Abstract: 【Abstract】 Objective To investigate the effect of pyrroloquinoline quinone （PQQ） on age-related skin aging in mice and its mechanisms. Methods Thirty Kunming mice were fed in specific pathogen-free condition, and equally divided into 3 groups: young group was fed with a normal diet for 8 months, old group was fed with a normal diet for 20 months to establish a mouse model of natural aging, and PQQ group was fed with PQQ-containing forages （4 milligrams of PQQ per kilogram of normal forages） for 20 months. After feeding, the mouse dorsal skin tissues were obtained, hematoxylin and eosin （HE） staining was performed to measure the epidermal and dermal thickness, Masson staining to detect changes in total skin collagen, immunohistochemical study to detect changes in expression of the proliferation marker Ki67, transmission electron microscopy to detect changes in autophagosomes in the mouse skin, and Western blot analysis to determine the expression of autophagy-related proteins Beclin1, LC3Ⅱ/LC3Ⅰ, and p62. Statistical analysis was carried out by using one-way analysis of variance for intergroup comparisons followed by least significant difference （LSD）-t test for multiple comparisons. Results HE and Masson staining showed that the epidermal and dermal thickness and the percentage of area of dermis stained positive for collagen among the total area of dermis in the tested region were significantly lower in the old group （15.67 ± 0.36 μm, 87.95 ± 11.86 μm, 22.12% ± 1.72%, respectively） than in the young group （29.37 ± 0.25 μm, 264.93 ± 10.34 μm, 45.03% ± 1.54%, respectively, all P＜0.05）, and significantly higher in the PQQ group （25.53 ± 0.47 μm, 145.01 ± 9.71 μm, 31.17% ± 1.20%, respectively） than in the old group （all P＜0.05）. Immunohistochemical study revealed that the expression of Ki67 was significantly lower in the old group （13.74% ± 3.06%） than in the young group （29.07% ± 2.79%, P＜0.05） and PQQ group （21.20% ± 1.47%, P＜0.05）. Transmission electron microscopy showed that the number of autophagosomes in the skin was significantly higher in the old group than in the young group （P＜0.05）, but significantly lower in the PQQ group than in the old group （P＜0.05）. As Western blot analysis revealed, the old group showed significantly decreased Beclin1 expression and LC3Ⅱ/LC3Ⅰratio, but significantly increased p62 expression compared with the young group（all P＜0.05）; compared with the old group, the PQQ group showed significantly increased Beclin1 expression and LC3Ⅱ/LC3Ⅰratio, but significantly decreased p62 expression（all P＜0.05）. Conclusion PQQ can delay the age-related skin aging in mice, likely by increasing the proliferative capacity of mouse skin cells and promoting skin autophagy.

Key words: Skin aging, PQQ cofactor, Cell proliferation, Autophagy, Collagen