{"gene":"GPR171","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2013,"finding":"GPR171 is the cognate receptor for the neuropeptide BigLEN (LENSSPQAPARRLLPP), coupling through Gαi/o to mediate BigLEN signaling in mouse hypothalamus and Neuro2A cells. The four C-terminal amino acids of BigLEN are sufficient to bind and activate GPR171, whereas the C-terminally truncated peptide LittleLEN does not activate it.","method":"Ligand-binding assays, receptor-activity assays, overexpression, shRNA knockdown, orphan GPCR deorphanization screen","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (binding, signaling, gain- and loss-of-function) in heterologous cells and in vivo; replicated across subsequent studies","pmids":["24043826"],"is_preprint":false},{"year":2013,"finding":"shRNA-mediated knockdown of hypothalamic GPR171 decreases BigLEN signaling and reduces food intake; combined knockdown plus BigLEN antibody neutralization nearly eliminates acute feeding in food-deprived mice, establishing the BigLEN-GPR171 system as a regulator of feeding and metabolism.","method":"shRNA knockdown in mouse hypothalamus, antibody neutralization, feeding behavior assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean in vivo knockdown with specific behavioral readout, complemented by antibody neutralization","pmids":["24043826"],"is_preprint":false},{"year":2016,"finding":"GPR171 is activated by the small-molecule agonist MS0015203, identified by virtual screening of a homology model of GPR171; selectivity confirmed against 80 other membrane proteins including family A GPCRs. Peripheral injection increases food intake and body weight in a GPR171-dependent manner (attenuated by hypothalamic shRNA knockdown).","method":"Virtual screen, radioligand binding to 80 GPCRs, shRNA knockdown, in vivo pharmacology","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — compound selectivity panel plus in vivo loss-of-function with defined behavioral phenotype","pmids":["27245612"],"is_preprint":false},{"year":2017,"finding":"GPR171 in the basolateral amygdala (BLA) mediates BigLEN-induced hyperpolarization of BLA pyramidal neurons; the small-molecule antagonist MS0021570_1 blocks BigLEN-mediated GPR171 activation in heterologous cells and in neurons, and lentiviral knockdown of GPR171 in the BLA reduces anxiety-like behavior and contextual fear conditioning.","method":"Electrophysiology (hyperpolarization assay), heterologous cell activation assay, DREADD-mediated neuronal activation, lentiviral shRNA knockdown, behavioral assays","journal":"Neuropsychopharmacology","confidence":"High","confidence_rationale":"Tier 2 — direct electrophysiological evidence plus in vivo lentiviral knockdown with defined behavioral readouts","pmids":["28425495"],"is_preprint":false},{"year":2019,"finding":"GPR171 is expressed in GABAergic neurons within the periaqueductal gray (PAG) and modulates mu-opioid receptor (but not delta-opioid receptor) signaling; GPR171 agonist enhances and antagonist reduces morphine-induced antinociception; receptor knockdown decreases mu-opioid receptor signaling.","method":"Immunofluorescence/colocalization, pharmacological agonist/antagonist administration, receptor knockdown, antinociception behavioral assays","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological modulation with defined receptor specificity and behavioral readout, single lab","pmids":["31308196"],"is_preprint":false},{"year":2021,"finding":"GPR171 protein expression is induced on T cells upon antigen stimulation; BigLEN binding to GPR171 suppresses TCR-mediated signaling pathways and inhibits T cell proliferation; GPR171 knockout mice exhibit enhanced antitumor immunity; GPR171 antagonism improves immune checkpoint blockade therapy.","method":"Western blot (protein induction), T cell activation assays, GPR171 knockout mice, tumor models, immune checkpoint blockade combination","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout plus pharmacological antagonism with multiple orthogonal immune and in vivo tumor readouts","pmids":["34615877"],"is_preprint":false},{"year":2021,"finding":"GPR171 is expressed in nociceptor subpopulations and, when activated by BigLEN or synthetic ligands, attenuates pain signals via Gi/o-coupled modulation of nociceptive ion channel activity, alleviating acute and pathologic pain.","method":"Immunostaining of DRG neurons, Gi/o pharmacology, ion channel functional assays, in vivo pain behavior","journal":"Biomedicines","confidence":"Medium","confidence_rationale":"Tier 2-3 — Gi/o coupling and ion channel modulation demonstrated, single lab","pmids":["33807709"],"is_preprint":false},{"year":2021,"finding":"GPR171 agonist MS15203 reduces CFA-induced inflammatory pain thermal hypersensitivity and CIPN-induced allodynia in male but not female mice; GPR171 protein levels in the PAG are decreased after neuropathic pain in males, and MS15203 treatment rescues PAG GPR171 protein levels.","method":"In vivo pharmacology, CFA and CIPN pain models, western blot of PAG tissue, sex-stratified behavioral analysis","journal":"Frontiers in pain research","confidence":"Medium","confidence_rationale":"Tier 2 — sex-stratified in vivo pharmacology with protein quantification, single lab","pmids":["35295419"],"is_preprint":false},{"year":2022,"finding":"GPR171 agonist MS15203 attenuates morphine tolerance in both male and female mice on the tail-flick (but not hotplate) test, and does not exacerbate morphine withdrawal during chronic treatment, indicating a test-dependent functional interaction with mu-opioid receptor signaling.","method":"Chronic morphine tolerance and withdrawal behavioral paradigms, tail-flick and hotplate tests, sex-stratified analysis","journal":"Behavioural pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — in vivo pharmacological interaction, single lab, two behavioral assays giving dissociable results","pmids":["35942845"],"is_preprint":false},{"year":2023,"finding":"GPR171 and its ligand ProSAAS are localized in