Calcium/Calmodulin-Dependent Protein Kinase II Activity Persists During Chronic β-Adrenoceptor Blockade in Experimental and Human Heart Failure

Abstract

Background— Considerable evidence suggests that calcium/calmodulin-dependent protein kinase II (CaMKII) overactivity plays a crucial role in the pathophysiology of heart failure (HF), a condition characterized by excessive β-adrenoceptor (β-AR) stimulation. Recent studies indicate a significant cross talk between β-AR signaling and CaMKII activation presenting CaMKII as a possible downstream mediator of detrimental β-AR signaling in HF. In this study, we investigated the effect of chronic β-AR blocker treatment on CaMKII activity in human and experimental HF. Methods and Results— Immunoblot analysis of myocardium from end-stage HF patients (n=12) and non-HF subjects undergoing cardiac surgery (n=12) treated with β-AR blockers revealed no difference in CaMKII activity when compared with non–β-AR blocker–treated patients. CaMKII activity was judged by analysis of CaMKII expression, autophosphorylation, and oxidation and by investigating the phosphorylation status of CaMKII downstream targets. To further evaluate these findings, CaMKIIδ C transgenic mice were treated with the β 1 -AR blocker metoprolol (270 mg/kg*d). Metoprolol significantly reduced transgene-associated mortality (n≥29; P <0.001), attenuated the development of cardiac hypertrophy (−14±6% heart weight/tibia length; P <0.05), and strongly reduced ventricular arrhythmias (−70±22% premature ventricular contractions; P <0.05). On a molecular level, metoprolol expectedly decreased protein kinase A–dependent phospholamban and ryanodine receptor 2 phosphorylation (−42±9% for P-phospholamban-S16 and −22±7% for P-ryanodine receptor 2-S2808; P <0.05). However, this was paralled neither by a reduction in CaMKII autophosphorylation, oxidation, and substrate binding nor a change in the phosphorylation of CaMKII downstream target proteins (n≥11). The lack of CaMKII modulation by β-AR blocker treatment was confirmed in healthy wild-type mice receiving metoprolol. Conclusions— Chronic β-AR blocker therapy in patients and in a mouse model of CaMKII-induced HF is not associated with a change in CaMKII activity. Thus, our data suggest that the molecular effects of β-AR blockers are not based on a modulation of CaMKII. Directly targeting CaMKII may, therefore, further improve HF therapy in addition to β-AR blockade.