{"gene":"FETUB","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2016,"finding":"Fetuin-B is a potent and highly specific inhibitor of the zona proteinase ovastacin (ASTL), which cleaves ZP2 and mediates definitive zona pellucida hardening. Genetic rescue experiments showed that fertility of Fetub-/- female mice was restored by additional ovastacin deficiency (Fetub-/-, Astl-/- double knockout), confirming ovastacin as the primary molecular target of fetuin-B in preventing premature ZP hardening.","method":"Genetic epistasis (double knockout mouse rescue), antisense oligonucleotide knockdown, IVF, immunoblot quantification of serum fetuin-B","journal":"Molecular human reproduction","confidence":"High","confidence_rationale":"Tier 1-2 — genetic rescue with double KO plus multiple orthogonal methods; replicated across multiple experimental arms","pmids":["27733488"],"is_preprint":false},{"year":2024,"finding":"FETUB physically interacts with insulin receptor-β (IRβ) in retinal cells. This interaction is increased under high-glucose conditions, and FETUB suppresses the insulin signaling (PI3K/Akt) pathway, promoting insulin resistance in BV2 microglia and Müller cells.","method":"Co-immunoprecipitation, FETUB recombinant protein treatment, FETUB shRNA knockdown, PI3K inhibitor rescue (LY294002), Western blotting","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional knockdown/overexpression with pathway inhibitor rescue; single lab","pmids":["39382879"],"is_preprint":false},{"year":2024,"finding":"FETUB promotes inflammation in diabetic retinopathy by activating microglia and the NF-κB signaling pathway. FETUB recombinant protein increased p-P65/P65 ratio and expression of TNF-α, VEGF, and IBA-1 in BV2 cells, while FETUB shRNA knockdown reduced these markers.","method":"FETUB recombinant protein treatment, FETUB shRNA knockdown, Western blotting, q-PCR, immunofluorescence, mouse DR model","journal":"Current eye research","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function with defined pathway readouts; single lab","pmids":["37883127"],"is_preprint":false},{"year":2025,"finding":"FETUB inhibits neprilysin (NEP) enzymatic activity. Bioinformatic docking, protein binding assays, and fluorescence substrate degradation experiments confirmed FETUB as a NEP inhibitor. Lung-specific FETUB knockdown in mice restored NEP activity, reduced neuropeptides CGRP and SP, and improved airway inflammation and hyperresponsiveness in asthma.","method":"Molecular docking, protein binding assay, fluorescence substrate degradation (in vitro NEP activity assay), AAV-mediated lung-specific FETUB knockdown mouse model, ELISA","journal":"International immunopharmacology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro enzymatic inhibition assay plus in vivo functional rescue with specific phenotypic readout","pmids":["40064057"],"is_preprint":false},{"year":2026,"finding":"FETUB promotes hepatocyte pyroptosis in metabolic-dysfunction-associated steatohepatitis (MASH) by downregulating adiponectin receptor 1 (AdipoR1), thereby activating the NLRP3 inflammasome/GSDMD pathway. Free fatty acid stimulation upregulated FETUB in primary hepatocytes, and FETUB blockade ameliorated hepatic steatosis, inflammation, ballooning, and fibrosis in HFD-induced mice.","method":"Primary mouse hepatocyte culture with FFA stimulation, FETUB blockade in HFD mouse model, Western blotting for NLRP3/GSDMD pathway components, histology","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo loss-of-function with defined molecular pathway; single lab","pmids":["41506566"],"is_preprint":false},{"year":2022,"finding":"FETUB transcription in hepatocytes is directly activated by leptin signaling through a STAT3-dependent mechanism. STAT3 binds to response elements on the FETUB promoter. VDR silencing releases FETUB expression, and 1α,25-(OH)2D3 reduces FETUB synthesis in a time- and dose-dependent manner in hepatocellular cells.","method":"In vitro leptin stimulation of primary hepatocytes and AML12 cells, STAT3 inhibition, VDR silencing, promoter binding analysis, VD supplementation in mice","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic transcriptional regulation with promoter binding and