Molecular events associated with apoptosis and proliferation induced by ultraviolet-B radiation in the skin of hairless mice

Background: It is recognized that UV radiation produced apoptotic cells (sun burn cells) in the epidermis of mice. However, the relationship between apoptosis and cell proliferation after UV exposure in the skin of hairless mice are still unclear. Objective: To investigate the effects of ultraviolet (UV) radiation on molecular events associated with apoptosis and proliferation in SKH1-hr mouse skin. Methods: Mice were irradiated with daily UVB exposure of 0. 1 or 0.25 J/cm² for 14 days. The skin tissues were analyzed at 2 and 24 h after the end irradiation for the presence of apoptotic cells and Bromodeoxyuridine (BrdU)-positive cells. We measured the expression of p53, p21, bcl-2, bax and E2F-1. Results: The results indicated that UVB irradiation caused to increase apoptotic cells in the epidermis of mice. The expression of p53 and p21 was increased at 2 and 24 h after irradiation compared with the control. UV radiation induced high levels of bax at 2 and 24 h after irradiation with a concomitant decrease in bcl-2 expression. The expression of E2F-1 in the skin was also increased at 2 and 24 h after irradiation. Coinciding with these changes, BrdU positive cells increased at 2 and 24 h after UVB exposure at the epidermis of hairless mice, which observed the apoptotic expression. Conclusion: These results suggest that UVB irradiation of mouse skin induces apoptosis and is mediated by the p53/p21/E2F-1/bax pathway and that the dead cells are replaced by hyperproliferative cells, leading to epidermal hyperplasia.