Characterization of Brain-Derived Extracellular Vesicle Lipids in Alzheimer’s Disease

Abstract

Lipid dyshomeostasis is associated with the most common form of dementia, Alzheimer's disease (AD). Substantial progress has been made in identifying positron emission tomography (PET) and cerebrospinal fluid (CSF) biomarkers for AD, but they have limited use as front-line, non-invasive diagnostic tools. Small extracellular vesicles (EVs) are released by all cell types and contain an enriched subset of their parental cell molecular composition, including lipids. EVs are released from the brain into the periphery, providing a potential source of tissue and disease specific lipid biomarkers. However, the EV lipidome of the central nervous system (CNS) is currently unknown and the potential of brain-derived EVs (BDEVs) to inform on lipid dyshomeostasis in AD remains unclear. The aim of this study was to reveal the lipid composition of BDEVs in human frontal cortex tissue, and to determine whether BDEVs in AD have altered lipid profiles compared to age-matched neurological controls (NC). Using semi-quantitative mass spectrometry, we describe the BDEV lipidome, covering 4 lipid categories, 17 lipid classes and 692 lipid molecules. Frontal cortex-derived BDEVs were enriched in glycerophosphoserine (PS) lipids, a characteristic of small EVs. Here we further report that BDEVs are enriched in ether-containing PS lipids, a finding that further establishes ether lipids as a feature of EVs. While no significant changes were detected in the frontal cortex in AD relative to neurological control subjects, the lipid profile of the BDEVs from AD tissue exhibited disease related differences. AD BDEVs had significantly altered glycerophospholipid (GP) and sphingolipid (SP) levels, specifically increased plasmalogen glycerophosphoethanolamine (PE-P) and decreased polyunsaturated fatty acyl containing lipids (PUFAs), and altered amide-linked acyl chain content in sphingomyelin (SM) and ceramide (Cer) lipids relative to vesicles from neurological control subjects. The most prominent alteration was a two-fold decrease in lipid species containing the anti-inflammatory/pro-resolving docosahexaenoic acid (DHA). The in-depth lipidome analysis provided in this study highlights the advantage of EVs over more complex tissues for improved detection of dysregulated lipids that may serve as potential biomarkers in the periphery.

Imaging flow cytometry challenges the usefulness of classically used extracellular vesicle labeling dyes and qualifies the novel dye Exoria for the labeling of mesenchymal stromal cell–extracellular vesicle preparations

“…Many studies have demonstrated that EV preparations from different cell sources vary in their lipid composition [45,46]. Such differences have been considered to serve as potential biomarkers for cancers such as colorectal cancer [47] and prostate cancer [48] as well as Alzheimer disease [49]. Furthermore, many groups have utilized such differences to selectively capture EVs by utilizing different lipid-binding molecules (i.e., cholera toxin B chain, Shiga toxin B subunit and annexin V) [50].…”

Imaging flow cytometry challenges the usefulness of classically used EV labelling dyes and qualifies that of a novel dye, named Exoria™ for the labelling of MSC-EV preparations

“…Many studies have demonstrated that EV preparations from different cell sources have varied lipid compositions (Skotland et al, 2019;Skotland et al, 2017). These differences have been studied as potential biomarkers for cancers such as colorectal cancer (Lydic et al, 2015), prostate cancer (Brzozowski et al, 2018) and Alzheimer disease (Su et al, 2020). Furthermore, many groups have utilized these differences to selectively capture EVs by utilizing different lipid binding molecules, i.e.…”

Balancing cholesterol in the brain: from synthesis to disposal

“…The precise molecular mechanisms of how the different ApoE isoforms and clusterin transport cholesterol in healthy brains versus in Alzheimer's disease still require further examination. The lipid and apolipoprotein composition of extracellular vesicles from healthy and diseased brains could be analyzed by comprehensive 'omic' studies [85]. These vesicles are reflective of intracellular contents, providing a non-invasive method of study.…”