ADAM23 (A Disintegrin And Metalloproteinase domain 23) is a catalytically inactive member of the ADAM family expressed primarily in the brain. Located on chromosome 2q33.3, ADAM23 plays critical roles in neuronal development, synaptic function, and cell-cell adhesion, with emerging associations to Alzheimer's Disease (AD) and Parkinson's Disease (PD)[1][2][3].
Unlike catalytically active ADAMs, ADAM23 functions primarily as a regulator of cell adhesion and signaling through its disintegrin and cysteine-rich domains. This "ligand" role allows ADAM23 to modulate interactions between neurons and their environment without direct proteolytic activity, making it a unique target for understanding neurodevelopment and neurodegeneration[4][5].
¶ Gene and Protein Structure
¶ Gene Location and Organization
The ADAM23 gene is located at chromosome 2q33.3, spanning approximately 15 kb of genomic DNA. Key identifiers include:
| Identifier |
Value |
| Gene Symbol |
ADAM23 |
| Full Name |
ADAM metallopeptidase domain 23 |
| NCBI Gene ID |
5385 |
| OMIM ID |
603346 |
| Ensembl ID |
ENSG00000108439 |
| UniProt ID |
O75077 |
| Chromosomal Location |
2q33.3 |
The gene consists of 24 exons encoding a type I transmembrane protein. The genomic region shows evolutionary conservation, particularly in the disintegrin and cysteine-rich domains[1].
¶ Protein Domain Architecture
ADAM23 contains the characteristic ADAM family domains, but with key differences due to its catalytic inactivity:
Signal Prodomain Metalloproteinase Disintegrin Cysteine-rich Transmembrane Cytoplasmic
peptide (inactive) domain region domain tail
↓ ↓ ↓ ↓ ↓ ↓ ↓
[1-19] [20-213] [214-463] [464-596] [597-666] [667-689] [690-834]
- Signal peptide (1-19): Directs protein to secretory pathway
- Prodomain (20-213): Maintains proper folding; contains cysteine switch
- Metalloproteinase domain (214-463): Contains critical mutations (E→D in active site) rendering it catalytically inactive. However, the domain structure is preserved and may contribute to protein stability.
- Disintegrin domain (464-596): High-affinity binding to integrins and other ADAMs. Contains the RGD motif recognition site.
- Cysteine-rich region (597-666): Contains multiple disulfide bonds stabilizing protein-protein interactions
- Transmembrane domain (667-689): Single-pass membrane anchor
- Cytoplasmic tail (690-834): Contains signaling motifs including:
- Proline-rich regions (PXXP motifs) for SH3 domain binding
- Potential phosphorylation sites
- PDZ domain-binding motif at C-terminus
The inactive metalloproteinase domain is a defining feature of ADAM23, distinguishing it from catalytically active ADAMs like ADAM17 and ADAM10. This inactivation results from critical residue substitutions in the zinc-binding motif[6].
ADAM23 functions as a key mediator of cell-cell and cell-matrix adhesion in the nervous system[7][8]:
The disintegrin domain of ADAM23 interacts with multiple integrin subunits:
- αvβ3: Vitronectin receptor expressed on neurons and glia
- α5β1: Fibronectin receptor
- α6β1: Laminin receptor
- α3β1: Collagen/laminin receptor
These interactions regulate:
- Neuronal migration during development
- Axon guidance and fasciculation
- Synapse formation and maintenance
- Glial-neuronal interactions
¶ Homophilic and Heterophilic Interactions
ADAM23 can engage in:
- Homophilic interactions: ADAM23-ADAM23 binding on adjacent cells
- Heterophilic interactions: Binding to other ADAM family members (e.g., ADAM11, ADAM22)
- Heterodimer formation: Complex formation with other disintegrin-containing proteins
During cortical development, ADAM23 regulates neuronal migration through multiple mechanisms[9]:
- Radial migration: Guides neurons along radial glial fibers from ventricular zone to cortical plate
- Terminal translocation: Controls final positioning of neurons in the cortical plate
- Layer-specific targeting: Expression patterns correlate with specific cortical layer formation
The disintegrin domain mediates interactions with the extracellular matrix and neighboring cells, providing guidance cues for migrating neurons.
