{"gene":"C3AR1","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":1996,"finding":"Human C3aR was cloned from U-937 cells and identified as a 482-residue GPCR with seven transmembrane helices and an unusually large second extracellular loop (~175 residues). Transfection of HEK-293 cells conferred specific C3a binding; co-transfection with Gα-16 in CHO cells enabled functional C3a-induced phosphoinositide hydrolysis, demonstrating G protein-coupled signaling.","method":"Expression cloning, radioligand binding, phosphoinositide hydrolysis assay in transfected cells","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — receptor cloned, ligand binding reconstituted, downstream signaling demonstrated in multiple cell lines","pmids":["8765043"],"is_preprint":false},{"year":1999,"finding":"Agonist-induced desensitization of C3aR involves rapid phosphorylation on serine and threonine residues (not tyrosine) by G protein-coupled receptor kinases (GRK2, GRK3, GRK5, GRK6). Overexpression of GRKs enhanced C3a-induced C3aR phosphorylation 1.5–1.9-fold and differentially reduced phospholipase C activity; antibody-mediated inhibition of endogenous GRK2/3 blocked C3aR phosphorylation. Endogenously expressed C3aR in HMC-1 mast cells also undergoes agonist-induced phosphorylation.","method":"Phosphorylation assays in RBL cells and COS-7, GRK overexpression/inhibition, phosphoamino acid analysis","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation with mutagenesis-level specificity, multiple GRK isoforms tested, endogenous validation","pmids":["10508278"],"is_preprint":false},{"year":1999,"finding":"An essential C3a ligand-binding site resides in the transmembrane core of guinea pig C3aR, not in the large extracellular loop. Mutation of Arg331 (in transmembrane region) to Ala or Gln completely abolished C3a binding, whereas mutations of Asp182, Asp309, Asp310, and large EC loop deletions did not eliminate binding.","method":"Site-directed mutagenesis, competitive radioligand binding assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with functional binding assay identifies critical residue","pmids":["10491297"],"is_preprint":false},{"year":2003,"finding":"The C3a-C3aR axis retains hematopoietic stem/progenitor cells (HSPCs) in bone marrow by increasing their responsiveness to SDF-1, thereby counteracting G-CSF-induced mobilization. C3-/- and C3aR-/- mice showed significantly enhanced G-CSF-induced HSPC mobilization. Chimeric mouse experiments revealed that C3aR deficiency on graft-derived (hematopoietic) cells, not host stromal cells, is responsible for increased mobilization.","method":"G-CSF mobilization in C3-/- and C3aR-/- mice, bone marrow chimeras, pharmacological C3aR antagonism (SB290157)","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + chimera experiments + pharmacological confirmation, multiple orthogonal approaches","pmids":["14604969"],"is_preprint":false},{"year":2007,"finding":"C3aR signaling on dendritic cells (DCs) is required for upregulating MHC and costimulatory molecule surface expression and for effective T cell priming against alloantigens. DCs lacking C3aR or treated with C3aR antagonist showed defective alloantigen-specific T cell priming and impaired skin allograft rejection. The alternative complement pathway (factor B-dependent, C4-independent) contributes C3a for this DC-autonomous allostimulation.","method":"C3aR-/- DC allostimulation assays, skin allograft rejection model, MHC/costimulatory molecule flow cytometry","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + antagonist + in vivo allograft model, multiple orthogonal readouts","pmids":["18056835"],"is_preprint":false},{"year":2009,"finding":"C3aR on HSPCs promotes their engraftment by augmenting matrix metalloprotease-9 (MMP-9) secretion and cell adhesion to stroma. C3aR-/- HSPCs showed delayed platelet/leukocyte recovery, reduced CFU-spleen formation, and decreased BM engraftment; they secreted less MMP-9 and had impaired stromal adhesion despite retaining C3a-enhanced SDF-1 responsiveness.","method":"Transplantation of C3aR-/- HSPCs, MMP-9 secretion assays, stromal adhesion assays, human CD34+ cord blood with SB290157 in NOD/SCID mice","journal":"Leukemia","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, pharmacological blockade in human cells, multiple functional readouts","pmids":["19357704"],"is_preprint":false},{"year":2012,"finding":"Absence of C3aR and C5aR signaling into CD4+ T cells leads to cessation of PI3Kγ/Akt/mTOR signaling, increased PKA activity, initiation of autoinductive TGF-β1 signaling, and induction of Foxp3+ regulatory T cells (iTreg). Endogenous TGF-β1 suppresses C3aR/C5aR signaling by preventing C3a/C5a production and upregulating the decoy receptor C5L2.","method":"C3aR/C5aR antagonism and KO in T cell cultures, PI3K/Akt/mTOR signaling assays, Foxp3 induction assays, autoimmune disease suppression","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + antagonists + defined signaling pathway, replicated in human cells","pmids":["23263555"],"is_preprint":false},{"year":2013,"finding":"C3AR1 (C3aR1) was identified as the receptor mediating TLQP-21 (a VGF-derived peptide) signaling in rodent CHO-K1 cells. Identification used genome-wide transcriptome sequencing of responsive cells, followed by validation with receptor-selective antagonists and siRNA knockdown. TLQP-21 signaling via C3AR1 is pertussis toxin-sensitive (Gi-coupled) and promotes RAW264.7 macrophage migration.","method":"Genome-wide RNAseq, siRNA knockdown, receptor antagonists, pertussis toxin sensitivity assay, cell migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — unbiased screen + siRNA + pharmacological validation + functional readout","pmids":["23940034"],"is_preprint":false},{"year":2014,"finding":"TLQP-21 is intrinsically disordered and undergoes a disorder-to-order transition adopting an α-helical conformation upon binding cells expressing C3aR1. The C-terminus is critical for receptor activation: a single R21A mutation or C-terminal amidation abolishes function. Human TLQP-21 (S20A substitution) activates human C3aR1 with lower potency than the rodent sequence.","method":"NMR/structural analysis, site-directed mutagenesis of TLQP-21, functional cell-based assays","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — structural characterization (NMR) plus mutagenesis with functional validation","pmids":["25456411"],"is_preprint":false},{"year":2014,"finding":"C3aR signaling protects myeloid and lymphoid cells from Listeria monocytogenes-induced apoptosis by suppressing Fas expression and caspase-3 activity while increasing Bcl-2 expression. C3aR-/- mice had increased bacterial burden, reduced survival, and increased TUNEL+ cells with elevated active caspase-3 and Fas, reduced Bcl-2, in spleen.","method":"Systemic L. monocytogenes infection of C3aR-/- mice, TUNEL staining, caspase-3/Fas/Bcl-2 Western blot/immunostaining","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined apoptotic molecular pathway, multiple orthogonal readouts","pmids":["24981453"],"is_preprint":false},{"year":2016,"finding":"C3aR-dependent NETosis (neutrophil extracellular trap formation) on neutrophils links complement activation triggered by circulating LPS to coagulation induction and N2 (pro-tumorigenic) neutrophil polarization in intestinal tumorigenesis. Increased circulating LPS upregulates C3aR on neutrophils, activating complement cascade leading to NETosis and coagulation.","method":"Mouse intestinal tumorigenesis models, neutrophil phenotyping, NET quantification, coagulation assays, complement pathway analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — multiple mechanistic steps established with genetic and functional assays in vivo","pmids":["26996437"],"is_preprint":false},{"year":2016,"finding":"TLQP-21 does not directly induce lipolysis but enhances β-adrenergic receptor-induced lipolysis through C3aR1, requiring Ca2+ mobilization and ERK-dependent activation of Hormone Sensitive Lipase (HSL). In vivo, chronic peripheral TLQP-21 reduces fat mass in diet-induced obese mice via β-adrenergic and C3aR1 co-activation.","method":"3T3-L1 adipocyte assays, genetic KO (C3aR1-/- and β-AR-deficient mice), Ca2+ mobilization, ERK/HSL phosphorylation, in vivo lipolysis","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro mechanistic dissection with multiple genetic KOs and defined signaling cascade","pmids":["28123945"],"is_preprint":false},{"year":2017,"finding":"C3aR1 expressed on surface of intestinal cells mediates C3a-driven intestinal stem cell expansion and organoid formation through Wnt signaling. C3- and C3aR1-deficient mice showed significantly reduced organoid formation; C3a promoted organoid growth and Lgr5/Ki67 expression in C3-deficient but not C3aR1-deficient mice, confirming receptor dependency.","method":"Intestinal organoid assays, C3-/- and C3aR1-/- mice, Wnt signaling reporters, Lgr5.egfp reporter mice","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO (two genes), ex vivo organoid assay, signaling pathway identified","pmids":["28928734"],"is_preprint":false},{"year":2017,"finding":"C3aR and C5aR are expressed by human and mouse pancreatic islet β-cells and α-cells. Activation of C3aR (and C5aR1) potentiated glucose-induced insulin secretion, increased intracellular Ca2+ and ATP generation, and protected islets from cytokine/palmitate-induced apoptosis. Glucose-conditioned islet media activated C3aR-driven β-arrestin recruitment.","method":"β-arrestin assay (DiscoverX), radioimmunoassay for insulin, Ca2+ imaging, ATP assay, apoptosis assay in human and mouse islets","journal":"Cellular and molecular life sciences","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal functional assays in primary human and mouse islets","pmids":["28921001"],"is_preprint":false},{"year":2018,"finding":"Platelet-expressed C3aR regulates distinct steps of thrombus formation (adhesion, spreading, Ca2+ influx) by mediating activation of the small GTPase Rap1b. Platelet-specific reconstitution experiments (C3aR-/- mice reconstituted with C3aR+/+ platelets) demonstrated that platelet C3aR specifically drives bleeding arrest, in vivo thrombosis, experimental stroke, and myocardial infarction outcomes. Rap1b was identified as a downstream effector by nano-LC-MS/MS.","method":"C3aR-/- mice, platelet reconstitution, intravital microscopy, in vitro platelet function assays, nano-LC-MS/MS for Rap1b identification","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + cell-specific reconstitution + MS-identified effector + multiple in vivo disease models","pmids":["29802205"],"is_preprint":false},{"year":2018,"finding":"C3-C3aR signaling activates STAT3 as a direct downstream target mediating tau pathogenesis. Deletion of C3ar1 in PS19 tauopathy mice rescued tau pathology, attenuated disease-associated microglia and neurotoxic astrocyte signatures, and reduced neuroinflammation, synaptic deficits, and neurodegeneration. RNA-seq identified a C3aR-dependent transcription factor network regulating the reactive glial switch.","method":"C3ar1-/- in PS19 tauopathy mice, RNA-seq, cell-type-specific transcriptomics, STAT3 signaling analysis","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with comprehensive transcriptomic + functional analysis, STAT3 identified as direct target","pmids":["30415998"],"is_preprint":false},{"year":2018,"finding":"The C3a-C3aR axis in smooth muscle cells promotes thoracic aortic dissection (TAD) by upregulating matrix metalloproteinase 2 (MMP2) expression. C3aR KO inhibited BAPN-induced TAD formation and reduced MMP2 expression. Recombinant C3a stimulation enhanced MMP2 expression and activation