{"gene":"LPIN1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2010,"finding":"Human LPIN1 encodes phosphatidate (PA) phosphatase (PAP1) activity; three isoforms (alpha, beta, gamma) purified from E. coli all require Mg2+ or Mn2+ ions and follow saturation kinetics for PA as substrate, with positive cooperative kinetics for PA surface concentration (Hill number ~2). Isoforms differ in turnover numbers (kcat: alpha 68.8, beta 42.8, gamma 5.7 s-1) and require at least one unsaturated fatty acyl moiety for maximum activity. Activity is inhibited by Ca2+, Zn2+, N-ethylmaleimide, propranolol, and sphingoid bases.","method":"Recombinant protein expression in E. coli, purification to near-homogeneity, in vitro enzyme kinetics in Triton X-100/PA mixed micelles","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with purified protein, comprehensive kinetic characterization with multiple substrates and inhibitors, isoform comparison","pmids":["20231281"],"is_preprint":false},{"year":2008,"finding":"LPIN1 mutations (identified by homozygosity mapping) cause loss of the muscle-specific phosphatidic acid phosphatase (PAP1) function, leading to accumulation of phosphatidic acid and lysophospholipids in muscle tissue and recurrent rhabdomyolysis. Phospholipid analysis of patient muscle biopsies directly demonstrated PA/lysophospholipid accumulation in the more severe genotypes.","method":"Homozygosity mapping, mutation identification in LPIN1, biochemical phospholipid analysis of patient muscle biopsies","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutation identification combined with direct biochemical substrate accumulation measurement in patient tissue, replicated across multiple families","pmids":["18817903"],"is_preprint":false},{"year":2008,"finding":"Schwann cell-specific deletion of Lpin1 leads to peripheral demyelination mediated by endoneurial accumulation of phosphatidic acid (PA), the substrate of the PAP1 enzyme. PA was shown to be a potent activator of the MEK-ERK pathway in Schwann cells, and MEK-ERK activation was required for PA-induced demyelination.","method":"Conditional knockout (Schwann cell-specific Lpin1 deletion), lipid biochemistry, cell signaling assays (MEK-ERK pathway activation), pharmacological inhibition of MEK-ERK","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific KO with defined phenotype, direct substrate accumulation measured, mechanistic pathway identified with pharmacological validation","pmids":["18559480"],"is_preprint":false},{"year":2011,"finding":"Lpin1 is a p53-responsive gene induced by DNA damage and glucose deprivation. p53 and Lpin1 regulate fatty acid oxidation in C2C12 myoblasts. Lpin1 expression in response to nutritional stress is controlled through the ROS-ATM-p53 pathway (p53 phosphorylation on Ser18 is ROS- and ATM-dependent), and this pathway is conserved in human cells.","method":"Genetic (p53 loss-of-function, ATM inhibition), ROS manipulation, chromatin immunoprecipitation (p53 binding to Lpin1 promoter), fatty acid oxidation assays in C2C12 cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP, genetic KO/KD, metabolic assay) in single lab establishing pathway position","pmids":["22055193"],"is_preprint":false},{"year":2015,"finding":"Pathogenic LPIN1 missense mutations (p.Leu635Pro and p.Arg725His) cause loss of phosphatidic acid phosphohydrolase (PAP) catalytic activity without diminishing substrate binding (kinetic analyses indicate loss of catalysis). p.Leu635Pro protein is less stable, aggregates in cytosol, and is targeted for proteasomal degradation, and shows abnormal subcellular localization in patient muscle. p.Arg725His retains transcriptional regulatory function but lacks PAP activity.","method":"Recombinant lipin 1 expression with patient mutations, PAP enzyme activity assays, kinetic analyses, Western blotting of patient muscle biopsy, immunohistochemical localization, proteasome inhibitor experiments","journal":"JIMD reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzyme assay with mutagenesis plus patient tissue Western blot and IHC, multiple orthogonal methods in single study","pmids":["25967228"],"is_preprint":false},{"year":2011,"finding":"A truncated Lpin1 protein lacking PAP1 activity (from a splice-site mutation causing frameshift and premature stop codon) is produced in Lpin1(1Hubr) rats and results in hypomyelination and mild lipodystrophy. Compensatory biochemical pathways substituting for missing PAP1 activity are activated, and a possible non-enzymatic Lpin1 function residing outside its PAP1 domain may contribute to the less severe phenotype compared to null mice.","method":"N-ethyl-N-nitrosourea mutagenesis, sequencing, PAP1 activity assays, histology, electrophysiology, biochemical pathway analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined truncation mutation, enzyme activity confirmed absent, multiple analytical methods in one study, single lab","pmids":["21715287"],"is_preprint":false},{"year":2016,"finding":"LPIN1 interacts with insulin receptor substrate 1 (IRS1) in an IGF-1-dependent manner and inhibits IRS1 serine phosphorylation, thereby preventing ubiquitin-dependent proteasomal and lysosomal degradation of IRS1. LPIN1 overexpression increases IRS1 abundance and activates RAF1-mediated signaling and AP-1 activity to promote mammary tumorigenesis.","method":"Co-immunoprecipitation, overexpression and knockdown in breast cancer cells, ubiquitination assays, proteasome/lysosome inhibitor experiments, in vivo syngeneic tumor model","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional assays (ubiquitination, signaling), in vitro and in vivo validation, single lab","pmids":["27729374"],"is_preprint":false},{"year":2021,"finding":"IL-33-induced COT-JNK1/2 signaling pathway regulates LPIN1 mRNA and protein expression by recruiting c-Jun to the LPIN1 promoter in breast cancer cells, providing a mechanism for transcriptional upregulation of LPIN1.","method":"qRT-PCR, Western blotting, chromatin immunoprecipitation (c-Jun binding to LPIN1 promoter), pharmacological inhibition of COT and JNK1/2, overexpression/knockdown","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus pathway inhibition experiments establishing promoter regulation mechanism, multiple orthogonal methods, single lab","pmids":["33946554"],"is_preprint":false},{"year":2021,"finding":"Cardiac-specific lipin 1 knockout (cs-Lpin1-/-) increases PA content in hearts and unexpectedly also elevates diacylglycerol and triglyceride. Loss of lipin 1 diminishes cardiac cardiolipin content and impairs mitochondrial respiration with pyruvate or succinate as substrates. Loss of lipin 1 dampens the cardiac inotropic response to dobutamine and exercise endurance, associated with reduced protein kinase A signaling.","method":"Cardiac-specific KO mouse model, lipidomics, mitochondrial respiration assays, dobutamine stress, exercise testing, protein kinase A signaling analysis, transverse aortic constriction","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — tissue-specific KO with multiple orthogonal readouts (lipidomics, mitochondrial function, signaling, physiology) in one rigorous