蛋白磷酸酶2A催化亚基甲基化调控在衰老发生机制中的作用

Protein phosphatase 2A (PP2A) is one of the most important protein serine/threonine phosphatase in mammalian cells. Methylation of the C-terminal leucine residue of the PP2A catalytic subunit (PP2A-C) plays a crucial role in regulating PP2A function. Methylation is catalyzed by a PP2A specific S-adenosyl methionine(SAM)-dependent enzyme, the leucine carboxyl methylatransferase (LCMT) and the carboxyl methyl group is hydrolyzed by a specific PP2A methylesterase (PME). Mammalian target of rapamycin compound 1(mTORC1) is a well known aging related signaling transduction pathway, which can be regulated by PP2A and oxdative stress. Preliminary results showed that levels of PP2A-C methylation are reversibly regulated by cellular redox status with associated changes in the composition of PP2A holoenzyme variants. In H2O2 induced-premature senescence cell, levels of PP2A-C decrease followed by PP2A-C demethylation. Therefore we proposed that oxidative stress regulate PP2A/PR61ε function by methylation/demethylation, which activate mTORC1 pathway and regulate aging procedure. In this study, we will investigate the regulation role of PP2A-C methylation in the mechanism of aging in vitro and vivo. Human diploid fibroblasts cell line will be used to induce replicative and premature senescence. The role of PP2A-C methylation will also be examined in animals which retardation of aging by dietary restriction and acceleration of aging by D-galactose. The question of can regulation of PP2A-C methylation by LCMT overexpression, PME inhibitor or redox reduction delay the procedure of aging or prevent aging related damage will also be addressed in this research. This study will help to answer some unknown questions in aging mechanism and also provide new clues for prevention and treatment of oxidative damage and aging related disease.

蛋白磷酸酶2A催化亚基（PP2A-C）游离羧基末端L309位点甲基化修饰对PP2A功能调控具有重要作用，该位点甲基化受亮氨酸甲基转移酶(LCMT)和羧基甲基酯酶（PME）催化调节。雷帕霉素的哺乳动物靶点复合物1信号传导通路(mTORC1）与衰老密切相关,其活性可受氧化应激和PP2A调控。前期研究发现PP2A-C甲基化受细胞内氧化还原状态调控,过氧化氢诱导细胞早衰过程细胞内PP2A-C水平下降，而甲基丢失处于变化早期。据此推测PP2A-C参与衰老调控。氧化应激诱导PP2A-C去甲基，调控PP2A/PR61ε功能,作用于mTORC1信号传导通路,参与衰老进程调控。本研究拟采用细胞实验与动物实验相结合，以人二倍体成纤维细胞和SD大鼠建立衰老细胞模型和衰老动物模型，探讨PP2A-C甲基化调控在衰老发生机制中的作用。本研究为深入理解衰老的发生过程与机制，以及氧化应激和衰老相关疾病的防治提供新的思路。

蛋白磷酸酶2A（PP2A）是细胞内重要的蛋白磷酸酶，与氧化应激及雷帕霉素的哺乳动物靶点复合物1（mTORC1）等多条衰老相关重要信号传导通路调控有关。蛋白磷酸酶2A催化亚基（PP2A-C）游离羧基末端L309位点甲基化修饰对PP2A活性及功能调控具有重要作用，该位点甲基化受亮氨酸甲基转移酶(LCMT1)和羧基甲基酯酶（PME1）催化调节。本研究从细胞及动物水平探讨PP2A-C甲基化在衰老过程及衰老相关机制调控中的作用。本项目研究结果显示，1.随着衰老的发生，PP2A-C甲基化修饰发生组织特异性改变，在体外复制性衰老及过氧化氢诱导的早衰细胞模型和体内衰老动物组织中均观察到PP2A-C甲基化修饰的改变，提示衰老过程伴随PP2A-C甲基化水平改变。2.氧化损伤及mTORC1信号传导通路调控是衰老发生重要机制，本项目研究结果显示氧化应激可改变细胞内PP2A-C甲基化水平，PP2A-C甲基化可调控氧化应激对mTORC1活性的抑制作用，提示PP2A甲基化在mTORC1通路相关衰老机制中可能发挥重要作用。3.饮食限制延缓实验动物衰老，本研究结果显示饮食限制可逆转衰老动物脏器PP2A-C甲基化改变，调节糖脂代谢水平，提示PP2A-C甲基化可作为衰老相关糖脂代谢紊乱调控的靶点。4.细胞水平血清饥饿可诱导PP2A-C剪切异构体表达，该异构体高表达可通过mTORC1信号传导通路而降低细胞基础自噬，提示PP2A-C参与mTORC1相关自噬调控。本项目研究探讨了PP2A-C甲基化与衰老及衰老发生机制的相互关系，提示PP2A-C甲基化可能作为衰老及衰老相关疾病防治的靶点，为进一步研究衰老及衰老相关疾病提供新的思路和线索。