Cardiac Myosins and Heart Failure

目的是建立与研究人类心脏收缩力和心力衰竭相关的动物模型。近期目标是探索在基础条件下以及在正常心血管功能受到挑战的条件下，兔心脏中α-肌球蛋白重链蛋白（α-MHC）上调的功能后果。稳定和升高的α-MHC水平将通过兔心脏中的心脏特异性转基因来实现，其肌球蛋白补体准确地反映了人类心肌的肌球蛋白补体，测试这种亚型存在对心血管功能的机制影响。我们假设改变α-MHC水平在基础条件下是相对良性的，并且在心脏衰竭时具有心脏保护作用。在特定目的1中，我们将定义心室中表达不同数量α-MHC的兔的表型。在基础条件下，将在运动、细胞、纤维和整个器官/动物水平上确定轻度和中度替代的影响。不同的TG兔将确定在“β-MHC”心脏中在基础条件下不同肌球蛋白同种型的生理重要性，并将检验在正常非应激条件下用高或低水平的β-MHC替代正常β-MHC补体是无害的假设。具体目标2将测试不同量的心室β-MHC对兔心脏耐受缺血的能力的影响。我们推测，稳定表达少量的β-MHC将有利于在缺血条件下维持心血管功能。然而，显著较高水平（40-50%）的α-MHC的表达可能会显著改变心肌细胞的生物化学，从而对器官耐受应激的能力产生负面影响。具体目标3将测试不同量的心室α-MHC对兔心脏耐受逐渐增加的后负荷的能力的影响，方法是在出生后不久通过经主动脉缩窄诱导压力超负荷，并允许动物在青少年和早期成年阶段“成长为”带状物。我们再次假设，在该模型中，用α-MHC进行适度替换将是有益的。具体目标4将测试不同量的心室α-MHC对兔心脏耐受起搏诱导的心力衰竭的能力的影响。我们的工作假设是表达α-MHC的TG动物将表现出显著更低的发病率和死亡率。与上述模型一起，它将提供α-MHC对肥大，扩张和衰竭发展的影响的全面图片。

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.