免疫蛋白酶体催化亚基β5i在动脉粥样硬化斑块形成中的作用机制

The immunoproteasome is the main complex to degrade cellular proteins, of which β5i is a key subunit with chymotrypsin-like activity. Many studies have confirmed that β5i plays a vital role in immune-inflammatory diseases, yet little is known about whether β5i is involved in atherosclerosis (AS), which is a chronic inflammatory disease featuring lipids swallowing by the macrophages and foam cell formation in the vessels. We previously found that β5i was induced, mainly in macrophages, in AS plaques. We also found PR-957, a specific inhibitor of β5i, attenuated AS with a dose-dependent effect. These data suggested that β5i could possibly modulate AS progression. In this study gene-deleted, inhibitor-treated and bone-marrow-transplanted animal and macrophage models will be used to further investigate the roles of β5i in AS, especially in macrophage lipid-swallowing and foam cell formation, and the mechanisms of β5i in modulation of macrophage phenotype turnover and its inflammatory responses. We hope to unveil the pathophysiological mechanisms of β5i in AS progression and provide new pharmaceutical target for AS control.

动脉粥样硬化(AS)是以动脉壁巨噬细胞脂质吞噬和泡沫细胞形成为特征的慢性炎症性疾病。免疫蛋白酶体催化亚基β5i具有糜蛋白酶样活性，在免疫炎症反应性疾病中发挥重要的调控作用。但是β5i在AS斑块形成中的作用尚不清楚。我们前期结果发现在AS斑块中β5i表达水平明显升高，主要位于AS斑块的巨噬细胞中；应用β5i抑制剂（PR-957）处理后可明显抑制高脂饮食诱导的AS斑块形成，并呈剂量依赖关系，这些结果提示β5i可能在AS斑块形成中发挥重要作用。本课题将在β5i基因敲除、抑制剂处理及骨髓移植的小鼠和培养的巨噬细胞中，明确β5i在AS形成中的作用；探讨β5i调节巨噬细胞脂质吞噬和泡沫细胞形成的机理；阐明β5i调控巨噬细胞表型（M1/M2）转化及其炎症反应的分子机制。最后阐明β5i调控AS进程的病理生理机制，为临床AS的防治提供新的药物靶点。

泛素-蛋白酶体系统（UPS）是真核细胞蛋白降解的主要方式，在心血管疾病发生发展中发挥关键作用。20S蛋白酶体复合物是UPS的蛋白降解核心，含β1、β2 和β5三个催化亚基。在炎症因子刺激下，这三个亚基可被诱导型亚基β1i、β2i 和β5i替代，组成免疫蛋白酶体。先前有报道指出，与无脑缺血症状人群相比，脑卒中患者颈动脉斑块内β5i表达明显升高，提示β5i可能与斑块不稳定性相关。然而，尚不明确β5i是否参与动脉粥样硬化斑块发生发展及其病理生理学机制。本研究首先在载脂蛋白E基因敲除（apoE KO）小鼠体内明确了β5i在动脉粥样硬化斑块内高表达，主要表达于斑块内巨噬细胞。在apoE KO小鼠体内敲除β5i或者给予β5i特异性抑制剂均显著抑制高脂饮食诱导的动脉粥样硬化。利用骨髓移植技术，我们进一步验证了巨噬细胞表达的β5i在动脉粥样硬化进程中的作用。最后，我们在培养的巨噬细胞内发现β5i可能是通过调节NF-κB抑制因子IκBα的降解和转入因子NF-κB的激活，抑制巨噬细胞c-mer原癌基因酪氨酸激酶（MERTK）表达和其介导的胞葬作用从而调控凋亡巨噬细胞聚集和坏死内核行成。本研究明确了β5i参与动脉粥样硬化进程及其病理生理学机制，为临床开发以β5i为调控动脉粥样硬化的新靶点提供了理论依据。