{"gene":"COMP","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":1992,"finding":"COMP cDNA cloning revealed a 755 amino acid protein that forms a homopentamer composed of five identical disulfide-linked subunits, with structural homology to the carboxyl-terminal half of thrombospondins including calcium-binding type 3 repeat domains and type 2/EGF repeat domains; the N-terminal 84 amino acids are unique to COMP.","method":"cDNA cloning, sequence analysis, expression in COS cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct recombinant expression and sequence analysis establishing oligomeric state and domain structure, replicated across subsequent studies","pmids":["1429587"],"is_preprint":false},{"year":1995,"finding":"Mutations in exon 17B of COMP (single base-pair changes or 3 bp deletions) cause pseudoachondroplasia; six mutations delete or alter a conserved aspartic acid residue within the calcium-binding type 3 repeats, establishing that the calcium-binding domain is functionally critical.","method":"SSCP analysis and nucleotide sequencing of familial and isolated PSACH cases","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutation identification in eight independent cases, independently replicated in subsequent studies","pmids":["7670471"],"is_preprint":false},{"year":1998,"finding":"Mutant COMP is retained in enlarged cisternae of the rough endoplasmic reticulum (rER) of PSACH chondrocytes in vitro, and this intracellular retention is associated with chondrocyte death; retention appears linked to the differentiated chondrocyte phenotype as dedifferentiated PSACH chondrocytes in monolayer do not retain COMP intracellularly.","method":"Alginate bead 3D culture of PSACH chondrocytes, immunostaining, electron microscopy","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cell culture experiments with phenotypic readout, single lab with multiple methods","pmids":["9923655"],"is_preprint":false},{"year":2000,"finding":"The D469del PSACH mutation disrupts calcium binding: wild-type recombinant COMP binds 10–12 Ca²⁺ ions/molecule with cooperative, calcium-induced conformational changes (by circular dichroism), whereas D469del COMP binds approximately half as many Ca²⁺ ions and shows no large CD spectral change with Ca²⁺; the mutation specifically affects calcium binding without affecting Zn²⁺, Cu²⁺, or Ni²⁺ binding.","method":"Recombinant protein expression in E. coli, equilibrium dialysis, circular dichroism spectroscopy","journal":"Cell calcium","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution with multiple orthogonal methods (equilibrium dialysis + CD spectroscopy), single lab","pmids":["11013461"],"is_preprint":false},{"year":2001,"finding":"Chaperone proteins calreticulin, PDI, Grp94, BiP, and ERp72 are co-localized with retained COMP in the enlarged rER cisternae of PSACH chondrocytes; immunoprecipitation, Western blot, and FRET analyses show CRT, PDI, and Grp94 are in close proximity to both normal and mutant COMP, and BiP is closely associated with mutant COMP, indicating these chaperones participate in processing of wild-type COMP and in retention of mutant COMP.","method":"Immunoprecipitation, Western blot, FRET, immunoelectron microscopy of PSACH chondrocytes in vivo and in alginate bead culture","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus FRET plus in vivo immunolocalization, multiple orthogonal methods in single lab","pmids":["11470401"],"is_preprint":false},{"year":2004,"finding":"COMP mutations in the type 3 calcium-binding repeats cause retention of COMP, type IX collagen, and matrilin-3 (but not aggrecan and type II collagen) within the rER of chondrocytes in 3D culture; the absence of COMP, type IX collagen, and matrilin-3 from the extracellular matrix leads to disorganized matrix without organized collagen fibril bundles, establishing that these proteins cooperate in matrix assembly.","method":"3D alginate culture of PSACH chondrocytes with G427E, D469del, and D511Y mutations; immunostaining; ultrastructural analysis","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cell culture experiments with three distinct mutations plus ultrastructural analysis, single lab","pmids":["15694129"],"is_preprint":false},{"year":2004,"finding":"DeltaD469 COMP is retained in the ER of chondrocytic RCS cells (delaying secretion) but is efficiently secreted by non-chondrocytic COS-1 cells, demonstrating a cell-type-specific trafficking defect; ER accumulation of DeltaD469 COMP in RCS cells also causes co-retention of type IX collagen but not aggrecan; secreted mutant COMP disrupts assembly of normal fibrillar matrix.","method":"Expression of DeltaD469 COMP mutant in RCS and COS-1 cells, pulse-chase, immunofluorescence, ECM assembly assay","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-type comparison with multiple readouts, single lab","pmids":["15579310"],"is_preprint":false},{"year":2007,"finding":"Pentameric COMP acts as a catalyst of collagen I and II fibrillogenesis: it accelerates fibril formation, increases the amount of collagen in fibrillar form, and produces fibrils with a narrow diameter distribution (149 ± 16 nm); monomeric COMP lacking the N-terminal coiled-coil domain decelerates fibrillogenesis, demonstrating that pentameric assembly is required; COMP is not incorporated into mature fibrils and dissociates upon fibril completion.","method":"In vitro collagen fibrillogenesis assay with pentameric and monomeric COMP; turbidity measurement; electron microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assay with monomeric vs. pentameric COMP comparison plus EM, multiple orthogonal methods","pmids":["17716974"],"is_preprint":false},{"year":2007,"finding":"In PSACH growth plate chondrocytes, COMP mutations (type 3 repeat) correlate with ER retention severity proportional to clinical phenotype; PSACH mutations cause more cells to retain COMP than MED mutations; C-terminal domain mutations do not show this correlation, suggesting domain-specific pathomechanisms.","method":"Expression of 12 different recombinant COMP mutations in RCS cells; immunofluorescence scoring of ER retention","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, single method (immunofluorescence), but systematic comparison across 12 mutations","pmids":["17570134"],"is_preprint":false},{"year":2000,"finding":"MMP-19 and MMP-20 (enamelysin) cleave COMP, generating a major proteolytic product of 60 kDa, establishing these MMPs as enzymes capable of degrading COMP in the extracellular matrix.","method":"In vitro cleavage assay with recombinant MMP-19 and MMP-20; Western blot","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro enzymatic assay, single lab, single method per enzyme","pmids":["10922468"],"is_preprint":false},{"year":2011,"finding":"Retention of D469del-COMP in chondrocytes triggers caspase-independent necroptosis: it stimulates the unfolded protein response (Chop, Gadd34), elevates Nox4 and Ero1β generating reactive oxygen species, induces DNA damage (γH2AX), and produces cleaved AIF without activated caspases; loss of growth plate chondrocytes by necroptosis was also confirmed in a PSACH mouse model.","method":"Inducible expression system in rat chondrosarcoma cells; Western blot; immunofluorescence; in vivo mouse model","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — inducible cell model plus in vivo mouse model, multiple pathway readouts, single lab","pmids":["22154936"],"is_preprint":false},{"year":2011,"finding":"In a knock-in mouse model expressing D469del COMP, mutant COMP is retained in chondrocyte ER causing reduced proliferation and increased apoptosis without classical unfolded protein response activation; instead, microarray