Evidence for adipocyte-derived extracellular vesicles in the human circulation

Abstract

Adipocyte-derived extracellular vesicles (EVs) may serve as novel endocrine mediators of adipose tissue and impact upon vascular health. However, it is unclear whether adipocyte-derived EVs are present in the human circulation. Therefore, the purpose of this study was to seek evidence for the presence of adipocyte-derived EVs in circulating plasma. Size exclusion chromatography of platelet-free plasma identified fractions 5-10 as containing EVs by a peak in particle concentration, which corresponded with the presence of EV and adipocyte proteins. Pooling fractions 5-10 and subjecting to ultracentrifugation yielded a plasma EV sample, as verified by transmission electron microscopy (TEM) showing EV structures and Western blotting for EV (e.g. CD9 and Alix) and adipocyte markers. Magnetic beads and a solid phase assay were used to deplete the EV sample of the four major families of circulating EVs: platelet-, leukocyte-, endothelial- and erythrocyte-derived EVs. Post-depletion samples from both techniques contained EV structures as visualized by TEM, as well as CD9, Alix and classic adipocyte proteins. Post-depletion samples also contained a range of other adipocyte proteins from an adipokine array. Adipocyte proteins and adipokines are expressed in optimally processed plasma EV samples, suggesting that adipocyte-derived EVs are secreted into the human circulation