{"gene":"GPR37","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1997,"finding":"GPR37 (hET(B)R-LP) encodes a 614-amino-acid seven-transmembrane GPCR with 52% similarity to endothelin type B receptor; when expressed in COS7 and HEK293 cells, recombinant hET(B)R-LP did not show significant binding of radiolabeled ET-1 or ET-3, and ET-1, ET-3, bombesin, and neuropeptide Y failed to produce Ca2+ mobilization or cAMP changes, indicating endothelins are NOT ligands for this receptor.","method":"Radioligand binding assay, Ca2+ mobilization assay, cAMP assay in transfected COS7/HEK293 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in transfected cells, single lab, negative result mechanistically informative (establishes endothelins are not ligands)","pmids":["9144577"],"is_preprint":false},{"year":2002,"finding":"GPR37 (Pael-R) is a substrate of the E3 ubiquitin ligase Parkin; Parkin specifically ubiquitinates unfolded/insoluble Pael-R and promotes its degradation, suppressing ER stress-induced cell death. Pael-R was identified as a Parkin-binding protein by yeast two-hybrid screening.","method":"Yeast two-hybrid, co-immunoprecipitation, in vitro ubiquitination assay, cell death assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Y2H, Co-IP, in vitro ubiquitination assay), replicated across multiple subsequent studies","pmids":["12150907"],"is_preprint":false},{"year":2002,"finding":"CHIP, Hsp70, Parkin, and GPR37 (Pael-R) form a complex in vitro and in vivo. CHIP promotes dissociation of Hsp70 from Parkin and Pael-R, facilitating Parkin-mediated Pael-R ubiquitination. CHIP enhanced Parkin-mediated in vitro ubiquitination of Pael-R even in the absence of Hsp70, acting as an E4-like co-factor.","method":"Co-immunoprecipitation, in vitro ubiquitination assay, in vitro complex reconstitution","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus Co-IP, multiple orthogonal methods in single rigorous study","pmids":["12150907"],"is_preprint":false},{"year":2003,"finding":"Panneuronal expression of GPR37 (Pael-R) in Drosophila causes age-dependent selective degeneration of dopaminergic neurons; coexpression of Parkin degrades Pael-R and suppresses its toxicity. Interfering with endogenous Drosophila Parkin promotes Pael-R accumulation and augments its toxicity, establishing Parkin as epistatic to Pael-R in this pathway.","method":"Drosophila transgenic overexpression and loss-of-function, DA neuron counting, immunostaining","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in intact organism, gain- and loss-of-function experiments, replicated by multiple labs","pmids":["12670421"],"is_preprint":false},{"year":2003,"finding":"Glup/PACRG (product of gene adjacent to Parkin) forms a large molecular chaperone complex containing Hsp70 and Hsp90, interacts with Pael-R, suppresses Pael-R-induced cell death, and facilitates inclusion body formation when the proteasome is inhibited; Glup knockdown attenuated inclusion formation and promoted cell death.","method":"Co-immunoprecipitation, siRNA knockdown, cell viability assay, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, siRNA knockdown with functional readout, single lab","pmids":["14532270"],"is_preprint":false},{"year":2006,"finding":"HRD1, a ubiquitin ligase expressed in substantia nigra dopaminergic neurons, interacts with GPR37 (Pael-R) through the HRD1 proline-rich region, promotes ubiquitination and degradation of Pael-R, and protects against Pael-R-induced apoptosis. siRNA knockdown of endogenous HRD1 induced Pael-R accumulation and caspase-3 activation.","method":"Co-immunoprecipitation, in vitro ubiquitination assay, siRNA knockdown, caspase-3 activation assay","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, ubiquitination assay, siRNA KD with functional readout), replicated by same group in multiple papers","pmids":["17059562"],"is_preprint":false},{"year":2006,"finding":"GPR37 (Pael-R) overexpression in mouse substantia nigra via adenoviral vectors caused ER stress and death of dopaminergic neurons in vivo. Dopaminergic neuronal death was enhanced in mice deficient in Parkin and the ER chaperone ORP150, and a dopamine synthesis inhibitor blocked neuronal death in parkin null mice, implicating both ER stress and dopamine toxicity in Pael-R-mediated neurodegeneration.","method":"Adenoviral in vivo expression, Parkin knockout mouse, ORP150 knockout mouse, pharmacological inhibition, immunohistochemistry","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological epistasis in vivo, multiple mouse models with defined phenotypic readout","pmids":["17116640"],"is_preprint":false},{"year":2007,"finding":"GPR37 (Pael-R) regulates dopamine metabolism in the nigrostriatal system: Pael-R knockout mice show ~60% striatal dopamine levels compared to wild-type, while Pael-R transgenic mice show increased striatal DOPAC and vesicular dopamine content. Pael-R transgenic nigrostriatal neurons are more vulnerable to PD-related neurotoxins.","method":"Knockout and transgenic mouse models, HPLC dopamine/DOPAC measurement, neurotoxin challenge","journal":"Neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss- and gain-of-function with biochemical readout, single lab","pmids":["17889953"],"is_preprint":false},{"year":2007,"finding":"Thioredoxin (TRX) suppresses Pael-R (GPR37)-induced neurotoxicity in Drosophila dopaminergic neurons; redox-defective TRX mutants still suppressed Pael-R toxicity, suggesting TRX chaperone activity (rather than antioxidant activity) is the primary mechanism of suppression.","method":"Drosophila transgenic coexpression, dopaminergic neuron counting, locomotor activity assay, mutagenesis of TRX active site","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with in vivo functional readout, single lab","pmids":["17301052"],"is_preprint":false},{"year":2008,"finding":"Parkin knockout/Pael-R transgenic double-mutant mice display early and progressive loss of dopaminergic and noradrenergic neurons, activation of the unfolded protein response (UPR), upregulation of dopamine and metabolites, and reduced mitochondrial complex I activity later in life — establishing Pael-R accumulation downstream of Parkin loss as mechanistically causing neurodegeneration.","method":"Double-mutant mouse model (Parkin KO × Pael-R Tg), stereological neuron counting, UPR markers, dopamine HPLC, mitochondrial complex I activity assay","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in vivo with multiple orthogonal phenotypic readouts","pmids":["18691389"],"is_preprint":false},{"year":2009,"finding":"N-terminal truncation of GPR37 (removal of first 210 or all N-terminal amino acids) dramatically enhances plasma membrane surface expression. Coexpression with adenosine A2A receptor or dopamine D2 receptor increases GPR37 surface expression; full-length GPR37 associates with D2R by co-immunoprecipitation, modestly altering D2R agonist/antagonist affinity. GPR37 also specifically interacts with PDZ scaffold syntenin-1, dramatically increasing GPR37 surface expression in HEK-293 cells.","method":"N-terminal truncation constructs, flow cytometry surface expression assay, co-immunoprecipitation, radioligand binding assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (truncation, Co-IP, radioligand binding), single lab","pmids":["19799451"],"is_preprint":false},{"year":2009,"finding":"AAV-mediated overexpression of rat Pael-R (GPR37) in the nigrostriatal system of adult rats causes rapid insoluble accumulation of the receptor, severe loss of nigral dopaminergic neurons and nigrostriatal fibers, striatal dopamine depletion, and spontaneous motor impairments; GABAergic neurons of the globus pallidus were unaffected, demonstrating selective dopaminergic vulnerability.","method":"Recombinant AAV (rAAV2/6) in vivo gene delivery, immunohistochemistry, behavioral testing (cylinder and stepping tests), dopamine HPLC","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gain-of-function with multiple phenotypic readouts, single lab","pmids":["19348945"],"is_preprint":false},{"year":2013,"finding":"GPR37 and GPR37L1 are receptors for prosaptide (active fragment of prosaposin/sulfated glycoprotein-1). Prosaptide promotes endocytosis of GPR37 and GPR37L1, binds both receptors, induces ERK phosphorylation in a pertussis toxin-sensitive manner, stimulates 35S-GTPγS binding, and inhibits forskolin-stimulated cAMP production in a GPR37/GPR37L1-dependent manner. Full-length prosaposin also activates GPR37 signaling. siRNA knockdown of GPR37 or GPR37L1 attenuates prosaptide/prosaposin-mediated astrocyte protection against oxidative stress.","method":"Receptor endocytosis assay, radioligand binding, ERK phosphorylation assay with pertussis toxin, 35S-GTPγS binding, cAMP assay, siRNA knockdown, cell viability assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal biochemical assays plus loss-of-function with functional readout in one study","pmids":["23690594"],"is_preprint":false},{"year":2013,"finding":"The C-terminal cysteine-rich domain of GPR37 controls its plasma membrane expression, signaling, and cytotoxicity. Deletion of six cysteine residues in this region promoted GPR37 plasma membrane expression and signaling without affecting receptor internalization, and protected against GPR37-mediated apoptosis and cell death.","method":"Site-directed mutagenesis/deletion constructs, flow cytometry surface expression, cell death/apoptosis assays","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with multiple functional readouts, single lab","pmids":["23398388"],"is_preprint":false},{"year":2014,"finding":"PICK1 interacts with GPR37 (PAELR) via its PDZ domain binding to the C-terminal PDZ motif of PAELR. Pull-down assays confirmed PICK1 is retained by GST-fused C-terminal PAELR from both heterologous cells and rat brain tissue. PICK1 overexpression reduces PAELR expression levels and reduces PAELR-induced cell death during rotenone treatment in a proteasome-dependent manner.","method":"GST pull-down, co-immunoprecipitation from rat brain tissue and transfected cells, cell viability assay, proteasome inhibitor treatment","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — reciprocal pull-down from native tissue plus functional cell death assay, single lab","pmids":["24749734"],"is_preprint":false},{"year":2018,"finding":"GABARAPL2 interacts with GPR37 (PAELR) via the GABAA binding site of GABARAPL2 and the cysteine-rich region (-CCCCCC-EEC) of the C-terminal of PAELR. Affinity chromatography confirmed Myc-GABARAPL2 is retained by GST-fused C-terminal PAELR. Transient transfection of GABARAPL2 reduces PAELR expression, suggesting autophagy-mediated regulation.","method":"GST affinity chromatography, in-silico modelling, transfection/Western blot","journal":"Neuroscience letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single pull-down method, single lab, no rescue experiment","pmids":["29496607"],"is_preprint":false},{"year":2019,"finding":"GPR37 signaling is required for the migration of olfactory ensheathing cells and GnRH neurons in the developing mouse olfactory system. Inhibition of GPR37 signaling in nasal explants attenuated GnRH neuronal migration and OEC movement. GPR37-deficient mice showed decreased olfactory bulb nerve layer and attenuated/delayed GnRH neuron migration into the brain.","method":"GPR37 knockout mouse, nasal explant cultures with GPR37 inhibition, immunocytochemistry, PCR","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus pharmacological inhibition in explants with cellular migration readout, single lab","pmids":["31143101"],"is_preprint":false},{"year":2024,"finding":"Osteocalcin (OCN), a bone-derived protein, activates GPR37 in a subpopulation of VTA GABAergic neurons to decrease potassium currents via GPR37-induced cAMP reduction and subsequent suppression of THIK-1 (K2P13.1) channels, increasing neuronal excitability. Knockout of GPR37 or conditional knockout in VTA GABAergic neurons delayed rapid visual escape response; reconstituting OCN-GPR37 signaling in VTA restored normal response.","method":"GPR37 knockout and conditional knockout mice, single-cell transcriptomics, patch-clamp electrophysiology, chemogenetics (HM4Di), behavioral assay (visual escape)","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic models with electrophysiology and behavioral readout, preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"GPR37 activation in TRPV1-lineage sensory neurons at the spinal level erases nociceptive sensitization. Intrathecal GPR37 agonists (TX14A and protectin D1) dose-dependently inhibited capsaicin-induced nociception acutely and long-term, and produced 'unpriming' in the hyperalgesic priming model. Global GPR37 KO and conditional KO in TRPV1-lineage neurons abolished these effects. Ex vivo Ca2+ imaging showed i.th. TX14A rescued dorsal horn interneurons from long-term potentiation/depression.","method":"GPR37 global knockout, conditional knockout (TRPV1-Cre), intrathecal pharmacology, behavioral nociceptive assays, ex vivo Ca2+ imaging of dorsal horn neurons","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus conditional KO with pharmacological and imaging readouts, preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"Protectin DX (PDX) activates GPR37 on macrophages to promote efferocytosis of apoptotic cells via calcium signaling. In a tibial fracture pain model, analgesic effects of PDX were abolished in Gpr37−/− mice. PDX binds GPR37 and induces calcium responses in peritoneal macrophages in a GPR37-dependent manner.","method":"GPR37 knockout mouse, in vivo fracture pain model, in vitro macrophage efferocytosis assay, calcium imaging, lipidomics","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with in vivo and in vitro functional readouts, preprint not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"GPR37 (Pael-R/PAELR) is an orphan GPCR predominantly expressed in the nervous system that acts as a substrate of the E3 ubiquitin ligase Parkin; when unfolded or overexpressed, it accumulates in the ER and triggers ER stress-induced dopaminergic neurodegeneration relevant to Parkinson's disease. Parkin, together with co-factors CHIP and Hsp70, ubiquitinates and degrades misfolded GPR37; the ER ubiquitin ligase HRD1 provides a parallel degradation pathway. When properly folded and trafficked to the plasma membrane — facilitated by N-terminal truncation, coexpression with D2R or A2AR, or interaction with syntenin-1 — GPR37 couples to Gi/o proteins and is activated by prosaptide/prosaposin to signal through ERK phosphorylation and cAMP inhibition, exerting neuroprotective and glioprotective effects. GPR37 also modulates dopamine metabolism, interacts with the dopamine transporter and D2R, regulates GnRH and olfactory ensheathing cell migration, controls pain sensitization via TRPV1-lineage spinal neurons, mediates macrophage efferocytosis in response to protectins, and in VTA GABAergic neurons mediates osteocalcin signaling to suppress THIK-1 K+ channels and increase neuronal excitability."},"narrative":{"mechanistic_narrative":"GPR37 (Pael-R) is a seven-transmembrane G protein-coupled receptor expressed predominantly in the nervous system whose dysfunction links protein quality control to dopaminergic neurodegeneration [PMID:9144577, PMID:12150907]. Although originally cloned for its similarity to the endothelin type B receptor, endothelins do not bind or activate it [PMID:9144577]. GPR37 is intrinsically prone to misfolding: when unfolded or overexpressed it accumulates in the ER and triggers ER stress and selective dopaminergic neuron death, a phenotype demonstrated in Drosophila, in mouse and rat substantia nigra, and exacerbated by loss of the ER chaperone ORP150 [PMID:12670421, PMID:17116640, PMID:19348945]. The receptor is a substrate of the Parkinson's disease E3 ubiquitin ligase Parkin, which ubiquitinates and degrades misfolded GPR37 to suppress ER stress-induced cell death; CHIP and Hsp70 act as co-factors that potentiate this ubiquitination, and the chaperone-associated proteins PACRG/Glup and thioredoxin further buffer GPR37 toxicity [PMID:12150907, PMID:14532270, PMID:17301052]. A parallel ER-associated ligase, HRD1, independently ubiquitinates and degrades GPR37 and protects against its apoptotic accumulation [PMID:17059562]. Loss of Parkin combined with GPR37 transgene expression causes early progressive loss of dopaminergic and noradrenergic neurons with UPR activation, establishing GPR37 accumulation downstream of Parkin loss as a cause of neurodegeneration [PMID:18691389]. GPR37 surface trafficking is gated by its cysteine-rich C-terminal domain and its N-terminus, and is enhanced by N-terminal truncation, co-expression with dopamine D2 or adenosine A2A receptors, and binding of the PDZ scaffold syntenin-1, while PICK1 and GABARAPL2 bind its C-terminus and lower receptor levels [PMID:19799451, PMID:23398388, PMID:24749734]. Once at the membrane, GPR37 functions as a Gi/o-coupled receptor activated by prosaptide/prosaposin, signaling through pertussis-toxin-sensitive ERK phosphorylation and inhibition of cAMP to confer cytoprotection against oxidative stress [PMID:23690594]. GPR37 additionally regulates striatal dopamine metabolism [PMID:17889953], guides olfactory ensheathing cell and GnRH neuron migration in development [PMID:31143101], and serves as a receptor for lipid and peptide ligands in pain and immune contexts.","teleology":[{"year":1997,"claim":"Cloning of an endothelin-receptor-like orphan GPCR resolved whether endothelins were its ligands, establishing GPR37 as a true orphan