| Symbol: | TYROBP |
| Also known as: | DAP12, KARAP, PLOSL |
| UniProt: | [O43914](https://www.uniprot.org/uniprot/O43914) |
| Gene: | [TYROBP](/genes/tyrobp) |
| MW: | 12.1 kDa |
| Location: | Cell membrane |
| PDB: | [1L1Y](https://www.rcsb.org/structure/1L1Y), [2L8H](https://www.rcsb.org/structure/2L8H) |
TYROBP (TYRO Protein Tyrosine Kinase-Binding Protein), commonly known as DAP12 (DNAX-Activation Protein 12), is a transmembrane signaling adaptor protein that plays critical roles in innate immunity and microglial function in the central nervous system. DAP12 partners with multiple immunoreceptors, most notably TREM2, to transduce activation signals that regulate microglial survival, phagocytosis, and inflammatory responses[1].
Mutations in TYROBP cause Nasu-Hakola disease (polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy, PLOSL), a rare autosomal recessive disorder characterized by presenile dementia and bone cysts. Additionally, DAP12 signaling is increasingly recognized as a key pathway in Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions[2][3].
TYROBP is a small 113-amino acid type I transmembrane protein:
Extracellular Domain (residues 1-35):
Transmembrane Domain (residues 36-56):
Cytoplasmic Domain (residues 57-113):
DAP12 pairs with multiple receptors in different cell types:
| Receptor | Cell Type | Function |
|---|---|---|
| TREM2 | Microglia | Phagocytosis, survival |
| TREM1 | Myeloid cells | Amplifies inflammation |
| SIRPβ1 | Macrophages | Adhesion, migration |
| MDL-1 | Myeloid cells | Cytokine production |
| NKp44 | NK cells | Cytotoxicity |
| SIGLEC-15 | Osteoclasts | Bone remodeling |
In microglia, DAP12 primarily partners with TREM2 to regulate:
Phagocytosis: DAP12-TREM2 signaling promotes clearance of:
Cell Survival: PI3K/AKT pathway activation downstream of DAP12 promotes microglial survival.
Migration: Chemotactic responses to damage signals require DAP12 signaling.
Metabolism: DAP12 regulates microglial metabolic adaptation during activation[6].
Proliferation: CSF1R-induced microglial proliferation is modulated by DAP12.
The canonical DAP12 signaling cascade involves:
Biallelic loss-of-function mutations in TYROBP cause Nasu-Hakola disease:
Clinical Features:
Pathology:
Mechanism: Loss of DAP12 function leads to:
DAP12-TREM2 signaling is critical in AD:
TREM2 Risk Variants: AD-associated TREM2 variants (R47H, R62H) impair DAP12 signaling.
Microglial Response to Aβ: DAP12 is required for:
DAM (Disease-Associated Microglia): The transcriptional shift to DAM phenotype requires intact DAP12-TREM2 signaling.
Neuroinflammation: DAP12 can also promote inflammatory responses that may be detrimental.
Synaptic Pruning: DAP12-TREM2 regulates complement-mediated synaptic pruning in AD[11].
DAP12 involvement in PD includes:
α-Synuclein Response: DAP12-TREM2 signaling regulates microglial responses to α-synuclein aggregates.
Neuroinflammation: DAP12 contributes to microglial activation in PD.
Neuroprotection: Some studies suggest DAP12 activation may be protective by promoting aggregate clearance[12].
In MS, DAP12 plays roles in:
Myelin Phagocytosis: DAP12 regulates microglial clearance of myelin debris.
Remyelination: Impaired DAP12 signaling may slow remyelination.
Neuroinflammation: DAP12 contributes to inflammatory responses in active lesions[13].
| Agent | Mechanism | Status |
|---|---|---|
| AL002 (Gantenerumab-like) | Anti-TREM2 agonist mAb | Phase II |
| DAP12 agonist antibodies | Direct DAP12 activation | Preclinical |
| Soluble TREM2 | Enhances DAP12 signaling | Clinical trials |
Receptor Agonists: Antibodies that cluster TREM2 and activate DAP12.
Soluble Ligands: Recombinant proteins that enhance DAP12-TREM2 signaling.
Small Molecule Activators: Compounds that enhance SYK activation downstream of DAP12[14].
Gene Therapy: Increasing TYROBP or TREM2 expression in microglia.
Balancing Activation: Overactivation may cause excessive inflammation.
Isoform Specificity: Need to target specific receptor-DAP12 pairs.
Timing: Optimal intervention window unclear.
Cell Type Effects: DAP12 is expressed in many immune cells; systemic effects possible[15].
| Interactor | Type | Function |
|---|---|---|
| TREM2 | Receptor | Primary CNS partner |
| TREM1 | Receptor | Inflammatory amplification |
| SYK | Kinase | ITAM signaling |
| ZAP70 | Kinase | ITAM signaling |
| PI3K | Kinase | Survival signaling |
| SRC kinases | Kinase | ITAM phosphorylation |
| GRB2 | Adaptor | RAS pathway |
| PLCγ | Enzyme | Ca2+ signaling |
Lanier LL, Corliss BC, Wu J, et al. Immunoreceptor DAP12 bearing a tyrosine-based activation motif is involved in activating NK cells. Nature. 1998. ↩︎
Paloneva J, Kestilä M, Wu J, et al. Loss-of-function mutations in TYROBP (DAP12) result in a presenile dementia with bone cysts. Nat Genet. 2000. ↩︎
Colonna M. TREMs in the immune system and beyond. Nat Rev Immunol. 2003. ↩︎
Feng J, Call ME, Wucherpfennig KW. The assembly of DAP12-TREM2 complex. Immunity. 2010. ↩︎
Hsieh CL, Koike M, Spusta SC, et al. A role for TREM2 ligands in the phagocytosis of apoptotic neuronal cells by microglia. J Neurochem. 2009. ↩︎
Ulland TK, Song WM, Huang SC, et al. TREM2 maintains microglial metabolic fitness in Alzheimer's disease. Cell. 2017. ↩︎
Turnbull IR, Gilfillan S, Cella M, et al. Cutting edge: TREM-2 attenuates macrophage activation. J Immunol. 2006. ↩︎
Paloneva J, Manninen T, Christman G, et al. Mutations in two genes encoding different subunits of a receptor signaling complex result in an identical disease phenotype. Am J Hum Genet. 2002. ↩︎
Thrash JC, Torbett BE, Carson MJ. Developmental regulation of TREM2 in the microglial response to neonatal hypoxia-ischemia. Dev Neurosci. 2009. ↩︎
Wang Y, Cella M, Mallinson K, et al. TREM2 lipid sensing sustains the microglial response in an Alzheimer's disease model. Cell. 2015. ↩︎
Filipello F, Morini R, Corradini I, et al. The Microglial Innate Immune Receptor TREM2 Is Required for Synapse Elimination and Normal Brain Connectivity. Immunity. 2018. ↩︎
Guerreiro R, Wojtas A, Bras J, et al. TREM2 variants in Alzheimer's disease. N Engl J Med. 2013. ↩︎
Takahashi K, Rochford CD, Neumann H. Clearance of apoptotic neurons without inflammation by microglial triggering receptor expressed on myeloid cells-2. J Exp Med. 2005. ↩︎
Schlepckow K, Monroe KM, Kleinberger G, et al. Enhancing TREM2 activity as a therapeutic approach. EMBO Mol Med. 2020. ↩︎
Cheng-Hathaway PJ, Reed-Geaghan EG, Jay TR, et al. The Trem2 R47H variant confers loss-of-function-like phenotypes in Alzheimer's disease. Mol Neurodegener. 2018. ↩︎