Proteomic profiling of tissue extracellular vesicles (EVs) identifies tissue EV markers and estimates the abundance of tissue EVs in the circulation

Extracellular vesicles (EVs) mediate cell-to-cell communication in endocrine, paracrine, and autocrine fashions, but their roles and transport in the body remain incompletely understood. It is suggested that EVs circulate in the body through the bloodstream, where EVs derived from various tissues are present. However, how much each tissue contributes to circulating EVs is largely unknown. Therefore, identifying tissue-specific EV markers is of importance for elucidating in vivo dynamics of tissue EVs. A key issue that hampers studying EVs in vivo is the lack of methodologies for collecting them from tissues. Here, we developed methods to isolate EVs from four different tissues, skeletal muscle, heart, liver, and adipose tissue, and performed proteomic analysis on their EVs. Unbiased and quantitative proteomic analysis revealed protein signatures of EVs from the four tissues and identified marker proteins specific to or highly enriched in EVs of each tissue. Furthermore, through comprehensive comparisons of the proteome from tissue and plasma EVs, we estimated the relative contribution of tissue EVs to circulating EVs. Our data suggest that adipose tissue-derived EVs are highly enriched, while skeletal muscle-derived EVs are only a minor population in circulating EVs. Collectively, our tissue EV proteome identified potential tissue EV markers and suggested that the abundance of tissue EVs in circulation highly depends on the original tissues.