study","pmids":["33986192"],"is_preprint":false},{"year":2022,"finding":"LPIN1 promotes triglyceride synthesis in buffalo mammary epithelial cells and is directly transcriptionally regulated by PPARγ binding to two PPAR response elements (PPRE1 and PPRE2) in the core LPIN1 promoter region (-666 to +42 bp). Site mutagenesis of these PPREs abolished PPARγ-driven LPIN1 transcription.","method":"Overexpression and lentivirus-mediated knockdown, promoter deletion analysis, site-directed mutagenesis of PPREs, dual-luciferase reporter assay, qRT-PCR, triglyceride content measurement","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter mutagenesis plus luciferase reporter and functional lipid assays, multiple orthogonal methods, single lab","pmids":["35149744"],"is_preprint":false},{"year":2017,"finding":"Human adipose tissue from LPIN1 biallelic loss-of-function mutation patients shows dramatically decreased lipin-1 protein and PAP activity, with compensatory increases in SREBP1, PPARG, and PGC1A expression, while adipose tissue develops without overt lipodystrophy and with normal qualitative lipid composition, indicating species-specific compensatory mechanisms.","method":"Histopathological analysis, PAP activity assay in patient adipose tissue biopsies, Western blotting, gene expression analysis, mesenchymal cell differentiation assays","journal":"Journal of lipid research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct enzyme activity measurement in patient tissue with multiple parallel analyses, single study","pmids":["28986436"],"is_preprint":false},{"year":2022,"finding":"LPIN1 induces gefitinib resistance in EGFR-mutant NSCLC cells by generating diacylglycerol upon gefitinib treatment, which activates protein kinase C delta and NF-κB in an LPIN1-dependent manner. LPIN1 also increases lipid droplet production. shRNA depletion or propranolol inhibition of LPIN1 reduced tumor growth in vivo.","method":"Overexpression and shRNA knockdown, DAG measurement, pharmacological inhibition (propranolol), PKC delta and NF-κB signaling assays, lipid droplet quantification, in vivo xenograft","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple signaling readouts plus in vivo validation, single lab with orthogonal genetic and pharmacological approaches","pmids":["35565351"],"is_preprint":false},{"year":2009,"finding":"Concurrent partial loss-of-function mutations in Lpin1 and NrCAM act synergistically (not additively) to cause severe peripheral neuropathy with transitory hindlimb paralysis. The Lpin1 mutation alone caused demyelination and aberrant myelin structures, while NrCAM mutation alone showed normal sciatic nerve morphology; the double mutant had more severe electrophysiological defects than either single mutant.","method":"N-ethyl-N-nitrosourea mutagenesis, linkage mapping, double-mutant analysis, behavioral testing, histology, electrophysiology","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis analysis with double mutants and single mutants compared by multiple phenotypic readouts, single study","pmids":["19793967"],"is_preprint":false},{"year":2025,"finding":"LPIN1 is required for normal hematopoietic stem/progenitor cell (HSPC) and leukemic stem cell (LSC) function. LPIN1 suppression reduces phosphatidylcholine and phosphatidylethanolamine while upregulating sphingomyelin, altering phospholipid homeostasis. LPIN1 knockdown inhibited proliferation of primary leukemic cells and normal HSPCs both in vitro and in xenotransplantation assays.","method":"LPIN1 knockdown (shRNA), lipidomics, in vitro proliferation assays, xenotransplantation in vivo assays, primary human AML samples","journal":"HemaSphere","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lipidomics plus in vitro and in vivo functional assays, single study with multiple orthogonal methods","pmids":["40265168"],"is_preprint":false},{"year":2026,"finding":"CXCL6 activates JNK, leading to inhibitory phosphorylation of the glucocorticoid receptor (GR), which prevents GR-dependent activation of the LPIN1 promoter, thereby suppressing LPIN1-PPARα axis in hepatocytes and impairing fatty acid oxidation. Lpin1 knockdown reversed the protective phenotype in Cxcl5-deficient mice, confirming LPIN1 suppression as the essential driver of CXCL6-mediated MASH progression.","method":"Genetic KO (Cxcl5-deficient mice), Lpin1 knockdown, JNK inhibition, GR phosphorylation analysis, promoter activity assays, hepatic lipid and gene expression analysis, in vivo diet-induced MASH model","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway established by KO + epistasis (Lpin1 KD in Cxcl5 KO) with multiple readouts, single lab","pmids":["42212316"],"is_preprint":false},{"year":2026,"finding":"CLIPPER, an enhancer-associated long noncoding RNA, regulates LPIN1 expression in cis in cardiomyocytes. Clipper or Lpin1 silencing stimulates productive mitochondrial fission (midzone positioning), decreases oxidative metabolism, reduces ROS production, dampens DNA damage, and creates conditions permissive for cardiomyocyte proliferation and cardiac regeneration after myocardial infarction.","method":"High-throughput lncRNA knockdown screen, in vivo Clipper knockdown after myocardial infarction, mitochondrial imaging (fission site positioning), metabolic assays, ROS measurement, cardiomyocyte proliferation assays","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KD with multiple orthogonal functional readouts (mitochondrial dynamics, bioenergetics, proliferation, cardiac function), single study","pmids":["41641546"],"is_preprint":false},{"year":2017,"finding":"hsa-miR-122-5p directly represses LPIN1 expression in hepatocytes, as confirmed by dual-luciferase reporter assay, qRT-PCR, and Western blot. LPIN1 is identified as a downstream target in the triacylglycerol synthesis pathway regulated by miR-122.","method":"Dual-luciferase reporter assay, qRT-PCR, Western blot in hepatocytes with miR-122 manipulation","journal":"Archives of Iranian medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, luciferase reporter plus expression analysis; pathway placement indirect","pmids":["28287811"],"is_preprint":false}],"current_model":"LPIN1 encodes lipin 1, a bifunctional protein: (1) a Mg2+/Mn2+-dependent phosphatidic acid (PA) phosphohydrolase (PAP1) that dephosphorylates PA to generate diacylglycerol—the committed step in triacylglycerol and membrane phospholipid biosynthesis—with isoform-specific kinetics; and (2) a transcriptional coactivator (acting via PPARα/PGC-1α) that regulates fatty acid oxidation gene expression. Loss of PAP1 activity causes PA accumulation in muscle and nerve, activating MEK-ERK signaling in Schwann cells to drive demyelination, and causing rhabdomyolysis. Lipin 1 is induced by the ROS-ATM-p53 pathway under nutritional stress to support fatty acid oxidation, is transcriptionally regulated by PPARγ (via PPRE elements) and by IL-33-COT-JNK1/2-c-Jun signaling, and is suppressed by CXCL6-JNK-mediated inhibition of the glucocorticoid receptor. Lipin 1 also stabilizes IRS1 by preventing its serine phosphorylation and ubiquitin-dependent degradation, and is required for phospholipid homeostasis in hematopoietic stem/progenitor cells and mitochondrial biogenesis in cardiomyocytes."