免疫蛋白酶体催化亚型PSMB8通过调节SERCA2a蛋白表达改善心肌收缩力的分子机制

The immunoproteasome catalytic subunit PSMB8 (LMP7) has chymotrypsin-like activity, which palys a critical role in degrading intracellular proteins. Sarcoplasmic reticulum calcium ATPase (SERCA2a) is a critical pump regulating calcium transfer and myocardial contractility, and is an effective therapeutic target of heart failure. Our prelimirary results showed that in transverse aortic constriction (TAC)-induced heart, PSMB8 protein level was significantly increased but SERCA2a protein expression was decreased. Treatment of mice with PSMB8 specific inhibitor PR-957 significantly reversed SERCA2a protein level, and improved the decreased myocardial contractility and heart failure induced by TAC. However, the pathophysiological mechanism for PSMB8 to decrease SERCA2a level and myocardial contractility in heat failure remains unknown. In the present study, we will apply TAC to induced heart failure in PSMB8 knockout and inhibitor-treated mice or phenylephrine (PE) to treated primary cardiomyocytes. We will investigate the effects of PSMB8 on myocardial contractility and hypertrophy, then eluciate the mechanism for PSMB8 to decrease SERCA2a protein and intracellular calcium levels. Our data will provide new evidence for potential therapeutic target of heart failure.

免疫蛋白酶体催化亚基PSMB8具有糜蛋白酶样活性，在细胞内蛋白质降解中发挥关键作用。肌浆网Ca2+-ATP酶2a（SERCA2a）是调节细胞钙稳态和心肌收缩力的重要蛋白以及心衰治疗的靶点。我们前期研究发现在主动脉弓缩窄术(TAC)诱导的心衰模型中，PSMB8蛋白水平增高，而SERCA2a蛋白水平降低。应用PSMB8抑制剂PR-957处理后可明显逆转SERCA2a的蛋白水平，显著改善TAC诱导的心肌收缩力降低和心衰。但是PSMB8是否通过降解SERCA2a导致心衰发生的分子机制不清楚。本课题将在PSMB8基因敲除、抑制剂处理的小鼠及培养的心肌细胞上，采用TAC术诱导心衰及苯肾上腺素（PE）处理心肌细胞，研究PSMB8对心肌收缩功能、心肌细胞肥大的影响；阐明PSMB8调节心肌SERCA2a蛋白水平及细胞内钙离子浓度的分子机制,为寻找防治心衰的新药靶点提供重要的依据。

没有有效的治疗，病理性心肌肥厚最终会导致心力衰竭。免疫蛋白酶体是与炎性疾病密切相关的，我们发现免疫蛋白酶体β5i表达和活性在血管紧张素II(Ang II)处理的心肌细胞、肥厚的小鼠及人的心脏中显著增高。敲除β5i抑制AngII和压力负荷诱导的心肌肥厚，反之β5i过表达加重这一效应。机制上发现β5i与自噬相关蛋白ATG5结合，促进泛素化ATG5降解，抑制自噬的激活,从而导致心脏肥大。此外,敲低ATG5抑制自噬扭转了β5i 敲除介导的心肌肥厚抑制作用。综上所述,本研究明确了β5i靶向ATG5和自噬从而调节心脏肥大的新生物学作用。调节β5i可能是治疗肥厚性心肌病的新治疗方法。