Effects of crocidolite asbestos on human bronchoepithelial-dependent fibroblast stimulation in coculture: the role of IL-6 and GM-CSF

Our plain-English summary of Effects of crocidolite asbestos on human bronchoepithelial-dependent fibroblast stimulation in coculture: the role of IL-6 and GM-CSF, by D.S. Lang, H. Schocker, S. Hockertz (Toxicology, 2001).

The study

• Authors: D.S. Lang, H. Schocker, S. Hockertz
• Journal: Toxicology
• Published: 2001;159(1-2):81-98
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cocultures of human pulmonary epithelial cells (BEAS-2B) and lung fibroblasts (WISTAR-38), representing two cell types of central regulatory potential in (chronic) lung disease, were used as an in vitro model to study the role of interleukin 6 (IL-6) and of granulocyte macrophage-colony stimulating factor (GM-CSF) in early fibrogenesis. For this purpose, epithelial cells were pre-exposed to UICC crocidolite asbestos fibers or titanium dioxide (TiO2) particles for 96 h and subsequently cocultured with fibroblasts for additional 72 h. Gene expression of IL-6 or GM-CSF in both cell types as well as of alpha1 procollagens types I and III in fibroblasts was determined by RT-PCR. Synthesis of IL-6, GM-CSF or collagen I was quantified using IL-6 bioassay or ELISA tests, respectively. Both mediators were directly induced in bronchoepithelial cells by crocidolite but not by TiO2. Likewise, steady-state mRNA levels of procollagens as well as collagen synthesis were upregulated in cocultured fibroblasts. As a result of coculture, cytokine concentrations were synergistically enhanced and further increased by crocidolite in a dose-dependent manner. Suppression of cytokine induction by corresponding neutralizing antibodies consistently abrogated collagen enhancement. Direct stimulation of fibroblast monocultures with recombinant human IL-6 or GM-CSF significantly increased collagen synthesis and transcription in a dose-dependent manner. Thus, our results demonstrate that crocidolite selectively stimulated production of IL-6 and GM-CSF in bronchoepithelial cells. In epithelial-fibroblast interactions, these mediators appear to play a key role in regulating fibroblast activity, indicating a close correlation between these cytokines and the fibrogenic potential of particulates.

In plain English

This was a laboratory (in vitro) study, not a study of people. The authors cocultured a human bronchial epithelial cell line (BEAS-2B) grown on membranes with human foetal lung fibroblasts (WISTAR-38) embedded in collagen gels. Only the epithelial cells were pre-exposed, for 96 hours, to UICC crocidolite asbestos fibres or to titanium dioxide (TiO2) particles. The particles were then removed and the cells were cocultured with the fibroblasts for a further 72 hours. Crocidolite, but not TiO2, raised epithelial gene expression of IL-6 and GM-CSF (1.5- and 2-fold above controls) and secretion of both cytokines, and coculture amplified secretion further. In the cocultured fibroblasts, procollagen type III and TGF beta 1 transcription rose 1.7- and 1.3-fold above controls. Neutralising IL-6 abolished the collagen increases, but anti-GM-CSF did not abolish the collagen type I increases. Recombinant IL-6 or GM-CSF alone raised fibroblast collagen synthesis and transcription. The authors concluded that these cytokines appear closely involved in asbestos-induced fibrosis.

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: In vitro cell culture experiment using indirect cocultures of two human lung cell lines, with particle exposure, RT-PCR, cytokine assays, antibody neutralisation and recombinant cytokine stimulation
• Who was studied: Human bronchial epithelial cell line BEAS-2B (passages 41-49) and human diploid embryonic lung fibroblast line WISTAR-38, both from ATCC, cultured in the authors' laboratory in Hamburg, Germany
• Exposure: UICC standard reference crocidolite asbestos fibres or titanium dioxide (TiO2, anatase) particles applied to the epithelial cells for 96 h at 2.2 and 11 micrograms/cm2 (crocidolite) and 4.4 and 22 micrograms/cm2 (TiO2). The article prints these as 'mg/cm2' because the micro symbol was lost.
• Main results:
  • In the bronchoepithelial cells, crocidolite pre-exposure raised IL-6 and GM-CSF gene expression 1.5-fold and 2-fold respectively above control values, in a dose-dependent manner
  • TiO2 pre-treatment produced no such change in cytokine mRNA in the epithelial cells
  • Coculture itself raised secreted cytokine levels above those of epithelial monocultures: 5-6-fold for GM-CSF and 16-18-fold for IL-6, across all asbestos dose levels
  • In the cocultured fibroblasts, alpha1 (III) procollagen and TGF beta 1 transcription rose 1.7-fold and 1.3-fold above controls
  • Neutralising antibody against IL-6 in the cocultures abolished the crocidolite-related rise in collagen type I production and gene expression in the fibroblasts
  • Anti-GM-CSF antibody, even at the highest dose, did not block the fibre-related increase of collagen type I in the fibroblasts
  • Adding recombinant human IL-6 directly to fibroblast monocultures increased collagen gene expression and synthesis
  • Recombinant human GM-CSF, at concentrations on average 100 times lower than those used for IL-6, also caused similar dose-dependent increases in the fibroblast monocultures
  • Cell injury was low in all treated cultures: LDH release stayed below 10% of maximal release
• The authors' conclusion: The authors concluded that their results suggest IL-6 and GM-CSF are closely involved in the pathogenesis of asbestos-induced fibrosis and may act as key mediators stimulating collagen synthesis
• Limitations the authors state:
  • The authors noted considerable variability in the measured collagen concentrations
  • The authors noted substantial variability in fibroblast cell densities among experiments
  • Coculture alone appeared to induce cytokine mRNA in the cocultured fibroblasts almost to its maximum, so crocidolite-related increases were concealed
  • The authors stated that further research is needed to determine whether such correlations generally determine the fibrotic potential of environmental substances

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Crocidolite, Fibroblast, Macrophage, UICC, Collagen, Cytokine, Fibrogenic.

Related studies

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• Lung mesothelial cell and fibroblast responses to pleural and alveolar macrophage supernatants and to lavage fluids from crocidolite-exposed rats — I.Y. Adamson, H. Prieditis, et al. (1997)
• Crocidolite asbestos and SV40 are cocarcinogens in human mesothelial cells and in causing mesothelioma in hamsters — B. Kroczynska, R. Cutrone, et al. (2006)
• Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos — S.A. Golladay, S.H. Park, et al. (1997)
• Crocidolite asbestos inhibits pentose phosphate oxidative pathway and glucose 6-phosphate dehydrogenase activity in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2002)
• Role of alphavbeta5 integrin receptor in endocytosis of crocidolite and its effect on intracellular glutathione levels in human lung epithelial (A549) cells — P. Pande, T.A. Mosleh, et al. (2006)

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