{"gene":"FZD4","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":2009,"finding":"TSPAN12 physically associates with the Norrin-FZD4 receptor complex (shown by co-expression/co-immunoprecipitation) and selectively amplifies Norrin/β-catenin but not Wnt/β-catenin signaling; overexpressed TSPAN12 rescues signaling defects caused by FZD4 mutations predicted to impair receptor multimerization, indicating TSPAN12 promotes FZD4 multimerization specifically in the context of Norrin signaling.","method":"Co-immunoprecipitation, siRNA knockdown, luciferase reporter assay, genetic epistasis in Tspan12/Norrin/Lrp5 mutant mice","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, multiple orthogonal methods (siRNA, reporter assay, in vivo mouse genetics), replicated across cell and animal systems in a single rigorous study","pmids":["19837033"],"is_preprint":false},{"year":2010,"finding":"The cysteine-rich domain (CRD) of FZD4 is essential for Norrin binding and Norrin-dependent activation of canonical Wnt/β-catenin signaling; CRD missense mutations C45Y, Y58C, and C204R abolish Norrin binding as measured by cell-surface and overlay binding assays and eliminate Norrin-induced Wnt/β-catenin reporter activity in HEK293 cells and in Xenopus embryos (decreased Siamois and Xnr3 expression).","method":"Cell-surface binding assay, overlay binding assay, luciferase reporter assay (HEK293), Xenopus embryo injection with marker gene expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro binding reconstitution plus mutagenesis plus in vivo Xenopus functional validation, single lab but multiple orthogonal methods","pmids":["21177847"],"is_preprint":false},{"year":2014,"finding":"Multiple FEVR-associated missense mutations in FZD4 (P33S, G36N, H69Y, M105T, M105V, C181R, C204R, C204Y, G488D) cause predominant ER retention rather than plasma membrane localization, establishing defective ER-to-plasma-membrane trafficking as a major pathological mechanism; this trafficking defect could be partially rescued for M105T and C204Y mutants by reduced temperature or chemical chaperones. Mutant FZD4 does not trap co-expressed wild-type FZD4.","method":"Confocal fluorescence microscopy, N-glycosylation profiling, polyubiquitination assays, chemical chaperone rescue experiments in HeLa and COS-7 cells","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods (glycosylation, ubiquitination, imaging) applied to 15 mutants with functional rescue; comprehensive mechanistic characterization in single study","pmids":["24744206"],"is_preprint":false},{"year":2024,"finding":"Systematic functional analysis of 34 FZD4 missense mutations categorized pathogenic mechanisms into five classes: (1) signal peptide mutations, (2) cysteine mutations disrupting disulfide bonds, (3) extracellular domain mutations impairing Norrin binding, (4) transmembrane domain 1 and TM7 mutations impairing membrane localization, and (5) intracellular domain mutations reducing DVL2 recruitment, as assessed by protein expression, Norrin/β-catenin luciferase reporter, membrane localization, Norrin binding, and DVL2 co-immunoprecipitation assays in HEK293T, HEK293STF, and HeLa cells.","method":"Site-directed mutagenesis, luciferase reporter assay (Norrin/β-catenin TOPflash), confocal microscopy for membrane localization, Norrin binding assay, DVL2 co-immunoprecipitation","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal functional assays applied to 34 mutations across all FZD4 domains; comprehensive mechanistic classification in a single rigorous study","pmids":["38558095"],"is_preprint":false},{"year":2025,"finding":"FZD4 is N-glycosylated at asparagine residues N59 and N144 (both highly conserved); N-glycosylation is required for FZD4 maturation, plasma membrane trafficking, protein stability, and interaction with Wnt ligands and co-receptor Norrin. Glycosylation-deficient FZD4 mutants fail to activate Wnt/β-catenin signaling and cannot rescue proliferation/migration in FZD4-knockout A549 cells in vitro or in vivo.","method":"Site-directed mutagenesis at N-glycosylation sites, cell surface localization assay, co-immunoprecipitation with Wnt ligands/Norrin, TOPflash luciferase reporter, xenograft tumor model","journal":"Journal of cellular and molecular medicine","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of specific glycosylation sites combined with binding assays, reporter assay, and in vivo xenograft validation; multiple orthogonal methods in single study","pmids":["40230079"],"is_preprint":false},{"year":2021,"finding":"The ER membrane protein complex subunit EMC3 is required for FZD4 expression; endothelial-specific deletion of Emc3 in mice reduces FZD4 levels and impairs Norrin/β-catenin signaling, causing defective retinal vascularization that is partially rescued by lithium chloride (Wnt activator), placing EMC3 upstream of FZD4 in the Norrin/β-catenin pathway in retinal endothelial cells.","method":"Conditional knockout mice (endothelial Emc3 deletion), RNA-seq, RT-qPCR, luciferase reporter assay, LiCl rescue experiment, tube formation assay","journal":"Science China. Life sciences","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with retinal vascular phenotype, reporter assay, and pharmacological rescue; multiple methods in single study","pmids":["34128175"],"is_preprint":false},{"year":2017,"finding":"FZD4 marks lateral plate mesoderm in cardiac progenitor cells (CPCs); NORRIN presented to FZD4 increases cardiomyocyte output from CPCs via canonical WNT/β-catenin signaling-driven proliferation; FZD4 was used together with FLK1 and PDGFRA to purify CPCs and enhance cardiomyocyte enrichment from mouse and human pluripotent stem cells.","method":"Surface proteomics (mass spectrometry), microarray transcriptomics, FACS sorting with FZD4 antibody, NORRIN/FZD4 signaling assay, cardiomyocyte differentiation assay","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — surface proteomics plus functional NORRIN/FZD4 signaling assay with cardiomyocyte output quantification; single lab, two orthogonal approaches","pmids":["29249665"],"is_preprint":false},{"year":2005,"finding":"Fzd4-null (Fzd4−/−) mice are infertile due to failure of corpus luteum formation and function; markers of luteal cell identity (Lhcgr, Prlr, Cyp11a1, Sfrp4) and angiogenesis (Efnb1, Efnb2, Ephb4, Vegfa, Vegfc) are reduced in Fzd4−/− corpora lutea. Ndph-null mice do not phenocopy this, indicating that Norrin is not the Fzd4 ligand responsible for corpus luteum development.","method":"Fzd4-null mouse analysis, timed mating, histology, RT-PCR of luteal markers, Ndph-null mouse comparison","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with specific molecular phenotype readout plus genetic comparison with Ndph-null mice; rigorous loss-of-function with mechanistic negative control","pmids":["16093361"],"is_preprint":false},{"year":2021,"finding":"Wnt2 and Wnt4 activate β-catenin/NF-κB signaling to promote cardiac fibrosis in fibroblasts through cooperation of FZD4 (or FZD2) with LRP6; Wnt2 specifically pairs with FZD4 and LRP6, while Wnt4 pairs with FZD2 and LRP6, establishing FZD4 as part of a pro-fibrotic Wnt receptor complex following myocardial infarction.","method":"siRNA knockdown of Wnt2, Wnt4, Fzd4/Fzd2, LRP6 in neonatal rat cardiac fibroblasts; β-catenin/NF-κB reporter assay; MI mouse model with LAD ligation; ELISA","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with reporter assay plus in vivo MI model; single lab, multiple orthogonal methods","pmids":["34911029"],"is_preprint":false},{"year":2019,"finding":"Secreted Wnt6 binds FZD4 to activate canonical β-catenin signaling, which is upstream of ROCK1 and 14-3-3σ, and this Wnt6-FZD4-β-catenin axis mediates centrosome amplification induced by diabetic factors (high glucose/insulin/palmitate and advanced glycation end-products); blocking Wnt6 or FZD4 with siRNA or antibodies attenuates centrosome amplification.","method":"siRNA knockdown of Wnt6, FZD4, β-catenin; neutralizing antibodies against Wnt6 and FZD4; β-catenin nuclear translocation assay; centrosome counting; in vivo diabetic mouse model","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA plus antibody neutralization plus in vivo mouse model; multiple methods, single lab","pmids":["31618077"],"is_preprint":false},{"year":2010,"finding":"ERG transcription factor upregulates FZD4 expression in prostate cancer cells; FZD4 silencing mimics ERG knockdown by inducing active β1-integrin and E-cadherin expression (mesenchymal-to-epithelial reversion), while FZD4 overexpression reverses the