title: Bacterial membrane vesicles deliver peptidoglycan to NOD1 in epithelial cells.
abstract: Gram-negative bacterial peptidoglycan is specifically recognized by the host intracellular sensor NOD1, resulting in the generation of innate immune responses. Although epithelial cells are normally refractory to external stimulation with peptidoglycan, these cells have been shown to respond in a NOD1-dependent manner to Gram-negative pathogens that can either invade or secrete factors into host cells. In the present work, we report that Gram-negative bacteria can deliver peptidoglycan to cytosolic NOD1 in host cells via a novel mechanism involving outer membrane vesicles (OMVs). We purified OMVs from the Gram-negative mucosal pathogens: Helicobacter pylori, Pseudomonas aeruginosa and Neisseria gonorrhoea and demonstrated that these peptidoglycan containing OMVs upregulated NF-kappaB and NOD1-dependent responses in vitro. These OMVs entered epithelial cells through lipid rafts thereby inducing NOD1-dependent responses in vitro. Moreover, OMVs delivered intragastrically to mice-induced innate and adaptive immune responses via a NOD1-dependent but TLR-independent mechanism. Collectively, our findings identify OMVs as a generalized mechanism whereby Gram-negative bacteria deliver peptidoglycan to cytosolic NOD1. We propose that OMVs released by bacteria in vivo may promote inflammation and pathology in infected hosts.
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Maria
authors.initials: M
authors.lastname: Kaparakis
authors.forename: Lynne
authors.initials: L
authors.lastname: Turnbull
authors.forename: Leticia
authors.initials: L
authors.lastname: Carneiro
authors.forename: Stephen
authors.initials: S
authors.lastname: Firth
authors.forename: Harold A
authors.initials: HA
authors.lastname: Coleman
authors.forename: Helena C
authors.initials: HC
authors.lastname: Parkington
authors.forename: Lionel
authors.initials: L
authors.lastname: Le Bourhis
authors.forename: Abdulgader
authors.initials: A
authors.lastname: Karrar
authors.forename: Jérôme
authors.initials: J
authors.lastname: Viala
authors.forename: Johnson
authors.initials: J
authors.lastname: Mak
authors.forename: Melanie L
authors.initials: ML
authors.lastname: Hutton
authors.forename: John K
authors.initials: JK
authors.lastname: Davies
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Crack
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Hertzog
authors.forename: Dana J
authors.initials: DJ
authors.lastname: Philpott
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Girardin
authors.forename: Cynthia B
authors.initials: CB
authors.lastname: Whitchurch
authors.forename: Richard L
authors.initials: RL
authors.lastname: Ferrero
mesh_terms: D000818:Animals; D004847:Epithelial Cells / Q000276:immunology*; D005260:Female; D006090:Gram-Negative Bacteria / Q000276:immunology*; D006367:HeLa Cells; D016480:Helicobacter pylori / Q000276:immunology; D006801:Humans; D008297:Male; D051379:Mice; D016328:NF-kappa B / Q000276:immunology*; D009343:Neisseria / Q000276:immunology; D053474:Nod1 Signaling Adaptor Protein / Q000276:immunology*; D010457:Peptidoglycan / Q000276:immunology / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000276:immunology; D022142:Secretory Vesicles / Q000276:immunology / Q000378:metabolism*
chemical_list: D016328:NF-kappa B; C119067:NOD1 protein, human; D053474:Nod1 Signaling Adaptor Protein; D010457:Peptidoglycan