ADAM23 localizes to synaptic membranes where it plays critical roles in synaptic formation, maintenance, and plasticity[10]:
- Recruits synaptic adhesion molecules to nascent synapses
- Promotes dendritic spine formation
- Facilitates presynaptic terminal differentiation
¶ Synaptic Maintenance
- Stabilizes synaptic contacts through adhesion interactions
- Regulates synaptic protein composition
- Maintains spine morphology
- Modulates activity-dependent structural changes
- Influences LTP (long-term potentiation)
- Affects learning and memory processes
ADAM23 participates in multiple signaling pathways:
- Intracellular calcium signaling: Modulates calcium dynamics at synapses
- MAPK/ERK pathway: Involved in neuronal differentiation and survival
- PI3K/Akt pathway: Promotes neuronal survival
- Rho GTPase signaling: Regulates cytoskeletal dynamics
ADAM23 exhibits dynamic expression patterns during development:
- Embryonic day 12-14 (E12-E14): Low expression in neural tube
- E15-E18: Increasing expression in cortical plate
- Postnatal day 0-7 (P0-P7): Peak expression in cortex and hippocampus
- P14-P21: Gradual decline to adult levels
This developmental profile suggests critical roles in cortical and hippocampal development[4].
In the adult brain, ADAM23 expression is highest in:
| Brain Region |
Expression Level |
Cell Types |
| Cerebral Cortex |
High |
Pyramidal neurons, interneurons |
| Hippocampus |
High |
CA1, CA3 pyramidal cells, dentate gyrus granule cells |
| Cerebellum |
Moderate |
Purkinje cells, granule cells |
| Subventricular Zone |
High |
Neural stem cells, transit-amplifying cells |
| Olfactory Bulb |
Moderate |
Mitral cells, granule cells |
| Thalamus |
Low-Moderate |
Thalamic relay neurons |
| Basal Ganglia |
Low-Moderate |
Medium spiny neurons |
- Neurons: Predominantly in soma and dendrites, enriched in dendritic spines
- Astrocytes: Limited expression, primarily at astrocyte-neuron interfaces
- Neural stem cells: High expression in subventricular zone progenitors
- Oligodendrocytes: Very low or absent
ADAM23 has emerged as a gene of interest in AD pathogenesis through multiple mechanisms[3][11][12]:
- Reduced ADAM23 expression in AD brain tissue (particularly in hippocampus and cortex)
- Correlation between ADAM23 levels and disease severity
- Expression changes in early vs. late AD stages
ADAM23 localizes to synaptic membranes where it may regulate:
- Synaptic protein composition: Altered levels of postsynaptic density proteins
- Spine morphology: Reduced spine density and abnormal spine shapes
- Synaptic signaling: Impaired glutamate receptor trafficking
While not directly involved in amyloid precursor protein (APP) processing:
- ADAM23 may influence amyloid-beta (Aβ) toxicity through synaptic effects
- Interactions with APP family proteins (APLP1, APLP2) are under investigation
- May affect neuronal vulnerability to Aβ-induced toxicity
Emerging evidence suggests potential interactions with tau protein pathology[13]:
- ADAM23 expression correlates with tau burden in some studies
- May affect tau-induced synaptic dysfunction
- Potential involvement in tau propagation mechanisms
Studies reveal ADAM23 promoter methylation changes in AD[14]:
- Hypermethylation associated with reduced expression
- Potential use as epigenetic biomarker
- Links to AD-related transcriptional dysregulation
ADAM23 involvement in PD is an emerging area of research[15]:
- Altered ADAM23 expression in substantia nigra dopaminergic neurons
- Potential role in dopaminergic neuron survival
- May affect vulnerability to PD-related stress
- Possible interactions with alpha-synuclein aggregation
- Effects on Lewy body formation
- May influence prion-like propagation
- ADAM23 in microglial-neuronal communication
