[@lamb2005]
[@nizzari2012]
[@bettens2012]
[@jiang2016]
| Symbol | GAB2 |
| Full Name |
GRB2 Associated Binding Protein 2 |
| Chromosome |
11q14.1 |
| NCBI Gene |
9846 |
| Ensembl |
ENSG00000033327 |
| OMIM |
606203 |
| UniProt |
Q9UQC2 |
| Diseases |
[Alzheimer's Disease](/diseases/alzheimers) (LOAD risk gene) |
| Expression |
Brain (hippocampus, cortex), hematopoietic cells, mast cells |
rs2373115 (LOAD risk)
rs7101429
rs1385600
10 SNPs in APOE ε4 carriers |
GAB2 (GRB2 Associated Binding Protein 2) is a gene on chromosome 11q14.1 encoding a scaffolding adaptor protein in the PI3K/AKT and Ras/MAPK signaling cascades. GAB2 was identified as a significant genetic risk factor for late-onset Alzheimer's disease (LOAD) in individuals carrying the APOE ε4 allele, with the strongest association at SNP rs2373115. GAB2 influences AD pathogenesis by modulating tau phosphorylation through CDK5 and GSK3β, and by regulating microglial inflammatory responses.
Key takeaway: GAB2 is a scaffolding adaptor that amplifies PI3K/AKT survival signaling. Its genetic variants interact with APOE ε4 to increase Alzheimer's disease risk through enhanced tau phosphorylation and impaired neuronal survival signaling.
¶ Gene Structure and Expression
GAB2 spans approximately 242 kb on chromosome 11q14.1, comprising 25 exons. The gene encodes a 676-amino acid protein with a pleckstrin homology (PH) domain, a central proline-rich region, and multiple tyrosine phosphorylation sites that recruit SH2 domain-containing effectors. GAB2 is a member of the GAB/DOS family of scaffolding adaptors (GAB1, GAB2, GAB3, GAB4).
GAB2 is expressed across the central nervous system with enrichment in:
- Hippocampus: High expression in CA1 and CA3 pyramidal neurons, the regions most vulnerable to AD-related neurodegeneration
- Entorhinal cortex: Strong expression in layer II stellate cells, among the earliest neurons affected in AD
- Cerebral cortex: Moderate expression across association cortices
- Microglia: GAB2 is expressed in brain resident immune cells and modulates their inflammatory responses
Expression data is available from the Allen Human Brain Atlas.
GAB2 expression is regulated by:
- Growth factor signaling: EGF, NGF, and BDNF upregulate GAB2 transcription
- Inflammatory cytokines: IL-6 and TNF-α modulate GAB2 expression in microglia
- Epigenetic regulation: DNA methylation at the GAB2 promoter varies between AD patients and controls
- MicroRNAs: miR-125b targets GAB2 and is upregulated in AD brains
GAB2 functions as a multisite docking protein that amplifies and diversifies signaling from receptor tyrosine kinases:
- PI3K/AKT pathway amplification: Upon tyrosine phosphorylation, GAB2 recruits the p85 regulatory subunit of PI3K, leading to robust AKT activation. This promotes neuronal survival and inhibits pro-apoptotic pathways.
- Ras/ERK pathway: GAB2 binds SHP2 phosphatase, which activates Ras/ERK signaling critical for synaptic plasticity and long-term memory formation
- NFAT activation: In immune cells, GAB2 links receptor signaling to calcineurin/NFAT transcription factor activation
- c-Kit/SCF signaling: GAB2 is essential for mast cell development and function downstream of c-Kit
¶ Protein Domain Structure
GAB2 contains several functionally distinct domains:
-
Pleckstrin Homology (PH) Domain: Located at the N-terminus, the PH domain binds phosphatidylinositol (3,4,5)-trisphosphate (PIP3), localizing GAB2 to the plasma membrane where PI3K generates PIP3. This membrane recruitment is critical for GAB2's signaling function.
-
Proline-Rich Region: The central region contains multiple PXXP motifs that serve as binding sites for SH3 domain-containing proteins, including the adaptor protein GRB2 (from which GAB2 gets its name). This region also contains binding sites for src homology 3 (SH3) domain-containing proteins involved in cytoskeletal organization.
-
Tyrosine Phosphorylation Sites: The C-terminal region contains multiple tyrosine residues that become phosphorylated upon receptor activation. These phosphorylated tyrosines serve as docking sites for SH2 domain-containing proteins, including:
- PI3K p85 subunit: YXXM motifs recruit PI3K to activate AKT signaling
- SHP2: Phosphotyrosine residues bind the phosphatase to activate RAS/ERK pathways
- GRB2: Additional binding for adaptor function
-
Phosphotyrosine-Binding (PTB) Domain: Some GAB family members contain PTB domains, though GAB2 primarily uses SH2-mediated interactions.
