{"gene":"C1QA","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":1999,"finding":"The cationic region comprising residues 14-26 of the C1qA polypeptide chain mediates C1q binding to anionic liposomes (and other immunoglobulin-independent activators of the classical pathway) through electrostatic interactions; peptides containing these residues inhibit C1q binding and complement activation in a charge-dependent, sequence-independent manner.","method":"In vitro saturation binding assay with purified C1q and anionic liposomes; inhibition by synthetic peptides; complement hemolysis assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with purified protein, peptide inhibition assays, and mechanistic mutagenesis-equivalent charge-titration experiments in a single study","pmids":["10209207"],"is_preprint":false},{"year":2001,"finding":"Bone marrow-derived cells of the monocyte-macrophage lineage are the primary source of serum C1q; transplantation of wild-type bone marrow into C1qa-/- mice fully reconstitutes serum C1q levels, while C1qa-/- bone marrow transplantation into wild-type mice ablates serum C1q over ~55 weeks.","method":"Bone marrow transplantation in C1qa-/- mice; Y chromosome-specific PCR for engraftment; serum C1q antigen measurement and C1 functional assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal bone marrow reconstitution with functional and antigenic readouts, clearly establishing cellular source","pmids":["11564823"],"is_preprint":false},{"year":2009,"finding":"Influenza A virus matrix protein M1 directly interacts with the globular region of C1qA via M1's N-terminal domain, blocking the C1qA–IgG interaction and inhibiting classical complement pathway-mediated hemolysis and virus neutralization in vitro, and promoting higher viral propagation in mouse lungs in vivo.","method":"Co-immunoprecipitation/pulldown of M1 with C1qA; domain-mapping with deletion constructs; in vitro hemolysis inhibition assay; in vivo mouse infection model","journal":"The Journal of general virology","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding assay with domain mapping, functional in vitro complement inhibition assay, and in vivo validation","pmids":["19656971"],"is_preprint":false},{"year":2012,"finding":"C1qA interacts with components of the RIG-I signaling pathway (RIG-I and VISA/MAVS) and enhances RIG-I–VISA-mediated IFN-β transcription as well as TBK1-mediated IFN-β promoter activation; overexpression of C1qA upregulates ISRE and NF-κB reporters, and C1qA counteracts the inhibitory effect of its receptor gC1qR on RIG-I signaling.","method":"Co-immunoprecipitation of C1qA with RIG-I pathway components; reporter gene assays (ISRE, NF-κB, IFN-β promoter) with overexpression; functional epistasis with gC1qR","journal":"Immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — single lab, Co-IP plus multiple reporter assays establishing pathway placement","pmids":["22260551"],"is_preprint":false},{"year":2017,"finding":"Microglia, not neurons or peripheral sources, are the dominant source of C1q in the brain; cell-specific deletion of C1qa in microglia (using C1qa FL/FL:Cx3cr1-CreERT2 mice) renders the brain virtually devoid of C1q while leaving liver, kidney, and plasma C1q unaffected.","method":"Conditional cell-type-specific knockout (Cre-lox); immunohistochemistry; QPCR; western blot in wild-type and AD model mice","journal":"Journal of neuroinflammation","confidence":"High","confidence_rationale":"Tier 2 — clean genetic loss-of-function with multiple orthogonal readouts and cell-type specificity confirmed across tissues","pmids":["28264694"],"is_preprint":false},{"year":2015,"finding":"C1qa is required for complement-mediated retinal ganglion cell (RGC) loss in a glaucoma model; ablation of C1qa in DBA/2NNia mice ameliorates RGC and optic nerve axonal loss and reduces microglial activation, establishing C1qa as a mediator of complement-driven neurodegeneration in the retina.","method":"C1qa congenic knockout in DBA/2NNia mice; retrograde fluorogold labeling and RGC counting; optic nerve semi-thin section grading; IOP measurement; microglial morphology analysis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple quantitative phenotypic readouts and mechanistic link to microglial activation","pmids":["26544197"],"is_preprint":false},{"year":2023,"finding":"METTL3-mediated m6A methylation of C1qA mRNA, read by YTHDF2, reduces C1qA expression in rituximab-resistant DLBCL cells; knockdown of METTL3 or YTHDF2 upregulates C1qA, restoring complement-dependent cytotoxicity and rituximab sensitivity both in vitro and in vivo.","method":"RNA pulldown and RIP-qPCR to identify m6A reader (YTHDF2) and writer (METTL3) for C1qA mRNA; KD/OE of C1qA, METTL3, YTHDF2 in DLBCL cells; in vitro and in vivo drug sensitivity assays","journal":"Cell death discovery","confidence":"High","confidence_rationale":"Tier 1-2 — RNA pulldown plus RIP-qPCR identifying writer/reader, functional rescue experiments in vitro and in vivo","pmids":["37907575"],"is_preprint":false},{"year":2021,"finding":"The classical complement pathway, initiated by C1qa, is required for host protection against mouse hepatitis virus A59; C1qa KO mice show significantly