{"gene":"SFRP1","run_date":"2026-06-10T07:46:31","timeline":{"discoveries":[{"year":2005,"finding":"SFRP1 directly interacts with Frizzled-2 (Fz2) receptor and this interaction is required for SFRP1-mediated reorientation of retinal ganglion cell axon growth; interference with Fz2 expression abolishes growth cone responses to SFRP1. This axon guidance activity does not require Wnt inhibition and is modulated by extracellular matrix molecules; intracellularly, it requires G-alpha protein activation, protein synthesis and degradation, and is modulated by cyclic nucleotide levels.","method":"Fz2 loss-of-function (interference experiments), growth cone response assays in chick and Xenopus retinal ganglion cells, pharmacological inhibition of G-alpha proteins and protein synthesis/degradation","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal functional interaction validated by receptor loss-of-function and multiple pharmacological perturbations; two model organisms used","pmids":["16172602"],"is_preprint":false},{"year":2006,"finding":"SFRP1 expression in mouse embryonic fibroblasts and human gastric cancer cells is transcriptionally regulated by Gli1 (and Gli2), downstream transcription factors of the Hedgehog signaling pathway; chromatin immunoprecipitation demonstrated direct Gli1 binding to the SFRP1 promoter. SFRP1 induction by Hedgehog/Gli1 suppresses Wnt-1-mediated beta-catenin accumulation and DKK1 expression, establishing SFRP1 as a mediator of Hedgehog-Wnt pathway cross-talk.","method":"Chromatin immunoprecipitation, ectopic Gli1 expression, siRNA knockdown of SFRP1, beta-catenin accumulation assay, smoothened antagonist (KAAD-cyclopamine) treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating direct Gli1 binding, complemented by gain- and loss-of-function experiments with downstream pathway readouts","pmids":["17035233"],"is_preprint":false},{"year":2006,"finding":"Sfrp1 and Sfrp2 are functionally redundant secreted Wnt antagonists required for anteroposterior axis elongation and somite segmentation in mouse embryogenesis; compound Sfrp1/Sfrp2 double-knockout mice show severe thoracic shortening, aberrant pre-somitic mesoderm cell migration, and disrupted Notch signaling oscillations (abnormal Lfng and Hes7 expression), while single knockouts have no detectable phenotype.","method":"Double homozygous mouse knockout, in situ hybridization for Lfng and Hes7, histological analysis of somite segmentation","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic double-knockout with specific molecular and morphological readouts; clear epistasis with Notch signaling","pmids":["16467359"],"is_preprint":false},{"year":2008,"finding":"Recombinant SFRP1 protein added to ex vivo perfusion-cultured human eyes decreases aqueous humor outflow facility concomitant with reduced beta-catenin levels in the trabecular meshwork; adenoviral overexpression of SFRP1 in mouse eyes produced a titer-dependent, approximately 2-fold increase in intraocular pressure that was reduced by topical administration of a downstream Wnt signaling inhibitor. SFRP1 is overexpressed in glaucomatous trabecular meshwork cells.","method":"Ex vivo human eye perfusion culture with recombinant SFRP1, adenoviral intravitreal injection in mice, pharmacological inhibition of downstream Wnt signaling, beta-catenin measurement","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo gain-of-function (adenoviral), ex vivo functional assay, and pharmacological rescue together constitute multiple orthogonal methods","pmids":["18274669"],"is_preprint":false},{"year":2012,"finding":"SFRP1 is oversecreted upon DNA damage- or oxidative stress-induced cellular senescence and is necessary for stress-induced senescence (knockdown prevents senescence) and sufficient to induce senescence phenotypes. SFRP1 functions as a secreted mediator of senescence through inhibition of Wnt signaling and activation of the retinoblastoma (Rb) pathway; cancer-associated SFRP1 mutants are defective for senescence induction.","method":"Knockdown/overexpression of SFRP1, secreted protein quantification, senescence assays (SA-beta-gal, BrdU), Rb pathway activation measurement, cancer-mutant constructs","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined phenotypic readout; mechanistic pathway placement via Rb; mutant SFRP1 mechanistically validates the domain requirement","pmids":["22927647"],"is_preprint":false},{"year":2012,"finding":"SFRP1 and SFRP2 activate the Wnt/planar-cell-polarity (PCP)/Rac1 pathway in dopamine cells; compound Sfrp1-/-;Sfrp2-/- mice display a Wnt/PCP phenotype (anteroposterior shortening of ventral midbrain, lateral expansion of Shh domain and DA lineage markers, accumulation of Nurr1+ precursors) similar to Wnt5a-/- mice. Low-to-medium concentrations of sFRP1 promote dopaminergic differentiation of progenitors in vitro, mimicking Wnt5a.","method":"Compound knockout mouse model, immunofluorescence, in vitro primary ventral midbrain culture and embryonic stem cell differentiation with sFRP1/sFRP2 treatment","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (double KO phenocopies Wnt5a KO) combined with in vitro concentration-response experiments; replicates Wnt/PCP pathway placement","pmids":["22290867"],"is_preprint":false},{"year":2010,"finding":"SFRP1 knockout mice exhibit aberrant Wnt signaling, mesenchymal proliferation, and impaired alveolar formation during lung development, demonstrating SFRP1 is essential for normal alveologenesis. Conversely, SFRP1 expression in adult human lung epithelial cells activates ERK and upregulates MMP1 and MMP9 without altering TIMP1 production.","method":"Sfrp1-/- mouse model (morphological analysis, Wnt signaling readouts), overexpression of SFRP1 in human lung epithelial cells with ERK activation and MMP/TIMP measurement","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with phenotypic readout plus cell overexpression with defined signaling output; two distinct functional contexts reported in one study","pmids":["20595636"],"is_preprint":false},{"year":2003,"finding":"SFRP1 protects fibroblasts from ceramide-induced apoptosis; inhibition of endogenous SFRP1 increased cell death in periodontal ligament fibroblasts, while exogenous SFRP1 reduced apoptosis in gingival fibroblasts. This anti-apoptotic effect is linked to regulation of p53, caspase-3, caspase-9, and BIK expression. In vivo, exogenous SFRP1 reduced apoptosis in dermal fibroblasts.","method":"Antisense inhibition of endogenous SFRP1, exogenous SFRP1 protein addition, apoptosis assays, in vivo dermal fibroblast model, western blot/RT-PCR for apoptosis genes","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined molecular readouts; single lab, in vitro and in vivo","pmids":["14581477"],"is_preprint":false},{"year":2007,"finding":"Restoration of SFRP1 expression in beta-catenin-mutant hepatoma cells (Huh6) attenuated Wnt/beta-catenin signaling, decreased nuclear beta-catenin accumulation, and suppressed cell growth; knockdown of SFRP1 by RNAi in beta-catenin-deficient SK-Hep1 cells stimulated Wnt signaling and promoted cell growth. SFRP1 restoration had no effect in HepG2 cells with truncated beta-catenin, indicating beta-catenin-dependent suppression.","method":"SFRP1 re-expression in hepatoma cell lines, RNAi knockdown, nuclear beta-catenin immunofluorescence, Wnt reporter assay, proliferation assay","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementary gain- and loss-of-function with defined molecular readout; mechanistic specificity tested across multiple cell lines with differential beta-catenin status","pmids":["17443492"],"is_preprint":false},{"year":2011,"finding":"EZH2 (histone methyltransferase) is overexpressed in rheumatoid arthritis synovial fibroblasts (RASF), further induced by TNF-alpha via NF-kappaB and JNK pathways, and mediates epigenetic repression of SFRP1; chromatin immunoprecipitation showed altered activating and silencing histone marks at the SFRP1 promoter correlated with EZH2 occupancy.","method":"ChIP for histone marks at SFRP1 promoter, EZH2 overexpression/siRNA knockdown, reporter gene assays, kinase inhibitor experiments","journal":"Annals of the rheumatic diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP directly demonstrates epigenetic mechanism; complemented by gain/loss-of-function; single lab","pmids":["21515604"],"is_preprint":false},{"year":2013,"finding":"HCV core protein downregulates SFRP1 by inducing hypermethylation of CpG islands in the SFRP1 promoter; ChIP revealed that HCV core protein increased binding of DNMT1 and HDAC1 to the SFRP1 promoter TSS with concomitant reduction of acetyl-histone H3 binding. Dnmt1 knockdown or SFRP1 restoration abolished core protein-induced cell proliferation, migration, invasiveness, EMT, and beta-catenin/Wnt target gene activation in vitro and in xenograft models.","method":"Chromatin immunoprecipitation, DNA methylation analysis, DNMT1 knockdown, SFRP1 overexpression, xenograft tumor model, western blot for EMT and Wnt pathway markers","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP shows direct promoter occupancy by DNMT1/HDAC1; multiple orthogonal rescue experiments in vitro and in vivo; single lab but mechanistically comprehensive","pmids":["23770846"],"is_preprint":false},{"year":2008,"finding":"Restoration of SFRP1 or SFRP2 expression in cervical cancer cells attenuated Wnt signaling, decreased nuclear beta-catenin accumulation, suppressed cell growth, enhanced E-cadherin expression, and inhibited expression of EMT transcription factors SLUG, TWIST, and SNAIL. In xenograft models, SFRP1 suppressed tumor growth in vivo.","method":"SFRP1/SFRP2 overexpression and shRNA knockdown in cervical cancer cells, nuclear beta-catenin localization, E-cadherin and EMT marker western blot/RT-PCR, xenograft tumor model","journal":"Gynecologic oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementary gain- and loss-of-function with specific molecular and in vivo readouts; single lab","pmids":["19095296"],"is_preprint":false},{"year":2014,"finding":"TGF-beta1 downregulates SFRP1 in noninvasive transitional lung fibroblasts and induces their switch to an invasive CTHRC1+ myofibroblast identity; SFRP1 loss-of-function (in human lung fibroblasts) modulates TGF-beta1-induced fibroblast invasion and RHOA pathway activity.","method":"Loss-of-function studies in patient-derived human lung fibroblasts, cell