Abstract
Background:
Pathogenic tau accumulation drives neurodegeneration in Alzheimer's disease (AD). Enhancing the aging brain's resilience to tau pathology would lead to novel therapeutic strategies. DAP12 (DNAX-activation protein 12), highly and selectively expressed by microglia, plays a crucial role in microglial immune responses. Previous studies have shown that tauopathy mice lacking DAP12 exhibit higher tau pathology but are protected from tau pathology-induced cognitive deficits. However, the exact mechanism behind this resilience remains elusive.
Methods:
We investigated the effects of DAP12 deletion on tau pathology, as well as tau-induced brain inflammation and neurodegeneration, in homozygous human Tau P301S transgenic mice. In addition, we conducted single-nucleus RNA sequencing of hippocampal tissues to examine cell type-specific transcriptomic changes at the single-cell level. Furthermore, we utilized the CellChat package to profile cell-cell communication in the mouse brain and investigated how these interactions are affected by tau pathology and Dap12 deletion.
Results:
We demonstrated that Dap12 deletion reduced tau processing in primary microglia and increased tau pathology in female tauopathy mice, with minimal effects on males. Despite this, Dap12 deletion markedly reduced brain inflammation, synapse loss, and demyelination, indicating enhanced resilience to tau toxicity. Single-cell transcriptomic profiling revealed that Dap12 deletion blocked tau-induced alterations in microglia, neurons, and oligodendrocytes. CellChat analysis identified aberrant tau-induced SLIT2 signaling from excitatory neurons to oligodendrocytes. Dap12 deletion suppressed Slit2 upregulation and mitigated demyelination, while lentiviral-Slit2 overexpression induced myelin loss in tauopathy mice. Elevated SLIT2 levels were associated with demyelination in tauopathy mouse model and human AD brains. Spatial transcriptomics revealed a spatial correlation of SLIT2 expression and tau pathology in AD brain tissue.
Conclusions:
Our study identifies a novel DAP12-dependent mechanistic link between upregulated Slit2 expression in excitatory neurons and oligodendrocyte-dependent myelination loss in tauopathy. Despite elevating tau load, the absence of microglial Dap12 ameliorates neuroinflammation and improves brain functions in tauopathy mice. Our study suggests that selectively targeting the toxic aspects of DAP12 signaling while preserving its beneficial functions may be a promising strategy to enhance brain resilience in AD.