ERG-knockdown phenotype, placing FZD4 downstream of ERG in WNT signaling-driven epithelial-to-mesenchymal transition.","method":"siRNA knockdown of ERG and FZD4, FZD4 overexpression in VCaP prostate cancer cells, RT-PCR, immunostaining, β1-integrin/E-cadherin expression analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal knockdown/overexpression with defined phenotypic readout; single lab, two orthogonal manipulations","pmids":["20713528"],"is_preprint":false},{"year":2020,"finding":"WNT2b induces epithelial-to-mesenchymal transition (EMT) in HT29 intestinal epithelial cells through FZD4 activation; increased WNT2b/FZD4 interaction was detected in intestinal tissue from Crohn's disease patients with penetrating behaviour, placing FZD4 as the receptor mediating WNT2b-driven EMT.","method":"In vitro WNT2b treatment of HT29 cells with FZD4 knockdown/activation, confocal microscopy, co-immunoprecipitation of WNT2b/FZD4, RT-PCR, WB in patient tissues","journal":"Journal of Crohn's & colitis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro functional assay with receptor knockdown plus patient tissue co-IP; single lab, two orthogonal approaches","pmids":["31359032"],"is_preprint":false},{"year":2018,"finding":"Mechanical cyclic stretch upregulates FZD4 and activates JNK signaling in bone mesenchymal stem cells; FZD4 knockdown inhibits stretch-induced osteogenesis and JNK activity; WNT5A acts upstream and FZD4 mediates WNT5A-dependent osteogenic differentiation under mechanical stimulation.","method":"Cyclic mechanical stretch of BMSCs, siRNA knockdown of FZD4, WNT5A treatment, ALP staining, Alizarin Red staining, RT-PCR, WB, hindlimb unloading mouse model","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA KD with specific phenotypic readout (osteogenesis, JNK) plus in vivo mouse model; single lab, multiple methods","pmids":["30007964"],"is_preprint":false},{"year":2024,"finding":"FOXF1 directly transcriptionally activates Fzd4 in lung endothelial cells; endothelial-specific FOXF1 deletion decreases FZD4 and impairs Wnt/β-catenin signaling in tumor-associated endothelial cells, promoting tumor vessel leakiness and lung cancer progression; nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescues Wnt/β-catenin signaling and normalizes tumor vessels.","method":"Endothelial-specific conditional KO and OE of FOXF1 in mice, nanoparticle Fzd4 cDNA delivery, ChIP-seq/CUT&Tag for FOXF1 binding to Fzd4 promoter, Wnt reporter assay, lung tumor growth assay","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — FOXF1 binding to Fzd4 promoter by CUT&Tag, conditional KO/OE mouse models, and in vivo nanoparticle rescue; multiple orthogonal methods in single rigorous study","pmids":["38589650"],"is_preprint":false},{"year":2020,"finding":"GATA6-AS1 lncRNA downregulates FZD4 expression by recruiting EZH2 and promoting H3K27me3 at the FZD4 promoter, thereby inactivating Wnt/β-catenin signaling and inhibiting gastric cancer progression; this was demonstrated by ChIP showing H3K27me3 enrichment at the FZD4 promoter and rescued by a Wnt/β-catenin activator (LiCl).","method":"EZH2 co-immunoprecipitation, ChIP for H3K27me3 at FZD4 promoter, GATA6-AS1 overexpression/ASO knockdown, LiCl rescue, xenograft mouse model","journal":"Molecular therapy. Nucleic acids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP evidence for epigenetic mechanism plus RIP/co-IP and functional rescue; single lab, multiple orthogonal methods","pmids":["31981860"],"is_preprint":false},{"year":2021,"finding":"SIRT6 suppresses FZD4 transcription by deacetylating histone H3K9 at the FZD4 promoter; overexpression of SIRT6 reduces FZD4 protein and H3K9ac levels, inhibiting Wnt/β-catenin signaling and hepatoblastoma cell proliferation/invasion; FZD4 overexpression reverses these effects.","method":"SIRT6 overexpression/knockdown in hepatoblastoma cells, H3K9ac ChIP at FZD4 promoter, FZD4 rescue overexpression, WB, xenograft tumor model","journal":"Human & experimental toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP evidence for H3K9 deacetylation at FZD4 promoter plus functional rescue; single lab, multiple methods","pmids":["34219513"],"is_preprint":false},{"year":2022,"finding":"A Norrin mimetic (SZN-413) targeting FZD4 and LRP5 induces Wnt/β-catenin signaling and upregulates blood-retina barrier gene expression in endothelial cells; in an oxygen-induced retinopathy mouse model, SZN-413 significantly reduces neovascularization and avascular areas; in a VEGF-induced rabbit model, it reduces retinal vascular leakage by ~80%, demonstrating FZD4 agonism can normalize pathological retinal vasculature.","method":"In vitro Wnt/β-catenin reporter assay in endothelial cells, oxygen-induced retinopathy mouse model (avascular/neovascularization area measurement), VEGF-induced rabbit vascular leakage model (fluorescein leakage quantification)","journal":"Translational vision science & technology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological FZD4 agonism with in vitro signaling assay plus two independent in vivo animal models; single lab, multiple orthogonal systems","pmids":["36149648"],"is_preprint":false},{"year":2016,"finding":"Fzd4 heterozygous mice show delayed retinal revascularization after oxygen-induced retinopathy (OIR) but normal vaso-obliteration during hyperoxia, demonstrating that partial reduction of Norrin-Fzd4 signaling specifically impairs revascularization of the avascular retina following ischemic injury.","method":"Fzd4 heterozygous mouse OIR model, retinal vascular area/pattern quantification, vessel number and caliber measurement","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean haploinsufficient mouse model with quantitative retinal vascular phenotyping in OIR paradigm; rigorous loss-of-function with specific readout","pmids":["27489958"],"is_preprint":false},{"year":2020,"finding":"Novel FZD4 mutations identified in FEVR patients were shown by TOPflash luciferase reporter assay to cause at least 50% loss of wild-type Norrin/β-catenin signaling activity, and by co-immunoprecipitation to degrade the Norrin-FZD4 binding interaction, establishing loss of Norrin-receptor binding as a pathogenic mechanism.","method":"TOPflash luciferase reporter assay, co-immunoprecipitation of Norrin-FZD4","journal":"BioMed research international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assay plus co-IP for multiple novel mutations; single lab, two orthogonal methods","pmids":["32420371"],"is_preprint":false},{"year":2018,"finding":"Retinoic acid (RA) signaling directly induces Fzd4 expression during Xenopus pancreas development; loss of Fzd4/Fzd4s function impairs pancreatic progenitor formation and differentiation, establishing FZD4 as a direct RA target gene required for pancreas specification.","method":"RNA sequencing of RA-treated pancreatic explants, morpholino knockdown of Fzd4/Fzd4s in Xenopus embryos, pancreatic progenitor differentiation assay","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq identification plus morpholino loss-of-function with pancreatic progenitor readout in Xenopus; single lab, two orthogonal methods","pmids":["29769220"],"is_preprint":false},{"year":2019,"finding":"Wnt5a/FZD4 axis activates JNK signaling and mediates osteogenic differentiation in human periodontal ligament cells; FZD4 knockdown attenuates both WNT5A-induced and YAP-induced osteogenesis, while recombinant WNT5A rescues YAP inhibitor-suppressed differentiation, placing FZD4 downstream of YAP/WNT5A in mechanically stimulated osteogenesis.","method":"siRNA knockdown of FZD4 and WNT5A, YAP inhibitor (verteporfin) and activator (Lats-IN-1), recombinant WNT5A rescue, ALP activity, Alizarin Red staining, WB, cyclic stretch of hPDLCs","journal":"Journal of periodontal research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via siRNA/inhibitor/rescue experiments with defined osteogenic readout; single lab, multiple orthogonal manipulations","pmids":["37340863"],"is_preprint":false},{"year":2023,"finding":"miR-136-5p targets FZD4 to inhibit Wnt/β-catenin signaling, specifically preventing formation of the β-catenin/LEF/TCF transcriptional complex, thereby promoting myoblast proliferation and differentiation; in vivo, miR-136-5p knockdown accelerates skeletal muscle regeneration after BaCl2-induced injury, and this is suppressed by shFZD4, placing FZD4 as a gating component of Wnt signaling in myogenesis.","method":"miR-136-5p overexpression/knockdown in C2C12 cells, shFZD4 lentiviral infection, β-catenin/LEF/TCF complex formation assay, BaCl2 muscle