S100A9 - S100 Calcium Binding Protein A9

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S100A9 Gene

Pathway Diagram

flowchart TD S100A9["S100A9"] Neuroinflammation["Neuroinflammation"] S100A9 -->|"involved_in"| Neuroinflammation APOPTOSIS["APOPTOSIS"] S100A9 -->|"exacerbates"| APOPTOSIS Inflammation["Inflammation"] S100A9 -->|"participates_in"| Inflammation TLR4["TLR4"] S100A9 -->|"binds"| TLR4 RAGE["RAGE"] S100A9 -->|"binds"| RAGE ALI["ALI"] S100A9 -->|"activates"| ALI ALDH1A1["ALDH1A1"] S100A9 -->|"activates"| ALDH1A1 brain_metastasis["brain metastasis"] S100A9 -->|"activates"| brain_metastasis HBV["HBV"] HBV -->|"associated with"| S100A9 style S100A9 fill:#1a237e,stroke:#4fc3f7,color:#4fc3f7 style Neuroinflammation fill:#e65100,stroke:#ff8a65,color:#ff8a65 style APOPTOSIS fill:#263238,stroke:#90a4ae,color:#90a4ae style Inflammation fill:#263238,stroke:#90a4ae,color:#90a4ae style TLR4 fill:#263238,stroke:#90a4ae,color:#90a4ae style RAGE fill:#263238,stroke:#90a4ae,color:#90a4ae style ALI fill:#4a0000,stroke:#ef5350,color:#ef5350 style ALDH1A1 fill:#1a237e,stroke:#4fc3f7,color:#4fc3f7 style brain_metastasis fill:#e65100,stroke:#ff8a65,color:#ff8a65 style HBV fill:#263238,stroke:#90a4ae,color:#90a4ae

Knowledge graph relationships for S100A9 (292 total edges in KG)

Introduction

S100A9 S100 Calcium Binding Protein A9 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

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S100A9 Gene

Pathway Diagram

Mermaid diagram (expand to render)

Knowledge graph relationships for S100A9 (292 total edges in KG)

Introduction

<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#f0f0f0;">Gene Overview</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>S100A9</td></tr>
<tr><td><strong>Full Name</strong></td><td>S100 Calcium Binding Protein A9</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>1q21.3</td></tr>
<tr><td><strong>Protein Product</strong></td><td>Calgranulin B (Myeloid-related Protein 14, MRP14)</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~13.2 kDa</td></tr>
<tr><td><strong>Gene Family</strong></td><td>S100 calcium-binding protein family</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ali" style="color:#ef9a9a">ALI</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/atherosclerosis" style="color:#ef9a9a">Atherosclerosis</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">138 edges</a></td>
</tr>
</table>
</div>

Overview

The S100A9 gene encodes Calgranulin B, also known as Myeloid-related Protein 14 (MRP14) or S100A9. Like its partner S100A8, S100A9 is a calcium-binding protein of the S100 family. S100A9 can form both homodimers and heterodimers with S100A8, with the S100A8/A9 heterodimer (calprotectin) being the biologically most active form. This protein plays critical roles in inflammation, immune defense, and more recently, in neurodegenerative diseases.

Gene Structure

The S100A9 gene is located in the S100 gene cluster on chromosome 1q21.3, adjacent to S100A8. The gene consists of 3 exons encoding a 113-amino acid protein. The promoter region contains binding sites for transcription factors including [NF-κB](/entities/nf-kb), AP-1, and C/EBP, allowing rapid induction during inflammation.

Protein Structure

The S100A9 protein contains:

EF-hand I (pseudo): N-terminal non-functional calcium-binding site
EF-hand II (canonical): C-terminal functional calcium-binding site
Hydrophobic patches: Mediate interaction with S100A8 and target proteins
C-terminal extension: Involved in dimerization and target recognition

The S100A8/A9 heterodimer (calprotectin) forms a structural basis for metal sequestration and receptor interactions.

Normal Function

S100A9, particularly as part of calprotectin (S100A8/A9), has diverse functions:

Antimicrobial defense: Withholds zinc and manganese from pathogens (nutritional immunity)

Pro-inflammatory signaling: Activates [TLR4](/entities/tlr4) and [RAGE](/genes/rage) receptors

Leukocyte recruitment: Chemotactic for neutrophils and monocytes

Oxidative stress response: Has antioxidant properties

[Apoptosis](/entities/apoptosis) regulation: Modulates intrinsic cell death pathways

Cytoskeletal dynamics: Affects neutrophil shape and movement

Expression Pattern

S100A9 is expressed in:

Neutrophils: Second most abundant cytosolic protein (40% of S100A8 amount)
Monocytes and macrophages: Induced during inflammation
Myeloid dendritic cells: At sites of immune activation
Activated [microglia](/entities/microglia): In neurodegenerative conditions
Certain epithelial cells: In inflamed tissues

Like S100A8, S100A9 expression is strongly induced by inflammatory cytokines and bacterial products.

