Calcium/calmodulin (Ca2+/CaM)-dependent protein kinase II (CaMKII) couples increases in cellular Ca2+ to fundamental responses in excitable cells. CaMKII was identified over 20 years ago by activation dependence on Ca2+/CaM, but recent evidence shows that CaMKII activity is also enhanced by pro-oxidant conditions. Here we show that oxidation of paired regulatory domain methionine residues sustains CaMKII activity in the absence of Ca2+/CaM. CaMKII is activated by angiotensin II (AngII)-induced oxidation, leading to apoptosis in cardiomyocytes both in vitro and in vivo. CaMKII oxidation is reversed by methionine sulfoxide reductase A (MsrA), and MsrA-/- mice show exaggerated CaMKII oxidation and myocardial apoptosis, impaired cardiac function, and increased mortality after myocardial infarction. Our data demonstrate a dynamic mechanism for CaMKII activation by oxidation and highlight the critical importance of oxidation-dependent CaMKII activation to AngII and ischemic myocardial apoptosis.

Rationale: The transverse tubule (T-tubule) system is the ultrastructural substrate for excitation-contraction coupling in ventricular myocytes; T-tubule disorganization and loss are linked to decreased contractility in end stage heart failure (HF). Objective: We sought to examine (1) whether pathological T-tubule remodeling occurs early in compensated hypertrophy and, if so, how it evolves during the transition from hypertrophy to HF; and (2) the role of junctophilin-2 in T-tubule remodeling. Methods and Results: We investigated T-tubule remodeling in relation to ventricular function during HF progression using state-of-the-art confocal imaging of T-tubules in intact hearts, using a thoracic aortic banding rat HF model. We developed a quantitative T-tubule power (TT power ) index to represent the integrity of T-tubule structure. We found that discrete local loss and global reorganization of the T-tubule system (leftward shift of TT power histogram) started early in compensated hypertrophy in left ventricular (LV) myocytes, before LV dysfunction, as detected by echocardiography. With progression from compensated hypertrophy to early and late HF, T-tubule remodeling spread from the LV to the right ventricle, and TT power histograms of both ventricles gradually shifted leftward. The mean LV TT power showed a strong correlation with ejection fraction and heart weight to body weight ratio. Over the progression to HF, we observed a gradual reduction in the expression of a junctophilin protein (JP-2) implicated in the formation of T-tubule/sarcoplasmic reticulum junctions. Furthermore, we found that JP-2 knockdown by gene silencing reduced T-tubule structure integrity in cultured adult ventricular myocytes. Conclusions: T-tubule remodeling in response to thoracic aortic banding stress begins before echocardiographically detectable LV dysfunction and progresses over the development of overt structural heart disease. LV T-tubule remodeling is closely associated with the severity of cardiac hypertrophy and predicts LV function. Thus, T-tubule remodeling may constitute a key mechanism underlying the transition from compensated hypertrophy to HF. (Circ Res. 2010;107:520-531.)Key Words: T-tubule Ⅲ myocardial remodeling Ⅲ hypertrophy Ⅲ heart failure Ⅲ confocal microscopy T he transverse tubules (T-tubules) are orderly invaginations of surface membrane along the Z-line regions, with regular spacing (Ϸ2 m) along the longitudinal axis of mammalian ventricular myocytes. The widely distributed, highly organized T-tubule system is essential for rapid electric excitation, initiation and synchronous triggering of sarcoplasmic reticulum (SR) Ca 2ϩ release, and, therefore, coordinated contraction of each contractile unit throughout the entire cytoplasm. The T-tubule system is thus an important determinant of cardiac cell function. [1][2][3] Heart failure (HF) is characterized by reduction of myocyte contractile function and defects in Ca 2ϩ handling (eg, blunted and dyssynchronous SR Ca 2ϩ release) in myocytes from HF models (includin...

Excessive activation of β-adrenergic, angiotensin II, and aldosterone (Aldo) signaling pathways promotes mortality after myocardial infarction (MI), while antagonist drugs targeting these pathways are core therapies for treating post-MI patients. Catecholamines and angiotensin II activate the multifunctional Ca2+/calmodulin-dependent protein kinase II (CaMKII), and CaMKII inhibition prevents isoproterenol- and angiotensin II-mediated cardiomyopathy. Here we show that Aldo exerts direct toxic actions on myocardium by oxidative activation of CaMKII, causing cardiac rupture and increased mortality in mice after MI. Aldo oxidizes CaMKII by recruiting NADPH oxidase, and oxidized CaMKII promotes matrix metalloproteinase 9 (Mmp9) expression in cardiomyocytes. Myocardial CaMKII inhibition, over-expression of methionine sulfoxide reductase A, an enzyme that reduces oxidized CaMKII, or NADPH oxidase inhibition prevented Aldo-enhanced post-MI cardiac rupture. These findings show oxidized myocardial CaMKII mediates cardiotoxic effects of Aldo on cardiac matrix and establish CaMKII as a nodal signal for the neurohumoral pathways associated with poor outcomes after MI.

In this experimental setting, calcineurin blockade with CsA prevented LV hypertrophy due to pressure overload. TAB mice treated with CsA maintain normal LV size and systolic function.