{"gene":"GFRAL","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2017,"finding":"GFRAL is the high-affinity receptor for GDF15; GDF15 binds GFRAL and genetic deletion of GFRAL abrogates GDF15-induced decreases in food intake and body weight in mice, establishing GFRAL as the bona fide receptor mediating metabolic effects of GDF15.","method":"Radioligand binding assay, GFRAL knockout mice, recombinant GDF15 administration","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — independently replicated by three separate groups in the same journal issue, using KO mice, binding assays, and in vivo functional readouts","pmids":["28846097","28846098","28846099"],"is_preprint":false},{"year":2017,"finding":"GFRAL requires association with the coreceptor RET to elicit intracellular signaling in response to GDF15 stimulation; GDF15-induced cell signaling requires the GFRAL-RET interaction.","method":"Cell-based signaling assays, co-receptor requirement demonstrated by loss-of-function and reconstitution experiments","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — independently replicated by three groups using cell signaling assays and genetic models","pmids":["28846097","28846098","28846099"],"is_preprint":false},{"year":2017,"finding":"Gfral mRNA is expressed specifically in neurons of the area postrema and nucleus of the solitary tract in the hindbrain (mouse, rat, monkey, human), and not in peripheral tissues, indicating GDF15-GFRAL regulation of food intake operates via a central mechanism.","method":"In situ hybridization, mRNA expression profiling, immunohistochemistry across species","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — replicated across three independent groups with in situ hybridization and expression profiling in multiple species","pmids":["28846097","28846098","28846099"],"is_preprint":false},{"year":2017,"finding":"Diet-induced obesity and insulin resistance are exacerbated in GFRAL-deficient mice, indicating a homeostatic role for GFRAL in metabolism.","method":"Gfral knockout mouse model, high-fat diet challenge, metabolic phenotyping","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean KO with defined metabolic phenotype, single lab but multiple metabolic readouts","pmids":["28846097"],"is_preprint":false},{"year":2005,"finding":"GFRAL (GRAL-A) protein localizes predominantly to the plasma membrane; overexpression of GFRAL-A protected PC12 cells and cultured hippocampal neurons from serum starvation-induced apoptosis, associated with inhibition of the JNK signaling pathway.","method":"Subcellular fractionation/immunofluorescence for localization; cell viability assays and JNK pathway analysis for neuroprotective function","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, overexpression system, pathway association without full mechanistic dissection","pmids":["16086688"],"is_preprint":false},{"year":2005,"finding":"GFRAL (GRAL) has two splice variants: full-length GRAL-A (2080 bp mRNA) and short GRAL-B (1833 bp mRNA), with primary CNS expression in adult mouse; GRAL-A shares ~30% amino acid identity with GFRα-3.","method":"cDNA cloning, sequence analysis, Northern blot/RT-PCR expression profiling","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab characterization of transcript variants and sequence homology","pmids":["16086688"],"is_preprint":false},{"year":2020,"finding":"Antagonistic monoclonal antibody 3P10 targeting GFRAL inhibits RET signaling by preventing the GDF15-driven interaction of RET with GFRAL on the cell surface; activation of the GFRAL-RET pathway induces expression of lipid metabolism genes in adipose tissue; peripheral chemical sympathectomy and loss of adipose triglyceride lipase protect mice from GDF15-induced weight loss, revealing a peripheral sympathetic axis by which GDF15 elicits lipolytic responses independently of anorexia.","method":"Antagonistic monoclonal antibody, RET signaling assays, sympathectomy, ATGL knockout mice, gene expression profiling in adipose tissue","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (antibody inhibition, genetic KO, sympathectomy, transcriptomics) in a single rigorous study","pmids":["32661391"],"is_preprint":false},{"year":2021,"finding":"Artificial activation of GFRAL-expressing neurons inhibited feeding, decreased gastric emptying, and promoted conditioned taste aversion (CTA). GFRAL neurons most strongly innervate the parabrachial nucleus targeting CGRP-expressing neurons, and silencing CGRPPBN neurons abrogated the aversive and anorexic effects of GDF-15, placing GFRAL neurons upstream of CGRPPBN in an aversive pathway.","method":"Chemogenetic activation (DREADD) of GFRAL neurons, conditional Gfral mice, TRAP-seq, CTA assay, CGRPPBN neuron silencing","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via conditional KO and chemogenetics with multiple orthogonal functional readouts, single lab","pmids":["33593916"],"is_preprint":false},{"year":2019,"finding":"Localized AAV-shRNA knockdown of GFRAL in the area postrema and nucleus of the solitary tract of mice commencing high-fat diet caused increased body weight and adiposity proportional to the degree of GFRAL knockdown, confirming AP/NTS as the major CNS site of GDF15 action.","method":"AAV-shRNA regional knockdown, quantitative immunohistochemistry, metabolic phenotyping","journal":"International journal of obesity (2005)","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — regional KO with defined metabolic phenotype and dose-response, single lab","pmids":["31152154"],"is_preprint":false},{"year":2022,"finding":"Membrane-bound MT1-MMP (MMP14) proteolytically inactivates GFRAL in GFRAL+ neurons; overnutrition-induced obesity increased MT1-MMP activation which suppressed GDF15-GFRAL signaling. Genetic ablation of MT1-MMP specifically in GFRAL+ neurons restored GFRAL expression and reduced weight gain. Depletion of GFRAL abolished the anti-obesity effects of MT1-MMP inhibition.","method":"Cell-specific conditional KO (MT1-MMP in GFRAL+ neurons), proteolytic cleavage assay, GFRAL KO epistasis, in vivo obesity models","journal":"Nature metabolism","confidence":"High","confidence_rationale":"Tier 2 / Moderate — epistasis with two conditional KO models, proteolytic assay, and in vivo functional readouts in a single rigorous study","pmids":["35177851"],"is_preprint":false},{"year":2024,"finding":"Direct acute infusion of GDF15 into the area postrema increased intravenous glucose tolerance and insulin sensitivity and lowered hepatic glucose production independently of food intake, weight, and plasma insulin; knockdown of GFRAL in the area postrema negated these effects and also negated metformin-induced glucose tolerance improvement.","method":"Intracranial infusion, GFRAL knockdown in area postrema, hyperinsulinemic-euglycemic clamp, conscious unrestrained rat model","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct CNS infusion with regional KD and clamp studies, single lab","pmids":["38064571"],"is_preprint":false},{"year":2024,"finding":"Cell-specific acute activation of GFRAL+ neurons caused hypothermia, torpor-like state, release of stress hormones, shift from glucose to lipid oxidation, impaired insulin sensitivity and glucose tolerance, decreased skeletal muscle glucose uptake, but augmented visceral fat glucose uptake.","method":"Chemogenetic