{"gene":"PCSK1N","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2000,"finding":"ProSAAS is a granin-like neuroendocrine peptide precursor that functions as an endogenous inhibitor of prohormone convertase 1 (PC1) with an IC50 of 590 nM, but does not inhibit PC2. When overexpressed in AtT-20 cells, proSAAS is secreted via the regulated pathway and substantially reduces processing of the endogenous prohormone POMC.","method":"In vitro PC1 inhibition assay, overexpression in AtT-20 cells, regulated secretion assay","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro enzymatic assay with IC50 measurement plus cell-based functional assay, foundational paper replicated by multiple subsequent studies","pmids":["10632593"],"is_preprint":false},{"year":2000,"finding":"The PC1 inhibitory region of proSAAS maps to an 8-12 residue region near the C terminus containing a critical Lys-Arg sequence. Synthetic peptides from this region are competitive inhibitors of PC1 with Ki values of 14-40 nM. ProSAAS selectively inhibits PC1 but not furin, PACE4, PC5A, or PC7. A GST fusion containing the inhibitory region binds the 71 kDa but not the 85 kDa form of PC1 at pH 5.5 but not pH 7.4; binding is partially Ca2+-dependent.","method":"In vitro competitive inhibition assay with synthetic peptides, GST pulldown, pH/calcium dependence experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with kinetic characterization, mutagenesis-equivalent systematic peptide mapping, replicated across multiple labs","pmids":["10816562"],"is_preprint":false},{"year":2000,"finding":"ProSAAS and 7B2 share structural and functional homology. The C-terminal 40-residue SAAS CT peptide contains a hexapeptide (previously identified by combinatorial library screening) that accounts for the majority of PC1 inhibitory potency, with nanomolar Ki. Recombinant PC1 can cleave the proSAAS CT peptide following the inhibitory hexapeptide, suggesting a self-inactivation mechanism.","method":"In vitro PC1 inhibition assay, sequence analysis, recombinant PC1 cleavage assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay with inhibition constants, multiple orthogonal methods, consistent with other labs","pmids":["10812060"],"is_preprint":false},{"year":2000,"finding":"ProSAAS is processed in mouse brain and pituitary into smaller peptides including little SAAS, PEN, and big LEN. Processing is slightly impaired in Cpe(fat/fat) mice, causing accumulation of partially processed peptides including a C-terminally extended form of PEN that inhibits PC1 activity.","method":"Radioimmunoassay, gel filtration, reverse-phase HPLC, mass spectrometry of brain/pituitary fractions from wild-type and Cpe(fat/fat) mice","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal analytical methods (RIA, MS, HPLC), replicated in subsequent studies","pmids":["11094058"],"is_preprint":false},{"year":2001,"finding":"The decapeptide proSAAS-(235-244) VLGALLRVKR is the most potent reversible competitive PC1 inhibitor with Ki ~9 nM. Systematic alanine-scanning mutagenesis identified that P1 Arg, P2 Lys, P4 Arg are critical for inhibition, while P3 Val and P5/P6/P1' Leu residues significantly affect potency and selectivity. The extended peptide proSAAS-(235-246) is a competitive substrate cleaved by PC1 at KR244. Circular dichroism revealed an extended poly-L-proline II type conformation for the most potent inhibitor.","method":"In vitro PC1 inhibition assay, alanine scanning mutagenesis of synthetic peptides, circular dichroism, molecular modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with kinetic characterization and structural analysis (CD), multiple orthogonal methods in single rigorous study","pmids":["11435430"],"is_preprint":false},{"year":2001,"finding":"PC2 and furin can each cleave recombinant proSAAS in vitro, rapidly removing the C-terminal inhibitory peptide. In PC2-null mouse brains, the C-terminal proSAAS peptide is not processed as efficiently as in wild-type, demonstrating that PC2 is partially responsible for this cleavage in vivo.","method":"In vitro cleavage assay with recombinant PC2 and furin, RIA analysis of brain extracts from PC2 null mice","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstitution validated by genetic knockout experiment in vivo","pmids":["11259501"],"is_preprint":false},{"year":2001,"finding":"The N-terminal domain of proSAAS (proSAAS-1-180) does not stabilize PC1 activity or protect it from thermal denaturation in vitro, unlike the effect of 7B2 N-terminal domain on PC2. Cotransfection of proSAAS-(1-225) or proSAAS-(1-180) with PC1 in HEK293 or CHO/PC1 cells reduced PC1 activity detected in medium without reducing PC1 mass, suggesting proSAAS-mediated inactivation. In AtT-20 cells, proSAAS-(1-225) slowed processing of POMC and proenkephalin.","method":"In vitro thermal denaturation assay, cotransfection in HEK293/CHO/AtT-20 cells, pulse-chase analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro assay plus multiple cell line cotransfection experiments, negative result for stabilization is rigorously established","pmids":["11719503"],"is_preprint":false},{"year":2002,"finding":"ProSAAS is processed in AtT-20 and PC12 cells into peptides including little SAAS, PEN, and big LEN via the regulated secretory pathway; secretion is stimulated by secretagogues. Because PC12 cells lack PC1 and PC2 yet efficiently cleave proSAAS, the initial cleavages do not require either enzyme. Long-term secretagogue treatment does not affect proSAAS mRNA, unlike PC1 mRNA which increases ~60-80%, indicating enzyme and inhibitor are independently regulated.","method":"Pulse-chase analysis with [3H]leucine, mass spectrometry, chromatography, RIA in AtT-20 and PC12 cells","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — pulse-chase plus MS plus RIA in two cell lines; PC12 (lacking PC1/PC2) provides clean genetic background for enzyme-independence conclusion","pmids":["11742530"],"is_preprint":false},{"year":2004,"finding":"In AtT-20 cells under pulse-chase conditions, proSAAS expression inhibits both C-terminal PC1 processing and POMC processing. In HEK293 cells, the SAAS CT peptide portion of chimeric constructs inhibits zymogen processing and decreases C-terminal PC1 processing. The PC1 propeptide expressed in trans reduces C-terminal PC1 processing and inhibits POMC processing.","method":"Pulse-chase analysis, transient transfection in AtT-20 and HEK293 cells, chimeric construct expression","journal":"The Journal of endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulse-chase in multiple cell lines, two orthogonal cell systems, single lab","pmids":["15283695"],"is_preprint":false},{"year":2008,"finding":"Non-mammalian proSAAS homologs from Xenopus and zebrafish (29-30% overall identity to mouse proSAAS) inhibit mouse PC1/3 with nanomolar inhibition constants. Two 14-16 residue hydrophobic segments (predicted alpha-helices) and sequences containing basic convertase cleavage sites are highly conserved across vertebrates, identifying these as functionally critical regions. Both non-mammalian proSAAS proteins are cleaved in vitro by PC2 and furin.","method":"In vitro PC1/3 inhibition assay, in vitro cleavage assay, sequence conservation analysis, in situ hybridization","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro inhibition assay with kinetics for non-mammalian orthologs, single lab, functional validation of conserved domains","pmids":["18948394"],"is_preprint":false},{"year":2010,"finding":"ProSAAS knockout mice show complete adult-like processing of prodynorphin in the prenatal brain instead of the incomplete processing seen in wild-type fetal brains where inhibitory proSAAS intermediates transiently accumulate, demonstrating that proSAAS directly regulates neuropeptide processing in vivo during embryonic development. Adult proSAAS knockout mice have normal peptide levels, suggesting PC1/3 activity is unaffected by proSAAS absence in adults. ProSAAS knockout mice exhibit decreased locomotion and male-specific 10-15% body weight decrease.","method":"Genetic knockout mouse model, peptidomics, glucose tolerance testing, behavioral analysis","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with specific molecular phenotype (prodynorphin processing), replicated across developmental and adult timepoints with peptidomics","pmids":["20367757"],"is_preprint":false},{"year":2011,"finding":"ProSAAS-derived peptides big LEN and PEN function as neuropeptides regulating food intake: intracerebroventricular injection of antibodies to big LEN or PEN significantly reduced food intake in fasted mice. Big LEN produced rapid and reversible inhibition of synaptic glutamate release in parvocellular