The role of estrogen and superoxide dismutase in cataractogenesis

Cataract is an opacification of the eye lens, constituting the major cause of blindness globally. Oxidative stress is a key factor in the formation of cataract and female gender is a known risk factor for age-related cataract. The aim of this thesis was to investigate the role of estrogen and the antioxidant enzyme superoxide dismutase (SOD) in cataractogenesis. Human lens epithelial cells (HLECs) obtained during cataract surgery at the Department of Ophthalmology at Sahlgrenska university hospital in Mölndal (SU/M) were used to study the effects of the major estrogen, 17β-estradiol (E2), on proliferation, cell viability, intracellular redox status, SOD and estrogen receptors (ERs). H2O2-induced oxidative stress was used to study the antioxidative properties of E2 in HLECs. Two genetic association studies were performed to investigate if genetic variations in estrogen-related and in SOD genes were associated with increased risk of cataract in an Estonian population, consisting of 492 patients with age-related cataract and 185 controls. Patients and controls were also recruited from the Eye Clinic at SU/M for a study on possible correlations between E2 levels and SOD activity. The effects of E2 at pharmacological concentrations in HLECs were; increased apoptosis and cell death, reduced cell viability and proliferation as well as increased intracellular levels of reactive oxygen species (ROS). At lower (physiologic) concentrations, increased proliferation, reduced cell death, stabilization of mitochondrial membrane potential and protection against oxidative stress by reduction of ROS were observed. At these concentrations total SOD activity was increased and protein expression levels of ERs were altered. However, no change in neither gene nor protein expression levels of SODs was seen. A linear correlation between increasing age and declining E2 serum levels was evident in cataract patients and controls. Men exhibited higher E2 levels compared to postmenopausal women. However, no correlation between serum levels of E2 and SOD activity was found in our study subjects. The genetic association studies showed that genetic variations in SOD and estrogen-related genes were not associated with increased risk of cataract. In conclusion, no correlation between SOD activity and E2 serum levels in cataract patients and controls was found and genetic variations in SOD or estrogen-related genes showed no association with increased risk of cataract in our subjects. The observed increase in SOD activity after exposure to E2 and reduction of ROS after preincubation with E2 in oxidatively stressed cells, support a role for E2 in the protection against oxidative stress in HLECs. The antioxidative effect of E2 in lens epithelial cells appears to be induced by non-genomic mechanisms

Effects of 17-Estradiol on Activity, Gene and Protein Expression of Superoxide Dismutases in Primary Cultured Human Lens Epithelial Cells

Purpose: Protective effects of estradiol against H2O2-induced oxidative stress have been demonstrated in lens epithelial cells. The purpose of this study was to investigate the effects of 17β-estradiol (E2) on the different superoxide dismutase (SOD) isoenzymes, SOD-1, SOD-2, and SOD-3, as well as estrogen receptors (ERs), ERα and ERβ, in primary cultured human lens epithelial cells (HLECs). Materials and methods: HLECs were exposed to 0.1 µM or 1 µM E2 for 1.5 h and 24 h after which the effects were studied. Protein expression and immunolocalization of SOD-1, SOD-2, ERα, and ERβ were studied with Western blot and immunocytochemistry. Total SOD activity was measured, and gene expression analyses were performed for SOD1, SOD2, and SOD3. Results: Increased SOD activity was seen after 1.5 h exposure to both 0.1 µM and 1 µM E2. There were no significant changes in protein or gene expression of the different SODs. Immunolabeling of SOD-1 was evident in the cytosol and nucleus; whereas, SOD-2 was localized in the mitochondria. Both ERα and ERβ were immunolocalized to the nucleus, and mitochondrial localization of ERβ was evident by colocalization with MitoTracker. Both ERα and ERβ showed altered protein expression levels after exposure to E2. Conclusions: The observed increase in SOD activity after exposure to E2 without accompanying increase in gene or protein expression supports a role for E2 in protection against oxidative stress mediated through non-genomic mechanisms