Ultraviolet radiation increases tropoelastin mRNA expression in the epidermis of human skin in vivo

Photoaged skin contains elastotic materials in the upper reticular dermis. This phenomenon is commonly known as solar elastosis. Little is known about the mechanisms leading to the accumulation of elastotic materials in photo aged skin, however. In this study, it was demonstrated that ultraviolet irr adiation induced tropoelastin mRNA expression in the keratinocytes of human skin in vivo and also in cultured human keratinocytes by in situ hybridiza tion acid reverse transcriptase polymerase chain reaction. It was also show n by northern blot analysis (n = 5) that there were increased tropoelastin mRNA levels in the forearm (sun-exposed) skin of elderly persons, compared with upper-inner arm (sun-protected) skin of the same individuals. As demon strated by in situ hybridization compared to sun-protected skin (upper-inne r arm) (n = 5), tropoelastin mRNA expression in photoaged skin was higher i n keratinocytes as well as in fibroblasts. Therefore, our results suggest t hat keratinocytes are another source of tropoelastin production after acute and chronic ultraviolet irradiation in human skin in vivo.