{"gene":"SIRT1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2001,"finding":"SIRT1 (hSIR2) functions as an NAD-dependent deacetylase that binds p53 and deacetylates it specifically at Lys382, reducing p53 transcriptional activity; a catalytically inactive SIRT1 mutant potentiates p53-dependent apoptosis and radiosensitivity.","method":"Co-immunoprecipitation, in vitro deacetylase assay, site-specific mutagenesis, overexpression in human cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical assay plus mutagenesis plus cellular functional readout, replicated by two independent groups (PMID 11672523 and 11672522)","pmids":["11672523","11672522"],"is_preprint":false},{"year":2002,"finding":"Nicotinamide noncompetitively inhibits both yeast Sir2 and human SIRT1 deacetylase activity in vitro (IC50 < 50 µM), acting by binding a conserved pocket adjacent to NAD+ and blocking NAD+ hydrolysis.","method":"In vitro deacetylase assay, kinetic analysis, yeast genetic experiments","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with kinetic mechanism and corroborating yeast genetics","pmids":["12297502"],"is_preprint":false},{"year":2003,"finding":"Resveratrol activates SIRT1 by lowering its Michaelis constant for both the acetylated substrate and NAD+, and increases cell survival by stimulating SIRT1-dependent deacetylation of p53.","method":"In vitro sirtuin activity assay, yeast lifespan assay, cell survival assay with SIRT1 overexpression","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzyme kinetics plus cellular functional validation","pmids":["12939617"],"is_preprint":false},{"year":2004,"finding":"SIRT1 physically interacts with FOXO3 (and FOXO3a) in response to oxidative stress and deacetylates FOXO3 in vitro and in cells; SIRT1 increases FOXO3's ability to induce cell cycle arrest and stress resistance while inhibiting FOXO3's pro-apoptotic activity.","method":"Co-immunoprecipitation, in vitro deacetylase assay, loss-of-function/gain-of-function in mammalian cells","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution plus cellular epistasis, multiple orthogonal methods","pmids":["14976264"],"is_preprint":false},{"year":2004,"finding":"SIRT1 deacetylates and represses the forkhead transcription factor FOXO3a and other mammalian forkhead factors, paralleling its effect on p53, thereby reducing forkhead-dependent apoptosis.","method":"Co-immunoprecipitation, in vitro deacetylase assay, transcriptional reporter assay, apoptosis assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro deacetylase assay plus cellular functional readouts, independent corroboration of FOXO regulation","pmids":["14980222"],"is_preprint":false},{"year":2004,"finding":"SIRT1 physically interacts with the RelA/p65 subunit of NF-κB and inhibits NF-κB-dependent transcription by deacetylating RelA/p65 at lysine 310, thereby sensitizing cells to TNFα-induced apoptosis.","method":"Co-immunoprecipitation, chromatin immunoprecipitation, in vitro deacetylase assay, transcriptional reporter assay","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 — biochemical and chromatin-based assays with site-specific lysine identification","pmids":["15152190"],"is_preprint":false},{"year":2004,"finding":"Caloric restriction induces SIRT1 expression in rat tissues and human cells; SIRT1 deacetylates Ku70, causing it to sequester the pro-apoptotic factor Bax away from mitochondria, thereby inhibiting stress-induced apoptosis.","method":"In vitro and in vivo CR experiments, co-immunoprecipitation, subcellular fractionation, apoptosis assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 1-2 — mechanistic substrate identification with functional consequence (Bax sequestration) in multiple models","pmids":["15205477"],"is_preprint":false},{"year":2004,"finding":"Sirt1 binds to and represses PPARγ target genes in white adipocytes by docking with co-repressors NCoR and SMRT, promoting fat mobilization; Sirt1+/− mice show compromised fatty acid mobilization upon fasting, and Sirt1 overexpression attenuates adipogenesis.","method":"Co-immunoprecipitation, ChIP, siRNA knockdown, Sirt1+/− mouse model, adipogenesis assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including in vivo genetic model","pmids":["15175761"],"is_preprint":false},{"year":2005,"finding":"SIRT1 directly interacts with and deacetylates PGC-1α in vitro and in vivo; a single amino acid mutation in SIRT1's ADP-ribosyltransferase domain abolishes the SIRT1–PGC-1α interaction while preserving SIRT1 binding to p53 and Foxo3a.","method":"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, NAD-dependent activity assay","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus domain mutagenesis plus in vivo validation","pmids":["15716268"],"is_preprint":false},{"year":2005,"finding":"SIRT1 forms a complex with PGC-1α and deacetylates PGC-1α at specific lysine residues in an NAD+-dependent manner in liver during fasting; SIRT1 induces gluconeogenic genes and hepatic glucose output through PGC-1α but does not regulate PGC-1α effects on mitochondrial genes.","method":"Co-immunoprecipitation, in vitro NAD+-dependent deacetylase assay, adenoviral overexpression, primary hepatocyte studies","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution plus in vivo hepatic genetic experiments","pmids":["15744310"],"is_preprint":false},{"year":2005,"finding":"Among the seven human SIRT proteins, SIRT1 is localized in the nucleus, shows in vitro deacetylase activity on histone H4 and p53 peptides, and is the primary deacetylase for cellular p53 (not shared by SIRT2–7); overexpression of any single SIRT does not extend replicative lifespan in normal human fibroblasts.","method":"Subcellular fractionation/immunofluorescence, in vitro peptide deacetylase assay, siRNA/overexpression, replicative lifespan assay","journal":"Molecular Biology of the Cell","confidence":"High","confidence_rationale":"Tier 1-2 — systematic comparative biochemical and cellular characterization of all seven human SIRTs","pmids":["16079181"],"is_preprint":false},{"year":2005,"finding":"Resveratrol activation of SIRT1 in vitro is entirely dependent on the presence of a covalently attached fluorophore on the substrate peptide; without fluorophore, resveratrol does not activate SIRT1 against native peptides, suggesting allosteric modulation is fluorophore-dependent.","method":"In vitro deacetylase assay with fluorophore-labeled and unlabeled peptide substrates, substrate competition studies, structural modeling","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — rigorous mechanistic biochemical study with multiple substrate variants","pmids":["15749705"],"is_preprint":false},{"year":2006,"finding":"E2F1 induces SIRT1 expression at the transcriptional level; SIRT1 binds to E2F1 and inhibits E2F1 transcriptional and apoptotic activities, forming a negative feedback loop; SIRT1 knockdown increases E2F1-dependent apoptosis and cellular sensitivity to etoposide.","method":"Co-immunoprecipitation, siRNA knockdown, reporter assay, apoptosis assay","journal":"Nature Cell Biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional genetic epistasis with defined apoptotic phenotype","pmids":["16892051"],"is_preprint":false},{"year":2006,"finding":"Resveratrol treatment of mice activates SIRT1, decreases PGC-1α acetylation and increases PGC-1α activity, inducing oxidative phosphorylation and mitochondrial biogenesis genes; resveratrol has no effect in SIRT1−/− MEFs, placing SIRT1 upstream of PGC-1α in the pathway.","method":"Mouse metabolic phenotyping, gene expression analysis, SIRT1−/− MEFs as genetic control, PGC-1α acetylation assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — in vivo model plus SIRT1 null epistasis, multiple orthogonal readouts","pmids":["17112576"],"is_preprint":false},{"year":2007,"finding":"SIRT1 interacts with LXRα and LXRβ and promotes their deacetylation at a single conserved lysine (K432 in LXRα, K433 in LXRβ) adjacent to AF2; deacetylation promotes subsequent LXR ubiquitination and upregulation of targets including ABCA1; K432 mutation eliminates LXRα activation by SIRT1.","method":"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, in vivo LXR target gene expression","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — site-specific mutagenesis plus in vitro biochemistry plus in vivo validation","pmids":["17936707"],"is_preprint":false},{"year":2007,"finding":"AROS (Active Regulator of SIRT1) is a nuclear protein that directly binds SIRT1 and enhances SIRT1-mediated deacetylation of p53 both in vitro and in vivo; an AROS-binding-defective SIRT1 mutant abolishes AROS-dependent p53 inactivation; AROS knockdown increases p21WAF1 expression and apoptosis.","method":"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, antisense knockdown, cell cycle and apoptosis assays","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution plus mutagenesis plus loss-of-function cellular phenotype","pmids":["17964266"],"is_preprint":false},{"year":2007,"finding":"SIRT1 physically complexes with the DNA repair protein Ku70 and deacetylates it; catalytically inactive SIRT1 fails to deacetylate Ku70 or enhance DNA strand-break repair, indicating that SIRT1 deacetylase activity is required for its DNA repair-promoting function.","method":"Co-immunoprecipitation, dominant-negative SIRT1 mutant, comet assay (DNA repair), acetylation immunoblot","journal":"Experimental & Molecular Medicine","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus catalytic mutant control plus functional DNA repair assay, single lab","pmids":["17334224"],"is_preprint":false},{"year":2007,"finding":"SIRT1 is upregulated in mouse models of Alzheimer's disease and ALS; in cell-based models, SIRT1 promotes neuronal survival and reduces acetylation of PGC-1α and p53; lentiviral SIRT1 injection in hippocampus of p25 transgenic mice conferred significant protection against neurodegeneration.","method":"In vivo mouse models (p25 transgenic, SOD1 ALS), lentiviral SIRT1 overexpression, acetylation immunoblot, neuronal survival assay","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 2 — in vivo gain-of-function with defined mechanistic substrate (PGC-1α, p53 deacetylation) and neuropathological phenotype","pmids":["17581637"],"is_preprint":false},{"year":2008,"finding":"miR-34a inhibits SIRT1 expression through a miR-34a binding site in the 3' UTR of SIRT1; miR-34a suppression of SIRT1 increases acetylated p53, upregulates p21 and PUMA, and leads to apoptosis in p53-WT colon cancer cells but not in p53-null cells, establishing a p53→miR-34a→SIRT1→p53 positive feedback loop.","method":"3' UTR reporter assay, siRNA/miRNA overexpression, acetylation immunoblot, apoptosis assay in p53-WT vs. p53-null cells","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — 3' UTR functional assay plus genetic epistasis (p53 null cells) plus multiple downstream readouts","pmids":["18755897"],"is_preprint":false},{"year":2008,"finding":"SIRT1 has a role in neurogenesis: oxidative stress and inflammation bias neuronal stem cell differentiation toward astrocytes by modulating Sirt1 activity, linking a longevity gene to neuronal stem cell fate decisions.","method":"Neuronal stem cell differentiation assay with SIRT1 modulation","journal":"Nature Cell Biology","confidence":"Medium","confidence_rationale":"Tier 2 — defined cellular phenotype (stem cell fate) with SIRT1 loss/gain of function, single study","pmids":["18379594"],"is_preprint":false},{"year":2008,"finding":"SIRT1 regulates autophagy: transient SIRT1 overexpression stimulates basal autophagy; SIRT1−/− MEFs fail to fully activate autophagy under starvation; wild-type but not deacetylase-inactive SIRT1 restores autophagy; SIRT1 forms a molecular complex with Atg5, Atg7, and Atg8 and directly deacetylates them in an NAD-dependent fashion in vitro.","method":"SIRT1 KO MEFs, reconstitution with WT vs. catalytic mutant SIRT1, co-immunoprecipitation with autophagy proteins, in vitro deacetylase assay, autophagy flux assay","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution with catalytic mutant plus genetic KO epistasis plus in vitro substrate deacetylation","pmids":["18296641"],"is_preprint":false},{"year":2008,"finding":"SIRT1 is an NAD+-dependent HDAC that associates with the CLOCK:BMAL1 chromatin complex at circadian promoters; genetic ablation or pharmacological inhibition of SIRT1 disrupts circadian transcription and acetylation of H3 and BMAL1; SIRT1 promotes deacetylation and degradation of PER2, connecting cellular NAD+ metabolism to the circadian clock.","method":"ChIP, SIRT1 KO cells/liver-specific mutant mice, pharmacological inhibition, PER2 acetylation and stability assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP, genetic KO, and biochemical assays in two independent studies (PMID 18662547 and 18662546)","pmids":["18662547","18662546"],"is_preprint":false},{"year":2008,"finding":"SIRT1 associates with the CLOCK:BMAL1 complex and is recruited to circadian promoters; it is required for high-magnitude circadian transcription of Bmal1, Rorgamma, Per2, and Cry1; SIRT1 promotes deacetylation and degradation of PER2, with NAD+ dependence linking cellular metabolism to clockwork.","method":"ChIP, SIRT1 KO cells, pharmacological inhibition, PER2 deacetylation assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP plus genetic KO plus biochemical substrate identification","pmids":["18662546"],"is_preprint":false},{"year":2008,"finding":"SIRT1 phosphorylation by cyclin B/Cdk1 at Thr530 and Ser540 is required for normal cell cycle progression; dephosphorylation of SIRT1 by phosphatases reduces its NAD+-dependent deacetylase activity; 13 in vivo phosphorylation sites on SIRT1 were identified by mass spectrometry.","method":"Mass spectrometry phosphosite mapping, in vitro phosphatase assay, cyclin B/Cdk1 kinase assay, cell cycle analysis with phospho-site mutants","journal":"PLoS One","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro kinase assay plus phospho-site mutagenesis plus cell cycle phenotype","pmids":["19107194"],"is_preprint":false},{"year":2008,"finding":"Sirt1 deficiency in mice markedly attenuates spermatogenesis: numbers of mature sperm and spermatogenic precursors are significantly reduced, DNA damage in sperm is elevated, and genes involved in spermatogenesis and protein sumoylation are dysregulated; Sirt1-deficient sperm show reduced fertilization efficiency.","method":"Sirt1 KO mouse model, sperm counting, TUNEL assay, microarray gene expression, in vitro fertilization","journal":"PLoS One","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined spermatogenic phenotype and molecular readouts, single lab","pmids":["18270565"],"is_preprint":false},{"year":2009,"finding":"AMPK enhances SIRT1 activity by increasing cellular NAD+ levels (not by direct phosphorylation), resulting in deacetylation of SIRT1 targets PGC-1α, FOXO1, and FOXO3a in mouse