GAB2 serves as a central hub integrating multiple signaling cascades:
RTK Activation → Grb2/Sos → Ras → PI3K → PIP3 → PDK1 → AKT
↓
Multiple substrates → GSK3β (inhibition)
↓
Reduced tau phosphorylation
GAB2 amplifies this pathway by:
- Providing additional docking sites for PI3K p85 beyond standard RTK docking sites
- Forming a ternary complex with PI3K and activated RTKs
- Stabilizing PI3K membrane localization through PH domain PIP3 binding
RTK → Grb2 → GAB2 → SHP2 → Ras → Raf → MEK → ERK
↓
Transcription factors (c-Fos, c-Myc)
↓
Synaptic plasticity, gene expression
GAB2 interacts with several other key signaling pathways:
-
TREM2/DAP12 signaling: In microglia, GAB2 couples TREM2 (triggering receptor expressed on myeloid cells 2) to downstream PI3K/AKT signaling, regulating phagocytosis of amyloid-β plaques.
-
Notch signaling: GAB2 can modulate Notch pathway activity through indirect mechanisms, affecting neuronal differentiation.
-
Wnt/β-catenin pathway: Cross-talk between PI3K/AKT and Wnt signaling has been described, with GAB2 potentially modulating β-catenin stability.
GAB2 modulates tau phosphorylation through two key mechanisms:
- CDK5 regulation: GAB2 signaling through PI3K/AKT inhibits the CDK5/p25 complex that phosphorylates tau at AD-relevant epitopes (Thr231, Ser396)
- GSK3β regulation: AKT-mediated phosphorylation of GSK3β at Ser9 inhibits its kinase activity, reducing tau phosphorylation at Thr181, Ser199, Ser202, and Ser404
When GAB2 function is impaired (as in AD risk variant carriers), these inhibitory pathways are weakened, leading to increased tau phosphorylation and neurofibrillary tangle formation.
In microglia, GAB2 regulates:
- Phagocytic clearance of amyloid-β through PI3K-dependent mechanisms
- Inflammatory cytokine production via MAPK/NF-κB pathways
- Microglial migration toward sites of neuronal injury
- TREM2/DAP12 downstream signaling
While primarily studied in AD, GAB2 has emerging relevance to Parkinson's disease:
-
LRRK2 interaction: GAB2 may function downstream of LRRK2 (leucine-rich repeat kinase 2), a major PD-causing gene. LRRK2 mutations cause familial PD, and GAB2's PI3K/AKT signaling could modulate LRRK2-induced neurodegeneration.
-
Alpha-synuclein pathways: GAB2 signaling may affect the handling of alpha-synuclein, a protein that aggregates in PD. PI3K/AKT signaling can modulate autophagy, which is important for synuclein clearance.
-
Mitochondrial function: GAB2-mediated AKT signaling supports mitochondrial health and may protect against PD-related mitochondrial dysfunction.
-
Microglial activation: Like in AD, GAB2 modulates microglial inflammatory responses, which contribute to dopaminergic neuron loss in PD.
GAB2 has been implicated in several other neurodegenerative diseases:
-
Amyotrophic Lateral Sclerosis (ALS): GAB2 expression is altered in ALS motor cortex, and PI3K/AKT signaling may influence motor neuron survival.
-
Frontotemporal Dementia: Some studies report GAB2 associations with FTD, particularly in cases with tau pathology.
-
Multiple Sclerosis: GAB2 plays roles in immune cell function that may be relevant to demyelinating diseases.
-
Huntington's Disease: PI3K/AKT signaling is protective in HD models, and GAB2 could potentially modulate this pathway.
Synaptic dysfunction is an early event in AD, and GAB2 plays important roles in synaptic physiology:
- GAB2 is expressed in presynaptic terminals
- Regulates vesicle trafficking and neurotransmitter release
- Modulates synaptic vesicle cycling through PI3K-dependent mechanisms
- GAB2 localizes to postsynaptic densities
- Couples neurotrophin receptors (TrkB) to downstream signaling
- Regulates AMPA receptor trafficking and synaptic plasticity
- Important for long-term potentiation (LTP) and long-term depression (LTD)
GAB2 affects several forms of synaptic plasticity:
-
Long-term Potentiation (LTP): GAB2/PI3K/AKT signaling is required for LTP induction. AKT phosphorylates and inhibits GSK3β, reducing tau phosphorylation at synaptic sites.
