Roles of microRNA-1 in hypoxia-induced apoptotic insults to neuronal cells.

Hypoxia is a common occurrence in brain tumors and traumatic brain injury. microRNA (miR)-1 participates in the regulation of brain development and neuronal function. Interestingly, miR-1 can mediate ischemia-induced injury to cardiomyocytes. This study was designed to evaluate the roles of miR-1 in hypoxia-induced insults to neurons and the possible mechanisms. Exposure of neuro-2a cells to oxygen/glucose deprivation (OGD) or cobalt chloride decreased cell viability and induced cell apoptosis in time-dependent manners. In parallel, OGD caused augmentation of cellular Bax and cytochrome c levels, a reduction in the mitochondrial membrane potential (MMP), activation of caspase-3, and fragmentation of DNA. miR-1 was induced in neuro-2a cells by OGD. Knocking down miR-1 expression using specific antisense inhibitors significantly alleviated OGD-induced neuronal death. Administration of OGD to neuro-2a cells induced heat-shock protein (HSP)-70 messenger (m)RNA and protein expressions. A bioinformatic search revealed that miR-1-specific binding elements exist in the 3'-untranslated region of HSP-70 mRNA. Overexpression of miR-1 simultaneously attenuated OGD-induced HSP-70 mRNA and protein expressions. In comparison, knocking down miR-1 expression synergistically enhanced OGD-induced HSP-70 mRNA. As to the mechanism, reducing miR-1 expression lowered OGD-induced alterations in the MMP, caspase-3 activation, DNA fragmentation, and cell apoptosis. Taken together, this study shows that miR-1 can target HSP-70 expression and consequently mediate hypoxia-induced apoptotic insults to neuro-2a cells via an intrinsic Bax-mitochondrion-caspase protease pathway.