Role in Disease

Alzheimer's Disease

S100A9 elevated in AD brain, colocalizing with amyloid plaques
Expressed by plaque-associated [microglia](/cell-types/microglia-neuroinflammation)
Contributes to neuroinflammation through:
TLR4/NF-κB pathway activation
Pro-inflammatory cytokine induction
[ROS](/entities/reactive-oxygen-species) production
Forms complexes with [Aβ](/proteins/amyloid-beta)
Detectable in CSF and plasma as biomarker
Genetic variants affect AD risk

Parkinson's Disease

Increased S100A9 in substantia nigra of PD patients
Associated with Lewy body pathology
Produced by activated microglia
Contributes to dopaminergic neuron degeneration
Correlates with disease duration and severity

Amyotrophic Lateral Sclerosis

S100A9 upregulated in ALS spinal cord
Expressed by reactive [astrocytes](/entities/astrocytes) and microglia
Contributes to motor neuron injury
Found in affected motor regions
Potential biomarker for disease progression

Multiple Sclerosis

S100A9/MSR in active MS lesions
Contributes to demyelination and axonal loss
Elevated in CSF during relapses
Predicts conversion from CIS to MS
Therapeutic target in development

Inflammatory Diseases

Rheumatoid arthritis: Biomarker of disease activity
Inflammatory bowel disease: Calprotectin standard clinical test
Psoriasis: Elevated in active disease
Cystic fibrosis: Lung inflammation marker

Therapeutic Implications

| Approach | Status | Notes |
|----------|--------|-------|
| Anti-S100A9 antibodies | Preclinical | Block inflammatory signaling |
| TLR4/RAGE antagonists | Clinical | Downstream pathway inhibition |
| Metal chelation therapy | Research | Target metal sequestration |
| Kinase inhibitors | Preclinical | JAK, [CDK5](/proteins/cdk5-protein) modulation |

Biomarker Applications

Calprotectin test: FDA-approved for IBD monitoring
Neurological disease: S100A8/A9 in CSF and plasma
Treatment monitoring: Levels change with therapy
Prognostic indicator: Correlates with outcomes

Key Research Directions

Receptor biology: Characterizing S100A9 receptors and signaling

Intracellular functions: Non-secreted roles in cell biology

Therapeutic targeting: Specific inhibitors and antibodies

Biomarker development: Validation in large cohorts

Genetic studies: GWAS for neurodegenerative diseases

Background

The study of S100A9 S100 Calcium Binding Protein A9 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 - S100A9](https://www.ncbi.nlm.nih.gov/gene)
[UniProt - S100A9](https://www.uniprot.org)
[PubMed](https://pubmed.ncbi.nlm.nih.gov)

References

[Wang S, et al, S100A8/A9 in inflammation and disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31249371/)

[Foell D, et al, S100A8 and S100A9 in inflammatory diseases (2007)](https://pubmed.ncbi.nlm.nih.gov/17721636/)

[Kerkhoff C, et al, S100A8/A9: a key regulator of neutrophil function (2012)](https://pubmed.ncbi.nlm.nih.gov/22959640/)

[Lei L, et al, S100A8/A9 in Alzheimer's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32988225/)

[Horvath I, et al, S100A8/A9 as biomarker in Parkinson's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34185892/)

[Vogl T, et al, S100A9: from biochemistry to clinical applications (2022)](https://pubmed.ncbi.nlm.nih.gov/35018867/)

[Chang HJ, et al, Calprotectin in neurological diseases (2021)](https://pubmed.ncbi.nlm.nih.gov/34744956/)

[Austermann J, et al, S100A9: therapeutic target in inflammation (2022)](https://pubmed.ncbi.nlm.nih.gov/35679931/)

Pathway Diagram

The following diagram shows the key molecular relationships involving S100A9 - S100 Calcium Binding Protein A9 discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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S100A9 - S100 Calcium Binding Protein A9

S100A9 Gene

Pathway Diagram

Introduction

S100A9 Gene

Pathway Diagram

Introduction

Overview

Gene Structure

Protein Structure

Normal Function

Expression Pattern

Role in Disease

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis

Multiple Sclerosis

Inflammatory Diseases

Therapeutic Implications

Biomarker Applications

Key Research Directions

Background

See Also

External Links

References

Pathway Diagram