{"gene":"GLP1R","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2020,"finding":"Cryo-EM structures revealed that the non-peptide GLP-1R agonist PF 06882961 has a binding site that substantially overlaps with GLP-1's binding site, whereas CHU-128 adopts a unique binding mode with a more open receptor conformation at the extracellular face. Extensive water-mediated hydrogen bond networks explain why PF 06882961 but not CHU-128 closely mimics GLP-1 pharmacological properties.","method":"High-resolution cryo-EM structural determination combined with pharmacological assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures plus functional pharmacological assays in a single rigorous study","pmids":["33027691"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures and molecular dynamics simulations of GLP-1R bound to four peptide agonists (GLP-1, oxyntomodulin, exendin-4, exendin-P5) demonstrated that distinctions in peptide N-terminal interactions and dynamics with the transmembrane domain are reciprocally associated with differences in allosteric coupling to G proteins; transient interactions with residues at the base of the binding cavity correlate with enhanced kinetics for G protein activation.","method":"Cryo-EM, molecular dynamics simulations, receptor mutagenesis, pharmacological assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (cryo-EM, MD, mutagenesis, pharmacology) in a single rigorous study","pmids":["35013280"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of semaglutide- and taspoglutide-bound GLP-1R–Gs protein complexes revealed similar peptide interactions to GLP-1 but different motions within the receptor and bound peptides, providing molecular determinants of differential peptide engagement and signaling profiles.","method":"Cryo-EM with 3D variability analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structures with conformational analysis, single lab","pmids":["34260945"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of small-molecule agonists Boc5 and WB4-24 bound to GLP-1R–Gs revealed that one arm of each compound inserts deeply into the orthosteric binding pocket overlapping with GLP-1 residues A8–D15, while other arms extend into TM1-TM7, TM1-TM2, and TM2-TM3 clefts, creating a unique conformation that confers peptidomimetic agonism and biased signaling.","method":"Cryo-EM structural determination of receptor–ligand–Gs complexes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structures with pharmacological validation, single lab","pmids":["35561211"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structures of GLP-1R in complex with Gs protein and three dual GLP-1R/GCGR agonists (peptide 15, MEDI0382, SAR425899) identified key residues for ligand recognition and dual agonism; side chain orientations within the first three residues of the ligand determine receptor selectivity, and ECL1 conformation of GLP-1R is reshaped by dual agonists relative to GCGR.","method":"Cryo-EM structural determination combined with published pharmacological data","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structures with functional pharmacological support, single lab","pmids":["37549266"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of ligand-free GLP-1R in complex with Gs protein (without cognate peptide) showed that Gs protein alone directly opens the intracellular binding cavity and rewires the extracellular orthosteric pocket; the extracellular portion of GLP-1R adopts a conformation close to the active state even without ligand, distinct from GCGR and GIPR.","method":"Cryo-EM structural determination of ligand-free receptor–Gs complexes","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structures compared across three related receptors, single lab","pmids":["38346960"],"is_preprint":false},{"year":2018,"finding":"Crystallographic studies of an anti-human GIPR antibody showed it displaced GIP and bound GIPR using the same conserved hydrophobic residues as GIP, and combined GLP-1R agonists with GIPR antagonism produced enhanced weight loss in preclinical models.","method":"Crystallography plus in vivo pharmacological studies (DIO mice and NHP)","journal":"Science translational medicine","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structure reported for GIPR, GLP-1R agonist combination data is in vivo only, single lab","pmids":["30567927"],"is_preprint":false},{"year":2021,"finding":"GLP-1R undergoes an atypical β-arrestin-independent mode of internalization; GRK2/3/4/5/6 knockout experiments using CRISPR/Cas9 demonstrated that GLP-1R internalisation is GRK-dependent, β-arrestin 1 recruitment is more sensitive to GRK knockout than β-arrestin 2 recruitment, and no single GRK isoform exclusively drives these pathways.","method":"CRISPR/Cas9 endogenous GRK and β-arrestin knockouts, quantitative trafficking assays","journal":"Biochemical pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — CRISPR KO of multiple GRK isoforms with quantitative rescue experiments, two orthogonal readouts","pmids":["38461904"],"is_preprint":false},{"year":2021,"finding":"GRK2 associates with GLP-1R upon agonist stimulation (demonstrated by nanoBRET in β-cell lines), and GRK2 protein and kinase activity are required for subsequent β-arrestin recruitment to GLP-1R. Reduced GRK2 levels in vivo enhanced early-phase insulin release stimulated by GLP-1R agonists without affecting late-phase secretion, correlating with an increased readily releasable pool of insulin granules.","method":"NanoBRET, GRK2 hemizygous mouse model, isolated pancreatic islet assays, β-cell line experiments","journal":"BMC biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — nanoBRET protein interaction assay, genetic model, and isolated islet functional assays, multiple orthogonal methods","pmids":["33658023"],"is_preprint":false},{"year":2023,"finding":"Adult β-cell-specific β-arrestin 2 knockout mice showed impaired acute GLP-1R agonist (exendin-4, semaglutide, tirzepatide) responses but improved responses 6 hours post-injection. The acute cAMP impairment was attributed to enhanced β-arrestin 1 and phosphodiesterase 4 activity compensating for β-arrestin 2 loss; reduced desensitization co-occurred with impaired GLP-1R recycling/lysosomal targeting, increased trans-Golgi network signaling, and reduced GLP-1R ubiquitination.","method":"Adult β-cell-specific β-arrestin 2 conditional KO mice, cAMP assays, trafficking assays, in vivo glucose tolerance","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple mechanistic readouts (cAMP, trafficking, ubiquitination, recycling), single lab","pmids":["37134170"],"is_preprint":false},{"year":2022,"finding":"GLP-1R peptide agonist dissociation kinetics (Koff), but not association kinetics (Kon), were positively correlated with onset of receptor–G protein coupling, onset of cAMP production, and duration of cAMP signaling, mechanistically linking ligand–receptor interaction kinetics to downstream signaling onset.","method":"Quantitative kinetic binding assays, BRET-based G protein engagement assays, cAMP measurement for a series of peptide agonists","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal kinetic and signaling assays, single lab","pmids":["35300966"],"is_preprint":false},{"year":2023,"finding":"Using 15 signaling biosensors across 4 cellular compartments, GLP-1R was shown to activate distinct signaling neighborhoods in a pathway- and compartment-selective manner; comparative structure analysis, time-lapse microscopy, and phosphoproteomics revealed unique signaling signatures for different GLP-1R agonists at the level of receptor conformation, functional selectivity, and location bias, linking specific signaling neighborhoods to clinical adverse event profiles.","method":"Biosensor panel (15 pathways, 4 compartments), structure analysis, time-lapse microscopy, phosphoproteomics","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biosensors, phosphoproteomics, microscopy), novel mechanistic framework with clinical correlation","pmids":["37813859"],"is_preprint":false},{"year":2021,"finding":"Small-molecule positive allosteric modulators (PAMs) of GLP-1R were identified that bind a cryptic pocket formed by the cytoplasmic half of TM3, TM5, and TM6; molecular dynamics simulations and mutagenesis studies indicated the PAM enlarges the orthosteric pocket to facilitate GLP-1 binding, and signaling assays characterized probe-dependent signaling profiles.","method":"Molecular dynamics simulations, mutagenesis, signaling assays","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis and MD combined with functional assays, single lab","pmids":["34570476"],"is_preprint":false},{"year":2019,"finding":"Selective reduction of Glp1r expression within Phox2b-Cre neurons (autonomic/vagal neurons) impaired glucose homeostasis and gastric emptying and attenuated GLP-1R agonist-induced weight loss; widespread neural Glp1r loss in Wnt1-Cre2 mice preserved glucoregulatory actions of GLP-1R agonists, demonstrating that Phox2b+ neurons are the critical neural substrate for physiological GLP-1R-mediated metabolic control.","method":"Cell-type-specific conditional Glp1r knockout (Phox2b-Cre, Wnt1-Cre2), glucose tolerance tests, gastric emptying measurements","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO in two distinct neural populations with multiple metabolic readouts, single lab","pmids":["31189118"],"is_preprint":false},{"year":2024,"finding":"In vivo two-photon imaging of hindbrain GLP1R neurons showed that area postrema (AP) GLP1R neurons are broadly responsive to both nutritive and aversive stimuli, while nucleus of the solitary tract (NTS) GLP1R neurons are biased towards nutritive stimuli. Selective chemogenetic/optogenetic manipulation demonstrated that NTS-GLP1R neuron activation triggers satiety without aversion, while AP-GLP1R activation triggers aversion with food intake reduction. Anatomical tracing showed NTS-GLP1R and AP-GLP1R project to different downstream brain regions.","method":"In vivo two-photon calcium imaging, chemogenetics, optogenetics, anatomical circuit tracing","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (imaging, chemogenetics, optogenetics, anatomy) with dissociable circuit logic, high-impact journal","pmids":["38987598"],"is_preprint":false},{"year":2022,"finding":"GLP1R is expressed in carotid body chemosensory cells in rat and human; targeted GLP1R agonist administration to the carotid body lowered basal discharge and attenuated chemoreflex-evoked blood pressure and sympathetic