miRNAs in Vesicles
Accumulating evidence supports the notion that extracellular miRNAs exhibit remarkable stability (Bertoia et al. 2015). It is assumed that this occurs though their presence in vesicles, protein and lipoprotein complexes. The release of cellular vesicles has emerged as a novel mechanism of intercellular communication. Most cells in response to stimulation or under basal conditions will form and secrete vesicles through a variety of processes. The released vesicles that may differ in size and content can transfer proteins, miRNAs or mRNA and can target recipient cells through membrane fusion, endocytosis or receptor-mediated binding (Loyer et al. 2014).
Apoptotic bodies (ABs) are the largest vesicles (>1 pm) that are released in the circulation upon cell apoptosis. ABs have been implicated in tissue repair and regeneration, and microarray analysis revealed that the miRNA content reflects their cellular origin (Zernecke et al. 2009). The transfer of miR-126 residing in ABs to endothelial cells in a mouse model of atherosclerosis had a protective effect mainly through the regulation of CXCL12 production and the recruitment of progenitor cells that promoted tissue repair (Zernecke et al. 2009). This effect was abolished when ABs from miR-126 null mice were applied indicating that miR-126 mediated the protective response.