Regulation and Function of Phosphodiesterase in the Heart

描述(由申请人提供)：环核苷酸磷酸二酯酶(PDE)通过催化分解反应，在调节单个环核苷酸池的大小、持续时间和分隔方面发挥重要作用。然而，PDE表达/活性改变与心功能不全之间的因果关系知之甚少。本项目的目的是了解PDE3A亚型在心脏基因表达和心力衰竭进展中的调节和作用。PDE3A是心肌细胞内重要的cAMP水解物之一。最近，我们发现PDE3A在人类和动物心力衰竭中的表达下调。PDE3A的下调通过持续诱导转录抑制因子ICER(可诱导的cAMP早期抑制因子)，从而抑制抗凋亡分子Bcl2的表达，从而与心肌细胞凋亡有关，这为慢性血管紧张素II(Ang II)和2-肾上腺素能受体(2-AR)刺激诱导心肌细胞凋亡提供了分子机制。有趣的是，持续的ICER诱导是由涉及PDE3A和ICER之间相互作用的正反馈机制(称为PDE3A-ICER反馈环)维持的。具体地说，ICER抑制PDE3A基因转录，PDE3A减少刺激cAMP/PKA信号，通过依赖PKA稳定ICER蛋白而导致ICER上调。除了促凋亡作用，我们的初步数据显示，持续的ICER诱导可能下调一些其他关键调节心肌细胞收缩功能和电生理的蛋白质。PDE3A是正反馈环的关键调节器，因为我们证明，保留PDE3A的功能可以终止反馈环，防止持续的ICER诱导。因此，我们假设PDE3A-ICER反馈环是心功能不全和心力衰竭的致病介质，维持PDE3A的表达和功能将是阻断PDE3A-ICER反馈环和防止心力衰竭进展的一个有吸引力的方法。为了验证这一假说，我们提出了三个目标，目标1：确定PDE3A-ICER反馈环在心肌细胞功能障碍中的作用和机制；目标2：确定刺激PDE3A基因表达从而防止PDE3A-ICER正反馈环的分子机制；目标3：确定在心力衰竭动物模型中恢复PDE3A功能是否能改善心功能。意义：这些发现将为心力衰竭发生的分子机制提供新的见解，并可能导致确定治疗心力衰竭的新治疗靶点。

DESCRIPTION (provided by applicant): Cyclic nucleotide phosphodiesterases (PDEs), by catalyzing the breakdown reaction, play essential roles in the regulation of the magnitude, duration, and compartmentation of individual cyclic nucleotide pools. However, little is known about the causal relationship between alterations of PDE expression/activity and cardiac dysfunctions. The objective of this project is to understand the regulation and function of PDE3A isoform in cardiac gene expression and the progression of heart failure. PDE3A is one of the important cAMP-hydrolyzing PDEs in cardiac myocytes. Recently, we found that the expression of PDE3A is downregulated in human and animal failing hearts. Downregulation of PDE3A is associated with myocyte apoptosis through sustained induction of a transcriptional repressor ICER (inducible cAMP early repressor) and thereby inhibition of anti- apoptotic molecule Bcl-2 expression, which provides the molecular mechanism for how chronic angiotensin II (Ang II) and 2-adrenergic receptor (2-AR) stimulation induce myocyte apoptosis. Interestingly, the sustained ICER induction is maintained by a positive feedback mechanism involving the interactions between PDE3A and ICER (referred to PDE3A-ICER feedback loop). Specifically, ICER represses PDE3A gene transcription and PDE3A reduction stimulates cAMP/PKA signaling, leading to ICER upregulation via PKA-dependent stabilization of ICER protein. In addition to the pro-apoptotic effect, our preliminary data show that sustained ICER induction may downregulate a number of other proteins that critically regulate myocyte contractile function and electrophysiology. PDE3A is a key regulator of the positive feedback loop since we demonstrated that preserving PDE3A function terminates the feedback loop and prevents the sustained ICER induction. Therefore, we hypothesize that the PDE3A-ICER feedback loop is a pathogenic mediator of cardiac dysfunction and heart failure, and maintaining PDE3A expression and function will be an attractive approach to block the PDE3A-ICER feedback loop and prevent the progression of heart failure. To test the hypothesis, we propose three aims, Aim 1: Determine the roles and mechanisms of the PDE3A-ICER feedback loop in cardiac myocyte dysfunction; Aim 2: Define the molecular mechanisms that stimulate PDE3A gene expression and thereby prevent the PDE3A-ICER positive feedback loop; Aim 3: Determine if restoring PDE3A function improves cardiac function in animal models of heart failure. Significance: The findings will provide novel insights into the molecular mechanisms underlying the development of heart failure, and may lead to the identification of novel therapeutic targets for treating heart failure.