skeletal muscle; this NAD+-mediated AMPK–SIRT1 axis explains convergent metabolic effects of both kinases.","method":"Skeletal muscle gene expression, NAD+ measurement, deacetylation assays, pharmacological and genetic AMPK manipulation","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — in vivo and cell-based experiments with multiple substrates and NAD+ mechanistic link, highly cited","pmids":["19262508"],"is_preprint":false},{"year":2009,"finding":"JNK1 phosphorylates SIRT1 at Ser27, Ser47, and Thr530 under oxidative stress conditions; this phosphorylation increases SIRT1 nuclear localization and enzymatic activity; notably, JNK1-phosphorylated SIRT1 shows substrate specificity: it deacetylates histone H3 but not p53.","method":"Co-immunoprecipitation of endogenous proteins, in vitro kinase assay, phospho-site mutagenesis, deacetylase activity assay, nuclear localization imaging","journal":"PLoS One","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro kinase reconstitution plus cellular functional readout, single lab","pmids":["20027304"],"is_preprint":false},{"year":2009,"finding":"SIRT1 associates with APE1 (apurinic/apyrimidinic endonuclease-1), deacetylates APE1 at lysines 6 and 7 in vitro and in vivo; SIRT1 knockdown increases cellular abasic DNA content and sensitizes cells to genotoxic death; SIRT1 activation promotes APE1 binding to XRCC1 and enhances BER pathway activity.","method":"Co-immunoprecipitation, in vitro deacetylase assay, siRNA knockdown, abasic site quantification, BER activity assay","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro reconstitution plus cellular epistasis, single lab","pmids":["19934257"],"is_preprint":false},{"year":2009,"finding":"Hepatocyte-specific SIRT1 deletion impairs PPARα signaling and fatty acid β-oxidation; SIRT1 interacts with PPARα and is required for PGC-1α coactivation of PPARα; liver-specific SIRT1 KO mice on high-fat diet develop hepatic steatosis, inflammation, and ER stress.","method":"Hepatocyte-specific Cre-lox SIRT1 KO mice, co-immunoprecipitation, gene expression, adenoviral SIRT1 overexpression, histopathology","journal":"Cell Metabolism","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific KO with clear metabolic phenotype plus molecular interaction data","pmids":["19356714"],"is_preprint":false},{"year":2010,"finding":"Laminar shear stress increases SIRT1 level and activity in endothelial cells; SIRT1 associates with eNOS and deacetylates it; AMPK-mediated phosphorylation of eNOS at Ser-633/1177 is required to prime SIRT1-induced eNOS deacetylation, enhancing NO production; AMPKα2−/− mice show increased eNOS acetylation in aorta.","method":"Co-immunoprecipitation, eNOS acetylation assay, AMPK inhibitor/eNOS phospho-site mutants, AMPKα2 KO mice, flow experiments","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — mechanistic epistasis (AMPK→eNOS phospho→SIRT1 deacetylation) validated in vivo with KO mice","pmids":["20479254"],"is_preprint":false},{"year":2010,"finding":"SIRT1 is essential for normal cognitive function and synaptic plasticity: SIRT1 KO mice show impaired learning, memory, classical conditioning, and spatial learning; these deficits correlate with defects in synaptic plasticity, decreased dendritic branching, reduced ERK1/2 phosphorylation, and altered expression of hippocampal genes involved in synaptic function, lipid metabolism, and myelination.","method":"SIRT1 KO mouse model, behavioral paradigms (fear conditioning, Morris water maze), LTP electrophysiology, Golgi staining of dendrites, gene expression","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple behavioral, electrophysiological, and molecular phenotypes","pmids":["20660252"],"is_preprint":false},{"year":2011,"finding":"SIRT1 deacetylates FOXO1 in pancreatic β-cells; SIRT1 activity determines whether FoxO1 drives a protective (GADD45α-mediated DNA repair) or proapoptotic (PUMA induction, caspase-3 cleavage) response to nitric oxide; SIRT1 inhibitors switch FoxO1-dependent protection to apoptosis.","method":"SIRT1 pharmacological inhibition, FoxO1 localization (nuclear translocation imaging), GADD45α/PUMA expression assay, caspase-3 assay in β-cells","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway placement with defined substrate (FoxO1) and opposing functional outcomes, single lab","pmids":["21196578"],"is_preprint":false},{"year":2011,"finding":"SIRT1 and SIRT3 deacetylate homologous substrates in their respective compartments: SIRT1 deacetylates AceCS1 and HMGCS1 in the cytoplasm, while SIRT3 deacetylates AceCS2 and HMGCS2 in mitochondria, revealing a pattern of substrate homology between cytoplasmic SIRT1 and mitochondrial SIRT3.","method":"In vitro deacetylase assay, phylogenetic analysis, fractionation","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution, single study","pmids":["21701047"],"is_preprint":false},{"year":2015,"finding":"SIRT1 deacetylates RORγt, the master transcription factor of Th17 cells, increasing RORγt transcriptional activity and enhancing Th17 cell generation; T cell-specific Sirt1 deletion suppresses Th17 differentiation and is protective in a mouse model of multiple sclerosis.","method":"Co-immunoprecipitation, in vitro deacetylase assay, T cell-specific Sirt1 KO mice, Th17 differentiation assay, EAE mouse model, hematopoietic chimera analysis","journal":"The Journal of Experimental Medicine","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical substrate identification plus conditional KO in vivo disease model plus mixed chimera epistasis","pmids":["25918343"],"is_preprint":false},{"year":2016,"finding":"SIRT1 stabilizes mitofusin 1 (MFN1) by deacetylating it; TIP60 acetyltransferase promotes MFN1 degradation, while SIRT1 deacetylase counteracts this; SIRT1 knockdown reduces MFN1 levels and mitochondrial elongation, while SIRT1 overexpression increases MFN1; under hypoxia, SIRT1 and MFN1 accumulate and mitochondria elongate.","method":"siRNA knockdown, SIRT1 overexpression, in vitro acetylation assay with TIP60 and SIRT1, immunoprecipitation, mitochondrial morphology imaging","journal":"Cellular Signalling","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro biochemical reconstitution plus cellular morphology phenotype, single lab","pmids":["28669827"],"is_preprint":false},{"year":2016,"finding":"HDAC4 stabilizes SIRT1 protein by enhancing its sumoylation, thereby increasing SIRT1 protein levels and delaying cellular senescence; HDAC4 knockdown leads to premature senescence in human fibroblasts.","method":"Co-immunoprecipitation, sumoylation assay, HDAC4 overexpression/knockdown, senescence assay (SA-β-gal)","journal":"Clinical and Experimental Pharmacology & Physiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — interaction and PTM data plus defined senescence phenotype, single lab","pmids":["26414199"],"is_preprint":false},{"year":2017,"finding":"SIRT1 activates fetal hemoglobin (γ-globin/HBG) gene expression by binding to the β-globin LCR and HBG promoters, promoting LCR-to-HBG promoter looping, increasing RNA Pol II and H4K16Ac at HBG promoter, and suppressing BCL11A, KLF1, HDAC1, and HDAC2 expression; small molecule SIRT1 activators SRT2104 and SRT1720 reactivate silenced HBG in adult erythroblasts.","method":"ChIP, chromosome conformation capture (looping assay), SIRT1 knockdown/overexpression, small molecule activators in primary human erythroblasts","journal":"American Journal of Hematology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and looping assay plus pharmacological activation in primary cells, single lab","pmids":["28776729"],"is_preprint":false},{"year":2018,"finding":"SIRT1 represses NF-κB-driven transcription of the AIM2 gene in cervical cancer cells by destabilizing RELB mRNA; SIRT1 knockdown derepresses AIM2 inflammasome-mediated pyroptosis, demonstrating a pro-tumorigenic role of SIRT1 through innate immune suppression.","method":"SIRT1 siRNA knockdown, SIRT1 restoration, AIM2 promoter/NF-κB reporter assay, RELB mRNA stability assay, pyroptosis assay, xenograft model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway (SIRT1→RELB→AIM2) with multiple functional assays, single lab","pmids":["29844574"],"is_preprint":false},{"year":2019,"finding":"SIRT1 mediates increased mitochondrial oxidative phosphorylation in CML leukemia stem cells (LSCs) via deacetylation of PGC-1α; genetic SIRT1 deletion in transgenic CML mice reduces LSC maintenance and enhances tyrosine kinase inhibitor efficacy; mitochondrial alterations are BCR-ABL kinase-independent.","method":"Conditional SIRT1 KO in CML transgenic mice, Seahorse metabolic profiling, PGC-1α acetylation assay, LSC functional assays","journal":"The Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional KO with defined metabolic mechanism (PGC-1α deacetylation) and LSC phenotype","pmids":["31180336"],"is_preprint":false},{"year":2019,"finding":"SIRT1 deacetylates STAT3, leading to STAT3 destabilization and degradation, thereby repressing FGB (fibrinogen beta chain) expression and inhibiting RCC tumor growth; overexpression of SIRT1 suppresses RCC proliferation in vitro and in vivo through this SIRT1-STAT3-FGB axis.","method":"Co-immunoprecipitation, STAT3 acetylation/ubiquitination assay, SIRT1 overexpression, luciferase reporter (FGB as STAT3 target), in vivo xenograft","journal":"Experimental Cell Research","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic substrate identification with in vitro and in vivo functional readout, single lab","pmids":["31201813"],"is_preprint":false},{"year":2019,"finding":"SIRT1 protects hypoxic cardiomyocytes via two pathways: (1) promoting autophagic flux through AMPK activation (blocked by compound C), and (2) reducing apoptosis through IRE1α pathway inhibition.","method":"Adenoviral SIRT1 overexpression/knockdown in H9C2 cells, pharmacological activator/inhibitor (SRT1720/EX-527), AMPK inhibitor (compound C), apoptosis assay (TUNEL, Annexin V), autophagic flux assay, in vivo hypoxic mouse model","journal":"International Journal of Molecular Medicine","confidence":"Medium","confidence_rationale":"Tier 2 — dual pathway placement with pharmacological epistasis in vitro and in vivo, single lab","pmids":["30864731"],"is_preprint":false},{"year":2020,"finding":"Macroautophagy mediates SIRT1 protein downregulation during senescence and ageing: nuclear SIRT1 is recognized as an autophagy substrate via the autophagy protein LC3, and is subjected to cytoplasmic autophagosome-lysosome degradation; this mechanism operates in multiple immune tissues in aged mice and in aged human CD8+CD28− T cells.","method":"Autophagy pathway inhibitors, LC3 interaction assay, subcellular fractionation, aged mouse tissue analysis, human T cell aging model","journal":"Nature Cell Biology","confidence":"High","confidence_rationale":"Tier 2 — mechanistic substrate identification (SIRT1 as LC3 cargo) replicated across multiple in vivo tissues and species","pmids":["32989246"],"is_preprint":false},{"year":2021,"finding":"ADNP and SIRT1 form a protein complex with two key interaction sites: one at the microtubule end-binding proteins EB1/EB3 and Tau level, and one at the DNA/chromatin site involving YY1, HDAC2, with sex- and age-dependent regulation of histone modifications; ADNP-SIRT1-EB1 correlation is specifically abolished in Alzheimer's and Parkinson's disease brain regions.","method":"Co-immunoprecipitation, single-cell RNA/protein expression, gene expression correlation analysis, postmortem brain tissue analysis","journal":"Molecular Psychiatry","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP interaction plus correlational expression data; mechanistic follow-up partial","pmids":["33967268"],"is_preprint":false}],"current_model":"SIRT1 is a nuclear, NAD+-dependent class III protein deacetylase that regulates a broad array of cellular processes by deacetylating histone (H3K9/K14, H4K16, BMAL1) and non-histone substrates (p53 at K382, FOXO1/3/4, NF-κB RelA/p65 at K310, PGC-1α, PPARα, LXRα/β at K432/433, RORγt, Ku70, APE1, Atg5/7/8, eNOS, STAT3, MFN1), whose activity is regulated by NAD+ availability, post-translational modifications (phosphorylation by cyclin B/Cdk1 and JNK1; sumoylation by HDAC4), protein interactions (AROS activates; DBC1 inhibits), miRNA-mediated repression (e.g., miR-34a targeting the 3' UTR), and autophagic degradation via LC3 during senescence; upstream, AMPK enhances SIRT1 activity by elevating cellular NAD+ levels, while SIRT1-mediated deacetylation of PGC-1α, FOXO factors, and NF-κB connects caloric sensing to metabolic reprogramming, stress resistance, circadian clock control, autophagy, DNA repair, immune regulation, and suppression of apoptosis."},"narrative":{"teleology":[{"year":2001,"claim":"The identification of SIRT1 as an NAD-dependent deacetylase that targets p53 at K382 established its enzymatic mechanism and linked it to apoptosis regulation, answering whether the yeast Sir2 longevity mechanism was conserved in mammals.","evidence":"In vitro deacetylase assay, co-IP, catalytic mutant analysis in human cells by two independent groups","pmids":["11672523","11672522"],"confidence":"High","gaps":["Crystal structure of SIRT1–p53 complex not yet resolved","Physiological context of p53 deacetylation in vivo not addressed"]},{"year":2002,"claim":"Demonstration that nicotinamide noncompetitively inhibits SIRT1 by blocking NAD⁺ hydrolysis established the first mechanistic model for endogenous feedback regulation of SIRT1 catalytic activity.","evidence":"Kinetic analysis of recombinant SIRT1 with corroborating yeast genetics","pmids":["12297502"],"confidence":"High","gaps":["In vivo relevance of nicotinamide concentrations for SIRT1 inhibition not established","Structural basis of nicotinamide binding pocket not resolved at that time"]},{"year":2004,"claim":"Rapid expansion of the SIRT1 substrate repertoire to include FOXO3a, NF-κB RelA/p65, and Ku70 revealed that SIRT1 is not merely a p53 deacetylase but a broad stress-responsive signaling node controlling apoptosis, inflammation, and DNA damage responses.","evidence":"In vitro deacetylase assays, co-IPs, ChIP, functional apoptosis/reporter assays, caloric restriction models across multiple labs","pmids":["14976264","14980222","15152190","15205477"],"confidence":"High","gaps":["Substrate selectivity determinants unknown","How SIRT1 discriminates among competing substrates in vivo not resolved"]},{"year":2004,"claim":"Discovery that SIRT1 represses PPARγ target genes in adipocytes via NCoR/SMRT recruitment, and that Sirt1 haploinsufficient mice have defective fat mobilization, established SIRT1 as a transcriptional co-repressor in metabolic regulation.","evidence":"ChIP, siRNA knockdown, Sirt1⁺/⁻ mouse fasting experiments, adipogenesis assay","pmids":["15175761"],"confidence":"High","gaps":["Full spectrum of SIRT1-regulated metabolic genes in adipose not mapped","Whether SIRT1 deacetylates PPARγ directly was not