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

The genetic associations of TREM2 loss-of-function variants with Alzheimer dis-ease (AD) indicate the protective roles of microglia in AD pathogenesis. Functional deficiencies of TREM2 disrupt microglial clustering around amyloid beta (A beta) plaques, impair their transcriptional response to AD, and worsen neuritic dystrophy. How-ever, the molecular mechanism underlying these phenotypes remains unclear. In this study, we investigated the pathological role of another AD risk gene, INPP5D, encoding a phosphoinositide PI(3,4,5)P-3 phosphatase expressed in microglia. In a Tyrobp-deficient TREM2 loss-of-function mouse model, Inpp5d haplodeficiency restored the association of microglia with A beta plaques, partially restored plaque compaction, and astrogliosis, and reduced phosphorylated tau(+) dystrophic neu-rites. Mechanistic analyses suggest that TREM2/TYROBP and INPP5D exert opposing effects on PI(3,4,5)P-3 signaling pathways as well as on phosphoproteins involved in the actin assembly. Our results suggest that INPP5D acts downstream of TREM2/TYROBP to regulate the microglial barrier against A beta toxicity, thereby modulates A beta-dependent pathological conversion of tau.