hypothalamic paraventricular neurons via a postsynaptic G protein-coupled receptor, releasing a retrograde synaptic messenger. Big LEN and PEN colocalize with neuropeptide Y in arcuate nucleus neurons.","method":"ICV antibody injection, whole-cell patch clamp electrophysiology, immunohistochemistry colocalization","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — electrophysiological functional assay plus in vivo antibody neutralization, multiple orthogonal methods establishing neuropeptide function","pmids":["22164236"],"is_preprint":false},{"year":2012,"finding":"Pax6 directly binds the Pcsk1n promoter and down-regulates proSAAS expression, as demonstrated by luciferase reporter assay, chromatin immunoprecipitation, and EMSA. Pax6 deficiency elevates proSAAS levels, which inhibits PC1/3 C-terminal cleavage and activity, thereby reducing proinsulin processing. Co-knockdown of Pax6 and Pcsk1n rescues the proinsulin processing defect caused by Pax6 knockdown alone.","method":"Luciferase reporter assay, ChIP, EMSA, RNAi knockdown, western blot, enzyme activity assay in MIN6 cells and Pax6 mutant mice","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (ChIP, EMSA, reporter assay, genetic rescue) establishing transcriptional regulation and epistatic pathway placement","pmids":["23056534"],"is_preprint":false},{"year":2013,"finding":"GPR171 is the receptor for the proSAAS-derived peptide BigLEN. BigLEN activates GPR171 via Gαi/o signaling in mouse hypothalamus and Neuro2A cells. The four C-terminal amino acids of BigLEN are sufficient to bind and activate GPR171. ShRNA knockdown of hypothalamic GPR171 decreases BigLEN signaling and alters food intake and metabolism. The BigLEN-GPR171 system is involved in regulation of feeding.","method":"Ligand-binding assay, receptor-activity assay, GPR171 overexpression and shRNA knockdown, in vivo feeding studies, orphan receptor screening","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — receptor deorphanization with binding assays, signaling assays, gain- and loss-of-function, in vivo validation","pmids":["24043826"],"is_preprint":false},{"year":2013,"finding":"ProSAAS functions as an anti-aggregant chaperone against Aβ(1-42) fibrillation in vitro at molar ratios of 1:10. ProSAAS co-immunoprecipitates with Aβ from APdE9 mouse brain lysates. The anti-aggregation function maps to residues 97-180. ProSAAS overexpression (lentiviral) or recombinant proSAAS in medium blocks Aβ(1-42)-induced neurocytotoxicity in Neuro2A cells.","method":"In vitro fibrillation assay (ThT), co-immunoprecipitation from mouse brain, structure-function analysis with truncation constructs, lentiviral overexpression, cytotoxicity assay","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstitution with domain mapping, co-IP from native tissue, cell-based neuroprotection assay, multiple orthogonal methods","pmids":["24102330"],"is_preprint":false},{"year":2013,"finding":"ProSAAS and 7B2 block human islet amyloid polypeptide (hIAPP) fibrillation in vitro. Structure-function studies mapped the anti-aggregation activity to a central region within 21-kDa 7B2 and the N-terminal region of proSAAS. Both chaperones blocked cytotoxic effects of exogenous hIAPP on Rin5f cells.","method":"In vitro fibrillation assay, structure-function truncation analysis, cell cytotoxicity assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution with domain mapping plus cell-based assay, single lab, two orthogonal methods","pmids":["24042052"],"is_preprint":false},{"year":2014,"finding":"Initial processing of proSAAS is mediated by furin (and/or furin-like enzymes) and carboxypeptidase D in the Golgi or trans-Golgi network; smaller peptide forms are generated by secretory granule prohormone convertases and carboxypeptidase E. Site-directed mutagenesis of the two furin consensus sites (P4 Arg→Lys) in proSAAS expressed in AtT-20 cells significantly increased colocalization of PEN and SAAS peptides, demonstrating that furin cleavage in the TGN sorts proSAAS fragments into distinct vesicles.","method":"Site-directed mutagenesis, AtT-20 transfection, immunofluorescence colocalization, subcellular fractionation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis with functional cellular readout (altered sorting), two orthogonal methods, mechanistic conclusion well-supported","pmids":["25148519"],"is_preprint":false},{"year":2016,"finding":"ProSAAS potently inhibits α-synuclein fibrillation in vitro; residues 158-180, containing a largely conserved element, are critical for this anti-aggregation activity. ProSAAS-encoding lentivirus blocks α-synuclein-induced cytotoxicity in primary cultures of nigral dopaminergic neurons, and recombinant proSAAS blocks α-synuclein cytotoxicity in SH-SY5Y cells. ProSAAS is associated with aggregated synuclein deposits in substantia nigra of Parkinson's disease patients.","method":"In vitro fibrillation assay, structure-function analysis, lentiviral overexpression in primary nigral cultures, recombinant protein cytotoxicity assay, immunohistochemistry on human tissue","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro assay with domain mapping, primary neuron functional assay, human tissue validation, multiple orthogonal methods","pmids":["27457957"],"is_preprint":false},{"year":2017,"finding":"The BigLEN-GPR171 system in the basolateral amygdala (BLA) regulates anxiety-like behavior and contextual fear conditioning. BigLEN hyperpolarizes BLA pyramidal neurons via GPR171. A small molecule GPR171 antagonist (MS0021570_1) blocks BigLEN-mediated hyperpolarization of BLA neurons and BigLEN-induced feeding; systemic or intra-BLA administration, or lentiviral knockdown of GPR171 in the BLA, reduces anxiety-like behavior and fear conditioning.","method":"Electrophysiology (BLA neuron hyperpolarization), virtual screening/homology modeling, small molecule pharmacology, lentiviral knockdown, in vivo behavioral assays","journal":"Neuropsychopharmacology","confidence":"High","confidence_rationale":"Tier 2 / Strong — electrophysiology, genetic knockdown, pharmacology, and in vivo behavior, multiple orthogonal methods in one study","pmids":["28425495"],"is_preprint":false},{"year":2017,"finding":"ProSAAS knockout mice fail to sensitize to cocaine or amphetamine (no locomotor sensitization), while rewarding effects (conditioned place preference) remain intact. Five of ten peptides significantly decreased in nucleus accumbens and VTA of cocaine-treated mice are derived from proSAAS, indicating cocaine modulates proSAAS peptide levels in specific brain regions.","method":"Quantitative peptidomics, proSAAS knockout mouse behavioral analysis (open field locomotion, sensitization, CPP)","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with specific behavioral phenotype plus quantitative peptidomics, single lab","pmids":["28881029"],"is_preprint":false},{"year":2020,"finding":"Cell stress (tunicamycin, thapsigargin, cobalt chloride hypoxic inducer, sodium arsenite) increases cellular proSAAS mRNA and protein in Neuro2A cells while paradoxically inhibiting proSAAS secretion, indicating that proSAAS is a stress-responsive secretory chaperone whose cellular retention is upregulated during ER and oxidative stress.","method":"qPCR, western blot, ELISA for secretion, pharmacological stress induction in Neuro2A cells","journal":"Cell stress & chaperones","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple stressors tested with mRNA and protein quantification, single lab, two orthogonal readouts","pmids":["32607937"],"is_preprint":false},{"year":2022,"finding":"Cytoplasmic expression of proSAAS generates membraneless ~2 μm spheres with liquid droplet-like properties that selectively sequester a C-terminally truncated form of TDP-43 via its prion-like domain. Three proSAAS sequences are required for sphere formation and TDP-43 encapsulation: a predicted coiled-coil, a conserved region (residues 158-169), and a positively charged sequence (residues 181-185). Lysine substitution in residues 181-185 causes nuclear translocation of proSAAS. ProSAAS expression confers cytoprotection against full-length TDP-43 toxicity in yeast.","method":"Fluorescence live cell imaging, site-directed mutagenesis, yeast toxicity assay, domain mapping with deletion/point mutant constructs","journal":"ACS chemical neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis with functional readout, live imaging of phase separation, yeast cytoprotection assay, multiple orthogonal methods in one study","pmids":["35549000"],"is_preprint":false},{"year":2022,"finding":"Lentiviral co-injection of proSAAS with human α-synuclein AAV into rat substantia nigra profoundly reduced motor