Abstract: 【Abstract】 Objective To investigate the counteractive effect of mouse dermal fibroblasts（MdFBs） during their adipogenic differentiation against Staphylococcus aureus infection, and to explore its mechanisms. Methods MdFBs were obtained from newborn C57BL/6 mice, and their adipogenic differentiation was induced by culture in an adipogenic medium for 48 hours. Real-time fluorescence-based quantitative PCR （RT-PCR） was performed to determine the mRNA expression of cathelicidin antimicrobial peptide （CAMP） on days 0 -6 during the adipogenic differentiation of MdFBs, and Western blot analysis to determine the protein expression of CAMP in the culture supernatant of MdFBs during their adipogenic differentiation. MdFBs were divided into 4 groups: co-stimulation group stimulated by S. aureus suspensions and cultured in an adipogenic medium, adipogenic control group cultured in an adipogenic medium, S. aureus-stimulation group stimulated by S. aureus suspensions and cultured in a common medium, and control group stimulated by phosphate-buffered saline and cultured in a common medium; Western blot analysis and RT-PCR were conducted to determine the protein and mRNA expression of CAMP. S. aureus (5 × 104 CFU/ml) was cultured with the culture supernatant of MdFBs after 5-day adipogenic differentiation (adipogenic group), and the growth activity was evaluated every 2 hours during 10 - 24 hours after the start of co-culture; S. aureus cultured with the culture supernatant of MdFBs in a common medium served as the normal control group, and that cultured with cell-free culture supernatant served as the negative control group. Differences between groups were assessed using unpaired t-test or analysis of variance. Results Significant differences were observed in the relative mRNA expression of CAMP among different time points (days 0, 1, 2, 4, and 6) during the adipogenic differentiation of MdFBs （1.14 ± 0.74, 68.04 ± 12.72, 683.12 ± 38.06, 1 390.68 ± 226.21, 454.57 ± 204.12, F = 50.08，P < 0.001）; the CAMP mRNA expression was significantly higher on days 1, 2, 4, and 6 than on day 0 （t = 9.09, 31.03, 10.63, 3.85, respectively, all P < 0.05）, and showed an initial rise and subsequent fall during days 0 - 6. The CAMP protein expression in the culture supernatant of MdFBs peaked on days 2 -5 and subsequently decreased. Significant differences were observed in the mRNA and protein expression of CAMP among the control group, S. aureus-stimulation group, adipogenic control group and co-stimulation group （mRNA: 0.08 ± 0.02, 0.38 ± 0.10, 0.49 ± 0.11, 0.80 ± 0.03, respectively, F = 43.25, P < 0.05; protein: 0.433 ± 0.176, 0.574 ± 0.176, 1.007 ± 0.176, 1.217 ± 0.176, respectively, F = 46.79, P < 0.05）, and the relative mRNA and protein expression of CAMP was significantly higher in the co-stimulation group than in the adipogenic control group, S. aureus-stimulation group and control group （all P < 0.05）. At 10 hours during culture, the growth activity of S. aureus was significantly lower in the adipogenic group （0.053 ± 0.015） than in the normal control group and negative control group （0.109 ± 0.015, 0.106 ± 0.015, t = 11.30, 13.26, respectively, both P < 0.05）; during 10 - 24 hours, the growth activity of S. aureus also showed a significant decrease in the adipogenic group compared with the normal control group and negative control group （all P < 0.05）. Conclusion MdFBs secreted CAMP during the adipogenic differentiation, and could inhibit the proliferation of S. aureus.

Key words: Fibroblasts, Mice, inbred C57BL, Staphylococcus aureus, Adipogenesis, Innate immunity, Cathelicidin antimicrobial peptide