title: Identification of bacterial muramyl dipeptide as activator of the NALP3/cryopyrin inflammasome.
abstract: Activation of caspase-1 and subsequent processing and secretion of the pro-inflammatory cytokine IL-1beta is triggered upon assembly of the inflammasome complex. It is generally believed that bacterial lipopolysaccharides (LPS) are activators of the inflammasome through stimulation of Toll-like receptor 4 (TLR4). Like TLRs, NALP3/Cryopyrin, which is a key component of the inflammasome, contains Leucine-Rich-Repeats (LRRs). LRRs are frequently used to sense bacterial components, thus raising the possibility that bacteria directly activate the inflammasome. Here, we show that bacterial peptidoglycans (PGN), but surprisingly not LPS, induce NALP3-mediated activation of caspase-1 and maturation of proIL-1beta. Activation is independent of TLRs because the PGN degradation product muramyl dipeptide (MDP), which is not sensed by TLRs, is the minimal-activating structure. Macrophages from a patient with Muckle-Wells syndrome, an autoinflammatory disease associated with mutations in the NALP3/Cryopyrin gene, show increased IL-1beta secretion in the presence of MDP. The activation of the NALP3-inflammasome by MDP may be the basis of the potent adjuvant activity of MDP.
authors.affiliation: Department of Biochemistry, University of Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Martinon
authors.forename: Laetitia
authors.initials: L
authors.lastname: Agostini
authors.forename: Etienne
authors.initials: E
authors.lastname: Meylan
authors.forename: Jürg
authors.initials: J
authors.lastname: Tschopp
mesh_terms: D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000378:metabolism*; D000686:Amyloidosis / Q000378:metabolism; D015551:Autoimmunity / Q000276:immunology; D002352:Carrier Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism*; D002478:Cells, Cultured; D002850:Chromatography, Gel; D006801:Humans; D007249:Inflammation / Q000276:immunology / Q000378:metabolism*; D007375:Interleukin-1 / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D010457:Peptidoglycan / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D013577:Syndrome; D014581:Urticaria / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D007375:Interleukin-1; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D010457:Peptidoglycan; D000119:Acetylmuramyl-Alanyl-Isoglutamine; D020170:Caspase 1