Exosomes are nanovesicles that have emerged as a new intercellular communication system for transporting proteins and RNAs; recent studies have shown that they play a role in many physiological and pathological processes such as immune regulation, cell differentiation, infection and cancer. By transferring proteins, mRNAs and microRNAs, exosomes act as information vehicles that alter the behavior of recipient cells. Compared to direct cell-cell contact or secreted factors, exosomes can affect recipient cells in more efficient ways. In whole adipose tissues, it has been shown that exosomes exist in supernatants of adipocytes and adipose stromal cells (ADSCs). Adipocyte exosomes are linked to lipid metabolism and obesity-related insulin resistance and exosomes secreted by ADSCs are involved in angiogenesis, immunomodulation and tumor development.
Roles of exosomes in obesity-related diseases.
(a) Exosomes taken in by small adipocytes result in enlargement of lipid droplets. In hypoxia, exosomes increase production of lipogenic enzymes (such as FASN, G6PD, ACC) and the size of lipid droplets. (b) Exosomes from obese individuals’ adipose tissue activates monocyte differentiation into macrophages and prompts secretion of inflamation factors IL-6 and TNF-α, resulting in insulin resistance in adipocytes and liver. (c) Exosomes from obese individuals’ adipocytes increase secretion of tissue inhibitor of metalloproteinases 1 (TIMP-1) and plasminogen activator inhibitor-1 (PAI-1) promoting liver fibrogenesis. (d) Exosomes released from dysfunctional and hypertrophic adipocytes impaire function of vascular endothelial cells, indicating the functions of exosomes in development of obesity-linked complications.