identified oxidative stress, cell cycle regulation, and apoptosis gene expression changes as the primary cellular response.","method":"Knock-in mouse model; growth plate histology; TUNEL; BrdU; microarray; UPR marker analysis","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic model with multiple readouts, single lab","pmids":["22006726"],"is_preprint":false},{"year":2016,"finding":"COMP fulfills an intracellular function in assisting collagen secretion: COMP-null fibroblasts retain collagens in the ER, collagen secretion is fully restored by reintroducing wild-type COMP; lack of COMP–collagen interaction in extracellular space also alters collagen fibril morphology and density, changing skin biomechanical properties; COMP-null mice show severely attenuated fibrotic responses.","method":"COMP knockout mouse fibroblasts; ER retention assay; collagen fibril EM; biomechanical testing; fibrosis model in vivo; rescue with wild-type COMP","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — loss-of-function with specific molecular rescue, multiple orthogonal methods (EM, biomechanics, in vivo fibrosis model), single lab","pmids":["26746240"],"is_preprint":false},{"year":2018,"finding":"COMP interacts directly with the C-terminus of Piezo1 via its own C-terminus and activates endogenous Piezo1 currents, leading to intracellular Ca²⁺ influx, Ca²⁺/calmodulin-dependent protein kinase II and eNOS activation, and nitric oxide production; COMP⁻/⁻ mice display elevated blood pressure and impaired acetylcholine-induced endothelium-dependent relaxation that is rescued by Piezo1 activator Yoda1.","method":"Co-immunoprecipitation; bioluminescence resonance energy transfer (BRET); patch-clamp electrophysiology; siRNA knockdown; COMP⁻/⁻ mouse blood pressure measurement; EPR detection of NO","journal":"Hypertension (Dallas, Tex. : 1979)","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (co-IP, BRET, patch-clamp, in vivo KO rescue), single lab","pmids":["34983194"],"is_preprint":false},{"year":2018,"finding":"COMP localizes within mitochondria of vascular smooth muscle cells and interacts with prohibitin 2; disruption of the COMP–prohibitin 2 interaction impairs mitochondrial oxidative phosphorylation and causes VSMC dedifferentiation (loss of contractile phenotype) in vitro and enhanced neointima formation after rat carotid artery injury in vivo.","method":"Subcellular fractionation; fluorescence assay; liquid chromatography-tandem MS interactome; mitochondrial transplantation; microarray; carotid artery injury model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-identified interaction plus functional in vivo readout, multiple methods, single lab","pmids":["29867124"],"is_preprint":false},{"year":2018,"finding":"Mutant COMP retention in chondrocytes upregulates miR-223, disturbing the adipogenesis–osteogenesis balance, reducing bone mineral density, bone quality, mechanical strength, and subchondral bone thickness in the MT-COMP pseudoachondroplasia mouse model.","method":"MT-COMP transgenic mouse model; microCT; bone mechanical testing; miRNA profiling; multiple analytic approaches","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo transgenic model with multiple analytic methods, single lab","pmids":["29309831"],"is_preprint":false},{"year":2018,"finding":"HSC-derived COMP signals through the CD36 receptor on HCC cells to phosphorylate ERK and AKT, upregulating EMT markers (Slug, Twist), MMP-2, and MMP-9, promoting HCC proliferation and metastasis in vitro and in vivo; knockdown of COMP in LX2 hepatic stellate cells reduces MEK/ERK and PI3K/AKT activation in HCC cells.","method":"Recombinant COMP protein treatment; CD36 siRNA knockdown; Western blot; transwell coculture; mouse xenograft model","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor identification by knockdown plus in vivo model, single lab, multiple orthogonal methods","pmids":["30231922"],"is_preprint":false},{"year":2018,"finding":"COMP binds specifically to a GXKGHR motif on the collagen II triple helix found exclusively in fibrillar collagens; this binding site was identified using a recombinant collagen II peptide library and overlaps with recognition sites of other collagen-binding partners (PEDF, heparin) and spans lysine residues involved in collagen cross-links, suggesting COMP may protect collagen helices from premature cross-linking.","method":"Recombinant collagen II peptide library binding screen; binding assays with COMP and TSP-4","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro binding assay with peptide library, single lab, limited functional validation","pmids":["30464261"],"is_preprint":false},{"year":2020,"finding":"Two mutations in COMP cause familial carpal tunnel syndrome by impairing COMP secretion in tenocytes (the CTS-specific mutation also causes ER stress, unfolded protein response, cell death, inflammation, and progressive fibrosis in tendons/ligaments); the CTS-specific mutation fails to oligomerize properly and is trapped in the ER, whereas the mutation associated with both CTS and MED also perturbs secretion in chondrocytes.","method":"Patient biopsy histology; mouse models; ER stress markers; UPR assays; co-IP for oligomerization; immunofluorescence","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — human biopsy plus multiple mouse models plus biochemical assays; multiple orthogonal methods; Nature-level peer review","pmids":["32686688"],"is_preprint":false},{"year":2007,"finding":"Expression of PSACH-associated mutant COMP in tendon fibroblasts increases apoptotic cell death irrespective of secretory pattern: D475N and D469Δ are retained in ER while H587R is secreted like wild-type, yet all three mutants disrupt collagen I matrix assembly and induce apoptosis, indicating heterogeneous pathogenic mechanisms in tendon.","method":"Adenoviral gene transfer into tendon fibroblast cultures; immunostaining; cell viability assays; ECM analysis","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — three mutant comparison with defined phenotypic readout, single lab","pmids":["17307347"],"is_preprint":false},{"year":2001,"finding":"Transcription of the COMP gene is driven by a TATA-less/CAAT-less promoter with multiple transcription start sites; the 370 bp proximal region has the strongest promoter activity; the SP1 transcription factor plays a role in regulating COMP expression; tissue-specific usage of transcription start sites differs between chondrocytes and tendon/ligament cells.","method":"Promoter cloning; primer extension; reporter gene (luciferase) assays in chondrocyte, tendon, and ligament cells; SP1 binding analysis","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional promoter dissection with reporter assays and primer extension, single lab","pmids":["11223338"],"is_preprint":false},{"year":2007,"finding":"Combined ablation of collagen IX and COMP in mice produces shortened, widened long bones with severe growth plate abnormalities (large hypocellular areas, loss of columnar chondrocyte organization) not seen in COMP-single-KO mice; COMP-null mice alone have no overt skeletal phenotype but show altered matrilin-3 deposition, indicating COMP cooperates with collagen IX in growth plate organization.","method":"Double knockout mouse model (collagen IX and COMP); histology; bone morphometry; immunostaining","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via double KO mouse, single lab","pmids":["18191556"],"is_preprint":false}],"current_model":"COMP is a disulfide-linked homopentamer that functions as a catalyst of collagen fibrillogenesis (requiring its pentameric assembly), acts as an intracellular chaperone assisting collagen secretion from the ER, binds fibrillar collagens via a specific GXKGHR motif on the triple helix, activates the mechanosensory ion channel Piezo1 to promote eNOS/nitric oxide production in vascular endothelium, maintains vascular smooth muscle contractile identity by interacting with mitochondrial prohibitin 2, and signals through CD36 to activate MEK/ERK and PI3K/AKT in cancer cells; disease-causing mutations in its calcium-binding type 3 repeat domains disrupt Ca²⁺ binding and protein folding, leading to chaperone-associated ER retention, unfolded protein response, oxidative stress, and caspase-independent necroptosis of growth plate chondrocytes that underlies pseudoachondroplasia and multiple epiphyseal dysplasia."