in mechanically stretched smooth muscle cells. MMP2-knockdown mice had reduced TAD formation.","method":"C3aR KO mice, BAPN-induced TAD model, MMP2 shRNA knockdown via AAV, in vitro C3a stimulation of stretched SMCs","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + downstream effector (MMP2) validated by independent KO, in vitro mechanistic confirmation","pmids":["29367209"],"is_preprint":false},{"year":2019,"finding":"C3aR1 exerts neuroprotection after spinal cord injury by acting as a physiological antagonist of CXCR2-driven neutrophil mobilization from bone marrow. Mechanistically, C3aR1 engages PTEN (a negative regulator of PI3K/AKT) to restrain CXCR2-driven BM neutrophil mobilization following trauma.","method":"C3aR1-/- mice with SCI model, PTEN pathway analysis, neutrophil mobilization assays, PI3K/AKT measurements","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + defined molecular pathway (PTEN/PI3K/CXCR2) + functional neuroprotection readout","pmids":["31045582"],"is_preprint":false},{"year":2019,"finding":"VEGFR2 survival and mitotic signaling requires concurrent C3aR1/C5aR1 and IL-6R-gp130 co-signaling. C3aR1/C5aR1 blockade totally abolished VEGFR2 auto-phosphorylation and downstream Src, ERK, AKT, mTOR, and STAT3 activation, and EC cell cycle entry. The four receptors are physically interactive as shown by Co-IP, confocal microscopy, ligand pulldown, and BRET assays. VEGF-A augments C3a/C5a/IL-6 production via p-Tyk2/p-STAT3.","method":"Co-immunoprecipitation, confocal microscopy, BRET, ligand pulldown, VEGFR2 phosphorylation assays, murine retinal angiogenesis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal physical interaction methods plus functional signaling assays and in vivo validation","pmids":["30765465"],"is_preprint":false},{"year":2019,"finding":"T cell-expressed C3aR1 induces CD8+ T cell proliferation, mTOR activation, and T-bet expression during allograft rejection. Host C3aR1 indirectly facilitates alloreactive CD8+ T cell expansion by amplifying APC costimulatory molecule expression and innate cytokine production. Demonstrated by reciprocal adoptive transfers of WT or C3ar1-/- CD8+ T cells.","method":"Cardiac allograft model, C3ar1-/- mice, reciprocal adoptive transfers, mTOR/T-bet signaling, flow cytometry","journal":"American journal of transplantation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal adoptive transfers establish cell-intrinsic vs. extrinsic mechanisms with defined downstream signaling","pmids":["30565852"],"is_preprint":false},{"year":2019,"finding":"B2 cell-autonomous autocrine C3aR1/C5aR1 signaling is required for follicular B2 cell activation, CD40 upregulation, IL-6 production, AID/Bcl-6 expression, and class switch recombination. B2 cells produce factor I and C3 and autophosphorylate CD19. C3ar1-/- mice produced only IgM after OVA immunization with no other isotypes.","method":"C3ar1-/- mice, OVA immunization, μMT reconstitution with WT/KO B2 cells, CSR analysis, factor I/C3 production assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + cell-autonomous reconstitution experiments + defined signaling components","pmids":["31217324"],"is_preprint":false},{"year":2020,"finding":"TLQP-21 increases motility and phagocytic capacity of murine microglia through C3aR1 signaling. Primary C3aR1-null microglia have impaired basal phagocytic function and do not respond to TLQP-21 or C3a super-agonist. RNA-seq of primary microglia revealed overlapping transcriptomic changes induced by TLQP-21 and C3a super-agonist, linked to cell migration and proliferation pathways. Human TLQP-21 similarly activates human microglia.","method":"Phagocytosis/migration assays, RNA-seq of C3aR1-null vs WT primary microglia, intracerebroventricular TLQP-21 in 5xFAD mice","journal":"Molecular neurodegeneration","confidence":"High","confidence_rationale":"Tier 2 — genetic KO controls, transcriptomic + functional assays, in vivo validation","pmids":["31924226"],"is_preprint":false},{"year":2020,"finding":"C3a-C3aR signaling in cancer-associated fibroblasts (CAFs) facilitates breast cancer lung metastasis by augmenting pro-metastatic cytokine secretion and extracellular matrix component expression via PI3K-AKT pathway activation.","method":"Ex vivo and in vivo assays, genetic and pharmacological C3aR blockade, PI3K-AKT signaling analysis in CAFs, mouse metastasis models","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic + pharmacological blockade with defined pathway, single lab","pmids":["31931851"],"is_preprint":false},{"year":2021,"finding":"Complement activation via the lectin pathway (MBL-dependent, C4-dependent) generates C3a which drives sarcoma progression and immunosuppression through C3aR on tumor-associated macrophages. C3aR deficiency (but not C5aR1 or C5aR2 deficiency) mirrors C3-/- phenotype. C3/C3aR deficiency reduces macrophage accumulation and functional skewing and increases T cell activation and anti-PD-1 response. Transcriptional profiling revealed enrichment of MHC II antigen presentation in C3-deficient macrophages.","method":"Systematic genetic KO (C3, MBL1/2, C4, C1q, factor B, C3aR, C5aR1, C5aR2), transplanted sarcoma models, transcriptional profiling of tumor-infiltrating macrophages","journal":"Nature cancer","confidence":"High","confidence_rationale":"Tier 2 — systematic comparison of multiple genetic KOs identifies pathway specificity; transcriptomic validation","pmids":["34505065"],"is_preprint":false},{"year":2021,"finding":"C3aR signaling on NK cells inhibits their infiltration into the tumor microenvironment by promoting direct physical interaction between C3aR and the integrin LFA-1, driving LFA-1 into a high-affinity conformation that decreases NK cell migration into tumors.","method":"C3aR blockade in NK cell tumor models, protein interaction assays (C3aR-LFA-1 co-localization/interaction), LFA-1 conformation assays","journal":"Cancer immunology research","confidence":"Medium","confidence_rationale":"Tier 2-3 — physical C3aR-LFA-1 interaction identified with functional consequence, single lab","pmids":["34819308"],"is_preprint":false},{"year":2021,"finding":"The purported C3aR antagonist SB290157 is actually a potent C3aR agonist in transfected cells and acts as a partial agonist at C5aR2 by mediating β-arrestin recruitment, leading to dampening of C5a-induced ERK signaling in primary macrophages. Its apparent antagonism of ligand-stimulated C3aR calcium flux is caused by potent β-arrestin-mediated receptor internalization.","method":"β-arrestin recruitment assays, ERK signaling assays in human and mouse primary macrophages, receptor internalization assays","journal":"Frontiers in pharmacology","confidence":"High","confidence_rationale":"Tier 2 — cell-based pharmacological characterization with multiple receptor and functional readouts","pmids":["33551801"],"is_preprint":false},{"year":2022,"finding":"C3aR signaling in the prefrontal cortex modulates synaptic pruning in depression via STAT3 activation. C3aR blockade inhibited hyperactivation of the microglial APT2/DHHC7 palmitoylation cycle, which mediates STAT3 translocation and proinflammatory cytokine expression, and attenuated excessive synaptic pruning. IL-1R/NF-κB signaling in astrocytes drives C3 release upstream of C3aR.","method":"Proteomic analysis, C3aR antagonist treatment in LPS/CUMS mouse models, STAT3/palmitoylation assays, synapse quantification","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2-3 — defined molecular pathway (APT2/DHHC7/STAT3) with pharmacological validation, single lab","pmids":["35715851"],"is_preprint":false},{"year":2022,"finding":"C3aR signaling contributes to renal interstitial fibrosis by promoting NLRP3 inflammasome activation and assembly in renal tubular epithelial cells. C3aR deficiency in UUO mice attenuated NLRP3 inflammasome activation and fibrosis; NLRP3 inhibition did not affect C3aR expression, placing C3aR upstream of NLRP3.","method":"C3aR-/- mice (UUO model), MCC950 NLRP3 inhibitor, Western blot, immunohistochemistry","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO + pharmacological dissection establishes C3aR→NLRP3 pathway order, single lab","pmids":["36041502"],"is_preprint":false},{"year":2022,"finding":"C3aR incorporating as a costimulatory domain in CAR-T cells (BB-ζ-C3aR) promotes Th17 phenotype expansion, memory T cell induction, and suppresses Tregs, enhancing antitumor efficacy. This demonstrates that C3aR signaling in T cells drives Th17 differentiation.","method":"CAR-T cell engineering, in vitro cytotoxicity, ALL/MM xenograft mouse models, T cell phenotyping","journal":"Journal of hematology & oncology","confidence":"Medium","confidence_rationale":"Tier 2 — defined functional consequence of C3aR signaling domain in engineered T cells with in vivo validation","pmids":["35597971"],"is_preprint":false},{"year":2022,"finding":"C3aR in astrocytes mediates A1 (neurotoxic) astrocyte polarization contributing to chronic post-thoracotomy pain. AAV-mediated C3aR knockdown in astrocytes inhibited LPS-induced A1 polarization, reduced C3/GFAP expression, alleviated mechanical withdrawal threshold, and increased neuroprotective A2 astrocytes.","method":"AAV2/9-rC3ar1 shRNA-GFAP in vivo knockdown, RT-PCR, Western blot, co-immunofluorescence, scRNA-seq, behavioral tests","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2 — cell-type-specific in vivo KD with defined phenotypic and molecular readouts","pmids":["36871753"],"is_preprint":false},{"year":2022,"finding":"CRISPR genome-scale screen identified C3aR as critical for macrophage capture of pathogenic fungi (Histoplasma, Candida, Coccidioides) but dispensable for phagocytosis of bacteria and latex beads. C3aR localizes to the early phagosome during Hc infection and coordinates actin-rich membrane protrusion formation promoting fungal capture. The ER membrane complex (EMC) promotes C3aR surface expression.","method":"Genome-scale CRISPR-Cas9 screen, C3aR-/- macrophages, live imaging of phagosome formation, actin dynamics assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1-2 — unbiased genome-scale screen + genetic KO + live imaging + multiple fungal species tested","pmids":["36174103"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM/crystal structures of C3a-bound C3aR and apo-C3aR were determined. Mutagenesis analysis revealed a conserved anaphylatoxin recognition pattern distinct from chemokine receptors, unique pocket topology mediating ligand selectivity for C3aR vs. C5aR1, and a common receptor activation mechanism between the two receptors.","method":"Cryo-EM structure determination of C3a-C3aR complex and apo-C3aR, mutagenesis, functional signaling assays","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 — structure determination with mutagenesis validation, defines molecular recognition mechanism","pmids":["37169960"],"is_preprint":false},{"year":2023,"finding":"C3aR1 couples preferentially to Gi/o/z proteins and recruits β-arrestins to cause internalization. TLQP-21 exhibits biased signaling toward Gi/o-mediated pathways relative to β-arrestin recruitment compared to C3a63-77. SB290157 acts as a potent C3aR1 agonist whose apparent antagonism of calcium flux is explained by β-arrestin-mediated receptor internalization. Ligand-mediated bias impacts Ca2+ influx, lipolysis in adipocytes, phagocytosis in microglia, and degranulation in mast cells.","method":"BRET G protein coupling assays, β-arrestin recruitment assays, internalization assays, adipocyte lipolysis, microglial phagocytosis, mast cell degranulation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — comprehensive G protein coupling characterization with multiple orthogonal