Identification of Novel Adipokines through Proteomic Profiling of Small Extracellular Vesicles Derived from Adipose Tissue.

Adipose tissue is regarded as a true endocrine organ that releases adipokines to regulate distant targets. Besides the well-studied secretory adipokines, the adipokines carried by small extracellular vesicles derived from adipose tissue (sEV-AT) have not been completely characterized yet. In this study, we conducted a complementary protein profiling on sEV-AT with label-free quantitative proteomic analysis (project accession: PXD013270). A total of 2607 sEV-AT proteins were identified, among which 328 proteins had been annotated as adipokines. Three undefined adipokine candidates (NPM3, STEAP3, and DAD1) were selected for further validation. These three proteins were expressed in both white and brown adipose tissues and upregulated during adipogenic differentiation in both 3T3-L1 cells and adipose-derived stromal/stem cells (ASCs). Expressions of NPM3 and DAD1 in sEV-AT were significantly decreased in obese subjects compared with lean controls, while obesity could not alter the expression of STEAP3. Our profiling study of the sEV-AT proteins expanded the list of adipokines and highlighted the pivotal role of adipokines specifically carried by sEVs in the regulation of multiple biological processes within adipose tissue.