MicroRNA-210 modulates endothelial cell response to hypoxia and inhibits the receptor tyrosine kinase ligand Ephrin-A3

MicroRNAs (miRNAs) are small non-proteincoding RNAs that function as negative gene expression regulators. In the present study, we investigated miRNAs role in endothelial cell response to hypoxia. We found that the expression of miR-210 progressively increased upon exposure to hypoxia. miR-210 overexpression in normoxic endothelial cells stimulated the formation of capillary-like structures on Matrigel and VEGF-driven cell migration. Conversely, miR-210 blockade via LNA-anti-miRNA transfection inhibited the formation of capillary-like structures stimulated by hypoxia and decreased cell migration in response to VEGF. miR-210 overexpression did not affect endothelial cell growth in both normoxia and hypoxia. However, antimiR– 210 transfection inhibited cell growth and induced apoptosis, both in normoxia and in hypoxia. We determined that one relevant target of miR-210 in hypoxia was Ephrin-A3, since miR-210 was necessary and sufficient to down-modulate its expression. Moreover, luciferase reporter assays showed that Ephrin- A3 was a direct target of miR-210. Ephrin-A3 modulation by miR-210 had significant functional consequences: indeed, the expression of an Ephrin-A3 allele that is not targeted by miR-210, prevented miR-210-mediated stimulation of both tubulogenesis and chemotaxis. We conclude that miR-210 upregulation is a crucial element of endothelial cell response to hypoxia, affecting cell survival, migration and differentiation.