The NLRP3 inflammasome is activated by nanoparticles through ATP, ADP and adenosine

Our plain-English summary of The NLRP3 inflammasome is activated by nanoparticles through ATP, ADP and adenosine, by L. Baron, A. Gombault, M. Fanny, et al (Cell Death & Disease, 2015).

The study

• Authors: L. Baron, A. Gombault, M. Fanny, B. Villeret, F. Savigny, N. Guillou, C. Panek, M. Le Bert, V. Lagente, F. Rassendren, N. Riteau, I. Couillin
• Journal: Cell Death & Disease
• Published: 2015;6(2):e1629
• Cited by: 181 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The NLR pyrin domain containing 3 (NLRP3) inflammasome is a major component of the innate immune system, but its mechanism of activation by a wide range of molecules remains largely unknown. Widely used nano-sized inorganic metal oxides such as silica dioxide (nano-SiO2) and titanium dioxide (nano-TiO2) activate the NLRP3 inflammasome in macrophages similarly to silica or asbestos micro-sized particles. By investigating towards the molecular mechanisms of inflammasome activation in response to nanoparticles, we show here that active adenosine triphosphate (ATP) release and subsequent ATP, adenosine diphosphate (ADP) and adenosine receptor signalling are required for inflammasome activation. Nano-SiO2 or nano-TiO2 caused a significant increase in P2Y1, P2Y2, A2A and/or A2B receptor expression, whereas the P2X7 receptor was downregulated. Interestingly, IL-1β secretion in response to nanoparticles is increased by enhanced ATP and ADP hydrolysis, whereas it is decreased by adenosine degradation or selective A2A or A2B receptor inhibition. Downstream of these receptors, our results show that nanoparticles activate the NLRP3 inflammasome via activation of PLC-InsP3 and/or inhibition of adenylate cyclase (ADCY)-cAMP pathways. Finally, a high dose of adenosine triggers inflammasome activation and IL-1β secretion through adenosine cellular uptake by nucleotide transporters and by its subsequent transformation in ATP by adenosine kinase. In summary, we show for the first time that extracellular adenosine activates the NLRP3 inflammasome by two ways: by interacting with adenosine receptors at nanomolar/micromolar concentrations and through cellular uptake by equilibrative nucleoside transporters at millimolar concentrations. These findings provide new molecular insights on the mechanisms of NLRP3 inflammasome activation and new therapeutic strategies to control inflammation.

In plain English

This was a laboratory study of how silica dioxide (nano-SiO2) and titanium dioxide (nano-TiO2) nanoparticles activate the NLRP3 inflammasome; asbestos was mentioned only as background, as a micro-sized particle previously shown to activate the inflammasome, and was not tested here. The authors used human THP1 macrophages and mouse bone-marrow-derived macrophages (including cells from P2X7-, P2X4- and P2Y2-deficient mice), plus intranasal instillation of nanoparticles (5 mg/kg) in C57BL/6 mice. Nano-SiO2 and nano-TiO2, but not nano-ZnO, triggered active ATP release in primed THP1 cells peaking at 3 to 4 hours, just before mature IL-1beta secretion. The connexin/pannexin channel blocker carbenoxolone, the connexin channel blocker flufenamic acid, the P2 receptor antagonists suramin and oATP, adenosine deaminase, and A2A, A2B or A3 receptor inhibitors each reduced IL-1beta; P2X7 or P2X4 deficiency gave no significant impairment, and the P2Y6 and P2Y12 antagonists had no effect, while the P2Y1 antagonist reduced IL-1beta induced by nano-SiO2 but not nano-TiO2. Adenosine at millimolar concentrations alone induced ATP release and IL-1beta, while the non-degradable analogue NECA did not. In mice, adenosine deaminase treatment reduced nano-SiO2-induced neutrophil influx, KC, MMP-9, MPO and IL-1beta.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study: in vitro experiments in human THP1 macrophages and mouse bone-marrow-derived macrophages, with an in vivo mouse lung instillation model
• Who was studied: Human monocyte/macrophage THP1 cells (including shRNA lines against NLRP3, ASC or lamin control), primary mouse bone-marrow-derived macrophages from C57BL/6 and P2X7-, P2X4- or P2Y2-deficient mice, and C57BL/6 mice aged eight to ten weeks (CNRS, Orleans, France)
• Exposure: Silica dioxide (nano-SiO2) and titanium dioxide (nano-TiO2) nanoparticles, with nano-ZnO as a comparison; 125 to 500 micrograms per ml in vitro and 5 mg/kg in vivo; plus ATP, ADP, adenosine, NECA, inosine and various receptor and enzyme inhibitors
• Main results:
  • In primed human THP1 macrophages, nano-SiO2 and nano-TiO2, but not nano-ZnO, caused active ATP release peaking at 3 to 4 hours, preceding mature IL-1beta secretion
  • In primed THP1 cells, the connexin/pannexin channel blocker carbenoxolone and the connexin channel blocker flufenamic acid reduced both ATP release and IL-1beta secretion after nano-SiO2 or nano-TiO2
  • In mouse BMDMs, the P2 receptor antagonists suramin and oATP dose-dependently reduced IL-1beta induced by nano-SiO2 or nano-TiO2
  • In mouse BMDMs, deficiency in P2X7 or P2X4 receptors did not significantly impair nanoparticle-induced IL-1beta production
  • In mouse BMDMs, the P2Y1 antagonist MRS2500 decreased IL-1beta induced by nano-SiO2 but not by nano-TiO2, while the P2Y6 antagonist MRS2578 and the P2Y12 antagonist MRS2395 had no effect
  • In mouse BMDMs, adenosine deaminase greatly reduced IL-1beta secretion induced by nano-SiO2 or nano-TiO2, whereas apyrase (hydrolysing ATP and ADP) slightly increased it
  • In mouse BMDMs, specific A2A, A2B and A3 receptor inhibitors decreased nanoparticle-induced IL-1beta secretion, while the A1 antagonist DPCPX had no effect
  • In THP1 cells, high (millimolar) doses of adenosine alone triggered ATP release and IL-1beta secretion, while equivalent doses of the non-degradable analogue NECA and of inosine did not
  • In mice, treatment with adenosine deaminase reduced nano-SiO2-induced neutrophil influx, KC and MMP-9 in BAL fluid and MPO and IL-1beta in lung at 6 hours
  • In mouse BMDMs, the PLC-beta inhibitor U73122 blocked nanoparticle-induced IL-1beta secretion
  • In mouse BMDMs, the adenylate cyclase activator forskolin dose-dependently inhibited nanoparticle-induced IL-1beta, while the adenylate cyclase inhibitor SQ22536 had no effect
• The authors' conclusion: The authors concluded that after tissue injury adenosine may activate the inflammasome through membrane receptor signalling, and that in chronic inflammation accumulated adenosine may act via cellular uptake and conversion into intracellular ATP, amplifying or prolonging inflammasome activation, suggesting possible therapeutic approaches
• Limitations the authors state:
  • The authors could not measure a significant ATP increase in supernatants of stimulated mouse bone-marrow-derived macrophages, unlike in the human THP1 line
  • The authors describe the proposed mechanism of sustained inflammasome activation by accumulating adenosine as based on their in vitro results

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Inflammation.

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