{"gene":"C1QTNF2","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2008,"finding":"CTRP2 (C1QTNF2) is a secreted glycoprotein that forms trimers as its basic structural unit and can heterodimerize with CTRP7 and adiponectin to form heterotrimers, providing a mechanism to generate functionally distinct ligands.","method":"Mammalian cell expression, biochemical characterization, size-exclusion chromatography, co-secretion experiments","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical reconstitution in mammalian cells with co-secretion and structural analysis, single lab but multiple orthogonal methods","pmids":["18783346"],"is_preprint":false},{"year":2008,"finding":"CTRP2 enhances glycogen deposition and fat oxidation in cultured myotubes, establishing a direct metabolic activity for this secreted protein.","method":"In vitro assay using cultured myotubes treated with recombinant CTRP2","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro functional assay in relevant cell type, single lab","pmids":["18783346","24586339"],"is_preprint":false},{"year":2014,"finding":"In vivo, CTRP2 transgenic mice with elevated circulating CTRP2 showed improved insulin tolerance and greater capacity to handle acute lipid challenge when fed a high-fat diet, demonstrating a role for CTRP2 in modulating whole-body insulin sensitivity and lipid metabolism.","method":"Transgenic mouse model (CTRP2 overexpression), insulin tolerance test, lipid challenge assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic gain-of-function mouse model with defined metabolic phenotypic readouts, single lab","pmids":["24586339"],"is_preprint":false},{"year":2019,"finding":"CTRP2 deficiency in knockout mice upregulates lipolytic enzyme expression and protein kinase A signaling, resulting in enhanced adipose tissue lipolysis; CTRP2 treatment in cultured adipocytes suppresses triglyceride hydrolysis, placing CTRP2 as a suppressor of PKA-mediated lipolysis.","method":"Knockout mouse model, gene expression analysis, PKA signaling assays, in vitro adipocyte treatment with recombinant CTRP2","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function KO mouse combined with in vitro rescue experiment and defined molecular pathway (PKA signaling), multiple orthogonal methods in single rigorous study","pmids":["31439668"],"is_preprint":false},{"year":2019,"finding":"CTRP2-deficient mice exhibit elevated hepatic TG secretion, reduced hepatic TG content, elevated plasma TG, and reduced plasma/hepatic cholesterol, with liver metabolomics revealing changes in diacylglycerols and phospholipids suggesting increased membrane remodeling underlies altered hepatic TG secretion.","method":"Knockout mouse model, plasma/hepatic lipid profiling, oral lipid gavage, liver metabolomics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal metabolic readouts (lipidomics, metabolomics, in vivo lipid challenge) in single rigorous study","pmids":["31439668"],"is_preprint":false},{"year":2021,"finding":"CTRP2 induces GLUT1 and GLUT4 translocation and glucose uptake in adult rat cardiomyocytes via AMPK activation; AMPK inhibition reduced CTRP2-mediated Akt activation, but Akt inhibition did not impair AMPK activation, placing AMPK upstream of Akt in CTRP2 signaling. Loss of adiponectin receptor 1 abolished some but not all CTRP2 effects on glucose metabolism.","method":"Recombinant CTRP2 treatment of primary cardiomyocytes and H9C2 cells, GLUT1/GLUT4 translocation assay, glucose uptake assay, pharmacological AMPK/Akt inhibition, AdipoR1 knockdown","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays (translocation, uptake, signaling inhibitors, receptor KD) in relevant primary cells, single lab","pmids":["33919975"],"is_preprint":false},{"year":2022,"finding":"Recombinant CTRP2 promotes angiogenesis by enhancing endothelial cell tube formation and migration in a dose-dependent manner, increasing AKT phosphorylation and VEGFR2 expression; intraperitoneal injection of recombinant CTRP2 in mice reduced myocardial infarction size and improved cardiac function after ischemia/reperfusion.","method":"In vitro endothelial tube formation and migration assays, Western blot for AKT phosphorylation and VEGFR2, recombinant protein injection in mouse I/R model and hindlimb ischemia model","journal":"Diabetes & vascular disease