{"gene":"ADGRF5","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2013,"finding":"GPR116 promotes breast cancer cell migration and invasion through the Gαq-p63RhoGEF-RhoA/Rac1 pathway, modulating lamellipodia formation and actin stress fibers in a RhoA- and Rac1-dependent manner.","method":"shRNA knockdown, ectopic overexpression, in vitro migration/invasion assays, mouse metastasis models, pathway analysis","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — clean KD and OE with defined cellular phenotype plus pathway placement, replicated in multiple cell lines and in vivo models","pmids":["24008316"],"is_preprint":false},{"year":2013,"finding":"GPR116 expression in alveolar type II (ATII) cells is required for maintaining normal pulmonary surfactant levels; global and conditional knockout mice develop progressive surfactant lipid and protein accumulation, labored breathing, and reduced lifespan.","method":"Global and conditional (cell-type-specific) Gpr116 knockout mice, bone marrow transplantation, histology, biochemical analysis of surfactant","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal genetic approaches (global KO, conditional KO, bone marrow transplant) with defined cellular phenotype, replicated across labs","pmids":["23684610"],"is_preprint":false},{"year":2013,"finding":"GPR116 functions as a molecular sensor of alveolar surfactant lipid pool size, regulating surfactant secretion; loss of GPR116 causes 12–30-fold accumulation of surfactant phospholipids and induces P2RY2 (purinergic receptor) expression in type II cells.","method":"Targeted Gpr116 knockout mice, lipid quantification, mRNA microarray, histology","journal":"American journal of respiratory cell and molecular biology","confidence":"High","confidence_rationale":"Tier 2 — independent replication of KO phenotype with defined molecular readouts","pmids":["23590306"],"is_preprint":false},{"year":2013,"finding":"Surfactant protein D (SP-D) was identified as a ligand of Ig-Hepta/GPR116 by co-expression and immunoprecipitation; GPR116 senses alveolar surfactant levels by monitoring SP-D and its signaling attenuates surfactant lipid/protein synthesis, secretion, and stimulates recycling/uptake.","method":"Co-expression and co-immunoprecipitation of SP-D with extracellular region of GPR116, radioactive tracer surfactant metabolism assays in KO vs WT mice","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 — ligand identified by pulldown/co-IP combined with in vivo metabolic tracer assays","pmids":["23922714"],"is_preprint":false},{"year":2006,"finding":"Ig-Hepta/GPR116 undergoes multiple proteolytic processing events: furin cleaves the proEGF2 region (residues 25–223) to generate EGF2 (residues 52–223), yielding four fragments (presequence, proEGF2/alpha, Ig-repeat beta-chain, TM7 gamma-chain); the alpha-fragment affects expression of certain mRNA species.","method":"Biochemical processing analysis, identification of furin cleavage site, mRNA expression assays","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro biochemical characterization of cleavage sites with mutagenesis-level detail, single lab","pmids":["16882675"],"is_preprint":false},{"year":2015,"finding":"Loss of Gpr116 in the lung results in macrophage activation, NF-κB nuclear translocation in alveolar macrophages, excessive ROS accumulation, and upregulation of MMP-2 and MMP-9 from alveolar macrophages, leading to emphysema-like pathology; increased monocyte chemotactic protein-1 (MCP-1) is observed in embryonic KO lungs prior to macrophage accumulation.","method":"Gpr116 knockout mouse model, bronchoalveolar lavage cytokine/lipid peroxide/MMP assays, NF-κB nuclear translocation assays, ROS detection, inhibitor experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple biochemical and cell-biology readouts in KO model with inhibitor validation, published in high-quality journal","pmids":["25778400"],"is_preprint":false},{"year":2015,"finding":"Endothelial-specific deletion of Gpr116 causes significant cerebral vascular leakage and attenuated pathological retinal vascular response in oxygen-induced retinopathy, demonstrating that Gpr116 modulates endothelial barrier properties in the CNS vasculature.","method":"Constitutive and endothelial-specific conditional Gpr116 knockout mice, vascular leakage assays, oxygen-induced retinopathy model","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific KO with defined vascular phenotype using multiple models","pmids":["26394398"],"is_preprint":false},{"year":2017,"finding":"GPR116 controls surfactant secretion and reuptake in alveolar type II (AT2) cells through Gq/11 signaling; synthetic tethered agonist peptides derived from the GPR116 ectodomain activated Gq/11-dependent inositol phosphate conversion, calcium mobilization, and cortical F-actin stabilization to inhibit surfactant secretion; AT2 cell-specific deletion of Gnaq/Gna11 phenocopied the Gpr116-/- surfactant accumulation phenotype.","method":"Synthetic agonist peptide assays, inositol phosphate conversion, calcium mobilization, F-actin assays, AT2 cell-specific Gnaq/Gna11 conditional KO, epistasis","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted Gq/11 pathway activation in vitro combined with in vivo genetic epistasis, multiple orthogonal methods","pmids":["28570277"],"is_preprint":false},{"year":2017,"finding":"Loss of GPR116 and ELTD1 (ADGRL4) together in endothelial cells causes aortic arch malformations, cardiac outflow tract defects, and renal thrombotic microangiopathy; endothelial-specific or neural crest-specific deletion of both did not fully recapitulate the phenotype, indicating non-endothelial/non-neural crest expression accounts for cardiovascular defects.","method":"Double-KO mouse model, endothelial-specific and neural crest-specific conditional KO, cardiovascular and renal histopathology","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis/double KO approach with defined phenotype, single lab","pmids":["28806758"],"is_preprint":false},{"year":2019,"finding":"Loss of ADGRF5 leads to airway inflammation including CCL2 upregulation specifically in lung endothelial cells; CCL2-mediated inflammation contributes to downstream inflammatory gene upregulation (S100a8, S100a9, Il5, Slc26a4), as shown by CCR2 inhibitor RS504393 treatment.","method":"Adgrf5 KO mouse model, qPCR/western blot in primary lung ECs, pharmacological inhibitor (RS504393) treatment, BALF analysis","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2-3 — primary cell experiments plus in vivo inhibitor rescue, single lab","pmids":["30654796"],"is_preprint":false},{"year":2019,"finding":"Adgrf5 is highly expressed in CNS endothelium and regulates retinal vascular patterning; Adgrf5 mutant retinae exhibit increased perivenous vascular density, abnormal projections to the inner plexus, and transient vascular protrusions into the inner retinal space, indicating a role in subretinal vascularization prevention.","method":"Adgrf5 knockout mouse retinal angiogenesis analysis, vascular morphometry, live imaging","journal":"Angiogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and KO phenotype with vascular functional readout, single lab","pmids":["31256320"],"is_preprint":false},{"year":2020,"finding":"Gpr116 is highly expressed in acid-secreting A-intercalated cells (A-ICs) of the