The Role of PARP-SIR2 Signaling in Heart Failure

描述（由申请人提供）：本研究的长期目标是了解PARP-Sir2a信号轴在心肌肥厚的发生和进展中的作用。PARP（聚adp核糖聚合酶）和Sir2a （ii类组蛋白去乙酰化酶，hdac）都是nada依赖的，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起着核心作用，被认为是氧化应激信号的核整合体。在心脏负荷增加时，PARP以与心脏肥厚强度成正比的线性方式被激活，在衰竭的心脏中大量表达PARP。PARP（-/-）小鼠免受缺血性损伤，并对压力过载产生减弱的肥厚反应。然而，PARP对心脏的有害作用背后的机制实际上是未知的。PARP通过将多个adp核糖单位从NAD转移到靶蛋白上，催化蛋白质的adp核糖基化。由于NAD对III类hdac的活性至关重要，因此人们认为PARP过度激活导致NAD的消耗会抑制ii类hdac的活性（例如Sir2a）。Sir2a被认为是一个长寿因素，并与卡路里限制介导的哺乳动物细胞存活率的增加有关。我们实验室最近获得的数据表明，这两种酶（PARP和Sir2a）的相互表达在心肌细胞存活/死亡和心脏肥厚到衰竭的进展中起着核心作用。例如，在动物和人类衰竭的心脏中，PARP的激活被发现与Sir2a活性的丧失有关。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心肌细胞的死亡；Sir2a的过表达保护心肌细胞免受Ang-ll和氧化应激介导的细胞死亡，并增强关键收缩基因（如心脏a-MHC基因）的表达。基于这些结果，我们认为在心肌应激过程中，PARP的诱导在氧化应激信号转化为肥厚以及随后心脏从肥厚到衰竭的过程中起着核心作用。该提议旨在验证肥大期间PARP过度激活由于细胞NAD耗竭而减弱Sir2a去乙酰化酶活性的假设。在氧化应激过程中，这些变化改变了细胞生存向细胞死亡的平衡，导致基因抑制和心肌细胞死亡，最终导致心室扩张和与心力衰竭相关的肌肉失代偿。该项目的成功结果将使我们能够理解Sir2a的作用，Sir2a在细胞肥大的发展过程中是许多细胞类型（包括神经元）的生存因子。因此，这些研究可能为心力衰竭的治疗提供新的策略。

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.