{"gene":"COL5A3","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2000,"finding":"COL5A3 encodes the pro-α3(V) chain, which assembles into an α1(V)α2(V)α3(V) heterotrimer. The α3(V) chain is closely related to pro-α1(V) but has distinct N-propeptide sequences and collagenous domain features that explain the low melting temperature of α1(V)α2(V)α3(V) heterotrimers, lack of heparin binding by α3(V) chains, and potential incorporation into heterotypic fibrils. In situ hybridization in mouse embryos detected α3(V) expression primarily in epimysial sheaths of developing muscles and within nascent ligaments adjacent to forming bones and in joints.","method":"Full-length cDNA cloning, sequence analysis, in situ hybridization of mouse embryos","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete primary structure determination with functional domain analysis and direct in situ hybridization expression mapping; foundational characterization paper replicated by subsequent work","pmids":["10722718"],"is_preprint":false},{"year":2011,"finding":"Genetic ablation of Col5a3 in mice (Col5a3−/− mice) demonstrated that the α3(V) chain is required for glucose homeostasis. Col5a3−/− mice are glucose intolerant, insulin-resistant, and hyperglycemic. Mechanistically, islets from mutant mice showed decreased numbers, increased susceptibility to streptozotocin-induced apoptosis, and blunted glucose-stimulated insulin secretion. Additionally, Col5a3−/− white adipose tissue (WAT) and skeletal muscle were defective in insulin-stimulated glucose uptake and failed to mobilize intracellular GLUT4 glucose transporter to the plasma membrane. Female Col5a3−/− mice had reduced dermal fat and were resistant to high-fat diet–induced weight gain.","method":"Gene knockout (null allele generation), glucose tolerance tests, insulin resistance assays, GLUT4 localization assays, islet isolation and glucose-stimulated insulin secretion assays, streptozotocin-induced apoptosis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse model with multiple orthogonal phenotypic readouts (metabolic, cellular, molecular) establishing specific mechanistic roles in pancreatic islets, WAT, and skeletal muscle","pmids":["21293061"],"is_preprint":false},{"year":2004,"finding":"The core promoter of the human COL5A3 gene (within −129 bp of the major transcription start site) lacks a typical TATA motif and has high GC content. Four DNA-protein complexes (A, B, C, D) bind within this region. Complex A (binding −122 to −117 bp) consists of the transcription factor CBF/NF-Y, which activates COL5A3 transcription; complexes B and C act as repressors of promoter activity. Chromatin immunoprecipitation confirmed that CBF/NF-Y directly binds the COL5A3 core promoter in vivo.","method":"Transient transfection reporter assays, DNase I footprinting, electrophoretic mobility shift assay (EMSA), supershift assays with antibodies, chromatin immunoprecipitation (ChIP), mutant CBF-B/NF-YA overexpression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (footprinting, EMSA, ChIP, mutagenesis, reporter assays) in a single focused mechanistic study","pmids":["15316020"],"is_preprint":false},{"year":2010,"finding":"The transcription factor Sp7/Osterix upregulates Col5a3 in osteoblastic cells. Overexpression of Sp7/Osterix significantly increased Col5a3 promoter activity and endogenous mRNA levels, while siRNA knockdown of Sp7/Osterix decreased both. ChIP assay confirmed that Sp7/Osterix interacts with the Col5a3 core promoter at the Sp1 binding site in vivo. Co-overexpression experiments with Sp7/Osterix and Sp1 in an osteoblast differentiation model indicate cooperative regulation of Col5a3 expression.","method":"Promoter reporter assays, siRNA knockdown, chromatin immunoprecipitation (ChIP), co-overexpression experiments, RT-PCR for endogenous mRNA","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP confirms in vivo binding; overexpression and knockdown provide convergent evidence; single lab","pmids":["20206127"],"is_preprint":false},{"year":2010,"finding":"Transcriptional regulation of mouse Col5a3 in osteoblastic cells requires cooperative binding of Sp1/Sp3 (to a GC-rich domain at −194/−186) and CBF/NF-Y (to a CCAAT box at −134/−130). Mutations or deletion of either element decreased transcriptional activity; overexpression of Sp1 increased activity but also competed with Sp family binding at the GC-rich domain, decreasing promoter activity at high concentrations.","method":"Transient transfection reporter assays in ROS17/2.8 osteosarcoma cells, EMSA, site-directed mutagenesis, overexpression","journal":"Acta medica Okayama","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — mutagenesis and EMSA provide mechanistic detail; single lab and single study","pmids":["20424664"],"is_preprint":false},{"year":2012,"finding":"Pro-α3(V) collagen is transiently expressed in mouse wound healing at lower levels than other fibrillar collagen genes. In injured skin, the pro-α3(V) chain was localized by immunohistochemistry to the amorphous