Aims: MicroRNAs (miRNAs) regulate various cardiac processes including cell proliferation and apoptosis. Pioglitazone (PIO), a peroxisome proliferator-activated receptor (PPAR)-gamma agonist, protects against myocardial ischaemia-reperfusion (IR) injury. We assessed the effects of PPAR-gamma activation on myocardial miRNA levels and the role of miRNAs in IR injury.
Methods and results: We evaluated the expression changes of miRNAs in the rat heart after PIO administration using miRNA arrays and then confirmed the result by northern blot. miR-29a and c levels decreased remarkably after 7-day treatment with PIO. In H9c2 cells, the effects of PIO and rosiglitazone on miR-29 expression levels were blocked by a selective PPAR-gamma inhibitor GW9662. Downregulation of miR-29 by antisense inhibitor or by PIO protected H9c2 cells from simulated IR injury, indicated as increased cell survival and decreased caspase-3 activity. In contrast, overexpressing miR-29 promoted apoptosis and completely blocked the protective effect of PIO. Antagomirs against miR-29a or -29c significantly reduced myocardial infarct size and apoptosis in hearts subjected to IR injury. Western blot analyses demonstrated that Mcl-2, an anti-apoptotic Bcl-2 family member, was increased by miR-29 inhibition.
Conclusion: Downregulation of miR-29 protected hearts against IR injury. The modulation of miRNAs can be achieved by pharmacological intervention. These findings provide a rationale for the development of miRNA-based strategies for the attenuation of IR injury.