Investigating the epigenetic regulation of manganese superoxide dismutase in aging rat tissue

Bayley, Cassidy
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The free radical theory of aging postulates that accumulation of oxidative damage in major cellular components is the predominant underlying cause of the aging phenotype. This damage is caused most commonly by reactive oxygen species (ROS) and antioxidant enzymes such as the superoxide dismutases (SOD) that neutralize ROS, are therefore vital. Manganese superoxide dismutase (MnSOD) is particularly critical as it is functional in the mitochondria, a major site for ROS generation. Numerous studies have demonstrated a tissue-specific decrease in the activity and mRNA levels of major antioxidants, including MnSOD, with aging, however the exact mechanism of this regulation is unclear. It was hypothesized that a general down-regulation of various antioxidant enzymes such as this may occur at the transcriptional level. In order to investigate SOD2 regulation, a comprehensively annotated rat SOD2 promoter region was established using the appropriate bioinformatics tools. Following this, SOD2 mRNA levels in tissues from young and old rat tissue were compared using quantitative PCR. The results showed increased and decreased SOD2 mRNA levels in old compared to young liver tissue and brain tissue, respectively, however these trends were not statistically significant. As MnSOD has been shown to be epigenetically downregulated in various age-related diseases it was hypothesized that the decrease in MnSOD mRNA levels seen in aging brain tissue may be a result of epigenetic regulation at the SOD2 (MnSOD gene) promoter, specifically, through DNA methylation. A methylation assay assessing the SOD2 gene promoter revealed no significant evidence of hypermethylation. Although this suggests that promoter methylation is an unlikely mechanism of SOD2 regulation in aging, further work would need to be implemented in order to prove this conclusively.
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2015