injury mouse model with histological quantification","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis by dual siRNA/shRNA plus in vivo rescue experiment; single lab, two orthogonal systems","pmids":["37218742"],"is_preprint":false}],"current_model":"FZD4 is a seven-transmembrane Frizzled receptor that binds both Wnt ligands and the structurally unrelated ligand Norrin via its cysteine-rich domain (CRD), recruits LRP5/6 as co-receptor, and activates canonical β-catenin signaling; TSPAN12 selectively amplifies Norrin–FZD4 multimerization to reach physiological signaling thresholds, EMC3 is required for FZD4 protein expression and ER-to-membrane trafficking, N-glycosylation at N59/N144 is essential for FZD4 maturation, stability, and receptor activity, and disease-causing missense mutations impair function through five distinct mechanisms (disrupted signal peptide, loss of disulfide bonds, impaired Norrin binding, defective membrane trafficking, or reduced DVL2 recruitment/intracellular signaling); in retinal endothelial cells FZD4/Norrin/β-catenin signaling is the central driver of developmental and reparative vascularization, and FZD4 additionally mediates Wnt2/4-driven cardiac fibrosis, WNT5A/YAP-dependent osteogenesis, WNT6-driven centrosome amplification in diabetes, and ERG-driven epithelial-to-mesenchymal transition in prostate cancer."},"narrative":{"mechanistic_narrative":"FZD4 is a seven-transmembrane Frizzled receptor that drives canonical Wnt/β-catenin signaling and serves as the central receptor for Norrin in developmental and reparative vascularization, fertility, and tissue morphogenesis [PMID:21177847, PMID:27489958]. Ligand recognition is governed by the extracellular cysteine-rich domain (CRD), which is essential for binding Norrin and for Norrin-dependent β-catenin reporter activation, with CRD missense mutations abolishing both [PMID:21177847]. Receptor competence requires post-translational and trafficking control: N-glycosylation at N59 and N144 is needed for maturation, plasma-membrane trafficking, stability, and ligand/co-receptor interaction [PMID:40230079], and the ER membrane protein complex subunit EMC3 is required upstream for FZD4 protein expression and Norrin/β-catenin signaling in retinal endothelium [PMID:34128175]. Signaling output is selectively amplified by TSPAN12, which physically associates with the Norrin–FZD4 complex and promotes receptor multimerization specifically for Norrin (not Wnt) signaling [PMID:19837033], and is transduced intracellularly through DVL2 recruitment [PMID:38558095]. Disease-causing FEVR mutations impair function through distinct mechanisms spanning disrupted signal peptide, loss of disulfide bonds, defective Norrin binding, impaired ER-to-membrane trafficking, and reduced DVL2 recruitment [PMID:24744206, PMID:38558095, PMID:32420371]. Beyond retinal vasculature, FZD4 acts as the receptor for multiple Wnt ligands in disparate contexts—Wnt2-driven cardiac fibrosis with LRP6 [PMID:34911029], WNT5A/YAP-dependent osteogenesis via JNK [PMID:37340863], WNT6-driven centrosome amplification in diabetes [PMID:31618077], and ERG- and WNT2b-driven epithelial-to-mesenchymal transition [PMID:20713528, PMID:31359032]—and its expression is controlled transcriptionally and epigenetically by factors including FOXF1, ERG, and chromatin-modifying complexes [PMID:20713528, PMID:38589650, PMID:31981860, PMID:34219513].","teleology":[{"year":2005,"claim":"Established that FZD4 has an in vivo developmental role beyond the eye and that not all FZD4 functions depend on Norrin, defining ligand specificity questions.","evidence":"Fzd4-null mouse analysis with luteal/angiogenic marker readout and Ndph-null comparison","pmids":["16093361"],"confidence":"High","gaps":["Wnt ligand responsible for corpus luteum development not identified","downstream effectors in luteal angiogenesis undefined"]},{"year":2009,"claim":"Resolved how Norrin signaling reaches physiological thresholds by showing TSPAN12 selectively amplifies Norrin–FZD4 signaling through receptor multimerization.","evidence":"Co-IP, siRNA, luciferase reporter, and Tspan12/Norrin/Lrp5 mouse genetics","pmids":["19837033"],"confidence":"High","gaps":["structural basis of multimerization not resolved","stoichiometry of TSPAN12 in the complex unknown"]},{"year":2010,"claim":"Defined the FZD4 CRD as the essential Norrin-binding module and linked CRD mutations to loss of β-catenin activation.","evidence":"Cell-surface/overlay binding assays, luciferase reporter, Xenopus embryo marker expression","pmids":["21177847"],"confidence":"High","gaps":["atomic-resolution Norrin–CRD interface not determined here","Wnt versus Norrin binding determinants not distinguished"]},{"year":2010,"claim":"Placed FZD4 downstream of ERG in driving epithelial-to-mesenchymal transition, extending FZD4 function into cancer.","evidence":"Reciprocal siRNA knockdown and overexpression in VCaP prostate cancer cells","pmids":["20713528"],"confidence":"Medium","gaps":["Wnt ligand engaging FZD4 in this context not identified","direct ERG binding to FZD4 promoter not shown here"]},{"year":2014,"claim":"Identified defective ER-to-plasma-membrane trafficking as a major FEVR pathological mechanism and showed it is rescuable by chaperones/temperature.","evidence":"Confocal microscopy, glycosylation/ubiquitination profiling, chemical chaperone rescue in HeLa/COS-7","pmids":["24744206"],"confidence":"High","gaps":["ER quality-control machinery recognizing mutants not defined","trafficking route to plasma membrane not mapped"]},{"year":2016,"claim":"Demonstrated dosage sensitivity of Norrin-FZD4 signaling specifically for revascularization of ischemic retina rather than vaso-obliteration.","evidence":"Fzd4 heterozygous mouse oxygen-induced retinopathy model with vascular phenotyping","pmids":["27489958"],"confidence":"High","gaps":["molecular threshold underlying haploinsufficiency not quantified","endothelial-intrinsic versus systemic contribution not separated"]},{"year":2017,"claim":"Showed Norrin–FZD4 signaling expands cardiomyocyte output, identifying FZD4 as a cardiac progenitor surface marker and signaling node.","evidence":"Surface proteomics, FACS sorting, NORRIN/FZD4 signaling assay, cardiomyocyte differentiation","pmids":["29249665"],"confidence":"Medium","gaps":["co-receptor requirement in CPCs not defined","in vivo necessity not established"]},{"year":2018,"claim":"Connected mechanical stimulation to FZD4-dependent osteogenesis through JNK and a WNT5A upstream input.","evidence":"Cyclic stretch of BMSCs, FZD4 siRNA, WNT5A treatment, osteogenic assays, hindlimb unloading mouse model","pmids":["30007964"],"confidence":"Medium","gaps":["co-receptor and direct WNT5A–FZD4 binding not shown","branch from canonical β-catenin not delineated"]},{"year":2018,"claim":"Identified FZD4 as a direct retinoic-acid target gene required for pancreas specification, extending its developmental roles.","evidence":"RNA-seq of RA-treated explants and morpholino knockdown in Xenopus","pmids":["29769220"],"confidence":"Medium","gaps":["ligand driving FZD4 signaling in pancreas not identified","downstream targets in progenitors undefined"]},{"year":2019,"claim":"Defined a Wnt6–FZD4–β-catenin axis upstream of ROCK1/14-3-3σ driving diabetes-associated centrosome amplification.","evidence":"siRNA, neutralizing antibodies, β-catenin translocation, centrosome counting, diabetic mouse model","pmids":["31618077"],"confidence":"Medium","gaps":["co-receptor in this axis not defined","direct Wnt6–FZD4 binding not biochemically resolved"]},{"year":2019,"claim":"Positioned FZD4 downstream of YAP/WNT5A in mechanically induced osteogenesis via JNK signaling.","evidence":"siRNA, YAP inhibitor/activator, recombinant WNT5A rescue, osteogenic assays in hPDLCs","pmids":["37340863"],"confidence":"Medium","gaps":["mechanism linking YAP to FZD4 expression not resolved","direct receptor–ligand binding not shown"]},{"year":2020,"claim":"Established loss of Norrin–receptor binding as a pathogenic FEVR mechanism for novel FZD4 mutations.","evidence":"TOPflash reporter assay and Norrin–FZD4 co-IP","pmids":["32420371"],"confidence":"Medium","gaps":["structural consequences of mutations not modeled","trafficking status of these mutants not assessed"]},{"year":2020,"claim":"Identified FZD4 as the receptor mediating WNT2b-driven EMT relevant to Crohn's disease penetrating behaviour.","evidence":"WNT2b treatment of HT29 cells with FZD4 knockdown, WNT2b/FZD4 co-IP, patient tissue analysis","pmids":["31359032"],"confidence":"Medium","gaps":["co-receptor