multiple cellular perturbations; single lab","pmids":["35896788"],"is_preprint":false},{"year":2018,"finding":"Vitamin D (1α,25-(OH)2D3) directly and negatively regulates FETUB synthesis in hepatocellular cells in a time- and dose-dependent manner, with the vitamin D receptor (VDR) being required, as VDR silencing releases FETUB expression. VD supplementation in juvenile mice reduced plasma FETUB.","method":"2D-electrophoretic proteomics, hepatocellular cell treatment with 1α,25-(OH)2D3, VDR silencing, mouse VD supplementation experiment, ELISA","journal":"The Journal of steroid biochemistry and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (cell culture, genetic silencing, in vivo) confirming VDR-mediated regulation; single lab","pmids":["29684480"],"is_preprint":false},{"year":2012,"finding":"Knockdown of FETUB in Chang liver cells using siRNA led to significant increase in expression of lipogenic genes and higher lipid levels, indicating FETUB plays a role in suppressing lipogenesis in hepatocytes.","method":"siRNA knockdown in Chang liver cells, lipid level measurement, gene expression analysis","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with defined cellular phenotype (lipid accumulation) and lipogenic gene expression; single lab","pmids":["22739111"],"is_preprint":false},{"year":2020,"finding":"Overexpression of FETUB in prostate cancer cells suppressed proliferation, migration, and invasion, promoted apoptosis, and inactivated the PI3K/AKT signaling pathway. Rescue with PI3K activator 740Y-P reversed the anti-tumor effects, placing FETUB upstream of PI3K/AKT.","method":"Lentiviral FETUB overexpression, in vitro migration/invasion assays, apoptosis assays, in vivo tumor xenograft, 740Y-P rescue experiment, Western blotting","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function plus pathway rescue in vitro and in vivo; single lab","pmids":["32892030"],"is_preprint":false},{"year":2026,"finding":"Granulosa cells do not synthesize fetuin-B (minimal FETUB transcription by RT-qPCR) but store, release, and re-internalize it. Fetuin-B was detected intracellularly (notably in filopodia) and peaked in supernatant on day 1 of culture, suggesting uptake from serum followed by regulated secretion.","method":"RT-qPCR, ELISA of granulosa cell supernatant and intracellular fractions, immunocytochemistry, comparison with HepG2 positive control","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (qPCR, ELISA, immunocytochemistry) establishing localization and transport; single lab","pmids":["41577932"],"is_preprint":false},{"year":2023,"finding":"Computational docking studies showed that FETUB inhibitor interactions with ovastacin (ASTL) involve hydrophobic interactions and H-bonding at specific residues (D198, L278 for hydrophobic; K93, R159, C281 for H-bonding), and SNPs at these positions affect FETUB-ASTL binding relevant to female infertility.","method":"In silico SNP analysis, molecular docking, Statistical Coupling Analysis","journal":"Frontiers in cell and developmental biology","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only, no experimental validation of specific residues","pmids":["37363721"],"is_preprint":false}],"current_model":"FETUB is a liver-derived glycoprotein and cysteine protease inhibitor that functions primarily as a potent inhibitor of ovastacin (ASTL), preventing premature zona pellucida hardening and thus enabling fertilization; it also inhibits neprilysin (NEP) enzymatic activity in the airway, interacts directly with insulin receptor-β to suppress PI3K/Akt insulin signaling, promotes inflammation via NF-κB/microglia activation and NLRP3/GSDMD-driven pyroptosis in metabolic and retinal disease contexts, and suppresses lipogenesis in hepatocytes, with its transcription in the liver regulated directly by the leptin-STAT3 axis and negatively by the vitamin D receptor."