},"narrative":{"mechanistic_narrative":"LPIN1 encodes lipin 1, a bifunctional Mg2+/Mn2+-dependent phosphatidic acid phosphohydrolase (PAP1) that catalyzes the committed, surface-cooperative dephosphorylation of phosphatidic acid (PA) to diacylglycerol at the heart of glycerolipid biosynthesis [PMID:20231281]. Three isoforms (alpha, beta, gamma) share this catalytic mechanism but differ in turnover, all requiring at least one unsaturated acyl chain and being inhibited by Ca2+, Zn2+, propranolol, and sphingoid bases [PMID:20231281]. Loss of PAP1 activity is directly pathogenic: biallelic LPIN1 mutations cause PA and lysophospholipid accumulation in muscle and recurrent rhabdomyolysis [PMID:18817903], and disease missense alleles abolish catalysis while sparing substrate binding, with one (p.Leu635Pro) destabilizing the protein and routing it to proteasomal degradation [PMID:25967228]. In the peripheral nervous system, Schwann-cell PA accumulation following Lpin1 loss activates MEK-ERK signaling to drive demyelination [PMID:18559480]. Beyond its enzymatic role, lipin 1 supports oxidative metabolism: it is induced under nutritional and genotoxic stress through the ROS-ATM-p53 pathway to sustain fatty acid oxidation [PMID:22055193], and in cardiomyocytes it is required for cardiolipin content, mitochondrial respiration, and the inotropic response [PMID:33986192]. Lipin 1 expression is set transcriptionally by PPARγ acting through promoter PPRE elements [PMID:35149744] and by GR-dependent activation feeding a LPIN1-PPARα fatty-acid-oxidation axis in hepatocytes [PMID:42212316]. In cancer contexts, lipin 1 stabilizes IRS1 by blocking its serine phosphorylation and ubiquitin-dependent degradation to promote RAF1/AP-1 signaling [PMID:27729374], and its DAG product activates PKCδ-NF-κB signaling [PMID:35565351]. Lipin 1 also maintains phospholipid homeostasis required for hematopoietic and leukemic stem/progenitor function [PMID:40265168].","teleology":[{"year":2008,"claim":"Established that LPIN1 loss-of-function is a Mendelian cause of recurrent rhabdomyolysis by removing muscle PAP1 activity and allowing its lipid substrate to accumulate, linking the gene's enzymatic role to human disease.","evidence":"Homozygosity mapping with biochemical phospholipid analysis of patient muscle biopsies","pmids":["18817903"],"confidence":"High","gaps":["Did not resolve why the metabolic defect manifests episodically as rhabdomyolysis","Did not establish the downstream signaling consequence of PA accumulation in muscle"]},{"year":2008,"claim":"Showed that the same PAP1 substrate, PA, when accumulated in Schwann cells acts as a signaling lipid driving demyelination, defining a mechanistic route from lipid imbalance to neuropathy.","evidence":"Schwann-cell-specific conditional Lpin1 knockout with lipid biochemistry and pharmacological MEK-ERK inhibition","pmids":["18559480"],"confidence":"High","gaps":["Did not identify the PA sensor upstream of MEK-ERK","Did not address whether the same mechanism operates in human neuropathy"]},{"year":2009,"claim":"Demonstrated that partial Lpin1 deficiency interacts non-additively with NrCAM mutation, indicating lipin 1's neuropathic effect can be modified by independent genetic loci.","evidence":"ENU mutagenesis, linkage mapping, and double-mutant electrophysiology in mice","pmids":["19793967"],"confidence":"Medium","gaps":["Mechanism of synergy between Lpin1 and NrCAM not defined","Relevance to human LPIN1 phenotypic variability untested"]},{"year":2010,"claim":"Reconstituted the catalytic identity of lipin 1 isoforms, defining LPIN1 as a Mg2+/Mn2+-dependent PA phosphohydrolase with surface-cooperative kinetics and isoform-specific turnover.","evidence":"Purified recombinant alpha/beta/gamma isoforms from E. coli with in vitro kinetics in mixed micelles","pmids":["20231281"],"confidence":"High","gaps":["Physiological division of labor among isoforms not established","Structural basis of catalysis and cooperativity not resolved"]},{"year":2011,"claim":"Placed LPIN1 induction within a stress-responsive transcriptional circuit, showing the ROS-ATM-p53 pathway upregulates it to support fatty acid oxidation under nutritional and genotoxic stress.","evidence":"p53/ATM genetic and pharmacological perturbation, ChIP of p53 at the Lpin1 promoter, and FAO assays in C2C12 cells","pmids":["22055193"],"confidence":"High","gaps":["Whether induced lipin 1 acts via PAP1 or coactivator function in this context not separated","In vivo relevance of the p53-Lpin1 axis not tested"]},{"year":2011,"claim":"Showed that a truncated PAP1-null Lpin1 in rats produces a milder phenotype than null mice, raising the possibility of compensatory pathways and a non-enzymatic function outside the PAP1 domain.","evidence":"ENU-derived splice mutant rat with PAP1 activity assays, histology, and electrophysiology","pmids":["21715287"],"confidence":"Medium","gaps":["The putative non-enzymatic function not molecularly defined","Compensatory pathways not identified"]},{"year":2015,"claim":"Dissected disease missense alleles to show catalysis can be lost while substrate binding and transcriptional regulatory function are retained, separating the enzymatic and regulatory roles of lipin 1.","evidence":"Recombinant mutant kinetics, patient muscle Western blot/IHC, and proteasome inhibitor experiments","pmids":["25967228"],"confidence":"High","gaps":["Structural explanation for selective loss of catalysis not provided","Contribution of retained regulatory function to milder phenotypes not quantified"]},{"year":2016,"claim":"Identified a non-enzymatic protein-protein function whereby LPIN1 binds IRS1 and blocks its degradation, coupling lipin 1 to growth-factor signaling and tumorigenesis.","evidence":"Co-IP, ubiquitination assays, knockdown/overexpression, and syngeneic tumor model in breast cancer cells","pmids":["27729374"],"confidence":"Medium","gaps":["Reciprocal/structural validation of the LPIN1-IRS1 interaction limited","Whether PAP1 activity is required for IRS1 stabilization not resolved"]},{"year":2017,"claim":"Showed human adipose tissue tolerates LPIN1 loss without lipodystrophy via compensatory SREBP1/PPARG/PGC1A upregulation, revealing species- and tissue-specific buffering of PAP1 deficiency.","evidence":"PAP activity assay, Western blot, and gene expression in patient adipose biopsies plus differentiation assays","pmids":["28986436"],"confidence":"Medium","gaps":["Molecular basis of compensation not mechanistically dissected","Long-term metabolic consequences in patients not assessed"]},{"year":2017,"claim":"Added post-transcriptional control by showing miR-122-5p directly represses LPIN1 in hepatocytes within the triacylglycerol synthesis pathway.","evidence":"Dual-luciferase reporter, qRT-PCR, and Western blot with miR-122 manipulation","pmids":["28287811"],"confidence":"Low","gaps":["Indirect pathway placement; functional lipid consequence not directly measured","Not independently confirmed in vivo"]},{"year":2021,"claim":"Defined a cardiac requirement for lipin 1 in maintaining