The Alzheimer’s disease protective P522R variant of PLCG2 , consistently enhances stimulus-dependent PLCγ2 activation, depleting substrate and altering cell function

Recent genome-wide association studies of Alzheimer’s disease (AD) have identified variants implicating immune pathways in disease development. A rare coding variant of , which encodes PLCγ2, shows a significant protective effect for AD (rs72824905, P522R, =5.38×10, Odds Ratio = 0.68). Molecular dynamic modelling of the PLCγ2-R522 variant, situated within the auto-inhibitory domain of PLCγ2, suggests a structural change to the protein. Through CRISPR-engineering we have generated novel -R522 harbouring human induced pluripotent cell lines (hiPSC) and a mouse knockin model, neither of which exhibits alterations in endogenous expression. Mouse microglia and macrophages and hiPSC-derived microglia-like cells with the R522 mutation, all demonstrate a consistent non-redundant hyperfunctionality in the context of normal expression of other PLC isoforms. This signalling alteration manifests as enhanced cellular Ca store release (∼20-40% increase) in response to physiologically-relevant stimuli (e.g. Fc receptor ligation and Aβ oligomers). This hyperfunctionality resulted in increased PIP depletion in the cells with the PLCγ2-R522 variant after exposure to stimuli and reduced basal detection of PIP levels . These PLCγ2-R522 associated abnormalities resulted in impairments to phagocytosis (fungal and bacterial particles) and enhanced endocytosis (Aβ oligomers and dextran). PLCγ2 sits downstream of disease relevant pathways, such as TREM2 and CSF1R and alterations in its activity, direct impacts cell function, which in the context of the inherent drugability of enzymes such as PLCγ2, raise the prospect of manipulation of PLCγ2 as a therapeutic target in Alzheimer’s Disease.