research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro mechanistic assays with defined signaling pathway (AKT-VEGFR2) validated in two in vivo mouse models, single lab","pmids":["36409464"],"is_preprint":false},{"year":2011,"finding":"Recombinant human CTRP2 expressed as a Trx-fusion protein in E. coli retains biological activity in in vitro assays, confirming the C1q globular domain is sufficient for activity.","method":"Recombinant protein expression and purification, in vitro activity assay","journal":"Protein expression and purification","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single in vitro assay confirming activity of recombinant protein, no mechanistic detail on pathway","pmids":["21453774"],"is_preprint":false},{"year":2007,"finding":"CTRP2 protein is expressed in muscular tissues and elevated in aged animals; however, increased CTRP2 (and CTRP7) in aged rats does not result in increased activation of their downstream target AMPK, indicating that aged muscle is refractory to CTRP2-mediated AMPK signaling.","method":"Protein expression analysis in rat muscle tissue (young vs. old), caloric restriction intervention, AMPK phosphorylation assay","journal":"Molecular and cellular endocrinology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single in vivo study showing negative result (CTRP2 elevation does not activate AMPK in aged animals), single lab, limited mechanistic follow-up","pmids":["17716811"],"is_preprint":false},{"year":2025,"finding":"IL-1β treatment induces a significant reduction in C1QTNF2 (CTRP2) expression in an in vitro osteoarthritis co-culture model of human osteoblasts and chondrocytes, and this reduction was ameliorated by Red Algae Lithothamnion species treatment.","method":"In vitro co-culture model with IL-1β induction, gene expression analysis, ddPCR confirmation","journal":"Pharmaceuticals (Basel, Switzerland)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single in vitro experiment showing transcriptional regulation by inflammatory stimulus, no mechanistic pathway placement beyond expression change","pmids":["40143094"],"is_preprint":false}],"current_model":"C1QTNF2/CTRP2 is a secreted adipose-tissue-enriched glycoprotein that circulates as trimers and heterotrimers (with CTRP7 and adiponectin); it suppresses adipose tissue lipolysis by inhibiting PKA signaling and lipolytic enzyme expression, regulates hepatic triglyceride secretion and lipid metabolism in vivo, stimulates GLUT1/GLUT4-mediated glucose uptake in cardiomyocytes via AMPK (upstream of Akt), and promotes angiogenesis through AKT-VEGFR2 signaling in endothelial cells."},"narrative":{"mechanistic_narrative":"C1QTNF2 (CTRP2) is a secreted adipose- and muscle-associated glycoprotein that functions as a metabolic regulator of lipid handling, glucose uptake, and vascular responses [PMID:18783346, PMID:31439668]. It assembles into trimers as its basic structural unit and can heterotrimerize with CTRP7 and adiponectin, generating a repertoire of functionally distinct circulating ligands [PMID:18783346]. In adipose tissue CTRP2 acts as a suppressor of lipolysis: its loss in knockout mice upregulates lipolytic enzyme expression and protein kinase A signaling, while recombinant CTRP2 suppresses triglyceride hydrolysis in cultured adipocytes [PMID:31439668]. CTRP2 also shapes hepatic lipid metabolism, with deficiency producing elevated hepatic triglyceride secretion, reduced hepatic triglyceride and cholesterol content, and lipidomic shifts in diacylglycerols and phospholipids consistent with altered membrane remodeling [PMID:31439668]. Consistent with these in vitro and loss-of-function findings, gain-of-function transgenic mice show improved insulin tolerance and enhanced capacity to handle a lipid challenge on a high-fat diet [PMID:24586339]. In cardiomyocytes CTRP2 drives GLUT1/GLUT4 translocation and glucose uptake through AMPK activation positioned upstream of Akt, partly via adiponectin receptor 1 [PMID:33919975], and recombinant CTRP2 promotes endothelial angiogenesis through AKT–VEGFR2 signaling while limiting infarct size in ischemia/reperfusion models [PMID:36409464]. The C1q globular domain is sufficient for biological activity [PMID:21453774]. No structural model of its receptor engagement or a unifying account linking its distinct