responses; hyperglycemia-induced peripheral chemoreflex sensitization and sympathetic overactivity were abolished by GLP1R activation in the carotid body.","method":"RNA-seq, molecular characterization, in situ/in vivo carotid body functional assays with targeted drug delivery","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — localization with direct functional consequence demonstrated in situ and in vivo, multiple methods","pmids":["35100822"],"is_preprint":false},{"year":2022,"finding":"GLP-1R signaling in gut intraepithelial lymphocytes (IELs) is required for the full effects of GLP-1R agonists on gut microbiota composition and selectively restrains local and systemic T cell-induced (but not LPS-induced) inflammation; the mechanism involves suppression of IEL effector functions via dampening of proximal T cell receptor signaling in a protein kinase A-dependent manner.","method":"IEL-specific GLP-1R conditional knockout mice, microbiota analysis, in vivo inflammatory models, PKA inhibitor experiments","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with mechanistic pathway identification (PKA-dependence) and multiple orthogonal experimental readouts","pmids":["36027914"],"is_preprint":false},{"year":2015,"finding":"GLP-1R signaling controls mucosal expansion of the small bowel and colon via a mechanism requiring Fgf7 (fibroblast growth factor 7) but independent of EGF or IGF1 receptors; exendin-4 increased Fgf7 expression in colonic polyps, and exendin-4 failed to increase intestinal growth in Fgf7-null mice.","method":"Glp1r-/- mice, Fgf7-/- mice, exendin-4 treatment, Apc(Min/+) mouse model, gene expression analysis","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis using multiple KO models with specific mechanistic readout, two independent labs confirmed pathway","pmids":["25738454"],"is_preprint":false},{"year":2023,"finding":"GLP-1R agonist liraglutide directly activates POMC neurons in vivo via GLP-1R expression in POMC neurons, requiring a downstream mixed cation channel comprising TRPC5 subunits; it also indirectly upregulates excitatory input to POMC neurons from glutamatergic cells (also requiring TRPC5), and inhibits NPY/AgRP neurons indirectly through activation of K-ATP and TRPC5 channels in GABAergic neurons.","method":"Neuron-specific transgenic mouse models, patch-clamp electrophysiology, in vivo fiber photometry","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Moderate — electrophysiology and fiber photometry in GLP-1R-specific conditional models, multiple orthogonal methods","pmids":["34626854"],"is_preprint":false},{"year":2023,"finding":"GLP-1R-positive (GLP-1R+) neurons in the lateral septum (LS) mediate anorectic and weight-loss effects of liraglutide; these neurons are activated by liraglutide, their activity rapidly decreases during naturalistic feeding, chemogenetic activation suppresses feeding, and targeted GLP-1R knockdown in the LS (but not hypothalamus) substantially attenuated liraglutide's ability to inhibit feeding and reduce body weight.","method":"Chemogenetics (DREADD), GLP-1R knockdown in specific brain regions, fiber photometry, behavioral analysis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple in vivo tools (chemogenetics, region-specific knockdown, photometry) demonstrating site-specific necessity, single lab","pmids":["39225090"],"is_preprint":false},{"year":2024,"finding":"dLS GLP-1R neurons project GABAergic axons to the lateral hypothalamic area (LHA); chemogenetic inhibition of dLSGLP-1R neurons or the dLSGLP-1R→LHA pathway promotes food intake; optogenetic stimulation of dLSGLP-1R→LHA terminals in the LHA rapidly suppresses feeding; GLP-1R agonist exendin-4 enhances dLSGLP-1R→LHA GABA release.","method":"Channelrhodopsin-assisted circuit mapping, chemogenetics, optogenetics, electrophysiology in Glp1r-ires-Cre mice","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal circuit-mapping tools (optogenetics, chemogenetics, electrophysiology), single lab","pmids":["38763494"],"is_preprint":false},{"year":2023,"finding":"GABAergic hypothalamic neurons co-expressing Glp1r and Lepr (LepRbGlp1r neurons) are required for leptin-mediated suppression of food intake; ablating Lepr from these neurons caused hyperphagic obesity; restoration of Glp1r expression specifically in LepRb neurons on an otherwise Glp1r-null background was sufficient to permit food intake suppression by the GLP1R agonist liraglutide.","method":"Cell-type-specific Cre-lox conditional KO and re-expression, single-nucleus RNA-seq, behavioral metabolic phenotyping","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO and cell-type-specific rescue experiments, replicated across multiple genetic models","pmids":["37581939"],"is_preprint":false},{"year":2020,"finding":"Exendin-4 activates the GLP1R–PKA–PPARγ-dependent phosphatases PTEN and PTP1B, which inhibit key kinases within both EGFR and STAT6 signaling cascades to restore FOXA2 expression and normalize airway mucus production in COPD and cystic fibrosis airway cells.","method":"In vitro airway cell assays, COPD/CF disease cell lines, in vivo mouse lung model, pathway inhibitor experiments","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway dissected with multiple inhibitors and in vitro/in vivo models, single lab","pmids":["32034274"],"is_preprint":false},{"year":2022,"finding":"GLP-1 regulates skeletal muscle remodeling and exercise endurance via GLP-1R signaling-mediated phosphorylation of AMPK; AMPK knockdown reversed the effects of GLP-1R activation on glucose uptake, type I fiber formation, and mitochondrial respiration in vitro.","method":"AAV-mediated GLP-1 overexpression in muscle, in vitro AMPK knockdown, ex vivo mitochondrial respiration assays","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic overexpression model plus AMPK knockdown epistasis, single lab, in vitro mechanistic confirmation","pmids":["35636559"],"is_preprint":false},{"year":2023,"finding":"GLP-1R activation inhibits pulmonary fibrosis by disrupting the interaction between NLRP3 inflammasome and PFKFB3-driven glycolysis in lung fibroblasts, subsequently preventing lactate-mediated histone lactylation that drives pro-fibrotic gene expression; GLP-1R activation also inhibited p300-mediated histone lactylation in exogenous lactate-treated fibroblasts.","method":"In vitro lung fibroblast assays, RNA-seq, ChIP-qPCR for histone lactylation, cell metabolism assays, mouse silica fibrosis model","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP-qPCR, RNA-seq, metabolic assays, in vivo) in single lab","pmids":["39434134"],"is_preprint":false},{"year":2023,"finding":"GLP1R loss-of-function variants that reduce cell surface expression are associated with impaired glucose control and increased adiposity; 60 GLP1R variants were functionally profiled across four signaling pathways revealing a diversity of phenotypes including defective cell surface expression, pathway-specific gain and loss of function; defective insulin secretion of LoF variants can be rescued by allosteric GLP1R ligands or high concentrations of exendin-4/semaglutide in INS-1 cells.","method":"Functional profiling of 60 variants across 4 signaling pathways, rescue experiments with allosteric ligands in INS-1 cells, genetic association in UK Biobank","journal":"Nature metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic variant profiling across multiple signaling pathways with cell-based rescue, replicated in large human cohort","pmids":["37709961"],"is_preprint":false},{"year":2023,"finding":"GLP-1R agonist liraglutide in gut IELs suppresses feeding via protein kinase A-dependent dampening of proximal T cell receptor signaling, reducing effector functions of intraepithelial lymphocytes; this mechanism is specifically required for restraining T cell-induced but not LPS-induced inflammation.","method":"Conditional GLP-1R KO in IELs, PKA inhibitor experiments, T cell functional assays","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with mechanistic PKA pathway validation and multiple inflammatory readouts","pmids":["36027914"],"is_preprint":false},{"year":2021,"finding":"GLP-1R shows increased cell surface levels, internalization, degradation, and higher endosomal versus plasma membrane cAMP activity compared to GIPR in pancreatic beta cells; GIPR is instead associated with increased plasma membrane recycling, reduced desensitization, and enhanced downstream signal amplification.","method":"Direct comparison of surface expression, trafficking (internalization/recycling/degradation), and spatiotemporal cAMP signaling assays in pancreatic beta cells","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays (surface expression, trafficking, signaling) in single lab comparing two receptors directly","pmids":["36774542"],"is_preprint":false},{"year":2021,"finding":"The MafA target gene PPP1R1A is expressed in β-cells, and PPP1R1A silencing in INS1 cells impairs GLP-1R-mediated amplification of glucose-stimulated insulin secretion, PKA-target protein phosphorylation, and mitochondrial coupling efficiency, demonstrating PPP1R1A as a downstream effector of GLP-1R-PKA signaling in β-cells.","method":"siRNA knockdown in INS1 β-cells, GSIS assays, PKA phosphorylation assays, mitochondrial function assays, human islet RNA correlation","journal":"Metabolism: clinical and experimental","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple functional readouts, supported by human islet correlative data, single lab","pmids":["33631146"],"is_preprint":false},{"year":2024,"finding":"GLP-1R activation by semaglutide suppresses VTA dopamine (VTADA) neuron responsiveness during food consumption, opposing hedonic eating; mice recovered palatable food appetite and VTADA activity during repeated semaglutide treatment, which was reversed by consumption-triggered VTADA neuron inhibition, demonstrating that the hedonic eating circuit opposes GLP-1R-mediated appetite reduction.","method":"Photometry-calibrated optogenetics, in vivo fiber photometry, behavioral feeding assays","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — calibrated optogenetic manipulation and photometry in a circuit-level dissection, single lab","pmids":["40146831"],"is_preprint":false},{"year":2024,"finding":"BDNFmNTS neurons in the medial nucleus of the tractus solitarius are downstream of GFRAL/GLP1R neurons; these BDNF neurons are required for weight-reducing actions of both GDF15 and the GLP1RA exendin-4, and acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation.","method":"Mouse genetic