[Mycoplasma pneumoniae toxin of community-acquired respiratory distress syndrome (CARDS) promotes autophagy of THP-1 cells and activates NLRP3 inflammasomes].

Objective To study the mechanism of community-acquired respiratory distress syndrome (CARDS) toxin of Mycoplasma pneumoniae (Mp) inducing THP-1 cell autophagy and the activation of pyrin domain containing the nucleotide-binding oligomerization domain-like receptor family 3 (NLRP3). Methods The recombinant CARDS (rCARDS) Mp toxin was obtained by Escherichia coli expression system, and THP-1 cells were treated with the toxin at the concentrations of 5 and 10 μg/mL for 20, 40 minutes, 1, 2 and 3 hours. The expression of autophagy-related proteins beclin-1, LC3II and P62 of THP-1 cells were determined by Western blot; the gene expression of NLRP3, caspase-1 and interleukin 1β (IL-1β) were detected by real-time quantitative PCR; and the level of reactive oxygen species (ROS) of THP-1 cells was tested by DCFH-DA staining. Results Compared with the control group, when treated with rCARDS toxin for 1 hour, the expression of beclin-1, LC3 and P62 significant increased. When treated with rCARDS toxin for 2 and 3 hours, the expression of beclin-1, LC3 and P62 significant decreased. When treated with rCARDS toxin for 20 and 40 minutes, the NLRP3 gene expression had no significant difference between the groups treated with the concentration of 5 and 10 μg/mL rCARDS toxin. NLRP3 gene expression in the groups treated with rCARDS toxin was higher than that in the control group in the whole experiment. When treated with rCARDS toxin for 1 hour and 2 hours, the NLRP3 gene expression of the 10 μg/mL group was significant higher than that in the 5 μg/mL group. When treated with rCARDS toxin for 3 hours, the NLRP3 gene expression of the 10 μg/mL group and 5 μg/mL group was lower than that in the groups treated for 2 hours. When treated with rCARDS toxin for 40 minutes, 1 hour and 2 hours, the caspase-1 mRNA expression of rCARDS toxin groups was higher than that in the control group. When treated for 40 minutes, 1, 2 and 3 hours, the caspase-1 gene expression of the 10 μg/mL group was significantly higher than that in the 5 μg/mL group. Compared to the control group, when treated with rCARDS toxin for 20 and 40 minutes, IL-1β gene expression had no significant difference. When the time prolonged to 1 hour and 3 hours, the levels of IL-1β mRNA expression and ROS had a significant increase in a dose-dependent manner in all groups. Conclusion CARDS Mp toxin can activate NLRP3 inflammasomes and induce cell autophagy in THP-1 cells.