Silica induces NLRP3 inflammasome activation in human lung epithelial cells

Part Fibre Toxicol. 2013 Feb 12;10:3. doi: 10.1186/1743-8977-10-3.

Abstract

Background: In myeloid cells the inflammasome plays a crucial role in innate immune defenses against pathogen- and danger-associated patterns such as crystalline silica. Respirable mineral particles impinge upon the lung epithelium causing irreversible damage, sustained inflammation and silicosis. In this study we investigated lung epithelial cells as a target for silica-induced inflammasome activation.

Methods: A human bronchial epithelial cell line (BEAS-2B) and primary normal human bronchial epithelial cells (NHBE) were exposed to toxic but nonlethal doses of crystalline silica over time to perform functional characterization of NLRP3, caspase-1, IL-1β, bFGF and HMGB1. Quantitative RT-PCR, caspase-1 enzyme activity assay, Western blot techniques, cytokine-specific ELISA and fibroblast (MRC-5 cells) proliferation assays were performed.

Results: We were able to show transcriptional and translational upregulation of the components of the NLRP3 intracellular platform, as well as activation of caspase-1. NLRP3 activation led to maturation of pro-IL-1β to secreted IL-1β, and a significant increase in the unconventional release of the alarmins bFGF and HMGB1. Moreover, release of bFGF and HMGB1 was shown to be dependent on particle uptake. Small interfering RNA experiments using siNLRP3 revealed the pivotal role of the inflammasome in diminished release of pro-inflammatory cytokines, danger molecules and growth factors, and fibroblast proliferation.

Conclusion: Our novel data indicate the presence and functional activation of the NLRP3 inflammasome by crystalline silica in human lung epithelial cells, which prolongs an inflammatory signal and affects fibroblast proliferation, mediating a cadre of lung diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics
  • Carrier Proteins / immunology*
  • Cell Culture Techniques
  • Cell Line
  • Cell Proliferation / drug effects
  • Dose-Response Relationship, Drug
  • Enzyme-Linked Immunosorbent Assay
  • Epithelial Cells / drug effects*
  • Epithelial Cells / immunology
  • Epithelial Cells / pathology
  • Fibroblasts / drug effects
  • Fibroblasts / immunology
  • Fibroblasts / pathology
  • Humans
  • Inflammasomes / biosynthesis
  • Inflammasomes / genetics
  • Inflammasomes / immunology*
  • Lung / drug effects*
  • Lung / immunology
  • Lung / pathology
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • Reverse Transcriptase Polymerase Chain Reaction
  • Silicon Dioxide / toxicity*
  • Up-Regulation

Substances

  • Carrier Proteins
  • Inflammasomes
  • NLR Family, Pyrin Domain-Containing 3 Protein
  • NLRP3 protein, human
  • Silicon Dioxide