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Microglial repopulation reverses cognitive-associated deficits in an Alzheimer’s disease model by restoring the BDNF signaling

ABSTRACT: Over the past decade, genetic evidence has demonstrated that microglial dysregulation is likely to play a central role in the development of Alzheimer's disease (AD). As resident immune cells in the brain, microglia become dystrophic and senescent during the chronic progression of AD. To explore whether replenishing the brain with new microglia is beneficial to AD, we employed a CSF1R inhibitor PLX3397 to deplete microglia and induce repopulation after the inhibitor withdrawal in 5xFAD transgenic mice. We observed that microglial repopulation ameliorates AD-associated cognitive deficits, accompanied by elevation of synaptic proteins and hippocampal long-term potentiation (LTP). In addition, microglial morphology is restored after microglial self-renewal, and amyloid pathology is reduced with long-term repopulation but not short-term. Transcriptome analysis showed that repopulating microglia in 5xFAD mice recovers a gene expression profile that is highly similar to microglia from WT mice. Notably, the neurotrophic signaling pathway and hippocampal neurogenesis dysregulated in the AD brain are restored after microglial replenishment. At last, we confirmed that microglial repopulation rescues brain-derived neurotrophic factor (BDNF) expression to contribute to synaptic plasticity. Together, we conclude that microglial self-renewal benefits AD brain by restoring the BDNF neurotrophic signaling pathway. Thus, the proper replenishment of microglia may be an effective and novel therapeutic strategy for ameliorating cognition impairment in AD.

ORGANISM(S): Mus musculus

PROVIDER: GSE223156 | GEO | 2023/07/24

REPOSITORIES: GEO

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Project description:Microglia are innate immune cells of the brain that perform phagocytic and inflammatory functions in disease conditions. Transcriptomic studies of acutely-isolated microglia have provided novel insights into their molecular and functional diversity in homeostatic and neurodegenerative disease states. State-of-the-art mass spectrometric methods can comprehensively characterize proteomic alterations in microglia in neurodegenerative disorders, potentially providing novel functionally-relevant molecular insights that are not provided by transcriptomics. However, proteomic profiling of adult primary microglia in neurodegenerative disease conditions has not been performed. We performed quantitative proteomic analyses of purified CD11b+ acutely-isolated microglia adult mice in normal, acute neuroinflammatory (LPS-treatment) and chronic neurodegenerative states (5xFAD model of Alzheimer’s disease [AD]) using tandem mass tag mass spectrometry. Differential expression analyses were performed to characterize specific microglial proteomic changes in 5xFAD mice and identify overlap with LPS-induced pro-inflammatory changes. Our results were also contrasted with existing proteomic data from wild-type mouse microglia and from existing microglial transcriptomic data from wild-type and 5xFAD mice. Neuropathological validation studies of select proteins were performed in human AD and 5xFAD brains. Of 4,133 proteins identified, 187 microglial proteins were differentially expressed in the 5xFAD mouse model of AD pathology, including proteins with previously known (Apoe, Clu and Htra1) as well as previously unreported relevance to AD biology (Cotl1 and Hexb). Proteins upregulated in 5xFAD microglia shared significant overlap with pro-inflammatory changes observed in LPS-treated mice. Several proteins increased in human AD brain were also upregulated by 5xFAD microglia (Aβ peptide, Apoe, Htra1, Cotl1 and Clu). Cotl1 was identified as a novel microglia-specific marker with increased expression and strong association with AD neuropathology. Apoe protein was also detected within plaque-associated microglia in which Apoe and Aβ were highly co-localized suggesting a role for Apoe in phagocytic clearance of Aβ. We report the first comprehensive comparative proteomic study of adult mouse microglia derived from acute neuroinflammatory and AD models, representing a valuable resource to the neuroscience research community. We highlight shared and unique microglial proteomic changes in acute neuroinflammatory, aging and AD mouse models in addition to identifying novel roles for microglial proteins in human neurodegeneration.

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Microglial repopulation reverses cognitive-associated deficits in an Alzheimer’s disease model by restoring the BDNF signaling

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