higher viral loads in the olfactory bulb, liver, and lungs, more severe histopathology, and elevated IFN-γ, MIP-1α, and MCP-1 compared to wild-type mice.","method":"CRISPR/Cas9-generated C1qa KO mice; MHV A59 infection model; viral load quantification; histopathology; immunohistochemistry; chemokine measurement","journal":"Journal of veterinary science","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with multiple orthogonal phenotypic readouts establishing antiviral role of the classical pathway","pmids":["34056877"],"is_preprint":false},{"year":2024,"finding":"C1qa mediates complement-driven synaptic pruning by activated microglia in Alzheimer's disease; elevated C1qA protein and mRNA in FAD4T mouse hippocampus coincides with microglial activation, reduced dendritic spine density, decreased PSD-95 and NMDAR1 levels, and impaired synaptic transmission.","method":"RNA-seq; immunofluorescence; patch-clamp electrophysiology; Golgi staining; western blot in FAD4T AD mouse model","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple orthogonal methods in a single lab; mechanistic link is correlative without direct C1qA KO rescue in this study","pmids":["38266812"],"is_preprint":false},{"year":2024,"finding":"C1qa knockout has both detrimental and beneficial effects on intracerebral hemorrhage-induced brain injury: C1qa KO mice show reduced hematoma erythrolysis and neutrophil infiltration but delayed hematoma clearance, reduced phagocytic multinuclear giant cell induction, and increased perihematomal neuronal damage; after thrombin injection, C1qa KO mice consistently show smaller lesion volumes, less neuronal loss, reduced neutrophil infiltration, and less blood-brain barrier damage.","method":"C1qa KO mouse model; autologous blood injection ICH model; thrombin injection model; MRI; immunohistochemistry","journal":"Translational stroke research","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with multiple in vivo endpoints; complex bidirectional phenotype","pmids":["39370487"],"is_preprint":false},{"year":2024,"finding":"NLRP12 forms a positive feedback loop with C1qA in tumor-associated macrophages (TAMs) that drives pro-tumor polarization via the LILRB4/NF-κB pathway; NLRP12 overexpression in macrophages promotes tumor cell malignant progression and suppresses T cell anti-tumor immunity, while NLRP12 KO reverses these effects.","method":"NLRP12 KO mice; NLRP12 overexpression in macrophages; LILRB4 knockdown; in vivo tumor growth assays; T cell proliferation and cytotoxicity assays","journal":"Cancer immunology, immunotherapy","confidence":"Medium","confidence_rationale":"Tier 2-3 — genetic KO and OE with multiple functional readouts; C1qA–NLRP12 feedback established by co-expression and functional epistasis but direct binding not demonstrated","pmids":["39527158"],"is_preprint":false},{"year":2025,"finding":"C1qA activity is required for activity-driven elimination of excessive intersegmental proprioceptive synaptic connections in the neonatal spinal cord; C1qa KO mice retain intersegmental monosynaptic responses at P11-13 (normally absent), phenocopying Nav1.6 cKO mice that have impaired proprioceptor activity and reduced C1qA expression in the ventral spinal cord.","method":"C1qa KO mice; Nav1.6 conditional KO mice; ex vivo spinal cord electrophysiology; immunofluorescence for C1qA expression","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with electrophysiological readout and genetic epistasis; preprint, single lab","pmids":[],"is_preprint":true},{"year":2025,"finding":"C1QA contributes to maintenance of basal beta-catenin-dependent (norrin/FZD4) signaling at the blood-retina barrier; C1qa KO exacerbates BRB dysfunction and cystoid edema in Tspan12 KO mice, and cell-based experiments indicate C1QA promotes FZD4 signaling to maintain barrier integrity.","method":"C1qa KO and Tspan12 KO compound mutant mice; MRI/aging study; BRB functional assay; ERG; microglia activation assessment; cell-based FZD4 signaling assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — genetic compound mutant with multiple in vivo readouts and cell-based mechanistic experiments; preprint, single lab","pmids":[],"is_preprint":true}],"current_model":"C1qA encodes the A chain of the C1q complement recognition molecule, which is produced predominantly by microglia in the brain and monocyte/macrophage-lineage cells in the periphery; the cationic region (residues 14-26) of C1qA mediates electrostatic binding to immunoglobulin-independent activators, and intracellularly C1qA enhances RIG-I antiviral signaling; C1q initiates classical complement pathway activation leading to opsonization, synaptic pruning, and neuronal protection or damage depending on context, and its expression is post-transcriptionally regulated by METTL3/YTHDF2-mediated m6A methylation."