pmid: '7561018'
C7
Introduction
C7 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
<div class="infobox infobox-gene"> [@uniprot]
<div class="infobox-header">Complement Component 7</div> [@staiko2019]
<div class="infobox-row"><span class="infobox-label">Gene Symbol</span><span class="infobox-value">C7</span></div> [@riddell2020]
<div class="infobox-row"><span class="infobox-label">Full Name</span><span class="infobox-value">Complement Component 7</span></div> [@gebbink2021]
<div class="infobox-row"><span class="infobox-label">Chromosomal Location</span><span class="infobox-value">5p13.1</span></div> [@rus2006]
<div class="infobox-row"><span class="infobox-label">NCBI Gene ID</span><span class="infobox-value">[719](https://www.ncbi.nlm.nih.gov/gene/719)</span></div> [@stahel2000]
<div class="infobox-row"><span class="infobox-label">OMIM</span><span class="infobox-value">[217070](https://omim.org/entry/217070)</span></div> [@michailidou2018]
<div class="infobox-row"><span class="infobox-label">Ensembl ID</span><span class="infobox-value">ENSG00000124429</span></div> [@watowich1995]
<div class="infobox-row"><span class="infobox-label">UniProt ID</span><span class="infobox-value">[P10643](https://www.uniprot.org/uniprot/P10643)</span></div>
<div class="infobox-row"><span class="infobox-label">Associated Diseases</span><span class="infobox-value">Complement Deficiency, Systemic Lupus Erythematosus</span></div>
</div>
Overview
The C7 gene encodes complement component 7, a terminal complement protein essential for membrane attack complex (MAC) formation in the innate immune system. C7 is a secreted glycoprotein that plays a critical role in the complement cascade, a series of proteins that enhance opsonization, inflammation, and cell lysis. The gene is located on chromosome 5p13.1 and encodes a protein of approximately 809 amino acids [1].
C7 is synthesized primarily in the liver as a single polypeptide chain that undergoes post-translational modifications to become a functional secreted protein. It circulates in plasma at concentrations of approximately 40-80 μg/mL in healthy individuals. The protein contains multiple thrombospondin type I repeats (TSRs) and a hydrophobic region that facilitates membrane insertion [2].
Function
The primary function of C7 is in the terminal pathway of the [complement system](/entities/complement-system). C7 binds to the C5b-6 complex to form C5b-6-7, which has the unique ability to insert into lipid bilayers of target cell membranes. This insertion is a critical step in the formation of the membrane attack complex (MAC), which creates a transmembrane pore leading to cell lysis.
The biological functions of C7 include:
Membrane Insertion: The C5b-6-7 complex can insert into cell membranes, initiating the formation of the MAC pore
Pore Formation: C7 provides the structural foundation for C8 and C9 addition to complete the MAC
Immune Defense: The MAC is crucial for defense against Neisseria infections (N. meningitidis, N. gonorrhoeae)
Immunomodulation: Sublytic MAC deposition can trigger inflammatory responses without cell deathDisease Associations
Alzheimer's Disease
The complement system, including terminal components, has been increasingly recognized in [Alzheimer's disease](/diseases/alzheimers-disease) pathogenesis. The MAC (C5b-9) is detected in AD brain tissue, particularly in association with amyloid plaques and in the cerebral vasculature. Research suggests that:
- MAC deposition on [neurons](/entities/neurons) may contribute to synaptic loss and neuronal damage [3]
- Complement activation products colocalize with neurofibrillary tangles
- The membrane attack complex may be involved in microvascular injury in AD
- Genetic variants in complement genes may modify AD risk [4]
Parkinson's Disease
Complement activation has been implicated in [Parkinson's disease](/diseases/parkinsons-disease) pathogenesis:
- MAC deposition has been observed in the substantia nigra of PD patients
- Microglial activation in PD is associated with complement upregulation
- C7 and other complement proteins are elevated in the CSF of PD patients
- The complement system may mediate neuroinflammation in PD [5]
Multiple Sclerosis and Demyelination
In multiple sclerosis and related demyelinating diseases:
- MAC-mediated demyelination is a key pathological mechanism
- Oligodendrocyte death can be complement-dependent
- Demyelinating lesions show complement deposition
