IRF8 Regulates Gram-Negative Bacteria-Mediated NLRP3 Inflammasome Activation and Cell Death

Inflammasomes are intracellular signaling complexes that are assembled in response to a variety of pathogenic or physiologic stimuli to initiate inflammatory responses. Ubiquitously present LPS in Gram-negative bacteria induces NLRP3 inflammasome activation that requires caspase-11. We have recently demonstrated that IFN regulatory factor (IRF) 8 was dispensable for caspase-11-mediated NLRP3 inflammasome activation during LPS transfection; however, its role in Gram-negative bacteria-mediated NLRP3 inflammasome activation remains unknown. In this study, we found that IRF8 promotes NLRP3 inflammasome activation in murine bone marrow-derived macrophages (BMDMs) infected with Gram-negative bacteria such as Citrobacter rodentium, Escherichia coli, or Pseudomonas aeruginosa mutant strain Delta popB. Moreover, BMDMs deficient in IRF8 showed substantially reduced caspase-11 activation and gasdermin D cleavage, which are required for NLRP3 inflammasome activation. Mechanistically, IRF8-mediated phosphorylation of IRF3 was required for Ifnb transcription, which in turn triggered the caspase-11-dependent NLRP3 inflammasome activation in the infected BMDMs. Overall, our findings suggest that IRF8 promotes NLRP3 inflammasome activation during infection with Gram-negative bacteria.