Ca2+-Influx Regulated Cardiac Hypertrophy, Arrhythmia and Myocyte Apoptosis

描述(申请人提供)：心律失常和泵衰竭是美国死亡率和发病率的主要原因。伴随心律失常的心肌肥厚是对血流动力学应激的常见初始反应，如高血压和心肌梗塞。持续的血流动力学应激会导致失代偿性心力衰竭。早期和代偿性肥厚时增强的肾上腺素能驱动所刺激的收缩能力的增强是通过促进细胞内钙循环，包括通过L型钙通道的钙内流增加(CAV12)。然而，Cavl.2在心脏病进展中的作用还不是很清楚。我们假设，钙内流增加有助于心肌肥厚、心律失常和心肌细胞凋亡的发展，最终导致心力衰竭。这一假设将在我们新建立的转基因(TG)小鼠品系中进行验证，这些品系在低水平或高水平过表达Cavl.2的Beta2a亚单位。我们的初步数据显示，低表达的TG小鼠出现心脏性猝死和肥大，而高表达的TG小鼠出现心力衰竭症状。血流动力学应激在低表达的TG小鼠中引起心力衰竭，在高表达的TG小鼠中加速心衰的发生。其具体目的是：1.确定钙离子内流的增加(使用低水平表达Cav1.2beta2a的转基因小鼠)是否足以增加心肌收缩能力，但不会导致肌浆网钙超载，是否可以诱导心肌细胞肥大而不引起细胞凋亡。2.确定足以引起肌浆网钙超载的钙内流增加(高水平表达Cav1.2beta2a的转基因小鼠)是否会导致心律失常和心肌细胞凋亡，从而导致心力衰竭，心泵功能降低，但心肌细胞收缩能力增加。这些研究将检验这样一种观点，即激活心肌细胞凋亡需要钙调节蛋白CaMK II依赖的磷酸化。3.研究Cav1.2beta2a低表达和高表达转基因小鼠细胞内钙内流增加是否加重/逆转血流动力学应激(主动脉缩窄和异丙肾上腺素输注)对心泵功能的不利影响，以及心力衰竭的发生。Cavl.2beta2a基因将在引入应激源之前或之后被激活。长期目标是确定治疗心脏病的新目标或战略。

DESCRIPTION (provided by applicant): Cardiac arrhythmia and pump failure are the leading causes of mortality and morbidity in the United States. Cardiac hypertrophy associated with arrhythmia is the common initial response to hemodynamic stress such as hypertension and myocardial infarction. Sustained hemodynamic stress leads to decompensated heart failure. Increased contractility stimulated by heightened adrenergic drive during early and compensated hypertrophy is brought about by enhancing intracellular Ca2+ cycling, including increased Ca2+ influx through the L-type Ca2+ channel (Cavl.2). However, the role of Cavl.2 in the progress of heart disease is not well understood. We hypothesize that increases in Ca2+ influx contribute to the development of cardiac hypertrophy, arrhythmia and myocyte apoptosis, which ultimately lead to heart failure. This hypothesis will be tested with our newly established transgenic (TG) mouse lines overexpressing the beta2a subunit of Cavl.2 at low or high levels. Our preliminary data show that low expression TG mice develop sudden cardiac death and hypertrophy while high expression TG mice have heart failure symptoms. Hemodynamic stress causes heart failure in low expression TG mice and precipitates the onset of heart failure in high expression TG mice. The specific aims are: 1. To determine if increases in Ca2+ influx (with a transgenic mouse line with low level expression of Cavl.2beta2a) that are sufficient to increase cardiac contractility, but do not induce SR Ca2+ overload, can induce myocyte hypertrophy without causing apoptosis. 2. To determine if increases in Ca2+ influx (transgenic mouse line with high level expression of Cavl.2beta2a) that are sufficient to cause SR Ca2+ overload induce cardiac arrhythmias and myocyte apoptosis, causing heart failure with depressed cardiac pump function, however, with increased myocyte contractility. These studies will test the idea that activation of myocyte apoptosis requires a CaMK II dependent phosphorylation of Ca2+ regulatory proteins. 3. To determine if increased Ca2+ influx (transgenic mouse lines with low and high expression of Cavl.2beta2a exacerbates/reverses the adverse effects of hemodynamic stress (aortic banding and isoproterenol infusion) on cardiac pump function, and the development of heart failure. The Cavl.2beta2a gene will be turned on either before or after the introduction of stressors. The long-term goal is to identify new targets or strategies for treating heart disease.