hippocampus, BLA, nucleus accumbens, prefrontal cortex, and VTA; in the VTA, GPR171 is primarily in dopamine neurons while ProSAAS is outside dopamine neurons. GPR171 agonist MS15203 does not activate VTA neurons (no c-Fos increase) and produces no conditioned place preference, indicating minimal reward liability.","method":"Immunohistochemistry, c-Fos quantification in VTA slices, conditioned place preference","journal":"Pharmacology, biochemistry, and behavior","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct localization with functional consequence (reward circuitry activation), single lab","pmids":["36933620"],"is_preprint":false},{"year":2025,"finding":"GPR171 deficiency promotes Th17 cell differentiation via the cAMP-pCREB-FABP5 axis and alters the lipidome profile of Th17 cells; BigLEN-triggered GPR171 activation inhibits Th17 differentiation in vitro; FABP5 blockade rescues the exacerbated colitis seen in Gpr171-/- mice.","method":"RNA-seq, lipidomics, cAMP/pCREB signaling assays, genetic knockout (Gpr171-/-), in vitro Th17 differentiation, FABP5 pharmacological blockade, DSS and T cell transfer colitis models","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 — mechanistic pathway (cAMP-pCREB-FABP5) defined by multiple orthogonal omics and genetic approaches with rescue experiment","pmids":["40074327"],"is_preprint":false},{"year":2025,"finding":"HIF-1α directly binds hypoxia response elements in the GPR171 promoter and drives GPR171 transcription in mast cells during H. pylori infection; GPR171 activation mediates CCL2 secretion via ERK1/2 signaling; loss or blockade of GPR171 reduces CCL2 and gastric mucosal inflammation.","method":"ChIP, dual-luciferase reporter assay, lentiviral knockdown, ELISA, western blot, in vivo H. pylori mouse model","journal":"Helicobacter","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP and reporter assay define transcriptional mechanism; loss-of-function and in vivo data support downstream ERK1/2-CCL2 pathway","pmids":["40320649"],"is_preprint":false},{"year":2026,"finding":"GPR171 (a P2Y-family GPCR) is expressed in hemogenic endothelium and hematopoietic stem/progenitor cells; its endogenous ligand (encoded by pcsk1nl/BigLEN) cooperates with GPR171 to enhance HSC generation. Mechanistically, GPR171 activates ERK1/2 and Notch signaling pathways independently and synergistically to promote embryonic HSC specification; GPR171-deficient zebrafish and mouse embryos show severe HSC deficits.","method":"Zebrafish gpr171 loss-of-function, genetic knockout mice, pharmacological BigLEN administration, ERK1/2 and Notch pathway assays, HSC quantification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — two vertebrate model systems (zebrafish and mouse KO), pharmacological rescue, and defined downstream signaling (ERK1/2 and Notch)","pmids":["41576080"],"is_preprint":false},{"year":2012,"finding":"Enforced expression of Gpr171 in myeloblastic 32D cells and primary Sca-1+ hematopoietic progenitors decreases myeloid marker expression and increases clonogenic colony formation; conversely, Gpr171 silencing reduces myeloid markers. In vivo, transplantation of Gpr171-overexpressing progenitors reduces Mac-1+Gr-1- myeloid cells, demonstrating that Gpr171 negatively regulates myeloid differentiation.","method":"Retroviral overexpression, shRNA silencing, colony-forming assays, in vivo bone marrow transplant","journal":"Experimental hematology","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function with in vitro and in vivo readouts, single lab","pmids":["23022127"],"is_preprint":false}],"current_model":"GPR171 is a Gαi/o-coupled GPCR that is activated by its endogenous neuropeptide ligand BigLEN (and mimicked by small-molecule agonists), and signals through multiple downstream pathways—including cAMP/pCREB/FABP5, ERK1/2, and Notch—to regulate diverse processes including hypothalamic feeding, anxiety and fear via basolateral amygdala hyperpolarization, mu-opioid receptor modulation in the periaqueductal gray, suppression of T cell (Th17 and TCR) responses, mast cell CCL2 secretion via HIF-1α-driven transcription and ERK1/2, and embryonic hematopoietic stem cell specification."},"narrative":{"teleology":[{"year":2012,"claim":"Before GPR171 was deorphanized, forced expression and silencing in hematopoietic progenitors revealed that GPR171 negatively regulates myeloid differentiation, providing the first indication of a non-neuronal developmental role.","evidence":"Retroviral overexpression and shRNA knockdown in 32D cells and Sca-1+ progenitors with colony assays and in vivo bone marrow transplant","pmids":["23022127"],"confidence":"Medium","gaps":["Ligand unknown at this time","Signaling pathway downstream of GPR171 in hematopoietic cells not identified","Single lab, not independently replicated"]},{"year":2013,"claim":"The identification of BigLEN as the endogenous ligand and Gαi/o as the coupling partner deorphanized GPR171, and hypothalamic knockdown established the BigLEN–GPR171 axis as a physiological regulator of feeding behavior.","evidence":"Binding/signaling assays in Neuro2A cells, shRNA knockdown in mouse hypothalamus, antibody neutralization, feeding behavior assays","pmids":["24043826"],"confidence":"High","gaps":["Structural basis of BigLEN–GPR171 interaction unresolved","Downstream intracellular effectors beyond Gαi/o not yet mapped","Genetic knockout model not available at this point"]},{"year":2016,"claim":"Discovery of the selective small-molecule agonist MS0015203 via virtual screening provided a pharmacological tool and confirmed GPR171 as a druggable target driving food intake and body weight in vivo.","evidence":"Homology-model virtual screen, selectivity panel (80 membrane proteins), hypothalamic shRNA knockdown plus peripheral MS0015203 injection","pmids":["27245612"],"confidence":"High","gaps":["No crystal or cryo-EM structure of GPR171","Metabolic consequences beyond acute feeding not explored","Mechanism of body-weight increase (central vs. peripheral) not