{"gene":"MCHR1","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":1999,"finding":"The orphan G-protein-coupled receptor SLC-1 (MCHR1) was identified as the cognate receptor for melanin-concentrating hormone (MCH); expressed in HEK293 cells, it binds MCH with sub-nanomolar affinity and is stimulated by MCH to mobilize intracellular Ca2+ and reduce forskolin-elevated cAMP levels, demonstrating coupling to both Gq and Gi pathways.","method":"Radioligand binding, Ca2+ mobilization assay, cAMP accumulation assay in HEK293 cells expressing recombinant SLC-1","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal functional assays (binding, Ca2+, cAMP) in recombinant system; independently replicated by three concurrent papers","pmids":["10421367"],"is_preprint":false},{"year":1999,"finding":"SLC-1 (MCHR1) expressed in Xenopus oocytes couples to both Gi (activating GIRK currents) and Gq (activating phospholipase C-dependent Ca2+-dependent Cl- currents) signaling pathways upon MCH stimulation.","method":"Xenopus oocyte expression system with GIRK co-expression; electrophysiological recording of GIRK and Ca2+-dependent Cl- currents","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in Xenopus oocytes with two distinct electrophysiological readouts; consistent with concurrent mammalian cell studies","pmids":["10471841"],"is_preprint":false},{"year":1999,"finding":"MCH was isolated and identified as the endogenous ligand of the rat and human SLC-1 (MCHR1) receptor, with an EC50 of ~0.2 nM for inhibition of forskolin-stimulated cAMP accumulation in CHO cells expressing SLC-1.","method":"Brain extract purification by HPLC, cAMP inhibition assay in CHO cells stably expressing rat and human SLC-1","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — endogenous ligand isolation with functional assay; replicated across multiple concurrent studies","pmids":["10441476"],"is_preprint":false},{"year":2001,"finding":"Structure-activity relationship studies defined MCH-(6-17) as the minimal sequence for full agonistic activity at MCHR1, with Met8, Arg11, and Tyr13 as essential residues; disruption of the disulfide bridge abolished agonistic activity and converted ligands to weak antagonists.","method":"cAMP inhibition assay and [35S]-GTPγS binding assay on HEK293 cells stably expressing human MCHR1, using 57 synthetic MCH analogues","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis/analog study with two orthogonal functional assays defining receptor contact residues","pmids":["11278733"],"is_preprint":false},{"year":2001,"finding":"The rat SLC-1 (MCHR1) receptor pharmacology closely parallels that of the human receptor, and agonist potency in the cAMP inhibition assay correlates strongly with binding affinity and in vivo feeding effects after ICV injection, establishing SLC-1 as the receptor mediating MCH-induced feeding behavior.","method":"cAMP inhibition assay and [125I]S36057 radioligand binding on rat recombinant SLC-1; ICV injection of MCH analogs with food intake measurement in rats","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 2 — reciprocal in vitro/in vivo correlation with multiple analogs; links receptor pharmacology directly to in vivo feeding phenotype","pmids":["11561073"],"is_preprint":false},{"year":2001,"finding":"In SK-MEL-37 human melanoma cells expressing endogenous SLC-1 (MCHR1), MCH inhibits cAMP accumulation and activates p42/p44 MAPK in a pertussis toxin-sensitive manner, indicating exclusive coupling to Gαi/Gαo in this cell context; Gαq-mediated Ca2+ mobilization was absent, showing cell-type-dependent G-protein selectivity.","method":"cAMP accumulation assay, MAPK activation assay, pertussis toxin treatment, Ca2+ measurement in SK-MEL-37 cells and CHO/293 cells overexpressing SLC-1","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal signaling assays with pharmacological dissection (pertussis toxin) in endogenously expressing cells","pmids":["11708774"],"is_preprint":false},{"year":2002,"finding":"Human immune cells (PBMCs) express functional MCHR1 that couples to both cAMP synthesis and calcium mobilization upon MCH stimulation; MCH treatment decreases CD3-stimulated PBMC proliferation in vitro, indicating an immunomodulatory role for MCH/MCHR1 signaling.","method":"RT-PCR, FACS, in vitro cAMP and Ca2+ assays, cell proliferation assay in human PBMCs","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays in primary human cells; single laboratory study","pmids":["12220661"],"is_preprint":false},{"year":2002,"finding":"Rhesus monkey MCH-R1 binds MCH with Kd of 6.5 nM and couples through both Gi/Go and Gq-type G proteins, mirroring human MCH-R1 coupling, while MCH-R2 utilizes exclusively the Gq signaling pathway.","method":"Radioligand binding assay, intracellular signaling characterization (cAMP and Ca2+) in cells expressing cloned monkey receptors","journal":"Peptides","confidence":"Medium","confidence_rationale":"Tier 2 — binding and functional assays with cloned receptor; single lab, confirms cross-species conservation of coupling","pmids":["12182940"],"is_preprint":false},{"year":2004,"finding":"A G34R coding SNP in MCHR1 present at 15% minor allele frequency in African-Americans does not alter receptor binding affinity or functional signaling (cAMP, Ca2+, MAPK) compared to wild-type MCHR1.","method":"Receptor binding assay, cAMP inhibition, Ca2+ mobilization, and MAPK activation assays in CHO cells expressing SNP-containing MCHR1 constructs","journal":"Obesity research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays on variant receptor; establishes functional neutrality of common variant","pmids":["15340116"],"is_preprint":false},{"year":2004,"finding":"Mice with genetic inactivation of MCHR1 (Mch1r-/-) develop osteoporosis with reduced cortical bone mass and increased serum c-telopeptide (marker of bone resorption), indicating that MCHR1 signaling is required for tonic stimulation of bone mass.","method":"MCHR1 knockout mouse generation, bone densitometry, serum c-telopeptide measurement","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with specific biochemical readout; single lab","pmids":["15147966"],"is_preprint":false},{"year":2005,"finding":"Mch1r-/- mice show significantly enhanced voluntary wheel running activity, and Pmch-/- mice show similar enhancement, demonstrating that endogenous MCH signaling through MCH1R plays an inhibitory role in regulating locomotor activity; naloxone suppresses wheel running in both genotypes, implicating opioid regulation downstream.","method":"Voluntary wheel running measurement in Mch1r-/- and Pmch-/- knockout mice; naloxone