},"narrative":{"teleology":[{"year":1999,"claim":"Identifying how C1q recognizes immunoglobulin-independent activators resolved a long-standing gap in understanding non-antibody-mediated classical pathway initiation: the cationic segment at residues 14–26 of C1qA mediates electrostatic binding to anionic surfaces.","evidence":"Saturation binding assays with purified C1q and anionic liposomes; charge-dependent peptide inhibition of complement hemolysis","pmids":["10209207"],"confidence":"High","gaps":["Whether this cationic region is sufficient for activator discrimination in vivo","No structural data on peptide–liposome interaction at atomic resolution"]},{"year":2001,"claim":"The cellular origin of circulating C1q was definitively established: bone marrow-derived monocyte-macrophage lineage cells are the primary source, resolving uncertainty about hepatocyte versus myeloid contributions.","evidence":"Reciprocal bone marrow transplantation in C1qa-knockout mice with serum C1q antigen and functional assays","pmids":["11564823"],"confidence":"High","gaps":["Relative contribution of tissue-resident versus circulating macrophages not dissected","No mechanism for transcriptional regulation of C1qa in myeloid cells"]},{"year":2009,"claim":"Demonstration that influenza A M1 protein directly binds the C1qA globular domain to block IgG interaction established a viral immune-evasion mechanism targeting the recognition step of the classical pathway.","evidence":"Co-immunoprecipitation with domain-mapping deletions; hemolysis inhibition in vitro; enhanced viral propagation in mouse lungs","pmids":["19656971"],"confidence":"High","gaps":["Structural basis of M1–C1qA interaction unresolved","Generalizability to other viral matrix proteins unknown"]},{"year":2012,"claim":"An unexpected intracellular role for C1qA emerged: it physically interacts with RIG-I and MAVS and enhances type I interferon signaling, placing C1qA in cytoplasmic antiviral innate immunity independently of extracellular complement.","evidence":"Co-immunoprecipitation of C1qA with RIG-I pathway components; ISRE, NF-κB, and IFN-β reporter assays with overexpression and epistasis with gC1qR","pmids":["22260551"],"confidence":"Medium","gaps":["Endogenous intracellular C1qA levels in relevant cell types not quantified","No loss-of-function validation of RIG-I enhancement","Single-lab finding not independently confirmed"]},{"year":2015,"claim":"C1qa was shown to be required for complement-mediated retinal ganglion cell loss in glaucoma, establishing the classical pathway as a driver of neurodegeneration in the eye.","evidence":"C1qa congenic knockout in DBA/2NNia glaucoma mice; retrograde RGC labeling; optic nerve grading; microglial morphology","pmids":["26544197"],"confidence":"High","gaps":["Whether C1q acts via opsonization or membrane attack complex not distinguished","Downstream effectors on microglia not identified"]},{"year":2017,"claim":"Cell-type-specific deletion proved microglia are the sole source of brain C1q, resolving whether peripheral or neuronal sources contribute.","evidence":"Conditional C1qa knockout in microglia (Cx3cr1-CreERT2); immunohistochemistry, qPCR, and western blot across tissues","pmids":["28264694"],"confidence":"High","gaps":["Signals that induce microglial C1qa upregulation in disease not defined","Whether astrocytes can produce C1q under extreme conditions not excluded"]},{"year":2021,"claim":"C1qa knockout mice showed dramatically increased viral loads and pathology upon coronavirus infection, establishing that classical complement pathway initiation via C1q is essential for antiviral defense in vivo.","evidence":"CRISPR-generated C1qa KO mice infected with MHV-A59; viral titers, histopathology, and cytokine profiling","pmids":["34056877"],"confidence":"High","gaps":["Whether protection is via opsonization, neutralization, or downstream C3b deposition not dissected","Applicability to human coronaviruses not tested"]},{"year":2023,"claim":"A post-transcriptional regulatory axis was uncovered: METTL3-mediated m6A modification of C1QA mRNA, read by YTHDF2, suppresses C1QA expression and confers rituximab resistance in lymphoma cells by reducing complement-dependent cytotoxicity.","evidence":"RIP-qPCR and RNA pulldown identifying METTL3/YTHDF2 on C1QA mRNA; knockdown/overexpression rescue of rituximab sensitivity in vitro and in vivo","pmids":["37907575"],"confidence":"High","gaps":["Specific m6A site(s) on C1QA mRNA not mapped","Whether this regulatory axis operates in macrophages or other C1q-producing cells unknown"]},{"year":2024,"claim":"Multiple studies extended C1qa's roles in neural injury and disease: C1qa mediates microglial synaptic pruning correlated with Alzheimer's pathology, exerts context-dependent effects in intracerebral hemorrhage, and participates in a pro-tumor feedback loop with NLRP12 in tumor-associated macrophages.","evidence":"FAD4T AD mouse model with electrophysiology and spine density (PMID:38266812); C1qa KO in ICH and thrombin injection models with MRI/IHC (PMID:39370487); NLRP12 KO and OE with tumor growth and T cell assays (PMID:39527158)","pmids":["38266812","39370487","39527158"],"confidence":"Medium","gaps":["Synaptic pruning link in AD is correlative without C1qa KO rescue in the same study","Bidirectional ICH phenotype mechanisms not resolved","Direct C1qA–NLRP12 physical interaction not demonstrated"]},{"year":null,"claim":"Key unresolved questions include the structural basis of C1qA interactions with diverse ligands, the signals that regulate microglial C1qa transcription in health and disease, and whether intracellular C1qA-RIG-I signaling operates at physiological expression levels.