Yu Ya-Chun, Kuo Chen-Ling, Cheng Wen-Ling, Liu Chin-San, Hsieh Mingli
Department of Life Science, Tunghai University, Taichung, Taiwan.
J Neurosci Res. 2009 Jun;87(8):1884-91. doi: 10.1002/jnr.22011.
Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant neurodegenerative disorder caused by polyglutamine expansion in the ataxin-3 protein that confers a toxic gain of function. Because of the late onset of the disease, we hypothesize that the accumulated oxidative stress or/and defective antioxidant enzyme ability may be contributory factors in the pathogenesis of MJD. In this study, we utilized SK-N-SH and COS7 cells stably transfected with full-length MJD with 78 polyglutamine repeats to examine any alterations in the antioxidant activity. We demonstrated a significant reduction in the ratio of GSH/GSSG and total glutathione content (GSH + 2x GSSG) in mutant MJD cells compared with the wild-type cells under normal or stressful conditions. We also showed that both SK-N-SH-MJD78 and COS7-MJD78-GFP cell lines have lower activities of catalase, glutathione reductase, and superoxide dismutase compared with the wild-type cell lines. In addition, it is known that, when cells are under oxidative stress, the mitochondrial DNA is prone to damage. Our results demonstrated that mitochondrial DNA copy numbers are decreased in mutant cells and SCA3 patients' samples compared with the normal controls. Furthermore, the amount of common mitochondrial DNA 4,977-bp deletion is higher in SCA3 patients compared with that in normal individuals. Overall, mutant ataxin-3 may influence the activity of enzymatic components to remove O(2)(-) and H(2)O(2) efficiently and promote mitochondrial DNA damage or depletion, which leads to dysfunction of mitochondria. Therefore, we suggest that the cell damage caused by greater oxidative stress in SCA3 mutant cells plays an important role, at least in part, in the disease progression.
马查多-约瑟夫病（MJD）/3型脊髓小脑共济失调（SCA3）是一种常染色体显性神经退行性疾病，由ataxin-3蛋白中的多聚谷氨酰胺扩增引起，这种扩增赋予了毒性功能获得。由于该疾病发病较晚，我们推测累积的氧化应激或/和抗氧化酶能力缺陷可能是MJD发病机制中的促成因素。在本研究中，我们利用稳定转染了含78个多聚谷氨酰胺重复序列的全长MJD的SK-N-SH和COS7细胞，来检测抗氧化活性的任何变化。我们证明，在正常或应激条件下，与野生型细胞相比，突变型MJD细胞中谷胱甘肽（GSH）/氧化型谷胱甘肽（GSSG）的比值以及总谷胱甘肽含量（GSH + 2x GSSG）显著降低。我们还表明，与野生型细胞系相比，SK-N-SH-MJD78和COS7-MJD78-GFP细胞系的过氧化氢酶、谷胱甘肽还原酶和超氧化物歧化酶活性均较低。此外，已知当细胞处于氧化应激状态时，线粒体DNA容易受损。我们的结果表明，与正常对照相比，突变细胞和SCA3患者样本中的线粒体DNA拷贝数减少。此外，SCA3患者中常见的4977碱基对线粒体DNA缺失量高于正常个体。总体而言，突变型ataxin-3可能会影响酶成分有效清除超氧阴离子（O(2)(-)）和过氧化氢（H(2)O(2)）的活性，并促进线粒体DNA损伤或耗竭，从而导致线粒体功能障碍。因此，我们认为SCA3突变细胞中更大的氧化应激所导致的细胞损伤至少在一定程度上在疾病进展中起重要作用。
