Gardnerella vaginalis induces NLRP3 inflammasome-mediated pyroptosis in macrophages and THP-1 monocytes

The vagina is colonized by a variety of microbes that serve vital roles in the maintenance of vaginal health. The purpose of the present study was to explore the underlying mechanism by which Gardnerella vaginalis (GV) can induce bacterial vaginosis (BV). The viability of primary mouse macrophages and THP-1 cells was detected using a Cell Counting Kit-8 assay. Lactate dehydrogenase and caspase-1 activity in the culture medium of macrophages and THP-1 cells were measured using a colorimetric assay and a caspase-1 activity assay kit, respectively. In the macrophages and THP-1 cells, the levels of TNF-alpha, IL-1 beta and IL-18 were detected using ELISA whereas reactive oxygen species (ROS) levels were detected using flow cytometry. The pyroptosis of macrophages and THP-1 cells was detected using calcein-AM/PI double staining. Expression of proteins associated with the nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain-containing protein 3 inflammasome (NLRP3), including NLRP3, apoptosis associated speck-like protein (ASC), caspase-1 and pro-caspase-1, were measured by western blotting and reverse transcription-quantitative PCR. GV significantly inhibited cell viability and increased LDH activity in macrophages and THP-1 cells. In addition, GV markedly promoted the production of TNF-alpha, IL-1 beta, IL-18 and ROS by macrophages and THP-1 cells. GV significantly promoted caspase-1 activation-mediated pyroptosis in macrophages and THP-1 cells. Treatment with GV significantly increased the protein and mRNA expression of NLRP3, ASC and caspase-1 in macrophages and THP-1 cells. To conclude, data from the present study suggest that G. vaginalis can induce BV by promoting NLRP3 inflammasome-mediated pyroptosis, which provides one of the molecular mechanisms by which G. vaginalis can induce BV.