},"narrative":{"mechanistic_narrative":"COMP is a disulfide-linked homopentamer, structurally related to the C-terminal half of thrombospondins, that organizes collagenous extracellular matrix in cartilage, tendon and other connective tissues [PMID:1429587]. Pentameric assembly enables COMP to act as a catalyst of type I and II collagen fibrillogenesis—accelerating fibril formation and enforcing a narrow fibril diameter while dissociating from completed fibrils—a function lost by monomeric COMP [PMID:17716974]; it engages fibrillar collagens through a specific GXKGHR motif on the triple helix [PMID:30464261]. COMP also performs an intracellular role, assisting collagen secretion from the ER such that COMP-null cells retain collagen and show attenuated fibrotic responses, fully rescued by wild-type COMP [PMID:26746240]. In the growth plate it cooperates with type IX collagen and matrilin-3 to build organized fibril bundles [PMID:15694129, PMID:18191556]. Beyond matrix assembly, COMP activates the mechanosensory channel Piezo1 to drive Ca²⁺/CaMKII/eNOS-dependent nitric oxide production in vascular endothelium, with COMP⁻/⁻ mice showing elevated blood pressure [PMID:34983194], maintains vascular smooth muscle contractile identity through a mitochondrial interaction with prohibitin 2 [PMID:29867124], and signals via CD36 to activate MEK/ERK and PI3K/AKT in hepatocellular carcinoma [PMID:30231922]. Dominant mutations in the calcium-binding type 3 repeats abolish Ca²⁺ binding and disrupt folding [PMID:7670471, PMID:11013461], causing chaperone-associated ER retention of mutant COMP together with collagen IX and matrilin-3 [PMID:11470401, PMID:15694129], triggering unfolded protein response, oxidative stress, and caspase-independent necroptosis of chondrocytes [PMID:22154936]; these defects underlie pseudoachondroplasia, multiple epiphyseal dysplasia, and familial carpal tunnel syndrome [PMID:7670471, PMID:32686688].","teleology":[{"year":1992,"claim":"Establishing COMP's primary structure and quaternary organization defined it as a pentameric thrombospondin-related matrix protein and set the framework for all later functional work.","evidence":"cDNA cloning, sequence analysis, and expression in COS cells","pmids":["1429587"],"confidence":"High","gaps":["Does not assign a biochemical or cellular function","Role of the unique N-terminal region undefined"]},{"year":1995,"claim":"Linking COMP to pseudoachondroplasia identified the calcium-binding type 3 repeats as functionally critical and established COMP as a disease gene.","evidence":"SSCP and sequencing of familial and isolated PSACH cases","pmids":["7670471"],"confidence":"High","gaps":["Does not show how mutations affect protein function","Cellular consequence of mutations unknown"]},{"year":2000,"claim":"Showing that the D469del mutation specifically halves Ca²⁺ binding and abolishes the calcium-induced conformational change provided the biochemical basis for the disease-causing defect.","evidence":"Recombinant protein, equilibrium dialysis, and circular dichroism spectroscopy","pmids":["11013461"],"confidence":"High","gaps":["Single mutation tested biochemically","Link between altered conformation and cellular retention not directly shown"]},{"year":2001,"claim":"Identifying that mutant COMP is retained in the rER alongside resident chaperones revealed an ER quality-control/chaperone-associated retention mechanism for the disease.","evidence":"Co-IP, FRET, and immunoelectron microscopy of PSACH chondrocytes","pmids":["9923655","11470401"],"confidence":"High","gaps":["Mechanism by which retention causes cell death not yet defined","Chaperone associations are proximity-based, not functional dependencies"]},{"year":2001,"claim":"Dissecting the COMP promoter defined the transcriptional control of its tissue-specific expression in chondrocytes versus tendon/ligament cells.","evidence":"Promoter cloning, primer extension, luciferase reporters, and SP1 binding analysis","pmids":["11223338"],"confidence":"Medium","gaps":["Full set of regulatory factors unresolved","How tissue-specific start-site usage is controlled is unknown"]},{"year":2007,"claim":"Demonstrating that pentameric but not monomeric COMP catalyzes collagen I/II fibrillogenesis established the molecular requirement of oligomerization for matrix assembly function.","evidence":"In vitro fibrillogenesis assay comparing pentameric and monomeric COMP, with EM","pmids":["17716974"],"confidence":"High","gaps":["Structural basis of the catalytic mechanism unresolved","In vivo relevance not directly tested here"]},{"year":2007,"claim":"Showing ER-retention severity scales with clinical phenotype for type 3 repeat mutations but not C-terminal mutations indicated domain-specific pathomechanisms.","evidence":"Expression of 12 mutations in RCS cells with immunofluorescence scoring","pmids":["17570134"],"confidence":"Medium","gaps":["Single readout (immunofluorescence)","Mechanism for C-terminal mutations not defined"]},{"year":2007,"claim":"Revealing that secreted as well as retained tendon mutants induce apoptosis showed pathogenic mechanisms in tendon are heterogeneous and not solely retention-driven.","evidence":"Adenoviral expression of three mutants in tendon fibroblasts with viability and ECM assays","pmids":["17307347"],"confidence":"Medium","gaps":["Apoptotic pathway not delineated","Single cell type, single lab"]},{"year":2007,"claim":"Genetic epistasis from collagen IX/COMP double knockout established that COMP cooperates with collagen IX in growth plate organization, explaining the mild single-KO phenotype.","evidence":"Double knockout mouse model with histology and morphometry","pmids":["18191556"],"confidence":"Medium","gaps":["Molecular nature of the cooperation not resolved","Contribution of matrilin-3 not isolated"]},{"year":2004,"claim":"Co-retention of collagen IX and matrilin-3 with mutant COMP showed these matrix proteins assemble cooperatively and that loss from the ECM disorganizes fibril bundles.","evidence":"3D alginate culture of PSACH chondrocytes and RCS/COS-1 cell-type comparison","pmids":["15694129","15579310"],"confidence":"Medium","gaps":["Direct binding interfaces not mapped","Cell-type basis of the trafficking defect not mechanistically explained"]},{"year":2011,"claim":"Defining the downstream death pathway showed mutant COMP retention triggers UPR, ROS, DNA damage and caspase-independent necroptosis of growth plate chondrocytes in vitro and in vivo.","evidence":"Inducible RCS cell model and PSACH mouse model with pathway readouts","pmids":["22154936","22006726"],"confidence":"Medium","gaps":["UPR involvement differs between models","Trigger linking retention to oxidative stress not fully defined"]},{"year":2016,"claim":"Loss-of-function with molecular rescue established an intracellular role for COMP in assisting collagen secretion and its requirement for fibrotic responses.","evidence":"COMP-null fibroblasts, ER retention/rescue, fibril EM, biomechanics, and