Novel Mechanism of SR Calcium Regulation in Cardiac Dysfunction

描述(申请人提供)：心力衰竭是美国和世界上最重要的疾病之一。心脏收缩功能丧失和对肾上腺素能刺激反应迟钝是衰竭心脏常见的病理生理学特征。心脏肌浆网钙循环是一个高度调节的过程，其异常在心力衰竭中起重要作用。最近，我们实验室发现了一种新的蛋白磷酸酶2C亚型(PP2Ce)，它具有以下有趣的特征。PP2Ce在心脏中高度表达，该蛋白特异性地定位于心肌细胞的SR膜。PP2Ce对p-PLN具有特异活性，对p-RyR2无明显影响。PP2Ce蛋白翻转速度快，在转录后水平上受2AR刺激显著诱导其表达。PP2Ce的表达抑制2AR介导的钙瞬变和收缩，并促进缺血/再灌注损伤后的失败。PP2Ce失活维持2AR诱导的收缩，保护I/R损伤，减轻压力超负荷所致的肥厚和心力衰竭。这些发现导致了我们令人兴奋的新假设，即PP2Ce是PLN的一种新的磷酸酶，在2AR信号转导和应激心脏功能调节中具有重要作用。在这个方案中，我们旨在揭示PP2Ce表达的调控机制和PP2Ce介导的信号转导的功能意义。具体地说，我们计划完成以下三个目标：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。特异性目的2：探讨PP2Ce基因表达的调控机制。我们将剖析PP2Ce蛋白表达的影响因素、PLN靶向和2AR介导的PP2Ce翻转调控。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的表达和失活对I/R损伤和压力超负荷的反应的功能影响。此外，我们还将确定PLN在PP2Ce介导的心脏保护和病理重塑中的功能意义。

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.