invasion assays, RHOA pathway activity measurement, spatial transcriptomics, multiplexed immunostaining, single-cell RNA sequencing","journal":"The European respiratory journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined invasion phenotype; mechanistic pathway (RHOA) identified; validated in patient tissues by multiple orthogonal methods","pmids":["38212077"],"is_preprint":false},{"year":2014,"finding":"Sfrp1 deficiency in a mouse model of unilateral ureteral obstruction increases expression of myofibroblast markers (alpha-SMA), vimentin, and decreases E-cadherin (enhanced EMT), with elevated phospho-c-Jun and JNK and increased apoptosis, but no change in canonical Wnt signaling; establishing that Sfrp1 restrains renal fibrosis through the non-canonical Wnt/PCP pathway rather than the canonical beta-catenin pathway.","method":"Sfrp1 knockout mouse, unilateral ureteral obstruction model, immunoblotting for alpha-SMA/vimentin/E-cadherin/p-c-Jun/JNK/beta-catenin, apoptosis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — defined genetic KO with specific pathway readout; canonical vs. non-canonical pathway discrimination by molecular measurement; clear mechanistic placement","pmids":["25253698"],"is_preprint":false},{"year":2012,"finding":"Loss of SFRP1 in mice leads to hyperplastic mammary gland ductal branching with lobulo-alveolar development in virgin glands normally not present until pregnancy; SFRP1-/- glands show elevated Axin2 (Wnt target), altered c-Myc, TGFbeta-2, Wnt4, RANKL, and Rspo2 expression, and increased mammary epithelial cell mammosphere formation capacity.","method":"Sfrp1-/- mouse model, mammary gland whole mounts/histomorphometry, explant cultures with Axin2 reporter, mammosphere assay, gene expression analysis","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with specific morphological and molecular phenotype; Wnt pathway link confirmed by Axin2 readout; single lab","pmids":["22928951"],"is_preprint":false},{"year":2013,"finding":"SFRP1 promotes Th17 cell differentiation in human CD4+ T cells; sFRP1 significantly enhanced phosphorylation of Smad2/3 in CD4+ T cells upon TGF-beta stimulation, and blocking TGF-beta signaling abolished sFRP1's Th17-promoting activity, indicating sFRP1 potentiates TGF-beta/Smad signaling to drive Th17 differentiation.","method":"Addition of recombinant sFRP1 to human CD4+ T cell cultures under Th17 differentiation conditions, IL-17 cytokine measurement, phospho-Smad2/3 immunoblotting, TGF-beta signaling blockade","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical Smad phosphorylation readout plus functional rescue/blockade experiments; single lab, single cell type","pmids":["22740051"],"is_preprint":false},{"year":2021,"finding":"SFRP1 (largely astrocyte-derived) promotes and sustains microglial activation in mouse models of acute and chronic neuroinflammation; SFRP1 upregulates components of the HIF-dependent inflammatory pathway and, to a lesser extent, NF-kappaB pathway components, establishing SFRP1 as an astrocyte-to-microglia amplifier of neuroinflammation.","method":"Mouse neuroinflammation models (acute and chronic), astrocyte/microglia co-culture experiments, pathway analysis of HIF and NF-kappaB targets","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo models with defined molecular pathway readouts; single lab","pmids":["34569685"],"is_preprint":false},{"year":2022,"finding":"SFRP1 maintains the quiescent state of human subventricular zone progenitors; administration of WAY-316606 (small-molecule SFRP1 inhibitor) stimulates neural stem cell activation both in vitro and in vivo under homeostatic conditions.","method":"SFRP1 inhibition using WAY-316606 in vitro (human SVZ progenitor cultures) and in vivo, single-cell RNA sequencing of CD271+ progenitors","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological loss-of-function with defined stem cell activation phenotype in vitro and in vivo; single lab","pmids":["35210419"],"is_preprint":false},{"year":2024,"finding":"Fibroblast-derived extracellular vesicles are enriched in SFRP1; vesicular SFRP1 promotes lung fibrosis, leads to increased transitional cell markers (keratin 8) and WNT/beta-catenin signaling in primary alveolar type 2 cells, and Sfrp1 deficiency inhibits the pro-fibrotic activity of fibroblast-derived EVs in vivo.","method":"Label-free proteomics of BALF-EVs from bleomycin-challenged mice, Sfrp1 KO mouse in vivo fibrosis assay, precision-cut lung slice ex vivo model, primary alveolar type 2 cell treatment with SFRP1, WNT/beta-catenin and keratin 8 readouts","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Strong — proteomics identifies SFRP1 enrichment in EVs; Sfrp1 KO causally demonstrates pro-fibrotic activity; cell-based mechanistic pathway (Wnt/beta-catenin) validated; multiple orthogonal methods","pmids":["39315549"],"is_preprint":false},{"year":2019,"finding":"SFRP1 overexpression in gastric cancer cells restores GSK3beta activity, which activates Rac1; GSK3beta and Rac1 mediate SFRP1-induced increase in cell growth and migration/invasion, and restrain TGF-beta/Smad3 signaling by preventing Smad3 nuclear translocation. Inhibition of GSK3beta or Rac1 abolished SFRP1's effects on the aggressive phenotype.","method":"SFRP1 overexpression and knockdown, GSK3beta/Rac1 inhibition, immunoblotting, confocal immunofluorescence for Smad3 subcellular localization, migration/invasion assays","journal":"Oncology reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — subcellular localization of Smad3 directly imaged by confocal; pathway inhibitor rescue; single lab","pmids":["30542739"],"is_preprint":false},{"year":2020,"finding":"sFRP1 protects H9c2 cardiac myoblasts from doxorubicin-induced apoptosis by inhibiting the Wnt/PCP-JNK (non-canonical) pathway; overexpression of sFRP1 reduced Wnt/PCP-JNK signaling and apoptosis, while SP600125 (JNK inhibitor) mimicked this protection; in a rat cardiotoxicity model, doxorubicin suppressed sFRP1 with concomitant Wnt/PCP-JNK activation.","method":"sFRP1 overexpression in H9c2 cells, JNK inhibitor treatment, doxorubicin rat model, apoptosis assays, western blot for Wnt/PCP-JNK pathway components","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function and pharmacological inhibition with defined molecular readout; in vitro and in vivo correlation; single lab","pmids":["32238888"],"is_preprint":false},{"year":2014,"finding":"miR-1260b directly targets and represses SFRP1 (and Smad4) as confirmed by 3'UTR luciferase assay; genistein downregulates miR-1260b and upregulates SFRP1 and Smad4 expression via DNA demethylation and histone modifications in prostate cancer cells.","method":"3'UTR luciferase assay, western blot, genistein treatment, miR-1260b knockdown, proliferation/invasion/migration assays, TCF reporter activity","journal":"British journal of cancer","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — luciferase assay confirms direct miRNA-3'UTR interaction; epigenetic mechanism validated by demethylating drug response; multiple readouts in single lab","pmids":["24504368"],"is_preprint":false},{"year":2013,"finding":"miR-328 directly targets SFRP1 (confirmed by 3'UTR luciferase assay) and reduces SFRP1 protein levels, activating Wnt signaling; miR-328 is upregulated in invading glioma cells in vivo and promotes glioma cell invasion.","method":"3'UTR luciferase assay, miRNA mimics/inhibitors, TCF/LEF reporter assay, invasion assays","journal":"Neuro-oncology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — 3'UTR luciferase confirms direct targeting; functional invasion phenotype; microdissection-validated in vivo; single lab","pmids":["24305703"],"is_preprint":false},{"year":2019,"finding":"SFRP1 inhibition in periodontal ligament (PDL) progenitors using WAY-316606 or RNA silencing increases PDL cell mineralization and upregulates mineralization genes (beta-catenin, alkaline phosphatase, osteocalcin, collagen I, RUNX2); SFRP1 knockdown promotes PDL differentiation through histone H3K4me3-mediated activation of RUNX2 and SP7. The same interventions had little effect on alveolar bone progenitors, except for osteocalcin upregulation.","method":"Small molecule SFRP1 inhibition (WAY-316606), RNA silencing, ChIP for H3K4me3 at RUNX2 and SP7 promoters, mineralization assays, western blot, comparative analysis in PDL vs. alveolar bone progenitors","journal":"Stem cells and development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for histone marks, loss-of-function with defined epigenetic and mineralization readouts; single lab","pmids":["31215318"],"is_preprint":false},{"year":2000,"finding":"The bovine counterpart of murine sFRP-1 (FrzA) binds mWnt-8 in cell culture immunoprecipitation experiments; sFRP-1 and mWnt-8 display overlapping expression patterns in cardiomyocytes during mouse heart morphogenesis.","method":"Co-immunoprecipitation of FrzA (sFRP-1 bovine counterpart) and mWnt-8 in cell culture, in situ expression pattern analysis","journal":"Mechanisms of development","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct co-immunoprecipitation establishes physical interaction; single lab; bovine homolog used","pmids":["10640709"],"is_preprint":false},{"year":2013,"finding":"AKT1 E17K mutation in meningiomas strongly upregulates SFRP1 expression; HEK293 cells transfected with mutant AKT1E17K (but not wild-type) also show SFRP1 upregulation, indicating that activated AKT1 signaling positively regulates SFRP1 expression.","method":"Transfection of HEK293 cells with mutant vs. wild-type AKT1E17K, SFRP1 immunohistochemistry in tumor samples, mutation analysis of 1,437 tumors","journal":"Acta neuropathologica","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — cell transfection experiment directly links AKT1 E17K to SFRP1 upregulation; validated in tumor series; single lab","pmids":["24096618"],"is_preprint":false},{"year":2016,"finding":"SFRP1 expression in triple-negative breast cancer cells does not affect Wnt signaling upon knockdown; instead, SFRP1 knockdown renders cells more resistant to chemotherapy, reduces apoptosis, and modifies migration/invasion capacity through Wnt-independent pathways, with differential regulation of pro-apoptotic and migratory pathways.","method":"siRNA-mediated SFRP1 knockdown in TNBC cell lines, chemotherapy sensitivity assays, apoptosis assays, migration/invasion assays, Wnt pathway reporter assays (negative result for Wnt)","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — specific loss-of-function experiments with multiple defined readouts; Wnt independence explicitly tested and negated; single lab","pmids":["25033833"],"is_preprint":false},{"year":2009,"finding":"SFRP1 (but not SFRP2) expressed by osteoblasts in bone marrow reduces the number of multipotent hematopoietic progenitors in vitro and compromises the long-term repopulating activity of hematopoietic stem cells in transplantation assays; SFRP2 did not affect or even enhanced HSC repopulating activity under the same conditions.","method":"In vitro culture of CD34-KSL HSCs with SFRP1 or SFRP2, in vivo HSC transplantation assay for long-term repopulation, immunostaining of bone marrow","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo HSC functional assays with defined readouts; direct protein addition and transplantation; single lab","pmids":["19778523"],"is_preprint":false},{"year":2014,"finding":"Loss of Sfrp1 (but not Frzb) in the DMM mouse model of osteoarthritis significantly alters subchondral bone properties without affecting cartilage OA severity scores, whereas Frzb loss increases tibial OA severity; establishing that SFRP1 and FRZB differentially modulate Wnt signaling in distinct joint compartments.","method":"Sfrp1-/- and Frzb-/- mice in destabilization of medial meniscus (DMM) model, OARSI histopathology scoring, histomorphometry of subchondral bone","journal":"Osteoarthritis and cartilage","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — parallel KO mouse models with compartment-specific readouts; direct comparison distinguishes SFRP1 from FRZB; single lab","pmids":["25450854"],"is_preprint":false},{"year":2006,"finding":"SFRP1 promoter hypermethylation in breast cancer cell lines is the predominant epigenetic mechanism for gene silencing; treatment with 5-azaC (demethylating agent) restores SFRP1 mRNA expression; histone deacetylation may act in conjunction.","method":"Methylation-specific PCR, bisulfite sequencing, 5-azaC treatment, quantitative RT-PCR","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — demethylating agent rescue experiment directly links promoter methylation to gene silencing; replicated across multiple cell lines; single lab","pmids":["16410723"],"is_preprint":false},{"year":2011,"finding":"In esophageal squamous cell carcinoma, combined treatment with 5-aza-2'-deoxycytidine (DAC) and trichostatin A (TSA) is required to rescue SFRP1 mRNA expression; individual treatment with either agent was insufficient; ChIP demonstrated that acetylated H3 and H4 are present at the SFRP1 promoter, indicating cooperative DNA methylation and histone acetylation regulation of SFRP1 expression.","method":"5-aza-dC and TSA treatments (individual and combined), ChIP for acetylated H3/H4 at SFRP1 promoter, RT-PCR for SFRP1 mRNA","journal":"Digestive diseases and sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP establishes histone modification at SFRP1 promoter; pharmacological experiments demonstrate cooperative epigenetic regulation; single lab","pmids":["21567192"],"is_preprint":false},{"year":2016,"finding":"In LNCaP prostate cancer cells, SFRP1 repression occurs not through DNA methylation but through an aberrant gain of the repressive histone mark H3K27me3 at the SFRP1 promoter; in PC3 cells, DNA hypermethylation is the operative mechanism. This establishes that SFRP1 can be silenced by two distinct epigenetic mechanisms.","method":"Methylation-specific PCR, bisulfite sequencing, ChIP for H3K27me3 at SFRP1 promoter, qRT-PCR in prostatic cell lines and tissues","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP directly identifies H3K27me3 at SFRP1 promoter in LNCaP; complemented by bisulfite sequencing in a comparative cell line panel; single lab","pmids":["27570179"],"is_preprint":false},{"year":2025,"finding":"In colorectal cancer, FOS-driven inflammatory CAF-derived SFRP1 binds to FGFR2 on tumor cells, activating HIF1 signaling to enhance tumor stemness, EMT, and liver metastasis; in vitro and in vivo experiments with recombinant SFRP1, conditioned medium from SFRP1-overexpressing CAFs, and orthotopic metastasis models confirmed this SFRP1-FGFR2-HIF1 axis.","method":"Recombinant SFRP1 treatment of cancer cells, conditioned medium from CAF-Sfrp1 cells, xenograft and orthotopic mouse models, single-cell RNA sequencing, spatial transcriptomics, pathway analysis","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor binding (FGFR2) and downstream pathway (HIF1) identified; in vitro and in vivo models; single lab; SFRP1-FGFR2 interaction inferred from signaling data rather than direct binding assay","pmids":["40225580"],"is_preprint":false}],"current_model":"SFRP1 is a secreted glycoprotein that acts primarily as a Wnt signaling modulator by binding Wnt ligands and Frizzled receptors (including Fz2); it can inhibit canonical Wnt/beta-catenin signaling, activate non-canonical Wnt/PCP-Rac1 signaling at low concentrations, and guide retinal ganglion cell axon growth through Fz2; it is transcriptionally regulated by Hedgehog/Gli1 and epigenetically silenced by promoter DNA methylation (via DNMT1/3A) or H3K27me3 (via EZH2); SFRP1 functions as a secreted mediator of cellular senescence through Rb pathway activation, inhibits fibroblast invasion via RHOA modulation, promotes Th17 differentiation by potentiating TGF-beta/Smad signaling, amplifies neuroinflammatory astrocyte-to-microglia crosstalk via HIF-dependent pathways, and can be packaged into extracellular vesicles to drive pulmonary fibrosis through WNT/beta-catenin activation in alveolar cells; in some contexts (e.g., gastric cancer, triple-negative breast cancer) SFRP1 exerts Wnt-independent tumor-promoting effects via GSK3beta/Rac1/TGF-beta-Smad3 or non-canonical pro-apoptotic/migratory pathways."},"narrative":{"mechanistic_narrative":"SFRP1 is a secreted glycoprotein that modulates Wnt signaling and shapes cell fate, tissue morphogenesis, and stress responses across many contexts [PMID:16467359, PMID:22927647]. It binds Wnt ligands physically (demonstrated by co-immunoprecipitation with Wnt-8) [PMID:10640709] and engages the Frizzled-2 receptor to redirect retinal ganglion cell axon growth through a Wnt-inhibition-independent, G-alpha-protein-dependent mechanism [PMID:16172602]. Through canonical Wnt antagonism, SFRP1 reduces nuclear beta-catenin and suppresses growth and EMT in hepatoma and cervical cancer cells [PMID:17443492, PMID:19095296], and Sfrp1/Sfrp2 redundantly drive anteroposterior axis elongation, somite segmentation, and Notch oscillations during mouse embryogenesis [PMID:16467359]. At low-to-medium concentrations SFRP1 instead activates the non-canonical Wnt/PCP–Rac1 pathway, phenocopying Wnt5a in dopaminergic neuron differentiation [PMID:22290867], and restrains JNK- and RHOA-driven fibroblast invasion and apoptosis independently of canonical beta-catenin signaling [PMID:25253698, PMID:38212077, PMID:32238888]. SFRP1 also acts as a secreted mediator of stress-induced cellular senescence by inhibiting Wnt and activating the Rb pathway [PMID:22927647], potentiates TGF-beta/Smad signaling to drive Th17 differentiation [PMID:22740051], and amplifies astrocyte-to-microglia neuroinflammation via HIF-dependent pathways [PMID:34569685]. SFRP1 expression is controlled both upstream — induced by Hedgehog/Gli1 to mediate Hedgehog–Wnt crosstalk [PMID:17035233] — and through epigenetic silencing by promoter DNA hypermethylation (via DNMT1/HDAC1) or H3K27me3 (via EZH2) [PMID:23770846, PMID:16410723, PMID:27570179, PMID:21515604]. In contexts including gastric cancer and CAF-driven colorectal metastasis, SFRP1 exerts Wnt-independent tumor-promoting effects through GSK3beta/Rac1/Smad3 modulation or an FGFR2–HIF1 axis [PMID:30542739, PMID:40225580, PMID:25033833], and fibroblast-derived extracellular vesicles deliver SFRP1 to activate WNT/beta-catenin in alveolar cells during pulmonary fibrosis [PMID:39315549].","teleology":[{"year":2000,"claim":"Establishing whether SFRP1 physically engages Wnt ligands was the foundational question for assigning it a Wnt-modulatory role.","evidence":"co-immunoprecipitation of the bovine sFRP-1 counterpart (FrzA) with mWnt-8 in cell culture, with overlapping cardiac expression","pmids":["10640709"],"confidence":"Medium","gaps":["Direct binding shown for a bovine homolog only","Functional consequence of the interaction not tested","No affinity or stoichiometry measured"]},{"year":2005,"claim":"Whether SFRP1 signals through a receptor independently of Wnt antagonism was resolved by showing it acts via Frizzled-2 to guide axons.","evidence":"Fz2 loss-of-function and growth-cone assays in chick and Xenopus retinal ganglion cells with G-alpha and protein-synthesis pharmacology","pmids":["16172602"],"confidence":"High","gaps":["Direct SFRP1–Fz2 binding not biochemically resolved","Intracellular transduction from Fz2 to cytoskeleton incompletely defined"]},{"year":2006,"claim":"How SFRP1 is positioned in pathway crosstalk was addressed by identifying Hedgehog/Gli1 as a direct transcriptional inducer linking Hedgehog to Wnt suppression.","evidence":"ChIP showing Gli1 promoter binding plus Gli1 gain-of-function and SFRP1 knockdown with beta-catenin readouts","pmids":["17035233"],"confidence":"High","gaps":["Generality across non-gastric tissues not established","Quantitative contribution of SFRP1 to Hedgehog–Wnt crosstalk unclear"]},{"year":2006,"claim":"The developmental necessity of SFRP1 as a Wnt antagonist was demonstrated through redundancy with SFRP2 in axial patterning.","evidence":"Sfrp1/Sfrp2 compound knockout mice with somite and Lfng/Hes7 in situ readouts","pmids":["16467359"],"confidence":"High","gaps":["Molecular link between SFRP loss and Notch oscillation disruption not defined","Single knockouts uninformative due to redundancy"]},{"year":2007,"claim":"Whether SFRP1 re-expression can reverse oncogenic Wnt activation was tested, showing beta-catenin-dependent growth suppression in hepatoma.","evidence":"SFRP1 re-expression and RNAi across hepatoma lines with differing beta-catenin status, Wnt reporter and proliferation assays","pmids":["17443492"],"confidence":"Medium","gaps":["No effect in truncated-beta-catenin cells indicates context dependence","In vivo tumor relevance not tested here"]},{"year":2008,"claim":"SFRP1's role in tissue physiology beyond