asymmetry, protected nigral TH-positive neurons and striatal TH-positive terminals, and reduced human α-synuclein protein levels. In a vagal α-synuclein transmission model, proSAAS AAV co-injection reduced α-synuclein-positive neurites in pons and caudal midbrain, demonstrating blockade of transsynaptic α-synuclein spread.","method":"Stereotaxic lentiviral/AAV injection in rat/mouse models, motor behavioral testing, nigral stereology, TH densitometry, immunohistochemistry","journal":"Journal of Parkinson's disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo lentiviral gain-of-function in two independent animal models with quantitative neuropathological and behavioral endpoints","pmids":["35527562"],"is_preprint":false},{"year":2022,"finding":"ProSAAS knockout mice display anxiety-like behaviors, reduced cued fear, impaired fear-potentiated startle, reduced water consumption, elevated respiratory exchange ratio during light phase (indicating decreased fat metabolism), and inability to shift circadian clock upon light pulse despite normal circadian activity patterns.","method":"Genetic knockout mouse model, behavioral testing battery (open field, light-dark, elevated zero maze, fear conditioning, startle), metabolic phenotyping, circadian light-pulse protocol","journal":"Genes, brain, and behavior","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean knockout with multiple specific behavioral and metabolic phenotypes, single lab","pmids":["35878875"],"is_preprint":false},{"year":2024,"finding":"ProSAAS protein levels in primary hippocampal neurons are substantially upregulated during homeostatic scaling (more so than 7B2 or CPE), while proSAAS mRNA remains static, suggesting translational or degradation control. ProSAAS is released upon depolarization of differentiated hippocampal cultures, supporting synaptic localization. Stereotaxic AAV2/1-mediated overexpression of proSAAS in the CA1 region of 5xFAD mice significantly reduces amyloid plaque burden.","method":"Western blotting, qPCR, depolarization-induced secretion assay, stereotaxic AAV injection in 5xFAD mice, immunohistochemistry","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo AAV overexpression with quantitative plaque burden readout plus in vitro secretion assay, single lab, two orthogonal methods","pmids":["39115041"],"is_preprint":false}],"current_model":"PCSK1N (proSAAS) is a granin-like neuroendocrine precursor protein that functions as a potent, selective, slow-binding competitive inhibitor of prohormone convertase 1/3 (PC1/3) via a C-terminal hexapeptide/decapeptide (Ki ~9-40 nM), is processed by furin in the trans-Golgi network and by PC2/carboxypeptidase E in secretory granules into neuropeptides (big LEN, PEN, little SAAS) that signal through GPRs (BigLEN→GPR171, involved in feeding and anxiety), and additionally acts as a secreted anti-aggregant chaperone that inhibits fibrillation of Aβ, α-synuclein, and hIAPP via a conserved hydrophobic region (residues 158-180) and is neuroprotective in models of Parkinson's and Alzheimer's disease."},"narrative":{"mechanistic_narrative":"PCSK1N (proSAAS) is a granin-like neuroendocrine precursor that serves dual roles as a selective endogenous inhibitor of prohormone convertase 1/3 (PC1/3) and as a source of bioactive neuropeptides governing feeding, anxiety, and metabolism [PMID:10632593, PMID:22164236]. Its inhibitory activity resides in a C-terminal decapeptide/hexapeptide that acts as a slow, reversible competitive inhibitor of PC1/3 with nanomolar Ki, depending on a critical Lys-Arg motif (P1 Arg, P2 Lys, P4 Arg) and adopting an extended polyproline II conformation, while sparing PC2, furin, and other convertases [PMID:10816562, PMID:10812060, PMID:11435430]. ProSAAS itself is cleaved by furin and carboxypeptidase D in the trans-Golgi network—an event that sorts fragments into distinct vesicles—and further processed by secretory-granule convertases (including PC2) and carboxypeptidase E into little SAAS, PEN, and big LEN [PMID:11094058, PMID:11259501, PMID:25148519]; PC1/3 can also clip off the inhibitory peptide in a self-inactivation reaction [PMID:10812060]. In vivo, proSAAS transiently restrains neuropeptide processing during development, regulating prodynorphin maturation in fetal brain, and its expression is repressed by the transcription factor Pax6, linking it to proinsulin processing in islet cells [PMID:20367757, PMID:23056534]. The liberated peptides act as neuropeptides: big LEN signals through the Gαi/o-coupled receptor GPR171 to inhibit feeding and, in the basolateral amygdala, to hyperpolarize pyramidal neurons and modulate anxiety and fear behavior [PMID:22164236, PMID:24043826, PMID:28425495]. Independently of its convertase-inhibitory role, proSAAS functions as a secreted, stress-responsive anti-aggregant chaperone that blocks fibrillation of Aβ, α-synuclein, and hIAPP through distinct hydrophobic regions, and is neuroprotective in cellular and rodent models of Alzheimer's and Parkinson's disease, including blockade of transsynaptic α-synuclein spread [PMID:24102330, PMID:27457957, PMID:35527562, PMID:39115041]. Cytoplasmic proSAAS can also form liquid droplet-like spheres that sequester truncated TDP-43 and confer cytoprotection against its toxicity [PMID:35549000].","teleology":[{"year":2000,"claim":"Established proSAAS as the first endogenous, selective inhibitor of PC1/3, defining its core biochemical identity and distinguishing it from the PC2 chaperone 7B2.","evidence":"In vitro PC1 inhibition assays with IC50/Ki measurement, synthetic peptide mapping, GST pulldown, and AtT-20 overexpression reducing POMC processing","pmids":["10632593","10816562","10812060"],"confidence":"High","gaps":["No co-crystal structure of the proSAAS peptide bound to PC1/3","Physiological consequence of inhibition in vivo not yet tested at this stage"]},{"year":2001,"claim":"Resolved the structural determinants of inhibition, identifying a decapeptide with Ki ~9 nM and the critical P1/P2/P4 basic residues plus a polyproline II conformation.","evidence":"Alanine-scanning mutagenesis of synthetic peptides, kinetic inhibition assays, and circular dichroism","pmids":["11435430"],"confidence":"High","gaps":["Conformation inferred from CD, not high-resolution structure","Does not address how the full-length precursor presents the inhibitory motif"]},{"year":2000,"claim":"Mapped how proSAAS is itself processed in brain and pituitary into smaller peptides, showing carboxypeptidase E shapes the inhibitory intermediate pool.","evidence":"RIA, gel filtration, HPLC, and MS of wild-type and Cpe(fat/fat) mouse tissue","pmids":["11094058"],"confidence":"High","gaps":["Functional roles of the individual peptide products not defined at this stage"]},{"year":2001,"claim":"Identified the convertases that inactivate proSAAS by removing its C-terminal inhibitory peptide, and showed its N-terminus does not stabilize PC1/3 (unlike 7B2 toward PC2).","evidence":"In vitro cleavage with recombinant PC2/furin, thermal denaturation assays, PC2-null brain RIA, and cell cotransfection","pmids":["11259501","11719503"],"confidence":"High","gaps":["Relative in vivo contributions of furin vs PC2 across tissues not fully quantified"]},{"year":2002,"claim":"Demonstrated that initial proSAAS cleavages and inhibitor expression are regulated independently of PC1/3, using PC12 cells lacking both convertases.","evidence":"Pulse-chase, MS, RIA in AtT-20 and PC12 cells with secretagogue stimulation","pmids":["11742530"],"confidence":"High","gaps":["Identity of the PC1/PC2-independent processing enzyme(s) not established"]},{"year":2008,"claim":"Showed cross-species conservation of inhibitory potency and identified two conserved hydrophobic helical segments as functionally critical regions.","evidence":"In vitro PC1/3 inhibition and cleavage assays with Xenopus/zebrafish orthologs, conservation analysis, in situ hybridization","pmids":["18948394"],"confidence":"Medium","gaps":["Function of the conserved hydrophobic segments beyond inhibition not yet linked to chaperone activity at this stage"]},{"year":2010,"claim":"Defined the in vivo role of proSAAS as a developmental brake on neuropeptide processing, with knockout revealing developmental and behavioral/metabolic phenotypes.","evidence":"ProSAAS knockout mice, peptidomics, behavioral and metabolic analysis","pmids":["20367757"],"confidence":"High","gaps":["Why adult PC1/3 activity appears normal despite developmental requirement not explained","Mechanism behind locomotor and body-weight phenotypes unresolved"]},{"year":2012,"claim":"Placed Pcsk1n in a transcriptional pathway, showing Pax6 represses it to permit proper PC1/3-dependent proinsulin