Aβ诱导表观遗传修饰抑制Ngn2表达在AD认知障碍中的作用及机制研究

In recent years, the accumulation of Aβ in the brain leading to neurons and synaptic plasticity lesion has been thought the main causes of Alzheimer's disease (AD) memory deficiency. However, the mechanism is unclear. Our previous studies have found that Ngn2 played an important role in neuron survival, synaptic plasticity and memory function after reperfusion injury. The previous studies found there are several CPGs in Ngn2 promotor region; the expression of Ngn2 mRNA was down-regulated in AD model; it also enhanced cytosine methylation and suppressed histone H3 acetylation in the Ngn2 promoter region. Latest researches have demonstrated Aβ can induce the expression of HDAC2 and MeCP2, which will repress the expression of target molecule and cause memory deficiency. There results strongly suggest Aβ could up-regulate the expression of HDAC2 and MeCP2 which will induce epigenetic suppression of Ngn2. Then it will cause neurons and synaptic plasticity lesion leading to memory deficiency. This project tries to observe the expression changes of Ngn2 and its function in learning and memory function in AD model. And then,we explore the mechanism of Ngn2 influenced by Aβ thouge the intervention effect of HDAC2、MeCP2. This project will provide new theoretical and experimental basis in Aβ induced-memory deficiency.

Aβ导致的神经元缺失和突触可塑性下降是AD认知障碍的主要原因但机制尚未阐明。新近研究发现Aβ通过增强组蛋白去乙酰化酶2(HDAC2)和甲基-CpG结合蛋白2(MeCP2)活性损害认知功能。我们前期发现，Ngn2具有促进脑缺血后神经元存活，突触形成和认知能力恢复的新功能；预实验显示在APP/PS1转基因小鼠中，海马区Ngn2启动子区甲基化水平增加，组蛋白H3乙酰化水平降低，Ngn2 mRNA及蛋白表达降低；上调Ngn2可促进认知功能恢复。因此推测：Aβ通过增强HDAC2和MeCP2活性抑制Ngn2表达，引起海马神经元缺失和突触可塑性下降损害认知功能。本研究拟从Aβ对Ngn2表达影响入手，研究Ngn2下调对海马神经元存活、突触可塑性及认知功能的作用，通过对HDAC2、MeCP2干预探索Aβ抑制Ngn2表达的分子机制。该课题将为认识Ngn2在AD认知障碍过程中的作用及机制提供新的理论和实验依据。

Aβ导致的神经元缺失和突触可塑性下降是AD认知障碍的主要原因，但相关机制尚未阐明。新近研究发现Aβ通过增强组蛋白去乙酰化酶2(HDAC2)和甲基-CpG结合蛋白2(MeCP2)活性损害认知功能。本研究Ngn2在AD模型中海马组织的表达变化及其对海马神经元存活及突触可塑性的作用，并通过对HDAC2、MeCP2干预探索Aβ抑制Ngn2表达的分子机制。结果显示，APP/PS1转基因小鼠模型（7月龄）的海马中Ngn2 mRNA及Ngn2蛋白表达下调；Aβ1-42处理后HT-22细胞中Ngn2蛋白的表达量下调；Ngn2过表达及TAT-Ngn2能够明显增强海马神经元活力，减少LDH释放，促进海马神经元存活。TAT-Ngn2腹腔注射后，TAT结构能够使TAT-Ngn2融合蛋白有效通过血脑屏障，并且分布于海马组织。TAT-Ngn2蛋白能够改善APP+/PS1+转基因小鼠的认知功能，增加APP+/PS1+转基因小鼠海马区SYN表达。Ngn2过表达及TAT-Ngn2对神经元凋亡的影响。APP+/PS1+转基因小鼠模型（7月龄）的海马中Ngn2启动子区甲基化水平及MECP2增加;Aβ1-42增加神经元细胞中Mecp2蛋白表达，减少Ngn2表达。APP+/PS1+转基因小鼠模型（7月龄）的海马中Ngn2启动子区组蛋白H3乙酰化水平减少； Aβ1-42增加神经元细胞中HDAC2，TSA增加Ngn2蛋白表达。综上，Aβ通过加强Mecp2及HDAC2活性，抑制Ngn2表达的分子机制。该课题的顺利实施及取得的研究成果初步揭示了Ngn2在AD认知障碍中的新作用，揭示了表观遗传调控对Ngn2表达影响的新机制，为AD的预防和治疗提供新的靶点和手段。同时，进一步明确TAT-Ngn2具有改善AD动物模型认知功能的作用，为将TAT-Ngn2开发成为一种新型有效的药物提供实验基础和科学依据。