{"gene":"HRH4","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2000,"finding":"HRH4 (HH4R) was cloned from human leukocyte cDNA and shown to inhibit forskolin-induced cAMP accumulation upon histamine stimulation, demonstrating Gi-coupled signaling. H3 agonists (NAMHA, RAMHA, imetit) bound specifically to HH4R and also inhibited cAMP accumulation, though with lower affinity than at H3R.","method":"Radioligand competition binding assays and functional cAMP accumulation assays in HH4R-expressing cells","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct functional reconstitution in recombinant cells with both binding and cAMP assays; foundational cloning paper replicated by subsequent work","pmids":["11118334"],"is_preprint":false},{"year":2010,"finding":"Species-specific ligand binding at H4R orthologs (human, mouse, rat, guinea pig, monkey, pig, dog) was determined by site-directed mutagenesis of chimeric human-pig H4R constructs, identifying specific amino acid residues that govern ligand affinity differences across species.","method":"Radioligand binding assays on recombinant H4R orthologs expressed in HEK293T cells; chimeric receptor construction and site-directed mutagenesis","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis combined with binding assays in recombinant system; multiple orthogonal approaches in single study","pmids":["20103609"],"is_preprint":false},{"year":2011,"finding":"Recombinant human H4R expressed in Sf9 insect cells was characterized in functional steady-state GTPase assays; clozapine was identified as a partial H4R agonist, providing evidence for functional selectivity (biased signaling) at H4R, with dissociations between binding affinity (pKi) and functional potency (pKB/pIC50) values.","method":"Radioligand competition binding and steady-state GTPase assays in Sf9 insect cells expressing recombinant hH4R; molecular docking","journal":"Naunyn-Schmiedeberg's archives of pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — functional GTPase assay in recombinant system, single lab, single study","pmids":["22033803"],"is_preprint":false},{"year":2012,"finding":"Homology modeling of H4R based on the H1R crystal structure combined with molecular dynamics identified that ligand binding at the orthosteric site involves a protonated NH interaction with Asp3.32 and an imidazole NH interaction with Glu5.46; Glu5.20 and Thr6.55 in H4R contribute to selectivity relative to H3R. Active-state MD simulations showed outward movement of the intracellular TM6 and conformational change of Tyr7.53 consistent with receptor activation.","method":"Homology modeling based on H1R crystal structure; molecular docking; molecular dynamics simulation","journal":"Journal of molecular graphics & modelling","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational modeling only, no experimental mutagenesis validation reported in abstract","pmids":["23220277"],"is_preprint":false},{"year":2013,"finding":"H4R is expressed in rat brain endothelial cells (RBE4 cell line) and its activation by histamine or immepip activates the ERK1/2 MAPK pathway; this effect was blocked by the H4R-selective inverse agonist/antagonist JNJ 7777120 but not by the H3R antagonist ciproxifan, demonstrating H4R-specific ERK1/2 signaling in brain endothelial cells.","method":"RT-PCR; sequencing; ERK1/2 phosphorylation assays in immortalized RBE4 rat brain endothelial cells with selective pharmacological antagonists; in vivo brain blood vessel experiments","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor identification by RT-PCR/sequencing plus functional signaling assay with selective antagonist dissection; replicated in vitro and in vivo","pmids":["23488566"],"is_preprint":false},{"year":2015,"finding":"Unconstrained molecular dynamics simulations of histamine binding to hH4R revealed the complete binding pathway from the extracellular side to the orthosteric binding site, showing that the positively charged amine moiety of histamine interacts electrostatically with Asp3.32 and the imidazole moiety forms hydrogen bonds with Glu5.46 and Gln7.42.","method":"Unconstrained molecular dynamics simulation","journal":"Bioorganic & medicinal chemistry letters","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational modeling only, no experimental mutagenesis validation reported in abstract","pmids":["25677665"],"is_preprint":false},{"year":2016,"finding":"H4R activation in human mast cells (HMC-1 and cord blood-derived mast cells) induces IL-13 and RANTES/CCL5 production via distinct signaling pathways: RANTES production was blocked by the MEK inhibitor PD98059 (ERK1/2 pathway), while IL-13 production was blocked by the PI3K inhibitor LY294002 (Akt pathway). H4R gene silencing by siRNA reduced histamine-induced phosphorylation of ERK1/2, Akt, and NF-κB-p65.","method":"H4R siRNA knockdown; pharmacological inhibitors (JNJ7777120, PD98059, LY294002, Bay117082); phosphorylation western blotting; ELISA for cytokines in HMC-1 and CBMCs","journal":"Journal of receptor and signal transduction research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown plus pharmacological inhibition of multiple pathway nodes; two orthogonal approaches, single lab","pmids":["27400655"],"is_preprint":false},{"year":2017,"finding":"H4R rs11662595 nonsynonymous polymorphism significantly decreased the ability of HRH4 to activate Gi protein, resulting in facilitation of EMT, increased cell proliferation, and invasion in A549 NSCLC cells; in vivo experiments in nu/nu mice confirmed that rs11662595 attenuated the anti-EMT effects of H4R agonist treatment.","method":"Transfection of wild-type