Acute reduction triggers increased microglial phagocytosis, slowing amyloid deposition in mice.

Heterozygous genetic variants within the gene show a strong association with increased Alzheimer's disease (AD) risk. Amyloid beta-depositing mouse models haploinsufficient or null for have identified important relationships among TREM2, microglia, and AD pathology; however, results are challenging to interpret in the context of varying microglial phenotypes and disease progression. We hypothesized that acute reduction may alter amyloid pathology and microglial responses independent of genetic deletion in mouse models. We developed antisense oligonucleotides (ASOs) that potently but transiently lower messenger RNA throughout the brain and administered them to APP/PS1 mice at varying stages of plaque pathology. Late-stage ASO-mediated knockdown significantly reduced plaque deposition and attenuated microglial association around plaque deposits when evaluated 1 mo after ASO injection. Changes in microglial gene signatures 1 wk after ASO administration and phagocytosis measured in ASO-treated cells together indicate that microglia may be activated with short-term reduction. These results suggest a time- and/or dose-dependent role for TREM2 in mediating plaque deposition and microglial responses in which loss of TREM2 function may be beneficial for microglial activation and plaque removal in an acute context.