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.
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