kidney; kidney-specific Gpr116 KO causes urinary acidification (decreased urine pH) with metabolic alkalosis, and loss of Gpr116 results in greater accumulation of V-ATPase proton pumps at the apical surface of A-ICs; a synthetic agonist peptide for Gpr116 inhibits proton flux in collecting duct intercalated cells.","method":"Kidney-specific KO mice, immunogold electron microscopy, synthetic agonist peptide treatment, split-open collecting duct proton flux assay, in situ receptor activation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including in situ peptide activation, immunogold EM, and functional flux assay in specific KO, single lab but highly rigorous","pmids":["33004624"],"is_preprint":false},{"year":2021,"finding":"Soluble FNDC4 (sFNDC4) directly and with high affinity binds to GPR116 in white adipose tissue, acting as its ligand; sFNDC4-GPR116 engagement promotes insulin signaling and insulin-mediated glucose uptake in white adipocytes; the protective effects of FcsFNDC4 on glucose tolerance in prediabetic mice require GPR116.","method":"Direct binding assay, GPR116 KO adipocytes, in vivo GPR116-dependent rescue assay with FcsFNDC4, glucose tolerance tests","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — ligand identified by direct binding assay, receptor-dependent in vivo rescue, multiple orthogonal methods","pmids":["34016966"],"is_preprint":false},{"year":2022,"finding":"GPR116 activation requires autocatalytic cleavage upstream of its tethered agonist (Stachel) sequence; a knock-in mouse expressing non-cleavable GPR116 phenocopies the pulmonary surfactant accumulation of GPR116 KO mice; key conserved amino acids in the tethered agonist sequence and extracellular loops 2/3 (ECL2/3) are essential for receptor activation; residues in TM7 mediate differential signaling strength between mouse and human GPR116.","method":"Knock-in non-cleavable mutant mice, site-directed mutagenesis, species-swapping approaches, in vitro tethered agonist assays, in vivo pulmonary phenotyping","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 — in vivo knock-in mutagenesis combined with in vitro mutagenesis and species-swap, multiple orthogonal methods","pmids":["36073784"],"is_preprint":false},{"year":2022,"finding":"GPR116 is essential for long-term maintenance of the skeletal muscle stem cell (MuSC) pool; Stachel peptide stimulation of GPR116 leads to strong interaction with β-arrestins; activated GPR116 increases nuclear localization of β-arrestin1, which interacts with CREB (cAMP response element binding protein) to regulate gene expression, thereby delaying MuSC activation and differentiation.","method":"Gpr116 conditional KO in MuSCs, Stachel peptide stimulation, β-arrestin interaction assays, nuclear fractionation, co-IP with CREB, MuSC self-renewal assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, nuclear fractionation, genetic KO with defined stem cell phenotype, multiple orthogonal methods","pmids":["36384129"],"is_preprint":false},{"year":2023,"finding":"GPR116 regulates NK cell antitumor function via the Gαq/HIF1α/NF-κB signaling pathway; GPR116 deficiency in NK cells enhances cytotoxicity with increased GzmB and IFNγ production.","method":"GPR116 KO mouse NK cell functional assays, in vitro and in vivo cytotoxicity assays, pathway inhibition experiments","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2-3 — KO with pathway placement and defined functional readouts, single lab","pmids":["36895027"],"is_preprint":false},{"year":2023,"finding":"GPR116 promotes ferroptosis in sepsis-induced liver injury by inhibiting the system Xc-/GSH/GPX4 pathway; hepatocyte-specific GPR116 deletion prevents hepatic ferroptosis and alleviates liver dysfunction; GPR116 aggravates mitochondrial damage and lipid peroxidation in hepatocytes.","method":"Hepatocyte-specific GPR116 KO mice, GPR116 overexpression, ferroptosis markers (GSH, GPX4, lipid peroxidation assays), mitochondrial damage assays","journal":"Cell biology and toxicology","confidence":"Medium","confidence_rationale":"Tier 2 — KO and OE with defined ferroptosis pathway placement, single lab","pmids":["37266730"],"is_preprint":false},{"year":2024,"finding":"GPR116 inhibits endoplasmic reticulum stress during acetaminophen-induced liver injury through interaction with β-arrestin1, which in turn inhibits BiP (binding immunoglobulin protein), a critical ER regulator; GPR116 activation by its ligand FNDC4 protects against early hepatotoxicity.","method":"Hepatocyte-specific GPR116 KO mice, GPR116 overexpression, co-immunoprecipitation of GPR116 with β-arrestin1 and BiP, RNA-seq, FNDC4 ligand treatment","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — co-IP identifying interaction partners with functional KO/OE readout, single lab","pmids":["39001944"],"is_preprint":false},{"year":2024,"finding":"GPR116 promotes breast cancer metastasis by inhibiting ERK1/2 via RhoA activation, reducing C/EBPβ phosphorylation at Thr235 and its nuclear translocation, thereby suppressing MMP8 transcription; loss of ADGRF5 increases MMP8 expression and CXCL8 secretion, polarizing tumor-associated neutrophils to the antitumor N1 phenotype.","method":"ADGRF5 knockdown in breast cancer cells, ERK1/2 phosphorylation assays, RhoA activation assays, C/EBPβ nuclear translocation assays, MMP8 promoter analysis, in vivo tumor models","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical assays placing ADGRF5 in defined pathway with in vivo validation, single lab","pmids":["38937435"],"is_preprint":false},{"year":2024,"finding":"GPR116 is involved in somatostatin release from pancreatic delta cells; whole-body GPR116 deficiency causes decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content, with glucose homeostasis maintained by compensatory modulation of insulin degradation.","method":"Whole-body and cell-specific GPR116 KO mouse models, somatostatin secretion assays, islet morphometry, insulin content measurement","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 — cell-specific and whole-body KO with defined secretory and morphological phenotypes, single lab","pmids":["38228886"],"is_preprint":false},{"year":2024,"finding":"ADGRF5 is specifically expressed in glomerular capillary endothelial cells; its deletion causes albuminuria, glomerular basement membrane defects, and altered expression of type IV collagens and KLF2 in glomerular endothelial cells.","method":"Adgrf5 KO mice, immunohistochemistry, electron microscopy, gene expression analysis in primary human glomerular ECs with ADGRF5 knockdown","journal":"Journal of the American Society of Nephrology","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with functional KO phenotype and human primary cell validation, single lab","pmids":["38844335"],"is_preprint":false},{"year":2025,"finding":"GPR116 acts as a hydrostatic pressure (HP) mechanosensor in liver sinusoidal endothelial cells (LSECs); using a hepatic hypertension-on-a-chip system, GPR116 was identified as the key HP sensor whose downstream mechanotransduction pathway drives endothelial injury; genetic silencing of GPR116 protected LSECs from HP-induced damage in vitro and in cirrhotic mice.","method":"Hepatic hypertension-on-a-chip (2D and 3D), genetic silencing of GPR116, in vivo cirrhotic mouse model, decoupled mechanical parameter