vs. rs11662595 mutant HRH4 in A549 cells; Gi protein activation assays; in vitro proliferation/invasion assays; in vivo xenograft mouse model","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mutagenesis (natural SNP) with functional Gi assay plus cellular and in vivo phenotypic readouts; single lab","pmids":["28847511"],"is_preprint":false},{"year":2018,"finding":"H4R activation in HMC-1 mast cells triggers intracellular Ca2+ release and degranulation, and induces IL-1β release via SAPK/JNK signaling; H4R siRNA knockdown inhibited histamine- and 4-methylhistamine-induced Ca2+ release, degranulation, and SAPK/JNK phosphorylation, and the JNK inhibitor SP600125 specifically blocked H4R-mediated IL-1β production.","method":"H4R siRNA knockdown; JNK inhibitor (SP600125); western blotting for SAPK/JNK phosphorylation; ELISA for IL-1β and IL-6; intracellular Ca2+ assay; degranulation assay in HMC-1 cells","journal":"Journal of receptor and signal transduction research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown plus selective pathway inhibitor; multiple readouts; single lab","pmids":["29863427"],"is_preprint":false},{"year":2018,"finding":"In vivo adoptive transfer experiments demonstrated that H4R on eosinophils mediates partial activation: transfer of H4R+/+ eosinophils into IL-5-deficient mice more effectively reversed DSS-induced colitis clinical phenotype (body weight loss, bleeding, stool consistency) than transfer of H4R-/- eosinophils, establishing a direct in vivo role for H4R in eosinophil-mediated colitis resolution.","method":"Adoptive transfer of H4R+/+ vs. H4R-/- eosinophils into IL-5-deficient BALB/c mice in DSS-induced colitis model; clinical scoring, histology, cytokine analysis","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout eosinophils with in vivo adoptive transfer and defined phenotypic readouts; single lab","pmids":["30319608"],"is_preprint":false},{"year":2011,"finding":"HRH4 overexpression in colorectal cancer cells caused growth arrest and induced cell cycle protein expression upon histamine exposure through a cAMP-dependent pathway; HRH4 stimulation also promoted 5-fluorouracil-induced apoptosis in HRH4-positive colorectal cells.","method":"Stable transfection of HRH4 in colorectal cancer cells; cell proliferation, colony formation, cell cycle, and apoptosis assays; immunoblotting; cAMP pathway analysis","journal":"BMC cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function with multiple cellular readouts and pathway identification; single lab","pmids":["21609450"],"is_preprint":false},{"year":2019,"finding":"H4R activation in rat brain microglia in vivo stimulates production of proinflammatory cytokines TNF-α and IL-1β; H4R agonist injection into the rat lateral ventricle induced microglial activation (Iba1 immunoreactivity) and cytokine release, and H4R antagonist partially abolished these effects, while H2R and H3R antagonists had opposite effects.","method":"Stereotaxic intracerebroventricular injection of histamine receptor agonists/antagonists; flow cytometry for receptor expression on microglia; Iba1 immunohistochemistry; ELISA and qRT-PCR for cytokines","journal":"Journal of neuroimmune pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological dissection with selective agonists/antagonists and multiple readouts; single lab","pmids":["31863333"],"is_preprint":false},{"year":2025,"finding":"Microglial-specific deletion of Hrh4 reverses cognitive deficits and reduces Aβ plaque, tauopathy, and microgliosis in aged 3xTg-AD mice by activating the cAMP/TGF-β1/Smad3 pathway to enhance microglial phagocytosis; these beneficial effects were abolished by inhibition of TGF-β receptor 1 signaling. Neuronal deletion of Hrh4 did not replicate these effects, establishing cell-type specificity.","method":"Conditional microglial-specific Hrh4 knockout mice; pharmacological rescue with VUF6002 (H4R antagonist); cognitive behavioral assays; transcriptomic analysis; Aβ/p-tau quantification; cAMP/TGF-β1/Smad3 pathway analysis","journal":"Advanced science","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic knockout plus pharmacological mimicry plus pathway mechanism (cAMP/TGF-β1/Smad3) with rescue experiment; multiple orthogonal methods","pmids":["41134085"],"is_preprint":false},{"year":2022,"finding":"H4R signaling in human lymphatic endothelial cells (LECs) in response to 4-methylhistamine requires extracellular Ca2+ entry through TRPV4; H4R activation sensitizes subsequent TRPV4 responses through a PLA2-dependent mechanism. TRPV4 activity is required downstream of H4R for NFATc1 translocation to the nucleus and cytoskeletal remodeling, but not for cytokine release.","method":"Ca2+ imaging with selective H4R antagonists; TRPV4 channel blockers; extracellular Ca2+ removal; NFATc1 nuclear translocation imaging; cytoskeletal assays; PLA2 inhibition in primary human LECs","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection with multiple selective tools plus mechanistic pathway (PLA2) in primary human cells; preprint, not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"HRH4 (H4R) is a Gi-coupled GPCR that inhibits cAMP accumulation upon histamine binding, with ligand recognition dependent on conserved residues Asp3.32, Glu5.46, and Gln7.42; in immune cells it signals through ERK1/2, Akt, NF-κB, and SAPK/JNK pathways to drive mast cell degranulation and cytokine release (IL-1β, IL-13, RANTES), activates microglia to release proinflammatory mediators, partially activates eosinophils in vivo, and in microglia specifically suppresses Alzheimer's disease pathology through a cAMP/TGF-β1/Smad3 axis that promotes Aβ and tau phagocytosis; in lymphatic endothelial cells H4R-evoked Ca2+ signaling is transduced via TRPV4 through a PLA2-dependent mechanism, leading to NFATc1 nuclear translocation and cytoskeletal remodeling."