processing.","evidence":"Luciferase reporter, ChIP, EMSA, RNAi, enzyme assays in MIN6 cells and Pax6 mutant mice with genetic rescue","pmids":["23056534"],"confidence":"High","gaps":["Whether other transcription factors regulate Pcsk1n in neurons unknown"]},{"year":2011,"claim":"Established proSAAS-derived big LEN and PEN as functional neuropeptides regulating food intake via a postsynaptic GPCR.","evidence":"ICV antibody neutralization, patch-clamp electrophysiology, immunohistochemical colocalization with NPY","pmids":["22164236"],"confidence":"High","gaps":["Receptor identity not yet defined in this study","Identity of the retrograde messenger unknown"]},{"year":2013,"claim":"Deorphanized GPR171 as the big LEN receptor signaling through Gαi/o to regulate feeding, defining the downstream signaling axis.","evidence":"Ligand binding, receptor activity assays, GPR171 gain/loss-of-function, in vivo feeding studies","pmids":["24043826"],"confidence":"High","gaps":["Receptors for other proSAAS peptides (PEN, little SAAS) not identified","Structural basis of big LEN-GPR171 binding not resolved"]},{"year":2013,"claim":"Revealed a second, processing-independent function of proSAAS as an anti-aggregant chaperone against amyloidogenic proteins, with domain mapping.","evidence":"ThT fibrillation assays, co-IP from APdE9 brain, truncation mapping, lentiviral and recombinant protein neuroprotection assays","pmids":["24102330","24042052"],"confidence":"High","gaps":["Molecular mechanism of fibrillation inhibition not structurally defined","Discrepant domain assignments (97-180 for Aβ; N-terminal for hIAPP) not reconciled"]},{"year":2014,"claim":"Clarified the subcellular processing route, showing furin/carboxypeptidase D cleavage in the TGN sorts proSAAS fragments into distinct secretory vesicles.","evidence":"Site-directed mutagenesis of furin sites, AtT-20 transfection, immunofluorescence colocalization, subcellular fractionation","pmids":["25148519"],"confidence":"High","gaps":["Sorting signals directing fragments to separate vesicles not defined"]},{"year":2016,"claim":"Extended the chaperone role to α-synuclein, localizing anti-aggregation activity to conserved residues 158-180 and providing human Parkinson's tissue and dopaminergic neuron evidence.","evidence":"In vitro fibrillation, structure-function mapping, lentiviral overexpression in primary nigral cultures, recombinant protein rescue, human substantia nigra immunohistochemistry","pmids":["27457957"],"confidence":"High","gaps":["Causal contribution of proSAAS deposition to human disease not established"]},{"year":2017,"claim":"Extended the big LEN-GPR171 axis to anxiety and fear circuits in the basolateral amygdala and provided a small-molecule antagonist.","evidence":"BLA electrophysiology, virtual screening, small-molecule pharmacology, lentiviral knockdown, in vivo behavior","pmids":["28425495"],"confidence":"High","gaps":["Endogenous source of big LEN in the BLA not mapped"]},{"year":2017,"claim":"Linked proSAAS peptides to psychostimulant behavioral plasticity, showing knockouts fail to develop locomotor sensitization.","evidence":"Quantitative peptidomics and proSAAS knockout behavioral testing (sensitization, CPP)","pmids":["28881029"],"confidence":"Medium","gaps":["Single lab; specific peptide(s) and receptors mediating the sensitization phenotype not identified"]},{"year":2020,"claim":"Identified proSAAS as a stress-responsive chaperone, with ER and oxidative stress raising cellular levels while paradoxically inhibiting its secretion.","evidence":"qPCR, western blot, secretion ELISA under pharmacological stress in Neuro2A cells","pmids":["32607937"],"confidence":"Medium","gaps":["Single lab; mechanism coupling stress to secretory retention unknown"]},{"year":2022,"claim":"Provided in vivo proof that proSAAS is neuroprotective and blocks transsynaptic α-synuclein spread in rodent Parkinson's models.","evidence":"Stereotaxic lentiviral/AAV co-injection in rat/mouse, motor testing, nigral stereology, TH densitometry, immunohistochemistry","pmids":["35527562"],"confidence":"High","gaps":["Whether protection requires secretion or extracellular chaperone activity not dissected"]},{"year":2022,"claim":"Revealed a phase-separation-based cytoprotective function, with cytoplasmic proSAAS forming droplet-like spheres that sequester truncated TDP-43.","evidence":"Live-cell fluorescence imaging, domain-mapping mutagenesis, yeast toxicity assay","pmids":["35549000"],"confidence":"High","gaps":["Physiological relevance of cytoplasmic proSAAS spheres in mammalian neurons unestablished"]},{"year":2022,"claim":"Expanded the knockout phenotype to anxiety, fear, metabolic, and circadian-shifting deficits, broadening proSAAS's behavioral footprint.","evidence":"ProSAAS knockout behavioral battery, metabolic phenotyping, circadian light-pulse protocol","pmids":["35878875"],"confidence":"Medium","gaps":["Single lab; which proSAAS peptides/circuits drive the circadian and metabolic phenotypes unclear"]},{"year":2024,"claim":"Linked synaptic, activity-dependent proSAAS regulation to amyloid clearance, showing translational upregulation during homeostatic scaling and plaque reduction in 5xFAD mice.","evidence":"Western blot, qPCR, depolarization secretion assay, stereotaxic AAV overexpression in 5xFAD CA1, immunohistochemistry","pmids":["39115041"],"confidence":"Medium","gaps":["Mechanism of translational/degradation control not defined","Single lab"]},{"year":null,"claim":"How proSAAS's two functional faces—convertase inhibition and anti-aggregant chaperone activity—are coordinated, and the structural basis of its substrate recognition for both convertases and amyloidogenic clients, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of proSAAS or its complexes","Receptors for proSAAS peptides other than big LEN not identified","Causal role in human neurodegenerative disease not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2,4]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[14,17,20,21]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[11,13,18]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[21]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[7,16]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[16]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,14,24]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[21]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,3,16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,13,18]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[11,18]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[14,17,22]}],"complexes":[],"partners":["PCSK1","PCSK2","FURIN","CPE","GPR171","PAX6","SNCA","APP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UHG2","full_name":"ProSAAS","aliases":["Proprotein convertase subtilisin/kexin type 1 inhibitor","Proprotein convertase 1 inhibitor","pro-SAAS"],"length_aa":260,"mass_kda":27.4,"function":"May function in the control of the neuroendocrine secretory pathway. Proposed be a specific endogenous inhibitor of PCSK1. ProSAAS and Big PEN-LEN, both containing the C-terminal inhibitory domain, but not the further processed peptides reduce PCSK1 activity in the endoplasmic reticulum and Golgi. It reduces the activity of the 84 kDa form but not the autocatalytically derived 66 kDa form of PCSK1. Subsequent processing of proSAAS may eliminate the inhibition. Slows down convertase-mediated processing of proopiomelanocortin and proenkephalin. May control the intracellular timing of PCSK1 rather than its total level of activity (By similarity) Endogenous ligand for GPR171. Neuropeptide involved in the regulation of feeding Endogenous ligand for GPR83. Neuropeptide involved in the regulation of feeding","subcellular_location":"Secreted; Golgi apparatus, trans-Golgi network","url":"https://www.uniprot.org/uniprotkb/Q9UHG2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PCSK1N","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PCSK1N","total_profiled":1310},"omim":[{"mim_id":"618925","title":"G PROTEIN-COUPLED RECEPTOR 171; GPR171","url":"https://www.omim.org/entry/618925"},{"mim_id":"300399","title":"PROPROTEIN CONVERTASE, SUBTILISIN/KEXIN-TYPE, 1, INHIBITOR OF; PCSK1N","url":"https://www.omim.org/entry/300399"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":782.7},{"tissue":"pituitary gland","ntpm":1213.3}],"url":"https://www.proteinatlas.org/search/PCSK1N"},"hgnc":{"alias_symbol":["SAAS","SgVIII","SCG8","proSAAS","PEN","BigLEN"],"prev_symbol":[]},"alphafold":{"accession":"Q9UHG2","domains":[{"cath_id":"1.20.5","chopping":"67-114","consensus_level":"medium","plddt":91.2085,"start":67,"end":114}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UHG2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UHG2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UHG2-F1-predicted_aligned_error_v6.png","plddt_mean":58.