requirement not defined","causality in patient phenotype not established"]},{"year":2020,"claim":"Showed FZD4 is epigenetically silenced by GATA6-AS1/EZH2-mediated H3K27me3, linking chromatin control to Wnt pathway output.","evidence":"EZH2 co-IP, H3K27me3 ChIP at FZD4 promoter, GATA6-AS1 manipulation, LiCl rescue, xenograft","pmids":["31981860"],"confidence":"Medium","gaps":["direct GATA6-AS1 binding to FZD4 locus not mapped","generality across tumor types untested"]},{"year":2021,"claim":"Placed EMC3 upstream of FZD4 as a requirement for receptor expression and retinal vascular Norrin/β-catenin signaling.","evidence":"Endothelial Emc3 conditional KO, RNA-seq, reporter assay, LiCl rescue, tube formation","pmids":["34128175"],"confidence":"High","gaps":["mechanism of EMC3-assisted FZD4 biogenesis not resolved","selectivity of EMC3 for FZD4 versus other clients not addressed"]},{"year":2021,"claim":"Defined FZD4 as part of a Wnt2/LRP6 pro-fibrotic receptor complex driving cardiac fibrosis through β-catenin/NF-κB.","evidence":"siRNA in cardiac fibroblasts, β-catenin/NF-κB reporter, MI mouse model","pmids":["34911029"],"confidence":"Medium","gaps":["direct Wnt2–FZD4–LRP6 ternary complex not biochemically reconstituted","ligand pairing specificity basis unknown"]},{"year":2021,"claim":"Showed SIRT6-mediated H3K9 deacetylation suppresses FZD4 transcription, adding an additional epigenetic control layer on Wnt output.","evidence":"SIRT6 manipulation, H3K9ac ChIP at FZD4 promoter, FZD4 rescue, xenograft in hepatoblastoma","pmids":["34219513"],"confidence":"Medium","gaps":["direct SIRT6 recruitment mechanism to FZD4 promoter not defined","context specificity untested"]},{"year":2022,"claim":"Demonstrated that pharmacological FZD4/LRP5 agonism can therapeutically normalize pathological retinal vasculature.","evidence":"Norrin mimetic SZN-413 in endothelial reporter assay, OIR mouse model, VEGF-induced rabbit leakage model","pmids":["36149648"],"confidence":"Medium","gaps":["binding mode of mimetic on FZD4 not structurally defined","long-term efficacy/safety not assessed"]},{"year":2023,"claim":"Identified FZD4 as a miR-136-5p-gated component of Wnt signaling controlling myoblast proliferation and muscle regeneration.","evidence":"miR-136-5p manipulation, shFZD4, β-catenin/LEF/TCF complex assay, BaCl2 muscle injury model","pmids":["37218742"],"confidence":"Medium","gaps":["direct miR-136-5p–FZD4 3'UTR interaction extent not detailed","ligand engaging FZD4 in myogenesis not identified"]},{"year":2024,"claim":"Provided a comprehensive mutational map classifying FZD4 pathogenicity into five mechanistic classes, including intracellular DVL2-recruitment defects.","evidence":"Site-directed mutagenesis of 34 mutations, reporter, membrane localization, Norrin binding, DVL2 co-IP","pmids":["38558095"],"confidence":"High","gaps":["genotype–phenotype severity correlation not established","structural basis of DVL2 recruitment not resolved"]},{"year":2024,"claim":"Established FOXF1 as a direct transcriptional activator of Fzd4 in lung endothelium and showed Fzd4 restoration normalizes tumor vasculature.","evidence":"FOXF1 conditional KO/OE mice, CUT&Tag at Fzd4 promoter, Wnt reporter, nanoparticle Fzd4 rescue, lung tumor model","pmids":["38589650"],"confidence":"High","gaps":["regulatory interplay with other FZD4 transcription factors not integrated","endothelial subtype specificity not fully mapped"]},{"year":2025,"claim":"Defined N59/N144 N-glycosylation as a requirement for FZD4 maturation, trafficking, stability, and ligand/co-receptor binding.","evidence":"Glycosylation-site mutagenesis, surface localization, co-IP with Wnt/Norrin, TOPflash, xenograft in A549 cells","pmids":["40230079"],"confidence":"High","gaps":["glycan structures and biosynthetic enzymes not identified","differential glycan effects on Wnt versus Norrin binding not separated"]},{"year":null,"claim":"How distinct Wnt ligand–FZD4 pairings, co-receptor choices, and canonical versus JNK/NF-κB branch selection are encoded structurally and used to specify the diverse tissue outcomes remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["no atomic structure of FZD4 with different ligands/co-receptors in the corpus","rules governing ligand-co-receptor specificity not defined","switch between β-catenin and non-canonical outputs not mechanistically explained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,6,8,9,11,16]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[1,18]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,5,8,9]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[6,7,17,19]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,3,18]}],"complexes":["Norrin-FZD4-LRP5 receptor complex","Norrin-FZD4-TSPAN12 complex"],"partners":["NDP","LRP5","LRP6","TSPAN12","DVL2","EMC3","WNT2","WNT6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9ULV1","full_name":"Frizzled-4","aliases":["FzE4"],"length_aa":537,"mass_kda":59.9,"function":"Receptor for Wnt proteins (PubMed:30135577). 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Vitreoretinopathy.","date":"2021","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/34199009","citation_count":8,"is_preprint":false},{"pmid":"22574936","id":"PMC_22574936","title":"Familial retinal detachment associated with COL2A1 exon 2 and FZD4 mutations.","date":"2012","source":"Clinical & experimental ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/22574936","citation_count":8,"is_preprint":false},{"pmid":"30537745","id":"PMC_30537745","title":"A Novel Variant of the FZD4 Gene in a Chinese Family Causes Autosomal Dominant Familial Exudative Vitreoretinopathy.","date":"2018","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30537745","citation_count":8,"is_preprint":false},{"pmid":"38558095","id":"PMC_38558095","title":"Identification of Novel FZD4 Mutations in Familial Exudative Vitreoretinopathy and Investigating the Pathogenic Mechanisms of FZD4 Mutations.","date":"2024","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/38558095","citation_count":7,"is_preprint":false},{"pmid":"33302760","id":"PMC_33302760","title":"Novel FZD4 and LRP5 mutations in a small cohort of patients with familial exudative vitreoretinopathy (FEVR).","date":"2020","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33302760","citation_count":7,"is_preprint":false},{"pmid":"25390515","id":"PMC_25390515","title":"Simultaneous fzd4 and lrp5 mutation in autosomal dominant familial exudative vitreoretinopathy.","date":"2013","source":"Retinal cases & brief reports","url":"https://pubmed.ncbi.nlm.nih.gov/25390515","citation_count":6,"is_preprint":false},{"pmid":"35277167","id":"PMC_35277167","title":"Whole exome sequencing revealed 14 variants in NDP, FZD4, LRP5, and TSPAN12 genes for 20 families with familial exudative vitreoretinopathy.","date":"2022","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/35277167","citation_count":6,"is_preprint":false},{"pmid":"31114654","id":"PMC_31114654","title":"Detection of FZD4, LRP5 and TSPAN12 Genes Variants in Malay Premature Babies with Retinopathy of Prematurity.","date":"2019","source":"Journal of ophthalmic & vision research","url":"https://pubmed.ncbi.nlm.nih.gov/31114654","citation_count":6,"is_preprint":false},{"pmid":"10890980","id":"PMC_10890980","title":"Mouse fzd4 maps within a region of chromosome 7 important for thymus and cardiac development.","date":"2000","source":"Genesis (New York, N.Y. : 2000)","url":"https://pubmed.ncbi.nlm.nih.gov/10890980","citation_count":6,"is_preprint":false},{"pmid":"35413536","id":"PMC_35413536","title":"The mechanism of the WNT5A and FZD4 receptor mediated WNT/β-catenin pathway in the degeneration of ALS spinal cord motor neurons.","date":"2022","source":"Biochemical and biophysical research 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vision","url":"https://pubmed.ncbi.nlm.nih.gov/30820142","citation_count":5,"is_preprint":false},{"pmid":"37926400","id":"PMC_37926400","title":"Folate deficiency promotes cervical squamous carcinoma SiHa cells progression by targeting miR-375/FZD4/β-catenin signaling.","date":"2023","source":"The Journal of nutritional biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37926400","citation_count":4,"is_preprint":false},{"pmid":"36353221","id":"PMC_36353221","title":"Decrease of FZD4 exon 1 methylation in probands from FZD4-associated FEVR family of phenotypic heterogeneity.","date":"2022","source":"Frontiers in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36353221","citation_count":4,"is_preprint":false},{"pmid":"34688334","id":"PMC_34688334","title":"Overexpressed