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

描述（由申请人提供）：心肌肌钙蛋白复合物（CTn）由心肌肌钙蛋白T（CTnT）、心肌肌钙蛋白I（CTnI）和心脏/慢骨骼肌肌钙蛋白C（CTnC）组成，其中，心肌肌钙蛋白T（CTnT）将复合物附着于细丝;心肌肌钙蛋白I（CTnI）参与抑制肌肉收缩，心脏/慢骨骼肌肌钙蛋白C（CTnC）结合Ca 2+并触发收缩。总之，CTn调节肌肉收缩，即，力发展、最大力发展和基础力的Ca 2+敏感性。心脏/慢骨骼肌肌钙蛋白C（C/SSTnC）是CTn中唯一在心脏和慢骨骼肌中表达和存在的组分。它被认为是横纹肌的主要Ca 2+传感器，并且一直是肥厚型（HCM）和扩张型（DCM）心肌病的靶点。HCM或DCM是由TnC基因突变引起的遗传性疾病，其特征在于心室壁的形态学变化和患病心脏的Ca 2+处理改变。肌钙蛋白中的HCM突变导致心肌肌丝对Ca 2+变得敏感，这与引起心律失常和心源性猝死有关。相反，与DCM相关的肌钙蛋白突变使肌丝对Ca 2+不敏感，这通常导致充血性心力衰竭。与心肌病相关的CTn突变已在心脏系统中被广泛研究。然而，心肌病C/SSTnC突变体也存在于慢骨骼肌的功能后果是未知的。本研究所要解决的问题是：与HCM和DCM相关的C/SSTnC突变在缓慢骨骼肌收缩调节中的功能后果是什么？它们与心肌中发现的那些相比如何？为了实现这一点，将使用体外系统以及用于测量力/pCa关系的带皮纤维。这些测量将在骨骼肌和心肌中进行。将对实验室中产生的HCM CTnC敲入小鼠进行表征，以确定完整和带皮纤维中突变的体内后果。该提案的目的是解决功能差异，在心脏和骨骼肌中的C/SSTnC突变的表型。这些研究将研究含有C/SSTnC突变的缓慢骨骼肌是否会出现与心脏中所见相似的骨骼异常，以及骨骼肌功能是否在突变敲除小鼠模型中发生改变。正在解决的问题是：骨骼系统中发生的变化是否与心肌中发生的变化相当？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乏的其他成分有助于挽救突变的影响？这些目标的成功执行将导致更好地了解与TnC基因突变相关的心脏与慢骨骼肌疾病。 公共卫生相关性：心脏/慢骨骼肌肌钙蛋白C（C/SSTnC）是CTn中唯一在心脏和慢骨骼肌中表达和存在的组分。该建议将阐明肌钙蛋白C突变体在缓慢骨骼肌中与肥厚型（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与心脏相似的骨骼异常，以及骨骼肌的功能是否会改变。我们将使用创新和新颖的方法，包括敲入小鼠，以提供关键的见解，这种疾病的骨骼肌。

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.