S-nitrosylation of calcium-handling proteins in cardiac adrenergic signaling and hypertrophy

Rationale: The regulation of calcium (Ca²⁺) homeostasis by β-adrenergic receptor (βAR) activation provides the essential underpinnings of sympathetic regulation of myocardial function, as well as a basis for understanding molecular events that result in hypertrophic signaling and heart failure. Sympathetic stimulation of the βAR not only induces protein phosphorylation but also activates nitric oxide-dependent signaling, which modulates cardiac contractility. Nonetheless, the role of nitric oxide in βAR-dependent regulation of Ca²⁺ handling has not yet been explicated fully. Objective: To elucidate the role of protein S-nitrosylation, a major transducer of nitric oxide bioactivity, on βAR-dependent alterations in cardiomyocyte Ca²⁺ handling and hypertrophy. Methods and Results: Using transgenic mice to titrate the levels of protein S-nitrosylation, we uncovered major roles for protein S-nitrosylation, in general, and for phospholamban and cardiac troponin C S-nitrosylation, in particular, in βAR-dependent regulation of Ca²⁺ homeostasis. Notably, S-nitrosylation of phospholamban consequent upon βAR stimulation is necessary for the inhibitory pentamerization of phospholamban, which activates sarcoplasmic reticulum Ca²⁺-ATPase and increases cytosolic Ca²⁺ transients. Coincident S-nitrosylation of cardiac troponin C decreases myocardial sensitivity to Ca²⁺. During chronic adrenergic stimulation, global reductions in cellular S-nitrosylation mitigate hypertrophic signaling resulting from Ca²⁺ overload. Conclusions: S-Nitrosylation operates in concert with phosphorylation to regulate many cardiac Ca²⁺-handling proteins, including phospholamban and cardiac troponin C, thereby playing an essential and previously unrecognized role in cardiac Ca²⁺ homeostasis. Manipulation of the S-nitrosylation level may prove therapeutic in heart failure.