D-丝氨酸-NMDAR-CaMKⅡ信号通路在砷致学习记忆损伤中作用的研究

Environmental arsenic exposure can seriously damage the children's intelligent development, but the toxicological mechanisms involved remains poorly understood. In our previous study of cytotoxicity in vitro suggested that arsenite might indirectly interfere the protein expression of N-methyl-D-aspartate receptor (NMDAR) and calmodulin-dependent protein kinaseⅡ(CaMKⅡ) through affecting the secretion of D-serine from astrocytes (AST) , NMDAR-CaMKII signaling pathway plays an import role in the formation of learning and memory, and D-serine is the importantly upper factor of this signaling pathway. If the metabolism of D-serine is abnormal in astrocyte exposed to arsenite, the transmission of information of NMDAR-CaMKII signaling pathway might inevitably be interfered, which could further affect the function of learning and memory. Therefore, the D-serine metabolism might be the initial target site of mental injury induced by arsenite. In present study, animal toxicity examination will be used and the technologies of electrophysiology, molecular biology and biochemistry will be applied, the main aim of this study is to explore the effects of arsenite on D-serine metabolism and D-serine-NMDAR-CaMKⅡ signaling pathway, and the results of the present study might provide scientific reference for the clarification of the initial target site and the definite mechanism of the learning and memory dysfunction induced by arsenite.

环境砷暴露严重损害儿童的智力发育，但其机制目前尚未阐明。我们前期的体外细胞毒理研究提示，砷可能通过影响星形胶质细胞（AST）对D-丝氨酸的分泌，间接干扰神经元内N-甲基-D-天冬氨酸受体（NMDAR）和钙调蛋白依赖性激酶Ⅱ（CaMKⅡ）蛋白的表达，NMDAR-CaMKⅡ信号通路在学习记忆形成中起关键作用，而D-丝氨酸是该信号通路的重要上游因子。如果砷暴露引起AST内D-丝氨酸的代谢异常，势必可干扰NMDAR-CaMKⅡ信号通路的信息传递，进而影响学习记忆功能。因此，D-丝氨酸代谢异常很可能是砷智力损伤的初始靶作用位点。本研究拟通过动物毒理试验研究方法，应用电生理学、分子生物学等技术从突触可塑性、基因转录和蛋白表达水平等深入探讨体内砷暴露对D-丝氨酸代谢及D-丝氨酸-NMDAR-CaMKII信号通路的影响，为揭示砷智力损伤的初始靶作用位点和阐明砷影响学习记忆损伤的确切机制提供科学的参考数据。

环境砷暴露严重损害儿童的智力发育，但其机制目前尚未阐明。本研究通过动物毒理试验研究方法，建立不同发育阶段小鼠仔鼠砷暴露模型，探讨体内砷暴露对D-丝氨酸代谢及D-丝氨酸- N-甲基-D-天冬氨酸受体(NMDAR)-钙调蛋白依赖性激酶Ⅱ(CaMKⅡ)信号通路的影响。本研究发现，砷暴露组仔鼠寻找水迷宫实验中平台的潜伏期时间明显延长，高剂量砷暴露组仔鼠在撤除平台后第Ⅱ象限停留时间明显减少，提示砷暴露可影响仔鼠学习和记忆能力；砷暴露可引起发育早期仔鼠海马神经突触的改变；砷能够引起发育早期仔鼠海马中D-丝氨酸代谢重要的代谢酶和转运体，丝氨酸消旋酶（SR）、D-氨基酸氧化酶（DAAO）和Na+非依赖型丙氨酸-丝氨酸-半胱氨酸转运体(asc-1)的mRNA及蛋白表达水平的明显改变，从而可能会影响D-丝氨酸代谢；砷能够使发育早期仔鼠海马中NMDAR亚单位NR1、NR2A和NR2B mRNA及蛋白表达水平明显降低，提示砷可影响学习记忆中关键受体NMDAR的水平；砷能够降低发育早期仔鼠海马中CaMKII蛋白表达水平及亚基CaMKIIα 和CaMKⅡβ mRNA水平；以上结果提示砷可能影响D-丝氨酸代谢和D-丝氨酸-NMDAR-CaMKII信号转导通路，进而损害学习记忆能力。