Initiation of Cardiac Hypertrophy

描述（由申请人提供）：在美国，心脏肥厚和心力衰竭是导致死亡的主要原因。然而，心脏病发病机制背后的分子过程尚未被完全理解。在几年的研究中，我们在自发性高血压大鼠中发现并分析了一种12kda的蛋白，肌营养蛋白（Myo），它可以刺激肌细胞生长。过去的资助期产生了这些新的观察结果：(1)Myo过表达导致心脏肥厚，并发展为心力衰竭，相关细胞因子/生长因子的分子谱在早期和晚期疾病中不同；(2) NFkappaB通路的激活是肌致心肌肥厚进展的必要条件；(3)慢性肥厚变为心力衰竭时，心肌细胞的细胞分裂和凋亡并行发生；(4) Myo过表达引发了p53显著、稳健的过表达，这表明p53在这一过程中可能发挥了作用。每一个发现都将为更多的研究提供肥沃的土壤，但我们在这个更新建议中选择关注Myo基因表达的开启和关闭的影响，并定义p53在肥厚过程中的作用。我们假设Myo在心肌肥厚开始时直接作用于心肌细胞，而在过渡到心力衰竭时，它与p53和其他细胞因子/生长因子协同作用。为了验证这一假设，我们提出了一种多学科方法来评估Myo基因表达或不表达的影响，方法是：(a)使用让控开关；(b)使用siRNA技术沉默Myo基因；或(c)常规给予心力衰竭患者的药物治疗。我们的具体目标是：(1)研究通过(a)使用四环素转激活系统或(b)使用siRNA沉默Myo基因来改变Myo基因表达的影响；(2)研究单个药物单独或联合使用对心肌肥厚发展为心力衰竭过程中与分子变化相关的肥厚程度的影响；(3)明确p53与Myo在肥厚及恶化为衰竭时的关系；(4)通过透射电子显微镜评估肥厚开始/进展到心力衰竭期间观察到的结构变化；(5)通过超声心动图确定心功能，将观察到的形态学和分子变化联系起来。这些发现对人类心脏病的治疗至关重要。再加上对心肌肥厚发展为心力衰竭的其他分子机制的研究，这些发现将促进更有效的干预，不仅在干预时间的决定上，而且在设计适当的分子基础疗法方面。

DESCRIPTION (provided by applicant): Cardiac hypertrophy and heart failure are leading causes of death in the United States. However, the molecular processes underlying the pathogenesis of heart disease have not been thoroughly understood. During investigations spanning several years we identified and profiled in spontaneously hypertensive rats a 12-kDa protein, myotrophin (Myo), that stimulates myocyte growth. The past funding period has yielded these novel observations: (1) Myo overexpression causes cardiac hypertrophy that devolves to heart failure, and the molecular profiles of associated cytokines/growth factors differ in early- vs. late-stage disease; (2) activation of the NFkappaB pathway is necessary for the progression of Myo-induced cardiac hypertrophy; (3) at the point when chronic hypertrophy becomes heart failure, cell division and apoptosis of cardiac myocytes occur in parallel; and (4) Myo overexpression elicits significant, robust overexpression of p53, highlighting a possible role of p53 in this process. Each finding would provide fertile ground for more investigation, but we chose in this renewal proposal to focus on the effects of turning Myo gene expression on and off and defining the role of p53 in the hypertrophic process. We hypothesize that Myo acts directly on myocyte during initiation of cardiac hypertrophy, whereas it acts in synergy with p53 and other cytokines/growth factors at the point of transition to heart failure. To test this hypothesis, we propose a multidisciplinary approach to evaluating the effects of the expression or nonexpression of the Myo gene by (a) using a let-control switch; (b) silencing the Myo gene using siRNA technology; or (c) administering pharmacological treatment conventionally given to humans with heart failure. Our specific aims are (1) to study the effects of altering Myo gene expression by either (a) using a tetracycline transactivation system or (b) silencing the Myo gene using siRNA; (2) to study the effects of individual pharmacologic agents, alone or in combination, on the degree of hypertrophy as it progresses to heart failure, associated with molecular changes; (3) to define what relationship p53 has to Myo in hypertrophy and when it worsens to failure; (4) to evaluate structural changes observed during initiation/progression of hypertrophy to heart failure by transmission electron microscopy and (5) to determine cardiac function by echocardiogram to correlate observed morphological and molecular changes. These findings bear crucially upon the treatment of heart disease in humans. Together with investigations into additional molecular mechanisms that underlie the progression of cardiac hypertrophy to heart failure, the findings will facilitate more effective intervention, not only in decisions regarding the timing of intervention, but also in the design of appropriate molecularly based therapies.