INPP5D modulates TREM2 loss‐of‐function phenotypes in a β‐amyloidosis mouse model

Abstract

AbstractBackgroundThe genetic associations of TREM2 loss‐of‐function variants with Alzheimer disease (AD) indicate the protective roles of microglia in AD pathogenesis. Functional deficiencies of TREM2 disrupt microglial clustering around amyloid β (Aβ) plaques, impair their transcriptional response to Aβ, and worsen neuritic dystrophy. However, the molecular mechanism underlying these phenotypes remains unclear.MethodsIn this study, we investigated the pathological role of another AD risk gene, INPP5D, encoding a phosphoinositide PI(3,4,5)P3 phosphatase expressed in microglia by crossing Tyrobp knockout, Inpp5d knockout and human mutant APP knockin mice.ResultIn a Tyrobp‐deficient TREM2 loss‐of‐function mouse model, Inpp5d haplodeficiency restored the association of microglia with Aβ plaques, partially restored plaque compaction and astrogliosis, and reduced phosphorylated tau+ dystrophic neurites. RNA‐sequencing of isolated microglia demonstrated that the expression of “disease‐associated microglia” genes is not responsible for these beneficial effects.ConclusionOur results suggest that INPP5D acts downstream of TREM2/TYROBP to regulate the microglial barrier against Aβ toxicity, thereby modulates Aβ‐dependent pathological conversion of tau.