Reactive oxygen species (ROS)-induced cardiac cell injury via expression changes of multiple genes plays a critical role in the pathogenesis of numerous heart diseases. MicroRNAs (miRNAs) comprise a novel class of endogenous, small, noncoding RNAs that negatively regulate about 30% of the genes in a cell via degradation or translational inhibition of their target mRNAs. Currently, the effects of ROS on miRNA expression and the roles of miRNAs in ROS-mediated injury on cardiac myocytes are uncertain. Using quantitative real-time RT-PCR (qRT-PCR), we demonstrated that microRNA-21 (miR-21) was upregulated in cardiac myocytes after treatment with hydrogen peroxide (H(2)O(2)). To determine the potential roles of miRNAs in H(2)O(2)-mediated gene regulation and cellular injury, miR-21 expression was downregulated by miR-21 inhibitor and upregulated by pre-miR-21. H(2)O(2)-induced cardiac cell death and apoptosis were increased by miR-21 inhibitor and was decreased by pre-miR-21. Programmed cell death 4 (PDCD4) that was regulated by miR-21 and was a direct target of miR-21 in cardiac myocytes. Pre-miR-21-mediated protective effect on cardiac myocyte injury was inhibited in H(2)O(2)-treated cardiac cells via adenovirus-mediated overexpression of PDCD4 without miR-21 binding site. Moreover, Activator protein 1 (AP-1) was a downstream signaling molecule of PDCD4 that was involved in miR-21-mediated effect on cardiac myocytes. The results suggest that miR-21 is sensitive to H(2)O(2) stimulation. miR-21 participates in H(2)O(2)-mediated gene regulation and functional modulation in cardiac myocytes. miR-21 might play an essential role in heart diseases related to ROS such as cardiac hypertrophy, heart failure, myocardial infarction, and myocardial ischemia/reperfusion injury.

MicroRNAs (miRNAs) are noncoding RNAs that impact almost every aspect of biology and disease. Until now, the cell-specific effects of miRNAs in cardiovascular system have not been established. In the current study, the cellular functions of miR-221 and miR-222 (miR-221/222) in vascular smooth muscle cells (VSMCs) and vascular endothelial cells (ECs) were compared. In cultured cells, we identified that the effects of miR-221/222 on proliferation, migration, and apoptosis are opposite between VSMCs and ECs. In VSMCs, miR-221/222 had effects of pro-proliferation, pro-migration, and anti-apoptosis. In contrast, miR-221/222 had effects of anti-proliferation, anti-migration, and pro-apoptosis in ECs. The different expression profiles of their target genes, p27(Kip1), p57(kip2), and c-kit between the two cell types might be related to the opposite effects. Finally, the opposite cellular effects of miR-221/222 were verified in vivo in balloon-injured rat carotid artery as demonstrated by different consequences in neointimal growth and re-endothelialization. The results suggest that the biological functions of miR-221/222 in vascular walls are cell-specific. The opposite cellular effects of miR-221/222 on VSMCs and ECs may have important therapeutic applications in many vascular diseases such as atherosclerosis and restenosis after angioplasty.