shown"]},{"year":2005,"claim":"Identification of PGC-1α as a direct SIRT1 substrate with site-specific deacetylation connected SIRT1 to hepatic gluconeogenesis and mitochondrial gene regulation, answering how caloric restriction signals converge on metabolic gene expression.","evidence":"In vitro deacetylase assay, domain mutagenesis, primary hepatocyte and fasting liver experiments","pmids":["15716268","15744310"],"confidence":"High","gaps":["Specific lysine residues on PGC-1α targeted by SIRT1 not fully mapped","Relative contributions of SIRT1 vs. other deacetylases to PGC-1α regulation in different tissues unclear"]},{"year":2005,"claim":"The finding that resveratrol activation of SIRT1 was fluorophore-dependent challenged the direct activator model and raised questions about the physiological relevance of small-molecule SIRT1 activation.","evidence":"Systematic comparison of fluorophore-labeled vs. unlabeled peptide substrates in in vitro deacetylase assays","pmids":["15749705"],"confidence":"High","gaps":["Whether resveratrol activates SIRT1 on full-length protein substrates remained debated","In vivo mechanism of resveratrol-SIRT1 axis not fully reconciled"]},{"year":2007,"claim":"Discovery of AROS as a direct SIRT1 activator and identification of LXRα/β as SIRT1 substrates at defined lysines expanded understanding of SIRT1 regulation and placed it in cholesterol/lipid homeostasis.","evidence":"Co-IP, in vitro deacetylase assay, AROS-binding-defective SIRT1 mutant, LXR K432 mutagenesis, in vivo target gene expression","pmids":["17964266","17936707"],"confidence":"High","gaps":["Relative contribution of AROS vs. DBC1 in different tissues not determined","Full physiological impact of SIRT1-LXR axis on reverse cholesterol transport not assessed"]},{"year":2008,"claim":"Three major biological roles were simultaneously established: SIRT1 promotes autophagy by deacetylating Atg5/7/8, entrains the circadian clock via the CLOCK:BMAL1 complex and PER2 deacetylation, and is subject to miR-34a-mediated post-transcriptional repression creating a p53–miR-34a–SIRT1 feedback loop.","evidence":"SIRT1 KO MEFs with reconstitution, ChIP at circadian promoters, liver-specific KO mice, 3′ UTR reporter assay, genetic epistasis in p53-null cells","pmids":["18296641","18662547","18662546","18755897"],"confidence":"High","gaps":["Relative importance of SIRT1 autophagy regulation vs. other autophagy deacetylases unclear","Whether SIRT1 circadian role is secondary to NAMPT/NAD⁺ oscillations not resolved"]},{"year":2008,"claim":"Mapping of 13 in vivo phosphorylation sites on SIRT1 and demonstration that cyclin B/Cdk1-mediated phosphorylation at T530/S540 is required for cell cycle progression established post-translational regulation as a key layer of SIRT1 control.","evidence":"Mass spectrometry, in vitro Cdk1 kinase assay, phosphosite mutant cell cycle analysis","pmids":["19107194"],"confidence":"High","gaps":["Functional significance of most of the 13 phosphosites not individually characterized","Phosphatase(s) responsible for SIRT1 dephosphorylation not identified"]},{"year":2009,"claim":"The finding that AMPK enhances SIRT1 activity by raising cellular NAD⁺ rather than by direct phosphorylation provided the mechanistic basis for metabolic convergence of AMPK and SIRT1 signaling on PGC-1α and FOXO targets.","evidence":"NAD⁺ measurements, deacetylation assays, pharmacological and genetic AMPK manipulation in skeletal muscle","pmids":["19262508"],"confidence":"High","gaps":["Whether AMPK–NAD⁺–SIRT1 axis operates identically across all tissues not established","Quantitative relationship between NAD⁺ fluctuations and SIRT1 activity thresholds unknown"]},{"year":2009,"claim":"Hepatocyte-specific SIRT1 deletion causing steatosis, inflammation, and ER stress under high-fat diet demonstrated that SIRT1-PPARα-PGC-1α cooperation is essential for hepatic lipid homeostasis in vivo.","evidence":"Liver-specific Cre-lox SIRT1 KO mice, co-IP of SIRT1-PPARα, gene expression, histopathology","pmids":["19356714"],"confidence":"High","gaps":["Whether SIRT1 directly deacetylates PPARα or acts solely as a PGC-1α co-regulator not fully resolved","Contribution of hepatic SIRT1 loss to systemic metabolic phenotypes not fully dissected"]},{"year":2010,"claim":"Demonstration that SIRT1 deacetylates eNOS downstream of AMPK-mediated phosphorylation, and that SIRT1 KO mice show impaired cognition and synaptic plasticity, extended SIRT1 functions to vascular biology and neuronal physiology.","evidence":"Co-IP, eNOS acetylation assay with AMPKα2 KO mice, SIRT1 KO mouse behavioral and electrophysiological analysis","pmids":["20479254","20660252"],"confidence":"High","gaps":["Direct neuronal substrates mediating synaptic plasticity defects not identified","Whether eNOS deacetylation is the primary mechanism of SIRT1 vascular protection not established"]},{"year":2015,"claim":"Identification of RORγt as a SIRT1 deacetylation substrate that enhances Th17 differentiation resolved how SIRT1 participates in adaptive immune regulation, with conditional T cell KO suppressing autoimmune disease.","evidence":"Co-IP, in vitro deacetylase assay, T cell-specific Sirt1 KO mice, EAE model, hematopoietic chimeras","pmids":["25918343"],"confidence":"High","gaps":["Whether SIRT1-RORγt axis operates in human Th17 biology not directly shown","Mechanism by which deacetylation increases RORγt activity not structurally resolved"]},{"year":2020,"claim":"Discovery that SIRT1 is itself degraded by macroautophagy via LC3 recognition during senescence and aging revealed a self-limiting feedback mechanism explaining age-dependent SIRT1 decline.","evidence":"Autophagy inhibitors, LC3 interaction assay, subcellular fractionation, aged mouse tissues, human CD8⁺CD28⁻ T cells","pmids":["32989246"],"confidence":"High","gaps":["Specific LC3-interacting region (LIR motif) on SIRT1 not mapped","Whether pharmacological autophagy inhibition can restore SIRT1 levels and reverse aging phenotypes not tested"]},{"year":null,"claim":"A unified structural and quantitative model integrating how SIRT1 discriminates among its >20 known substrates in different cellular contexts, and how its multiple post-translational modifications (phosphorylation, sumoylation) combinatorially tune substrate selectivity, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length SIRT1 structure with native substrate bound","Quantitative kinetic parameters for most substrates lacking","How tissue-specific SIRT1 functions are programmed despite ubiquitous expression is mechanistically unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3,4,5,8,9,14,20,27,33,34,39]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[5,7,12,21,22,36]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[10,21]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[10,15,26,36,41]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[20,40]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,3,4,6,12]},{"term_id":"R-HSA-9909396","term_label":"Circadian clock","supporting_discovery_ids":[21,22]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[16,27]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7,9,13,28]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[33,37]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,25,29]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[21,36]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[23]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[7,12,36]}],"complexes":["CLOCK:BMAL1 complex"],"partners":["TP53","FOXO3","RELA","PPARGC1A","PPARA","XRCC6","CLOCK","AROS"],"other_free_text":[]},"mechanistic_narrative":"SIRT1 is a nuclear NAD⁺-dependent class III protein deacetylase that couples cellular metabolic state to chromatin remodeling, transcription factor activity, DNA repair, autophagy, and circadian clock function by deacetylating both histone (H3, H4K16) and non-histone substrates. Key non-histone substrates include p53 (K382), FOXO1/3a, NF-κB RelA/p65 (K310), PGC-1α, PPARα, LXRα/β (K432/K433), RORγt, Ku70, APE1, Atg5/7/8, eNOS, STAT3, and MFN1, through which SIRT1 regulates apoptosis, gluconeogenesis, fatty acid oxidation, mitochondrial biogenesis, inflammation, Th17 differentiation, base excision repair, and autophagy [PMID:11672523, PMID:14976264, PMID:15152190, PMID:15744310, PMID:18296641, PMID:25918343, PMID:18662547]. SIRT1 enzymatic activity is controlled by NAD⁺ availability (indirectly regulated by AMPK), phosphorylation by cyclin B/Cdk1 and JNK1, sumoylation promoted by HDAC4, binding of the activator AROS and the inhibitor DBC1, and transcriptional/post-transcriptional regulation including miR-34a-mediated repression and autophagic degradation via LC3 during senescence [PMID:19262508, PMID:19107194, PMID:17964266, PMID:18755897, PMID:32989246]. SIRT1 associates with the CLOCK:BMAL1 complex at circadian promoters, deacetylates BMAL1 and PER2, and is essential for high-amplitude circadian transcription, thereby linking NAD⁺ metabolism to the molecular clock [PMID:18662547, PMID:18662546]."},"prefetch_data":{"uniprot":{"accession":"Q96EB6","full_name":"NAD-dependent protein deacetylase sirtuin-1","aliases":["NAD-dependent protein deacylase sirtuin-1","Regulatory protein SIR2 homolog 1","SIR2-like protein 1","hSIR2"],"length_aa":747,"mass_kda":81.7,"function":"NAD-dependent protein deacetylase that links transcriptional regulation directly to intracellular energetics and participates in the coordination of several separated cellular functions such as cell cycle, response to DNA damage, metabolism, apoptosis and autophagy (PubMed:11672523, PubMed:12006491, PubMed:14976264, PubMed:14980222, PubMed:15126506, PubMed:15152190, PubMed:15205477, PubMed:15469825, PubMed:15692560, PubMed:16079181, PubMed:16166628, PubMed:16892051, PubMed:16998810, PubMed:17283066, PubMed:17290224, PubMed:17334224, PubMed:17505061, PubMed:17612497, PubMed:17620057, PubMed:17936707, PubMed:18203716, PubMed:18296641, PubMed:18662546, PubMed:18687677, PubMed:19188449, PubMed:19220062, PubMed:19364925, PubMed:19690166, PubMed:19934257, PubMed:20097625, PubMed:20100829, PubMed:20203304, PubMed:20375098, PubMed:20620956, PubMed:20670893, PubMed:20817729, PubMed:20955178, PubMed:21149730, PubMed:21245319, PubMed:21471201, PubMed:21504832, PubMed:21555002, PubMed:21698133, PubMed:21701047, PubMed:21775285, PubMed:21807113, PubMed:21841822, PubMed:21890893, PubMed:21947282, PubMed:22274616, PubMed:22918831, PubMed:24415752, PubMed:24824780, PubMed:29681526, PubMed:29765047, PubMed:30409912). Can modulate chromatin function through deacetylation of histones and can promote alterations in the methylation of histones and DNA, leading to transcriptional repression (PubMed:15469825). Deacetylates a broad range of transcription factors and coregulators, thereby regulating target gene expression positively and negatively (PubMed:14976264, PubMed:14980222, PubMed:15152190). Serves as a sensor of the cytosolic ratio of NAD(+)/NADH which is altered by glucose deprivation and metabolic changes associated with caloric restriction (PubMed:15205477). Is essential in skeletal muscle cell differentiation and in response to low nutrients mediates the inhibitory effect on skeletal myoblast differentiation which also involves 5'-AMP-activated protein kinase (AMPK) and nicotinamide phosphoribosyltransferase (NAMPT) (By similarity). Component of the eNoSC (energy-dependent nucleolar silencing) complex, a complex that mediates silencing of rDNA in response to intracellular energy status and acts by recruiting histone-modifying enzymes (PubMed:18485871). The eNoSC complex is able to sense the energy status of cell: upon glucose starvation, elevation of NAD(+)/NADP(+) ratio activates SIRT1, leading to histone H3 deacetylation followed by dimethylation of H3 at 'Lys-9' (H3K9me2) by SUV39H1 and the formation of silent chromatin in the rDNA locus (PubMed:18485871, PubMed:21504832). Deacetylates 'Lys-266' of SUV39H1, leading to its activation (PubMed:21504832). Inhibits skeletal muscle differentiation by deacetylating PCAF and MYOD1 (PubMed:19188449). Deacetylates H2A and 'Lys-26' of H1-4 (PubMed:15469825). Deacetylates 'Lys-16' of histone H4 (in vitro). Involved in NR0B2/SHP corepression function through chromatin remodeling: Recruited to LRH1 target gene promoters by NR0B2/SHP thereby stimulating histone H3 and H4 deacetylation leading to transcriptional repression (PubMed:20375098). Proposed to contribute to genomic integrity via positive regulation of telomere length; however, reports on localization to pericentromeric heterochromatin are conflicting (By similarity). Proposed to play a role in constitutive heterochromatin (CH) formation and/or maintenance through regulation of the available pool of nuclear SUV39H1 (PubMed:15469825, PubMed:18004385). Upon oxidative/metabolic stress decreases SUV39H1 degradation by inhibiting SUV39H1 polyubiquitination by MDM2 (PubMed:18004385, PubMed:21504832). This increase in SUV39H1 levels enhances SUV39H1 turnover in CH, which in turn seems to accelerate renewal of the heterochromatin which correlates with greater genomic integrity during stress response (PubMed:18004385, PubMed:21504832). Deacetylates 'Lys-382' of p53/TP53 and impairs its ability to induce transcription-dependent proapoptotic program and modulate cell senescence (PubMed:11672523, PubMed:12006491, PubMed:22542455). Deacetylates TAF1B and thereby represses rDNA transcription by the RNA polymerase I (By similarity). Deacetylates MYC, promotes the association of MYC with MAX and decreases MYC stability leading to compromised transformational capability (PubMed:19364925, PubMed:21807113). Deacetylates FOXO3 in response to oxidative stress thereby increasing its ability to induce cell cycle arrest and resistance to oxidative stress but inhibiting FOXO3-mediated induction of apoptosis transcriptional activity; also leading to FOXO3 ubiquitination and protesomal degradation (PubMed:14976264, PubMed:14980222, PubMed:21841822). Appears to have a similar effect on MLLT7/FOXO4 in regulation of transcriptional activity and apoptosis (PubMed:15126506). Deacetylates DNMT1; thereby impairs DNMT1 methyltransferase-independent transcription repressor activity, modulates DNMT1 cell cycle regulatory function and DNMT1-mediated gene silencing (PubMed:21947282). Deacetylates RELA/NF-kappa-B p65 thereby inhibiting its transactivating potential and augments apoptosis in response to TNF (PubMed:15152190). Deacetylates HIF1A, KAT5/TIP60, RB1 and HIC1 (PubMed:17283066, PubMed:17620057, PubMed:20100829, PubMed:20620956). Deacetylates FOXO1 resulting in its nuclear retention and enhancement of its transcriptional activity leading to increased gluconeogenesis in liver (PubMed:15692560). Inhibits E2F1 transcriptional activity and apoptotic function, possibly by deacetylation (PubMed:16892051). Involved in HES1- and HEY2-mediated transcriptional repression (PubMed:12535671). In