BDNF前肽片段调控Alzheimer疾病模型海马gamma振荡的突触环路机制研究

Brain-derived neurotrophic factor (BDNF) play an important role in the development of neuron circuit and synaptic plasticity. The expression of BDNF pro-peptide in hippocampal CA3 region is similar with BDNF mature form, but which is dramatically increased compared to BDNF mature form in Alzheimer’s disease (AD). However, it is unclear about the biological functions of BDNF pro-peptide. BDNF pro-peptide facilitates LTD in hippocampus and regulates the normal function of neurons. According to the preliminary study, we presume that BDNF pro-peptide regulates synaptic transmission and hippocampal function as a negative regulator, but the underlying synaptic mechanism is unclear. Therefore, we aim to investigate: ⑴ the effect of BDNF pro-peptide on gamma oscillation, the changes of excitatory/inhibitory balance of neural networks and synaptic transmission mediated by BDNF pro-peptide in hippocampal CA3 area, the effect of BDNF pro-peptide on gamma oscillation-associated learning and memory and emotion; ⑵ the molecular and electrophysiological mechanism of BDNF pro-peptide mediating the changes of AD-related learning and memory and emotion by knockdown of BDNF pro-peptide binding receptor. This study will identify potential molecular targets that could prevent or delay AD-related neurological dysfunction.

脑源性神经营养因子（BDNF）参与调节神经环路发育和突触可塑性，而BDNF前肽片段在海马CA3区含量与BDNF的成熟形式相同，甚至在老年痴呆症（AD）患者脑中表达高于BDNF成熟形式的数倍，研究证实 BDNF前肽片段能够易化海马LTD，影响突触正常结构形成。结合我们的前期研究基础，我们推测BDNF前肽片段在海马脑区可能作为负性调节因子来调控突触传递进而影响海马功能，但其中涉及的突触机制尚不明确。因此本项目拟通过在体、离体电生理记录、分子生物学和免疫组织化学等研究手段，探讨：⑴ BDNF前肽片段对海马CA3区gamma振荡的调控作用、对神经网络兴奋/抑制平衡及突触传递的影响、对gamma振荡相关的学习记忆及情绪的调控作用；⑵通过对BDNF前肽片段结合受体的敲减，研究BDNF前肽片段介导AD相关学习记忆及情绪改变的分子和电生理机制，发现可阻止或延缓AD相关神经功能减退的分子靶点。

在本项目研究中，我们通过制备纯化的BDNF pro-peptide，体外和体内模拟了海马神经元在网络活动激活时释放 BDNF pro-peptide后，该前肽片段与海马兴奋性锥体神经元和抑制性中间神经元 p75NTR 相结合，通过激活CDK5信号通路，调控神经网络中兴奋与抑制平衡，作为负性调节因子来调节海马神经网络中神经元的突触传递和振荡活动，并损伤与之相关的学习与记忆行为；AD 相关的海马 gamma 振荡活动衰退及与振荡相关的行为学改变与 BDNF pro-peptide 的作用相关，而CDK5信号通路介导了该作用。通过应用CDK5抑制剂和二甲双胍抑制CDK5信号通路的激活可能减弱 BDNF pro-peptide 的作用进而逆转 AD 相关的海马 gamma振荡及LTP活动的衰退和AD鼠学习记忆功能障碍。这些发现使我们对于BDNF前体片段通过调控神经突触可塑性及gamma网络振荡活动从而影响学习记忆功能的认识得到了进一步的增强，同时也使促进了我们对于调控脑的学习记忆功能的分子机制的认识，对AD的临床提供了新的靶点和治疗策略。