pharmacological challenge; dynorphin mRNA measurement","journal":"Regulatory peptides","confidence":"Medium","confidence_rationale":"Tier 2 — two independent KO mouse lines with quantitative locomotor assay and pharmacological probe; single lab","pmids":["15544841"],"is_preprint":false},{"year":2006,"finding":"MCHR1 null mutant mice display anxiolytic-like behavior across multiple behavioral paradigms (open field, elevated plus maze, social interaction, stress-induced hyperthermia); baseline serotonin levels in the prefrontal cortex are lower in MCHR1 KO mice, and forced swim-induced 5-HT efflux is absent, placing MCHR1 upstream of serotonergic transmission in modulating anxiety.","method":"MCHR1 knockout mouse behavioral testing (open field, EPM, social interaction, SIH), in vivo microdialysis for serotonin measurement in prefrontal cortex","journal":"Neuropsychopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with behavioral battery and in vivo neurochemical readout; single lab","pmids":["15988472"],"is_preprint":false},{"year":2006,"finding":"A neuroblastoma-derived cell line (I3.4.2) with high endogenous MCHR1 expression shows MCH-stimulated Ca2+ mobilization that is insensitive to pertussis toxin and absent cAMP signaling, indicating that in neural-derived cells MCHR1 signals preferentially through Gαq rather than Gαi/o.","method":"Pertussis toxin treatment, Ca2+ mobilization assay, cAMP accumulation assay in IMR32-derived neuronal cell line expressing native MCHR1","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection with pertussis toxin in native neural-expressing cells; single lab","pmids":["16524757"],"is_preprint":false},{"year":2020,"finding":"MCHR1 protein localizes abundantly to primary cilia on neurons throughout the murine CNS, as determined by immunohistochemistry with a validated specific antibody; ciliary MCHR1 co-localizes with diverse neurochemical markers (TH, calretinin, kisspeptin, estrogen receptor, OT, AVP, CRF), suggesting non-synaptic volume transmission as a predominant mode of MCH signaling.","method":"Immunohistochemistry with specificity-validated antibody, multiple neurochemical marker co-localization in rat and mouse CNS","journal":"Journal of neuroscience research","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with validated antibody across brain regions; single lab but comprehensive mapping","pmids":["32530066"],"is_preprint":false},{"year":2021,"finding":"The ciliary transition zone protein AHI1 is required for trafficking of MCHR1 into neuronal primary cilia; Ahi1-/- neurons show reduced ciliary MCHR1 with normal total and surface expression, and have significantly decreased cAMP and ERK signaling downstream of MCH stimulation, demonstrating that ciliary localization of MCHR1 is necessary for its signaling.","method":"Neuronal cultures from Ahi1+/+ and Ahi1-/- embryonic mice, immunofluorescence for ciliary MCHR1, cAMP assay, ERK phosphorylation assay after MCH stimulation","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple orthogonal signaling readouts (cAMP, ERK) directly linking ciliary localization to signaling; strong mechanistic conclusion","pmids":["33741721"],"is_preprint":false},{"year":2021,"finding":"PDGF-BB directly binds MCHR1 in membrane fractions of normal human dermal fibroblasts (confirmed by surface plasmon resonance), upregulates MCHR1 expression, and signals through MCHR1 to modulate intracellular cAMP and induce TGFβ1 and CTGF expression; MCHR1 silencing blocks these profibrotic responses.","method":"Co-IP/membrane fraction binding, surface plasmon resonance, MCHR1 siRNA knockdown, cAMP assay, TGFβ1/CTGF mRNA and protein measurement in normal human dermal fibroblasts","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 — SPR binding confirmation plus KD phenotype with multiple readouts; novel non-MCH ligand for MCHR1; single lab","pmids":["34912333"],"is_preprint":false},{"year":2022,"finding":"MRAP2 interacts with MCHR1 (confirmed by co-immunoprecipitation and bimolecular fluorescence complementation) and inhibits MCHR1-mediated intracellular Ca2+ signaling; the C-terminal domain of MRAP2 is required for this pharmacological modulation and for effects on MCHR1 membrane transport.","method":"Co-immunoprecipitation, bimolecular fluorescence complementation, Ca2+ signaling assay with MRAP2 truncation constructs","journal":"Frontiers in endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal interaction confirmed by two methods with domain mapping; single lab","pmids":["35311242"],"is_preprint":false},{"year":2012,"finding":"MCHR1 mRNA is expressed in thyroid follicular cells; MCH1R-knockout mice exhibit reduced circulating thyroid hormones (T4, fT4, T3, rT3) with elevated TRH and TSH, and upon TSH challenge their thyroids secrete lower amounts of T4, demonstrating that MCHR1 signaling is required for normal thyroid hormone secretion.","method":"RT-PCR for thyroid MCHR1 expression, MCH1R knockout mouse phenotyping (serum hormone measurements), TSH challenge experiment, 125I secretion assay","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with functional endocrine challenge assay; single lab","pmids":["23024261"],"is_preprint":false},{"year":2022,"finding":"Intrahippocampal MCH administration impairs memory consolidation and decreases hippocampal MCHR1 and TrkB receptor expression without altering BDNF or NMDA receptor subunit levels; co-administration with MCHR1 antagonist ATC-0175 reverses memory impairment, placing MCHR1 activation upstream of TrkB downregulation in hippocampal memory consolidation.","method":"Bilateral intrahippocampal MCH microinjection in rats, novel object recognition test, elevated plus maze, Western blot/qPCR for MCHR1, TrkB, BDNF, NR1, NR2A, NR2B; pharmacological rescue with MCHR1 antagonist","journal":"Progress in neuro-psychopharmacology & biological psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological challenge with antagonist rescue and molecular readouts; single lab","pmids":["36565982"],"is_preprint":false}],"current_model":"MCHR1 (SLC-1/GPR24) is a Gi/o- and Gq-coupled GPCR that binds MCH with sub-nanomolar affinity, inhibits cAMP accumulation and mobilizes intracellular Ca2+ in a cell-type-dependent manner; it localizes predominantly to neuronal primary cilia where AHI1-dependent ciliary trafficking is required for full downstream cAMP and ERK signaling; it also interacts with MRAP2 (which inhibits its Ca2+ signaling via its C-terminus) and can be engaged by PDGF-BB to drive fibrotic signaling, while in vivo it tonically regulates feeding, locomotion, anxiety/mood via serotonergic transmission, bone homeostasis, thyroid hormone secretion, and hippocampal memory consolidation."