Heart failure is one of the most important diseases in the US and the world. Loss of contractility and blunted response to adrenergic stimulation are common pathophysiological features of a failing heart. Cardiac SR calcium cycling is a highly regulated process and its abnormalities play a major role in heart failure. Recently, our laboratory has identified a novel isoform of protein phosphatase 2C (PP2Ce) which has the following interesting features. PP2Ce is highly expressed in heart and the protein is targeted specifically on SR membrane of cardiomyocytes. PP2Ce has specific activity towards p-PLN without significant impact on p-RyR2. PP2Ce protein has a rapid turn- over rate and its expression is significantly induced by prolonged 2AR stimulation at post-transcriptional level. PP2Ce expression suppresses 2AR mediated induction in calcium transients and contractility, and promotes failure following ischemia/reperfusion injury. PP2Ce inactivation sustains 2AR induced contractility, protects against I/R injury and attenuates pressure-overload induced hypertrophy and heart failure. These findings lead to our exciting new hypothesis that PP2Ce is a novel phosphatase of PLN with a significant contribution to 2AR signaling and functional regulation in stressed hearts. In this proposal, we aim to uncover the regulatory mechanisms of PP2Ce expression and the functional significance of PP2Ce mediated signaling. Specifically, we plan to accomplish the following three aims:
Specific aim 1 : To investigate the molecular basis and cellular impact of PP2Ce-mediated PLN dephosphorylation. We will determine the interaction between PP2Ce and PLN, and the impact of PP2Ce expression/inactivation on SR calcium homeostasis.
Specific aim 2 : To investigate the regulatory mechanism of PP2Ce expression. We will dissect the contributing factors in PP2Ce protein expression, PLN targeting and 2AR mediated regulation of its turn-over.
Specific aim 3 : To determine the functional role of PP2Ce activity in intact heart. We will determine the functional impact of PP2Ce expression and inactivation in response to I/R injury and pressure-overload. In addition, we will determine functional significance of PLN in PP2Ce mediated cardiac protection and pathological remodeling.
Cardiac SR calcium regulation and dysfunction is critically important to cardiomyocyte contractility under basal and diseased conditions. Investigation of a novel phosphatase for PLN, a key regulator of SR calcium cycling can bring new insights to the regulatory network in this process and helps to explore new avenues of therapy for heart failure.
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