Abstract 3734: Regulation of Novel Micrornas Identified in End-stage Human Heart Failure
microRNAs (miRNAs) are short, non-coding RNA molecules which pair with specific ‘target’ mRNAs and act as negative regulators of gene expression by inhibiting mRNA translation or promoting mRNA degradation. Recent studies have uncovered the important roles these tiny regulatory molecules play in diverse aspects of cardiac function. Chronic stress on the heart leads to altered signaling that results in remodeling from adaptive to maladaptive hypertrophy transitioning into dilated cardiomyopathy (DCM). To identify altered miRNAs in human DCM, we have carried out a comprehensive analysis on miRNA expression profiles from 50 human DCM patient samples and 20 non-failing human hearts. Our studies using a miRNA microarray showed significant alterations in 8 miRNAs. Off which two of the altered miRNAs are novel (miRNA-7 and -378) and have not been implicated in heart failure. We hypothesized that these two novel miRNAs are critical for normal cardiac function and downregulation of these miRNAs leads to upregulation of deleterious pathways contributing to cardiac dysfunction and heart failure. Since we have used end-stage human DCM samples, we tested whether alterations in these novel miRNAs is a “cause” or “effect” of heart failure by subjecting C57BL/6 mice to transverse aortic constriction (TAC) for 1, 2, 3, 4, 7 and 12 days. Real time expression analysis (RT-PCR) of these miRNAs showed significant downregulation as early as 24 hrs (1 day) of TAC which was sustained even after 12 days of banding suggesting that these miRNAs may be a contributing factor in the initiation of heart failure and not the effect of heart failure. Bioinformatic analysis showed that targets of these two novel miRNAs regulate critical signaling networks and experimental validation of these targets performed on human DCM, mouse TAC and cells stably expressing miRNA-7 or -378 will be discussed in the presentation. To further understand the mechanism of regulation of these miRNAs, we have analyzed the promoters of miRNA 7 and 378 and identified Hes-1 as the major repressor that leads to the downregulation of these miRNAs during end stage heart failure/TAC. In summary, we have identified two novel miRNAs whose dysregulation may play a critical role in cardiac dysfunction.