Abstract 14349: Conditional Dicer Deletion in Adult Hearts Induces miR15b Expression, Mitochondrial Dysfunction and Oxidative Stress
Dicer, an endonuclease required for the processing of miRNA to their mature form. A central role of miRNA in cardiac development and function has been proposed. Decreased levels of Dicer have been noted in heart failure patients with specific cardiomyopathy. The acute effects of dicer deficiency on the function of the adult heart and underlying mechanisms remain to be elucidated. We hypothesized that arrest of miRNA maturation and change in miRNA levels upon cardiac-specific Dicer deletion in adult animals result in rapid loss of cardiac function caused by mitochondrial dysfunction and oxidative stress.
Methods: Condition deletion of dicer in heart was achieved by injecting tamoxifen to double-transgenic Myh6-cre/Esr1-Dicerfl/fl mice developed in our laboratory. Heart function was determined using gated cardiac 11.7T MRI and echocardiography. Tamoxifen injection effectively depleted Dicer protein in myocardium. Such depletion resulted in rapid and significant (p<0.05, n=5) decrease in ejection fraction (32±9%↓), stroke volume (23±7%↓) and cardiac output (28.3±6%↓) in Dicer−/− compared to Dicer+/+ mice. Studies with isolated mitochondria showed significant decrease in RCR (p<0.05, n=4) indicating mitochondrial dysfuntion. Such compromise in mitochondrial function was associated with increased tissue oxidative stress in Dicer−/− mice as assessed by a significant increase in TBARS (p<0.05, n=3) and GSSG/GSH ratio (p<0.05, n=4). miRNA profiling array data show significant (p<0.05, n=3) change in the levels of a number of miRNAs including miR-1, miR-133 a&b, miR-142–3p and miR-15b. miR15b was one of miR that was induced upon dicer deletion in heart. In silico predicted targets of miR15b are involved in mitochondrial and cardioprotective functions. Cardiomyocyte (HL-1) cells transfected with miR-15b mimic showed significantly (p<0.05, n=4) compromised mitochondrial membrane potential measured by JC-1 flowcytometry and TMRM/PMPI ratio.
Conclusions: This study provides first evidence that acute depletion of Dicer in adult mice results in miR15b mediated mitochondrial dysfunction and oxidative stress which is followed by acute loss of cardiac functions.
- © 2010 by American Heart Association, Inc.