Alzheimer’s disease-associated protective variant Plcg2-P522R modulates peripheral macrophage function in a sex-dimorphic manner

ABSTRACT Genome-wide association studies have identified a protective mutation in the phospholipase C gamma 2 (PLCG2) gene which confers protection against Alzheimer’s disease (AD)-associated cognitive decline. Therefore, PLCG2, which is primarily expressed in immune cells, has become a target of interest for potential therapeutic intervention. The protective allele, known as P522R, has been shown to be hyper-morphic in microglia, increasing phagocytosis of amyloid-beta (Aβ), and increasing the release of inflammatory cytokines. However, the effect of this protective mutation on peripheral tissue-resident macrophages, and the extent to which sex modifies this effect, has yet to be assessed. Herein, we show that peripheral macrophages carrying the P522R mutation do indeed show functional differences compared to their wild-type (WT) counterparts, however, these alterations occur in a sex-dependent manner. In macrophages from females, the P522R mutation increases lysosomal protease activity, cytokine secretion, and gene expression associated with cytokine secretion and apoptosis. In contrast, in macrophages from males, the mutation causes decreased phagocytosis and lysosomal protease activity, modest increases in cytokine secretion, and induction of gene expression associated with negative regulation of the immune response. Taken together, these results suggest that the mutation may be conferring different effects dependent on sex and cell type, and highlight the importance of considering sex as a biological variable when assessing the effects of genetic variants and implications for potential immune system-targeted therapies. Competing Interest Statement The authors have declared no competing interest. Footnotes Manuscript has been revised in response to reviewer comments. Analysis now mainly focuses on within-sex comparisons. Figures, text, and supplement are all revised. LIST OF ABBREVIATIONS - PLCG2 - phospholipase C gamma 2 - AD - Alzheimer’s disease - Aβ - amyloid-beta - TREM2 - triggering receptor expressed on myeloid cells 2 - TLR - toll-like receptor - PIP2 - phosphatidylinositol (4,5) bisphosphate - DAG - diacylglycerol - IP3 - inositol 1,4,5 triphosphate - LPM - large peritoneal macrophage - SPM - small peritoneal macrophage - WT - wild-type - PBS - phosphate buffered saline - FMOC - fluorescence minus one control - MSD - MesoScale Discovery - LLOD - lower limit of detection - SEM - standard error of the mean - MHCII - major histocompatibility complex II - LPS - lipopolysaccharide - DEG - differentially expressed gene