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of MCH as the endogenous ligand of the orphan receptor SLC-1 resolved the receptor's pharmacological identity and established its dual Gi/o–Gq coupling, providing the molecular basis for all subsequent MCH signaling studies.","evidence":"Radioligand binding, Ca²⁺ mobilization, cAMP inhibition in HEK293/CHO cells; GIRK and Cl⁻ current recording in Xenopus oocytes","pmids":["10421367","10471841","10441476"],"confidence":"High","gaps":["G-protein coupling selectivity in native tissues not yet addressed","No structural basis for sub-nanomolar MCH binding"]},{"year":2001,"claim":"Structure-activity analysis of MCH analogs defined the minimal active peptide core (residues 6–17), essential contact residues, and the requirement for the disulfide bridge, while correlating in vitro potency with in vivo feeding responses—linking receptor pharmacology to the orexigenic phenotype.","evidence":"57 synthetic MCH analogs tested by cAMP and GTPγS assays in HEK293 cells; ICV injection of analogs with food intake measurement in rats","pmids":["11278733","11561073"],"confidence":"High","gaps":["No receptor mutagenesis to identify contact residues on the MCHR1 side","Downstream intracellular pathways mediating feeding behavior undefined"]},{"year":2001,"claim":"Demonstration that cell-type context dictates MCHR1's G-protein selectivity—exclusive Gi/o coupling in melanoma cells versus Gq-dominant coupling in neuronal cells—established that MCHR1 signaling output is not fixed but depends on the cellular G-protein repertoire.","evidence":"cAMP, Ca²⁺, and MAPK assays with pertussis toxin in SK-MEL-37 melanoma cells and IMR32-derived neuroblastoma cells expressing endogenous MCHR1","pmids":["11708774","16524757"],"confidence":"High","gaps":["Mechanism determining G-protein selectivity (e.g., receptor phosphorylation state, scaffold proteins) unknown","In vivo relevance of cell-type-dependent coupling not established"]},{"year":2004,"claim":"MCHR1 knockout mice revealed an unexpected requirement for MCH/MCHR1 signaling in bone homeostasis, demonstrating that MCHR1 tonically stimulates bone mass and that its loss leads to osteoporosis with increased bone resorption.","evidence":"MCHR1 KO mouse bone densitometry and serum c-telopeptide measurement","pmids":["15147966"],"confidence":"Medium","gaps":["Whether MCHR1 acts directly on osteoblasts/osteoclasts or indirectly via CNS pathways is unknown","No rescue experiment performed"]},{"year":2005,"claim":"Behavioral phenotyping of MCHR1-null and PMCH-null mice established that endogenous MCH–MCHR1 signaling tonically suppresses locomotor activity and promotes anxiety-like behavior, with serotonergic transmission as a downstream mediator of the anxiolytic phenotype.","evidence":"Voluntary wheel running in two independent KO lines; behavioral battery (open field, EPM, social interaction, SIH) plus in vivo microdialysis for 5-HT in prefrontal cortex of MCHR1 KO mice","pmids":["15544841","15988472"],"confidence":"Medium","gaps":["Neuronal subpopulations mediating the locomotor versus anxiety phenotypes not identified","Circuit-level mechanism linking MCHR1 to serotonergic neuron firing not resolved"]},{"year":2012,"claim":"Discovery of MCHR1 expression in thyroid follicular cells and the hypothyroid phenotype of MCHR1 KO mice extended the receptor's physiological roles beyond the CNS, demonstrating a direct requirement for MCHR1 in thyroid hormone secretion.","evidence":"RT-PCR for thyroid MCHR1; KO mouse serum hormone levels; TSH challenge and ¹²⁵I secretion assay","pmids":["23024261"],"confidence":"Medium","gaps":["Intracellular signaling pathway in thyroid cells (Gi vs Gq) not characterized","Whether MCH is delivered to thyroid via circulation or local production is unknown"]},{"year":2020,"claim":"Comprehensive mapping of MCHR1 to neuronal primary cilia across the CNS reframed the receptor's signaling mode, suggesting volume transmission rather than synaptic signaling as its predominant activation mechanism in the brain.","evidence":"Immunohistochemistry with validated antibody and neurochemical marker co-localization across rat and mouse brain regions","pmids":["32530066"],"confidence":"Medium","gaps":["Functional consequence of ciliary versus non-ciliary MCHR1 signaling not yet distinguished in vivo","Source and diffusion dynamics of MCH reaching cilia not characterized"]},{"year":2021,"claim":"Demonstrating that AHI1 is required for MCHR1 ciliary trafficking and that loss of ciliary MCHR1 attenuates cAMP and ERK signaling established the primary cilium as a necessary signaling platform for MCHR1, connecting ciliopathy biology to MCH signaling.","evidence":"Ahi1 KO neuronal cultures; immunofluorescence for ciliary MCHR1; cAMP and ERK phosphorylation assays after MCH stimulation","pmids":["33741721"],"confidence":"High","gaps":["Whether AHI1 loss phenocopies MCHR1 KO behavioral phenotypes in vivo not tested","Additional ciliary trafficking machinery for MCHR1 beyond AHI1 not identified"]},{"year":2021,"claim":"Identification of PDGF-BB as a non-canonical MCHR1 ligand that drives profibrotic signaling expanded the receptor's functional repertoire beyond neuropeptide signaling into tissue fibrosis.","evidence":"SPR binding, co-IP in dermal fibroblast membranes, MCHR1 siRNA knockdown with TGFβ1/CTGF readouts","pmids":["34912333"],"confidence":"Medium","gaps":["PDGF-BB binding site on MCHR1 relative to MCH binding site not mapped","Independent replication of PDGF-BB as a direct MCHR1 ligand not yet reported","In vivo relevance of PDGF-BB–MCHR1 interaction in fibrotic disease not established"]},{"year":2022,"claim":"Discovery that MRAP2 physically interacts with MCHR1 and inhibits its Ca²⁺ signaling via its C-terminal domain identified the first accessory protein that modulates MCHR1 pharmacology, and intrahippocampal MCHR1 activation was shown to impair memory consolidation through TrkB downregulation.","evidence":"Co-IP and BiFC for MRAP2–MCHR1 interaction with domain truncations; intrahippocampal MCH microinjection with antagonist rescue and Western blot in rats","pmids":["35311242","36565982"],"confidence":"Medium","gaps":["Stoichiometry and structural basis of MRAP2–MCHR1 complex unknown","Mechanism linking MCHR1 activation to TrkB downregulation not elucidated","Whether MRAP2 modulation occurs in vivo in neurons not tested"]},{"year":null,"claim":"Key unresolved questions include the structural basis for MCH and PDGF-BB binding to MCHR1, the in vivo contribution of ciliary versus non-ciliary receptor pools to distinct physiological functions, and the cell-intrinsic determinants of G-protein coupling selectivity.