Investigation of the molecular mechanisms of cardiac failure focusing on the Z-disc abnormalities

心力衰竭是一种由供氧所需心输出量不足所定义的疾病状态。最严重的心力衰竭包括肥厚性心肌病（HCM）和扩张性心肌病（DCM）。我们已经确定了HCM和/或DCM的疾病基因，并提出心力衰竭与z盘功能异常之间的联系。在本研究中，我们旨在识别与心力衰竭相关的Z-disc异常，揭示Z-disc异常导致心力衰竭的分子机制，并获得抑制Z-disc异常功能的策略。主要议题如下：(1) HCM患者存在TCAP突变，DCM患者存在TCAP、CRYAB和FHL2突变。此外，在限制性心肌病（RCM）中发现了MYPN突变。TCAP、CRYAB、FHL2和MYPN编码z波段或i波段成分，进一步支持Z-I波段功能异常的病理作用。(2) TTN突变破坏了与FHL2和CRYAB的相互作用，表明TTN与FHL2和CRYAB的相互作用对心肌功能很重要。(3) RCM中发现的MYPN突变破坏了大鼠心肌细胞肌原纤维的形成，提示MYPN在心肌肉瘤形成中的功能作用。(4) Cypher/ZASP与代谢酶结合，Cyper/ZASP突变破坏了这种相互作用，在心肌细胞应激时发现代谢酶定位在Z-I带区。这些发现提示了z波段的一种新功能。(5) PP1M的一个小抑制亚基M21增加了心肌收缩的钙敏感性，过表达M21的转基因小鼠出现猝死和心肌肥厚并伴有心肌细胞紊乱，这与HCM的临床观察结果非常相似。m21转基因小鼠可作为HCM的良好动物模型，提示钙敏感性升高是HCM发生的原因。

Heart failure is a disease condition defined by insufficient cardiac output required for oxygen supply. Causes of the most severe heart failure include hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). We have identified disease genes for HCM and/or DCM and suggested the linkage between the heart failure, and abnormality in Z-disc function. In this study, we aimed to identify the Z-disc abnormalities associated with heart failure and to reveal the molecular mechanisms of heart failure caused by the Z-disc abnormalities as well as to obtain a strategy to suppress the abnormal function of Z-disc. Main topics were as follows. (1) TCAP mutations were found in the patients with HCM and mutations in TCAP, CRYAB and FHL2 were, found in the patients with DCM. In addition MYPN mutation was found in restrictive cardiomyopathy, (RCM). TCAP, CRYAB, FHL2 and MYPN encoded components of Z-band or I-band, further supporting the pathological roles of abnormalities in the Z-I band function. (2) TTN mutations impaired interaction with FHL2 and CRYAB, suggesting the interaction of TTN with FHL2 and CRYAB was important for cardiac muscle function. (3) MYPN mutation found in RCM impaired formation of myofibrils in rat cardiomyocytes, suggesting the functional role of MYPN in cardiac sarcomerogenesis. (4) Cypher/ZASP bound to a metabolic enzyme and Cyper/ZASP mutations disrupted this interaction, and the metabolic enzyme was found to localized into Z-I band region upon stress to cardiomyocytes. These findings suggested a novel function of Z-band. (5) M21, a small inhibitory subunit of PP1M, increased calcium sensitivity of cardiac muscle contraction, and M21-overexpressing transgenic mice showed sudden death and cardiac hypertrophy accompanied by myocyte-disarrays, which were closely similar to the clinical observations in HCM. The M21-transgenic mice would be a good animal model for HCM and indicated that the increased calcium sensitivity was the cause of HCM.