},"narrative":{"teleology":[{"year":2012,"claim":"Establishing that FETUB has a hepatocyte-intrinsic metabolic function: siRNA knockdown in liver cells showed FETUB suppresses lipogenic gene expression and lipid accumulation, revealing it as a negative regulator of lipogenesis beyond its known protease-inhibitor identity.","evidence":"siRNA knockdown in Chang liver cells with lipid and gene expression readouts","pmids":["22739111"],"confidence":"Medium","gaps":["Downstream lipogenic targets not identified","No in vivo confirmation of anti-lipogenic role","Mechanism of lipogenesis suppression unknown"]},{"year":2016,"claim":"Identifying the primary physiological target of fetuin-B: genetic rescue experiments showed that fertility defects of Fetub-knockout female mice are entirely dependent on ovastacin (ASTL), establishing fetuin-B as the endogenous inhibitor that prevents premature zona pellucida hardening and is essential for fertilization.","evidence":"Fetub−/−; Astl−/− double-knockout rescue in mice, antisense oligonucleotide knockdown, IVF assays","pmids":["27733488"],"confidence":"High","gaps":["Structural basis of FETUB–ovastacin interaction not experimentally resolved","Whether fetuin-B also inhibits other metzincin proteinases in vivo unknown"]},{"year":2018,"claim":"Demonstrating transcriptional control of FETUB by vitamin D signaling: 1α,25-(OH)₂D₃ suppresses FETUB expression in hepatocellular cells in a VDR-dependent manner, providing a regulatory link between vitamin D status and circulating fetuin-B levels.","evidence":"Hepatocellular cell treatment with calcitriol, VDR silencing, mouse vitamin D supplementation, ELISA","pmids":["29684480"],"confidence":"Medium","gaps":["VDR binding site on FETUB promoter not mapped","Physiological significance of VDR-FETUB axis in whole-organism metabolism unclear"]},{"year":2020,"claim":"Revealing FETUB as an upstream suppressor of PI3K/AKT signaling with tumor-suppressive consequences: overexpression in prostate cancer cells inhibited proliferation and invasion, effects reversed by a PI3K activator, placing FETUB functionally upstream of PI3K/AKT.","evidence":"Lentiviral overexpression, xenograft model, 740Y-P rescue, Western blot","pmids":["32892030"],"confidence":"Medium","gaps":["Direct molecular target mediating PI3K suppression in cancer cells not identified","Not confirmed in additional cancer types","Endogenous FETUB expression in prostate tissue not characterized"]},{"year":2022,"claim":"Linking leptin–STAT3 signaling to FETUB transcription: leptin stimulates FETUB expression in hepatocytes through STAT3 binding to the FETUB promoter, integrating fetuin-B into the adiposity–liver cross-talk axis.","evidence":"Leptin stimulation of primary hepatocytes/AML12 cells, STAT3 inhibition, promoter binding analysis","pmids":["35896788"],"confidence":"Medium","gaps":["Quantitative contribution of STAT3 versus other transcription factors not resolved","In vivo validation of leptin–FETUB axis in obesity models limited"]},{"year":2024,"claim":"Establishing a direct physical interaction between FETUB and insulin receptor-β and its functional consequence: FETUB binds IRβ, and this interaction increases under high glucose, suppressing PI3K/Akt signaling and promoting insulin resistance and NF-κB-mediated inflammation in retinal microglia and Müller cells.","evidence":"Co-immunoprecipitation, recombinant FETUB and shRNA knockdown in BV2 and Müller cells, PI3K inhibitor rescue, Western blot, diabetic retinopathy mouse model","pmids":["39382879","37883127"],"confidence":"Medium","gaps":["Binding interface between FETUB and IRβ not mapped","Whether FETUB–IRβ interaction occurs in non-retinal tissues in vivo unknown","Independent replication needed"]},{"year":2025,"claim":"Expanding protease-inhibitor repertoire: FETUB directly inhibits neprilysin (NEP) enzymatic activity, and lung-specific FETUB knockdown in asthma models restored NEP activity, reduced neuropeptide accumulation, and alleviated airway inflammation and hyperresponsiveness.","evidence":"Molecular docking, protein binding assay, fluorescence substrate NEP activity assay, AAV-mediated lung-specific FETUB knockdown in mice","pmids":["40064057"],"confidence":"High","gaps":["Kinetic parameters (Ki) of FETUB–NEP inhibition not reported","Whether FETUB inhibits NEP in other tissues not tested"]},{"year":2026,"claim":"Elucidating FETUB's role in MASH-associated pyroptosis: free fatty acids upregulate FETUB in hepatocytes, which downregulates AdipoR1 to activate the NLRP3/GSDMD pyroptotic pathway; FETUB blockade ameliorates steatohepatitis