title: Serum amyloid A activates the NLRP3 inflammasome via P2X7 receptor and a cathepsin B-sensitive pathway.
abstract: Serum amyloid A (SAA) is an acute-phase protein, the serum levels of which can increase up to 1000-fold during inflammation. SAA has a pathogenic role in amyloid A-type amyloidosis, and increased serum levels of SAA correlate with the risk for cardiovascular diseases. IL-1β is a key proinflammatory cytokine, and its secretion is strictly controlled by the inflammasomes. We studied the role of SAA in the regulation of IL-1β production and activation of the inflammasome cascade in human and mouse macrophages, as well as in THP-1 cells. SAA could provide a signal for the induction of pro-IL-1β expression and for inflammasome activation, resulting in secretion of mature IL-1β. Blocking TLR2 and TLR4 attenuated SAA-induced expression of IL1B, whereas inhibition of caspase-1 and the ATP receptor P2X(7) abrogated the release of mature IL-1β. NLRP3 inflammasome consists of the NLRP3 receptor and the adaptor protein apoptosis-associated speck-like protein containing CARD (a caspase-recruitment domain) (ASC). SAA-mediated IL-1β secretion was markedly reduced in ASC(-/-) macrophages, and silencing NLRP3 decreased IL-1β secretion, confirming NLRP3 as the SAA-responsive inflammasome. Inflammasome activation was dependent on cathepsin B activity, but it was not associated with lysosomal destabilization. SAA also induced secretion of cathepsin B and ASC. In conclusion, SAA can induce the expression of pro-IL-1β and activation of the NLRP3 inflammasome via P2X(7) receptor and a cathepsin B-sensitive pathway. Thus, during systemic inflammation, SAA may promote the production of IL-1β in tissues. Furthermore, the SAA-induced secretion of active cathepsin B may lead to extracellular processing of SAA and, thus, potentially to the development of amyloid A amyloidosis.
authors.affiliation: Wihuri Research Institute, 00140 Helsinki, Finland. kari.eklund@wri.fi
authors.forename: Katri
authors.initials: K
authors.lastname: Niemi
authors.forename: Laura
authors.initials: L
authors.lastname: Teirilä
authors.forename: Jani
authors.initials: J
authors.lastname: Lappalainen
authors.forename: Kristiina
authors.initials: K
authors.lastname: Rajamäki
authors.forename: Marc H
authors.initials: MH
authors.lastname: Baumann
authors.forename: Katariina
authors.initials: K
authors.lastname: Öörni
authors.forename: Henrik
authors.initials: H
authors.lastname: Wolff
authors.forename: Petri T
authors.initials: PT
authors.lastname: Kovanen
authors.forename: Sampsa
authors.initials: S
authors.lastname: Matikainen
authors.forename: Kari K
authors.initials: KK
authors.lastname: Eklund
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D004151:Dipeptides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D058847:Inflammasomes / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D034622:RNA Interference; D058486:Receptors, Purinergic P2X7 / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000685:Serum Amyloid A Protein / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: C400541:CA 074 methyl ester; D002352:Carrier Proteins; D004151:Dipeptides; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D058486:Receptors, Purinergic P2X7; D011994:Recombinant Proteins; D000685:Serum Amyloid A Protein; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D002401:Cathepsin B; D020170:Caspase 1