Role of serum- and glucocorticoid-regulated kinase-1 in electrical remodeling

描述(由申请人提供)：不利的心脏重构是心力衰竭和心律失常的常见前奏，但人们对介导这一转变的信号机制知之甚少。血清和糖皮质激素调节的激酶-1(SGK1)是一种依赖PI3K的激酶，在病理性肥厚和心力衰竭(HF)中被激活，但在生理性肥厚中不被激活。SGK1与其他依赖PI3K的激酶如Akt1共享一些下游底物(如GSK3和Foxo3)，但也具有独特的下游作用，包括调节离子通道如钾通道和心脏钠通道SCN5A。虽然我们之前已经证明SGK1在体外调节心肌细胞(CM)的生存和生长，但它在体内CM中的作用以及慢性SGK1激活或抑制的影响在很大程度上是未知的。为了在体内解决这些问题，我们培育了心脏特异的转基因(TG)小鼠，表达SGK1激酶的结构性活性(CA)或显性阴性(DN)形式。SGK1-CATG小鼠表现出自发性和诱发性心律失常，而SGK1-DNTG小鼠在基线状态下表现正常。在横行主动脉缩窄(TAC)诱导的心肌肥厚和心力衰竭模型中，SGK1-dN TGS对心功能障碍和纤维化具有显著的保护作用。SGK1激活导致SCN5A蛋白的翻译后修饰和亚细胞分布发生显著变化。这与通道动力学和门控的改变以及晚期钠电流和动作电位时程的增加有关。本研究的主要目的是了解SGK1在病理性肥厚和心力衰竭背景下的电重构中的作用。这一建议基于四个假设：1)CMS中SGK1的慢性激活是HF不利电重构的重要中介，2)CMS中SGK1的抑制将减轻不利的重构，3)改变SCN5A功能和终末是这些效应的重要贡献者，以及4)其他新的SGK1底物也在观察到的表型中发挥作用。为了验证这些假设，我们将利用在基线和肥厚和/或心力衰竭模型中具有CM特异性SGK1-CA或-DN表达的小鼠。在目标1中，我们将研究激活或抑制SGK1对基础状态和主动脉缩窄后电重构的影响。在目标2中，我们将定义与所观察到的电生理表型有关的细胞机制。最后，在目标3中，我们将通过对已知下游通路的集中询问和对新效应器的消减筛选来描述调节这些表型的分子机制。心律失常仍然是心力衰竭发病率和死亡率的重要原因。了解SGK1在心力衰竭的不良电重构和心律失常并发症中的作用，可以为这一重要疾病提供新的治疗方法。

DESCRIPTION (provided by applicant): Adverse cardiac remodeling is a common prelude to heart failure and arrhythmia, but little is known about the signaling mechanisms that mediate this transition. Serum- and glucocorticoid-regulated kinase-1 (SGK1) is a PI3-kinase (PI3K)-dependent kinase that is activated in pathological hypertrophy and heart failure (HF) but not in physiological hypertrophy. SGK1 shares some downstream substrates (e.g. GSK3 and Foxo3) with other PI3K-dependent kinases, such as Akt1, but also has unique downstream effects including modulation of ion channels such as potassium channels and the cardiac sodium channel, SCN5a. While we have previously shown that SGK1 regulates cardiomyocyte (CM) survival and growth in vitro, its role in CM in vivo and the effects of chronic SGK1 activation or inhibition are largely unknown. To address these questions in vivo, we generated cardiac-specific transgenic (TG) mice expressing either a constitutively active (CA) or dominant negative (DN) form of the SGK1 kinase. While SGK1-CA TG mice exhibit spontaneous and inducible arrhythmias, SGK1-DN TG mice appear normal at baseline. In a model of cardiac hypertrophy and heart failure induced by transverse aortic constriction (TAC), SGK1-DN TGs are substantially protected against cardiac dysfunction and fibrosis. SGK1 activation led to significant alterations in post-translational modification and subcellular distribution of SCN5a protein. This was associated with altered channel kinetics and gating, as well as an increase in late sodium current (INaL) and action potential duration (APD). The major goal of this proposal is to understand the role of SGK1 in electrical remodeling in the context of pathological hypertrophy and HF. This proposal is based on four hypotheses: 1) that chronic activation of SGK1 in CMs is an important mediator of adverse electrical remodeling in HF, 2) that inhibition of SGK1 in CMs will mitigate adverse remodeling, 3) that altered SCN5a function and INaL are important contributors to these effects, and 4) that other novel SGK1 substrates also play a role in the observed phenotypes. To test these hypotheses, we will utilize mice with CM-specific expression of SGK1-CA or -DN at baseline and in models of hypertrophy and/or HF. In Aim 1, we will examine the effects of activating or inhibiting SGK1 on electrical remodeling at baseline and after aortic banding. In Aim 2, we will define the cellular mechanisms responsible for the observed electrophysiological phenotypes. Finally, in Aim 3, we will delineate the molecular mechanisms mediating these phenotypes through focused interrogation of known downstream pathways, and subtractive screens for novel effectors. Arrhythmia remains an important cause of morbidity and mortality in HF. Understanding the role of SGK1 in adverse electrical remodeling and arrhythmic complications of HF could yield novel therapeutic approaches for this important condition.