dissected"]},{"year":2017,"claim":"Electrophysiological recordings and behavioral assays in the basolateral amygdala demonstrated that GPR171 mediates BigLEN-induced neuronal hyperpolarization and contributes to anxiety and fear conditioning, extending its CNS role beyond feeding.","evidence":"Patch-clamp electrophysiology, antagonist MS0021570_1, lentiviral shRNA in BLA, conditioned fear and anxiety behavioral assays","pmids":["28425495"],"confidence":"High","gaps":["Ion channel identity mediating hyperpolarization not determined","Circuit-level mechanism (interneuron vs. projection neuron contribution) unclear"]},{"year":2019,"claim":"Localization of GPR171 on GABAergic PAG neurons and its selective modulation of mu-opioid (but not delta-opioid) receptor signaling established a functional cross-talk relevant to pain processing.","evidence":"Immunofluorescence colocalization, pharmacological agonist/antagonist in vivo, receptor knockdown, antinociception assays","pmids":["31308196"],"confidence":"Medium","gaps":["Physical interaction or heterodimerization with mu-opioid receptor not demonstrated","Single lab; independent replication needed","Molecular mechanism of selectivity over delta-opioid receptor unknown"]},{"year":2021,"claim":"Demonstration that GPR171 is induced on activated T cells, suppresses TCR signaling and proliferation, and that knockout mice show enhanced antitumor immunity revealed GPR171 as an immune checkpoint–like receptor.","evidence":"Western blot, T cell activation assays, Gpr171 knockout mice, syngeneic tumor models, combination with anti-PD-1","pmids":["34615877"],"confidence":"High","gaps":["Precise TCR signaling node inhibited by GPR171 not identified","Human T cell relevance not established in this study","Whether GPR171 acts cell-autonomously vs. via paracrine BigLEN not resolved"]},{"year":2021,"claim":"GPR171 expression in nociceptor DRG subpopulations and its Gi/o-mediated attenuation of nociceptive ion channel activity extended the receptor's pain-modulatory role to the peripheral nervous system, complementing the central PAG findings.","evidence":"Immunostaining of DRG, Gi/o pharmacology, ion channel functional assays, in vivo pain behavior","pmids":["33807709","35295419"],"confidence":"Medium","gaps":["Specific ion channel targets not molecularly identified","Sex-dependent efficacy (male > female) not mechanistically explained","Single lab findings"]},{"year":2022,"claim":"Chronic GPR171 agonism attenuated morphine tolerance without worsening withdrawal, refining the functional interaction with mu-opioid receptor signaling and suggesting therapeutic potential.","evidence":"Chronic morphine tolerance and withdrawal paradigms, tail-flick and hotplate tests, sex-stratified analysis","pmids":["35942845"],"confidence":"Medium","gaps":["Assay-dependent result (tail-flick but not hotplate) unexplained mechanistically","Single lab","Molecular basis of GPR171–MOR cross-talk still unknown"]},{"year":2023,"claim":"Mapping GPR171 and ProSAAS across limbic/reward circuits and showing that GPR171 agonism does not activate VTA dopamine neurons or produce conditioned place preference addressed reward-liability concerns for therapeutic development.","evidence":"Immunohistochemistry in hippocampus/BLA/NAc/PFC/VTA, c-Fos quantification, conditioned place preference","pmids":["36933620"],"confidence":"Medium","gaps":["Functional role of GPR171 on VTA dopamine neurons remains undefined","Single lab; no self-administration data"]},{"year":2025,"claim":"Definition of the cAMP–pCREB–FABP5 axis downstream of GPR171 in Th17 cells, combined with lipidomic remodeling and rescue of colitis by FABP5 blockade, provided the first detailed intracellular signaling pathway linking GPR171 to adaptive immune regulation.","evidence":"RNA-seq, lipidomics, cAMP/pCREB assays, Gpr171−/− mice, in vitro Th17 differentiation, FABP5 inhibitor, DSS and T cell transfer colitis models","pmids":["40074327"],"confidence":"High","gaps":["Whether the cAMP–pCREB–FABP5 axis operates in other T cell subsets not tested","Lipid species functionally driving Th17 fate not individually validated"]},{"year":2025,"claim":"ChIP and reporter assays showed HIF-1α directly activates GPR171 transcription in mast cells, and GPR171 drives CCL2 secretion via ERK1/2, connecting GPR171 to innate immune inflammation during H. pylori infection.","evidence":"ChIP on GPR171 promoter, dual-luciferase reporter, lentiviral knockdown, ELISA, western blot, H. pylori mouse model","pmids":["40320649"],"confidence":"High","gaps":["Whether HIF-1α regulation of GPR171 occurs in other cell types not addressed","BigLEN source in gastric mucosa not identified"]},{"year":2026,"claim":"Demonstration that GPR171 synergistically activates ERK1/2 and Notch in hemogenic endothelium to specify HSCs, with deficiency causing severe HSC deficits in zebrafish and mouse, established a developmental hematopoietic function conserved across vertebrates.","evidence":"Zebrafish gpr171 loss-of-function, mouse genetic knockout, pharmacological BigLEN rescue, ERK1/2 and Notch pathway assays, HSC quantification","pmids":["41576080"],"confidence":"High","gaps":["Whether GPR171 is required for adult definitive hematopoiesis not tested","How ERK1/2 and Notch are independently and synergistically engaged is mechanistically unresolved"]},{"year":null,"claim":"Major open questions include the structural basis of BigLEN and small-molecule binding, the molecular mechanism of GPR171–mu-opioid receptor cross-talk, the identity of the ion channels modulated in nociceptors, and whether GPR171 immune-checkpoint functions translate to human cancer immunotherapy.","evidence":"","pmids":[],"confidence":"High","gaps":["No experimentally determined GPR171 structure","Physical basis of mu-opioid receptor modulation unresolved","Human clinical validation of immune checkpoint role absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,3,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,8,13]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5,6]}],"pathway":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,10,11,12]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,10,11]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[12,13]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[3,4,9]}],"complexes":[],"partners":["PCSK1N","OPRM1","HIF1A","FABP5"],"other_free_text":[]},"mechanistic_narrative":"GPR171 is a Gαi/o-coupled receptor of the P2Y GPCR family that transduces signals from its endogenous neuropeptide ligand BigLEN (derived from ProSAAS/PCSK1N) to regulate feeding behavior, pain modulation, anxiety, immune cell function, and hematopoietic stem cell specification. Activation by BigLEN or synthetic agonists inhibits cAMP production and engages downstream ERK1/2, cAMP–pCREB–FABP5, and Notch signaling cascades in a context-dependent manner: in the hypothalamus it promotes food intake, in basolateral amygdala pyramidal neurons it drives hyperpolarization linked to anxiety and fear, in the periaqueductal gray it positively modulates mu-opioid receptor signaling and antinociception, and in T cells it suppresses TCR-mediated proliferation and Th17 differentiation [PMID:24043826, PMID:28425495, PMID:31308196, PMID:34615877, PMID:40074327]. GPR171 deficiency in mice enhances antitumor immunity and exacerbates Th17-driven colitis through derepression of the cAMP–pCREB–FABP5 lipid-metabolic axis, while in mast cells HIF-1α–driven GPR171 transcription mediates CCL2 secretion via ERK1/2 during Helicobacter pylori infection [PMID:34615877, PMID:40074327, PMID:40320649]. GPR171 is also required for embryonic hematopoietic stem cell specification, where it synergistically activates ERK1/2 and Notch pathways in hemogenic endothelium, and its loss in zebrafish and mouse embryos causes severe HSC deficits [PMID:41576080, PMID:23022127]."},"prefetch_data":{"uniprot":{"accession":"O14626","full_name":"G-protein coupled receptor 171","aliases":["G-protein coupled receptor H963"],"length_aa":319,"mass_kda":36.8,"function":"G-protein coupled receptor for Big LEN, a 16-amino acid neuropeptide produced from the precursor protein, proSAAS (encoded by PCSK1N). Acts through a G(i)-alpha-mediated pathway in response to Big LEN. Big LEN-GPR171 system plays an important role in regulating feeding and metabolism. Also plays a role in modulating fear and anxiety-like behaviors in the basolateral amygdala. Big LEN-GPR171 modulates the mu-type opioid receptor signaling and antinociception (By similarity). Acts as a negative regulator T cell function (PubMed:34615877)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O14626/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPR171","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GPR171","total_profiled":1310},"omim":[{"mim_id":"618925","title":"G PROTEIN-COUPLED RECEPTOR 171; GPR171","url":"https://www.omim.org/entry/618925"},{"mim_id":"618872","title":"NIZON-ISIDOR SYNDROME; NIZIDS","url":"https://www.omim.org/entry/618872"},{"mim_id":"611318","title":"MEDIATOR COMPLEX SUBUNIT 12-LIKE; MED12L","url":"https://www.omim.org/entry/611318"},{"mim_id":"300399","title":"PROPROTEIN CONVERTASE, SUBTILISIN/KEXIN-TYPE, 1, INHIBITOR OF; PCSK1N","url":"https://www.omim.org/entry/300399"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":12.1},{"tissue":"lymphoid tissue","ntpm":20.1}],"url":"https://www.proteinatlas.org/search/GPR171"},"hgnc":{"alias_symbol":["H963"],"prev_symbol":[]},"alphafold":{"accession":"O14626","domains":[{"cath_id":"1.20.1070.10","chopping":"13-317","consensus_level":"high","plddt":89.3076,"start":13,"end":317}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14626","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14626-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14626-F1-predicted_aligned_error_v6.png","plddt_mean":87.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPR171","jax_strain_url":"https://www.jax.org/strain/search?query=GPR171"},"sequence":{"accession":"O14626","fasta_url":"https://rest.uniprot.org/uniprotkb/O14626.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14626/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14626"}},"corpus_meta":[{"pmid":"24043826","id":"PMC_24043826","title":"GPR171 is a hypothalamic G protein-coupled receptor for BigLEN, a neuropeptide involved in feeding.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/24043826","citation_count":71,"is_preprint":false},{"pmid":"27245612","id":"PMC_27245612","title":"Identification of a small-molecule ligand that activates the neuropeptide receptor GPR171 and increases food intake.","date":"2016","source":"Science signaling","url":"https://pubmed.ncbi.nlm.nih.gov/27245612","citation_count":29,"is_preprint":false},{"pmid":"28425495","id":"PMC_28425495","title":"The BigLEN-GPR171 Peptide Receptor System Within the Basolateral Amygdala Regulates Anxiety-Like Behavior and Contextual Fear Conditioning.","date":"2017","source":"Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/28425495","citation_count":26,"is_preprint":false},{"pmid":"34615877","id":"PMC_34615877","title":"The GPR171 pathway suppresses T cell activation and limits antitumor immunity.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34615877","citation_count":24,"is_preprint":false},{"pmid":"26760963","id":"PMC_26760963","title":"GPR171 expression enhances proliferation and metastasis of lung cancer cells.