non-fibrillar region rather than fine or dense fibrils. The pro-α3(V) chain co-localized with heparan sulfate in the injured skin, suggesting a functional interaction via an acidic segment of the pro-α3(V) chain.","method":"RT-PCR, in situ hybridization, immunohistochemistry, electron microscopy, wound healing mouse model","journal":"Connective tissue research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (RT-PCR, ISH, IHC, EM) establishing subcellular/matrix localization with functional implication; single lab","pmids":["22214369"],"is_preprint":false},{"year":2012,"finding":"Reconstituted fibrils from the α1(V)α2(V)α3(V) (Vp123) subtype of type V collagen showed D-periodic banding at 34°C (~45 nm width) but lost banding pattern when reconstituted at 37°C, and banded fibrils reconstituted at 34°C lost their characteristic pattern within 60 min at 37°C. In contrast, α1(V)2α2(V) (Vp112) fibrils maintained banding at 37°C. This thermal instability of Vp123 banding suggests that α3(V)-containing trimers exist not only as periodic banded fibrils but also as non-fibrillar meshwork structures.","method":"Pepsin treatment of human placenta collagen, fibril reconstitution, transmission electron microscopy at multiple temperatures","journal":"Connective tissue research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution with EM characterization; single study, single lab","pmids":["23092503"],"is_preprint":false},{"year":2009,"finding":"miR-29b directly targets the 3'-UTR of COL5A3 mRNA to repress its expression. Luciferase reporter assays showed that miR-29b decreased and anti-miR-29b increased activity of COL5A3 3'-UTR sequences. miR-29b also decreased endogenous COL5A3 gene expression in osteoblastic cells.","method":"3'-UTR luciferase reporter assays, anti-miR-29b transfection, endogenous gene expression measurement","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct 3'-UTR reporter assay plus endogenous mRNA measurement; replicated in a second independent study (PMID:20194304)","pmids":["19342382","20194304"],"is_preprint":false},{"year":2010,"finding":"miR-29b suppresses COL5A3 expression via its 3'-UTR in renal medullary epithelial cells, as shown by luciferase reporter assay. Knockdown of miR-29b in SS-13(BN) rat kidneys resulted in upregulation of Col5a3 mRNA, supporting direct post-transcriptional regulation.","method":"3'-UTR luciferase reporter assay, in vivo miR-29b knockdown in rat kidneys, real-time PCR for collagen gene expression","journal":"Hypertension","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assay plus in vivo knockdown with mRNA readout; replicates finding from PMID:19342382","pmids":["20194304"],"is_preprint":false},{"year":2020,"finding":"miR-29a directly suppresses COL5A3 expression at the translational level in human pancreatic stellate cells (hPSCs), as demonstrated by Western blot after miR-29a mimic transfection. COL5A3 was identified as one of eight key direct targets of miR-29a in PSCs, placing COL5A3 in the ECM remodeling/collagen biosynthesis pathway regulated by miR-29a in the PDAC tumor microenvironment.","method":"RNAseq transcriptome analysis, Western blot after miR-29a mimic transfection in hPSCs","journal":"BMC cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein-level validation by Western blot plus transcriptome analysis; single lab","pmids":["32660466"],"is_preprint":false},{"year":2025,"finding":"CRISPR knockdown of COL5A3 in human white adipose tissue cell lines significantly increased lipid accumulation (fold change = 1.72, p = 0.0028), establishing a functional role for COL5A3 in suppressing adipogenesis in human adipocytes.","method":"CRISPR knockdown in human white adipose tissue cell lines, lipid accumulation assay (Oil Red O or equivalent)","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean CRISPR KD with quantitative cellular phenotype; single study, confirmed in both preprint and peer-reviewed publication","pmids":["40912257","39371160"],"is_preprint":false},{"year":2025,"finding":"Col5a3 interference (siRNA knockdown) in 3T3-L1 preadipocytes promoted cell proliferation but inhibited differentiation into mature adipocytes, as measured by CCK-8, EdU staining, cell cycle detection, triglyceride assay, and Oil Red O staining. RNA-seq of differentiated adipocytes after Col5a3 interference identified 368 DEGs, with the most significant enrichment in the oxidative phosphorylation pathway, suggesting Col5a3 promotes adipogenesis partly through this pathway.","method":"siRNA knockdown in 3T3-L1 cells, CCK-8 proliferation assay, EdU staining, cell cycle analysis, RT-qPCR, Western blot, triglyceride assay, Oil Red O staining, RNA-seq","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in a single focused mechanistic study; single lab, mechanistic pathway assignment is speculative per authors","pmids":["40004494"],"is_preprint":false}],"current_model":"COL5A3 encodes the pro-α3(V) collagen chain, which assembles into α1(V)α2(V)α3(V) heterotrimers that form thermally less stable fibrils and non-fibrillar meshwork structures in the ECM; its transcription is activated cooperatively by CBF/NF-Y and Sp1, and further upregulated by Sp7/Osterix in osteoblasts, while being post-transcriptionally repressed by miR-29 family members via 3'-UTR binding; genetic deletion in mice causes glucose intolerance, insulin resistance, defective GLUT4 mobilization, and impaired pancreatic islet function, and knockdown in adipocytes increases lipid accumulation, indicating that COL5A3 plays critical roles in regulating collagen fibril geometry, metabolic tissue function, and adipogenesis."