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of full-length C1q or C1qA–ligand complexes","Transcriptional regulation of C1qa in microglia largely uncharacterized","Intracellular RIG-I-enhancing function awaits independent replication and endogenous-level validation"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,5,7]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,1,2,5,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,5,7,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,10]}],"complexes":["C1 complex (C1q/C1r/C1s)"],"partners":["C1QB","C1QC","DDX58","MAVS","NLRP12","YTHDF2","METTL3"],"other_free_text":[]},"mechanistic_narrative":"C1QA encodes the A chain of complement component C1q, the pattern-recognition molecule that initiates the classical complement pathway, functioning in innate immunity, synaptic pruning, and tissue homeostasis. Serum C1q is produced primarily by monocyte-macrophage lineage cells, while brain C1q derives exclusively from microglia; the cationic region (residues 14–26) of C1qA mediates electrostatic binding to immunoglobulin-independent activators, and the globular head domain engages IgG as well as viral proteins such as influenza M1 [PMID:10209207, PMID:11564823, PMID:28264694, PMID:19656971]. C1q-initiated classical pathway activation is required for antiviral defense, complement-dependent cytotoxicity of tumor cells, microglial synaptic pruning during development and neurodegeneration, and modulation of neuroinflammatory injury, with C1qa knockout in mice conferring context-dependent protection or exacerbation of pathology in glaucoma, intracerebral hemorrhage, and Alzheimer's disease models [PMID:26544197, PMID:34056877, PMID:39370487, PMID:38266812]. C1QA mRNA is post-transcriptionally regulated by METTL3-mediated m6A methylation read by YTHDF2, and intracellularly C1qA enhances RIG-I/MAVS-dependent interferon-β signaling independently of extracellular complement activation [PMID:37907575, PMID:22260551]."},"prefetch_data":{"uniprot":{"accession":"P02745","full_name":"Complement C1q subcomponent subunit A","aliases":[],"length_aa":245,"mass_kda":26.0,"function":"Core component of the complement C1 complex, a multiprotein complex that initiates the classical pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:34155115, PubMed:6249812, PubMed:6776418). The classical complement pathway is initiated by the C1Q subcomplex of the C1 complex, which specifically binds IgG or IgM immunoglobulins complexed with antigens, forming antigen-antibody complexes on the surface of pathogens: C1QA, together with C1QB and C1QC, specifically recognizes and binds the Fc regions of IgG or IgM via its C1q domain (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:6776418). Immunoglobulin-binding activates the proenzyme C1R, which cleaves C1S, initiating the proteolytic cascade of the complement system (PubMed:29449492). The C1Q subcomplex is activated by a hexamer of IgG complexed with antigens, while it is activated by a pentameric IgM (PubMed:19706439, PubMed:24626930, PubMed:29449492). The C1Q subcomplex also recognizes and binds phosphatidylserine exposed on the surface of cells undergoing programmed cell death, possibly promoting activation of the complement system (PubMed:18250442)","subcellular_location":"Secreted; Cell surface","url":"https://www.uniprot.org/uniprotkb/P02745/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C1QA","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C1QA","total_profiled":1310},"omim":[{"mim_id":"614330","title":"COMPLEMENT COMPONENT 1, q SUBCOMPONENT-LIKE 2; C1QL2","url":"https://www.omim.org/entry/614330"},{"mim_id":"614285","title":"C1q- AND TUMOR NECROSIS FACTOR-RELATED PROTEIN 9; C1QTNF9","url":"https://www.omim.org/entry/614285"},{"mim_id":"614148","title":"C1q- AND TUMOR NECROSIS FACTOR-RELATED PROTEIN 9B; C1QTNF9B","url":"https://www.omim.org/entry/614148"},{"mim_id":"614147","title":"C1q- AND TUMOR NECROSIS FACTOR-RELATED PROTEIN 8; C1QTNF8","url":"https://www.omim.org/entry/614147"},{"mim_id":"613652","title":"C1q DEFICIENCY 1; C1QD1","url":"https://www.omim.org/entry/613652"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"choroid plexus","ntpm":604.1},{"tissue":"lymphoid tissue","ntpm":1056.2}],"url":"https://www.proteinatlas.org/search/C1QA"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P02745","domains":[{"cath_id":"2.60.120.40","chopping":"114-242","consensus_level":"high","plddt":94.9244,"start":114,"end":242}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P02745","model_url":"https://alphafold.ebi.ac.uk/files/AF-P02745-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P02745-F1-predicted_aligned_error_v6.png","plddt_mean":82.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C1QA","jax_strain_url":"https://www.jax.org/strain/search?query=C1QA"},"sequence":{"accession":"P02745","fasta_url":"https://rest.uniprot.org/uniprotkb/P02745.