C3 — Complement Component 3

C3 — Complement Component 3

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">C3 — Complement Component 3</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>C3</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>C3 — Complement Component 3</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=C3" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/alzheimers_disease" style="color:#ef9a9a">ALZHEIMERS_DISEASE</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's Disease</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's disease</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">281 edges</a></td>
</tr>
</table>

C3 — Complement Component 3 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Official Symbol: C3 [@complement2021] Official Full Name: Complement Component 3 [@als2021] Gene ID: 735 [@alternative2020] Chromosomal Location: 19p13.3 [@therapeutic2021] Protein: Complement C3

Pathway Diagram

C3 — Complement Component 3

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">C3 — Complement Component 3</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>C3</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>C3 — Complement Component 3</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=C3" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/alzheimers_disease" style="color:#ef9a9a">ALZHEIMERS_DISEASE</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's Disease</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">Alzheimer's disease</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">281 edges</a></td>
</tr>
</table>

C3 — Complement Component 3 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

Official Symbol: C3 [@complement2021] Official Full Name: Complement Component 3 [@als2021] Gene ID: 735 [@alternative2020] Chromosomal Location: 19p13.3 [@therapeutic2021] Protein: Complement C3

Pathway Diagram

Overview

The C3 gene encodes complement component 3 (C3), the central protein of the [complement system](/entities/complement-system). C3 is the most abundant complement protein in serum and plays a pivotal role in all three complement activation pathways (classical, lectin, and alternative). Upon activation, C3 is cleaved into C3a (anaphylatoxin) and C3b (opsonin), which mediate downstream immune responses.

Gene Structure

The C3 gene spans approximately 42 kb on chromosome 19p13.3 and consists of 41 exons. The coding sequence is distributed across multiple exons, with alternative splicing producing multiple isoforms. The gene encodes a 1,663 amino acid preproprotein that undergoes significant post-translational modification.

Protein Structure

C3 is synthesized as a preproprotein consisting of:

• Alpha chain (~110 kDa)
• Beta chain (~70 kDa)
• Disulfide bonds linking the chains

• C3a: 9 kDa anaphylatoxin
• C3b: 176 kDa opsonin

Molecular Function

C3 and its fragments mediate multiple immune functions:

• Opsonization: C3b covalently binds to pathogen surfaces, marking them for phagocytosis
• Anaphylatoxin activity: C3a triggers mast cell degranulation and inflammation
• Immune complex clearance: C3b facilitates removal of immune complexes
• B cell activation: C3d acts as a adjuvant for B cell receptor signaling
• Alternative pathway amplification: C3bBb convertase generates more C3b

Expression Pattern

C3 is primarily synthesized in the liver (hepatocytes) but also produced locally by:

• Macrophages and monocytes
• [Microglia](/entities/microglia) and [astrocytes](/entities/astrocytes) in the brain
• Dendritic cells
• Endothelial cells
• Adipocytes

Role in Neurodegeneration

Alzheimer's Disease

• C3 is elevated in AD brain and CSF
• C3b localizes to amyloid plaques and NFT
• Complement-mediated synaptic pruning contributes to memory loss
• C3a receptor signaling affects microglial activation

Parkinson's Disease

• C3 is upregulated in substantia nigra
• Complement activation contributes to dopaminergic neuron death
• C3a may modulate neuroinflammation

Amyotrophic Lateral Sclerosis

• C3 is increased in ALS spinal cord
• Complement activation accelerates motor neuron degeneration
• C5-C5aR signaling implicated in ALS pathogenesis

Multiple Sclerosis

• C3 contributes to demyelination
• Complement inhibitors reduce disease severity in animal models
• C3a drives pro-inflammatory microglial activation

Age-Related Macular Degeneration

• C3 variants increase AMD risk
• Complement activation in retinal pigment epithelium

Therapeutic Implications

C3 is a promising therapeutic target:

• C3 inhibitors: Pegylated C3 inhibitor (PEG-C3) in development
• Compstatin analogs: Cyclic peptides inhibiting C3 cleavage
• C3a receptor antagonists: Block pro-inflammatory signaling
• Gene therapy: AAV-delivered C3 inhibitors

Animal Models

• C3 knockout mice: Viable but susceptible to infections
• C3 transgenic mice: Show enhanced pathology in neurodegenerative models
• C3a receptor knockout: Protected against neuroinflammation

Background

The study of C3 — Complement Component 3 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

• [C3 Gene Database](https://www.ncbi.nlm.nih.gov/gene/735)
• [UniProt P01024](https://www.uniprot.org/uniprot/P01024)
• [OMIM 120700](https://www.omim.org/entry/120700)
• [Human Protein Atlas](https://www.proteinatlas.org/ENSG00000125730-C3)

References

Related Hypotheses

From the [SciDEX Exchange](/exchange) — scored by multi-agent debate

• [SASP-Mediated Complement Cascade Amplification](/hypothesis/h-58e4635a) — <span style="color:#81c784;font-weight:600">0.71</span> · Target: C1Q/C3

Pathway Diagram

The following diagram shows the key molecular relationships involving C3 — Complement Component 3 discovered through SciDEX knowledge graph analysis: