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肌营养不良蛋白-糖蛋白复合物成分的遗传缺陷有关。例如，肌营养不良蛋白基因突变导致Duchenne和Becker肌营养不良患者心肌病发病率高，并可引起x连锁扩张型心肌病。肌聚糖基因的突变是导致肢带肌营养不良的原因，并且通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，肠病毒感染，与肌营养不良蛋白-糖蛋白复合物的破坏联系起来。因此，越来越多的证据表明，肌营养不良蛋白-糖蛋白复合物在遗传性和获得性心肌病的发生中起着关键作用。肌营养不良聚糖是肌营养不良蛋白-糖蛋白复合物的关键成分，该复合物将细胞骨架蛋白肌营养不良蛋白与细胞外基质蛋白层粘连蛋白-2连接起来。最近对无三聚糖酐的胚胎干细胞进行的实验表明，三聚糖酐是基底膜组装所必需的，而不是心肌细胞分化所必需的。肌糖苷与肌糖苷异常密切相关，最近对肌糖苷缺失小鼠的研究表明，肌糖苷相关心肌病的潜在机制是由于血管平滑肌功能障碍。该项目的总体目标是验证肌营养不良蛋白-糖蛋白复合物功能障碍可导致扩张型至扩张型心肌病的假设。我们计划验证以下三个假设：1)心肌细胞中肌糖异常蛋白的破坏足以破坏正常的基底膜组装并诱发心肌病；2)血管平滑肌肌糖功能的破坏是诱发心肌病的充分必要条件，血管平滑肌基因改变是诱发心肌病的充分必要条件；2)血管平滑肌肌糖功能的破坏是诱发肌糖复合物基因改变引起的心肌病的充分和必要条件；3)心肌细胞中肌营养不良蛋白的分裂在肠病毒感染的心肌病中起重要作用。为了直接检测三聚糖酐在心脏中的功能，我们在第一个特定目标中提出了实验，以规避三聚糖酐无效突变的早期致命性，从而分析三聚糖酐在心脏基底膜组装和心脏功能中的作用。第二个目的是研究肌聚糖对心脏血管平滑肌中肌聚糖复合物的调节作用。为此目的，将产生平滑肌中三角肌聚糖特异性缺乏的小鼠。具体目的3和4鉴定肠病毒蛋白酶2A介导的肌营养不良蛋白的裂解机制，并确定这种裂解在完整心脏中的意义。在这些特定目标中概述的互补方法将产生对肌营养不良蛋白-糖蛋白复合物在遗传性和获得性心肌病中的作用的新理解。

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.