assays and multiple cell types","pmids":["38072064"],"is_preprint":false},{"year":2023,"finding":"C3aR deletion in microglia rescues dysregulated lipid profiles and improves microglial phagocytic and clustering abilities in Alzheimer's disease. C3ar1-null microglia show lower HIF-1α expression, resistance to hypoxia-mimetic-induced metabolic changes, and reduced lipid droplet accumulation, with improved receptor recycling and Aβ phagocytosis. A heightened C3aR/HIF-1α signaling axis underlies microglial metabolic dysfunction in AD.","method":"C3ar1-KI reporter mouse, C3ar1-KO × APP-KI mice, primary microglial cultures, transcriptomic analysis, lipid profiling, phagocytosis assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with transcriptomic, metabolic, and functional validation, knockin reporter characterization","pmids":["37317973"],"is_preprint":false},{"year":2023,"finding":"C3aR-initiated signaling is a critical mechanism of podocyte injury in membranous nephropathy. C3aR antagonists and C3AR gene silencing in primary human podocytes (in a glomerulus-on-a-chip model) reduced MN serum-induced oxidative stress and prevented albumin leakage; inhibition of MAC formation did not affect permselectivity. C3aR antagonist prevented proteinuria in a mouse MN model.","method":"Glomerulus-on-a-chip with primary human podocytes, C3AR siRNA knockdown, C3aR antagonist, mouse MN model, proteinuria measurement","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 1-2 — human organ-on-chip reconstitution + genetic silencing + in vivo validation, establishes C3aR as primary mediator over MAC","pmids":["38227377"],"is_preprint":false},{"year":2024,"finding":"In NPM1-mutated AML, C3aR stimulation with C3a activates ERK1/2 and increases AML cell survival. C3AR is specifically expressed on NPM1-mutated AML cells (including leukemic stem cells co-marked by GPR56) but absent from normal hematopoietic stem/progenitor cells. Anti-C3AR antibodies elicit NK cell-mediated killing of AML cells ex vivo.","method":"Flow cytometry screen (362 markers), scRNA-seq, C3a stimulation/ERK1/2 assay, antibody-mediated NK cell killing, xenotransplantation","journal":"Blood advances","confidence":"High","confidence_rationale":"Tier 2 — unbiased surface marker screen + defined ERK signaling + functional killing assay + xenotransplantation","pmids":["36383712"],"is_preprint":false},{"year":2024,"finding":"NFAT1 in tumor-associated macrophages transcriptionally activates C3 expression, increasing C3a secretion which binds C3aR and promotes M2-like macrophage polarization by activating TIM-3. C3a/C3aR also activates the Ca2+-NFAT1 pathway forming a positive feedback loop sustaining M2 polarization and promoting mesenchymal transition of glioma stem cells.","method":"Nfat1-/- mouse glioma model, C3aR inhibitor, TIM-3 blocking, Ca2+ signaling assays, transcriptional activity assays","journal":"Cancer immunology research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO + pharmacological inhibition + defined feedback circuit, single lab","pmids":["38289255"],"is_preprint":false},{"year":2024,"finding":"Male adipocyte-specific C3aR1 KO mice exhibit enhanced white adipose tissue thermogenesis and increased respiration, while female adipocyte-specific C3aR1 KO mice display decreased brown fat thermogenesis and cold intolerance, revealing sexual dimorphism in the adipsin/C3a/C3aR1 axis in regulating adaptive thermogenesis.","method":"Adipocyte-specific C3aR1 KO mice (male and female), Adipsin-KO mice, metabolic phenotyping, cold tolerance tests","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific KO with sex-stratified metabolic phenotyping, defines cell-autonomous role","pmids":["38713526"],"is_preprint":false},{"year":2024,"finding":"C3aR modulates susceptibility to LPS-induced depressive-like behaviors through regulation of glutamatergic neuronal excitability in the medial prefrontal cortex. C3aR deletion or antagonism in mPFC confers resilience; re-expression of C3aR in mPFC neurons of KO mice restores susceptibility. C3aR-null mPFC glutamatergic neurons display hyperexcitability upon LPS, which is anti-depressant.","method":"C3aR KO mice, intra-mPFC AAV C3aR antagonism/expression, chemogenetic manipulation of mPFCGlu neurons, electrophysiology, behavioral tests","journal":"Progress in neurobiology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + viral rescue + electrophysiology + behavioral pharmacology, multiple orthogonal approaches","pmids":["38641040"],"is_preprint":false},{"year":2024,"finding":"C3a promotes neuronal apoptosis and α-synuclein pathology in Parkinson's disease through C3aR-mediated modulation of GSK3β. Complement C3 is released from astrocytes (TLR2/NF-κB dependent), and astrocyte-neuron communication via C3/C3aR influences neuronal apoptosis and α-syn pathology in PD models.","method":"α-syn PFF mouse models, C3 overexpression/knockdown, TLR2/NF-κB inhibition in primary astrocytes, GSK3β activity assays","journal":"Brain, behavior, and immunity","confidence":"Medium","confidence_rationale":"Tier 2-3 — pathway placed (TLR2/NF-κB→C3→C3aR→GSK3β) with in vivo models, single lab","pmids":["39288893"],"is_preprint":false},{"year":2024,"finding":"C3a exacerbates neuroinflammation after subarachnoid hemorrhage via the C3aR-ERK-P2X7-NLRP3 inflammasome signaling axis. C3aR engagement promotes ATP efflux by activating ERK1/2 phosphorylation, which activates P2X7, leading to NLRP3 inflammasome assembly. C3aR interference reduced LDH, IL-1β, caspase-1, NLRP3, ASC oligomerization, and ATP release in BV-2 cells.","method":"BV-2 cell heme stimulation model, C3aR siRNA, ERK inhibitor, P2X7 antagonist (JNJ-55308942), in vivo SB290157 in SAH mice","journal":"Inflammation","confidence":"Medium","confidence_rationale":"Tier 2 — stepwise pathway dissection with specific inhibitors at each node, in vitro + in vivo validation","pmids":["39528767"],"is_preprint":false}],"current_model":"C3aR1 (C3AR1) is a Gi/o/z-coupled seven-transmembrane GPCR that binds complement fragment C3a and the VGF-derived peptide TLQP-21 via a critical transmembrane binding site (Arg331); ligand binding triggers GRK2/3-mediated phosphorylation and β-arrestin-dependent internalization, while productive Gi/o signaling activates PI3Kγ/Akt/mTOR, ERK, Ca2+ mobilization, and STAT3 downstream of the receptor. In immune cells, C3aR1 on dendritic cells upregulates MHC and costimulatory molecules for T cell priming, on T cells drives mTOR/T-bet-dependent CD8+ proliferation and Th17/memory differentiation, on platelets activates Rap1b to regulate thrombus formation, on macrophages coordinates actin-dependent phagocytic capture of fungi via phagosomal localization, and on neutrophils engages PTEN to antagonize CXCR2-driven bone marrow mobilization; in the CNS, microglial C3aR1 regulates a HIF-1α–driven metabolic/lipid axis, activates STAT3 to sustain reactive glial states in tauopathy, and modulates synaptic pruning and glutamatergic neuronal excitability; in metabolic tissues, adipocyte C3aR1 enhances β-adrenergic-induced lipolysis through Ca2+/ERK/HSL and regulates thermogenesis in a sexually dimorphic manner; C3aR1 can also engage VEGFR2, PDGFR, and EGFR in a physical receptor complex requiring concurrent IL-6R-gp130 co-signaling, and structurally adopts a unique anaphylatoxin recognition mode distinct from chemokine receptors as revealed by cryo-EM."},"narrative":{"teleology":[{"year":1996,"claim":"Cloning of C3aR established it as a 482-residue GPCR with an unusually large second extracellular loop that couples to G proteins to transduce C3a signals, answering the fundamental question of the molecular identity of the C3a receptor.","evidence":"Expression cloning from U-937 cells, radioligand binding and phosphoinositide hydrolysis in transfected HEK-293 and CHO cells","pmids":["8765043"],"confidence":"High","gaps":["Endogenous G protein coupling specificity not determined","Downstream signaling cascades beyond phosphoinositide hydrolysis unknown","Three-dimensional structure unresolved"]},{"year":1999,"claim":"Identification of Arg331 as the essential transmembrane ligand-binding residue and GRK2/3/5/6 as the kinases mediating agonist-induced receptor desensitization resolved how C3aR recognizes C3a and how signaling is terminated.","evidence":"Site-directed mutagenesis with radioligand binding; GRK overexpression/inhibition with phosphorylation and PLC assays in RBL, COS-7, and HMC-1 cells","pmids":["10491297","10508278"],"confidence":"High","gaps":["Full complement of phosphorylation sites not mapped","β-arrestin involvement in internalization not yet demonstrated","Whether the large EC loop contributes to binding affinity or selectivity remained unclear"]},{"year":2003,"claim":"Demonstrating that C3aR on hematopoietic cells retains stem/progenitor cells in bone marrow by enhancing SDF-1 responsiveness established the first non-inflammatory physiological role for C3aR in hematopoiesis.","evidence":"G-CSF mobilization assays in C3⁻/⁻ and C3aR⁻/⁻ mice, bone marrow chimeras, SB290157 pharmacology","pmids":["14604969"],"confidence":"High","gaps":["Intracellular signaling linking C3aR to SDF-1 sensitization not delineated","Note: SB290157 later shown to be a C3aR agonist, complicating pharmacological interpretation"]},{"year":2007,"claim":"Showing that DC-intrinsic C3aR signaling upregulates MHC and costimulatory molecules for effective T cell priming established C3aR as a bridge between innate complement activation and adaptive immunity.","evidence":"C3aR⁻/⁻ DC allostimulation assays, skin allograft rejection model, flow cytometry","pmids":["18056835"],"confidence":"High","gaps":["Exact signaling pathway within DCs not defined","Whether C3aR acts similarly in tolerogenic DC contexts unknown"]},{"year":2012,"claim":"Establishing that cessation of C3aR/C5aR signaling in CD4⁺ T cells triggers PI3Kγ/Akt/mTOR collapse and autoinductive TGF-β1–driven Foxp3⁺ iTreg induction defined C3aR as a tonic suppressor of regulatory T cell differentiation.","evidence":"C3aR/C5aR antagonism and KO in T cell cultures, PI3K/Akt/mTOR and Foxp3 assays, autoimmune disease models","pmids":["23263555"],"confidence":"High","gaps":["Relative contributions of C3aR versus C5aR not fully dissected","Whether this mechanism operates in all tissue microenvironments unclear"]},{"year":2013,"claim":"Identification of C3aR1 as the receptor for VGF-derived TLQP-21 via an unbiased transcriptomic screen revealed that C3aR1 is a dual-ligand GPCR with functions extending beyond complement.","evidence":"Genome-wide RNAseq of responsive CHO-K1 cells, siRNA knockdown, pertussis toxin sensitivity, macrophage migration assay","pmids":["23940034"],"confidence":"High","gaps":["Structural basis of TLQP-21 versus C3a recognition at C3aR not determined","Physiological contexts where TLQP-21/C3aR signaling dominates over C3a/C3aR not established"]},{"year":2014,"claim":"Structural characterization of TLQP-21 binding and functional dissection of C3aR's anti-apoptotic role during Listeria infection expanded understanding of ligand recognition and protective immune functions.","evidence":"NMR of TLQP-21, mutagenesis of C-terminal residues; C3aR⁻/⁻ mice infected with L. monocytogenes, Fas/Bcl-2/caspase-3 analysis","pmids":["25456411","24981453"],"confidence":"High","gaps":["Anti-apoptotic signaling cascade downstream of C3aR not fully mapped","Whether TLQP-21 and C3a compete for the same binding site unclear"]},{"year":2016,"claim":"Two studies showed C3aR enhances β-adrenergic lipolysis via Ca²⁺/ERK/HSL in adipocytes and drives neutrophil NETosis linking complement to coagulation in tumorigenesis, revealing tissue-specific effector