Mitochondrial DNA Repair Processes In Oxidative Stress And Aging

线粒体功能障碍被认为是衰老和年龄相关性退化的重要促成因素。我们和其他人正在研究核DNA损伤和线粒体功能障碍之间的关系。我们发现，某些DNA修复疾病与神经变性，如科凯恩综合征，着色性干皮病A组（XPA）和共济失调毛细血管扩张症（A-T）具有线粒体表型，其特征在于增加线粒体膜电位，增加活性氧产生和减少线粒体自噬，异常线粒体的降解途径。这种线粒体应激反应似乎是由PARP 1的持续激活引发的，导致细胞NAD+水平降低。线粒体异常也与NAD+-SIRT 1-PGC-α轴的抑制相关。PARP、其PARylate的靶蛋白和辅因子NAD+在细胞核至线粒体的信号级联中起关键作用，这与线粒体功能障碍有关。我们发现，这些线粒体表型可以在各种实验系统和物种中被PARP 1抑制剂或NAD+前体部分拯救，这表明了进化上保守的机制。我们正在寻求核线粒体信号网络的药理学调节，我们相信这将是预防和治疗年龄相关疾病的一种有前途的新方法。目前的研究表明，PARP 1的抑制、SIRT 1的激活或使用NAD+前体如烟酰胺核苷或烟酰胺单核苷酸肽恢复NAD+，都使线粒体表型正常化。 Aprataxin（APTX）是碱基切除修复（BER）途径中的酶，其从DNA末端去除5AMP基团。这些加合物是由于连接失败或碱基修饰而产生的。APTX突变的人会出现共济失调伴动眼运动性失用症1型（AOA 1），这是一种进行性脊髓小脑共济失调。APTX在细胞核和线粒体DNA稳定性中发挥作用，然而，线粒体功能在AOA 1细胞中尚未得到很好的表征。我们发现，APTX缺乏损害线粒体形态，网络的形成，和线粒体自噬。因此，我们调查了调节线粒体形态的基因，发现APTX缺陷细胞中OPA 1表达受损。这项工作加强了DNA修复缺陷和线粒体改变之间的关联，并进一步证实线粒体功能障碍是越来越多的遗传多样性神经退行性疾病的特征。

Mitochondrial dysfunction is recognized as an important contributing factor for aging and age-related degeneration. We and others are investigating the relationship between nuclear DNA damage and mitochondrial dysfunction. We find that certain DNA repair disorders with neurodegeneration like Cockayne Syndrome, Xeroderma pigmentosum group A (XPA) and Ataxia Telangiectasia (A-T) have a mitochondrial phenotype characterized by increased mitochondrial membrane potential, increased reactive oxygen species generation and decreased mitophagy, the degradation pathway for abnormal mitochondria. This mitochondrial stress response appears to be initiated by persistent activation of PARP1 leading to diminished cellular NAD+ levels. The mitochondrial abnormalities also correlate with inhibition of the NAD+-SIRT1-PGC-alpha axis. PARPs, the target proteins they PARylate, and the cofactor NAD+ play critical roles in the nucleus to mitochondria signaling cascade, which is linked to mitochondrial dysfunction. We showed that these mitochondrial phenotypes can be partially rescued by PARP1 inhibitors or NAD+ precursors in various experimental systems and species, suggesting an evolutionarily conserved mechanism. We are pursuing pharmacological modulation of the nuclear-mitochondrial signaling network which we believe will be a promising novel approach for the prevention and treatment of age-associated diseases. Current research shows that inhibition of PARP1, activation of SIRT1 or restoration of NAD+ using NAD+ precursors like nicotinamide riboside or nicotinamide mononucleotide, all normalize mitochondrial phenotypes. Aprataxin (APTX) is an enzyme in the base excision repair (BER) pathway that removes 5AMP groups from DNA ends. These adducts are created as a result of abortive ligation or base modifications. People with mutations in APTX develop ataxia with oculomotor apraxia type 1 (AOA1) and it is a progressive spinocerebellar ataxia. APTX functions in both nuclear and mitochondrial DNA stability, however, mitochondrial function has not been well characterized in AOA1 cells. We found that APTX deficiency impairs mitochondrial morphology, network formation, and mitophagy. Thus, we surveyed genes that modulate mitochondrial morphology and found that OPA1 expression was impaired in APTX-deficient cells. This works strengthens the associations between defective DNA repair and mitochondrial alterations and further corroborates that mitochondrial dysfunction is a characteristic of an increasing number of genetically diverse neurodegenerative disorders.