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26760963","citation_count":19,"is_preprint":false},{"pmid":"23022127","id":"PMC_23022127","title":"Gpr171, a putative P2Y-like receptor, negatively regulates myeloid differentiation in murine hematopoietic progenitors.","date":"2012","source":"Experimental hematology","url":"https://pubmed.ncbi.nlm.nih.gov/23022127","citation_count":18,"is_preprint":false},{"pmid":"35295419","id":"PMC_35295419","title":"GPR171 Agonist Reduces Chronic Neuropathic and Inflammatory Pain in Male, But Not Female Mice.","date":"2021","source":"Frontiers in pain research (Lausanne, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/35295419","citation_count":17,"is_preprint":false},{"pmid":"31308196","id":"PMC_31308196","title":"Opioid-Induced Signaling and Antinociception Are Modulated by the Recently Deorphanized Receptor, GPR171.","date":"2019","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/31308196","citation_count":13,"is_preprint":false},{"pmid":"40074327","id":"PMC_40074327","title":"GPR171 restrains intestinal inflammation by suppressing FABP5-mediated Th17 cell differentiation and lipid metabolism.","date":"2025","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/40074327","citation_count":11,"is_preprint":false},{"pmid":"36212434","id":"PMC_36212434","title":"DIRAS3, GPR171 and RAC2 were identified as the key molecular patterns associated with brain metastasis of breast cancer.","date":"2022","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/36212434","citation_count":10,"is_preprint":false},{"pmid":"33807709","id":"PMC_33807709","title":"GPR171 Activation Modulates Nociceptor Functions, Alleviating Pathologic Pain.","date":"2021","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/33807709","citation_count":10,"is_preprint":false},{"pmid":"35942845","id":"PMC_35942845","title":"GPR171 activation regulates morphine tolerance but not withdrawal in a test-dependent manner in mice.","date":"2022","source":"Behavioural pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35942845","citation_count":3,"is_preprint":false},{"pmid":"40320649","id":"PMC_40320649","title":"HIF-1α-Induced GPR171 Expression Mediates CCL2 Secretion by Mast Cells to Promote Gastric Inflammation During Helicobacter pylori Infection.","date":"2025","source":"Helicobacter","url":"https://pubmed.ncbi.nlm.nih.gov/40320649","citation_count":2,"is_preprint":false},{"pmid":"36933620","id":"PMC_36933620","title":"A small molecule ligand for the novel pain target, GPR171, produces minimal reward in mice.","date":"2023","source":"Pharmacology, biochemistry, and behavior","url":"https://pubmed.ncbi.nlm.nih.gov/36933620","citation_count":2,"is_preprint":false},{"pmid":"41576080","id":"PMC_41576080","title":"Gpr171 regulates embryonic hematopoietic stem cell emergence via ERK1/2 and Notch signaling.","date":"2026","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41576080","citation_count":0,"is_preprint":false},{"pmid":"40450835","id":"PMC_40450835","title":"ProSAAS neuropeptides and receptors GPR171 and GPR83: Potential therapeutic applications for pain, anxiety, and body weight regulation.","date":"2025","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/40450835","citation_count":0,"is_preprint":false},{"pmid":"40318809","id":"PMC_40318809","title":"GPR171 is necessary for normal physiological functions and mood-related behaviors in males, but not females.","date":"2025","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/40318809","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9501,"output_tokens":3440,"usd":0.040051},"stage2":{"model":"claude-opus-4-6","input_tokens":6839,"output_tokens":3214,"usd":0.171818},"total_usd":0.211869,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"GPR171 is the cognate receptor for the neuropeptide BigLEN (LENSSPQAPARRLLPP), coupling through Gαi/o to mediate BigLEN signaling in mouse hypothalamus and Neuro2A cells. The four C-terminal amino acids of BigLEN are sufficient to bind and activate GPR171, whereas the C-terminally truncated peptide LittleLEN does not activate it.\",\n      \"method\": \"Ligand-binding assays, receptor-activity assays, overexpression, shRNA knockdown, orphan GPCR deorphanization screen\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (binding, signaling, gain- and loss-of-function) in heterologous cells and in vivo; replicated across subsequent studies\",\n      \"pmids\": [\"24043826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"shRNA-mediated knockdown of hypothalamic GPR171 decreases BigLEN signaling and reduces food intake; combined knockdown plus BigLEN antibody neutralization nearly eliminates acute feeding in food-deprived mice, establishing the BigLEN-GPR171 system as a regulator of feeding and metabolism.\",\n      \"method\": \"shRNA knockdown in mouse hypothalamus, antibody neutralization, feeding behavior assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean in vivo knockdown with specific behavioral readout, complemented by antibody neutralization\",\n      \"pmids\": [\"24043826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GPR171 is activated by the small-molecule agonist MS0015203, identified by virtual screening of a homology model of GPR171; selectivity confirmed against 80 other membrane proteins including family A GPCRs. Peripheral injection increases food intake and body weight in a GPR171-dependent manner (attenuated by hypothalamic shRNA knockdown).\",\n      \"method\": \"Virtual screen, radioligand binding to 80 GPCRs, shRNA knockdown, in vivo pharmacology\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — compound selectivity panel plus in vivo loss-of-function with defined behavioral phenotype\",\n      \"pmids\": [\"27245612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPR171 in the basolateral amygdala (BLA) mediates BigLEN-induced hyperpolarization of BLA pyramidal neurons; the small-molecule antagonist MS0021570_1 blocks BigLEN-mediated GPR171 activation in heterologous cells and in neurons, and lentiviral knockdown of GPR171 in the BLA reduces anxiety-like behavior and contextual fear conditioning.\",\n      \"method\": \"Electrophysiology (hyperpolarization assay), heterologous cell activation assay, DREADD-mediated neuronal activation, lentiviral shRNA knockdown, behavioral assays\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct electrophysiological evidence plus in vivo lentiviral knockdown with defined behavioral readouts\",\n      \"pmids\": [\"28425495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPR171 is expressed in GABAergic neurons within the periaqueductal gray (PAG) and modulates mu-opioid receptor (but not delta-opioid receptor) signaling; GPR171 agonist enhances and antagonist reduces morphine-induced antinociception; receptor knockdown decreases mu-opioid receptor signaling.