Abstract: XU Dan*, LIU Tong-yun, YUAN Rui-hong, TU Ying, GU Hua, HE Li. *Department of Dermatology, First Affiliated Hospital of Kunming Medical University, Kunming 650032, China Corresponding author: HE Li, Email: heli2662@yahoo.com.cn 【Abstract】 Objective To estimate the effect of different doses of ultraviolet （UV） radiation on the proliferation of and apoptosis in kertatinocytes, as well as on the expression of p53, matrix metalloproteinase-2 （MMP2） and -9 （MMP9） in actinic keratosis（AK） lesions and normal human skin. Methods Tissue specimens were obtained from the lesions of 20 patients with AK and sun-exposed normal skin of 20 healthy human subjects, and subjected to an air-exposed culture. Each of the specimens was divided into 4 areas to remain untreated （control area） or be irradiated with UV of 5, 10 and 20 J/cm2 （irradiated areas） for 4 consecutive days. After another 24-hour culture, the tissue cultures were collected followed by the evaluation of apoptosis in and proliferation of keratinocytes by using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling （TUNEL） and Ki-67 staining, and determination of mRNA and protein expressions of p53, MMP2 and MMP9 by using real time PCR and immunohistochemistry respectively. Results A statistical increase was observed in the percentage of apoptotic cells in the normal skin irradiated with UV of 10 and 20 J/cm2 （46.8% ± 2.1% and 56.7% ± 2.4%, both P < 0.05） and in the AK lesions irradiated with UV of 20 J/cm2（43.5% ± 1.5%, P < 0.05） compared with the corresponding unirradiated tissues. The normal skin showed a higher percentage of apoptotic cells than the lesional skin after irradiation with UV of 10 and 20 J/cm2 （both P < 0.05）. The percentage of Ki-67-positive cells was significantly decreased in the normal skin after irradiation with UV of 20 J/cm2 （3.34% ± 0.76%, P < 0.05）, but experienced no statistical changes in the lesional skin after different doses of UV irradiation （all P > 0.05）. There was a statistical elevation in the expression of p53 mRNA （5 J/cm2: 1.106 ± 0.025, 10 J/cm2: 1.259 ± 0.045, 20 J/cm2: 1.425 ± 0.053, all P < 0.05） and protein（10 J/cm2: 0.1169 ± 0.0032, 20 J/cm2: 0.1454 ± 0.0047, both P < 0.05） in the normal skin, but a statistical reduction in the expression of p53 mRNA（10 J/cm2: 0.611 ± 0.050, 20 J/cm2: 0.578 ± 0.070, both P < 0.05） and protein（20 J/cm2: 0.0404 ± 0.0027, P< 0.05） in the lesional skin after irradiation compared with the corresponding unirradiated skin tissues. Further more, a statistical increment was observed in MMP2 mRNA and protein expression in normal skin irradiated with UV of 10 J/cm2 （1.086 ± 0.013, 0.0843 ± 0.0024, respectively, both P < 0.05） and 20 J/cm2 （1.417 ± 0.036, 0.1236 ± 0.0042, respectively, both P < 0.05） and in lesional skin irradiated with UV of 20 J/cm2 （1.296 ± 0.028, 0.0744 ± 0.0032, respectively, both P < 0.05）, as well as in MMP9 mRNA and protein expression in normal skin irradiated with UV of 20 J/cm2 （1.395 ± 0.026, 0.3065 ± 0.0162, respectively, both P < 0.05） and in lesional skin irradiated with UV of 10 J/cm2 （1.298 ± 0.035, 0.0992 ± 0.0053, respectively, both P < 0.05） and 20 J/cm2 （1.286 ± 0.032, 0.1010 ± 0.0063, respectively, both P < 0.05） compared with the corresponding unirradiated tissues. Conclusion Ultraviolet may accelerate the progression of AK by down-regulating p53 expression but up-regulating MMP2 and MMP9 expression. 【Key words】 Actinic keratosis; Ultraviolet rays; Genes，p53; Matrix metalloproteinase 2; Matrix metalloproteinase 9

Key words: Sun protection factor