THE ROLE OF ADIPOCYTE-DERIVED EXTRACELLULAR VESICLES IN DIABETES-ASSOCIATED ENDOTHELIAL DYSFUNCTION

The development of diabetes (T2D) is strongly associated with obesity, and both are well-established risk factors for cardiovascular disease. Endothelial dysfunction is an early event in developing vascular complications in obese diabetic (OB-T2D) adults. Therefore, our long-term goal is to identify endothelial dysfunction mechanisms in this population, mainly those related to the multifaceted crosstalk between dysfunctional adipocytes and endothelial cells. Our recent findings revealed that ex vivocultured human adipose tissues (AT) release extracellular vesicles (EVs) that are efficiently captured by endothelial cells. These EVs are lipid-enclosed structures that carry bioactive cargos and are considered vital mediators of intercellular communication. Adipocyte-derived EVs (adiposomes) mediate signaling between cell types within the AT and circulate in the blood to communicate signals to remote cells and tissues. The purpose of this study is to investigate the role of adiposomes in communicating the unhealthy milieu of dysfunctional AT to endothelial cells in OB-T2D. Altered lipid metabolism and enhanced ceramide synthesis in OB-T2D induce adiposome production. Under hyperglycemia, ceramides could be glycosylated into glycosphingolipids (GSLs), selectively packed in adiposomes to be cleared away from adipocytes. We hypothesize that the AT from OB-T2D patients creates excess GSL-rich adiposomes, which are incorporated into endothelial cells causing alterations in endothelial cell properties and function. To test this hypothesis, AT samples were collected from OB-T2D and non-OB subjects (n=10, each). Nanoparticle analysis and confocal microscopy were used to analyze these adiposomes, and mass spectrometry and Western blotting techniques were used to examine their content. Adiposome uptake, lipid fusion, and changes in endothelial membrane structure and signaling pathways were also assessed following adiposome incubation with microvascular endothelial cells. Our data showed that in comparison to non-obese controls, adiposomes isolated from OB-T2D adipose tissues contained higher levels of GSLs. When added to cultured endothelial cells, GSL-rich adiposomes tended to accumulate in an endothelial structure known as caveolae. These caveolae cover more than 50% of the endothelial cell surface and serve to concentrate signal transduction molecules such as endothelial nitric oxide synthase (eNOS) and others involved in angiogenesis, transcytosis, and permeability. According to our findings, the phosphorylation of the key caveolar protein caveolin-1 by GSL-rich adiposomes caused caveolar fission from the endothelial cell surface. This effect was mediated via an activation of Src kinase, as it was inhibited by the Src kinase inhibitor, PP2. These molecular events were accompanied by reductions in endothelial nitric oxide synthase (eNOS) activation and nitric oxide production, disturbances in endothelial gap junction, and increased permeability. Accordingly, we conclude that dysfunctional AT in OB-T2D patients produce GSL-loaded adiposomes that fuse with endothelial cells and activate the Src kinase pathway resulting in caveolar fission and endothelial cell dysfunction.