},"narrative":{"mechanistic_narrative":"HRH4 (H4R) is a Gi-coupled histamine receptor that signals primarily in immune and neural cell types to drive inflammatory effector programs [PMID:11118334]. Cloned from human leukocytes, it inhibits forskolin-induced cAMP accumulation upon histamine binding, with ligand recognition centered on the orthosteric residues Asp3.32, Glu5.46, and Gln7.42 [PMID:11118334]; functional and binding analyses across orthologs and recombinant systems define species-specific affinity determinants and ligand-dependent functional selectivity at the receptor [PMID:20103609, PMID:22033803]. In mast cells, H4R activation couples to distinct downstream cascades to direct effector output: ERK1/2 drives RANTES/CCL5 production, Akt drives IL-13, NF-κB-p65 is engaged downstream of histamine, and SAPK/JNK signaling mediates intracellular Ca2+ release, degranulation, and IL-1β release [PMID:27400655, PMID:29863427]. The receptor extends this proinflammatory role to the nervous system, where H4R activation in microglia stimulates TNF-α and IL-1β production and microglial activation in vivo [PMID:31863333], yet microglial-specific Hrh4 deletion paradoxically reverses cognitive deficits and reduces Aβ and tau pathology in AD model mice by engaging a cAMP/TGF-β1/Smad3 axis that enhances phagocytosis [PMID:41134085]. H4R also functions in non-hematopoietic contexts, activating ERK1/2 in brain endothelial cells [PMID:23488566], modulating cAMP-dependent growth arrest and chemosensitivity in colorectal cancer cells [PMID:21609450], and influencing EMT and proliferation in lung cancer cells in a manner attenuated by the rs11662595 polymorphism that impairs Gi activation [PMID:28847511].","teleology":[{"year":2000,"claim":"Established the molecular identity and signaling output of HRH4, answering whether the leukocyte-derived receptor was a functional histamine receptor and how it transduces signal.","evidence":"Cloning from human leukocyte cDNA with radioligand binding and cAMP accumulation assays in recombinant cells","pmids":["11118334"],"confidence":"High","gaps":["Did not define native cell-type signaling beyond cAMP","Cross-reactivity with H3 agonists left ligand selectivity unresolved"]},{"year":2010,"claim":"Mapped the structural basis of species-divergent ligand affinity, addressing why pharmacology differs across H4R orthologs.","evidence":"Chimeric human-pig receptor constructs and site-directed mutagenesis with radioligand binding in HEK293T cells","pmids":["20103609"],"confidence":"High","gaps":["Residue mapping did not address downstream signaling consequences","No active-state structural model"]},{"year":2011,"claim":"Demonstrated functional selectivity (biased signaling) at H4R, addressing whether binding affinity predicts signaling output.","evidence":"Radioligand binding and steady-state GTPase assays with clozapine in Sf9 insect cells; molecular docking","pmids":["22033803"],"confidence":"Medium","gaps":["Single-lab, single-study GTPase readout","Bias not validated in native cells"]},{"year":2011,"claim":"Revealed a tumor-suppressive role in colorectal cancer, asking whether H4R signaling alters proliferation and drug response.","evidence":"Stable HRH4 transfection in colorectal cancer cells with proliferation, cell-cycle, apoptosis, and cAMP pathway assays","pmids":["21609450"],"confidence":"Medium","gaps":["Overexpression model may not reflect endogenous receptor levels","Mechanism linking cAMP to cell-cycle arrest not fully resolved"]},{"year":2012,"claim":"Computationally defined orthosteric binding contacts and an activation-associated conformational change, framing the structural mechanism of recognition.","evidence":"Homology modeling on the H1R crystal structure with molecular dynamics simulation","pmids":["23220277"],"confidence":"Low","gaps":["Computational only, no experimental mutagenesis validation","Predicted selectivity residues untested functionally"]},{"year":2013,"claim":"Identified H4R-specific ERK1/2 activation in brain endothelial cells, extending receptor function beyond hematopoietic cells.","evidence":"RT-PCR/sequencing and ERK1/2 phosphorylation assays with selective antagonists in RBE4 cells and in vivo","pmids":["23488566"],"confidence":"Medium","gaps":["Downstream physiological consequence in vasculature unclear","G-protein coupling in this context not directly tested"]},{"year":2015,"claim":"Resolved the complete histamine binding pathway and key contact residues, refining the recognition mechanism.","evidence":"Unconstrained molecular dynamics simulation of histamine binding to hH4R","pmids":["25677665"],"confidence":"Low","gaps":["Computational only, no experimental validation","Does not address signaling conformations"]},{"year":2016,"claim":"Dissected branched effector signaling in mast cells, answering which pathway drives which cytokine.","evidence":"H4R siRNA knockdown and pathway-selective inhibitors with phosphoblotting and cytokine ELISA in HMC-1 and CBMCs","pmids":["27400655"],"confidence":"Medium","gaps":["Single lab","Direct receptor-to-kinase coupling steps not defined"]},{"year":2017,"claim":"Linked a natural HRH4 polymorphism to impaired Gi activation and pro-tumor phenotype, connecting genetic variation to function in lung cancer.","evidence":"Wild-type vs. rs11662595 mutant transfection with Gi activation, invasion/proliferation assays, and xenograft model","pmids":["28847511"],"confidence":"Medium","gaps":["Single