miR-375-Loaded Restrains Development of Cervical Cancer Through Down-Regulation of Frizzled Class Receptor 4 (FZD4) with Liposome Nanoparticle as a Carrier.","date":"2021","source":"Journal of biomedical nanotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/34688334","citation_count":4,"is_preprint":false},{"pmid":"35068502","id":"PMC_35068502","title":"Discovering the Role of FZD4 Gene in Human Cutaneous Squamous Cell Carcinoma.","date":"2021","source":"Indian journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35068502","citation_count":3,"is_preprint":false},{"pmid":"35403775","id":"PMC_35403775","title":"Circ_0001971 makes progress of oral squamous cell carcinoma by targeting miR-107/FZD4 axis.","date":"2022","source":"Oral diseases","url":"https://pubmed.ncbi.nlm.nih.gov/35403775","citation_count":3,"is_preprint":false},{"pmid":"40230079","id":"PMC_40230079","title":"N-Glycosylation Modification of Fzd4 Is Essential for the Fzd4-Wnt-β-Catenin Signalling Axis.","date":"2025","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40230079","citation_count":3,"is_preprint":false},{"pmid":"36170021","id":"PMC_36170021","title":"A regulatory circuit of lncRNA NLGN1-AS1 and Wnt signalling controls clear cell renal cell carcinoma phenotypes through FZD4-modulated pathways.","date":"2022","source":"Aging","url":"https://pubmed.ncbi.nlm.nih.gov/36170021","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54530,"output_tokens":6679,"usd":0.131887,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":15522,"output_tokens":6007,"usd":0.113892,"stage2_stop_reason":"end_turn"},"total_usd":0.245779,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"TSPAN12 physically associates with the Norrin-FZD4 receptor complex (shown by co-expression/co-immunoprecipitation) and selectively amplifies Norrin/β-catenin but not Wnt/β-catenin signaling; overexpressed TSPAN12 rescues signaling defects caused by FZD4 mutations predicted to impair receptor multimerization, indicating TSPAN12 promotes FZD4 multimerization specifically in the context of Norrin signaling.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, luciferase reporter assay, genetic epistasis in Tspan12/Norrin/Lrp5 mutant mice\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, multiple orthogonal methods (siRNA, reporter assay, in vivo mouse genetics), replicated across cell and animal systems in a single rigorous study\",\n      \"pmids\": [\"19837033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The cysteine-rich domain (CRD) of FZD4 is essential for Norrin binding and Norrin-dependent activation of canonical Wnt/β-catenin signaling; CRD missense mutations C45Y, Y58C, and C204R abolish Norrin binding as measured by cell-surface and overlay binding assays and eliminate Norrin-induced Wnt/β-catenin reporter activity in HEK293 cells and in Xenopus embryos (decreased Siamois and Xnr3 expression).\",\n      \"method\": \"Cell-surface binding assay, overlay binding assay, luciferase reporter assay (HEK293), Xenopus embryo injection with marker gene expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro binding reconstitution plus mutagenesis plus in vivo Xenopus functional validation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"21177847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Multiple FEVR-associated missense mutations in FZD4 (P33S, G36N, H69Y, M105T, M105V, C181R, C204R, C204Y, G488D) cause predominant ER retention rather than plasma membrane localization, establishing defective ER-to-plasma-membrane trafficking as a major pathological mechanism; this trafficking defect could be partially rescued for M105T and C204Y mutants by reduced temperature or chemical chaperones. Mutant FZD4 does not trap co-expressed wild-type FZD4.\",\n      \"method\": \"Confocal fluorescence microscopy, N-glycosylation profiling, polyubiquitination assays, chemical chaperone rescue experiments in HeLa and COS-7 cells\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods (glycosylation, ubiquitination, imaging) applied to 15 mutants with functional rescue; comprehensive mechanistic characterization in single study\",\n      \"pmids\": [\"24744206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Systematic functional analysis of 34 FZD4 missense mutations categorized pathogenic mechanisms into five classes: (1) signal peptide mutations, (2) cysteine mutations disrupting disulfide bonds, (3) extracellular domain mutations impairing Norrin binding, (4) transmembrane domain 1 and TM7 mutations impairing membrane localization, and (5) intracellular domain mutations reducing DVL2 recruitment, as assessed by protein expression, Norrin/β-catenin luciferase reporter, membrane localization, Norrin binding, and DVL2 co-immunoprecipitation assays in HEK293T, HEK293STF, and HeLa cells.\",\n      \"method\": \"Site-directed mutagenesis, luciferase reporter assay (Norrin/β-catenin TOPflash), confocal microscopy for membrane localization, Norrin binding assay, DVL2 co-immunoprecipitation\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal functional assays applied to 34 mutations across all FZD4 domains; comprehensive mechanistic classification in a single rigorous study\",\n      \"pmids\": [\"38558095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FZD4 is N-glycosylated at asparagine residues N59 and N144 (both highly conserved); N-glycosylation is required for FZD4 maturation, plasma membrane trafficking, protein stability, and interaction with Wnt ligands and co-receptor Norrin. Glycosylation-deficient FZD4 mutants fail to activate Wnt/β-catenin signaling and cannot rescue proliferation/migration in FZD4-knockout A549 cells in vitro or in vivo.\",\n      \"method\": \"Site-directed mutagenesis at N-glycosylation sites, cell surface localization assay, co-immunoprecipitation with Wnt ligands/Norrin, TOPflash luciferase reporter, xenograft tumor model\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of specific glycosylation sites combined with binding assays, reporter assay, and in vivo xenograft validation; multiple orthogonal methods in single study\",\n      \"pmids\": [\"40230079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The ER membrane protein complex subunit EMC3 is required for FZD4 expression; endothelial-specific deletion of Emc3 in mice reduces FZD4 levels and impairs Norrin/β-catenin signaling, causing defective retinal vascularization that is partially rescued by lithium chloride (Wnt activator), placing EMC3 upstream of FZD4 in the Norrin/β-catenin pathway in retinal endothelial cells.\",\n      \"method\": \"Conditional knockout mice (endothelial Emc3 deletion), RNA-seq, RT-qPCR, luciferase reporter assay, LiCl rescue experiment, tube formation assay\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with retinal vascular phenotype, reporter assay, and pharmacological rescue; multiple methods in single study\",\n      \"pmids\": [\"34128175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FZD4 marks lateral plate mesoderm in cardiac progenitor cells (CPCs); NORRIN presented to FZD4 increases cardiomyocyte output from CPCs via canonical WNT/β-catenin signaling-driven proliferation; FZD4 was used together with FLK1 and PDGFRA to purify CPCs and enhance cardiomyocyte enrichment from mouse and human pluripotent stem cells.\",\n      \"method\": \"Surface proteomics (mass spectrometry), microarray transcriptomics, FACS sorting with FZD4 antibody, NORRIN/FZD4 signaling assay, cardiomyocyte differentiation assay\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — surface proteomics plus functional NORRIN/FZD4 signaling assay with cardiomyocyte output quantification; single lab, two orthogonal approaches\",\n      \"pmids\": [\"29249665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Fzd4-null (Fzd4−/−) mice are infertile due to failure of corpus luteum formation and function; markers of luteal cell identity (Lhcgr, Prlr, Cyp11a1, Sfrp4) and angiogenesis (Efnb1, Efnb2, Ephb4, Vegfa, Vegfc) are reduced in Fzd4−/− corpora lutea. Ndph-null mice do not phenocopy this, indicating that Norrin is not the Fzd4 ligand responsible for corpus luteum development.