1A.02

Abstract

Objective: Circulating microRNAs may be markers of cardiac damage or dysfunction. miR-208a has heart-specific expression since its host gene – myosin heavy chain MYH6, dominant cardiac myosin motor is also heart-specific and its expression maintains proper cardiac output. Our aim was to evaluate miR-208a and MYH6 as key contributing factors involved in hypertrophic heart dysfunction. Design and method: 18–20 weeks old male Wistar rats were treated for 8 days with isoproterenol (ISO; N=12; 5 mg/kg intraperitoneally) or vehicle (CON; N=12). Relative expressions of cardiac myosin heavy chains (MYH6, MYH7, MYH7B), markers of cardiac damage (natriuretic peptides ANP, BNP) and heart-related microRNAs miR-1, miR-133a, miR-208a, miR-499 were analyzed using quantitative real-time PCR in samples from left ventricle, microRNAs also in venous blood. Cardiac hypertrophy and dysfunction was quantified with heart gravimetry and left heart catheterization, respectively. Results: Treatment with isoproterenol induced cardiac hypertrophy (heart mass increased by +36% vs. CON (P<0.01) and 53% mortality associated with cardiovascular dysfunction characterized by a deteriorated peak left ventricular pressure and rate of isovolumetric pressure change during contraction (+dP/dt) compared to CON (−8% and −27% resp., P < 0.01). Gene expression of cardiac myosin heavy chain MYH6 in left ventricles was decreased by −61% indicating myosin switching in contractile apparatus. Cardiac dysfunction was further confirmed by 10-fold increase of atrial natriuretic peptide (ANP; P<0.01). Cardiac levels of microRNAs miR-1, miR-133a, miR-208a, miR-499 were strongly decreased (−71%, −65%, −59%, −75% resp., P < 0.01). Plasma levels of the same microRNAs were unchanged except for the cardio-specific miR-208a that showed a significant, 56-fold increase (P<0.01). ROC curve for detection of cardiac hypertrophy based on plasma miR-208a had a corresponding AUC = 98.8% (95% confidence interval, 85.3% – 100%). Conclusions: Cardiac hypertrophy was associated with a decrease of several heart-related gene-regulatory microRNAs expression in the heart. Increased miR-208a in plasma is a strong predictor of cardiac hypertrophy. Isoproterenol induced heart damage also involves decrease in expression of dominant cardiac myosin motor MYH6 which is the host gene of miR-208a. In summary, miR-208a and myosin heavy chain MYH6 are key factors in hypertrophic heart dysfunction.