CaMKII was suggested to mediate ischemic myocardial injury and adverse cardiac remodeling. Here, we investigated the roles of different CaMKII isoforms and splice variants in ischemia/reperfusion (I/R) injury by the use of new genetic CaMKII mouse models. Although CaMKIIδC was upregulated 1 day after I/R injury, cardiac damage 1 day after I/R was neither affected in CaMKIIδ-deficient mice, CaMKIIδ-deficient mice in which the splice variants CaMKIIδB and C were re-expressed, nor in cardiomyocyte-specific CaMKIIδ/γ double knockout mice (DKO). In contrast, 5 weeks after I/R, DKO mice were protected against extensive scar formation and cardiac dysfunction, which was associated with reduced leukocyte infiltration and attenuated expression of members of the chemokine (C-C motif) ligand family, in particular CCL3 (macrophage inflammatory protein-1α, MIP-1α). Intriguingly, CaMKII was sufficient and required to induce CCL3 expression in isolated cardiomyocytes, indicating a cardiomyocyte autonomous effect. We propose that CaMKII-dependent chemoattractant signaling explains the effects on post-I/R remodeling. Taken together, we demonstrate that CaMKII is not critically involved in acute I/R-induced damage but in the process of post-infarct remodeling and inflammatory processes.

Significance In failing hearts, norepinephrine (NE) net release and endothelin-1 (ET1) levels are increased. ET1 receptor antagonists were successfully used in preclinical heart failure (HF) studies, but clinical studies did not show beneficial effects in HF patients. We found that mice lacking endothelin receptor A (ET A ) only in sympathetic neurons but not in cardiomyocytes were protected from the development of HF. Mechanistically, the presynaptic reuptake of NE within the heart was preserved in mice lacking ET A only in sympathetic neurons. These data provide an explanation of why patients in clinical studies do not benefit from ET1 receptor antagonists, because these patients are usually treated with β blockers, which interfere with the mechanism of action identified here.

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