The Alzheimer's disease-associated protective Plcγ2-P522R variant promotes beneficial microglial functions

BackgroundMicroglia-specific genetic variants are enriched in several neurodegenerative diseases, including Alzheimers disease (AD), implicating a central role for alterations of the innate immune system in the disease etiology. A rare coding variant in the PLCG2 gene (rs72824905, p.P522R) selectively expressed in microglia and macrophages was recently identified and shown to reduce the risk for AD. MethodsTo assess the role of this variant in the context of immune cell functions, we generated a Plc{gamma}2-P522R knock-in (KI) mouse model using CRISPR/Cas9 gene editing. ResultsFunctional analyses of macrophages derived from homozygous KI mice and wild type (WT) littermates revealed that the P522R variant potentiates the primary function of Plc{gamma}2 as a Pip2-metabolizing enzyme. This was associated with improved survival, enhanced phagocytic activity, and increased acute inflammatory response of the KI cells. Enhanced phagocytosis was also observed in mouse BV2 microglia-like cells overexpressing human PLC{gamma}2-P522R, but not in PLC{gamma}2-WT expressing cells. Furthermore, the brain mRNA signature together with microglia-specific PET imaging indicated microglia activation in Plc{gamma}2-P522R KI mice. ConclusionThus, we have delineated cellular mechanisms of the protective Plc{gamma}2-P522R variant, which provide further support for the emerging idea that activated microglia exert protective functions in AD.