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P02745/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P02745"}},"corpus_meta":[{"pmid":"28264694","id":"PMC_28264694","title":"Cell-specific deletion of C1qa identifies 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C4 Transcripts in the Midbrain of People With Schizophrenia.","date":"2020","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/33133060","citation_count":75,"is_preprint":false},{"pmid":"12630757","id":"PMC_12630757","title":"Homozygous single nucleotide polymorphism of the complement C1QA gene is associated with decreased levels of C1q in patients with subacute cutaneous lupus erythematosus.","date":"2003","source":"Lupus","url":"https://pubmed.ncbi.nlm.nih.gov/12630757","citation_count":66,"is_preprint":false},{"pmid":"10209207","id":"PMC_10209207","title":"C1q binding to liposomes is surface charge dependent and is inhibited by peptides consisting of residues 14-26 of the human C1qA chain in a sequence independent manner.","date":"1999","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/10209207","citation_count":56,"is_preprint":false},{"pmid":"19656971","id":"PMC_19656971","title":"Influenza A virus M1 blocks the classical complement pathway through interacting with C1qA.","date":"2009","source":"The Journal of general virology","url":"https://pubmed.ncbi.nlm.nih.gov/19656971","citation_count":42,"is_preprint":false},{"pmid":"38266812","id":"PMC_38266812","title":"Cognitive impairment in Alzheimer's disease FAD4T mouse model: Synaptic loss facilitated by activated microglia via C1qA.","date":"2024","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38266812","citation_count":29,"is_preprint":false},{"pmid":"16465510","id":"PMC_16465510","title":"The pattern of clinical breast cancer metastasis correlates with a single nucleotide polymorphism in the C1qA component of complement.","date":"2006","source":"Immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/16465510","citation_count":26,"is_preprint":false},{"pmid":"22260551","id":"PMC_22260551","title":"The complement C1qA enhances retinoic acid-inducible gene-I-mediated immune signalling.","date":"2012","source":"Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/22260551","citation_count":25,"is_preprint":false},{"pmid":"20332777","id":"PMC_20332777","title":"Common germ-line polymorphism of C1QA and breast cancer survival.","date":"2010","source":"British journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/20332777","citation_count":16,"is_preprint":false},{"pmid":"31019999","id":"PMC_31019999","title":"C1QA and C1QC modify age-at-onset in familial amyloid polyneuropathy patients.","date":"2019","source":"Annals of clinical and translational neurology","url":"https://pubmed.ncbi.nlm.nih.gov/31019999","citation_count":15,"is_preprint":false},{"pmid":"20560256","id":"PMC_20560256","title":"Hereditary C1q deficiency: a new family with C1qA deficiency.","date":"2010","source":"The Turkish journal of 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saturation binding assay with purified C1q and anionic liposomes; inhibition by synthetic peptides; complement hemolysis assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with purified protein, peptide inhibition assays, and mechanistic mutagenesis-equivalent charge-titration experiments in a single study\",\n      \"pmids\": [\"10209207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Bone marrow-derived cells of the monocyte-macrophage lineage are the primary source of serum C1q; transplantation of wild-type bone marrow into C1qa-/- mice fully reconstitutes serum C1q levels, while C1qa-/- bone marrow transplantation into wild-type mice ablates serum C1q over ~55 weeks.\",\n      \"method\": \"Bone marrow transplantation in C1qa-/- mice; Y chromosome-specific PCR for engraftment; serum C1q antigen measurement and C1 functional assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal bone marrow reconstitution with functional and antigenic readouts, clearly establishing cellular source\",\n      \"pmids\": [\"11564823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Influenza A virus matrix protein M1 directly interacts with the globular region of C1qA via M1's N-terminal domain, blocking the C1qA–IgG interaction and inhibiting classical complement pathway-mediated hemolysis and virus neutralization in vitro, and promoting higher viral propagation in mouse lungs in vivo.\",\n      \"method\": \"Co-immunoprecipitation/pulldown of M1 with C1qA; domain-mapping with deletion constructs; in vitro hemolysis inhibition assay; in vivo mouse infection model\",\n      \"journal\": \"The Journal of general virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding assay with domain mapping, functional in vitro complement inhibition assay, and in vivo validation\",\n      \"pmids\": [\"19656971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"C1qA interacts with components of the RIG-I signaling pathway (RIG-I and VISA/MAVS) and enhances RIG-I–VISA-mediated IFN-β transcription as well as TBK1-mediated IFN-β promoter activation; overexpression of C1qA upregulates ISRE and NF-κB reporters, and C1qA counteracts the inhibitory effect of its receptor gC1qR on RIG-I signaling.