Ubiquitin receptors and cardiac proteotoxicity

描述（由申请人提供）：心脏中错误折叠蛋白质水平的增加与充血性心力衰竭（CHF）的大子集相关，CHF是几乎所有心脏病的最终共同途径，并困扰着数百万美国人的生活。大多数细胞蛋白质的靶向去除主要通过泛素-蛋白酶体系统（UPS）完成，其通过两个步骤降解蛋白质：（1）通过称为泛素化的过程将泛素（Ub）链连接到靶蛋白分子;（2）通过蛋白酶体降解泛素化蛋白。心脏UPS功能障碍与常见原因的CHF相关，并且经常指示的缺陷是两个步骤之间的解偶联，如通过在患病心肌中增加的泛素化蛋白水平与升高或正常的蛋白酶体肽酶活性的矛盾共存所表明的。然而，很少有人知道的解偶联的分子基础和病理生理意义。Ub受体的UBL-UBA家族（Ubiquilin 1、Rad 23、Ddi 1）旨在为蛋白酶体募集泛素化蛋白，从而促进偶联。到目前为止，这些Ub受体在哺乳动物心脏中的作用还没有阐明。我们的初步研究表明，心脏Ubqln 1蛋白在缺血性心脏病或扩张型心肌病的人类终末期CHF中以及结蛋白相关心肌病（DRC）的小鼠模型中显着增加，这是一种真正的心肌病，由错误折叠蛋白表达增加引起。我们的初步数据还表明，Ubqln 1促进蛋白酶体降解泛素化的错误折叠的蛋白质，而不改变蛋白酶体的活动。因此，我们假设Ubqln 1上调通过增强泛素化错误折叠蛋白向蛋白酶体的募集以进行降解来保护心肌细胞免受蛋白毒性。一组独特的遗传改变的小鼠以及人诱导多能干细胞（hiPSC）衍生的心肌细胞将用于询问心肌细胞中的Ubqln 1和蛋白酶体功能，以研究Ubqln 1在DRC进展中的作用，心肌缺血/再灌注（I/R）损伤和I/R后R小鼠心脏重塑，并检验Ubqln 1作为穿梭Ub受体将泛素化错误折叠蛋白募集到蛋白酶体中进行降解的假设，从而防止心肌细胞中的蛋白毒性。这项工作的完成有望提高我们对心脏蛋白质质量控制的理解，并为开发新的策略提供新的分子靶点，以对抗蛋白毒性增加的心脏疾病，这是越来越多的建议CHF的主要致病因素。

DESCRIPTION (provided by applicant): Increased levels of misfolded proteins in the heart are associated with a large subset of congestive heart failure (CHF), the final common pathway for virtually all heart diseases and afflicting the life of millions of Americans. Targeted removal of most cellular proteins is primarily done by the ubiquitin-proteasome system (UPS) which degrades a protein via two steps: (1) attachment of a chain of ubiquitin (Ub) to a target protein molecule via a process known as ubiquitination; (2) degradation of the ubiquitinated protein by the proteasome. Cardiac UPS dysfunction is associated with CHF of common causes and a frequently indicated defect is an uncoupling between the two steps, as suggested by the paradoxical co-existence of increased levels of ubiquitinated proteins with elevated or normal proteasomal peptidase activities in diseased myocardium. However, little is known about the molecular basis and pathophysiological significance of the uncoupling. The UBL-UBA family of Ub receptors (Ubiquilin1, Rad23, Ddi1) are purport to recruit ubiquitinated proteins for the proteasome, thereby promoting the coupling. To date, the role of none of these Ub receptors in mammalian hearts is elucidated. Our pilot studies reveal that cardiac Ubqln1 proteins were remarkably increased in human end-stage CHF from ischemic heart disease or dilated cardiomyopathy and in mouse models of desmin-related cardiomyopathy (DRC), a bona fide cardiomyopathy caused by increased expression of misfolded proteins. Our preliminary data also suggest that Ubqln1 promotes proteasomal degradation of ubiquitinated misfolded proteins without altering proteasome activities. Hence, we hypothesize that Ubqln1 up-regulation protects against proteotoxicity in cardiomyocytes by enhancing the recruitment of ubiquitinated misfolded proteins to the proteasome for degradation. A unique set of genetically altered mice as well as human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes will be used to interrogate Ubqln1 and proteasome functions in cardiomyocytes to investigate the role of Ubqln1 in the DRC progression, myocardial ischemia/reperfusion (I/R) injury and post I/R cardiac remodeling in mice and to test the hypothesis that Ubqln1 functions as a shuttling Ub receptor to recruit ubiquitinated misfolded proteins to the proteasome for degradation, thereby protecting against proteotoxicity in cardiomyocytes. The completion of this work is expected to improve our understanding of cardiac protein quality control and provide new molecular targets for developing new strategies to fight cardiac disease with increased proteotoxicity, an increasingly suggested major pathogenic factor of CHF.