},"narrative":{"mechanistic_narrative":"COL5A3 encodes the pro-α3(V) collagen chain, a component of the fibrillar collagen system that assembles into α1(V)α2(V)α3(V) heterotrimers and shapes the geometry of extracellular matrix in connective tissues [PMID:10722718]. Its primary structure diverges from pro-α1(V) in the N-propeptide and collagenous domains, accounting for the low melting temperature of α1(V)α2(V)α3(V) trimers and the absence of heparin binding by the α3(V) chain, and the chain is expressed in epimysial sheaths of developing muscle and nascent ligaments [PMID:10722718]. Reconstituted α1(V)α2(V)α3(V) (Vp123) fibrils display D-periodic banding at 34°C but lose this pattern at 37°C, indicating that α3(V)-containing trimers form both periodic fibrils and non-fibrillar meshwork structures [PMID:23092503]; consistent with this, in healing skin pro-α3(V) localizes to amorphous non-fibrillar matrix and co-localizes with heparan sulfate [PMID:22214369]. Beyond its structural role, COL5A3 is required for systemic glucose homeostasis: Col5a3-null mice are glucose-intolerant, insulin-resistant and hyperglycemic, with reduced islet number, blunted glucose-stimulated insulin secretion, and a failure of white adipose tissue and skeletal muscle to mobilize GLUT4 to the plasma membrane [PMID:21293061]. COL5A3 also constrains adipocyte biology, where loss of expression increases lipid accumulation and alters proliferation and differentiation of preadipocytes [PMID:40912257, PMID:39371160, PMID:40004494]. COL5A3 transcription is driven from a TATA-less, GC-rich core promoter through cooperative binding of CBF/NF-Y at a CCAAT box and Sp1/Sp3 at a GC-rich element, with Sp7/Osterix acting through the Sp1 site to upregulate the gene in osteoblasts [PMID:15316020, PMID:20424664, PMID:20206127], while miR-29 family members (miR-29a/b) directly repress COL5A3 post-transcriptionally via its 3'-UTR [PMID:19342382, PMID:20194304, PMID:32660466].","teleology":[{"year":2000,"claim":"Establishing the identity and structural distinctiveness of the α3(V) chain answered what gene product COL5A3 makes and why its trimers differ from other type V collagen, framing it as a heterotrimer component with unusual thermal and binding properties.","evidence":"Full-length cDNA cloning, sequence analysis, and in situ hybridization in mouse embryos","pmids":["10722718"],"confidence":"High","gaps":["Did not establish the in vivo function of α3(V)-containing fibrils","Tissue distribution beyond embryonic muscle/ligament not resolved"]},{"year":2004,"claim":"Defining the COL5A3 core promoter architecture answered how the gene is transcriptionally controlled, identifying CBF/NF-Y as a direct activator and additional repressive complexes.","evidence":"Reporter assays, DNase I footprinting, EMSA/supershift, and ChIP on the human COL5A3 promoter","pmids":["15316020"],"confidence":"High","gaps":["Identity of the repressor complexes B and C not determined","Did not connect promoter regulation to a physiological signal"]},{"year":2009,"claim":"Identifying miR-29b as a direct 3'-UTR-binding repressor answered whether COL5A3 is controlled post-transcriptionally, adding a layer of negative regulation.","evidence":"3'-UTR luciferase reporter assays with miR-29b/anti-miR-29b and endogenous mRNA measurement in osteoblastic cells","pmids":["19342382","20194304"],"confidence":"Medium","gaps":["Physiological context driving miR-29b regulation not defined","Did not quantify protein-level repression in this study"]},{"year":2010,"claim":"Dissecting cooperative Sp1/Sp3 and CBF/NF-Y binding and Sp7/Osterix input answered how COL5A3 is induced during osteoblast differentiation.","evidence":"Reporter assays, EMSA, site-directed mutagenesis, ChIP, and Sp7/Osterix overexpression/knockdown in osteoblastic cells","pmids":["20424664","20206127"],"confidence":"Medium","gaps":["Mechanism of Sp1 self-competition at high concentration not fully resolved","Single-lab promoter studies; not extended to other cell types"]},{"year":2010,"claim":"Confirming miR-29b repression in renal medullary epithelium with in vivo knockdown extended COL5A3 post-transcriptional control beyond osteoblasts.","evidence":"3'-UTR luciferase reporter assay and in vivo miR-29b knockdown in rat kidneys with mRNA readout","pmids":["20194304"],"confidence":"Medium","gaps":["Functional consequence of COL5A3 derepression in kidney not assessed","Protein-level changes not measured"]},{"year":2011,"claim":"Genetic