\",\n      \"method\": \"Co-immunoprecipitation of C1qA with RIG-I pathway components; reporter gene assays (ISRE, NF-κB, IFN-β promoter) with overexpression; functional epistasis with gC1qR\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — single lab, Co-IP plus multiple reporter assays establishing pathway placement\",\n      \"pmids\": [\"22260551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Microglia, not neurons or peripheral sources, are the dominant source of C1q in the brain; cell-specific deletion of C1qa in microglia (using C1qa FL/FL:Cx3cr1-CreERT2 mice) renders the brain virtually devoid of C1q while leaving liver, kidney, and plasma C1q unaffected.\",\n      \"method\": \"Conditional cell-type-specific knockout (Cre-lox); immunohistochemistry; QPCR; western blot in wild-type and AD model mice\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic loss-of-function with multiple orthogonal readouts and cell-type specificity confirmed across tissues\",\n      \"pmids\": [\"28264694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"C1qa is required for complement-mediated retinal ganglion cell (RGC) loss in a glaucoma model; ablation of C1qa in DBA/2NNia mice ameliorates RGC and optic nerve axonal loss and reduces microglial activation, establishing C1qa as a mediator of complement-driven neurodegeneration in the retina.\",\n      \"method\": \"C1qa congenic knockout in DBA/2NNia mice; retrograde fluorogold labeling and RGC counting; optic nerve semi-thin section grading; IOP measurement; microglial morphology analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple quantitative phenotypic readouts and mechanistic link to microglial activation\",\n      \"pmids\": [\"26544197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL3-mediated m6A methylation of C1qA mRNA, read by YTHDF2, reduces C1qA expression in rituximab-resistant DLBCL cells; knockdown of METTL3 or YTHDF2 upregulates C1qA, restoring complement-dependent cytotoxicity and rituximab sensitivity both in vitro and in vivo.\",\n      \"method\": \"RNA pulldown and RIP-qPCR to identify m6A reader (YTHDF2) and writer (METTL3) for C1qA mRNA; KD/OE of C1qA, METTL3, YTHDF2 in DLBCL cells; in vitro and in vivo drug sensitivity assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — RNA pulldown plus RIP-qPCR identifying writer/reader, functional rescue experiments in vitro and in vivo\",\n      \"pmids\": [\"37907575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The classical complement pathway, initiated by C1qa, is required for host protection against mouse hepatitis virus A59; C1qa KO mice show significantly higher viral loads in the olfactory bulb, liver, and lungs, more severe histopathology, and elevated IFN-γ, MIP-1α, and MCP-1 compared to wild-type mice.\",\n      \"method\": \"CRISPR/Cas9-generated C1qa KO mice; MHV A59 infection model; viral load quantification; histopathology; immunohistochemistry; chemokine measurement\",\n      \"journal\": \"Journal of veterinary science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with multiple orthogonal phenotypic readouts establishing antiviral role of the classical pathway\",\n      \"pmids\": [\"34056877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C1qa mediates complement-driven synaptic pruning by activated microglia in Alzheimer's disease; elevated C1qA protein and mRNA in FAD4T mouse hippocampus coincides with microglial activation, reduced dendritic spine density, decreased PSD-95 and NMDAR1 levels, and impaired synaptic transmission.\",\n      \"method\": \"RNA-seq; immunofluorescence; patch-clamp electrophysiology; Golgi staining; western blot in FAD4T AD mouse model\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple orthogonal methods in a single lab; mechanistic link is correlative without direct C1qA KO rescue in this study\",\n      \"pmids\": [\"38266812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C1qa knockout has both detrimental and beneficial effects on intracerebral hemorrhage-induced brain injury: C1qa KO mice show reduced hematoma erythrolysis and neutrophil infiltration but delayed hematoma clearance, reduced phagocytic multinuclear giant cell induction, and increased perihematomal neuronal damage; after thrombin injection, C1qa KO mice consistently show smaller lesion volumes, less neuronal loss, reduced neutrophil infiltration, and less blood-brain barrier damage.\",\n      \"method\": \"C1qa KO mouse model; autologous blood injection ICH model; thrombin injection model; MRI; immunohistochemistry\",\n      \"journal\": \"Translational stroke research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple in vivo endpoints; complex bidirectional phenotype\",\n      \"pmids\": [\"39370487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NLRP12 forms a positive feedback loop with C1qA in tumor-associated macrophages (TAMs) that drives pro-tumor polarization via the LILRB4/NF-κB pathway; NLRP12 overexpression in macrophages promotes tumor cell malignant progression and suppresses T cell anti-tumor immunity, while NLRP12 KO reverses these effects.