title: Cholesterol crystals induce complement-dependent inflammasome activation and cytokine release.
abstract: Inflammation is associated with development of atherosclerosis, and cholesterol crystals (CC) have long been recognized as a hallmark of atherosclerotic lesions. CC appear early in the atheroma development and trigger inflammation by NLRP3 inflammasome activation. In this study we hypothesized whether CC employ the complement system to activate inflammasome/caspase-1, leading to release of mature IL-1β, and whether complement activation regulates CC-induced cytokine production. In this study we describe that CC activated both the classical and alternative complement pathways, and C1q was found to be crucial for the activation. CC employed C5a in the release of a number of cytokines in whole blood, including IL-1β and TNF. CC induced minimal amounts of cytokines in C5-deficient whole blood, until reconstituted with C5. Furthermore, C5a and TNF in combination acted as a potent primer for CC-induced IL-1β release by increasing IL-1β transcripts. CC-induced complement activation resulted in upregulation of complement receptor 3 (CD11b/CD18), leading to phagocytosis of CC. Also, CC mounted a complement-dependent production of reactive oxygen species and active caspase-1. We conclude that CC employ the complement system to induce cytokines and activate the inflammasome/caspase-1 by regulating several cellular responses in human monocytes. In light of this, complement inhibition might be an interesting therapeutic approach for treatment of atherosclerosis.
authors.affiliation: Centre of Molecular Inflammation Research, Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim N-7491, Norway;
authors.forename: Eivind O
authors.initials: EO
authors.lastname: Samstad
authors.forename: Nathalie
authors.initials: N
authors.lastname: Niyonzima
authors.forename: Stig
authors.initials: S
authors.lastname: Nymo
authors.forename: Marie H
authors.initials: MH
authors.lastname: Aune
authors.forename: Liv
authors.initials: L
authors.lastname: Ryan
authors.forename: Siril S
authors.initials: SS
authors.lastname: Bakke
authors.forename: Knut T
authors.initials: KT
authors.lastname: Lappegård
authors.forename: Ole-Lars
authors.initials: OL
authors.lastname: Brekke
authors.forename: John D
authors.initials: JD
authors.lastname: Lambris
authors.forename: Jan K
authors.initials: JK
authors.lastname: Damås
authors.forename: Eicke
authors.initials: E
authors.lastname: Latz
authors.forename: Tom E
authors.initials: TE
authors.lastname: Mollnes
authors.forename: Terje
authors.initials: T
authors.lastname: Espevik
mesh_terms: D015153:Blotting, Western; D020170:Caspase 1 / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism / Q000494:pharmacology*; D003167:Complement Activation / Q000187:drug effects / Q000276:immunology; D015922:Complement C1q / Q000276:immunology / Q000378:metabolism; D003182:Complement C5 / Q000276:immunology / Q000378:metabolism; D015936:Complement C5a / Q000276:immunology / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000187:drug effects / Q000276:immunology; D003171:Complement Pathway, Classical / Q000187:drug effects / Q000276:immunology; D003165:Complement System Proteins / Q000276:immunology* / Q000378:metabolism; D016207:Cytokines / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D058847:Inflammasomes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000276:immunology / Q000378:metabolism; D018613:Microscopy, Confocal; D009000:Monocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis / Q000276:immunology; D017382:Reactive Oxygen Species / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism
chemical_list: D003182:Complement C5; D016207:Cytokines; D058847:Inflammasomes; D053583:Interleukin-1beta; D016177:Macrophage-1 Antigen; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D015922:Complement C1q; D015936:Complement C5a; D003165:Complement System Proteins; D002784:Cholesterol; D020170:Caspase 1