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M.S. Cortina, W.J. Lukiw, W.C. Gordon, N.G. Bazan; Bright Light Triggers DNA Repair and Up-regulates Photoreceptor DNA Polymerase and ß . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5134.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Bright light triggers a biphasic response in nuclear DNA fragmentation after 24 h and 48h, suggesting the existence of a photoreceptor-repair mechanism that may explain the temporary disappearance of fragmented DNA following the first peak (IOVS, Gordon et al., 2002). Here we looked at the mitochondrial DNA-repair enzyme, DNA polymerase γ, and the nuclear DNA-repair enzyme, DNA polymerase ß, to determine whether light damage activates a repair response in photoreceptors. Methods: Sprague-Dawley rats dark adapted 2 days were light treated 5 h and returned to darkness. Animals were killed at 6-h intervals; right eyes were sectioned for immunohistochemistry, left retinas were prepared for Western blot analysis. Protein was quantified by Bradford micro assay. Goat polyclonal anti-DNA polymerase γ and anti-DNA polymerase ß were used. Bound primary antibody was detected by anti-mouse IgG peroxidase-linked secondary antibody, developed, and analyzed. Bands for DNA polymerases ß and γ were detected at 39 kDa and 140 kDa, respectively. Results: Time courses from 0-72 h after light as well as 10 days and dark controls were analyzed by Western blot. A single peak occurred for DNA polymerase γ at 6 h after light, with a 2-fold decrease by 12 h and continued decrease to dark levels at 54 h. DNA polymerase ß peaked at 24 h and similarly decreased to control levels at 72 h. These data are supported by immunohistochemistry that localized both repair enzymes in photoreceptors. Conclusions: During light damage, DNA-repair enzymes are induced. The increase in the mitochondria-specific enzyme, DNA polymerase γ, precedes that of the nuclear enzyme, DNA polymerase ß, suggesting that mitochondrial injury leads to nuclear damage. However, these enzymes peak only once, suggesting that DNA is repaired initially, but insufficiently, triggering a second wave of DNA damage in photoreceptor nuclei resulting in cell death. These enzymes may provide novel pharmacologic targets to enhance DNA repair and rescue photoreceptors in retinal degenerative diseases. (NEI, EY05121)
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