**8. EV release in health and disease**

A myriad of different mechanisms have been shown to contribute to EV release in various types of cells. These mechanisms include specialized roles of proteins

#### *Mechanisms of Extracellular Vesicle Biogenesis, Cargo Loading, and Release DOI: http://dx.doi.org/10.5772/intechopen.100458*

including Rab proteins, SNARE proteins, small GTPases of the Rho/Rac/cdc42 family, and diacyl glycerol kinase α. These mechanisms also include posttranslational modifications of EV cargo proteins, inhibition of various kinases, and activation of cell surface receptors. Different Rab proteins play specialized roles in regulating exosome transport between different cellular compartments. For example, Rab5 and Rab7 are important in delivering cargo to the early endosomes, while Rab27 is involved in membrane docking to promote fusion, while Rab11 and Rab35 are involved in MVE secretion [42]. The process by which exosomes bud off the plasma membrane is accomplished with the activation of the ARF6 protein [43].

The specific inhibition of protein kinase C, but not protein kinase D in cultured human aortic endothelial cells resulted in both an increase in EV size and increase in EV release [18]. It is still not known whether the increase in EV release is a direct consequence of decreased Protein Kinase C (PKC) activity or a indirect consequence resulting from other proteins that are regulated by PKC activity. Also, it is likely that various mechanisms that regulate PKC activity such as diacylglycerol (DAG) also regulate EV size and release. This could provide a feedback mechanism by which EVs that are released by one cell type and taken up by another cell type can regulate the release of EVs in the recipient cells.

Pharmacological activation of specific G-protein coupled receptors (GPCRs) from trophoblast cells was shown to trigger the release of EVs [17]. Activation of CCKBR, TAS2R14, cholinergic muscarinic 1 and 3, and angiotensin II receptors, each increased EV release without affecting the overall size of the EVs [17]. Also, EV release by the calcium ionophore, A23187, was less robust when compared to receptor-mediated stimulation [17]. These finding warrant the investigation on whether activation of other GPCRs can mediate EV release.