cooperation with MYCN seems to be involved in transcriptional repression of DUSP6/MAPK3 leading to MYCN stabilization by phosphorylation at 'Ser-62' (PubMed:21698133). Deacetylates MEF2D (PubMed:16166628). Required for antagonist-mediated transcription suppression of AR-dependent genes which may be linked to local deacetylation of histone H3 (PubMed:17505061). Represses HNF1A-mediated transcription (By similarity). Required for the repression of ESRRG by CREBZF (PubMed:19690166). Deacetylates NR1H3 and NR1H2 and deacetylation of NR1H3 at 'Lys-434' positively regulates transcription of NR1H3:RXR target genes, promotes NR1H3 proteasomal degradation and results in cholesterol efflux; a promoter clearing mechanism after reach round of transcription is proposed (PubMed:17936707). Involved in lipid metabolism: deacetylates LPIN1, thereby inhibiting diacylglycerol synthesis (PubMed:20817729, PubMed:29765047). Implicated in regulation of adipogenesis and fat mobilization in white adipocytes by repression of PPARG which probably involves association with NCOR1 and SMRT/NCOR2 (By similarity). Deacetylates p300/EP300 and PRMT1 (By similarity). Deacetylates ACSS2 leading to its activation, and HMGCS1 deacetylation (PubMed:21701047). Involved in liver and muscle metabolism. Through deacetylation and activation of PPARGC1A is required to activate fatty acid oxidation in skeletal muscle under low-glucose conditions and is involved in glucose homeostasis (PubMed:23142079). Involved in regulation of PPARA and fatty acid beta-oxidation in liver. Involved in positive regulation of insulin secretion in pancreatic beta cells in response to glucose; the function seems to imply transcriptional repression of UCP2. Proposed to deacetylate IRS2 thereby facilitating its insulin-induced tyrosine phosphorylation. Deacetylates SREBF1 isoform SREBP-1C thereby decreasing its stability and transactivation in lipogenic gene expression (PubMed:17290224, PubMed:20817729). Involved in DNA damage response by repressing genes which are involved in DNA repair, such as XPC and TP73, deacetylating XRCC6/Ku70, and facilitating recruitment of additional factors to sites of damaged DNA, such as SIRT1-deacetylated NBN can recruit ATM to initiate DNA repair and SIRT1-deacetylated XPA interacts with RPA2 (PubMed:15205477, PubMed:16998810, PubMed:17334224, PubMed:17612497, PubMed:20670893, PubMed:21149730). Also involved in DNA repair of DNA double-strand breaks by homologous recombination and specifically single-strand annealing independently of XRCC6/Ku70 and NBN (PubMed:15205477, PubMed:17334224, PubMed:20097625). Promotes DNA double-strand breaks by mediating deacetylation of SIRT6 (PubMed:32538779). Transcriptional suppression of XPC probably involves an E2F4:RBL2 suppressor complex and protein kinase B (AKT) signaling. Transcriptional suppression of TP73 probably involves E2F4 and PCAF. Deacetylates WRN thereby regulating its helicase and exonuclease activities and regulates WRN nuclear translocation in response to DNA damage (PubMed:18203716). Deacetylates APEX1 at 'Lys-6' and 'Lys-7' and stimulates cellular AP endonuclease activity by promoting the association of APEX1 to XRCC1 (PubMed:19934257). Catalyzes deacetylation of ERCC4/XPF, thereby impairing interaction with ERCC1 and nucleotide excision repair (NER) (PubMed:32034146). Increases p53/TP53-mediated transcription-independent apoptosis by blocking nuclear translocation of cytoplasmic p53/TP53 and probably redirecting it to mitochondria. Deacetylates XRCC6/Ku70 at 'Lys-539' and 'Lys-542' causing it to sequester BAX away from mitochondria thereby inhibiting stress-induced apoptosis. Is involved in autophagy, presumably by deacetylating ATG5, ATG7 and MAP1LC3B/ATG8 (PubMed:18296641). Deacetylates AKT1 which leads to enhanced binding of AKT1 and PDK1 to PIP3 and promotes their activation (PubMed:21775285). Proposed to play role in regulation of STK11/LBK1-dependent AMPK signaling pathways implicated in cellular senescence which seems to involve the regulation of the acetylation status of STK11/LBK1. Can deacetylate STK11/LBK1 and thereby increase its activity, cytoplasmic localization and association with STRAD; however, the relevance of such activity in normal cells is unclear (PubMed:18687677, PubMed:20203304). In endothelial cells is shown to inhibit STK11/LBK1 activity and to promote its degradation. Deacetylates SMAD7 at 'Lys-64' and 'Lys-70' thereby promoting its degradation. Deacetylates CIITA and augments its MHC class II transactivation and contributes to its stability (PubMed:21890893). Deacetylates MECOM/EVI1 (PubMed:21555002). Deacetylates PML at 'Lys-487' and this deacetylation promotes PML control of PER2 nuclear localization (PubMed:22274616). During the neurogenic transition, represses selective NOTCH1-target genes through histone deacetylation in a BCL6-dependent manner and leading to neuronal differentiation. Regulates the circadian expression of several core clock genes, including BMAL1, RORC, PER2 and CRY1 and plays a critical role in maintaining a controlled rhythmicity in histone acetylation, thereby contributing to circadian chromatin remodeling (PubMed:18662546). Deacetylates BMAL1 and histones at the circadian gene promoters in order to facilitate repression by inhibitory components of the circadian oscillator (By similarity). Deacetylates PER2, facilitating its ubiquitination and degradation by the proteasome (By similarity). Protects cardiomyocytes against palmitate-induced apoptosis (By similarity). Deacetylates XBP1 isoform 2; deacetylation decreases protein stability of XBP1 isoform 2 and inhibits its transcriptional activity (PubMed:20955178). Deacetylates PCK1 and directs its activity toward phosphoenolpyruvate production promoting gluconeogenesis (PubMed:30193097). Involved in the CCAR2-mediated regulation of PCK1 and NR1D1 (PubMed:24415752). Deacetylates CTNB1 at 'Lys-49' (PubMed:24824780). In POMC (pro-opiomelanocortin) neurons, required for leptin-induced activation of PI3K signaling (By similarity). Deacetylates SOX9; promoting SOX9 nuclear localization and transactivation activity (By similarity). Involved in the regulation of centrosome duplication: deacetylates CENATAC in G1 phase, allowing for SASS6 accumulation on the centrosome and subsequent procentriole assembly (PubMed:31722219). Deacetylates NDC80/HEC1 (PubMed:30409912). In addition to protein deacetylase activity, also acts as a protein-lysine deacylase by mediating protein delactylation, depropionylation and decrotonylation (PubMed:28497810, PubMed:38512451). Mediates depropionylation of Osterix (SP7) (By similarity). Catalyzes decrotonylation of histones; it however does not represent a major histone decrotonylase (PubMed:28497810). Mediates protein delactylation of TEAD1 and YAP1 (PubMed:38512451) Deacetylates 'Lys-382' of p53/TP53, however with lower activity than isoform 1. In combination, the two isoforms exert an additive effect. Isoform 2 regulates p53/TP53 expression and cellular stress response and is in turn repressed by p53/TP53 presenting a SIRT1 isoform-dependent auto-regulatory loop Catalytically inactive 75SirT1 may be involved in regulation of apoptosis. May be involved in protecting chondrocytes from apoptotic death by associating with cytochrome C and interfering with apoptosome assembly (Microbial infection) In case of HIV-1 infection, interacts with and deacetylates the viral Tat protein. 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[\"19262508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"miR-34a inhibits SIRT1 expression through a binding site within the 3' UTR of SIRT1 mRNA, leading to increased acetylated p53, induction of p21 and PUMA, and ultimately apoptosis in a p53-dependent manner, forming part of a p53-miR-34a-SIRT1 positive feedback loop.\",\n      \"method\": \"miR-34a overexpression/inhibition, 3' UTR reporter assays, siRNA knockdown of SIRT1, apoptosis assays in p53 WT and null colon cancer cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with functional readouts; highly cited foundational study\",\n      \"pmids\": [\"18755897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 interacts with and deacetylates LXR proteins at a conserved lysine (K432 in LXRα, K433 in LXRβ), promoting subsequent LXR ubiquitination and positively regulating LXR target genes including ABCA1; mutations at K432 eliminate LXRα activation by SIRT1.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylation assay, site-directed mutagenesis, loss-of-function in vivo; gene expression analysis of LXR targets\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro deacetylation assay combined with mutagenesis and in vivo validation\",\n      \"pmids\": [\"17936707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"AROS (active regulator of SIRT1) is a nuclear protein that directly binds SIRT1 and enhances SIRT1-mediated deacetylation of p53 both in vitro and in vivo, inhibiting p53-mediated transcriptional activity; AROS binding-defective SIRT1 mutants cannot cooperate with AROS to inactivate p53.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylation assay, SIRT1 mutant constructs, antisense knockdown of AROS, cell cycle and apoptosis assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro assay with mutagenesis and functional cellular readouts in a single rigorous study\",\n      \"pmids\": [\"17964266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"E2F1 induces SIRT1 expression at the transcriptional level; SIRT1 in turn binds to E2F1 and inhibits E2F1 transcriptional and apoptotic activities, forming a negative feedback loop that modulates cellular sensitivity to DNA damage.\",\n      \"method\": \"Transcriptional reporter assays, co-immunoprecipitation, siRNA knockdown of SIRT1, etoposide-induced DNA damage assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal regulation demonstrated with multiple orthogonal methods including pulldown, reporter, and functional siRNA experiments\",\n      \"pmids\": [\"16892051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 physically complexes with DNA repair protein Ku70, leading to its deacetylation in a catalytic-activity-dependent manner; SIRT1 overexpression enhances repair of radiation-induced DNA strand breaks, while catalytically inactive SIRT1 fails to do so.\",\n      \"method\": \"Co-immunoprecipitation, SIRT1 overexpression and siRNA knockdown, dominant-negative catalytically inactive SIRT1 mutant, DNA repair assay after radiation\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — catalytic mutant confirms mechanism-dependence; multiple functional readouts\",\n      \"pmids\": [\"17334224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"APE1 is a SIRT1 substrate; SIRT1 associates with APE1 (interaction increased with genotoxic stress), deacetylates APE1 at lysines 6 and 7 in vitro and in vivo, and promotes APE1 binding to XRCC1 and BER activity; SIRT1 knockdown increases cellular abasic DNA content and sensitizes cells to genotoxic stress.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylation assay (SIRT1 + APE1), site identification by mutagenesis, SIRT1 siRNA knockdown, resveratrol/nicotinamide modulation, abasic site assay, XRCC1 binding assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with site-specific mutagenesis and multiple functional readouts\",\n      \"pmids\": [\"19934257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 is phosphorylated in vivo at 13 residues identified by mass spectrometry; dephosphorylation by phosphatases decreases NAD+-dependent deacetylase activity in vitro; CyclinB/Cdk1 forms a complex with and phosphorylates SIRT1 at T530 and S540, and mutation of these residues disturbs normal cell cycle progression and fails to rescue proliferation defects in SIRT1-deficient cells.\",\n      \"method\": \"In vivo mass spectrometry phosphosite identification, in vitro phosphatase assay, in vitro kinase assay with CyclinB/Cdk1, site-directed mutagenesis, cell cycle analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mass spectrometry identification plus in vitro kinase assay and functional mutagenesis\",\n      \"pmids\": [\"19107194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"JNK1 physically interacts with SIRT1 under oxidative stress conditions (co-IP of endogenous proteins) and phosphorylates SIRT1 at Ser27, Ser47, and Thr530, increasing SIRT1 nuclear localization and enzymatic activity; JNK1 phosphorylation of SIRT1 shows substrate selectivity, promoting deacetylation of histone H3 but not p53.\",\n      \"method\": \"Co-immunoprecipitation of endogenous proteins, in vitro kinase assay, nuclear localization assay, SIRT1 enzymatic activity assay, substrate-specific deacetylation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro kinase assay with site mapping and functional activity readouts\",\n      \"pmids\": [\"20027304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Laminar/pulsatile shear stress increases SIRT1 level and activity in endothelial cells; SIRT1 associates with eNOS and promotes eNOS deacetylation, enhancing NO production; AMPK phosphorylation of eNOS is required to prime SIRT1-induced eNOS deacetylation, demonstrated by AMPK inhibitor and eNOS phospho-site mutants; AMPKα2−/− mice show higher eNOS acetylation in vivo.\",\n      \"method\": \"Laminar/oscillatory flow experiments in cultured ECs; co-immunoprecipitation (SIRT1-eNOS); AMPK inhibitor; eNOS phospho-site mutants; in vivo AMPKα2 KO mouse comparison\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, mutagenesis, in vitro and in vivo corroborating evidence\",\n      \"pmids\": [\"20479254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"During senescence and in vivo aging, nuclear SIRT1 protein is recognized as an autophagy substrate, exported to the cytoplasm, and degraded via the autophagosome-lysosome pathway through interaction with LC3; this contributes to SIRT1 protein downregulation in spleen, thymus, hematopoietic stem/progenitor cells in aged mice, and CD8+CD28- T cells from aged humans.\",\n      \"method\": \"Cellular fractionation, autophagy flux assays, LC3 interaction studies, lysosome inhibition, in vivo tissue analysis in aged mice, human aged T cell analysis\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in vitro and in vivo, replicated across tissues and species\",\n      \"pmids\": [\"32989246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIRT1 deacetylates RORγt, the master transcription factor of Th17 cells, increasing RORγt transcriptional activity and enhancing Th17 cell generation and function; T cell-specific Sirt1 deletion and pharmacologic SIRT1 inhibitors suppress Th17 differentiation and are protective in a mouse model of multiple sclerosis.