Trichomonas vaginalis Induces IL-1 beta Production in a Human Prostate Epithelial Cell Line by Activating the NLRP3 Inflammasome Via Reactive Oxygen Species and Potassium Ion Efflux

Abstract

BACKGROUND. Trichomonas vaginalis is a sexually transmitted protozoan parasite that causes vaginitis in women, and urethritis and prostatitis in men. IL-1 beta is synthesized as immature pro-IL-1 beta, which is cleaved by activated caspase-1. Caspase-1 is, in turn, activated by a multi-protein complex known as an inflammasome. In this study, we investigated the inflammatory response of a prostate epithelial cell line (RWPE-1) to T. vaginalis and, specifically, the capacity of T. vaginalis to activate the NLRP3 inflammasome. METHODS. RWPE-1 cells were stimulated by live T. vaginalis, and subsequent expression of pro-IL-1 beta, IL-1 beta, NLRP3, ASC and caspase-1 was determined by real-time PCR and Western blotting. IL-1 beta and caspase-1 production was also measured by ELISA. To evaluate the effects of NLRP3 and caspase-1 on IL-1 beta production, the activated RWPE-1 cells were transfected with small interfering RNAs to silence the NLRP3 and caspase-1 genes. Activation of the NLRP3 inflammasome was observed by fluorescence microscopy. Intracellular reactive oxygen species (ROS) were evaluated by spectrofluorometry. RESULTS. When RWPE-1 cells were stimulated with live T. vaginalis, the mRNA and protein expression of IL-1 beta, NLRP3, ASC, and caspase-1 increased. Moreover, silencing of NLRP3 and caspase-1 attenuated T. vaginalis-induced IL-1 beta secretion. The NADPH oxidase inhibitor DPI and high extracellular potassium ion suppressed the production of IL-1 beta, caspase-1, and the expression of NLRP3 and ASC proteins. The specific NF-kappa B inhibitor, Bay 11-7082, inhibited IL-1 beta production, and also inhibited the production of caspase-1, ASC and NLRP3 proteins. CONCLUSIONS. T. vaginalis induces the formation of the NLRP3 inflammasome in human prostate epithelial cells via ROS and potassium ion efflux, and this results in IL-1 beta production. This is the first evidence for activation of the NLRP3 inflammasome in the inflammatory response by prostate epithelial cells infected with T. vaginalis.