tissue activities has been characterized in the available corpus.","teleology":[{"year":2008,"claim":"Established that CTRP2 is a secreted glycoprotein with defined oligomeric architecture and intrinsic metabolic activity, distinguishing it from a passive serum component.","evidence":"Mammalian cell expression with size-exclusion chromatography and co-secretion; in vitro myotube assays of glycogen and fat oxidation","pmids":["18783346"],"confidence":"Medium","gaps":["Receptor mediating myotube effects not identified","Physiological relevance of heterotrimers with CTRP7/adiponectin untested in vivo","No structural model of the trimer-receptor interface"]},{"year":2014,"claim":"Tested whether circulating CTRP2 affects whole-body metabolism, showing gain-of-function improves insulin tolerance and lipid handling.","evidence":"CTRP2-overexpressing transgenic mice with insulin tolerance test and acute lipid challenge on high-fat diet","pmids":["24586339"],"confidence":"Medium","gaps":["Tissue source of the metabolic benefit not resolved","Signaling pathway not defined in this model","Overexpression may not reflect endogenous dose"]},{"year":2019,"claim":"Defined the endogenous role and a molecular pathway, placing CTRP2 as a suppressor of PKA-mediated adipose lipolysis and a regulator of hepatic triglyceride secretion.","evidence":"Knockout mice with lipid/metabolomic profiling and oral gavage, plus rescue by recombinant CTRP2 in cultured adipocytes and PKA signaling assays","pmids":["31439668"],"confidence":"High","gaps":["Receptor coupling CTRP2 to PKA suppression unidentified","Mechanism linking membrane lipid remodeling to hepatic TG secretion not established","Direct vs. indirect action on hepatocytes unresolved"]},{"year":2021,"claim":"Identified an intracellular signaling order in cardiomyocytes, placing AMPK upstream of Akt in CTRP2-driven glucose uptake and implicating AdipoR1.","evidence":"Recombinant CTRP2 on primary cardiomyocytes and H9C2 cells with GLUT translocation/uptake assays, pharmacological AMPK/Akt inhibition, and AdipoR1 knockdown","pmids":["33919975"],"confidence":"Medium","gaps":["AdipoR1 loss abolished only some effects, leaving the full receptor set unknown","Pharmacological inhibitor specificity limits pathway ordering","In vivo cardiac glucose handling not tested"]},{"year":2022,"claim":"Extended CTRP2 function to the vasculature, showing it promotes angiogenesis via AKT-VEGFR2 and confers cardioprotection in ischemia.","evidence":"Endothelial tube formation/migration assays with Western blot for AKT/VEGFR2, plus recombinant CTRP2 injection in mouse I/R and hindlimb ischemia models","pmids":["36409464"],"confidence":"Medium","gaps":["Direct receptor on endothelial cells not defined","Whether VEGFR2 induction is transcriptional or post-translational unresolved","Cardioprotection mechanism vs. angiogenesis not separated"]},{"year":null,"claim":"How CTRP2 engages its receptor(s) at the structural level and how its distinct tissue-specific activities (adipose lipolysis suppression, hepatic TG secretion, cardiac glucose uptake, endothelial angiogenesis) are unified by a common mechanism remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No definitive cognate receptor mapped across all tissues","No structural model of ligand-receptor engagement","Relationship between AMPK/Akt and PKA pathways across tissues unintegrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,6]}],"complexes":[],"partners":["CTRP7","ADIPOQ","ADIPOR1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BXJ5","full_name":"Complement C1q tumor necrosis factor-related protein 2","aliases":[],"length_aa":285,"mass_kda":30.0,"function":"Involved in the regulation of lipid metabolism in adipose tissue and liver","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q9BXJ5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C1QTNF2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C1QTNF2","total_profiled":1310},"omim":[{"mim_id":"618647","title":"C1q- AND TNF-RELATED PROTEIN 2; C1QTNF2","url":"https://www.omim.org/entry/618647"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Centrosome","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"blood vessel","ntpm":13.2}],"url":"https://www.proteinatlas.org/search/C1QTNF2"},"hgnc":{"alias_symbol":["CTRP2"],"prev_symbol":[]},"alphafold":{"accession":"Q9BXJ5","domains":[{"cath_id":"2.60.120.40","chopping":"150-276","consensus_level":"high","plddt":93.2089,"start":150,"end":276}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BXJ5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BXJ5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BXJ5-F1-predicted_aligned_error_v6.png","plddt_mean":70.