PP2A-C 甲基化在锰诱导学习记忆损伤中的作用研究

The methylation of the C- terminal leucine residue of the PP2A catalytic subunit is important for PP2A catalytic activity, which is regulated by a one-carbon metabolism cycle. Abnormal hyperphosphorylation of tau is strongly associated with learning and memory dysfunction. Activating PP2A to dephosphorylate tau is a potential therapeutic target for neurodegenerative diseases. Excessive manganese exposure induces abnormal tau hyperphosphorylation, which might contribute to learning and memory impairment. Our previous studies show that PP2A-C methylation decreased upon manganese exposure, which implies a crucial role for PP2A-C methylation in manganese neurotoxicity. In view of these results, we presumed that learning and memory impaired by manganese might be due to PP2A catalytic subunit demethylation and loss of its catalytic activity, which leads to tau hyperphosphorylation through one-carbon metabolism disruption. The present study is designed to investigate the regulatory role of PP2A-C methylation through one-carbon metabolism in the mechanism of learning and memory impairment induced by manganese in vivo and vitro. We also discuss the pathways of PP2A-C methylation regulation by manganese and its effects on tau phosphorylation and learning and memory lesion. This study will provide insight into manganese neurotoxicity and new strategies for prevention and treatment of learning and memory damage by manganese or neurodegenerative diseases.

一碳循环调控蛋白磷酸酶2A催化亚基(PP2A-C)甲基化且对PP2A活性具有重要作用。tau过度磷酸化与学习记忆障碍相关，活化PP2A行使去磷酸化维持tau平衡是神经退行性疾病潜在的治疗靶点。锰可诱导学习记忆损伤，与tau磷酸化异常有关。前期研究发现锰暴露诱导PP2A-C甲基化下降，提示PP2A-C甲基化在锰神经毒性中可能发挥重要作用。根据前期结果及文献推测锰通过干扰一碳代谢循环诱导PP2A-C去甲基化，PP2A活性下降，致tau蛋白磷酸化异常，学习记忆损伤。本研究拟通过细胞实验与动物实验相结合，研究一碳代谢循环调控PP2A-C甲基化在锰诱导的学习记忆损伤中的作用，探讨锰对PP2A-C甲基化调控的方式，并进一步研究调控PP2A-C甲基化水平对锰诱导tau蛋白磷酸化及学习记忆损伤的影响。本研究为深入理解锰神经毒性，有效防治锰诱导的学习记忆损伤及相关神经退行性疾病提供新思路。

职业或环境过量锰暴露是以tau过度磷酸化为特征的阿尔兹海默症的危险因素之一。蛋白磷酸酶2A（PP2A）是细胞内重要的蛋白磷酸酶，执行去磷酸作用，与神经退行性病变相关。蛋白磷酸酶2A 催化亚基（PP2Ac）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。甲基供体S-腺苷甲硫氨酸（SAM）在亮氨酸甲基转移酶(LCMT1)和羧基甲基酯酶（PME1）可逆性的催化作用下修饰该位点甲基化并调节PP2A的活性。本研究从细胞及动物水平探讨PP2Ac甲基化在锰诱导学习记忆损伤及其相关机制调控中的作用。项目研究结果显示：1.体外试验提示染锰诱导神经细胞tau过磷酸化/损伤与增加氧化应激、干扰一碳循环代谢、改变PP2A-C甲基化修饰有关。2.甲硫氨酸补充改善锰诱导的神经细胞损伤，机制与其作为抗氧化剂及甲基供体改善PP2Ac甲基化有关。3.进一步的LCMT1过表达细胞转染结果及PME1抑制剂ABL127干预试验表明， PP2Ac甲基化调控是锰诱导神经细胞损伤的重要机制。本项目研究结果显示氧化应激及一碳代谢循环可改变细胞内PP2Ac 甲基化水平。PP2Ac甲基化降低，PP2Ac去甲基化升高在锰诱导的细胞损伤中可能发挥重要作用。4.实验动物研究结果显示染锰诱导的学习记忆损伤与脑组织PP2Ac甲基化改变及tau过度磷酸化有关，提示PP2Ac甲基化是锰诱导tau过磷酸化、学习记忆障碍的关键事件。本项目研究探讨了tau过度磷酸化与锰诱导的学习记忆障碍及发生机制的相互关系，提示PP2Ac可能作为锰诱导的神经损伤防治的靶点，为进一步研究神经退行性病变提供新的思路和线索