Novel Nuclear GRK5 Activity in the heart: Good or Bad?

心力衰竭(HF)是一个主要的健康问题，也是心脏损伤后的病理终点 以心泵功能和肌力储备丧失为特征的。通常，心肌肥厚会发生。 在心脏应激或损伤之后，在心力衰竭发作之前和造成心力衰竭的原因。这一病理过程也可能 涉及修复或再生机制的丧失，这与心脏损伤一起导致泵 失败了。G蛋白偶联受体(GPCRs)在心脏功能调节中起关键作用，包括 是心脏肥大过程中的关键角色。GPCR受到由以下因素触发的监管 磷酸化和随后的脱敏通过一组被称为GPCRKs(GRKs)的激酶家族来实现。 脱敏会导致下游信号的丢失。越来越清楚的是，GRK可以 在调节心肌信号和功能方面起着关键作用。GRK的行动似乎变成了 尤其是在心脏功能受损的情况下，如肥厚和衰竭。 心脏中含量最丰富的GRK是GRK2(或PARK1)，GRKS是第二种在 心脏。GRK2和GRKS已被证明在人类心力衰竭和动物中都上调 心肌肥厚和心力衰竭模型。通过使用转基因小鼠，我们已经证明了小鼠 心脏中过表达的GRK2与过表达的GRKS具有不同的表型。在过去的几年里 十年来，我们的研究一直集中在GRK2上，我们已经表明，在衰竭的心脏中抑制其活性 是有益的。来自我们实验室的新数据现在表明，GRKS也是肥厚患者的潜在靶点 而衰竭的心脏及其在心脏中的作用应该得到更深入的探讨。具体地说，我们发现 与心脏GRK2过表达的小鼠和野生型对照小鼠不同，转基因小鼠心脏水平增加 GRK的人不能像现在这样忍受由横主动脉收缩(TAG)造成的慢性压力超负荷 迅速失代偿、心衰和早逝。有趣的是，GRKS，而不是GRK2，已经被证明驻留在 细胞核可与DNA结合，提示其可能在基因调控中发挥作用 抄写。由于基因转录事件与心肌肥厚密切相关，因此新的核 GRKS的作用可能与GRKS转基因小鼠的异常肥大反应有关。 事实上，我们有初步证据表明，GRKS可以与第二类组蛋白相互作用并使其磷酸化 脱乙酰酶(HDAC)是已知在心脏疾病中起关键作用的主要转录抑制因子。 肥大。在这个项目中，我们计划测试我们的中心假设，即GRKS在 心肌细胞的信号和功能，包括在心脏损伤反应中的关键作用，由于其 核内的定位和活动。我们检验这一假设的相关具体目标是：[1] 确定心肌GRKS的体内需求量及其在心脏对心脏损伤反应中的活性； [2]以可诱导的肌细胞靶向表达GRKS突变体的转基因小鼠为特征 保持在核外(GRK5ANLS)或保持在核内(GRK5ANES)，并确定 核型与非核型GRKS在心肌肥厚和心衰中的作用；以及[3]确定其机制。 心肌细胞GRKS核定位的作用，包括其对HDAC功能和心脏基因的潜在调节 使用体外细胞模型系统转录并将知识应用于上述小鼠 模特们。这些研究将利用我们PPG小组中现有的模型和专业知识来学习 更多关于GRKS在受损心肌中的作用以及它是否确实是一个潜在的新分子 追求治疗心力衰竭的新治疗策略的目标。此外，通过这个PPG内部的互动， 我们有机会研究核GRKS活动是否可能参与修复 流程。

Heart failure (HF) is a major health problem and the pathological endpoint after cardiac injury that is characterized by a loss of cardiac pump function and inotropic reserve. Often, myocardial hypertrophy occurs after cardiac stress or injury preceding and contributing to the onset of HF. This pathological process may also involve a loss of repair or regeneration mechanisms, which combined with the cardiac injury results in pump failure. G protein-coupled receptors (GPCRs) play a critical role in the regulation of heart function including being key players in the cardiac hypertrophic process. GPCRs undergo regulation triggered by phosphorylation and subsequent desensitization via a family of kinases known as GPCR kinases (GRKs). Desensitization leads to the loss of downstream signaling. It is becoming increasingly clear that GRKs can play a critical role in modulating myocardial signaling and function. The actions of GRKs appear to become especially important during conditions of compromised heart function such as in hypertrophy and failure. The most abundant GRK in the heart is GRK2 (or PARK1) and GRKS is a second GRK highly expressed in the heart. Both GRK2 and GRKS have been shown to be up-regulated in human HF and also in animal models of cardiac hypertrophy and HF. Through the use of transgenic mice, we have shown that mice overexpressing GRK2 in the heart have a different phenotype from those overexpressing GRKS. Over the last decade, our research has focused on GRK2 and we have shown that inhibition of its activity in the failing heart is beneficial. Novel data from our lab has now shown that GRKS is also a potential target in the hypertrophied and failing heart and its role in the heart should be explored in more depth. Specifically, we have found that unlike cardiac GRK2 overexpressors and wild-type control mice, transgenic mice with increased cardiac levels of GRKS do not tolerate chronic pressure overload exerted by transverse aortic constriction (TAG) as there is rapid decompensation, HF and early death. Interestingly, GRKS, but not GRK2, has been shown to reside in the nucleus of cells and can bind to DMA suggesting that it may play a role in the regulation of gene transcription. Since gene transcriptional events are tightly linked to myocardial hypertrophy, novel nuclear effects of GRKS may be involved in the abnormal hypertrophic response seen in GRKS transgenic mice. Indeed, we have preliminary evidence that GRKS can interact with and phosphorylate Class II histone deacetylases (HDACs), which are major transcriptional repressers known to play a critical role in cardiac hypertrophy. In this project, we plan to test our Central Hypothesis, which is that GRKS plays a novel role in cardiomyocyte signaling and function, including a critical role in the hearts response to injury, due to its localization and activity in the nucleus. Our associated Specific Aims to test this hypothesis are: [1] To determine the in vivo requirement of myocardial GRKS and its activity in the heart's response to cardiac injury; [2] To characterize transgenic mice with inducible myocyte-targeted expression of GRKS mutants that are either kept out of the nucleus (GRK5ANLS) or kept in the nucleus (GRK5ANES) and to determine the role of nuclear vs. non-nuclear GRKS function in cardiac hypertrophy and HF; and [3] To determine the mechanistic role of myocyte GRKS nuclear localization, including its potential regulation of HDAC function and cardiac gene transcription using in vitro cellular model systems and applying knowledge to our above-described mouse models. These studies will take advantage of the models and expertise present within our PPG group to learn more about the role of GRKS in compromised myocardium and whether it is indeed a potential new molecule to target in pursuit of novel therapeutic strategies for treating HF. Moreover, through interactions within this PPG group we have the opportunity to study whether nuclear GRKS activity may be involved in the repair processes.