Abstract: Objective To observe the effect of solar infrared ray (IR) radiation on the expressions of c-Jun and collagens I and III
in cultured human skin fibroblasts (HSFs) and explore the molecular mechanism by which IR radiation causes aging of the
skin. Methods Primarily cultured HSFs exposed to IR radiation were examined for changes of the cell viability with MTT
assay. The mRNA and protein expressions of c-Jun and collagens I and III was detected with real-time quantitative PCR and
immunocytochemistry. Results MTT assay showed that IR irradiation caused inhibition of cell proliferation compared with the
control cells. The mRNA and protein expression of collagen I was decreased significantly by IR irradiation with the increase of
the irradiation dose (P<0.01). HSFs irradiated by IR for 12 h showed a dose-dependent reduction of the expression of collagen
type III mRNA and protein (P<0.05, P<0.01), but the expression increased dose-dependently in response to IR exposure for 24 h
(P<0.05 or 0.01). IR irradiation enhanced the mRNA and protein expression of c-Jun in a dose-dependence manner (P<0.05 or
0.01). Conclusion IR irradiation can increase the expression of c-Jun, inhibit the expression of collagen I, and cause disturbance
in collagen III expression in human skin fibroblasts, which may be one of the mechanism of IR radiation to initiate and
promote skin photoaging.