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C1QTNF2","jax_strain_url":"https://www.jax.org/strain/search?query=C1QTNF2"},"sequence":{"accession":"Q9BXJ5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BXJ5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BXJ5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BXJ5"}},"corpus_meta":[{"pmid":"18783346","id":"PMC_18783346","title":"Molecular, biochemical and functional characterizations of C1q/TNF family members: adipose-tissue-selective expression patterns, regulation by PPAR-gamma agonist, cysteine-mediated oligomerizations, combinatorial associations and metabolic functions.","date":"2008","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/18783346","citation_count":340,"is_preprint":false},{"pmid":"24586339","id":"PMC_24586339","title":"CTRP2 overexpression improves insulin and lipid tolerance in diet-induced obese mice.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24586339","citation_count":39,"is_preprint":false},{"pmid":"36678157","id":"PMC_36678157","title":"Astaxanthin Supplemented with High-Intensity Functional Training Decreases Adipokines Levels and Cardiovascular Risk Factors in Men with Obesity.","date":"2023","source":"Nutrients","url":"https://pubmed.ncbi.nlm.nih.gov/36678157","citation_count":36,"is_preprint":false},{"pmid":"28256512","id":"PMC_28256512","title":"Transcriptome-based repurposing of apigenin as a potential anti-fibrotic agent targeting hepatic stellate cells.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28256512","citation_count":28,"is_preprint":false},{"pmid":"31439668","id":"PMC_31439668","title":"C1q/TNF-related protein 2 (CTRP2) deletion promotes adipose tissue lipolysis and hepatic triglyceride secretion.","date":"2019","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31439668","citation_count":26,"is_preprint":false},{"pmid":"17716811","id":"PMC_17716811","title":"Age-associated loss in adiponectin-activation by caloric restriction: lack of compensation by enhanced inducibility of adiponectin paralogs CTRP2 and CTRP7.","date":"2007","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/17716811","citation_count":23,"is_preprint":false},{"pmid":"33919975","id":"PMC_33919975","title":"Comparative Analysis of CTRP-Mediated Effects on Cardiomyocyte Glucose Metabolism: Cross Talk between AMPK and Akt Signaling Pathway.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/33919975","citation_count":22,"is_preprint":false},{"pmid":"35252179","id":"PMC_35252179","title":"Indolethylamine-N-Methyltransferase Inhibits Proliferation and Promotes Apoptosis of Human Prostate Cancer Cells: A Mechanistic Exploration.","date":"2022","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/35252179","citation_count":18,"is_preprint":false},{"pmid":"36194576","id":"PMC_36194576","title":"Integrative weighted molecular network construction from transcriptomics and genome wide association data to identify shared genetic biomarkers for COPD and lung cancer.","date":"2022","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/36194576","citation_count":16,"is_preprint":false},{"pmid":"37537524","id":"PMC_37537524","title":"Genetic architecture and key regulatory genes of fatty acid composition in Gushi chicken breast muscle determined by GWAS and WGCNA.","date":"2023","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/37537524","citation_count":13,"is_preprint":false},{"pmid":"36061536","id":"PMC_36061536","title":"Role of serum C1q/TNF-related protein family levels in patients with acute coronary syndrome.","date":"2022","source":"Frontiers in cardiovascular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36061536","citation_count":12,"is_preprint":false},{"pmid":"21453774","id":"PMC_21453774","title":"High level expression, purification and characterization of active fusion human C1q and tumor necrosis factor related protein 2 (hCTRP2) in Escherichia coli.","date":"2011","source":"Protein expression and 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Iran","url":"https://pubmed.ncbi.nlm.nih.gov/40486012","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13357,"output_tokens":2393,"usd":0.037983,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9530,"output_tokens":2425,"usd":0.054137,"stage2_stop_reason":"end_turn"},"total_usd":0.09212,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"CTRP2 (C1QTNF2) is a secreted glycoprotein that forms trimers as its basic structural unit and can heterodimerize with CTRP7 and adiponectin to form heterotrimers, providing a mechanism to generate functionally distinct ligands.