C7

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.

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:

Disease 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

Membrane Attack Complex Formation

The complement cascade leads to MAC assembly:

C7 Structure

C7 has distinct structural features:

Regulation

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:

Therapeutic Potential

Complement inhibition strategies:

References

• 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