pathways.","evidence":"3T3-L1 adipocyte assays with C3aR1⁻/⁻ and β-AR⁻/⁻ mice; mouse intestinal tumor models with NET quantification and coagulation assays","pmids":["28123945","26996437"],"confidence":"High","gaps":["Whether lipolytic and NET pathways share common proximal signaling steps unknown","Biased agonism at C3aR in these contexts not explored"]},{"year":2017,"claim":"Discovery that C3aR drives intestinal stem cell expansion through Wnt and potentiates glucose-stimulated insulin secretion in β-cells extended C3aR's roles to tissue regeneration and metabolic hormone regulation.","evidence":"Intestinal organoids from C3⁻/⁻ and C3aR1⁻/⁻ mice with Lgr5 reporters; β-arrestin and insulin secretion assays in primary human/mouse islets","pmids":["28928734","28921001"],"confidence":"High","gaps":["Mechanism linking C3aR to Wnt pathway activation not defined","Whether islet C3aR engagement is paracrine or autocrine not fully resolved"]},{"year":2018,"claim":"Identification of Rap1b as the platelet C3aR effector for thrombus formation and STAT3 as the microglial C3aR effector sustaining neuroinflammatory glial states in tauopathy established cell-type–specific downstream signaling nodes.","evidence":"Platelet-specific reconstitution in C3aR⁻/⁻ mice with nano-LC-MS/MS for Rap1b; C3ar1⁻/⁻ × PS19 tauopathy mice with RNA-seq and STAT3 analysis","pmids":["29802205","30415998"],"confidence":"High","gaps":["How C3aR activates Rap1b (direct vs. intermediate) not determined","Whether STAT3 activation is Gi-dependent or β-arrestin-dependent in microglia not distinguished"]},{"year":2019,"claim":"Multiple studies demonstrated C3aR's engagement with PTEN to antagonize CXCR2-driven neutrophil mobilization, physical complex formation with VEGFR2/PDGFR/EGFR requiring IL-6R-gp130 co-signaling, T cell-intrinsic mTOR/T-bet activation for CD8⁺ expansion, and B2 cell-autonomous class-switch recombination—collectively establishing C3aR as a signaling integrator across diverse cellular contexts.","evidence":"C3aR1⁻/⁻ SCI models with PTEN pathway analysis; Co-IP/BRET/confocal for VEGFR2 complex; adoptive transfers of C3ar1⁻/⁻ T cells in cardiac allografts; C3ar1⁻/⁻ OVA immunization with B cell reconstitution","pmids":["31045582","30765465","30565852","31217324"],"confidence":"High","gaps":["Structural basis of the C3aR-VEGFR2-gp130 complex not resolved","How C3aR-PTEN interaction is spatially organized in neutrophils unknown","Relative importance of T cell-intrinsic vs. DC-mediated C3aR in vivo not quantified"]},{"year":2020,"claim":"Demonstrating that TLQP-21 and C3a super-agonist induce overlapping transcriptomic changes in microglia that enhance motility and phagocytosis confirmed C3aR1 as a shared receptor mediating neuropeptide and complement-driven microglial activation.","evidence":"RNA-seq of C3aR1⁻/⁻ vs. WT primary microglia, phagocytosis/migration assays, intracerebroventricular TLQP-21 in 5xFAD mice","pmids":["31924226"],"confidence":"High","gaps":["Whether TLQP-21 and C3a produce distinct signaling biases in microglia not fully resolved","Physiological TLQP-21 concentrations in brain parenchyma not established"]},{"year":2021,"claim":"Systematic genetic dissection showed that lectin-pathway-generated C3a signals specifically through C3aR (not C5aR1/C5aR2) to skew tumor-associated macrophages toward immunosuppression in sarcoma, while SB290157 was unmasked as a C3aR agonist whose apparent antagonism arises from β-arrestin-mediated internalization—fundamentally revising pharmacological interpretations of prior studies.","evidence":"Systematic KO panel (C3, MBL, C4, C1q, factor B, C3aR, C5aR1, C5aR2) in transplanted sarcoma; β-arrestin recruitment/internalization assays for SB290157 in primary macrophages","pmids":["34505065","33551801"],"confidence":"High","gaps":["How many prior SB290157-based conclusions require reinterpretation not catalogued","Whether C3aR-specific antagonists free of agonist activity exist not established"]},{"year":2022,"claim":"A CRISPR genome-scale screen identified C3aR as selectively required for macrophage phagosomal capture of pathogenic fungi via actin-dependent membrane protrusions, revealing a pathogen-specific innate immune function distinct from general phagocytosis.","evidence":"Genome-scale CRISPR screen in macrophages, C3aR⁻/⁻ validation, live imaging of phagosome formation with Histoplasma/Candida/Coccidioides","pmids":["36174103"],"confidence":"High","gaps":["Fungal ligand or opsonin that triggers phagosomal C3aR not identified","Whether C3aR phagosomal localization requires EMC-dependent trafficking not fully resolved"]},{"year":2023,"claim":"Cryo-EM structures of C3a-bound and apo C3aR revealed a unique anaphylatoxin recognition mode distinct from chemokine receptors, and comprehensive G protein coupling profiling established Gi/o/z preference with ligand-dependent biased agonism between C3a and TLQP-21, resolving long-standing questions about receptor activation and selectivity.","evidence":"Cryo-EM/crystal structures with mutagenesis; BRET G protein coupling, β-arrestin recruitment, internalization assays across multiple cell types","pmids":["37169960","38072064"],"confidence":"High","gaps":["Structure of TLQP-21–bound C3aR not determined","Structural basis for β-arrestin-biased versus G protein-biased signaling not resolved"]},{"year":2023,"claim":"Microglial C3aR deletion rescued lipid dysregulation and phagocytic dysfunction in AD via suppression of a HIF-1α–driven metabolic axis, while C3aR was identified as the primary mediator of podocyte injury in membranous nephropathy over MAC—extending C3aR's pathogenic roles to metabolic reprogramming and kidney disease.","evidence":"C3ar1-KO × APP-KI mice with lipid profiling, HIF-1α analysis, phagocytosis assays; human podocyte glomerulus-on-a-chip with C3AR siRNA, mouse MN model","pmids":["37317973","38227377"],"confidence":"High","gaps":["How C3aR activates HIF-1α in microglia not mechanistically defined","Whether C3aR-driven podocyte injury involves the same STAT3 or ERK pathways as other cell types unknown"]},{"year":2024,"claim":"C3aR was shown to regulate glutamatergic neuronal excitability in the prefrontal cortex, control sexually dimorphic adaptive thermogenesis in adipocytes, promote ERK-dependent AML cell survival as a targetable surface marker on NPM1-mutated leukemic stem cells, and modulate GSK3β-dependent α-synuclein pathology—demonstrating the breadth of cell-type–specific C3aR functions.","evidence":"C3aR KO with viral rescue and electrophysiology in mPFC; adipocyte-specific C3aR1 KO with sex-stratified metabolic phenotyping; flow cytometry screen of 362 markers on AML cells with ERK assays and anti-C3AR antibody NK killing; α-syn PFF models with GSK3β analysis","pmids":["38641040","38713526","36383712","39288893"],"confidence":"High","gaps":["How C3aR modulates ion channel properties in glutamatergic neurons unknown","Mechanism of sexual dimorphism in adipocyte C3aR1 thermogenic signaling not defined","Whether anti-C3AR antibodies are effective in vivo in AML not demonstrated"]},{"year":null,"claim":"Key unresolved questions include the structural basis of TLQP-21 binding and biased agonism at C3aR, the molecular mechanism by which C3aR activates HIF-1α in microglia, how phagosomal C3aR recognizes fungal pathogens, the identity of downstream ion channel targets in neurons, and whether C3aR-selective antagonists devoid of agonist activity can be developed for therapeutic use.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Structure of TLQP-21–C3aR complex not determined","Mechanism of C3aR-HIF-1α coupling in microglia unknown","In vivo therapeutic potential of anti-C3AR antibodies in AML not tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,31]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,30,35]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[30]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,6,9,19,20,23,30]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,11,15,18,32]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[14]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[11,33,37]}],"complexes":[],"partners":["C3A","TLQP-21","GRK2","GRK3","RAP1B","VEGFR2","LFA-1","STAT3"],"other_free_text":[]},"mechanistic_narrative":"C3AR1 encodes a seven-transmembrane Gi/o/z-coupled GPCR that senses complement fragment C3a and the neuropeptide TLQP-21, transducing signals through PI3K/Akt/mTOR, ERK, Ca²⁺ mobilization, STAT3, and β-arrestin–dependent internalization to regulate immune cell activation, hemostasis, neuroinflammation, and metabolism [PMID:8765043, PMID:38072064, PMID:23263555, PMID:30415998]. In innate and adaptive immunity, C3aR1 on dendritic cells upregulates MHC/costimulatory molecules for T cell priming, drives CD8⁺ T cell proliferation via mTOR/T-bet, promotes Th17 differentiation and B cell class-switch recombination, coordinates actin-dependent phagosomal capture of pathogenic fungi in macrophages, and activates Rap1b in platelets to regulate thrombus formation [PMID:18056835, PMID:30565852, PMID:31217324, PMID:36174103, PMID:29802205]. In the central nervous system, microglial C3aR1 sustains reactive glial states in tauopathy through STAT3, governs a HIF-1α–driven metabolic–lipid axis that impairs Aβ phagocytosis in Alzheimer's disease, modulates synaptic pruning, and controls glutamatergic neuronal excitability in the prefrontal cortex [PMID:30415998, PMID:37317973, PMID:35715851, PMID:38641040]. In adipose tissue, C3aR1 enhances β-adrenergic–induced lipolysis through Ca²⁺/ERK/HSL and regulates adaptive thermogenesis in a sexually dimorphic manner [PMID:28123945, PMID:38713526]."},"prefetch_data":{"uniprot":{"accession":"Q16581","full_name":"C3a anaphylatoxin chemotactic receptor","aliases":[],"length_aa":482,"mass_kda":53.9,"function":"Receptor for the chemotactic and inflammatory peptide anaphylatoxin C3a, stimulating chemotaxis, granule enzyme release and superoxide anion production (PubMed:12871936, PubMed:37852260, PubMed:8702752). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors, such as adenylate cyclase (PubMed:37852260). C3AR1 is coupled to G(i)/G(o) (GNAI1 or GNAO1) G alpha proteins and mediates inhibition of adenylate cyclase (PubMed:37852260)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q16581/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C3AR1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C3AR1","total_profiled":1310},"omim":[{"mim_id":"605246","title":"COMPLEMENT COMPONENT 3a RECEPTOR 1; C3AR1","url":"https://www.omim.org/entry/605246"},{"mim_id":"601665","title":"OBESITY","url":"https://www.omim.org/entry/601665"},{"mim_id":"600807","title":"ASTHMA, SUSCEPTIBILITY TO","url":"https://www.omim.org/entry/600807"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":37.8}],"url":"https://www.proteinatlas.org/search/C3AR1"},"hgnc":{"alias_symbol":["C3AR","AZ3B"],"prev_symbol":[]},"alphafold":{"accession":"Q16581","domains":[{"cath_id":"1.20.1070.10","chopping":"20-177_328-458","consensus_level":"medium","plddt":89.8178,"start":20,"end":458}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16581","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16581-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16581-F1-predicted_aligned_error_v6.png","plddt_mean":68.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C3AR1","jax_strain_url":"https://www.jax.org/strain/search?query=C3AR1"},"sequence":{"accession":"Q16581","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16581.