Objective: To investigate the effect of different dosages of ultraviolet A (UVA) on the proliferation and inducible nitric oxide synthase (iNOS)/nitric oxide (NO) system of human skin fibroblasts and to study the mechanism of skin photoaging.
Methods: Fibroblasts from normal skin cultured in vitro were irradiated with 1, 5, and 10 J/cm(2) of UVA, respectively. The proliferation activity, expression of iNOS mRNA/protein and NO production of human skin fibroblasts at different time points after irradiation of different dosages of UVA were measured by MTT assay, RT-PCR, Western blotting, and Griess reaction, respectively.
Results: The survival rate of normal fibroblasts with time increase during 72 h. Low level of iNOS mRNA/protein expression and NO production was detected in normal human skin fibroblasts. But at each time point after 5 and 10 J/cm(2) dosage of UVA, the decrease of cell survival rate and the increase of iNOS mRNA/protein expression and NO production became more significant than those in the control group at the same time and 1 J/cm(2) UVA-irradiated group. There were significant differences (P<0.01 or P<0.05), which were most significant at 24 h after UVA irradiation. There was significant difference compared with that at 48 h and 72 h after the same UVA dosage (P<0.01).
Conclusion: UVA can inhibit the proliferation activity of human skin fibroblasts. It might be related to the up-regulation of iNOS gene expression and the over-secretion of NO induced by UVA.