Disease Progression-Dependent Effects of TREM2 Deficiency in a Mouse Model of Alzheimer's Disease

Abstract

Neuroinflammation is an important contributor to Alzheimer's disease (AD) pathogenesis, as underscored by the recent identification of immune-related genetic risk factors for AD, including coding variants in the gene TREM2 (triggering receptor expressed on myeloid cells 2). Understanding TREM2 function promises to provide important insights into how neuroinflammation contributes to AD pathology. However, studies so far have produced seemingly conflicting results, with reports that amyloid pathology can be both decreased and increased in TREM2-deficient AD mouse models. In this study, we unify these previous findings by demonstrating that TREM2 deficiency ameliorates amyloid pathology early, but exacerbates it late in disease progression in the APPPS1–21 mouse model of AD. We also demonstrate that TREM2 deficiency decreases plaque-associated myeloid cell accumulation by reducing cell proliferation, specifically late in pathology. In addition, TREM2 deficiency reduces myeloid cell internalization of amyloid throughout pathology, but decreases inflammation-related gene transcript levels selectively late in disease progression. Together, these results suggest that TREM2 plays distinct functional roles at different stages in AD pathology.