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16581/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16581"}},"corpus_meta":[{"pmid":"30415998","id":"PMC_30415998","title":"Complement C3aR 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identified as a 482-residue GPCR with seven transmembrane helices and an unusually large second extracellular loop (~175 residues). Transfection of HEK-293 cells conferred specific C3a binding; co-transfection with Gα-16 in CHO cells enabled functional C3a-induced phosphoinositide hydrolysis, demonstrating G protein-coupled signaling.\",\n      \"method\": \"Expression cloning, radioligand binding, phosphoinositide hydrolysis assay in transfected cells\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — receptor cloned, ligand binding reconstituted, downstream signaling demonstrated in multiple cell lines\",\n      \"pmids\": [\"8765043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Agonist-induced desensitization of C3aR involves rapid phosphorylation on serine and threonine residues (not tyrosine) by G protein-coupled receptor kinases (GRK2, GRK3, GRK5, GRK6). Overexpression of GRKs enhanced C3a-induced C3aR phosphorylation 1.5–1.9-fold and differentially reduced phospholipase C activity; antibody-mediated inhibition of endogenous GRK2/3 blocked C3aR phosphorylation. Endogenously expressed C3aR in HMC-1 mast cells also undergoes agonist-induced phosphorylation.\",\n      \"method\": \"Phosphorylation assays in RBL cells and COS-7, GRK overexpression/inhibition, phosphoamino acid analysis\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation with mutagenesis-level specificity, multiple GRK isoforms tested, endogenous validation\",\n      \"pmids\": [\"10508278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"An essential C3a ligand-binding site resides in the transmembrane core of guinea pig C3aR, not in the large extracellular loop. Mutation of Arg331 (in transmembrane region) to Ala or Gln completely abolished C3a binding, whereas mutations of Asp182, Asp309, Asp310, and large EC loop deletions did not eliminate binding.\",\n      \"method\": \"Site-directed mutagenesis, competitive radioligand binding assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with functional binding assay identifies critical residue\",\n      \"pmids\": [\"10491297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The C3a-C3aR axis retains hematopoietic stem/progenitor cells (HSPCs) in bone marrow by increasing their responsiveness to SDF-1, thereby counteracting G-CSF-induced mobilization. C3-/- and C3aR-/- mice showed significantly enhanced G-CSF-induced HSPC mobilization. Chimeric mouse experiments revealed that C3aR deficiency on graft-derived (hematopoietic) cells, not host stromal cells, is responsible for increased mobilization.\",\n      \"method\": \"G-CSF mobilization in C3-/- and C3aR-/- mice, bone marrow chimeras, pharmacological C3aR antagonism (SB290157)\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + chimera experiments + pharmacological confirmation, multiple orthogonal approaches\",\n      \"pmids\": [\"14604969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"C3aR signaling on dendritic cells (DCs) is required for upregulating MHC and costimulatory molecule surface expression and for effective T cell priming against alloantigens. DCs lacking C3aR or treated with C3aR antagonist showed defective alloantigen-specific T cell priming and impaired skin allograft rejection. The alternative complement pathway (factor B-dependent, C4-independent) contributes C3a for this DC-autonomous allostimulation.\",\n      \"method\": \"C3aR-/- DC allostimulation assays, skin allograft rejection model, MHC/costimulatory molecule flow cytometry\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + antagonist + in vivo allograft model, multiple orthogonal readouts\",\n      \"pmids\": [\"18056835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"C3aR on HSPCs promotes their engraftment by augmenting matrix metalloprotease-9 (MMP-9) secretion and cell adhesion to stroma. C3aR-/- HSPCs showed delayed platelet/leukocyte recovery, reduced CFU-spleen formation, and decreased BM engraftment; they secreted less MMP-9 and had impaired stromal adhesion despite retaining C3a-enhanced SDF-1 responsiveness.\",\n      \"method\": \"Transplantation of C3aR-/- HSPCs, MMP-9 secretion assays, stromal adhesion assays, human CD34+ cord blood with SB290157 in NOD/SCID mice\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, pharmacological blockade in human cells, multiple functional readouts\",\n      \"pmids\": [\"19357704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Absence of C3aR and C5aR signaling into CD4+ T cells leads to cessation of PI3Kγ/Akt/mTOR signaling, increased PKA activity, initiation of autoinductive TGF-β1 signaling, and induction of Foxp3+ regulatory T cells (iTreg). Endogenous TGF-β1 suppresses C3aR/C5aR signaling by preventing C3a/C5a production and upregulating the decoy receptor C5L2.\",\n      \"method\": \"C3aR/C5aR antagonism and KO in T cell cultures, PI3K/Akt/mTOR signaling assays, Foxp3 induction assays, autoimmune disease suppression\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + antagonists + defined signaling pathway, replicated in human cells\",\n      \"pmids\": [\"23263555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"C3AR1 (C3aR1) was identified as the receptor mediating TLQP-21 (a VGF-derived peptide) signaling in rodent CHO-K1 cells. Identification used genome-wide transcriptome sequencing of responsive cells, followed by validation with receptor-selective antagonists and siRNA knockdown. TLQP-21 signaling via C3AR1 is pertussis toxin-sensitive (Gi-coupled) and promotes RAW264.7 macrophage migration.\",\n      \"method\": \"Genome-wide RNAseq, siRNA knockdown, receptor antagonists, pertussis toxin sensitivity assay, cell migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — unbiased screen + siRNA + pharmacological validation + functional readout\",\n      \"pmids\": [\"23940034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLQP-21 is intrinsically disordered and undergoes a disorder-to-order transition adopting an α-helical conformation upon binding cells expressing C3aR1. The C-terminus is critical for receptor activation: a single R21A mutation or C-terminal amidation abolishes function. Human TLQP-21 (S20A substitution) activates human C3aR1 with lower potency than the rodent sequence.\",\n      \"method\": \"NMR/structural analysis, site-directed mutagenesis of TLQP-21, functional cell-based assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural characterization (NMR) plus mutagenesis with functional validation\",\n      \"pmids\": [\"25456411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"C3aR signaling protects myeloid and lymphoid cells from Listeria monocytogenes-induced apoptosis by suppressing Fas expression and caspase-3 activity while increasing Bcl-2 expression. C3aR-/- mice had increased bacterial burden, reduced survival, and increased TUNEL+ cells with elevated active caspase-3 and Fas, reduced Bcl-2, in spleen.\",\n      \"method\": \"Systemic L. monocytogenes infection of C3aR-/- mice, TUNEL staining, caspase-3/Fas/Bcl-2 Western blot/immunostaining\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined apoptotic molecular pathway, multiple orthogonal readouts\",\n      \"pmids\": [\"24981453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"C3aR-dependent NETosis (neutrophil extracellular trap formation) on neutrophils links complement activation triggered by circulating LPS to coagulation induction and N2 (pro-tumorigenic) neutrophil polarization in intestinal tumorigenesis. Increased circulating LPS upregulates C3aR on neutrophils, activating complement cascade leading to NETosis and coagulation.\",\n      \"method\": \"Mouse intestinal tumorigenesis models, neutrophil phenotyping, NET quantification, coagulation assays, complement pathway analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mechanistic steps established with genetic and functional assays in vivo\",\n      \"pmids\": [\"26996437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TLQP-21 does not directly induce lipolysis but enhances β-adrenergic receptor-induced lipolysis through C3aR1, requiring Ca2+ mobilization and ERK-dependent activation of Hormone Sensitive Lipase (HSL). In vivo, chronic peripheral TLQP-21 reduces fat mass in diet-induced obese mice via β-adrenergic and C3aR1 co-activation.\",\n      \"method\": \"3T3-L1 adipocyte assays, genetic KO (C3aR1-/- and β-AR-deficient mice), Ca2+ mobilization, ERK/HSL phosphorylation, in vivo lipolysis\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro mechanistic dissection with multiple genetic KOs and defined signaling cascade\",\n      \"pmids\": [\"28123945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"C3aR1 expressed on surface of intestinal cells mediates C3a-driven intestinal stem cell expansion and organoid formation through Wnt signaling. C3- and C3aR1-deficient mice showed significantly reduced organoid formation; C3a promoted organoid growth and Lgr5/Ki67 expression in C3-deficient but not C3aR1-deficient mice, confirming receptor dependency.\",\n      \"method\": \"Intestinal organoid assays, C3-/- and C3aR1-/- mice, Wnt signaling reporters, Lgr5.egfp reporter mice\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO (two genes), ex vivo organoid assay, signaling pathway identified\",\n      \"pmids\": [\"28928734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"C3aR and C5aR are expressed by human and mouse pancreatic islet β-cells and α-cells. Activation of C3aR (and C5aR1) potentiated glucose-induced insulin secretion, increased intracellular Ca2+ and ATP generation, and protected islets from cytokine/palmitate-induced apoptosis. Glucose-conditioned islet media activated C3aR-driven β-arrestin recruitment.\",\n      \"method\": \"β-arrestin assay (DiscoverX), radioimmunoassay for insulin, Ca2+ imaging, ATP assay, apoptosis assay in human and mouse islets\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal functional assays in primary human and mouse islets\",\n      \"pmids\": [\"28921001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Platelet-expressed C3aR regulates distinct steps of thrombus formation (adhesion, spreading, Ca2+ influx) by mediating activation of the small GTPase Rap1b. Platelet-specific reconstitution experiments (C3aR-/- mice reconstituted with C3aR+/+ platelets) demonstrated that platelet C3aR specifically drives bleeding arrest, in vivo thrombosis, experimental stroke, and myocardial infarction outcomes. Rap1b was identified as a downstream effector by nano-LC-MS/MS.\",\n      \"method\": \"C3aR-/- mice, platelet reconstitution, intravital microscopy, in vitro platelet function assays, nano-LC-MS/MS for Rap1b identification\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + cell-specific reconstitution + MS-identified effector + multiple in vivo disease models\",\n      \"pmids\": [\"29802205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"C3-C3aR signaling activates STAT3 as a direct downstream target mediating tau pathogenesis. Deletion of C3ar1 in PS19 tauopathy mice rescued tau pathology, attenuated disease-associated microglia and neurotoxic astrocyte signatures, and reduced neuroinflammation, synaptic deficits, and neurodegeneration. RNA-seq identified a C3aR-dependent transcription factor network regulating the reactive glial switch.