Abstract P183: Cardiac Deletion of CaMKII Delta and Gamma Protects Against Heart Failure Despite Activation of Calcineurin Signaling

Abstract

CaMKII delta and gamma are the major CaMKII genes expressed in the heart, and both are up-regulated in response to pressure overload. Recently, we have demonstrated that CaMKII delta single knockout mice are protected against cardiac hypertrophy and remodeling. However, the role of CaMKII gamma and potential redundant functions of CaMKII delta and gamma are still elusive. The aim of the present study was to evaluate the function of CaMKII delta and gamma by a cardiomyocyte-specific double knockout mouse model(delta/gamma-CKO). Strikingly, whereas delta and gamma single knockout mice displayed only slightly reduced levels of cardiac phospholamban (PLN) phosphorylation at the CaMKII phosphorylation site threonin 17, in delta/gamma-CKO mice there was almost no residual PLN-threonin-17 phosphorylation detectable. Surprisingly and in contrast to delta and gamma single knockout mice, delta/gamma-CKO mice did develop cardiac hypertrophy after transverse aortic constriction (TAC). Despite cardiac hypertrophy we observed markedly reduced cardiac fibrosis and apoptosis. Microarray analysis revealed a distinct different gene expression profile pointing to an activation of calcineurin in delta/gamma-CKO mice after TAC. Phosphorylation of calcineurin at serine 197, which leads to an inactivation of its enzymatic activity, was almost abolished in delta/gamma-CKO mice. To test the therapeutical implications of a complete myocardial CaMKII knockout, an tamoxifen-inducible knockout system was established. Knockout of CaMKII delta and gamma was induced by administration of tamoxifen three weeks after TAC surgery. Whereas control mice did develop overt heart failure and cardiac remodeling 16 weeks after TAC, delta/gamma-iCKO mice recovered from cardiac dysfunction. Taken together, our mouse genetic studies demonstrate that CaMKII delta and gamma are promising drug targets to restore cardiac function after pathological stress. These data also unmask a cross talk of CaMKII to endogenous calcineurin signaling, which results in adaptive cardiac hypertrophy and not pathological remodeling.