Alveolar cell stretching in the presence of fibrous particles induces interleukin-8 responses

Our plain-English summary of Alveolar cell stretching in the presence of fibrous particles induces interleukin-8 responses, by A. Tsuda, B.K. Stringer, S.M. Mijailovich, et al (American Journal of Respiratory Cell and Molecular Biology, 1999).

The study

• Authors: A. Tsuda, B.K. Stringer, S.M. Mijailovich, R.A. Rogers, K. Hamada, M.L. Gray
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1999;21(4):455-62
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Inhalation of fibrous particulates is strongly associated with lung injury, but the molecular and cellular mechanisms that could explain the fiber-induced pathogenesis are not fully understood. We hypothesized that the physical stress exerted on the alveolar epithelium by the deposited fibers is greatly enhanced by the tidal cyclic motion of the epithelial cells that is associated with breathing, and that this initial mechanical interaction triggers a subsequent cell response. To test this hypothesis, we developed a dynamic model of fiber-induced cell injury using a cell-stretcher device. We exposed a cyclically stretched monolayer of the human alveolar epithelial cell line A549 to glass or crocidolite asbestos fibers for 8 h and then measured the production of the proinflammatory cytokine interleukin (IL)-8 as a readout of fiber-induced cell injury. Cyclic stretching significantly increased IL-8 production in the fiber-treated cultures, suggesting that the physical stress on the cells caused by the fibers was indeed enhanced by the motion. Coating of the asbestos fibers with fibronectin, a glycoprotein abundant in the alveolar lining fluid, further increased the fiber-induced cell response when the cells were cyclically stretched. This response was, however, significantly reduced by introducing into the culture medium, before fiber treatment, soluble RGD (Arg-Gly-Asp)-containing peptides, which specifically block binding to integrin receptors upon RGD attachment. These results suggested that adhesive interactions between protein-coated fibers and cell surface molecules are involved in the fiber-induced pathogenic process. Our novel findings indicate the importance of physical insults in fiber-induced cell stress, and bring to the forefront the need to study the mechanisms involved in this process.

In plain English

This laboratory study used a human lung cell line (A549, from an alveolar epithelial tumor) grown on a stretchable membrane. To mimic breathing, some cultures were stretched by 5% ten times per minute for 8 hours, and others were left still. Cells were exposed to UICC crocidolite asbestos or glass fibers (MMVF-10), plain or coated with fibronectin, a protein found in lung lining fluid. The authors measured interleukin-8 (IL-8), an inflammatory signal, as a marker of cell stress. Stretching alone did not raise IL-8. Glass fibers caused a slight, not statistically significant rise in still cells but a significant rise in stretched cells. Crocidolite raised IL-8 in still cells, and stretching significantly increased this. Fibronectin coating greatly increased the asbestos response but had no appreciable effect on the glass response. In stretched cells, RGD peptides, which block integrin receptors on the cell surface, reduced IL-8 from coated asbestos by 70%. The authors concluded that the lung's breathing motion may be very important in enhancing a fiber's ability to mechanically injure cells or alter their responses.

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 laboratory experiment on cultured cells using a cell-stretching device (no humans or animals studied)
• Who was studied: Human alveolar epithelial tumor cell line A549 (from the American Type Culture Collection), grown as monolayers on stretchable silicone membranes
• Exposure: UICC crocidolite asbestos or glass fibers (manmade vitreous fiber MMVF-10), uncoated or coated with fibronectin. Fibers were applied at a dose printed as '10 mg/cm2' (see text problems). Cells were cyclically stretched (5% strain, 10 times per minute, 8 h) or kept static. Some stretched cultures were pretreated with RGD peptides. TNF-alpha was used as a non-particle comparison stimulus.
• Main results:
  • Cells without fibers: cyclic stretching alone did not raise IL-8 above the levels in static cultures.
  • Uncoated glass fibers: a slight, not statistically significant IL-8 increase in static cells. In stretched cells the increase was statistically significant (P = 0.0006).
  • Uncoated crocidolite asbestos: induced IL-8 in static cells. Stretching significantly enhanced this response (P = 0.015).
  • Fibronectin coating: the coating on asbestos stayed nearly constant across 2, 5 and 10 washings (fluorescence 131.95, 131.96, 132.61). The coating on glass fell over the same washings (139.44, 105.44, 92.93).
  • Fibronectin-coated fibers: stretching significantly enhanced IL-8 for both coated glass (P = 0.02) and coated crocidolite (P = 0.018). Coating greatly enhanced the asbestos response but had no appreciable effect on the glass response.
  • TNF-alpha-treated cells: stretching did not further increase the IL-8 response.
  • Stretched cells given fibronectin-coated asbestos: RGD peptide pretreatment significantly reduced IL-8 (P = 0.002), a 70% inhibition (0.68 versus 2.25 ng/ml, mean plus or minus SEM, with versus without RGD). In static cultures, RGD had no significant effect.
  • Dose response with fibronectin-coated asbestos (5, 10 and 20 per square centimetre of culture surface): IL-8 showed a trend toward rising with dose in both static and stretched cells, with wide variation. Stretched cultures consistently produced more IL-8 than static ones.
• The authors' conclusion: The authors concluded that the enhanced response in stretched cells suggests the lung's cyclic breathing motion may be very important in enhancing a fiber's ability to mechanically injure cells or alter cell responses. They also concluded that adhesive interactions between protein-coated fibers and cell surface receptors may be involved.
• Limitations the authors state:
  • The dose-response data showed wide variation.
  • Whether particles of identical chemistry but different shape would give different responses was not tested and awaits future investigation.

Topics

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

Medical terms in this study, explained in our Lexicon: Epithelium, Crocidolite, Cytokine, Glycoprotein.

Related studies

• IL-8 response of cyclically stretching alveolar epithelial cells exposed to non-fibrous particles — S.M. Mijailovich, K. Hamada, et al. (2007)
• Mechanisms of silica-induced IL-8 release from A549 cells: initial kinase-activation does not require EGFR activation or particle uptake — J. Øvrevik, M. Refsnes, et al. (2006)
• Interleukin 1 production and accessory cell function of rat alveolar macrophages exposed to mineral dust particles — Y. Oghiso, Y. Kubota (1987)
• Interleukin-1-mediated release of interleukin-8 by asbestos-stimulated human pleural mesothelial cells — D.E. Griffith, E.J. Miller, et al. (1994)
• Response of bovine alveolar macrophages in vitro to welding fume particles — L.R. White, A.B. Marthinsen, et al. (1983)
• Asbestos fibre length-dependent detachment injury to alveolar epithelial cells in vitro: role of a fibronectin-binding receptor — K. Donaldson, B.G. Miller, et al. (1993)

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