MicroRNA-21 protects neurons from ischemic death

MicroRNAs are small RNAs that attenuate protein expression by complementary binding to the 3'-UTR of a target mRNA. Currently, very little is known about microRNAs after cerebral ischemia. In particular, microRNA-21 (miR-21) is a strong antiapoptotic factor in some biological systems. We investigated the role of miR-21 after stroke in the rat. We employed in situ hybridization and laser capture microdissection in combination with real-time RT-PCR to investigate the expression of miR-21 after stroke. In situ hybridization revealed that miR-21 expression was upregulated in neurons of the ischemic boundary zone, and quantitative real-time RT-PCR analysis revealed that stroke increased mature miR-21 levels by approximately threefold in neurons isolated from the ischemic boundary zone by laser capture microdissection as compared with homologous contralateral neurons 2 days (n = 4; P < 0.05) and 7 days (n = 3; P < 0.05) after stroke. In vitro, overexpression of miR-21 in cultured cortical neurons substantially suppressed oxygen and glucose deprivation-induced apoptotic cell death, whereas attenuation of endogenous miR-21 by antisense inhibition exacerbated cell death after oxygen and glucose deprivation. Moreover, overexpression of miR-21 in neurons significantly reduced FASLG levels, and introduction of an miR-21 mimic into 293-HEK cells substantially reduced luciferase activity in a reporter system containing the 3'-UTR of Faslg. Our data indicate that overexpression of miR-21 protects against ischemic neuronal death, and that downregulation of FASLG, a tumor necrosis factor-α family member and an important cell death-inducing ligand whose gene is targeted by miR-21, probably mediates the neuroprotective effect. These novel findings suggest that miR-21 may be an attractive therapeutic molecule for treatment of stroke.