| Oxidative damage to mitochondrial DNA has been implicated as a causative factor in many disease processes and in aging. Because different cell types have demonstrated varying abilities for repairing this damage, we have investigated the effects of enhancing mtDNA repair in two cell types that are relatively deficient in repair. Specifically, the enzyme that repairs the mutagenic lesion 8-oxoguanine in the nucleus, called 8-oxoguanine DNA glycosylase (OGG), was targeted to mitochondria. A vector containing this gene fused to a mitochondrial transport sequence was used to transfect human cell lines. Localization of the protein and enzyme activity were analyzed. Then mtDNA repair was evaluated. Finally, the effect of changes in mtDNA repair was studied with several viability assays. Initial studies employed an isolate of HeLa cells with inefficient mtDNA repair, and subsequent experiments were done with Cockayne syndrome A fibroblasts. We hypothesized that increasing levels of OGG, a critical DNA repair enzyme, in mitochondria could alter the ability of the cell to repair oxidative damage to mtDNA. As a result, cell sensitivity to oxidative stress might also be changed. Targeting OGG exclusively to mitochondria in HeLa cells resulted in more efficient mtDNA repair and better cellular resistance to oxidative insult. Cockayne Syndrome A fibroblasts were protected by additional mitochondrial OGG as well. Therefore, targeting of DNA repair enzymes to mitochondria appears to have potential as a therapeutic procedure for combating the accumulation of mtDNA damage observed with aging and other degenerative conditions. |
