Xu Jing, Zhang Quan-Guang, Li Chong, Zhang Guang-Yi
Research Center for Biochemistry and Molecular Biology, The Jiangsu Key Laboratory of Brain Disease Bioinformation, Xuzhou Medical College, Jiangsu, People's Republic of China.
Hippocampus. 2007;17(7):525-37. doi: 10.1002/hipo.20289.
Previous studies have shown that subtoxic NMDA moderated the neuronal survival in vitro and vivo. We performed this experiment to clarify the precise mechanism underlie subtoxic NMDA delayed neuronal death in ischemic brain injury. We found that pretreatment of NMDA (100 mg/kg) increased the number of the surviving CA1 pyramidal cells of hippocampus at 5 days of reperfusion. This dose of NMDA could also enhance Akt activation after ischemia/reperfusion (I/R). Here, we examined the possible mechanism that NMDA induced Akt activation. On the one hand, we found NMDA receptor-mediated Akt activation was associated with increased expression of BDNF (brain-derived neurotrophic factor) and activation of its high-affinity receptor TrkB after I/R in the hippocampus CA1 region, which could be held down by TrkB receptor antagonist K252a. On the other hand, we found that NMDA enhanced the binding of Ca2+-dependent calmodulin (CaM) to p85 (the regulation subunit of PI-3K), which led to the activation of Akt. W-13, an active CaM inhibitor, prevented the combination of CaM and p85 and subsequent Akt activation. Furthermore, NMDA receptor-mediated Akt activation was reversed by combined treatment with LY294002, the specific blockade of PI-3K. Taken together, our results suggested that subtoxic NMDA exerts the neuroprotective effect via activation of prosurvival PI-3K/Akt pathway against ischemic brain injury, and BDNF-TrkB signaling and Ca2+-dependent CaM cascade might contribute to NMDA induced activation of PI-3K/Akt pathway.
先前的研究表明，亚毒性剂量的N-甲基-D-天冬氨酸（NMDA）在体外和体内均能调节神经元存活。我们进行了本实验，以阐明亚毒性NMDA在缺血性脑损伤中延迟神经元死亡的精确机制。我们发现，用NMDA（100mg/kg）预处理可增加再灌注5天时海马CA1区存活锥体细胞的数量。该剂量的NMDA还可增强缺血/再灌注（I/R）后Akt的激活。在此，我们研究了NMDA诱导Akt激活的可能机制。一方面，我们发现NMDA受体介导的Akt激活与海马CA1区I/R后脑源性神经营养因子（BDNF）表达增加及其高亲和力受体TrkB的激活有关，而TrkB受体拮抗剂K252a可抑制这种作用。另一方面，我们发现NMDA增强了钙依赖性钙调蛋白（CaM）与p85（磷脂酰肌醇-3激酶的调节亚基）的结合，从而导致Akt激活。活性CaM抑制剂W-13可阻止CaM与p85的结合及随后的Akt激活。此外，PI-3K特异性阻滞剂LY294002联合处理可逆转NMDA受体介导的Akt激活。综上所述，我们的结果表明，亚毒性NMDA通过激活促存活的PI-3K/Akt信号通路对缺血性脑损伤发挥神经保护作用，BDNF-TrkB信号通路和钙依赖性CaM级联反应可能参与了NMDA诱导的PI-3K/Akt信号通路激活。
