FoxO3a转录因子在β淀粉样蛋白诱导的突触损伤中的作用及机制研究

Synaptic injury indueced by β amyloid (Aβ) is one of early characteristics of Alzheirmer's disease(AD) and highly related with recognitive impairment. However, the involved molecules are only beginning to be unveiled.FoxO3a transcription factor is a multifunctional protein involved in many cellular functions including neuronal differentiation,apoptosis and metabolism, but its role in Aβ-induced synaptic injury is still far from fully understood. Our previous studies have indicated that FoxO3a negatively regulated neurite outgrowth and extension induced by nerve growth factor, further studies showed that Aβ enhanced the protein level of FoxO3a, decreased the phosphorylation and increased the nuclear location of FoxO3a. Most importantly,Aβ inhibited the expression of synapse-related proteins, while knocking down the level of FoxO3a attenuated the effect of Aβ partially.These results have indicated that FoxO3a may play a role in the process of synaptic injury induced by Aβ.On the basis of the above work, we will investigate the mechanisms responsible for the alteration of the phosphorylation of FoxO3a after treatment with Aβ,the role of FoxO3a in the synaptic injury induced by Aβ and the related signaling pathway will be studied as well, moreover,we will also look for the downstream target of FoxO3a involved in this action by gene chip technique.Our research aims to provide evidences for the involvment of FoxO3a in the synaptic injury induced by Aβ and the process of learning and memeory,it may also offer possible intervention targets for the treatment of AD.

β淀粉样蛋白(Aβ)诱导的神经突触损伤是阿尔茨海默病(AD)早期特征之一，与认知功能下降直接相关，但哪些分子参与这一过程还知之甚少。FoxO3a转录因子广泛参与神经细胞的分化、凋亡、代谢等调控，但是否介导Aβ诱导的神经突触损伤还不清楚。我们前期发现过表达FoxO3a抑制神经细胞突起的生长延伸，进一步研究发现Aβ可促进FoxO3a表达、降低FoxO3a磷酸化并增加FoxO3a入核；重要的是Aβ可降低突触相关蛋白的水平，而敲除FoxO3a则可部分逆转Aβ的作用，这些结果提示FoxO3a可能参与Aβ诱导的突触损伤。本项目将在以上工作基础上，研究Aβ影响FoxO3a磷酸化机制、FoxO3a在Aβ诱导突触损伤中的作用及其作用的信号通路，并利用基因芯片技术寻找FoxO3a对突触损伤作用的下游基因。本项目的研究将为FoxO3a参与Aβ诱导的突触损伤及学习记忆提供依据并为AD的治疗提供可能的干预靶点。

神经突触的损伤被认为是阿尔茨海默病（AD）导致认知功能下降的直接原因。研究AD发病过程中，有哪些分子参与神经突触损伤将有利于揭示AD发生的机制并针对这些分子对突触的损伤进程进行干预。FoxO3a转录因子参与神经突起的生长延伸过程，但FoxO3a在AD进程中，与突触损伤的关系还不清楚。在本项目中，我们分别采用Aβ处理PC12细胞及原代培养神经元，考察FoxO3a的表达、磷酸化水平、细胞内定位及突触蛋白表达的变化；并建立大鼠海马Aβ注射及APP/PS1动物模型，整体水平上考察皮层及海马组织中FoxO3a及突触相关蛋白的水平。进一步分别在离体和在体上敲低FoxO3a的水平，考察突触相关蛋白的变化，以证实FoxO3a参与Aβ对PSD95的抑制作用；在此基础上进一步考察相关信号通路的变化。我们发现在Aβ处理的PC12细胞及神经元中、Aβ海马注射及APP/PS1动物脑组织中均可见FoxO3a的表达显著增加、磷酸化水平下降且FoxO3a多定位于细胞核内，而突触相关蛋白如PSD95的表达则显著下降。进一步发现Aβ处理细胞后Akt的磷酸化下降，在APP/PS1转基因鼠内，Akt、GSK3β及p38MAPK的磷酸化水平显著下降。而在PC12细胞内敲低FoxO3a的表达，则可以削弱Aβ抑制PSD95的作用以及Aβ对Akt磷酸化的抑制作用，在APP/PS1转基因鼠中通过注射含FoxO3a shRNA的AAV载体敲低FoxO3a表达同样可以获得这一结果。因此，我们的结果表明在AD细胞及动物模型中，FoxO3a对突触相关蛋白PSD95的表达起负性调控作用。综上，项目的研究结果为以FoxO3a为靶点开发新型改善认知障碍的药物提供了实验依据。