Poly(ADP-ribose) polymerase offers protection against oxidative and alkylation damage to the nuclear and mitochondrial genomes of the retinal pigment epithelium

Purpose: To investigate the role of poly(ADP-ribose)-polymerase (PARP) in protecting against oxidative (H2O2) and alkylation (MMS) damage to the nDNA and mtDNA genomes of the retinal pigment epithelium (RPE). We further hypothesized that PARP ribosylation enzymatic activity is required to facilitate efficient nDNA and mtDNA repair to enable the RPE to survive chronic oxidative stress exposure. Methods: Cellular sensitivity to H2O2 and MMS was determined by the MTT and LDH assays. PARP ribosyl(ation) activity was inhibited by supplementation of 3-aminobenzamide (competitive PARP inhibitor). The susceptibility and repair capacities of nuclear and mitochondrial genomes were assessed by quantitative PCR and PARP activity assessed using an enzyme assay. Results: This study demonstrated that cells lacking ribosyl(ation) activity had a significantly lower lesion repair capacity in both nDNA and mtDNA (p < 0.05), which culminated in reduced cell viability after H2O2 exposure only (p < 0.05). Furthermore, the mtDNA demonstrated a significantly greater sensitivity compared to nDNA to both oxidative and alkylation damage (p < 0.05). Conclusion: PARP activity has an important role in providing the RPE with the high oxidative tolerance required for this cell type to survive the constant reactive oxygen species attack in vivo for several decades. Copyright (C) 2007 S. Karger AG, Basel