APOPTOSIS AND CONTRACTILITY IN ISCHEMIC CARDIOMYOPATHY

缺血性心肌病是心力衰竭最常见的病因，但导致失代偿性左心功能不全的因素尚不清楚。尽管已有大量研究集中于脑梗塞后的不可逆性损伤，但许多患者的心力衰竭症状与存活的功能障碍或“冬眠”心肌有关。病理学研究支持这样的观点，即功能障碍的程度经常超过尸检发现的结构性纤维化量。申请人的初步研究再现了慢性LAD狭窄猪冬眠心肌的生理特征。虽然这种情况发生在左心功能正常且无梗死的情况下，但3个月后局部心肌细胞凋亡增加，30%的心肌细胞丢失和代偿性心肌细胞肥大。在分子水平上，存在SR钙摄取蛋白的区域性下调。这些变化是由可逆性缺血(即心绞痛)引起的，在整体左心室功能正常的情况下，与终末期心力衰竭中发现的异常相同。因此，这项应用的总体假设是，心肌细胞凋亡和SR功能障碍发生在冠脉血流储备慢性减少的区域，并且是缺血性心肌病发病机制中的早期事件而不是晚期事件。目的1明确细胞凋亡介导的心肌细胞丢失和可逆性心肌缺血对冬眠心肌的影响。一个双血管狭窄模型将被用来确定舒张期拉伸和功能障碍区域的大小是如何调节细胞凋亡和左心室重塑的。目的2将确定缺血和正常区域细胞凋亡的时间进程与促和抗凋亡蛋白Bax和Bcl2的表达的关系，这将在体内以区域为基础进行量化。目的3明确细胞凋亡介导的心肌细胞丢失和SR蛋白表达改变对冬眠心肌血管重建术和碱性成纤维细胞生长因子-5刺激血管生成后功能可逆性的影响程度。目的4将确定是否可以通过β受体阻滞剂、在心肌细胞丢失发生之前刺激血管生成和体内过表达Bcl2来从药理上阻止细胞凋亡和SR蛋白表达的改变。这种综合的方法应该能更好地了解导致缺血性左心室功能障碍进展的事件，而此时可以使用血运重建和体内基因转移等治疗干预措施来阻断进行性心肌细胞丢失、收缩功能障碍和不可逆转的结构性纤维化。

Ischemic cardiomyopathy is the most common etiological cause of heart failure but the factors responsible for initiating decompensated LV dysfunction are unknown. Although considerable work has focused on irreversible injury following infarction, many patients have symptoms of heart failure in association with viable dysfunctional or "hibernating" myocardium. Pathological studies support the notion that the degree of dysfunction frequently exceeds the amount of structural fibrosis identified at postmortem exam. Preliminary studies by the applicant have reproduced the physiological features of hibernating myocardium in pigs with a chronic LAD stenosis. While this occurs with normal LV function and without infarction, there is increased regional myocyte apoptosis, a 30 percent loss of myocytes and compensatory myocyte hypertrophy after a period of 3 months. At the molecular level, there is a regional downregulation of SR calcium uptake proteins. These changes, arising from reversible ischemia (i.e. angina pectoris) and with normal global LV function, are identical to the abnormalities found in end-stage heart failure. Thus, the overall hypothesis of this application is that myocyte apoptosis and SR dysfunction arise in areas with chronically reduced coronary flow reserve and are early rather than late events in the pathogenesis of ischemic cardiomyopathy. Aim 1 will define the role of apoptosis mediated myocyte loss and LV remodeling from reversible ischemia in hibernating myocardium. A 2-vessel stenosis model that progresses to global LV dysfunction with LV dilatation and increased LV filling pressure will be used to determine how diastolic stretch and the size of the dysfunctional region modulates apoptosis and LV remodeling. Aim 2 will identify the temporal progression of apoptosis in ischemic and normal regions in relation to the expression of the pro- and anti-apoptotic proteins Bax and Bcl-2 which will be quantified in vivo on a regional basis. Aim 3 will define the extent that apoptosis mediated myocyte loss and altered SR protein expression affects the reversibility of function in hibernating myocardium after surgical revascularization and after stimulating angiogenesis with basic fibroblast growth factor (FGF-5). Aim 4 will determine whether apoptosis and altered SR protein expression can be prevented pharmacologically with beta blockade, by stimulating angiogenesis prior to the development of myocyte loss and by overexpressing Bcl-2 in vivo. This integrative approach should provide a better understanding of the events that lead to the progression of ischemic LV dysfunction at a time when therapeutic interventions such as revascularization and in vivo gene transfer can be used to interrupt the progressive myocyte loss, contractile dysfunction and irreversible structural fibrosis.