Mitochondria-targeted Ogg1 and Aconitase-2 Prevent Oxidant-induced Mitochondrial DNA Damage in Alveolar Epithelial Cells

Background: Mitochondrial Ogg1 prevents oxidant (H2O2 and asbestos)-induced Aco-2 degradation and apoptosis. Results: Oxidant stress caused preferential AEC mtDNA > nuclear DNA damage, mt-p53 translocation, and apoptosis; effects were blocked by mt-hOgg1 or Aco-2. Conclusion: mt-hOgg1 and Aco-2 preserve AEC mtDNA, preventing oxidant-induced p53 activation and apoptosis. Significance: mt-hOgg1/Aco-2 effects on mtDNA may be an innovative target for preventing degenerative diseases. Mitochondria-targeted human 8-oxoguanine DNA glycosylase (mt-hOgg1) and aconitase-2 (Aco-2) each reduce oxidant-induced alveolar epithelial cell (AEC) apoptosis, but it is unclear whether protection occurs by preventing AEC mitochondrial DNA (mtDNA) damage. Using quantitative PCR-based measurements of mitochondrial and nuclear DNA damage, mtDNA damage was preferentially noted in AEC after exposure to oxidative stress (e.g. amosite asbestos (5-25 g/cm(2)) or H2O2 (100-250 m)) for 24 h. Overexpression of wild-type mt-hOgg1 or mt-long / 317-323 hOgg1 mutant incapable of DNA repair (mt-hOgg1-Mut) each blocked A549 cell oxidant-induced mtDNA damage, mitochondrial p53 translocation, and intrinsic apoptosis as assessed by DNA fragmentation and cleaved caspase-9. In contrast, compared with controls, knockdown of Ogg1 (using Ogg1 shRNA in A549 cells or primary alveolar type 2 cells from ogg1(-/-) mice) augmented mtDNA lesions and intrinsic apoptosis at base line, and these effects were increased further after exposure to oxidative stress. Notably, overexpression of Aco-2 reduced oxidant-induced mtDNA lesions, mitochondrial p53 translocation, and apoptosis, whereas siRNA for Aco-2 (siAco-2) enhanced mtDNA damage, mitochondrial p53 translocation, and apoptosis. Finally, siAco-2 attenuated the protective effects of mt-hOgg1-Mut but not wild-type mt-hOgg1 against oxidant-induced mtDNA damage and apoptosis. Collectively, these data demonstrate a novel role for mt-hOgg1 and Aco-2 in preserving AEC mtDNA integrity, thereby preventing oxidant-induced mitochondrial dysfunction, p53 mitochondrial translocation, and intrinsic apoptosis. Furthermore, mt-hOgg1 chaperoning of Aco-2 in preventing oxidant-mediated mtDNA damage and apoptosis may afford an innovative target for the molecular events underlying oxidant-induced toxicity.