lab","Clinical relevance of the SNP not established in patient cohorts here"]},{"year":2018,"claim":"Established SAPK/JNK as the route for H4R-driven Ca2+ release, degranulation, and IL-1β in mast cells.","evidence":"H4R siRNA knockdown and JNK inhibitor with phosphoblotting, ELISA, Ca2+ and degranulation assays in HMC-1 cells","pmids":["29863427"],"confidence":"Medium","gaps":["Single lab","Coupling between Gi/cAMP and JNK not mechanistically bridged"]},{"year":2018,"claim":"Provided in vivo genetic evidence that eosinophil H4R contributes to colitis resolution, defining a tissue-level effector role.","evidence":"Adoptive transfer of H4R+/+ vs H4R-/- eosinophils into IL-5-deficient mice in DSS colitis","pmids":["30319608"],"confidence":"Medium","gaps":["Molecular signaling in eosinophils not delineated","Single lab"]},{"year":2019,"claim":"Demonstrated that microglial H4R drives proinflammatory cytokine release in vivo, opposing H2R/H3R.","evidence":"Intracerebroventricular agonist/antagonist injection with Iba1 IHC, flow cytometry, ELISA and qRT-PCR in rat","pmids":["31863333"],"confidence":"Medium","gaps":["Intracellular signaling pathway not resolved","Single lab"]},{"year":2025,"claim":"Defined cell-type-specific microglial H4R control of AD pathology via a cAMP/TGF-β1/Smad3 phagocytic axis, establishing therapeutic logic of receptor blockade.","evidence":"Conditional microglial Hrh4 knockout, pharmacological rescue with VUF6002, behavioral/transcriptomic/pathology readouts with TGF-βR1 inhibition rescue in 3xTg-AD mice","pmids":["41134085"],"confidence":"High","gaps":["Reconciliation with proinflammatory microglial role not fully resolved","Human relevance untested"]},{"year":2022,"claim":"Identified TRPV4 as a Ca2+-entry effector downstream of H4R in lymphatic endothelial cells via a PLA2-dependent mechanism.","evidence":"Ca2+ imaging, TRPV4 blockers, extracellular Ca2+ removal, NFATc1 translocation and cytoskeletal assays with PLA2 inhibition in primary human LECs (preprint)","pmids":[],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Direct physical coupling of H4R to TRPV4 not shown"]},{"year":null,"claim":"How H4R's dual proinflammatory and protective roles in microglia are reconciled at the signaling level, and how Gi/cAMP coupling bifurcates into the divergent ERK/Akt/JNK/NF-κB and TGF-β1/Smad3 outputs, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experimental structure of active H4R-G-protein complex in the corpus","Context-dependent switch between inflammatory and phagocytic programs uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,8,9,11]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H3N8","full_name":"Histamine H4 receptor","aliases":["AXOR35","G-protein coupled receptor 105","GPRv53","Pfi-013","SP9144"],"length_aa":390,"mass_kda":44.5,"function":"G protein-coupled receptor primarily expressed in immune cells such as mast cells, eosinophils, basophils, dendritic cells and neutrophils that plays a key role in immune and inflammatory responses (PubMed:26948974). Mediates chemotaxis of immune cells to sites of inflammation or injury by responding to histamine (PubMed:26948974). Activation by histamine also influences the release of proinflammatory cytokines such as TNF, CCL4, IL6 and IFN-gamma (PubMed:29600327, PubMed:31583075). Ligand binding induces a conformation change that triggers signaling via G(i)/GNAI1 leading to decreased intracellular cAMP levels by inhibiting adenylate cyclase activity (PubMed:39333117). In addition, plays a role in the control of renal reabsorption processes, particularly albumin uptake (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9H3N8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HRH4","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/HRH4","total_profiled":1310},"omim":[{"mim_id":"606792","title":"HISTAMINE RECEPTOR H4; HRH4","url":"https://www.omim.org/entry/606792"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Not detected","tissue_distribution":"Not detected","driving_tissues":[],"url":"https://www.proteinatlas.org/search/HRH4"},"hgnc":{"alias_symbol":["H4R","HH4R","AXOR35","GPCR105","GPRv53"],"prev_symbol":[]},"alphafold":{"accession":"Q9H3N8","domains":[{"cath_id":"1.20.1070.10","chopping":"13-212_289-375","consensus_level":"high","plddt":88.2891,"start":13,"end":375}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3N8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3N8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3N8-F1-predicted_aligned_error_v6.png","plddt_mean":76.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HRH4","jax_strain_url":"https://www.jax.org/strain/search?query=HRH4"},"sequence":{"accession":"Q9H3N8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H3N8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H3N8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3N8"}},"corpus_meta":[{"pmid":"11118334","id":"PMC_11118334","title":"Molecular cloning and characterization of a new human histamine receptor, HH4R.","date":"2000","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/11118334","citation_count":277,"is_preprint":false},{"pmid":"16299042","id":"PMC_16299042","title":"Selective expression of histamine receptors H1R, H2R, and H4R, but not H3R, in the human intestinal tract.","date":"2005","source":"Gut","url":"https://pubmed.ncbi.nlm.nih.gov/16299042","citation_count":129,"is_preprint":false},{"pmid":"25102165","id":"PMC_25102165","title":"Modulation of behavior by the histaminergic system: lessons from HDC-, H3R- and H4R-deficient mice.","date":"2014","source":"Neuroscience and biobehavioral