regulation","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — novel microfluidic system identifying mechanosensor role with in vivo validation, single lab","pmids":["41237250"],"is_preprint":false},{"year":2026,"finding":"Endothelial ADGRF5/GPR116 is required for sustained thermogenic remodeling of brown adipose tissue (BAT) during prolonged cold exposure; endothelial deletion impairs thermogenic capacity, induces endothelial transcriptional reprogramming with EndMT-like features, and disrupts endothelial-adipocyte paracrine signaling that supports full thermogenic adipocyte adaptation.","method":"Inducible endothelial-specific ADGRF5 KO mice, snRNA-seq, vascular functional assays, CellChat/NicheNet cell-cell communication modeling, cold exposure challenges","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — cell-type-specific inducible KO with snRNA-seq and functional vascular assays, single lab","pmids":["41796902"],"is_preprint":false},{"year":2012,"finding":"Adipose tissue-specific deletion of Gpr116 causes glucose intolerance and insulin resistance, hepatosteatosis, reduced circulating adiponectin, and increased serum resistin, establishing a role for GPR116 in adipocyte biology and systemic energy homeostasis.","method":"Adipose tissue-specific conditional Gpr116 KO mice, glucose and insulin tolerance tests, serum adipokine measurements, liver histology","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — conditional KO with defined metabolic phenotypes, single lab","pmids":["22971422"],"is_preprint":false}],"current_model":"ADGRF5/GPR116 is an adhesion GPCR that undergoes autocatalytic cleavage to expose a tethered agonist (Stachel) sequence, which activates the receptor through interactions with extracellular loops 2/3 and TM7, primarily coupling to Gαq/11 signaling to regulate surfactant secretion/reuptake in alveolar type II cells, V-ATPase trafficking in renal intercalated cells, and actin/RhoA/Rac1-dependent cell motility; it also signals through β-arrestin1 nuclear functions to maintain muscle stem cell quiescence, and acts as a mechanosensor in endothelial cells to preserve barrier integrity and tissue homeostasis across lung, kidney, vasculature, and metabolic tissues."},"narrative":{"teleology":[{"year":2006,"claim":"Establishing that GPR116 undergoes multi-step proteolytic processing—including furin cleavage of the proEGF2 region—provided the first biochemical framework for its ectodomain maturation, though the functional significance of individual fragments was unclear.","evidence":"Biochemical processing analysis and furin cleavage site identification in vitro","pmids":["16882675"],"confidence":"Medium","gaps":["Functional consequence of each fragment not established","GAIN domain autocleavage not yet distinguished from furin processing","In vivo relevance of processing not tested"]},{"year":2012,"claim":"Adipose-specific deletion revealed that GPR116 is required for systemic glucose homeostasis and adipokine regulation, broadening the receptor's role beyond lung to metabolic tissues.","evidence":"Adipose-specific conditional KO mice with glucose/insulin tolerance tests and serum adipokine measurements","pmids":["22971422"],"confidence":"Medium","gaps":["Downstream signaling pathway in adipocytes not defined","Direct versus indirect metabolic effects not resolved","Single lab"]},{"year":2013,"claim":"Multiple independent knockout studies converged on GPR116 as a critical sensor of alveolar surfactant pool size in type II pneumocytes, with loss causing massive surfactant accumulation, and SP-D was identified as an extracellular ligand engaging the ectodomain to couple surfactant sensing to secretion/reuptake control.","evidence":"Global and conditional Gpr116 KO mice from multiple labs; SP-D co-IP with GPR116 ectodomain; radioactive tracer surfactant metabolism; lipid quantification and mRNA microarray","pmids":["23684610","23590306","23922714"],"confidence":"High","gaps":["SP-D as ligand confirmed by co-IP but direct binding affinity not measured with purified components","Downstream G-protein coupling in AT2 cells not yet identified","Mechanism by which GPR116 distinguishes surfactant pool size unknown"]},{"year":2013,"claim":"In parallel, GPR116 was placed in the Gαq–p63RhoGEF–RhoA/Rac1 signaling axis controlling cancer cell migration, providing the first pathway-level resolution of downstream effectors.","evidence":"shRNA knockdown and overexpression in breast cancer cell lines, in vitro migration/invasion assays, mouse metastasis model","pmids":["24008316"],"confidence":"High","gaps":["Whether Gαq coupling in cancer cells reflects normal physiology unresolved","Direct Gαq interaction not shown biochemically at this stage"]},{"year":2015,"claim":"GPR116 loss was shown to trigger secondary inflammatory cascades—macrophage activation with NF-κB translocation, ROS, and MMP upregulation in lung, and endothelial barrier compromise in CNS vasculature—extending its role from surfactant homeostasis to tissue protection.","evidence":"Gpr116 KO mice with bronchoalveolar lavage, NF-κB/ROS assays, MMP measurements; endothelial-specific conditional KO with vascular leakage assays and oxygen-induced retinopathy model","pmids":["25778400","26394398"],"confidence":"High","gaps":["Whether inflammatory phenotype is cell-autonomous or secondary to surfactant excess not fully dissected","Endothelial ligand/activation mechanism unknown"]},{"year":2017,"claim":"The Gαq/11 pathway was definitively established as the effector coupling downstream of GPR116 in AT2 cells: synthetic Stachel peptides activated Gq-dependent IP turnover and calcium flux, and AT2-specific Gnaq/Gna11 double KO phenocopied the surfactant defect, resolving the core signaling mechanism.","evidence":"Synthetic tethered agonist peptide assays, IP conversion, calcium mobilization, F-actin imaging, AT2-specific Gnaq/Gna11 conditional KO epistasis","pmids":["28570277"],"confidence":"High","gaps":["Whether Gαq/11 is the sole G-protein effector or whether Gα12/13 contributes not tested","Endogenous ligand-triggered versus constitutive activation balance unclear"]},{"year":2019,"claim":"Lung endothelial cells were identified as a source of CCL2-driven inflammation upon ADGRF5 loss, and retinal vascular patterning defects in KO mice established an endothelial-autonomous role in angiogenic regulation.","evidence":"Adgrf5 KO mice with primary lung EC gene expression, CCR2 inhibitor rescue; KO retinal angiogenesis analysis","pmids":["30654796","31256320"],"confidence":"Medium","gaps":["Endothelial GPR116 ligand and downstream signaling pathway not identified","CCL2 upregulation mechanism in ECs not resolved"]},{"year":2020,"claim":"GPR116 was shown to regulate renal acid–base balance by controlling apical V-ATPase accumulation in intercalated cells, with synthetic Stachel peptide directly inhibiting proton flux, demonstrating a second epithelial tissue where GPR116 governs vesicular trafficking.","evidence":"Kidney-specific KO mice, immunogold EM, split-open collecting duct proton flux assay with synthetic agonist peptide","pmids":["33004624"],"confidence":"High","gaps":["G-protein coupling in intercalated cells not confirmed","Endogenous trigger for GPR116 activation in kidney unknown","Whether V-ATPase trafficking is direct or secondary not established"]},{"year":2021,"claim":"Soluble