Implication of RPE-derived exosomes in blood vessel formation under stress conditions
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Retinal pigment epithelium
Epitelio pigmentario de la retina
Retinal pigment epithelium (RPE) has a crucial role in the physiology and pathophysiology of the retina due to its location and metabolism. Oxidative damage has been demonstrated as a pathogenic mechanism in several retinal diseases, and reactive oxygen species (ROS) are certainly important by-products ethanol metabolism. Autophagy and exosome secretion are known to play important roles in a variety of physiological and disease states, including the development of neovascular agerelated macular degeneration (NV AMD). Previous studies have demonstrated that these cellular mechanisms share common pathways of activation. Low oxidative damage in ARPE-19, a humanRPE cell line, alters both autophagy and exosome biogenesis. Moreover, oxidative stress modifies the protein and genetic cargo of exosomes, possibly affecting the fate of surrounding cells. In order to understand the connection between these two mechanisms and their impact on angiogenesis, stressed ARPE-19 cells were treated with a siRNA targeting Atg7, a key protein for the formation of autophagosomes. Subsequently, we observed the formation of multivesicular bodies and the release of exosomes, which were found to be decreased in number. RPE-released exosomes contained VEGFR2 as part of their cargo. This receptor for VEGF - which is critical for the development of new blood vessels in NV AMD - was increased in exosome populations released from ARPE-19 cells under oxidative stress. While stressed-RPE exosomes enhanced tube formation of endothelial cells, exosomes became ineffective after silencing VEGFR2 in ARPE-19 cells and were, as a result, unable to influence angiogenesis. Moreover, vessel sprouting in the presence of stressed-RPE exosomes seems to follow a VEGF independent pathway. In view of these results, we propose that abnormal vessel growth correlates with VEGFR2-expression.