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of MCHR1 bound to MCH or any ligand","In vivo cell-type-specific conditional knockout studies are lacking","Determinants of Gi vs Gq selectivity in native neurons remain uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,12,16]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,15,16]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[13,14]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,5,14]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[11,13,18]}],"complexes":[],"partners":["MCH","AHI1","MRAP2","PDGF-BB"],"other_free_text":[]},"mechanistic_narrative":"MCHR1 (SLC-1/GPR24) is a G-protein-coupled receptor for melanin-concentrating hormone (MCH) that integrates energy balance, locomotion, anxiety, memory, bone homeostasis, and thyroid function through cell-type-dependent coupling to Gi/o and Gq signaling cascades. MCHR1 binds MCH with sub-nanomolar affinity and, depending on cellular context, inhibits cAMP accumulation via pertussis toxin-sensitive Gi/o proteins, mobilizes intracellular Ca²⁺ via Gq, and activates p42/p44 MAPK; in neuronal cells expressing endogenous receptor, signaling can be exclusively Gq-mediated [PMID:10421367, PMID:11708774, PMID:16524757]. In the CNS, MCHR1 localizes predominantly to neuronal primary cilia, and AHI1-dependent ciliary trafficking is required for downstream cAMP and ERK signaling, establishing the cilium as a critical signaling platform for this receptor [PMID:32530066, PMID:33741721]. MCHR1 is modulated by the accessory protein MRAP2, whose C-terminus inhibits MCHR1-mediated Ca²⁺ signaling and membrane transport, and can also be engaged by the non-canonical ligand PDGF-BB to drive profibrotic gene expression in dermal fibroblasts [PMID:35311242, PMID:34912333]."},"prefetch_data":{"uniprot":{"accession":"Q99705","full_name":"Melanin-concentrating hormone receptor 1","aliases":["G-protein coupled receptor 24","MCH-1R","MCH1R","MCHR","SLC-1","Somatostatin receptor-like protein"],"length_aa":353,"mass_kda":38.9,"function":"Receptor for melanin-concentrating hormone, coupled to both G proteins that inhibit adenylyl cyclase and G proteins that activate phosphoinositide hydrolysis","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q99705/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MCHR1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MCHR1","total_profiled":1310},"omim":[{"mim_id":"611424","title":"ZINC FINGER MYND DOMAIN-CONTAINING PROTEIN 19; ZMYND19","url":"https://www.omim.org/entry/611424"},{"mim_id":"606151","title":"BBS2 GENE; BBS2","url":"https://www.omim.org/entry/606151"},{"mim_id":"606111","title":"MELANIN-CONCENTRATING HORMONE RECEPTOR 2; MCHR2","url":"https://www.omim.org/entry/606111"},{"mim_id":"601751","title":"MELANIN-CONCENTRATING HORMONE RECEPTOR 1; MCHR1","url":"https://www.omim.org/entry/601751"},{"mim_id":"600374","title":"BBS4 GENE; BBS4","url":"https://www.omim.org/entry/600374"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":9.3},{"tissue":"endometrium 1","ntpm":5.5},{"tissue":"ovary","ntpm":9.9}],"url":"https://www.proteinatlas.org/search/MCHR1"},"hgnc":{"alias_symbol":["SLC1","MCH1R"],"prev_symbol":["GPR24"]},"alphafold":{"accession":"Q99705","domains":[{"cath_id":"1.20.1070.10","chopping":"103-392","consensus_level":"high","plddt":91.272,"start":103,"end":392}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99705","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99705-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99705-F1-predicted_aligned_error_v6.png","plddt_mean":84.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MCHR1","jax_strain_url":"https://www.jax.org/strain/search?query=MCHR1"},"sequence":{"accession":"Q99705","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99705.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99705/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99705"}},"corpus_meta":[{"pmid":"10421367","id":"PMC_10421367","title":"Melanin-concentrating hormone is the cognate ligand for the orphan G-protein-coupled receptor SLC-1.","date":"1999","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/10421367","citation_count":418,"is_preprint":false},{"pmid":"10762350","id":"PMC_10762350","title":"The distribution of the mRNA and protein products of the melanin-concentrating hormone (MCH) receptor gene, slc-1, in the central nervous system of the rat.","date":"2000","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10762350","citation_count":240,"is_preprint":false},{"pmid":"10471841","id":"PMC_10471841","title":"Identification of melanin concentrating hormone (MCH) as the natural ligand for the orphan somatostatin-like receptor 1 (SLC-1).","date":"1999","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/10471841","citation_count":163,"is_preprint":false},{"pmid":"10441476","id":"PMC_10441476","title":"Isolation and identification of melanin-concentrating hormone as the endogenous ligand of the SLC-1 receptor.","date":"1999","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10441476","citation_count":145,"is_preprint":false},{"pmid":"17675291","id":"PMC_17675291","title":"SLC1 and SLC4 encode partially redundant acyl-coenzyme A 1-acylglycerol-3-phosphate O-acyltransferases of budding yeast.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17675291","citation_count":102,"is_preprint":false},{"pmid":"17237257","id":"PMC_17237257","title":"Efficacy of the MCHR1 antagonist N-[3-(1-{[4-(3,4-difluorophenoxy)phenyl]methyl}(4-piperidyl))-4-methylphenyl]-2-methylpropanamide (SNAP 94847) in mouse models of anxiety and depression following acute and chronic administration is independent of hippocampal neurogenesis.","date":"2007","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/17237257","citation_count":100,"is_preprint":false},{"pmid":"24240778","id":"PMC_24240778","title":"SLC1 glutamate transporters.","date":"2013","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24240778","citation_count":85,"is_preprint":false},{"pmid":"24586162","id":"PMC_24586162","title":"The Chlamydia trachomatis type III secretion chaperone Slc1 engages multiple early effectors, including TepP, a tyrosine-phosphorylated protein required for the recruitment of CrkI-II to nascent inclusions and innate immune signaling.","date":"2014","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/24586162","citation_count":83,"is_preprint":false},{"pmid":"15988472","id":"PMC_15988472","title":"Genetic