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

描述（由申请人提供）：不良心脏重构是心力衰竭和心律失常的常见前奏，但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激酶-1 （SGK1）是PI3K激酶（PI3K）依赖性激酶，在病理性肥厚和心力衰竭（HF）中激活，但在生理性肥厚中不激活。SGK1与其他pi3k依赖性激酶（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，包括钾通道和心脏钠通道SCN5a等离子通道的调节。虽然我们之前已经证明SGK1在体外调节心肌细胞（CM）的存活和生长，但其在体内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，我们产生了心脏特异性转基因（TG）小鼠，表达构成型活性（CA）或显性阴性（DN）形式的SGK1激酶。SGK1-CA TG小鼠表现出自发性和诱导性心律失常，而SGK1-DN TG小鼠在基线时表现正常。在横断主动脉缩窄（TAC）引起的心脏肥厚和心力衰竭模型中，SGK1-DN tg基本上可以防止心功能障碍和纤维化。SGK1激活导致SCN5a蛋白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的改变以及后期钠电流（INaL）和动作电位持续时间（APD）的增加有关。本提案的主要目标是了解SGK1在病理性肥大和心衰背景下的电重构中的作用。该建议基于四个假设：1)CMs中SGK1的慢性激活是HF不良电重构的重要介质，2)CMs中SGK1的抑制将减轻不良重构，3)SCN5a功能和INaL的改变是这些影响的重要因素，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，我们将在基线和肥大和/或HF模型中使用SGK1-CA或-DN在cm特异性表达的小鼠。在目的1中，我们将研究激活或抑制SGK1对基线和主动脉束带后电重构的影响。在目标2中，我们将定义负责观察到的电生理表型的细胞机制。最后，在Aim 3中，我们将通过对已知下游途径的集中询问和对新型效应物的减法筛选来描述介导这些表型的分子机制。心律不齐仍然是心衰发病和死亡的重要原因。了解SGK1在心衰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.