JBC：发现舞蹈病神经元线粒体DNA氧化损伤的机制

亨廷顿氏舞蹈病是一种常染色体显性遗传的神经退行性疾病，主要表现为运动障碍、认知和精神紊乱，一般在发病后10-15年内死亡。该疾病的病理特征是大脑纹状体神经元的渐进性丢失，但亨廷顿基因突变导致纹状体神经元选择性死亡的机制还不清楚，目前也没有任何治疗手段。前人一系列研究发现，与大脑其他区域相比，舞蹈病病人的纹状体区具有显着升高的氧化应激水平，然而氧化应激的来源和机制目前不清楚。

中科院动物所唐铁山研究组利用酵母人工染色体转基因舞蹈病（HD）模型鼠研究了HD细胞中线粒体Ca2+稳态失衡与线粒体氧化损伤之间的关系，结果表明HD细胞线粒体基质中Ca2+浓度和活性氧的水平都显着高于对照野生细胞，提示HD线粒体中的Ca2+稳态和活性氧信号都发生了紊乱。如果阻断线粒体Ca2+摄入也同样阻断了线粒体中活性氧水平的升高，表明HD细胞线粒体中氧化压力的增高依赖于线粒体Ca2+的摄入。同样的结果也在HD小鼠模型的纹状体神经元和HD病人成纤维细胞中得到。

更为重要的是，HD细胞中线粒体Ca2+过量摄入可以直接导致线粒体基因组DNA（mtDNA）损伤的显着升高。因此依赖于线粒体Ca2+摄入的氧化应激和氧化损伤积累最终会导致线粒体的功能障碍和神经细胞死亡。这项研究首次证实了舞蹈病神经元线粒体Ca2+过度摄入/氧化应激/mtDNA损伤三者之间存在的确切因果关系。本研究也提示降低线粒体Ca2+摄入可以作为HD治疗的一个策略。鉴于Ca2+信号异常在多种神经退行性疾病（如阿尔兹海默病、帕金森病、脊髓小脑共济失调症等）的病理发生中发挥着重要作用，本研究结果对于上述疾病治疗手段的开发也具有重要的借鉴意义。

该成果于2012年12月17日在线发表于J Biol Chem。研究组博士研究生王久强为该论文第一作者，唐铁山研究员为通讯作者。合作者有北京大学程和平教授、膜重点室孙钦秒和陈佺研究员以及北京基因组研究所郭彩霞研究员。该研究得到了科技部、国家自然科学基金委和中国科学院的资助。

doi: 10.1074/jbc.M112.407726
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Dysregulation of Mitochondrial Calcium Signaling and Superoxide Flashes Cause Mitochondrial Genomic DNA Damage in Huntington's Disease

Jiu-Qiang Wang1, Qian Chen1, Xianhua Wang2, Qiao-Chu Wang1, Yun Wang1, He-Ping Cheng2, Caixia Guo1, Qinmiao Sun1, Quan Chen1 and Tie-Shan Tang1,*

SUMMARY Huntingtons disease (HD) is an inherited, fatal neurodegenerative disorder characterized by the progressive loss of striatal medium spiny neurons. Indications of oxidative stress are apparent in brain tissues from both HD patients and HD mouse models; however, the origin of this oxidant stress remains a mystery. Here, we used a yeast artificial chromosome transgenic mouse model of HD (YAC128) to investigate the potential connections between dysregulation of cytosolic Ca2+ signaling and mitochondrial oxidative damage in HD cells. We found that YAC128 embryonic fibroblasts (MEFs) exhibit a strikingly higher level of mitochondrial matrix Ca2+ loading and elevated superoxide generation compared to WT cells, indicating that both mitochondrial Ca2+ signaling and superoxide generation are dysregulated in HD cells. The excessive mitochondrial oxidant stress is critically dependent on mitochondrial Ca2+ loading in HD cells, since blocking mitochondrial Ca2+ uptake abolished elevated superoxide generation. Similar results were obtained using neurons from HD model mice and fibroblast cells from HD patient. More importantly, mitochondrial Ca2+ loading in HD cells caused a 2-fold higher level of mitochondrial genomic DNA (mtDNA) damage due to the excessive oxidant generation. This study provides strong evidence to support a new causal link between dysregulated mitochondrial Ca2+ signaling, elevated mitochondrial oxidant stress and mtDNA damage in HD. Our results also indicate that reducing mitochondrial Ca2+ uptake could be a therapeutic strategy for HD.