cardiolipin, mitochondrial respiration, and contractile reserve, broadening its role beyond bulk glycerolipid synthesis.","evidence":"Cardiac-specific KO mouse with lipidomics, mitochondrial respiration, dobutamine/exercise testing, and PKA analysis","pmids":["33986192"],"confidence":"High","gaps":["Mechanism linking lipin 1 to cardiolipin homeostasis not defined","Reason for paradoxical DAG/TG elevation despite PAP1 loss unexplained"]},{"year":2021,"claim":"Identified IL-33-COT-JNK1/2-c-Jun signaling as a transcriptional activator of LPIN1, connecting inflammatory signaling to lipin 1 expression in cancer.","evidence":"ChIP of c-Jun at the LPIN1 promoter with pathway inhibition and expression analysis in breast cancer cells","pmids":["33946554"],"confidence":"Medium","gaps":["Downstream metabolic/signaling output of induced LPIN1 not fully traced","In vivo confirmation limited"]},{"year":2022,"claim":"Established direct PPARγ-driven transcription of LPIN1 through defined promoter PPRE elements, linking nuclear receptor control to triglyceride synthesis.","evidence":"Promoter deletion, PPRE site-directed mutagenesis, luciferase reporter, and TG measurement in buffalo mammary epithelial cells","pmids":["35149744"],"confidence":"Medium","gaps":["Conservation of these PPREs in human LPIN1 not addressed","Interplay with other transcriptional regulators not examined"]},{"year":2022,"claim":"Showed LPIN1 confers gefitinib resistance in EGFR-mutant NSCLC by generating DAG that activates PKCδ-NF-κB and promotes lipid droplet formation, implicating its enzymatic product in drug resistance.","evidence":"Knockdown/overexpression, DAG measurement, propranolol inhibition, signaling assays, and xenografts","pmids":["35565351"],"confidence":"Medium","gaps":["Direct demonstration that PAP1 catalysis produces the signaling DAG pool not isolated","Specificity of propranolol effects not fully controlled"]},{"year":2025,"claim":"Demonstrated that LPIN1 is required for phospholipid homeostasis and proliferation of normal and leukemic hematopoietic stem/progenitor cells, extending its role to stem cell biology.","evidence":"shRNA knockdown, lipidomics, and in vitro/xenotransplant proliferation assays in primary human AML and HSPCs","pmids":["40265168"],"confidence":"Medium","gaps":["Whether the requirement is catalytic or via the coactivator/IRS1 functions not resolved","Therapeutic window between LSC and HSPC dependence not defined"]},{"year":2026,"claim":"Placed LPIN1 as the essential effector of CXCL6-JNK-GR signaling in hepatocytes, where its suppression of the LPIN1-PPARα axis impairs fatty acid oxidation and drives MASH progression.","evidence":"Cxcl5-deficient mice with Lpin1 knockdown epistasis, GR phosphorylation analysis, and diet-induced MASH model","pmids":["42212316"],"confidence":"Medium","gaps":["Distinction between PAP1 and coactivator contributions to FAO not made","Direct GR occupancy at LPIN1 promoter not fully characterized"]},{"year":2026,"claim":"Showed cis-regulation of LPIN1 by the enhancer-associated lncRNA CLIPPER controls mitochondrial fission, oxidative metabolism, and cardiomyocyte proliferative capacity after infarction.","evidence":"lncRNA knockdown screen, in vivo Clipper knockdown post-MI, mitochondrial imaging, and proliferation assays","pmids":["41641546"],"confidence":"Medium","gaps":["Mechanism by which lipin 1 level governs mitochondrial fission not defined","Whether enzymatic activity mediates the regenerative phenotype untested"]},{"year":null,"claim":"It remains unresolved how lipin 1's enzymatic PAP1 activity, its transcriptional coactivator role, and its protein-stabilizing (IRS1) function are differentially deployed across tissues, and what structural features govern isoform-specific catalysis.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking catalysis to the regulatory functions","No systematic separation-of-function study across tissues","Mechanism of subcellular targeting and membrane engagement unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,4,10]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,8,9]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[3,7,9,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,6,11]}],"complexes":[],"partners":["IRS1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q14693","full_name":"Phosphatidate phosphatase LPIN1","aliases":["Lipin-1"],"length_aa":890,"mass_kda":98.7,"function":"Acts as a magnesium-dependent phosphatidate phosphatase enzyme which catalyzes the conversion of phosphatidic acid to diacylglycerol during triglyceride, phosphatidylcholine and phosphatidylethanolamine biosynthesis and therefore controls the metabolism of fatty acids at different levels (PubMed:20231281, PubMed:23426360, PubMed:29765047, PubMed:31695197). Is involved in adipocyte differentiation (By similarity). Recruited at the mitochondrion outer membrane and is involved in mitochondrial fission by converting phosphatidic acid to diacylglycerol (By similarity). Acts also as nuclear transcriptional coactivator for PPARGC1A/PPARA regulatory pathway to modulate lipid metabolism gene expression (By similarity)","subcellular_location":"Cytoplasm, cytosol; Endoplasmic reticulum membrane; Nucleus membrane","url":"https://www.uniprot.org/uniprotkb/Q14693/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LPIN1","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LPIN1","total_profiled":1310},"omim":[{"mim_id":"616869","title":"C-TERMINAL DOMAIN NUCLEAR ENVELOPE PHOSPHATASE 1 REGULATORY SUBUNIT 1; CNEP1R1","url":"https://www.omim.org/entry/616869"},{"mim_id":"615096","title":"MICRO RNA 217; MIR217","url":"https://www.omim.org/entry/615096"},{"mim_id":"614960","title":"PHOSPHOLIPASE D FAMILY, MEMBER 6; PLD6","url":"https://www.omim.org/entry/614960"},{"mim_id":"610684","title":"C-TERMINAL DOMAIN NUCLEAR ENVELOPE PHOSPHATASE 1; CTDNEP1","url":"https://www.omim.org/entry/610684"},{"mim_id":"605520","title":"LIPIN 3; LPIN3","url":"https://www.omim.org/entry/605520"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":180.0},{"tissue":"tongue","ntpm":128.3}],"url":"https://www.proteinatlas.org/search/LPIN1"},"hgnc":{"alias_symbol":["KIAA0188"],"prev_symbol":[]},"alphafold":{"accession":"Q14693","domains":[{"cath_id":"2.60.40,2.60.40","chopping":"27-108_625-670","consensus_level":"medium","plddt":85.4867,"start":27,"end":670},{"cath_id":"-","chopping":"465-546","consensus_level":"high","plddt":87.441,"start":465,"end":546},{"cath_id":"3.40.50.1000","chopping":"672-856","consensus_level":"medium","plddt":85.3422,"start":672,"end":856}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14693","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14693-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14693-F1-predicted_aligned_error_v6.png","plddt_mean":60.41},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LPIN1","jax_strain_url":"https://www.jax.org/strain/search?query=LPIN1"},"sequence":{"accession":"Q14693","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14693.