FNDC4 was identified as a high-affinity ligand for GPR116 in adipocytes, coupling receptor engagement to enhanced insulin signaling and glucose uptake—providing the first ligand-receptor pair validated by direct binding and in vivo receptor-dependent rescue.","evidence":"Direct binding assay, GPR116 KO adipocytes, in vivo FcsFNDC4 rescue requiring GPR116, glucose tolerance tests in prediabetic mice","pmids":["34016966"],"confidence":"High","gaps":["Whether FNDC4 and SP-D compete for the same binding site unknown","Signaling pathway downstream of FNDC4–GPR116 not fully resolved","Tissue-specific ligand hierarchy not determined"]},{"year":2022,"claim":"The requirement for autocatalytic ectodomain cleavage was proven in vivo: a non-cleavable GPR116 knock-in phenocopied the KO, and systematic mutagenesis mapped the Stachel sequence and ECL2/3 residues essential for activation, with TM7 residues governing species-specific signaling strength.","evidence":"Non-cleavable knock-in mice, site-directed mutagenesis, species-swapping, in vitro tethered agonist assays, in vivo pulmonary phenotyping","pmids":["36073784"],"confidence":"High","gaps":["No crystal/cryo-EM structure of GPR116 available","Whether cleavage occurs constitutively or is regulated by ligand binding unknown"]},{"year":2022,"claim":"A β-arrestin1-dependent, G-protein-independent signaling arm was uncovered in muscle stem cells: GPR116 Stachel activation drives β-arrestin1 nuclear translocation and CREB interaction to maintain quiescence, revealing biased signaling capacity.","evidence":"Conditional KO in MuSCs, Stachel peptide stimulation, β-arrestin interaction assays, nuclear fractionation, co-IP with CREB, self-renewal assays","pmids":["36384129"],"confidence":"High","gaps":["Whether β-arrestin and Gαq arms are simultaneously active or represent biased agonism in different tissues not tested","Transcriptional targets of β-arrestin1–CREB complex not catalogued"]},{"year":2023,"claim":"GPR116's Gαq coupling was extended to NK cells (regulating cytotoxicity via HIF1α/NF-κB) and to hepatocyte ferroptosis (via system Xc−/GSH/GPX4 suppression), revealing broad tissue-specific effector pathway engagement.","evidence":"GPR116 KO mouse NK cell assays with pathway inhibitors; hepatocyte-specific KO/OE with ferroptosis marker assays","pmids":["36895027","37266730"],"confidence":"Medium","gaps":["NK cell role based on single lab","Ferroptosis role based on single lab with no independent replication","Direct Gαq coupling in hepatocytes not biochemically confirmed"]},{"year":2024,"claim":"GPR116 was identified as a hydrostatic pressure mechanosensor in liver sinusoidal endothelial cells and was further shown to maintain glomerular endothelial integrity, regulate breast cancer immune evasion via RhoA–ERK–C/EBPβ–MMP8, and participate in pancreatic delta cell somatostatin release and beta cell mass maintenance.","evidence":"Hepatic hypertension-on-a-chip with GPR116 silencing and cirrhotic mouse validation; glomerular EC KO with EM and gene expression; breast cancer cell KD with ERK/RhoA assays and tumor models; pancreatic KO with secretion assays and islet morphometry; β-arrestin1–BiP co-IP in hepatocytes","pmids":["41237250","38844335","38937435","38228886","39001944"],"confidence":"Medium","gaps":["Mechanosensor activation mechanism (conformational change under pressure) not elucidated","Whether glomerular and hepatic endothelial roles share common signaling axis unknown","Pancreatic delta cell signaling pathway not characterized"]},{"year":null,"claim":"Key unresolved questions include the structural basis of tethered agonist–receptor activation (no high-resolution structure exists), the hierarchy and tissue specificity of multiple reported ligands (SP-D, FNDC4, mechanical force), and whether G-protein versus β-arrestin biased signaling is determined by ligand identity, tissue context, or receptor processing state.","evidence":"","pmids":[],"confidence":"High","gaps":["No cryo-EM or crystal structure of GPR116","Ligand competition or cooperativity between SP-D, FNDC4, and mechanical stimuli not tested","Biased agonism determinants unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[7,11,13,21]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[2,3,21]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[14,15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,7,11,13]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,13]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,2,7,11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,9,15]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[12,23]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[11]}],"complexes":[],"partners":["GNAQ","GNA11","ARRB1","SFTPD","FNDC4","CREB1","RHOA","RAC1"],"other_free_text":[]},"mechanistic_narrative":"ADGRF5 (GPR116) is an adhesion G protein-coupled receptor that functions as a molecular sensor across multiple epithelial, endothelial, and mesenchymal tissues, integrating extracellular cues—including surfactant protein D, soluble FNDC4, and hydrostatic pressure—to regulate secretory homeostasis, barrier integrity, and metabolic signaling. Autocatalytic cleavage of the ectodomain exposes a tethered agonist (Stachel) sequence that activates the receptor through interactions with extracellular loops 2/3 and TM7, coupling primarily to Gαq/11 to drive inositol phosphate turnover, calcium mobilization, and cortical F-actin stabilization; a non-cleavable knock-in phenocopies the knockout surfactant accumulation [PMID:36073784, PMID:28570277]. In alveolar type II cells, ADGRF5–Gαq/11 signaling restrains surfactant secretion and promotes reuptake, and its loss causes massive phospholipid accumulation, macrophage activation, and emphysema-like pathology [PMID:23684610, PMID:25778400]; in renal intercalated cells it controls apical V-ATPase trafficking and acid secretion [PMID:33004624], while in endothelium it maintains CNS vascular barrier integrity, glomerular basement membrane composition, and acts as a hydrostatic pressure mechanosensor [PMID:26394398, PMID:38844335, PMID:41237250]. Beyond Gαq, ADGRF5 signals through β-arrestin1 nuclear translocation to interact with CREB and maintain muscle stem cell quiescence, and engages RhoA/Rac1 to regulate cell motility [PMID:36384129, PMID:24008316]."},"prefetch_data":{"uniprot":{"accession":"Q8IZF2","full_name":"Adhesion G protein-coupled receptor F5","aliases":["G-protein coupled receptor 116"],"length_aa":1346,"mass_kda":149.5,"function":"Adhesion G protein-coupled receptor (PubMed:28570277). In alveolar type II (ATII or AT2) cells, required for normal lung surfactant homeostasis (PubMed:28570277). Modulation of both surfactant secretion and uptake by ATII cells is mediated by the downstream activation of GNAQ/GNA11 proteins and may be a consequence of increased cortical F-actin assembly induced by ADGRF5 activation (PubMed:28570277). In the kidney, may play a role in the regulation of acid excretion into the primary urine, possibly by regulating the surface expression of V-ATPase proton pump (By similarity). As a receptor for soluble FNDC4 (sFNDC4), required for proper systemic glucose tolerance, specifically sensitizing white adipose tissue to insulin. Also plays a role in sFNDC4-induced decrease of local inflammation in white adipose tissue (PubMed:34016966)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8IZF2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ADGRF5","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ADGRF5","total_profiled":1310},"omim":[{"mim_id":"620874","title":"ADHESION G PROTEIN-COUPLED RECEPTOR F5; ADGRF5","url":"https://www.omim.org/entry/620874"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in 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global and conditional knockout mice develop progressive surfactant lipid and protein accumulation, labored breathing, and reduced lifespan.