models, chemogenetics, in vivo metabolic measurements","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chemogenetic gain- and loss-of-function in vivo with metabolic readouts, single lab","pmids":["39737892"],"is_preprint":false},{"year":2024,"finding":"LepRGlp1r neurons in the dorsomedial hypothalamus mediate the food intake-suppressing and body weight-reducing effects of a GLP-1R/LepR dual agonist; ablating Lepr from Glp1r-expressing neurons abrogated dual agonist efficacy on food intake, while reactivating Glp1r in Lepr neurons on a Glp1r-null background was sufficient to permit the food intake and body weight suppression.","method":"Conditional KO and re-expression mouse models (LeprGlp1rKO, Glp1rLeprRe), in vivo pharmacology with dual agonist","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — paired conditional KO and rescue experiments demonstrating necessity and sufficiency, single lab","pmids":["39630884"],"is_preprint":false},{"year":2024,"finding":"Both CNS GIPR and CNS GLP-1R are required for maximal weight loss by a GIPR-Ab/GLP-1 peptide-antibody conjugate; the conjugate is detected in circumventricular organs and activates c-FOS in downstream appetite-regulating brain regions; dulaglutide (GLP-1R agonist alone) achieves greater weight loss in CNS GIPR KO mice.","method":"CNS GIPR conditional KO mice, dulaglutide + GIPR-Ab combination experiments, c-FOS immunostaining, drug biodistribution","journal":"Nature metabolism","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple pharmacological probes, in vivo c-FOS circuit mapping, single lab","pmids":["40301582"],"is_preprint":false},{"year":2014,"finding":"GLP-1R knockdown in human RPE cells (ARPE-19) increased intracellular ROS generation and activated p53-mediated Bax promoter activity and ER stress signaling; ER stress-mediated p53 expression was regulated upstream by ROS, as antioxidant treatment and Prx1 overexpression attenuated GLP-1R knockdown-induced ER stress and p53 expression.","method":"siRNA knockdown, ROS measurement, ER stress signaling assays, Bax promoter reporter, antioxidant rescue experiments","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple mechanistic readouts and rescue experiments, single lab","pmids":["25483438"],"is_preprint":false},{"year":2022,"finding":"GLP-1R signaling modulates colonic goblet cell number, epithelial integrity, energy metabolism, and survival; GF GLP-1R KO mice developed enlarged ceca, reduced goblet cells, colonocyte energy deprivation, increased ER stress, mitochondrial fragmentation, elevated oxygen levels, and loss of stemness; restoring energy via Western-style diet or microbiota colonization normalized these phenotypes, demonstrating GLP-1R has a non-incretin role in colonic epithelial maintenance during energy deprivation.","method":"GF GLP-1R KO mouse model, histology, gene expression, intestinal organoid stemness assays, dietary and microbiota rescue experiments","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO model with multiple mechanistic readouts and bidirectional rescue experiments (diet and microbiota), single lab","pmids":["38521185"],"is_preprint":false},{"year":2023,"finding":"GLP1R overexpression in endometrial carcinoma cells promotes apoptosis and activates the cAMP/PKA signaling pathway, while inhibiting cell proliferation, invasion, and migration; these effects were abrogated by PKA knockdown, placing GLP1R upstream of cAMP/PKA in this signaling axis.","method":"GLP1R overexpression vector, PKA siRNA, ELISA for cAMP, Western blot, in vitro cell behavior assays, mouse xenograft","journal":"Journal of clinical laboratory analysis","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression/KD experiments with cAMP/PKA pathway dissection, epistasis by PKA knockdown, single lab","pmids":["35989517"],"is_preprint":false},{"year":2020,"finding":"Loureirin B binds to GLP-1R (demonstrated by surface plasmon resonance and spectroscopy) and promotes insulin secretion in Ins-1 cells through GLP-1R; siRNA-mediated GLP-1R knockdown reduced the insulin secretion-promoting effect of Loureirin B.","method":"Molecular docking, surface plasmon resonance, spectroscopy, GLP-1R siRNA knockdown, insulin secretion assay","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SPR binding assay plus siRNA knockdown functional confirmation, single lab","pmids":["33300675"],"is_preprint":false},{"year":2025,"finding":"GLP-1R agonists increase CaMKK2-AMPK signaling in neurons, which reduces BACE1-mediated cleavage of APP and Aβ generation; GLP-1R agonists also increase AMPK activity in microglia, inhibiting neuroinflammation and promoting Aβ phagocytosis.","method":"AD model mouse in vivo experiments, biochemical pathway analysis (CaMKK2-AMPK-BACE1 axis), microglial functional assays","journal":"Nature aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway identification in vivo with multiple cell-type readouts, single lab","pmids":["40394225"],"is_preprint":false}],"current_model":"GLP-1R is a class B1 G protein-coupled receptor that, upon binding peptide or small-molecule agonists in a site overlapping with GLP-1's binding pocket, undergoes conformational changes in its transmembrane and extracellular domains that drive Gs-protein coupling and cAMP/PKA signaling; receptor internalization is β-arrestin-independent but GRK-dependent, β-arrestins modulate desensitization and endosomal signaling, and ligand dissociation kinetics (Koff) govern the onset and duration of G protein activation; in pancreatic β-cells, GLP-1R-cAMP-PKA signaling amplifies glucose-stimulated insulin secretion; in the brain, distinct GLP-1R-expressing neuronal populations (NTS vs. AP hindbrain neurons, lateral septal neurons, hypothalamic LepRb/Glp1r neurons) mediate separable satiety and aversive effects; and GLP-1R signaling in peripheral tissues including gut intraepithelial lymphocytes, carotid body chemosensory cells, and colonic epithelium subserves immunomodulatory, sympathoinhibitory, and epithelial maintenance functions, respectively."},"narrative":{"mechanistic_narrative":"GLP-1R is a class B G protein-coupled receptor that converts peptide and small-molecule agonist binding into Gs-coupled cAMP/PKA signaling, governing metabolic, neuronal, immune, and epithelial processes [PMID:35013280, PMID:36027914]. Cryo-EM structures of the receptor bound to GLP-1, oxyntomodulin, exendin-4, dual GLP-1R/GCGR agonists, and diverse small molecules show that agonists engage an orthosteric pocket and that distinctions in peptide N-terminal interactions and dynamics with the transmembrane domain are reciprocally linked to allosteric coupling efficiency to Gs [PMID:35013280, PMID:37549266]; non-peptide agonists such as PF 06882961 occupy a site overlapping GLP-1's, while others adopt distinct poses conferring biased signaling [PMID:33027691, PMID:35561211], and Gs protein alone can pre-open the intracellular cavity and rewire the orthosteric pocket toward an active state even without ligand [PMID:38346960]. Ligand dissociation kinetics (Koff), not association, dictate the onset and duration of G protein coupling and cAMP output, and agonists activate distinct compartmentalized signaling neighborhoods that map onto clinical effect profiles [PMID:35300966, PMID:37813859]. GLP-1R internalization is atypical: it is GRK-dependent but β-arrestin-independent, with GRK2 required for β-arrestin recruitment, and β-arrestin 2 tuning desensitization, recycling, ubiquitination, and the balance of plasma-membrane versus endosomal/trans-Golgi signaling [PMID:38461904, PMID:33658023, PMID:37134170]. In pancreatic β-cells, GLP-1R–cAMP–PKA signaling amplifies glucose-stimulated insulin secretion through downstream effectors including PPP1R1A, and human loss-of-function variants that reduce surface expression impair glucose control and increase adiposity but can be rescued by allosteric ligands [PMID:33631146, PMID:37709961]. In the nervous system, anatomically distinct GLP-1R neuronal populations partition function: NTS neurons drive satiety without aversion while area postrema neurons drive aversion, hypothalamic LepRb/Glp1r and lateral septal GABAergic neurons projecting to the lateral hypothalamus mediate anorexia, and GLP-1R activation suppresses VTA dopamine responses to oppose hedonic eating [PMID:38987598, PMID:37581939, PMID:38763494, PMID:40146831]. In peripheral tissues, GLP-1R signaling restrains intraepithelial-lymphocyte T cell receptor signaling via PKA, sustains colonic epithelial maintenance and intestinal mucosal growth through an Fgf7-dependent pathway, and modulates carotid body chemoreflex and sympathetic output [PMID:36027914, PMID:38521185, PMID:25738454, PMID:35100822].","teleology":[{"year":2018,"claim":"Established that GLP-1R agonism could be combined with GIPR antagonism to enhance metabolic efficacy, framing GLP-1R within the incretin pharmacology landscape.","evidence":"Crystallography of an anti-GIPR antibody plus in vivo studies in DIO mice and non-human primates","pmids":["30567927"],"confidence":"Medium","gaps":["GLP-1R structure itself not resolved here","combination mechanism inferred from in vivo weight loss only"]},{"year":2020,"claim":"Resolved how non-peptide agonists engage GLP-1R, showing that pharmacological mimicry of GLP-1 depends on whether a small molecule occupies the overlapping orthosteric pocket and reconstitutes its water-mediated hydrogen-bond network.","evidence":"High-resolution cryo-EM of PF 06882961- and CHU-128-bound receptor with pharmacological assays","pmids":["33027691"],"confidence":"High","gaps":["Does not map full conformational trajectory to G protein coupling","limited to two compounds"]},{"year":2021,"claim":"Defined the molecular basis of differential peptide engagement among clinical agonists, linking distinct receptor and peptide motions to differing signaling profiles.","evidence":"Cryo-EM with 3D variability analysis of semaglutide- and taspoglutide-bound GLP-1R–Gs complexes","pmids":["34260945"],"confidence":"High","gaps":["Static structures only partially capture dynamics","signaling consequences inferred"]},{"year":2022,"claim":"Connected peptide N-terminal transmembrane interactions to allosteric Gs coupling kinetics, explaining how subtle ligand differences tune G protein activation.","evidence":"Cryo-EM, molecular dynamics, mutagenesis and pharmacology across four peptide agonists","pmids":["35013280"],"confidence":"High","gaps":["Kinetic correlations not validated against in vivo signaling outcomes"]},{"year":2022,"claim":"Showed that ligand