and optogenetic activation of GFRAL+ neurons, metabolomics, transcriptomics, glucose uptake assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal activation methods with defined physiological readouts, single lab","pmids":["38507407"],"is_preprint":false},{"year":2022,"finding":"In a mouse model of muscle-specific mitochondrial dysfunction, GFRAL is required for systemic energy metabolism via daytime-restricted anorexia; GFRAL signaling mediates hypothalamic corticotropin-releasing hormone induction (without elevated corticosterone) and governs anxiety-like behavior.","method":"GFRAL KO crossed with muscle mitochondrial dysfunction mouse model, behavioral assays, hypothalamic gene expression analysis","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic epistasis with defined behavioral and endocrine phenotypes, single lab","pmids":["36271504"],"is_preprint":false},{"year":2022,"finding":"A neutralizing monoclonal antibody to GFRAL prevented cisplatin-induced decrease in wheel running (fatigue behavior) in mice, demonstrating that the GDF15/GFRAL axis mediates chemotherapy-induced fatigue.","method":"Anti-GFRAL neutralizing antibody, voluntary wheel running assay, mGDF15-Fc administration","journal":"Brain, behavior, and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pharmacological blockade with behavioral readout, single lab","pmids":["36427806"],"is_preprint":false},{"year":2020,"finding":"In endothelial cells, MIC-1/GDF15 promotes angiogenesis via MEK/ERK- and PI3K/Akt-dependent pathways; siRNA knockdown of GFRAL abrogated these MIC-1 signaling events, identifying GFRAL as an endothelial cell receptor for MIC-1.","method":"siRNA knockdown of GFRAL in endothelial cells, angiogenesis assays, signaling pathway analysis (MEK/ERK, PI3K/Akt)","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, siRNA knockdown with functional angiogenesis assays; GFRAL peripheral expression contested by other studies","pmids":["33151561"],"is_preprint":false},{"year":2020,"finding":"In pancreatic ductal adenocarcinoma cells, GFRAL mediates GDF-15-induced tumor cell proliferation and metastasis; overexpression of GFRAL in pancreatic cancer cells enhanced GDF-15 biological effects.","method":"GFRAL overexpression, GDF-15 knockdown, xenotransplantation in nude mice, in vitro proliferation assays","journal":"Aging","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, overexpression/KD in cancer cell lines; GFRAL peripheral expression is contested by other papers in this corpus","pmids":["33201838"],"is_preprint":false},{"year":2023,"finding":"GDF-15 inhibits ADP-induced human platelet aggregation through binding to GFRAL on platelets and signaling via the GFRAL/RET complex, inhibiting AKT and ERK activation; immunoprecipitation confirmed GFRAL as the binding partner of GDF-15 on platelets.","method":"Platelet aggregation assay, receptor microarray, immunoprecipitation, ERK/AKT pathway analysis, RET agonist/inhibitor experiments","journal":"Biomolecules","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, peripheral GFRAL expression on platelets contested by other studies in this corpus; mechanistic pathway established by Co-IP and signaling assays","pmids":["38254638"],"is_preprint":false},{"year":2023,"finding":"A peptide antagonist of GFRAL (GRASP) developed by library screening binds GFRAL (confirmed by surface plasmon resonance and flow cytometry) and blocks GDF15-mediated RET recruitment; in vivo GRASP attenuated GDF15-induced nausea and anorexia in rats.","method":"Peptide library screen, surface plasmon resonance, flow cytometry, in vivo rat anorexia model","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vitro binding (SPR) plus in vivo functional validation, single lab","pmids":["37506293"],"is_preprint":false},{"year":2023,"finding":"GDF15 C-terminal peptide fragments bind the extracellular domain of GFRAL (SPOT arrays) and inhibit GFRAL activity in cells expressing the GFRAL/RET receptor complex in the micromolar range, identifying the C-terminus of GDF15 as the GFRAL-binding region.","method":"SPOT peptide arrays, solid-phase peptide synthesis, functional cell assays with GFRAL/RET-expressing cells","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — peptide binding mapped to GFRAL extracellular domain with functional cell assays, single lab","pmids":["37495041"],"is_preprint":false},{"year":2024,"finding":"BDNFmNTS neurons in the medial nucleus of the tractus solitarius are required downstream of GFRAL/GLP1R neurons for weight-reducing actions of GDF15; acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation.","method":"Genetic ablation of BDNFmNTS neurons, chemogenetic activation, GDF15 and Exendin-4 treatment, metabolic phenotyping","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with chemogenetics and pharmacological tools, multiple functional readouts, single lab","pmids":["39737892"],"is_preprint":false},{"year":2026,"finding":"GDF15 suppresses autoimmune T cell responses through GFRAL activation on brainstem neurons, leading to β-adrenergic signaling and norepinephrine synthesis in the spleen, which decreases integrin expression on T cells required for blood-brain barrier transmigration; chemogenetic activation of GFRAL+ neurons recapitulated these neuroimmune effects.","method":"GDF15 KO mice, recombinant GDF15, neuronal gene delivery, chemogenetic activation of GFRAL+ neurons, norepinephrine measurement, integrin expression analysis, preclinical MS models","journal":"Nature immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (genetic KO, chemogenetics, gene delivery, pharmacology) with defined neuroimmune mechanism, single lab","pmids":["41540266"],"is_preprint":false},{"year":2025,"finding":"Bicyclic peptide tandems mimicking homodimeric GDF15 bind GFRAL with picomolar affinity and inhibit GDF15-GFRAL protein-protein interaction to prevent RET-induced intracellular signaling, as confirmed in a functional cell signaling assay; structural data guided conversion of monomeric hits to tandem molecules.","method":"Phage display, structure-guided design, binding affinity measurement, functional cell signaling assay, pharmacokinetic analysis","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — structure-guided design with functional validation in cell assay, single lab","pmids":["41066664"],"is_preprint":false},{"year":2024,"finding":"GFRAL expression, assessed using Gfral:eGFP reporter mice, single-molecule FISH, and scRNA-seq, is overwhelmingly restricted to the brainstem AP/NTS; Gfral-labelled cells were not reliably detected in other brain regions or peripheral tissues using three independent detection methods.","method":"Gfral:eGFP reporter mice, single-molecule fluorescence in situ hybridization (smFISH), scRNA-seq of human tissues","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — three orthogonal detection methods across mouse and human tissues, directly contradicts reports of peripheral GFRAL expression","pmids":["39608751"],"is_preprint":false},{"year":2025,"finding":"In melanoma cells, CAF-derived GDF15 binds GFRAL, promoting RET phosphorylation and downstream signaling that increases tumor cell stemness and secretion of CCL18 and TGF-β, inducing macrophage M2 polarization; confirmed by co-immunoprecipitation.","method":"Co-immunoprecipitation, chromatin immunoprecipitation, luciferase