The Role of the Proteasome in Troponin related Cardiomyopathies

描述（由申请人提供）：尽管在心脏病的诊断和治疗方面取得了重大进展，但心肌病仍然是发达国家最常见的死亡原因。心肌肌钙蛋白T（cTnT）突变导致约7%的家族性肥厚型心肌病（FHC）病例。携带这些FHC相关cTnT突变的患者显示出猝死的高发生率，而没有在具有其他蛋白质突变的FHC患者中观察到的左心室心壁的经典增加。这项建议的重点是蛋白酶体在肌钙蛋白相关的心肌病中的作用。调节心脏蛋白酶体的分子机制及其在心肌病中的作用尚不清楚。转基因小鼠表达的突变体（I79 N）cTnT与FHC表现出的变化，在翻译后修饰的蛋白酶体亚基和活性的蛋白酶体，但没有引起显着的变化，在蛋白酶体亚基的表达研究。观察到蛋白酶体磷酸化水平的变化伴随着所有三种20 S和26 S蛋白酶体活性的降低。了解蛋白酶体系统在心肌病中的重要性是至关重要的，以便能够正确地靶向这种关键的蛋白水解复合物，以获得未来的心血管益处。与20 S蛋白酶体相关的关键磷酸酶的量在从I79 N心脏分离的20 S蛋白酶体中也减少。这是很重要的，因为我们的研究结果还表明，激酶和磷酸酶与心脏内的蛋白酶体复合物是重要的调节剂的蛋白酶体的活性，心脏蛋白酶体是不同于其他组织的蛋白酶体。根据我们的研究结果，我们假设：1）肌丝Ca 2+敏感性显著增加（>0.1pCa单位）有助于信号传导的细胞改变，导致蛋白酶体功能障碍，这导致泛素化蛋白增加和心脏功能障碍，2）肌钙蛋白中的一些FHC相关突变直接影响这些蛋白质被蛋白酶体降解的能力并改变蛋白酶体活性，和3）激酶和磷酸酶在肌钙蛋白相关的心肌病中作为蛋白酶体复合物的相关蛋白发挥作用;它们作为蛋白酶体亚蛋白质组的一部分在调节蛋白酶体功能中起关键作用。为了研究这些假设，我们将研究三个具体目标：1）描述20 S和26 S蛋白酶体在肌钙蛋白相关心肌病中的作用，2）表征肌钙蛋白相关心肌病中蛋白酶体复合物的时间分布，3）表征心肌病诱导的26 S蛋白酶体磷酸化变化。 公共卫生相关性：家族性肥厚型心肌病（FHC）是最常见的遗传性心脏病，患病率至少为0.2%，是青少年和年轻人（尤其是运动员）猝死的最常见原因。泛素蛋白酶体系统（UPS）的功能障碍与压力超负荷诱导的心肌肥厚、缺血/再灌注和充血性心力衰竭有关。研究蛋白酶体在FHC中的作用将对蛋白酶体在心肌病中的功能提供重要的见解。

DESCRIPTION (provided by applicant): Despite significant advances in diagnosis and treatment of heart diseases, cardiomyopathies remain the most prevalent cause of death in developed countries. Mutations in cardiac troponin T (cTnT) are responsible for ~7% of all familial hypertrophic cardiomyopathy (FHC) cases. Patients carrying these FHC related cTnT mutations show a high incidence of sudden death without the classical increase in the left ventricular heart wall seen in FHC patients with mutations in other proteins. This proposal focuses on the role of the proteasome in troponin related cardiomyopathies. The molecular mechanisms that regulate the cardiac proteasome and their role in cardiomyopathies are unknown. Transgenic mice expressing a mutant (I79N) cTnT that is associated with FHC exhibited changes in both post-translational modifications of proteasome subunits and the activity of the proteasome, but did not cause significant changes in the expression of the proteasome subunits investigated. Changes in phosphorylation levels of the proteasome were observed concomitant with decreases in all three 20S and 26S proteasome activities. It is critical to understand the importance of the proteasome system in cardiomyopathies to be able to properly target this key proteolytic complex for future cardiovascular benefit. The amount of a key phosphatase associated with the 20S proteasome is also decreased in 20S proteasomes isolated from I79N hearts. This is important since our results also suggest that the kinases and phosphatases associated with the proteasome complex inside the heart are important modulators of the proteasome activity, and that the cardiac proteasome is unlike proteasomes from other tissues. Based upon our results we hypothesize: 1) Significant increases in myofilament Ca2+-sensitivity (>0.1pCa units) contribute to cellular alterations in signaling that lead to proteasome dysfunction which results in increased ubiquitinated proteins and cardiac dysfunction, 2) Some FHC related mutations in troponin directly affect the ability of these proteins to be degraded by the proteasome and alter proteasome activity, and 3) Kinases and phosphatases function as associating proteins for proteasomal complexes in the Troponin-related cardiomyopathies; they play a critical role in modulating the proteasomal function as part of the proteasomal subproteome. To investigate these hypotheses we will investigate three specific aims: 1) To Delineate the Roles of the 20S and 26S Proteasomes in Troponin-related Cardiomyopathies, 2) To Characterize the Temporal Profile of the Proteasome complexes in Troponin-related Cardiomyopathies, and 3) To Characterize Cardiomyopathy Induced Phosphorylation Changes in 26S Proteasomes. PUBLIC HEALTH RELEVANCE: Familial hypertrophic cardiomyopathy (FHC) is the most common inherited heart disease with a prevalence of at least 0.2% and is the most common cause of sudden death in adolescents and young adults, especially in athletes. Dysfunction of the ubiquitin proteasome system (UPS) has been associated pressure overload induced hypertrophy, ischemia/reperfusion, and congestive heart failure. Investigating the role of the proteasome in FHC will give critical insights into proteasomal function in cardiomyopathies.