title: Oxidative metabolism enables Salmonella evasion of the NLRP3 inflammasome.
abstract: Microbial infection triggers assembly of inflammasome complexes that promote caspase-1-dependent antimicrobial responses. Inflammasome assembly is mediated by members of the nucleotide binding domain leucine-rich repeat (NLR) protein family that respond to cytosolic bacterial products or disruption of cellular processes. Flagellin injected into host cells by invading Salmonella induces inflammasome activation through NLRC4, whereas NLRP3 is required for inflammasome activation in response to multiple stimuli, including microbial infection, tissue damage, and metabolic dysregulation, through mechanisms that remain poorly understood. During systemic infection, Salmonella avoids NLRC4 inflammasome activation by down-regulating flagellin expression. Macrophages exhibit delayed NLRP3 inflammasome activation after Salmonella infection, suggesting that Salmonella may evade or prevent the rapid activation of the NLRP3 inflammasome. We therefore screened a Salmonella Typhimurium transposon library to identify bacterial factors that limit NLRP3 inflammasome activation. Surprisingly, absence of the Salmonella TCA enzyme aconitase induced rapid NLRP3 inflammasome activation. This inflammasome activation correlated with elevated levels of bacterial citrate, and required mitochondrial reactive oxygen species and bacterial citrate synthase. Importantly, Salmonella lacking aconitase displayed NLRP3- and caspase-1/11-dependent attenuation of virulence, and induced elevated serum IL-18 in wild-type mice. Together, our data link Salmonella genes controlling oxidative metabolism to inflammasome activation and suggest that NLRP3 inflammasome evasion promotes systemic Salmonella virulence.
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine; and 2 Immunology Graduate Group and 3 Cell and Molecular Biology Graduate Group, University of Pennsylvania, Kennett Square, PA 19104.
authors.forename: Meghan A
authors.initials: MA
authors.lastname: Wynosky-Dolfi
authors.forename: Annelise G
authors.initials: AG
authors.lastname: Snyder
authors.forename: Naomi H
authors.initials: NH
authors.lastname: Philip
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Doonan
authors.forename: Maya C
authors.initials: MC
authors.lastname: Poffenberger
authors.forename: Daina
authors.initials: D
authors.lastname: Avizonis
authors.forename: Erin E
authors.initials: EE
authors.lastname: Zwack
authors.forename: Amber M
authors.initials: AM
authors.lastname: Riblett
authors.forename: Baofeng
authors.initials: B
authors.lastname: Hu
authors.forename: Till
authors.initials: T
authors.lastname: Strowig
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
authors.forename: Russell G
authors.initials: RG
authors.lastname: Jones
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Freedman
authors.forename: Igor E
authors.initials: IE
authors.lastname: Brodsky
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D058947:Bacterial Secretion Systems; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D002952:Citric Acid Cycle; D005798:Genes, Bacterial / Q000235:genetics; D057131:Immune Evasion / Q000276:immunology*; D007109:Immunity; D058847:Inflammasomes / Q000378:metabolism*; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D012481:Salmonella Infections, Animal / Q000276:immunology / Q000473:pathology; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; D058947:Bacterial Secretion Systems; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D058847:Inflammasomes; C512299:Ipaf protein, mouse; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D017382:Reactive Oxygen Species; D007521:Isocitrate Dehydrogenase; D002950:Citrate (si)-Synthase; D000154:Aconitate Hydratase