Abstract 19199: Cardiomyocyte Enriched MicroRNA, Mir-378, Regulates Hypertrophy Agonists Stimulated Growth of Cardiac Myocytes

MicroRNAs are small non-coding RNAs that have emerged as important negative regulators of gene expression. We recently described miR-378 as a cardiomyocyte enriched miRNA that targets IGF1/IGF1R signaling and regulates post-natal cardiac remodeling ( JBC 287(16):12913-26, 2012 ). In this study we tested the hypothesis that miR-378 regulates cardiomyocyte growth induced by hypertrophy stimuli. To test miR-378 involvement in cardiac hypertrophy, pressure overload was induced in adult mice by transverse aortic constriction (TAC) for 2 wks or 8 wks. TAC produced about 40% increase in HW / tibia length ratio with no overt cardiac dysfunction at 2 wks (hypertrophy, H group) and 30% reduction in %FS at 8 wks (heart failure, HF group). Expression of miR-378 was reduced by about 50% in H group but it was induced by 1.2-fold in HF group. Deficiency of miR-378 (30% to 60%) was also noted when neonatal rat ventricular cardiomyocytes (NRVM) were exposed to hypertrophy agonists, phenylephrine (PE, 20uM), AngII (100 nM) or isoproterenol (10 uM) for 48 h. Inhibition of miR-378 in NRVM by 378-antimiR, resulted in enhanced PE stimulated cardiomyocyte growth as reflected by 25% increase in cardiomyocyte size by WGA staining. We also noted significatly more induction of ANF in response to PE treatment in 378-antimiR transfected NRVM as compared to scramble control. Conversely, over-expression of miR-378 by 378-mimic in NRVM led to significant inhibition of PE induced [3] Leu incorporation and ANF induction. It also counteracted PE-stimulated activation of Ras and downstream signaling cascade such as pERK1/2, p70S6K and pAKT. One of the well accepted markers of pathological remodeling is nuclear translocation of NFATC which activates hypertrophy gene program in response to hypertrophy stimulus. By confocal imaging we found 378-mimic totally obliterated nuclear occupancy of NFATC 48 h after PE treatment. Data indicate that deficiency of miR-378 contributes to the development of cardiac hypertrophy, and by inhibiting Ras-signaling, miR-378 acts as an anti-hypertrophy microRNA. Our findings implicate that over-expression of miR-378 will counteract pathological remodeling and protect the heart from maladaptive hypertrophy and heart failure.