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

最近的研究表明，神经系统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。越来越多的结果表明，DNA损伤可能会减少与学习、记忆和神经元存活相关的基因的转录表达，从而启动大脑老化和发病机制的程序。在本研究中，我们重点研究了神经退行性疾病的DNA修复和损伤反应的分子基础。我们对表达突变的Huntingtin外显子1片段蛋白的神经元制备的可溶性核蛋白进行了蛋白质组学分析，发现mHTT降低了核HMGB1蛋白水平的浓度。我们还发现，在亨廷顿病的病理中，核HMGB1的减少导致了DNA双链断裂(DDSB)介导的神经元损伤。利用高表达DNA修复/损伤反应基因的转基因小鼠和苍蝇动物，我们发现DNA修复的改善显著恢复了亨廷顿病的病理症状。此外，我们还研究了HMGB1和DDSB在小鼠脑老化过程中区域和细胞类型的特异性变化。HMGB1定位于神经元和星形胶质细胞的细胞核，其蛋白水平随年龄变化而变化。在衰老过程中，HMGB1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在老化过程中没有明显变化。这些结果表明HMGB1在神经元和星形胶质细胞之间的表达存在差异调节，提示核HMGB1的减少可能与DDSB介导的衰老脑内神经元功能障碍有关。我们的研究结果可能为我们开发针对各种神经退行性疾病的新疗法提供有效的策略。

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.