OXIDATIVE STRESS,REPAIR OF OXIDIZED GUANINES IN AGED CELLS

活性氧（ROS）通过改变维持细胞稳态的细胞信号级联反应导致组织功能下降，并通过诱导包括DNA在内的细胞成分损伤，与病因学和衰老有关。8-氧鸟嘌呤（8-oxoG）和开环嘌呤（FapyG）是ROS诱导的两种丰富的致突变性和毒性碱基损伤，主要由8-氧鸟嘌呤- dna糖基酶（OGGI）修复，其剪接变体OGGI- 1a和OGG1-2a分别靶向细胞核和线粒体（mr）。在ogg - 14小鼠细胞中，这些病变在细胞核和mtDNA中积累，与突变增强和自发性桐状癌相关。同时，缺乏OGG 1-1 a的有效核输入和衰老加速小鼠基因组中损伤的积累支持8-oxoG/FapyG参与衰老过程的病因学。矛盾的是，细胞核和mtDNA中8-oxoG/FapyG的年龄依赖性积累没有发生OGG1总活性的下降。我们的研究结果表明，衰老细胞中OGG 1-2a的mt输入较差，因此很大一部分酶仍然结合在外mt膜上。此外，在衰老细胞中，活性氧诱导的OGG1-1 - a的核积累被延迟。

Reactive oxygen species (ROS) are implicated in the etiology &aging by causing a decline in tissue functions due to altered cellular signaling cascades that maintain cellular homeostasis, and by inducing damage to cellular components, including DNA. 8-Oxoguanine (8-oxoG), and ring-opened purine (FapyG), the two abundant mutagenic and toxic base lesions induced by ROS, are repaired primarily by 8-oxoG-DNA glycosylase (OGGI), with spliced variants, OGGI-1 a and OGG1-2a, targeted to nucleus and mitochondria (mr), respectively. In ogg 14-mouse cells, these lesions accumulate in both nuclear and mtDNA, associated with enhanced mutagenesis, and spontaneous tung carcinoma. At the same time, lack of efficient nuclear import of OGG 1-1 a and accumulation of damage in the genome of senescence-accelerated mice support the etiologic involvement of 8-oxoG/FapyG in aging processes. Paradoxically, age-dependent accumulation of 8-oxoG/FapyG in nuclear and mtDNA occurs without a decline in total OGG1 activity. This discrepancy could be explained by our results showing poor mt import of OGG 1-2a in senescent cells so that a significant fraction of the enzyme remains bound to the outer mt membrane. Furthermore, nuclear accumulation of OGG1-1 a induced by ROS is delayed in the aged cells. The central hypothesis of this project is that toxic and mutagenic oxidative DNA lesions accumulate due to a decreased ability of aged cells to maintain normal levels of OGG 1 in the nucleus and mt thereby causing a decline in tissue functions. Using a variety of cellular, molecular and transgenic approaches, and in collaboration with P1 and P2, we will test our hypothesis with the following aims: 1) to explore the mechanism of age-dependent deficiency in repair of oxidative lesions after oxidative challenge; 2) to validate the preliminary observation that the delay in OGG1 nuclear accumulation is linked to its covalent modification (e.g., acetylation) identified in OGG1-la; and 3) to confirm that accumulation of 8-oxoG/FapyG in the mtDNA of aged cells is indeed due to reduced repair caused by inefficient targeting of OGG1-2a to the mt matrix, which is affected by ROS. These studies will shed significant light on the accumulation of the major mutagenic and toxic lesions in the aging process. The long-term objective is to develop intervention strategies to ameliorate an age-associated decrease in repair of mutagenic DNA lesions in the nucleus and rot, and thus to delay the decline in mitochondria and cellular functions.