Kajitani Kosuke, Yamaguchi Hiroo, Dan Yukihiko, Furuichi Masato, Kang Dongchon, Nakabeppu Yusaku
Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan.
J Neurosci. 2006 Feb 8;26(6):1688-98. doi: 10.1523/JNEUROSCI.4948-05.2006.
Enhanced oxidative stress has been implicated in the excitotoxicity of the CNS, and 8-oxo-7,8-dihydro-guanine (8-oxoG), a major type of oxidative damage in nucleic acids, was reported to be accumulated in the rat hippocampus after kainate administration. We herein showed that the 8-oxoG levels in mitochondrial DNA and cellular RNA increased significantly in the CA3 subregion of the mouse hippocampus 6-12 h after kainate administration but returned to basal levels within a few days. Laser-scanning confocal microscopy revealed the 8-oxoG accumulation in mitochondrial DNA to be remarkable in CA3 microglia, whereas that in nuclear DNA or cellular RNA was also detected in the CA3 pyramidal cells and astrocytes. 8-oxoG accumulation in cellular DNA or RNA should be suppressed by MutT homolog 1 (MTH1) with 8-oxo-dGTPase (8-oxo-7,8-dihydro-2'-deoxyguanosine triphosphatase) activity and 8-oxoG-DNA glycosylase 1 (OGG1) with 8-oxoG DNA glycosylase activity. We thus examined the expression level of MTH1 and OGG1 in the mouse hippocampus after kainate administration. The Mth1 mRNA level decreased soon after kainate administration and then quickly recovered beyond the basal level, and a continuously increased MTH1 protein level was observed, whereas the Ogg1 mRNA level remained constant. MTH1-null and wild-type mice exhibited a similar degree of CA3 neuron loss after kainate administration; however, the 8-oxoG levels that accumulated in mitochondrial DNA and cellular RNA in the CA3 microglia significantly increased in the MTH1-null mice in comparison with wild-type mice, thus demonstrating that MTH1 efficiently suppresses the accumulation of 8-oxoG in both cellular DNA and RNA in the hippocampus, especially in microglia, caused by excitotoxicity.
增强的氧化应激与中枢神经系统的兴奋性毒性有关，据报道，核酸中主要的氧化损伤类型8-氧代-7,8-二氢鸟嘌呤（8-氧代鸟嘌呤，8-oxoG）在给予海藻酸后在大鼠海马体中积累。我们在此表明，给予海藻酸后6-12小时，小鼠海马体CA3亚区线粒体DNA和细胞RNA中的8-氧代鸟嘌呤水平显著升高，但在几天内恢复到基础水平。激光扫描共聚焦显微镜显示，CA3小胶质细胞中线粒体DNA中的8-氧代鸟嘌呤积累显著，而在CA3锥体细胞和星形胶质细胞中也检测到核DNA或细胞RNA中的8-氧代鸟嘌呤积累。具有8-氧代-dGTPase（8-氧代-7,8-二氢-2'-脱氧鸟苷三磷酸酶）活性的MutT同源物1（MTH1）和具有8-氧代鸟嘌呤DNA糖基化酶活性的8-氧代鸟嘌呤-DNA糖基化酶1（OGG1）应抑制细胞DNA或RNA中的8-氧代鸟嘌呤积累。因此，我们检测了给予海藻酸后小鼠海马体中MTH1和OGG1的表达水平。给予海藻酸后，Mth1 mRNA水平很快下降，然后迅速恢复到基础水平以上，并观察到MTH1蛋白水平持续升高，而Ogg1 mRNA水平保持不变。MTH1基因敲除小鼠和野生型小鼠在给予海藻酸后表现出相似程度的CA3神经元损失；然而，与野生型小鼠相比，MTH1基因敲除小鼠CA3小胶质细胞线粒体DNA和细胞RNA中积累的8-氧代鸟嘌呤水平显著升高，从而表明MTH1有效地抑制了由兴奋性毒性引起的海马体中细胞DNA和RNA，尤其是小胶质细胞中8-氧代鸟嘌呤的积累。