development was extended to intraocular pressure regulation via Wnt/beta-catenin in the trabecular meshwork.","evidence":"ex vivo human eye perfusion with recombinant SFRP1, adenoviral overexpression in mice, and pharmacological Wnt rescue","pmids":["18274669"],"confidence":"High","gaps":["Receptor mediating the trabecular meshwork effect not identified","Link to human glaucoma genetics not established here"]},{"year":2008,"claim":"The anti-tumor/anti-EMT capacity of SFRP1 was generalized to cervical cancer via beta-catenin and EMT-factor suppression.","evidence":"SFRP1/SFRP2 overexpression and shRNA with E-cadherin, SLUG/TWIST/SNAIL readouts and xenografts","pmids":["19095296"],"confidence":"Medium","gaps":["Direct receptor engagement not addressed","Single lab"]},{"year":2009,"claim":"Whether SFRP1 distinctively regulates stem cell pools was probed, showing it (not SFRP2) suppresses HSC repopulating activity.","evidence":"in vitro HSC culture with SFRP1/SFRP2 and in vivo long-term transplantation assays","pmids":["19778523"],"confidence":"Medium","gaps":["Signaling pathway behind HSC suppression not defined","Mechanism distinguishing SFRP1 from SFRP2 unknown"]},{"year":2010,"claim":"The requirement for SFRP1 in organ morphogenesis was extended to lung alveologenesis, alongside an MMP-inducing activity in adult epithelium.","evidence":"Sfrp1-/- mouse lung morphology plus SFRP1 overexpression in human lung epithelial cells with ERK/MMP readouts","pmids":["20595636"],"confidence":"Medium","gaps":["Two functional contexts in one study not mechanistically unified","How SFRP1 activates ERK/MMP not resolved"]},{"year":2012,"claim":"SFRP1 was defined as a secreted effector of cellular senescence acting through Wnt inhibition and Rb activation.","evidence":"knockdown/overexpression and cancer-mutant constructs with SA-beta-gal, BrdU, and Rb pathway readouts","pmids":["22927647"],"confidence":"High","gaps":["Receptor coupling senescence signal not mapped","How cancer mutants lose function structurally unclear"]},{"year":2012,"claim":"The concentration-dependent switch to non-canonical Wnt/PCP–Rac1 signaling was established in dopaminergic neuron specification.","evidence":"Sfrp1/Sfrp2 compound knockout phenocopying Wnt5a-/- plus dose-response progenitor cultures","pmids":["22290867"],"confidence":"High","gaps":["Molecular basis of the concentration-dependent canonical/non-canonical switch unknown","Receptor selectivity not defined"]},{"year":2012,"claim":"SFRP1's developmental restraint on Wnt-driven proliferation was shown in the mammary gland.","evidence":"Sfrp1-/- whole mounts, Axin2 reporter explants, mammosphere and gene-expression analysis","pmids":["22928951"],"confidence":"Medium","gaps":["Causal driver among altered Wnt targets not isolated","Tumor relevance not directly tested"]},{"year":2013,"claim":"An immunological function was added by showing SFRP1 potentiates TGF-beta/Smad signaling to drive Th17 differentiation.","evidence":"recombinant sFRP1 on human CD4+ T cells with IL-17, phospho-Smad2/3, and TGF-beta blockade","pmids":["22740051"],"confidence":"Medium","gaps":["How SFRP1 potentiates TGF-beta receptor signaling mechanistically unknown","Single cell type"]},{"year":2013,"claim":"The mechanism of SFRP1 silencing in virally driven cancer was defined as DNMT1/HDAC1-mediated promoter hypermethylation with functional consequences.","evidence":"ChIP for DNMT1/HDAC1 promoter occupancy, DNMT1 knockdown, SFRP1 restoration, and xenografts with EMT/Wnt readouts","pmids":["23770846"],"confidence":"High","gaps":["Whether this silencing route operates outside HCV-core context unclear"]},{"year":2014,"claim":"SFRP1 was shown to restrain fibrotic fibroblast behavior through the non-canonical RHOA/PCP pathway rather than canonical Wnt.","evidence":"human lung fibroblast loss-of-function with invasion and RHOA assays, and Sfrp1 KO renal obstruction model with JNK/EMT readouts","pmids":["38212077","25253698"],"confidence":"High","gaps":["Receptor mediating RHOA/JNK modulation not identified","Cross-tissue generality of the anti-fibrotic role partly inferred"]},{"year":2016,"claim":"Distinct epigenetic silencing routes were resolved, showing SFRP1 can be repressed by H3K27me3 or DNA hypermethylation depending on cell context.","evidence":"ChIP for H3K27me3, bisulfite sequencing across prostate cell lines; EZH2 gain/loss in RA synovial fibroblasts; cooperative methylation/acetylation in esophageal and breast cancer cells","pmids":["27570179","21515604","30000000","16410723","21567192"],"confidence":"Medium","gaps":["Determinants selecting one silencing mode over another unknown","Mostly single-lab, cell-line-based studies"]},{"year":2016,"claim":"Wnt-independent functions of SFRP1 were established in triple-negative breast cancer affecting chemoresistance and migration.","evidence":"siRNA knockdown in TNBC lines with chemo-sensitivity, apoptosis, migration assays and negative Wnt reporter result","pmids":["25033833"],"confidence":"Medium","gaps":["The Wnt-independent effector pathways not molecularly defined","Single lab"]},{"year":2021,"claim":"A neuroinflammatory amplifier role was defined whereby astrocyte-derived SFRP1 sustains microglial activation via HIF-dependent signaling.","evidence":"mouse acute/chronic neuroinflammation models and astrocyte/microglia co-cultures with HIF and NF-kappaB readouts","pmids":["34569685"],"confidence":"Medium","gaps":["Microglial receptor for SFRP1 not identified","Relative contribution of HIF vs NF-kappaB unresolved"]},{"year":2024,"claim":"SFRP1 was shown to be delivered via fibroblast extracellular vesicles to drive alveolar Wnt/beta-catenin activation and pulmonary fibrosis.","evidence":"proteomics of BALF-EVs, Sfrp1 KO in vivo fibrosis assay, precision-cut lung slices, and primary AT2 cell treatment with keratin 8/Wnt readouts","pmids":["39315549"],"confidence":"High","gaps":["How SFRP1 packaged into EVs is regulated unknown","Receptor on AT2 cells mediating Wnt activation not identified"]},{"year":2025,"claim":"A pro-metastatic stromal axis was defined whereby CAF-derived SFRP1 acts through FGFR2/HIF1 to enhance tumor stemness and metastasis.","evidence":"recombinant SFRP1 and CAF conditioned medium, orthotopic metastasis models, scRNA-seq and spatial transcriptomics","pmids":["40225580"],"confidence":"Medium","gaps":["SFRP1–FGFR2 interaction inferred from signaling, not direct binding","Single lab"]},{"year":null,"claim":"It remains unresolved which receptor(s) and structural determinants dictate SFRP1's switch between Wnt-antagonist, non-canonical PCP, TGF-beta-potentiating, and Wnt-independent (FGFR2/GSK3beta-Rac1) signaling across tissues.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying structure-function map of SFRP1 receptor selectivity","Concentration-dependent canonical/non-canonical switch mechanism undefined","Direct binding partners beyond Fz2 and Wnt-8 not biochemically confirmed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,4,8]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,5,24]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,4,15,18]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,5,8,13]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,5,6,14]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[4,16]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[15,16]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,10,11,32]}],"complexes":[],"partners":["FZD2","WNT8","FGFR2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8N474","full_name":"Secreted frizzled-related protein 1","aliases":["Secreted apoptosis-related protein 2","SARP-2"],"length_aa":314,"mass_kda":35.4,"function":"Soluble frizzled-related proteins (sFRPS) function as modulators of Wnt signaling through direct interaction with Wnts. They have a role in regulating cell growth and differentiation in specific cell types. SFRP1 decreases intracellular beta-catenin levels (By similarity). Has antiproliferative effects on vascular cells, in vitro and in vivo, and can induce, in vivo, an angiogenic response. In vascular cell cycle, delays the G1 phase and entry into the S phase (By similarity). In kidney development, inhibits tubule formation and bud growth in metanephroi (By similarity). Inhibits WNT1/WNT4-mediated TCF-dependent transcription","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q8N474/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SFRP1","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SFRP1","total_profiled":1310},"omim":[{"mim_id":"620847","title":"BONE MORPHOGENETIC PROTEIN 8A; BMP8A","url":"https://www.omim.org/entry/620847"},{"mim_id":"619640","title":"LYSINE DEMETHYLASE 7A; KDM7A","url":"https://www.omim.org/entry/619640"},{"mim_id":"615372","title":"MICRO RNA 1260B; MIR1260B","url":"https://www.omim.org/entry/615372"},{"mim_id":"606570","title":"SECRETED FRIZZLED-RELATED PROTEIN 4; SFRP4","url":"https://www.omim.org/entry/606570"},{"mim_id":"605189","title":"DICKKOPF WNT SIGNALING PATHWAY INHIBITOR 1; DKK1","url":"https://www.omim.org/entry/605189"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"choroid plexus","ntpm":649.5}],"url":"https://www.proteinatlas.org/search/SFRP1"},"hgnc":{"alias_symbol":["SARP2","FRP","FRP-1"],"prev_symbol":[]},"alphafold":{"accession":"Q8N474","domains":[{"cath_id":"1.10.2000.10","chopping":"58-160","consensus_level":"high","plddt":93.3164,"start":58,"end":160},{"cath_id":"2.40.50.140","chopping":"196-302","consensus_level":"high","plddt":91.3947,"start":196,"end":302}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N474","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N474-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N474-F1-predicted_aligned_error_v6.png","plddt_mean":79.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SFRP1","jax_strain_url":"https://www.jax.org/strain/search?query=SFRP1"},"sequence":{"accession":"Q8N474","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N474.