\",\n      \"method\": \"Immunofluorescence/colocalization, pharmacological agonist/antagonist administration, receptor knockdown, antinociception behavioral assays\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological modulation with defined receptor specificity and behavioral readout, single lab\",\n      \"pmids\": [\"31308196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR171 protein expression is induced on T cells upon antigen stimulation; BigLEN binding to GPR171 suppresses TCR-mediated signaling pathways and inhibits T cell proliferation; GPR171 knockout mice exhibit enhanced antitumor immunity; GPR171 antagonism improves immune checkpoint blockade therapy.\",\n      \"method\": \"Western blot (protein induction), T cell activation assays, GPR171 knockout mice, tumor models, immune checkpoint blockade combination\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus pharmacological antagonism with multiple orthogonal immune and in vivo tumor readouts\",\n      \"pmids\": [\"34615877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR171 is expressed in nociceptor subpopulations and, when activated by BigLEN or synthetic ligands, attenuates pain signals via Gi/o-coupled modulation of nociceptive ion channel activity, alleviating acute and pathologic pain.\",\n      \"method\": \"Immunostaining of DRG neurons, Gi/o pharmacology, ion channel functional assays, in vivo pain behavior\",\n      \"journal\": \"Biomedicines\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Gi/o coupling and ion channel modulation demonstrated, single lab\",\n      \"pmids\": [\"33807709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR171 agonist MS15203 reduces CFA-induced inflammatory pain thermal hypersensitivity and CIPN-induced allodynia in male but not female mice; GPR171 protein levels in the PAG are decreased after neuropathic pain in males, and MS15203 treatment rescues PAG GPR171 protein levels.\",\n      \"method\": \"In vivo pharmacology, CFA and CIPN pain models, western blot of PAG tissue, sex-stratified behavioral analysis\",\n      \"journal\": \"Frontiers in pain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — sex-stratified in vivo pharmacology with protein quantification, single lab\",\n      \"pmids\": [\"35295419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPR171 agonist MS15203 attenuates morphine tolerance in both male and female mice on the tail-flick (but not hotplate) test, and does not exacerbate morphine withdrawal during chronic treatment, indicating a test-dependent functional interaction with mu-opioid receptor signaling.\",\n      \"method\": \"Chronic morphine tolerance and withdrawal behavioral paradigms, tail-flick and hotplate tests, sex-stratified analysis\",\n      \"journal\": \"Behavioural pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — in vivo pharmacological interaction, single lab, two behavioral assays giving dissociable results\",\n      \"pmids\": [\"35942845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPR171 and its ligand ProSAAS are localized in hippocampus, BLA, nucleus accumbens, prefrontal cortex, and VTA; in the VTA, GPR171 is primarily in dopamine neurons while ProSAAS is outside dopamine neurons. GPR171 agonist MS15203 does not activate VTA neurons (no c-Fos increase) and produces no conditioned place preference, indicating minimal reward liability.\",\n      \"method\": \"Immunohistochemistry, c-Fos quantification in VTA slices, conditioned place preference\",\n      \"journal\": \"Pharmacology, biochemistry, and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct localization with functional consequence (reward circuitry activation), single lab\",\n      \"pmids\": [\"36933620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR171 deficiency promotes Th17 cell differentiation via the cAMP-pCREB-FABP5 axis and alters the lipidome profile of Th17 cells; BigLEN-triggered GPR171 activation inhibits Th17 differentiation in vitro; FABP5 blockade rescues the exacerbated colitis seen in Gpr171-/- mice.\",\n      \"method\": \"RNA-seq, lipidomics, cAMP/pCREB signaling assays, genetic knockout (Gpr171-/-), in vitro Th17 differentiation, FABP5 pharmacological blockade, DSS and T cell transfer colitis models\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway (cAMP-pCREB-FABP5) defined by multiple orthogonal omics and genetic approaches with rescue experiment\",\n      \"pmids\": [\"40074327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HIF-1α directly binds hypoxia response elements in the GPR171 promoter and drives GPR171 transcription in mast cells during H. pylori infection; GPR171 activation mediates CCL2 secretion via ERK1/2 signaling; loss or blockade of GPR171 reduces CCL2 and gastric mucosal inflammation.\",\n      \"method\": \"ChIP, dual-luciferase reporter assay, lentiviral knockdown, ELISA, western blot, in vivo H. pylori mouse model\",\n      \"journal\": \"Helicobacter\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP and reporter assay define transcriptional mechanism; loss-of-function and in vivo data support downstream ERK1/2-CCL2 pathway\",\n      \"pmids\": [\"40320649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GPR171 (a P2Y-family GPCR) is expressed in hemogenic endothelium and hematopoietic stem/progenitor cells; its endogenous ligand (encoded by pcsk1nl/BigLEN) cooperates with GPR171 to enhance HSC generation. Mechanistically, GPR171 activates ERK1/2 and Notch signaling pathways independently and synergistically to promote embryonic HSC specification; GPR171-deficient zebrafish and mouse embryos show severe HSC deficits.