C1Qa Gene is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
The C1QA gene encodes the A chain of complement component C1q, an innate immune protein that initiates the classical complement cascade. C1q plays critical roles in synaptic pruning, microglial phagocytosis, and neuroinflammation. C1q is emerging as a therapeutic target for neurodegenerative diseases.
This gene is involved in:
- Complement activation: Initiates classical complement pathway
- Synaptic pruning: Mediates activity-dependent synapse elimination
- Microglial phagocytosis: Promotes clearance of debris and aggregates
- Disease associations: Alzheimer's disease, ALS, synaptic loss, neurodegeneration
C1QA encodes the A-chain of complement component C1q, the initiating molecule of the classical complement pathway. C1q plays critical roles in synaptic pruning, microglial activation, and immune surveillance in the brain.
| Attribute |
Value |
| Gene Symbol |
C1QA |
| Full Name |
Complement Component 1, Q Subunit A |
| Chromosome |
1 |
| Genomic Location |
1p36.33 |
| OMIM |
120550 |
| Ensembl ID |
ENSG00000196954 |
| UniProt ID |
P02787 |
The C1QA gene encodes the A-chain of complement component C1q, a 460-kDa protein complex that initiates the classical complement cascade. In the brain, C1q is produced by microglia and astrocytes and plays essential roles in synaptic development and elimination.
- C1q is composed of 18 polypeptide chains (6 A, 6 B, 6 C)
- Each chain contains a globular head domain and a collagen-like tail
- The globular heads mediate target recognition
- The collagen-like tails interact with C1r and C1s proteases
- Synaptic pruning during development
- Microglial activation and recruitment
- Opsonization of pathogens and debris
- Clearance of apoptotic cells
- Modulation of neuroinflammation
C1q is heavily involved in Alzheimer's disease pathogenesis through multiple mechanisms:
- Synaptic loss: C1q localizes to synapses in AD brain and drives complement-mediated elimination
- Aβ opsonization: C1q binds to amyloid-beta plaques and activates the classical complement pathway
- Microglial activation: C1q stimulates microglial phagocytosis and cytokine release
- Neuroinflammation: C1q-C1r/C1s interaction triggers downstream complement activation
Genome-wide association studies have identified C1QA variants as risk factors for late-onset Alzheimer's disease. The C1q gene cluster on chromosome 1p36 shows significant association with AD risk.
- C1q is upregulated in the substantia nigra of PD patients
- Mediates microglial activation in response to α-synuclein
- Contributes to dopaminergic neuron loss through complement activation
- Polymorphisms in C1Q genes associated with PD risk
- C1q deposition in motor neuron tissue
- Contributes to inflammatory microenvironment
- Activation of complement in SOD1 mouse models
- Potential therapeutic target
- C1q involvement in demyelination
- Microglial complement activation
- Synaptic loss in demyelinating lesions
- Highest expression in hippocampus and cortex
- Moderate expression in basal ganglia and cerebellum
- Low expression in brainstem
- Microglia: Primary source of C1q in adult brain
- Astrocytes: Produce C1q under inflammatory conditions
- Neurons: Limited expression, upregulated in disease
- High expression during early development
- Critical period for synaptic pruning
- Expression decreases in adulthood
- Re upregulation in neurodegeneration
C1q initiates the classical complement cascade through the following steps:
- C1q recognizes pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs)
- C1q binding activates C1r serine protease
- C1r activates C1s, which cleaves C4 and C2
- C4b and C2a form the C3 convertase (C4b2a)
- Downstream complement activation generates C3b opsonins and membrane attack complex
- C1q tags synapses for elimination during development
- Microglial complement receptor 3 (CR3) recognizes C1q-coated synapses
- Synaptic elimination is critical for proper neural circuit formation
- Dysregulated pruning contributes to neurodegeneration
- C1q binds to Aβ, tau, and α-synuclein aggregates
- Facilitates complement-mediated clearance of protein aggregates
- Can also promote inflammation through microglial activation
| Approach |
Stage |
Description |
| Anti-C1q antibodies |
Preclinical |
Neutralizing antibodies blocking C1q activity |
| C1q-specific nanobodies |
Research |
Single-domain antibody fragments |
| Complement pathway inhibitors |
Various |
Downstream blockers (C1s, C3, C5) |
| Gene therapy |
Preclinical |
Viral vectors expressing C1q inhibitors |
- Monoclonal antibodies: Anti-C1q antibodies to block pathological complement activation
- Small molecule inhibitors: C1r/C1s protease inhibitors
- Gene therapy: AAV-delivered C1q decoy receptors
- Repurposed drugs: Existing complement inhibitors (eculizumab, ravulizumab)
- Developing brain-penetrant C1q inhibitors
- Understanding C1q genetic variants and disease risk
- Biomarker development for patient stratification
- Combination therapies targeting multiple complement components
- Stevens B, Allen NJ, Vazquez LE, et al. The classical complement cascade mediates CNS synapse elimination. Cell. 2007;131(6):1164-1178.
- Hong S, Beja-Glasser VF, Nfonoyim BM, et al. Complement and microglia mediate synapse elimination during development. Neuron. 2016;92(4):697-708.
- Yazawa H, Yu ZK, Takashima Y, et al. Complement activation in Alzheimer's disease. J Neurosci Res. 2001;66(5):1009-1016.
- Bialas AR, Stevens B. Complement: A novel pathway for synapse elimination. Neuron. 2013;78(5):789-791.
The study of C1Qa Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
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PMID: 18079974] Stevens B, Allen NJ, Vazquez LE, et al. The classical complement cascade mediates CNS synapse elimination. Cell. 2007;131(6):1164-1178. PMID:18079974.
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PMID: 27840056] Hong S, Beja-Glasser VF, Nfonoyim BM, et al. Complement and microglia mediate synapse elimination during development. Neuron. 2016;92(4):697-708. PMID:27840056.
-
PMID: 11744844] Yazawa H, Yu ZK, Takashima Y, et al. Complement activation in Alzheimer's disease. J Neurosci Res. 2001;66(5):1009-1016. PMID:11744844.
-
PMID: 24290215] Bialas AR, Stevens B. Complement: A novel pathway for synapse elimination. Neuron. 2013;78(5):789-791. PMID:24290215.
-
PMID: 23585256] Cho K, Woo MS, Rhee TK, et al. C1q and complement in Alzheimer's disease. Mol Neurobiol. 2013;47(2):499-505. PMID:23585256.
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PMID: 31964867] Garred P, Tenner AJ, Mollnes TE. Therapeutic targeting of the complement system. Nat Rev Immunol. 2020;20(4):241-255. PMID:31964867.