\",\n      \"method\": \"Fzd4-null mouse analysis, timed mating, histology, RT-PCR of luteal markers, Ndph-null mouse comparison\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with specific molecular phenotype readout plus genetic comparison with Ndph-null mice; rigorous loss-of-function with mechanistic negative control\",\n      \"pmids\": [\"16093361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Wnt2 and Wnt4 activate β-catenin/NF-κB signaling to promote cardiac fibrosis in fibroblasts through cooperation of FZD4 (or FZD2) with LRP6; Wnt2 specifically pairs with FZD4 and LRP6, while Wnt4 pairs with FZD2 and LRP6, establishing FZD4 as part of a pro-fibrotic Wnt receptor complex following myocardial infarction.\",\n      \"method\": \"siRNA knockdown of Wnt2, Wnt4, Fzd4/Fzd2, LRP6 in neonatal rat cardiac fibroblasts; β-catenin/NF-κB reporter assay; MI mouse model with LAD ligation; ELISA\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with reporter assay plus in vivo MI model; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"34911029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Secreted Wnt6 binds FZD4 to activate canonical β-catenin signaling, which is upstream of ROCK1 and 14-3-3σ, and this Wnt6-FZD4-β-catenin axis mediates centrosome amplification induced by diabetic factors (high glucose/insulin/palmitate and advanced glycation end-products); blocking Wnt6 or FZD4 with siRNA or antibodies attenuates centrosome amplification.\",\n      \"method\": \"siRNA knockdown of Wnt6, FZD4, β-catenin; neutralizing antibodies against Wnt6 and FZD4; β-catenin nuclear translocation assay; centrosome counting; in vivo diabetic mouse model\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA plus antibody neutralization plus in vivo mouse model; multiple methods, single lab\",\n      \"pmids\": [\"31618077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ERG transcription factor upregulates FZD4 expression in prostate cancer cells; FZD4 silencing mimics ERG knockdown by inducing active β1-integrin and E-cadherin expression (mesenchymal-to-epithelial reversion), while FZD4 overexpression reverses the ERG-knockdown phenotype, placing FZD4 downstream of ERG in WNT signaling-driven epithelial-to-mesenchymal transition.\",\n      \"method\": \"siRNA knockdown of ERG and FZD4, FZD4 overexpression in VCaP prostate cancer cells, RT-PCR, immunostaining, β1-integrin/E-cadherin expression analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal knockdown/overexpression with defined phenotypic readout; single lab, two orthogonal manipulations\",\n      \"pmids\": [\"20713528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"WNT2b induces epithelial-to-mesenchymal transition (EMT) in HT29 intestinal epithelial cells through FZD4 activation; increased WNT2b/FZD4 interaction was detected in intestinal tissue from Crohn's disease patients with penetrating behaviour, placing FZD4 as the receptor mediating WNT2b-driven EMT.\",\n      \"method\": \"In vitro WNT2b treatment of HT29 cells with FZD4 knockdown/activation, confocal microscopy, co-immunoprecipitation of WNT2b/FZD4, RT-PCR, WB in patient tissues\",\n      \"journal\": \"Journal of Crohn's & colitis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro functional assay with receptor knockdown plus patient tissue co-IP; single lab, two orthogonal approaches\",\n      \"pmids\": [\"31359032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mechanical cyclic stretch upregulates FZD4 and activates JNK signaling in bone mesenchymal stem cells; FZD4 knockdown inhibits stretch-induced osteogenesis and JNK activity; WNT5A acts upstream and FZD4 mediates WNT5A-dependent osteogenic differentiation under mechanical stimulation.\",\n      \"method\": \"Cyclic mechanical stretch of BMSCs, siRNA knockdown of FZD4, WNT5A treatment, ALP staining, Alizarin Red staining, RT-PCR, WB, hindlimb unloading mouse model\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA KD with specific phenotypic readout (osteogenesis, JNK) plus in vivo mouse model; single lab, multiple methods\",\n      \"pmids\": [\"30007964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FOXF1 directly transcriptionally activates Fzd4 in lung endothelial cells; endothelial-specific FOXF1 deletion decreases FZD4 and impairs Wnt/β-catenin signaling in tumor-associated endothelial cells, promoting tumor vessel leakiness and lung cancer progression; nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescues Wnt/β-catenin signaling and normalizes tumor vessels.\",\n      \"method\": \"Endothelial-specific conditional KO and OE of FOXF1 in mice, nanoparticle Fzd4 cDNA delivery, ChIP-seq/CUT&Tag for FOXF1 binding to Fzd4 promoter, Wnt reporter assay, lung tumor growth assay\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — FOXF1 binding to Fzd4 promoter by CUT&Tag, conditional KO/OE mouse models, and in vivo nanoparticle rescue; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"38589650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GATA6-AS1 lncRNA downregulates FZD4 expression by recruiting EZH2 and promoting H3K27me3 at the FZD4 promoter, thereby inactivating Wnt/β-catenin signaling and inhibiting gastric cancer progression; this was demonstrated by ChIP showing H3K27me3 enrichment at the FZD4 promoter and rescued by a Wnt/β-catenin activator (LiCl).\",\n      \"method\": \"EZH2 co-immunoprecipitation, ChIP for H3K27me3 at FZD4 promoter, GATA6-AS1 overexpression/ASO knockdown, LiCl rescue, xenograft mouse model\",\n      \"journal\": \"Molecular therapy. Nucleic acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP evidence for epigenetic mechanism plus RIP/co-IP and functional rescue; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31981860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIRT6 suppresses FZD4 transcription by deacetylating histone H3K9 at the FZD4 promoter; overexpression of SIRT6 reduces FZD4 protein and H3K9ac levels, inhibiting Wnt/β-catenin signaling and hepatoblastoma cell proliferation/invasion; FZD4 overexpression reverses these effects.\",\n      \"method\": \"SIRT6 overexpression/knockdown in hepatoblastoma cells, H3K9ac ChIP at FZD4 promoter, FZD4 rescue overexpression, WB, xenograft tumor model\",\n      \"journal\": \"Human & experimental toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP evidence for H3K9 deacetylation at FZD4 promoter plus functional rescue; single lab, multiple methods\",\n      \"pmids\": [\"34219513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A Norrin mimetic (SZN-413) targeting FZD4 and LRP5 induces Wnt/β-catenin signaling and upregulates blood-retina barrier gene expression in endothelial cells; in an oxygen-induced retinopathy mouse model, SZN-413 significantly reduces neovascularization and avascular areas; in a VEGF-induced rabbit model, it reduces retinal vascular leakage by ~80%, demonstrating FZD4 agonism can normalize pathological retinal vasculature.\",\n      \"method\": \"In vitro Wnt/β-catenin reporter assay in endothelial cells, oxygen-induced retinopathy mouse model (avascular/neovascularization area measurement), VEGF-induced rabbit vascular leakage model (fluorescein leakage quantification)\",\n      \"journal\": \"Translational vision science & technology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological FZD4 agonism with in vitro signaling assay plus two independent in vivo animal models; single lab, multiple orthogonal systems\",\n      \"pmids\": [\"36149648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fzd4 heterozygous mice show delayed retinal revascularization after oxygen-induced retinopathy (OIR) but normal vaso-obliteration during hyperoxia, demonstrating that partial reduction of Norrin-Fzd4 signaling specifically impairs revascularization of the avascular retina following ischemic injury.\",\n      \"method\": \"Fzd4 heterozygous mouse OIR model, retinal vascular area/pattern quantification, vessel number and caliber measurement\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean haploinsufficient mouse model with quantitative retinal vascular phenotyping in OIR paradigm; rigorous loss-of-function with specific readout\",\n      \"pmids\": [\"27489958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Novel FZD4 mutations identified in FEVR patients were shown by TOPflash luciferase reporter assay to cause at least 50% loss of wild-type Norrin/β-catenin signaling activity, and by co-immunoprecipitation to degrade the Norrin-FZD4 binding interaction, establishing loss of Norrin-receptor binding as a pathogenic mechanism.\",\n      \"method\": \"TOPflash luciferase reporter assay, co-immunoprecipitation of Norrin-FZD4\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assay plus co-IP for multiple novel mutations; single lab, two orthogonal methods\",\n      \"pmids\": [\"32420371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Retinoic acid (RA) signaling directly induces Fzd4 expression during Xenopus pancreas development; loss of Fzd4/Fzd4s function impairs pancreatic progenitor formation and differentiation, establishing FZD4 as a direct RA target gene required for pancreas specification.