\",\n      \"method\": \"T cell-specific SIRT1 KO mice, pharmacological SIRT1 inhibitors, mixed hematopoietic chimera analysis, deacetylation assay, Th17 differentiation assays, MS mouse model\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with mechanistic substrate identification and in vivo disease model\",\n      \"pmids\": [\"25918343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIRT1 deacetylates the cytoplasmic enzyme AceCS1 (Acetyl-CoA Synthetase 1), paralleling the mitochondrial SIRT3-mediated deacetylation of AceCS2, and also deacetylates HMGCS1 in the cytoplasm, paralleling SIRT3-mediated deacetylation of HMGCS2 in mitochondria.\",\n      \"method\": \"In vitro deacetylation assay, comparison between cytoplasmic SIRT1 and mitochondrial SIRT3 substrate pairs\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay but single lab, limited follow-up mechanistic validation\",\n      \"pmids\": [\"21701047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIRT1 promotes deacetylation and stabilization of mitofusin 1 (MFN1), thereby promoting mitochondrial elongation; TIP60 acetyltransferase acetylates MFN1 reducing its stability, while SIRT1 counteracts TIP60-mediated acetylation; SIRT1 knockdown significantly reduces MFN1 levels and SIRT1 overexpression increases them; this mechanism operates under hypoxic conditions.\",\n      \"method\": \"SIRT1 siRNA and overexpression, TIP60 overexpression, in vitro acetylation assay with TIP60 ± SIRT1, nicotinamide inhibition, MFN1 protein stability assay, mitochondrial morphology analysis\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of acetylation/deacetylation, single lab\",\n      \"pmids\": [\"28669827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HDAC4 enhances endogenous SIRT1 expression by increasing SIRT1 sumoylation, thereby stabilizing SIRT1 protein levels and delaying cellular senescence; HDAC4 overexpression delays senescence while HDAC4 knockdown causes premature senescence in human fibroblasts.\",\n      \"method\": \"HDAC4 overexpression and knockdown, sumoylation assay for SIRT1, SIRT1 protein stability measurement, senescence assays (SA-β-gal)\",\n      \"journal\": \"Clinical and experimental pharmacology & physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — sumoylation assay with functional consequence; single lab\",\n      \"pmids\": [\"26414199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIRT1 regulates FoxO1-dependent transcriptional activity in pancreatic β-cells responding to nitric oxide; SIRT1 inhibition shifts FoxO1-mediated responses from cytoprotective (GADD45α expression/DNA repair) to proapoptotic (PUMA accumulation, caspase-3 cleavage).\",\n      \"method\": \"SIRT1 inhibitors (in β-cells), FoxO1 localization/transcriptional assays, GADD45α and PUMA expression, caspase-3 cleavage, DNA repair assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional readouts with pharmacologic SIRT1 manipulation; single lab\",\n      \"pmids\": [\"21196578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT1 mediates increased mitochondrial oxidative phosphorylation in CML leukemia stem cells (LSCs) via its substrate PGC-1α; genetic deletion of SIRT1 in transgenic CML mice reduces leukemia development and alters mitochondrial function in a kinase-independent manner, while TKI treatment further inhibits CML hematopoiesis in SIRT1-deleted mice.\",\n      \"method\": \"Genetic SIRT1 deletion in transgenic CML mice, mitochondrial respiration assays, PGC-1α substrate analysis, tyrosine kinase inhibitor combination studies\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with defined metabolic phenotype and substrate (PGC-1α) identification\",\n      \"pmids\": [\"31180336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIRT1 activates fetal hemoglobin (HBG) gene expression by binding to the β-globin locus control region (LCR) and HBG promoters, promoting LCR-to-HBG promoter looping, increasing RNA Pol II and H4K16Ac at HBG promoters, and suppressing expression of HBG suppressors BCL11A, KLF1, HDAC1, and HDAC2.\",\n      \"method\": \"SIRT1 knockdown and overexpression in primary erythroid cells, ChIP (SIRT1 binding), chromosome conformation assays (looping), small-molecule SIRT1 activators (SRT2104, SRT1720), gene expression analysis\",\n      \"journal\": \"American journal of hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and looping data plus functional gene expression and pharmacological validation; single lab\",\n      \"pmids\": [\"28776729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT1 destabilizes STAT3 by deacetylating it, leading to STAT3 degradation and reduced transcription of FGB; this SIRT1-STAT3-FGB axis suppresses renal cell carcinoma tumorigenesis in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, luciferase reporter assay (FGB as STAT3 target), SIRT1 overexpression/knockdown, in vitro and in vivo proliferation assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP combined with functional rescue experiments; single lab\",\n      \"pmids\": [\"31201813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"C/EBPα directly binds to a consensus C/EBPα binding site in the SIRT1 promoter and transcriptionally upregulates SIRT1 expression during adipogenesis; C/EBPα knockdown decreases SIRT1 protein levels in preadipocytes.\",\n      \"method\": \"Promoter deletion analysis, gel shift assay (EMSA), chromatin immunoprecipitation (ChIP), C/EBPα overexpression and siRNA knockdown\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple chromatin-level methods (ChIP, EMSA, promoter deletion) in a single lab study\",\n      \"pmids\": [\"20157332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ADNP and SIRT1 interact at two key sites: at the microtubule end-binding proteins EB1/EB3 and at a shared DNA binding motif with YY1 and HDAC2; this ADNP-SIRT1 complex regulates microtubule dynamics and histone methylation in age- and sex-dependent manner, with the interaction disrupted in Alzheimer's and Parkinson's disease brain regions.\",\n      \"method\": \"Co-immunoprecipitation, single-cell RNA/protein analysis, gene expression correlation, postmortem human brain analysis\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single pulldown/co-IP with correlative expression data; limited mechanistic follow-up\",\n      \"pmids\": [\"33967268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Circ-SIRT1 (hsa_circ_0093884) stabilizes SIRT1 mRNA by binding to its 3'-UTR (sponging miR-3681-3p/miR-5195-3p) and stabilizes SIRT1 protein by recruiting USP22 deubiquitinase to promote SIRT1 deubiquitination, thereby promoting cardiomyocyte proliferation and protecting against cardiac hypertrophy.\",\n      \"method\": \"Adenovirus and LNA-mediated gain/loss of circ-SIRT1 function, RNA pulldown, miRNA sponge assay, USP22 co-IP/deubiquitination assay, SIRT1 protein stability assay, in vitro and in vivo cardiac function assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — USP22 deubiquitination assay with functional rescue; single lab, multiple methods\",\n      \"pmids\": [\"34759275\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIRT1 is an NAD+-dependent deacetylase that deacetylates numerous histone and non-histone substrates (including p53, FOXO transcription factors, PGC-1α, LXR, RORγt, eNOS, APE1, Ku70, STAT3, and MFN1) to regulate metabolism, DNA repair, apoptosis, inflammation, and mitochondrial biogenesis; its activity is controlled by substrate availability (NAD+/NADH ratio), direct phosphorylation (by CyclinB/Cdk1 and JNK1), sumoylation (stabilizing), autophagy-mediated protein degradation, and protein–protein interactions with activators (AROS) and upstream regulators (AMPK, E2F1), while its mRNA is post-transcriptionally repressed by miR-34a downstream of p53 in a feedback loop.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"SIRT1 (hSIR2) functions as an NAD-dependent deacetylase that binds p53 and deacetylates it specifically at Lys382, reducing p53 transcriptional activity; a catalytically inactive SIRT1 mutant potentiates p53-dependent apoptosis and radiosensitivity.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, site-specific mutagenesis, overexpression in human cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assay plus mutagenesis plus cellular functional readout, replicated by two independent groups (PMID 11672523 and 11672522)\",\n      \"pmids\": [\"11672523\", \"11672522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Nicotinamide noncompetitively inhibits both yeast Sir2 and human SIRT1 deacetylase activity in vitro (IC50 < 50 µM), acting by binding a conserved pocket adjacent to NAD+ and blocking NAD+ hydrolysis.\",\n      \"method\": \"In vitro deacetylase assay, kinetic analysis, yeast genetic experiments\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with kinetic mechanism and corroborating yeast genetics\",\n      \"pmids\": [\"12297502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Resveratrol activates SIRT1 by lowering its Michaelis constant for both the acetylated substrate and NAD+, and increases cell survival by stimulating SIRT1-dependent deacetylation of p53.\",\n      \"method\": \"In vitro sirtuin activity assay, yeast lifespan assay, cell survival assay with SIRT1 overexpression\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzyme kinetics plus cellular functional validation\",\n      \"pmids\": [\"12939617\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SIRT1 physically interacts with FOXO3 (and FOXO3a) in response to oxidative stress and deacetylates FOXO3 in vitro and in cells; SIRT1 increases FOXO3's ability to induce cell cycle arrest and stress resistance while inhibiting FOXO3's pro-apoptotic activity.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, loss-of-function/gain-of-function in mammalian cells\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution plus cellular epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"14976264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SIRT1 deacetylates and represses the forkhead transcription factor FOXO3a and other mammalian forkhead factors, paralleling its effect on p53, thereby reducing forkhead-dependent apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, transcriptional reporter assay, apoptosis assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro deacetylase assay plus cellular functional readouts, independent corroboration of FOXO regulation\",\n      \"pmids\": [\"14980222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SIRT1 physically interacts with the RelA/p65 subunit of NF-κB and inhibits NF-κB-dependent transcription by deacetylating RelA/p65 at lysine 310, thereby sensitizing cells to TNFα-induced apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation, in vitro deacetylase assay, transcriptional reporter assay\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical and chromatin-based assays with site-specific lysine identification\",\n      \"pmids\": [\"15152190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Caloric restriction induces SIRT1 expression in rat tissues and human cells; SIRT1 deacetylates Ku70, causing it to sequester the pro-apoptotic factor Bax away from mitochondria, thereby inhibiting stress-induced apoptosis.\",\n      \"method\": \"In vitro and in vivo CR experiments, co-immunoprecipitation, subcellular fractionation, apoptosis assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mechanistic substrate identification with functional consequence (Bax sequestration) in multiple models\",\n      \"pmids\": [\"15205477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Sirt1 binds to and represses PPARγ target genes in white adipocytes by docking with co-repressors NCoR and SMRT, promoting fat mobilization; Sirt1+/− mice show compromised fatty acid mobilization upon fasting, and Sirt1 overexpression attenuates adipogenesis.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, siRNA knockdown, Sirt1+/− mouse model, adipogenesis assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including in vivo genetic model\",\n      \"pmids\": [\"15175761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SIRT1 directly interacts with and deacetylates PGC-1α in vitro and in vivo; a single amino acid mutation in SIRT1's ADP-ribosyltransferase domain abolishes the SIRT1–PGC-1α interaction while preserving SIRT1 binding to p53 and Foxo3a.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, NAD-dependent activity assay\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus domain mutagenesis plus in vivo validation\",\n      \"pmids\": [\"15716268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SIRT1 forms a complex with PGC-1α and deacetylates PGC-1α at specific lysine residues in an NAD+-dependent manner in liver during fasting; SIRT1 induces gluconeogenic genes and hepatic glucose output through PGC-1α but does not regulate PGC-1α effects on mitochondrial genes.\",\n      \"method\": \"Co-immunoprecipitation, in vitro NAD+-dependent deacetylase assay, adenoviral overexpression, primary hepatocyte studies\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic reconstitution plus in vivo hepatic genetic experiments\",\n      \"pmids\": [\"15744310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Among the seven human SIRT proteins, SIRT1 is localized in the nucleus, shows in vitro deacetylase activity on histone H4 and p53 peptides, and is the primary deacetylase for cellular p53 (not shared by SIRT2–7); overexpression of any single SIRT does not extend replicative lifespan in normal human fibroblasts.\",\n      \"method\": \"Subcellular fractionation/immunofluorescence, in vitro peptide deacetylase assay, siRNA/overexpression, replicative lifespan assay\",\n      \"journal\": \"Molecular Biology of the Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic comparative biochemical and cellular characterization of all seven human SIRTs\",\n      \"pmids\": [\"16079181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Resveratrol activation of SIRT1 in vitro is entirely dependent on the presence of a covalently attached fluorophore on the substrate peptide; without fluorophore, resveratrol does not activate SIRT1 against native peptides, suggesting allosteric modulation is fluorophore-dependent.\",\n      \"method\": \"In vitro deacetylase assay with fluorophore-labeled and unlabeled peptide substrates, substrate competition studies, structural modeling\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous mechanistic biochemical study with multiple substrate variants\",\n      \"pmids\": [\"15749705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"E2F1 induces SIRT1 expression at the transcriptional level; SIRT1 binds to E2F1 and inhibits E2F1 transcriptional and apoptotic activities, forming a negative feedback loop; SIRT1 knockdown increases E2F1-dependent apoptosis and cellular sensitivity to etoposide.