receptor.","evidence":"Radioligand binding, Ca2+ and cAMP assays in transfected COS7/HEK293 cells","pmids":["9144577"],"confidence":"Medium","gaps":["No endogenous ligand identified at this stage","No cellular function or localization defined"]},{"year":2002,"claim":"Identification of GPR37 as a Parkin substrate connected an orphan GPCR to Parkinson's disease protein quality control, defining how misfolded GPR37 is cleared to prevent ER stress death.","evidence":"Yeast two-hybrid, Co-IP, in vitro ubiquitination and cell death assays; CHIP/Hsp70 complex reconstitution","pmids":["12150907"],"confidence":"High","gaps":["Degradation studied in overexpression contexts","Physiological substrate role of folded receptor not addressed"]},{"year":2003,"claim":"In vivo genetic epistasis in Drosophila established that GPR37 accumulation selectively kills dopaminergic neurons and that Parkin acts upstream to suppress this toxicity.","evidence":"Drosophila transgenic gain- and loss-of-function with DA neuron counting","pmids":["12670421"],"confidence":"High","gaps":["Mechanism of dopaminergic selectivity unresolved","Endogenous ligand and signaling not involved in toxicity readout"]},{"year":2003,"claim":"Discovery of PACRG/Glup as a chaperone-complex partner showed GPR37 handling involves Hsp70/Hsp90 machinery directing it to inclusion bodies or death.","evidence":"Co-IP, siRNA knockdown, cell viability and immunofluorescence","pmids":["14532270"],"confidence":"Medium","gaps":["Single lab","In vivo relevance of inclusion formation not tested"]},{"year":2006,"claim":"Identification of HRD1 revealed a Parkin-independent ER-associated degradation route for GPR37, explaining parallel clearance of the misfolded receptor.","evidence":"Co-IP, in vitro ubiquitination, siRNA knockdown with caspase-3 readout","pmids":["17059562"],"confidence":"High","gaps":["Relative contribution of HRD1 versus Parkin in vivo unquantified"]},{"year":2006,"claim":"In vivo overexpression in mouse substantia nigra established that GPR37 causes ER stress and dopamine-dependent neuron death, mechanistically separating ER stress and dopamine toxicity components.","evidence":"Adenoviral expression, Parkin and ORP150 KO mice, dopamine synthesis inhibition, IHC","pmids":["17116640"],"confidence":"High","gaps":["Link between ER stress and dopamine toxicity not molecularly defined"]},{"year":2007,"claim":"Knockout and transgenic mice showed GPR37 regulates nigrostriatal dopamine levels and neurotoxin vulnerability, indicating a physiological role beyond misfolding toxicity.","evidence":"KO/Tg mice, HPLC dopamine/DOPAC, neurotoxin challenge","pmids":["17889953"],"confidence":"Medium","gaps":["Mechanism linking GPR37 to dopamine handling unknown","Single lab"]},{"year":2007,"claim":"Thioredoxin was shown to suppress GPR37 toxicity through chaperone rather than antioxidant activity, refining the protein-folding basis of GPR37 neurotoxicity.","evidence":"Drosophila coexpression with TRX active-site mutagenesis, DA neuron and locomotor readouts","pmids":["17301052"],"confidence":"Medium","gaps":["Direct TRX-GPR37 interaction not shown","Single lab"]},{"year":2008,"claim":"A Parkin KO × GPR37 transgenic double mutant placed GPR37 accumulation downstream of Parkin loss as causal for progressive neurodegeneration with UPR and complex I deficits.","evidence":"Double-mutant mice, stereology, UPR markers, dopamine HPLC, complex I assay","pmids":["18691389"],"confidence":"High","gaps":["Whether complex I deficit is direct or secondary not resolved"]},{"year":2009,"claim":"Mapping of trafficking determinants showed N-terminal truncation, D2R/A2AR coexpression, and syntenin-1 binding promote GPR37 surface delivery, explaining how the misfolding-prone receptor reaches the membrane.","evidence":"Truncation constructs, flow cytometry, Co-IP, radioligand binding","pmids":["19799451"],"confidence":"Medium","gaps":["Functional consequence of D2R heterocomplex on signaling unclear","Single lab"]},{"year":2009,"claim":"AAV overexpression in adult rat nigrostriatum reproduced selective dopaminergic loss and motor deficits, validating GPR37 accumulation as a mammalian PD-relevant lesion.","evidence":"rAAV2/6 delivery, IHC, behavioral tests, dopamine HPLC","pmids":["19348945"],"confidence":"Medium","gaps":["Endogenous receptor levels in pathology not addressed","Single lab"]},{"year":2013,"claim":"Identification of prosaptide/prosaposin as agonists deorphanized GPR37, defining it as a Gi/o-coupled cytoprotective receptor signaling via ERK and cAMP inhibition.","evidence":"Endocytosis, radioligand binding, ERK with PTX, GTPγS, cAMP, siRNA, cell viability","pmids":["23690594"],"confidence":"High","gaps":["Structural basis of ligand binding not defined","In vivo signaling outputs not mapped"]},{"year":2013,"claim":"The C-terminal cysteine-rich domain was shown to govern surface expression, signaling, and cytotoxicity, identifying a structural switch between toxic and functional receptor states.","evidence":"Cysteine deletion mutants, flow cytometry, apoptosis/death assays","pmids":["23398388"],"confidence":"Medium","gaps":["Single lab","Native regulation of these cysteines unknown"]},{"year":2014,"claim":"PICK1 was identified as a PDZ partner that lowers GPR37 levels and reduces its toxicity proteasome-dependently, adding a scaffold-linked regulatory layer.","evidence":"GST pull-down from brain and cells, Co-IP, viability under rotenone, proteasome inhibition","pmids":["24749734"],"confidence":"Medium","gaps":["Mechanism of PICK1-directed degradation unclear","Single lab"]},{"year":2018,"claim":"GABARAPL2 binding to the GPR37 C-terminus implicated autophagy in regulating receptor levels.","evidence":"GST affinity chromatography, in-silico modeling, transfection/Western","pmids":["29496607"],"confidence":"Low","gaps":["Single pull-down method without rescue","Autophagic degradation not directly demonstrated"]},{"year":2019,"claim":"GPR37 signaling was found to drive olfactory ensheathing cell and GnRH neuron migration, establishing a developmental morphogenetic role.","evidence":"GPR37 KO mice, nasal explant inhibition, immunocytochemistry, PCR","pmids":["31143101"],"confidence":"Medium","gaps":["Downstream migratory signaling pathway unknown","Single lab"]},{"year":2024,"claim":"Osteocalcin was shown to activate GPR37 in VTA GABAergic neurons to suppress THIK-1 channels via cAMP reduction, linking a bone-derived ligand to neuronal excitability and behavior.","evidence":"GPR37 KO and conditional KO, scRNA-seq, patch-clamp, chemogenetics, visual escape behavior (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","Direct OCN-GPR37 binding not shown"]},{"year":2025,"claim":"GPR37 activation by lipid mediators in TRPV1-lineage sensory neurons and macrophages was shown to resolve nociceptive sensitization and promote efferocytosis, expanding its ligand repertoire to specialized pro-resolving mediators.","evidence":"Global and conditional GPR37 KO, intrathecal pharmacology, behavioral and Ca2+ imaging, macrophage efferocytosis (preprints)","pmids":[],"confidence":"Medium","gaps":["Preprints not yet peer-reviewed","Receptor coupling in these cell types not fully defined"]},{"year":null,"claim":"How GPR37 reconciles its misfolding-driven neurotoxic accumulation with its physiological ligand-activated cytoprotective and excitability-modulating signaling remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of GPR37 with any ligand","Quantitative balance of degradation pathways in disease unknown","Mechanism linking same receptor to both death and protection unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[12,17]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[12]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,6]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[10,13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,6]}],"complexes":["Parkin–CHIP–Hsp70–GPR37 complex"],"partners":["PARK2","STUB1","HSPA1A","SYNJ2BP","HRD1","PICK1","DRD2","GABARAPL2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15354","full_name":"Prosaposin receptor GPR37","aliases":["Endothelin B receptor-like protein 1","ETBR-LP-1","G-protein coupled receptor 37","Parkin-associated endothelin receptor-like receptor","PAELR"],"length_aa":613,"mass_kda":67.1,"function":"G-protein-coupled receptor that plays a role in several physiological pathways such as resolution of inflammatory pain and oligodendrocyte differentiation (By similarity). Acts as a receptor for several ligands including prosaposin, osteocalcin or neuroprotectin D1. Ligand binding induces endocytosis, followed by an ERK phosphorylation cascade (PubMed:11439185, PubMed:23690594). Acts as a receptor for osteocalcin (OCN) to regulate oligodendrocyte differentiation and central nervous system myelination. Mechanistically, plays