PIP2 depletion and altered endocytosis caused by expression of Alzheimer's disease‐protective variant PLCγ2 R522

• Published in: The EMBO journal 2021-09, Vol.40 (17), p.e105603-n/a
• Main Authors: Maguire, Emily, Menzies, Georgina E, Phillips, Thomas, Sasner, Michael, Williams, Harriet M, Czubala, Magdalena A, Evans, Neil, Cope, Emma L, Sims, Rebecca, Howell, Gareth R, Lloyd‐Evans, Emyr, Williams, Julie, Allen, Nicholas D, Taylor, Philip R
• Format: Article
• Language: English
• Subjects: Alzheimer Disease - genetics; Alzheimer's disease; Amyloid beta-Peptides - metabolism; Animals; Calcium; Calcium ions; Cell culture; Cell Line; Cell lines; Cells, Cultured; Depletion; EMBO24; EMBO27; Endocytosis; Fc receptors; Genomes; Humans; Hyperactivity; Isoforms; Macrophages; Macrophages - metabolism; Mice; Mice, Inbred C57BL; Microglia; Mutation; Mutation, Missense; Neurodegenerative diseases; Neuroglia - metabolism; Oligomers; Phagocytes; Phagocytosis; Phosphatidylinositol 4,5-diphosphate; Phosphatidylinositol 4,5-Diphosphate - metabolism; PIP2; PLCG2; Pluripotency; Protein Kinase C - genetics; Protein Kinase C - metabolism; Substrates
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2020105603

Variants identified in genome‐wide association studies have implicated immune pathways in the development of Alzheimer’s disease (AD). Here, we investigated the mechanistic basis for protection from AD associated with PLCγ2 R522, a rare coding variant of the PLCG2 gene. We studied the variant's role in macrophages and microglia of newly generated PLCG2 ‐R522‐expressing human induced pluripotent cell lines (hiPSC) and knockin mice, which exhibit normal endogenous PLCG2 expression. In all models, cells expressing the R522 mutation show a consistent non‐redundant hyperfunctionality in the context of normal expression of other PLC isoforms. This manifests as enhanced release of cellular calcium ion stores in response to physiologically relevant stimuli like Fc‐receptor ligation or exposure to Aβ oligomers. Expression of the PLCγ2‐R522 variant resulted in increased stimulus‐dependent PIP 2 depletion and reduced basal PIP 2 levels in vivo . Furthermore, it was associated with impaired phagocytosis and enhanced endocytosis. PLCγ2 acts downstream of other AD‐related factors, such as TREM2 and CSF1R, and alterations in its activity directly impact cell function. The inherent druggability of enzymes such as PLCγ2 raises the prospect of PLCγ2 manipulation as a future therapeutic approach in AD. SYNOPSIS The Alzheimer’s disease protective variant of PLCG2, R522, is hyperfunctional and alters endocytic and phagocytic uptake by macrophages and microglia. Hyperfunctionality of the R522 variant can lead to substrate depletion, which would have implications for therapeutic approaches. We observed a clear consistent increase in enzymatic activation in both human and mouse microglia and macrophages due to the Alzheimer’s disease protective variant of PLCG2 (R522). Hyperactivity of PLCγ2‐R522 results in substrate depletion in macrophages and microglia. Cells expressing the R522 variant exhibit alterations in the phagocytic and endocytic activities. Graphical Abstract Expression analyses in hIPSCs and knock‐in mice implicate enhanced Ca 2+ release and stimulus‐dependent PIP2 depletion in macrophages and microglia in Alzheimer's disease protection associated with a rare PLCG2 coding variant.