in vivo.","evidence":"Primary hepatocyte FFA stimulation, FETUB blockade in HFD mouse model, NLRP3/GSDMD pathway Western blot, histology","pmids":["41506566"],"confidence":"Medium","gaps":["Mechanism by which FETUB downregulates AdipoR1 not defined","Single lab; independent replication needed"]},{"year":2026,"claim":"Clarifying fetuin-B handling in the reproductive system: granulosa cells do not synthesize fetuin-B but internalize it from serum and re-secrete it in a regulated manner, indicating a paracrine delivery mechanism to the oocyte.","evidence":"RT-qPCR, ELISA, immunocytochemistry of cultured granulosa cells versus HepG2 control","pmids":["41577932"],"confidence":"Medium","gaps":["Receptor or uptake mechanism for fetuin-B internalization by granulosa cells unknown","Functional consequence of regulated release timing not tested"]},{"year":null,"claim":"The structural basis of FETUB's dual protease inhibition (ovastacin and neprilysin), the molecular mechanism by which it modulates IRβ and AdipoR1, and whether its metabolic and inflammatory effects are mediated through a single or multiple receptor interactions remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of FETUB or FETUB–target complexes","No unified model connecting protease-inhibitor and receptor-modulatory functions","Tissue-specific contributions of circulating versus locally released FETUB not dissected"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,1,8]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7,4]}],"complexes":[],"partners":["ASTL","MME","INSR","ADIPOR1","STAT3"],"other_free_text":[]},"mechanistic_narrative":"FETUB encodes fetuin-B, a liver-secreted glycoprotein that functions as a cysteine protease inhibitor with broad roles in fertility, metabolic homeostasis, and inflammation. Its best-characterized function is potent inhibition of the metalloproteinase ovastacin (ASTL), preventing premature zona pellucida hardening; genetic epistasis in mice confirmed that the infertility of Fetub-knockout females is fully rescued by concomitant ovastacin deficiency [PMID:27733488]. FETUB also inhibits neprilysin (NEP) enzymatic activity in the airway, where its knockdown restores NEP function and alleviates asthma-related inflammation [PMID:40064057], and it physically interacts with insulin receptor-β to suppress PI3K/Akt signaling, promoting insulin resistance and NF-κB-driven inflammation in retinal and microglial cells [PMID:39382879, PMID:37883127]. Hepatic FETUB transcription is positively regulated by the leptin–STAT3 axis and negatively regulated by the vitamin D receptor, and FETUB modulates hepatocyte lipogenesis and pyroptosis through the NLRP3/GSDMD pathway [PMID:35896788, PMID:29684480, PMID:22739111, PMID:41506566]."},"prefetch_data":{"uniprot":{"accession":"Q9UGM5","full_name":"Fetuin-B","aliases":["16G2","Fetuin-like protein IRL685","Gugu"],"length_aa":382,"mass_kda":42.1,"function":"Protease inhibitor required for egg fertilization. Required to prevent premature zona pellucida hardening before fertilization, probably by inhibiting the protease activity of ASTL, a protease that mediates the cleavage of ZP2 and triggers zona pellucida hardening (By similarity)","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q9UGM5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FETUB","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FETUB","total_profiled":1310},"omim":[{"mim_id":"605954","title":"FETUIN B; FETUB","url":"https://www.omim.org/entry/605954"},{"mim_id":"138680","title":"ALPHA-2-HS-GLYCOPROTEIN; AHSG","url":"https://www.omim.org/entry/138680"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"liver","ntpm":219.3}],"url":"https://www.proteinatlas.org/search/FETUB"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9UGM5","domains":[{"cath_id":"3.10.450.10","chopping":"30-144_310-364","consensus_level":"high","plddt":89.4418,"start":30,"end":364},{"cath_id":"3.10.450.10","chopping":"154-218_233-257","consensus_level":"high","plddt":92.0817,"start":154,"end":257}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UGM5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UGM5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UGM5-F1-predicted_aligned_error_v6.png","plddt_mean":81.