Downregulation of microRNA-519 promotes angiogenesis induced by cerebral ischemia via upregulating HIF-1α expression

Angiogenesis is a crucial process for brain tissue repair and remodeling after brain injury. It has been demonstrated that microRNA (miRNA or miR) expression profiles are altered in tissues under hypoxic-ischemic conditions. However, its role in angiogenesis subsequent to cerebral ischemia is not fully understood. The present study was aimed to investigate the role of miR-519 in angiogenesis and the molecular mechanisms mediated by HIF-1 alpha in an in vitro model for cerebral ischemia. Firstly, a rat middle cerebral artery occlusion (MCAO) model was established, and the results from microarray selection and qRT-PCR demonstrated that the expression levels of miR-519 were significantly decreased in the rat cerebral following MCAO. On the other hand, human umbilical vein endothelial cells (HUVECs) were exposed to low oxygen conditions and showed that hypoxia significantly downregulated miR519 expression levels. After transfection of HUVECs with miR-519 mimic, hypoxia-induced tube formation and cell migration were markedly attenuated. The results indicated that miR-519 inhibited angiogenesis by decreasing cell migration and tube formation. Furthermore, in HEK 293 cells, results from the luciferase reporter assay revealed that miR-519 directly targeted the 3' untranslated region (3'-UTR) of HIF-1 alpha and that miR-519 regulated the protein expression of HIF-1 alpha. Additionally, in vivo studies demonstrated that HIF-1 alpha expression was markedly increased in the cerebral ischemic groups, and confirmed that a negative correlation existed between miR-519 and HIF-1 alpha expression. To further analyze this effect, a pCDNA-HIF-1 alpha plasmid was transfected into the normoxic and hypoxic HUVECs, and it was revealed that the inhibitory effect of miR-519 on angiogenesis was attenuated by the overexpression of HIF-1 alpha. It is, therefore, concluded that downregulation of miR-519 promotes angiogenesis in response to cerebral ischemic injury, which is achieved partially by upregulating HIF-1 alpha expression. However, furthermore studies are necessary to verify this point.