\",\n      \"method\": \"Zebrafish gpr171 loss-of-function, genetic knockout mice, pharmacological BigLEN administration, ERK1/2 and Notch pathway assays, HSC quantification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two vertebrate model systems (zebrafish and mouse KO), pharmacological rescue, and defined downstream signaling (ERK1/2 and Notch)\",\n      \"pmids\": [\"41576080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Enforced expression of Gpr171 in myeloblastic 32D cells and primary Sca-1+ hematopoietic progenitors decreases myeloid marker expression and increases clonogenic colony formation; conversely, Gpr171 silencing reduces myeloid markers. In vivo, transplantation of Gpr171-overexpressing progenitors reduces Mac-1+Gr-1- myeloid cells, demonstrating that Gpr171 negatively regulates myeloid differentiation.\",\n      \"method\": \"Retroviral overexpression, shRNA silencing, colony-forming assays, in vivo bone marrow transplant\",\n      \"journal\": \"Experimental hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with in vitro and in vivo readouts, single lab\",\n      \"pmids\": [\"23022127\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPR171 is a Gαi/o-coupled GPCR that is activated by its endogenous neuropeptide ligand BigLEN (and mimicked by small-molecule agonists), and signals through multiple downstream pathways—including cAMP/pCREB/FABP5, ERK1/2, and Notch—to regulate diverse processes including hypothalamic feeding, anxiety and fear via basolateral amygdala hyperpolarization, mu-opioid receptor modulation in the periaqueductal gray, suppression of T cell (Th17 and TCR) responses, mast cell CCL2 secretion via HIF-1α-driven transcription and ERK1/2, and embryonic hematopoietic stem cell specification.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GPR171 is a Gαi/o-coupled receptor of the P2Y GPCR family that transduces signals from its endogenous neuropeptide ligand BigLEN (derived from ProSAAS/PCSK1N) to regulate feeding behavior, pain modulation, anxiety, immune cell function, and hematopoietic stem cell specification. Activation by BigLEN or synthetic agonists inhibits cAMP production and engages downstream ERK1/2, cAMP–pCREB–FABP5, and Notch signaling cascades in a context-dependent manner: in the hypothalamus it promotes food intake, in basolateral amygdala pyramidal neurons it drives hyperpolarization linked to anxiety and fear, in the periaqueductal gray it positively modulates mu-opioid receptor signaling and antinociception, and in T cells it suppresses TCR-mediated proliferation and Th17 differentiation [PMID:24043826, PMID:28425495, PMID:31308196, PMID:34615877, PMID:40074327]. GPR171 deficiency in mice enhances antitumor immunity and exacerbates Th17-driven colitis through derepression of the cAMP–pCREB–FABP5 lipid-metabolic axis, while in mast cells HIF-1α–driven GPR171 transcription mediates CCL2 secretion via ERK1/2 during Helicobacter pylori infection [PMID:34615877, PMID:40074327, PMID:40320649]. GPR171 is also required for embryonic hematopoietic stem cell specification, where it synergistically activates ERK1/2 and Notch pathways in hemogenic endothelium, and its loss in zebrafish and mouse embryos causes severe HSC deficits [PMID:41576080, PMID:23022127].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Before GPR171 was deorphanized, forced expression and silencing in hematopoietic progenitors revealed that GPR171 negatively regulates myeloid differentiation, providing the first indication of a non-neuronal developmental role.\",\n      \"evidence\": \"Retroviral overexpression and shRNA knockdown in 32D cells and Sca-1+ progenitors with colony assays and in vivo bone marrow transplant\",\n      \"pmids\": [\"23022127\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ligand unknown at this time\", \"Signaling pathway downstream of GPR171 in hematopoietic cells not identified\", \"Single lab, not independently replicated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The identification of BigLEN as the endogenous ligand and Gαi/o as the coupling partner deorphanized GPR171, and hypothalamic knockdown established the BigLEN–GPR171 axis as a physiological regulator of feeding behavior.\",\n      \"evidence\": \"Binding/signaling assays in Neuro2A cells, shRNA knockdown in mouse hypothalamus, antibody neutralization, feeding behavior assays\",\n      \"pmids\": [\"24043826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of BigLEN–GPR171 interaction unresolved\", \"Downstream intracellular effectors beyond Gαi/o not yet mapped\", \"Genetic knockout model not available at this point\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery of the selective small-molecule agonist MS0015203 via virtual screening provided a pharmacological tool and confirmed GPR171 as a druggable target driving food intake and body weight in vivo.\",\n      \"evidence\": \"Homology-model virtual screen, selectivity panel (80 membrane proteins), hypothalamic shRNA knockdown plus peripheral MS0015203 injection\",\n      \"pmids\": [\"27245612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of GPR171\", \"Metabolic consequences beyond acute feeding not explored\", \"Mechanism of body-weight increase (central vs. peripheral) not dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Electrophysiological recordings and behavioral assays in the basolateral amygdala demonstrated that GPR171 mediates BigLEN-induced neuronal hyperpolarization and contributes to anxiety and fear conditioning, extending its CNS role beyond feeding.\",\n      \"evidence\": \"Patch-clamp electrophysiology, antagonist MS0021570_1, lentiviral shRNA in BLA, conditioned fear and anxiety behavioral assays\",\n      \"pmids\": [\"28425495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ion channel identity mediating hyperpolarization not determined\", \"Circuit-level mechanism (interneuron vs. projection neuron contribution) unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Localization of GPR171 on GABAergic PAG neurons and its selective modulation of mu-opioid (but not delta-opioid) receptor signaling established a functional cross-talk relevant to pain processing.