Cardiac Myosins and Heart Failure

其目的是建立与研究人类心脏收缩能力和心力衰竭相关的动物模型。近期目标是探索兔心脏α-肌球蛋白重链蛋白(α-MHC)上调的功能后果，无论是在基础条件下还是在正常心血管功能受到挑战的条件下。通过在兔心脏中进行心脏特异性转基因，将实现稳定和升高的α-MHC水平，其肌球蛋白补体准确地反映了人类心肌的肌球蛋白补体，测试了该亚型存在对心血管功能的机制影响。我们假设，在基础条件下，改变α-MHC水平将是相对良性的，并且在心力衰竭时具有心脏保护作用。在特定的目标1中，我们将定义在脑室表达不同数量的α-MHC的兔的表型。低水平和中等水平替代的效果将在基础条件下在运动、细胞、纤维和整个器官/动物水平上确定。不同的TG兔将在基础条件下确定不同肌球蛋白亚型在“β-MHC”心脏中的生理重要性，并将检验在正常非应激条件下用高水平或低水平的β-MHC取代正常的β-MHC补体是无害的假设。特定目标2将测试不同数量的脑室β-MHC对兔心脏耐受缺血能力的影响。我们假设，在缺血条件下，稳定表达少量的β-MHC将有利于维持心血管功能。然而，较高水平的α-MHC表达(40%-50%)可能会极大地改变心肌细胞的生化，从而对器官耐受应激的能力产生负面影响。具体目标3将测试不同数量的脑室α-MHC对兔心脏承受逐渐增加的负荷的能力的影响，方法是在出生后不久通过经主动脉缩窄诱导压力超负荷，并允许动物在青春期和成年期早期“成长为”该带。我们再一次假设，在这个模型中，适度替换α-MHC将是有益的。特定目标4将测试不同数量的脑室α-MHC对兔心脏耐受起搏引起的心力衰竭的能力的影响。我们的工作假设是，表达甘油三酯的α-MHC动物的发病率和死亡率将显著降低。与上面的模型一起，它将提供一个关于α-MHC在肥大、扩张和衰竭发展过程中的作用的全面图景。

The objective is to create animal models that are relevant to studying human cardiac contractility and heart failure. The immediate goals are to explore the functional consequences of up-regulation of the alpha-myosin heavy chain protein (alpha-MHC) in the rabbit heart, both under basal conditions as well as under conditions when normal cardiovascular function is challenged. Stable and elevated levels of alpha-MHC will be achieved by cardiac-specific transgenesis in the rabbit heart, whose myosin complement accurately reflects that of the human myocardium, testing the mechanistic implications of this isoform's presence for cardiovascular function. We hypothesize that altering alpha-MHC levels will be relatively benign under basal conditions and cardioprotective as the heart fails. In SPECIFIC AIM 1, we will define the phenotypes of rabbits with varying amounts of alpha-MHC being expressed in the ventricle. The effects of both low and moderate replacement will be determined at the motor, cellular, fiber and whole organ/animal levels under basal conditions. The different TG rabbits will establish the physiological importance of the different myosin isoforms under basal conditions in a "beta-MHC" heart and will test the hypothesis that replacement of the normal beta-MHC complement with either high or low levels of beta-MHC is innocuous under normal unstressed conditions. Specific Aim 2 will test the effects of varying amounts of ventricular beta-MHC on the ability of the rabbit heart to tolerate ischemia. We hypothesize that stable expression of low amounts of beta-MHC will be beneficial for maintaining cardiovascular function under ischemic conditions. However, expression of alpha-MHC at significantly higher levels (40-50%) may alter cardiomyocyte biochemistry so dramatically as to negatively impact on the organ's ability to tolerate stress. Specific Aim 3 will test the effects of varying amounts of ventricular alpha-MHC on the ability of the rabbit heart to tolerate gradual increase in aflerload, by inducing pressure-overload via trans-aortic coarctation soon after birth and allowing the animals to "grow into" the band during the adolescent and early adult stages. Again we hypothesize that in this model, modest replacement with alpha-MHC will be beneficial. Specific Aim 4 will test the effects of varying amounts of ventricular alpha-MHC on the ability of the rabbit heart to tolerate pacing induced heart failure. Our working hypothesis is that the alpha-MHC expressing TG animals will exhibit significantly less morbidity and mortality. Together with the models above, it will provide a comprehensive picture of the alpha-MHC's effects on the development of hypertrophy, dilation and failure.