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCSK1N","jax_strain_url":"https://www.jax.org/strain/search?query=PCSK1N"},"sequence":{"accession":"Q9UHG2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UHG2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UHG2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UHG2"}},"corpus_meta":[{"pmid":"10632593","id":"PMC_10632593","title":"Identification 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When overexpressed in AtT-20 cells, proSAAS is secreted via the regulated pathway and substantially reduces processing of the endogenous prohormone POMC.\",\n      \"method\": \"In vitro PC1 inhibition assay, overexpression in AtT-20 cells, regulated secretion assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro enzymatic assay with IC50 measurement plus cell-based functional assay, foundational paper replicated by multiple subsequent studies\",\n      \"pmids\": [\"10632593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The PC1 inhibitory region of proSAAS maps to an 8-12 residue region near the C terminus containing a critical Lys-Arg sequence. Synthetic peptides from this region are competitive inhibitors of PC1 with Ki values of 14-40 nM. ProSAAS selectively inhibits PC1 but not furin, PACE4, PC5A, or PC7. A GST fusion containing the inhibitory region binds the 71 kDa but not the 85 kDa form of PC1 at pH 5.5 but not pH 7.4; binding is partially Ca2+-dependent.\",\n      \"method\": \"In vitro competitive inhibition assay with synthetic peptides, GST pulldown, pH/calcium dependence experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with kinetic characterization, mutagenesis-equivalent systematic peptide mapping, replicated across multiple labs\",\n      \"pmids\": [\"10816562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"ProSAAS and 7B2 share structural and functional homology. The C-terminal 40-residue SAAS CT peptide contains a hexapeptide (previously identified by combinatorial library screening) that accounts for the majority of PC1 inhibitory potency, with nanomolar Ki. Recombinant PC1 can cleave the proSAAS CT peptide following the inhibitory hexapeptide, suggesting a self-inactivation mechanism.\",\n      \"method\": \"In vitro PC1 inhibition assay, sequence analysis, recombinant PC1 cleavage assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay with inhibition constants, multiple orthogonal methods, consistent with other labs\",\n      \"pmids\": [\"10812060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"ProSAAS is processed in mouse brain and pituitary into smaller peptides including little SAAS, PEN, and big LEN. Processing is slightly impaired in Cpe(fat/fat) mice, causing accumulation of partially processed peptides including a C-terminally extended form of PEN that inhibits PC1 activity.\",\n      \"method\": \"Radioimmunoassay, gel filtration, reverse-phase HPLC, mass spectrometry of brain/pituitary fractions from wild-type and Cpe(fat/fat) mice\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal analytical methods (RIA, MS, HPLC), replicated in subsequent studies\",\n      \"pmids\": [\"11094058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The decapeptide proSAAS-(235-244) VLGALLRVKR is the most potent reversible competitive PC1 inhibitor with Ki ~9 nM. Systematic alanine-scanning mutagenesis identified that P1 Arg, P2 Lys, P4 Arg are critical for inhibition, while P3 Val and P5/P6/P1' Leu residues significantly affect potency and selectivity. The extended peptide proSAAS-(235-246) is a competitive substrate cleaved by PC1 at KR244. Circular dichroism revealed an extended poly-L-proline II type conformation for the most potent inhibitor.\",\n      \"method\": \"In vitro PC1 inhibition assay, alanine scanning mutagenesis of synthetic peptides, circular dichroism, molecular modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with kinetic characterization and structural analysis (CD), multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"11435430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PC2 and furin can each cleave recombinant proSAAS in vitro, rapidly removing the C-terminal inhibitory peptide. In PC2-null mouse brains, the C-terminal proSAAS peptide is not processed as efficiently as in wild-type, demonstrating that PC2 is partially responsible for this cleavage in vivo.\",\n      \"method\": \"In vitro cleavage assay with recombinant PC2 and furin, RIA analysis of brain extracts from PC2 null mice\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstitution validated by genetic knockout experiment in vivo\",\n      \"pmids\": [\"11259501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The N-terminal domain of proSAAS (proSAAS-1-180) does not stabilize PC1 activity or protect it from thermal denaturation in vitro, unlike the effect of 7B2 N-terminal domain on PC2. Cotransfection of proSAAS-(1-225) or proSAAS-(1-180) with PC1 in HEK293 or CHO/PC1 cells reduced PC1 activity detected in medium without reducing PC1 mass, suggesting proSAAS-mediated inactivation. In AtT-20 cells, proSAAS-(1-225) slowed processing of POMC and proenkephalin.\",\n      \"method\": \"In vitro thermal denaturation assay, cotransfection in HEK293/CHO/AtT-20 cells, pulse-chase analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro assay plus multiple cell line cotransfection experiments, negative result for stabilization is rigorously established\",\n      \"pmids\": [\"11719503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ProSAAS is processed in AtT-20 and PC12 cells into peptides including little SAAS, PEN, and big LEN via the regulated secretory pathway; secretion is stimulated by secretagogues. Because PC12 cells lack PC1 and PC2 yet efficiently cleave proSAAS, the initial cleavages do not require either enzyme. Long-term secretagogue treatment does not affect proSAAS mRNA, unlike PC1 mRNA which increases ~60-80%, indicating enzyme and inhibitor are independently regulated.\",\n      \"method\": \"Pulse-chase analysis with [3H]leucine, mass spectrometry, chromatography, RIA in AtT-20 and PC12 cells\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — pulse-chase plus MS plus RIA in two cell lines; PC12 (lacking PC1/PC2) provides clean genetic background for enzyme-independence conclusion\",\n      \"pmids\": [\"11742530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In AtT-20 cells under pulse-chase conditions, proSAAS expression inhibits both C-terminal PC1 processing and POMC processing. In HEK293 cells, the SAAS CT peptide portion of chimeric constructs inhibits zymogen processing and decreases C-terminal PC1 processing. The PC1 propeptide expressed in trans reduces C-terminal PC1 processing and inhibits POMC processing.\",\n      \"method\": \"Pulse-chase analysis, transient transfection in AtT-20 and HEK293 cells, chimeric construct expression\",\n      \"journal\": \"The Journal of endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulse-chase in multiple cell lines, two orthogonal cell systems, single lab\",\n      \"pmids\": [\"15283695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Non-mammalian proSAAS homologs from Xenopus and zebrafish (29-30% overall identity to mouse proSAAS) inhibit mouse PC1/3 with nanomolar inhibition constants. Two 14-16 residue hydrophobic segments (predicted alpha-helices) and sequences containing basic convertase cleavage sites are highly conserved across vertebrates, identifying these as functionally critical regions. Both non-mammalian proSAAS proteins are cleaved in vitro by PC2 and furin.\",\n      \"method\": \"In vitro PC1/3 inhibition assay, in vitro cleavage assay, sequence conservation analysis, in situ hybridization\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro inhibition assay with kinetics for non-mammalian orthologs, single lab, functional validation of conserved domains\",\n      \"pmids\": [\"18948394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ProSAAS knockout mice show complete adult-like processing of prodynorphin in the prenatal brain instead of the incomplete processing seen in wild-type fetal brains where inhibitory proSAAS intermediates transiently accumulate, demonstrating that proSAAS directly regulates neuropeptide processing in vivo during embryonic development. Adult proSAAS knockout mice have normal peptide levels, suggesting PC1/3 activity is unaffected by proSAAS absence in adults. ProSAAS knockout mice exhibit decreased locomotion and male-specific 10-15% body weight decrease.