reporter assay, lentiviral transfection, flow cytometry, recombinant protein rescue, Cre-loxP KO mice","journal":"Journal for immunotherapy of cancer","confidence":"Low","confidence_rationale":"Tier 3 / Weak — peripheral GFRAL expression on melanoma cells contested by PMID 39608751; mechanistic Co-IP data from single lab","pmids":["40555562"],"is_preprint":false},{"year":2024,"finding":"GFRAL silencing by shRNA in the area postrema/NTS of ALS model mice (hSOD1G93A) induced weight gain, reduced adipose tissue wasting, ameliorated motor function and muscle atrophy, and prolonged survival; microglial depletion reduced brainstem GDF15 expression and lipolytic gene expression in adipose tissue, suggesting microglial involvement in mediating GFRAL-dependent effects.","method":"shRNA regional knockdown, PLX5622 microglial depletion, body weight and motor function assays, lipolytic gene expression analysis","journal":"Brain, behavior, and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — regional KD with functional phenotypes including survival, plus microglial depletion experiment; single lab","pmids":["39672239"],"is_preprint":false}],"current_model":"GFRAL is a plasma membrane-localized, brainstem-restricted (area postrema/NTS) receptor that binds GDF15 with high affinity and requires recruitment of the coreceptor RET to initiate intracellular signaling, activating downstream pathways (ERK, AKT, RET kinase); this GFRAL-RET complex mediates GDF15-induced suppression of food intake and body weight via aversive neural circuits projecting to CGRP+ parabrachial and BDNF+ mNTS neurons, drives a peripheral sympathetic-lipolytic axis in adipose tissue, modulates glucose homeostasis through area postrema neurons, and is negatively regulated by MT1-MMP-mediated proteolytic cleavage of GFRAL in GFRAL+ neurons during obesity."},"narrative":{"mechanistic_narrative":"GFRAL is the high-affinity receptor for GDF15 and the molecular gateway through which this cytokine controls feeding, energy balance, and aversive physiology [PMID:28846097, PMID:28846098, PMID:28846099]. Ligand binding occurs through the GFRAL extracellular domain, which engages the C-terminus of GDF15 [PMID:37495041], but GFRAL itself has no intrinsic signaling capacity: productive responses require GDF15-driven recruitment of the coreceptor RET to GFRAL, which then activates ERK and AKT signaling [PMID:28846097, PMID:28846098, PMID:28846099, PMID:32661391]. Expression of GFRAL is overwhelmingly restricted to neurons of the brainstem area postrema and nucleus of the solitary tract, with no reliable detection in peripheral tissues across multiple species and orthogonal methods [PMID:28846097, PMID:28846098, PMID:28846099, PMID:39608751]; regional knockdown in the AP/NTS recapitulates and worsens diet-induced obesity, establishing this circuit as the principal site of GDF15 action [PMID:31152154, PMID:28846097]. Activated GFRAL neurons project most strongly to CGRP-expressing parabrachial neurons to drive conditioned taste aversion and anorexia, and act through BDNF-expressing mNTS neurons to reduce food intake and promote fatty acid oxidation [PMID:33593916, PMID:39737892]. Beyond central anorexia, the GFRAL-RET axis engages a peripheral sympathetic-lipolytic program in adipose tissue that contributes to weight loss independently of feeding [PMID:32661391], modulates glucose homeostasis and insulin sensitivity via area postrema neurons (including effects required for metformin action) [PMID:38064571], and broadly regulates systemic energy metabolism, body temperature, and aversive/anxiety-like states [PMID:38507407, PMID:36271504]. GFRAL signaling is negatively regulated by membrane-bound MT1-MMP (MMP14), which proteolytically inactivates GFRAL in GFRAL+ neurons during overnutrition, dampening GDF15 responsiveness in obesity [PMID:35177851]. The pathway mediates pathological states including chemotherapy-induced fatigue [PMID:36427806], and GFRAL is an actively pursued therapeutic target, with antagonist antibodies, peptides, and bicyclic mimetics that block GDF15-driven RET recruitment [PMID:32661391, PMID:37506293, PMID:41066664].","teleology":[{"year":2017,"claim":"Establishing the orphan receptor for the metabolic cytokine GDF15 was the central question; identifying GFRAL as the high-affinity GDF15 receptor that is genetically required for GDF15-induced anorexia defined the entire axis.","evidence":"Radioligand binding, GFRAL knockout mice, and recombinant GDF15 administration, replicated across three groups","pmids":["28846097","28846098","28846099"],"confidence":"High","gaps":["Did not resolve the structural basis of binding","Intracellular signaling mechanism not yet defined at this stage"]},{"year":2017,"claim":"Because GFRAL lacks an obvious signaling module, how it transmits a signal was unknown; demonstrating an obligatory requirement for the coreceptor RET established the two-component receptor architecture.","evidence":"Cell-based signaling assays with loss-of-function and reconstitution","pmids":["28846097","28846098","28846099"],"confidence":"High","gaps":["Stoichiometry and assembly order of the GFRAL-RET complex not defined","Downstream effectors only partially mapped"]},{"year":2017,"claim":"Where GDF15 acts was unresolved; restricting GFRAL expression to brainstem AP/NTS neurons across species localized the entire GDF15 metabolic effect to a central circuit.","evidence":"In situ hybridization and expression profiling across mouse, rat, monkey, and human","pmids":["28846097","28846098","28846099"],"confidence":"High","gaps":["Did not map downstream neural projections","Did not exclude low-level expression detectable only by more sensitive methods"]},{"year":2017,"claim":"Whether GFRAL had a homeostatic role beyond pharmacological GDF15 was unknown; KO mice on high-fat diet showed exacerbated obesity and insulin resistance, defining an endogenous metabolic function.","evidence":"Gfral knockout mice with high-fat diet challenge and metabolic phenotyping","pmids":["28846097"],"confidence":"High","gaps":["Did not establish the endogenous GDF15 source driving this tone","Circuit-level basis not addressed"]},{"year":2019,"claim":"To confirm AP/NTS as the operative CNS site rather than an expression correlate, regional knockdown was required; localized AAV-shRNA in AP/NTS produced dose-dependent weight gain.","evidence":"AAV-shRNA regional knockdown with quantitative IHC and metabolic phenotyping","pmids":["31152154"],"confidence":"Medium","gaps":["Single lab","Downstream circuit not addressed"]},{"year":2020,"claim":"Whether GDF15-induced weight loss was purely anorexic was unresolved; an antagonist antibody plus sympathectomy and ATGL-KO revealed a peripheral sympathetic-lipolytic axis acting independently of food intake.","evidence":"Antagonistic mAb 3P10, chemical sympathectomy, ATGL knockout, and adipose transcriptomics","pmids":["32661391"],"confidence":"High","gaps":["Neural relay from GFRAL neurons to sympathetic output not delineated","Relative contribution of lipolysis vs anorexia to total weight loss not quantified"]},{"year":2021,"claim":"The downstream circuit for aversion and anorexia was unknown; chemogenetic and epistasis experiments placed GFRAL neurons upstream of CGRP parabrachial neurons in an aversive pathway.","evidence":"DREADD activation of