Effects of variation in superoxide dismutases (SOD) on oxidative stress and apoptosis in lens epithelium

• Published in: Experimental eye research Vol. 79; no. 6; pp. 859 - 868
• Main Authors: Reddy, V.N., Kasahara, E., Hiraoka, M., Lin, L.-R., Ho, Y.-S.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-12-2004
• Subjects: Animals; apoptosis; Apoptosis - physiology; Caspase 3; Caspases - metabolism; cataract; Cells, Cultured; CuZnSOD; DNA Damage; DNA strand breaks; Epithelial Cells - cytology; Epithelial Cells - enzymology; Gene Expression Regulation, Enzymologic - physiology; gene regulation; human lens epithelium; Hydrogen Peroxide - pharmacology; Lens Capsule, Crystalline - cytology; Lens Capsule, Crystalline - enzymology; Lens Capsule, Crystalline - physiology; Mice; Mice, Knockout; Mice, Transgenic; mitochondria; MnSOD; oxidative stress; Oxidative Stress - physiology; reactive oxygen species; Reactive Oxygen Species - metabolism; Superoxide Dismutase - genetics; Superoxide Dismutase - metabolism; Superoxide Dismutase - physiology; Superoxide Dismutase-1; transgenic mouse models; CuZnSOD; cataract; gene regulation; mitochondria; MnSOD; reactive oxygen species; apoptosis; human lens epithelium; DNA strand breaks; oxidative stress; transgenic mouse models
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2004.04.005

Among the critical antioxidant enzymes that protect the cells against oxidative stress are superoxide dismutases: CuZnSOD (
Sod1) and MnSOD (
Sod2). The latter is also implicated in apoptosis. To determine the importance of these enzymes in protection against reactive oxygen species (ROS) in the lens, we analysed DNA strand breaks in lens epithelium from transgenic and knockout (
Sod1) mice following exposure to H
2O
2 in organ culture. Since
Sod2 knockouts do not survive, comparison was made of lenses of partially-deficient (heterozygote) for
Sod2 and the wild-type controls which have twice the enzyme level. Antioxidant potential of
Sod2 was also studied in human lens epithelial cells (SRA01/04) in which the enzyme was up- and down-regulated by transfection with plasmids containing sense and antisense human cDNA for MnSOD. DNA strand breaks in the epithelium of
Sod1 knockouts and
Sod2 heterozygotes were much greater than in the corresponding wild-type or in transgenic mice over-expressing the enzymes when the lenses were exposed to H
2O
2. The functional role of
Sod2 in apoptosis was examined in cultured human lens epithelial cells. Cells with higher enzyme levels were more resistant to the cytotoxic effects of H
2O
2, O
2
− and UV–B radiation. Furthermore,
Sod2-deficient cells showed dramatic mitochondrial damage, cytochrome C leakage, caspase 3 activation and increased apoptotic cell death when they were challenged with O
2
−. Thus, mitochondrial enzyme (
Sod2) deficiency plays an important role in the initiation of apoptosis in the lens epithelium.