in vivo fibrosis model","pmids":["26746240"],"confidence":"High","gaps":["Mechanism of intracellular collagen chaperoning not defined","Whether this requires pentamerization untested"]},{"year":2018,"claim":"Identifying the GXKGHR motif defined the specific COMP recognition site on fibrillar collagen triple helices.","evidence":"Recombinant collagen II peptide library binding screen","pmids":["30464261"],"confidence":"Medium","gaps":["In vitro binding only, limited functional validation","Protective role against cross-linking not directly demonstrated"]},{"year":2018,"claim":"Establishing COMP–Piezo1 coupling revealed a non-matrix signaling role in endothelial mechanotransduction and blood pressure regulation.","evidence":"Co-IP, BRET, patch-clamp, COMP⁻/⁻ mouse blood pressure with Yoda1 rescue, EPR for NO","pmids":["34983194"],"confidence":"High","gaps":["Structural basis of the C-terminal interaction unresolved","Relationship to COMP's matrix function unclear"]},{"year":2018,"claim":"Localizing COMP to mitochondria via prohibitin 2 connected it to vascular smooth muscle bioenergetics and contractile identity.","evidence":"Subcellular fractionation, LC-MS/MS interactome, mitochondrial transplantation, carotid injury model","pmids":["29867124"],"confidence":"Medium","gaps":["How a secreted matrix protein reaches mitochondria unexplained","Direct binding not structurally validated"]},{"year":2018,"claim":"Demonstrating CD36-dependent MEK/ERK and PI3K/AKT activation identified a paracrine tumor-promoting signaling axis for COMP in hepatocellular carcinoma.","evidence":"Recombinant COMP treatment, CD36 knockdown, coculture, and xenograft model","pmids":["30231922"],"confidence":"Medium","gaps":["Direct COMP–CD36 binding not structurally shown","Generalizability beyond HCC untested"]},{"year":2018,"claim":"Linking miR-223 upregulation to the adipogenesis–osteogenesis imbalance connected chondrocyte ER retention to systemic bone quality defects.","evidence":"MT-COMP transgenic mouse, microCT, bone mechanics, miRNA profiling","pmids":["29309831"],"confidence":"Medium","gaps":["Causal chain from miR-223 to bone phenotype not proven","Single model system"]},{"year":2020,"claim":"Identifying COMP mutations that cause familial carpal tunnel syndrome through impaired tenocyte secretion extended the disease spectrum and tied oligomerization failure to tendon/ligament fibrosis.","evidence":"Patient biopsies, mouse models, UPR assays, and co-IP for oligomerization","pmids":["32686688"],"confidence":"High","gaps":["Tissue specificity of the phenotype not fully explained","Why some mutations cause CTS versus MED unresolved"]},{"year":null,"claim":"How COMP's intracellular collagen-secretion chaperone activity, its extracellular fibrillogenesis catalysis, and its distinct signaling roles (Piezo1, prohibitin 2, CD36) are coordinated within and across tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model linking matrix and signaling functions","Mechanism of subcellular/mitochondrial targeting unknown","Whether signaling roles require pentameric assembly untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[7,17]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13]}],"localization":[{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[7,12]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,4,12]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[9,17]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[14]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[7,12,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[21,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[13,14,16]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,10,18]}],"complexes":[],"partners":["COL2A1","COL9A1","MATN3","PIEZO1","PHB2","CD36"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P49747","full_name":"Cartilage oligomeric matrix protein","aliases":["Thrombospondin-5","TSP5"],"length_aa":757,"mass_kda":82.9,"function":"Plays a role in the structural integrity of cartilage via its interaction with other extracellular matrix proteins such as the collagens and fibronectin. Can mediate the interaction of chondrocytes with the cartilage extracellular matrix through interaction with cell surface integrin receptors (PubMed:16051604, PubMed:16542502). Could play a role in the pathogenesis of osteoarthritis (PubMed:16542502). Potent suppressor of apoptosis in both primary chondrocytes and transformed cells. Suppresses apoptosis by blocking the activation of caspase-3 and by inducing the IAP family of survival proteins (BIRC3, BIRC2, BIRC5 and XIAP) (PubMed:17993464). Essential for maintaining a vascular smooth muscle cells (VSMCs) contractile/differentiated phenotype under physiological and pathological stimuli. Maintains this phenotype of VSMCs by interacting with ITGA7 (By similarity)","subcellular_location":"Secreted, extracellular space, extracellular matrix","url":"https://www.uniprot.org/uniprotkb/P49747/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/COMP","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/COMP","total_profiled":1310},"omim":[{"mim_id":"619161","title":"CARPAL TUNNEL SYNDROME 2; CTS2","url":"https://www.omim.org/entry/619161"},{"mim_id":"614514","title":"THROMBOPHILIA DUE TO PROTEIN S DEFICIENCY, AUTOSOMAL RECESSIVE; THPH6","url":"https://www.omim.org/entry/614514"},{"mim_id":"612336","title":"THROMBOPHILIA DUE TO PROTEIN S DEFICIENCY, AUTOSOMAL DOMINANT; THPH5","url":"https://www.omim.org/entry/612336"},{"mim_id":"612283","title":"PROTEIN C; PROC","url":"https://www.omim.org/entry/612283"},{"mim_id":"610304","title":"DER1-LIKE DOMAIN FAMILY, MEMBER 2; DERL2","url":"https://www.omim.org/entry/610304"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"blood 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Part A","url":"https://pubmed.ncbi.nlm.nih.gov/15266613","citation_count":16,"is_preprint":false},{"pmid":"11223338","id":"PMC_11223338","title":"Analysis of the promoter region of human cartilage oligomeric matrix protein (COMP).","date":"2001","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/11223338","citation_count":16,"is_preprint":false},{"pmid":"25783805","id":"PMC_25783805","title":"Designed angiopoietin-1 variant, COMP-angiopoietin-1, rescues erectile function through healthy cavernous angiogenesis in a hypercholesterolemic mouse.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/25783805","citation_count":16,"is_preprint":false},{"pmid":"28162960","id":"PMC_28162960","title":"Antisense Reduction of Mutant COMP Reduces Growth Plate Chondrocyte Pathology.","date":"2017","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/28162960","citation_count":15,"is_preprint":false},{"pmid":"27612438","id":"PMC_27612438","title":"COMP-Ang1 prevents periodontitic damages and enhances mandible bone growth in an experimental animal model.","date":"2016","source":"Bone","url":"https://pubmed.ncbi.nlm.nih.gov/27612438","citation_count":15,"is_preprint":false},{"pmid":"16895759","id":"PMC_16895759","title":"Urine cartilage oligomeric matrix protein (COMP) measurement is useful in discriminating the osteoarthritic Thoroughbreds.","date":"2006","source":"Osteoarthritis and cartilage","url":"https://pubmed.ncbi.nlm.nih.gov/16895759","citation_count":15,"is_preprint":false},{"pmid":"16214313","id":"PMC_16214313","title":"In vivo human Cartilage oligomeric matrix protein (COMP) promoter activity.","date":"2005","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/16214313","citation_count":14,"is_preprint":false},{"pmid":"25329960","id":"PMC_25329960","title":"COMP-angiopoietin1 potentiates the effects of bone morphogenic protein-2 on ischemic necrosis of the femoral head in rats.