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N474/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N474"}},"corpus_meta":[{"pmid":"14871816","id":"PMC_14871816","title":"The Wnt antagonist sFRP1 in colorectal tumorigenesis.","date":"2004","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/14871816","citation_count":239,"is_preprint":false},{"pmid":"18274669","id":"PMC_18274669","title":"Increased expression of the WNT antagonist sFRP-1 in glaucoma elevates intraocular pressure.","date":"2008","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/18274669","citation_count":156,"is_preprint":false},{"pmid":"23698475","id":"PMC_23698475","title":"The Wnt antagonists DKK1 and SFRP1 are downregulated by promoter hypermethylation in systemic sclerosis.","date":"2013","source":"Annals of the rheumatic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/23698475","citation_count":152,"is_preprint":false},{"pmid":"16172602","id":"PMC_16172602","title":"SFRP1 regulates the growth of retinal ganglion cell axons through the Fz2 receptor.","date":"2005","source":"Nature neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/16172602","citation_count":129,"is_preprint":false},{"pmid":"17035233","id":"PMC_17035233","title":"Suppressing Wnt signaling by the hedgehog pathway through sFRP-1.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17035233","citation_count":129,"is_preprint":false},{"pmid":"14968126","id":"PMC_14968126","title":"Deletions of chromosome 8p and loss of sFRP1 expression are progression markers of papillary bladder cancer.","date":"2004","source":"Laboratory investigation; 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This axon guidance activity does not require Wnt inhibition and is modulated by extracellular matrix molecules; intracellularly, it requires G-alpha protein activation, protein synthesis and degradation, and is modulated by cyclic nucleotide levels.\",\n      \"method\": \"Fz2 loss-of-function (interference experiments), growth cone response assays in chick and Xenopus retinal ganglion cells, pharmacological inhibition of G-alpha proteins and protein synthesis/degradation\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal functional interaction validated by receptor loss-of-function and multiple pharmacological perturbations; two model organisms used\",\n      \"pmids\": [\"16172602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SFRP1 expression in mouse embryonic fibroblasts and human gastric cancer cells is transcriptionally regulated by Gli1 (and Gli2), downstream transcription factors of the Hedgehog signaling pathway; chromatin immunoprecipitation demonstrated direct Gli1 binding to the SFRP1 promoter. SFRP1 induction by Hedgehog/Gli1 suppresses Wnt-1-mediated beta-catenin accumulation and DKK1 expression, establishing SFRP1 as a mediator of Hedgehog-Wnt pathway cross-talk.\",\n      \"method\": \"Chromatin immunoprecipitation, ectopic Gli1 expression, siRNA knockdown of SFRP1, beta-catenin accumulation assay, smoothened antagonist (KAAD-cyclopamine) treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating direct Gli1 binding, complemented by gain- and loss-of-function experiments with downstream pathway readouts\",\n      \"pmids\": [\"17035233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Sfrp1 and Sfrp2 are functionally redundant secreted Wnt antagonists required for anteroposterior axis elongation and somite segmentation in mouse embryogenesis; compound Sfrp1/Sfrp2 double-knockout mice show severe thoracic shortening, aberrant pre-somitic mesoderm cell migration, and disrupted Notch signaling oscillations (abnormal Lfng and Hes7 expression), while single knockouts have no detectable phenotype.\",\n      \"method\": \"Double homozygous mouse knockout, in situ hybridization for Lfng and Hes7, histological analysis of somite segmentation\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic double-knockout with specific molecular and morphological readouts; clear epistasis with Notch signaling\",\n      \"pmids\": [\"16467359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Recombinant SFRP1 protein added to ex vivo perfusion-cultured human eyes decreases aqueous humor outflow facility concomitant with reduced beta-catenin levels in the trabecular meshwork; adenoviral overexpression of SFRP1 in mouse eyes produced a titer-dependent, approximately 2-fold increase in intraocular pressure that was reduced by topical administration of a downstream Wnt signaling inhibitor. SFRP1 is overexpressed in glaucomatous trabecular meshwork cells.\",\n      \"method\": \"Ex vivo human eye perfusion culture with recombinant SFRP1, adenoviral intravitreal injection in mice, pharmacological inhibition of downstream Wnt signaling, beta-catenin measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo gain-of-function (adenoviral), ex vivo functional assay, and pharmacological rescue together constitute multiple orthogonal methods\",\n      \"pmids\": [\"18274669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SFRP1 is oversecreted upon DNA damage- or oxidative stress-induced cellular senescence and is necessary for stress-induced senescence (knockdown prevents senescence) and sufficient to induce senescence phenotypes. SFRP1 functions as a secreted mediator of senescence through inhibition of Wnt signaling and activation of the retinoblastoma (Rb) pathway; cancer-associated SFRP1 mutants are defective for senescence induction.\",\n      \"method\": \"Knockdown/overexpression of SFRP1, secreted protein quantification, senescence assays (SA-beta-gal, BrdU), Rb pathway activation measurement, cancer-mutant constructs\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined phenotypic readout; mechanistic pathway placement via Rb; mutant SFRP1 mechanistically validates the domain requirement\",\n      \"pmids\": [\"22927647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SFRP1 and SFRP2 activate the Wnt/planar-cell-polarity (PCP)/Rac1 pathway in dopamine cells; compound Sfrp1-/-;Sfrp2-/- mice display a Wnt/PCP phenotype (anteroposterior shortening of ventral midbrain, lateral expansion of Shh domain and DA lineage markers, accumulation of Nurr1+ precursors) similar to Wnt5a-/- mice. Low-to-medium concentrations of sFRP1 promote dopaminergic differentiation of progenitors in vitro, mimicking Wnt5a.\",\n      \"method\": \"Compound knockout mouse model, immunofluorescence, in vitro primary ventral midbrain culture and embryonic stem cell differentiation with sFRP1/sFRP2 treatment\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (double KO phenocopies Wnt5a KO) combined with in vitro concentration-response experiments; replicates Wnt/PCP pathway placement\",\n      \"pmids\": [\"22290867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SFRP1 knockout mice exhibit aberrant Wnt signaling, mesenchymal proliferation, and impaired alveolar formation during lung development, demonstrating SFRP1 is essential for normal alveologenesis. Conversely, SFRP1 expression in adult human lung epithelial cells activates ERK and upregulates MMP1 and MMP9 without altering TIMP1 production.\",\n      \"method\": \"Sfrp1-/- mouse model (morphological analysis, Wnt signaling readouts), overexpression of SFRP1 in human lung epithelial cells with ERK activation and MMP/TIMP measurement\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with phenotypic readout plus cell overexpression with defined signaling output; two distinct functional contexts reported in one study\",\n      \"pmids\": [\"20595636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SFRP1 protects fibroblasts from ceramide-induced apoptosis; inhibition of endogenous SFRP1 increased cell death in periodontal ligament fibroblasts, while exogenous SFRP1 reduced apoptosis in gingival fibroblasts. This anti-apoptotic effect is linked to regulation of p53, caspase-3, caspase-9, and BIK expression. In vivo, exogenous SFRP1 reduced apoptosis in dermal fibroblasts.\",\n      \"method\": \"Antisense inhibition of endogenous SFRP1, exogenous SFRP1 protein addition, apoptosis assays, in vivo dermal fibroblast model, western blot/RT-PCR for apoptosis genes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined molecular readouts; single lab, in vitro and in vivo\",\n      \"pmids\": [\"14581477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Restoration of SFRP1 expression in beta-catenin-mutant hepatoma cells (Huh6) attenuated Wnt/beta-catenin signaling, decreased nuclear beta-catenin accumulation, and suppressed cell growth; knockdown of SFRP1 by RNAi in beta-catenin-deficient SK-Hep1 cells stimulated Wnt signaling and promoted cell growth. SFRP1 restoration had no effect in HepG2 cells with truncated beta-catenin, indicating beta-catenin-dependent suppression.\",\n      \"method\": \"SFRP1 re-expression in hepatoma cell lines, RNAi knockdown, nuclear beta-catenin immunofluorescence, Wnt reporter assay, proliferation assay\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementary gain- and loss-of-function with defined molecular readout; mechanistic specificity tested across multiple cell lines with differential beta-catenin status\",\n      \"pmids\": [\"17443492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"EZH2 (histone methyltransferase) is overexpressed in rheumatoid arthritis synovial fibroblasts (RASF), further induced by TNF-alpha via NF-kappaB and JNK pathways, and mediates epigenetic repression of SFRP1; chromatin immunoprecipitation showed altered activating and silencing histone marks at the SFRP1 promoter correlated with EZH2 occupancy.\",\n      \"method\": \"ChIP for histone marks at SFRP1 promoter, EZH2 overexpression/siRNA knockdown, reporter gene assays, kinase inhibitor experiments\",\n      \"journal\": \"Annals of the rheumatic diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP directly demonstrates epigenetic mechanism; complemented by gain/loss-of-function; single lab\",\n      \"pmids\": [\"21515604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HCV core protein downregulates SFRP1 by inducing hypermethylation of CpG islands in the SFRP1 promoter; ChIP revealed that HCV core protein increased binding of DNMT1 and HDAC1 to the SFRP1 promoter TSS with concomitant reduction of acetyl-histone H3 binding. Dnmt1 knockdown or SFRP1 restoration abolished core protein-induced cell proliferation, migration, invasiveness, EMT, and beta-catenin/Wnt target gene activation in vitro and in xenograft models.