Ectopic Expression of miR‐424(322)/503 Triggers Acute and Reversible Dilated Cardiomyopathy

Abstract

Background Cardiovascular disease is the topmost cause of death worldwide before cancer, chronic respiratory diseases, Alzheimer's and kidney diseases. Dilated cardiomyopathy (DCM) is one of the most common cardiovascular diseases with an estimated prevalence of 1 in 2500 individuals. DCM is clinically characterized by ventricular chamber dilation and systolic dysfunction eventually leading to heart failure. MicroRNAs have been shown to play an integral role in regulating the progression of cardiomyopathy along with heart failure and as a result have become novel targets for therapy. Previously, our lab has shown that the miR-424(322)/503 is highly enriched in embryonic heart during early cardiac development but its expression drops to very low level after birth. Interestingly, other studies have revealed the upregulation of miR-424(322)/503 in failing human hearts. However, the relation between miR-424(322)/503 and heart failure is not yet known. Methods and results To understand the role of miR-424(322)/503 in adult heart, we created tetracycline-controlled cardiomyocyte-specific miR-424(322)/503 expressing transgenic mice (Tg). miR-424(322)/503 was induced in Tg and wildtype (Wt) mice (8 weeks) using doxycycline containing chow continuously for a month. Cardiac function was monitored every week using transthoracic echocardiography. The hearts were then harvested for molecular and histological analyses. Echocardiographic analysis revealed continuous deterioration of cardiac function in Tg mice starting from 2 weeks of doxycycline induction. This was evidenced by significant decrease in ejection fraction and fractional shortening from 46±1.9% and 22±1.09% at week 2 to 15±2.7% and 6±1.2% at week 4, respectively. Cardiac failure markers (ANP and BNP) were also found to be upregulated by 8-10 folds in Tg as compared to Wt hearts. Further analysis with tissue staining in Tg hearts exhibited dilated chambers with thin ventricular wall, presence of fibrosis and disorganized myocytes; a phenotype consistent with DCM. Next, to further see the causative role of miR-424(322)/503 and determine if miR-424(322)/503 is required for heart failure progression, mice were fed with doxycycline chow for 2 weeks, which is the time-point when the heart failure started to occur, and then continued with normal chow. We observed that the heart function had recovered as indicated by improvement in ejection fraction and fractional shortening from 31.94±7.55% and 14.98±3.95% in week 3 to 51.27±5.02% and 25.79±2.92% in week 12, respectively. ANP and BNP levels dropped significantly in week 12 compared to weeks 2-3. This suggests that miR-424(322)/503 plays a role in DCM progression. Conclusion Overall, this is the first study showing that upregulated miR-424(322)/503 in the heart is sufficient to lead to DCM and miR-424(322)/503 induced heart failure is reversible. Thus, this study supports miR-424(322)/503 as a novel potential therapeutic target for DCM.