TREM2-H157Y Increases Soluble TREM2 Production and Reduces Amyloid Pathology

The p.H157Y variant of TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) has been reported to increase Alzheimers disease (AD) risk. This mutation in the extracellular domain of TREM2 localizes at the cleavage site, leading to enhanced shedding. Here, we generated a novel Trem2 H157Y knock-in mouse model to investigate how this H157Y mutation impacts TREM2 proteolytic processing, synaptic function, and AD-related amyloid pathology. Consistent with previous in vitro findings, TREM2-H157Y increases the amount of soluble TREM2 (sTREM2) in the cortex and serum of mutant mice compared to the wild type controls. Interestingly, the Trem2 H157Y variant enhances synaptic plasticity without affecting microglial density and morphology. In the presence of amyloid pathology, TREM2-H157Y surprisingly accelerates A{beta} clearance and reduces amyloid burden and microgliosis. Taken together, our findings support a beneficial effect of the Trem2 H157Y mutation in synaptic function and in mitigating amyloid pathology. Considering the genetic association of TREM2 p.H157Y with AD, we speculate TREM2-H157Y might increase AD risk through an amyloid-independent pathway, as such its effects on tauopathy and neurodegeneration merit further investigation.