- Potential modulation of neuroinflammatory responses
ADAM23 mutations and dysregulation are associated with:
- Lissencephaly spectrum: Cortical malformation disorders
- Intellectual disability: Cognitive impairment with or without seizures
- Autism spectrum disorders: Some cases associated with ADAM23 variants
- Epilepsy: Temporal lobe epilepsy linked to ADAM23 expression changes[16]
Interestingly, ADAM23 functions as a tumor suppressor in some contexts:
- Reduced expression in gliomas
- Epigenetic silencing in certain cancers
- Potential prognostic value
ADAM23 interacts with numerous proteins to mediate its functions[17]:
| Partner |
Interaction Domain |
Functional Consequence |
| Integrins (αvβ3, α5β1, α6β1) |
Disintegrin |
Cell adhesion and migration |
| ADAM11 |
Disintegrin |
Homophilic adhesion |
| ADAM22 |
Disintegrin |
Heterophilic interactions |
| APP/APLP family |
Unknown |
Potential signaling complex |
| PSD-95 |
Cytoplasmic |
Synaptic localization |
| Grb2 |
Cytoplasmic |
Signal transduction |
| p130Cas |
Cytoplasmic |
Adhesion signaling |
ADAM23 integrates into cellular signaling networks:
- Focal adhesion kinase (FAK) pathway: Integrin-mediated adhesion signaling
- Src family kinases: Downstream adhesion signaling
- PI3K/Akt pathway: Survival signaling
- MAPK/ERK pathway: Differentiation and growth signaling
ADAM23 has potential as a disease biomarker:
-
Cerebrospinal fluid (CSF) ADAM23:
- Altered levels in AD and PD
- Potential for disease diagnosis
- Correlation with disease progression
-
Blood-based markers:
- Exosomal ADAM23
- Peripheral blood monocyte expression
ADAM23-based therapeutic strategies include:
- Gene therapy: Modulating ADAM23 expression to protect synaptic function
- Protein engineering: Soluble ADAM23 domains as decoy receptors
- Small molecule modulators: Compounds targeting ADAM23-integrin interactions
- Antibody-based approaches: Agonists or antagonists of ADAM23 function
- Brain penetration required
- Selectivity for ADAM23 vs. other ADAMs
- Maintaining proper folding and trafficking
ADAM23 global knockout:
- Viable but with neurological phenotypes
- Impaired spatial learning and memory
- Altered synaptic plasticity
- Abnormal cortical development in some models
- ADAM23 overexpression: Enhanced synaptic function
- Reporter lines: Visualization of ADAM23 expression patterns
- Conditional knockouts: Cell-type-specific deletion
- ADAM23 in APP/PS1 mice: Crosses with AD models
- ADAM23 in α-synuclein models: PD-related studies
- Understanding catalytic inactivity: Why is ADAM23 catalytically inactive and what is the functional significance?
- Identifying all protein partners: Comprehensive interactome mapping
- Determining disease mechanisms: How does ADAM23 contribute to AD and PD?
- Developing therapeutic approaches: Targeting ADAM23 for neuroprotection
- Single-cell RNA-seq to characterize ADAM23 expression
- Cryo-EM to determine ADAM23 structure
- CRISPR screening to identify genetic interactions
- Patient-derived iPSC neurons for disease modeling
ADAM23 is a catalytically inactive ADAM family member with critical functions in the developing and adult nervous system. Through its disintegrin and cysteine-rich domains, ADAM23 mediates cell-cell and cell-matrix adhesion, regulates neuronal migration and cortical development, and plays essential roles in synaptic formation and plasticity. Altered ADAM23 expression in Alzheimer's and Parkinson's disease suggests potential involvement in neurodegeneration, though the precise mechanisms remain under investigation. As a non-proteolytic ADAM, ADAM23 offers unique opportunities for therapeutic targeting through modulation of adhesion-based signaling rather than catalytic activity.