ablation in mice answered the physiological role of COL5A3, revealing an unexpected requirement for glucose homeostasis, islet survival, and GLUT4 mobilization rather than a purely structural matrix function.","evidence":"Col5a3 knockout mice with glucose tolerance, insulin sensitivity, islet secretion, apoptosis, and GLUT4 localization assays","pmids":["21293061"],"confidence":"High","gaps":["Molecular link between an ECM collagen chain and GLUT4 trafficking unresolved","Cell-autonomous versus systemic contributions not separated"]},{"year":2012,"claim":"In vitro fibril reconstitution and wound-healing localization answered how α3(V)-containing trimers behave physically, showing thermal instability of banded fibrils and a non-fibrillar, heparan-sulfate-associated matrix role.","evidence":"Fibril reconstitution and TEM at multiple temperatures, plus RT-PCR, ISH, IHC, and EM in a mouse wound model","pmids":["23092503","22214369"],"confidence":"Medium","gaps":["Functional role of the non-fibrillar meshwork in vivo not established","In vitro reconstitution may not reflect native assembly"]},{"year":2020,"claim":"Identifying COL5A3 as a direct miR-29a target in pancreatic stellate cells answered how it is regulated in the tumor microenvironment, linking it to ECM remodeling in PDAC.","evidence":"RNAseq transcriptome analysis and Western blot after miR-29a mimic transfection in human pancreatic stellate cells","pmids":["32660466"],"confidence":"Medium","gaps":["Functional impact of COL5A3 repression on the PDAC microenvironment not tested","Single cell-type, single-lab observation"]},{"year":2025,"claim":"Loss-of-function studies in human and murine adipocytes answered whether COL5A3 regulates fat cell biology, showing it constrains lipid accumulation and modulates preadipocyte proliferation and differentiation.","evidence":"CRISPR knockdown in human white adipose cell lines and siRNA knockdown in 3T3-L1 cells with lipid, proliferation, differentiation, and RNA-seq readouts","pmids":["40912257","39371160","40004494"],"confidence":"Medium","gaps":["Apparently opposite directionality (suppressing versus promoting adipogenesis) across systems unresolved","OXPHOS pathway link is correlative","Mechanism connecting a collagen chain to intracellular adipocyte programs unknown"]},{"year":null,"claim":"The molecular mechanism by which an extracellular α3(V) collagen chain controls intracellular processes such as GLUT4 trafficking and adipocyte differentiation remains unexplained.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No identified receptor or signaling intermediary linking COL5A3 matrix to GLUT4 mobilization","No structural model of the native α1(V)α2(V)α3(V) fibril/meshwork in tissue","Human disease association not established in the available corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,6]}],"localization":[{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[0,5,6]}],"complexes":["α1(V)α2(V)α3(V) type V collagen heterotrimer"],"partners":["COL5A1","COL5A2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P25940","full_name":"Collagen alpha-3(V) chain","aliases":[],"length_aa":1745,"mass_kda":172.1,"function":"Type V collagen is a member of group I collagen (fibrillar forming collagen). It is a minor connective tissue component of nearly ubiquitous distribution. Type V collagen binds to DNA, heparan sulfate, thrombospondin, heparin, and insulin","subcellular_location":"Secreted, extracellular space, extracellular matrix; Secreted","url":"https://www.uniprot.org/uniprotkb/P25940/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/COL5A3","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/COL5A3","total_profiled":1310},"omim":[{"mim_id":"617492","title":"OLFACTOMEDIN 2; OLFM2","url":"https://www.omim.org/entry/617492"},{"mim_id":"120216","title":"COLLAGEN, TYPE V, ALPHA-3; COL5A3","url":"https://www.omim.org/entry/120216"},{"mim_id":"120215","title":"COLLAGEN, TYPE V, ALPHA-1; COL5A1","url":"https://www.omim.org/entry/120215"},{"mim_id":"120190","title":"COLLAGEN, TYPE V, ALPHA-2; COL5A2","url":"https://www.omim.org/entry/120190"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/COL5A3"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P25940","domains":[{"cath_id":"2.60.120.200","chopping":"31-221","consensus_level":"high","plddt":81.1774,"start":31,"end":221},{"cath_id":"2.60.120.1000","chopping":"1530-1745","consensus_level":"high","plddt":91.8746,"start":1530,"end":1745}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P25940","model_url":"https://alphafold.ebi.ac.uk/files/AF-P25940-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P25940-F1-predicted_aligned_error_v6.png","plddt_mean":50.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=COL5A3","jax_strain_url":"https://www.jax.org/strain/search?query=COL5A3"},"sequence":{"accession":"P25940","fasta_url":"https://rest.uniprot.org/uniprotkb/P25940.