reviews","url":"https://pubmed.ncbi.nlm.nih.gov/25102165","citation_count":58,"is_preprint":false},{"pmid":"20103609","id":"PMC_20103609","title":"Molecular determinants of ligand binding to H4R species variants.","date":"2010","source":"Molecular 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immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30319608","citation_count":6,"is_preprint":false},{"pmid":"22201741","id":"PMC_22201741","title":"Computerized modeling techniques predict the 3D structure of H₄R: facts and fiction.","date":"2012","source":"Frontiers in bioscience (Landmark edition)","url":"https://pubmed.ncbi.nlm.nih.gov/22201741","citation_count":5,"is_preprint":false},{"pmid":"34064490","id":"PMC_34064490","title":"Production of IL-31 in CD45RO+CLA+H4R+ T Cells in Atopic Dermatitis.","date":"2021","source":"Journal of clinical medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34064490","citation_count":5,"is_preprint":false},{"pmid":"27697645","id":"PMC_27697645","title":"Dibenzo[b,f][1,4]oxazepines and dibenzo[b,e]oxepines: Influence of the chlorine substitution pattern on the pharmacology at the H1R, H4R, 5-HT2AR and other selected GPCRs.","date":"2016","source":"Pharmacological 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N-(2-Aminoethyl)-5-Chloro-1H-Indole-2-Carboxamide (Compound A) in a Mouse Model of Allergic Asthma.","date":"2020","source":"Immunological investigations","url":"https://pubmed.ncbi.nlm.nih.gov/31985316","citation_count":0,"is_preprint":false},{"pmid":"39732275","id":"PMC_39732275","title":"The H4R antagonist, JNJ-7777120 treatments ameliorate mild traumatic brain injury by reducing oxidative damage, inflammatory and apoptotic responses through blockage of the ERK1/2/NF-κB pathway in a rat model.","date":"2024","source":"Experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/39732275","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.25.690563","title":"TRPV4 Promotes Histamine Receptor Signaling in Lymphatic Endothelial 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H3 agonists (NAMHA, RAMHA, imetit) bound specifically to HH4R and also inhibited cAMP accumulation, though with lower affinity than at H3R.\",\n      \"method\": \"Radioligand competition binding assays and functional cAMP accumulation assays in HH4R-expressing cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct functional reconstitution in recombinant cells with both binding and cAMP assays; foundational cloning paper replicated by subsequent work\",\n      \"pmids\": [\"11118334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Species-specific ligand binding at H4R orthologs (human, mouse, rat, guinea pig, monkey, pig, dog) was determined by site-directed mutagenesis of chimeric human-pig H4R constructs, identifying specific amino acid residues that govern ligand affinity differences across species.\",\n      \"method\": \"Radioligand binding assays on recombinant H4R orthologs expressed in HEK293T cells; chimeric receptor construction and site-directed mutagenesis\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis combined with binding assays in recombinant system; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"20103609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Recombinant human H4R expressed in Sf9 insect cells was characterized in functional steady-state GTPase assays; clozapine was identified as a partial H4R agonist, providing evidence for functional selectivity (biased signaling) at H4R, with dissociations between binding affinity (pKi) and functional potency (pKB/pIC50) values.\",\n      \"method\": \"Radioligand competition binding and steady-state GTPase assays in Sf9 insect cells expressing recombinant hH4R; molecular docking\",\n      \"journal\": \"Naunyn-Schmiedeberg's archives of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — functional GTPase assay in recombinant system, single lab, single study\",\n      \"pmids\": [\"22033803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Homology modeling of H4R based on the H1R crystal structure combined with molecular dynamics identified that ligand binding at the orthosteric site involves a protonated NH interaction with Asp3.32 and an imidazole NH interaction with Glu5.46; Glu5.20 and Thr6.55 in H4R contribute to selectivity relative to H3R. Active-state MD simulations showed outward movement of the intracellular TM6 and conformational change of Tyr7.53 consistent with receptor activation.\",\n      \"method\": \"Homology modeling based on H1R crystal structure; molecular docking; molecular dynamics simulation\",\n      \"journal\": \"Journal of molecular graphics & modelling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational modeling only, no experimental mutagenesis validation reported in abstract\",\n      \"pmids\": [\"23220277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"H4R is expressed in rat brain endothelial cells (RBE4 cell line) and its activation by histamine or immepip activates the ERK1/2 MAPK pathway; this effect was blocked by the H4R-selective inverse agonist/antagonist JNJ 7777120 but not by the H3R antagonist ciproxifan, demonstrating H4R-specific ERK1/2 signaling in brain endothelial cells.\",\n      \"method\": \"RT-PCR; sequencing; ERK1/2 phosphorylation assays in immortalized RBE4 rat brain endothelial cells with selective pharmacological antagonists; in vivo brain blood vessel experiments\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor identification by RT-PCR/sequencing plus functional signaling assay with selective antagonist dissection; replicated in vitro and in vivo\",\n      \"pmids\": [\"23488566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Unconstrained molecular dynamics simulations of histamine binding to hH4R revealed the complete binding pathway from the extracellular side to the orthosteric binding site, showing that the positively charged amine moiety of histamine interacts electrostatically with Asp3.32 and the imidazole moiety forms hydrogen bonds with Glu5.46 and Gln7.42.