GFRAL neurons, conditional Gfral mice, TRAP-seq, CTA, and CGRP-PBN silencing","pmids":["33593916"],"confidence":"High","gaps":["Neurotransmitter identity of GFRAL neuron output not defined","Did not address parallel non-aversive branches"]},{"year":2022,"claim":"How GFRAL responsiveness is downregulated in obesity was unknown; identifying MT1-MMP as a proteolytic inactivator of GFRAL revealed a negative-regulatory mechanism that blunts GDF15 signaling during overnutrition.","evidence":"GFRAL+ neuron-specific MT1-MMP conditional KO, proteolytic cleavage assay, and GFRAL-KO epistasis","pmids":["35177851"],"confidence":"High","gaps":["Cleavage site and fragment fate not defined","Trigger linking overnutrition to MT1-MMP activation not resolved"]},{"year":2022,"claim":"Whether GFRAL mediates pathological wasting and behavior beyond diet was open; muscle-mitochondrial-dysfunction and chemotherapy models showed GFRAL drives anorexia, CRH induction, anxiety-like behavior, and fatigue.","evidence":"GFRAL KO crosses, behavioral assays, hypothalamic gene expression, and anti-GFRAL neutralizing antibody with wheel-running","pmids":["36271504","36427806"],"confidence":"Medium","gaps":["Circuit basis of CRH induction and fatigue not mapped","Single lab per phenotype"]},{"year":2023,"claim":"The ligand-receptor binding interface and tractability for antagonism were undefined; peptide mapping localized binding to the GDF15 C-terminus/GFRAL extracellular domain and yielded functional antagonists.","evidence":"SPOT/peptide arrays, SPR, flow cytometry, and in vivo rat anorexia models for GRASP and C-terminal fragments","pmids":["37495041","37506293"],"confidence":"Medium","gaps":["High-resolution structure of the complex not solved here","Potency in the micromolar range for some agents"]},{"year":2024,"claim":"Whether GDF15-GFRAL controls glucose homeostasis independently of weight was unresolved; AP infusion and regional knockdown showed GFRAL is required for GDF15- and metformin-driven glucose tolerance improvements.","evidence":"Intracranial GDF15 infusion, AP-specific GFRAL knockdown, and hyperinsulinemic-euglycemic clamp in rats","pmids":["38064571"],"confidence":"Medium","gaps":["Efferent pathway controlling hepatic glucose production not defined","Single lab"]},{"year":2024,"claim":"The breadth of physiology controlled by GFRAL neurons and their downstream relay were incompletely defined; activation studies and BDNF-mNTS epistasis revealed thermoregulatory/torpor effects and a required BDNF-mNTS node.","evidence":"Chemogenetic/optogenetic activation of GFRAL+ neurons with metabolomics; genetic ablation and activation of BDNF-mNTS neurons","pmids":["38507407","39737892"],"confidence":"Medium","gaps":["Integration of CGRP-PBN and BDNF-mNTS branches not reconciled","Single lab per study"]},{"year":2024,"claim":"Whether reported peripheral GFRAL expression is real was contested; three orthogonal detection methods confirmed expression is overwhelmingly restricted to brainstem AP/NTS and not peripheral tissues.","evidence":"Gfral:eGFP reporter mice, smFISH, and scRNA-seq across mouse and human tissues","pmids":["39608751"],"confidence":"High","gaps":["Cannot fully exclude rare or transient peripheral expression below detection","Does not adjudicate every individual peripheral claim"]},{"year":2025,"claim":"Whether the central GFRAL axis intersects systemic immunity and disease was unknown; brainstem GFRAL activation was shown to suppress autoimmune T cell responses via splenic β-adrenergic signaling, and regional knockdown improved ALS outcomes.","evidence":"GDF15 KO, chemogenetic GFRAL+ activation, norepinephrine/integrin analysis in MS models; AP/NTS shRNA knockdown with microglial depletion in hSOD1G93A mice","pmids":["41540266","39672239"],"confidence":"Medium","gaps":["Efferent neuroimmune relay incompletely defined","Single lab per disease model"]},{"year":2025,"claim":"Therapeutic blockade of the GDF15-GFRAL interface remained to be optimized; structure-guided bicyclic peptide tandems mimicking dimeric GDF15 bound GFRAL at picomolar affinity and blocked RET recruitment.","evidence":"Phage display, structure-guided design, affinity measurement, and functional cell signaling assay","pmids":["41066664"],"confidence":"Medium","gaps":["In vivo efficacy not established in this study","Single lab"]},{"year":null,"claim":"How the GFRAL-RET complex is assembled at atomic resolution and how its divergent outputs (CGRP-PBN aversion, BDNF-mNTS anorexia, sympathetic lipolysis, glucose control, neuroimmune signaling) are routed through distinct GFRAL neuron subpopulations remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of the ternary GDF15-GFRAL-RET complex","Molecular logic dividing aversive vs metabolic vs immune branches unknown","Identity and connectivity of GFRAL neuron subtypes not fully resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,1,18]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,4,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,6]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,10,11]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[2,7,19]}],"complexes":["GFRAL-RET coreceptor complex"],"partners":["GDF15","RET","MMP14"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6UXV0","full_name":"GDNF family receptor alpha-like","aliases":[],"length_aa":394,"mass_kda":44.5,"function":"Brainstem-restricted receptor for GDF15 hormone, which triggers an aversive response, characterized by nausea, vomiting, and/or loss of appetite in response to various stresses (PubMed:28846097, PubMed:28846098, PubMed:28846099, PubMed:28953886, PubMed:36630958). The aversive response is both required to reduce continuing exposure to those stresses at the time of exposure and to promote avoidance behavior in the future (PubMed:28846097, PubMed:28846098, PubMed:28846099, PubMed:28953886, PubMed:36630958). The GDF15-GFRAL aversive response is triggered by stresses, such as anticancer drugs (camptothecin or cisplatin), cancers or drugs such as metformin (PubMed:32661391). Upon interaction with its ligand, GDF15, mediates the GDF15-induced autophosphorylation and activation of the RET tyrosine kinase receptor, leading to activation of MAPK- and AKT- signaling pathways (PubMed:31535977, PubMed:32661391). Ligand-binding activates GFRAL-expressing neurons localized in the area postrema and nucleus tractus solitarius of the brainstem (By similarity). The GDF15-GFRAL signal induces expression of genes involved in metabolism, such as lipid metabolism in adipose tissues (PubMed:32661391)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q6UXV0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GFRAL","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GFRAL","total_profiled":1310},"omim":[{"mim_id":"617837","title":"GDNF FAMILY RECEPTOR ALPHA-LIKE PROTEIN; GFRAL","url":"https://www.omim.org/entry/617837"},{"mim_id":"605312","title":"GROWTH/DIFFERENTIATION FACTOR 15; GDF15","url":"https://www.omim.org/entry/605312"},{"mim_id":"604446","title":"PHOSPHOTRIESTERASE-RELATED PROTEIN; PTER","url":"https://www.omim.org/entry/604446"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"},{"location":"Actin filaments","reliability":"Additional"},{"location":"Focal adhesion sites","reliability":"Additional"}],"tissue_specificity":"Not detected","tissue_distribution":"Not detected","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GFRAL"},"hgnc":{"alias_symbol":["GRAL","UNQ9356","bA360D14.1"],"prev_symbol":["C6orf144"]},"alphafold":{"accession":"Q6UXV0","domains":[{"cath_id":"-","chopping":"25-98","consensus_level":"high","plddt":85.0464,"start":25,"end":98},{"cath_id":"1.10.220","chopping":"128-207","consensus_level":"medium","plddt":88.3697,"start":128,"end":207},{"cath_id":"1.10.220.110","chopping":"215-324","consensus_level":"medium","plddt":92.6548,"start":215,"end":324}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXV0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXV0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXV0-F1-predicted_aligned_error_v6.png","plddt_mean":76.