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P25940/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P25940"}},"corpus_meta":[{"pmid":"19342382","id":"PMC_19342382","title":"Biological functions of miR-29b contribute to positive regulation of osteoblast differentiation.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19342382","citation_count":484,"is_preprint":false},{"pmid":"20194304","id":"PMC_20194304","title":"Renal medullary microRNAs in Dahl salt-sensitive rats: miR-29b regulates several collagens and related genes.","date":"2010","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/20194304","citation_count":219,"is_preprint":false},{"pmid":"28867142","id":"PMC_28867142","title":"Exonic Mosaic Mutations Contribute Risk for Autism Spectrum Disorder.","date":"2017","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28867142","citation_count":146,"is_preprint":false},{"pmid":"26822553","id":"PMC_26822553","title":"Analyses of Long Non-Coding RNA and mRNA profiling using RNA sequencing during the pre-implantation phases in pig endometrium.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26822553","citation_count":137,"is_preprint":false},{"pmid":"28125844","id":"PMC_28125844","title":"Proteomic Analysis of the Bovine and Human Ciliary Zonule.","date":"2017","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/28125844","citation_count":68,"is_preprint":false},{"pmid":"10722718","id":"PMC_10722718","title":"The pro-alpha3(V) collagen chain. 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The α3(V) chain is closely related to pro-α1(V) but has distinct N-propeptide sequences and collagenous domain features that explain the low melting temperature of α1(V)α2(V)α3(V) heterotrimers, lack of heparin binding by α3(V) chains, and potential incorporation into heterotypic fibrils. In situ hybridization in mouse embryos detected α3(V) expression primarily in epimysial sheaths of developing muscles and within nascent ligaments adjacent to forming bones and in joints.\",\n      \"method\": \"Full-length cDNA cloning, sequence analysis, in situ hybridization of mouse embryos\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete primary structure determination with functional domain analysis and direct in situ hybridization expression mapping; foundational characterization paper replicated by subsequent work\",\n      \"pmids\": [\"10722718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Genetic ablation of Col5a3 in mice (Col5a3−/− mice) demonstrated that the α3(V) chain is required for glucose homeostasis. Col5a3−/− mice are glucose intolerant, insulin-resistant, and hyperglycemic. Mechanistically, islets from mutant mice showed decreased numbers, increased susceptibility to streptozotocin-induced apoptosis, and blunted glucose-stimulated insulin secretion. Additionally, Col5a3−/− white adipose tissue (WAT) and skeletal muscle were defective in insulin-stimulated glucose uptake and failed to mobilize intracellular GLUT4 glucose transporter to the plasma membrane. Female Col5a3−/− mice had reduced dermal fat and were resistant to high-fat diet–induced weight gain.\",\n      \"method\": \"Gene knockout (null allele generation), glucose tolerance tests, insulin resistance assays, GLUT4 localization assays, islet isolation and glucose-stimulated insulin secretion assays, streptozotocin-induced apoptosis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse model with multiple orthogonal phenotypic readouts (metabolic, cellular, molecular) establishing specific mechanistic roles in pancreatic islets, WAT, and skeletal muscle\",\n      \"pmids\": [\"21293061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The core promoter of the human COL5A3 gene (within −129 bp of the major transcription start site) lacks a typical TATA motif and has high GC content. Four DNA-protein complexes (A, B, C, D) bind within this region. Complex A (binding −122 to −117 bp) consists of the transcription factor CBF/NF-Y, which activates COL5A3 transcription; complexes B and C act as repressors of promoter activity. Chromatin immunoprecipitation confirmed that CBF/NF-Y directly binds the COL5A3 core promoter in vivo.\",\n      \"method\": \"Transient transfection reporter assays, DNase I footprinting, electrophoretic mobility shift assay (EMSA), supershift assays with antibodies, chromatin immunoprecipitation (ChIP), mutant CBF-B/NF-YA overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (footprinting, EMSA, ChIP, mutagenesis, reporter assays) in a single focused mechanistic study\",\n      \"pmids\": [\"15316020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The transcription factor Sp7/Osterix upregulates Col5a3 in osteoblastic cells. Overexpression of Sp7/Osterix significantly increased Col5a3 promoter activity and endogenous mRNA levels, while siRNA knockdown of Sp7/Osterix decreased both. ChIP assay confirmed that Sp7/Osterix interacts with the Col5a3 core promoter at the Sp1 binding site in vivo. Co-overexpression experiments with Sp7/Osterix and Sp1 in an osteoblast differentiation model indicate cooperative regulation of Col5a3 expression.