dissociation kinetics, rather than association, govern the timing and persistence of receptor–G protein coupling and cAMP output.","evidence":"Quantitative kinetic binding, BRET G protein engagement, and cAMP assays for a peptide agonist series","pmids":["35300966"],"confidence":"Medium","gaps":["Single lab, in vitro only","physiological relevance of Koff to insulin secretion not tested"]},{"year":2022,"claim":"Identified a druggable cryptic allosteric pocket in the cytoplasmic half of TM3/TM5/TM6 that enlarges the orthosteric site to facilitate GLP-1 binding.","evidence":"Molecular dynamics, mutagenesis and signaling assays for small-molecule positive allosteric modulators","pmids":["34570476"],"confidence":"Medium","gaps":["No experimental structure of PAM-bound receptor","probe-dependence limits generalization"]},{"year":2024,"claim":"Revealed that small-molecule agonists Boc5 and WB4-24 achieve peptidomimetic and biased signaling by inserting into both the orthosteric pocket and distinct transmembrane clefts.","evidence":"Cryo-EM of receptor–ligand–Gs complexes with pharmacological validation","pmids":["35561211"],"confidence":"High","gaps":["Bias quantified in vitro, not linked to in vivo outcomes"]},{"year":2023,"claim":"Defined determinants of GLP-1R versus GCGR selectivity in dual agonists, showing ligand N-terminal side chains and ECL1 reshaping control dual agonism.","evidence":"Cryo-EM of receptor–Gs with three dual GLP-1R/GCGR agonists","pmids":["37549266"],"confidence":"High","gaps":["Selectivity rules derived from limited ligand set"]},{"year":2024,"claim":"Demonstrated that Gs protein alone can pre-activate GLP-1R by opening the intracellular cavity and rewiring the orthosteric pocket, distinguishing it from GCGR and GIPR.","evidence":"Cryo-EM of ligand-free GLP-1R–Gs complexes compared across three receptors","pmids":["38346960"],"confidence":"High","gaps":["Functional significance of ligand-independent pre-coupling in cells unknown"]},{"year":2021,"claim":"Established the atypical trafficking logic of GLP-1R, showing internalization is GRK-dependent but β-arrestin-independent and that GRK2 is required for β-arrestin recruitment and tunes insulin release kinetics.","evidence":"CRISPR GRK/β-arrestin knockouts, nanoBRET, GRK2 hemizygous mice and isolated islet assays","pmids":["38461904","33658023"],"confidence":"High","gaps":["No single GRK isoform assigned exclusive role","GRK2 islet effects on early-phase secretion mechanism partly correlative"]},{"year":2021,"claim":"Contrasted GLP-1R and GIPR trafficking, showing GLP-1R favors internalization, degradation and endosomal cAMP whereas GIPR favors recycling and signal amplification.","evidence":"Parallel surface expression, trafficking, and spatiotemporal cAMP assays in β-cells","pmids":["36774542"],"confidence":"Medium","gaps":["Single lab comparison","in vivo consequences not addressed"]},{"year":2021,"claim":"Identified PPP1R1A as a downstream effector linking GLP-1R–PKA signaling to amplification of glucose-stimulated insulin secretion and mitochondrial coupling.","evidence":"siRNA knockdown in INS1 cells with GSIS, PKA phosphorylation and mitochondrial assays plus human islet correlation","pmids":["33631146"],"confidence":"Medium","gaps":["Single lab","mechanism of PPP1R1A action on secretion not fully defined"]},{"year":2023,"claim":"Showed β-arrestin 2 controls the temporal phases of GLP-1R signaling in β-cells, balancing desensitization, recycling, ubiquitination and compartmentalized cAMP.","evidence":"Adult β-cell-specific β-arrestin 2 conditional KO with cAMP, trafficking and glucose tolerance assays","pmids":["37134170"],"confidence":"High","gaps":["Compensation by β-arrestin 1/PDE4 complicates clean attribution"]},{"year":2023,"claim":"Mapped the spatiotemporal signaling diversity of GLP-1R agonists across pathways and compartments, linking signaling neighborhoods to clinical adverse-event profiles.","evidence":"15-biosensor panel across four compartments, structure analysis, microscopy and phosphoproteomics","pmids":["37813859"],"confidence":"High","gaps":["Clinical correlations associative, not causal"]},{"year":2023,"claim":"Connected human GLP1R genetic variation to metabolic disease, showing loss-of-function variants reduce surface expression and impair glucose control, with rescue by allosteric ligands.","evidence":"Functional profiling of 60 variants across four pathways, INS-1 rescue, UK Biobank association","pmids":["37709961"],"confidence":"High","gaps":["Not all variant phenotypes validated in vivo"]},{"year":2019,"claim":"Localized the critical neural substrate for physiological GLP-1R metabolic control to Phox2b+ autonomic/vagal neurons.","evidence":"Cell-type-specific conditional Glp1r knockouts (Phox2b-Cre, Wnt1-Cre2) with glucose tolerance and gastric emptying assays","pmids":["31189118"],"confidence":"High","gaps":["Does not resolve downstream circuit","single lab"]},{"year":2023,"claim":"Established hypothalamic LepRb/Glp1r and lateral septal GLP-1R neurons as necessary and sufficient mediators of GLP-1R agonist anorexia.","evidence":"Conditional KO and re-expression, chemogenetics, region-specific knockdown and fiber photometry","pmids":["37581939","39225090"],"confidence":"High","gaps":["Integration across hypothalamic and septal nodes not fully mapped"]},{"year":2024,"claim":"Dissociated satiety from aversion at the circuit level, showing NTS-GLP1R neurons drive satiety without aversion while AP-GLP1R neurons drive aversion, and traced dLS-GLP1R GABAergic projections to the lateral hypothalamus.","evidence":"Two-photon calcium imaging, chemogenetics, optogenetics and circuit tracing","pmids":["38987598","38763494"],"confidence":"High","gaps":["Downstream effector neurons of each population incompletely defined"]},{"year":2024,"claim":"Identified the hedonic eating circuit opposing GLP-1R-driven appetite reduction, showing GLP-1R activation suppresses VTA dopamine responses to food.","evidence":"Photometry-calibrated optogenetics and feeding behavior with semaglutide","pmids":["40146831"],"confidence":"High","gaps":["Receptor locus on VTA circuit not fully resolved"]},{"year":2024,"claim":"Placed BDNFmNTS neurons downstream of GFRAL/GLP1R neurons as a required node for GLP-1R agonist weight loss, and showed CNS GIPR plus GLP-1R cooperate for maximal weight loss.","evidence":"Genetic and chemogenetic gain/loss-of-function, c-FOS mapping, drug biodistribution","pmids":["39737892","40301582"],"confidence":"Medium","gaps":["BDNFmNTS findings single lab","molecular coupling between receptors and BDNF neurons unresolved"]},{"year":2024,"claim":"Showed dual GLP-1R/LepR agonism acts through dorsomedial hypothalamic LepRGlp1r neurons, with re-expression on a null background sufficient for efficacy.","evidence":"Conditional KO and re-expression mouse models with dual agonist pharmacology","pmids":["39630884"],"confidence":"High","gaps":["Downstream projection targets not defined"]},{"year":2022,"claim":"Defined peripheral immunomodulatory and chemosensory roles, showing GLP-1R restrains intraepithelial-lymphocyte TCR signaling via PKA and modulates carotid body chemoreflex and sympathetic output.","evidence":"IEL-specific conditional KO with PKA inhibitors and microbiota analysis; carotid body RNA-seq and in vivo functional assays","pmids":["36027914","35100822","31189118"],"confidence":"High","gaps":["Carotid body receptor signaling pathway less detailed than IEL PKA axis"]},{"year":2015,"claim":"Established a non-incretin epithelial role, showing GLP-1R controls intestinal mucosal growth through Fgf7, independent of EGF/IGF1 receptors, and later colonic epithelial maintenance during energy deprivation.","evidence":"Glp1r-/- and Fgf7-/- mice with exendin-4 and Apc(Min/+) models; GF GLP-1R KO with organoid and dietary/microbiota rescue","pmids":["25738454","38521185"],"confidence":"High","gaps":["Receptor-expressing cell type driving Fgf7 induction not fully resolved"]},{"year":2025,"claim":"Extended GLP-1R signaling to neuroprotection, showing agonists engage CaMKK2-AMPK to reduce BACE1-mediated APP cleavage and Aβ generation while promoting microglial Aβ phagocytosis.","evidence":"AD model mice with biochemical CaMKK2-AMPK-BACE1 pathway analysis and microglial assays","pmids":["40394225"],"confidence":"Medium","gaps":["Single lab","direct receptor-to-CaMKK2 coupling mechanism not defined"]},{"year":null,"claim":"How agonist-specific receptor conformations and compartmentalized signaling neighborhoods translate into the divergent therapeutic and adverse effects across distinct β-cell, neuronal, immune, and epithelial cell types remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking biased signaling to cell-type-specific physiology","in vivo causal link between Koff/location bias and clinical outcomes untested","molecular effectors downstream of cAMP/PKA characterized only in selected tissues"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,5,11]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,25,27]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[9,27]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal 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\"discoveries\": [\n    {\n      \"year\": 2020,\n      \"finding\": \"Cryo-EM structures revealed that the non-peptide GLP-1R agonist PF 06882961 has a binding site that substantially overlaps with GLP-1's binding site, whereas CHU-128 adopts a unique binding mode with a more open receptor conformation at the extracellular face. Extensive water-mediated hydrogen bond networks explain why PF 06882961 but not CHU-128 closely mimics GLP-1 pharmacological properties.\",\n      \"method\": \"High-resolution cryo-EM structural determination combined with pharmacological assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures plus functional pharmacological assays in a single rigorous study\",\n      \"pmids\": [\"33027691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures and molecular dynamics simulations of GLP-1R bound to four peptide agonists (GLP-1, oxyntomodulin, exendin-4, exendin-P5) demonstrated that distinctions in peptide N-terminal interactions and dynamics with the transmembrane domain are reciprocally associated with differences in allosteric coupling to G proteins; transient interactions with residues at the base of the binding cavity correlate with enhanced kinetics for G protein activation.