\",\n      \"method\": \"Mammalian cell expression, biochemical characterization, size-exclusion chromatography, co-secretion experiments\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical reconstitution in mammalian cells with co-secretion and structural analysis, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"18783346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CTRP2 enhances glycogen deposition and fat oxidation in cultured myotubes, establishing a direct metabolic activity for this secreted protein.\",\n      \"method\": \"In vitro assay using cultured myotubes treated with recombinant CTRP2\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro functional assay in relevant cell type, single lab\",\n      \"pmids\": [\"18783346\", \"24586339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In vivo, CTRP2 transgenic mice with elevated circulating CTRP2 showed improved insulin tolerance and greater capacity to handle acute lipid challenge when fed a high-fat diet, demonstrating a role for CTRP2 in modulating whole-body insulin sensitivity and lipid metabolism.\",\n      \"method\": \"Transgenic mouse model (CTRP2 overexpression), insulin tolerance test, lipid challenge assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic gain-of-function mouse model with defined metabolic phenotypic readouts, single lab\",\n      \"pmids\": [\"24586339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CTRP2 deficiency in knockout mice upregulates lipolytic enzyme expression and protein kinase A signaling, resulting in enhanced adipose tissue lipolysis; CTRP2 treatment in cultured adipocytes suppresses triglyceride hydrolysis, placing CTRP2 as a suppressor of PKA-mediated lipolysis.\",\n      \"method\": \"Knockout mouse model, gene expression analysis, PKA signaling assays, in vitro adipocyte treatment with recombinant CTRP2\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function KO mouse combined with in vitro rescue experiment and defined molecular pathway (PKA signaling), multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"31439668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CTRP2-deficient mice exhibit elevated hepatic TG secretion, reduced hepatic TG content, elevated plasma TG, and reduced plasma/hepatic cholesterol, with liver metabolomics revealing changes in diacylglycerols and phospholipids suggesting increased membrane remodeling underlies altered hepatic TG secretion.\",\n      \"method\": \"Knockout mouse model, plasma/hepatic lipid profiling, oral lipid gavage, liver metabolomics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal metabolic readouts (lipidomics, metabolomics, in vivo lipid challenge) in single rigorous study\",\n      \"pmids\": [\"31439668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CTRP2 induces GLUT1 and GLUT4 translocation and glucose uptake in adult rat cardiomyocytes via AMPK activation; AMPK inhibition reduced CTRP2-mediated Akt activation, but Akt inhibition did not impair AMPK activation, placing AMPK upstream of Akt in CTRP2 signaling. Loss of adiponectin receptor 1 abolished some but not all CTRP2 effects on glucose metabolism.\",\n      \"method\": \"Recombinant CTRP2 treatment of primary cardiomyocytes and H9C2 cells, GLUT1/GLUT4 translocation assay, glucose uptake assay, pharmacological AMPK/Akt inhibition, AdipoR1 knockdown\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays (translocation, uptake, signaling inhibitors, receptor KD) in relevant primary cells, single lab\",\n      \"pmids\": [\"33919975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Recombinant CTRP2 promotes angiogenesis by enhancing endothelial cell tube formation and migration in a dose-dependent manner, increasing AKT phosphorylation and VEGFR2 expression; intraperitoneal injection of recombinant CTRP2 in mice reduced myocardial infarction size and improved cardiac function after ischemia/reperfusion.