Proteomic Analysis of Extracellular Vesicles Released by Adipocytes of Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

Extracellular vesicles (EVs) such as exosomes are secretory vesicles that act as autocrine, paracrine, or endocrine messengers; mediate intercellular cross-talk; and carry a cargo of various proteins. Because EVs can be transported to recipient cells via circulation, many researchers have been studying EVs from immune cells or cancer cells. Adipocytes are also considered endocrine cells and secrete adipokines such as adiponectin, regulating a variety of intracellular signaling pathways. Expansion of adipose tissue in obesity alters adipokine secretion, thereby increasing the risk of metabolic diseases. Characterization of adipocyte-derived exosomes is necessary to explain the communication between adipocytes and other cell types. In the present study, to identify proteins associated with adipocyte-derived exosomes, we isolated exosomes from adipose tissue of obese diabetic and obese nondiabetic rats. We identified proteins by analyzing exosomes from obese rats with type 2 diabetes and their matched control littermates using nano-liquid chromatography with tandem mass spectrometry coupled with label-free relative quantification. We identified 509 proteins from adipocytes including 81 known adipokines; similar to 78 % of all the identified proteins were categorized as exosome-associated proteins. Among the protein profiles, we uncovered 128 upregulated and 72 downregulated proteins, which are differentially expressed in OLETF adipocyte-derived exosomes. This study seems to demonstrate for the first time hundreds of proteins in exosomes released by adipocytes in obese rats and rats with type 2 diabetes. Thus, protein profiles of exosomes from adipocytes possibly indicate the transmission of signals as part of cell-cell communication and should further our understanding of obesity- and diabetes-related diseases.