Extracellular vesicles (EV) are sub-micron circulating vesicles found in all bodily fluids and in all species so far tested. They have also recently been identified in seawater and it has further been shown that they are released from microorganisms and may participate in interspecies communication in the gut. EV are typically composed of a lipid bilayer formed from the plasma membrane and which encases a cargo that can include genetic material, proteins, and lipids. At least two different processes of formation and release have been described in mammalian cells. The exosome population (50 to 150nm size) are produced via a lyso-endosomal pathway, while microvesicles (100 to 1000nm) are formed by budding of the plasma membrane in a calcium dependent process. Both pathways are highly regulated and appear to be conserved amongst different species. EV release has been shown to be upregulated in a number of human chronic diseases including cardiovascular disease, metabolic disorders, obesity, and cancer; evaluation of their presence in veterinary samples may aid diagnosis in the future. Researchers from the Royal Veterinary College provide insight into the formation of EV and their detection in bodily fluids from different veterinary species and how they may provide a novel addition to the veterinary toolkit of the future.
Mechanisms of extracellular vesicle production and release from cells
Extracellular vesicles include exosomes, microvesicles, and apoptotic bodies (not shown on this diagram). A. Microvesicles (MVs) are approximately 100nm to 1 µm in size, whilst exosomes are 50-150nm in diameter. MVs are released by membrane budding and are decorated with a number of cell surface molecules specific to the parent cell from which they were released and may also have exposed phosphatidyl serine on their outer membrane. B. Exosomes are formed within multivesicular bodies (MVBs) and are released following the fusion of MVB with the plasma membrane. Exosomes have surface markers including CD81, CD63. EV carry cargo including protein, lipids, miRNAs, and mRNAs, which they can deliver to their target cells.