EC-SOD induces apoptosis through COX-2 and galectin-7 in the epidermis

Extracellular superoxide dismutase (EC-SOD) is an anti-oxidant enzyme found in the extracellular matrix of tissues, and plays an important role in the prevention of many diseases caused by oxidative stress. However, other functions of EC-SOD in epidermis are not well known.

We investigated the functions of EC-SOD in epidermis using keratinocyte cell line and EC-SOD transgenic mice.

Expression of galectin-7 in pEC-SOD transfected cells or skin of EC-SOD transgenic mice was detected by western blot analysis. The percentage of apoptotic cells was determined by propidium iodide staining and subsequent FACS analysis. COX-2 siRNA or scrambled siRNA was transfected into HaCaT cells and western blot analysis was performed to detect pro-apoptotic protein levels.

The epidermis of EC-SOD transgenic mice was thinner than wild type mice. In addition, we showed that the thin epidermis of EC-SOD transgenic mice results from the apoptosis of epidermal cells. To elucidate which molecules are involved in EC-SOD-induced apoptosis, we utilized two-dimensional electrophoresis; the results showed that the epidermis of EC-SOD transgenic mice produces more galectin-7, a pro-apoptotic factor, than the wild type. Furthermore, we showed that the transfection of EC-SOD-expressing plasmids induces the production of galectin-7, and pro-apoptotic proteins in keratinocytes. This suggests that EC-SOD induces apoptosis through increased galectin-7 expression. Finally, we demonstrated that EC-SOD-induced galectin-7 results from the production of COX-2.

Our results imply that EC-SOD plays a role not only as a reactive oxygen species scavenger, but also as a pro-apoptotic factor via COX-2/galectin-7 pathways in the epidermis.