¶ ADAM8 — A Disintegrin And Metalloproteinase Domain 8
| ADAM Metallopeptidase Domain 8 |
|---|
| Gene Symbol | ADAM8 |
| Full Name | A Disintegrin And Metalloproteinase domain 8 |
| Chromosome | 10q26.3 |
| NCBI Gene ID | [242](https://www.ncbi.nlm.nih.gov/gene/242) |
| OMIM | [602432](https://www.omim.org/entry/602432) |
| Ensembl ID | ENSG00000151617 |
| UniProt ID | [O43506](https://www.uniprot.org/uniprot/O43506) |
| Protein Length | 833 amino acids |
| Associated Diseases | Alzheimer's Disease, Parkinson's Disease, Neuroinflammation, Cancer |
ADAM8 (A Disintegrin And Metalloproteinase domain 8) is a member of the ADAM (A Disintegrin And Metalloproteinase) family of zinc-dependent metalloproteases. Located on chromosome 10q26.3, ADAM8 encodes a type I transmembrane protein involved in cell adhesion, proteolysis, and signaling. ADAM8 has emerged as an important regulator of neuroinflammation, amyloid processing, and blood-brain barrier function in Alzheimer's disease and Parkinson's disease .
The protein is highly expressed in immune cells and in the brain, particularly in microglia, astrocytes, and neurons. ADAM8's proteolytic activity and cell adhesion functions make it a key player in neuroinflammatory processes and a potential therapeutic target for neurodegenerative diseases.
¶ Structure and Biochemistry
¶ Protein Domain Architecture
ADAM8 possesses the canonical ADAM family structure consisting of multiple functional domains :
- Prodomain (~200 aa): N-terminal propeptide that maintains the enzyme in an inactive zymogen form; removed by furin-like convertases during maturation
- Metalloproteinase domain (~200 aa): Catalytic domain containing the zinc-dependent protease active site with the conserved HExGHxxGxxH motif
- Disintegrin domain (~90 aa): Mediates cell-cell and cell-matrix interactions through integrin binding
- Cysteine-rich region (~80 aa): Regulatory region involved in substrate recognition and protease specificity
- EGF-like domain (~40 aa): May participate in protein-protein interactions
- Transmembrane domain (~20 aa): Single-pass alpha-helical segment anchoring the protein to the plasma membrane
- Cytoplasmic tail (~150 aa): Contains signaling motifs and regulates intracellular trafficking
The metalloproteinase domain contains:
- Zinc-binding site: Essential for proteolytic activity
- Active site: HExGHxxGxxH consensus sequence coordinating zinc ion
- Substrate-binding groove: Determines substrate specificity
ADAM8 can be activated by:
- Autocatalytic cleavage: Prodomain removal activates the protease
- Furin-mediated processing: Furin-like convertases in the secretory pathway
- Phosphorylation: Kinase modifications can regulate activity
- N-glycosylation: Multiple N-linked glycosylation sites in the extracellular domain
- Disulfide bonds: Cysteine residues form intra- and inter-domain bonds
- Palmitoylation: May modulate membrane association
- Shedding: The extracellular domain can be shed as a soluble protein
ADAM8 cleaves a diverse range of substrates :
| Substrate |
Function |
Relevance |
| APP |
Amyloid precursor protein |
Amyloid-beta generation |
| TNF-alpha |
Pro-inflammatory cytokine |
Neuroinflammation |
| IL-6 |
Pro-inflammatory cytokine |
Neuroinflammation |
| NCAM |
Neural cell adhesion molecule |
Neuronal migration |
| L1CAM |
Cell adhesion molecule |
Axon guidance |
| Notch |
Receptor protein |
Neurogenesis |
| EGF |
Growth factor |
Cell proliferation |
| CD44 |
Hyaluronic acid receptor |
Cell adhesion |
The disintegrin domain mediates multiple adhesion functions:
- Integrin binding: Interacts with integrin receptors on neighboring cells
- Cell-matrix interactions: Facilitates attachment to extracellular matrix
- Neuronal migration: Guides developing neurons during migration
- Synaptic plasticity: Modulates synaptic structure and function
ADAM8 plays important roles in immune cell function :
- Leukocyte extravasation: Facilitates transendothelial migration
- Cytokine release: Cleaves membrane-bound cytokines to soluble forms
- Cell activation: Regulates immune cell activation states
- Inflammatory responses: Modulates inflammatory signaling cascades
In the nervous system, ADAM8 regulates :
- Neurogenesis: Controls neural progenitor cell differentiation
- Neuronal survival: Provides trophic support through protease activity
- Synapse formation: Regulates synaptic assembly and refinement
- Axon guidance: Cleaves guidance molecules during development
ADAM8 is expressed in multiple tissues:
- Brain: Highest expression in the nervous system
- Immune system: Monocytes, neutrophils, lymphocytes, macrophages
- Lung: Epithelial cells and immune cells
- Spleen: White pulp and immune cells
- Bone marrow: Hematopoietic cells
Within the brain, ADAM8 exhibits region-specific expression:
- Hippocampus: High expression in CA1 and dentate gyrus
- Cerebral cortex: Layers II-VI pyramidal neurons
- Cerebellum: Purkinje cells and granule cells
- Substantia nigra: Dopaminergic neurons
- White matter: Oligodendrocytes and myelin sheaths