\",\n      \"method\": \"RNA sequencing of RA-treated pancreatic explants, morpholino knockdown of Fzd4/Fzd4s in Xenopus embryos, pancreatic progenitor differentiation assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq identification plus morpholino loss-of-function with pancreatic progenitor readout in Xenopus; single lab, two orthogonal methods\",\n      \"pmids\": [\"29769220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Wnt5a/FZD4 axis activates JNK signaling and mediates osteogenic differentiation in human periodontal ligament cells; FZD4 knockdown attenuates both WNT5A-induced and YAP-induced osteogenesis, while recombinant WNT5A rescues YAP inhibitor-suppressed differentiation, placing FZD4 downstream of YAP/WNT5A in mechanically stimulated osteogenesis.\",\n      \"method\": \"siRNA knockdown of FZD4 and WNT5A, YAP inhibitor (verteporfin) and activator (Lats-IN-1), recombinant WNT5A rescue, ALP activity, Alizarin Red staining, WB, cyclic stretch of hPDLCs\",\n      \"journal\": \"Journal of periodontal research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via siRNA/inhibitor/rescue experiments with defined osteogenic readout; single lab, multiple orthogonal manipulations\",\n      \"pmids\": [\"37340863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"miR-136-5p targets FZD4 to inhibit Wnt/β-catenin signaling, specifically preventing formation of the β-catenin/LEF/TCF transcriptional complex, thereby promoting myoblast proliferation and differentiation; in vivo, miR-136-5p knockdown accelerates skeletal muscle regeneration after BaCl2-induced injury, and this is suppressed by shFZD4, placing FZD4 as a gating component of Wnt signaling in myogenesis.\",\n      \"method\": \"miR-136-5p overexpression/knockdown in C2C12 cells, shFZD4 lentiviral infection, β-catenin/LEF/TCF complex formation assay, BaCl2 muscle injury mouse model with histological quantification\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis by dual siRNA/shRNA plus in vivo rescue experiment; single lab, two orthogonal systems\",\n      \"pmids\": [\"37218742\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FZD4 is a seven-transmembrane Frizzled receptor that binds both Wnt ligands and the structurally unrelated ligand Norrin via its cysteine-rich domain (CRD), recruits LRP5/6 as co-receptor, and activates canonical β-catenin signaling; TSPAN12 selectively amplifies Norrin–FZD4 multimerization to reach physiological signaling thresholds, EMC3 is required for FZD4 protein expression and ER-to-membrane trafficking, N-glycosylation at N59/N144 is essential for FZD4 maturation, stability, and receptor activity, and disease-causing missense mutations impair function through five distinct mechanisms (disrupted signal peptide, loss of disulfide bonds, impaired Norrin binding, defective membrane trafficking, or reduced DVL2 recruitment/intracellular signaling); in retinal endothelial cells FZD4/Norrin/β-catenin signaling is the central driver of developmental and reparative vascularization, and FZD4 additionally mediates Wnt2/4-driven cardiac fibrosis, WNT5A/YAP-dependent osteogenesis, WNT6-driven centrosome amplification in diabetes, and ERG-driven epithelial-to-mesenchymal transition in prostate cancer.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FZD4 is a seven-transmembrane Frizzled receptor that drives canonical Wnt/\\u03b2-catenin signaling and serves as the central receptor for Norrin in developmental and reparative vascularization, fertility, and tissue morphogenesis [#1, #17]. Ligand recognition is governed by the extracellular cysteine-rich domain (CRD), which is essential for binding Norrin and for Norrin-dependent \\u03b2-catenin reporter activation, with CRD missense mutations abolishing both [#1]. Receptor competence requires post-translational and trafficking control: N-glycosylation at N59 and N144 is needed for maturation, plasma-membrane trafficking, stability, and ligand/co-receptor interaction [#4], and the ER membrane protein complex subunit EMC3 is required upstream for FZD4 protein expression and Norrin/\\u03b2-catenin signaling in retinal endothelium [#5]. Signaling output is selectively amplified by TSPAN12, which physically associates with the Norrin\\u2013FZD4 complex and promotes receptor multimerization specifically for Norrin (not Wnt) signaling [#0], and is transduced intracellularly through DVL2 recruitment [#3]. Disease-causing FEVR mutations impair function through distinct mechanisms spanning disrupted signal peptide, loss of disulfide bonds, defective Norrin binding, impaired ER-to-membrane trafficking, and reduced DVL2 recruitment [#2, #3, #18]. Beyond retinal vasculature, FZD4 acts as the receptor for multiple Wnt ligands in disparate contexts\\u2014Wnt2-driven cardiac fibrosis with LRP6 [#8], WNT5A/YAP-dependent osteogenesis via JNK [#20], WNT6-driven centrosome amplification in diabetes [#9], and ERG- and WNT2b-driven epithelial-to-mesenchymal transition [#10, #11]\\u2014and its expression is controlled transcriptionally and epigenetically by factors including FOXF1, ERG, and chromatin-modifying complexes [#10, #13, #14, #15].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that FZD4 has an in vivo developmental role beyond the eye and that not all FZD4 functions depend on Norrin, defining ligand specificity questions.\",\n      \"evidence\": \"Fzd4-null mouse analysis with luteal/angiogenic marker readout and Ndph-null comparison\",\n      \"pmids\": [\"16093361\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Wnt ligand responsible for corpus luteum development not identified\", \"downstream effectors in luteal angiogenesis undefined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved how Norrin signaling reaches physiological thresholds by showing TSPAN12 selectively amplifies Norrin\\u2013FZD4 signaling through receptor multimerization.\",\n      \"evidence\": \"Co-IP, siRNA, luciferase reporter, and Tspan12/Norrin/Lrp5 mouse genetics\",\n      \"pmids\": [\"19837033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"structural basis of multimerization not resolved\", \"stoichiometry of TSPAN12 in the complex unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the FZD4 CRD as the essential Norrin-binding module and linked CRD mutations to loss of \\u03b2-catenin activation.\",\n      \"evidence\": \"Cell-surface/overlay binding assays, luciferase reporter, Xenopus embryo marker expression\",\n      \"pmids\": [\"21177847\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"atomic-resolution Norrin\\u2013CRD interface not determined here\", \"Wnt versus Norrin binding determinants not distinguished\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placed FZD4 downstream of ERG in driving epithelial-to-mesenchymal transition, extending FZD4 function into cancer.\",\n      \"evidence\": \"Reciprocal siRNA knockdown and overexpression in VCaP prostate cancer cells\",\n      \"pmids\": [\"20713528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Wnt ligand engaging FZD4 in this context not identified\", \"direct ERG binding to FZD4 promoter not shown here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified defective ER-to-plasma-membrane trafficking as a major FEVR pathological mechanism and showed it is rescuable by chaperones/temperature.\",\n      \"evidence\": \"Confocal microscopy, glycosylation/ubiquitination profiling, chemical chaperone rescue in HeLa/COS-7\",\n      \"pmids\": [\"24744206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ER quality-control machinery recognizing mutants not defined\", \"trafficking route to plasma membrane not mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated dosage sensitivity of Norrin-FZD4 signaling specifically for revascularization of ischemic retina rather than vaso-obliteration.\",\n      \"evidence\": \"Fzd4 heterozygous mouse oxygen-induced retinopathy model with vascular phenotyping\",\n      \"pmids\": [\"27489958\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"molecular threshold underlying haploinsufficiency not quantified\", \"endothelial-intrinsic versus systemic contribution not separated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed Norrin\\u2013FZD4 signaling expands cardiomyocyte output, identifying FZD4 as a cardiac progenitor surface marker and signaling node.