\",\n      \"method\": \"Cryo-EM, molecular dynamics simulations, receptor mutagenesis, pharmacological assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (cryo-EM, MD, mutagenesis, pharmacology) in a single rigorous study\",\n      \"pmids\": [\"35013280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of semaglutide- and taspoglutide-bound GLP-1R–Gs protein complexes revealed similar peptide interactions to GLP-1 but different motions within the receptor and bound peptides, providing molecular determinants of differential peptide engagement and signaling profiles.\",\n      \"method\": \"Cryo-EM with 3D variability analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structures with conformational analysis, single lab\",\n      \"pmids\": [\"34260945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of small-molecule agonists Boc5 and WB4-24 bound to GLP-1R–Gs revealed that one arm of each compound inserts deeply into the orthosteric binding pocket overlapping with GLP-1 residues A8–D15, while other arms extend into TM1-TM7, TM1-TM2, and TM2-TM3 clefts, creating a unique conformation that confers peptidomimetic agonism and biased signaling.\",\n      \"method\": \"Cryo-EM structural determination of receptor–ligand–Gs complexes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structures with pharmacological validation, single lab\",\n      \"pmids\": [\"35561211\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of GLP-1R in complex with Gs protein and three dual GLP-1R/GCGR agonists (peptide 15, MEDI0382, SAR425899) identified key residues for ligand recognition and dual agonism; side chain orientations within the first three residues of the ligand determine receptor selectivity, and ECL1 conformation of GLP-1R is reshaped by dual agonists relative to GCGR.\",\n      \"method\": \"Cryo-EM structural determination combined with published pharmacological data\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structures with functional pharmacological support, single lab\",\n      \"pmids\": [\"37549266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of ligand-free GLP-1R in complex with Gs protein (without cognate peptide) showed that Gs protein alone directly opens the intracellular binding cavity and rewires the extracellular orthosteric pocket; the extracellular portion of GLP-1R adopts a conformation close to the active state even without ligand, distinct from GCGR and GIPR.\",\n      \"method\": \"Cryo-EM structural determination of ligand-free receptor–Gs complexes\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structures compared across three related receptors, single lab\",\n      \"pmids\": [\"38346960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Crystallographic studies of an anti-human GIPR antibody showed it displaced GIP and bound GIPR using the same conserved hydrophobic residues as GIP, and combined GLP-1R agonists with GIPR antagonism produced enhanced weight loss in preclinical models.\",\n      \"method\": \"Crystallography plus in vivo pharmacological studies (DIO mice and NHP)\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure reported for GIPR, GLP-1R agonist combination data is in vivo only, single lab\",\n      \"pmids\": [\"30567927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GLP-1R undergoes an atypical β-arrestin-independent mode of internalization; GRK2/3/4/5/6 knockout experiments using CRISPR/Cas9 demonstrated that GLP-1R internalisation is GRK-dependent, β-arrestin 1 recruitment is more sensitive to GRK knockout than β-arrestin 2 recruitment, and no single GRK isoform exclusively drives these pathways.\",\n      \"method\": \"CRISPR/Cas9 endogenous GRK and β-arrestin knockouts, quantitative trafficking assays\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO of multiple GRK isoforms with quantitative rescue experiments, two orthogonal readouts\",\n      \"pmids\": [\"38461904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GRK2 associates with GLP-1R upon agonist stimulation (demonstrated by nanoBRET in β-cell lines), and GRK2 protein and kinase activity are required for subsequent β-arrestin recruitment to GLP-1R. Reduced GRK2 levels in vivo enhanced early-phase insulin release stimulated by GLP-1R agonists without affecting late-phase secretion, correlating with an increased readily releasable pool of insulin granules.\",\n      \"method\": \"NanoBRET, GRK2 hemizygous mouse model, isolated pancreatic islet assays, β-cell line experiments\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — nanoBRET protein interaction assay, genetic model, and isolated islet functional assays, multiple orthogonal methods\",\n      \"pmids\": [\"33658023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Adult β-cell-specific β-arrestin 2 knockout mice showed impaired acute GLP-1R agonist (exendin-4, semaglutide, tirzepatide) responses but improved responses 6 hours post-injection. The acute cAMP impairment was attributed to enhanced β-arrestin 1 and phosphodiesterase 4 activity compensating for β-arrestin 2 loss; reduced desensitization co-occurred with impaired GLP-1R recycling/lysosomal targeting, increased trans-Golgi network signaling, and reduced GLP-1R ubiquitination.\",\n      \"method\": \"Adult β-cell-specific β-arrestin 2 conditional KO mice, cAMP assays, trafficking assays, in vivo glucose tolerance\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple mechanistic readouts (cAMP, trafficking, ubiquitination, recycling), single lab\",\n      \"pmids\": [\"37134170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GLP-1R peptide agonist dissociation kinetics (Koff), but not association kinetics (Kon), were positively correlated with onset of receptor–G protein coupling, onset of cAMP production, and duration of cAMP signaling, mechanistically linking ligand–receptor interaction kinetics to downstream signaling onset.\",\n      \"method\": \"Quantitative kinetic binding assays, BRET-based G protein engagement assays, cAMP measurement for a series of peptide agonists\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal kinetic and signaling assays, single lab\",\n      \"pmids\": [\"35300966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using 15 signaling biosensors across 4 cellular compartments, GLP-1R was shown to activate distinct signaling neighborhoods in a pathway- and compartment-selective manner; comparative structure analysis, time-lapse microscopy, and phosphoproteomics revealed unique signaling signatures for different GLP-1R agonists at the level of receptor conformation, functional selectivity, and location bias, linking specific signaling neighborhoods to clinical adverse event profiles.\",\n      \"method\": \"Biosensor panel (15 pathways, 4 compartments), structure analysis, time-lapse microscopy, phosphoproteomics\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biosensors, phosphoproteomics, microscopy), novel mechanistic framework with clinical correlation\",\n      \"pmids\": [\"37813859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Small-molecule positive allosteric modulators (PAMs) of GLP-1R were identified that bind a cryptic pocket formed by the cytoplasmic half of TM3, TM5, and TM6; molecular dynamics simulations and mutagenesis studies indicated the PAM enlarges the orthosteric pocket to facilitate GLP-1 binding, and signaling assays characterized probe-dependent signaling profiles.\",\n      \"method\": \"Molecular dynamics simulations, mutagenesis, signaling assays\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis and MD combined with functional assays, single lab\",\n      \"pmids\": [\"34570476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Selective reduction of Glp1r expression within Phox2b-Cre neurons (autonomic/vagal neurons) impaired glucose homeostasis and gastric emptying and attenuated GLP-1R agonist-induced weight loss; widespread neural Glp1r loss in Wnt1-Cre2 mice preserved glucoregulatory actions of GLP-1R agonists, demonstrating that Phox2b+ neurons are the critical neural substrate for physiological GLP-1R-mediated metabolic control.\",\n      \"method\": \"Cell-type-specific conditional Glp1r knockout (Phox2b-Cre, Wnt1-Cre2), glucose tolerance tests, gastric emptying measurements\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO in two distinct neural populations with multiple metabolic readouts, single lab\",\n      \"pmids\": [\"31189118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In vivo two-photon imaging of hindbrain GLP1R neurons showed that area postrema (AP) GLP1R neurons are broadly responsive to both nutritive and aversive stimuli, while nucleus of the solitary tract (NTS) GLP1R neurons are biased towards nutritive stimuli. Selective chemogenetic/optogenetic manipulation demonstrated that NTS-GLP1R neuron activation triggers satiety without aversion, while AP-GLP1R activation triggers aversion with food intake reduction. Anatomical tracing showed NTS-GLP1R and AP-GLP1R project to different downstream brain regions.\",\n      \"method\": \"In vivo two-photon calcium imaging, chemogenetics, optogenetics, anatomical circuit tracing\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (imaging, chemogenetics, optogenetics, anatomy) with dissociable circuit logic, high-impact journal\",\n      \"pmids\": [\"38987598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GLP1R is expressed in carotid body chemosensory cells in rat and human; targeted GLP1R agonist administration to the carotid body lowered basal discharge and attenuated chemoreflex-evoked blood pressure and sympathetic responses; hyperglycemia-induced peripheral chemoreflex sensitization and sympathetic overactivity were abolished by GLP1R activation in the carotid body.\",\n      \"method\": \"RNA-seq, molecular characterization, in situ/in vivo carotid body functional assays with targeted drug delivery\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — localization with direct functional consequence demonstrated in situ and in vivo, multiple methods\",\n      \"pmids\": [\"35100822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GLP-1R signaling in gut intraepithelial lymphocytes (IELs) is required for the full effects of GLP-1R agonists on gut microbiota composition and selectively restrains local and systemic T cell-induced (but not LPS-induced) inflammation; the mechanism involves suppression of IEL effector functions via dampening of proximal T cell receptor signaling in a protein kinase A-dependent manner.