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14693/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14693"}},"corpus_meta":[{"pmid":"18492828","id":"PMC_18492828","title":"ACSL1, AGPAT6, FABP3, LPIN1, and SLC27A6 are the most abundant isoforms in bovine mammary tissue and their expression is affected by stage of lactation.","date":"2008","source":"The Journal of nutrition","url":"https://pubmed.ncbi.nlm.nih.gov/18492828","citation_count":183,"is_preprint":false},{"pmid":"18817903","id":"PMC_18817903","title":"Mutations in LPIN1 cause recurrent acute myoglobinuria in childhood.","date":"2008","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18817903","citation_count":173,"is_preprint":false},{"pmid":"22055193","id":"PMC_22055193","title":"ROS-mediated p53 induction of Lpin1 regulates fatty acid oxidation in response to nutritional stress.","date":"2011","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/22055193","citation_count":159,"is_preprint":false},{"pmid":"20231281","id":"PMC_20231281","title":"Characterization of the human LPIN1-encoded phosphatidate phosphatase isoforms.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20231281","citation_count":132,"is_preprint":false},{"pmid":"18559480","id":"PMC_18559480","title":"Phosphatidic acid mediates demyelination in Lpin1 mutant mice.","date":"2008","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/18559480","citation_count":121,"is_preprint":false},{"pmid":"20583302","id":"PMC_20583302","title":"LPIN1 gene mutations: a major cause of severe rhabdomyolysis in early childhood.","date":"2010","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/20583302","citation_count":102,"is_preprint":false},{"pmid":"31162914","id":"PMC_31162914","title":"Exosomal miR-451a Functions as a Tumor Suppressor in Hepatocellular Carcinoma by Targeting LPIN1.","date":"2019","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and 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Isoforms differ in turnover numbers (kcat: alpha 68.8, beta 42.8, gamma 5.7 s-1) and require at least one unsaturated fatty acyl moiety for maximum activity. Activity is inhibited by Ca2+, Zn2+, N-ethylmaleimide, propranolol, and sphingoid bases.\",\n      \"method\": \"Recombinant protein expression in E. coli, purification to near-homogeneity, in vitro enzyme kinetics in Triton X-100/PA mixed micelles\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with purified protein, comprehensive kinetic characterization with multiple substrates and inhibitors, isoform comparison\",\n      \"pmids\": [\"20231281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"LPIN1 mutations (identified by homozygosity mapping) cause loss of the muscle-specific phosphatidic acid phosphatase (PAP1) function, leading to accumulation of phosphatidic acid and lysophospholipids in muscle tissue and recurrent rhabdomyolysis. Phospholipid analysis of patient muscle biopsies directly demonstrated PA/lysophospholipid accumulation in the more severe genotypes.\",\n      \"method\": \"Homozygosity mapping, mutation identification in LPIN1, biochemical phospholipid analysis of patient muscle biopsies\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutation identification combined with direct biochemical substrate accumulation measurement in patient tissue, replicated across multiple families\",\n      \"pmids\": [\"18817903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Schwann cell-specific deletion of Lpin1 leads to peripheral demyelination mediated by endoneurial accumulation of phosphatidic acid (PA), the substrate of the PAP1 enzyme. PA was shown to be a potent activator of the MEK-ERK pathway in Schwann cells, and MEK-ERK activation was required for PA-induced demyelination.\",\n      \"method\": \"Conditional knockout (Schwann cell-specific Lpin1 deletion), lipid biochemistry, cell signaling assays (MEK-ERK pathway activation), pharmacological inhibition of MEK-ERK\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific KO with defined phenotype, direct substrate accumulation measured, mechanistic pathway identified with pharmacological validation\",\n      \"pmids\": [\"18559480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Lpin1 is a p53-responsive gene induced by DNA damage and glucose deprivation. p53 and Lpin1 regulate fatty acid oxidation in C2C12 myoblasts. Lpin1 expression in response to nutritional stress is controlled through the ROS-ATM-p53 pathway (p53 phosphorylation on Ser18 is ROS- and ATM-dependent), and this pathway is conserved in human cells.\",\n      \"method\": \"Genetic (p53 loss-of-function, ATM inhibition), ROS manipulation, chromatin immunoprecipitation (p53 binding to Lpin1 promoter), fatty acid oxidation assays in C2C12 cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP, genetic KO/KD, metabolic assay) in single lab establishing pathway position\",\n      \"pmids\": [\"22055193\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Pathogenic LPIN1 missense mutations (p.Leu635Pro and p.Arg725His) cause loss of phosphatidic acid phosphohydrolase (PAP) catalytic activity without diminishing substrate binding (kinetic analyses indicate loss of catalysis). p.Leu635Pro protein is less stable, aggregates in cytosol, and is targeted for proteasomal degradation, and shows abnormal subcellular localization in patient muscle. p.Arg725His retains transcriptional regulatory function but lacks PAP activity.\",\n      \"method\": \"Recombinant lipin 1 expression with patient mutations, PAP enzyme activity assays, kinetic analyses, Western blotting of patient muscle biopsy, immunohistochemical localization, proteasome inhibitor experiments\",\n      \"journal\": \"JIMD reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzyme assay with mutagenesis plus patient tissue Western blot and IHC, multiple orthogonal methods in single study\",\n      \"pmids\": [\"25967228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A truncated Lpin1 protein lacking PAP1 activity (from a splice-site mutation causing frameshift and premature stop codon) is produced in Lpin1(1Hubr) rats and results in hypomyelination and mild lipodystrophy. Compensatory biochemical pathways substituting for missing PAP1 activity are activated, and a possible non-enzymatic Lpin1 function residing outside its PAP1 domain may contribute to the less severe phenotype compared to null mice.\",\n      \"method\": \"N-ethyl-N-nitrosourea mutagenesis, sequencing, PAP1 activity assays, histology, electrophysiology, biochemical pathway analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined truncation mutation, enzyme activity confirmed absent, multiple analytical methods in one study, single lab\",\n      \"pmids\": [\"21715287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LPIN1 interacts with insulin receptor substrate 1 (IRS1) in an IGF-1-dependent manner and inhibits IRS1 serine phosphorylation, thereby preventing ubiquitin-dependent proteasomal and lysosomal degradation of IRS1. LPIN1 overexpression increases IRS1 abundance and activates RAF1-mediated signaling and AP-1 activity to promote mammary tumorigenesis.