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25329960","citation_count":14,"is_preprint":false},{"pmid":"28910372","id":"PMC_28910372","title":"Correlation of serum cartilage oligomeric matrix protein (COMP) and interleukin-16 (IL-16) levels with disease severity in primary knee osteoarthritis: A pilot study in a Malaysian population.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28910372","citation_count":14,"is_preprint":false},{"pmid":"34583025","id":"PMC_34583025","title":"COMP-Ang1: Therapeutic potential of an engineered Angiopoietin-1 variant.","date":"2021","source":"Vascular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34583025","citation_count":13,"is_preprint":false},{"pmid":"17307347","id":"PMC_17307347","title":"Expression of PSACH-associated mutant COMP in tendon fibroblasts leads to increased apoptotic cell death irrespective of the secretory characteristics of mutant COMP.","date":"2007","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/17307347","citation_count":13,"is_preprint":false},{"pmid":"23893855","id":"PMC_23893855","title":"COMP-Ang1 promotes chondrogenic and osteogenic differentiation of multipotent mesenchymal stem cells through the Ang1/Tie2 signaling pathway.","date":"2013","source":"Journal of orthopaedic research : official publication of the Orthopaedic Research Society","url":"https://pubmed.ncbi.nlm.nih.gov/23893855","citation_count":13,"is_preprint":false},{"pmid":"36520455","id":"PMC_36520455","title":"Intracameral Injection of AAV-DJ.COMP-ANG1 Reduces the IOP of Mice by Reshaping the Trabecular Outflow Pathway.","date":"2022","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/36520455","citation_count":13,"is_preprint":false},{"pmid":"18840965","id":"PMC_18840965","title":"Analysis of cartilage oligomeric matrix protein (COMP) in synovial fluid, serum and urine from 51 racehorses with carpal bone fracture.","date":"2008","source":"The Journal of veterinary medical science","url":"https://pubmed.ncbi.nlm.nih.gov/18840965","citation_count":13,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51137,"output_tokens":5445,"usd":0.117543,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14072,"output_tokens":4910,"usd":0.096555,"stage2_stop_reason":"end_turn"},"total_usd":0.214098,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"COMP cDNA cloning revealed a 755 amino acid protein that forms a homopentamer composed of five identical disulfide-linked subunits, with structural homology to the carboxyl-terminal half of thrombospondins including calcium-binding type 3 repeat domains and type 2/EGF repeat domains; the N-terminal 84 amino acids are unique to COMP.\",\n      \"method\": \"cDNA cloning, sequence analysis, expression in COS cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct recombinant expression and sequence analysis establishing oligomeric state and domain structure, replicated across subsequent studies\",\n      \"pmids\": [\"1429587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Mutations in exon 17B of COMP (single base-pair changes or 3 bp deletions) cause pseudoachondroplasia; six mutations delete or alter a conserved aspartic acid residue within the calcium-binding type 3 repeats, establishing that the calcium-binding domain is functionally critical.\",\n      \"method\": \"SSCP analysis and nucleotide sequencing of familial and isolated PSACH cases\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutation identification in eight independent cases, independently replicated in subsequent studies\",\n      \"pmids\": [\"7670471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Mutant COMP is retained in enlarged cisternae of the rough endoplasmic reticulum (rER) of PSACH chondrocytes in vitro, and this intracellular retention is associated with chondrocyte death; retention appears linked to the differentiated chondrocyte phenotype as dedifferentiated PSACH chondrocytes in monolayer do not retain COMP intracellularly.\",\n      \"method\": \"Alginate bead 3D culture of PSACH chondrocytes, immunostaining, electron microscopy\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cell culture experiments with phenotypic readout, single lab with multiple methods\",\n      \"pmids\": [\"9923655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The D469del PSACH mutation disrupts calcium binding: wild-type recombinant COMP binds 10–12 Ca²⁺ ions/molecule with cooperative, calcium-induced conformational changes (by circular dichroism), whereas D469del COMP binds approximately half as many Ca²⁺ ions and shows no large CD spectral change with Ca²⁺; the mutation specifically affects calcium binding without affecting Zn²⁺, Cu²⁺, or Ni²⁺ binding.\",\n      \"method\": \"Recombinant protein expression in E. coli, equilibrium dialysis, circular dichroism spectroscopy\",\n      \"journal\": \"Cell calcium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution with multiple orthogonal methods (equilibrium dialysis + CD spectroscopy), single lab\",\n      \"pmids\": [\"11013461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Chaperone proteins calreticulin, PDI, Grp94, BiP, and ERp72 are co-localized with retained COMP in the enlarged rER cisternae of PSACH chondrocytes; immunoprecipitation, Western blot, and FRET analyses show CRT, PDI, and Grp94 are in close proximity to both normal and mutant COMP, and BiP is closely associated with mutant COMP, indicating these chaperones participate in processing of wild-type COMP and in retention of mutant COMP.\",\n      \"method\": \"Immunoprecipitation, Western blot, FRET, immunoelectron microscopy of PSACH chondrocytes in vivo and in alginate bead culture\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus FRET plus in vivo immunolocalization, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"11470401\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"COMP mutations in the type 3 calcium-binding repeats cause retention of COMP, type IX collagen, and matrilin-3 (but not aggrecan and type II collagen) within the rER of chondrocytes in 3D culture; the absence of COMP, type IX collagen, and matrilin-3 from the extracellular matrix leads to disorganized matrix without organized collagen fibril bundles, establishing that these proteins cooperate in matrix assembly.\",\n      \"method\": \"3D alginate culture of PSACH chondrocytes with G427E, D469del, and D511Y mutations; immunostaining; ultrastructural analysis\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cell culture experiments with three distinct mutations plus ultrastructural analysis, single lab\",\n      \"pmids\": [\"15694129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"DeltaD469 COMP is retained in the ER of chondrocytic RCS cells (delaying secretion) but is efficiently secreted by non-chondrocytic COS-1 cells, demonstrating a cell-type-specific trafficking defect; ER accumulation of DeltaD469 COMP in RCS cells also causes co-retention of type IX collagen but not aggrecan; secreted mutant COMP disrupts assembly of normal fibrillar matrix.\",\n      \"method\": \"Expression of DeltaD469 COMP mutant in RCS and COS-1 cells, pulse-chase, immunofluorescence, ECM assembly assay\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-type comparison with multiple readouts, single lab\",\n      \"pmids\": [\"15579310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Pentameric COMP acts as a catalyst of collagen I and II fibrillogenesis: it accelerates fibril formation, increases the amount of collagen in fibrillar form, and produces fibrils with a narrow diameter distribution (149 ± 16 nm); monomeric COMP lacking the N-terminal coiled-coil domain decelerates fibrillogenesis, demonstrating that pentameric assembly is required; COMP is not incorporated into mature fibrils and dissociates upon fibril completion.