The Role of PARP-SIR2 Signaling in Heart Failure

描述（由申请方提供）：本研究的长期目标是了解PARP-Sir 2a信号传导轴在心脏肥大发作和进展中的作用。PARP（聚ADP-核糖聚合酶）和Sir 2a（III类组蛋白脱乙酰酶，HDAC）都是NAD依赖性的、氧化还原敏感的染色质重塑酶。它们在细胞存活和基因调控中发挥核心作用，被认为是氧化应激信号的核整合子。在心脏的工作负荷增加期间，PARP以与心脏肥大的强度成比例的线性方式被激活，并且在衰竭的心脏中发生大量PARP表达。PARP（-/-）小鼠免受缺血性损伤，并对压力超负荷产生减弱的肥大反应。然而，PARP在心脏中的有害作用背后的机制实际上是未知的。PARP通过将多个ADP-核糖单元从NAD转移到靶蛋白来催化蛋白质的ADP-核糖基化。由于NAD对于III类HDAC的活性是必不可少的，因此认为通过PARP过度活化而消耗NAD抑制了III类HDAC的活性（例如，Sir2a）。Sir 2a被认为是一种长寿因子，并且与卡路里限制介导的哺乳动物细胞存活率的增加有关。我们实验室获得的最新数据表明，这两种酶（PARP和Sir 2a）的相互表达在心肌细胞存活/死亡和心肌肥厚向衰竭的进展中起着核心作用。例如，在动物和人类的衰竭心脏中，发现PARP激活与Sir 2a活性的丧失相关。在培养的心肌细胞中，PARP过表达导致基因转录的大量抑制和肌细胞细胞死亡; Sir 2a的过表达保护肌细胞免受Ang-II和氧化应激介导的细胞死亡，并增强关键收缩基因的表达，例如，心脏a-MHC基因。基于这些结果，我们认为在心肌应激期间，PARP的诱导在氧化应激信号向肥大的转化以及随后的心脏从肥大向衰竭的进展中起着核心作用。该提议旨在检验肥大期间PARP过度活化由于细胞NAD耗竭而减弱Sir 2a脱乙酰酶活性的假设。这些变化在氧化应激期间将平衡从细胞存活转移到细胞死亡，导致基因抑制和肌细胞死亡，最终导致与衰竭心脏相关的腔室扩张和肌肉失代偿。该项目的成功结果将使我们能够了解Sir 2a的作用，它被认为是细胞肥大发展过程中许多细胞类型（包括神经元）的生存因子。因此，这些研究可能为心力衰竭的管理提供新的策略。

DESCRIPTION (provided by applicant): The long-term goal of this study is to understand the role of PARP-Sir2a axis of signaling in the onset and progression of cardiac hypertrophy. Both PARP (poly-ADP-ribose polymerase) and Sir2a (Class-Ill histone deacetylase, HDACs) are NAD-dependent, redox-sensitive, chromatin remodeling enzymes. They play a central role in cell survival and gene regulation, and are considered to be the nuclear integrators of oxidative-stress signaling. During increased work load on the heart, PARP is activated in a linear fashion proportional to the intensity of cardiac hypertrophy, and massive PARP expression occurs in failing hearts. PARP (-/-) mice are protected from ischemic insults, and produce an attenuated hypertrophic response to pressure overload. However, the mechanism behind the deleterious effect of PARP in hearts is virtually unknown. PARP catalyzes ADP-ribosylation of proteins by transferring multiple ADP-ribose units from NAD to the target protein. Since NAD is essential for the activity of class III HDACs, it is believed that the depletion of NAD by PARP over-activation represses the activity of class-Ill HDACs (e.g., Sir2a). Sir2a is considered to be a longevity factor, and is implicated in calorie restriction-mediated increases in mammalian cell-survival. Recent data obtained in our laboratory indicate that a reciprocal expression of these two enzymes (PARP & Sir2a) plays a central role in myocyte cell-survival/death and the progression of cardiac hypertrophy to failure. For example, in failing hearts of both animals and humans, PARP activation was found to be associated with the loss of Sir2a activity. In cultured cardiac myocytes, PARP over-expression resulted in massive repression of gene transcription and myocyte cell-death; over expression of Sir2a protected myocytes from Ang-ll and oxidative-stress mediated cell-death, and enhanced the expression of key contractile genes, e.g., the cardiac a-MHC gene. Based on these results, we believe that during myocardial stress, induction of PARP plays a central role in the translation of oxidative-stress signals to hypertrophy and, subsequently, to the heart's progression from hypertrophy to failure. This proposal is designed to test the hypothesis that PARP over activation during hypertrophy attenuates Sir2a deacetylase activity due to cellular NAD depletion. These changes shift the balance from cell-survival towards cell death during oxidative stress, resulting in gene repression and myocyte cell death, which eventually lead to chamber dilation and muscle decompensation associated with the failing heart. A successful outcome of this project will allow us to understand the role of Sir2a, which is implicated as a survival factor for many cell-types (including neurons) during the development of cell hypertrophy. As such, these studies are likely to provide new strategies for the management of heart failure.