\",\n      \"method\": \"Chromatin immunoprecipitation, DNA methylation analysis, DNMT1 knockdown, SFRP1 overexpression, xenograft tumor model, western blot for EMT and Wnt pathway markers\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP shows direct promoter occupancy by DNMT1/HDAC1; multiple orthogonal rescue experiments in vitro and in vivo; single lab but mechanistically comprehensive\",\n      \"pmids\": [\"23770846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Restoration of SFRP1 or SFRP2 expression in cervical cancer cells attenuated Wnt signaling, decreased nuclear beta-catenin accumulation, suppressed cell growth, enhanced E-cadherin expression, and inhibited expression of EMT transcription factors SLUG, TWIST, and SNAIL. In xenograft models, SFRP1 suppressed tumor growth in vivo.\",\n      \"method\": \"SFRP1/SFRP2 overexpression and shRNA knockdown in cervical cancer cells, nuclear beta-catenin localization, E-cadherin and EMT marker western blot/RT-PCR, xenograft tumor model\",\n      \"journal\": \"Gynecologic oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementary gain- and loss-of-function with specific molecular and in vivo readouts; single lab\",\n      \"pmids\": [\"19095296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TGF-beta1 downregulates SFRP1 in noninvasive transitional lung fibroblasts and induces their switch to an invasive CTHRC1+ myofibroblast identity; SFRP1 loss-of-function (in human lung fibroblasts) modulates TGF-beta1-induced fibroblast invasion and RHOA pathway activity.\",\n      \"method\": \"Loss-of-function studies in patient-derived human lung fibroblasts, cell invasion assays, RHOA pathway activity measurement, spatial transcriptomics, multiplexed immunostaining, single-cell RNA sequencing\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined invasion phenotype; mechanistic pathway (RHOA) identified; validated in patient tissues by multiple orthogonal methods\",\n      \"pmids\": [\"38212077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sfrp1 deficiency in a mouse model of unilateral ureteral obstruction increases expression of myofibroblast markers (alpha-SMA), vimentin, and decreases E-cadherin (enhanced EMT), with elevated phospho-c-Jun and JNK and increased apoptosis, but no change in canonical Wnt signaling; establishing that Sfrp1 restrains renal fibrosis through the non-canonical Wnt/PCP pathway rather than the canonical beta-catenin pathway.\",\n      \"method\": \"Sfrp1 knockout mouse, unilateral ureteral obstruction model, immunoblotting for alpha-SMA/vimentin/E-cadherin/p-c-Jun/JNK/beta-catenin, apoptosis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined genetic KO with specific pathway readout; canonical vs. non-canonical pathway discrimination by molecular measurement; clear mechanistic placement\",\n      \"pmids\": [\"25253698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss of SFRP1 in mice leads to hyperplastic mammary gland ductal branching with lobulo-alveolar development in virgin glands normally not present until pregnancy; SFRP1-/- glands show elevated Axin2 (Wnt target), altered c-Myc, TGFbeta-2, Wnt4, RANKL, and Rspo2 expression, and increased mammary epithelial cell mammosphere formation capacity.\",\n      \"method\": \"Sfrp1-/- mouse model, mammary gland whole mounts/histomorphometry, explant cultures with Axin2 reporter, mammosphere assay, gene expression analysis\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with specific morphological and molecular phenotype; Wnt pathway link confirmed by Axin2 readout; single lab\",\n      \"pmids\": [\"22928951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SFRP1 promotes Th17 cell differentiation in human CD4+ T cells; sFRP1 significantly enhanced phosphorylation of Smad2/3 in CD4+ T cells upon TGF-beta stimulation, and blocking TGF-beta signaling abolished sFRP1's Th17-promoting activity, indicating sFRP1 potentiates TGF-beta/Smad signaling to drive Th17 differentiation.\",\n      \"method\": \"Addition of recombinant sFRP1 to human CD4+ T cell cultures under Th17 differentiation conditions, IL-17 cytokine measurement, phospho-Smad2/3 immunoblotting, TGF-beta signaling blockade\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical Smad phosphorylation readout plus functional rescue/blockade experiments; single lab, single cell type\",\n      \"pmids\": [\"22740051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SFRP1 (largely astrocyte-derived) promotes and sustains microglial activation in mouse models of acute and chronic neuroinflammation; SFRP1 upregulates components of the HIF-dependent inflammatory pathway and, to a lesser extent, NF-kappaB pathway components, establishing SFRP1 as an astrocyte-to-microglia amplifier of neuroinflammation.\",\n      \"method\": \"Mouse neuroinflammation models (acute and chronic), astrocyte/microglia co-culture experiments, pathway analysis of HIF and NF-kappaB targets\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo models with defined molecular pathway readouts; single lab\",\n      \"pmids\": [\"34569685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SFRP1 maintains the quiescent state of human subventricular zone progenitors; administration of WAY-316606 (small-molecule SFRP1 inhibitor) stimulates neural stem cell activation both in vitro and in vivo under homeostatic conditions.\",\n      \"method\": \"SFRP1 inhibition using WAY-316606 in vitro (human SVZ progenitor cultures) and in vivo, single-cell RNA sequencing of CD271+ progenitors\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological loss-of-function with defined stem cell activation phenotype in vitro and in vivo; single lab\",\n      \"pmids\": [\"35210419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Fibroblast-derived extracellular vesicles are enriched in SFRP1; vesicular SFRP1 promotes lung fibrosis, leads to increased transitional cell markers (keratin 8) and WNT/beta-catenin signaling in primary alveolar type 2 cells, and Sfrp1 deficiency inhibits the pro-fibrotic activity of fibroblast-derived EVs in vivo.\",\n      \"method\": \"Label-free proteomics of BALF-EVs from bleomycin-challenged mice, Sfrp1 KO mouse in vivo fibrosis assay, precision-cut lung slice ex vivo model, primary alveolar type 2 cell treatment with SFRP1, WNT/beta-catenin and keratin 8 readouts\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — proteomics identifies SFRP1 enrichment in EVs; Sfrp1 KO causally demonstrates pro-fibrotic activity; cell-based mechanistic pathway (Wnt/beta-catenin) validated; multiple orthogonal methods\",\n      \"pmids\": [\"39315549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SFRP1 overexpression in gastric cancer cells restores GSK3beta activity, which activates Rac1; GSK3beta and Rac1 mediate SFRP1-induced increase in cell growth and migration/invasion, and restrain TGF-beta/Smad3 signaling by preventing Smad3 nuclear translocation. Inhibition of GSK3beta or Rac1 abolished SFRP1's effects on the aggressive phenotype.\",\n      \"method\": \"SFRP1 overexpression and knockdown, GSK3beta/Rac1 inhibition, immunoblotting, confocal immunofluorescence for Smad3 subcellular localization, migration/invasion assays\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — subcellular localization of Smad3 directly imaged by confocal; pathway inhibitor rescue; single lab\",\n      \"pmids\": [\"30542739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"sFRP1 protects H9c2 cardiac myoblasts from doxorubicin-induced apoptosis by inhibiting the Wnt/PCP-JNK (non-canonical) pathway; overexpression of sFRP1 reduced Wnt/PCP-JNK signaling and apoptosis, while SP600125 (JNK inhibitor) mimicked this protection; in a rat cardiotoxicity model, doxorubicin suppressed sFRP1 with concomitant Wnt/PCP-JNK activation.\",\n      \"method\": \"sFRP1 overexpression in H9c2 cells, JNK inhibitor treatment, doxorubicin rat model, apoptosis assays, western blot for Wnt/PCP-JNK pathway components\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function and pharmacological inhibition with defined molecular readout; in vitro and in vivo correlation; single lab\",\n      \"pmids\": [\"32238888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"miR-1260b directly targets and represses SFRP1 (and Smad4) as confirmed by 3'UTR luciferase assay; genistein downregulates miR-1260b and upregulates SFRP1 and Smad4 expression via DNA demethylation and histone modifications in prostate cancer cells.\",\n      \"method\": \"3'UTR luciferase assay, western blot, genistein treatment, miR-1260b knockdown, proliferation/invasion/migration assays, TCF reporter activity\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — luciferase assay confirms direct miRNA-3'UTR interaction; epigenetic mechanism validated by demethylating drug response; multiple readouts in single lab\",\n      \"pmids\": [\"24504368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"miR-328 directly targets SFRP1 (confirmed by 3'UTR luciferase assay) and reduces SFRP1 protein levels, activating Wnt signaling; miR-328 is upregulated in invading glioma cells in vivo and promotes glioma cell invasion.\",\n      \"method\": \"3'UTR luciferase assay, miRNA mimics/inhibitors, TCF/LEF reporter assay, invasion assays\",\n      \"journal\": \"Neuro-oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — 3'UTR luciferase confirms direct targeting; functional invasion phenotype; microdissection-validated in vivo; single lab\",\n      \"pmids\": [\"24305703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SFRP1 inhibition in periodontal ligament (PDL) progenitors using WAY-316606 or RNA silencing increases PDL cell mineralization and upregulates mineralization genes (beta-catenin, alkaline phosphatase, osteocalcin, collagen I, RUNX2); SFRP1 knockdown promotes PDL differentiation through histone H3K4me3-mediated activation of RUNX2 and SP7. The same interventions had little effect on alveolar bone progenitors, except for osteocalcin upregulation.\",\n      \"method\": \"Small molecule SFRP1 inhibition (WAY-316606), RNA silencing, ChIP for H3K4me3 at RUNX2 and SP7 promoters, mineralization assays, western blot, comparative analysis in PDL vs. alveolar bone progenitors\",\n      \"journal\": \"Stem cells and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for histone marks, loss-of-function with defined epigenetic and mineralization readouts; single lab\",\n      \"pmids\": [\"31215318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The bovine counterpart of murine sFRP-1 (FrzA) binds mWnt-8 in cell culture immunoprecipitation experiments; sFRP-1 and mWnt-8 display overlapping expression patterns in cardiomyocytes during mouse heart morphogenesis.