Extracellular nanovesicles secreted by human osteosarcoma cells promote angiogenesis

Angiogenesis involves a number of different players among which extracellular nanovesicles (EVs) have recently been proposed as an efficient cargo of pro-angiogenic mediators. Angiogenesis plays a key role in osteosarcoma (OS) development and progression. Acidity is a hallmark of malignancy in a variety of cancers, including sarcomas, as a result of an increased energetic metabolism. The aim of this study was to investigate the role of EVs derived from osteosarcoma cells on angiogenesis and whether extracellular acidity, generated by tumor metabolism, could influence EVs activity. For this purpose, we purified and characterized EVs from OS cells maintained at either acidic or neutral pH. The ability of EVs to induce angiogenesis was assessed in vitro by endothelial cell tube formation and in vivo using chicken chorioallantoic membrane. Our findings demonstrated that EVs derived from osteosarcoma cells maintained either in acidic or neutral conditions induced angiogenesis. The results showed that miRNA and protein content of EVs cargo are correlated with pro-angiogenic activity and this activity is increased by the acidity of tumor microenvironment. This study provides evidence that EVs released by human osteosarcoma cells act as carriers of active angiogenic stimuli that are able to promote endothelial cell functions relevant to angiogenesis.