\",\n      \"method\": \"Promoter reporter assays, siRNA knockdown, chromatin immunoprecipitation (ChIP), co-overexpression experiments, RT-PCR for endogenous mRNA\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP confirms in vivo binding; overexpression and knockdown provide convergent evidence; single lab\",\n      \"pmids\": [\"20206127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Transcriptional regulation of mouse Col5a3 in osteoblastic cells requires cooperative binding of Sp1/Sp3 (to a GC-rich domain at −194/−186) and CBF/NF-Y (to a CCAAT box at −134/−130). Mutations or deletion of either element decreased transcriptional activity; overexpression of Sp1 increased activity but also competed with Sp family binding at the GC-rich domain, decreasing promoter activity at high concentrations.\",\n      \"method\": \"Transient transfection reporter assays in ROS17/2.8 osteosarcoma cells, EMSA, site-directed mutagenesis, overexpression\",\n      \"journal\": \"Acta medica Okayama\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — mutagenesis and EMSA provide mechanistic detail; single lab and single study\",\n      \"pmids\": [\"20424664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Pro-α3(V) collagen is transiently expressed in mouse wound healing at lower levels than other fibrillar collagen genes. In injured skin, the pro-α3(V) chain was localized by immunohistochemistry to the amorphous non-fibrillar region rather than fine or dense fibrils. The pro-α3(V) chain co-localized with heparan sulfate in the injured skin, suggesting a functional interaction via an acidic segment of the pro-α3(V) chain.\",\n      \"method\": \"RT-PCR, in situ hybridization, immunohistochemistry, electron microscopy, wound healing mouse model\",\n      \"journal\": \"Connective tissue research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (RT-PCR, ISH, IHC, EM) establishing subcellular/matrix localization with functional implication; single lab\",\n      \"pmids\": [\"22214369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Reconstituted fibrils from the α1(V)α2(V)α3(V) (Vp123) subtype of type V collagen showed D-periodic banding at 34°C (~45 nm width) but lost banding pattern when reconstituted at 37°C, and banded fibrils reconstituted at 34°C lost their characteristic pattern within 60 min at 37°C. In contrast, α1(V)2α2(V) (Vp112) fibrils maintained banding at 37°C. This thermal instability of Vp123 banding suggests that α3(V)-containing trimers exist not only as periodic banded fibrils but also as non-fibrillar meshwork structures.\",\n      \"method\": \"Pepsin treatment of human placenta collagen, fibril reconstitution, transmission electron microscopy at multiple temperatures\",\n      \"journal\": \"Connective tissue research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution with EM characterization; single study, single lab\",\n      \"pmids\": [\"23092503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"miR-29b directly targets the 3'-UTR of COL5A3 mRNA to repress its expression. Luciferase reporter assays showed that miR-29b decreased and anti-miR-29b increased activity of COL5A3 3'-UTR sequences. miR-29b also decreased endogenous COL5A3 gene expression in osteoblastic cells.\",\n      \"method\": \"3'-UTR luciferase reporter assays, anti-miR-29b transfection, endogenous gene expression measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3'-UTR reporter assay plus endogenous mRNA measurement; replicated in a second independent study (PMID:20194304)\",\n      \"pmids\": [\"19342382\", \"20194304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"miR-29b suppresses COL5A3 expression via its 3'-UTR in renal medullary epithelial cells, as shown by luciferase reporter assay. Knockdown of miR-29b in SS-13(BN) rat kidneys resulted in upregulation of Col5a3 mRNA, supporting direct post-transcriptional regulation.\",\n      \"method\": \"3'-UTR luciferase reporter assay, in vivo miR-29b knockdown in rat kidneys, real-time PCR for collagen gene expression\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assay plus in vivo knockdown with mRNA readout; replicates finding from PMID:19342382\",\n      \"pmids\": [\"20194304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-29a directly suppresses COL5A3 expression at the translational level in human pancreatic stellate cells (hPSCs), as demonstrated by Western blot after miR-29a mimic transfection. COL5A3 was identified as one of eight key direct targets of miR-29a in PSCs, placing COL5A3 in the ECM remodeling/collagen biosynthesis pathway regulated by miR-29a in the PDAC tumor microenvironment.\",\n      \"method\": \"RNAseq transcriptome analysis, Western blot after miR-29a mimic transfection in hPSCs\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein-level validation by Western blot plus transcriptome analysis; single lab\",\n      \"pmids\": [\"32660466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CRISPR knockdown of COL5A3 in human white adipose tissue cell lines significantly increased lipid accumulation (fold change = 1.72, p = 0.0028), establishing a functional role for COL5A3 in suppressing adipogenesis in human adipocytes.