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

描述（由申请人提供）：心脏肌钙蛋白复合物（CTn）由心脏肌钙蛋白T （CTnT）组成，将复合物附着在细丝上；心肌肌钙蛋白I (CTnI)，参与抑制肌肉收缩和心脏/慢骨肌钙蛋白C (CTnC)，结合Ca2+并触发收缩。综上所述，CTn调节肌肉收缩，即Ca2+对力发展、最大力发展和基础力的敏感性。心肌/慢骨骼肌肌钙蛋白C （C/SSTnC）是唯一在心肌和慢骨骼肌中表达和存在的CTn成分。它被认为是横纹肌的主要Ca2+传感器，并已成为肥厚（HCM）和扩张型（DCM）心肌病的目标。HCM或DCM是由TnC基因突变引起的遗传性疾病，其特征是心室壁的形态学改变和患病心脏Ca2+处理的改变。肌钙蛋白的HCM突变导致心肌肌丝对Ca2+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Ca2+脱敏，这通常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，在慢骨骼肌中也存在心肌病C/SSTnC突变的功能后果尚不清楚。本次拨款要解决的问题是：与HCM和DCM相关的C/SSTnC突变在骨骼肌缓慢收缩调节中的功能后果是什么？它们与心肌中的相比如何？为了实现这一目标，将利用体外系统以及将用于测量力/pCa关系的剥皮纤维。这些测量将在骨骼肌和心肌中进行。在实验室中产生的HCM CTnC敲入小鼠将被表征，以确定完整和剥皮纤维突变的体内后果。本提案的目的是解决心脏和骨骼肌中C/SSTnC突变表型基础的功能差异。这些研究将探讨含有C/SSTnC突变的缓慢骨骼肌是否会出现与心脏中类似的骨骼异常，以及骨骼肌的功能是否会在突变敲敲小鼠模型中发生改变。正在解决的问题是：发生在骨骼系统中的变化是否与发生在心肌中的变化相当？如果慢骨骼肌的功能变化似乎微乎其微，那么在心肌调节中缺失的哪些额外成分有助于挽救突变的影响？这些目标的成功实施将有助于更好地理解与TnC基因突变相关的心脏与慢骨骼肌疾病。

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.