a negative role in oligodendrocyte differentiation and myelination during development via activation of the ERK1/2 signaling pathway. Therefore, regulates the stability of myelin or resistance of myelin itself to demyelination. Upon activation by neuroprotectin D1 (NPD1), promotes the activation of phagocytosis in macrophages as well as the shift in cytokine release toward an anti-inflammatory profile, and thus helps to reverse inflammatory pain. In addition, the increased macrophage phagocytosis mediates protection against sepsis upon pathogen infection. Additionally, extracellular vesicles derived from efferocyte express prosaposin, which binds to macrophage GPR37 to increase expression of the efferocytosis receptor TIM4 via an ERK-AP1-dependent signaling axis, leading to increased macrophage efferocytosis efficiency and accelerated resolution of inflammation (By similarity). May also act as a maturation factor of LRP6, protecting LRP6 from the endoplasmic reticulum (ER)-associated protein degradation (ERAD) and thereby promoting the Wnt/beta-catenin signaling pathway (PubMed:28341812)","subcellular_location":"Cell projection, dendrite; Synapse; Cell membrane; Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/O15354/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPR37","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/GPR37","total_profiled":1310},"omim":[{"mim_id":"621533","title":"NEURODEVELOPMENTAL DISORDER WITH SEIZURES AND IMPAIRED INTELLECTUAL AND LANGUAGE DEVELOPMENT; NEDSIL","url":"https://www.omim.org/entry/621533"},{"mim_id":"618487","title":"G PROTEIN-COUPLED RECEPTOR 151; GPR151","url":"https://www.omim.org/entry/618487"},{"mim_id":"617630","title":"G PROTEIN-COUPLED RECEPTOR 37-LIKE 1; GPR37L1","url":"https://www.omim.org/entry/617630"},{"mim_id":"611176","title":"JNK/MAPK8-ASSOCIATED MEMBRANE PROTEIN; JKAMP","url":"https://www.omim.org/entry/611176"},{"mim_id":"602583","title":"G PROTEIN-COUPLED RECEPTOR 37; GPR37","url":"https://www.omim.org/entry/602583"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Nuclear membrane","reliability":"Uncertain"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":67.2},{"tissue":"retina","ntpm":36.2}],"url":"https://www.proteinatlas.org/search/GPR37"},"hgnc":{"alias_symbol":["EDNRBL","hET(B)R-LP","PAELR"],"prev_symbol":[]},"alphafold":{"accession":"O15354","domains":[{"cath_id":"1.20.1070.10","chopping":"256-400_419-573","consensus_level":"high","plddt":82.7383,"start":256,"end":573}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15354","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15354-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15354-F1-predicted_aligned_error_v6.png","plddt_mean":61.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPR37","jax_strain_url":"https://www.jax.org/strain/search?query=GPR37"},"sequence":{"accession":"O15354","fasta_url":"https://rest.uniprot.org/uniprotkb/O15354.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15354/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15354"}},"corpus_meta":[{"pmid":"12150907","id":"PMC_12150907","title":"CHIP is associated with Parkin, a gene responsible for familial Parkinson's disease, and enhances its ubiquitin ligase activity.","date":"2002","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/12150907","citation_count":405,"is_preprint":false},{"pmid":"12670421","id":"PMC_12670421","title":"Parkin suppresses dopaminergic neuron-selective neurotoxicity induced by Pael-R in Drosophila.","date":"2003","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/12670421","citation_count":301,"is_preprint":false},{"pmid":"12676955","id":"PMC_12676955","title":"Parkin facilitates the elimination of expanded polyglutamine proteins and leads to preservation of proteasome function.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12676955","citation_count":231,"is_preprint":false},{"pmid":"23690594","id":"PMC_23690594","title":"GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23690594","citation_count":194,"is_preprint":false},{"pmid":"16539653","id":"PMC_16539653","title":"Suppressive effects of 4-phenylbutyrate on the aggregation of Pael receptors and endoplasmic reticulum stress.","date":"2006","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16539653","citation_count":152,"is_preprint":false},{"pmid":"14991825","id":"PMC_14991825","title":"Pael-R is accumulated in Lewy bodies of Parkinson's disease.","date":"2004","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/14991825","citation_count":125,"is_preprint":false},{"pmid":"24250222","id":"PMC_24250222","title":"Pathway Analysis of ChIP-Seq-Based NRF1 Target Genes Suggests a Logical Hypothesis of their Involvement in the Pathogenesis of Neurodegenerative Diseases.","date":"2013","source":"Gene regulation and systems biology","url":"https://pubmed.ncbi.nlm.nih.gov/24250222","citation_count":117,"is_preprint":false},{"pmid":"19339245","id":"PMC_19339245","title":"Identification of a novel Zn2+-binding domain in the autosomal recessive juvenile Parkinson-related E3 ligase parkin.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19339245","citation_count":109,"is_preprint":false},{"pmid":"23710284","id":"PMC_23710284","title":"Endoplasmic reticulum stress and Parkinson's disease: the role of HRD1 in averting apoptosis in neurodegenerative disease.","date":"2013","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/23710284","citation_count":103,"is_preprint":false},{"pmid":"12691660","id":"PMC_12691660","title":"Parkin: a multipurpose neuroprotective agent?","date":"2003","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/12691660","citation_count":93,"is_preprint":false},{"pmid":"17116640","id":"PMC_17116640","title":"Pael receptor induces death of dopaminergic neurons in the substantia nigra via endoplasmic reticulum stress and dopamine toxicity, which is enhanced under condition of parkin inactivation.","date":"2006","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17116640","citation_count":89,"is_preprint":false},{"pmid":"17059562","id":"PMC_17059562","title":"A ubiquitin ligase HRD1 promotes the degradation of Pael receptor, a substrate of Parkin.","date":"2006","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17059562","citation_count":78,"is_preprint":false},{"pmid":"22223342","id":"PMC_22223342","title":"Protective effects of 4-phenylbutyrate derivatives on the neuronal cell death and endoplasmic reticulum stress.","date":"2012","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/22223342","citation_count":69,"is_preprint":false},{"pmid":"19799451","id":"PMC_19799451","title":"GPR37 surface expression enhancement via N-terminal truncation or protein-protein interactions.","date":"2009","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19799451","citation_count":60,"is_preprint":false},{"pmid":"14532270","id":"PMC_14532270","title":"A product of the human gene adjacent to parkin is a component of Lewy bodies and suppresses Pael receptor-induced cell death.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14532270","citation_count":59,"is_preprint":false},{"pmid":"9144577","id":"PMC_9144577","title":"A novel endothelin receptor type-B-like gene enriched in the brain.","date":"1997","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/9144577","citation_count":57,"is_preprint":false},{"pmid":"14579121","id":"PMC_14579121","title":"Pael receptor, endoplasmic reticulum stress, and Parkinson's disease.","date":"2003","source":"Journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/14579121","citation_count":55,"is_preprint":false},{"pmid":"23251443","id":"PMC_23251443","title":"Mutation in Parkinson disease-associated, G-protein-coupled receptor 37 (GPR37/PaelR) is related to autism spectrum disorder.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23251443","citation_count":48,"is_preprint":false},{"pmid":"18691389","id":"PMC_18691389","title":"Pael-R transgenic mice crossed with parkin deficient mice displayed progressive and selective catecholaminergic neuronal loss.","date":"2008","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18691389","citation_count":48,"is_preprint":false},{"pmid":"19348945","id":"PMC_19348945","title":"Targeted overexpression of the parkin substrate Pael-R in the nigrostriatal system of adult rats to model Parkinson's disease.","date":"2009","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/19348945","citation_count":48,"is_preprint":false},{"pmid":"31963327","id":"PMC_31963327","title":"TGF-β/Smad3 Signalling Modulates GABA Neurotransmission: Implications in Parkinson's Disease.