Die Bedeutung der Proteinkinase A und der Ca2+/Calmodulin abhängigen Proteinkinase II für das Sarkoplasmatische Retikulum Kalziumleck in der humanen Hypertrophie und Herzinsuffizienz

Abstract

Sarcoplasmic reticulum (SR) Ca2+ leak through ryanodine receptor type 2 (RyR2) hyperphosphorylation is a key pathomechanism in human heart failure (HF). The resulting increased spontaneous diastolic calcium release promotes arrhythmic events and compromises cardiac contractility. Protein kinase A (PKA) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) have been identified as potential mediators of RyR2 dysregulation, but their respective contribution to the development of HF has been controversially discussed. Sossalla et al. (Circulation 2010) demonstrated that inhibition of CaMKII in human HF reduces SR Ca2+ leak and improves contractility. The present work is the first to comprehensively investigate the role of both kinases in the transition from human afterload-induced hypertrophy to HF. Analyses of RyR2 expression and phosphorylation demonstrated increased RyR2 expression in compensated afterload-induced hypertrophy compared to healthy donor hearts. Relative RyR2 phosphorylation was not significantly altered at the specific phosphorylation sites of either PKA or CaMKII. In HF, however, there was a pronounced CaMKII-dependent hyperphosphorylation of RyR2 at an unchanged RyR2 expression, whereas PKA-dependent regulation was not detectable. This finding was independent from previous β-blocker treatment. In addition, Ca2+ cycling was investigated by epifluorescence and confocal laser scanning microscopy in isolated cardiomyocytes from both pathologies. In HF, the SR Ca2+ leak was nearly doubled in comparison to compensated cardiac hypertrophy. This was associated with a significant reduction of systolic Ca2+ release and SR Ca2+ load. Accordingly, in cardiac hypertrophy inhibitors of both kinases reduced the SR Ca2+ leak. In HF, CaMKII inhibition but not inhibition of PKA yielded a reduction of the SR Ca2+ leak. Moreover, PKA inhibition further reduced SR Ca2+ load and systolic Ca2+ transients. In conclusion, these results show that in compensated hypertrophy both CaMKII and PKA functionally regulate RyR2 and may induce SR Ca2+ leak. In the transition from hypertrophy to HF, the diastolic Ca2+ leak increases and disturbed Ca2+ cycling occurs. This is associated with an increase in CaMKII- but not PKA-dependent RyR2 phosphorylation. Inhibition of CaMKII may thus represent a promising therapeutic approach for the treatment of arrhythmias and contractile dysfunction in human HF.