A preliminary study on Candida albicans-induced pyroptosis of murine bone marrow-derived macrophages / 中华皮肤科杂志

ABSTRACT

Objective:To investigate the effect of Candida albicans ( C. albicans) on pyroptosis of murine bone marrow-derived macrophages (BMDMs) . Methods:Live-cell imaging was used to observe morphologic changes of in vitro C. albicans-infected BMDMs (multiplicity of infection [MOI] = 50) so as to evaluate whether pyroptosis occurred. Cultured BMDMs were divided into a control group and a C. albicans group, which were treated with phosphate-buffered saline and C. albicans suspensions respectively for 6 hours; then, real-time fluorescence-based quantitative PCR was performed to determine the mRNA expression of NOD-like receptor pyrin domain containing 3 (NLRP3), interleukin (IL) -1β and IL-18, and Western blot analysis to determine the protein expression and cleavage levels of NLRP3, caspase-1 and gasdermin D (GSDMD). BMDMs were cultured with C. albicans suspensions for different durations (0, 10, 15, 20, and 25 hours), and enzyme-linked immunosorbent assay was conducted to detect secretion levels of IL-1β and IL-18. Cultured wild-type BMDMs and GSDMD-knockout BMDMs were treated with C. albicans suspensions for 15 minutes, and then rates of phagocytosis of C. albicans by wild-type BMDMs and GSDMD-knockout BMDMs were estimated by flow cytometry; after 6-hour treatment with C. albicans, flow cytometry and lactate dehydrogenase (LDH) release assay were performed to assess mortality rates of wild-type BMDMs and GSDMD-knockout BMDMs. In addition, some wild-type BMDMs and GSDMD-knockout BMDMs were separately divided into blank control group, control group, maximum enzyme activity-sample control group, IL-1β alone group, C. albicans alone group, and IL-1β + C. albicans group, and cell mortality rates were detected by the LDH release assay after treatment with IL-1β and/or C. albicans. Statistical analysis was carried out by using unpaired t test, Kruskal-Wallis test, analysis of variance, and other statistical methods. Results:After in vitro treatment with C. albicans, swelling and ballooning with large bubbles blowing from the plasma membrane occurred in BMDMs, suggesting the occurrence of cell pyroptosis; compared with the control group, the C. albicans group showed significantly increased mRNA expression levels of NLRP3 and IL-1β after 6-hour treatment with C. albicans ( t = 13.02, 17.51, respectively, P = or < 0.001), but no significant change in the IL-18 mRNA expression level ( P = 0.486), and Western blot analysis showed that C. albicans could increase the expression of NLRP3 inflammasomes, as well as cleaved caspase-1 and GSDMD. After the treatment with C. albicans for different durations (0, 10, 15, 20, and 25 hours), the secretion level of IL-1β by BMDMs gradually increased over time ( H = 12.90, P = 0.012), while the secretion level of IL-18 did not significantly change ( F = 0.48, P = 0.753), and the secretion level of IL-1β was significantly lower in the GSDMD-knockout BMDM group than in the wild-type BMDM group ( F = 24.22, P = 0.008). After 15-minute in vitro treatment with C. albicans, the phagocytosis rate of C. albicans was significantly lower in the GSDMD-knockout BMDM group (50.3% ± 1.10%) than in the wild-type BMDM group (58.53% ± 1.19%, t = 5.09, P = 0.007) ; after 6-hour treatment with C. albicans, the cell mortality rate was significantly higher in the GSDMD-knockout BMDM group than in the wild-type BMDM group (flow cytometry 38.40% ± 0.50% vs. 34.37% ± 0.52%, t = 4.72, P = 0.009; LDH release assay 22.52% ± 0.18% vs. 12.48% ± 0.15%, t = 42.36, P < 0.001) ; the cell mortality rates of wild-type BMDMs and GSDMD-knockout BMDMs both significantly decreased in the IL-1β + C. albicans groups compared with the C. albicans groups (both P < 0.001) . Conclusion:Pyroptosis could be induced in murine BMDMs after C. albicans infection, which promotes the release of IL-1β and may reduce the mortality rate of macrophages by improving their immune activity.