Exosomes

D ow nloaded from DOI: 10.1161/CIRCULATIONAHA.112.146738 2 In multicellular organisms, cells communicate with each other via extracellular molecules such as nucleotides, lipids, short peptides, or proteins. These molecules are released in the extracellular space to bind to receptors on other cells, thus modifying intracellular signaling in the recipient cells. In addition to these single molecules, cells also release in their extracellular environment a series of complex structures called membrane vesicles, which contain numerous proteins, lipids, and even nucleic acids1. Although known for several decades to exist, membrane vesicles have long been thought of as mere cell debris. Over the past few years, however, accumulated evidence has shown that vesicles can affect the cells they encounter by acting as signaling vehicles containing a cell-specific cargo of proteins, lipids, and genetic material that are moved to other cells where they alter function and physiology. The topic of extracellula