Trem2 restrains the enhancement of tau accumulation and neurodegeneration by -amyloid pathology

Loss-of-function TREM2 mutations strongly increase Alzheimer's disease (AD) risk. Trem2 deletion has revealed protective Trem2 functions in preclinicalmodels of beta-amyloidosis, a prominent feature of pre-diagnosis AD stages. How TREM2 influences later AD stages characterized by tau-mediated neurodegeneration is unclear. To understand Trem2 function in the context of both beta-amyloid and tau pathologies, we examined Trem2 deficiency in the pR5-183 mouse model expressing mutant tau alone or in TauPS2APP mice, in which beta-amyloid pathology exacerbates tau pathology and neurodegeneration. Single-cell RNA sequencing in these models revealed robust disease-associated microglia (DAM) activation in TauPS2APP mice that was amyloid-dependent and Trem2-dependent. In the presence of beta-amyloid pathology, Trem2 deletion further exacerbated tau accumulation and spreading and promoted brain atrophy. Without beta-amyloid pathology, Trem2 deletion did not affect these processes. Therefore, TREM2 may slow AD progression and reduce tau-driven neurodegeneration by restricting the degree to which b-amyloid facilitates the spreading of pathogenic tau.