MAD2B介导的神经元细胞周期再进入在糖尿病认知功能障碍中的作用及其机制

Cognitive impairment is the main clinical manifestation of diabetic encephalopathy and a serious threat to the quality of life for diabetic patients, but its pathogenic mechanism has not been completely understood. It has been reported that cell cycle re-entry of post-mitotic neurons is involved in the development of numerous central nervous system diseases. However, it is still unknown whether cell cycle re-entry is involved in the pathogenesis of cognitive impairment related to diabetes. Our preliminary data showed that the expression of mitotic arrest deficient-like 2 (MAD2B) was elevated significantly upon the exposure to high glucose in vitro, which was accompanied by increased number of neurons re-entered cell cycle. Inhibition of MAD2B prevented cell cycle re-entry of neurons, suggesting that MAD2B plays a vital role in inducing cell cycle re-entry of neurons. According to bioinformatic analysis, we found that MAD2B might be phosphorylated by 5'-AMP dependent protein kinase (AMPK), which is necessary for its degradation. On the basis of these previous experiments, we plan to investigate the significance of MAD2B-mediated cell cycle re-entry of neurons in the pathogenesis of cognitive impairment in diabetes and the role of AMPK in regulating MAD2B phosphorylation, by using cultured neurons and conditional knockout mice. Through these studies, we expect to deepen the current understanding of the mechanism of diabetic encephalopathy and provide experimental evidence for it intervention.

认知功能障碍是糖尿病脑病的主要临床表现，严重影响患者生活质量。研究表明，神经元细胞周期再进入是多种神经系统疾病进程中的早期细胞事件，但其在糖尿病认知功能障碍中的作用及机制尚未阐明。我们的前期研究发现：高糖环境可诱导神经元有丝分裂阻滞缺陷蛋白（MAD2B）表达升高，并伴随神经元细胞周期再进入和神经元数目减少；而敲低MAD2B可抑制该过程，提示MAD2B是介导高糖所致神经元细胞周期再进入的关键分子。生物信息学分析和预实验结果进一步发现，MAD2B的磷酸化和降解可能受AMPK调控。在上述前期研究结果基础上，本项目拟采用体外细胞模型和神经元特异性基因敲除小鼠等为研究对象，深入探讨MAD2B介导的神经元细胞周期再进入在糖尿病认知功能障碍进程中的病理生理意义以及AMPK对MAD2B磷酸化和降解的调控机理，以期深化目前对糖尿病认知功能障碍发病机理的认识并为其早期防治提供新的理论依据。

认知功能障碍是糖尿病脑病的主要临床表现，但其机制尚未阐明。本项目主要研究结果如下：（1）高糖环境可诱导神经元有丝分裂阻滞缺陷蛋白（MAD2B）表达升高，并伴随神经元细胞周期再进入和神经元数目减少；而敲低MAD2B可抑制该过程，提示MAD2B是介导高糖所致神经元细胞周期再进入的关键分子；（2）在神经元内高糖主要抑制MAD2B的降解，进而导致其表达升高。同时高糖可以抑制AMPK的活性。而激活AMPK显著降低高糖所致的神经元凋亡和MAD2B表达，这提示MAD2B的表达水平与AMPK的活性密切相关；进一步研究发现MAD2B主要通过泛素蛋白酶体途径降解。而激活AMPK促进MAD2B的泛素化和降解。这些结果均提示，激活AMPK信号通路可能是治疗高糖所致神经元损伤和认知功能障碍的新策略；（4）OGD/R诱导MAD2B的表达，导致cyclinB1在神经元内堆积，促进神经元细胞周期再进入。而二甲双胍可以逆转上述效应。因此，二甲双胍可能通过调控MAD2B的表达，进而改善脑缺血再灌注损伤；（5）CORT刺激导致MAD2B下降。过表达MAD2B，在基础水平不影响小鼠的抑郁行为。但在给予不可预知刺激时，可以增加小鼠的抗抑郁能力。其机制可能是通过影响GRM4的表达来实现其抗抑郁作用。综上所述，这些研究结果表明MAD2B在糖尿病脑病认知功能障碍中发挥重要作用。并且拓展研究提示，MAD2B亦参与脑缺血再灌注损伤和抑郁症的发生发展。