\",\n      \"method\": \"NLRP12 KO mice; NLRP12 overexpression in macrophages; LILRB4 knockdown; in vivo tumor growth assays; T cell proliferation and cytotoxicity assays\",\n      \"journal\": \"Cancer immunology, immunotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic KO and OE with multiple functional readouts; C1qA–NLRP12 feedback established by co-expression and functional epistasis but direct binding not demonstrated\",\n      \"pmids\": [\"39527158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"C1qA activity is required for activity-driven elimination of excessive intersegmental proprioceptive synaptic connections in the neonatal spinal cord; C1qa KO mice retain intersegmental monosynaptic responses at P11-13 (normally absent), phenocopying Nav1.6 cKO mice that have impaired proprioceptor activity and reduced C1qA expression in the ventral spinal cord.\",\n      \"method\": \"C1qa KO mice; Nav1.6 conditional KO mice; ex vivo spinal cord electrophysiology; immunofluorescence for C1qA expression\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with electrophysiological readout and genetic epistasis; preprint, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"C1QA contributes to maintenance of basal beta-catenin-dependent (norrin/FZD4) signaling at the blood-retina barrier; C1qa KO exacerbates BRB dysfunction and cystoid edema in Tspan12 KO mice, and cell-based experiments indicate C1QA promotes FZD4 signaling to maintain barrier integrity.\",\n      \"method\": \"C1qa KO and Tspan12 KO compound mutant mice; MRI/aging study; BRB functional assay; ERG; microglia activation assessment; cell-based FZD4 signaling assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic compound mutant with multiple in vivo readouts and cell-based mechanistic experiments; preprint, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"C1qA encodes the A chain of the C1q complement recognition molecule, which is produced predominantly by microglia in the brain and monocyte/macrophage-lineage cells in the periphery; the cationic region (residues 14-26) of C1qA mediates electrostatic binding to immunoglobulin-independent activators, and intracellularly C1qA enhances RIG-I antiviral signaling; C1q initiates classical complement pathway activation leading to opsonization, synaptic pruning, and neuronal protection or damage depending on context, and its expression is post-transcriptionally regulated by METTL3/YTHDF2-mediated m6A methylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"C1QA encodes the A chain of complement component C1q, the pattern-recognition molecule that initiates the classical complement pathway, functioning in innate immunity, synaptic pruning, and tissue homeostasis. Serum C1q is produced primarily by monocyte-macrophage lineage cells, while brain C1q derives exclusively from microglia; the cationic region (residues 14–26) of C1qA mediates electrostatic binding to immunoglobulin-independent activators, and the globular head domain engages IgG as well as viral proteins such as influenza M1 [PMID:10209207, PMID:11564823, PMID:28264694, PMID:19656971]. C1q-initiated classical pathway activation is required for antiviral defense, complement-dependent cytotoxicity of tumor cells, microglial synaptic pruning during development and neurodegeneration, and modulation of neuroinflammatory injury, with C1qa knockout in mice conferring context-dependent protection or exacerbation of pathology in glaucoma, intracerebral hemorrhage, and Alzheimer's disease models [PMID:26544197, PMID:34056877, PMID:39370487, PMID:38266812]. C1QA mRNA is post-transcriptionally regulated by METTL3-mediated m6A methylation read by YTHDF2, and intracellularly C1qA enhances RIG-I/MAVS-dependent interferon-β signaling independently of extracellular complement activation [PMID:37907575, PMID:22260551].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying how C1q recognizes immunoglobulin-independent activators resolved a long-standing gap in understanding non-antibody-mediated classical pathway initiation: the cationic segment at residues 14–26 of C1qA mediates electrostatic binding to anionic surfaces.\",\n      \"evidence\": \"Saturation binding assays with purified C1q and anionic liposomes; charge-dependent peptide inhibition of complement hemolysis\",\n      \"pmids\": [\"10209207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this cationic region is sufficient for activator discrimination in vivo\", \"No structural data on peptide–liposome interaction at atomic resolution\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The cellular origin of circulating C1q was definitively established: bone marrow-derived monocyte-macrophage lineage cells are the primary source, resolving uncertainty about hepatocyte versus myeloid contributions.\",\n      \"evidence\": \"Reciprocal bone marrow transplantation in C1qa-knockout mice with serum C1q antigen and functional assays\",\n      \"pmids\": [\"11564823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of tissue-resident versus circulating macrophages not dissected\", \"No mechanism for transcriptional regulation of C1qa in myeloid cells\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that influenza A M1 protein directly binds the C1qA globular domain to block IgG interaction established a viral immune-evasion mechanism targeting the recognition step of the classical pathway.