Abstract 13467: Loss of MiR-144/451 Cluster Impairs Ischemic Preconditioning-Mediated Cardioprotection via Targeting Rac-1
Background: We previously reported that the miR-144/451 cluster was significantly upregulated in mouse hearts upon six cycles of 4-min ischemia, via coronary artery occlusion, followed by 4-min reperfusion in vivo. Furthermore, overexpression of miR-144/451 protects cardiomyocytes against simulated ischemia/reperfusion (I/R)-induced injury. However, whether increased miR-144 and miR-451 facilitate ischemic preconditioning (IPC)-mediated cardioprotection is totally unknown.
Methods and Results: Given that miR-144 and miR-451 are 100-bp apart and transcribed on a single precursor RNA, we employed a miR-144/451 knockout (KO) mouse model for this study. We observed that miR-144/451-KO mice were healthy and showed no apparent cardiac morphological or pathological abnormalities. Upon in vivo IPC (four cycles of 4-min I/R) followed by 30-min ischemia/24-h reperfusion, the miR-144/451-KO hearts displayed the similar infarction size as the sham groups (44±6% vs. 41±4%, n=9, P>0.05); whereas wild-type hearts subjected to IPC followed by I/R showed smaller infarction size (6±2%), as related to the sham operation (25±3%, n=11, P<0.001). These data suggest that the miR-144/451 cluster is required for IPC-elicited cardioprotection. Using Target-Scan software, gene array and western-blot analysis, we observed that Rac-1, an essential component of NADPH oxidase, was mostly upregulated (2.3-fold) in KO hearts among the three bona fide targets (Rac-1, 14-3-3ζ, and CUGBP2) for both miR-144 and miR-451. Accordingly, reactive oxygen species (ROS) levels were markedly increased by 2.5-fold in KO hearts upon IPC, compared to 1.5-fold increase in IPC-WT hearts (n=6, P<0.01), suggesting excessive generation of ROS in IPC-KO hearts. Pre-treatment of KO hearts with Rac-1 inhibitor NSC23766 (20mg/kg, ip) reduced IPC-triggered ROS levels and restored IPC-elicited cardioprotection (n=7).
Conclusion: These data indicate that loss of miR-144/451 cluster causes upregulation of Rac-1, consequently generates large amount of ROS during IPC, which contributes to the impaired IPC efficacy. Our findings, for the first time, suggest that the miR-144/451 cluster is involved in the IPC-elicited cardioprotection.
- © 2011 by American Heart Association, Inc.