Caveolin介导AMPA受体过度内化在脆性X综合症异常突触可塑性中的机制研究

Fragile X syndrome (FXS) is one of the most common inherited mental retardation diseases. Exploring the pathogenesis and therapeutic approach of FXS is an important social and clinical problem. Classsic mGluR theory suggested that mGluR1/5-dependent protein synthesis might be exaggerated in the absence of FMRP, which promoted AMPAR to translocate from the membrane into cytoplasm, leading exaggerated LTD in hippocampus.Our research group first found FMRP binding Cav-1 mRNA to supress its translation, and CAV1 was overexpressed in Fmr1 knockout (KO) mice, as an animal model of fragile X syndrome. We further confirmed that CAV1 coupled with mGluR1/5. However, the signaling pathway of CAV1 regulates LTD function after mGluR1/5 activation has not yet been elucidated. The present projectbased on the mGluR theory, in order to explore the functions of CAV1 in exaggerated mGluR-LTD in Fmr1 KO mice and the mechanisms of its invovled AMPAR internalizationby using electrophysiological, molecular biological, pharmacological, and behavioral methods. It will be helpful to expand the internalization mechanisms of postsynaptic glutamate receptors in the process of learning and memory, and provide new drug targets for the prevention and treatment of fragile X syndrome.

脆性X综合症是临床最常见的遗传性智力低下症，探索其发病机制及治疗途径是社会和临床都急需解决的一个重要课题。经典mGluR理论认为，FMRP的缺失引起mGluR1/5依赖性翻译过表达，导致突触后谷氨酸AMPA受体从细胞膜向胞浆转移加强，表现为海马中mGluR依赖的LTD增加。我们课题组首先发现FMRP结合Cav-1 mRNA抑制其翻译，在脆性X综合症动物模型Fmr1基因敲除小鼠中CAV1表达水平升高，并证实了CAV1偶联mGluR1/5，但目前关于激活mGluR1/5后CAV1调控LTD形成的作用和信号通路仍未阐明。本项目拟基于mGluR理论，综合利用电生理、分子生物学、药理学和行为学等手段系统研究CAV1在Fmr1 KO小鼠中异常mGluR-LTD的作用及其介导AMPA受体过度内化的机制。本项目拓展了学习记忆过程中突触后谷氨酸受体的内化机制，同时为脆性X综合症的防治提供新的药物靶标。

脆性X综合征（FXS）是引起智力障碍的重要原因和发生孤独症的主要单基因疾病。经典代谢型谷氨酸（mGluR）理论认为，FMRP缺失导致mGluR5过度激活与异常突触可塑性有关。但是，其中AMPA受体异常转运的分子机制尚不清楚。在这里，我们发现只有mGluR依赖的长时程抑制仅在青春期的Fmr1 KO小鼠海马中增大，而NMDAR依赖的长时程抑制在所有年龄的Fmr1 KO海马中均正常。这种不同发育阶段的变化与形成小窝所必需的caveolin-1（Cav1）的表达水平不同有关。与Cav1在AMPA受体转运中的作用一致，我们发现干扰Cav1表达可降低Fmr1 KO小鼠中增强的mGluR-LTD。此外，干扰Cav1减少了PKC介导的GluA2丝氨酸880位点的过多磷酸化，这并不需要NMDAR参与。我们进一步发现激动剂DHPG可诱导GluA2在细胞膜脂筏中再分配，并依赖于胆固醇的插入。由于发现胆固醇在海马神经元过度积累，我们使用250和500mg/kg甲基-β-环糊精（Mβ-CD）皮下注射能显著改善Fmr1 KO小鼠的活动过度、海马依赖性恐惧记忆和空间记忆缺陷。我们的研究结果表明Cav1的功能障碍导致了海马中mGluR-LTD的增强，并且破坏小窝形成中的胆固醇可以恢复FXS小鼠的正常行为。