\",\n      \"method\": \"Co-immunoprecipitation, overexpression and knockdown in breast cancer cells, ubiquitination assays, proteasome/lysosome inhibitor experiments, in vivo syngeneic tumor model\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional assays (ubiquitination, signaling), in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"27729374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IL-33-induced COT-JNK1/2 signaling pathway regulates LPIN1 mRNA and protein expression by recruiting c-Jun to the LPIN1 promoter in breast cancer cells, providing a mechanism for transcriptional upregulation of LPIN1.\",\n      \"method\": \"qRT-PCR, Western blotting, chromatin immunoprecipitation (c-Jun binding to LPIN1 promoter), pharmacological inhibition of COT and JNK1/2, overexpression/knockdown\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus pathway inhibition experiments establishing promoter regulation mechanism, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"33946554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cardiac-specific lipin 1 knockout (cs-Lpin1-/-) increases PA content in hearts and unexpectedly also elevates diacylglycerol and triglyceride. Loss of lipin 1 diminishes cardiac cardiolipin content and impairs mitochondrial respiration with pyruvate or succinate as substrates. Loss of lipin 1 dampens the cardiac inotropic response to dobutamine and exercise endurance, associated with reduced protein kinase A signaling.\",\n      \"method\": \"Cardiac-specific KO mouse model, lipidomics, mitochondrial respiration assays, dobutamine stress, exercise testing, protein kinase A signaling analysis, transverse aortic constriction\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — tissue-specific KO with multiple orthogonal readouts (lipidomics, mitochondrial function, signaling, physiology) in one rigorous study\",\n      \"pmids\": [\"33986192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"LPIN1 promotes triglyceride synthesis in buffalo mammary epithelial cells and is directly transcriptionally regulated by PPARγ binding to two PPAR response elements (PPRE1 and PPRE2) in the core LPIN1 promoter region (-666 to +42 bp). Site mutagenesis of these PPREs abolished PPARγ-driven LPIN1 transcription.\",\n      \"method\": \"Overexpression and lentivirus-mediated knockdown, promoter deletion analysis, site-directed mutagenesis of PPREs, dual-luciferase reporter assay, qRT-PCR, triglyceride content measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter mutagenesis plus luciferase reporter and functional lipid assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"35149744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Human adipose tissue from LPIN1 biallelic loss-of-function mutation patients shows dramatically decreased lipin-1 protein and PAP activity, with compensatory increases in SREBP1, PPARG, and PGC1A expression, while adipose tissue develops without overt lipodystrophy and with normal qualitative lipid composition, indicating species-specific compensatory mechanisms.\",\n      \"method\": \"Histopathological analysis, PAP activity assay in patient adipose tissue biopsies, Western blotting, gene expression analysis, mesenchymal cell differentiation assays\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct enzyme activity measurement in patient tissue with multiple parallel analyses, single study\",\n      \"pmids\": [\"28986436\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"LPIN1 induces gefitinib resistance in EGFR-mutant NSCLC cells by generating diacylglycerol upon gefitinib treatment, which activates protein kinase C delta and NF-κB in an LPIN1-dependent manner. LPIN1 also increases lipid droplet production. shRNA depletion or propranolol inhibition of LPIN1 reduced tumor growth in vivo.\",\n      \"method\": \"Overexpression and shRNA knockdown, DAG measurement, pharmacological inhibition (propranolol), PKC delta and NF-κB signaling assays, lipid droplet quantification, in vivo xenograft\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple signaling readouts plus in vivo validation, single lab with orthogonal genetic and pharmacological approaches\",\n      \"pmids\": [\"35565351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Concurrent partial loss-of-function mutations in Lpin1 and NrCAM act synergistically (not additively) to cause severe peripheral neuropathy with transitory hindlimb paralysis. The Lpin1 mutation alone caused demyelination and aberrant myelin structures, while NrCAM mutation alone showed normal sciatic nerve morphology; the double mutant had more severe electrophysiological defects than either single mutant.\",\n      \"method\": \"N-ethyl-N-nitrosourea mutagenesis, linkage mapping, double-mutant analysis, behavioral testing, histology, electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis analysis with double mutants and single mutants compared by multiple phenotypic readouts, single study\",\n      \"pmids\": [\"19793967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LPIN1 is required for normal hematopoietic stem/progenitor cell (HSPC) and leukemic stem cell (LSC) function. LPIN1 suppression reduces phosphatidylcholine and phosphatidylethanolamine while upregulating sphingomyelin, altering phospholipid homeostasis. LPIN1 knockdown inhibited proliferation of primary leukemic cells and normal HSPCs both in vitro and in xenotransplantation assays.\",\n      \"method\": \"LPIN1 knockdown (shRNA), lipidomics, in vitro proliferation assays, xenotransplantation in vivo assays, primary human AML samples\",\n      \"journal\": \"HemaSphere\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lipidomics plus in vitro and in vivo functional assays, single study with multiple orthogonal methods\",\n      \"pmids\": [\"40265168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CXCL6 activates JNK, leading to inhibitory phosphorylation of the glucocorticoid receptor (GR), which prevents GR-dependent activation of the LPIN1 promoter, thereby suppressing LPIN1-PPARα axis in hepatocytes and impairing fatty acid oxidation. Lpin1 knockdown reversed the protective phenotype in Cxcl5-deficient mice, confirming LPIN1 suppression as the essential driver of CXCL6-mediated MASH progression.\",\n      \"method\": \"Genetic KO (Cxcl5-deficient mice), Lpin1 knockdown, JNK inhibition, GR phosphorylation analysis, promoter activity assays, hepatic lipid and gene expression analysis, in vivo diet-induced MASH model\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway established by KO + epistasis (Lpin1 KD in Cxcl5 KO) with multiple readouts, single lab\",\n      \"pmids\": [\"42212316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CLIPPER, an enhancer-associated long noncoding RNA, regulates LPIN1 expression in cis in cardiomyocytes. Clipper or Lpin1 silencing stimulates productive mitochondrial fission (midzone positioning), decreases oxidative metabolism, reduces ROS production, dampens DNA damage, and creates conditions permissive for cardiomyocyte proliferation and cardiac regeneration after myocardial infarction.