Epigallocatechin-3-Gallate Accelerates Relaxation and Ca(2+) Transient Decay and Desensitizes Myofilaments in Healthy and Mybpc3-Targeted Knock-in Cardiomyopathic Mice

Background: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac muscle disease with left ventricular hypertrophy, interstitial fibrosis and diastolic dysfunction. Increased myofilament Ca(2+) sensitivity could be the underlying cause of diastolic dysfunction. Epigallocatechin-3-gallate (EGCg), a catechin found in green tea, has been reported to decrease myofilament Ca(2+) sensitivity in HCM models with troponin mutations. However, whether this is also the case for HCM-associated thick filament mutations is not known. Therefore, we evaluated whether EGCg affects the behavior of cardiomyocytes and myofilaments of an HCM mouse model carrying a gene mutation in cardiac myosin-binding protein C and exhibiting both increased myofilament Ca(2+) sensitivity and diastolic dysfunction. Methods and Results: Acute effects of EGCg were tested on fractional sarcomere shortening and Ca(2+) transients in intact ventricular myocytes and on force-Ca(2+) relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI) and wild-type (WT) mice. Fractional sarcomere shortening and Ca(2+) transients were analyzed at 37°C under 1-Hz pacing in the absence or presence of EGCg (1.8 μM). At baseline and in the absence of Fura-2, KI cardiomyocytes displayed lower diastolic sarcomere length, higher fractional sarcomere shortening, longer time to peak shortening and time to 50% relengthening than WT cardiomyocytes. In WT and KI neither diastolic sarcomere length nor fractional sarcomere shortening were influenced by EGCg treatment, but relaxation time was reduced, to a greater extent in KI cells. EGCg shortened time to peak Ca(2+) and Ca(2+) transient decay in Fura-2-loaded WT and KI cardiomyocytes. EGCg did not influence phosphorylation of phospholamban. In skinned cardiac muscle strips, EGCg (30 μM) decreased Ca(2+) sensitivity in both groups. Conclusion: EGCg hastened relaxation and Ca(2+) transient decay to a larger extent in KI than in WT cardiomyocytes. This effect could be partially explained by myofilament Ca(2+) desensitization.