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Enrichment of Astrocyte-Derived Extracellular Vesicles from Human Plasma
Published on: August 3, 2022
Multi-Omics Analysis of Microglial Extracellular Vesicles From Human Alzheimer's Disease Brain Tissue Reveals
Whitaker Cohn1, Mikhail Melnik2, Calvin Huang2
1Drug Discovery Lab, Department of Neurology, University of California, Los Angeles, Los Angeles, CA, United States.
Abstract:
Alzheimer's disease (AD) is the most common cause of dementia, yet there is no cure or diagnostics available prior to the onset of clinical symptoms. Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are released from almost all types of cell. Genome-wide association studies have linked multiple AD genetic risk factors to microglia-specific pathways. It is plausible that microglia-derived EVs may play a role in the progression of AD by contributing to the dissemination of insoluble pathogenic proteins, such as tau and Aβ. Despite the potential utility of EVs as a diagnostic tool, our knowledge of human brain EV subpopulations is limited. Here we present a method for isolating microglial CD11b-positive small EVs from cryopreserved human brain tissue, as well as an integrated multiomics analysis of microglial EVs enriched from the parietal cortex of four late-stage AD (Braak V-VI) and three age-matched normal/low pathology (NL) cases. This integrated analysis revealed 1,000 proteins, 594 lipids, and 105 miRNAs using shotgun proteomics, targeted lipidomics, and NanoString nCounter technology, respectively. The results showed a significant reduction in the abundance of homeostatic microglia markers P2RY12 and TMEM119, and increased levels of disease-associated microglia markers FTH1 and TREM2, in CD11b-positive EVs from AD brain compared to NL cases. Tau abundance was significantly higher in AD brain-derived microglial EVs. These changes were accompanied by the upregulation of synaptic and neuron-specific proteins in the AD group. Levels of free cholesterol were elevated in microglial EVs from the AD brain. Lipidomic analysis also revealed a proinflammatory lipid profile, endolysosomal dysfunction, and a significant AD-associated decrease in levels of docosahexaenoic acid (DHA)-containing polyunsaturated lipids, suggesting a potential defect in acyl-chain remodeling. Additionally, four miRNAs associated with immune and cellular senescence signaling pathways were significantly upregulated in the AD group. Our data suggest that loss of the homeostatic microglia signature in late AD stages may be accompanied by endolysosomal impairment and the release of undigested neuronal and myelin debris, including tau, through extracellular vesicles. We suggest that the analysis of microglia-derived EVs has merit for identifying novel EV-associated biomarkers and providing a framework for future larger-scale multiomics studies on patient-derived cell-type-specific EVs.
Insights
Researchers developed a method to isolate microglial extracellular vesicles (EVs) from human brain tissue. Analysis revealed elevated tau and altered lipid profiles in EVs from Alzheimer
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Alzheimer's disease (AD) is the most common cause of dementia, lacking early diagnostic tools or cures.
- Microglia, the brain's immune cells, are implicated in AD pathogenesis, with their derived extracellular vesicles (EVs) potentially playing a role in disease progression.
- Current understanding of human brain EV subpopulations, particularly those derived from microglia, is limited.
Purpose of the Study:
- To develop a method for isolating microglial CD11b-positive small EVs from cryopreserved human brain tissue.
- To perform an integrated multiomics analysis of these EVs from late-stage AD and normal/low pathology (NL) cases.
- To identify potential EV-associated biomarkers for Alzheimer's disease.
Main Methods:
- Isolation of microglial CD11b-positive small EVs from human parietal cortex tissue.
- Integrated multiomics analysis including shotgun proteomics, targeted lipidomics, and miRNA profiling (NanoString nCounter).
- Comparison of EV composition between four late-stage AD (Braak V-VI) and three age-matched NL cases.
Main Results:
- Significant reduction in homeostatic microglia markers (P2RY12, TMEM119) and increase in disease-associated markers (FTH1, TREM2) in AD-derived EVs.
- Elevated tau protein levels and upregulation of synaptic/neuron-specific proteins in EVs from AD brains.
- Alterations in lipid profiles, including increased free cholesterol, a proinflammatory signature, endolysosomal dysfunction, and decreased docosahexaenoic acid (DHA)-containing lipids in AD EVs.
Conclusions:
- Loss of homeostatic microglia signature in late AD stages is associated with endolysosomal impairment and release of neuronal/myelin debris via EVs.
- Microglia-derived EVs carry tau and other pathological molecules, suggesting their role in AD progression.
- Analysis of microglia-derived EVs shows promise for identifying novel biomarkers and warrants further large-scale multiomics studies on patient-derived EVs.