\",\n      \"method\": \"High-throughput lncRNA knockdown screen, in vivo Clipper knockdown after myocardial infarction, mitochondrial imaging (fission site positioning), metabolic assays, ROS measurement, cardiomyocyte proliferation assays\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KD with multiple orthogonal functional readouts (mitochondrial dynamics, bioenergetics, proliferation, cardiac function), single study\",\n      \"pmids\": [\"41641546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"hsa-miR-122-5p directly represses LPIN1 expression in hepatocytes, as confirmed by dual-luciferase reporter assay, qRT-PCR, and Western blot. LPIN1 is identified as a downstream target in the triacylglycerol synthesis pathway regulated by miR-122.\",\n      \"method\": \"Dual-luciferase reporter assay, qRT-PCR, Western blot in hepatocytes with miR-122 manipulation\",\n      \"journal\": \"Archives of Iranian medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, luciferase reporter plus expression analysis; pathway placement indirect\",\n      \"pmids\": [\"28287811\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LPIN1 encodes lipin 1, a bifunctional protein: (1) a Mg2+/Mn2+-dependent phosphatidic acid (PA) phosphohydrolase (PAP1) that dephosphorylates PA to generate diacylglycerol—the committed step in triacylglycerol and membrane phospholipid biosynthesis—with isoform-specific kinetics; and (2) a transcriptional coactivator (acting via PPARα/PGC-1α) that regulates fatty acid oxidation gene expression. Loss of PAP1 activity causes PA accumulation in muscle and nerve, activating MEK-ERK signaling in Schwann cells to drive demyelination, and causing rhabdomyolysis. Lipin 1 is induced by the ROS-ATM-p53 pathway under nutritional stress to support fatty acid oxidation, is transcriptionally regulated by PPARγ (via PPRE elements) and by IL-33-COT-JNK1/2-c-Jun signaling, and is suppressed by CXCL6-JNK-mediated inhibition of the glucocorticoid receptor. Lipin 1 also stabilizes IRS1 by preventing its serine phosphorylation and ubiquitin-dependent degradation, and is required for phospholipid homeostasis in hematopoietic stem/progenitor cells and mitochondrial biogenesis in cardiomyocytes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LPIN1 encodes lipin 1, a bifunctional Mg2+/Mn2+-dependent phosphatidic acid phosphohydrolase (PAP1) that catalyzes the committed, surface-cooperative dephosphorylation of phosphatidic acid (PA) to diacylglycerol at the heart of glycerolipid biosynthesis [#0]. Three isoforms (alpha, beta, gamma) share this catalytic mechanism but differ in turnover, all requiring at least one unsaturated acyl chain and being inhibited by Ca2+, Zn2+, propranolol, and sphingoid bases [#0]. Loss of PAP1 activity is directly pathogenic: biallelic LPIN1 mutations cause PA and lysophospholipid accumulation in muscle and recurrent rhabdomyolysis [#1], and disease missense alleles abolish catalysis while sparing substrate binding, with one (p.Leu635Pro) destabilizing the protein and routing it to proteasomal degradation [#4]. In the peripheral nervous system, Schwann-cell PA accumulation following Lpin1 loss activates MEK-ERK signaling to drive demyelination [#2]. Beyond its enzymatic role, lipin 1 supports oxidative metabolism: it is induced under nutritional and genotoxic stress through the ROS-ATM-p53 pathway to sustain fatty acid oxidation [#3], and in cardiomyocytes it is required for cardiolipin content, mitochondrial respiration, and the inotropic response [#8]. Lipin 1 expression is set transcriptionally by PPARγ acting through promoter PPRE elements [#9] and by GR-dependent activation feeding a LPIN1-PPARα fatty-acid-oxidation axis in hepatocytes [#14]. In cancer contexts, lipin 1 stabilizes IRS1 by blocking its serine phosphorylation and ubiquitin-dependent degradation to promote RAF1/AP-1 signaling [#6], and its DAG product activates PKCδ-NF-κB signaling [#11]. Lipin 1 also maintains phospholipid homeostasis required for hematopoietic and leukemic stem/progenitor function [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that LPIN1 loss-of-function is a Mendelian cause of recurrent rhabdomyolysis by removing muscle PAP1 activity and allowing its lipid substrate to accumulate, linking the gene's enzymatic role to human disease.\",\n      \"evidence\": \"Homozygosity mapping with biochemical phospholipid analysis of patient muscle biopsies\",\n      \"pmids\": [\"18817903\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve why the metabolic defect manifests episodically as rhabdomyolysis\", \"Did not establish the downstream signaling consequence of PA accumulation in muscle\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed that the same PAP1 substrate, PA, when accumulated in Schwann cells acts as a signaling lipid driving demyelination, defining a mechanistic route from lipid imbalance to neuropathy.\",\n      \"evidence\": \"Schwann-cell-specific conditional Lpin1 knockout with lipid biochemistry and pharmacological MEK-ERK inhibition\",\n      \"pmids\": [\"18559480\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the PA sensor upstream of MEK-ERK\", \"Did not address whether the same mechanism operates in human neuropathy\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that partial Lpin1 deficiency interacts non-additively with NrCAM mutation, indicating lipin 1's neuropathic effect can be modified by independent genetic loci.\",\n      \"evidence\": \"ENU mutagenesis, linkage mapping, and double-mutant electrophysiology in mice\",\n      \"pmids\": [\"19793967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of synergy between Lpin1 and NrCAM not defined\", \"Relevance to human LPIN1 phenotypic variability untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Reconstituted the catalytic identity of lipin 1 isoforms, defining LPIN1 as a Mg2+/Mn2+-dependent PA phosphohydrolase with surface-cooperative kinetics and isoform-specific turnover.\",\n      \"evidence\": \"Purified recombinant alpha/beta/gamma isoforms from E. coli with in vitro kinetics in mixed micelles\",\n      \"pmids\": [\"20231281\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological division of labor among isoforms not established\", \"Structural basis of catalysis and cooperativity not resolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placed LPIN1 induction within a stress-responsive transcriptional circuit, showing the ROS-ATM-p53 pathway upregulates it to support fatty acid oxidation under nutritional and genotoxic stress.\",\n      \"evidence\": \"p53/ATM genetic and pharmacological perturbation, ChIP of p53 at the Lpin1 promoter, and FAO assays in C2C12 cells\",\n      \"pmids\": [\"22055193\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether induced lipin 1 acts via PAP1 or coactivator function in this context not separated\", \"In vivo relevance of the p53-Lpin1 axis not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed that a truncated PAP1-null Lpin1 in rats produces a milder phenotype than null mice, raising the possibility of compensatory pathways and a non-enzymatic function outside the PAP1 domain.