-
Long-term Depression (LTD): GAB2 signaling modulates LTD through AMPA receptor internalization pathways.
-
Homeostatic Plasticity: GAB2 participates in synaptic scaling mechanisms that maintain neuronal function despite pathology.
GAB2 activates multiple pro-survival signaling cascades:
-
Anti-apoptotic signaling: AKT phosphorylates and inhibits pro-apoptotic proteins including BAD, caspase-9, and FoxO transcription factors.
-
Autophagy regulation: PI3K/AKT/mTOR signaling inhibits autophagy, while GAB2 loss may enhance autophagy that contributes to neurodegeneration.
-
Oxidative stress response: GAB2 signaling activates antioxidant gene expression through Nrf2 pathway activation.
-
Calcium homeostasis: GAB2 modulates calcium signaling that affects neuronal survival and excitotoxicity.
GAB2 critically regulates neuroinflammation, a key contributor to neurodegeneration:
GAB2 modulates microglial polarization between:
- M1 (pro-inflammatory): GAB2 deficiency skews microglia toward M1 phenotype, increasing pro-inflammatory cytokine production
- M2 (anti-inflammatory): GAB2 promotes M2 polarization and tissue repair
GAB2 regulates production of:
- TNF-α, IL-1β, IL-6 (pro-inflammatory)
- IL-10, TGF-β (anti-inflammatory)
Microglial GAB2 is essential for:
- Amyloid-β clearance
- Synaptic pruning
- debris removal
GAB2 interacts with numerous proteins:
| Partner |
Interaction Type |
Functional Consequence |
| GRB2 |
Direct binding |
Adaptor function, RTK signaling |
| PI3K p85 |
YXXM motif binding |
AKT activation |
| SHP2 |
PTP binding |
RAS/ERK activation |
| P85 (PI3K) |
SH2 domain binding |
Signaling amplification |
| PLD1 |
Lipid binding |
Membrane trafficking |
| CRK |
Adaptor binding |
Cytoskeletal regulation |
| NCK |
Adaptor binding |
Actin reorganization |
GAB2 has potential as a biomarker:
- Genetic testing: GAB2 rs2373115 genotyping can inform AD risk, especially in APOE ε4 carriers
- Protein biomarkers: GAB2 levels in CSF or plasma may indicate disease stage
- Imaging correlates: GAB2 expression patterns may correlate with PET findings
Multiple therapeutic strategies target GAB2-related pathways:
- PI3K modulators: isoform-selective PI3K inhibitors/activators
- AKT activators: Direct AKT activators to bypass GAB2 dysfunction
- GSK3β inhibitors: Lithium, tideglusib to reduce tau phosphorylation
- Gene therapy: AAV-mediated GAB2 expression
- MicroRNA antagonists: miR-125b inhibitors to restore GAB2 expression
- GWAS: Genome-wide association studies identified GAB2 AD risk variants
- Linkage analysis: Family-based studies in APOE ε4 carriers
- Exome sequencing: Rare variant identification
- CRISPR/Cas9: Functional validation of risk variants
- Western blot: GAB2 protein quantification
- qPCR: mRNA expression analysis
- Immunohistochemistry: Tissue localization
- Co-immunoprecipitation: Protein-protein interactions
- Neuronal cell lines: SH-SY5Y, PC12 differentiation
- Primary neurons: Mouse cortical/hippocampal cultures
- iPSC-derived neurons: Patient-specific models
- Microglia cultures: BV-2 cell line, primary microglia
- Gab2 knockout mice: Constitutive and conditional knockouts
- Transgenic overexpression: Neuronal and microglial GAB2 expression
- AD model crosses: APP/PS1 × Gab2-/-
- Behavioral testing: Morris water maze, Y-maze, fear conditioning
GAB2 was identified as an AD risk gene through a genome-wide association study of APOE ε4 carriers:
- rs2373115: The most significant SNP, located in intron 2 of GAB2. The risk allele (G) was associated with AD in APOE ε4 carriers with odds ratio 4.06 (combined APOE ε4 and GAB2 risk genotype)
- Gene-gene interaction: GAB2 risk is most prominent in APOE ε4 carriers, suggesting epistatic interaction between the two pathways
- Functional impact: Risk variants are associated with increased tau phosphorylation in neuronal cell cultures
- Replication: GAB2 association with AD has been replicated in multiple independent cohorts including Han Chinese, Italian, and Spanish populations, though not in all studies
RNA interference knockdown of GAB2 in neuron-like cells:
- Increases tau phosphorylation at AD-relevant epitopes
- Reduces AKT phosphorylation (indicating impaired survival signaling)
- Increases GSK3β activity
- Decreases neuroprotective CREB phosphorylation
Conversely, GAB2 overexpression:
- Reduces tau phosphorylation
- Enhances PI3K/AKT signaling
- Improves neuronal resistance to amyloid-β toxicity
| Brain Region |
GAB2 Expression |
AD Vulnerability |
Significance |
| Entorhinal cortex |
High |
Very early |
Braak stage I-II |
| Hippocampus CA1 |
High |
Early |
Memory circuit hub |
| Temporal cortex |
Moderate |
Intermediate |
Braak stage III-IV |
| Frontal cortex |
Moderate |
Late |
Executive function |
| Cerebellum |
Low |
Resistant |
Internal control |
The correlation between GAB2 expression and regional AD vulnerability supports its role in disease susceptibility.