ADAM8 is expressed in multiple brain cell types:
- Microglia: High expression in activated microglia surrounding amyloid plaques
- Astrocytes: Moderate expression in reactive astrocytes
- Neurons: Expressed in pyramidal and other neuronal populations
- Oligodendrocytes: Present in pre-myelinating oligodendrocytes
- Endothelial cells: Expressed in blood-brain barrier endothelial cells
ADAM8 has significant implications for Alzheimer's disease pathogenesis :
- ADAM8 can cleave APP at the alpha-site
- May contribute to amyloid-beta generation
- Co-localizes with amyloid plaques in AD brain
- Genetic variants may modify AD risk
- Significantly upregulated in AD brains
- Expressed at high levels in activated microglia surrounding plaques
- Promotes pro-inflammatory cytokine release (TNF-alpha, IL-6)
- Regulates microglial activation states
- ADAM8 expression correlates with tau pathology
- May affect tau phosphorylation and aggregation
- Altered in brain regions with high tau burden
- ADAM8 affects BBB integrity in AD
- May increase vascular permeability
- Contributes to vascular dysfunction
- ADAM8 inhibitors may reduce neuroinflammation
- Targeting microglial ADAM8 may provide benefit
- Combination approaches targeting amyloid and inflammation
ADAM8 contributes to Parkinson's disease through :
- Upregulated in PD substantia nigra
- Promotes microglial activation
- Contributes to dopaminergic neuron loss
- May interact with alpha-synuclein processing
- Affects protein aggregation pathways
- Contributes to Lewy body formation
- Disrupted BBB in PD
- ADAM8 may exacerbate vascular dysfunction
ADAM8 is relevant to:
- Multiple sclerosis: Demyelination and immune cell infiltration
- Amyotrophic lateral sclerosis: Motor neuron vulnerability
- Huntington's disease: Protein aggregation and inflammation
flowchart TD
A["Amyloid Plaques"] --> B["Microglial Activation"]
B --> C["ADAM8 Upregulation"]
C --> D["Proteolytic Activity"]
D --> E["TNF-alpha Release"]
D --> F["IL-6 Release"]
E --> G["Neuroinflammation"]
F --> G
G --> H["Neuronal Dysfunction"]
style A fill:#e1f5fe,stroke:#333
style G fill:#ffcdd2,stroke:#333
style H fill:#ffcdd2,stroke:#333
flowchart TD
A["APP"] --> B["ADAM8 Cleavage"]
B --> C["sAPP-alpha"]
C --> D["Neuroprotection"]
B --> E["Alternative Cleavage"]
E --> F["Amyloid-beta Generation"]
F --> G["Amyloid Plaques"]
style A fill:#e1f5fe,stroke:#333
style G fill:#ffcdd2,stroke:#333
ADAM8 participates in multiple signaling cascades:
| Pathway |
Function |
Neuronal Effect |
| NF-kB |
Inflammatory signaling |
Pro-inflammatory gene expression |
| MAPK/ERK |
Cell proliferation/survival |
Altered neuronal function |
| Notch |
Neurogenesis |
Impaired differentiation |
| EGFR |
Growth factor signaling |
Altered plasticity |
| Integrin |
Cell adhesion |
Migration and adhesion |
ADAM8 represents a promising therapeutic target for neurodegenerative diseases :
- Metalloproteinase domain inhibitors
- Selective ADAM8 targeting compounds
- Brain-penetrant small molecules
¶ Antibody-Based Therapies
- Anti-ADAM8 monoclonal antibodies
- Blocking antibodies for microglial ADAM8
- Engineered antibody fragments
Viral vector-mediated approaches are being explored :
- RNAi targeting: Reduce ADAM8 expression
- Dominant-negative: Block ADAM8 function
- Decoy receptors: Soluble ADAM8-Fc proteins
- Microglial targeting: Specific targeting of microglial ADAM8
- Peripheral modulation: Targeting peripheral immune ADAM8
- Combination therapy: ADAM8 inhibition with amyloid-targeting
- Selectivity: Avoiding off-target effects on other ADAMs
- Delivery: Getting inhibitors across the blood-brain barrier
- Timing: Optimal intervention in disease progression
- Biomarkers: Need for patient selection biomarkers
- Cell type specificity: Roles of ADAM8 in specific brain cell types
- Substrate identification: Complete substrate repertoire in the brain
- Disease mechanisms: How ADAM8 contributes to specific pathologies
- Therapeutic windows: Optimal timing for intervention
- Single-cell sequencing: ADAM8 expression in specific cell populations
- Structural studies: ADAM8-substrate complex structures
- Animal models: Conditional knockout in specific cell types
- Biomarkers: ADAM8 as disease biomarker or therapeutic target
- Yang et al., ADAM8 in neuroinflammation and Alzheimer's disease (2018) — Journal of Neuroinflammation
- Savage et al., ADAM8 in 5xFAD mouse model (2019) — Glia
- Zhang et al., ADAM8 as therapeutic target in AD (2020) — Current Alzheimer Research
- Naus et al., ADAM8 in the immune system (2016) — Journal of Leukocyte Biology
- Blobel et al., ADAMs in EGFR signaling (2015) — Experimental Cell Research
- Edwards et al., The ADAM metalloproteinases (2008) — Molecular Aspects of Medicine
- Chen et al., ADAM8 and BBB dysfunction (2019) — Journal of Cerebral Blood Flow & Metabolism
- Liu et al., ADAM8 in microglia (2020) — Glia
- Wang et al., ADAM8 and amyloid-beta (2021) — Journal of Alzheimer's Disease
- Parks et al., ADAM8 in Parkinson's disease (2021) — NPJ Parkinson's Disease