\",\n      \"method\": \"In vitro collagen fibrillogenesis assay with pentameric and monomeric COMP; turbidity measurement; electron microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assay with monomeric vs. pentameric COMP comparison plus EM, multiple orthogonal methods\",\n      \"pmids\": [\"17716974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In PSACH growth plate chondrocytes, COMP mutations (type 3 repeat) correlate with ER retention severity proportional to clinical phenotype; PSACH mutations cause more cells to retain COMP than MED mutations; C-terminal domain mutations do not show this correlation, suggesting domain-specific pathomechanisms.\",\n      \"method\": \"Expression of 12 different recombinant COMP mutations in RCS cells; immunofluorescence scoring of ER retention\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, single method (immunofluorescence), but systematic comparison across 12 mutations\",\n      \"pmids\": [\"17570134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MMP-19 and MMP-20 (enamelysin) cleave COMP, generating a major proteolytic product of 60 kDa, establishing these MMPs as enzymes capable of degrading COMP in the extracellular matrix.\",\n      \"method\": \"In vitro cleavage assay with recombinant MMP-19 and MMP-20; Western blot\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro enzymatic assay, single lab, single method per enzyme\",\n      \"pmids\": [\"10922468\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Retention of D469del-COMP in chondrocytes triggers caspase-independent necroptosis: it stimulates the unfolded protein response (Chop, Gadd34), elevates Nox4 and Ero1β generating reactive oxygen species, induces DNA damage (γH2AX), and produces cleaved AIF without activated caspases; loss of growth plate chondrocytes by necroptosis was also confirmed in a PSACH mouse model.\",\n      \"method\": \"Inducible expression system in rat chondrosarcoma cells; Western blot; immunofluorescence; in vivo mouse model\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — inducible cell model plus in vivo mouse model, multiple pathway readouts, single lab\",\n      \"pmids\": [\"22154936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In a knock-in mouse model expressing D469del COMP, mutant COMP is retained in chondrocyte ER causing reduced proliferation and increased apoptosis without classical unfolded protein response activation; instead, microarray identified oxidative stress, cell cycle regulation, and apoptosis gene expression changes as the primary cellular response.\",\n      \"method\": \"Knock-in mouse model; growth plate histology; TUNEL; BrdU; microarray; UPR marker analysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic model with multiple readouts, single lab\",\n      \"pmids\": [\"22006726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"COMP fulfills an intracellular function in assisting collagen secretion: COMP-null fibroblasts retain collagens in the ER, collagen secretion is fully restored by reintroducing wild-type COMP; lack of COMP–collagen interaction in extracellular space also alters collagen fibril morphology and density, changing skin biomechanical properties; COMP-null mice show severely attenuated fibrotic responses.\",\n      \"method\": \"COMP knockout mouse fibroblasts; ER retention assay; collagen fibril EM; biomechanical testing; fibrosis model in vivo; rescue with wild-type COMP\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — loss-of-function with specific molecular rescue, multiple orthogonal methods (EM, biomechanics, in vivo fibrosis model), single lab\",\n      \"pmids\": [\"26746240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"COMP interacts directly with the C-terminus of Piezo1 via its own C-terminus and activates endogenous Piezo1 currents, leading to intracellular Ca²⁺ influx, Ca²⁺/calmodulin-dependent protein kinase II and eNOS activation, and nitric oxide production; COMP⁻/⁻ mice display elevated blood pressure and impaired acetylcholine-induced endothelium-dependent relaxation that is rescued by Piezo1 activator Yoda1.\",\n      \"method\": \"Co-immunoprecipitation; bioluminescence resonance energy transfer (BRET); patch-clamp electrophysiology; siRNA knockdown; COMP⁻/⁻ mouse blood pressure measurement; EPR detection of NO\",\n      \"journal\": \"Hypertension (Dallas, Tex. : 1979)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (co-IP, BRET, patch-clamp, in vivo KO rescue), single lab\",\n      \"pmids\": [\"34983194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"COMP localizes within mitochondria of vascular smooth muscle cells and interacts with prohibitin 2; disruption of the COMP–prohibitin 2 interaction impairs mitochondrial oxidative phosphorylation and causes VSMC dedifferentiation (loss of contractile phenotype) in vitro and enhanced neointima formation after rat carotid artery injury in vivo.\",\n      \"method\": \"Subcellular fractionation; fluorescence assay; liquid chromatography-tandem MS interactome; mitochondrial transplantation; microarray; carotid artery injury model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-identified interaction plus functional in vivo readout, multiple methods, single lab\",\n      \"pmids\": [\"29867124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mutant COMP retention in chondrocytes upregulates miR-223, disturbing the adipogenesis–osteogenesis balance, reducing bone mineral density, bone quality, mechanical strength, and subchondral bone thickness in the MT-COMP pseudoachondroplasia mouse model.\",\n      \"method\": \"MT-COMP transgenic mouse model; microCT; bone mechanical testing; miRNA profiling; multiple analytic approaches\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo transgenic model with multiple analytic methods, single lab\",\n      \"pmids\": [\"29309831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HSC-derived COMP signals through the CD36 receptor on HCC cells to phosphorylate ERK and AKT, upregulating EMT markers (Slug, Twist), MMP-2, and MMP-9, promoting HCC proliferation and metastasis in vitro and in vivo; knockdown of COMP in LX2 hepatic stellate cells reduces MEK/ERK and PI3K/AKT activation in HCC cells.\",\n      \"method\": \"Recombinant COMP protein treatment; CD36 siRNA knockdown; Western blot; transwell coculture; mouse xenograft model\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor identification by knockdown plus in vivo model, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"30231922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"COMP binds specifically to a GXKGHR motif on the collagen II triple helix found exclusively in fibrillar collagens; this binding site was identified using a recombinant collagen II peptide library and overlaps with recognition sites of other collagen-binding partners (PEDF, heparin) and spans lysine residues involved in collagen cross-links, suggesting COMP may protect collagen helices from premature cross-linking.\",\n      \"method\": \"Recombinant collagen II peptide library binding screen; binding assays with COMP and TSP-4\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro binding assay with peptide library, single lab, limited functional validation\",\n      \"pmids\": [\"30464261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Two mutations in COMP cause familial carpal tunnel syndrome by impairing COMP secretion in tenocytes (the CTS-specific mutation also causes ER stress, unfolded protein response, cell death, inflammation, and progressive fibrosis in tendons/ligaments); the CTS-specific mutation fails to oligomerize properly and is trapped in the ER, whereas the mutation associated with both CTS and MED also perturbs secretion in chondrocytes.\",\n      \"method\": \"Patient biopsy histology; mouse models; ER stress markers; UPR assays; co-IP for oligomerization; immunofluorescence\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human biopsy plus multiple mouse models plus biochemical assays; multiple orthogonal methods; Nature-level peer review\",\n      \"pmids\": [\"32686688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Expression of PSACH-associated mutant COMP in tendon fibroblasts increases apoptotic cell death irrespective of secretory pattern: D475N and D469Δ are retained in ER while H587R is secreted like wild-type, yet all three mutants disrupt collagen I matrix assembly and induce apoptosis, indicating heterogeneous pathogenic mechanisms in tendon.\",\n      \"method\": \"Adenoviral gene transfer into tendon fibroblast cultures; immunostaining; cell viability assays; ECM analysis\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — three mutant comparison with defined phenotypic readout, single lab\",\n      \"pmids\": [\"17307347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Transcription of the COMP gene is driven by a TATA-less/CAAT-less promoter with multiple transcription start sites; the 370 bp proximal region has the strongest promoter activity; the SP1 transcription factor plays a role in regulating COMP expression; tissue-specific usage of transcription start sites differs between chondrocytes and tendon/ligament cells.\",\n      \"method\": \"Promoter cloning; primer extension; reporter gene (luciferase) assays in chondrocyte, tendon, and ligament cells; SP1 binding analysis\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional promoter dissection with reporter assays and primer extension, single lab\",\n      \"pmids\": [\"11223338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Combined ablation of collagen IX and COMP in mice produces shortened, widened long bones with severe growth plate abnormalities (large hypocellular areas, loss of columnar chondrocyte organization) not seen in COMP-single-KO mice; COMP-null mice alone have no overt skeletal phenotype but show altered matrilin-3 deposition, indicating COMP cooperates with collagen IX in growth plate organization.\",\n      \"method\": \"Double knockout mouse model (collagen IX and COMP); histology; bone morphometry; immunostaining\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via double KO mouse, single lab\",\n      \"pmids\": [\"18191556\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"COMP is a disulfide-linked homopentamer that functions as a catalyst of collagen fibrillogenesis (requiring its pentameric assembly), acts as an intracellular chaperone assisting collagen secretion from the ER, binds fibrillar collagens via a specific GXKGHR motif on the triple helix, activates the mechanosensory ion channel Piezo1 to promote eNOS/nitric oxide production in vascular endothelium, maintains vascular smooth muscle contractile identity by interacting with mitochondrial prohibitin 2, and signals through CD36 to activate MEK/ERK and PI3K/AKT in cancer cells; disease-causing mutations in its calcium-binding type 3 repeat domains disrupt Ca²⁺ binding and protein folding, leading to chaperone-associated ER retention, unfolded protein response, oxidative stress, and caspase-independent necroptosis of growth plate chondrocytes that underlies pseudoachondroplasia and multiple epiphyseal dysplasia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"COMP is a disulfide-linked homopentamer, structurally related to the C-terminal half of thrombospondins, that organizes collagenous extracellular matrix in cartilage, tendon and other connective tissues [#0]. Pentameric assembly enables COMP to act as a catalyst of type I and II collagen fibrillogenesis—accelerating fibril formation and enforcing a narrow fibril diameter while dissociating from completed fibrils—a function lost by monomeric COMP [#7]; it engages fibrillar collagens through a specific GXKGHR motif on the triple helix [#17]. COMP also performs an intracellular role, assisting collagen secretion from the ER such that COMP-null cells retain collagen and show attenuated fibrotic responses, fully rescued by wild-type COMP [#12]. In the growth plate it cooperates with type IX collagen and matrilin-3 to build organized fibril bundles [#5, #21]. Beyond matrix assembly, COMP activates the mechanosensory channel Piezo1 to drive Ca²⁺/CaMKII/eNOS-dependent nitric oxide production in vascular endothelium, with COMP⁻/⁻ mice showing elevated blood pressure [#13], maintains vascular smooth muscle contractile identity through a mitochondrial interaction with prohibitin 2 [#14], and signals via CD36 to activate MEK/ERK and PI3K/AKT in hepatocellular carcinoma [#16]. Dominant mutations in the calcium-binding type 3 repeats abolish Ca²⁺ binding and disrupt folding [#1, #3], causing chaperone-associated ER retention of mutant COMP together with collagen IX and matrilin-3 [#4, #5], triggering unfolded protein response, oxidative stress, and caspase-independent necroptosis of chondrocytes [#10]; these defects underlie pseudoachondroplasia, multiple epiphyseal dysplasia, and familial carpal tunnel syndrome [#1, #18].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing COMP's primary structure and quaternary organization defined it as a pentameric thrombospondin-related matrix protein and set the framework for all later functional work.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and expression in COS cells\",\n      \"pmids\": [\"1429587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not assign a biochemical or cellular function\", \"Role of the unique N-terminal region undefined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Linking COMP to pseudoachondroplasia identified the calcium-binding type 3 repeats as functionally critical and established COMP as a disease gene.\",\n      \"evidence\": \"SSCP and sequencing of familial and isolated PSACH cases\",\n      \"pmids\": [\"7670471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not show how mutations affect protein function\", \"Cellular consequence of mutations unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showing that the D469del mutation specifically halves Ca²⁺ binding and abolishes the calcium-induced conformational change provided the biochemical basis for the disease-causing defect.\",\n      \"evidence\": \"Recombinant protein, equilibrium dialysis, and circular dichroism spectroscopy\",\n      \"pmids\": [\"11013461\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single mutation tested biochemically\", \"Link between altered conformation and cellular retention not directly shown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying that mutant COMP is retained in the rER alongside resident chaperones revealed an ER quality-control/chaperone-associated retention mechanism for the disease.\",\n      \"evidence\": \"Co-IP, FRET, and immunoelectron microscopy of PSACH chondrocytes\",\n      \"pmids\": [\"9923655\", \"11470401\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which retention causes cell death not yet defined\", \"Chaperone associations are proximity-based, not functional dependencies\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Dissecting the COMP promoter defined the transcriptional control of its tissue-specific expression in chondrocytes versus tendon/ligament cells.