The Role of Cardiomyopathic Troponin C Mutations in Skeletal and Cardiac Muscle C

说明(申请人提供)：心肌肌钙蛋白复合体(CTN)由心肌肌钙蛋白T(CTnT)、心肌肌钙蛋白I(CTnI)和心脏/慢肌肌钙蛋白C(CTNC)组成，cTnT与钙结合并触发收缩，cTnI参与抑制肌肉收缩。总之，CTN调节肌肉收缩，即对力发展、最大力发展和基础力的钙敏感性。心肌/慢速骨骼肌钙蛋白C(C/SSTnC)是CTN在心肌和慢速骨骼肌中表达和存在的唯一成分。它被认为是横纹肌的主要钙感受器，是肥厚型(HCM)和扩张型(DCM)心肌病的靶标。HCM或DCM是由TNC基因突变引起的遗传性疾病，其特征是室壁的形态变化和病变心脏的钙处理改变。肌钙蛋白的HCM突变导致心肌肌丝对钙敏感，这可能导致心律失常和心源性猝死。相比之下，与扩张型心肌病相关的肌钙蛋白突变会使肌丝对钙离子不敏感，而钙离子往往会导致充血性心力衰竭。与心肌病相关的CTN突变在心脏系统中已被广泛研究。然而，心肌病C/SSTnC突变也存在于慢速骨骼肌中，其功能后果尚不清楚。这项资助要解决的问题是：与HCM和DCM相关的C/SSTnC突变在调节缓慢的骨骼肌收缩中的功能后果是什么？它们与在心肌中发现的那些相比如何？为了实现这一点，将利用体外系统以及将被用来测量力/PCA关系的带皮纤维。这些测量将在骨骼肌和心肌中进行。在实验室培育的一只HCM cTNC敲入小鼠将被鉴定，以确定这种突变在完整和有皮肤的纤维中的体内后果。这项建议的目的是解决心肌和骨骼肌中C/SSTnC突变表型背后的功能差异。这些研究将调查含有C/SSTnC突变的缓慢骨骼肌是否会出现类似于心脏的骨骼异常，以及在突变敲击小鼠模型中，骨骼肌的功能是否发生改变。正在解决的问题是：骨骼系统中发生的变化与心肌中发生的变化可比性吗？如果慢速骨骼肌的功能变化似乎很小，那么在心肌调节中缺失的其他哪些成分有助于挽救突变的影响？这些目标的成功实现将有助于更好地理解与TNC基因突变相关的心脏和慢速骨骼肌疾病。 公共卫生相关性：心肌/慢骨骼肌钙蛋白C(C/SSTnC)是CTN中唯一在心肌和慢骨骼肌中表达和存在的成分。这一建议将阐明肌钙蛋白C突变与慢速骨骼肌肥厚型(HCM)和扩张型(DCM)心肌病相关的生理后果。这些研究将调查含有C/SSTnC突变的缓慢骨骼肌是否会出现类似于心脏的骨骼异常，以及骨骼肌的功能是否会发生改变。我们将使用创新和新颖的方法，包括转基因小鼠，为骨骼肌中的这种疾病提供关键的见解。

DESCRIPTION (provided by applicant): The cardiac troponin complex (CTn) is made up of cardiac troponin T (CTnT), that attaches the complex to the thin filament; cardiac troponin I (CTnI), involved in the inhibition of muscle contraction and cardiac/slow skeletal troponin C (CTnC), that binds Ca2+ and triggers contraction. Altogether, the CTn, regulates muscle contraction, i.e., Ca2+ sensitivity of force development, maximal force development and basal force. Cardiac/Slow Skeletal Troponin C (C/SSTnC) is the only component of CTn that is expressed and present in both cardiac and slow skeletal muscles. It is considered the primary Ca2+ sensor of striated muscle and has been a target of Hypertrophic (HCM) and Dilated (DCM) Cardiomyopathies. HCM or DCM are genetic disorders caused by the mutations in the TnC gene that are characterized by morphological changes in the ventricular walls and altered Ca2+ handling of the diseased heart. HCM mutations in troponin cause the cardiac myofilament to become sensitized to Ca2+ which is implicated as causing arrhythmias and sudden cardiac death. In contrast, troponin mutations related to DCM desensitize myofilaments to Ca2+ which often leads to congestive heart failure. CTn mutations related to cardiomyopathy have been extensively studied in the cardiac system. However, the functional consequences of cardiomyopathic C/SSTnC mutants also present in slow skeletal muscle are unknown. The question to be addressed in this grant is: What are the functional consequences of C/SSTnC mutations linked to HCM and DCM in the regulation of slow skeletal muscle contraction? How do they compare to those found in cardiac muscle? To accomplish this, in vitro systems will be utilized as well as skinned fibers which will be used to measure the force/pCa relationship. These measurements will be performed in both skeletal and cardiac muscles. An HCM CTnC knock-in mouse generated in the laboratory will be characterized to determine the in vivo consequences of the mutation in intact and skinned fibers. The aims of this proposal address the functional differences that underlie the phenotypes of C/SSTnC mutations in cardiac and skeletal muscles. These studies will investigate whether slow skeletal muscle containing C/SSTnC mutations develops skeletal abnormalities similar to those seen in the heart and whether the function of skeletal muscle is altered in the mutation-knock in mouse model. The questions that are being addressed are: Is the change that occurs in the skeletal system comparable to changes that occur in cardiac muscle? If the functional changes in slow skeletal muscle appear minimal what additional components absent in the regulation of cardiac muscle assist in rescuing the effects of the mutation? Successful execution of these aims will lead to a better understanding of cardiac versus slow skeletal muscle disorders associated with mutations in the TnC gene. PUBLIC HEALTH RELEVANCE: Cardiac/Slow Skeletal Troponin C (C/SSTnC) is the only component of CTn that is expressed and present in both cardiac and slow skeletal muscles. This proposal will elucidate the physiological consequences of troponin C mutants related to Hypertrophic (HCM) and dilated (DCM) cardiomyopathy in slow skeletal muscle. These studies will investigate whether slow skeletal muscle containing C/SSTnC mutations develops skeletal abnormalities similar to those seen in the heart and whether the function of skeletal muscle is altered. We will use innovative and novel approaches including knock-in mice to provide critical insights into this disease in skeletal muscle.