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, reporter assay, apoptosis assay\",\n      \"journal\": \"Nature Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional genetic epistasis with defined apoptotic phenotype\",\n      \"pmids\": [\"16892051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Resveratrol treatment of mice activates SIRT1, decreases PGC-1α acetylation and increases PGC-1α activity, inducing oxidative phosphorylation and mitochondrial biogenesis genes; resveratrol has no effect in SIRT1−/− MEFs, placing SIRT1 upstream of PGC-1α in the pathway.\",\n      \"method\": \"Mouse metabolic phenotyping, gene expression analysis, SIRT1−/− MEFs as genetic control, PGC-1α acetylation assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model plus SIRT1 null epistasis, multiple orthogonal readouts\",\n      \"pmids\": [\"17112576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 interacts with LXRα and LXRβ and promotes their deacetylation at a single conserved lysine (K432 in LXRα, K433 in LXRβ) adjacent to AF2; deacetylation promotes subsequent LXR ubiquitination and upregulation of targets including ABCA1; K432 mutation eliminates LXRα activation by SIRT1.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, in vivo LXR target gene expression\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — site-specific mutagenesis plus in vitro biochemistry plus in vivo validation\",\n      \"pmids\": [\"17936707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"AROS (Active Regulator of SIRT1) is a nuclear protein that directly binds SIRT1 and enhances SIRT1-mediated deacetylation of p53 both in vitro and in vivo; an AROS-binding-defective SIRT1 mutant abolishes AROS-dependent p53 inactivation; AROS knockdown increases p21WAF1 expression and apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, site-directed mutagenesis, antisense knockdown, cell cycle and apoptosis assays\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution plus mutagenesis plus loss-of-function cellular phenotype\",\n      \"pmids\": [\"17964266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 physically complexes with the DNA repair protein Ku70 and deacetylates it; catalytically inactive SIRT1 fails to deacetylate Ku70 or enhance DNA strand-break repair, indicating that SIRT1 deacetylase activity is required for its DNA repair-promoting function.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative SIRT1 mutant, comet assay (DNA repair), acetylation immunoblot\",\n      \"journal\": \"Experimental & Molecular Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus catalytic mutant control plus functional DNA repair assay, single lab\",\n      \"pmids\": [\"17334224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIRT1 is upregulated in mouse models of Alzheimer's disease and ALS; in cell-based models, SIRT1 promotes neuronal survival and reduces acetylation of PGC-1α and p53; lentiviral SIRT1 injection in hippocampus of p25 transgenic mice conferred significant protection against neurodegeneration.\",\n      \"method\": \"In vivo mouse models (p25 transgenic, SOD1 ALS), lentiviral SIRT1 overexpression, acetylation immunoblot, neuronal survival assay\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo gain-of-function with defined mechanistic substrate (PGC-1α, p53 deacetylation) and neuropathological phenotype\",\n      \"pmids\": [\"17581637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"miR-34a inhibits SIRT1 expression through a miR-34a binding site in the 3' UTR of SIRT1; miR-34a suppression of SIRT1 increases acetylated p53, upregulates p21 and PUMA, and leads to apoptosis in p53-WT colon cancer cells but not in p53-null cells, establishing a p53→miR-34a→SIRT1→p53 positive feedback loop.\",\n      \"method\": \"3' UTR reporter assay, siRNA/miRNA overexpression, acetylation immunoblot, apoptosis assay in p53-WT vs. p53-null cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — 3' UTR functional assay plus genetic epistasis (p53 null cells) plus multiple downstream readouts\",\n      \"pmids\": [\"18755897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 has a role in neurogenesis: oxidative stress and inflammation bias neuronal stem cell differentiation toward astrocytes by modulating Sirt1 activity, linking a longevity gene to neuronal stem cell fate decisions.\",\n      \"method\": \"Neuronal stem cell differentiation assay with SIRT1 modulation\",\n      \"journal\": \"Nature Cell Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined cellular phenotype (stem cell fate) with SIRT1 loss/gain of function, single study\",\n      \"pmids\": [\"18379594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 regulates autophagy: transient SIRT1 overexpression stimulates basal autophagy; SIRT1−/− MEFs fail to fully activate autophagy under starvation; wild-type but not deacetylase-inactive SIRT1 restores autophagy; SIRT1 forms a molecular complex with Atg5, Atg7, and Atg8 and directly deacetylates them in an NAD-dependent fashion in vitro.\",\n      \"method\": \"SIRT1 KO MEFs, reconstitution with WT vs. catalytic mutant SIRT1, co-immunoprecipitation with autophagy proteins, in vitro deacetylase assay, autophagy flux assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution with catalytic mutant plus genetic KO epistasis plus in vitro substrate deacetylation\",\n      \"pmids\": [\"18296641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 is an NAD+-dependent HDAC that associates with the CLOCK:BMAL1 chromatin complex at circadian promoters; genetic ablation or pharmacological inhibition of SIRT1 disrupts circadian transcription and acetylation of H3 and BMAL1; SIRT1 promotes deacetylation and degradation of PER2, connecting cellular NAD+ metabolism to the circadian clock.\",\n      \"method\": \"ChIP, SIRT1 KO cells/liver-specific mutant mice, pharmacological inhibition, PER2 acetylation and stability assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP, genetic KO, and biochemical assays in two independent studies (PMID 18662547 and 18662546)\",\n      \"pmids\": [\"18662547\", \"18662546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 associates with the CLOCK:BMAL1 complex and is recruited to circadian promoters; it is required for high-magnitude circadian transcription of Bmal1, Rorgamma, Per2, and Cry1; SIRT1 promotes deacetylation and degradation of PER2, with NAD+ dependence linking cellular metabolism to clockwork.\",\n      \"method\": \"ChIP, SIRT1 KO cells, pharmacological inhibition, PER2 deacetylation assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP plus genetic KO plus biochemical substrate identification\",\n      \"pmids\": [\"18662546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIRT1 phosphorylation by cyclin B/Cdk1 at Thr530 and Ser540 is required for normal cell cycle progression; dephosphorylation of SIRT1 by phosphatases reduces its NAD+-dependent deacetylase activity; 13 in vivo phosphorylation sites on SIRT1 were identified by mass spectrometry.\",\n      \"method\": \"Mass spectrometry phosphosite mapping, in vitro phosphatase assay, cyclin B/Cdk1 kinase assay, cell cycle analysis with phospho-site mutants\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro kinase assay plus phospho-site mutagenesis plus cell cycle phenotype\",\n      \"pmids\": [\"19107194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Sirt1 deficiency in mice markedly attenuates spermatogenesis: numbers of mature sperm and spermatogenic precursors are significantly reduced, DNA damage in sperm is elevated, and genes involved in spermatogenesis and protein sumoylation are dysregulated; Sirt1-deficient sperm show reduced fertilization efficiency.\",\n      \"method\": \"Sirt1 KO mouse model, sperm counting, TUNEL assay, microarray gene expression, in vitro fertilization\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined spermatogenic phenotype and molecular readouts, single lab\",\n      \"pmids\": [\"18270565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"AMPK enhances SIRT1 activity by increasing cellular NAD+ levels (not by direct phosphorylation), resulting in deacetylation of SIRT1 targets PGC-1α, FOXO1, and FOXO3a in mouse skeletal muscle; this NAD+-mediated AMPK–SIRT1 axis explains convergent metabolic effects of both kinases.\",\n      \"method\": \"Skeletal muscle gene expression, NAD+ measurement, deacetylation assays, pharmacological and genetic AMPK manipulation\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and cell-based experiments with multiple substrates and NAD+ mechanistic link, highly cited\",\n      \"pmids\": [\"19262508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"JNK1 phosphorylates SIRT1 at Ser27, Ser47, and Thr530 under oxidative stress conditions; this phosphorylation increases SIRT1 nuclear localization and enzymatic activity; notably, JNK1-phosphorylated SIRT1 shows substrate specificity: it deacetylates histone H3 but not p53.\",\n      \"method\": \"Co-immunoprecipitation of endogenous proteins, in vitro kinase assay, phospho-site mutagenesis, deacetylase activity assay, nuclear localization imaging\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro kinase reconstitution plus cellular functional readout, single lab\",\n      \"pmids\": [\"20027304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SIRT1 associates with APE1 (apurinic/apyrimidinic endonuclease-1), deacetylates APE1 at lysines 6 and 7 in vitro and in vivo; SIRT1 knockdown increases cellular abasic DNA content and sensitizes cells to genotoxic death; SIRT1 activation promotes APE1 binding to XRCC1 and enhances BER pathway activity.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, siRNA knockdown, abasic site quantification, BER activity assay\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution plus cellular epistasis, single lab\",\n      \"pmids\": [\"19934257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Hepatocyte-specific SIRT1 deletion impairs PPARα signaling and fatty acid β-oxidation; SIRT1 interacts with PPARα and is required for PGC-1α coactivation of PPARα; liver-specific SIRT1 KO mice on high-fat diet develop hepatic steatosis, inflammation, and ER stress.\",\n      \"method\": \"Hepatocyte-specific Cre-lox SIRT1 KO mice, co-immunoprecipitation, gene expression, adenoviral SIRT1 overexpression, histopathology\",\n      \"journal\": \"Cell Metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific KO with clear metabolic phenotype plus molecular interaction data\",\n      \"pmids\": [\"19356714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Laminar shear stress increases SIRT1 level and activity in endothelial cells; SIRT1 associates with eNOS and deacetylates it; AMPK-mediated phosphorylation of eNOS at Ser-633/1177 is required to prime SIRT1-induced eNOS deacetylation, enhancing NO production; AMPKα2−/− mice show increased eNOS acetylation in aorta.\",\n      \"method\": \"Co-immunoprecipitation, eNOS acetylation assay, AMPK inhibitor/eNOS phospho-site mutants, AMPKα2 KO mice, flow experiments\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic epistasis (AMPK→eNOS phospho→SIRT1 deacetylation) validated in vivo with KO mice\",\n      \"pmids\": [\"20479254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SIRT1 is essential for normal cognitive function and synaptic plasticity: SIRT1 KO mice show impaired learning, memory, classical conditioning, and spatial learning; these deficits correlate with defects in synaptic plasticity, decreased dendritic branching, reduced ERK1/2 phosphorylation, and altered expression of hippocampal genes involved in synaptic function, lipid metabolism, and myelination.\",\n      \"method\": \"SIRT1 KO mouse model, behavioral paradigms (fear conditioning, Morris water maze), LTP electrophysiology, Golgi staining of dendrites, gene expression\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple behavioral, electrophysiological, and molecular phenotypes\",\n      \"pmids\": [\"20660252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIRT1 deacetylates FOXO1 in pancreatic β-cells; SIRT1 activity determines whether FoxO1 drives a protective (GADD45α-mediated DNA repair) or proapoptotic (PUMA induction, caspase-3 cleavage) response to nitric oxide; SIRT1 inhibitors switch FoxO1-dependent protection to apoptosis.\",\n      \"method\": \"SIRT1 pharmacological inhibition, FoxO1 localization (nuclear translocation imaging), GADD45α/PUMA expression assay, caspase-3 assay in β-cells\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway placement with defined substrate (FoxO1) and opposing functional outcomes, single lab\",\n      \"pmids\": [\"21196578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIRT1 and SIRT3 deacetylate homologous substrates in their respective compartments: SIRT1 deacetylates AceCS1 and HMGCS1 in the cytoplasm, while SIRT3 deacetylates AceCS2 and HMGCS2 in mitochondria, revealing a pattern of substrate homology between cytoplasmic SIRT1 and mitochondrial SIRT3.\",\n      \"method\": \"In vitro deacetylase assay, phylogenetic analysis, fractionation\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution, single study\",\n      \"pmids\": [\"21701047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIRT1 deacetylates RORγt, the master transcription factor of Th17 cells, increasing RORγt transcriptional activity and enhancing Th17 cell generation; T cell-specific Sirt1 deletion suppresses Th17 differentiation and is protective in a mouse model of multiple sclerosis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deacetylase assay, T cell-specific Sirt1 KO mice, Th17 differentiation assay, EAE mouse model, hematopoietic chimera analysis\",\n      \"journal\": \"The Journal of Experimental Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical substrate identification plus conditional KO in vivo disease model plus mixed chimera epistasis\",\n      \"pmids\": [\"25918343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIRT1 stabilizes mitofusin 1 (MFN1) by deacetylating it; TIP60 acetyltransferase promotes MFN1 degradation, while SIRT1 deacetylase counteracts this; SIRT1 knockdown reduces MFN1 levels and mitochondrial elongation, while SIRT1 overexpression increases MFN1; under hypoxia, SIRT1 and MFN1 accumulate and mitochondria elongate.\",\n      \"method\": \"siRNA knockdown, SIRT1 overexpression, in vitro acetylation assay with TIP60 and SIRT1, immunoprecipitation, mitochondrial morphology imaging\",\n      \"journal\": \"Cellular Signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro biochemical reconstitution plus cellular morphology phenotype, single lab\",\n      \"pmids\": [\"28669827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HDAC4 stabilizes SIRT1 protein by enhancing its sumoylation, thereby increasing SIRT1 protein levels and delaying cellular senescence; HDAC4 knockdown leads to premature senescence in human fibroblasts.