TYROBP (TYRO Binding Protein), also known as DAP12 (DNAX-activating protein 12), is a critical adaptor protein that mediates signaling in microglia and other immune cells. TYROBP forms a signaling complex with TREM2 (Triggering Receptor Expressed on Myeloid Cells 2), and both genes are strongly associated with Alzheimer's disease (AD) risk 1. This pathway page explores the molecular mechanisms by which TYROBP/DAP12 influences microglial function, neuroinflammation, and neurodegeneration in AD.
¶ Gene and Protein Structure
The TYROBP gene encodes a type I transmembrane adaptor protein consisting of:
- An extracellular N-terminal domain
- A single transmembrane domain (with a charged aspartic acid residue)
- An intracellular ITAM (Immunoreceptor Tyrosine-based Activation Motif)
TYROBP is expressed primarily in:
- Microglia (highest expression)
- Macrophages
- Monocytes
- Dendritic cells
- Osteoclasts
- Some subsets of NK cells
In the brain, TYROBP is almost exclusively expressed in microglia, where it partners with TREM2 2.
flowchart TD
A[TREM2 Ligands] --> B[Aβ plaques]
A --> C[APOE]
A --> D[Lipids]
A --> D1[Dead cells]
B --> E[TREM2 receptor]
C --> E
D --> E
D1 --> E
E --> F[TREM2-TYROBP complex]
F --> G[ITAM phosphorylation]
G --> H[SYK recruitment]
H --> I[SRC family kinases]
I --> J[PI3K/AKT pathway]
I --> K[ERK/MAPK pathway]
I --> L[NF-κB pathway]
I --> M[Calcium signaling]
J --> N[Cell survival & proliferation]
K --> O[Gene transcription]
L --> P[Inflammatory response]
M --> Q[ cytoskeletal reorganization]
N --> R[Microglial activation]
O --> R
P --> R
Q --> R
- PI3K/AKT Pathway: Promotes cell survival, proliferation, and metabolic fitness
- ERK/MAPK Pathway: Regulates gene expression and cellular differentiation
- NF-κB Pathway: Controls inflammatory gene transcription
- Calcium Signaling: Mediates cytoskeletal reorganization and phagocytosis
flowchart TD
A[TREM2-TYROBP signaling] --> B[Actin cytoskeleton remodeling]
B --> C[Phagocytic cup formation]
C --> D[Target recognition]
D --> E[Aβ particles]
D --> E1[Apoptotic cells]
D --> E2[Debris]
E --> F[Phagosome formation]
E1 --> F
E2 --> F
F --> G[Phagosome maturation]
G --> H[ lysosomal degradation]
H --> I[Antigen presentation]
J[AD Risk Variants] --> K[Impaired SYK activation]
K --> L[Reduced phagocytic capacity]
L --> M[Aβ accumulation]
- Aβ clearance: TYROBP signaling is essential for microglial phagocytosis of amyloid plaques
- Cell debris removal: Critical for clearing dead neurons and synaptic fragments
- Immune surveillance: Maintains baseline microglial activity
flowchart TD
A[TREM2-TYROBP] --> B[Pro-inflammatory signaling]
B --> C[NF-κB activation]
C --> D[TNF-α production]
C --> D1[IL-1β production]
C --> D2[IL-6 production]
A --> E[Anti-inflammatory signaling]
E --> F[IL-10 production]
E --> F1[TGF-β production]
G[AD Risk Variants] --> H[Dysregulated inflammation]
H --> I[Chronic neuroinflammation]
I --> J[Neuronal dysfunction]
G --> K[Impaired homeostatic signaling]
K --> L[Reduced phagocytosis]
L --> M[Toxic Aβ accumulation]
M --> J
TYROBP signaling has complex, context-dependent effects on inflammation:
- Pro-inflammatory: Can drive production of cytokines (TNF-α, IL-1β, IL-6)
- Anti-inflammatory: Can promote anti-inflammatory responses (IL-10, TGF-β)
- Homeostatic: Essential for maintaining normal microglial surveillance and response
The balance depends on:
- Ligand context (Aβ vs. apoptotic cells vs. healthy tissue)
- Cellular environment (cytokines, growth factors)
- Disease stage (early vs. late AD)
- TYROBP is significantly associated with AD risk (GWAS p < 5×10⁻⁸) 1
- The AD risk allele leads to reduced TYROBP expression
- Expression quantitative trait loci (eQTLs) in brain tissue
- TREM2 and TYROBP are co-expressed in microglia
- TREM2 risk variants (R47H, R62H) impair signaling through TYROBP
- This explains the similar phenotypic effects of TREM2 and TYROBP variants
¶ Pathway: TYROBP and Tau Pathology
flowchart TD
A[TYROBP signaling] --> B[Microglial activation]
B --> C[Phagocytosis of tau aggregates]
B --> D[Secretion of inflammatory mediators]
C --> E[Tau clearance]
D --> F[tau phosphorylation]
G[Impaired TYROBP] --> H[Reduced tau clearance]
H --> I[Tau aggregation]
I --> J[NFT formation]
G --> K[Excessive inflammation]
K --> L[神经元 stress]
L --> J
- Small molecule agonists: Develop compounds that enhance TYROBP signaling
- Gene therapy: Increase TYROBP expression in microglia
- Protein replacement: Deliver functional TYROBP protein
| Approach |
Status |
Description |
| TREM2 agonists |
Phase 1/2 |
Enhance upstream signaling |
| SYK inhibitors |
Preclinical |
Modulate downstream signaling |
| Anti-inflammatory |
Various |
Reduce excessive inflammation |
- TYROBP and AD risk (2014)
- TREM2 and TYROBP expression in human brain (2015)
- TREM2-TYROBP signaling in microglia (2017)
- Microglial AD risk genes (2019)