\",\n      \"method\": \"IEL-specific GLP-1R conditional knockout mice, microbiota analysis, in vivo inflammatory models, PKA inhibitor experiments\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with mechanistic pathway identification (PKA-dependence) and multiple orthogonal experimental readouts\",\n      \"pmids\": [\"36027914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GLP-1R signaling controls mucosal expansion of the small bowel and colon via a mechanism requiring Fgf7 (fibroblast growth factor 7) but independent of EGF or IGF1 receptors; exendin-4 increased Fgf7 expression in colonic polyps, and exendin-4 failed to increase intestinal growth in Fgf7-null mice.\",\n      \"method\": \"Glp1r-/- mice, Fgf7-/- mice, exendin-4 treatment, Apc(Min/+) mouse model, gene expression analysis\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis using multiple KO models with specific mechanistic readout, two independent labs confirmed pathway\",\n      \"pmids\": [\"25738454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP-1R agonist liraglutide directly activates POMC neurons in vivo via GLP-1R expression in POMC neurons, requiring a downstream mixed cation channel comprising TRPC5 subunits; it also indirectly upregulates excitatory input to POMC neurons from glutamatergic cells (also requiring TRPC5), and inhibits NPY/AgRP neurons indirectly through activation of K-ATP and TRPC5 channels in GABAergic neurons.\",\n      \"method\": \"Neuron-specific transgenic mouse models, patch-clamp electrophysiology, in vivo fiber photometry\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology and fiber photometry in GLP-1R-specific conditional models, multiple orthogonal methods\",\n      \"pmids\": [\"34626854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP-1R-positive (GLP-1R+) neurons in the lateral septum (LS) mediate anorectic and weight-loss effects of liraglutide; these neurons are activated by liraglutide, their activity rapidly decreases during naturalistic feeding, chemogenetic activation suppresses feeding, and targeted GLP-1R knockdown in the LS (but not hypothalamus) substantially attenuated liraglutide's ability to inhibit feeding and reduce body weight.\",\n      \"method\": \"Chemogenetics (DREADD), GLP-1R knockdown in specific brain regions, fiber photometry, behavioral analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vivo tools (chemogenetics, region-specific knockdown, photometry) demonstrating site-specific necessity, single lab\",\n      \"pmids\": [\"39225090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"dLS GLP-1R neurons project GABAergic axons to the lateral hypothalamic area (LHA); chemogenetic inhibition of dLSGLP-1R neurons or the dLSGLP-1R→LHA pathway promotes food intake; optogenetic stimulation of dLSGLP-1R→LHA terminals in the LHA rapidly suppresses feeding; GLP-1R agonist exendin-4 enhances dLSGLP-1R→LHA GABA release.\",\n      \"method\": \"Channelrhodopsin-assisted circuit mapping, chemogenetics, optogenetics, electrophysiology in Glp1r-ires-Cre mice\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal circuit-mapping tools (optogenetics, chemogenetics, electrophysiology), single lab\",\n      \"pmids\": [\"38763494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GABAergic hypothalamic neurons co-expressing Glp1r and Lepr (LepRbGlp1r neurons) are required for leptin-mediated suppression of food intake; ablating Lepr from these neurons caused hyperphagic obesity; restoration of Glp1r expression specifically in LepRb neurons on an otherwise Glp1r-null background was sufficient to permit food intake suppression by the GLP1R agonist liraglutide.\",\n      \"method\": \"Cell-type-specific Cre-lox conditional KO and re-expression, single-nucleus RNA-seq, behavioral metabolic phenotyping\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO and cell-type-specific rescue experiments, replicated across multiple genetic models\",\n      \"pmids\": [\"37581939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Exendin-4 activates the GLP1R–PKA–PPARγ-dependent phosphatases PTEN and PTP1B, which inhibit key kinases within both EGFR and STAT6 signaling cascades to restore FOXA2 expression and normalize airway mucus production in COPD and cystic fibrosis airway cells.\",\n      \"method\": \"In vitro airway cell assays, COPD/CF disease cell lines, in vivo mouse lung model, pathway inhibitor experiments\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway dissected with multiple inhibitors and in vitro/in vivo models, single lab\",\n      \"pmids\": [\"32034274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GLP-1 regulates skeletal muscle remodeling and exercise endurance via GLP-1R signaling-mediated phosphorylation of AMPK; AMPK knockdown reversed the effects of GLP-1R activation on glucose uptake, type I fiber formation, and mitochondrial respiration in vitro.\",\n      \"method\": \"AAV-mediated GLP-1 overexpression in muscle, in vitro AMPK knockdown, ex vivo mitochondrial respiration assays\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic overexpression model plus AMPK knockdown epistasis, single lab, in vitro mechanistic confirmation\",\n      \"pmids\": [\"35636559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP-1R activation inhibits pulmonary fibrosis by disrupting the interaction between NLRP3 inflammasome and PFKFB3-driven glycolysis in lung fibroblasts, subsequently preventing lactate-mediated histone lactylation that drives pro-fibrotic gene expression; GLP-1R activation also inhibited p300-mediated histone lactylation in exogenous lactate-treated fibroblasts.\",\n      \"method\": \"In vitro lung fibroblast assays, RNA-seq, ChIP-qPCR for histone lactylation, cell metabolism assays, mouse silica fibrosis model\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP-qPCR, RNA-seq, metabolic assays, in vivo) in single lab\",\n      \"pmids\": [\"39434134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP1R loss-of-function variants that reduce cell surface expression are associated with impaired glucose control and increased adiposity; 60 GLP1R variants were functionally profiled across four signaling pathways revealing a diversity of phenotypes including defective cell surface expression, pathway-specific gain and loss of function; defective insulin secretion of LoF variants can be rescued by allosteric GLP1R ligands or high concentrations of exendin-4/semaglutide in INS-1 cells.\",\n      \"method\": \"Functional profiling of 60 variants across 4 signaling pathways, rescue experiments with allosteric ligands in INS-1 cells, genetic association in UK Biobank\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic variant profiling across multiple signaling pathways with cell-based rescue, replicated in large human cohort\",\n      \"pmids\": [\"37709961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP-1R agonist liraglutide in gut IELs suppresses feeding via protein kinase A-dependent dampening of proximal T cell receptor signaling, reducing effector functions of intraepithelial lymphocytes; this mechanism is specifically required for restraining T cell-induced but not LPS-induced inflammation.\",\n      \"method\": \"Conditional GLP-1R KO in IELs, PKA inhibitor experiments, T cell functional assays\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with mechanistic PKA pathway validation and multiple inflammatory readouts\",\n      \"pmids\": [\"36027914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GLP-1R shows increased cell surface levels, internalization, degradation, and higher endosomal versus plasma membrane cAMP activity compared to GIPR in pancreatic beta cells; GIPR is instead associated with increased plasma membrane recycling, reduced desensitization, and enhanced downstream signal amplification.\",\n      \"method\": \"Direct comparison of surface expression, trafficking (internalization/recycling/degradation), and spatiotemporal cAMP signaling assays in pancreatic beta cells\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays (surface expression, trafficking, signaling) in single lab comparing two receptors directly\",\n      \"pmids\": [\"36774542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The MafA target gene PPP1R1A is expressed in β-cells, and PPP1R1A silencing in INS1 cells impairs GLP-1R-mediated amplification of glucose-stimulated insulin secretion, PKA-target protein phosphorylation, and mitochondrial coupling efficiency, demonstrating PPP1R1A as a downstream effector of GLP-1R-PKA signaling in β-cells.\",\n      \"method\": \"siRNA knockdown in INS1 β-cells, GSIS assays, PKA phosphorylation assays, mitochondrial function assays, human islet RNA correlation\",\n      \"journal\": \"Metabolism: clinical and experimental\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple functional readouts, supported by human islet correlative data, single lab\",\n      \"pmids\": [\"33631146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GLP-1R activation by semaglutide suppresses VTA dopamine (VTADA) neuron responsiveness during food consumption, opposing hedonic eating; mice recovered palatable food appetite and VTADA activity during repeated semaglutide treatment, which was reversed by consumption-triggered VTADA neuron inhibition, demonstrating that the hedonic eating circuit opposes GLP-1R-mediated appetite reduction.\",\n      \"method\": \"Photometry-calibrated optogenetics, in vivo fiber photometry, behavioral feeding assays\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — calibrated optogenetic manipulation and photometry in a circuit-level dissection, single lab\",\n      \"pmids\": [\"40146831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"BDNFmNTS neurons in the medial nucleus of the tractus solitarius are downstream of GFRAL/GLP1R neurons; these BDNF neurons are required for weight-reducing actions of both GDF15 and the GLP1RA exendin-4, and acute activation of BDNFmNTS neurons is sufficient to reduce food intake and drive fatty acid oxidation.\",\n      \"method\": \"Mouse genetic models, chemogenetics, in vivo metabolic measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chemogenetic gain- and loss-of-function in vivo with metabolic readouts, single lab\",\n      \"pmids\": [\"39737892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LepRGlp1r neurons in the dorsomedial hypothalamus mediate the food intake-suppressing and body weight-reducing effects of a GLP-1R/LepR dual agonist; ablating Lepr from Glp1r-expressing neurons abrogated dual agonist efficacy on food intake, while reactivating Glp1r in Lepr neurons on a Glp1r-null background was sufficient to permit the food intake and body weight suppression.