New therapeutic approach for heart failure using HB-EGF mediated signal transduction

扩张型心肌病是心血管领域最重要的疾病。在本研究项目中，我们的重点是确定新的心力衰竭治疗靶点。我们建立了缺乏生长因子HB-EGF的小鼠。这些小鼠自发发生心力衰竭，其病理和生理表型与人类扩张型心肌病非常相似。利用该动物模型和人类心肌病病例，我们检测了表达谱，并筛选出参与心力衰竭病理生理的候选基因。其中，我们重点研究了一种新的心肌特异性肌球蛋白轻链激酶cardiac-MLCK，该激酶在体内和体外均特异性表达于心脏和磷酸盐心肌特异性肌球蛋白轻链。cardiac-MLCK基因敲低可导致斑马鱼心脏发育严重受损，提示其在心脏发育中的重要作用。同样在大鼠培养的心肌细胞中，降低cardiac-MLCK的表达导致心肌肌节组装受损。这些数据表明，心肌MLCK是心肌肌球蛋白轻链不可缺少的激酶，对肌节组装至关重要。由于心力衰竭时心肌细胞MLCK表达严重下调，因此心脏MLCK的减少可能会导致肌节组装不足，从而导致心脏功能障碍。事实上，已知心肌肌球蛋白轻链（其是心肌MLCK的底物）的突变导致心肌病，表明这种底物-激酶反应对于肌节组装是重要的，并且其损伤导致心肌病。结论：利用心衰模型动物和人的心肌细胞表达谱，我们可以成功地克隆出心衰治疗的新靶点心肌MLCK。心肌MLCK是心肌病的潜在靶点。我们现在正在使用相同的数据库筛选其他治疗靶点。

Dilated Cardiomyopathy is most important disease in cardiovascular field. In this research project, we focused on the identification of new therapeutic targets of heart failure. We established mice lacking growth factor HB-EGF. These mice suffered heart failure spontaneously and the pathological and physiological phenotypes are quite similar to these of human dilated cardiomyopahty. Using this animal model and human cases of cardiomyopaty, we examined the expression profile and screened out candidate genes which involved in the pathophysiology of heart failure. Among them we focused on the novel cardiac specific myosin light chain kinase named cardiac-MLCK This novel kinase was specifically expressed in heart and phsphorirates cardiac specific myosin light chain both in vivo and in vitro. Knock down of cardiac-MLCK in zebrafish caused sever impairment of cardiac development, suggesting its important role of cardiac development. Also in rat cultured cardiomyocytes, reducing expression of cardiac-MLCK caused impairment of cardiac sarcomere assembly. These data suggests that cardiac-MLCK is indispensable kinase of cardiac myosin light chain and essential for sarcomere assembly. Since MLCK expression was severely downregulated in cardiomyocyte in heart failure, reduced cardiac-MLCK may cause the insufficient sarcomere assembly resulting heart dysfunction. In fact the mutation of cardiac myosin light chain which is substrate of cardiac-MLCK is known to cause cardiomyopathy, indicating this substrate-kinase reaction is important for sarcomere assembly and its impairment causes cardiomyopathy. In conclusion we could successfully cloned out new therapeutic target of heart failure, cardiac-MLCK, using expression profiling of heart failure samples of model animal and human. Cardiac MLCK is potential target for cardiomyopathy. We are now screening other therapeutic targets using the same data base.