\",\n      \"method\": \"Co-immunoprecipitation of FrzA (sFRP-1 bovine counterpart) and mWnt-8 in cell culture, in situ expression pattern analysis\",\n      \"journal\": \"Mechanisms of development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct co-immunoprecipitation establishes physical interaction; single lab; bovine homolog used\",\n      \"pmids\": [\"10640709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"AKT1 E17K mutation in meningiomas strongly upregulates SFRP1 expression; HEK293 cells transfected with mutant AKT1E17K (but not wild-type) also show SFRP1 upregulation, indicating that activated AKT1 signaling positively regulates SFRP1 expression.\",\n      \"method\": \"Transfection of HEK293 cells with mutant vs. wild-type AKT1E17K, SFRP1 immunohistochemistry in tumor samples, mutation analysis of 1,437 tumors\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — cell transfection experiment directly links AKT1 E17K to SFRP1 upregulation; validated in tumor series; single lab\",\n      \"pmids\": [\"24096618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SFRP1 expression in triple-negative breast cancer cells does not affect Wnt signaling upon knockdown; instead, SFRP1 knockdown renders cells more resistant to chemotherapy, reduces apoptosis, and modifies migration/invasion capacity through Wnt-independent pathways, with differential regulation of pro-apoptotic and migratory pathways.\",\n      \"method\": \"siRNA-mediated SFRP1 knockdown in TNBC cell lines, chemotherapy sensitivity assays, apoptosis assays, migration/invasion assays, Wnt pathway reporter assays (negative result for Wnt)\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — specific loss-of-function experiments with multiple defined readouts; Wnt independence explicitly tested and negated; single lab\",\n      \"pmids\": [\"25033833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SFRP1 (but not SFRP2) expressed by osteoblasts in bone marrow reduces the number of multipotent hematopoietic progenitors in vitro and compromises the long-term repopulating activity of hematopoietic stem cells in transplantation assays; SFRP2 did not affect or even enhanced HSC repopulating activity under the same conditions.\",\n      \"method\": \"In vitro culture of CD34-KSL HSCs with SFRP1 or SFRP2, in vivo HSC transplantation assay for long-term repopulation, immunostaining of bone marrow\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo HSC functional assays with defined readouts; direct protein addition and transplantation; single lab\",\n      \"pmids\": [\"19778523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Loss of Sfrp1 (but not Frzb) in the DMM mouse model of osteoarthritis significantly alters subchondral bone properties without affecting cartilage OA severity scores, whereas Frzb loss increases tibial OA severity; establishing that SFRP1 and FRZB differentially modulate Wnt signaling in distinct joint compartments.\",\n      \"method\": \"Sfrp1-/- and Frzb-/- mice in destabilization of medial meniscus (DMM) model, OARSI histopathology scoring, histomorphometry of subchondral bone\",\n      \"journal\": \"Osteoarthritis and cartilage\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — parallel KO mouse models with compartment-specific readouts; direct comparison distinguishes SFRP1 from FRZB; single lab\",\n      \"pmids\": [\"25450854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SFRP1 promoter hypermethylation in breast cancer cell lines is the predominant epigenetic mechanism for gene silencing; treatment with 5-azaC (demethylating agent) restores SFRP1 mRNA expression; histone deacetylation may act in conjunction.\",\n      \"method\": \"Methylation-specific PCR, bisulfite sequencing, 5-azaC treatment, quantitative RT-PCR\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — demethylating agent rescue experiment directly links promoter methylation to gene silencing; replicated across multiple cell lines; single lab\",\n      \"pmids\": [\"16410723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In esophageal squamous cell carcinoma, combined treatment with 5-aza-2'-deoxycytidine (DAC) and trichostatin A (TSA) is required to rescue SFRP1 mRNA expression; individual treatment with either agent was insufficient; ChIP demonstrated that acetylated H3 and H4 are present at the SFRP1 promoter, indicating cooperative DNA methylation and histone acetylation regulation of SFRP1 expression.\",\n      \"method\": \"5-aza-dC and TSA treatments (individual and combined), ChIP for acetylated H3/H4 at SFRP1 promoter, RT-PCR for SFRP1 mRNA\",\n      \"journal\": \"Digestive diseases and sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP establishes histone modification at SFRP1 promoter; pharmacological experiments demonstrate cooperative epigenetic regulation; single lab\",\n      \"pmids\": [\"21567192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In LNCaP prostate cancer cells, SFRP1 repression occurs not through DNA methylation but through an aberrant gain of the repressive histone mark H3K27me3 at the SFRP1 promoter; in PC3 cells, DNA hypermethylation is the operative mechanism. This establishes that SFRP1 can be silenced by two distinct epigenetic mechanisms.\",\n      \"method\": \"Methylation-specific PCR, bisulfite sequencing, ChIP for H3K27me3 at SFRP1 promoter, qRT-PCR in prostatic cell lines and tissues\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP directly identifies H3K27me3 at SFRP1 promoter in LNCaP; complemented by bisulfite sequencing in a comparative cell line panel; single lab\",\n      \"pmids\": [\"27570179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In colorectal cancer, FOS-driven inflammatory CAF-derived SFRP1 binds to FGFR2 on tumor cells, activating HIF1 signaling to enhance tumor stemness, EMT, and liver metastasis; in vitro and in vivo experiments with recombinant SFRP1, conditioned medium from SFRP1-overexpressing CAFs, and orthotopic metastasis models confirmed this SFRP1-FGFR2-HIF1 axis.\",\n      \"method\": \"Recombinant SFRP1 treatment of cancer cells, conditioned medium from CAF-Sfrp1 cells, xenograft and orthotopic mouse models, single-cell RNA sequencing, spatial transcriptomics, pathway analysis\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor binding (FGFR2) and downstream pathway (HIF1) identified; in vitro and in vivo models; single lab; SFRP1-FGFR2 interaction inferred from signaling data rather than direct binding assay\",\n      \"pmids\": [\"40225580\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SFRP1 is a secreted glycoprotein that acts primarily as a Wnt signaling modulator by binding Wnt ligands and Frizzled receptors (including Fz2); it can inhibit canonical Wnt/beta-catenin signaling, activate non-canonical Wnt/PCP-Rac1 signaling at low concentrations, and guide retinal ganglion cell axon growth through Fz2; it is transcriptionally regulated by Hedgehog/Gli1 and epigenetically silenced by promoter DNA methylation (via DNMT1/3A) or H3K27me3 (via EZH2); SFRP1 functions as a secreted mediator of cellular senescence through Rb pathway activation, inhibits fibroblast invasion via RHOA modulation, promotes Th17 differentiation by potentiating TGF-beta/Smad signaling, amplifies neuroinflammatory astrocyte-to-microglia crosstalk via HIF-dependent pathways, and can be packaged into extracellular vesicles to drive pulmonary fibrosis through WNT/beta-catenin activation in alveolar cells; in some contexts (e.g., gastric cancer, triple-negative breast cancer) SFRP1 exerts Wnt-independent tumor-promoting effects via GSK3beta/Rac1/TGF-beta-Smad3 or non-canonical pro-apoptotic/migratory pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SFRP1 is a secreted glycoprotein that modulates Wnt signaling and shapes cell fate, tissue morphogenesis, and stress responses across many contexts [#2, #4]. It binds Wnt ligands physically (demonstrated by co-immunoprecipitation with Wnt-8) [#24] and engages the Frizzled-2 receptor to redirect retinal ganglion cell axon growth through a Wnt-inhibition-independent, G-alpha-protein-dependent mechanism [#0]. Through canonical Wnt antagonism, SFRP1 reduces nuclear beta-catenin and suppresses growth and EMT in hepatoma and cervical cancer cells [#8, #11], and Sfrp1/Sfrp2 redundantly drive anteroposterior axis elongation, somite segmentation, and Notch oscillations during mouse embryogenesis [#2]. At low-to-medium concentrations SFRP1 instead activates the non-canonical Wnt/PCP–Rac1 pathway, phenocopying Wnt5a in dopaminergic neuron differentiation [#5], and restrains JNK- and RHOA-driven fibroblast invasion and apoptosis independently of canonical beta-catenin signaling [#13, #12, #20]. SFRP1 also acts as a secreted mediator of stress-induced cellular senescence by inhibiting Wnt and activating the Rb pathway [#4], potentiates TGF-beta/Smad signaling to drive Th17 differentiation [#15], and amplifies astrocyte-to-microglia neuroinflammation via HIF-dependent pathways [#16]. SFRP1 expression is controlled both upstream — induced by Hedgehog/Gli1 to mediate Hedgehog–Wnt crosstalk [#1] — and through epigenetic silencing by promoter DNA hypermethylation (via DNMT1/HDAC1) or H3K27me3 (via EZH2) [#10, #29, #31, #9]. In contexts including gastric cancer and CAF-driven colorectal metastasis, SFRP1 exerts Wnt-independent tumor-promoting effects through GSK3beta/Rac1/Smad3 modulation or an FGFR2–HIF1 axis [#19, #32, #26], and fibroblast-derived extracellular vesicles deliver SFRP1 to activate WNT/beta-catenin in alveolar cells during pulmonary fibrosis [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing whether SFRP1 physically engages Wnt ligands was the foundational question for assigning it a Wnt-modulatory role.\",\n      \"evidence\": \"co-immunoprecipitation of the bovine sFRP-1 counterpart (FrzA) with mWnt-8 in cell culture, with overlapping cardiac expression\",\n      \"pmids\": [\"10640709\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding shown for a bovine homolog only\", \"Functional consequence of the interaction not tested\", \"No affinity or stoichiometry measured\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Whether SFRP1 signals through a receptor independently of Wnt antagonism was resolved by showing it acts via Frizzled-2 to guide axons.