\",\n      \"method\": \"Global and conditional (cell-type-specific) Gpr116 knockout mice, bone marrow transplantation, histology, biochemical analysis of surfactant\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal genetic approaches (global KO, conditional KO, bone marrow transplant) with defined cellular phenotype, replicated across labs\",\n      \"pmids\": [\"23684610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPR116 functions as a molecular sensor of alveolar surfactant lipid pool size, regulating surfactant secretion; loss of GPR116 causes 12–30-fold accumulation of surfactant phospholipids and induces P2RY2 (purinergic receptor) expression in type II cells.\",\n      \"method\": \"Targeted Gpr116 knockout mice, lipid quantification, mRNA microarray, histology\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — independent replication of KO phenotype with defined molecular readouts\",\n      \"pmids\": [\"23590306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Surfactant protein D (SP-D) was identified as a ligand of Ig-Hepta/GPR116 by co-expression and immunoprecipitation; GPR116 senses alveolar surfactant levels by monitoring SP-D and its signaling attenuates surfactant lipid/protein synthesis, secretion, and stimulates recycling/uptake.\",\n      \"method\": \"Co-expression and co-immunoprecipitation of SP-D with extracellular region of GPR116, radioactive tracer surfactant metabolism assays in KO vs WT mice\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ligand identified by pulldown/co-IP combined with in vivo metabolic tracer assays\",\n      \"pmids\": [\"23922714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ig-Hepta/GPR116 undergoes multiple proteolytic processing events: furin cleaves the proEGF2 region (residues 25–223) to generate EGF2 (residues 52–223), yielding four fragments (presequence, proEGF2/alpha, Ig-repeat beta-chain, TM7 gamma-chain); the alpha-fragment affects expression of certain mRNA species.\",\n      \"method\": \"Biochemical processing analysis, identification of furin cleavage site, mRNA expression assays\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro biochemical characterization of cleavage sites with mutagenesis-level detail, single lab\",\n      \"pmids\": [\"16882675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss of Gpr116 in the lung results in macrophage activation, NF-κB nuclear translocation in alveolar macrophages, excessive ROS accumulation, and upregulation of MMP-2 and MMP-9 from alveolar macrophages, leading to emphysema-like pathology; increased monocyte chemotactic protein-1 (MCP-1) is observed in embryonic KO lungs prior to macrophage accumulation.\",\n      \"method\": \"Gpr116 knockout mouse model, bronchoalveolar lavage cytokine/lipid peroxide/MMP assays, NF-κB nuclear translocation assays, ROS detection, inhibitor experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical and cell-biology readouts in KO model with inhibitor validation, published in high-quality journal\",\n      \"pmids\": [\"25778400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Endothelial-specific deletion of Gpr116 causes significant cerebral vascular leakage and attenuated pathological retinal vascular response in oxygen-induced retinopathy, demonstrating that Gpr116 modulates endothelial barrier properties in the CNS vasculature.\",\n      \"method\": \"Constitutive and endothelial-specific conditional Gpr116 knockout mice, vascular leakage assays, oxygen-induced retinopathy model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KO with defined vascular phenotype using multiple models\",\n      \"pmids\": [\"26394398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPR116 controls surfactant secretion and reuptake in alveolar type II (AT2) cells through Gq/11 signaling; synthetic tethered agonist peptides derived from the GPR116 ectodomain activated Gq/11-dependent inositol phosphate conversion, calcium mobilization, and cortical F-actin stabilization to inhibit surfactant secretion; AT2 cell-specific deletion of Gnaq/Gna11 phenocopied the Gpr116-/- surfactant accumulation phenotype.\",\n      \"method\": \"Synthetic agonist peptide assays, inositol phosphate conversion, calcium mobilization, F-actin assays, AT2 cell-specific Gnaq/Gna11 conditional KO, epistasis\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted Gq/11 pathway activation in vitro combined with in vivo genetic epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"28570277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Loss of GPR116 and ELTD1 (ADGRL4) together in endothelial cells causes aortic arch malformations, cardiac outflow tract defects, and renal thrombotic microangiopathy; endothelial-specific or neural crest-specific deletion of both did not fully recapitulate the phenotype, indicating non-endothelial/non-neural crest expression accounts for cardiovascular defects.\",\n      \"method\": \"Double-KO mouse model, endothelial-specific and neural crest-specific conditional KO, cardiovascular and renal histopathology\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis/double KO approach with defined phenotype, single lab\",\n      \"pmids\": [\"28806758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of ADGRF5 leads to airway inflammation including CCL2 upregulation specifically in lung endothelial cells; CCL2-mediated inflammation contributes to downstream inflammatory gene upregulation (S100a8, S100a9, Il5, Slc26a4), as shown by CCR2 inhibitor RS504393 treatment.\",\n      \"method\": \"Adgrf5 KO mouse model, qPCR/western blot in primary lung ECs, pharmacological inhibitor (RS504393) treatment, BALF analysis\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — primary cell experiments plus in vivo inhibitor rescue, single lab\",\n      \"pmids\": [\"30654796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Adgrf5 is highly expressed in CNS endothelium and regulates retinal vascular patterning; Adgrf5 mutant retinae exhibit increased perivenous vascular density, abnormal projections to the inner plexus, and transient vascular protrusions into the inner retinal space, indicating a role in subretinal vascularization prevention.\",\n      \"method\": \"Adgrf5 knockout mouse retinal angiogenesis analysis, vascular morphometry, live imaging\",\n      \"journal\": \"Angiogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and KO phenotype with vascular functional readout, single lab\",\n      \"pmids\": [\"31256320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Gpr116 is highly expressed in acid-secreting A-intercalated cells (A-ICs) of the kidney; kidney-specific Gpr116 KO causes urinary acidification (decreased urine pH) with metabolic alkalosis, and loss of Gpr116 results in greater accumulation of V-ATPase proton pumps at the apical surface of A-ICs; a synthetic agonist peptide for Gpr116 inhibits proton flux in collecting duct intercalated cells.