\",\n      \"evidence\": \"ENU-derived splice mutant rat with PAP1 activity assays, histology, and electrophysiology\",\n      \"pmids\": [\"21715287\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The putative non-enzymatic function not molecularly defined\", \"Compensatory pathways not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Dissected disease missense alleles to show catalysis can be lost while substrate binding and transcriptional regulatory function are retained, separating the enzymatic and regulatory roles of lipin 1.\",\n      \"evidence\": \"Recombinant mutant kinetics, patient muscle Western blot/IHC, and proteasome inhibitor experiments\",\n      \"pmids\": [\"25967228\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural explanation for selective loss of catalysis not provided\", \"Contribution of retained regulatory function to milder phenotypes not quantified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified a non-enzymatic protein-protein function whereby LPIN1 binds IRS1 and blocks its degradation, coupling lipin 1 to growth-factor signaling and tumorigenesis.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, knockdown/overexpression, and syngeneic tumor model in breast cancer cells\",\n      \"pmids\": [\"27729374\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reciprocal/structural validation of the LPIN1-IRS1 interaction limited\", \"Whether PAP1 activity is required for IRS1 stabilization not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed human adipose tissue tolerates LPIN1 loss without lipodystrophy via compensatory SREBP1/PPARG/PGC1A upregulation, revealing species- and tissue-specific buffering of PAP1 deficiency.\",\n      \"evidence\": \"PAP activity assay, Western blot, and gene expression in patient adipose biopsies plus differentiation assays\",\n      \"pmids\": [\"28986436\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of compensation not mechanistically dissected\", \"Long-term metabolic consequences in patients not assessed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Added post-transcriptional control by showing miR-122-5p directly represses LPIN1 in hepatocytes within the triacylglycerol synthesis pathway.\",\n      \"evidence\": \"Dual-luciferase reporter, qRT-PCR, and Western blot with miR-122 manipulation\",\n      \"pmids\": [\"28287811\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Indirect pathway placement; functional lipid consequence not directly measured\", \"Not independently confirmed in vivo\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined a cardiac requirement for lipin 1 in maintaining cardiolipin, mitochondrial respiration, and contractile reserve, broadening its role beyond bulk glycerolipid synthesis.\",\n      \"evidence\": \"Cardiac-specific KO mouse with lipidomics, mitochondrial respiration, dobutamine/exercise testing, and PKA analysis\",\n      \"pmids\": [\"33986192\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking lipin 1 to cardiolipin homeostasis not defined\", \"Reason for paradoxical DAG/TG elevation despite PAP1 loss unexplained\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified IL-33-COT-JNK1/2-c-Jun signaling as a transcriptional activator of LPIN1, connecting inflammatory signaling to lipin 1 expression in cancer.\",\n      \"evidence\": \"ChIP of c-Jun at the LPIN1 promoter with pathway inhibition and expression analysis in breast cancer cells\",\n      \"pmids\": [\"33946554\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream metabolic/signaling output of induced LPIN1 not fully traced\", \"In vivo confirmation limited\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established direct PPARγ-driven transcription of LPIN1 through defined promoter PPRE elements, linking nuclear receptor control to triglyceride synthesis.\",\n      \"evidence\": \"Promoter deletion, PPRE site-directed mutagenesis, luciferase reporter, and TG measurement in buffalo mammary epithelial cells\",\n      \"pmids\": [\"35149744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conservation of these PPREs in human LPIN1 not addressed\", \"Interplay with other transcriptional regulators not examined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed LPIN1 confers gefitinib resistance in EGFR-mutant NSCLC by generating DAG that activates PKCδ-NF-κB and promotes lipid droplet formation, implicating its enzymatic product in drug resistance.\",\n      \"evidence\": \"Knockdown/overexpression, DAG measurement, propranolol inhibition, signaling assays, and xenografts\",\n      \"pmids\": [\"35565351\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that PAP1 catalysis produces the signaling DAG pool not isolated\", \"Specificity of propranolol effects not fully controlled\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated that LPIN1 is required for phospholipid homeostasis and proliferation of normal and leukemic hematopoietic stem/progenitor cells, extending its role to stem cell biology.\",\n      \"evidence\": \"shRNA knockdown, lipidomics, and in vitro/xenotransplant proliferation assays in primary human AML and HSPCs\",\n      \"pmids\": [\"40265168\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the requirement is catalytic or via the coactivator/IRS1 functions not resolved\", \"Therapeutic window between LSC and HSPC dependence not defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Placed LPIN1 as the essential effector of CXCL6-JNK-GR signaling in hepatocytes, where its suppression of the LPIN1-PPARα axis impairs fatty acid oxidation and drives MASH progression.\",\n      \"evidence\": \"Cxcl5-deficient mice with Lpin1 knockdown epistasis, GR phosphorylation analysis, and diet-induced MASH model\",\n      \"pmids\": [\"42212316\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Distinction between PAP1 and coactivator contributions to FAO not made\", \"Direct GR occupancy at LPIN1 promoter not fully characterized\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed cis-regulation of LPIN1 by the enhancer-associated lncRNA CLIPPER controls mitochondrial fission, oxidative metabolism, and cardiomyocyte proliferative capacity after infarction.\",\n      \"evidence\": \"lncRNA knockdown screen, in vivo Clipper knockdown post-MI, mitochondrial imaging, and proliferation assays\",\n      \"pmids\": [\"41641546\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which lipin 1 level governs mitochondrial fission not defined\", \"Whether enzymatic activity mediates the regenerative phenotype untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how lipin 1's enzymatic PAP1 activity, its transcriptional coactivator role, and its protein-stabilizing (IRS1) function are differentially deployed across tissues, and what structural features govern isoform-specific catalysis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking catalysis to the regulatory functions\", \"No systematic separation-of-function study across tissues\", \"Mechanism of subcellular targeting and membrane engagement unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 4, 10]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 8, 9]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3, 7, 9, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 6, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"IRS1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}