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GFRAL","jax_strain_url":"https://www.jax.org/strain/search?query=GFRAL"},"sequence":{"accession":"Q6UXV0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UXV0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UXV0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXV0"}},"corpus_meta":[{"pmid":"28846097","id":"PMC_28846097","title":"GFRAL 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GDF15 binds GFRAL and genetic deletion of GFRAL abrogates GDF15-induced decreases in food intake and body weight in mice, establishing GFRAL as the bona fide receptor mediating metabolic effects of GDF15.\",\n      \"method\": \"Radioligand binding assay, GFRAL knockout mice, recombinant GDF15 administration\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independently replicated by three separate groups in the same journal issue, using KO mice, binding assays, and in vivo functional readouts\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GFRAL requires association with the coreceptor RET to elicit intracellular signaling in response to GDF15 stimulation; GDF15-induced cell signaling requires the GFRAL-RET interaction.\",\n      \"method\": \"Cell-based signaling assays, co-receptor requirement demonstrated by loss-of-function and reconstitution experiments\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independently replicated by three groups using cell signaling assays and genetic models\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Gfral mRNA is expressed specifically in neurons of the area postrema and nucleus of the solitary tract in the hindbrain (mouse, rat, monkey, human), and not in peripheral tissues, indicating GDF15-GFRAL regulation of food intake operates via a central mechanism.\",\n      \"method\": \"In situ hybridization, mRNA expression profiling, immunohistochemistry across species\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — replicated across three independent groups with in situ hybridization and expression profiling in multiple species\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Diet-induced obesity and insulin resistance are exacerbated in GFRAL-deficient mice, indicating a homeostatic role for GFRAL in metabolism.\",\n      \"method\": \"Gfral knockout mouse model, high-fat diet challenge, metabolic phenotyping\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined metabolic phenotype, single lab but multiple metabolic readouts\",\n      \"pmids\": [\"28846097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GFRAL (GRAL-A) protein localizes predominantly to the plasma membrane; overexpression of GFRAL-A protected PC12 cells and cultured hippocampal neurons from serum starvation-induced apoptosis, associated with inhibition of the JNK signaling pathway.\",\n      \"method\": \"Subcellular fractionation/immunofluorescence for localization; cell viability assays and JNK pathway analysis for neuroprotective function\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, overexpression system, pathway association without full mechanistic dissection\",\n      \"pmids\": [\"16086688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GFRAL (GRAL) has two splice variants: full-length GRAL-A (2080 bp mRNA) and short GRAL-B (1833 bp mRNA), with primary CNS expression in adult mouse; GRAL-A shares ~30% amino acid identity with GFRα-3.\",\n      \"method\": \"cDNA cloning, sequence analysis, Northern blot/RT-PCR expression profiling\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab characterization of transcript variants and sequence homology\",\n      \"pmids\": [\"16086688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Antagonistic monoclonal antibody 3P10 targeting GFRAL inhibits RET signaling by preventing the GDF15-driven interaction of RET with GFRAL on the cell surface; activation of the GFRAL-RET pathway induces expression of lipid metabolism genes in adipose tissue; peripheral chemical sympathectomy and loss of adipose triglyceride lipase protect mice from GDF15-induced weight loss, revealing a peripheral sympathetic axis by which GDF15 elicits lipolytic responses independently of anorexia.\",\n      \"method\": \"Antagonistic monoclonal antibody, RET signaling assays, sympathectomy, ATGL knockout mice, gene expression profiling in adipose tissue\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (antibody inhibition, genetic KO, sympathectomy, transcriptomics) in a single rigorous study\",\n      \"pmids\": [\"32661391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Artificial activation of GFRAL-expressing neurons inhibited feeding, decreased gastric emptying, and promoted conditioned taste aversion (CTA). GFRAL neurons most strongly innervate the parabrachial nucleus targeting CGRP-expressing neurons, and silencing CGRPPBN neurons abrogated the aversive and anorexic effects of GDF-15, placing GFRAL neurons upstream of CGRPPBN in an aversive pathway.\",\n      \"method\": \"Chemogenetic activation (DREADD) of GFRAL neurons, conditional Gfral mice, TRAP-seq, CTA assay, CGRPPBN neuron silencing\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via conditional KO and chemogenetics with multiple orthogonal functional readouts, single lab\",\n      \"pmids\": [\"33593916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Localized AAV-shRNA knockdown of GFRAL in the area postrema and nucleus of the solitary tract of mice commencing high-fat diet caused increased body weight and adiposity proportional to the degree of GFRAL knockdown, confirming AP/NTS as the major CNS site of GDF15 action.\",\n      \"method\": \"AAV-shRNA regional knockdown, quantitative immunohistochemistry, metabolic phenotyping\",\n      \"journal\": \"International journal of obesity (2005)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — regional KO with defined metabolic phenotype and dose-response, single lab\",\n      \"pmids\": [\"31152154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Membrane-bound MT1-MMP (MMP14) proteolytically inactivates GFRAL in GFRAL+ neurons; overnutrition-induced obesity increased MT1-MMP activation which suppressed GDF15-GFRAL signaling. Genetic ablation of MT1-MMP specifically in GFRAL+ neurons restored GFRAL expression and reduced weight gain. Depletion of GFRAL abolished the anti-obesity effects of MT1-MMP inhibition.