Molecular mechanisms of neuropathogenesis associated with the defects of DNA repair system

近年来的研究表明，神经系统中DNA修复/损伤反应机制的缺陷与各种神经退行性疾病的病理机制密切相关。越来越多的研究结果表明，DNA损伤可能会降低参与学习、记忆和神经元存活的基因的转录表达，从而启动脑老化和发病机制。本研究旨在探讨神经退行性疾病中DNA修复和损伤反应的分子基础，对表达突变型亨廷顿蛋白外显子1片段（mHtt）的神经元进行可溶性核蛋白质组学分析，发现mHtt降低了核HMGB 1蛋白水平。我们还发现，减少核HMGB 1导致DNA双链断裂（DDSB）介导的神经元损伤亨廷顿氏病的病理。使用过表达DNA修复/损伤反应基因的小鼠和苍蝇的基因转基因动物，我们发现DNA修复的改善显著地恢复了亨廷顿病病理学的症状。此外，我们还研究了小鼠脑老化过程中HMGB 1和DDSB积累的区域和细胞类型特异性变化。HMGB 1定位于神经元和星形胶质细胞的细胞核中，并且在不同脑区的蛋白水平随年龄而变化。HMGB 1在神经元中减少，而在星形胶质细胞中增加。相反，DDSB在神经元中显著积累，但在星形胶质细胞中没有显著变化。这些结果表明，HMGB 1在神经元和星形胶质细胞中的表达存在差异，提示细胞核HMGB 1的减少可能与DDSB介导的神经元功能障碍有关，我们的研究结果可能为开发新的神经退行性疾病的治疗方法提供有效的策略。

Recent studies have shown that the defect of DNA repair/damage response mechanism in the nervous system closely associate with pathology underlying various neurodegenerative diseases. Accumulating results suggest that DNA damage may reduce transcriptional expression of genes involved in learning, memory and neuronal survival to initiate a program of brain ageing and pathogenesis. In this study, we focused on the molecular basis of DNA repair and damage responses underlying neurodegenerative diseases.We performed a proteome analysis of soluble nuclear proteins prepared from neurons expressing mutant huntingtin exon 1 fragment protein which contains abnormally expanded poly-glutamine repeat (mHtt), and found that mHtt reduces the concentration of nuclear HMGB1 protein level. We also found that the reduction of nuclear HMGB1 causes DNA double-strand break (DDSB)-mediated neuronal damage in Huntinton's disease pathology. Using gene transgenic animals of mouse and fly that overexpressing DNA repair/damage response genes, we found that the improvement of DNA repair significantly recovers the symptoms of Huntinton's disease pathology. Furthermore, we investigated the regional and cell-type specific changes of HMGB1 and DDSB accumulation during the aging of mouse brain. HMGB1 is localized in the nuclei of neurons and astrocytes, and the protein level changes in various brain regions age-dependently. HMGB1 reduces in neurons, whereas it increases in astrocytes during aging. In contrast, DDSB remarkably accumulates in neurons, but it does not change significantly in astrocytes during aging. These results indicate that HMGB1 expression is differentially regulated between neuron and astrocyte, and suggest that the reduction of nuclear HMGB1 might be associated with DDSB-mediated neuronal dysfunction in the aging brain.Our findings might provide us an effective strategy for developing new therapeutics against various neurodegenerative disorders.