Protective variant in PLCγ2 mitigates Alzheimer’s disease associated pathology via enhancing beneficial microglia functions

PLCγ2-P522R (phospholipase C gamma 2, proline 522 to arginine) is a protective variant that reduces the risk for late onset Alzheimer’s disease (LOAD). Recently, it was shown to decrease β-amyloid pathology in 5XFAD mouse model of AD. In this study, our goal was to investigate the protective functions of PLCγ2-P522R variant in less aggressive mouse model of AD as well as to assess underlying mechanisms at the molecular and cellular level using mouse and human microglia models. The effects of the protective PLCγ2-P522R variant on microglia activation, AD-related β-amyloid and neuronal pathologies, as well as behavioral changes were investigated in PLCγ2-P522R knock-in mice crossbred with an APP/PS1 mouse model of AD. Transcriptomic, proteomic, and functional studies were carried out in cultured and acutely isolated adult PLCγ2-P522R mouse microglia to study molecular mechanisms. Finally, microglia-like cell models generated from blood and skin biopsy samples of the PLCγ2-P522R variant carriers were employed to translate the key findings in human cells. Our results demonstrate that the PLCγ2-P522R variant reduces brain β-amyloid plaque burden of APP/PS1 mice. Simultaneously, PLCγ2-P522R variant increased non-proinflammatory microglia activation and microglia clustering around β-amyloid plaques, leading to reduced β-amyloid plaque-associated neuronal dystrophy. In cultured mouse primary microglia, PLCγ2-P522R variant decreased accumulation of large lipid droplets, reduced cell stress, and increased acute response to strong inflammatory stimuli. Transcriptomic and proteomic analyses in acutely isolated adult mouse microglia as well as in human monocyte-derived microglial cells showed that PLCγ2-P522R upregulates mitochondrial fatty acid oxidation and downregulates inflammatory/interferon signaling pathways. Accordingly, PLCγ2-P522R increased mitochondrial respiration in iPSC -derived microglial cells. Together, these findings suggest that PLCγ2-P522R variant exerts protection against AD-associated β-amyloid and neuronal pathologies via enhancing microglial barrier formation around β-amyloid plaques, but suppressing pro-inflammatory activation. Observed changes in fatty acid metabolism and mitochondrial flexibility as well as the downregulation of genes involved in inflammatory signaling pathways suggest that these protective effects of the PLCγ2-P522R variant are mediated through an anti-ageing mechanism. APP/PS1xPLCG2-P522R knock in mice (n=4) and respective APP/PS1 control animals (n=4) were sacrificed and transcardially perfused with saline at the age 13-months. Half of the brain was dissected into regional blocks and snap frozed in liquid nitrogen. Temporo-occipital cortex was then homogenized on DPBS and an aliquot was subjected to RNA sequencing (see protocol section). The whole brain of subset of above-described mice was used for acute CD11b+ microglia isolation utilizing magnetic bead-based isolation and subjected to RNA sequencing. Wildtype animals without the AD background were included as controls in the above mentioned analyses. Similarly, CD11b+ microglia isolated from 13-month-old PLCG2-P522R knock in (n=4) and wildtype (n=3) mice without the AD background were used for RNA sequencing studies.