\",\n      \"method\": \"C3ar1-/- in PS19 tauopathy mice, RNA-seq, cell-type-specific transcriptomics, STAT3 signaling analysis\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with comprehensive transcriptomic + functional analysis, STAT3 identified as direct target\",\n      \"pmids\": [\"30415998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The C3a-C3aR axis in smooth muscle cells promotes thoracic aortic dissection (TAD) by upregulating matrix metalloproteinase 2 (MMP2) expression. C3aR KO inhibited BAPN-induced TAD formation and reduced MMP2 expression. Recombinant C3a stimulation enhanced MMP2 expression and activation in mechanically stretched smooth muscle cells. MMP2-knockdown mice had reduced TAD formation.\",\n      \"method\": \"C3aR KO mice, BAPN-induced TAD model, MMP2 shRNA knockdown via AAV, in vitro C3a stimulation of stretched SMCs\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + downstream effector (MMP2) validated by independent KO, in vitro mechanistic confirmation\",\n      \"pmids\": [\"29367209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"C3aR1 exerts neuroprotection after spinal cord injury by acting as a physiological antagonist of CXCR2-driven neutrophil mobilization from bone marrow. Mechanistically, C3aR1 engages PTEN (a negative regulator of PI3K/AKT) to restrain CXCR2-driven BM neutrophil mobilization following trauma.\",\n      \"method\": \"C3aR1-/- mice with SCI model, PTEN pathway analysis, neutrophil mobilization assays, PI3K/AKT measurements\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + defined molecular pathway (PTEN/PI3K/CXCR2) + functional neuroprotection readout\",\n      \"pmids\": [\"31045582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"VEGFR2 survival and mitotic signaling requires concurrent C3aR1/C5aR1 and IL-6R-gp130 co-signaling. C3aR1/C5aR1 blockade totally abolished VEGFR2 auto-phosphorylation and downstream Src, ERK, AKT, mTOR, and STAT3 activation, and EC cell cycle entry. The four receptors are physically interactive as shown by Co-IP, confocal microscopy, ligand pulldown, and BRET assays. VEGF-A augments C3a/C5a/IL-6 production via p-Tyk2/p-STAT3.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy, BRET, ligand pulldown, VEGFR2 phosphorylation assays, murine retinal angiogenesis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal physical interaction methods plus functional signaling assays and in vivo validation\",\n      \"pmids\": [\"30765465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"T cell-expressed C3aR1 induces CD8+ T cell proliferation, mTOR activation, and T-bet expression during allograft rejection. Host C3aR1 indirectly facilitates alloreactive CD8+ T cell expansion by amplifying APC costimulatory molecule expression and innate cytokine production. Demonstrated by reciprocal adoptive transfers of WT or C3ar1-/- CD8+ T cells.\",\n      \"method\": \"Cardiac allograft model, C3ar1-/- mice, reciprocal adoptive transfers, mTOR/T-bet signaling, flow cytometry\",\n      \"journal\": \"American journal of transplantation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal adoptive transfers establish cell-intrinsic vs. extrinsic mechanisms with defined downstream signaling\",\n      \"pmids\": [\"30565852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"B2 cell-autonomous autocrine C3aR1/C5aR1 signaling is required for follicular B2 cell activation, CD40 upregulation, IL-6 production, AID/Bcl-6 expression, and class switch recombination. B2 cells produce factor I and C3 and autophosphorylate CD19. C3ar1-/- mice produced only IgM after OVA immunization with no other isotypes.\",\n      \"method\": \"C3ar1-/- mice, OVA immunization, μMT reconstitution with WT/KO B2 cells, CSR analysis, factor I/C3 production assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + cell-autonomous reconstitution experiments + defined signaling components\",\n      \"pmids\": [\"31217324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLQP-21 increases motility and phagocytic capacity of murine microglia through C3aR1 signaling. Primary C3aR1-null microglia have impaired basal phagocytic function and do not respond to TLQP-21 or C3a super-agonist. RNA-seq of primary microglia revealed overlapping transcriptomic changes induced by TLQP-21 and C3a super-agonist, linked to cell migration and proliferation pathways. Human TLQP-21 similarly activates human microglia.\",\n      \"method\": \"Phagocytosis/migration assays, RNA-seq of C3aR1-null vs WT primary microglia, intracerebroventricular TLQP-21 in 5xFAD mice\",\n      \"journal\": \"Molecular neurodegeneration\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO controls, transcriptomic + functional assays, in vivo validation\",\n      \"pmids\": [\"31924226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"C3a-C3aR signaling in cancer-associated fibroblasts (CAFs) facilitates breast cancer lung metastasis by augmenting pro-metastatic cytokine secretion and extracellular matrix component expression via PI3K-AKT pathway activation.\",\n      \"method\": \"Ex vivo and in vivo assays, genetic and pharmacological C3aR blockade, PI3K-AKT signaling analysis in CAFs, mouse metastasis models\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic + pharmacological blockade with defined pathway, single lab\",\n      \"pmids\": [\"31931851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Complement activation via the lectin pathway (MBL-dependent, C4-dependent) generates C3a which drives sarcoma progression and immunosuppression through C3aR on tumor-associated macrophages. C3aR deficiency (but not C5aR1 or C5aR2 deficiency) mirrors C3-/- phenotype. C3/C3aR deficiency reduces macrophage accumulation and functional skewing and increases T cell activation and anti-PD-1 response. Transcriptional profiling revealed enrichment of MHC II antigen presentation in C3-deficient macrophages.\",\n      \"method\": \"Systematic genetic KO (C3, MBL1/2, C4, C1q, factor B, C3aR, C5aR1, C5aR2), transplanted sarcoma models, transcriptional profiling of tumor-infiltrating macrophages\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic comparison of multiple genetic KOs identifies pathway specificity; transcriptomic validation\",\n      \"pmids\": [\"34505065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C3aR signaling on NK cells inhibits their infiltration into the tumor microenvironment by promoting direct physical interaction between C3aR and the integrin LFA-1, driving LFA-1 into a high-affinity conformation that decreases NK cell migration into tumors.\",\n      \"method\": \"C3aR blockade in NK cell tumor models, protein interaction assays (C3aR-LFA-1 co-localization/interaction), LFA-1 conformation assays\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — physical C3aR-LFA-1 interaction identified with functional consequence, single lab\",\n      \"pmids\": [\"34819308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The purported C3aR antagonist SB290157 is actually a potent C3aR agonist in transfected cells and acts as a partial agonist at C5aR2 by mediating β-arrestin recruitment, leading to dampening of C5a-induced ERK signaling in primary macrophages. Its apparent antagonism of ligand-stimulated C3aR calcium flux is caused by potent β-arrestin-mediated receptor internalization.\",\n      \"method\": \"β-arrestin recruitment assays, ERK signaling assays in human and mouse primary macrophages, receptor internalization assays\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-based pharmacological characterization with multiple receptor and functional readouts\",\n      \"pmids\": [\"33551801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C3aR signaling in the prefrontal cortex modulates synaptic pruning in depression via STAT3 activation. C3aR blockade inhibited hyperactivation of the microglial APT2/DHHC7 palmitoylation cycle, which mediates STAT3 translocation and proinflammatory cytokine expression, and attenuated excessive synaptic pruning. IL-1R/NF-κB signaling in astrocytes drives C3 release upstream of C3aR.\",\n      \"method\": \"Proteomic analysis, C3aR antagonist treatment in LPS/CUMS mouse models, STAT3/palmitoylation assays, synapse quantification\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — defined molecular pathway (APT2/DHHC7/STAT3) with pharmacological validation, single lab\",\n      \"pmids\": [\"35715851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C3aR signaling contributes to renal interstitial fibrosis by promoting NLRP3 inflammasome activation and assembly in renal tubular epithelial cells. C3aR deficiency in UUO mice attenuated NLRP3 inflammasome activation and fibrosis; NLRP3 inhibition did not affect C3aR expression, placing C3aR upstream of NLRP3.\",\n      \"method\": \"C3aR-/- mice (UUO model), MCC950 NLRP3 inhibitor, Western blot, immunohistochemistry\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + pharmacological dissection establishes C3aR→NLRP3 pathway order, single lab\",\n      \"pmids\": [\"36041502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C3aR incorporating as a costimulatory domain in CAR-T cells (BB-ζ-C3aR) promotes Th17 phenotype expansion, memory T cell induction, and suppresses Tregs, enhancing antitumor efficacy. This demonstrates that C3aR signaling in T cells drives Th17 differentiation.\",\n      \"method\": \"CAR-T cell engineering, in vitro cytotoxicity, ALL/MM xenograft mouse models, T cell phenotyping\",\n      \"journal\": \"Journal of hematology & oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined functional consequence of C3aR signaling domain in engineered T cells with in vivo validation\",\n      \"pmids\": [\"35597971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C3aR in astrocytes mediates A1 (neurotoxic) astrocyte polarization contributing to chronic post-thoracotomy pain. AAV-mediated C3aR knockdown in astrocytes inhibited LPS-induced A1 polarization, reduced C3/GFAP expression, alleviated mechanical withdrawal threshold, and increased neuroprotective A2 astrocytes.\",\n      \"method\": \"AAV2/9-rC3ar1 shRNA-GFAP in vivo knockdown, RT-PCR, Western blot, co-immunofluorescence, scRNA-seq, behavioral tests\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific in vivo KD with defined phenotypic and molecular readouts\",\n      \"pmids\": [\"36871753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRISPR genome-scale screen identified C3aR as critical for macrophage capture of pathogenic fungi (Histoplasma, Candida, Coccidioides) but dispensable for phagocytosis of bacteria and latex beads. C3aR localizes to the early phagosome during Hc infection and coordinates actin-rich membrane protrusion formation promoting fungal capture. The ER membrane complex (EMC) promotes C3aR surface expression.\",\n      \"method\": \"Genome-scale CRISPR-Cas9 screen, C3aR-/- macrophages, live imaging of phagosome formation, actin dynamics assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — unbiased genome-scale screen + genetic KO + live imaging + multiple fungal species tested\",\n      \"pmids\": [\"36174103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM/crystal structures of C3a-bound C3aR and apo-C3aR were determined. Mutagenesis analysis revealed a conserved anaphylatoxin recognition pattern distinct from chemokine receptors, unique pocket topology mediating ligand selectivity for C3aR vs. C5aR1, and a common receptor activation mechanism between the two receptors.\",\n      \"method\": \"Cryo-EM structure determination of C3a-C3aR complex and apo-C3aR, mutagenesis, functional signaling assays\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structure determination with mutagenesis validation, defines molecular recognition mechanism\",\n      \"pmids\": [\"37169960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C3aR1 couples preferentially to Gi/o/z proteins and recruits β-arrestins to cause internalization. TLQP-21 exhibits biased signaling toward Gi/o-mediated pathways relative to β-arrestin recruitment compared to C3a63-77. SB290157 acts as a potent C3aR1 agonist whose apparent antagonism of calcium flux is explained by β-arrestin-mediated receptor internalization. Ligand-mediated bias impacts Ca2+ influx, lipolysis in adipocytes, phagocytosis in microglia, and degranulation in mast cells.