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FETUB","jax_strain_url":"https://www.jax.org/strain/search?query=FETUB"},"sequence":{"accession":"Q9UGM5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UGM5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UGM5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UGM5"}},"corpus_meta":[{"pmid":"17494914","id":"PMC_17494914","title":"Microarray 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research","url":"https://pubmed.ncbi.nlm.nih.gov/41887668","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":30675,"output_tokens":2716,"usd":0.066382},"stage2":{"model":"claude-opus-4-6","input_tokens":6078,"output_tokens":2505,"usd":0.139522},"total_usd":0.205904,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"Fetuin-B is a potent and highly specific inhibitor of the zona proteinase ovastacin (ASTL), which cleaves ZP2 and mediates definitive zona pellucida hardening. Genetic rescue experiments showed that fertility of Fetub-/- female mice was restored by additional ovastacin deficiency (Fetub-/-, Astl-/- double knockout), confirming ovastacin as the primary molecular target of fetuin-B in preventing premature ZP hardening.\",\n      \"method\": \"Genetic epistasis (double knockout mouse rescue), antisense oligonucleotide knockdown, IVF, immunoblot quantification of serum fetuin-B\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic rescue with double KO plus multiple orthogonal methods; replicated across multiple experimental arms\",\n      \"pmids\": [\"27733488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FETUB physically interacts with insulin receptor-β (IRβ) in retinal cells. This interaction is increased under high-glucose conditions, and FETUB suppresses the insulin signaling (PI3K/Akt) pathway, promoting insulin resistance in BV2 microglia and Müller cells.\",\n      \"method\": \"Co-immunoprecipitation, FETUB recombinant protein treatment, FETUB shRNA knockdown, PI3K inhibitor rescue (LY294002), Western blotting\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional knockdown/overexpression with pathway inhibitor rescue; single lab\",\n      \"pmids\": [\"39382879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FETUB promotes inflammation in diabetic retinopathy by activating microglia and the NF-κB signaling pathway. FETUB recombinant protein increased p-P65/P65 ratio and expression of TNF-α, VEGF, and IBA-1 in BV2 cells, while FETUB shRNA knockdown reduced these markers.\",\n      \"method\": \"FETUB recombinant protein treatment, FETUB shRNA knockdown, Western blotting, q-PCR, immunofluorescence, mouse DR model\",\n      \"journal\": \"Current eye research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with defined pathway readouts; single lab\",\n      \"pmids\": [\"37883127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FETUB inhibits neprilysin (NEP) enzymatic activity. Bioinformatic docking, protein binding assays, and fluorescence substrate degradation experiments confirmed FETUB as a NEP inhibitor. Lung-specific FETUB knockdown in mice restored NEP activity, reduced neuropeptides CGRP and SP, and improved airway inflammation and hyperresponsiveness in asthma.\",\n      \"method\": \"Molecular docking, protein binding assay, fluorescence substrate degradation (in vitro NEP activity assay), AAV-mediated lung-specific FETUB knockdown mouse model, ELISA\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro enzymatic inhibition assay plus in vivo functional rescue with specific phenotypic readout\",\n      \"pmids\": [\"40064057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FETUB promotes hepatocyte pyroptosis in metabolic-dysfunction-associated steatohepatitis (MASH) by downregulating adiponectin receptor 1 (AdipoR1), thereby activating the NLRP3 inflammasome/GSDMD pathway. Free fatty acid stimulation upregulated FETUB in primary hepatocytes, and FETUB blockade ameliorated hepatic steatosis, inflammation, ballooning, and fibrosis in HFD-induced mice.