inactivation of melanin-concentrating hormone receptor subtype 1 (MCHR1) in mice exerts anxiolytic-like behavioral effects.","date":"2006","source":"Neuropsychopharmacology : official 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and SAR study of pyrrolo[3,4-b]pyridin-7(6H)-one derivatives as melanin concentrating hormone receptor 1 (MCH-R1) antagonists.","date":"2013","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/23411080","citation_count":5,"is_preprint":false},{"pmid":"32329245","id":"PMC_32329245","title":"PyRod Enables Rational Homology Model-based Virtual Screening Against MCHR1.","date":"2020","source":"Molecular informatics","url":"https://pubmed.ncbi.nlm.nih.gov/32329245","citation_count":5,"is_preprint":false},{"pmid":"12680590","id":"PMC_12680590","title":"Different structural requirements for melanin-concentrating hormone (MCH) interacting with rat MCH-R1 (SLC-1) and mouse B16 cell MCH-R.","date":"2003","source":"Journal of receptor and signal transduction research","url":"https://pubmed.ncbi.nlm.nih.gov/12680590","citation_count":5,"is_preprint":false},{"pmid":"26022839","id":"PMC_26022839","title":"Dihydropyrrolopyrazol-6-one MCHR1 antagonists for the treatment of obesity: Insights on in vivo efficacy from a novel FLIPR assay setup.","date":"2015","source":"Bioorganic & medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/26022839","citation_count":4,"is_preprint":false},{"pmid":"23024261","id":"PMC_23024261","title":"Disruption of the melanin-concentrating hormone receptor 1 (MCH1R) affects thyroid function.","date":"2012","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/23024261","citation_count":4,"is_preprint":false},{"pmid":"28025230","id":"PMC_28025230","title":"Mechanisms for Hepatobiliary Toxicity in Rats Treated with an Antagonist of Melanin Concentrating Hormone Receptor 1 (MCHR1).","date":"2016","source":"Toxicological sciences : an official journal of the Society of Toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/28025230","citation_count":4,"is_preprint":false},{"pmid":"39892319","id":"PMC_39892319","title":"The 1-acylglycerol-3-phosphate acyltransferase Slc1 is required to regulate mitochondria and lipid droplets.","date":"2025","source":"Microbiological research","url":"https://pubmed.ncbi.nlm.nih.gov/39892319","citation_count":3,"is_preprint":false},{"pmid":"29948643","id":"PMC_29948643","title":"SNAPshots of the MCHR1: a Comparison Between the PET-Tracers [18F]FE@SNAP and [11C]SNAP-7941.","date":"2019","source":"Molecular imaging and biology","url":"https://pubmed.ncbi.nlm.nih.gov/29948643","citation_count":3,"is_preprint":false},{"pmid":"36565982","id":"PMC_36565982","title":"Acute intrahippocampal administration of melanin-concentrating hormone impairs memory consolidation and decreases the expression of MCHR-1 and TrkB receptors.","date":"2022","source":"Progress in neuro-psychopharmacology & biological psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/36565982","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":40896,"output_tokens":4612,"usd":0.095934},"stage2":{"model":"claude-opus-4-6","input_tokens":8104,"output_tokens":3013,"usd":0.173767},"total_usd":0.269701,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"The orphan G-protein-coupled receptor SLC-1 (MCHR1) was identified as the cognate receptor for melanin-concentrating hormone (MCH); expressed in HEK293 cells, it binds MCH with sub-nanomolar affinity and is stimulated by MCH to mobilize intracellular Ca2+ and reduce forskolin-elevated cAMP levels, demonstrating coupling to both Gq and Gi pathways.\",\n      \"method\": \"Radioligand binding, Ca2+ mobilization assay, cAMP accumulation assay in HEK293 cells expressing recombinant SLC-1\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal functional assays (binding, Ca2+, cAMP) in recombinant system; independently replicated by three concurrent papers\",\n      \"pmids\": [\"10421367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"SLC-1 (MCHR1) expressed in Xenopus oocytes couples to both Gi (activating GIRK currents) and Gq (activating phospholipase C-dependent Ca2+-dependent Cl- currents) signaling pathways upon MCH stimulation.\",\n      \"method\": \"Xenopus oocyte expression system with GIRK co-expression; electrophysiological recording of GIRK and Ca2+-dependent Cl- currents\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in Xenopus oocytes with two distinct electrophysiological readouts; consistent with concurrent mammalian cell studies\",\n      \"pmids\": [\"10471841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"MCH was isolated and identified as the endogenous ligand of the rat and human SLC-1 (MCHR1) receptor, with an EC50 of ~0.2 nM for inhibition of forskolin-stimulated cAMP accumulation in CHO cells expressing SLC-1.\",\n      \"method\": \"Brain extract purification by HPLC, cAMP inhibition assay in CHO cells stably expressing rat and human SLC-1\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — endogenous ligand isolation with functional assay; replicated across multiple concurrent studies\",\n      \"pmids\": [\"10441476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Structure-activity relationship studies defined MCH-(6-17) as the minimal sequence for full agonistic activity at MCHR1, with Met8, Arg11, and Tyr13 as essential residues; disruption of the disulfide bridge abolished agonistic activity and converted ligands to weak antagonists.\",\n      \"method\": \"cAMP inhibition assay and [35S]-GTPγS binding assay on HEK293 cells stably expressing human MCHR1, using 57 synthetic MCH analogues\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis/analog study with two orthogonal functional assays defining receptor contact residues\",\n      \"pmids\": [\"11278733\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The rat SLC-1 (MCHR1) receptor pharmacology closely parallels that of the human receptor, and agonist potency in the cAMP inhibition assay correlates strongly with binding affinity and in vivo feeding effects after ICV injection, establishing SLC-1 as the receptor mediating MCH-induced feeding behavior.\",\n      \"method\": \"cAMP inhibition assay and [125I]S36057 radioligand binding on rat recombinant SLC-1; ICV injection of MCH analogs with food intake measurement in rats\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal in vitro/in vivo correlation with multiple analogs; links receptor pharmacology directly to in vivo feeding phenotype\",\n      \"pmids\": [\"11561073\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In SK-MEL-37 human melanoma cells expressing endogenous SLC-1 (MCHR1), MCH inhibits cAMP accumulation and activates p42/p44 MAPK in a pertussis toxin-sensitive manner, indicating exclusive coupling to Gαi/Gαo in this cell context; Gαq-mediated Ca2+ mobilization was absent, showing cell-type-dependent G-protein selectivity.