Abstract 5321: Dicer Depletion in Adult Hearts Induces Oxidative Stress, Mitochondrial Dysfunction and Causes Rapid Loss of Cardiac Function

Abstract

Introduction. Dicer, an RNAse III endonuclease, plays a key role in the processing of miRNA into their functional mature form. A number of recent reports point towards a central role of miRNA in cardiac development and function. However, the short-term effects of dicer deficiency on the function of the adult heart and underlying mechanisms remain to be elucidated. Oxidative stress and dysregulated mitochondrial function are known to play a major role in acute cardiac pathologies. Hypothesis . Arrest of miR maturation by heart-specific dicer knock-out in adult animals result in rapid loss of cardiac function caused by mitochondrial dysfunction and oxidative stress. Methods . Mice homozygous for Dicer-floxed alleles (Dicer fl/fl ) and transgenic Myh6-cre/Esr1 mice were crossed to generate double-transgenic (Myh6-cre/Esr1-Dicer fl/fl ) mice. At 8 weeks of age Myh6-cre/Esr1-Dicer fl/fl mice were treated with vehicle or tamoxifen (tam; 20 mg/kg per day) daily ip injections for five consecutive days. To determine the acute functional consequences of Dicer depletion, heart function was determined using gated cardiac MRI and echocardiography. Myocardial miR profiling was performed using a bead array system. Candidate miRs were verified using quantitative PCR. Results . Tam injection for 5 days effectively depleted Dicer protein in myocardium. miRNA array data show significant (p< 0.05, n=3) decrease in the levels of a number of abundant mature miRNA including miR-1, miR-133 a&b. Following 5 days of Tam injection, a significant (p< 0.05, n=5) decrease in ejection fraction (32±9%↓), stroke volume (23±7%↓) and cardiac output (28.3±6%↓) was noted in Dicer −/− compared to Dicer +/+ mice. Studies with isolated mitochondria showed a significant decrease in energy dependent pore opening and increase in uncoupled mitochondria in the heart of Dicer −/− mice. Such compromise in mitochondrial function was associated with structural disintegration and increased (30±7.5%↑; p<0.05, n=3) tissue oxidative stress. Conclusions . This study provides first evidence demonstrating that depletion of dicer in adult mice results in mitochondrial dysfunction and oxidative stress in the myocardium which is followed by acute loss of cardiac functions.