\",\n      \"method\": \"Genetic knockout mouse model, peptidomics, glucose tolerance testing, behavioral analysis\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with specific molecular phenotype (prodynorphin processing), replicated across developmental and adult timepoints with peptidomics\",\n      \"pmids\": [\"20367757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ProSAAS-derived peptides big LEN and PEN function as neuropeptides regulating food intake: intracerebroventricular injection of antibodies to big LEN or PEN significantly reduced food intake in fasted mice. Big LEN produced rapid and reversible inhibition of synaptic glutamate release in parvocellular hypothalamic paraventricular neurons via a postsynaptic G protein-coupled receptor, releasing a retrograde synaptic messenger. Big LEN and PEN colocalize with neuropeptide Y in arcuate nucleus neurons.\",\n      \"method\": \"ICV antibody injection, whole-cell patch clamp electrophysiology, immunohistochemistry colocalization\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — electrophysiological functional assay plus in vivo antibody neutralization, multiple orthogonal methods establishing neuropeptide function\",\n      \"pmids\": [\"22164236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Pax6 directly binds the Pcsk1n promoter and down-regulates proSAAS expression, as demonstrated by luciferase reporter assay, chromatin immunoprecipitation, and EMSA. Pax6 deficiency elevates proSAAS levels, which inhibits PC1/3 C-terminal cleavage and activity, thereby reducing proinsulin processing. Co-knockdown of Pax6 and Pcsk1n rescues the proinsulin processing defect caused by Pax6 knockdown alone.\",\n      \"method\": \"Luciferase reporter assay, ChIP, EMSA, RNAi knockdown, western blot, enzyme activity assay in MIN6 cells and Pax6 mutant mice\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (ChIP, EMSA, reporter assay, genetic rescue) establishing transcriptional regulation and epistatic pathway placement\",\n      \"pmids\": [\"23056534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPR171 is the receptor for the proSAAS-derived peptide BigLEN. BigLEN activates GPR171 via Gαi/o signaling in mouse hypothalamus and Neuro2A cells. The four C-terminal amino acids of BigLEN are sufficient to bind and activate GPR171. ShRNA knockdown of hypothalamic GPR171 decreases BigLEN signaling and alters food intake and metabolism. The BigLEN-GPR171 system is involved in regulation of feeding.\",\n      \"method\": \"Ligand-binding assay, receptor-activity assay, GPR171 overexpression and shRNA knockdown, in vivo feeding studies, orphan receptor screening\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — receptor deorphanization with binding assays, signaling assays, gain- and loss-of-function, in vivo validation\",\n      \"pmids\": [\"24043826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ProSAAS functions as an anti-aggregant chaperone against Aβ(1-42) fibrillation in vitro at molar ratios of 1:10. ProSAAS co-immunoprecipitates with Aβ from APdE9 mouse brain lysates. The anti-aggregation function maps to residues 97-180. ProSAAS overexpression (lentiviral) or recombinant proSAAS in medium blocks Aβ(1-42)-induced neurocytotoxicity in Neuro2A cells.\",\n      \"method\": \"In vitro fibrillation assay (ThT), co-immunoprecipitation from mouse brain, structure-function analysis with truncation constructs, lentiviral overexpression, cytotoxicity assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstitution with domain mapping, co-IP from native tissue, cell-based neuroprotection assay, multiple orthogonal methods\",\n      \"pmids\": [\"24102330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ProSAAS and 7B2 block human islet amyloid polypeptide (hIAPP) fibrillation in vitro. Structure-function studies mapped the anti-aggregation activity to a central region within 21-kDa 7B2 and the N-terminal region of proSAAS. Both chaperones blocked cytotoxic effects of exogenous hIAPP on Rin5f cells.\",\n      \"method\": \"In vitro fibrillation assay, structure-function truncation analysis, cell cytotoxicity assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution with domain mapping plus cell-based assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"24042052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Initial processing of proSAAS is mediated by furin (and/or furin-like enzymes) and carboxypeptidase D in the Golgi or trans-Golgi network; smaller peptide forms are generated by secretory granule prohormone convertases and carboxypeptidase E. Site-directed mutagenesis of the two furin consensus sites (P4 Arg→Lys) in proSAAS expressed in AtT-20 cells significantly increased colocalization of PEN and SAAS peptides, demonstrating that furin cleavage in the TGN sorts proSAAS fragments into distinct vesicles.\",\n      \"method\": \"Site-directed mutagenesis, AtT-20 transfection, immunofluorescence colocalization, subcellular fractionation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis with functional cellular readout (altered sorting), two orthogonal methods, mechanistic conclusion well-supported\",\n      \"pmids\": [\"25148519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ProSAAS potently inhibits α-synuclein fibrillation in vitro; residues 158-180, containing a largely conserved element, are critical for this anti-aggregation activity. ProSAAS-encoding lentivirus blocks α-synuclein-induced cytotoxicity in primary cultures of nigral dopaminergic neurons, and recombinant proSAAS blocks α-synuclein cytotoxicity in SH-SY5Y cells. ProSAAS is associated with aggregated synuclein deposits in substantia nigra of Parkinson's disease patients.\",\n      \"method\": \"In vitro fibrillation assay, structure-function analysis, lentiviral overexpression in primary nigral cultures, recombinant protein cytotoxicity assay, immunohistochemistry on human tissue\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro assay with domain mapping, primary neuron functional assay, human tissue validation, multiple orthogonal methods\",\n      \"pmids\": [\"27457957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The BigLEN-GPR171 system in the basolateral amygdala (BLA) regulates anxiety-like behavior and contextual fear conditioning. BigLEN hyperpolarizes BLA pyramidal neurons via GPR171. A small molecule GPR171 antagonist (MS0021570_1) blocks BigLEN-mediated hyperpolarization of BLA neurons and BigLEN-induced feeding; systemic or intra-BLA administration, or lentiviral knockdown of GPR171 in the BLA, reduces anxiety-like behavior and fear conditioning.\",\n      \"method\": \"Electrophysiology (BLA neuron hyperpolarization), virtual screening/homology modeling, small molecule pharmacology, lentiviral knockdown, in vivo behavioral assays\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — electrophysiology, genetic knockdown, pharmacology, and in vivo behavior, multiple orthogonal methods in one study\",\n      \"pmids\": [\"28425495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ProSAAS knockout mice fail to sensitize to cocaine or amphetamine (no locomotor sensitization), while rewarding effects (conditioned place preference) remain intact. Five of ten peptides significantly decreased in nucleus accumbens and VTA of cocaine-treated mice are derived from proSAAS, indicating cocaine modulates proSAAS peptide levels in specific brain regions.\",\n      \"method\": \"Quantitative peptidomics, proSAAS knockout mouse behavioral analysis (open field locomotion, sensitization, CPP)\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with specific behavioral phenotype plus quantitative peptidomics, single lab\",\n      \"pmids\": [\"28881029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cell stress (tunicamycin, thapsigargin, cobalt chloride hypoxic inducer, sodium arsenite) increases cellular proSAAS mRNA and protein in Neuro2A cells while paradoxically inhibiting proSAAS secretion, indicating that proSAAS is a stress-responsive secretory chaperone whose cellular retention is upregulated during ER and oxidative stress.\",\n      \"method\": \"qPCR, western blot, ELISA for secretion, pharmacological stress induction in Neuro2A cells\",\n      \"journal\": \"Cell stress & chaperones\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple stressors tested with mRNA and protein quantification, single lab, two orthogonal readouts\",\n      \"pmids\": [\"32607937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cytoplasmic expression of proSAAS generates membraneless ~2 μm spheres with liquid droplet-like properties that selectively sequester a C-terminally truncated form of TDP-43 via its prion-like domain. Three proSAAS sequences are required for sphere formation and TDP-43 encapsulation: a predicted coiled-coil, a conserved region (residues 158-169), and a positively charged sequence (residues 181-185). Lysine substitution in residues 181-185 causes nuclear translocation of proSAAS. ProSAAS expression confers cytoprotection against full-length TDP-43 toxicity in yeast.