MEF2 在细胞衰老中的调节作用及机制研究

Myocyte enhancer factor 2 (MEF2) is involved in various tissue formation and cell proliferation, and is closely associated with aging-related diseases. However, it is still unclear whether MEF2 plays important roles in cellular senescence. In our previous study, we discovered that the single nucleotide polymorphisms （SNPs） in the promoter of MEF2A affect the promoter activity, and the frequency distribution of the SNPs is significantly different between the patients with coronary artery disease (CAD) and health controls, suggested that change in the expression of MEF2A may be implicated in the pathogenesis of aging-related diseases, such as coronary artery disease (CAD). Additionally, MEF2A was significantly down-regulated in the senescent vascular cells induced by H2O2, and increased senescent cells in the MEF2A-specific siRNA transfected group were observed. Accordingly, we hypothesize that down-regulation of MEF2 will accelerate cell senescence. To test the hypothesis above, this project will focus on the following aspects: 1) The influence of change in the expression level of MEF2 on the progress of cell senescence; 2) The molecular mechanism of MEF2 involved in cell senescence. 3) The association between promoter activity, epigenetic change of MEF2 and cell senescence. 4) The association between the polymorphisms and methylation state in the promoter of MEF2 and the aging-related diseases, such as atherosclerosis. The completion of this project will generate an original theory for the molecular regulation of cell senescence, provide new targets for early diagnosis and prevention for aging-related disease, and develop a novel methodology.

肌细胞增强因子2(MEF2)参与多种组织形成及细胞增殖，与多种老年相关疾病密切相关，然而其在细胞衰老中的作用并未被揭示。我们前期研究发现：MEF2A的启动子单核苷酸多态（SNPs）导致启动子活性改变，且在冠心病患者和健康人群中的频率分布存在显著差异，提示MEF2A的表达改变可能与冠心病等老年性疾病的发生发展有关；此外，在H2O2诱导的衰老血管内皮细胞中，MEF2A的表达显著下调，siRNA抑制MEF2A的表达可加速细胞衰老。据此，我们提出“MEF2的表达下调将加速细胞衰老”的假说。为证实以上假说，项目拟研究：1）MEF2的表达改变对细胞衰老进程的影响；2）MEF2参与细胞衰老的分子机制；3）MEF2启动子活性及甲基化改变与细胞衰老的关系；4）MEF2启动子多态及甲基化状况与动脉粥样硬化等老年病的关系。为细胞衰老的分子调控机制提供新理论，为老年病的早期诊断及防治提供新靶标、发展新方法。

MEF2在细胞增殖、心脏发育及冠心病等老年性疾病的发生发展中扮演重要角色，然而它在老年性疾病发生发展中的机制尚未明确。本项目通过以下研究阐明了MEF2A的表达调控对人冠状动脉内皮细胞衰老进程的影响，从而揭示了MEF2A在老年性疾病发生发展中的可能机制。具体研究如下:1)检测细胞复制性衰老或诱导性衰老过程中MEF2A的表达变化；2）MEF2A的表达改变对细胞衰老表型的影响；3）鉴定MEF2A调控细胞衰老的信号网络；4）阐明MEF2A启动子区的遗传多态对MEF2A表达的影响。研究发现：1）人冠状动脉内皮细胞(HCAEC)经过连续传代后,MEF2A的表达水平没有显著下降,但抑制MEF2A的表达后促进了细胞衰老，细胞增殖能力下降；2）过表达MEF2A后，细胞增殖能力增强，可抵抗慢病毒转染诱导的细胞死亡；3）抑制MEF2A的表达后，与细胞紧密连接、粘附连接及内皮细胞功能相关的基因表达下调，下调基因涉及到氧化磷酸化、自噬调节及细胞粘附分子等信号通路。在下调的基因网络中涉及到3个重要的中心分子（PIK3CG，PRKCB和FOS）。4）HCAEC经过连续传代后，未发现MEF2A的表达下调，但发现GAPDH的表达下调。抑制GAPDH的表达可明显加速细胞衰老；5）MEF2A启动子区的多态位点可影响其转录活性，但对H2O2和晚期糖基化终产物等诱导因素的反应性没有明显差异。本研究提示MEF2A在血管内皮细胞中的表达稳定对维持细胞增殖及防止细胞诱导凋亡方面发挥重要作用，MEF2A对细胞连接、细胞粘附分子的调控作用可能与细胞凋亡及衰老有关；GAPDH在维持细胞增殖，防止细胞衰老中扮演更重要的角色。本研究发现的慢病毒诱导的内皮细胞死亡提示病毒感染可能加速血管病变，导致早发性冠心病，MEF2A高表达的个体也许能抵抗病毒诱导的内皮细胞死亡，从而保护血管。本研究为冠心病等老年性疾病的发生机制研究提供了新方向，为冠心病等老年性疾病的防治提供了新思路，本研究还提示病毒感染也许是诱发心血管疾病的又一风险因子。