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31963327","citation_count":44,"is_preprint":false},{"pmid":"26635605","id":"PMC_26635605","title":"Drug Discovery Opportunities at the Endothelin B Receptor-Related Orphan G Protein-Coupled Receptors, GPR37 and GPR37L1.","date":"2015","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/26635605","citation_count":42,"is_preprint":false},{"pmid":"17889953","id":"PMC_17889953","title":"Pael receptor is involved in dopamine metabolism in the nigrostriatal system.","date":"2007","source":"Neuroscience research","url":"https://pubmed.ncbi.nlm.nih.gov/17889953","citation_count":39,"is_preprint":false},{"pmid":"17301052","id":"PMC_17301052","title":"Thioredoxin suppresses Parkin-associated endothelin receptor-like receptor-induced neurotoxicity and extends longevity in Drosophila.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17301052","citation_count":35,"is_preprint":false},{"pmid":"18344614","id":"PMC_18344614","title":"Novel functions of ubiquitin ligase HRD1 with transmembrane and proline-rich domains.","date":"2008","source":"Journal of pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/18344614","citation_count":35,"is_preprint":false},{"pmid":"18241051","id":"PMC_18241051","title":"Immunohistochemical localization of a ubiquitin ligase HRD1 in murine brain.","date":"2008","source":"Journal of neuroscience research","url":"https://pubmed.ncbi.nlm.nih.gov/18241051","citation_count":34,"is_preprint":false},{"pmid":"23398388","id":"PMC_23398388","title":"The Parkinson's disease-associated GPR37 receptor-mediated cytotoxicity is controlled by its intracellular cysteine-rich domain.","date":"2013","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23398388","citation_count":31,"is_preprint":false},{"pmid":"28629580","id":"PMC_28629580","title":"Folding Underlies Bidirectional Role of GPR37/Pael-R in Parkinson Disease.","date":"2017","source":"Trends in pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/28629580","citation_count":28,"is_preprint":false},{"pmid":"25169131","id":"PMC_25169131","title":"A low level of GPR37 is associated with human hepatocellular carcinoma progression and poor patient survival.","date":"2014","source":"Pathology, research and practice","url":"https://pubmed.ncbi.nlm.nih.gov/25169131","citation_count":28,"is_preprint":false},{"pmid":"29083378","id":"PMC_29083378","title":"Neuroprotection by Endoplasmic Reticulum Stress-Induced HRD1 and Chaperones: Possible Therapeutic Targets for Alzheimer's and Parkinson's Disease.","date":"2016","source":"Medical sciences (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/29083378","citation_count":19,"is_preprint":false},{"pmid":"25862943","id":"PMC_25862943","title":"Adenosine A2A receptor-mediated control of pilocarpine-induced tremulous jaw movements is Parkinson's disease-associated GPR37 receptor-dependent.","date":"2015","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/25862943","citation_count":17,"is_preprint":false},{"pmid":"31143101","id":"PMC_31143101","title":"GPR37 Signaling Modulates Migration of Olfactory Ensheathing Cells and Gonadotropin Releasing Hormone Cells in Mice.","date":"2019","source":"Frontiers in cellular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/31143101","citation_count":12,"is_preprint":false},{"pmid":"23208051","id":"PMC_23208051","title":"[Molecular pharmacological studies on the protection mechanism against endoplasmic reticulum stress-induced neurodegenerative disease].","date":"2012","source":"Yakugaku zasshi : Journal of the Pharmaceutical Society of Japan","url":"https://pubmed.ncbi.nlm.nih.gov/23208051","citation_count":12,"is_preprint":false},{"pmid":"24749734","id":"PMC_24749734","title":"The protein interacting with C-kinase (PICK1) interacts with and attenuates parkin-associated endothelial-like (PAEL) receptor-mediated cell death.","date":"2014","source":"Journal of neurochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24749734","citation_count":11,"is_preprint":false},{"pmid":"27252059","id":"PMC_27252059","title":"[Physiological Roles of Ubiquitin Ligases Related to the Endoplasmic Reticulum].","date":"2016","source":"Yakugaku zasshi : Journal of the Pharmaceutical Society of Japan","url":"https://pubmed.ncbi.nlm.nih.gov/27252059","citation_count":8,"is_preprint":false},{"pmid":"29496607","id":"PMC_29496607","title":"A novel modelling mechanism of PAEL receptor and GABARAPL2 interaction involved in Parkinson's disease.","date":"2018","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/29496607","citation_count":7,"is_preprint":false},{"pmid":"24694815","id":"PMC_24694815","title":"[Pharmacological studies on neurodegenerative diseases focusing on refolding and degradation of unfolded proteins in the endoplasmic reticulum].","date":"2014","source":"Yakugaku zasshi : Journal of the Pharmaceutical Society of Japan","url":"https://pubmed.ncbi.nlm.nih.gov/24694815","citation_count":7,"is_preprint":false},{"pmid":"22898202","id":"PMC_22898202","title":"Downregulation of Pael-R expression in a Parkinson's disease cell model reduces apoptosis.","date":"2012","source":"Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia","url":"https://pubmed.ncbi.nlm.nih.gov/22898202","citation_count":6,"is_preprint":false},{"pmid":"38852645","id":"PMC_38852645","title":"5-Phenyl valeric acid attenuates α-synuclein aggregation and endoplasmic reticulum stress in rotenone-induced Parkinson's disease rats: A molecular mechanistic study.","date":"2024","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/38852645","citation_count":5,"is_preprint":false},{"pmid":"15572843","id":"PMC_15572843","title":"[Protective effects of HRD1 and 4-phenylbutyric acid against neuronal cell death].","date":"2004","source":"Nihon yakurigaku zasshi. Folia pharmacologica Japonica","url":"https://pubmed.ncbi.nlm.nih.gov/15572843","citation_count":4,"is_preprint":false},{"pmid":"17251065","id":"PMC_17251065","title":"Cloning and developmental expression of a chick G-protein-coupled receptor SCGPR1.","date":"2006","source":"Gene expression patterns : GEP","url":"https://pubmed.ncbi.nlm.nih.gov/17251065","citation_count":3,"is_preprint":false},{"pmid":"15572841","id":"PMC_15572841","title":"[Neurodegeneration caused by ER stress?--the pathogenetic mechanisms underlying AR-JP].","date":"2004","source":"Nihon yakurigaku zasshi. Folia pharmacologica Japonica","url":"https://pubmed.ncbi.nlm.nih.gov/15572841","citation_count":2,"is_preprint":false},{"pmid":"25206827","id":"PMC_25206827","title":"The Pael-R gene does not mediate the changes in rotenone-induced Parkinson's disease model cells.","date":"2014","source":"Neural regeneration research","url":"https://pubmed.ncbi.nlm.nih.gov/25206827","citation_count":1,"is_preprint":false},{"pmid":"18210841","id":"PMC_18210841","title":"[Animal models for familial Parkinson's disease].","date":"2007","source":"Rinsho shinkeigaku = Clinical neurology","url":"https://pubmed.ncbi.nlm.nih.gov/18210841","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.25.690482","title":"Spinal-level activation of GPR37 in TRPV1-expressing sensory neurons erases nociceptive system sensitization in murine models","date":"2025-11-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.25.690482","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.11.10.687700","title":"Protectin DX resolves fracture-induced postoperative pain in mice via neuronal signaling and GPR37-activated macrophage efferocytosis","date":"2025-11-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.10.687700","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.10.20.683538","title":"Protectin D1/GPR37 signaling enhances macrophage-dependent efferocytosis to attenuate experimental abdominal aortic aneurysm formation","date":"2025-10-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.20.683538","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.08.12.607510","title":"A bone-derived protein primes rapid visual escape via GPR37 receptor in a subpopulation of VTA GABAergic neurons","date":"2024-08-13","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.12.607510","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.07.26.605282","title":"Gz Enhanced Signal Transduction assaY (G  <sub>Z</sub>  ESTY) for GPCR deorphanization","date":"2024-07-26","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.26.605282","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":25409,"output_tokens":5416,"usd":0.078733,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13807,"output_tokens":5018,"usd":0.097242,"stage2_stop_reason":"end_turn"},"total_usd":0.175975,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"GPR37 (hET(B)R-LP) encodes a 614-amino-acid seven-transmembrane GPCR with 52% similarity to endothelin type B receptor; when expressed in COS7 and HEK293 cells, recombinant hET(B)R-LP did not show significant binding of radiolabeled ET-1 or ET-3, and ET-1, ET-3, bombesin, and neuropeptide Y failed to produce Ca2+ mobilization or cAMP changes, indicating endothelins are NOT ligands for this receptor.