\",\n      \"method\": \"cAMP accumulation assay, MAPK activation assay, pertussis toxin treatment, Ca2+ measurement in SK-MEL-37 cells and CHO/293 cells overexpressing SLC-1\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal signaling assays with pharmacological dissection (pertussis toxin) in endogenously expressing cells\",\n      \"pmids\": [\"11708774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Human immune cells (PBMCs) express functional MCHR1 that couples to both cAMP synthesis and calcium mobilization upon MCH stimulation; MCH treatment decreases CD3-stimulated PBMC proliferation in vitro, indicating an immunomodulatory role for MCH/MCHR1 signaling.\",\n      \"method\": \"RT-PCR, FACS, in vitro cAMP and Ca2+ assays, cell proliferation assay in human PBMCs\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays in primary human cells; single laboratory study\",\n      \"pmids\": [\"12220661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rhesus monkey MCH-R1 binds MCH with Kd of 6.5 nM and couples through both Gi/Go and Gq-type G proteins, mirroring human MCH-R1 coupling, while MCH-R2 utilizes exclusively the Gq signaling pathway.\",\n      \"method\": \"Radioligand binding assay, intracellular signaling characterization (cAMP and Ca2+) in cells expressing cloned monkey receptors\",\n      \"journal\": \"Peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — binding and functional assays with cloned receptor; single lab, confirms cross-species conservation of coupling\",\n      \"pmids\": [\"12182940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"A G34R coding SNP in MCHR1 present at 15% minor allele frequency in African-Americans does not alter receptor binding affinity or functional signaling (cAMP, Ca2+, MAPK) compared to wild-type MCHR1.\",\n      \"method\": \"Receptor binding assay, cAMP inhibition, Ca2+ mobilization, and MAPK activation assays in CHO cells expressing SNP-containing MCHR1 constructs\",\n      \"journal\": \"Obesity research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays on variant receptor; establishes functional neutrality of common variant\",\n      \"pmids\": [\"15340116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Mice with genetic inactivation of MCHR1 (Mch1r-/-) develop osteoporosis with reduced cortical bone mass and increased serum c-telopeptide (marker of bone resorption), indicating that MCHR1 signaling is required for tonic stimulation of bone mass.\",\n      \"method\": \"MCHR1 knockout mouse generation, bone densitometry, serum c-telopeptide measurement\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific biochemical readout; single lab\",\n      \"pmids\": [\"15147966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Mch1r-/- mice show significantly enhanced voluntary wheel running activity, and Pmch-/- mice show similar enhancement, demonstrating that endogenous MCH signaling through MCH1R plays an inhibitory role in regulating locomotor activity; naloxone suppresses wheel running in both genotypes, implicating opioid regulation downstream.\",\n      \"method\": \"Voluntary wheel running measurement in Mch1r-/- and Pmch-/- knockout mice; naloxone pharmacological challenge; dynorphin mRNA measurement\",\n      \"journal\": \"Regulatory peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two independent KO mouse lines with quantitative locomotor assay and pharmacological probe; single lab\",\n      \"pmids\": [\"15544841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"MCHR1 null mutant mice display anxiolytic-like behavior across multiple behavioral paradigms (open field, elevated plus maze, social interaction, stress-induced hyperthermia); baseline serotonin levels in the prefrontal cortex are lower in MCHR1 KO mice, and forced swim-induced 5-HT efflux is absent, placing MCHR1 upstream of serotonergic transmission in modulating anxiety.\",\n      \"method\": \"MCHR1 knockout mouse behavioral testing (open field, EPM, social interaction, SIH), in vivo microdialysis for serotonin measurement in prefrontal cortex\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with behavioral battery and in vivo neurochemical readout; single lab\",\n      \"pmids\": [\"15988472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A neuroblastoma-derived cell line (I3.4.2) with high endogenous MCHR1 expression shows MCH-stimulated Ca2+ mobilization that is insensitive to pertussis toxin and absent cAMP signaling, indicating that in neural-derived cells MCHR1 signals preferentially through Gαq rather than Gαi/o.\",\n      \"method\": \"Pertussis toxin treatment, Ca2+ mobilization assay, cAMP accumulation assay in IMR32-derived neuronal cell line expressing native MCHR1\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection with pertussis toxin in native neural-expressing cells; single lab\",\n      \"pmids\": [\"16524757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MCHR1 protein localizes abundantly to primary cilia on neurons throughout the murine CNS, as determined by immunohistochemistry with a validated specific antibody; ciliary MCHR1 co-localizes with diverse neurochemical markers (TH, calretinin, kisspeptin, estrogen receptor, OT, AVP, CRF), suggesting non-synaptic volume transmission as a predominant mode of MCH signaling.\",\n      \"method\": \"Immunohistochemistry with specificity-validated antibody, multiple neurochemical marker co-localization in rat and mouse CNS\",\n      \"journal\": \"Journal of neuroscience research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with validated antibody across brain regions; single lab but comprehensive mapping\",\n      \"pmids\": [\"32530066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The ciliary transition zone protein AHI1 is required for trafficking of MCHR1 into neuronal primary cilia; Ahi1-/- neurons show reduced ciliary MCHR1 with normal total and surface expression, and have significantly decreased cAMP and ERK signaling downstream of MCH stimulation, demonstrating that ciliary localization of MCHR1 is necessary for its signaling.