Mitochondrial Reactive Oxygen Species Mediate Metabolic Stability

Oxidative phosphorylation (OXPHOS) is the metabolic pathway in mitochondria that produces the large majority of ATP used by the cell. Superoxide, a reactive oxygen species (ROS), is generated during OXPHOS when electrons are prematurely transferred to oxygen. Although ROS are necessary for certain cell signaling pathways, they are generally thought to be damaging to the cell. Cells can protect themselves against oxidative damage using antioxidant enzymes that break down superoxide and other ROS. Antioxidants are currently used as therapeutics for a number of diseases, but so far, mitochondria targeted antioxidants have not been well characterized for this purpose. Manganese superoxide dismutase (SOD2) is an antioxidant enzyme found in mitochondria that converts superoxide into hydrogen peroxide. This project focuses on mice that overexpress SOD2. Microarray analysis of gene expression in these mice showed potentially defective OXPHOS gene expression. Preliminary studies confirmed reductions of complexes II and III in the SOD2 samples by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and a reduction of complex II assembly in the SOD2 liver samples by blue native PAGE. Current studies have shown that SOD2 mice have reduced assembly of complex II and V by BN-PAGE, but unchanged assembly of complexes I and III by the same method. To follow up on these results, activity assays indicate a decrease in complex II activity and a potential increase in complex I activity. Aconitase showed an increase in activity in SOD2 samples as well. Taken together, this implicates that overexpression of SOD2 causes defects in OXPHOS.