Extracellular superoxide dismutase tissue distribution and the patterns of superoxide dismutase mRNA expression following ultraviolet irradiation on mouse skin

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Abstract
Superoxide dismutases (SODs) are believed to play a crucial role in protecting cells against oxygen toxicity. There are three forms of SOD: cytosolic Cu–Zn SOD, mitochondrial Mn SOD, and extracellular SOD (EC SOD). Extracellular SOD is primarily a tissue enzyme, but the role of EC SOD in skin is unclear. Therefore, this study investigated the distribution of EC SOD in the skin using immunohistochemistry and examining the patterns of EC SOD gene expression following ultraviolet (UV) irradiation in comparison with those of Cu–Zn SOD and Mn SOD in mouse dorsal skin using Northern blot analysis. Immunohistochemical analysis showed that EC SOD was abundantly located in the epidermis as well as in the dermis, but the gene expression of EC SOD mRNA was more abundant in the dermis than in the epidermis. The gene expression levels of all three types of SODs after UV irradiation were induced differently according to the type and UV irradiation dose. The EC SOD mRNA expression level was increased relatively later than that of Cu–Zn SOD and Mn SOD. The EC SOD mRNA level was significantly higher at 6 h and 48 h after UVA irradiation and psoralen plus ultraviolet-A treatment, respectively. Ultraviolet-B irradiation increased the EC SOD mRNA expression level, with maximum at 48 h. These suggest that EC SOD participates in the majority of antioxidant systems in the skin, and it may have different defensive roles from Cu–Zn SOD and Mn SOD against UV-induced injury of the skin.