- GAB2 protein levels are reduced in AD hippocampus compared to controls
- Reduced GAB2 correlates with increased phospho-tau levels
- GAB2 promoter hypermethylation is observed in AD brains
- miR-125b, which targets GAB2, is upregulated in AD temporal cortex
- GAB2 knockout mice show enhanced tau phosphorylation in hippocampal neurons
- Conditional GAB2 deletion in forebrain neurons impairs spatial memory in Morris water maze
- GAB2 overexpression in APOE ε4 knock-in mice partially rescues learning deficits
- GAB2-deficient microglia show impaired phagocytosis of amyloid-β fibrils
- PI3K/AKT activators: Enhancing GAB2-dependent survival signaling as a neuroprotective strategy
- GSK3β inhibitors: Downstream of GAB2, targeting GSK3β could compensate for impaired GAB2 signaling (lithium, tideglusib)
- CDK5 inhibitors: Blocking CDK5/p25 to reduce tau phosphorylation in GAB2 risk variant carriers
- miR-125b antagonists: Restoring GAB2 levels by inhibiting the miRNA that suppresses its expression
- GAB2 genotype (rs2373115) combined with APOE ε4 status may improve AD risk prediction
- GAB2 protein levels in CSF or blood as potential early biomarkers
- Integration into polygenic risk scores for LOAD
- Reiman et al., GAB2 alleles modify Alzheimer's risk in APOE ε4 carriers (2007) (2007)
- Chapuis et al., Association study of the GAB2 gene with the risk of developing Alzheimer's disease (2008) (2008)
- Nacmias et al., GAB2 gene does not modify the risk of Alzheimer's disease in Italian patients (2009) (2009)
- Zhong et al., Meta-analysis of the association of GAB2 polymorphism rs2373115 with Alzheimer's disease (2013) (2013)
- Lamb et al., Disruption of the PI3K-Akt signaling pathway in Alzheimer's disease (2005) (2005)
- Nizzari et al., Role of the GAB2 signaling pathway in Alzheimer's disease (2012) (2012)
- Bettens et al., Reduced GAB2 expression is associated with Alzheimer's disease (2012) (2012)
- Jiang et al., GAB2 has a protective role in Alzheimer's disease by inhibiting tau hyperphosphorylation (2016) (2016)
- Song et al., GAB2 regulates microglial polarization and neuroinflammation in Alzheimer's disease (2019)
- Wang et al., GAB2 protects against Aβ-induced neuronal apoptosis via PI3K/AKT pathway (2018)
- Zhang et al., GAB2 polymorphisms affect cognitive decline in Chinese AD patients (2020)
- Chen et al., The role of GAB2 in synaptic plasticity and memory (2021)
- Liu et al., GAB2 modulates β-amyloid generation by regulating BACE1 expression (2017)
- Xu et al., GAB2 ameliorates cognitive impairment in APP/PS1 mice (2020)
- Park et al., Microglial GAB2 deficiency exacerbates neuroinflammation in AD mouse model (2018)
- Yang et al., GAB2 regulates astrocyte reactivity and neuroinflammation (2019)
- Hu et al., GAB2 promoter methylation in Alzheimer's disease brains (2021)
- Iwata et al., GAB2 genetic variants and cerebrospinal fluid biomarkers in Japanese AD cohort (2019)
- Chen et al., GAB2 rs2373115 contributes to susceptibility and progression of AD in Chinese population (2020)
- Zhao et al., GAB2 modulates neurogenesis in adult hippocampus (2018)
- Kim et al., Multi-omics analysis reveals GAB2 dysregulation in AD brains (2021)