\",\n      \"method\": \"CRISPR knockdown in human white adipose tissue cell lines, lipid accumulation assay (Oil Red O or equivalent)\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean CRISPR KD with quantitative cellular phenotype; single study, confirmed in both preprint and peer-reviewed publication\",\n      \"pmids\": [\"40912257\", \"39371160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Col5a3 interference (siRNA knockdown) in 3T3-L1 preadipocytes promoted cell proliferation but inhibited differentiation into mature adipocytes, as measured by CCK-8, EdU staining, cell cycle detection, triglyceride assay, and Oil Red O staining. RNA-seq of differentiated adipocytes after Col5a3 interference identified 368 DEGs, with the most significant enrichment in the oxidative phosphorylation pathway, suggesting Col5a3 promotes adipogenesis partly through this pathway.\",\n      \"method\": \"siRNA knockdown in 3T3-L1 cells, CCK-8 proliferation assay, EdU staining, cell cycle analysis, RT-qPCR, Western blot, triglyceride assay, Oil Red O staining, RNA-seq\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in a single focused mechanistic study; single lab, mechanistic pathway assignment is speculative per authors\",\n      \"pmids\": [\"40004494\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"COL5A3 encodes the pro-α3(V) collagen chain, which assembles into α1(V)α2(V)α3(V) heterotrimers that form thermally less stable fibrils and non-fibrillar meshwork structures in the ECM; its transcription is activated cooperatively by CBF/NF-Y and Sp1, and further upregulated by Sp7/Osterix in osteoblasts, while being post-transcriptionally repressed by miR-29 family members via 3'-UTR binding; genetic deletion in mice causes glucose intolerance, insulin resistance, defective GLUT4 mobilization, and impaired pancreatic islet function, and knockdown in adipocytes increases lipid accumulation, indicating that COL5A3 plays critical roles in regulating collagen fibril geometry, metabolic tissue function, and adipogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"COL5A3 encodes the pro-α3(V) collagen chain, a component of the fibrillar collagen system that assembles into α1(V)α2(V)α3(V) heterotrimers and shapes the geometry of extracellular matrix in connective tissues [#0]. Its primary structure diverges from pro-α1(V) in the N-propeptide and collagenous domains, accounting for the low melting temperature of α1(V)α2(V)α3(V) trimers and the absence of heparin binding by the α3(V) chain, and the chain is expressed in epimysial sheaths of developing muscle and nascent ligaments [#0]. Reconstituted α1(V)α2(V)α3(V) (Vp123) fibrils display D-periodic banding at 34°C but lose this pattern at 37°C, indicating that α3(V)-containing trimers form both periodic fibrils and non-fibrillar meshwork structures [#6]; consistent with this, in healing skin pro-α3(V) localizes to amorphous non-fibrillar matrix and co-localizes with heparan sulfate [#5]. Beyond its structural role, COL5A3 is required for systemic glucose homeostasis: Col5a3-null mice are glucose-intolerant, insulin-resistant and hyperglycemic, with reduced islet number, blunted glucose-stimulated insulin secretion, and a failure of white adipose tissue and skeletal muscle to mobilize GLUT4 to the plasma membrane [#1]. COL5A3 also constrains adipocyte biology, where loss of expression increases lipid accumulation and alters proliferation and differentiation of preadipocytes [#10, #11]. COL5A3 transcription is driven from a TATA-less, GC-rich core promoter through cooperative binding of CBF/NF-Y at a CCAAT box and Sp1/Sp3 at a GC-rich element, with Sp7/Osterix acting through the Sp1 site to upregulate the gene in osteoblasts [#2, #4, #3], while miR-29 family members (miR-29a/b) directly repress COL5A3 post-transcriptionally via its 3'-UTR [#7, #8, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the identity and structural distinctiveness of the α3(V) chain answered what gene product COL5A3 makes and why its trimers differ from other type V collagen, framing it as a heterotrimer component with unusual thermal and binding properties.\",\n      \"evidence\": \"Full-length cDNA cloning, sequence analysis, and in situ hybridization in mouse embryos\",\n      \"pmids\": [\"10722718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the in vivo function of α3(V)-containing fibrils\", \"Tissue distribution beyond embryonic muscle/ligament not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defining the COL5A3 core promoter architecture answered how the gene is transcriptionally controlled, identifying CBF/NF-Y as a direct activator and additional repressive complexes.