\",\n      \"method\": \"Fluorescence live cell imaging, site-directed mutagenesis, yeast toxicity assay, domain mapping with deletion/point mutant constructs\",\n      \"journal\": \"ACS chemical neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis with functional readout, live imaging of phase separation, yeast cytoprotection assay, multiple orthogonal methods in one study\",\n      \"pmids\": [\"35549000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Lentiviral co-injection of proSAAS with human α-synuclein AAV into rat substantia nigra profoundly reduced motor asymmetry, protected nigral TH-positive neurons and striatal TH-positive terminals, and reduced human α-synuclein protein levels. In a vagal α-synuclein transmission model, proSAAS AAV co-injection reduced α-synuclein-positive neurites in pons and caudal midbrain, demonstrating blockade of transsynaptic α-synuclein spread.\",\n      \"method\": \"Stereotaxic lentiviral/AAV injection in rat/mouse models, motor behavioral testing, nigral stereology, TH densitometry, immunohistochemistry\",\n      \"journal\": \"Journal of Parkinson's disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo lentiviral gain-of-function in two independent animal models with quantitative neuropathological and behavioral endpoints\",\n      \"pmids\": [\"35527562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ProSAAS knockout mice display anxiety-like behaviors, reduced cued fear, impaired fear-potentiated startle, reduced water consumption, elevated respiratory exchange ratio during light phase (indicating decreased fat metabolism), and inability to shift circadian clock upon light pulse despite normal circadian activity patterns.\",\n      \"method\": \"Genetic knockout mouse model, behavioral testing battery (open field, light-dark, elevated zero maze, fear conditioning, startle), metabolic phenotyping, circadian light-pulse protocol\",\n      \"journal\": \"Genes, brain, and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean knockout with multiple specific behavioral and metabolic phenotypes, single lab\",\n      \"pmids\": [\"35878875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ProSAAS protein levels in primary hippocampal neurons are substantially upregulated during homeostatic scaling (more so than 7B2 or CPE), while proSAAS mRNA remains static, suggesting translational or degradation control. ProSAAS is released upon depolarization of differentiated hippocampal cultures, supporting synaptic localization. Stereotaxic AAV2/1-mediated overexpression of proSAAS in the CA1 region of 5xFAD mice significantly reduces amyloid plaque burden.\",\n      \"method\": \"Western blotting, qPCR, depolarization-induced secretion assay, stereotaxic AAV injection in 5xFAD mice, immunohistochemistry\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo AAV overexpression with quantitative plaque burden readout plus in vitro secretion assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"39115041\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCSK1N (proSAAS) is a granin-like neuroendocrine precursor protein that functions as a potent, selective, slow-binding competitive inhibitor of prohormone convertase 1/3 (PC1/3) via a C-terminal hexapeptide/decapeptide (Ki ~9-40 nM), is processed by furin in the trans-Golgi network and by PC2/carboxypeptidase E in secretory granules into neuropeptides (big LEN, PEN, little SAAS) that signal through GPRs (BigLEN→GPR171, involved in feeding and anxiety), and additionally acts as a secreted anti-aggregant chaperone that inhibits fibrillation of Aβ, α-synuclein, and hIAPP via a conserved hydrophobic region (residues 158-180) and is neuroprotective in models of Parkinson's and Alzheimer's disease.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PCSK1N (proSAAS) is a granin-like neuroendocrine precursor that serves dual roles as a selective endogenous inhibitor of prohormone convertase 1/3 (PC1/3) and as a source of bioactive neuropeptides governing feeding, anxiety, and metabolism [#0, #11]. Its inhibitory activity resides in a C-terminal decapeptide/hexapeptide that acts as a slow, reversible competitive inhibitor of PC1/3 with nanomolar Ki, depending on a critical Lys-Arg motif (P1 Arg, P2 Lys, P4 Arg) and adopting an extended polyproline II conformation, while sparing PC2, furin, and other convertases [#1, #2, #4]. ProSAAS itself is cleaved by furin and carboxypeptidase D in the trans-Golgi network—an event that sorts fragments into distinct vesicles—and further processed by secretory-granule convertases (including PC2) and carboxypeptidase E into little SAAS, PEN, and big LEN [#3, #5, #16]; PC1/3 can also clip off the inhibitory peptide in a self-inactivation reaction [#2]. In vivo, proSAAS transiently restrains neuropeptide processing during development, regulating prodynorphin maturation in fetal brain, and its expression is repressed by the transcription factor Pax6, linking it to proinsulin processing in islet cells [#10, #12]. The liberated peptides act as neuropeptides: big LEN signals through the G\\u03b1i/o-coupled receptor GPR171 to inhibit feeding and, in the basolateral amygdala, to hyperpolarize pyramidal neurons and modulate anxiety and fear behavior [#11, #13, #18]. Independently of its convertase-inhibitory role, proSAAS functions as a secreted, stress-responsive anti-aggregant chaperone that blocks fibrillation of A\\u03b2, \\u03b1-synuclein, and hIAPP through distinct hydrophobic regions, and is neuroprotective in cellular and rodent models of Alzheimer's and Parkinson's disease, including blockade of transsynaptic \\u03b1-synuclein spread [#14, #17, #22, #24]. Cytoplasmic proSAAS can also form liquid droplet-like spheres that sequester truncated TDP-43 and confer cytoprotection against its toxicity [#21].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established proSAAS as the first endogenous, selective inhibitor of PC1/3, defining its core biochemical identity and distinguishing it from the PC2 chaperone 7B2.\",\n      \"evidence\": \"In vitro PC1 inhibition assays with IC50/Ki measurement, synthetic peptide mapping, GST pulldown, and AtT-20 overexpression reducing POMC processing\",\n      \"pmids\": [\"10632593\", \"10816562\", \"10812060\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of the proSAAS peptide bound to PC1/3\", \"Physiological consequence of inhibition in vivo not yet tested at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved the structural determinants of inhibition, identifying a decapeptide with Ki ~9 nM and the critical P1/P2/P4 basic residues plus a polyproline II conformation.\",\n      \"evidence\": \"Alanine-scanning mutagenesis of synthetic peptides, kinetic inhibition assays, and circular dichroism\",\n      \"pmids\": [\"11435430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformation inferred from CD, not high-resolution structure\", \"Does not address how the full-length precursor presents the inhibitory motif\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapped how proSAAS is itself processed in brain and pituitary into smaller peptides, showing carboxypeptidase E shapes the inhibitory intermediate pool.\",\n      \"evidence\": \"RIA, gel filtration, HPLC, and MS of wild-type and Cpe(fat/fat) mouse tissue\",\n      \"pmids\": [\"11094058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional roles of the individual peptide products not defined at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified the convertases that inactivate proSAAS by removing its C-terminal inhibitory peptide, and showed its N-terminus does not stabilize PC1/3 (unlike 7B2 toward PC2).\",\n      \"evidence\": \"In vitro cleavage with recombinant PC2/furin, thermal denaturation assays, PC2-null brain RIA, and cell cotransfection\",\n      \"pmids\": [\"11259501\", \"11719503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo contributions of furin vs PC2 across tissues not fully quantified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated that initial proSAAS cleavages and inhibitor expression are regulated independently of PC1/3, using PC12 cells lacking both convertases.