Effects of Ultraviolet Irradiation on Cellular Senescence in Keratinocytes Versus Fibroblasts.

Aging is a biologic process characterized by time-dependent functional declines that are influenced by oxidative stress-induced inflammatory reactions. In particular, ultraviolet (UV) irradiation plays a key role in cellular senescence in photo-aged skin. However, the cellular senescence of epidermal keratinocytes and dermal fibroblasts by UV irradiation may differ depending on the exposure time and dosage of UV irradiation. Therefore, the purpose of the study was to evaluate and compare the effects of UV irradiation on cellular senescence in human epidermal keratinocytes (HaCaT) and human dermal fibroblasts (HDFs). After cell viability test, 200 mJ/cm UV irradiation was used in this study. To evaluate the reactive oxygen species and reactive nitrogen species production, the levels of glutathione (GSH) and nitrite (NO2) were measured. We also performed reverse transcription-polymerase chain reaction, Western blot analysis, and senescence-associated beta-galactosidase assay. An overall decrease in GSH and an increase in NO2 were observed in the HaCaT and HDF cells. However, the time-line and dose-dependent effects varied. Higher expressions of tumor necrosis factor-α, inducible nitric oxide synthase, and interleukin-1β than that of the control group were observed in both cells. The HDF cells showed high levels of matrix metallopeptidase 9 and neutral endopeptidase protein but low levels of SIRT1 and procollagen I. The expression of nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) was increased in the HaCaT cells, but not in the HDF cells. The NF-κB peaked at 1 hour after UV irradiation in the HaCaT cells. The "turning-on" signal was faster in the irradiated HaCaT cells.