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The Nucleotide-Binding Domain and Leucine-Rich Repeat Protein–3 Inflammasome Is Not Activated in Airway Smooth Muscle Upon Toll-Like Receptor–2 Ligation

Authors: Hatem Alkhouri; Hanna Im; Mostafizur Rahman; Nowshin N. Rumzhum; Jeremy A. Hirota; Christopher D. Pascoe; Brian G. Oliver; +3 Authors

The Nucleotide-Binding Domain and Leucine-Rich Repeat Protein–3 Inflammasome Is Not Activated in Airway Smooth Muscle Upon Toll-Like Receptor–2 Ligation

Abstract

Inflammasomes have emerged as playing key roles in inflammation and innate immunity. A growing body of evidence has suggested that the nucleotide-binding domain and leucine-rich repeat protein-3 (NLRP3) inflammasome is important in chronic airway diseases such as asthma and chronic obstructive pulmonary disease. Inflammasome activation results, in part, in pro-IL-1β processing and the secretion of the proinflammatory cytokine IL-1β. Because asthma exacerbations are associated with elevated concentrations of secreted IL-1β, we addressed whether the NLRP3 inflammasome is activated under in vitro conditions that mimic infectious exacerbations in asthma. Primary cultures of airway smooth muscle (ASM) cells were treated with infectious stimuli (mimicked using the Toll-like receptor-2 agonist Pam3CSK4, a synthetic bacterial lipopeptide). Whereas Pam3CSK4 robustly up-regulated ASM cytokine expression in response to TNF-α and significantly enhanced IL-1β mRNA expression, we were unable to detect IL-1β in the cell supernatants. Thus, IL-1β was not secreted and therefore was unable to act in an autocrine manner to promote the amplification of ASM inflammatory responses. Moreover, Toll-like receptor-2 ligation did not enhance NLRP3 or caspase-1 expression in ASM cells, and NLRP3 and caspase-1 protein were not present in the ASM layer of tracheal sections from human donors. In conclusion, these data demonstrate that the enhanced synthetic function of ASM cells, induced by infectious exacerbations of airway inflammation, is NLRP3 inflammasome-independent and IL-1β-independent. Activation of the NLRP3 inflammasome by invading pathogens may prove cell type-specific in exacerbations of airway inflammation in asthma.

Keywords

Inflammation, Inflammasomes, Nucleotides, Tumor Necrosis Factor-alpha, Caspase 1, Interleukin-1beta, Myocytes, Smooth Muscle, Muscle, Smooth, Toll-Like Receptor 2, Protein Structure, Tertiary, Lipopeptides, NLR Family, Pyrin Domain-Containing 3 Protein, Humans, Carrier Proteins, Cells, Cultured, Protein Binding

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
7
Average
Average
Average
bronze