\",\n      \"method\": \"BRET G protein coupling assays, β-arrestin recruitment assays, internalization assays, adipocyte lipolysis, microglial phagocytosis, mast cell degranulation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — comprehensive G protein coupling characterization with multiple orthogonal assays and multiple cell types\",\n      \"pmids\": [\"38072064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C3aR deletion in microglia rescues dysregulated lipid profiles and improves microglial phagocytic and clustering abilities in Alzheimer's disease. C3ar1-null microglia show lower HIF-1α expression, resistance to hypoxia-mimetic-induced metabolic changes, and reduced lipid droplet accumulation, with improved receptor recycling and Aβ phagocytosis. A heightened C3aR/HIF-1α signaling axis underlies microglial metabolic dysfunction in AD.\",\n      \"method\": \"C3ar1-KI reporter mouse, C3ar1-KO × APP-KI mice, primary microglial cultures, transcriptomic analysis, lipid profiling, phagocytosis assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with transcriptomic, metabolic, and functional validation, knockin reporter characterization\",\n      \"pmids\": [\"37317973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C3aR-initiated signaling is a critical mechanism of podocyte injury in membranous nephropathy. C3aR antagonists and C3AR gene silencing in primary human podocytes (in a glomerulus-on-a-chip model) reduced MN serum-induced oxidative stress and prevented albumin leakage; inhibition of MAC formation did not affect permselectivity. C3aR antagonist prevented proteinuria in a mouse MN model.\",\n      \"method\": \"Glomerulus-on-a-chip with primary human podocytes, C3AR siRNA knockdown, C3aR antagonist, mouse MN model, proteinuria measurement\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — human organ-on-chip reconstitution + genetic silencing + in vivo validation, establishes C3aR as primary mediator over MAC\",\n      \"pmids\": [\"38227377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In NPM1-mutated AML, C3aR stimulation with C3a activates ERK1/2 and increases AML cell survival. C3AR is specifically expressed on NPM1-mutated AML cells (including leukemic stem cells co-marked by GPR56) but absent from normal hematopoietic stem/progenitor cells. Anti-C3AR antibodies elicit NK cell-mediated killing of AML cells ex vivo.\",\n      \"method\": \"Flow cytometry screen (362 markers), scRNA-seq, C3a stimulation/ERK1/2 assay, antibody-mediated NK cell killing, xenotransplantation\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — unbiased surface marker screen + defined ERK signaling + functional killing assay + xenotransplantation\",\n      \"pmids\": [\"36383712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NFAT1 in tumor-associated macrophages transcriptionally activates C3 expression, increasing C3a secretion which binds C3aR and promotes M2-like macrophage polarization by activating TIM-3. C3a/C3aR also activates the Ca2+-NFAT1 pathway forming a positive feedback loop sustaining M2 polarization and promoting mesenchymal transition of glioma stem cells.\",\n      \"method\": \"Nfat1-/- mouse glioma model, C3aR inhibitor, TIM-3 blocking, Ca2+ signaling assays, transcriptional activity assays\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + pharmacological inhibition + defined feedback circuit, single lab\",\n      \"pmids\": [\"38289255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Male adipocyte-specific C3aR1 KO mice exhibit enhanced white adipose tissue thermogenesis and increased respiration, while female adipocyte-specific C3aR1 KO mice display decreased brown fat thermogenesis and cold intolerance, revealing sexual dimorphism in the adipsin/C3a/C3aR1 axis in regulating adaptive thermogenesis.\",\n      \"method\": \"Adipocyte-specific C3aR1 KO mice (male and female), Adipsin-KO mice, metabolic phenotyping, cold tolerance tests\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific KO with sex-stratified metabolic phenotyping, defines cell-autonomous role\",\n      \"pmids\": [\"38713526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C3aR modulates susceptibility to LPS-induced depressive-like behaviors through regulation of glutamatergic neuronal excitability in the medial prefrontal cortex. C3aR deletion or antagonism in mPFC confers resilience; re-expression of C3aR in mPFC neurons of KO mice restores susceptibility. C3aR-null mPFC glutamatergic neurons display hyperexcitability upon LPS, which is anti-depressant.\",\n      \"method\": \"C3aR KO mice, intra-mPFC AAV C3aR antagonism/expression, chemogenetic manipulation of mPFCGlu neurons, electrophysiology, behavioral tests\",\n      \"journal\": \"Progress in neurobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + viral rescue + electrophysiology + behavioral pharmacology, multiple orthogonal approaches\",\n      \"pmids\": [\"38641040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C3a promotes neuronal apoptosis and α-synuclein pathology in Parkinson's disease through C3aR-mediated modulation of GSK3β. Complement C3 is released from astrocytes (TLR2/NF-κB dependent), and astrocyte-neuron communication via C3/C3aR influences neuronal apoptosis and α-syn pathology in PD models.\",\n      \"method\": \"α-syn PFF mouse models, C3 overexpression/knockdown, TLR2/NF-κB inhibition in primary astrocytes, GSK3β activity assays\",\n      \"journal\": \"Brain, behavior, and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pathway placed (TLR2/NF-κB→C3→C3aR→GSK3β) with in vivo models, single lab\",\n      \"pmids\": [\"39288893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C3a exacerbates neuroinflammation after subarachnoid hemorrhage via the C3aR-ERK-P2X7-NLRP3 inflammasome signaling axis. C3aR engagement promotes ATP efflux by activating ERK1/2 phosphorylation, which activates P2X7, leading to NLRP3 inflammasome assembly. C3aR interference reduced LDH, IL-1β, caspase-1, NLRP3, ASC oligomerization, and ATP release in BV-2 cells.\",\n      \"method\": \"BV-2 cell heme stimulation model, C3aR siRNA, ERK inhibitor, P2X7 antagonist (JNJ-55308942), in vivo SB290157 in SAH mice\",\n      \"journal\": \"Inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — stepwise pathway dissection with specific inhibitors at each node, in vitro + in vivo validation\",\n      \"pmids\": [\"39528767\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"C3aR1 (C3AR1) is a Gi/o/z-coupled seven-transmembrane GPCR that binds complement fragment C3a and the VGF-derived peptide TLQP-21 via a critical transmembrane binding site (Arg331); ligand binding triggers GRK2/3-mediated phosphorylation and β-arrestin-dependent internalization, while productive Gi/o signaling activates PI3Kγ/Akt/mTOR, ERK, Ca2+ mobilization, and STAT3 downstream of the receptor. In immune cells, C3aR1 on dendritic cells upregulates MHC and costimulatory molecules for T cell priming, on T cells drives mTOR/T-bet-dependent CD8+ proliferation and Th17/memory differentiation, on platelets activates Rap1b to regulate thrombus formation, on macrophages coordinates actin-dependent phagocytic capture of fungi via phagosomal localization, and on neutrophils engages PTEN to antagonize CXCR2-driven bone marrow mobilization; in the CNS, microglial C3aR1 regulates a HIF-1α–driven metabolic/lipid axis, activates STAT3 to sustain reactive glial states in tauopathy, and modulates synaptic pruning and glutamatergic neuronal excitability; in metabolic tissues, adipocyte C3aR1 enhances β-adrenergic-induced lipolysis through Ca2+/ERK/HSL and regulates thermogenesis in a sexually dimorphic manner; C3aR1 can also engage VEGFR2, PDGFR, and EGFR in a physical receptor complex requiring concurrent IL-6R-gp130 co-signaling, and structurally adopts a unique anaphylatoxin recognition mode distinct from chemokine receptors as revealed by cryo-EM.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"C3AR1 encodes a seven-transmembrane Gi/o/z-coupled GPCR that senses complement fragment C3a and the neuropeptide TLQP-21, transducing signals through PI3K/Akt/mTOR, ERK, Ca²⁺ mobilization, STAT3, and β-arrestin–dependent internalization to regulate immune cell activation, hemostasis, neuroinflammation, and metabolism [PMID:8765043, PMID:38072064, PMID:23263555, PMID:30415998]. In innate and adaptive immunity, C3aR1 on dendritic cells upregulates MHC/costimulatory molecules for T cell priming, drives CD8⁺ T cell proliferation via mTOR/T-bet, promotes Th17 differentiation and B cell class-switch recombination, coordinates actin-dependent phagosomal capture of pathogenic fungi in macrophages, and activates Rap1b in platelets to regulate thrombus formation [PMID:18056835, PMID:30565852, PMID:31217324, PMID:36174103, PMID:29802205]. In the central nervous system, microglial C3aR1 sustains reactive glial states in tauopathy through STAT3, governs a HIF-1α–driven metabolic–lipid axis that impairs Aβ phagocytosis in Alzheimer's disease, modulates synaptic pruning, and controls glutamatergic neuronal excitability in the prefrontal cortex [PMID:30415998, PMID:37317973, PMID:35715851, PMID:38641040]. In adipose tissue, C3aR1 enhances β-adrenergic–induced lipolysis through Ca²⁺/ERK/HSL and regulates adaptive thermogenesis in a sexually dimorphic manner [PMID:28123945, PMID:38713526].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Cloning of C3aR established it as a 482-residue GPCR with an unusually large second extracellular loop that couples to G proteins to transduce C3a signals, answering the fundamental question of the molecular identity of the C3a receptor.\",\n      \"evidence\": \"Expression cloning from U-937 cells, radioligand binding and phosphoinositide hydrolysis in transfected HEK-293 and CHO cells\",\n      \"pmids\": [\"8765043\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous G protein coupling specificity not determined\", \"Downstream signaling cascades beyond phosphoinositide hydrolysis unknown\", \"Three-dimensional structure unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of Arg331 as the essential transmembrane ligand-binding residue and GRK2/3/5/6 as the kinases mediating agonist-induced receptor desensitization resolved how C3aR recognizes C3a and how signaling is terminated.\",\n      \"evidence\": \"Site-directed mutagenesis with radioligand binding; GRK overexpression/inhibition with phosphorylation and PLC assays in RBL, COS-7, and HMC-1 cells\",\n      \"pmids\": [\"10491297\", \"10508278\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full complement of phosphorylation sites not mapped\", \"β-arrestin involvement in internalization not yet demonstrated\", \"Whether the large EC loop contributes to binding affinity or selectivity remained unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating that C3aR on hematopoietic cells retains stem/progenitor cells in bone marrow by enhancing SDF-1 responsiveness established the first non-inflammatory physiological role for C3aR in hematopoiesis.