Ubiquitin receptors and cardiac proteotoxicity

描述(申请人提供)：心脏中错误折叠蛋白水平的增加与充血性心力衰竭(CHF)的一大部分有关，充血性心力衰竭是几乎所有心脏疾病的最终共同途径，困扰着数百万美国人的生活。大多数细胞蛋白的靶向去除主要是由泛素-蛋白酶体系统(UPS)完成的，该系统通过两个步骤降解蛋白质：(1)通过泛素化过程将泛素链(Ub)连接到目标蛋白质分子上；(2)通过蛋白酶体降解泛素化的蛋白质。心脏UPS功能障碍与常见原因的CHF有关，一个经常被指出的缺陷是这两个步骤之间的脱钩，这一点从病变心肌中泛素化蛋白水平升高与蛋白酶体多肽酶活性正常或升高的矛盾共存中得到了提示。然而，对解偶联的分子基础和病理生理学意义知之甚少。UbL-UBA家族的Ub受体(Ubiquilin1，RAD23，Ddi1)被认为是为蛋白酶体招募泛素化的蛋白质，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不清楚。我们的初步研究表明，在人类缺血性心脏病或扩张型心肌病所致的终末期CHF以及结蛋白相关心肌病(DRC)小鼠模型中，心脏Ubqln1蛋白显著增加。DRC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，Ubqln1促进了泛素化错误折叠蛋白的蛋白酶体降解，而不改变蛋白酶体的活性。因此，我们假设，Ubqln1上调通过促进泛素化的错误折叠蛋白重新聚集到蛋白酶体进行降解来保护心肌细胞免受蛋白毒性。一组独特的转基因小鼠以及人类诱导多能干细胞(HiPSC)来源的心肌细胞将被用来询问心肌细胞中的Ubqln1和蛋白酶体功能，以研究Ubqln1在小鼠DRC进展、心肌缺血/再灌注(I/R)损伤和I/R后心脏重构中的作用，并测试Ubqln1作为穿梭Ub受体的功能，从而将泛素化的错误折叠蛋白募集到蛋白酶体进行降解，从而保护心肌细胞免受蛋白毒性的影响。这项工作的完成有望提高我们对心脏蛋白质量控制的理解，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病，蛋白毒性是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.