\",\n      \"method\": \"Neuronal cultures from Ahi1+/+ and Ahi1-/- embryonic mice, immunofluorescence for ciliary MCHR1, cAMP assay, ERK phosphorylation assay after MCH stimulation\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal signaling readouts (cAMP, ERK) directly linking ciliary localization to signaling; strong mechanistic conclusion\",\n      \"pmids\": [\"33741721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PDGF-BB directly binds MCHR1 in membrane fractions of normal human dermal fibroblasts (confirmed by surface plasmon resonance), upregulates MCHR1 expression, and signals through MCHR1 to modulate intracellular cAMP and induce TGFβ1 and CTGF expression; MCHR1 silencing blocks these profibrotic responses.\",\n      \"method\": \"Co-IP/membrane fraction binding, surface plasmon resonance, MCHR1 siRNA knockdown, cAMP assay, TGFβ1/CTGF mRNA and protein measurement in normal human dermal fibroblasts\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — SPR binding confirmation plus KD phenotype with multiple readouts; novel non-MCH ligand for MCHR1; single lab\",\n      \"pmids\": [\"34912333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MRAP2 interacts with MCHR1 (confirmed by co-immunoprecipitation and bimolecular fluorescence complementation) and inhibits MCHR1-mediated intracellular Ca2+ signaling; the C-terminal domain of MRAP2 is required for this pharmacological modulation and for effects on MCHR1 membrane transport.\",\n      \"method\": \"Co-immunoprecipitation, bimolecular fluorescence complementation, Ca2+ signaling assay with MRAP2 truncation constructs\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction confirmed by two methods with domain mapping; single lab\",\n      \"pmids\": [\"35311242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MCHR1 mRNA is expressed in thyroid follicular cells; MCH1R-knockout mice exhibit reduced circulating thyroid hormones (T4, fT4, T3, rT3) with elevated TRH and TSH, and upon TSH challenge their thyroids secrete lower amounts of T4, demonstrating that MCHR1 signaling is required for normal thyroid hormone secretion.\",\n      \"method\": \"RT-PCR for thyroid MCHR1 expression, MCH1R knockout mouse phenotyping (serum hormone measurements), TSH challenge experiment, 125I secretion assay\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with functional endocrine challenge assay; single lab\",\n      \"pmids\": [\"23024261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Intrahippocampal MCH administration impairs memory consolidation and decreases hippocampal MCHR1 and TrkB receptor expression without altering BDNF or NMDA receptor subunit levels; co-administration with MCHR1 antagonist ATC-0175 reverses memory impairment, placing MCHR1 activation upstream of TrkB downregulation in hippocampal memory consolidation.\",\n      \"method\": \"Bilateral intrahippocampal MCH microinjection in rats, novel object recognition test, elevated plus maze, Western blot/qPCR for MCHR1, TrkB, BDNF, NR1, NR2A, NR2B; pharmacological rescue with MCHR1 antagonist\",\n      \"journal\": \"Progress in neuro-psychopharmacology & biological psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological challenge with antagonist rescue and molecular readouts; single lab\",\n      \"pmids\": [\"36565982\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MCHR1 (SLC-1/GPR24) is a Gi/o- and Gq-coupled GPCR that binds MCH with sub-nanomolar affinity, inhibits cAMP accumulation and mobilizes intracellular Ca2+ in a cell-type-dependent manner; it localizes predominantly to neuronal primary cilia where AHI1-dependent ciliary trafficking is required for full downstream cAMP and ERK signaling; it also interacts with MRAP2 (which inhibits its Ca2+ signaling via its C-terminus) and can be engaged by PDGF-BB to drive fibrotic signaling, while in vivo it tonically regulates feeding, locomotion, anxiety/mood via serotonergic transmission, bone homeostasis, thyroid hormone secretion, and hippocampal memory consolidation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MCHR1 (SLC-1/GPR24) is a G-protein-coupled receptor for melanin-concentrating hormone (MCH) that integrates energy balance, locomotion, anxiety, memory, bone homeostasis, and thyroid function through cell-type-dependent coupling to Gi/o and Gq signaling cascades. MCHR1 binds MCH with sub-nanomolar affinity and, depending on cellular context, inhibits cAMP accumulation via pertussis toxin-sensitive Gi/o proteins, mobilizes intracellular Ca²⁺ via Gq, and activates p42/p44 MAPK; in neuronal cells expressing endogenous receptor, signaling can be exclusively Gq-mediated [PMID:10421367, PMID:11708774, PMID:16524757]. In the CNS, MCHR1 localizes predominantly to neuronal primary cilia, and AHI1-dependent ciliary trafficking is required for downstream cAMP and ERK signaling, establishing the cilium as a critical signaling platform for this receptor [PMID:32530066, PMID:33741721]. MCHR1 is modulated by the accessory protein MRAP2, whose C-terminus inhibits MCHR1-mediated Ca²⁺ signaling and membrane transport, and can also be engaged by the non-canonical ligand PDGF-BB to drive profibrotic gene expression in dermal fibroblasts [PMID:35311242, PMID:34912333].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of MCH as the endogenous ligand of the orphan receptor SLC-1 resolved the receptor's pharmacological identity and established its dual Gi/o–Gq coupling, providing the molecular basis for all subsequent MCH signaling studies.\",\n      \"evidence\": \"Radioligand binding, Ca²⁺ mobilization, cAMP inhibition in HEK293/CHO cells; GIRK and Cl⁻ current recording in Xenopus oocytes\",\n      \"pmids\": [\"10421367\", \"10471841\", \"10441476\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"G-protein coupling selectivity in native tissues not yet addressed\",\n        \"No structural basis for sub-nanomolar MCH binding\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Structure-activity analysis of MCH analogs defined the minimal active peptide core (residues 6–17), essential contact residues, and the requirement for the disulfide bridge, while correlating in vitro potency with in vivo feeding responses—linking receptor pharmacology to the orexigenic phenotype.\",\n      \"evidence\": \"57 synthetic MCH analogs tested by cAMP and GTPγS assays in HEK293 cells; ICV injection of analogs with food intake measurement in rats\",\n      \"pmids\": [\"11278733\", \"11561073\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No receptor mutagenesis to identify contact residues on the MCHR1 side\",\n        \"Downstream intracellular pathways mediating feeding behavior undefined\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that cell-type context dictates MCHR1's G-protein selectivity—exclusive Gi/o coupling in melanoma cells versus Gq-dominant coupling in neuronal cells—established that MCHR1 signaling output is not fixed but depends on the cellular G-protein repertoire.