\",\n      \"evidence\": \"G-CSF mobilization assays in C3⁻/⁻ and C3aR⁻/⁻ mice, bone marrow chimeras, SB290157 pharmacology\",\n      \"pmids\": [\"14604969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Intracellular signaling linking C3aR to SDF-1 sensitization not delineated\", \"Note: SB290157 later shown to be a C3aR agonist, complicating pharmacological interpretation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing that DC-intrinsic C3aR signaling upregulates MHC and costimulatory molecules for effective T cell priming established C3aR as a bridge between innate complement activation and adaptive immunity.\",\n      \"evidence\": \"C3aR⁻/⁻ DC allostimulation assays, skin allograft rejection model, flow cytometry\",\n      \"pmids\": [\"18056835\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact signaling pathway within DCs not defined\", \"Whether C3aR acts similarly in tolerogenic DC contexts unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing that cessation of C3aR/C5aR signaling in CD4⁺ T cells triggers PI3Kγ/Akt/mTOR collapse and autoinductive TGF-β1–driven Foxp3⁺ iTreg induction defined C3aR as a tonic suppressor of regulatory T cell differentiation.\",\n      \"evidence\": \"C3aR/C5aR antagonism and KO in T cell cultures, PI3K/Akt/mTOR and Foxp3 assays, autoimmune disease models\",\n      \"pmids\": [\"23263555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of C3aR versus C5aR not fully dissected\", \"Whether this mechanism operates in all tissue microenvironments unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identification of C3aR1 as the receptor for VGF-derived TLQP-21 via an unbiased transcriptomic screen revealed that C3aR1 is a dual-ligand GPCR with functions extending beyond complement.\",\n      \"evidence\": \"Genome-wide RNAseq of responsive CHO-K1 cells, siRNA knockdown, pertussis toxin sensitivity, macrophage migration assay\",\n      \"pmids\": [\"23940034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of TLQP-21 versus C3a recognition at C3aR not determined\", \"Physiological contexts where TLQP-21/C3aR signaling dominates over C3a/C3aR not established\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Structural characterization of TLQP-21 binding and functional dissection of C3aR's anti-apoptotic role during Listeria infection expanded understanding of ligand recognition and protective immune functions.\",\n      \"evidence\": \"NMR of TLQP-21, mutagenesis of C-terminal residues; C3aR⁻/⁻ mice infected with L. monocytogenes, Fas/Bcl-2/caspase-3 analysis\",\n      \"pmids\": [\"25456411\", \"24981453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Anti-apoptotic signaling cascade downstream of C3aR not fully mapped\", \"Whether TLQP-21 and C3a compete for the same binding site unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Two studies showed C3aR enhances β-adrenergic lipolysis via Ca²⁺/ERK/HSL in adipocytes and drives neutrophil NETosis linking complement to coagulation in tumorigenesis, revealing tissue-specific effector pathways.\",\n      \"evidence\": \"3T3-L1 adipocyte assays with C3aR1⁻/⁻ and β-AR⁻/⁻ mice; mouse intestinal tumor models with NET quantification and coagulation assays\",\n      \"pmids\": [\"28123945\", \"26996437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether lipolytic and NET pathways share common proximal signaling steps unknown\", \"Biased agonism at C3aR in these contexts not explored\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that C3aR drives intestinal stem cell expansion through Wnt and potentiates glucose-stimulated insulin secretion in β-cells extended C3aR's roles to tissue regeneration and metabolic hormone regulation.\",\n      \"evidence\": \"Intestinal organoids from C3⁻/⁻ and C3aR1⁻/⁻ mice with Lgr5 reporters; β-arrestin and insulin secretion assays in primary human/mouse islets\",\n      \"pmids\": [\"28928734\", \"28921001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking C3aR to Wnt pathway activation not defined\", \"Whether islet C3aR engagement is paracrine or autocrine not fully resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of Rap1b as the platelet C3aR effector for thrombus formation and STAT3 as the microglial C3aR effector sustaining neuroinflammatory glial states in tauopathy established cell-type–specific downstream signaling nodes.\",\n      \"evidence\": \"Platelet-specific reconstitution in C3aR⁻/⁻ mice with nano-LC-MS/MS for Rap1b; C3ar1⁻/⁻ × PS19 tauopathy mice with RNA-seq and STAT3 analysis\",\n      \"pmids\": [\"29802205\", \"30415998\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How C3aR activates Rap1b (direct vs. intermediate) not determined\", \"Whether STAT3 activation is Gi-dependent or β-arrestin-dependent in microglia not distinguished\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Multiple studies demonstrated C3aR's engagement with PTEN to antagonize CXCR2-driven neutrophil mobilization, physical complex formation with VEGFR2/PDGFR/EGFR requiring IL-6R-gp130 co-signaling, T cell-intrinsic mTOR/T-bet activation for CD8⁺ expansion, and B2 cell-autonomous class-switch recombination—collectively establishing C3aR as a signaling integrator across diverse cellular contexts.\",\n      \"evidence\": \"C3aR1⁻/⁻ SCI models with PTEN pathway analysis; Co-IP/BRET/confocal for VEGFR2 complex; adoptive transfers of C3ar1⁻/⁻ T cells in cardiac allografts; C3ar1⁻/⁻ OVA immunization with B cell reconstitution\",\n      \"pmids\": [\"31045582\", \"30765465\", \"30565852\", \"31217324\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the C3aR-VEGFR2-gp130 complex not resolved\", \"How C3aR-PTEN interaction is spatially organized in neutrophils unknown\", \"Relative importance of T cell-intrinsic vs. DC-mediated C3aR in vivo not quantified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that TLQP-21 and C3a super-agonist induce overlapping transcriptomic changes in microglia that enhance motility and phagocytosis confirmed C3aR1 as a shared receptor mediating neuropeptide and complement-driven microglial activation.\",\n      \"evidence\": \"RNA-seq of C3aR1⁻/⁻ vs. WT primary microglia, phagocytosis/migration assays, intracerebroventricular TLQP-21 in 5xFAD mice\",\n      \"pmids\": [\"31924226\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TLQP-21 and C3a produce distinct signaling biases in microglia not fully resolved\", \"Physiological TLQP-21 concentrations in brain parenchyma not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic genetic dissection showed that lectin-pathway-generated C3a signals specifically through C3aR (not C5aR1/C5aR2) to skew tumor-associated macrophages toward immunosuppression in sarcoma, while SB290157 was unmasked as a C3aR agonist whose apparent antagonism arises from β-arrestin-mediated internalization—fundamentally revising pharmacological interpretations of prior studies.\",\n      \"evidence\": \"Systematic KO panel (C3, MBL, C4, C1q, factor B, C3aR, C5aR1, C5aR2) in transplanted sarcoma; β-arrestin recruitment/internalization assays for SB290157 in primary macrophages\",\n      \"pmids\": [\"34505065\", \"33551801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How many prior SB290157-based conclusions require reinterpretation not catalogued\", \"Whether C3aR-specific antagonists free of agonist activity exist not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A CRISPR genome-scale screen identified C3aR as selectively required for macrophage phagosomal capture of pathogenic fungi via actin-dependent membrane protrusions, revealing a pathogen-specific innate immune function distinct from general phagocytosis.\",\n      \"evidence\": \"Genome-scale CRISPR screen in macrophages, C3aR⁻/⁻ validation, live imaging of phagosome formation with Histoplasma/Candida/Coccidioides\",\n      \"pmids\": [\"36174103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Fungal ligand or opsonin that triggers phagosomal C3aR not identified\", \"Whether C3aR phagosomal localization requires EMC-dependent trafficking not fully resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM structures of C3a-bound and apo C3aR revealed a unique anaphylatoxin recognition mode distinct from chemokine receptors, and comprehensive G protein coupling profiling established Gi/o/z preference with ligand-dependent biased agonism between C3a and TLQP-21, resolving long-standing questions about receptor activation and selectivity.\",\n      \"evidence\": \"Cryo-EM/crystal structures with mutagenesis; BRET G protein coupling, β-arrestin recruitment, internalization assays across multiple cell types\",\n      \"pmids\": [\"37169960\", \"38072064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of TLQP-21–bound C3aR not determined\", \"Structural basis for β-arrestin-biased versus G protein-biased signaling not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Microglial C3aR deletion rescued lipid dysregulation and phagocytic dysfunction in AD via suppression of a HIF-1α–driven metabolic axis, while C3aR was identified as the primary mediator of podocyte injury in membranous nephropathy over MAC—extending C3aR's pathogenic roles to metabolic reprogramming and kidney disease.\",\n      \"evidence\": \"C3ar1-KO × APP-KI mice with lipid profiling, HIF-1α analysis, phagocytosis assays; human podocyte glomerulus-on-a-chip with C3AR siRNA, mouse MN model\",\n      \"pmids\": [\"37317973\", \"38227377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How C3aR activates HIF-1α in microglia not mechanistically defined\", \"Whether C3aR-driven podocyte injury involves the same STAT3 or ERK pathways as other cell types unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"C3aR was shown to regulate glutamatergic neuronal excitability in the prefrontal cortex, control sexually dimorphic adaptive thermogenesis in adipocytes, promote ERK-dependent AML cell survival as a targetable surface marker on NPM1-mutated leukemic stem cells, and modulate GSK3β-dependent α-synuclein pathology—demonstrating the breadth of cell-type–specific C3aR functions.\",\n      \"evidence\": \"C3aR KO with viral rescue and electrophysiology in mPFC; adipocyte-specific C3aR1 KO with sex-stratified metabolic phenotyping; flow cytometry screen of 362 markers on AML cells with ERK assays and anti-C3AR antibody NK killing; α-syn PFF models with GSK3β analysis\",\n      \"pmids\": [\"38641040\", \"38713526\", \"36383712\", \"39288893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How C3aR modulates ion channel properties in glutamatergic neurons unknown\", \"Mechanism of sexual dimorphism in adipocyte C3aR1 thermogenic signaling not defined\", \"Whether anti-C3AR antibodies are effective in vivo in AML not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of TLQP-21 binding and biased agonism at C3aR, the molecular mechanism by which C3aR activates HIF-1α in microglia, how phagosomal C3aR recognizes fungal pathogens, the identity of downstream ion channel targets in neurons, and whether C3aR-selective antagonists devoid of agonist activity can be developed for therapeutic use.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structure of TLQP-21–C3aR complex not determined\", \"Mechanism of C3aR-HIF-1α coupling in microglia unknown\", \"In vivo therapeutic potential of anti-C3AR antibodies in AML not tested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 31]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 30, 35]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [30]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 6, 9, 19, 20, 23, 30]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 11, 15, 18, 32]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [11, 33, 37]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"C3a\",\n      \"TLQP-21\",\n      \"GRK2\",\n      \"GRK3\",\n      \"RAP1B\",\n      \"VEGFR2\",\n      \"LFA-1\",\n      \"STAT3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}