\",\n      \"method\": \"Primary mouse hepatocyte culture with FFA stimulation, FETUB blockade in HFD mouse model, Western blotting for NLRP3/GSDMD pathway components, histology\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo loss-of-function with defined molecular pathway; single lab\",\n      \"pmids\": [\"41506566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FETUB transcription in hepatocytes is directly activated by leptin signaling through a STAT3-dependent mechanism. STAT3 binds to response elements on the FETUB promoter. VDR silencing releases FETUB expression, and 1α,25-(OH)2D3 reduces FETUB synthesis in a time- and dose-dependent manner in hepatocellular cells.\",\n      \"method\": \"In vitro leptin stimulation of primary hepatocytes and AML12 cells, STAT3 inhibition, VDR silencing, promoter binding analysis, VD supplementation in mice\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic transcriptional regulation with promoter binding and multiple cellular perturbations; single lab\",\n      \"pmids\": [\"35896788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Vitamin D (1α,25-(OH)2D3) directly and negatively regulates FETUB synthesis in hepatocellular cells in a time- and dose-dependent manner, with the vitamin D receptor (VDR) being required, as VDR silencing releases FETUB expression. VD supplementation in juvenile mice reduced plasma FETUB.\",\n      \"method\": \"2D-electrophoretic proteomics, hepatocellular cell treatment with 1α,25-(OH)2D3, VDR silencing, mouse VD supplementation experiment, ELISA\",\n      \"journal\": \"The Journal of steroid biochemistry and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (cell culture, genetic silencing, in vivo) confirming VDR-mediated regulation; single lab\",\n      \"pmids\": [\"29684480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Knockdown of FETUB in Chang liver cells using siRNA led to significant increase in expression of lipogenic genes and higher lipid levels, indicating FETUB plays a role in suppressing lipogenesis in hepatocytes.\",\n      \"method\": \"siRNA knockdown in Chang liver cells, lipid level measurement, gene expression analysis\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular phenotype (lipid accumulation) and lipogenic gene expression; single lab\",\n      \"pmids\": [\"22739111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Overexpression of FETUB in prostate cancer cells suppressed proliferation, migration, and invasion, promoted apoptosis, and inactivated the PI3K/AKT signaling pathway. Rescue with PI3K activator 740Y-P reversed the anti-tumor effects, placing FETUB upstream of PI3K/AKT.\",\n      \"method\": \"Lentiviral FETUB overexpression, in vitro migration/invasion assays, apoptosis assays, in vivo tumor xenograft, 740Y-P rescue experiment, Western blotting\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function plus pathway rescue in vitro and in vivo; single lab\",\n      \"pmids\": [\"32892030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Granulosa cells do not synthesize fetuin-B (minimal FETUB transcription by RT-qPCR) but store, release, and re-internalize it. Fetuin-B was detected intracellularly (notably in filopodia) and peaked in supernatant on day 1 of culture, suggesting uptake from serum followed by regulated secretion.\",\n      \"method\": \"RT-qPCR, ELISA of granulosa cell supernatant and intracellular fractions, immunocytochemistry, comparison with HepG2 positive control\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (qPCR, ELISA, immunocytochemistry) establishing localization and transport; single lab\",\n      \"pmids\": [\"41577932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Computational docking studies showed that FETUB inhibitor interactions with ovastacin (ASTL) involve hydrophobic interactions and H-bonding at specific residues (D198, L278 for hydrophobic; K93, R159, C281 for H-bonding), and SNPs at these positions affect FETUB-ASTL binding relevant to female infertility.