- Therapeutic strategies targeting complement are being explored [6]
Other Neurodegenerative Conditions
- Amyotrophic Lateral Sclerosis (ALS): Complement activation is observed in ALS motor [cortex](/brain-regions/cortex) and spinal cord
- Frontotemporal Dementia: MAC deposition found in FTD brain tissue
- Huntington's Disease: Complement proteins upregulated in HD brain
Expression
Tissue Distribution
- Liver: Primary site of complement protein synthesis
- Brain: Expressed by [astrocytes](/entities/astrocytes) and [microglia](/cell-types/microglia-neuroinflammation), particularly under inflammatory conditions
- Kidney: Local synthesis in glomerular cells
- Lung: Expression in alveolar epithelial cells
- Immune cells: Monocytes and macrophages can produce C7
Regulation
C7 expression is regulated by:
- Inflammatory cytokines (IL-6, TNF-α, IFN-γ) upregulate hepatic C7 synthesis
- Acute phase response increases C7 levels 2-3 fold
- Glucocorticoids can suppress complement expression
- Aging is associated with dysregulated complement activity
Clinical Significance
C7 Deficiency
Complete C7 deficiency is rare but leads to:
- Severe susceptibility to Neisseria infections
- Increased risk of meningitis and sepsis
- Generally normal immune function otherwise
Therapeutic Implications
Given the role of complement in neurodegeneration, complement inhibitors are being investigated:
- Eculizumab and ravulizumab (anti-C5) are approved for other conditions
- Anti-C7 therapeutics are in development
- Gene therapy approaches for complement deficiency are experimental
Molecular Mechanisms
The complement cascade leads to MAC assembly:
Mermaid diagram (expand to render)
C7 Structure
C7 has distinct structural features:
N-terminal domain: Interaction with C5b-6
Thiolester domain: Covalent bonding
C-terminal domain: Membrane interactionRegulation
C7 activity is tightly controlled:
- Fluid phase: Limited to prevent self-damage
- Membrane regulation: CD55, CD59 control
- Soluble regulators: Vitronectin, clusterin
Genetics
Common Variants
- Various single nucleotide polymorphisms (SNPs) in the C7 gene have been identified
- Some variants may affect complement activity levels
- Associations with autoimmune diseases (SLE, rheumatoid arthritis) reported
Population Genetics
Disease Associations Summary
C7 and complement in neurodegeneration:
| Disease | Evidence | Role |
|---------|----------|------|
| Alzheimer's | Strong | Synaptic pruning, amyloid clearance |
| Parkinson's | Moderate | Dopaminergic neuron vulnerability |
| ALS | Moderate | Motor neuron complement activation |
| MS | Strong | Demyelination, lesion formation |
Summary
Core Points
C7 is a terminal complement component:
MAC formation: Essential for membrane pore formation
Immune defense: Bacterial killing, cell lysis
Neuroinflammation: Synaptic elimination, disease
Therapeutic target: Drug development activeTherapeutic Potential
Complement inhibition strategies:
C5 inhibitors: Eculizumab, ravulizumab
C1q inhibitors: In development
C3 inhibitors: In development
MAC inhibitors: Future directionsReferences
- C7 shows moderate polymorphism across populations
- Deficiency alleles are rare (1:1,000,000)
Background
The study of C7 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.
External Links
- [NCBI Gene: C7](https://www.ncbi.nlm.nih.gov/gene/719)
- [UniProt: C7](https://www.uniprot.org/uniprot/P10643)
- [OMIM: C7](https://omim.org/entry/217070)
- [Ensembl: C7](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124429)
- [GeneCards: C7](https://www.genecards.org/cgi-bin/carddisp.pl?gene=C7)
References
Unknown, NCBI Gene: C7 (719) (n.d.)
Unknown, UniProt: Complement component C7 (P10643) (n.d.)
[Staiko et al., Complement activation in Alzheimer's disease (2019) (2019)](https://doi.org/10.1007/s00401-019-01998-x)
[Riddell et al., Complement in Alzheimer's disease (2020) (2020)](https://doi.org/10.1016/j.jneuroim.2020.577258)
[Gebbink et al., Complement activation in Parkinson's disease (2021) (2021)](https://doi.org/10.1007/s00401-021-02285-4)
[Rus et al., Complement in demyelinating disease (2006) (2006)](https://doi.org/10.1093/brain/awl006)
[Stahel et al., Complement membrane attack complex (2000) (2000)](https://doi.org/10.1016/s0165-5728(00)
[Michailidou et al., Complement C7 and Alzheimer disease risk (2018) (2018)](https://pubmed.ncbi.nlm.nih.gov/29561451/)
[Watowich et al., Structure and function of complement component C7 (1995) (1995)](https://pubmed.ncbi.nlm.nih.gov/7561018/)