\",\n      \"method\": \"Cell-specific conditional KO (MT1-MMP in GFRAL+ neurons), proteolytic cleavage assay, GFRAL KO epistasis, in vivo obesity models\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with two conditional KO models, proteolytic assay, and in vivo functional readouts in a single rigorous study\",\n      \"pmids\": [\"35177851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Direct acute infusion of GDF15 into the area postrema increased intravenous glucose tolerance and insulin sensitivity and lowered hepatic glucose production independently of food intake, weight, and plasma insulin; knockdown of GFRAL in the area postrema negated these effects and also negated metformin-induced glucose tolerance improvement.\",\n      \"method\": \"Intracranial infusion, GFRAL knockdown in area postrema, hyperinsulinemic-euglycemic clamp, conscious unrestrained rat model\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct CNS infusion with regional KD and clamp studies, single lab\",\n      \"pmids\": [\"38064571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cell-specific acute activation of GFRAL+ neurons caused hypothermia, torpor-like state, release of stress hormones, shift from glucose to lipid oxidation, impaired insulin sensitivity and glucose tolerance, decreased skeletal muscle glucose uptake, but augmented visceral fat glucose uptake.\",\n      \"method\": \"Chemogenetic and optogenetic activation of GFRAL+ neurons, metabolomics, transcriptomics, glucose uptake assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal activation methods with defined physiological readouts, single lab\",\n      \"pmids\": [\"38507407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In a mouse model of muscle-specific mitochondrial dysfunction, GFRAL is required for systemic energy metabolism via daytime-restricted anorexia; GFRAL signaling mediates hypothalamic corticotropin-releasing hormone induction (without elevated corticosterone) and governs anxiety-like behavior.\",\n      \"method\": \"GFRAL KO crossed with muscle mitochondrial dysfunction mouse model, behavioral assays, hypothalamic gene expression analysis\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic epistasis with defined behavioral and endocrine phenotypes, single lab\",\n      \"pmids\": [\"36271504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A neutralizing monoclonal antibody to GFRAL prevented cisplatin-induced decrease in wheel running (fatigue behavior) in mice, demonstrating that the GDF15/GFRAL axis mediates chemotherapy-induced fatigue.\",\n      \"method\": \"Anti-GFRAL neutralizing antibody, voluntary wheel running assay, mGDF15-Fc administration\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pharmacological blockade with behavioral readout, single lab\",\n      \"pmids\": [\"36427806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In endothelial cells, MIC-1/GDF15 promotes angiogenesis via MEK/ERK- and PI3K/Akt-dependent pathways; siRNA knockdown of GFRAL abrogated these MIC-1 signaling events, identifying GFRAL as an endothelial cell receptor for MIC-1.\",\n      \"method\": \"siRNA knockdown of GFRAL in endothelial cells, angiogenesis assays, signaling pathway analysis (MEK/ERK, PI3K/Akt)\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, siRNA knockdown with functional angiogenesis assays; GFRAL peripheral expression contested by other studies\",\n      \"pmids\": [\"33151561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In pancreatic ductal adenocarcinoma cells, GFRAL mediates GDF-15-induced tumor cell proliferation and metastasis; overexpression of GFRAL in pancreatic cancer cells enhanced GDF-15 biological effects.\",\n      \"method\": \"GFRAL overexpression, GDF-15 knockdown, xenotransplantation in nude mice, in vitro proliferation assays\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, overexpression/KD in cancer cell lines; GFRAL peripheral expression is contested by other papers in this corpus\",\n      \"pmids\": [\"33201838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GDF-15 inhibits ADP-induced human platelet aggregation through binding to GFRAL on platelets and signaling via the GFRAL/RET complex, inhibiting AKT and ERK activation; immunoprecipitation confirmed GFRAL as the binding partner of GDF-15 on platelets.\",\n      \"method\": \"Platelet aggregation assay, receptor microarray, immunoprecipitation, ERK/AKT pathway analysis, RET agonist/inhibitor experiments\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, peripheral GFRAL expression on platelets contested by other studies in this corpus; mechanistic pathway established by Co-IP and signaling assays\",\n      \"pmids\": [\"38254638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A peptide antagonist of GFRAL (GRASP) developed by library screening binds GFRAL (confirmed by surface plasmon resonance and flow cytometry) and blocks GDF15-mediated RET recruitment; in vivo GRASP attenuated GDF15-induced nausea and anorexia in rats.\",\n      \"method\": \"Peptide library screen, surface plasmon resonance, flow cytometry, in vivo rat anorexia model\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vitro binding (SPR) plus in vivo functional validation, single lab\",\n      \"pmids\": [\"37506293\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GDF15 C-terminal peptide fragments bind the extracellular domain of GFRAL (SPOT arrays) and inhibit GFRAL activity in cells expressing the GFRAL/RET receptor complex in the micromolar range, identifying the C-terminus of GDF15 as the GFRAL-binding region.\",\n      \"method\": \"SPOT peptide arrays, solid-phase peptide synthesis, functional cell assays with GFRAL/RET-expressing cells\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — peptide binding mapped to GFRAL extracellular domain with functional cell assays, single lab\",\n      \"pmids\": [\"37495041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"BDNFmNTS neurons in the medial nucleus of the tractus solitarius are required downstream of GFRAL/GLP1R neurons for weight-reducing actions of GDF15; acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation.\",\n      \"method\": \"Genetic ablation of BDNFmNTS neurons, chemogenetic activation, GDF15 and Exendin-4 treatment, metabolic phenotyping\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with chemogenetics and pharmacological tools, multiple functional readouts, single lab\",\n      \"pmids\": [\"39737892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GDF15 suppresses autoimmune T cell responses through GFRAL activation on brainstem neurons, leading to β-adrenergic signaling and norepinephrine synthesis in the spleen, which decreases integrin expression on T cells required for blood-brain barrier transmigration; chemogenetic activation of GFRAL+ neurons recapitulated these neuroimmune effects.\",\n      \"method\": \"GDF15 KO mice, recombinant GDF15, neuronal gene delivery, chemogenetic activation of GFRAL+ neurons, norepinephrine measurement, integrin expression analysis, preclinical MS models\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (genetic KO, chemogenetics, gene delivery, pharmacology) with defined neuroimmune mechanism, single lab\",\n      \"pmids\": [\"41540266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Bicyclic peptide tandems mimicking homodimeric GDF15 bind GFRAL with picomolar affinity and inhibit GDF15-GFRAL protein-protein interaction to prevent RET-induced intracellular signaling, as confirmed in a functional cell signaling assay; structural data guided conversion of monomeric hits to tandem molecules.