\",\n      \"method\": \"Conditional KO and re-expression mouse models (LeprGlp1rKO, Glp1rLeprRe), in vivo pharmacology with dual agonist\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — paired conditional KO and rescue experiments demonstrating necessity and sufficiency, single lab\",\n      \"pmids\": [\"39630884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Both CNS GIPR and CNS GLP-1R are required for maximal weight loss by a GIPR-Ab/GLP-1 peptide-antibody conjugate; the conjugate is detected in circumventricular organs and activates c-FOS in downstream appetite-regulating brain regions; dulaglutide (GLP-1R agonist alone) achieves greater weight loss in CNS GIPR KO mice.\",\n      \"method\": \"CNS GIPR conditional KO mice, dulaglutide + GIPR-Ab combination experiments, c-FOS immunostaining, drug biodistribution\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple pharmacological probes, in vivo c-FOS circuit mapping, single lab\",\n      \"pmids\": [\"40301582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GLP-1R knockdown in human RPE cells (ARPE-19) increased intracellular ROS generation and activated p53-mediated Bax promoter activity and ER stress signaling; ER stress-mediated p53 expression was regulated upstream by ROS, as antioxidant treatment and Prx1 overexpression attenuated GLP-1R knockdown-induced ER stress and p53 expression.\",\n      \"method\": \"siRNA knockdown, ROS measurement, ER stress signaling assays, Bax promoter reporter, antioxidant rescue experiments\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple mechanistic readouts and rescue experiments, single lab\",\n      \"pmids\": [\"25483438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GLP-1R signaling modulates colonic goblet cell number, epithelial integrity, energy metabolism, and survival; GF GLP-1R KO mice developed enlarged ceca, reduced goblet cells, colonocyte energy deprivation, increased ER stress, mitochondrial fragmentation, elevated oxygen levels, and loss of stemness; restoring energy via Western-style diet or microbiota colonization normalized these phenotypes, demonstrating GLP-1R has a non-incretin role in colonic epithelial maintenance during energy deprivation.\",\n      \"method\": \"GF GLP-1R KO mouse model, histology, gene expression, intestinal organoid stemness assays, dietary and microbiota rescue experiments\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO model with multiple mechanistic readouts and bidirectional rescue experiments (diet and microbiota), single lab\",\n      \"pmids\": [\"38521185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GLP1R overexpression in endometrial carcinoma cells promotes apoptosis and activates the cAMP/PKA signaling pathway, while inhibiting cell proliferation, invasion, and migration; these effects were abrogated by PKA knockdown, placing GLP1R upstream of cAMP/PKA in this signaling axis.\",\n      \"method\": \"GLP1R overexpression vector, PKA siRNA, ELISA for cAMP, Western blot, in vitro cell behavior assays, mouse xenograft\",\n      \"journal\": \"Journal of clinical laboratory analysis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression/KD experiments with cAMP/PKA pathway dissection, epistasis by PKA knockdown, single lab\",\n      \"pmids\": [\"35989517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Loureirin B binds to GLP-1R (demonstrated by surface plasmon resonance and spectroscopy) and promotes insulin secretion in Ins-1 cells through GLP-1R; siRNA-mediated GLP-1R knockdown reduced the insulin secretion-promoting effect of Loureirin B.\",\n      \"method\": \"Molecular docking, surface plasmon resonance, spectroscopy, GLP-1R siRNA knockdown, insulin secretion assay\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SPR binding assay plus siRNA knockdown functional confirmation, single lab\",\n      \"pmids\": [\"33300675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GLP-1R agonists increase CaMKK2-AMPK signaling in neurons, which reduces BACE1-mediated cleavage of APP and Aβ generation; GLP-1R agonists also increase AMPK activity in microglia, inhibiting neuroinflammation and promoting Aβ phagocytosis.\",\n      \"method\": \"AD model mouse in vivo experiments, biochemical pathway analysis (CaMKK2-AMPK-BACE1 axis), microglial functional assays\",\n      \"journal\": \"Nature aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway identification in vivo with multiple cell-type readouts, single lab\",\n      \"pmids\": [\"40394225\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GLP-1R is a class B1 G protein-coupled receptor that, upon binding peptide or small-molecule agonists in a site overlapping with GLP-1's binding pocket, undergoes conformational changes in its transmembrane and extracellular domains that drive Gs-protein coupling and cAMP/PKA signaling; receptor internalization is β-arrestin-independent but GRK-dependent, β-arrestins modulate desensitization and endosomal signaling, and ligand dissociation kinetics (Koff) govern the onset and duration of G protein activation; in pancreatic β-cells, GLP-1R-cAMP-PKA signaling amplifies glucose-stimulated insulin secretion; in the brain, distinct GLP-1R-expressing neuronal populations (NTS vs. AP hindbrain neurons, lateral septal neurons, hypothalamic LepRb/Glp1r neurons) mediate separable satiety and aversive effects; and GLP-1R signaling in peripheral tissues including gut intraepithelial lymphocytes, carotid body chemosensory cells, and colonic epithelium subserves immunomodulatory, sympathoinhibitory, and epithelial maintenance functions, respectively.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GLP-1R is a class B G protein-coupled receptor that converts peptide and small-molecule agonist binding into Gs-coupled cAMP/PKA signaling, governing metabolic, neuronal, immune, and epithelial processes [#1, #16]. Cryo-EM structures of the receptor bound to GLP-1, oxyntomodulin, exendin-4, dual GLP-1R/GCGR agonists, and diverse small molecules show that agonists engage an orthosteric pocket and that distinctions in peptide N-terminal interactions and dynamics with the transmembrane domain are reciprocally linked to allosteric coupling efficiency to Gs [#1, #4]; non-peptide agonists such as PF 06882961 occupy a site overlapping GLP-1's, while others adopt distinct poses conferring biased signaling [#0, #3], and Gs protein alone can pre-open the intracellular cavity and rewire the orthosteric pocket toward an active state even without ligand [#5]. Ligand dissociation kinetics (Koff), not association, dictate the onset and duration of G protein coupling and cAMP output, and agonists activate distinct compartmentalized signaling neighborhoods that map onto clinical effect profiles [#10, #11]. GLP-1R internalization is atypical: it is GRK-dependent but β-arrestin-independent, with GRK2 required for β-arrestin recruitment, and β-arrestin 2 tuning desensitization, recycling, ubiquitination, and the balance of plasma-membrane versus endosomal/trans-Golgi signaling [#7, #8, #9]. In pancreatic β-cells, GLP-1R–cAMP–PKA signaling amplifies glucose-stimulated insulin secretion through downstream effectors including PPP1R1A, and human loss-of-function variants that reduce surface expression impair glucose control and increase adiposity but can be rescued by allosteric ligands [#28, #25]. In the nervous system, anatomically distinct GLP-1R neuronal populations partition function: NTS neurons drive satiety without aversion while area postrema neurons drive aversion, hypothalamic LepRb/Glp1r and lateral septal GABAergic neurons projecting to the lateral hypothalamus mediate anorexia, and GLP-1R activation suppresses VTA dopamine responses to oppose hedonic eating [#14, #21, #20, #29]. In peripheral tissues, GLP-1R signaling restrains intraepithelial-lymphocyte T cell receptor signaling via PKA, sustains colonic epithelial maintenance and intestinal mucosal growth through an Fgf7-dependent pathway, and modulates carotid body chemoreflex and sympathetic output [#16, #34, #17, #15].\",\n  \"teleology\": [\n    {\n      \"year\": 2018,\n      \"claim\": \"Established that GLP-1R agonism could be combined with GIPR antagonism to enhance metabolic efficacy, framing GLP-1R within the incretin pharmacology landscape.\",\n      \"evidence\": \"Crystallography of an anti-GIPR antibody plus in vivo studies in DIO mice and non-human primates\",\n      \"pmids\": [\"30567927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GLP-1R structure itself not resolved here\", \"combination mechanism inferred from in vivo weight loss only\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved how non-peptide agonists engage GLP-1R, showing that pharmacological mimicry of GLP-1 depends on whether a small molecule occupies the overlapping orthosteric pocket and reconstitutes its water-mediated hydrogen-bond network.\",\n      \"evidence\": \"High-resolution cryo-EM of PF 06882961- and CHU-128-bound receptor with pharmacological assays\",\n      \"pmids\": [\"33027691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not map full conformational trajectory to G protein coupling\", \"limited to two compounds\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the molecular basis of differential peptide engagement among clinical agonists, linking distinct receptor and peptide motions to differing signaling profiles.\",\n      \"evidence\": \"Cryo-EM with 3D variability analysis of semaglutide- and taspoglutide-bound GLP-1R–Gs complexes\",\n      \"pmids\": [\"34260945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Static structures only partially capture dynamics\", \"signaling consequences inferred\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected peptide N-terminal transmembrane interactions to allosteric Gs coupling kinetics, explaining how subtle ligand differences tune G protein activation.\",\n      \"evidence\": \"Cryo-EM, molecular dynamics, mutagenesis and pharmacology across four peptide agonists\",\n      \"pmids\": [\"35013280\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetic correlations not validated against in vivo signaling outcomes\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed that ligand dissociation kinetics, rather than association, govern the timing and persistence of receptor–G protein coupling and cAMP output.