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A. Wang, T. J. Lukas, M. Yuan, A. H. Neufeld; Increased Mitochondrial Dna Damage and Down-Regulation of Dna Repair Enzymes in Aged Retina and Rpe/Choroid. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3971.
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© ARVO (1962-2015); The Authors (2016-present)
In the CNS, increased mitochondrial DNA (mtDNA) damage is associated with aging and may underlie, contribute or increase the susceptibility to neurodegenerative diseases. Because of the focus on the photoreceptors and the RPE/choroid as cells relevant to age-related macular degeneration (AMD) and RGCs as cells relevant to glaucoma, we examined young and old retinas and RPE/choroid, harvested from rodent eyes, for DNA damage and for changes in selected DNA repair enzymes.
Immunohistochemical labeling and quantitative ELISA for the oxidative DNA damage marker, 8-hydroxy-2’-deoxy-guanosine (8-OHdG) were measured in young (5mos) and old (25mos) rodent retinas and RPE/choroid. Expression of 8-OHdG was co-localized with the mitochondrial enzyme superoxide dismutase (MnSOD). mtDNA and nDNA damage was determined by quantitative PCR. Levels of several DNA repair enzymes were determined using qRT-PCR, Western blots and immunohistochemistry. AP sites were determined in DNA from young and old retinas.
Immunohistochemical labeling for 8-OHdG increased in old rodent photoreceptors, RGCs and RPE/choroid. Quantitative ELISA confirmed increased levels of 8-OHdG. 8-OHdG co-localized with MnSOD, suggesting damage to mtDNA. Measurements of nDNA and mtDNA lesions indicated that DNA damage is primarily in mtDNA in old retinas and RPE/choroid. Increased mtDNA damage may be due to decreased levels of DNA repair enzymes in the aged retina and RPE/choroid. DNA repair enzymes, poly (ADP-ribose) polymerase 1 (PARP1), 8-oxoguanine-DNA glycosylase 1 (OGG1), mutY homolog (MYH), were decreased in photoreceptors, RGCs and RPE/choroid from old animals compared to young animals. Fewer AP sites in old retinas were consistent with the overall decrease in DNA glycosylase with age.
Our results show that there is increased mtDNA damage in photoreceptors, RGCs and RPE/choroid in old animals, which is likely due to decreased DNA repair capacity. mtDNA damage in the retinas and RPE/choroid may be a susceptibility factor that underlies the development of AMD and glaucoma.
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