\",\n      \"method\": \"Kidney-specific KO mice, immunogold electron microscopy, synthetic agonist peptide treatment, split-open collecting duct proton flux assay, in situ receptor activation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including in situ peptide activation, immunogold EM, and functional flux assay in specific KO, single lab but highly rigorous\",\n      \"pmids\": [\"33004624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Soluble FNDC4 (sFNDC4) directly and with high affinity binds to GPR116 in white adipose tissue, acting as its ligand; sFNDC4-GPR116 engagement promotes insulin signaling and insulin-mediated glucose uptake in white adipocytes; the protective effects of FcsFNDC4 on glucose tolerance in prediabetic mice require GPR116.\",\n      \"method\": \"Direct binding assay, GPR116 KO adipocytes, in vivo GPR116-dependent rescue assay with FcsFNDC4, glucose tolerance tests\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ligand identified by direct binding assay, receptor-dependent in vivo rescue, multiple orthogonal methods\",\n      \"pmids\": [\"34016966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR116 activation requires autocatalytic cleavage upstream of its tethered agonist (Stachel) sequence; a knock-in mouse expressing non-cleavable GPR116 phenocopies the pulmonary surfactant accumulation of GPR116 KO mice; key conserved amino acids in the tethered agonist sequence and extracellular loops 2/3 (ECL2/3) are essential for receptor activation; residues in TM7 mediate differential signaling strength between mouse and human GPR116.\",\n      \"method\": \"Knock-in non-cleavable mutant mice, site-directed mutagenesis, species-swapping approaches, in vitro tethered agonist assays, in vivo pulmonary phenotyping\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vivo knock-in mutagenesis combined with in vitro mutagenesis and species-swap, multiple orthogonal methods\",\n      \"pmids\": [\"36073784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR116 is essential for long-term maintenance of the skeletal muscle stem cell (MuSC) pool; Stachel peptide stimulation of GPR116 leads to strong interaction with β-arrestins; activated GPR116 increases nuclear localization of β-arrestin1, which interacts with CREB (cAMP response element binding protein) to regulate gene expression, thereby delaying MuSC activation and differentiation.\",\n      \"method\": \"Gpr116 conditional KO in MuSCs, Stachel peptide stimulation, β-arrestin interaction assays, nuclear fractionation, co-IP with CREB, MuSC self-renewal assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, nuclear fractionation, genetic KO with defined stem cell phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"36384129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPR116 regulates NK cell antitumor function via the Gαq/HIF1α/NF-κB signaling pathway; GPR116 deficiency in NK cells enhances cytotoxicity with increased GzmB and IFNγ production.\",\n      \"method\": \"GPR116 KO mouse NK cell functional assays, in vitro and in vivo cytotoxicity assays, pathway inhibition experiments\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — KO with pathway placement and defined functional readouts, single lab\",\n      \"pmids\": [\"36895027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPR116 promotes ferroptosis in sepsis-induced liver injury by inhibiting the system Xc-/GSH/GPX4 pathway; hepatocyte-specific GPR116 deletion prevents hepatic ferroptosis and alleviates liver dysfunction; GPR116 aggravates mitochondrial damage and lipid peroxidation in hepatocytes.\",\n      \"method\": \"Hepatocyte-specific GPR116 KO mice, GPR116 overexpression, ferroptosis markers (GSH, GPX4, lipid peroxidation assays), mitochondrial damage assays\",\n      \"journal\": \"Cell biology and toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO and OE with defined ferroptosis pathway placement, single lab\",\n      \"pmids\": [\"37266730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPR116 inhibits endoplasmic reticulum stress during acetaminophen-induced liver injury through interaction with β-arrestin1, which in turn inhibits BiP (binding immunoglobulin protein), a critical ER regulator; GPR116 activation by its ligand FNDC4 protects against early hepatotoxicity.\",\n      \"method\": \"Hepatocyte-specific GPR116 KO mice, GPR116 overexpression, co-immunoprecipitation of GPR116 with β-arrestin1 and BiP, RNA-seq, FNDC4 ligand treatment\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — co-IP identifying interaction partners with functional KO/OE readout, single lab\",\n      \"pmids\": [\"39001944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPR116 promotes breast cancer metastasis by inhibiting ERK1/2 via RhoA activation, reducing C/EBPβ phosphorylation at Thr235 and its nuclear translocation, thereby suppressing MMP8 transcription; loss of ADGRF5 increases MMP8 expression and CXCL8 secretion, polarizing tumor-associated neutrophils to the antitumor N1 phenotype.\",\n      \"method\": \"ADGRF5 knockdown in breast cancer cells, ERK1/2 phosphorylation assays, RhoA activation assays, C/EBPβ nuclear translocation assays, MMP8 promoter analysis, in vivo tumor models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays placing ADGRF5 in defined pathway with in vivo validation, single lab\",\n      \"pmids\": [\"38937435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPR116 is involved in somatostatin release from pancreatic delta cells; whole-body GPR116 deficiency causes decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content, with glucose homeostasis maintained by compensatory modulation of insulin degradation.\",\n      \"method\": \"Whole-body and cell-specific GPR116 KO mouse models, somatostatin secretion assays, islet morphometry, insulin content measurement\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-specific and whole-body KO with defined secretory and morphological phenotypes, single lab\",\n      \"pmids\": [\"38228886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ADGRF5 is specifically expressed in glomerular capillary endothelial cells; its deletion causes albuminuria, glomerular basement membrane defects, and altered expression of type IV collagens and KLF2 in glomerular endothelial cells.\",\n      \"method\": \"Adgrf5 KO mice, immunohistochemistry, electron microscopy, gene expression analysis in primary human glomerular ECs with ADGRF5 knockdown\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional KO phenotype and human primary cell validation, single lab\",\n      \"pmids\": [\"38844335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR116 acts as a hydrostatic pressure (HP) mechanosensor in liver sinusoidal endothelial cells (LSECs); using a hepatic hypertension-on-a-chip system, GPR116 was identified as the key HP sensor whose downstream mechanotransduction pathway drives endothelial injury; genetic silencing of GPR116 protected LSECs from HP-induced damage in vitro and in cirrhotic mice.