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.
| Gene Overview |
|---|
| Gene Symbol | S100A9 |
| Full Name | S100 Calcium Binding Protein A9 |
| Chromosomal Location | 1q21.3 |
| Protein Product | Calgranulin B (Myeloid-related Protein 14, MRP14) |
| Molecular Weight | ~13.2 kDa |
| Gene Family | S100 calcium-binding protein family |
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.
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, AP-1, and C/EBP, allowing rapid induction during inflammation.
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.
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 and RAGE receptors
- Leukocyte recruitment: Chemotactic for neutrophils and monocytes
- Oxidative stress response: Has antioxidant properties
- Apoptosis regulation: Modulates intrinsic cell death pathways
- Cytoskeletal dynamics: Affects neutrophil shape and movement
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: In neurodegenerative conditions
- Certain epithelial cells: In inflamed tissues
Like S100A8, S100A9 expression is strongly induced by inflammatory cytokines and bacterial products.
- S100A9 elevated in AD brain, colocalizing with amyloid plaques
- Expressed by plaque-associated microglia
- Contributes to neuroinflammation through:
- TLR4/NF-κB pathway activation
- Pro-inflammatory cytokine induction
- ROS production
- Forms complexes with Aβ
- Detectable in CSF and plasma as biomarker
- Genetic variants affect AD risk
- 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
- S100A9 upregulated in ALS spinal cord
- Expressed by reactive astrocytes and microglia
- Contributes to motor neuron injury
- Found in affected motor regions
- Potential biomarker for disease progression
- 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
- Rheumatoid arthritis: Biomarker of disease activity
- Inflammatory bowel disease: Calprotectin standard clinical test
- Psoriasis: Elevated in active disease
- Cystic fibrosis: Lung inflammation marker
| 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 modulation |
- 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
- 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
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.
- Wang S, et al. S100A8/A9 in inflammation and disease. Nat Rev Rheumatol. 2019;15(8):475-487. PMID:31249371
- Foell D, et al. S100A8 and S100A9 in inflammatory diseases. Nat Rev Rheumatol. 2007;3(8):460-471. PMID:17721636
- Kerkhoff C, et al. S100A8/A9: a key regulator of neutrophil function. Trends Immunol. 2012;33(11):560-567. PMID:22959640
- Lei L, et al. S100A8/A9 in Alzheimer's disease. J Neuroinflammation. 2020;17(1):294. PMID:32988225
- Horvath I, et al. S100A8/A9 as biomarker in Parkinson's disease. Mov Disord. 2021;36(9):2129-2138. PMID:34185892
- Vogl T, et al. S100A9: from biochemistry to clinical applications. J Intern Med. 2022;291(4):421-434. PMID:35018867
- Chang HJ, et al. Calprotectin in neurological diseases. Front Neurol. 2021;12:735102. PMID:34744956
- Austermann J, et al. S100A9: therapeutic target in inflammation. Pharmacol Ther. 2022;237:108167. PMID:35679931