\",\n      \"method\": \"In silico SNP analysis, molecular docking, Statistical Coupling Analysis\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no experimental validation of specific residues\",\n      \"pmids\": [\"37363721\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FETUB is a liver-derived glycoprotein and cysteine protease inhibitor that functions primarily as a potent inhibitor of ovastacin (ASTL), preventing premature zona pellucida hardening and thus enabling fertilization; it also inhibits neprilysin (NEP) enzymatic activity in the airway, interacts directly with insulin receptor-β to suppress PI3K/Akt insulin signaling, promotes inflammation via NF-κB/microglia activation and NLRP3/GSDMD-driven pyroptosis in metabolic and retinal disease contexts, and suppresses lipogenesis in hepatocytes, with its transcription in the liver regulated directly by the leptin-STAT3 axis and negatively by the vitamin D receptor.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FETUB encodes fetuin-B, a liver-secreted glycoprotein that functions as a cysteine protease inhibitor with broad roles in fertility, metabolic homeostasis, and inflammation. Its best-characterized function is potent inhibition of the metalloproteinase ovastacin (ASTL), preventing premature zona pellucida hardening; genetic epistasis in mice confirmed that the infertility of Fetub-knockout females is fully rescued by concomitant ovastacin deficiency [PMID:27733488]. FETUB also inhibits neprilysin (NEP) enzymatic activity in the airway, where its knockdown restores NEP function and alleviates asthma-related inflammation [PMID:40064057], and it physically interacts with insulin receptor-β to suppress PI3K/Akt signaling, promoting insulin resistance and NF-κB-driven inflammation in retinal and microglial cells [PMID:39382879, PMID:37883127]. Hepatic FETUB transcription is positively regulated by the leptin–STAT3 axis and negatively regulated by the vitamin D receptor, and FETUB modulates hepatocyte lipogenesis and pyroptosis through the NLRP3/GSDMD pathway [PMID:35896788, PMID:29684480, PMID:22739111, PMID:41506566].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing that FETUB has a hepatocyte-intrinsic metabolic function: siRNA knockdown in liver cells showed FETUB suppresses lipogenic gene expression and lipid accumulation, revealing it as a negative regulator of lipogenesis beyond its known protease-inhibitor identity.\",\n      \"evidence\": \"siRNA knockdown in Chang liver cells with lipid and gene expression readouts\",\n      \"pmids\": [\"22739111\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream lipogenic targets not identified\", \"No in vivo confirmation of anti-lipogenic role\", \"Mechanism of lipogenesis suppression unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identifying the primary physiological target of fetuin-B: genetic rescue experiments showed that fertility defects of Fetub-knockout female mice are entirely dependent on ovastacin (ASTL), establishing fetuin-B as the endogenous inhibitor that prevents premature zona pellucida hardening and is essential for fertilization.\",\n      \"evidence\": \"Fetub−/−; Astl−/− double-knockout rescue in mice, antisense oligonucleotide knockdown, IVF assays\",\n      \"pmids\": [\"27733488\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FETUB–ovastacin interaction not experimentally resolved\", \"Whether fetuin-B also inhibits other metzincin proteinases in vivo unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating transcriptional control of FETUB by vitamin D signaling: 1α,25-(OH)₂D₃ suppresses FETUB expression in hepatocellular cells in a VDR-dependent manner, providing a regulatory link between vitamin D status and circulating fetuin-B levels.\",\n      \"evidence\": \"Hepatocellular cell treatment with calcitriol, VDR silencing, mouse vitamin D supplementation, ELISA\",\n      \"pmids\": [\"29684480\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"VDR binding site on FETUB promoter not mapped\", \"Physiological significance of VDR-FETUB axis in whole-organism metabolism unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealing FETUB as an upstream suppressor of PI3K/AKT signaling with tumor-suppressive consequences: overexpression in prostate cancer cells inhibited proliferation and invasion, effects reversed by a PI3K activator, placing FETUB functionally upstream of PI3K/AKT.