Role of Manganese Superoxide Dismutase (SOD2) in Protection Against Oxidative Stress and Apoptosis

Abstract

Abstract: : Purpose: Among the key antioxidant enzymes that protect the lens against oxidative damage is superoxide dismutase. It has been reported that apoptotic cell death occurs in lens epithelium of cataract patients. MnSOD (SOD2) localized in the mitochondria may play a role in apoptosis. Here, we have investigated the relationship of SOD2 levels in human lens epithelial cells to oxidative stress and apoptosis. Methods: SOD2 levels in human lens epithelial cell cultures (SRA 01/04) were up– and down regulated by transfection with sense– and antisense cDNA for SOD2. The susceptibility of the cells to oxidative stress was evaluated by exposing them to photochemically generated O₂^– and measuring DNA strand breaks. Mitochondrial damage was visualized by electron microscopy and cytochrome C leakage was established by immunoblotting. Apoptosis was quantified by tunel assay, activation of Caspase 3 and by flow cytometry of Annexin V–FITC staining of the cells. Results: Cells with higher levels of the enzyme were more resistant to oxidative stress compared to the cells in which the enzyme was down–regulated. SOD2–deficient cells showed loss of mitochondria and membrane damage when challenged with O₂^–. Furthermore, they showed greater number of tunnel positive cells, enhanced cytochrome C leakage from mitochondria into cell cytoplasm, and activation of Caspase 3 as compared to non–transfected cells or those with elevated level of the enzyme. Conclusions: These findings demonstrate the protective effect of SOD2 on oxidation–induced apoptosis of lens epithelial cells. Under conditions of decreased enzyme expression or its loss from mitochondria, increased accumulation of reactive oxygen species may result in apoptosis leading to cataract formation.

Keywords: antioxidants • apoptosis/cell death • cataract