Hou Sheng T, Jiang Susan X, Aylsworth Amy, Ferguson Graeme, Slinn Jacqueline, Hu Houwen, Leung Thomas, Kappler Joachim, Kaibuchi Kozo
Experimental NeuroTherapeutics Laboratory, Institute for Biological Sciences, National Research Council Canada, Ottawa, Ontario, Canada.
J Neurochem. 2009 Nov;111(3):870-81. doi: 10.1111/j.1471-4159.2009.06375.x. Epub 2009 Sep 7.
Intracellular calcium influx through NMDA receptors triggers a cascade of deleterious signaling events which lead to neuronal death in neurological conditions such as stroke. However, it is not clear as to the molecular mechanism underlying early damage response from axons and dendrites which are important in maintaining a network essential for the survival of neurons. Here, we examined changes of axons treated with glutamate and showed the appearance of betaIII-tubulin positive varicosities on axons before the appearance of neuronal death. Dizocilpine blocked the occurrence of varicosities on axons suggesting that these microstructures were mediated by NMDA receptor activities. Despite early increased expression of pCaMKII and pMAPK after just 10 min of glutamate treatment, only inhibitors to Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and calpain prevented the occurrence of axonal varicosities. In contrast, inhibitors to Rho kinase, mitogen-activated protein kinase and phosphoinositide 3-kinase were not effective, nor were they able to rescue neurons from death, suggesting CaMKII and calpain are important in axon survival. Activated CaMKII directly phosphorylates collapsin response mediator protein (CRMP) 2 which is independent of calpain-mediated cleavage of CRMP2. Over-expression of CRMP2, but not the phosphorylation-resistant mutant CRMP2-T555A, increased axonal resistance to glutamate toxicity with reduced numbers of varicosities. The levels of both pCRMP2 and pCaMKII were also increased robustly within early time points in ischemic brains and which correlated with the appearance of axonal varicosities in the ischemic neurons. Collectively, these studies demonstrated an important role for CaMKII in modulating the integrity of axons through CRMP2 during excitotoxicity-induced neuronal death.
通过N-甲基-D-天冬氨酸（NMDA）受体的细胞内钙内流会引发一系列有害的信号事件，这些事件会导致诸如中风等神经疾病中的神经元死亡。然而，对于轴突和树突早期损伤反应的分子机制尚不清楚，而轴突和树突对于维持神经元存活所必需的网络至关重要。在此，我们检测了用谷氨酸处理的轴突的变化，并显示在神经元死亡出现之前轴突上出现了βIII-微管蛋白阳性膨体。地佐环平可阻止轴突上膨体的出现，这表明这些微观结构是由NMDA受体活性介导的。尽管在谷氨酸处理仅10分钟后，pCaMKII和pMAPK的表达就早期增加，但只有钙/钙调蛋白依赖性蛋白激酶II（CaMKII）和钙蛋白酶的抑制剂能阻止轴突膨体的出现。相比之下，Rho激酶、丝裂原活化蛋白激酶和磷酸肌醇3激酶的抑制剂无效，也不能挽救神经元免于死亡，这表明CaMKII和钙蛋白酶在轴突存活中很重要。活化的CaMKII直接磷酸化塌陷反应介导蛋白（CRMP）2，这独立于钙蛋白酶介导的CRMP2裂解。CRMP2的过表达，而不是磷酸化抗性突变体CRMP2-T555A，增加了轴突对谷氨酸毒性的抗性，同时减少了膨体的数量。在缺血性脑的早期时间点，pCRMP2和pCaMKII的水平也显著增加，这与缺血性神经元中轴突膨体的出现相关。总体而言，这些研究证明了CaMKII在兴奋性毒性诱导的神经元死亡过程中通过CRMP2调节轴突完整性方面的重要作用。
