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

描述（由申请人提供）：不良心脏重塑是心力衰竭和心律失常的常见前奏，但对介导这种转变的信号传导机制知之甚少。血清和糖皮质激素调节激酶-1（SGK 1）是一种PI 3-激酶（PI 3 K）依赖性激酶，在病理性肥大和心力衰竭（HF）中被激活，但在生理性肥大中不被激活。SGK 1与其他PI 3 K依赖性激酶（如Akt 1）共享一些下游底物（如GSK 3和Foxo 3），但也具有独特的下游效应，包括调节离子通道（如钾通道和心脏钠通道SCN 5a）。 虽然我们以前已经表明，SGK 1调节心肌细胞（CM）的存活和生长在体外，其在CM中的作用在体内和慢性SGK 1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，我们产生了心脏特异性转基因（TG）小鼠表达组成型活性（CA）或显性阴性（DN）形式的SGK 1激酶。虽然SGK 1-CA TG小鼠表现出自发性和诱导性心律失常，但SGK 1-DN TG小鼠在基线时表现正常。在由横向主动脉缩窄（TAC）诱导的心脏肥大和心力衰竭模型中，SGK 1-DN TG基本上保护免于心脏功能障碍和纤维化。SGK 1激活导致SCN 5a蛋白的翻译后修饰和亚细胞分布的显著改变。这与通道动力学和门控改变以及迟发钠电流（INaL）和动作电位时程（APD）增加有关。该提案的主要目标是了解SGK 1在病理性肥大和HF背景下的电重构中的作用。 该提议基于四个假设：1）CM中SGK 1的慢性激活是HF中不良电重构的重要介质，2）CM中SGK 1的抑制将减轻不良重构，3）改变的SCN 5a功能和INaL是这些效应的重要贡献者，以及4）其他新型SGK 1底物也在观察到的表型中发挥作用。为了检验这些假设，我们将利用在基线和肥大和/或HF模型中具有SGK 1-CA或-DN的CM特异性表达的小鼠。在目标1中，我们将研究激活或抑制SGK 1对基线和主动脉结扎后电重构的影响。在目标2中，我们将定义负责所观察到的电生理表型的细胞机制。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物的消减筛选来描绘介导这些表型的分子机制。 心律失常仍然是HF发病率和死亡率的重要原因。了解SGK 1在HF的不良电重构和脑血管并发症中的作用可能会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.