Abstract 16546: microRNA(miR)-451 Regulates Cardiac Growth and Myocardial Reactive Oxidative Species (ROS) Level via Nrf2 and AMPK Pathways

Abstract

The role of miR-451 in certain cardiac diseases was recently reported including ischemia/reperfusion and hypertrophic cardiomyopathy. Oxidative stress is known to involve in the above diseases. Currently the relationship between miR-451 and cardiac oxidative stress is unknown. We thus hypothesize that miR-451 act as a key mediator for cardiac hypertrophy via regulating myocardial ROS level and antioxidant pathways. We first compared the heart/body weight (HW/BW) ratio between age- & gender-matched miR-451 knockout (KO) and wild-type (WT) mice. Increase of HW/BW was found in KO mice (6.1±0.1 vs 4.8±0.1 mg/g in WT, p<0.01). Expression of fetal genes ANF (2.9-fold↑) and β-MHC (4.0-fold↑) was also significantly increased in KO hearts, as well as the ROS level (2.3-fold↑, p<0.05) in KO hearts. Consistently, both the protein expression and activation levels of the oxidation-regulating gene Nrf2 decreased the same extent (~33%↓, p<0.05) in KO hearts. In contrast, the protein expression of the direct antioxidants HO-1 and SOD3 were found significantly increased in KO hearts, suggesting a compensatory mechanism to quench the increased cardiac ROS. Since we previously showed that phosphorylation (p) of AMPKα was inhibited in cardiac hypertrophy, thus the p-AMPKα level was tested and found significantly (76%↓, p<0.05) decreased in KO heart, consistent with the hypertrophy in KO heart. In order to further explore the relationship between Nrf2 and AMPKα, cultured adult rat ventricular myocytes (ARVM) was treated with an Nrf2 activator sulforaphane, which induced 1.4-fold increase in p-AMPKα (p<0.01); whereas the AMPK activator AICAR didn’t affect Nrf2 expression in ARVM, suggesting Nrf2 is upstream from AMPK. When miR-451 mimics were overexpressed in cultured cardiac myocytes, Nrf2 was significantly increased (2.3-fold↑, p<0.05) with overexpression of miR-451 mimics vs control, suggesting miR-451 regulates Nrf2 expression. Taken together, our data show that miR-451 activates cardiac Nrf2 and its downstream AMPK signaling pathway; whereas antioxidants HO-1 and SOD3 act as compensatory mechanism for increased cardiac ROS when miR-451 is defect. miR-451 plays a novel protective role against cardiac oxidative stress, and also mediates cardiac hypertrophy.