\",\n      \"method\": \"Radioligand binding assay, Ca2+ mobilization assay, cAMP assay in transfected COS7/HEK293 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in transfected cells, single lab, negative result mechanistically informative (establishes endothelins are not ligands)\",\n      \"pmids\": [\"9144577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GPR37 (Pael-R) is a substrate of the E3 ubiquitin ligase Parkin; Parkin specifically ubiquitinates unfolded/insoluble Pael-R and promotes its degradation, suppressing ER stress-induced cell death. Pael-R was identified as a Parkin-binding protein by yeast two-hybrid screening.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, in vitro ubiquitination assay, cell death assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Y2H, Co-IP, in vitro ubiquitination assay), replicated across multiple subsequent studies\",\n      \"pmids\": [\"12150907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CHIP, Hsp70, Parkin, and GPR37 (Pael-R) form a complex in vitro and in vivo. CHIP promotes dissociation of Hsp70 from Parkin and Pael-R, facilitating Parkin-mediated Pael-R ubiquitination. CHIP enhanced Parkin-mediated in vitro ubiquitination of Pael-R even in the absence of Hsp70, acting as an E4-like co-factor.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, in vitro complex reconstitution\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus Co-IP, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"12150907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Panneuronal expression of GPR37 (Pael-R) in Drosophila causes age-dependent selective degeneration of dopaminergic neurons; coexpression of Parkin degrades Pael-R and suppresses its toxicity. Interfering with endogenous Drosophila Parkin promotes Pael-R accumulation and augments its toxicity, establishing Parkin as epistatic to Pael-R in this pathway.\",\n      \"method\": \"Drosophila transgenic overexpression and loss-of-function, DA neuron counting, immunostaining\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in intact organism, gain- and loss-of-function experiments, replicated by multiple labs\",\n      \"pmids\": [\"12670421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Glup/PACRG (product of gene adjacent to Parkin) forms a large molecular chaperone complex containing Hsp70 and Hsp90, interacts with Pael-R, suppresses Pael-R-induced cell death, and facilitates inclusion body formation when the proteasome is inhibited; Glup knockdown attenuated inclusion formation and promoted cell death.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, cell viability assay, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, siRNA knockdown with functional readout, single lab\",\n      \"pmids\": [\"14532270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HRD1, a ubiquitin ligase expressed in substantia nigra dopaminergic neurons, interacts with GPR37 (Pael-R) through the HRD1 proline-rich region, promotes ubiquitination and degradation of Pael-R, and protects against Pael-R-induced apoptosis. siRNA knockdown of endogenous HRD1 induced Pael-R accumulation and caspase-3 activation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, siRNA knockdown, caspase-3 activation assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, ubiquitination assay, siRNA KD with functional readout), replicated by same group in multiple papers\",\n      \"pmids\": [\"17059562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GPR37 (Pael-R) overexpression in mouse substantia nigra via adenoviral vectors caused ER stress and death of dopaminergic neurons in vivo. Dopaminergic neuronal death was enhanced in mice deficient in Parkin and the ER chaperone ORP150, and a dopamine synthesis inhibitor blocked neuronal death in parkin null mice, implicating both ER stress and dopamine toxicity in Pael-R-mediated neurodegeneration.\",\n      \"method\": \"Adenoviral in vivo expression, Parkin knockout mouse, ORP150 knockout mouse, pharmacological inhibition, immunohistochemistry\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological epistasis in vivo, multiple mouse models with defined phenotypic readout\",\n      \"pmids\": [\"17116640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GPR37 (Pael-R) regulates dopamine metabolism in the nigrostriatal system: Pael-R knockout mice show ~60% striatal dopamine levels compared to wild-type, while Pael-R transgenic mice show increased striatal DOPAC and vesicular dopamine content. Pael-R transgenic nigrostriatal neurons are more vulnerable to PD-related neurotoxins.\",\n      \"method\": \"Knockout and transgenic mouse models, HPLC dopamine/DOPAC measurement, neurotoxin challenge\",\n      \"journal\": \"Neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss- and gain-of-function with biochemical readout, single lab\",\n      \"pmids\": [\"17889953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Thioredoxin (TRX) suppresses Pael-R (GPR37)-induced neurotoxicity in Drosophila dopaminergic neurons; redox-defective TRX mutants still suppressed Pael-R toxicity, suggesting TRX chaperone activity (rather than antioxidant activity) is the primary mechanism of suppression.\",\n      \"method\": \"Drosophila transgenic coexpression, dopaminergic neuron counting, locomotor activity assay, mutagenesis of TRX active site\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with in vivo functional readout, single lab\",\n      \"pmids\": [\"17301052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Parkin knockout/Pael-R transgenic double-mutant mice display early and progressive loss of dopaminergic and noradrenergic neurons, activation of the unfolded protein response (UPR), upregulation of dopamine and metabolites, and reduced mitochondrial complex I activity later in life — establishing Pael-R accumulation downstream of Parkin loss as mechanistically causing neurodegeneration.\",\n      \"method\": \"Double-mutant mouse model (Parkin KO × Pael-R Tg), stereological neuron counting, UPR markers, dopamine HPLC, mitochondrial complex I activity assay\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in vivo with multiple orthogonal phenotypic readouts\",\n      \"pmids\": [\"18691389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"N-terminal truncation of GPR37 (removal of first 210 or all N-terminal amino acids) dramatically enhances plasma membrane surface expression. Coexpression with adenosine A2A receptor or dopamine D2 receptor increases GPR37 surface expression; full-length GPR37 associates with D2R by co-immunoprecipitation, modestly altering D2R agonist/antagonist affinity. GPR37 also specifically interacts with PDZ scaffold syntenin-1, dramatically increasing GPR37 surface expression in HEK-293 cells.\",\n      \"method\": \"N-terminal truncation constructs, flow cytometry surface expression assay, co-immunoprecipitation, radioligand binding assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (truncation, Co-IP, radioligand binding), single lab\",\n      \"pmids\": [\"19799451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"AAV-mediated overexpression of rat Pael-R (GPR37) in the nigrostriatal system of adult rats causes rapid insoluble accumulation of the receptor, severe loss of nigral dopaminergic neurons and nigrostriatal fibers, striatal dopamine depletion, and spontaneous motor impairments; GABAergic neurons of the globus pallidus were unaffected, demonstrating selective dopaminergic vulnerability.\",\n      \"method\": \"Recombinant AAV (rAAV2/6) in vivo gene delivery, immunohistochemistry, behavioral testing (cylinder and stepping tests), dopamine HPLC\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gain-of-function with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"19348945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPR37 and GPR37L1 are receptors for prosaptide (active fragment of prosaposin/sulfated glycoprotein-1). Prosaptide promotes endocytosis of GPR37 and GPR37L1, binds both receptors, induces ERK phosphorylation in a pertussis toxin-sensitive manner, stimulates 35S-GTPγS binding, and inhibits forskolin-stimulated cAMP production in a GPR37/GPR37L1-dependent manner. Full-length prosaposin also activates GPR37 signaling. siRNA knockdown of GPR37 or GPR37L1 attenuates prosaptide/prosaposin-mediated astrocyte protection against oxidative stress.