\",\n      \"method\": \"Unconstrained molecular dynamics simulation\",\n      \"journal\": \"Bioorganic & medicinal chemistry letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational modeling only, no experimental mutagenesis validation reported in abstract\",\n      \"pmids\": [\"25677665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"H4R activation in human mast cells (HMC-1 and cord blood-derived mast cells) induces IL-13 and RANTES/CCL5 production via distinct signaling pathways: RANTES production was blocked by the MEK inhibitor PD98059 (ERK1/2 pathway), while IL-13 production was blocked by the PI3K inhibitor LY294002 (Akt pathway). H4R gene silencing by siRNA reduced histamine-induced phosphorylation of ERK1/2, Akt, and NF-κB-p65.\",\n      \"method\": \"H4R siRNA knockdown; pharmacological inhibitors (JNJ7777120, PD98059, LY294002, Bay117082); phosphorylation western blotting; ELISA for cytokines in HMC-1 and CBMCs\",\n      \"journal\": \"Journal of receptor and signal transduction research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown plus pharmacological inhibition of multiple pathway nodes; two orthogonal approaches, single lab\",\n      \"pmids\": [\"27400655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"H4R rs11662595 nonsynonymous polymorphism significantly decreased the ability of HRH4 to activate Gi protein, resulting in facilitation of EMT, increased cell proliferation, and invasion in A549 NSCLC cells; in vivo experiments in nu/nu mice confirmed that rs11662595 attenuated the anti-EMT effects of H4R agonist treatment.\",\n      \"method\": \"Transfection of wild-type vs. rs11662595 mutant HRH4 in A549 cells; Gi protein activation assays; in vitro proliferation/invasion assays; in vivo xenograft mouse model\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mutagenesis (natural SNP) with functional Gi assay plus cellular and in vivo phenotypic readouts; single lab\",\n      \"pmids\": [\"28847511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"H4R activation in HMC-1 mast cells triggers intracellular Ca2+ release and degranulation, and induces IL-1β release via SAPK/JNK signaling; H4R siRNA knockdown inhibited histamine- and 4-methylhistamine-induced Ca2+ release, degranulation, and SAPK/JNK phosphorylation, and the JNK inhibitor SP600125 specifically blocked H4R-mediated IL-1β production.\",\n      \"method\": \"H4R siRNA knockdown; JNK inhibitor (SP600125); western blotting for SAPK/JNK phosphorylation; ELISA for IL-1β and IL-6; intracellular Ca2+ assay; degranulation assay in HMC-1 cells\",\n      \"journal\": \"Journal of receptor and signal transduction research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown plus selective pathway inhibitor; multiple readouts; single lab\",\n      \"pmids\": [\"29863427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In vivo adoptive transfer experiments demonstrated that H4R on eosinophils mediates partial activation: transfer of H4R+/+ eosinophils into IL-5-deficient mice more effectively reversed DSS-induced colitis clinical phenotype (body weight loss, bleeding, stool consistency) than transfer of H4R-/- eosinophils, establishing a direct in vivo role for H4R in eosinophil-mediated colitis resolution.\",\n      \"method\": \"Adoptive transfer of H4R+/+ vs. H4R-/- eosinophils into IL-5-deficient BALB/c mice in DSS-induced colitis model; clinical scoring, histology, cytokine analysis\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout eosinophils with in vivo adoptive transfer and defined phenotypic readouts; single lab\",\n      \"pmids\": [\"30319608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"HRH4 overexpression in colorectal cancer cells caused growth arrest and induced cell cycle protein expression upon histamine exposure through a cAMP-dependent pathway; HRH4 stimulation also promoted 5-fluorouracil-induced apoptosis in HRH4-positive colorectal cells.\",\n      \"method\": \"Stable transfection of HRH4 in colorectal cancer cells; cell proliferation, colony formation, cell cycle, and apoptosis assays; immunoblotting; cAMP pathway analysis\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function with multiple cellular readouts and pathway identification; single lab\",\n      \"pmids\": [\"21609450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"H4R activation in rat brain microglia in vivo stimulates production of proinflammatory cytokines TNF-α and IL-1β; H4R agonist injection into the rat lateral ventricle induced microglial activation (Iba1 immunoreactivity) and cytokine release, and H4R antagonist partially abolished these effects, while H2R and H3R antagonists had opposite effects.\",\n      \"method\": \"Stereotaxic intracerebroventricular injection of histamine receptor agonists/antagonists; flow cytometry for receptor expression on microglia; Iba1 immunohistochemistry; ELISA and qRT-PCR for cytokines\",\n      \"journal\": \"Journal of neuroimmune pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological dissection with selective agonists/antagonists and multiple readouts; single lab\",\n      \"pmids\": [\"31863333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Microglial-specific deletion of Hrh4 reverses cognitive deficits and reduces Aβ plaque, tauopathy, and microgliosis in aged 3xTg-AD mice by activating the cAMP/TGF-β1/Smad3 pathway to enhance microglial phagocytosis; these beneficial effects were abolished by inhibition of TGF-β receptor 1 signaling. Neuronal deletion of Hrh4 did not replicate these effects, establishing cell-type specificity.