\",\n      \"evidence\": \"Pulse-chase, MS, RIA in AtT-20 and PC12 cells with secretagogue stimulation\",\n      \"pmids\": [\"11742530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the PC1/PC2-independent processing enzyme(s) not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed cross-species conservation of inhibitory potency and identified two conserved hydrophobic helical segments as functionally critical regions.\",\n      \"evidence\": \"In vitro PC1/3 inhibition and cleavage assays with Xenopus/zebrafish orthologs, conservation analysis, in situ hybridization\",\n      \"pmids\": [\"18948394\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function of the conserved hydrophobic segments beyond inhibition not yet linked to chaperone activity at this stage\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the in vivo role of proSAAS as a developmental brake on neuropeptide processing, with knockout revealing developmental and behavioral/metabolic phenotypes.\",\n      \"evidence\": \"ProSAAS knockout mice, peptidomics, behavioral and metabolic analysis\",\n      \"pmids\": [\"20367757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why adult PC1/3 activity appears normal despite developmental requirement not explained\", \"Mechanism behind locomotor and body-weight phenotypes unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placed Pcsk1n in a transcriptional pathway, showing Pax6 represses it to permit proper PC1/3-dependent proinsulin processing.\",\n      \"evidence\": \"Luciferase reporter, ChIP, EMSA, RNAi, enzyme assays in MIN6 cells and Pax6 mutant mice with genetic rescue\",\n      \"pmids\": [\"23056534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other transcription factors regulate Pcsk1n in neurons unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established proSAAS-derived big LEN and PEN as functional neuropeptides regulating food intake via a postsynaptic GPCR.\",\n      \"evidence\": \"ICV antibody neutralization, patch-clamp electrophysiology, immunohistochemical colocalization with NPY\",\n      \"pmids\": [\"22164236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor identity not yet defined in this study\", \"Identity of the retrograde messenger unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Deorphanized GPR171 as the big LEN receptor signaling through G\\u03b1i/o to regulate feeding, defining the downstream signaling axis.\",\n      \"evidence\": \"Ligand binding, receptor activity assays, GPR171 gain/loss-of-function, in vivo feeding studies\",\n      \"pmids\": [\"24043826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptors for other proSAAS peptides (PEN, little SAAS) not identified\", \"Structural basis of big LEN-GPR171 binding not resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a second, processing-independent function of proSAAS as an anti-aggregant chaperone against amyloidogenic proteins, with domain mapping.\",\n      \"evidence\": \"ThT fibrillation assays, co-IP from APdE9 brain, truncation mapping, lentiviral and recombinant protein neuroprotection assays\",\n      \"pmids\": [\"24102330\", \"24042052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of fibrillation inhibition not structurally defined\", \"Discrepant domain assignments (97-180 for A\\u03b2; N-terminal for hIAPP) not reconciled\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Clarified the subcellular processing route, showing furin/carboxypeptidase D cleavage in the TGN sorts proSAAS fragments into distinct secretory vesicles.\",\n      \"evidence\": \"Site-directed mutagenesis of furin sites, AtT-20 transfection, immunofluorescence colocalization, subcellular fractionation\",\n      \"pmids\": [\"25148519\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals directing fragments to separate vesicles not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended the chaperone role to \\u03b1-synuclein, localizing anti-aggregation activity to conserved residues 158-180 and providing human Parkinson's tissue and dopaminergic neuron evidence.\",\n      \"evidence\": \"In vitro fibrillation, structure-function mapping, lentiviral overexpression in primary nigral cultures, recombinant protein rescue, human substantia nigra immunohistochemistry\",\n      \"pmids\": [\"27457957\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal contribution of proSAAS deposition to human disease not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended the big LEN-GPR171 axis to anxiety and fear circuits in the basolateral amygdala and provided a small-molecule antagonist.\",\n      \"evidence\": \"BLA electrophysiology, virtual screening, small-molecule pharmacology, lentiviral knockdown, in vivo behavior\",\n      \"pmids\": [\"28425495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous source of big LEN in the BLA not mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked proSAAS peptides to psychostimulant behavioral plasticity, showing knockouts fail to develop locomotor sensitization.\",\n      \"evidence\": \"Quantitative peptidomics and proSAAS knockout behavioral testing (sensitization, CPP)\",\n      \"pmids\": [\"28881029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; specific peptide(s) and receptors mediating the sensitization phenotype not identified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified proSAAS as a stress-responsive chaperone, with ER and oxidative stress raising cellular levels while paradoxically inhibiting its secretion.\",\n      \"evidence\": \"qPCR, western blot, secretion ELISA under pharmacological stress in Neuro2A cells\",\n      \"pmids\": [\"32607937\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; mechanism coupling stress to secretory retention unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided in vivo proof that proSAAS is neuroprotective and blocks transsynaptic \\u03b1-synuclein spread in rodent Parkinson's models.\",\n      \"evidence\": \"Stereotaxic lentiviral/AAV co-injection in rat/mouse, motor testing, nigral stereology, TH densitometry, immunohistochemistry\",\n      \"pmids\": [\"35527562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether protection requires secretion or extracellular chaperone activity not dissected\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed a phase-separation-based cytoprotective function, with cytoplasmic proSAAS forming droplet-like spheres that sequester truncated TDP-43.\",\n      \"evidence\": \"Live-cell fluorescence imaging, domain-mapping mutagenesis, yeast toxicity assay\",\n      \"pmids\": [\"35549000\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of cytoplasmic proSAAS spheres in mammalian neurons unestablished\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Expanded the knockout phenotype to anxiety, fear, metabolic, and circadian-shifting deficits, broadening proSAAS's behavioral footprint.\",\n      \"evidence\": \"ProSAAS knockout behavioral battery, metabolic phenotyping, circadian light-pulse protocol\",\n      \"pmids\": [\"35878875\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; which proSAAS peptides/circuits drive the circadian and metabolic phenotypes unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked synaptic, activity-dependent proSAAS regulation to amyloid clearance, showing translational upregulation during homeostatic scaling and plaque reduction in 5xFAD mice.\",\n      \"evidence\": \"Western blot, qPCR, depolarization secretion assay, stereotaxic AAV overexpression in 5xFAD CA1, immunohistochemistry\",\n      \"pmids\": [\"39115041\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of translational/degradation control not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How proSAAS's two functional faces—convertase inhibition and anti-aggregant chaperone activity—are coordinated, and the structural basis of its substrate recognition for both convertases and amyloidogenic clients, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of proSAAS or its complexes\", \"Receptors for proSAAS peptides other than big LEN not identified\", \"Causal role in human neurodegenerative disease not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [14, 17, 20, 21]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [11, 13, 18]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [7, 16]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 14, 24]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 3, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 13, 18]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [11, 18]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [14, 17, 22]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PCSK1\", \"PCSK2\", \"FURIN\", \"CPE\", \"GPR171\", \"PAX6\", \"SNCA\", \"APP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}