Publication: Priming is dispensable for NLRP3 inflammasome activation in human monocytes in vitro
Authors
Martín Sánchez, María Rosario Fátima ; Gritsenko, Anna ; Yu, Shi ; Díaz del Olmo, Inés ; Nichols, Eva María ; Davis, Daniel M. ; Brough, David ; López Castejón, Gloria
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Publisher
Frontiers Media
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DOI
https://doi.org/10.3389/fimmu.2020.565924
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info:eu-repo/semantics/article
Description
Abstract
Interleukin (IL)-18 and IL-1b are potent pro-inflammatory cytokines that contribute toinflammatory conditions such as rheumatoid arthritis and Alzheimer’s disease. They areproduced as inactive precursors that are activated by large macromolecular complexescalled inflammasomes upon sensing damage or pathogenic signals. NLRP3inflammasome activation is regarded to require a priming step that causes NLRP3 andIL-1b gene upregulation, and also NLRP3 post-translational licencing. A subsequentactivation step leads to the assembly of the complex and the cleavage of pro-IL-18 andpro-IL-1b by caspase-1 into their mature forms, allowing their release. Here we show thathuman monocytes, but not monocyte derived macrophages, are able to form canonicalNLRP3 inflammasomes in the absence of priming. NLRP3 activator nigericin caused theprocessing and release of constitutively expressed IL-18 in an unprimed setting. This wasmediated by the canonical NLRP3 inflammasome that was dependent on K + and Cl−efflux and led to ASC oligomerization, caspase-1 and Gasdermin-D (GSDMD) cleavage.IL-18 release was impaired by the NLRP3 inhibitor MCC950 and by the absence ofNLRP3, but also by deficiency of GSDMD, suggesting that pyroptosis is the mechanism ofrelease. This work highlights the readiness of the NLRP3 inflammasome to assemble inthe absence of priming in human monocytes and hence contribute to the very early stagesof the inflammatory response when IL-1b has not yet been produced. It is important toconsider the unprimed setting when researching the mechanisms of NLRP3 activation, asto not overshadow the pathways that occur in the absence of priming stimuli, which mightonly enhance this response.
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Citation
Front. Immunol., 30 September 2020, Volume 11 - 565924
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