\",\n      \"method\": \"Receptor endocytosis assay, radioligand binding, ERK phosphorylation assay with pertussis toxin, 35S-GTPγS binding, cAMP assay, siRNA knockdown, cell viability assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal biochemical assays plus loss-of-function with functional readout in one study\",\n      \"pmids\": [\"23690594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The C-terminal cysteine-rich domain of GPR37 controls its plasma membrane expression, signaling, and cytotoxicity. Deletion of six cysteine residues in this region promoted GPR37 plasma membrane expression and signaling without affecting receptor internalization, and protected against GPR37-mediated apoptosis and cell death.\",\n      \"method\": \"Site-directed mutagenesis/deletion constructs, flow cytometry surface expression, cell death/apoptosis assays\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with multiple functional readouts, single lab\",\n      \"pmids\": [\"23398388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PICK1 interacts with GPR37 (PAELR) via its PDZ domain binding to the C-terminal PDZ motif of PAELR. Pull-down assays confirmed PICK1 is retained by GST-fused C-terminal PAELR from both heterologous cells and rat brain tissue. PICK1 overexpression reduces PAELR expression levels and reduces PAELR-induced cell death during rotenone treatment in a proteasome-dependent manner.\",\n      \"method\": \"GST pull-down, co-immunoprecipitation from rat brain tissue and transfected cells, cell viability assay, proteasome inhibitor treatment\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — reciprocal pull-down from native tissue plus functional cell death assay, single lab\",\n      \"pmids\": [\"24749734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GABARAPL2 interacts with GPR37 (PAELR) via the GABAA binding site of GABARAPL2 and the cysteine-rich region (-CCCCCC-EEC) of the C-terminal of PAELR. Affinity chromatography confirmed Myc-GABARAPL2 is retained by GST-fused C-terminal PAELR. Transient transfection of GABARAPL2 reduces PAELR expression, suggesting autophagy-mediated regulation.\",\n      \"method\": \"GST affinity chromatography, in-silico modelling, transfection/Western blot\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pull-down method, single lab, no rescue experiment\",\n      \"pmids\": [\"29496607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPR37 signaling is required for the migration of olfactory ensheathing cells and GnRH neurons in the developing mouse olfactory system. Inhibition of GPR37 signaling in nasal explants attenuated GnRH neuronal migration and OEC movement. GPR37-deficient mice showed decreased olfactory bulb nerve layer and attenuated/delayed GnRH neuron migration into the brain.\",\n      \"method\": \"GPR37 knockout mouse, nasal explant cultures with GPR37 inhibition, immunocytochemistry, PCR\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus pharmacological inhibition in explants with cellular migration readout, single lab\",\n      \"pmids\": [\"31143101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Osteocalcin (OCN), a bone-derived protein, activates GPR37 in a subpopulation of VTA GABAergic neurons to decrease potassium currents via GPR37-induced cAMP reduction and subsequent suppression of THIK-1 (K2P13.1) channels, increasing neuronal excitability. Knockout of GPR37 or conditional knockout in VTA GABAergic neurons delayed rapid visual escape response; reconstituting OCN-GPR37 signaling in VTA restored normal response.\",\n      \"method\": \"GPR37 knockout and conditional knockout mice, single-cell transcriptomics, patch-clamp electrophysiology, chemogenetics (HM4Di), behavioral assay (visual escape)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic models with electrophysiology and behavioral readout, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR37 activation in TRPV1-lineage sensory neurons at the spinal level erases nociceptive sensitization. Intrathecal GPR37 agonists (TX14A and protectin D1) dose-dependently inhibited capsaicin-induced nociception acutely and long-term, and produced 'unpriming' in the hyperalgesic priming model. Global GPR37 KO and conditional KO in TRPV1-lineage neurons abolished these effects. Ex vivo Ca2+ imaging showed i.th. TX14A rescued dorsal horn interneurons from long-term potentiation/depression.\",\n      \"method\": \"GPR37 global knockout, conditional knockout (TRPV1-Cre), intrathecal pharmacology, behavioral nociceptive assays, ex vivo Ca2+ imaging of dorsal horn neurons\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus conditional KO with pharmacological and imaging readouts, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Protectin DX (PDX) activates GPR37 on macrophages to promote efferocytosis of apoptotic cells via calcium signaling. In a tibial fracture pain model, analgesic effects of PDX were abolished in Gpr37−/− mice. PDX binds GPR37 and induces calcium responses in peritoneal macrophages in a GPR37-dependent manner.\",\n      \"method\": \"GPR37 knockout mouse, in vivo fracture pain model, in vitro macrophage efferocytosis assay, calcium imaging, lipidomics\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with in vivo and in vitro functional readouts, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GPR37 (Pael-R/PAELR) is an orphan GPCR predominantly expressed in the nervous system that acts as a substrate of the E3 ubiquitin ligase Parkin; when unfolded or overexpressed, it accumulates in the ER and triggers ER stress-induced dopaminergic neurodegeneration relevant to Parkinson's disease. Parkin, together with co-factors CHIP and Hsp70, ubiquitinates and degrades misfolded GPR37; the ER ubiquitin ligase HRD1 provides a parallel degradation pathway. When properly folded and trafficked to the plasma membrane — facilitated by N-terminal truncation, coexpression with D2R or A2AR, or interaction with syntenin-1 — GPR37 couples to Gi/o proteins and is activated by prosaptide/prosaposin to signal through ERK phosphorylation and cAMP inhibition, exerting neuroprotective and glioprotective effects. GPR37 also modulates dopamine metabolism, interacts with the dopamine transporter and D2R, regulates GnRH and olfactory ensheathing cell migration, controls pain sensitization via TRPV1-lineage spinal neurons, mediates macrophage efferocytosis in response to protectins, and in VTA GABAergic neurons mediates osteocalcin signaling to suppress THIK-1 K+ channels and increase neuronal excitability.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPR37 (Pael-R) is a seven-transmembrane G protein-coupled receptor expressed predominantly in the nervous system whose dysfunction links protein quality control to dopaminergic neurodegeneration [#0, #1]. Although originally cloned for its similarity to the endothelin type B receptor, endothelins do not bind or activate it [#0]. GPR37 is intrinsically prone to misfolding: when unfolded or overexpressed it accumulates in the ER and triggers ER stress and selective dopaminergic neuron death, a phenotype demonstrated in Drosophila, in mouse and rat substantia nigra, and exacerbated by loss of the ER chaperone ORP150 [#3, #6, #11]. The receptor is a substrate of the Parkinson's disease E3 ubiquitin ligase Parkin, which ubiquitinates and degrades misfolded GPR37 to suppress ER stress-induced cell death; CHIP and Hsp70 act as co-factors that potentiate this ubiquitination, and the chaperone-associated proteins PACRG/Glup and thioredoxin further buffer GPR37 toxicity [#1, #2, #4, #8]. A parallel ER-associated ligase, HRD1, independently ubiquitinates and degrades GPR37 and protects against its apoptotic accumulation [#5]. Loss of Parkin combined with GPR37 transgene expression causes early progressive loss of dopaminergic and noradrenergic neurons with UPR activation, establishing GPR37 accumulation downstream of Parkin loss as a cause of neurodegeneration [#9]. GPR37 surface trafficking is gated by its cysteine-rich C-terminal domain and its N-terminus, and is enhanced by N-terminal truncation, co-expression with dopamine D2 or adenosine A2A receptors, and binding of the PDZ scaffold syntenin-1, while PICK1 and GABARAPL2 bind its C-terminus and lower receptor levels [#10, #13, #14]. Once at the membrane, GPR37 functions as a Gi/o-coupled receptor activated by prosaptide/prosaposin, signaling through pertussis-toxin-sensitive ERK phosphorylation and inhibition of cAMP to confer cytoprotection against oxidative stress [#12]. GPR37 additionally regulates striatal dopamine metabolism [#7], guides olfactory ensheathing cell and GnRH neuron migration in development [#16], and serves as a receptor for lipid and peptide ligands in pain and immune contexts [#17, #18, #19].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Cloning of an endothelin-receptor-like orphan GPCR resolved whether endothelins were its ligands, establishing GPR37 as a true orphan receptor.