UV-induced apoptosis in rat skin.

Sunburn cells appear in the epidermis after UVB irradiation and are histologically suggested to be keratinocytes undergoing apoptosis. We here show a known biochemical process of apoptosis, genomic DNA fragmentation, in rat skin. UVB irradiation induced sunburn cells in the epidermis of rat skin at a lower dosage and the cleavage of genome DNA to nucleosomal size units at dosages of more than 0.3 J/cm2. The fragmented DNA observed could be driven from the epidermis though the involvement of DNA in dermal cells cannot be neglected. PUVA treatment also induced sunburn cells and the fragmentation of genome DNA. The extent of DNA fragmentation by UVB irradiation was enhanced depending on the dosage and peaked at 12-24 h after the irradiation. The induction of the DNA fragmentation observed in this study indicates the presence of a common pathway related to the DNA damage-induced apoptosis in the skin, and might become a useful marker in the course of in vivo studies on the physiological role of apoptotic process in the skin.