\",\n      \"method\": \"Hepatic hypertension-on-a-chip (2D and 3D), genetic silencing of GPR116, in vivo cirrhotic mouse model, decoupled mechanical parameter regulation\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — novel microfluidic system identifying mechanosensor role with in vivo validation, single lab\",\n      \"pmids\": [\"41237250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Endothelial ADGRF5/GPR116 is required for sustained thermogenic remodeling of brown adipose tissue (BAT) during prolonged cold exposure; endothelial deletion impairs thermogenic capacity, induces endothelial transcriptional reprogramming with EndMT-like features, and disrupts endothelial-adipocyte paracrine signaling that supports full thermogenic adipocyte adaptation.\",\n      \"method\": \"Inducible endothelial-specific ADGRF5 KO mice, snRNA-seq, vascular functional assays, CellChat/NicheNet cell-cell communication modeling, cold exposure challenges\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific inducible KO with snRNA-seq and functional vascular assays, single lab\",\n      \"pmids\": [\"41796902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Adipose tissue-specific deletion of Gpr116 causes glucose intolerance and insulin resistance, hepatosteatosis, reduced circulating adiponectin, and increased serum resistin, establishing a role for GPR116 in adipocyte biology and systemic energy homeostasis.\",\n      \"method\": \"Adipose tissue-specific conditional Gpr116 KO mice, glucose and insulin tolerance tests, serum adipokine measurements, liver histology\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined metabolic phenotypes, single lab\",\n      \"pmids\": [\"22971422\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ADGRF5/GPR116 is an adhesion GPCR that undergoes autocatalytic cleavage to expose a tethered agonist (Stachel) sequence, which activates the receptor through interactions with extracellular loops 2/3 and TM7, primarily coupling to Gαq/11 signaling to regulate surfactant secretion/reuptake in alveolar type II cells, V-ATPase trafficking in renal intercalated cells, and actin/RhoA/Rac1-dependent cell motility; it also signals through β-arrestin1 nuclear functions to maintain muscle stem cell quiescence, and acts as a mechanosensor in endothelial cells to preserve barrier integrity and tissue homeostasis across lung, kidney, vasculature, and metabolic tissues.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ADGRF5 (GPR116) is an adhesion G protein-coupled receptor that functions as a molecular sensor across multiple epithelial, endothelial, and mesenchymal tissues, integrating extracellular cues—including surfactant protein D, soluble FNDC4, and hydrostatic pressure—to regulate secretory homeostasis, barrier integrity, and metabolic signaling. Autocatalytic cleavage of the ectodomain exposes a tethered agonist (Stachel) sequence that activates the receptor through interactions with extracellular loops 2/3 and TM7, coupling primarily to Gαq/11 to drive inositol phosphate turnover, calcium mobilization, and cortical F-actin stabilization; a non-cleavable knock-in phenocopies the knockout surfactant accumulation [PMID:36073784, PMID:28570277]. In alveolar type II cells, ADGRF5–Gαq/11 signaling restrains surfactant secretion and promotes reuptake, and its loss causes massive phospholipid accumulation, macrophage activation, and emphysema-like pathology [PMID:23684610, PMID:25778400]; in renal intercalated cells it controls apical V-ATPase trafficking and acid secretion [PMID:33004624], while in endothelium it maintains CNS vascular barrier integrity, glomerular basement membrane composition, and acts as a hydrostatic pressure mechanosensor [PMID:26394398, PMID:38844335, PMID:41237250]. Beyond Gαq, ADGRF5 signals through β-arrestin1 nuclear translocation to interact with CREB and maintain muscle stem cell quiescence, and engages RhoA/Rac1 to regulate cell motility [PMID:36384129, PMID:24008316].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing that GPR116 undergoes multi-step proteolytic processing—including furin cleavage of the proEGF2 region—provided the first biochemical framework for its ectodomain maturation, though the functional significance of individual fragments was unclear.\",\n      \"evidence\": \"Biochemical processing analysis and furin cleavage site identification in vitro\",\n      \"pmids\": [\"16882675\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of each fragment not established\", \"GAIN domain autocleavage not yet distinguished from furin processing\", \"In vivo relevance of processing not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Adipose-specific deletion revealed that GPR116 is required for systemic glucose homeostasis and adipokine regulation, broadening the receptor's role beyond lung to metabolic tissues.\",\n      \"evidence\": \"Adipose-specific conditional KO mice with glucose/insulin tolerance tests and serum adipokine measurements\",\n      \"pmids\": [\"22971422\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream signaling pathway in adipocytes not defined\", \"Direct versus indirect metabolic effects not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Multiple independent knockout studies converged on GPR116 as a critical sensor of alveolar surfactant pool size in type II pneumocytes, with loss causing massive surfactant accumulation, and SP-D was identified as an extracellular ligand engaging the ectodomain to couple surfactant sensing to secretion/reuptake control.\",\n      \"evidence\": \"Global and conditional Gpr116 KO mice from multiple labs; SP-D co-IP with GPR116 ectodomain; radioactive tracer surfactant metabolism; lipid quantification and mRNA microarray\",\n      \"pmids\": [\"23684610\", \"23590306\", \"23922714\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SP-D as ligand confirmed by co-IP but direct binding affinity not measured with purified components\", \"Downstream G-protein coupling in AT2 cells not yet identified\", \"Mechanism by which GPR116 distinguishes surfactant pool size unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"In parallel, GPR116 was placed in the Gαq–p63RhoGEF–RhoA/Rac1 signaling axis controlling cancer cell migration, providing the first pathway-level resolution of downstream effectors.\",\n      \"evidence\": \"shRNA knockdown and overexpression in breast cancer cell lines, in vitro migration/invasion assays, mouse metastasis model\",\n      \"pmids\": [\"24008316\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Gαq coupling in cancer cells reflects normal physiology unresolved\", \"Direct Gαq interaction not shown biochemically at this stage\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"GPR116 loss was shown to trigger secondary inflammatory cascades—macrophage activation with NF-κB translocation, ROS, and MMP upregulation in lung, and endothelial barrier compromise in CNS vasculature—extending its role from surfactant homeostasis to tissue protection.\",\n      \"evidence\": \"Gpr116 KO mice with bronchoalveolar lavage, NF-κB/ROS assays, MMP measurements; endothelial-specific conditional KO with vascular leakage assays and oxygen-induced retinopathy model\",\n      \"pmids\": [\"25778400\", \"26394398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether inflammatory phenotype is cell-autonomous or secondary to surfactant excess not fully dissected\", \"Endothelial ligand/activation mechanism unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The Gαq/11 pathway was definitively established as the effector coupling downstream of GPR116 in AT2 cells: synthetic Stachel peptides activated Gq-dependent IP turnover and calcium flux, and AT2-specific Gnaq/Gna11 double KO phenocopied the surfactant defect, resolving the core signaling mechanism.