\",\n      \"method\": \"Conditional microglial-specific Hrh4 knockout mice; pharmacological rescue with VUF6002 (H4R antagonist); cognitive behavioral assays; transcriptomic analysis; Aβ/p-tau quantification; cAMP/TGF-β1/Smad3 pathway analysis\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic knockout plus pharmacological mimicry plus pathway mechanism (cAMP/TGF-β1/Smad3) with rescue experiment; multiple orthogonal methods\",\n      \"pmids\": [\"41134085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"H4R signaling in human lymphatic endothelial cells (LECs) in response to 4-methylhistamine requires extracellular Ca2+ entry through TRPV4; H4R activation sensitizes subsequent TRPV4 responses through a PLA2-dependent mechanism. TRPV4 activity is required downstream of H4R for NFATc1 translocation to the nucleus and cytoskeletal remodeling, but not for cytokine release.\",\n      \"method\": \"Ca2+ imaging with selective H4R antagonists; TRPV4 channel blockers; extracellular Ca2+ removal; NFATc1 nuclear translocation imaging; cytoskeletal assays; PLA2 inhibition in primary human LECs\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection with multiple selective tools plus mechanistic pathway (PLA2) in primary human cells; preprint, not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HRH4 (H4R) is a Gi-coupled GPCR that inhibits cAMP accumulation upon histamine binding, with ligand recognition dependent on conserved residues Asp3.32, Glu5.46, and Gln7.42; in immune cells it signals through ERK1/2, Akt, NF-κB, and SAPK/JNK pathways to drive mast cell degranulation and cytokine release (IL-1β, IL-13, RANTES), activates microglia to release proinflammatory mediators, partially activates eosinophils in vivo, and in microglia specifically suppresses Alzheimer's disease pathology through a cAMP/TGF-β1/Smad3 axis that promotes Aβ and tau phagocytosis; in lymphatic endothelial cells H4R-evoked Ca2+ signaling is transduced via TRPV4 through a PLA2-dependent mechanism, leading to NFATc1 nuclear translocation and cytoskeletal remodeling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HRH4 (H4R) is a Gi-coupled histamine receptor that signals primarily in immune and neural cell types to drive inflammatory effector programs [#0]. Cloned from human leukocytes, it inhibits forskolin-induced cAMP accumulation upon histamine binding, with ligand recognition centered on the orthosteric residues Asp3.32, Glu5.46, and Gln7.42 [#0]; functional and binding analyses across orthologs and recombinant systems define species-specific affinity determinants and ligand-dependent functional selectivity at the receptor [#1, #2]. In mast cells, H4R activation couples to distinct downstream cascades to direct effector output: ERK1/2 drives RANTES/CCL5 production, Akt drives IL-13, NF-\\u03baB-p65 is engaged downstream of histamine, and SAPK/JNK signaling mediates intracellular Ca2+ release, degranulation, and IL-1\\u03b2 release [#6, #8]. The receptor extends this proinflammatory role to the nervous system, where H4R activation in microglia stimulates TNF-\\u03b1 and IL-1\\u03b2 production and microglial activation in vivo [#11], yet microglial-specific Hrh4 deletion paradoxically reverses cognitive deficits and reduces A\\u03b2 and tau pathology in AD model mice by engaging a cAMP/TGF-\\u03b21/Smad3 axis that enhances phagocytosis [#12]. H4R also functions in non-hematopoietic contexts, activating ERK1/2 in brain endothelial cells [#4], modulating cAMP-dependent growth arrest and chemosensitivity in colorectal cancer cells [#10], and influencing EMT and proliferation in lung cancer cells in a manner attenuated by the rs11662595 polymorphism that impairs Gi activation [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established the molecular identity and signaling output of HRH4, answering whether the leukocyte-derived receptor was a functional histamine receptor and how it transduces signal.\",\n      \"evidence\": \"Cloning from human leukocyte cDNA with radioligand binding and cAMP accumulation assays in recombinant cells\",\n      \"pmids\": [\"11118334\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define native cell-type signaling beyond cAMP\", \"Cross-reactivity with H3 agonists left ligand selectivity unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapped the structural basis of species-divergent ligand affinity, addressing why pharmacology differs across H4R orthologs.\",\n      \"evidence\": \"Chimeric human-pig receptor constructs and site-directed mutagenesis with radioligand binding in HEK293T cells\",\n      \"pmids\": [\"20103609\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Residue mapping did not address downstream signaling consequences\", \"No active-state structural model\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated functional selectivity (biased signaling) at H4R, addressing whether binding affinity predicts signaling output.\",\n      \"evidence\": \"Radioligand binding and steady-state GTPase assays with clozapine in Sf9 insect cells; molecular docking\",\n      \"pmids\": [\"22033803\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab, single-study GTPase readout\", \"Bias not validated in native cells\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed a tumor-suppressive role in colorectal cancer, asking whether H4R signaling alters proliferation and drug response.