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，我们重点研究了心力衰竭新的治疗靶点的确定。我们建立了缺乏生长因子HB-EGF的小鼠。这些小鼠自发地发生心力衰竭，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，我们检测了该基因的表达谱，并筛选出与心力衰竭病理生理相关的候选基因。其中，我们重点研究了一种新的心脏特异性肌球蛋白轻链激酶，命名为心脏-MLCK，这种新的激酶在体内和体外都特异性地在心脏和肌球蛋白轻链中表达。斑马鱼心脏MLCK基因敲除后，心脏发育受到严重损害，提示其在心脏发育中起重要作用。在培养的大鼠心肌细胞中，减少心脏MLCK的表达也会导致心肌肌节组装的损害。这些数据表明，心脏MLCK是心肌肌球蛋白轻链不可缺少的一种激酶，是肌节组装所必需的。由于心力衰竭时心肌细胞中MLCK的表达严重下调，心脏MLCK的减少可能导致肌节组装不足，从而导致心功能不全。事实上，作为心脏MLCK底物的心肌肌球蛋白轻链的突变已被认为是引起心肌病的原因，这表明这种底物-激酶反应对肌节的组装很重要，它的损伤会导致心肌病。综上所述，我们可以利用模型动物和人的心力衰竭样本的表达谱，成功地克隆出心力衰竭的新治疗靶点-心脏MLCK。心肌MLCK是治疗心肌病的潜在靶点。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.