Garcia M, Charvin D, Caboche J
Laboratoire Signalisation Neuronale et Régulations Géniques, Unité Mixte de Recherche 7102, Université Pierre et Marie Curie, 9 quai Saint Bernard, 75005 Paris, France.
Neuroscience. 2004;127(4):859-70. doi: 10.1016/j.neuroscience.2004.05.054.
Huntington's disease (HD) is an autosomal neurodegenerative disorder, caused by expansion of a glutamine repeat in the Huntingtin protein. Pathogenesis in HD includes the cytoplasmic cleavage of Huntingtin and release of an amino-terminal fragment capable of nuclear localization, where expanded-Huntingtin (Exp-Htt) might lead to aberrant transcriptional regulation, neuronal dysfunction and degeneration. Recent evidence, from hippocampal cell lines, also implicates altered interaction of Exp-Htt with components of the c-Jun N-terminal kinase (JNK) cascade. However, there is yet no proven implication of the JNK/c-Jun module in degeneration of striatal neurons, the more vulnerable cell population, in HD. In the present study, we used primary striatal neurons in culture to analyze c-Jun activation by Exp-Htt. Green fluorescent protein (GFP)-tagged exon 1 of human Huntingtin either in its normal (25Q, normal-Htt) or expanded (103Q, Exp-Htt) version was transiently transfected in these cells. We first set out, in our conditions, the time course of striatal degeneration produced by Exp-Htt, and found it occurred rapidly. At 48 h post-transfection, 60% of striatal neurons expressing Exp-Htt had apoptotic characteristics including DNA fragmentation and neuritic retraction. Most of these neurons also showed nuclear aggregates of GFP-Exp Htt. Kinetics of c-Jun activation were tested in transfected cells using immunocytochemical detection of phospho-c-Jun. We found a significant activation and induction of c-Jun in Exp-Htt but not normal-Htt-transfected neurons. Of interest, these events occurred prior to nuclear translocation of Exp-Htt. Finally, overexpression of a dominant negative version of c-Jun, as well as pharmacological inhibition of JNK strongly protected against DNA fragmentation and neuritic retraction induced by Exp-Htt. Thus our data suggest that c-Jun activation and induction, is an early event in the pathogenesis of HD, occurring prior to formation of nuclear aggregates of Exp-Htt.
亨廷顿舞蹈症（HD）是一种常染色体显性神经退行性疾病，由亨廷顿蛋白中谷氨酰胺重复序列的扩增引起。HD的发病机制包括亨廷顿蛋白的细胞质裂解和能够进行核定位的氨基末端片段的释放，其中扩增的亨廷顿蛋白（Exp-Htt）可能导致异常的转录调控、神经元功能障碍和变性。来自海马细胞系的最新证据还表明，Exp-Htt与c-Jun氨基末端激酶（JNK）级联反应的成分之间的相互作用发生了改变。然而，JNK/c-Jun模块在HD中更易受损的细胞群体——纹状体神经元变性中的作用尚未得到证实。在本研究中，我们使用培养的原代纹状体神经元来分析Exp-Htt对c-Jun的激活作用。将带有绿色荧光蛋白（GFP）标签的人亨廷顿蛋白第1外显子的正常（25Q，正常-Htt）或扩增（103Q，Exp-Htt）版本瞬时转染到这些细胞中。我们首先在我们的实验条件下确定了Exp-Htt引起的纹状体变性的时间进程，发现其发生迅速。转染后48小时，60%表达Exp-Htt的纹状体神经元具有凋亡特征，包括DNA片段化和神经突回缩。这些神经元中的大多数还显示出GFP-Exp Htt的核聚集。使用磷酸化c-Jun的免疫细胞化学检测在转染细胞中测试c-Jun激活的动力学。我们发现Exp-Htt转染的神经元中c-Jun有显著激活和诱导，而正常-Htt转染的神经元中则没有。有趣的是，这些事件发生在Exp-Htt核转位之前。最后，c-Jun显性负性版本的过表达以及JNK的药理学抑制强烈保护细胞免受Exp-Htt诱导的DNA片段化和神经突回缩。因此，我们的数据表明，c-Jun的激活和诱导是HD发病机制中的一个早期事件，发生在Exp-Htt核聚集形成之前。
