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Bulk RNA-seq of adult homeostatic microglia from 4 brain regions

ABSTRACT: To compare microglial regional heterogeneity, we generated bulk RNA-seq profiles of postnatal day 60 microglia, sorted by TMEM119+ (also CD45lowCD11b+), from cortex (CTX), cerebellum (CB), hippocampus (HIP), striatum (STR) regions. For each sample, 3000 microglia were FACS sorted into RLT lysis buffer for total RNA extraction, followed by Smart-seq library preparation and Illumina Nextseq (sequence depth 10-20 million per sample). Consistent with our scRNA-seq data, samples from 4 regions were highly correlated (R>0.99), and individual samples did not cluster according to tissue origins, suggesting striking similarities between homeostatic microglia from different brain regions. Moreover, we could not detect any differentially expressed genes (FDR < 0.05) between regions from the bulk samples. These data suggest that classical adult microglia with homeostatic signatures (e.g. Tmem119), as the most dominant microglial population in the healthy brain, have little transcriptomic heterogeneity across brain regions.

ORGANISM(S): Mus musculus

PROVIDER: GSE123021 | GEO | 2018/12/31

REPOSITORIES: GEO

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Project description:Alzheimer’s Disease (AD) is the most common cause of dementia in the elderly population without a cure or early diagnostics currently available. Despite the demonstrated ability of extracellular vesicles (EVs) to spread tau and Aβ pathology in AD models and their potential utility as a diagnostic and treatment-monitoring tool, our knowledge of human brain EV subpopulations, their molecular composition and roles in disease progression is very limited. Genome-wide association studies linked multiple AD genetic risk factors to microglia-specific pathways suggesting a potential role of microglia-derived EVs in AD progression. Here we are presenting a method for isolation of microglial CD11b-positive small EVs from cryopreserved human brain tissue and multi-omics analysis of the EVs from the parietal cortex of 4 late-stage AD (Braak V-VI) and 3 age-matched normal/low pathology (NL) cases. We identified a total of 1000 proteins by quantitative proteomics, analyzed 594 individual lipid species by targeted lipidomics, and 105 miRNAs using a NanoString miRNA expression panel. We found significant reduction in abundance of homeostatic microglia markers, P2RY12 and TMEM119, and increased levels of disease associated microglia markers, FTH1 and TREM2, in microglial EVs from AD brain compared to NL cases. Protein tau abundance was also significantly higher in AD brain-derived microglial EVs. These changes were accompanied by upregulation of synaptic and neuron-specific proteins in the AD group. Levels of free-cholesterol were elevated in microglial EVs from AD brain. Lipidomic analysis also revealed a pro-inflammatory lipid profile, endolysosomal dysfunction and significant AD-associated decrease in levels of docosahexaenoic acid (DHA)-containing polyunsaturated lipids of different classes, suggesting a potential defect in acyl-chain remodeling. Several immune pathways and senescence were among the top pathways controlled by 4 miRNAs significantly upregulated in the AD group. Our data suggest that loss of the homeostatic microglia signature in late AD stages may accompany endolysosomal impairment and release of undigested neuronal and myelin debris, including tau, through extracellular vesicles. These data validate a method of isolation of small cell-type specific EVs from human brain tissue, suggests new potential EV-associated markers and disease-related pathways, and provides a framework for future large-scale multi-omics study.

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Bulk RNA-seq of adult homeostatic microglia from 4 brain regions

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