\",\n      \"evidence\": \"Radioligand binding, Ca2+ and cAMP assays in transfected COS7/HEK293 cells\",\n      \"pmids\": [\"9144577\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No endogenous ligand identified at this stage\", \"No cellular function or localization defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of GPR37 as a Parkin substrate connected an orphan GPCR to Parkinson's disease protein quality control, defining how misfolded GPR37 is cleared to prevent ER stress death.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, in vitro ubiquitination and cell death assays; CHIP/Hsp70 complex reconstitution\",\n      \"pmids\": [\"12150907\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degradation studied in overexpression contexts\", \"Physiological substrate role of folded receptor not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"In vivo genetic epistasis in Drosophila established that GPR37 accumulation selectively kills dopaminergic neurons and that Parkin acts upstream to suppress this toxicity.\",\n      \"evidence\": \"Drosophila transgenic gain- and loss-of-function with DA neuron counting\",\n      \"pmids\": [\"12670421\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of dopaminergic selectivity unresolved\", \"Endogenous ligand and signaling not involved in toxicity readout\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery of PACRG/Glup as a chaperone-complex partner showed GPR37 handling involves Hsp70/Hsp90 machinery directing it to inclusion bodies or death.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, cell viability and immunofluorescence\",\n      \"pmids\": [\"14532270\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"In vivo relevance of inclusion formation not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of HRD1 revealed a Parkin-independent ER-associated degradation route for GPR37, explaining parallel clearance of the misfolded receptor.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitination, siRNA knockdown with caspase-3 readout\",\n      \"pmids\": [\"17059562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of HRD1 versus Parkin in vivo unquantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"In vivo overexpression in mouse substantia nigra established that GPR37 causes ER stress and dopamine-dependent neuron death, mechanistically separating ER stress and dopamine toxicity components.\",\n      \"evidence\": \"Adenoviral expression, Parkin and ORP150 KO mice, dopamine synthesis inhibition, IHC\",\n      \"pmids\": [\"17116640\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Link between ER stress and dopamine toxicity not molecularly defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Knockout and transgenic mice showed GPR37 regulates nigrostriatal dopamine levels and neurotoxin vulnerability, indicating a physiological role beyond misfolding toxicity.\",\n      \"evidence\": \"KO/Tg mice, HPLC dopamine/DOPAC, neurotoxin challenge\",\n      \"pmids\": [\"17889953\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking GPR37 to dopamine handling unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Thioredoxin was shown to suppress GPR37 toxicity through chaperone rather than antioxidant activity, refining the protein-folding basis of GPR37 neurotoxicity.\",\n      \"evidence\": \"Drosophila coexpression with TRX active-site mutagenesis, DA neuron and locomotor readouts\",\n      \"pmids\": [\"17301052\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct TRX-GPR37 interaction not shown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"A Parkin KO × GPR37 transgenic double mutant placed GPR37 accumulation downstream of Parkin loss as causal for progressive neurodegeneration with UPR and complex I deficits.\",\n      \"evidence\": \"Double-mutant mice, stereology, UPR markers, dopamine HPLC, complex I assay\",\n      \"pmids\": [\"18691389\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether complex I deficit is direct or secondary not resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapping of trafficking determinants showed N-terminal truncation, D2R/A2AR coexpression, and syntenin-1 binding promote GPR37 surface delivery, explaining how the misfolding-prone receptor reaches the membrane.\",\n      \"evidence\": \"Truncation constructs, flow cytometry, Co-IP, radioligand binding\",\n      \"pmids\": [\"19799451\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of D2R heterocomplex on signaling unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"AAV overexpression in adult rat nigrostriatum reproduced selective dopaminergic loss and motor deficits, validating GPR37 accumulation as a mammalian PD-relevant lesion.\",\n      \"evidence\": \"rAAV2/6 delivery, IHC, behavioral tests, dopamine HPLC\",\n      \"pmids\": [\"19348945\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous receptor levels in pathology not addressed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of prosaptide/prosaposin as agonists deorphanized GPR37, defining it as a Gi/o-coupled cytoprotective receptor signaling via ERK and cAMP inhibition.\",\n      \"evidence\": \"Endocytosis, radioligand binding, ERK with PTX, GTPγS, cAMP, siRNA, cell viability\",\n      \"pmids\": [\"23690594\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ligand binding not defined\", \"In vivo signaling outputs not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The C-terminal cysteine-rich domain was shown to govern surface expression, signaling, and cytotoxicity, identifying a structural switch between toxic and functional receptor states.\",\n      \"evidence\": \"Cysteine deletion mutants, flow cytometry, apoptosis/death assays\",\n      \"pmids\": [\"23398388\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Native regulation of these cysteines unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"PICK1 was identified as a PDZ partner that lowers GPR37 levels and reduces its toxicity proteasome-dependently, adding a scaffold-linked regulatory layer.\",\n      \"evidence\": \"GST pull-down from brain and cells, Co-IP, viability under rotenone, proteasome inhibition\",\n      \"pmids\": [\"24749734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of PICK1-directed degradation unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"GABARAPL2 binding to the GPR37 C-terminus implicated autophagy in regulating receptor levels.\",\n      \"evidence\": \"GST affinity chromatography, in-silico modeling, transfection/Western\",\n      \"pmids\": [\"29496607\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single pull-down method without rescue\", \"Autophagic degradation not directly demonstrated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"GPR37 signaling was found to drive olfactory ensheathing cell and GnRH neuron migration, establishing a developmental morphogenetic role.\",\n      \"evidence\": \"GPR37 KO mice, nasal explant inhibition, immunocytochemistry, PCR\",\n      \"pmids\": [\"31143101\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream migratory signaling pathway unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Osteocalcin was shown to activate GPR37 in VTA GABAergic neurons to suppress THIK-1 channels via cAMP reduction, linking a bone-derived ligand to neuronal excitability and behavior.\",\n      \"evidence\": \"GPR37 KO and conditional KO, scRNA-seq, patch-clamp, chemogenetics, visual escape behavior (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not yet peer-reviewed\", \"Direct OCN-GPR37 binding not shown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"GPR37 activation by lipid mediators in TRPV1-lineage sensory neurons and macrophages was shown to resolve nociceptive sensitization and promote efferocytosis, expanding its ligand repertoire to specialized pro-resolving mediators.\",\n      \"evidence\": \"Global and conditional GPR37 KO, intrathecal pharmacology, behavioral and Ca2+ imaging, macrophage efferocytosis (preprints)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprints not yet peer-reviewed\", \"Receptor coupling in these cell types not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GPR37 reconciles its misfolding-driven neurotoxic accumulation with its physiological ligand-activated cytoprotective and excitability-modulating signaling remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of GPR37 with any ligand\", \"Quantitative balance of degradation pathways in disease unknown\", \"Mechanism linking same receptor to both death and protection unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [12, 17]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [10, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 6]}\n    ],\n    \"complexes\": [\"Parkin–CHIP–Hsp70–GPR37 complex\"],\n    \"partners\": [\"PARK2\", \"STUB1\", \"HSPA1A\", \"SYNJ2BP\", \"HRD1\", \"PICK1\", \"DRD2\", \"GABARAPL2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}