Novel Mechanism of SR Calcium Regulation in Cardiac Dysfunction

描述（由申请人提供）：心力衰竭是美国和世界上最重要的疾病之一。收缩力丧失和对肾上腺素能刺激反应迟钝是心力衰竭的常见病理生理特征。心脏SR钙循环是一个高度调控的过程，其异常在心力衰竭中起重要作用。最近，我们的实验室发现了一种新的蛋白磷酸酶2C （PP2Ce）异构体，它具有以下有趣的特征。PP2Ce在心脏中高表达，并特异性靶向于心肌细胞SR膜。PP2Ce对p-PLN具有特异性活性，对p-RyR2无显著影响。PP2Ce蛋白具有快速的翻转速率，在转录后水平上，长时间的2AR刺激可显著诱导其表达。PP2Ce表达抑制2AR介导的钙瞬态和收缩性的诱导，并促进缺血/再灌注损伤后的衰竭。PP2Ce失活维持2AR诱导的收缩力，防止I/R损伤，减轻压力过载诱导的肥厚和心力衰竭。这些发现导致了我们令人兴奋的新假设，即PP2Ce是PLN的一种新型磷酸酶，在应激心脏中对2AR信号传导和功能调节有重要贡献。本研究旨在揭示PP2Ce表达的调控机制以及PP2Ce介导的信号转导的功能意义。具体而言，我们计划实现以下三个目标：具体目标1：研究pp2ce介导的PLN去磷酸化的分子基础和细胞影响。我们将确定PP2Ce和PLN之间的相互作用，以及PP2Ce表达/失活对SR钙稳态的影响。目的2：探讨PP2Ce表达的调控机制。我们将剖析PP2Ce蛋白表达、PLN靶向和2AR介导的其翻转调节的影响因素。具体目的3：确定PP2Ce活性在完整心脏中的功能作用。我们将确定PP2Ce表达和失活对I/R损伤和压力过载的功能影响。此外，我们将确定PLN在PP2Ce介导的心脏保护和病理重构中的功能意义。

DESCRIPTION (provided by applicant): 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.