\",\n      \"evidence\": \"Synthetic tethered agonist peptide assays, IP conversion, calcium mobilization, F-actin imaging, AT2-specific Gnaq/Gna11 conditional KO epistasis\",\n      \"pmids\": [\"28570277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Gαq/11 is the sole G-protein effector or whether Gα12/13 contributes not tested\", \"Endogenous ligand-triggered versus constitutive activation balance unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Lung endothelial cells were identified as a source of CCL2-driven inflammation upon ADGRF5 loss, and retinal vascular patterning defects in KO mice established an endothelial-autonomous role in angiogenic regulation.\",\n      \"evidence\": \"Adgrf5 KO mice with primary lung EC gene expression, CCR2 inhibitor rescue; KO retinal angiogenesis analysis\",\n      \"pmids\": [\"30654796\", \"31256320\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endothelial GPR116 ligand and downstream signaling pathway not identified\", \"CCL2 upregulation mechanism in ECs not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"GPR116 was shown to regulate renal acid–base balance by controlling apical V-ATPase accumulation in intercalated cells, with synthetic Stachel peptide directly inhibiting proton flux, demonstrating a second epithelial tissue where GPR116 governs vesicular trafficking.\",\n      \"evidence\": \"Kidney-specific KO mice, immunogold EM, split-open collecting duct proton flux assay with synthetic agonist peptide\",\n      \"pmids\": [\"33004624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G-protein coupling in intercalated cells not confirmed\", \"Endogenous trigger for GPR116 activation in kidney unknown\", \"Whether V-ATPase trafficking is direct or secondary not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Soluble FNDC4 was identified as a high-affinity ligand for GPR116 in adipocytes, coupling receptor engagement to enhanced insulin signaling and glucose uptake—providing the first ligand-receptor pair validated by direct binding and in vivo receptor-dependent rescue.\",\n      \"evidence\": \"Direct binding assay, GPR116 KO adipocytes, in vivo FcsFNDC4 rescue requiring GPR116, glucose tolerance tests in prediabetic mice\",\n      \"pmids\": [\"34016966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FNDC4 and SP-D compete for the same binding site unknown\", \"Signaling pathway downstream of FNDC4–GPR116 not fully resolved\", \"Tissue-specific ligand hierarchy not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The requirement for autocatalytic ectodomain cleavage was proven in vivo: a non-cleavable GPR116 knock-in phenocopied the KO, and systematic mutagenesis mapped the Stachel sequence and ECL2/3 residues essential for activation, with TM7 residues governing species-specific signaling strength.\",\n      \"evidence\": \"Non-cleavable knock-in mice, site-directed mutagenesis, species-swapping, in vitro tethered agonist assays, in vivo pulmonary phenotyping\",\n      \"pmids\": [\"36073784\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal/cryo-EM structure of GPR116 available\", \"Whether cleavage occurs constitutively or is regulated by ligand binding unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A β-arrestin1-dependent, G-protein-independent signaling arm was uncovered in muscle stem cells: GPR116 Stachel activation drives β-arrestin1 nuclear translocation and CREB interaction to maintain quiescence, revealing biased signaling capacity.\",\n      \"evidence\": \"Conditional KO in MuSCs, Stachel peptide stimulation, β-arrestin interaction assays, nuclear fractionation, co-IP with CREB, self-renewal assays\",\n      \"pmids\": [\"36384129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether β-arrestin and Gαq arms are simultaneously active or represent biased agonism in different tissues not tested\", \"Transcriptional targets of β-arrestin1–CREB complex not catalogued\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"GPR116's Gαq coupling was extended to NK cells (regulating cytotoxicity via HIF1α/NF-κB) and to hepatocyte ferroptosis (via system Xc−/GSH/GPX4 suppression), revealing broad tissue-specific effector pathway engagement.\",\n      \"evidence\": \"GPR116 KO mouse NK cell assays with pathway inhibitors; hepatocyte-specific KO/OE with ferroptosis marker assays\",\n      \"pmids\": [\"36895027\", \"37266730\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NK cell role based on single lab\", \"Ferroptosis role based on single lab with no independent replication\", \"Direct Gαq coupling in hepatocytes not biochemically confirmed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"GPR116 was identified as a hydrostatic pressure mechanosensor in liver sinusoidal endothelial cells and was further shown to maintain glomerular endothelial integrity, regulate breast cancer immune evasion via RhoA–ERK–C/EBPβ–MMP8, and participate in pancreatic delta cell somatostatin release and beta cell mass maintenance.\",\n      \"evidence\": \"Hepatic hypertension-on-a-chip with GPR116 silencing and cirrhotic mouse validation; glomerular EC KO with EM and gene expression; breast cancer cell KD with ERK/RhoA assays and tumor models; pancreatic KO with secretion assays and islet morphometry; β-arrestin1–BiP co-IP in hepatocytes\",\n      \"pmids\": [\"41237250\", \"38844335\", \"38937435\", \"38228886\", \"39001944\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanosensor activation mechanism (conformational change under pressure) not elucidated\", \"Whether glomerular and hepatic endothelial roles share common signaling axis unknown\", \"Pancreatic delta cell signaling pathway not characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of tethered agonist–receptor activation (no high-resolution structure exists), the hierarchy and tissue specificity of multiple reported ligands (SP-D, FNDC4, mechanical force), and whether G-protein versus β-arrestin biased signaling is determined by ligand identity, tissue context, or receptor processing state.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cryo-EM or crystal structure of GPR116\", \"Ligand competition or cooperativity between SP-D, FNDC4, and mechanical stimuli not tested\", \"Biased agonism determinants unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [7, 11, 13, 21]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [2, 3, 21]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [14, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 7, 11, 13]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 7, 12, 14, 15]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2, 7, 11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 9, 15]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [12, 23]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GNAQ\",\n      \"GNA11\",\n      \"ARRB1\",\n      \"SFTPD\",\n      \"FNDC4\",\n      \"CREB1\",\n      \"RHOA\",\n      \"RAC1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}