Analysis of signal transduction system in ischemic neuronal death

已知ERK、p38、JNK属于同一家族，即丝裂原活化蛋白激酶(MAP Kinase)。这些激酶被磷酸化的级联激活，导致分化、细胞增殖和细胞死亡，如细胞凋亡。尤其是ERK与细胞增殖和生长密切相关，而JNKad p38则与细胞死亡密切相关。在目前的研究中，我们利用全脑缺血来研究这些激酶是否与CA1迟发性神经元死亡有关。通过大鼠前脑缺血和免疫印迹实验，我们检测了大鼠海马CA1区、齿状回和大脑皮质中这些激酶的磷酸化状态，并与组织学结果进行了相关性分析。在此模型中神经元死亡的CA1区，观察到ERK磷酸化的双相增加，而在其他区域仅在5min时观察到早期增加。在诱导缺血耐受后，这种双相增加是最小的。仅在30min时，JNK在CA1和齿状回有短暂的磷酸化。关于p38，只有皮质表现出增强的磷酸化。这些结果表明，只有持续性的磷酸化与全脑缺血后缺血性神经元损伤的区域分布有关。然而，脑缺血后蛋白质合成受到明显抑制。由于ERK激活转录因子并诱导其他基因，ERK的磷酸化是否真的诱导蛋白质诱导神经元死亡仍有待进一步研究。

It is known that ERK, p38, JNK belong to the same family, mitogen-activated protein kinases (MAP kinase). These kinases are activated by a phosphorylation cascade, leading to differentiation, cell proliferation, and cell death such as apoptosis. In particular, ERK is intimately related to proliferation and growth, whereas JNK ad p38 are involved in cell death. In the current study, we investigated whether these kinases are involved in delayed neuronal death in CA1 using global forebrain ischemia. By using rat forebrain ischemia and immunoblotting for samples obtained from hippocampal CA1, dentate gyrus, and cortex, we examined the phosphorylation state of these kinases and correlated with histological outcome. In the CA1 region, where neurons die in this model, biphasic increase of phosphorylation of ERK was observed, whereas in the other regions only early increase at 5 min was noted. Following induction of ischemic tolerance, this biphasic increase was minimal. JNK phosphorylation was transiently observed at 30 min only in CA1 and dentate gyrus. With regard to p38, only cortex showed increased phosphorylation. These results indicate that only persistent phosphorylation was correlated with regional distribution of ischemic neuronal injury following global ischemia. However, protein synthesis is markedly inhibited after ischemia. Since ERK activates transcription factors and induces other genes, whether ERK phosphorylation in fact induces proteins to induce neuronal death remains to be determined by further study.