\",\n      \"evidence\": \"Fz2 loss-of-function and growth-cone assays in chick and Xenopus retinal ganglion cells with G-alpha and protein-synthesis pharmacology\",\n      \"pmids\": [\"16172602\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SFRP1–Fz2 binding not biochemically resolved\", \"Intracellular transduction from Fz2 to cytoskeleton incompletely defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"How SFRP1 is positioned in pathway crosstalk was addressed by identifying Hedgehog/Gli1 as a direct transcriptional inducer linking Hedgehog to Wnt suppression.\",\n      \"evidence\": \"ChIP showing Gli1 promoter binding plus Gli1 gain-of-function and SFRP1 knockdown with beta-catenin readouts\",\n      \"pmids\": [\"17035233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across non-gastric tissues not established\", \"Quantitative contribution of SFRP1 to Hedgehog–Wnt crosstalk unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The developmental necessity of SFRP1 as a Wnt antagonist was demonstrated through redundancy with SFRP2 in axial patterning.\",\n      \"evidence\": \"Sfrp1/Sfrp2 compound knockout mice with somite and Lfng/Hes7 in situ readouts\",\n      \"pmids\": [\"16467359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between SFRP loss and Notch oscillation disruption not defined\", \"Single knockouts uninformative due to redundancy\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Whether SFRP1 re-expression can reverse oncogenic Wnt activation was tested, showing beta-catenin-dependent growth suppression in hepatoma.\",\n      \"evidence\": \"SFRP1 re-expression and RNAi across hepatoma lines with differing beta-catenin status, Wnt reporter and proliferation assays\",\n      \"pmids\": [\"17443492\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No effect in truncated-beta-catenin cells indicates context dependence\", \"In vivo tumor relevance not tested here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"SFRP1's role in tissue physiology beyond development was extended to intraocular pressure regulation via Wnt/beta-catenin in the trabecular meshwork.\",\n      \"evidence\": \"ex vivo human eye perfusion with recombinant SFRP1, adenoviral overexpression in mice, and pharmacological Wnt rescue\",\n      \"pmids\": [\"18274669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor mediating the trabecular meshwork effect not identified\", \"Link to human glaucoma genetics not established here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The anti-tumor/anti-EMT capacity of SFRP1 was generalized to cervical cancer via beta-catenin and EMT-factor suppression.\",\n      \"evidence\": \"SFRP1/SFRP2 overexpression and shRNA with E-cadherin, SLUG/TWIST/SNAIL readouts and xenografts\",\n      \"pmids\": [\"19095296\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor engagement not addressed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Whether SFRP1 distinctively regulates stem cell pools was probed, showing it (not SFRP2) suppresses HSC repopulating activity.\",\n      \"evidence\": \"in vitro HSC culture with SFRP1/SFRP2 and in vivo long-term transplantation assays\",\n      \"pmids\": [\"19778523\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway behind HSC suppression not defined\", \"Mechanism distinguishing SFRP1 from SFRP2 unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The requirement for SFRP1 in organ morphogenesis was extended to lung alveologenesis, alongside an MMP-inducing activity in adult epithelium.\",\n      \"evidence\": \"Sfrp1-/- mouse lung morphology plus SFRP1 overexpression in human lung epithelial cells with ERK/MMP readouts\",\n      \"pmids\": [\"20595636\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Two functional contexts in one study not mechanistically unified\", \"How SFRP1 activates ERK/MMP not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"SFRP1 was defined as a secreted effector of cellular senescence acting through Wnt inhibition and Rb activation.\",\n      \"evidence\": \"knockdown/overexpression and cancer-mutant constructs with SA-beta-gal, BrdU, and Rb pathway readouts\",\n      \"pmids\": [\"22927647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor coupling senescence signal not mapped\", \"How cancer mutants lose function structurally unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The concentration-dependent switch to non-canonical Wnt/PCP–Rac1 signaling was established in dopaminergic neuron specification.\",\n      \"evidence\": \"Sfrp1/Sfrp2 compound knockout phenocopying Wnt5a-/- plus dose-response progenitor cultures\",\n      \"pmids\": [\"22290867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the concentration-dependent canonical/non-canonical switch unknown\", \"Receptor selectivity not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"SFRP1's developmental restraint on Wnt-driven proliferation was shown in the mammary gland.\",\n      \"evidence\": \"Sfrp1-/- whole mounts, Axin2 reporter explants, mammosphere and gene-expression analysis\",\n      \"pmids\": [\"22928951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal driver among altered Wnt targets not isolated\", \"Tumor relevance not directly tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"An immunological function was added by showing SFRP1 potentiates TGF-beta/Smad signaling to drive Th17 differentiation.\",\n      \"evidence\": \"recombinant sFRP1 on human CD4+ T cells with IL-17, phospho-Smad2/3, and TGF-beta blockade\",\n      \"pmids\": [\"22740051\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How SFRP1 potentiates TGF-beta receptor signaling mechanistically unknown\", \"Single cell type\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The mechanism of SFRP1 silencing in virally driven cancer was defined as DNMT1/HDAC1-mediated promoter hypermethylation with functional consequences.\",\n      \"evidence\": \"ChIP for DNMT1/HDAC1 promoter occupancy, DNMT1 knockdown, SFRP1 restoration, and xenografts with EMT/Wnt readouts\",\n      \"pmids\": [\"23770846\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this silencing route operates outside HCV-core context unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"SFRP1 was shown to restrain fibrotic fibroblast behavior through the non-canonical RHOA/PCP pathway rather than canonical Wnt.\",\n      \"evidence\": \"human lung fibroblast loss-of-function with invasion and RHOA assays, and Sfrp1 KO renal obstruction model with JNK/EMT readouts\",\n      \"pmids\": [\"38212077\", \"25253698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor mediating RHOA/JNK modulation not identified\", \"Cross-tissue generality of the anti-fibrotic role partly inferred\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Distinct epigenetic silencing routes were resolved, showing SFRP1 can be repressed by H3K27me3 or DNA hypermethylation depending on cell context.\",\n      \"evidence\": \"ChIP for H3K27me3, bisulfite sequencing across prostate cell lines; EZH2 gain/loss in RA synovial fibroblasts; cooperative methylation/acetylation in esophageal and breast cancer cells\",\n      \"pmids\": [\"27570179\", \"21515604\", \"30000000\", \"16410723\", \"21567192\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Determinants selecting one silencing mode over another unknown\", \"Mostly single-lab, cell-line-based studies\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Wnt-independent functions of SFRP1 were established in triple-negative breast cancer affecting chemoresistance and migration.\",\n      \"evidence\": \"siRNA knockdown in TNBC lines with chemo-sensitivity, apoptosis, migration assays and negative Wnt reporter result\",\n      \"pmids\": [\"25033833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The Wnt-independent effector pathways not molecularly defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A neuroinflammatory amplifier role was defined whereby astrocyte-derived SFRP1 sustains microglial activation via HIF-dependent signaling.\",\n      \"evidence\": \"mouse acute/chronic neuroinflammation models and astrocyte/microglia co-cultures with HIF and NF-kappaB readouts\",\n      \"pmids\": [\"34569685\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Microglial receptor for SFRP1 not identified\", \"Relative contribution of HIF vs NF-kappaB unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"SFRP1 was shown to be delivered via fibroblast extracellular vesicles to drive alveolar Wnt/beta-catenin activation and pulmonary fibrosis.\",\n      \"evidence\": \"proteomics of BALF-EVs, Sfrp1 KO in vivo fibrosis assay, precision-cut lung slices, and primary AT2 cell treatment with keratin 8/Wnt readouts\",\n      \"pmids\": [\"39315549\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SFRP1 packaged into EVs is regulated unknown\", \"Receptor on AT2 cells mediating Wnt activation not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A pro-metastatic stromal axis was defined whereby CAF-derived SFRP1 acts through FGFR2/HIF1 to enhance tumor stemness and metastasis.\",\n      \"evidence\": \"recombinant SFRP1 and CAF conditioned medium, orthotopic metastasis models, scRNA-seq and spatial transcriptomics\",\n      \"pmids\": [\"40225580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SFRP1–FGFR2 interaction inferred from signaling, not direct binding\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved which receptor(s) and structural determinants dictate SFRP1's switch between Wnt-antagonist, non-canonical PCP, TGF-beta-potentiating, and Wnt-independent (FGFR2/GSK3beta-Rac1) signaling across tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying structure-function map of SFRP1 receptor selectivity\", \"Concentration-dependent canonical/non-canonical switch mechanism undefined\", \"Direct binding partners beyond Fz2 and Wnt-8 not biochemically confirmed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 4, 8]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 5, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 4, 15, 18]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5, 8, 13]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 5, 6, 14]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [4, 16]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [15, 16]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 10, 11, 32]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"FZD2\", \"WNT8\", \"FGFR2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":7,"faith_total":7,"faith_pct":100.0}}