Abstract: Yang Ziliang*, Luo Dan, Qian Qihong, Du Na, Yu Xiuqin, Wang Miaomiao, Min Wei. *Department of Dermatology, First Affiliated Hospital of Soochow University, Suzhou 215006, China Corresponding author: Min Wei, Email: minwei@suda.edu.cn 【Abstract】 Objective To evaluate the protective effect of astragaloside Ⅳ against ultraviolet B （UVB）-induced photodamage to human HaCaT keratinocytes, and to investigate its mechanisms. Methods Cultured immortalized human HaCaT keratinocytes were divided into four groups: blank control group receiving untreated, UVB group irradiated with 50 mJ/cm2 UVB, astragaloside Ⅳ group treated with astragaloside Ⅳ, UVB + astragaloside Ⅳ group treated with astragaloside Ⅳ for 24 hours before and after 50 mJ/cm2 of UVB radiation. The concentration of astragaloside Ⅳ ranged from 10 to 200 mg/L in cell proliferation assay, and according to the results of proliferation assay, 20 mg/L was determined as the optimal concentration in the other assays. At 24 hours after UVB radiation, cell counting kit-8 （CCK8） assay was performed to evaluate cellular proliferative activity, flow cytometry to determine intracellular reactive oxygen species （ROS） levels, and Western blot to measure the expression levels of p53, p38, matrix metalloproteinase-9 （MMP-9） and high mobility group Al （HMGA-1） protein in HaCaT cells. Results Compared with the control group, astragaloside Ⅳ at 10 and 20 mg/L had no inhibitory effect （F = 1.32, P > 0.05）, while astragaloside Ⅳ at 50, 100 and 200 mg/L showed significantly inhibitory effect （F = 20.20, P < 0.05）, on the proliferation of HaCaT cells. In addition, cellular proliferative activity in the UVB group was significantly lower than that in the control group （F = 99.00, P < 0.01）. Compared with the UVB group, cellular proliferative activity increased to different degrees in HaCaT cells treated with both UVB and astragaloside Ⅳ of 10－200 mg/L （F = 19.08, P < 0.01）, with the strongest increase observed in those treated with UVB and astragaloside Ⅳ of 20 mg/L. Further experiments revealed reduced intracellular ROS levels in the UVB + astragaloside Ⅳ （20 mg/L） group compared with the UVB group （t = 21.12, P < 0.01）. Western blot assay showed that the expression levels of p53, p38, MMP-9 and HMGA-1 protein were significantly higher in the UVB group than in the control group （all P < 0.01）, but significantly lower in the UVB + astragaloside Ⅳ （20 mg/L） group than in the UVB group （all P < 0.01）. Conclusion Astragaloside Ⅳ can effectively protect keratinocytes from UVB-induced photodamage.

Key words: Astragalus membranaceus, Ultraviolet rays, Keratinocytes, Reactive oxygen species