\",\n      \"evidence\": \"Lentiviral overexpression, xenograft model, 740Y-P rescue, Western blot\",\n      \"pmids\": [\"32892030\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target mediating PI3K suppression in cancer cells not identified\", \"Not confirmed in additional cancer types\", \"Endogenous FETUB expression in prostate tissue not characterized\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linking leptin–STAT3 signaling to FETUB transcription: leptin stimulates FETUB expression in hepatocytes through STAT3 binding to the FETUB promoter, integrating fetuin-B into the adiposity–liver cross-talk axis.\",\n      \"evidence\": \"Leptin stimulation of primary hepatocytes/AML12 cells, STAT3 inhibition, promoter binding analysis\",\n      \"pmids\": [\"35896788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quantitative contribution of STAT3 versus other transcription factors not resolved\", \"In vivo validation of leptin–FETUB axis in obesity models limited\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Establishing a direct physical interaction between FETUB and insulin receptor-β and its functional consequence: FETUB binds IRβ, and this interaction increases under high glucose, suppressing PI3K/Akt signaling and promoting insulin resistance and NF-κB-mediated inflammation in retinal microglia and Müller cells.\",\n      \"evidence\": \"Co-immunoprecipitation, recombinant FETUB and shRNA knockdown in BV2 and Müller cells, PI3K inhibitor rescue, Western blot, diabetic retinopathy mouse model\",\n      \"pmids\": [\"39382879\", \"37883127\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding interface between FETUB and IRβ not mapped\", \"Whether FETUB–IRβ interaction occurs in non-retinal tissues in vivo unknown\", \"Independent replication needed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Expanding protease-inhibitor repertoire: FETUB directly inhibits neprilysin (NEP) enzymatic activity, and lung-specific FETUB knockdown in asthma models restored NEP activity, reduced neuropeptide accumulation, and alleviated airway inflammation and hyperresponsiveness.\",\n      \"evidence\": \"Molecular docking, protein binding assay, fluorescence substrate NEP activity assay, AAV-mediated lung-specific FETUB knockdown in mice\",\n      \"pmids\": [\"40064057\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetic parameters (Ki) of FETUB–NEP inhibition not reported\", \"Whether FETUB inhibits NEP in other tissues not tested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Elucidating FETUB's role in MASH-associated pyroptosis: free fatty acids upregulate FETUB in hepatocytes, which downregulates AdipoR1 to activate the NLRP3/GSDMD pyroptotic pathway; FETUB blockade ameliorates steatohepatitis in vivo.\",\n      \"evidence\": \"Primary hepatocyte FFA stimulation, FETUB blockade in HFD mouse model, NLRP3/GSDMD pathway Western blot, histology\",\n      \"pmids\": [\"41506566\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which FETUB downregulates AdipoR1 not defined\", \"Single lab; independent replication needed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Clarifying fetuin-B handling in the reproductive system: granulosa cells do not synthesize fetuin-B but internalize it from serum and re-secrete it in a regulated manner, indicating a paracrine delivery mechanism to the oocyte.\",\n      \"evidence\": \"RT-qPCR, ELISA, immunocytochemistry of cultured granulosa cells versus HepG2 control\",\n      \"pmids\": [\"41577932\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor or uptake mechanism for fetuin-B internalization by granulosa cells unknown\", \"Functional consequence of regulated release timing not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of FETUB's dual protease inhibition (ovastacin and neprilysin), the molecular mechanism by which it modulates IRβ and AdipoR1, and whether its metabolic and inflammatory effects are mediated through a single or multiple receptor interactions remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of FETUB or FETUB–target complexes\", \"No unified model connecting protease-inhibitor and receptor-modulatory functions\", \"Tissue-specific contributions of circulating versus locally released FETUB not dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 1, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ASTL\", \"MME\", \"INSR\", \"ADIPOR1\", \"STAT3\"],\n    \"other_free_text\": []\n  }\n}\n```"}