Bacterial RNA and small antiviral compounds activate caspase-1 through cryopyrin/Nalp3

Abstract

Missense mutations in the CIAS1 gene cause three autoinflammatory disorders: familial cold autoinflammatory syndrome, Muckle-Wells syndrome and neonatal-onset multiple-system inflammatory disease 1 . Cryopyrin (also called Nalp3), the product of CIAS1, is a member of the NOD-LRR protein family that has been linked to the activation of intracellular host defence signalling pathways 2,3 . Cryopyrin forms a multi-protein complex termed 'the inflammasome', which contains the apoptosisassociated speck-like protein (ASC) and caspase-1, and promotes caspase-1 activation and processing of pro-interleukin (IL)-1b (ref. 4). Here we show the effect of cryopyrin deficiency on inflammasome function and immune responses. Cryopyrin and ASC are essential for caspase-1 activation and IL-1b and IL-18 production in response to bacterial RNA and the imidazoquinoline compounds R837 and R848. In contrast, secretion of tumournecrosis factor-a and IL-6, as well as activation of NF-kB and mitogen-activated protein kinases (MAPKs) were unaffected by cryopyrin deficiency. Furthermore, we show that Toll-like receptors and cryopyrin control the secretion of IL-1b and IL-18 through different intracellular pathways. These results reveal a critical role for cryopyrin in host defence through bacterial RNA-mediated activation of caspase-1, and provide insights regarding the pathogenesis of autoinflammatory syndromes.To define the role of cryopyrin in inflammatory responses, we generated cryopyrin-deficient mice by homologous recombination using a targeting construct to replace exons I and II of the cryopyrin gene (Cias1), which encode the pyrin domain of cryopyrin that is essential for effector function of the protein ( Supplementary Fig. 1). Cias1 2/2 mice were fertile and appeared healthy when housed in a standard specific pathogen-free environment.We initially investigated the role of cryopyrin in caspase-1-dependent IL-1b secretion using thioglycollate-elicited peritoneal macrophages and bone marrow-derived macrophages (BMDMs) and multiple bacterial and synthetic ligands. Stimulation of peritoneal macrophages or BMDMs with several TLR2 and TLR4 agonists, including diacylated (Pam 2 CGDPKHPHSF) and triacylated (Pam 3 CSK 4 ) synthetic lipopeptides, lipoteichoic acid, highly purified lipopolysaccharide (LPS) and lipid A induced comparable levels of IL-1b in wild-type and Cias1 2/2 macrophages ( Fig. 1a and Supplementary Fig. 2). Similar results were obtained when macrophages were stimulated with bacterial ligands and treated briefly with ATP ( Supplementary Fig. 3), a signal that enhances the secretion of IL-1b in pre-stimulated macrophages 5 . Incubation of macrophages with muramyl dipeptide (MDP) did not induce secretion of IL-1b above background levels in wild-type and Cias1 2/2 macrophages, even after addition of ATP ( Fig. 1a; see also Supplementary Fig. 3). Furthermore, production of interferon-a induced by several viruses was unimpaired in macrophages and dendritic cells from Cias1 2/2 mice ( Supplementary Fig. 4).Notably, secretion o...

Engagement of NOD2 has a dual effect on proIL‐1β mRNA transcription and secretion of bioactive IL‐1β

“…Furthermore, it has to be realized that data from cell lines and overexpression models are not always compatible with data obtained from freshly isolated human cells. In addition, differences exist between NALP3 -/-mice and human cells [12,33,34], and between NOD2 -/-mice and cells obtained from Crohn's disease patients homozygous for the NOD2fs allele [7,35].…”

Inflammatory caspases and inflammasomes: master switches of inflammation

“…In this study, caspase-1 activation was monitored in presence of extracellular ATP, and is therefore likely to depend on P2X 7 activation. 84 Other agents that decrease intracellular potassium levels such as the potassium ionophore nigericine and maitotoxin, a potent marine toxin, depend on the NALP3-based inflammasome for caspase-1 activation. 81 NALP3 and ASC are also required for caspase-1 activation by the Gram-positive bacteria Staphylococcus aureus and Listeria monocytogenes.…”

Aldara activates TLR7-independent immune defence

“…37) are produced upon treatment with Aldara. It was shown that IMQ activates the inflammasome in murine peritoneal macrophages, 38 but such evidence is lacking for keratinocytes. Exposure of primary human keratinocytes to Aldara in vitro induced the release of cleaved caspase-1 (caspase-1 CARD domain), mature IL-1b (IL-1b p17) and IL-18 (IL-18 p17) into the cell-culture supernatant (Fig.…”