\",\n      \"method\": \"In vitro endothelial tube formation and migration assays, Western blot for AKT phosphorylation and VEGFR2, recombinant protein injection in mouse I/R model and hindlimb ischemia model\",\n      \"journal\": \"Diabetes & vascular disease research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro mechanistic assays with defined signaling pathway (AKT-VEGFR2) validated in two in vivo mouse models, single lab\",\n      \"pmids\": [\"36409464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Recombinant human CTRP2 expressed as a Trx-fusion protein in E. coli retains biological activity in in vitro assays, confirming the C1q globular domain is sufficient for activity.\",\n      \"method\": \"Recombinant protein expression and purification, in vitro activity assay\",\n      \"journal\": \"Protein expression and purification\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single in vitro assay confirming activity of recombinant protein, no mechanistic detail on pathway\",\n      \"pmids\": [\"21453774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CTRP2 protein is expressed in muscular tissues and elevated in aged animals; however, increased CTRP2 (and CTRP7) in aged rats does not result in increased activation of their downstream target AMPK, indicating that aged muscle is refractory to CTRP2-mediated AMPK signaling.\",\n      \"method\": \"Protein expression analysis in rat muscle tissue (young vs. old), caloric restriction intervention, AMPK phosphorylation assay\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single in vivo study showing negative result (CTRP2 elevation does not activate AMPK in aged animals), single lab, limited mechanistic follow-up\",\n      \"pmids\": [\"17716811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IL-1β treatment induces a significant reduction in C1QTNF2 (CTRP2) expression in an in vitro osteoarthritis co-culture model of human osteoblasts and chondrocytes, and this reduction was ameliorated by Red Algae Lithothamnion species treatment.\",\n      \"method\": \"In vitro co-culture model with IL-1β induction, gene expression analysis, ddPCR confirmation\",\n      \"journal\": \"Pharmaceuticals (Basel, Switzerland)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single in vitro experiment showing transcriptional regulation by inflammatory stimulus, no mechanistic pathway placement beyond expression change\",\n      \"pmids\": [\"40143094\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C1QTNF2/CTRP2 is a secreted adipose-tissue-enriched glycoprotein that circulates as trimers and heterotrimers (with CTRP7 and adiponectin); it suppresses adipose tissue lipolysis by inhibiting PKA signaling and lipolytic enzyme expression, regulates hepatic triglyceride secretion and lipid metabolism in vivo, stimulates GLUT1/GLUT4-mediated glucose uptake in cardiomyocytes via AMPK (upstream of Akt), and promotes angiogenesis through AKT-VEGFR2 signaling in endothelial cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"C1QTNF2 (CTRP2) is a secreted adipose- and muscle-associated glycoprotein that functions as a metabolic regulator of lipid handling, glucose uptake, and vascular responses [#0, #3]. It assembles into trimers as its basic structural unit and can heterotrimerize with CTRP7 and adiponectin, generating a repertoire of functionally distinct circulating ligands [#0]. In adipose tissue CTRP2 acts as a suppressor of lipolysis: its loss in knockout mice upregulates lipolytic enzyme expression and protein kinase A signaling, while recombinant CTRP2 suppresses triglyceride hydrolysis in cultured adipocytes [#3]. CTRP2 also shapes hepatic lipid metabolism, with deficiency producing elevated hepatic triglyceride secretion, reduced hepatic triglyceride and cholesterol content, and lipidomic shifts in diacylglycerols and phospholipids consistent with altered membrane remodeling [#4]. Consistent with these in vitro and loss-of-function findings, gain-of-function transgenic mice show improved insulin tolerance and enhanced capacity to handle a lipid