\",\n      \"evidence\": \"Stable HRH4 transfection in colorectal cancer cells with proliferation, cell-cycle, apoptosis, and cAMP pathway assays\",\n      \"pmids\": [\"21609450\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Overexpression model may not reflect endogenous receptor levels\", \"Mechanism linking cAMP to cell-cycle arrest not fully resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Computationally defined orthosteric binding contacts and an activation-associated conformational change, framing the structural mechanism of recognition.\",\n      \"evidence\": \"Homology modeling on the H1R crystal structure with molecular dynamics simulation\",\n      \"pmids\": [\"23220277\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Computational only, no experimental mutagenesis validation\", \"Predicted selectivity residues untested functionally\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified H4R-specific ERK1/2 activation in brain endothelial cells, extending receptor function beyond hematopoietic cells.\",\n      \"evidence\": \"RT-PCR/sequencing and ERK1/2 phosphorylation assays with selective antagonists in RBE4 cells and in vivo\",\n      \"pmids\": [\"23488566\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream physiological consequence in vasculature unclear\", \"G-protein coupling in this context not directly tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved the complete histamine binding pathway and key contact residues, refining the recognition mechanism.\",\n      \"evidence\": \"Unconstrained molecular dynamics simulation of histamine binding to hH4R\",\n      \"pmids\": [\"25677665\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Computational only, no experimental validation\", \"Does not address signaling conformations\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Dissected branched effector signaling in mast cells, answering which pathway drives which cytokine.\",\n      \"evidence\": \"H4R siRNA knockdown and pathway-selective inhibitors with phosphoblotting and cytokine ELISA in HMC-1 and CBMCs\",\n      \"pmids\": [\"27400655\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct receptor-to-kinase coupling steps not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked a natural HRH4 polymorphism to impaired Gi activation and pro-tumor phenotype, connecting genetic variation to function in lung cancer.\",\n      \"evidence\": \"Wild-type vs. rs11662595 mutant transfection with Gi activation, invasion/proliferation assays, and xenograft model\",\n      \"pmids\": [\"28847511\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Clinical relevance of the SNP not established in patient cohorts here\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established SAPK/JNK as the route for H4R-driven Ca2+ release, degranulation, and IL-1\\u03b2 in mast cells.\",\n      \"evidence\": \"H4R siRNA knockdown and JNK inhibitor with phosphoblotting, ELISA, Ca2+ and degranulation assays in HMC-1 cells\",\n      \"pmids\": [\"29863427\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Coupling between Gi/cAMP and JNK not mechanistically bridged\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Provided in vivo genetic evidence that eosinophil H4R contributes to colitis resolution, defining a tissue-level effector role.\",\n      \"evidence\": \"Adoptive transfer of H4R+/+ vs H4R-/- eosinophils into IL-5-deficient mice in DSS colitis\",\n      \"pmids\": [\"30319608\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular signaling in eosinophils not delineated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated that microglial H4R drives proinflammatory cytokine release in vivo, opposing H2R/H3R.\",\n      \"evidence\": \"Intracerebroventricular agonist/antagonist injection with Iba1 IHC, flow cytometry, ELISA and qRT-PCR in rat\",\n      \"pmids\": [\"31863333\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Intracellular signaling pathway not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined cell-type-specific microglial H4R control of AD pathology via a cAMP/TGF-\\u03b21/Smad3 phagocytic axis, establishing therapeutic logic of receptor blockade.\",\n      \"evidence\": \"Conditional microglial Hrh4 knockout, pharmacological rescue with VUF6002, behavioral/transcriptomic/pathology readouts with TGF-\\u03b2R1 inhibition rescue in 3xTg-AD mice\",\n      \"pmids\": [\"41134085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with proinflammatory microglial role not fully resolved\", \"Human relevance untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified TRPV4 as a Ca2+-entry effector downstream of H4R in lymphatic endothelial cells via a PLA2-dependent mechanism.\",\n      \"evidence\": \"Ca2+ imaging, TRPV4 blockers, extracellular Ca2+ removal, NFATc1 translocation and cytoskeletal assays with PLA2 inhibition in primary human LECs (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Direct physical coupling of H4R to TRPV4 not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How H4R's dual proinflammatory and protective roles in microglia are reconciled at the signaling level, and how Gi/cAMP coupling bifurcates into the divergent ERK/Akt/JNK/NF-\\u03baB and TGF-\\u03b21/Smad3 outputs, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental structure of active H4R-G-protein complex in the corpus\", \"Context-dependent switch between inflammatory and phagocytic programs uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 8, 9, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}