Low-Dose UVA Radiation-Induced Adaptive Response in Cultured Human Dermal Fibroblasts

Objective. To investigate the mechanism of the adaptive response induced by low-dose ultraviolet A (UVA) radiation. Methods. Cultured dermal fibroblasts were irradiated by a lethal dose of UVA (86.4 J/cm2) with preirradiation of single or repetitive low dose of UVA (7.2 J/cm2). Alterations of cellular morphology were observed by light microscope and electron microscope. Cell cycle and cellular apoptosis were assayed by flow cytometer. The extent of DNA damage was determined by single-cell gel electrophoresis (SCGE). Results. The cultured dermal fibroblasts, with pretreatment of single or repetitive irradiation of 7.2 J/cm2 UVA relieved toxic reaction of cellular morphology and arrest of cell cycle, decreased apoptosis ratio, reduced DNA chain breakage, and accelerated DNA repair caused by subsequent 86.4 J/cm2 UVA irradiation. Compared with nonpretreatment groups, all those differences were significant (P<0.01 or P<0.05). Conclusions. The adaptation reaction might depend on the accumulated dose of low-dose UVA irradiation. Low-dose UVA radiation might induce adaptive response that may protect cultured dermal fibroblasts from the subsequent challenged dose of UVA damage. The duration and protective capability of the adaptive reaction might be related to the accumulated dose of low-dose UVA Irradiation