Abstract

Objective

This study was designed to evaluate whether p62/SQSTM1 (hereafter referred to as p62) is involved in the immune response of macrophages against challenge by Candida albicans (C. albicans).

Methods

We cultured bone marrow-derived macrophages (BMDMs) to investigate the immune response to challenge by C. albicans. The p62 gene was knocked down by transfection with p62 small interfering RNA (siRNA) in the p62 siRNA group. BMDMs transfected with nonsense siRNA served as the negative control (NC) group. These two groups of BMDMs were challenged with C. albicans in vitro. We detected p62 expression through quantitative reverse transcription PCR and western blotting. The phagocytosis ability of BMDMs was evaluated by flow cytometry and microscopic examination using an Olympus FV1000 laser scanning confocal microscope. Moreover, we determined the level of reactive oxygen species (ROS) in BMDMs. The mRNA levels of proinflammatory cytokines were determined by quantitative reverse transcription PCR.

Results

After stimulation by C. albicans, the relative expression of p62 mRNA was increased in a dose-dependent manner, the relative expression of p62 and the ratio of BMDMs to C. albicans is 1.893 ± 0.2156 (1:1, P < 0.05), 2.873 ± 0.4787 (1:3, P < 0.05) and 3.556 ± 0.2892 (1:5, P < 0.01). The p62 protein level was also increased. After transfection with p62 siRNA, the mRNA and protein levels of p62 were significantly decreased in BMDMs (P < 0.05). After 0.5, 1 and 2 hours of co-culture of BMDMs with C. albicans, flow cytometry showed that the phagocytosis rates of C. albicans by BMDMs were significantly lower in the p62 siRNA group than in the NC group (39.70 ± 1.69% vs. 55.23 ± 0.72%, 46.70 ± 0.89% vs. 60.80 ± 1.78%, 51.90 ± 0.98% vs. 64.43 ± 2.0%, respectively, all P < 0.05). Consistent results were seen in the production of ROS (4269 ± 392.6 vs. 13426 ± 1859.7, 4967 ± 721.2 vs. 13687 ± 2611.2, 7647 ± 1950.0 vs. 17719 ± 1814.2, respectively, all P < 0.05). The ROS levels were higher in BMDMs of the NC group than in BMDMs transfected with p62 siRNA at 0.5, 1, and 2 hours after treatment with C. albicans. BMDMs was co-cultured with C. albicans for 4 and 12 hours, the mRNA levels of interleukin-1β and interleukin-18 in NCs were also higher than p62 siRNA group, interleukin-1β: (6.14 ± 1.63 vs. 12.12 ± 0.54, 8.81 ± 0.86 vs. 26.2 ± 4.67, respectively, all P < 0.05), IL-18: (0.38 ± 0.02 vs. 0.97 ± 0.06, 0.44 ± 0.02 vs. 2.23 ± 0.46, respectively, all P < 0.05).

Conclusion

p62 plays an important role in the process of phagocytosis in BMDMs challenged by C. albicans through ROS production and expression of proinflammatory cytokines.