Abstract: Jia Xiaoxiao, Hu Wenting, Wang Min, Hua You, Gao Yali, Geng Qingwei, Li Liuyu, Song Xiuzu Department of Dermatology, Hangzhou Third Hospital, Zhejiang Chinese Medical University, Hangzhou 310009, China Corresponding author: Song Xiuzu, Email: songxiuzu@sina.com 【Abstract】 Objective To evaluate the effect of tea polyphenol epigallocatechin gallate（EGCG）on ultraviolet B （UVB）-induced skin pigmentation, transfer and degradation of melanosomes in mice, and to explore the role of autophagy in the mechanism of melanosome degradation. Methods A total of 32 ears from 16 female C57/BL6 mice were randomly and equally divided into 4 groups: acetone control group topically treated with acetone solution daily, EGCG group topically treated with 10 g/L EGCG acetone solution daily, UVB irradiation group irradiated with 500 mJ/cm2 UVB once a day and 2 hours later topically treated with acetone solution, UVB + EGCG group irradiated with 500 mJ/cm2 UVB once a day and 2 hours later topically treated with EGCG acetone solution. Ten days later, all the mice were sacrificed, and skin tissue samples were collected from the ears. Transmission electron microscopy was performed to observe ultrastructural changes of melanosomes and autophagosomes, immunohistochemical study to measure of protease-activated receptor 2 （PAR2） and microtubule-associated protein light chain 3 （LC3） in the epidermis, and Western blot analysis to determine the protein of PAR2, Ras-related protein Rab27a and LC3 in the epidermis. Results There was a significant difference in the number of melanosomes and autophagosomes among the acetone control group, EGCG group, UVB irradiation group and UVB + EGCG group （H = 12.249, 13.888, respectively, both P < 0.05）. Compared with the acetone control group, the UVB irradiation group showed significantly increased number of melanosomes （1.85 ± 0.32 vs. 1.00 ± 0.41, P < 0.05）and autophagosomes （1.94 ± 0.64 vs.1.00 ± 0.46, P < 0.05） in epidermal keratinocytes in mouse skin. Compared with the UVB irradiation group, the UVB + EGCG group showed significantly decreased number of melanosomes（1.30 ± 0.44, P < 0.05）, but significantly increased number of autophagosomes（3.03 ± 0.75, P < 0.05）. Immunohistochemical study showed a significant difference in the level of PAR2 in the epidermis among the 4 groups （H = 18.700, P < 0.05）, and the of PAR2 was significantly lower in the UVB + EGCG group than in the UVB irradiation group （7.94 ± 4.57 vs. 12.54 ± 3.07, Z = 2.143, P < 0.05）. However, the 4 groups all showed a low level of LC3, and there was no significant difference among the 4 groups （H = 5.051, P > 0.05）. Western blot analysis revealed significant differences in the protein of PAR2 and Rab27a, as well as in the LC3-Ⅱ/LC3-Ⅰratio, among the 4 groups（F = 18.739, 25.967, 24.022, respectively, all P < 0.05）. Compared with the UVB irradiation group, the UVB + EGCG group showed significantly decreased of PAR2 （0.91 ± 0.54 vs. 3.12 ± 0.61, P < 0.05） and Rab27a （0.99 ± 0.16 vs. 1.42 ± 0.07, P < 0.05）, but significantly increased LC3-Ⅱ/LC3-Ⅰratio （1.67 ± 0.08 vs. 1.24 ± 0.07, P < 0.05）. Conclusion Topical EGCG treatment can effectively suppress UVB-induced skin pigmentation, which may be related to the inhibition of melanosome transfer and promotion of melanosome autophagy.