\",\n      \"evidence\": \"Co-immunoprecipitation with domain-mapping deletions; hemolysis inhibition in vitro; enhanced viral propagation in mouse lungs\",\n      \"pmids\": [\"19656971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of M1–C1qA interaction unresolved\", \"Generalizability to other viral matrix proteins unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"An unexpected intracellular role for C1qA emerged: it physically interacts with RIG-I and MAVS and enhances type I interferon signaling, placing C1qA in cytoplasmic antiviral innate immunity independently of extracellular complement.\",\n      \"evidence\": \"Co-immunoprecipitation of C1qA with RIG-I pathway components; ISRE, NF-κB, and IFN-β reporter assays with overexpression and epistasis with gC1qR\",\n      \"pmids\": [\"22260551\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous intracellular C1qA levels in relevant cell types not quantified\", \"No loss-of-function validation of RIG-I enhancement\", \"Single-lab finding not independently confirmed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"C1qa was shown to be required for complement-mediated retinal ganglion cell loss in glaucoma, establishing the classical pathway as a driver of neurodegeneration in the eye.\",\n      \"evidence\": \"C1qa congenic knockout in DBA/2NNia glaucoma mice; retrograde RGC labeling; optic nerve grading; microglial morphology\",\n      \"pmids\": [\"26544197\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether C1q acts via opsonization or membrane attack complex not distinguished\", \"Downstream effectors on microglia not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Cell-type-specific deletion proved microglia are the sole source of brain C1q, resolving whether peripheral or neuronal sources contribute.\",\n      \"evidence\": \"Conditional C1qa knockout in microglia (Cx3cr1-CreERT2); immunohistochemistry, qPCR, and western blot across tissues\",\n      \"pmids\": [\"28264694\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals that induce microglial C1qa upregulation in disease not defined\", \"Whether astrocytes can produce C1q under extreme conditions not excluded\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"C1qa knockout mice showed dramatically increased viral loads and pathology upon coronavirus infection, establishing that classical complement pathway initiation via C1q is essential for antiviral defense in vivo.\",\n      \"evidence\": \"CRISPR-generated C1qa KO mice infected with MHV-A59; viral titers, histopathology, and cytokine profiling\",\n      \"pmids\": [\"34056877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether protection is via opsonization, neutralization, or downstream C3b deposition not dissected\", \"Applicability to human coronaviruses not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A post-transcriptional regulatory axis was uncovered: METTL3-mediated m6A modification of C1QA mRNA, read by YTHDF2, suppresses C1QA expression and confers rituximab resistance in lymphoma cells by reducing complement-dependent cytotoxicity.\",\n      \"evidence\": \"RIP-qPCR and RNA pulldown identifying METTL3/YTHDF2 on C1QA mRNA; knockdown/overexpression rescue of rituximab sensitivity in vitro and in vivo\",\n      \"pmids\": [\"37907575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific m6A site(s) on C1QA mRNA not mapped\", \"Whether this regulatory axis operates in macrophages or other C1q-producing cells unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Multiple studies extended C1qa's roles in neural injury and disease: C1qa mediates microglial synaptic pruning correlated with Alzheimer's pathology, exerts context-dependent effects in intracerebral hemorrhage, and participates in a pro-tumor feedback loop with NLRP12 in tumor-associated macrophages.\",\n      \"evidence\": \"FAD4T AD mouse model with electrophysiology and spine density (PMID:38266812); C1qa KO in ICH and thrombin injection models with MRI/IHC (PMID:39370487); NLRP12 KO and OE with tumor growth and T cell assays (PMID:39527158)\",\n      \"pmids\": [\"38266812\", \"39370487\", \"39527158\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Synaptic pruning link in AD is correlative without C1qa KO rescue in the same study\", \"Bidirectional ICH phenotype mechanisms not resolved\", \"Direct C1qA–NLRP12 physical interaction not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of C1qA interactions with diverse ligands, the signals that regulate microglial C1qa transcription in health and disease, and whether intracellular C1qA-RIG-I signaling operates at physiological expression levels.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of full-length C1q or C1qA–ligand complexes\", \"Transcriptional regulation of C1qa in microglia largely uncharacterized\", \"Intracellular RIG-I-enhancing function awaits independent replication and endogenous-level validation\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10]}\n    ],\n    \"complexes\": [\n      \"C1 complex (C1q/C1r/C1s)\"\n    ],\n    \"partners\": [\n      \"C1QB\",\n      \"C1QC\",\n      \"DDX58\",\n      \"MAVS\",\n      \"NLRP12\",\n      \"YTHDF2\",\n      \"METTL3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}