\",\n      \"method\": \"Co-immunoprecipitation, sumoylation assay, HDAC4 overexpression/knockdown, senescence assay (SA-β-gal)\",\n      \"journal\": \"Clinical and Experimental Pharmacology & Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — interaction and PTM data plus defined senescence phenotype, single lab\",\n      \"pmids\": [\"26414199\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIRT1 activates fetal hemoglobin (γ-globin/HBG) gene expression by binding to the β-globin LCR and HBG promoters, promoting LCR-to-HBG promoter looping, increasing RNA Pol II and H4K16Ac at HBG promoter, and suppressing BCL11A, KLF1, HDAC1, and HDAC2 expression; small molecule SIRT1 activators SRT2104 and SRT1720 reactivate silenced HBG in adult erythroblasts.\",\n      \"method\": \"ChIP, chromosome conformation capture (looping assay), SIRT1 knockdown/overexpression, small molecule activators in primary human erythroblasts\",\n      \"journal\": \"American Journal of Hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and looping assay plus pharmacological activation in primary cells, single lab\",\n      \"pmids\": [\"28776729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SIRT1 represses NF-κB-driven transcription of the AIM2 gene in cervical cancer cells by destabilizing RELB mRNA; SIRT1 knockdown derepresses AIM2 inflammasome-mediated pyroptosis, demonstrating a pro-tumorigenic role of SIRT1 through innate immune suppression.\",\n      \"method\": \"SIRT1 siRNA knockdown, SIRT1 restoration, AIM2 promoter/NF-κB reporter assay, RELB mRNA stability assay, pyroptosis assay, xenograft model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway (SIRT1→RELB→AIM2) with multiple functional assays, single lab\",\n      \"pmids\": [\"29844574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT1 mediates increased mitochondrial oxidative phosphorylation in CML leukemia stem cells (LSCs) via deacetylation of PGC-1α; genetic SIRT1 deletion in transgenic CML mice reduces LSC maintenance and enhances tyrosine kinase inhibitor efficacy; mitochondrial alterations are BCR-ABL kinase-independent.\",\n      \"method\": \"Conditional SIRT1 KO in CML transgenic mice, Seahorse metabolic profiling, PGC-1α acetylation assay, LSC functional assays\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo conditional KO with defined metabolic mechanism (PGC-1α deacetylation) and LSC phenotype\",\n      \"pmids\": [\"31180336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT1 deacetylates STAT3, leading to STAT3 destabilization and degradation, thereby repressing FGB (fibrinogen beta chain) expression and inhibiting RCC tumor growth; overexpression of SIRT1 suppresses RCC proliferation in vitro and in vivo through this SIRT1-STAT3-FGB axis.\",\n      \"method\": \"Co-immunoprecipitation, STAT3 acetylation/ubiquitination assay, SIRT1 overexpression, luciferase reporter (FGB as STAT3 target), in vivo xenograft\",\n      \"journal\": \"Experimental Cell Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic substrate identification with in vitro and in vivo functional readout, single lab\",\n      \"pmids\": [\"31201813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT1 protects hypoxic cardiomyocytes via two pathways: (1) promoting autophagic flux through AMPK activation (blocked by compound C), and (2) reducing apoptosis through IRE1α pathway inhibition.\",\n      \"method\": \"Adenoviral SIRT1 overexpression/knockdown in H9C2 cells, pharmacological activator/inhibitor (SRT1720/EX-527), AMPK inhibitor (compound C), apoptosis assay (TUNEL, Annexin V), autophagic flux assay, in vivo hypoxic mouse model\",\n      \"journal\": \"International Journal of Molecular Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — dual pathway placement with pharmacological epistasis in vitro and in vivo, single lab\",\n      \"pmids\": [\"30864731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Macroautophagy mediates SIRT1 protein downregulation during senescence and ageing: nuclear SIRT1 is recognized as an autophagy substrate via the autophagy protein LC3, and is subjected to cytoplasmic autophagosome-lysosome degradation; this mechanism operates in multiple immune tissues in aged mice and in aged human CD8+CD28− T cells.\",\n      \"method\": \"Autophagy pathway inhibitors, LC3 interaction assay, subcellular fractionation, aged mouse tissue analysis, human T cell aging model\",\n      \"journal\": \"Nature Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic substrate identification (SIRT1 as LC3 cargo) replicated across multiple in vivo tissues and species\",\n      \"pmids\": [\"32989246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ADNP and SIRT1 form a protein complex with two key interaction sites: one at the microtubule end-binding proteins EB1/EB3 and Tau level, and one at the DNA/chromatin site involving YY1, HDAC2, with sex- and age-dependent regulation of histone modifications; ADNP-SIRT1-EB1 correlation is specifically abolished in Alzheimer's and Parkinson's disease brain regions.\",\n      \"method\": \"Co-immunoprecipitation, single-cell RNA/protein expression, gene expression correlation analysis, postmortem brain tissue analysis\",\n      \"journal\": \"Molecular Psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP interaction plus correlational expression data; mechanistic follow-up partial\",\n      \"pmids\": [\"33967268\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIRT1 is a nuclear, NAD+-dependent class III protein deacetylase that regulates a broad array of cellular processes by deacetylating histone (H3K9/K14, H4K16, BMAL1) and non-histone substrates (p53 at K382, FOXO1/3/4, NF-κB RelA/p65 at K310, PGC-1α, PPARα, LXRα/β at K432/433, RORγt, Ku70, APE1, Atg5/7/8, eNOS, STAT3, MFN1), whose activity is regulated by NAD+ availability, post-translational modifications (phosphorylation by cyclin B/Cdk1 and JNK1; sumoylation by HDAC4), protein interactions (AROS activates; DBC1 inhibits), miRNA-mediated repression (e.g., miR-34a targeting the 3' UTR), and autophagic degradation via LC3 during senescence; upstream, AMPK enhances SIRT1 activity by elevating cellular NAD+ levels, while SIRT1-mediated deacetylation of PGC-1α, FOXO factors, and NF-κB connects caloric sensing to metabolic reprogramming, stress resistance, circadian clock control, autophagy, DNA repair, immune regulation, and suppression of apoptosis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SIRT1 is an NAD+-dependent protein deacetylase that serves as a central integrator of metabolic, stress, and inflammatory signaling by deacetylating a broad array of histone and non-histone substrates. It deacetylates p53, FOXO1/3a, PGC-1α, LXR, RORγt, eNOS, STAT3, Ku70, APE1, and MFN1, thereby coordinating transcription, DNA base-excision and double-strand break repair, mitochondrial biogenesis and dynamics, cholesterol efflux, Th17 differentiation, and endothelial nitric oxide production [PMID:17936707, PMID:19934257, PMID:17334224, PMID:25918343, PMID:20479254, PMID:28669827]. SIRT1 enzymatic activity is tuned by intracellular NAD+ levels (coupled to AMPK), stimulatory phosphorylation by CyclinB/Cdk1 and JNK1, the co-activator AROS, sumoylation-dependent protein stabilization, and autophagy-mediated degradation during senescence and aging [PMID:19262508, PMID:19107194, PMID:20027304, PMID:17964266, PMID:26414199, PMID:32989246]. Its expression is transcriptionally induced by E2F1 and C/EBPα and post-transcriptionally repressed by miR-34a in a p53-dependent positive-feedback loop that links SIRT1 loss to apoptosis [PMID:16892051, PMID:20157332, PMID:18755897].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing that SIRT1 participates in a transcriptional feedback loop with E2F1 answered how SIRT1 expression is coupled to the DNA-damage response and revealed that SIRT1 can directly inhibit a transcription factor that drives its own expression.\",\n      \"evidence\": \"Transcriptional reporter assays, co-immunoprecipitation, and siRNA knockdown after etoposide treatment in human cells\",\n      \"pmids\": [\"16892051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether E2F1 is directly deacetylated by SIRT1 or inhibited through another mechanism was not resolved\", \"Relative contribution of E2F1 vs. other transcription factors to SIRT1 induction in non-cancer cells is unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of LXR, Ku70, and the co-activator AROS as SIRT1 partners broadened the enzyme's substrate repertoire from p53/FOXOs to cholesterol metabolism (LXR-ABCA1 axis) and DNA double-strand break repair (Ku70), and revealed that an accessory protein (AROS) can allosterically enhance SIRT1 catalytic activity toward p53.\",\n      \"evidence\": \"In vitro deacetylation assays with site-directed mutagenesis (LXR K432, Ku70), co-IP, catalytically inactive SIRT1 mutant, AROS binding-defective SIRT1 mutants, radiation-induced DNA repair assays\",\n      \"pmids\": [\"17936707\", \"17334224\", \"17964266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of AROS–SIRT1 interaction unknown\", \"Whether SIRT1-Ku70 deacetylation affects NHEJ fidelity versus efficiency was not distinguished\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that miR-34a post-transcriptionally represses SIRT1 downstream of p53 established a positive-feedback loop (p53→miR-34a⊣SIRT1⊣p53) explaining how p53 activation can be amplified through SIRT1 downregulation, and that CyclinB/Cdk1 phosphorylation at T530/S540 is required for SIRT1's cell-cycle functions showed the first direct link between cell-cycle kinases and sirtuin activity.\",\n      \"evidence\": \"3′-UTR reporter assays, miR-34a overexpression/inhibition in p53-WT and null cells; mass spectrometry phosphosite mapping, in vitro CyclinB/Cdk1 kinase assay, phospho-site mutagenesis with cell-cycle rescue\",\n      \"pmids\": [\"18755897\", \"19107194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contribution of individual phosphosites beyond T530/S540 to SIRT1 activity was not dissected\", \"Whether miR-34a-SIRT1 axis operates equivalently in non-epithelial tissues was not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that AMPK increases SIRT1 activity by raising NAD+ levels, JNK1 phosphorylates SIRT1 under oxidative stress with substrate-selective consequences, and APE1 is a direct SIRT1 substrate in base-excision repair collectively established SIRT1 as a stress-responsive enzyme whose substrate selectivity is modulated by upstream kinases and metabolic state.\",\n      \"evidence\": \"AMPK genetic/pharmacological manipulation with NAD+ measurement in mouse skeletal muscle; endogenous co-IP and in vitro JNK1 kinase assay with substrate-selective deacetylation readouts; in vitro APE1 deacetylation at K6/K7 with mutagenesis and abasic-site quantification\",\n      \"pmids\": [\"19262508\", \"20027304\", \"19934257\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How JNK1 phosphorylation alters SIRT1 substrate selectivity at the structural level is unknown\", \"Relative contribution of SIRT1-APE1 axis vs. other BER regulators in vivo is not quantified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showing that SIRT1 deacetylates eNOS downstream of AMPK-mediated priming phosphorylation under shear stress placed SIRT1 at the intersection of mechanotransduction and vascular NO production, while identification of C/EBPα as a transcriptional activator of the SIRT1 promoter extended understanding of tissue-specific SIRT1 expression control during adipogenesis.\",\n      \"evidence\": \"Co-IP of SIRT1–eNOS in endothelial cells, AMPK inhibitor and eNOS phospho-mutants, AMPKα2 KO mice; ChIP and EMSA on SIRT1 promoter with C/EBPα in preadipocytes\",\n      \"pmids\": [\"20479254\", \"20157332\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIRT1-eNOS axis contributes to atheroprotection independently of other SIRT1 substrates in vivo is unresolved\", \"Tissue-specific combinatorial transcriptional regulation of SIRT1 beyond E2F1 and C/EBPα is incomplete\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extension of SIRT1 substrates to cytoplasmic metabolic enzymes (AceCS1, HMGCS1) and demonstration that SIRT1 modulates the cytoprotective vs. proapoptotic balance of FoxO1 in pancreatic β-cells clarified compartment-specific metabolic roles and substrate-specific functional outcomes.\",\n      \"evidence\": \"In vitro deacetylation of AceCS1/HMGCS1 comparing SIRT1 and SIRT3; pharmacological SIRT1 inhibition in β-cells with GADD45α/PUMA/caspase-3 readouts\",\n      \"pmids\": [\"21701047\", \"21196578\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo physiological relevance of SIRT1-AceCS1 deacetylation vs. SIRT3 pathway not established\", \"How SIRT1 directs FoxO1 toward survival vs. death gene programs at the molecular level is not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of RORγt as a SIRT1 substrate in Th17 cells, where deacetylation enhances RORγt activity and Th17 differentiation, revealed an unexpected pro-inflammatory role for SIRT1 and showed that T cell-specific Sirt1 deletion protects against autoimmune neuroinflammation.\",\n      \"evidence\": \"T cell-specific SIRT1 KO mice, SIRT1 inhibitors, Th17 differentiation assays, EAE mouse model\",\n      \"pmids\": [\"25918343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIRT1 deacetylates other Th17-specific transcription factors besides RORγt is unknown\", \"Acetylation site(s) on RORγt targeted by SIRT1 were not mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing that HDAC4 stabilizes SIRT1 protein through enhanced sumoylation, delaying cellular senescence, added post-translational modification cross-talk (sumoylation) to the network regulating SIRT1 protein turnover.\",\n      \"evidence\": \"HDAC4 overexpression/knockdown, sumoylation and protein stability assays, SA-β-gal senescence assays in human fibroblasts\",\n      \"pmids\": [\"26414199\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The specific SUMO sites on SIRT1 stabilized by HDAC4 were not mapped\", \"Whether HDAC4 acts on a SUMO E3 ligase or directly on SIRT1 is unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that SIRT1 deacetylates MFN1 to promote mitochondrial elongation under hypoxia, and that SIRT1 binds the β-globin LCR to activate fetal hemoglobin expression via chromatin looping, expanded SIRT1 functions to mitochondrial dynamics and erythroid gene regulation.\",\n      \"evidence\": \"In vitro TIP60/SIRT1 acetylation–deacetylation assay on MFN1 with morphology readout; ChIP and chromosome conformation capture at the β-globin locus in primary erythroid cells with SIRT1 activators\",\n      \"pmids\": [\"28669827\", \"28776729\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acetylation site(s) on MFN1 targeted by SIRT1 were not identified\", \"Whether SIRT1 binding at the LCR is direct or complex-mediated is uncertain\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of STAT3 as a deacetylation target linking SIRT1 to STAT3 degradation and FGB transcription, and demonstration that SIRT1 deletion impairs leukemia stem cell mitochondrial metabolism via PGC-1α, extended SIRT1 roles to cancer-specific metabolic dependencies.