Pathologic Role of MicroRNA‐365 in the Heart

Abstract

Cardiac remodeling occurs in many cardiovascular diseases. It can severely impair ventricular function and increase the risk for arrhythmias. A better understanding of cardiac signaling regulatory mechanisms is critical for development of novel and effective treatment approaches. MicroRNAs (miRNAs) are important regulators in cardiac development and disease. It was reported that miRNA‐365 is 2.8‐fold up‐regulated in the left ventricular tissue from patients undergoing heart transplantation due to end‐stage heart failure (Thum T et. al, Circulation 2007). Using phenotypic screen of 230 synthetic miRNAs, miRNA‐365 was identified as one of four hypertrophy‐modulating miRNAs (Jentzsch et al., Jour Mol Cell Card 2012). However, to date, miRNA‐365 has not been functionally characterized in the heart. The goal of this on‐going study is to delineate the functional importance and regulatory mechanisms of miRNA‐365 in the heart. Using adult rats, we found increase of miRNA‐365 expression in the infarcted area than in the remote area and sham control only 7 days after myocardial infarction. MiRNA‐365 is also up‐regulated in neonatal rat ventricular myocytes stimulated with phenylephrine. Overexpression of miRNA‐365 in culture significantly increases both the size of neonatal cardiac myocytes and atrial natriuretic factor (ANF) expression. In contrast, ANF expression is markedly reduced by miRNA‐365 knockdown. We generated a transgenic mouse model with cardiac specific, α myosin heavy chain‐driven overexpression of miRNA‐365. Significant increase of ANF expression in ventricules with cardiac specific overexpression of miRNA‐365 suggests the activation of hypertrophy signaling. Our ex vivo optical mapping data suggest that ventricular tachycardia (VT) is highly inducible in the heart with cardiac specific overexpression of miRNA‐365 and spatially discordant calcium alternans is the major driven force for the VT events. Importantly, this spatially discordant calcium alternans can be eliminated by Dantrolene, suggesting uncontrolled SR calcium release during excitation‐contraction coupling may contribute to the VT induction. Our data further show that spatially discordant calcium alternans can be changed back to concordant calcium alternans by mitoTEMPO, suggesting that increased mitochondrial reactive oxygen species could be the upstream of the uncontrolled SR calcium release. These findings are supported by single cell patch clamps, in which the isolated myocytes from miRNA‐365 overexpressing hearts show increased early after depolarizations (EAD), which are majorly due to elevated cytosolic calcium concentrations. Taken together, our results suggest miRNA‐365 has a critical pathologic role in the heart and may regulate both structural and electrical cardiac remodeling, which warrants further investigation.Support or Funding InformationAmerican Heart Association (AHA) Founders Affiliate Pre‐doctoral Fellowship; COBRE for CardioPulmonary Vascular Biology