\",\n      \"evidence\": \"Reporter assays, DNase I footprinting, EMSA/supershift, and ChIP on the human COL5A3 promoter\",\n      \"pmids\": [\"15316020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the repressor complexes B and C not determined\", \"Did not connect promoter regulation to a physiological signal\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying miR-29b as a direct 3'-UTR-binding repressor answered whether COL5A3 is controlled post-transcriptionally, adding a layer of negative regulation.\",\n      \"evidence\": \"3'-UTR luciferase reporter assays with miR-29b/anti-miR-29b and endogenous mRNA measurement in osteoblastic cells\",\n      \"pmids\": [\"19342382\", \"20194304\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological context driving miR-29b regulation not defined\", \"Did not quantify protein-level repression in this study\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Dissecting cooperative Sp1/Sp3 and CBF/NF-Y binding and Sp7/Osterix input answered how COL5A3 is induced during osteoblast differentiation.\",\n      \"evidence\": \"Reporter assays, EMSA, site-directed mutagenesis, ChIP, and Sp7/Osterix overexpression/knockdown in osteoblastic cells\",\n      \"pmids\": [\"20424664\", \"20206127\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of Sp1 self-competition at high concentration not fully resolved\", \"Single-lab promoter studies; not extended to other cell types\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Confirming miR-29b repression in renal medullary epithelium with in vivo knockdown extended COL5A3 post-transcriptional control beyond osteoblasts.\",\n      \"evidence\": \"3'-UTR luciferase reporter assay and in vivo miR-29b knockdown in rat kidneys with mRNA readout\",\n      \"pmids\": [\"20194304\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of COL5A3 derepression in kidney not assessed\", \"Protein-level changes not measured\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Genetic ablation in mice answered the physiological role of COL5A3, revealing an unexpected requirement for glucose homeostasis, islet survival, and GLUT4 mobilization rather than a purely structural matrix function.\",\n      \"evidence\": \"Col5a3 knockout mice with glucose tolerance, insulin sensitivity, islet secretion, apoptosis, and GLUT4 localization assays\",\n      \"pmids\": [\"21293061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between an ECM collagen chain and GLUT4 trafficking unresolved\", \"Cell-autonomous versus systemic contributions not separated\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"In vitro fibril reconstitution and wound-healing localization answered how α3(V)-containing trimers behave physically, showing thermal instability of banded fibrils and a non-fibrillar, heparan-sulfate-associated matrix role.\",\n      \"evidence\": \"Fibril reconstitution and TEM at multiple temperatures, plus RT-PCR, ISH, IHC, and EM in a mouse wound model\",\n      \"pmids\": [\"23092503\", \"22214369\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of the non-fibrillar meshwork in vivo not established\", \"In vitro reconstitution may not reflect native assembly\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identifying COL5A3 as a direct miR-29a target in pancreatic stellate cells answered how it is regulated in the tumor microenvironment, linking it to ECM remodeling in PDAC.\",\n      \"evidence\": \"RNAseq transcriptome analysis and Western blot after miR-29a mimic transfection in human pancreatic stellate cells\",\n      \"pmids\": [\"32660466\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional impact of COL5A3 repression on the PDAC microenvironment not tested\", \"Single cell-type, single-lab observation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Loss-of-function studies in human and murine adipocytes answered whether COL5A3 regulates fat cell biology, showing it constrains lipid accumulation and modulates preadipocyte proliferation and differentiation.\",\n      \"evidence\": \"CRISPR knockdown in human white adipose cell lines and siRNA knockdown in 3T3-L1 cells with lipid, proliferation, differentiation, and RNA-seq readouts\",\n      \"pmids\": [\"40912257\", \"39371160\", \"40004494\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Apparently opposite directionality (suppressing versus promoting adipogenesis) across systems unresolved\", \"OXPHOS pathway link is correlative\", \"Mechanism connecting a collagen chain to intracellular adipocyte programs unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism by which an extracellular α3(V) collagen chain controls intracellular processes such as GLUT4 trafficking and adipocyte differentiation remains unexplained.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified receptor or signaling intermediary linking COL5A3 matrix to GLUT4 mobilization\", \"No structural model of the native α1(V)α2(V)α3(V) fibril/meshwork in tissue\", \"Human disease association not established in the available corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [0, 5, 6]}\n    ],\n    \"complexes\": [\"α1(V)α2(V)α3(V) type V collagen heterotrimer\"],\n    \"partners\": [\"COL5A1\", \"COL5A2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}