\",\n      \"method\": \"Phage display, structure-guided design, binding affinity measurement, functional cell signaling assay, pharmacokinetic analysis\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — structure-guided design with functional validation in cell assay, single lab\",\n      \"pmids\": [\"41066664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GFRAL expression, assessed using Gfral:eGFP reporter mice, single-molecule FISH, and scRNA-seq, is overwhelmingly restricted to the brainstem AP/NTS; Gfral-labelled cells were not reliably detected in other brain regions or peripheral tissues using three independent detection methods.\",\n      \"method\": \"Gfral:eGFP reporter mice, single-molecule fluorescence in situ hybridization (smFISH), scRNA-seq of human tissues\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — three orthogonal detection methods across mouse and human tissues, directly contradicts reports of peripheral GFRAL expression\",\n      \"pmids\": [\"39608751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In melanoma cells, CAF-derived GDF15 binds GFRAL, promoting RET phosphorylation and downstream signaling that increases tumor cell stemness and secretion of CCL18 and TGF-β, inducing macrophage M2 polarization; confirmed by co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation, chromatin immunoprecipitation, luciferase reporter assay, lentiviral transfection, flow cytometry, recombinant protein rescue, Cre-loxP KO mice\",\n      \"journal\": \"Journal for immunotherapy of cancer\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — peripheral GFRAL expression on melanoma cells contested by PMID 39608751; mechanistic Co-IP data from single lab\",\n      \"pmids\": [\"40555562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GFRAL silencing by shRNA in the area postrema/NTS of ALS model mice (hSOD1G93A) induced weight gain, reduced adipose tissue wasting, ameliorated motor function and muscle atrophy, and prolonged survival; microglial depletion reduced brainstem GDF15 expression and lipolytic gene expression in adipose tissue, suggesting microglial involvement in mediating GFRAL-dependent effects.\",\n      \"method\": \"shRNA regional knockdown, PLX5622 microglial depletion, body weight and motor function assays, lipolytic gene expression analysis\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — regional KD with functional phenotypes including survival, plus microglial depletion experiment; single lab\",\n      \"pmids\": [\"39672239\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GFRAL is a plasma membrane-localized, brainstem-restricted (area postrema/NTS) receptor that binds GDF15 with high affinity and requires recruitment of the coreceptor RET to initiate intracellular signaling, activating downstream pathways (ERK, AKT, RET kinase); this GFRAL-RET complex mediates GDF15-induced suppression of food intake and body weight via aversive neural circuits projecting to CGRP+ parabrachial and BDNF+ mNTS neurons, drives a peripheral sympathetic-lipolytic axis in adipose tissue, modulates glucose homeostasis through area postrema neurons, and is negatively regulated by MT1-MMP-mediated proteolytic cleavage of GFRAL in GFRAL+ neurons during obesity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GFRAL is the high-affinity receptor for GDF15 and the molecular gateway through which this cytokine controls feeding, energy balance, and aversive physiology [#0]. Ligand binding occurs through the GFRAL extracellular domain, which engages the C-terminus of GDF15 [#18], but GFRAL itself has no intrinsic signaling capacity: productive responses require GDF15-driven recruitment of the coreceptor RET to GFRAL, which then activates ERK and AKT signaling [#1, #6]. Expression of GFRAL is overwhelmingly restricted to neurons of the brainstem area postrema and nucleus of the solitary tract, with no reliable detection in peripheral tissues across multiple species and orthogonal methods [#2, #22]; regional knockdown in the AP/NTS recapitulates and worsens diet-induced obesity, establishing this circuit as the principal site of GDF15 action [#8, #3]. Activated GFRAL neurons project most strongly to CGRP-expressing parabrachial neurons to drive conditioned taste aversion and anorexia, and act through BDNF-expressing mNTS neurons to reduce food intake and promote fatty acid oxidation [#7, #19]. Beyond central anorexia, the GFRAL-RET axis engages a peripheral sympathetic-lipolytic program in adipose tissue that contributes to weight loss independently of feeding [#6], modulates glucose homeostasis and insulin sensitivity via area postrema neurons (including effects required for metformin action) [#10], and broadly regulates systemic energy metabolism, body temperature, and aversive/anxiety-like states [#11, #12]. GFRAL signaling is negatively regulated by membrane-bound MT1-MMP (MMP14), which proteolytically inactivates GFRAL in GFRAL+ neurons during overnutrition, dampening GDF15 responsiveness in obesity [#9]. The pathway mediates pathological states including chemotherapy-induced fatigue [#13], and GFRAL is an actively pursued therapeutic target, with antagonist antibodies, peptides, and bicyclic mimetics that block GDF15-driven RET recruitment [#6, #17, #21].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Establishing the orphan receptor for the metabolic cytokine GDF15 was the central question; identifying GFRAL as the high-affinity GDF15 receptor that is genetically required for GDF15-induced anorexia defined the entire axis.\",\n      \"evidence\": \"Radioligand binding, GFRAL knockout mice, and recombinant GDF15 administration, replicated across three groups\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of binding\", \"Intracellular signaling mechanism not yet defined at this stage\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Because GFRAL lacks an obvious signaling module, how it transmits a signal was unknown; demonstrating an obligatory requirement for the coreceptor RET established the two-component receptor architecture.\",\n      \"evidence\": \"Cell-based signaling assays with loss-of-function and reconstitution\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and assembly order of the GFRAL-RET complex not defined\", \"Downstream effectors only partially mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Where GDF15 acts was unresolved; restricting GFRAL expression to brainstem AP/NTS neurons across species localized the entire GDF15 metabolic effect to a central circuit.\",\n      \"evidence\": \"In situ hybridization and expression profiling across mouse, rat, monkey, and human\",\n      \"pmids\": [\"28846097\", \"28846098\", \"28846099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map downstream neural projections\", \"Did not exclude low-level expression detectable only by more sensitive methods\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Whether GFRAL had a homeostatic role beyond pharmacological GDF15 was unknown; KO mice on high-fat diet showed exacerbated obesity and insulin resistance, defining an endogenous metabolic function.