APOE4 Alters the Inflammatory and Metabolic Properties of Extracellular Vesicles of Induced Pluripotent Stem Cell-derived Astrocytes and Mesenchymal Stromal Cells

Background Apolipoprotein E (APOE) is a lipid transporter whose variant, APOE4 , is the strongest genetic predictor of Alzheimer’s disease development. APOE’s role as a lipid transporter is disrupted with E4 due to differences in its binding affinity, altering APOE’s preferred lipid substrate. This alters the cholesterol homeostasis of neural cells such as astrocytes, leading to lipid droplet formation, a driver of neuroinflammation. In addition, APOE has been identified as a cargo protein carried within extracellular vesicles (EVs), including exosomes, suggesting EVs play a role in regulating neural lipid metabolism. However, the extent and further results of APOE disruption of EV excretion and cargo are not well-established. Methods This study seeks to identify differences in EV secretion and bioactivity between APOE3 and APOE4 genotypes in various cell types and the role they play in Alzheimer’s disease pathogenesis. Human pluripotent potent stem cell-derived astrocytes (iASs) and mesenchymal stromal cells (iMSCs) with homozygous APOE3 and homozygous APOE44 cellswere derived and the secreted EVs were characterized. Results Our results indicate that EV secretion was comparable in APOE3 and APOE4 cells, although decreased expression of the endosomal sorting complex required for transport (ESCRT) dependent and independent genes in APOE4 cells was observed. When treating THP-1 cells, an innate inflammatory capability is observed across cell types in APOE4 EVs, increasing the levels of NF-κB activation significantly compared to untreated controls. Quantitative lipidomics revealed increased levels of total lipid and lipid classes involved in the mediation of lipid stress in APOE4 EVs. In addition, lipids involved in EV biogenesis are dysregulated. KEGG analysis showed upregulation of functional pathways of interest in Alzheimer’s Disease progression, including efferocytosis, choline metabolism, and bile acid synthesis. Conclusions Our results suggest that APOE4 may affect the lipid cargo of the EVs, which is hypothesized to be a result of endosomal trafficking via interruptions in both ESCRT dependent and independent biogenesis pathways. Furthermore, disrupted lipid metabolism in APOE4 could affect ESCRT-independent EV formation. APOE4 derived EVs have innate inflammatory properties that are exacerbated in the presence of excess fatty acid. This study paves the way for understanding the role of EVs in mediating inflammation and lipid metabolism in APOE4 related Alzheimer’s disease.