\",\n      \"evidence\": \"Co-IP and STAT3 degradation assays in renal cell carcinoma; genetic SIRT1 deletion in transgenic CML mice with mitochondrial respiration assays\",\n      \"pmids\": [\"31201813\", \"31180336\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific acetyl-lysine(s) on STAT3 deacetylated by SIRT1 were not mapped\", \"Whether SIRT1-PGC-1α dependency is shared across leukemia subtypes is unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstration that SIRT1 is selectively exported from the nucleus and degraded via autophagy during senescence and aging, through direct LC3 interaction, revealed a mechanism for age-dependent SIRT1 loss that is distinct from transcriptional or miRNA-mediated downregulation.\",\n      \"evidence\": \"Cellular fractionation, autophagy flux assays, LC3 interaction studies, lysosome inhibition in cultured cells; validation in aged mouse tissues and human aged CD8+CD28- T cells\",\n      \"pmids\": [\"32989246\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The LC3-interacting region (LIR) on SIRT1 was not precisely mapped\", \"Whether pharmacological autophagy inhibition can restore SIRT1 levels and function in aged tissues is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive structural model of how post-translational modifications (phosphorylation, sumoylation, ubiquitination) and protein partners (AROS, ADNP) converge to determine SIRT1 substrate selectivity in a context-dependent manner remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of full-length SIRT1 in complex with a regulatory partner exists\", \"How JNK1 phosphorylation confers substrate selectivity (H3 but not p53) at the structural level is unknown\", \"Relative contributions of autophagy vs. miR-34a vs. proteasomal pathways to SIRT1 turnover in specific tissues and aging contexts are not quantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 3, 5, 6, 8, 9, 11, 13, 18]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4, 17]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 8, 10, 17]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [10, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [8, 17]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [1, 15]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 17]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FOXO1\",\n      \"PGC1A\",\n      \"LXR\",\n      \"XRCC5\",\n      \"APEX1\",\n      \"NOS3\",\n      \"AROS\",\n      \"RORC\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SIRT1 is a nuclear NAD⁺-dependent class III protein deacetylase that couples cellular metabolic state to chromatin remodeling, transcription factor activity, DNA repair, autophagy, and circadian clock function by deacetylating both histone (H3, H4K16) and non-histone substrates. Key non-histone substrates include p53 (K382), FOXO1/3a, NF-κB RelA/p65 (K310), PGC-1α, PPARα, LXRα/β (K432/K433), RORγt, Ku70, APE1, Atg5/7/8, eNOS, STAT3, and MFN1, through which SIRT1 regulates apoptosis, gluconeogenesis, fatty acid oxidation, mitochondrial biogenesis, inflammation, Th17 differentiation, base excision repair, and autophagy [PMID:11672523, PMID:14976264, PMID:15152190, PMID:15744310, PMID:18296641, PMID:25918343, PMID:18662547]. SIRT1 enzymatic activity is controlled by NAD⁺ availability (indirectly regulated by AMPK), phosphorylation by cyclin B/Cdk1 and JNK1, sumoylation promoted by HDAC4, binding of the activator AROS and the inhibitor DBC1, and transcriptional/post-transcriptional regulation including miR-34a-mediated repression and autophagic degradation via LC3 during senescence [PMID:19262508, PMID:19107194, PMID:17964266, PMID:18755897, PMID:32989246]. SIRT1 associates with the CLOCK:BMAL1 complex at circadian promoters, deacetylates BMAL1 and PER2, and is essential for high-amplitude circadian transcription, thereby linking NAD⁺ metabolism to the molecular clock [PMID:18662547, PMID:18662546].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"The identification of SIRT1 as an NAD-dependent deacetylase that targets p53 at K382 established its enzymatic mechanism and linked it to apoptosis regulation, answering whether the yeast Sir2 longevity mechanism was conserved in mammals.\",\n      \"evidence\": \"In vitro deacetylase assay, co-IP, catalytic mutant analysis in human cells by two independent groups\",\n      \"pmids\": [\"11672523\", \"11672522\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of SIRT1–p53 complex not yet resolved\", \"Physiological context of p53 deacetylation in vivo not addressed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstration that nicotinamide noncompetitively inhibits SIRT1 by blocking NAD⁺ hydrolysis established the first mechanistic model for endogenous feedback regulation of SIRT1 catalytic activity.\",\n      \"evidence\": \"Kinetic analysis of recombinant SIRT1 with corroborating yeast genetics\",\n      \"pmids\": [\"12297502\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of nicotinamide concentrations for SIRT1 inhibition not established\", \"Structural basis of nicotinamide binding pocket not resolved at that time\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Rapid expansion of the SIRT1 substrate repertoire to include FOXO3a, NF-κB RelA/p65, and Ku70 revealed that SIRT1 is not merely a p53 deacetylase but a broad stress-responsive signaling node controlling apoptosis, inflammation, and DNA damage responses.\",\n      \"evidence\": \"In vitro deacetylase assays, co-IPs, ChIP, functional apoptosis/reporter assays, caloric restriction models across multiple labs\",\n      \"pmids\": [\"14976264\", \"14980222\", \"15152190\", \"15205477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate selectivity determinants unknown\", \"How SIRT1 discriminates among competing substrates in vivo not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery that SIRT1 represses PPARγ target genes in adipocytes via NCoR/SMRT recruitment, and that Sirt1 haploinsufficient mice have defective fat mobilization, established SIRT1 as a transcriptional co-repressor in metabolic regulation.\",\n      \"evidence\": \"ChIP, siRNA knockdown, Sirt1⁺/⁻ mouse fasting experiments, adipogenesis assay\",\n      \"pmids\": [\"15175761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full spectrum of SIRT1-regulated metabolic genes in adipose not mapped\", \"Whether SIRT1 deacetylates PPARγ directly was not shown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of PGC-1α as a direct SIRT1 substrate with site-specific deacetylation connected SIRT1 to hepatic gluconeogenesis and mitochondrial gene regulation, answering how caloric restriction signals converge on metabolic gene expression.\",\n      \"evidence\": \"In vitro deacetylase assay, domain mutagenesis, primary hepatocyte and fasting liver experiments\",\n      \"pmids\": [\"15716268\", \"15744310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific lysine residues on PGC-1α targeted by SIRT1 not fully mapped\", \"Relative contributions of SIRT1 vs. other deacetylases to PGC-1α regulation in different tissues unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The finding that resveratrol activation of SIRT1 was fluorophore-dependent challenged the direct activator model and raised questions about the physiological relevance of small-molecule SIRT1 activation.\",\n      \"evidence\": \"Systematic comparison of fluorophore-labeled vs. unlabeled peptide substrates in in vitro deacetylase assays\",\n      \"pmids\": [\"15749705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether resveratrol activates SIRT1 on full-length protein substrates remained debated\", \"In vivo mechanism of resveratrol-SIRT1 axis not fully reconciled\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery of AROS as a direct SIRT1 activator and identification of LXRα/β as SIRT1 substrates at defined lysines expanded understanding of SIRT1 regulation and placed it in cholesterol/lipid homeostasis.\",\n      \"evidence\": \"Co-IP, in vitro deacetylase assay, AROS-binding-defective SIRT1 mutant, LXR K432 mutagenesis, in vivo target gene expression\",\n      \"pmids\": [\"17964266\", \"17936707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of AROS vs. DBC1 in different tissues not determined\", \"Full physiological impact of SIRT1-LXR axis on reverse cholesterol transport not assessed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Three major biological roles were simultaneously established: SIRT1 promotes autophagy by deacetylating Atg5/7/8, entrains the circadian clock via the CLOCK:BMAL1 complex and PER2 deacetylation, and is subject to miR-34a-mediated post-transcriptional repression creating a p53–miR-34a–SIRT1 feedback loop.\",\n      \"evidence\": \"SIRT1 KO MEFs with reconstitution, ChIP at circadian promoters, liver-specific KO mice, 3′ UTR reporter assay, genetic epistasis in p53-null cells\",\n      \"pmids\": [\"18296641\", \"18662547\", \"18662546\", \"18755897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance of SIRT1 autophagy regulation vs. other autophagy deacetylases unclear\", \"Whether SIRT1 circadian role is secondary to NAMPT/NAD⁺ oscillations not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mapping of 13 in vivo phosphorylation sites on SIRT1 and demonstration that cyclin B/Cdk1-mediated phosphorylation at T530/S540 is required for cell cycle progression established post-translational regulation as a key layer of SIRT1 control.\",\n      \"evidence\": \"Mass spectrometry, in vitro Cdk1 kinase assay, phosphosite mutant cell cycle analysis\",\n      \"pmids\": [\"19107194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of most of the 13 phosphosites not individually characterized\", \"Phosphatase(s) responsible for SIRT1 dephosphorylation not identified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The finding that AMPK enhances SIRT1 activity by raising cellular NAD⁺ rather than by direct phosphorylation provided the mechanistic basis for metabolic convergence of AMPK and SIRT1 signaling on PGC-1α and FOXO targets.\",\n      \"evidence\": \"NAD⁺ measurements, deacetylation assays, pharmacological and genetic AMPK manipulation in skeletal muscle\",\n      \"pmids\": [\"19262508\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AMPK–NAD⁺–SIRT1 axis operates identically across all tissues not established\", \"Quantitative relationship between NAD⁺ fluctuations and SIRT1 activity thresholds unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Hepatocyte-specific SIRT1 deletion causing steatosis, inflammation, and ER stress under high-fat diet demonstrated that SIRT1-PPARα-PGC-1α cooperation is essential for hepatic lipid homeostasis in vivo.\",\n      \"evidence\": \"Liver-specific Cre-lox SIRT1 KO mice, co-IP of SIRT1-PPARα, gene expression, histopathology\",\n      \"pmids\": [\"19356714\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIRT1 directly deacetylates PPARα or acts solely as a PGC-1α co-regulator not fully resolved\", \"Contribution of hepatic SIRT1 loss to systemic metabolic phenotypes not fully dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstration that SIRT1 deacetylates eNOS downstream of AMPK-mediated phosphorylation, and that SIRT1 KO mice show impaired cognition and synaptic plasticity, extended SIRT1 functions to vascular biology and neuronal physiology.\",\n      \"evidence\": \"Co-IP, eNOS acetylation assay with AMPKα2 KO mice, SIRT1 KO mouse behavioral and electrophysiological analysis\",\n      \"pmids\": [\"20479254\", \"20660252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct neuronal substrates mediating synaptic plasticity defects not identified\", \"Whether eNOS deacetylation is the primary mechanism of SIRT1 vascular protection not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of RORγt as a SIRT1 deacetylation substrate that enhances Th17 differentiation resolved how SIRT1 participates in adaptive immune regulation, with conditional T cell KO suppressing autoimmune disease.\",\n      \"evidence\": \"Co-IP, in vitro deacetylase assay, T cell-specific Sirt1 KO mice, EAE model, hematopoietic chimeras\",\n      \"pmids\": [\"25918343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIRT1-RORγt axis operates in human Th17 biology not directly shown\", \"Mechanism by which deacetylation increases RORγt activity not structurally resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Discovery that SIRT1 is itself degraded by macroautophagy via LC3 recognition during senescence and aging revealed a self-limiting feedback mechanism explaining age-dependent SIRT1 decline.\",\n      \"evidence\": \"Autophagy inhibitors, LC3 interaction assay, subcellular fractionation, aged mouse tissues, human CD8⁺CD28⁻ T cells\",\n      \"pmids\": [\"32989246\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific LC3-interacting region (LIR motif) on SIRT1 not mapped\", \"Whether pharmacological autophagy inhibition can restore SIRT1 levels and reverse aging phenotypes not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A unified structural and quantitative model integrating how SIRT1 discriminates among its >20 known substrates in different cellular contexts, and how its multiple post-translational modifications (phosphorylation, sumoylation) combinatorially tune substrate selectivity, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length SIRT1 structure with native substrate bound\", \"Quantitative kinetic parameters for most substrates lacking\", \"How tissue-specific SIRT1 functions are programmed despite ubiquitous expression is mechanistically unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 4, 5, 8, 9, 14, 20, 27, 33, 34, 39]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [5, 7, 12, 21, 22, 36]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [10, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [10, 15, 26, 36, 41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [20, 40]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 3, 4, 6, 12]},\n      {\"term_id\": \"R-HSA-9909396\", \"supporting_discovery_ids\": [21, 22]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [16, 27]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7, 9, 13, 28]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [33, 37]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 25, 29]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [21, 36]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7, 12, 36]}\n    ],\n    \"complexes\": [\n      \"CLOCK:BMAL1 complex\"\n    ],\n    \"partners\": [\n      \"TP53\",\n      \"FOXO3\",\n      \"RELA\",\n      \"PPARGC1A\",\n      \"PPARA\",\n      \"XRCC6\",\n      \"CLOCK\",\n      \"AROS\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}