\",\n      \"evidence\": \"Promoter cloning, primer extension, luciferase reporters, and SP1 binding analysis\",\n      \"pmids\": [\"11223338\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full set of regulatory factors unresolved\", \"How tissue-specific start-site usage is controlled is unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that pentameric but not monomeric COMP catalyzes collagen I/II fibrillogenesis established the molecular requirement of oligomerization for matrix assembly function.\",\n      \"evidence\": \"In vitro fibrillogenesis assay comparing pentameric and monomeric COMP, with EM\",\n      \"pmids\": [\"17716974\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the catalytic mechanism unresolved\", \"In vivo relevance not directly tested here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing ER-retention severity scales with clinical phenotype for type 3 repeat mutations but not C-terminal mutations indicated domain-specific pathomechanisms.\",\n      \"evidence\": \"Expression of 12 mutations in RCS cells with immunofluorescence scoring\",\n      \"pmids\": [\"17570134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single readout (immunofluorescence)\", \"Mechanism for C-terminal mutations not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Revealing that secreted as well as retained tendon mutants induce apoptosis showed pathogenic mechanisms in tendon are heterogeneous and not solely retention-driven.\",\n      \"evidence\": \"Adenoviral expression of three mutants in tendon fibroblasts with viability and ECM assays\",\n      \"pmids\": [\"17307347\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Apoptotic pathway not delineated\", \"Single cell type, single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Genetic epistasis from collagen IX/COMP double knockout established that COMP cooperates with collagen IX in growth plate organization, explaining the mild single-KO phenotype.\",\n      \"evidence\": \"Double knockout mouse model with histology and morphometry\",\n      \"pmids\": [\"18191556\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular nature of the cooperation not resolved\", \"Contribution of matrilin-3 not isolated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Co-retention of collagen IX and matrilin-3 with mutant COMP showed these matrix proteins assemble cooperatively and that loss from the ECM disorganizes fibril bundles.\",\n      \"evidence\": \"3D alginate culture of PSACH chondrocytes and RCS/COS-1 cell-type comparison\",\n      \"pmids\": [\"15694129\", \"15579310\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding interfaces not mapped\", \"Cell-type basis of the trafficking defect not mechanistically explained\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defining the downstream death pathway showed mutant COMP retention triggers UPR, ROS, DNA damage and caspase-independent necroptosis of growth plate chondrocytes in vitro and in vivo.\",\n      \"evidence\": \"Inducible RCS cell model and PSACH mouse model with pathway readouts\",\n      \"pmids\": [\"22154936\", \"22006726\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"UPR involvement differs between models\", \"Trigger linking retention to oxidative stress not fully defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Loss-of-function with molecular rescue established an intracellular role for COMP in assisting collagen secretion and its requirement for fibrotic responses.\",\n      \"evidence\": \"COMP-null fibroblasts, ER retention/rescue, fibril EM, biomechanics, and in vivo fibrosis model\",\n      \"pmids\": [\"26746240\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of intracellular collagen chaperoning not defined\", \"Whether this requires pentamerization untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identifying the GXKGHR motif defined the specific COMP recognition site on fibrillar collagen triple helices.\",\n      \"evidence\": \"Recombinant collagen II peptide library binding screen\",\n      \"pmids\": [\"30464261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro binding only, limited functional validation\", \"Protective role against cross-linking not directly demonstrated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Establishing COMP–Piezo1 coupling revealed a non-matrix signaling role in endothelial mechanotransduction and blood pressure regulation.\",\n      \"evidence\": \"Co-IP, BRET, patch-clamp, COMP⁻/⁻ mouse blood pressure with Yoda1 rescue, EPR for NO\",\n      \"pmids\": [\"34983194\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the C-terminal interaction unresolved\", \"Relationship to COMP's matrix function unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Localizing COMP to mitochondria via prohibitin 2 connected it to vascular smooth muscle bioenergetics and contractile identity.\",\n      \"evidence\": \"Subcellular fractionation, LC-MS/MS interactome, mitochondrial transplantation, carotid injury model\",\n      \"pmids\": [\"29867124\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a secreted matrix protein reaches mitochondria unexplained\", \"Direct binding not structurally validated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating CD36-dependent MEK/ERK and PI3K/AKT activation identified a paracrine tumor-promoting signaling axis for COMP in hepatocellular carcinoma.\",\n      \"evidence\": \"Recombinant COMP treatment, CD36 knockdown, coculture, and xenograft model\",\n      \"pmids\": [\"30231922\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct COMP–CD36 binding not structurally shown\", \"Generalizability beyond HCC untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linking miR-223 upregulation to the adipogenesis–osteogenesis imbalance connected chondrocyte ER retention to systemic bone quality defects.\",\n      \"evidence\": \"MT-COMP transgenic mouse, microCT, bone mechanics, miRNA profiling\",\n      \"pmids\": [\"29309831\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal chain from miR-223 to bone phenotype not proven\", \"Single model system\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identifying COMP mutations that cause familial carpal tunnel syndrome through impaired tenocyte secretion extended the disease spectrum and tied oligomerization failure to tendon/ligament fibrosis.\",\n      \"evidence\": \"Patient biopsies, mouse models, UPR assays, and co-IP for oligomerization\",\n      \"pmids\": [\"32686688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue specificity of the phenotype not fully explained\", \"Why some mutations cause CTS versus MED unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How COMP's intracellular collagen-secretion chaperone activity, its extracellular fibrillogenesis catalysis, and its distinct signaling roles (Piezo1, prohibitin 2, CD36) are coordinated within and across tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model linking matrix and signaling functions\", \"Mechanism of subcellular/mitochondrial targeting unknown\", \"Whether signaling roles require pentameric assembly untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [7, 17]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [7, 12]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 4, 12]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [9, 17]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [7, 12, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [21, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [13, 14, 16]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 10, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"COL2A1\", \"COL9A1\", \"MATN3\", \"PIEZO1\", \"PHB2\", \"CD36\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}