Dystrophin-glyoprotein complex and dilated cardiomyopathy

扩张型心肌病是一种多因素疾病，包括遗传性和获得性心肌病。最近的实验表明，人类遗传性心肌病可能与营养不良蛋白-糖蛋白复合体成分的遗传缺陷有关。例如，dystrophin基因的突变会导致Duchenne和Becker肌营养不良症的高发病率，并可能导致X连锁扩张型心肌病。肌聚糖基因的突变是导致肢体带状肌营养不良症的原因，并经常与心肌病密切相关。此外，我们的初步数据将获得性心肌病、肠道病毒感染与营养不良蛋白-糖蛋白复合体的破坏联系在一起。因此，越来越多的证据表明，营养不良蛋白-糖蛋白复合体在遗传性和获得性心肌病的发生中起着关键作用。抗肌营养不良多糖是抗肌营养不良蛋白-糖蛋白复合体的关键成分，该复合体连接细胞骨架蛋白抗肌营养不良蛋白和细胞外基质蛋白层粘连蛋白-2。最近对营养不良蛋白聚糖缺失的ES细胞的实验表明，营养不良蛋白聚糖是基底膜组装所必需的，但不是心肌细胞分化所必需的。肌聚糖与肌营养不良蛋白聚糖相互作用密切，最近对肌聚糖缺失小鼠的研究表明，肌糖相关心肌病的潜在机制是由于血管平滑肌功能障碍所致。该项目的总体目标是检验营养不良蛋白-糖蛋白复合体功能障碍可导致扩张型到扩张型心肌病的假说。我们计划检验以下三个假设：1)心肌细胞中肌营养不良蛋白聚糖的破坏足以扰乱正常的基底膜组装并导致心肌病；2)血管平滑肌肌营养不良蛋白聚糖功能的破坏是诱导心肌病的充分和必要的条件，而血管平滑肌肌营养不良蛋白的基因改变是诱发心肌病的充分和必要的条件；2)血管平滑肌肌糖蛋白功能的破坏是诱导心肌病的充分且必要的条件；以及3)心肌细胞中肌营养不良蛋白的切割与肠道病毒感染的心肌病密切相关。为了直接研究肌营养不良蛋白聚糖在心脏中的功能，我们提出了第一个特定目的的实验，目的是绕过肌营养不良蛋白聚糖零突变的早期致命性，以分析肌营养不良蛋白聚糖在心脏基底膜组装和心功能中的作用。第二个目的是研究心脏血管平滑肌中的肌聚糖对肌营养不良蛋白聚糖复合体的调节。为了达到这一目的，将产生一种在平滑肌中存在特殊的肌聚糖缺乏的小鼠。特异性目标3和4确定肠道病毒蛋白酶2A介导的Dystrophin切割的机制，并确定这种切割在完整心脏中的意义。在这些特定的目的中概述的互补方法将产生对dystrophin-糖蛋白复合体在遗传性和获得性心肌病中的作用的新的理解。

Dilated cardiomyopathy is a multi-factorial disease that includes both the hereditary and acquired forms of cardiomyopathy. Recent experiments have shown that hereditary cardiomyopathy in humans can be associated with genetic defects in components of the dystrophin-glycoprotein complex. For example, mutations in the dystrophin gene lead to a high incidence of cardiomyopathy in Duchenne and Becker muscular dystrophy, and can caused X-linked dilated cardiomyopathy. Mutations in the genes for the sarcoglycans are responsible for limb girdle muscular dystrophy and are often quite associated with cardiomyopathy. In addition, our preliminary data links an acquired form of cardiomyopathy, enteroviral infection, with disruption of the dystrophin-glycoprotein complex. Thus, evidence is accumulating that the dystrophin-glycoprotein complex has a critical role in the genesis of hereditary and acquired cardiomyopathy. Dystroglycan is a key component of the dystrophin- glycoprotein complex that links the cytoskeletal protein dystrophin to the extracellular matrix protein laminin-2. Recent experiments with dystroglycan null ES cells have demonstrated that dystroglycan is required for basement membrane assembly but not cardiac myocyte differentiation. Sarcoglycans interact closely with dystroglycan and recent studies of sarcoglycan null mice have suggested that the underlying mechanism of sarcoglycan related cardiomyopathy is due to the dysfunction of vascular smooth muscle. The overall goal of this project is to test the hypothesis that the dysfunction of the dystrophin-glycoprotein complex can lead to dilated to dilated cardiomyopathy. We plan to test the following three hypotheses: 1) disruption of dystroglycan in the cardiac myocyte is sufficient to disrupt normal basement membrane assembly and induce cardiomyopathy; 2) disruption of sarcoglycan function in the vascular smooth muscle is sufficient and necessary to induce the cardiomyopathy that occurs with genetic alteration of the vascular smooth muscle is sufficient and necessary to induce the cardiomyopathy; 2) disruption of sarcoglycan function in the vascular smooth muscle is sufficient and necessary to induce the cardiomyopathy that occurs with genetic alteration of the sarcoglycan complex; and 3) cleavage of dystrophin in the cardiac myocyte contributes significantly to to the cardiomyopathy of enteroviral infection. To directly examine dystroglycan's function in the heart we have proposed experiments in the first specific aim to circumvent the early lethality of dystroglycan null mutation in order to analyze dystroglycan's role in cardiac basement membrane assembly and cardiac function.. The second aim is to investigate the regulation of the dystroglycan complex by the sarcoglycans in vascular smooth muscle of the heart. For this aim mice with a specific deficiency in delta-sarcoglycan in smooth muscle will be produced. Specific aims three and four identify the mechanisms of enteroviral protease 2A mediated cleavage of dystrophin and determine the significance of this cleavage in the intact heart. The complimentary approach is outlined in these specific aims will yield a new understanding of the role of dystrophin-glycoprotein complex in both hereditary and acquired cardiomyopathy.