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We introduce a new method for mesoscopic modeling of protein diffusion in an entire cell. This method is based on the construction of a three-dimensional digital model cell from confocal microscopy data. The model cell is segmented into the cytoplasm, nucleus, plasma membrane, and nuclear envelope, in which environment protein motion is modeled by fully numerical mesoscopic methods. Finer cellular structures that cannot be resolved with the imaging technique, which significantly affect protein motion, are accounted for in this method by assigning an effective, position-dependent porosity to the cell. This porosity can also be determined by confocal microscopy using the equilibrium distribution of a non-binding fluorescent protein. Distinction can now be made within this method between diffusion in the liquid phase of the cell (cytosol/nucleosol) and the cytoplasm/nucleoplasm. Here we applied the method to analyze fluorescence recovery after photobleach (FRAP) experiments in which the diffusion coefficient of a freely-diffusing model protein was determined for two different cell lines, and to explain the clear difference typically observed between conventional FRAP results and those of fluorescence correlation spectroscopy (FCS). A large difference was found in the FRAP experiments between diffusion in the cytoplasm/nucleoplasm and in the cytosol/nucleosol, for all of which the diffusion coefficients were determined. The cytosol results were found to be in very good agreement with those by FCS.

Background Phospholipase C gamma 2, proline 522 to arginine (PLCγ2-P522R) is a protective variant that reduces the risk of Alzheimer’s disease (AD). Recently, it was shown to mitigate β-amyloid pathology in a 5XFAD mouse model of AD. Here, we investigated the protective functions of the PLCγ2-P522R variant in a less aggressive APP/PS1 mouse model of AD and assessed the underlying cellular mechanisms using mouse and human microglial models. Methods The effects of the protective PLCγ2-P522R variant on microglial activation, AD-associated β-amyloid and neuronal pathologies, and behavioral changes were investigated in PLCγ2-P522R knock-in variant mice crossbred with APP/PS1 mice. Transcriptomic, proteomic, and functional studies were carried out using microglia isolated from mice carrying the PLCγ2-P522R variant. Finally, microglia-like cell models generated from human blood and skin biopsy samples of PLCγ2-P522R variant carriers were employed. Results The PLCγ2-P522R variant decreased β-amyloid plaque count and coverage in female APP/PS1 mice. Moreover, the PLCγ2-P522R variant promoted anxiety in these mice. The area of the microglia around β-amyloid plaques was also increased in mice carrying the PLCγ2-P522R variant, while β-amyloid plaque-associated neuronal dystrophy and the levels of certain cytokines, including IL-6 and IL-1β, were reduced. These alterations were revealed through [18F]FEPPA PET imaging and behavioral studies, as well as various cytokine immunoassays, transcriptomic and proteomic analyses, and immunohistochemical analyses using mouse brain tissues. In cultured mouse primary microglia, the PLCγ2-P522R variant reduced the size of lipid droplets. Furthermore, transcriptomic and proteomic analyses revealed that the PLCγ2-P522R variant regulated key targets and pathways involved in lipid metabolism, mitochondrial fatty acid oxidation, and inflammatory/interferon signaling in acutely isolated adult mouse microglia and human monocyte-derived microglia-like cells. Finally, the PLCγ2-P522R variant also increased mitochondrial respiration in human iPSC-derived microglia. Conclusions These findings suggest that the PLCγ2-P522R variant exerts protective effects against β-amyloid and neuronal pathologies by increasing microglial responsiveness to β-amyloid plaques in APP/PS1 mice. The changes observed in lipid/fatty acid and mitochondrial metabolism revealed by the omics and metabolic assessments of mouse and human microglial models suggest that the protective effects of the PLCγ2-P522R variant are potentially associated with increased metabolic capacity of microglia.

Phospholipase C gamma 2, proline 522 to arginine (PLC[gamma]2-P522R) is a protective variant that reduces the risk of Alzheimer's disease (AD). Recently, it was shown to mitigate [beta]-amyloid pathology in a 5XFAD mouse model of AD. Here, we investigated the protective functions of the PLC[gamma]2-P522R variant in a less aggressive APP/PS1 mouse model of AD and assessed the underlying cellular mechanisms using mouse and human microglial models. The effects of the protective PLC[gamma]2-P522R variant on microglial activation, AD-associated [beta]-amyloid and neuronal pathologies, and behavioral changes were investigated in PLC[gamma]2-P522R knock-in variant mice crossbred with APP/PS1 mice. Transcriptomic, proteomic, and functional studies were carried out using microglia isolated from mice carrying the PLC[gamma]2-P522R variant. Finally, microglia-like cell models generated from human blood and skin biopsy samples of PLC[gamma]2-P522R variant carriers were employed. The PLC[gamma]2-P522R variant decreased [beta]-amyloid plaque count and coverage in female APP/PS1 mice. Moreover, the PLC[gamma]2-P522R variant promoted anxiety in these mice. The area of the microglia around [beta]-amyloid plaques was also increased in mice carrying the PLC[gamma]2-P522R variant, while [beta]-amyloid plaque-associated neuronal dystrophy and the levels of certain cytokines, including IL-6 and IL-1[beta], were reduced. These alterations were revealed through [18F]FEPPA PET imaging and behavioral studies, as well as various cytokine immunoassays, transcriptomic and proteomic analyses, and immunohistochemical analyses using mouse brain tissues. In cultured mouse primary microglia, the PLC[gamma]2-P522R variant reduced the size of lipid droplets. Furthermore, transcriptomic and proteomic analyses revealed that the PLC[gamma]2-P522R variant regulated key targets and pathways involved in lipid metabolism, mitochondrial fatty acid oxidation, and inflammatory/interferon signaling in acutely isolated adult mouse microglia and human monocyte-derived microglia-like cells. Finally, the PLC[gamma]2-P522R variant also increased mitochondrial respiration in human iPSC-derived microglia. These findings suggest that the PLC[gamma]2-P522R variant exerts protective effects against [beta]-amyloid and neuronal pathologies by increasing microglial responsiveness to [beta]-amyloid plaques in APP/PS1 mice. The changes observed in lipid/fatty acid and mitochondrial metabolism revealed by the omics and metabolic assessments of mouse and human microglial models suggest that the protective effects of the PLC[gamma]2-P522R variant are potentially associated with increased metabolic capacity of microglia.

PLCγ2-P522R (phospholipase C gamma 2, proline 522 to arginine) is a protective variant that reduces the risk for late onset Alzheimer’s disease. 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 a less aggressive mouse model of AD as well as to assess the 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 APP/PS1 AD model mice. 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 to human cells. Our results demonstrate that the PLCγ2-P522R variant reduced 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 and 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.