\",\n      \"evidence\": \"cAMP, Ca²⁺, and MAPK assays with pertussis toxin in SK-MEL-37 melanoma cells and IMR32-derived neuroblastoma cells expressing endogenous MCHR1\",\n      \"pmids\": [\"11708774\", \"16524757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism determining G-protein selectivity (e.g., receptor phosphorylation state, scaffold proteins) unknown\",\n        \"In vivo relevance of cell-type-dependent coupling not established\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"MCHR1 knockout mice revealed an unexpected requirement for MCH/MCHR1 signaling in bone homeostasis, demonstrating that MCHR1 tonically stimulates bone mass and that its loss leads to osteoporosis with increased bone resorption.\",\n      \"evidence\": \"MCHR1 KO mouse bone densitometry and serum c-telopeptide measurement\",\n      \"pmids\": [\"15147966\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether MCHR1 acts directly on osteoblasts/osteoclasts or indirectly via CNS pathways is unknown\",\n        \"No rescue experiment performed\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Behavioral phenotyping of MCHR1-null and PMCH-null mice established that endogenous MCH–MCHR1 signaling tonically suppresses locomotor activity and promotes anxiety-like behavior, with serotonergic transmission as a downstream mediator of the anxiolytic phenotype.\",\n      \"evidence\": \"Voluntary wheel running in two independent KO lines; behavioral battery (open field, EPM, social interaction, SIH) plus in vivo microdialysis for 5-HT in prefrontal cortex of MCHR1 KO mice\",\n      \"pmids\": [\"15544841\", \"15988472\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Neuronal subpopulations mediating the locomotor versus anxiety phenotypes not identified\",\n        \"Circuit-level mechanism linking MCHR1 to serotonergic neuron firing not resolved\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery of MCHR1 expression in thyroid follicular cells and the hypothyroid phenotype of MCHR1 KO mice extended the receptor's physiological roles beyond the CNS, demonstrating a direct requirement for MCHR1 in thyroid hormone secretion.\",\n      \"evidence\": \"RT-PCR for thyroid MCHR1; KO mouse serum hormone levels; TSH challenge and ¹²⁵I secretion assay\",\n      \"pmids\": [\"23024261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Intracellular signaling pathway in thyroid cells (Gi vs Gq) not characterized\",\n        \"Whether MCH is delivered to thyroid via circulation or local production is unknown\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Comprehensive mapping of MCHR1 to neuronal primary cilia across the CNS reframed the receptor's signaling mode, suggesting volume transmission rather than synaptic signaling as its predominant activation mechanism in the brain.\",\n      \"evidence\": \"Immunohistochemistry with validated antibody and neurochemical marker co-localization across rat and mouse brain regions\",\n      \"pmids\": [\"32530066\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional consequence of ciliary versus non-ciliary MCHR1 signaling not yet distinguished in vivo\",\n        \"Source and diffusion dynamics of MCH reaching cilia not characterized\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that AHI1 is required for MCHR1 ciliary trafficking and that loss of ciliary MCHR1 attenuates cAMP and ERK signaling established the primary cilium as a necessary signaling platform for MCHR1, connecting ciliopathy biology to MCH signaling.\",\n      \"evidence\": \"Ahi1 KO neuronal cultures; immunofluorescence for ciliary MCHR1; cAMP and ERK phosphorylation assays after MCH stimulation\",\n      \"pmids\": [\"33741721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether AHI1 loss phenocopies MCHR1 KO behavioral phenotypes in vivo not tested\",\n        \"Additional ciliary trafficking machinery for MCHR1 beyond AHI1 not identified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of PDGF-BB as a non-canonical MCHR1 ligand that drives profibrotic signaling expanded the receptor's functional repertoire beyond neuropeptide signaling into tissue fibrosis.\",\n      \"evidence\": \"SPR binding, co-IP in dermal fibroblast membranes, MCHR1 siRNA knockdown with TGFβ1/CTGF readouts\",\n      \"pmids\": [\"34912333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"PDGF-BB binding site on MCHR1 relative to MCH binding site not mapped\",\n        \"Independent replication of PDGF-BB as a direct MCHR1 ligand not yet reported\",\n        \"In vivo relevance of PDGF-BB–MCHR1 interaction in fibrotic disease not established\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that MRAP2 physically interacts with MCHR1 and inhibits its Ca²⁺ signaling via its C-terminal domain identified the first accessory protein that modulates MCHR1 pharmacology, and intrahippocampal MCHR1 activation was shown to impair memory consolidation through TrkB downregulation.\",\n      \"evidence\": \"Co-IP and BiFC for MRAP2–MCHR1 interaction with domain truncations; intrahippocampal MCH microinjection with antagonist rescue and Western blot in rats\",\n      \"pmids\": [\"35311242\", \"36565982\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Stoichiometry and structural basis of MRAP2–MCHR1 complex unknown\",\n        \"Mechanism linking MCHR1 activation to TrkB downregulation not elucidated\",\n        \"Whether MRAP2 modulation occurs in vivo in neurons not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for MCH and PDGF-BB binding to MCHR1, the in vivo contribution of ciliary versus non-ciliary receptor pools to distinct physiological functions, and the cell-intrinsic determinants of G-protein coupling selectivity.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of MCHR1 bound to MCH or any ligand\",\n        \"In vivo cell-type-specific conditional knockout studies are lacking\",\n        \"Determinants of Gi vs Gq selectivity in native neurons remain uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 12, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 15, 16]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [13, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 1, 5, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 5, 14]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [11, 13, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"MCH\",\n      \"AHI1\",\n      \"MRAP2\",\n      \"PDGF-BB\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}