\",\n      \"evidence\": \"Quantitative kinetic binding, BRET G protein engagement, and cAMP assays for a peptide agonist series\",\n      \"pmids\": [\"35300966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, in vitro only\", \"physiological relevance of Koff to insulin secretion not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified a druggable cryptic allosteric pocket in the cytoplasmic half of TM3/TM5/TM6 that enlarges the orthosteric site to facilitate GLP-1 binding.\",\n      \"evidence\": \"Molecular dynamics, mutagenesis and signaling assays for small-molecule positive allosteric modulators\",\n      \"pmids\": [\"34570476\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental structure of PAM-bound receptor\", \"probe-dependence limits generalization\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed that small-molecule agonists Boc5 and WB4-24 achieve peptidomimetic and biased signaling by inserting into both the orthosteric pocket and distinct transmembrane clefts.\",\n      \"evidence\": \"Cryo-EM of receptor–ligand–Gs complexes with pharmacological validation\",\n      \"pmids\": [\"35561211\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Bias quantified in vitro, not linked to in vivo outcomes\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined determinants of GLP-1R versus GCGR selectivity in dual agonists, showing ligand N-terminal side chains and ECL1 reshaping control dual agonism.\",\n      \"evidence\": \"Cryo-EM of receptor–Gs with three dual GLP-1R/GCGR agonists\",\n      \"pmids\": [\"37549266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity rules derived from limited ligand set\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated that Gs protein alone can pre-activate GLP-1R by opening the intracellular cavity and rewiring the orthosteric pocket, distinguishing it from GCGR and GIPR.\",\n      \"evidence\": \"Cryo-EM of ligand-free GLP-1R–Gs complexes compared across three receptors\",\n      \"pmids\": [\"38346960\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of ligand-independent pre-coupling in cells unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established the atypical trafficking logic of GLP-1R, showing internalization is GRK-dependent but β-arrestin-independent and that GRK2 is required for β-arrestin recruitment and tunes insulin release kinetics.\",\n      \"evidence\": \"CRISPR GRK/β-arrestin knockouts, nanoBRET, GRK2 hemizygous mice and isolated islet assays\",\n      \"pmids\": [\"38461904\", \"33658023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No single GRK isoform assigned exclusive role\", \"GRK2 islet effects on early-phase secretion mechanism partly correlative\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Contrasted GLP-1R and GIPR trafficking, showing GLP-1R favors internalization, degradation and endosomal cAMP whereas GIPR favors recycling and signal amplification.\",\n      \"evidence\": \"Parallel surface expression, trafficking, and spatiotemporal cAMP assays in β-cells\",\n      \"pmids\": [\"36774542\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab comparison\", \"in vivo consequences not addressed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified PPP1R1A as a downstream effector linking GLP-1R–PKA signaling to amplification of glucose-stimulated insulin secretion and mitochondrial coupling.\",\n      \"evidence\": \"siRNA knockdown in INS1 cells with GSIS, PKA phosphorylation and mitochondrial assays plus human islet correlation\",\n      \"pmids\": [\"33631146\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"mechanism of PPP1R1A action on secretion not fully defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed β-arrestin 2 controls the temporal phases of GLP-1R signaling in β-cells, balancing desensitization, recycling, ubiquitination and compartmentalized cAMP.\",\n      \"evidence\": \"Adult β-cell-specific β-arrestin 2 conditional KO with cAMP, trafficking and glucose tolerance assays\",\n      \"pmids\": [\"37134170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensation by β-arrestin 1/PDE4 complicates clean attribution\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapped the spatiotemporal signaling diversity of GLP-1R agonists across pathways and compartments, linking signaling neighborhoods to clinical adverse-event profiles.\",\n      \"evidence\": \"15-biosensor panel across four compartments, structure analysis, microscopy and phosphoproteomics\",\n      \"pmids\": [\"37813859\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Clinical correlations associative, not causal\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected human GLP1R genetic variation to metabolic disease, showing loss-of-function variants reduce surface expression and impair glucose control, with rescue by allosteric ligands.\",\n      \"evidence\": \"Functional profiling of 60 variants across four pathways, INS-1 rescue, UK Biobank association\",\n      \"pmids\": [\"37709961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Not all variant phenotypes validated in vivo\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Localized the critical neural substrate for physiological GLP-1R metabolic control to Phox2b+ autonomic/vagal neurons.\",\n      \"evidence\": \"Cell-type-specific conditional Glp1r knockouts (Phox2b-Cre, Wnt1-Cre2) with glucose tolerance and gastric emptying assays\",\n      \"pmids\": [\"31189118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve downstream circuit\", \"single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established hypothalamic LepRb/Glp1r and lateral septal GLP-1R neurons as necessary and sufficient mediators of GLP-1R agonist anorexia.\",\n      \"evidence\": \"Conditional KO and re-expression, chemogenetics, region-specific knockdown and fiber photometry\",\n      \"pmids\": [\"37581939\", \"39225090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Integration across hypothalamic and septal nodes not fully mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dissociated satiety from aversion at the circuit level, showing NTS-GLP1R neurons drive satiety without aversion while AP-GLP1R neurons drive aversion, and traced dLS-GLP1R GABAergic projections to the lateral hypothalamus.\",\n      \"evidence\": \"Two-photon calcium imaging, chemogenetics, optogenetics and circuit tracing\",\n      \"pmids\": [\"38987598\", \"38763494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector neurons of each population incompletely defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified the hedonic eating circuit opposing GLP-1R-driven appetite reduction, showing GLP-1R activation suppresses VTA dopamine responses to food.\",\n      \"evidence\": \"Photometry-calibrated optogenetics and feeding behavior with semaglutide\",\n      \"pmids\": [\"40146831\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor locus on VTA circuit not fully resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed BDNFmNTS neurons downstream of GFRAL/GLP1R neurons as a required node for GLP-1R agonist weight loss, and showed CNS GIPR plus GLP-1R cooperate for maximal weight loss.\",\n      \"evidence\": \"Genetic and chemogenetic gain/loss-of-function, c-FOS mapping, drug biodistribution\",\n      \"pmids\": [\"39737892\", \"40301582\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"BDNFmNTS findings single lab\", \"molecular coupling between receptors and BDNF neurons unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed dual GLP-1R/LepR agonism acts through dorsomedial hypothalamic LepRGlp1r neurons, with re-expression on a null background sufficient for efficacy.\",\n      \"evidence\": \"Conditional KO and re-expression mouse models with dual agonist pharmacology\",\n      \"pmids\": [\"39630884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream projection targets not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined peripheral immunomodulatory and chemosensory roles, showing GLP-1R restrains intraepithelial-lymphocyte TCR signaling via PKA and modulates carotid body chemoreflex and sympathetic output.\",\n      \"evidence\": \"IEL-specific conditional KO with PKA inhibitors and microbiota analysis; carotid body RNA-seq and in vivo functional assays\",\n      \"pmids\": [\"36027914\", \"35100822\", \"31189118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Carotid body receptor signaling pathway less detailed than IEL PKA axis\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established a non-incretin epithelial role, showing GLP-1R controls intestinal mucosal growth through Fgf7, independent of EGF/IGF1 receptors, and later colonic epithelial maintenance during energy deprivation.\",\n      \"evidence\": \"Glp1r-/- and Fgf7-/- mice with exendin-4 and Apc(Min/+) models; GF GLP-1R KO with organoid and dietary/microbiota rescue\",\n      \"pmids\": [\"25738454\", \"38521185\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor-expressing cell type driving Fgf7 induction not fully resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended GLP-1R signaling to neuroprotection, showing agonists engage CaMKK2-AMPK to reduce BACE1-mediated APP cleavage and Aβ generation while promoting microglial Aβ phagocytosis.\",\n      \"evidence\": \"AD model mice with biochemical CaMKK2-AMPK-BACE1 pathway analysis and microglial assays\",\n      \"pmids\": [\"40394225\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"direct receptor-to-CaMKK2 coupling mechanism not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How agonist-specific receptor conformations and compartmentalized signaling neighborhoods translate into the divergent therapeutic and adverse effects across distinct β-cell, neuronal, immune, and epithelial cell types remains unresolved.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking biased signaling to cell-type-specific physiology\", \"in vivo causal link between Koff/location bias and clinical outcomes untested\", \"molecular effectors downstream of cAMP/PKA characterized only in selected tissues\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 5, 11]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 25, 27]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [9, 27]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 10, 11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [28, 25]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [14, 21, 19]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [16, 26]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [7, 9]}\n    ],\n    \"complexes\": [\"GLP-1R\\u2013Gs protein complex\"],\n    \"partners\": [\"GNAS\", \"GRK2\", \"ARRB1\", \"ARRB2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}