\",\n      \"evidence\": \"Immunofluorescence colocalization, pharmacological agonist/antagonist in vivo, receptor knockdown, antinociception assays\",\n      \"pmids\": [\"31308196\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physical interaction or heterodimerization with mu-opioid receptor not demonstrated\", \"Single lab; independent replication needed\", \"Molecular mechanism of selectivity over delta-opioid receptor unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstration that GPR171 is induced on activated T cells, suppresses TCR signaling and proliferation, and that knockout mice show enhanced antitumor immunity revealed GPR171 as an immune checkpoint–like receptor.\",\n      \"evidence\": \"Western blot, T cell activation assays, Gpr171 knockout mice, syngeneic tumor models, combination with anti-PD-1\",\n      \"pmids\": [\"34615877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise TCR signaling node inhibited by GPR171 not identified\", \"Human T cell relevance not established in this study\", \"Whether GPR171 acts cell-autonomously vs. via paracrine BigLEN not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"GPR171 expression in nociceptor DRG subpopulations and its Gi/o-mediated attenuation of nociceptive ion channel activity extended the receptor's pain-modulatory role to the peripheral nervous system, complementing the central PAG findings.\",\n      \"evidence\": \"Immunostaining of DRG, Gi/o pharmacology, ion channel functional assays, in vivo pain behavior\",\n      \"pmids\": [\"33807709\", \"35295419\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific ion channel targets not molecularly identified\", \"Sex-dependent efficacy (male > female) not mechanistically explained\", \"Single lab findings\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Chronic GPR171 agonism attenuated morphine tolerance without worsening withdrawal, refining the functional interaction with mu-opioid receptor signaling and suggesting therapeutic potential.\",\n      \"evidence\": \"Chronic morphine tolerance and withdrawal paradigms, tail-flick and hotplate tests, sex-stratified analysis\",\n      \"pmids\": [\"35942845\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Assay-dependent result (tail-flick but not hotplate) unexplained mechanistically\", \"Single lab\", \"Molecular basis of GPR171–MOR cross-talk still unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapping GPR171 and ProSAAS across limbic/reward circuits and showing that GPR171 agonism does not activate VTA dopamine neurons or produce conditioned place preference addressed reward-liability concerns for therapeutic development.\",\n      \"evidence\": \"Immunohistochemistry in hippocampus/BLA/NAc/PFC/VTA, c-Fos quantification, conditioned place preference\",\n      \"pmids\": [\"36933620\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of GPR171 on VTA dopamine neurons remains undefined\", \"Single lab; no self-administration data\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Definition of the cAMP–pCREB–FABP5 axis downstream of GPR171 in Th17 cells, combined with lipidomic remodeling and rescue of colitis by FABP5 blockade, provided the first detailed intracellular signaling pathway linking GPR171 to adaptive immune regulation.\",\n      \"evidence\": \"RNA-seq, lipidomics, cAMP/pCREB assays, Gpr171−/− mice, in vitro Th17 differentiation, FABP5 inhibitor, DSS and T cell transfer colitis models\",\n      \"pmids\": [\"40074327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the cAMP–pCREB–FABP5 axis operates in other T cell subsets not tested\", \"Lipid species functionally driving Th17 fate not individually validated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"ChIP and reporter assays showed HIF-1α directly activates GPR171 transcription in mast cells, and GPR171 drives CCL2 secretion via ERK1/2, connecting GPR171 to innate immune inflammation during H. pylori infection.\",\n      \"evidence\": \"ChIP on GPR171 promoter, dual-luciferase reporter, lentiviral knockdown, ELISA, western blot, H. pylori mouse model\",\n      \"pmids\": [\"40320649\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HIF-1α regulation of GPR171 occurs in other cell types not addressed\", \"BigLEN source in gastric mucosa not identified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Demonstration that GPR171 synergistically activates ERK1/2 and Notch in hemogenic endothelium to specify HSCs, with deficiency causing severe HSC deficits in zebrafish and mouse, established a developmental hematopoietic function conserved across vertebrates.\",\n      \"evidence\": \"Zebrafish gpr171 loss-of-function, mouse genetic knockout, pharmacological BigLEN rescue, ERK1/2 and Notch pathway assays, HSC quantification\",\n      \"pmids\": [\"41576080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GPR171 is required for adult definitive hematopoiesis not tested\", \"How ERK1/2 and Notch are independently and synergistically engaged is mechanistically unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the structural basis of BigLEN and small-molecule binding, the molecular mechanism of GPR171–mu-opioid receptor cross-talk, the identity of the ion channels modulated in nociceptors, and whether GPR171 immune-checkpoint functions translate to human cancer immunotherapy.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimentally determined GPR171 structure\", \"Physical basis of mu-opioid receptor modulation unresolved\", \"Human clinical validation of immune checkpoint role absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 8, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 10, 11, 12]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 10, 11]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [12, 13]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [3, 4, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PCSK1N\",\n      \"OPRM1\",\n      \"HIF1A\",\n      \"FABP5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}