\",\n      \"evidence\": \"Gfral knockout mice with high-fat diet challenge and metabolic phenotyping\",\n      \"pmids\": [\"28846097\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the endogenous GDF15 source driving this tone\", \"Circuit-level basis not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"To confirm AP/NTS as the operative CNS site rather than an expression correlate, regional knockdown was required; localized AAV-shRNA in AP/NTS produced dose-dependent weight gain.\",\n      \"evidence\": \"AAV-shRNA regional knockdown with quantitative IHC and metabolic phenotyping\",\n      \"pmids\": [\"31152154\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Downstream circuit not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether GDF15-induced weight loss was purely anorexic was unresolved; an antagonist antibody plus sympathectomy and ATGL-KO revealed a peripheral sympathetic-lipolytic axis acting independently of food intake.\",\n      \"evidence\": \"Antagonistic mAb 3P10, chemical sympathectomy, ATGL knockout, and adipose transcriptomics\",\n      \"pmids\": [\"32661391\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Neural relay from GFRAL neurons to sympathetic output not delineated\", \"Relative contribution of lipolysis vs anorexia to total weight loss not quantified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The downstream circuit for aversion and anorexia was unknown; chemogenetic and epistasis experiments placed GFRAL neurons upstream of CGRP parabrachial neurons in an aversive pathway.\",\n      \"evidence\": \"DREADD activation of GFRAL neurons, conditional Gfral mice, TRAP-seq, CTA, and CGRP-PBN silencing\",\n      \"pmids\": [\"33593916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Neurotransmitter identity of GFRAL neuron output not defined\", \"Did not address parallel non-aversive branches\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"How GFRAL responsiveness is downregulated in obesity was unknown; identifying MT1-MMP as a proteolytic inactivator of GFRAL revealed a negative-regulatory mechanism that blunts GDF15 signaling during overnutrition.\",\n      \"evidence\": \"GFRAL+ neuron-specific MT1-MMP conditional KO, proteolytic cleavage assay, and GFRAL-KO epistasis\",\n      \"pmids\": [\"35177851\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cleavage site and fragment fate not defined\", \"Trigger linking overnutrition to MT1-MMP activation not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Whether GFRAL mediates pathological wasting and behavior beyond diet was open; muscle-mitochondrial-dysfunction and chemotherapy models showed GFRAL drives anorexia, CRH induction, anxiety-like behavior, and fatigue.\",\n      \"evidence\": \"GFRAL KO crosses, behavioral assays, hypothalamic gene expression, and anti-GFRAL neutralizing antibody with wheel-running\",\n      \"pmids\": [\"36271504\", \"36427806\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Circuit basis of CRH induction and fatigue not mapped\", \"Single lab per phenotype\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The ligand-receptor binding interface and tractability for antagonism were undefined; peptide mapping localized binding to the GDF15 C-terminus/GFRAL extracellular domain and yielded functional antagonists.\",\n      \"evidence\": \"SPOT/peptide arrays, SPR, flow cytometry, and in vivo rat anorexia models for GRASP and C-terminal fragments\",\n      \"pmids\": [\"37495041\", \"37506293\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"High-resolution structure of the complex not solved here\", \"Potency in the micromolar range for some agents\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Whether GDF15-GFRAL controls glucose homeostasis independently of weight was unresolved; AP infusion and regional knockdown showed GFRAL is required for GDF15- and metformin-driven glucose tolerance improvements.\",\n      \"evidence\": \"Intracranial GDF15 infusion, AP-specific GFRAL knockdown, and hyperinsulinemic-euglycemic clamp in rats\",\n      \"pmids\": [\"38064571\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Efferent pathway controlling hepatic glucose production not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The breadth of physiology controlled by GFRAL neurons and their downstream relay were incompletely defined; activation studies and BDNF-mNTS epistasis revealed thermoregulatory/torpor effects and a required BDNF-mNTS node.\",\n      \"evidence\": \"Chemogenetic/optogenetic activation of GFRAL+ neurons with metabolomics; genetic ablation and activation of BDNF-mNTS neurons\",\n      \"pmids\": [\"38507407\", \"39737892\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Integration of CGRP-PBN and BDNF-mNTS branches not reconciled\", \"Single lab per study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Whether reported peripheral GFRAL expression is real was contested; three orthogonal detection methods confirmed expression is overwhelmingly restricted to brainstem AP/NTS and not peripheral tissues.\",\n      \"evidence\": \"Gfral:eGFP reporter mice, smFISH, and scRNA-seq across mouse and human tissues\",\n      \"pmids\": [\"39608751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cannot fully exclude rare or transient peripheral expression below detection\", \"Does not adjudicate every individual peripheral claim\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Whether the central GFRAL axis intersects systemic immunity and disease was unknown; brainstem GFRAL activation was shown to suppress autoimmune T cell responses via splenic β-adrenergic signaling, and regional knockdown improved ALS outcomes.\",\n      \"evidence\": \"GDF15 KO, chemogenetic GFRAL+ activation, norepinephrine/integrin analysis in MS models; AP/NTS shRNA knockdown with microglial depletion in hSOD1G93A mice\",\n      \"pmids\": [\"41540266\", \"39672239\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Efferent neuroimmune relay incompletely defined\", \"Single lab per disease model\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Therapeutic blockade of the GDF15-GFRAL interface remained to be optimized; structure-guided bicyclic peptide tandems mimicking dimeric GDF15 bound GFRAL at picomolar affinity and blocked RET recruitment.\",\n      \"evidence\": \"Phage display, structure-guided design, affinity measurement, and functional cell signaling assay\",\n      \"pmids\": [\"41066664\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo efficacy not established in this study\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the GFRAL-RET complex is assembled at atomic resolution and how its divergent outputs (CGRP-PBN aversion, BDNF-mNTS anorexia, sympathetic lipolysis, glucose control, neuroimmune signaling) are routed through distinct GFRAL neuron subpopulations remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the ternary GDF15-GFRAL-RET complex\", \"Molecular logic dividing aversive vs metabolic vs immune branches unknown\", \"Identity and connectivity of GFRAL neuron subtypes not fully resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 1, 18]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 4, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 10, 11]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 7, 19]}\n    ],\n    \"complexes\": [\"GFRAL-RET coreceptor complex\"],\n    \"partners\": [\"GDF15\", \"RET\", \"MMP14\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}