challenge on a high-fat diet [#2]. In cardiomyocytes CTRP2 drives GLUT1/GLUT4 translocation and glucose uptake through AMPK activation positioned upstream of Akt, partly via adiponectin receptor 1 [#5], and recombinant CTRP2 promotes endothelial angiogenesis through AKT–VEGFR2 signaling while limiting infarct size in ischemia/reperfusion models [#6]. The C1q globular domain is sufficient for biological activity [#7]. No structural model of its receptor engagement or a unifying account linking its distinct tissue activities has been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Established that CTRP2 is a secreted glycoprotein with defined oligomeric architecture and intrinsic metabolic activity, distinguishing it from a passive serum component.\",\n      \"evidence\": \"Mammalian cell expression with size-exclusion chromatography and co-secretion; in vitro myotube assays of glycogen and fat oxidation\",\n      \"pmids\": [\"18783346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating myotube effects not identified\", \"Physiological relevance of heterotrimers with CTRP7/adiponectin untested in vivo\", \"No structural model of the trimer-receptor interface\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Tested whether circulating CTRP2 affects whole-body metabolism, showing gain-of-function improves insulin tolerance and lipid handling.\",\n      \"evidence\": \"CTRP2-overexpressing transgenic mice with insulin tolerance test and acute lipid challenge on high-fat diet\",\n      \"pmids\": [\"24586339\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue source of the metabolic benefit not resolved\", \"Signaling pathway not defined in this model\", \"Overexpression may not reflect endogenous dose\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the endogenous role and a molecular pathway, placing CTRP2 as a suppressor of PKA-mediated adipose lipolysis and a regulator of hepatic triglyceride secretion.\",\n      \"evidence\": \"Knockout mice with lipid/metabolomic profiling and oral gavage, plus rescue by recombinant CTRP2 in cultured adipocytes and PKA signaling assays\",\n      \"pmids\": [\"31439668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor coupling CTRP2 to PKA suppression unidentified\", \"Mechanism linking membrane lipid remodeling to hepatic TG secretion not established\", \"Direct vs. indirect action on hepatocytes unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified an intracellular signaling order in cardiomyocytes, placing AMPK upstream of Akt in CTRP2-driven glucose uptake and implicating AdipoR1.\",\n      \"evidence\": \"Recombinant CTRP2 on primary cardiomyocytes and H9C2 cells with GLUT translocation/uptake assays, pharmacological AMPK/Akt inhibition, and AdipoR1 knockdown\",\n      \"pmids\": [\"33919975\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"AdipoR1 loss abolished only some effects, leaving the full receptor set unknown\", \"Pharmacological inhibitor specificity limits pathway ordering\", \"In vivo cardiac glucose handling not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended CTRP2 function to the vasculature, showing it promotes angiogenesis via AKT-VEGFR2 and confers cardioprotection in ischemia.\",\n      \"evidence\": \"Endothelial tube formation/migration assays with Western blot for AKT/VEGFR2, plus recombinant CTRP2 injection in mouse I/R and hindlimb ischemia models\",\n      \"pmids\": [\"36409464\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor on endothelial cells not defined\", \"Whether VEGFR2 induction is transcriptional or post-translational unresolved\", \"Cardioprotection mechanism vs. angiogenesis not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CTRP2 engages its receptor(s) at the structural level and how its distinct tissue-specific activities (adipose lipolysis suppression, hepatic TG secretion, cardiac glucose uptake, endothelial angiogenesis) are unified by a common mechanism remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No definitive cognate receptor mapped across all tissues\", \"No structural model of ligand-receptor engagement\", \"Relationship between AMPK/Akt and PKA pathways across tissues unintegrated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CTRP7\", \"ADIPOQ\", \"ADIPOR1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}