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Effect of Bacteroides fragilis administration on microglia in WT and the APP-PS1 model of Alzheimer's disease [Bfrag]

ABSTRACT: The gut microbiota and innate immune system play critical roles in Alzheimer’s disease (AD). Bacteroides is elevated in AD patients and correlates with cerebrospinal fluid levels of Aβ and tau. We found that increased amyloid-β (Aβ) plaques in Bacteroides fragilis treated APP/PS1-21 mice were associated with altered cortical expression Aβ processing genes. B. fragilis suppressed peripheral CD4+ T cell production of GM-CSF and IL-4 and transcriptional changes in microglia related to GM-CSF and IL-4 signaling, phagocytosis, and protein degradation. Furthermore, B. fragilis impaired the microglial uptake of intracranially injected Aβ42, whereas Erysipelotrichaceae strains increased uptake. Depleting murine Bacteroidetes with metronidazole decreased amyloid load in aged 5xFAD mice, increased CD4+ T cell GM-CSF production, and activated microglial pathways related to cytokine signaling, phagocytosis and lysosomal degradation. These data suggest that the gut microbiome may contribute to AD pathogenesis by suppressing peripheral cytokines and microglia phagocytic function, leading to impaired immune-mediated Aβ clearance.

ORGANISM(S): Mus musculus

PROVIDER: GSE215438 | GEO | 2024/10/12

REPOSITORIES: GEO

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Project description:Background: ABCA1 has recently been identified as a novel genetic risk factor for Alzheimer’s disease. The major known role of ABCA1 in the brain is to transfer lipids onto lipid poor APOE. Given that APOEε4 is the strongest genetic risk factor for developing late onset Alzheimer’s disease, this recent finding implicates the cholesterol homeostatic pathway in the onset/progression of Alzheimer’s disease. microRNAs (miRs) are small RNA species that negatively regulate expression of their target genes. ABCA1 is regulated by miR-33, and loss of this miR significantly increases protein levels of ABCA1 and increases the lipidation of APOE. However, it is unknown if loss of miR-33 and subsequent increase in ABCA1 protein levels ameliorates amyloid pathology. Methods: We generated miR-33+/+;APP/PS1 and miR-33-/-;APP/PS1 mice to determine changes in amyloid-beta (Aβ) peptides and amyloid plaque formation utilizing biochemical and histological analyses. In addition to amyloid pathology, we assessed if deletion of miR-33 altered the activation of glial cells in the brains of these mice. We utilized in vitro methods to determine if miR-33 alters the phagocytosis of Aβ aggregates. We utilized RNA-sequencing and mass spectrometry to identify the transcriptome and proteome regulation by miR-33 in the context of amyloid pathology. Results: Deletion of miR-33 dramatically reduces insoluble Aβ peptide levels and the deposition of amyloid plaques in APP/PS1 mice. In addition, we identified that astrocyte and microglial activation is markedly decreased in miR-33-/-;APP/PS1 mice through histological analyses. Intriguingly, we show that loss of miR-33 results in amyloid plaques that are more compact, potentially implicating enhanced microglial phagocytosis. We confirm in vitro that loss of miR-33 significantly increases microglial phagocytosis of Aβ aggregates. Our multi-omics analyses reveal that deletion of miR-33 regulates immune response in the context of amyloid pathology. Interestingly, we identified that WNT/Beta-catenin signaling is significantly upregulated in miR-33-/-;APP/PS1 mice. Conclusion: We confirm that the deletion of miR-33 increases APOE lipidation and significantly reduces amyloid pathology as well as glial activation in APP/PS1 mice. Our results agree with previous work identifying APOE lipidation as an important modulator of amyloid pathology. We show, for the first time, that loss of miR-33 increases the phagocytosis of Aβ by microglia. In total, we identify miR-33 as a promising target for the amelioration of amyloid pathology.

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Effect of Bacteroides fragilis administration on microglia in WT and the APP-PS1 model of Alzheimer's disease [Bfrag]

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