NMDA受体不同亚单位在肌萎缩侧索硬化发病机制中的作用

Amyotrophic lateral sclerosis (ALS) is a serious lethal motor neurons degenerative disease. Glutamate excitotoxicity is the major cause of ALS. Activation of N-methyl-D-aspartate (NMDA) receptors, an ionotropic glutamate receptor, brings about intracellular calcium overload, which induces a great deal oxidative enzymes and leads to neurons degeneration after glutamate injury. The course shows that NMDA receptors activation plays a key role in glutamate injury. However, NMDA receptor inhibitors do not show neuroprotective effects. Previous studies showed that NMDA receptors were made up of different subunits, of which NR2AR (NR2A-containing NMDA receptors) and NR2BR (NR2B-containing receptors) differed widely on the distribution and function, but what roles they played in pathogenesis of ALS were still not clear. Our study is designed to make clear the role of NR2AR and NR2BR activation in pathogenesis of ALS, including the activities of NR2AR and NR2BR during different course of chronic glutamate injury, whether inducing the typical pathological changes of ALS, and the impact of neuronal survival/death state, as well as the intracellular signaling pathways inducing neuronal degeneration. Our previous study found that NR2AR/PTEN/TDP-43 signaling pathway activation had a neuroprotective effect in the early stage of chronic glutamate injury.The result has been accepted by Journal of Cell Science (IF 6.290). Next, we will focuse on the effect of NR2BR in ALS pathogenesis. We expect that NR2AR and NR2BR activation occurs in different phases of chronic glutamate injury, NR2AR activities in early stage has neuroprotective effects, on the contrary NR2BR activities in late stage induces neuronal degeneration. Activation of NR2BR in the late stage of chronic glutamate injury will induce pathological change of ALS, including motor neurons apoptosis, abnormal TDP-43 cytoplasmic inclusions, and most obviously TDP-43 sequestrated from nuclear. NR2BR activation induces neuodegeneration through PTEN upregulation/ CREB downregulation/ TDP-43 downregulation signaling pathway. Our results will provide new ideas for the pathogenesis research of ALS, and provide new drug targets for ALS treatment.

肌萎缩侧索硬化（ALS)是一种致死性的运动神经元变性疾病，谷氨酸兴奋毒性损伤是ALS最重要的发病原因。谷氨酸损伤后通过激活NMDA受体（一种亲离子型谷氨酸受体）使细胞内钙超载造成神经元变性死亡，但临床上NMDA受体抑制剂并未产生神经保护作用。进一步研究表明NMDA受体由不同亚单位构成，其中NR2AR和NR2BR在分布和功能上有很大差异，但二者发挥作用的机制至今未明。我们的研究旨在明确NR2AR和NR2BR在ALS发病机制中的作用，包括慢性谷氨酸损伤后NR2AR和NR2BR的活动情况，激活后能否引起ALS的典型病理改变，对神经元生存/死亡状态的影响，以及引起改变的细胞内信号传导通路。我们前期的研究发现慢性谷氨酸损伤早期NR2AR/PTEN/TDP-43信号通路激活具有神经保护作用，下一步将明确NR2BR在谷氨酸损伤中的作用。我们的研究结果将为ALS发病机制及治疗提供新思路和新途径。

一、项目背景. TDP-43蛋白异常积聚是最新发现的肌萎缩侧索硬化（Amyotrophic lateral sclerosis， ALS）的特征性病理改变，TDP-43作为一种DNA/RNA结合蛋白，正常情况下存在于细胞核中，ALS患者运动神经元中TDP-43转移至胞浆并形成包涵体，产生神经毒性，但造成TDP-43异常积聚的原因不明。我们的研究致力于TDP-43积聚的发生机制，以及寻找减轻积聚的方法。. 癌基因DJ-1与神经变性疾病密切相关，其突变与常染色体隐性遗传的Parkinson病有关，DJ-1蛋白可通过抗氧化及抑制凋亡对神经细胞产生保护。SOD1基因突变造成蛋白毒性功能获得是ALS的重要发病机制，在SOD1转基因ALS模型鼠中发现，DJ-1可结合到突变SOD1上，减轻其毒性作用。DJ-1是否能够抑制TDP-43蛋白积聚，目前尚缺乏研究。.二、主要研究内容. 环境因素与TDP-43异常积聚的关系，含NR2B亚单位的NMDA受体激活与TDP-43异常的关系，DJ-1减轻TDP-43积聚的机制。.三、重要结果. 1. 谷氨酸兴奋毒性损伤和氧化应激可造成TDP-43异常积聚. 2. Ifenprodil减轻TDP-43的异常积聚，对神经元起保护作用. 3. DJ-1能结合到TDP-43包涵体上，并抑制其异常积聚. 4. DJ-1通过丝裂原活化蛋白激酶途径抑制TDP-43的积聚. 5. DJ-1功能异常加剧TDP-43积聚.四、关键数据及科学意义. 谷氨酸兴奋毒性损伤和氧化应激损伤均能造成TDP-43异常积聚，说明环境因素在TDP-43异常中的重要作用。自2006年发现TDP-43异常是ALS的根本病理改变以来，研究集中于寻找相关基因突变，尽管已经发现超过100种的突变可造成TDP-43片段化并异常积聚，但存在突变的ALS患者仅占5%。我们的研究表明，多种环境因素可造成TDP-43异常积聚，为ALS及神经变性病的机制研究提供了新的思路。. 在我们的氧化应激ALS模型中，DJ-1能够结合到TDP-43包涵体上抑制其积聚，从而发挥对神经元的保护作用。既往的研究中，DJ-1能够抑制多种和神经变性相关的异常蛋白积聚。提示DJ-1作为一种重要的分子伴侣，可能成为治疗神经变性疾病的未来方向。