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

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE277167 | GEO | 2024/09/16

REPOSITORIES: GEO

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Project description:Background Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer’s disease (AD). In vitro, microglia preferentially upregulate iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of knocking down microglial iron import gene, Slc11a2, on AD-related cognitive decline and microglial transcriptional phenotype. Methods In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1Cre-ERT2;Slc11a2flfl;APP/PS1+ or – mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b+ microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted. Results DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2KD APP/PS1 females displayed significant increases in genes Enpp2, Ttr, and iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2KD cells from APP/PS1 females also exhibited decreased expression of markers related to disease-associated microglia (DAMs), such as Apoe, Ctsb, Csf1, and Hif1α. Conclusions This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in female microglia and cognitive deficits in Slc11a2KD APP/PS1 mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

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

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