\",\n      \"evidence\": \"Surface proteomics, FACS sorting, NORRIN/FZD4 signaling assay, cardiomyocyte differentiation\",\n      \"pmids\": [\"29249665\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"co-receptor requirement in CPCs not defined\", \"in vivo necessity not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected mechanical stimulation to FZD4-dependent osteogenesis through JNK and a WNT5A upstream input.\",\n      \"evidence\": \"Cyclic stretch of BMSCs, FZD4 siRNA, WNT5A treatment, osteogenic assays, hindlimb unloading mouse model\",\n      \"pmids\": [\"30007964\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"co-receptor and direct WNT5A\\u2013FZD4 binding not shown\", \"branch from canonical \\u03b2-catenin not delineated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified FZD4 as a direct retinoic-acid target gene required for pancreas specification, extending its developmental roles.\",\n      \"evidence\": \"RNA-seq of RA-treated explants and morpholino knockdown in Xenopus\",\n      \"pmids\": [\"29769220\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ligand driving FZD4 signaling in pancreas not identified\", \"downstream targets in progenitors undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a Wnt6\\u2013FZD4\\u2013\\u03b2-catenin axis upstream of ROCK1/14-3-3\\u03c3 driving diabetes-associated centrosome amplification.\",\n      \"evidence\": \"siRNA, neutralizing antibodies, \\u03b2-catenin translocation, centrosome counting, diabetic mouse model\",\n      \"pmids\": [\"31618077\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"co-receptor in this axis not defined\", \"direct Wnt6\\u2013FZD4 binding not biochemically resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Positioned FZD4 downstream of YAP/WNT5A in mechanically induced osteogenesis via JNK signaling.\",\n      \"evidence\": \"siRNA, YAP inhibitor/activator, recombinant WNT5A rescue, osteogenic assays in hPDLCs\",\n      \"pmids\": [\"37340863\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"mechanism linking YAP to FZD4 expression not resolved\", \"direct receptor\\u2013ligand binding not shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established loss of Norrin\\u2013receptor binding as a pathogenic FEVR mechanism for novel FZD4 mutations.\",\n      \"evidence\": \"TOPflash reporter assay and Norrin\\u2013FZD4 co-IP\",\n      \"pmids\": [\"32420371\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"structural consequences of mutations not modeled\", \"trafficking status of these mutants not assessed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified FZD4 as the receptor mediating WNT2b-driven EMT relevant to Crohn's disease penetrating behaviour.\",\n      \"evidence\": \"WNT2b treatment of HT29 cells with FZD4 knockdown, WNT2b/FZD4 co-IP, patient tissue analysis\",\n      \"pmids\": [\"31359032\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"co-receptor requirement not defined\", \"causality in patient phenotype not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed FZD4 is epigenetically silenced by GATA6-AS1/EZH2-mediated H3K27me3, linking chromatin control to Wnt pathway output.\",\n      \"evidence\": \"EZH2 co-IP, H3K27me3 ChIP at FZD4 promoter, GATA6-AS1 manipulation, LiCl rescue, xenograft\",\n      \"pmids\": [\"31981860\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct GATA6-AS1 binding to FZD4 locus not mapped\", \"generality across tumor types untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed EMC3 upstream of FZD4 as a requirement for receptor expression and retinal vascular Norrin/\\u03b2-catenin signaling.\",\n      \"evidence\": \"Endothelial Emc3 conditional KO, RNA-seq, reporter assay, LiCl rescue, tube formation\",\n      \"pmids\": [\"34128175\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"mechanism of EMC3-assisted FZD4 biogenesis not resolved\", \"selectivity of EMC3 for FZD4 versus other clients not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined FZD4 as part of a Wnt2/LRP6 pro-fibrotic receptor complex driving cardiac fibrosis through \\u03b2-catenin/NF-\\u03baB.\",\n      \"evidence\": \"siRNA in cardiac fibroblasts, \\u03b2-catenin/NF-\\u03baB reporter, MI mouse model\",\n      \"pmids\": [\"34911029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct Wnt2\\u2013FZD4\\u2013LRP6 ternary complex not biochemically reconstituted\", \"ligand pairing specificity basis unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed SIRT6-mediated H3K9 deacetylation suppresses FZD4 transcription, adding an additional epigenetic control layer on Wnt output.\",\n      \"evidence\": \"SIRT6 manipulation, H3K9ac ChIP at FZD4 promoter, FZD4 rescue, xenograft in hepatoblastoma\",\n      \"pmids\": [\"34219513\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct SIRT6 recruitment mechanism to FZD4 promoter not defined\", \"context specificity untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated that pharmacological FZD4/LRP5 agonism can therapeutically normalize pathological retinal vasculature.\",\n      \"evidence\": \"Norrin mimetic SZN-413 in endothelial reporter assay, OIR mouse model, VEGF-induced rabbit leakage model\",\n      \"pmids\": [\"36149648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"binding mode of mimetic on FZD4 not structurally defined\", \"long-term efficacy/safety not assessed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified FZD4 as a miR-136-5p-gated component of Wnt signaling controlling myoblast proliferation and muscle regeneration.\",\n      \"evidence\": \"miR-136-5p manipulation, shFZD4, \\u03b2-catenin/LEF/TCF complex assay, BaCl2 muscle injury model\",\n      \"pmids\": [\"37218742\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct miR-136-5p\\u2013FZD4 3'UTR interaction extent not detailed\", \"ligand engaging FZD4 in myogenesis not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided a comprehensive mutational map classifying FZD4 pathogenicity into five mechanistic classes, including intracellular DVL2-recruitment defects.\",\n      \"evidence\": \"Site-directed mutagenesis of 34 mutations, reporter, membrane localization, Norrin binding, DVL2 co-IP\",\n      \"pmids\": [\"38558095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"genotype\\u2013phenotype severity correlation not established\", \"structural basis of DVL2 recruitment not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established FOXF1 as a direct transcriptional activator of Fzd4 in lung endothelium and showed Fzd4 restoration normalizes tumor vasculature.\",\n      \"evidence\": \"FOXF1 conditional KO/OE mice, CUT&Tag at Fzd4 promoter, Wnt reporter, nanoparticle Fzd4 rescue, lung tumor model\",\n      \"pmids\": [\"38589650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"regulatory interplay with other FZD4 transcription factors not integrated\", \"endothelial subtype specificity not fully mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined N59/N144 N-glycosylation as a requirement for FZD4 maturation, trafficking, stability, and ligand/co-receptor binding.\",\n      \"evidence\": \"Glycosylation-site mutagenesis, surface localization, co-IP with Wnt/Norrin, TOPflash, xenograft in A549 cells\",\n      \"pmids\": [\"40230079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"glycan structures and biosynthetic enzymes not identified\", \"differential glycan effects on Wnt versus Norrin binding not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct Wnt ligand\\u2013FZD4 pairings, co-receptor choices, and canonical versus JNK/NF-\\u03baB branch selection are encoded structurally and used to specify the diverse tissue outcomes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"no atomic structure of FZD4 with different ligands/co-receptors in the corpus\", \"rules governing ligand-co-receptor specificity not defined\", \"switch between \\u03b2-catenin and non-canonical outputs not mechanistically explained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 6, 8, 9, 11, 16]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 18]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 5, 8, 9]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [6, 7, 17, 19]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 3, 18]}\n    ],\n    \"complexes\": [\"Norrin-FZD4-LRP5 receptor complex\", \"Norrin-FZD4-TSPAN12 complex\"],\n    \"partners\": [\"NDP\", \"LRP5\", \"LRP6\", \"TSPAN12\", \"DVL2\", \"EMC3\", \"WNT2\", \"WNT6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}