MicroRNA-155 Promotes Myocardial Infarction-Induced Apoptosis by Targeting RNA-Binding Protein QKI.

Acute myocardial infarction (AMI) is the leading cause of sudden death worldwide. MicroRNA-155 (miR-155) has been reported to target antiapoptotic genes in various diseases models, but the functional role of miR-155 in response to MI injury needs further investigations. This study investigated the role of miR-155 in myocardial ischemia injury. TUNEL and flow cytometry were performed to measure cell apoptosis. Western blot analysis was employed to detect protein expressions of Bcl-2, XIAP, Bax, and caspase-3. qRT-PCR was used to quantify miRNA levels. We showed that miR-155 was dynamically elevated in murine hearts subjected to MI and in neonatal rat ventricular cardiomyocyte (NRVM) injury induced by hydrogen peroxide (HO). In response to HO, the silencing of miR-155 using AMO-155 (antisense inhibitor oligodeoxyribonucleotides) significantly increased cell viability and reduced cell apoptosis. Moreover, AMO-155 reversed the HO-induced downregulation of Bcl-2 and XIAP and upregulation of Bax and cleaved-caspase-3. Further study revealed that AMO-155 resulted in a decrease of HO-induced JC-1-labelled monomeric cell number. In addition, AMO-155 markedly decreased infarct size, ameliorated impaired cardiac function, and significantly reduced apoptotic cell percentages in MI mice heart. The RNA-binding protein Quaking (QKI) was predicted as a target gene of miR-155 through bioinformatic analysis, and AMO-155 attenuated the downregulation of QKI in HO-treated cardiomyocytes and MI mice heart. Knockdown of QKI by siRNA abolished the antiapoptotic effects of AMO-155. Taken together, miR-155 is upregulated in the MI heart and NRVMs in response to HO stress, and downregulating of miR-155 protects cardiomyocytes against apoptosis. Mechanistically, it is probably due to the repression of QKI signaling pathway.