Mst1和Mst2激酶调节吞噬细胞抗氧化应激的作用机制研究

Phagocytes are specialized immune cells that engulf harmful microorganisms and destroy them in phagosomes. Recent studies have found that the kinases Mst1 and Mst2 functioned to control ROS production in phagocytes to kill pathogens. However, how phagocytes maintaining redox homeostasis to against oxidative damage and apoptosis has remained unclear. Recently, we found that kinases Mst1/2 double knockout phagocytes (cDKO) showed higher level of ROS and significantly increased apoptosis than wildtype. Treated with ROS scavenger, apoptosis was remarkable decreased in cDKO phagocytes. Meanwhile, Mst1/2 can regulate the activation of Nrf2 and probably the initiation of the antioxidant gene transcription to protect the cells from oxidative damage and apoptosis. Further study shows that the nucleo-cytoplasmic ratio and protein level of Nrf2 were also decreased in cDKO phagocytes. Meanwhile, Mst1/2 can regulate the activation of Nrf2 and probably the initiation of the antioxidant gene transcription to protect the cells from oxidative damage and apoptosis. Further study shows that the nucleo-cytoplasmic ratio and protein level of Nrf2 were also decreased in cDKO phagocytes. This grant will clarify the mechanism of the kinases Mst1/2 regulates redox homeostasis and activation of Nrf2 in phagocytes at the molecular, cellular and whole animal level, which will further elucidate the pathogenesis of pathogenic bacteria induced septicopyemia and phagocytes immunodeficiency disease.

致病菌引发的感染性疾病是临床治疗的一项难题。申请人在Nature Immunology第一作者的研究工作揭示了激酶Mst1/2在调控吞噬细胞释放活性氧进而杀伤和清除细菌的过程中发挥着重要作用。然而，吞噬细胞维持氧化还原稳态以抵御氧化损伤和细胞凋亡的调控机制并不完全清楚。申请人前期未发表的数据显示，激酶Mst1/2缺失的吞噬细胞内活性氧ROS水平升高、凋亡显著增加；进一步发现了Mst1/2缺失的吞噬细胞中调控抗氧化转录因子Nrf2的入核比例和蛋白水平都有显著下降，从而导致细胞处于氧化应激状态。在本基金中，我们将分子、细胞水平上，阐明Mst1/2对于转录因子Nrf2的活性调节机制；解析Mst1/2-Nrf2通路在吞噬细胞的抗氧化应激和细胞凋亡及宿主抗感染的功能作用，为病原体感染引发的脓毒血症和吞噬细胞免疫缺陷疾病的研究提供理论基础。

活性氧是天然免疫系统重要组分，在天然免疫系统清除胞内的细菌的过程中有着重要作用。巨噬细胞内活性氧有着两方面的功能，一方面，活性氧可以辅助巨噬细胞清除吞噬到胞内的细菌；另一方面，由于活性氧的自身的强氧化能力，过量的活性氧会对细胞组分（例如DNA、脂质和蛋白质）产生氧化损伤，从而导致细胞损伤、细胞老化和细胞死亡。因此，巨噬细胞中活性氧的稳态维持至关重要，但是目前对巨噬细胞内抗氧化应激调控的具体分子机制还不清楚。.Hippo信号通路是一条在哺乳动物中保守的信号通路，Hippo信号通路的关键激酶Mst1/2在调节巨噬细胞中活性氧的释放和细菌杀伤中发挥重要的作用。本项目研究发现激酶Mst1/2可以感应细胞内的活性氧信号，并且通过调节转录因子Nrf2的蛋白稳定性，从而清除过度的活性氧，保护细胞自身免受氧化损伤。.活性氧作为一个生理信号，可以募集Mst1/2和Keap1(kelch like ECH associated protein 1)到活性氧的产生部位，例如线粒体。在线粒体膜上，活性氧激活Mst1/2，促进Mst1/2磷酸化Keap1，破坏Keap1的二聚化，从而保护Nrf2免受泛素化降解，进而保护细胞免受氧化损伤。因此，Mst1/2缺失的巨噬细胞会出现更多的氧化损伤、细胞老化和细胞死亡。综上所述，我们证明了Mst1/2-Keap1-Nrf2的信号调控机制，在巨噬细胞感知活性氧启动抗氧化应激反应过程发挥重要作用。