Expression and activity of urokinase and its receptor in endothelial and pulmonary epithelial cells exposed to asbestos

Our plain-English summary of Expression and activity of urokinase and its receptor in endothelial and pulmonary epithelial cells exposed to asbestos, by A. Barchowsky, R.R. Roussel, R.J. Krieser, et al (Toxicology and Applied Pharmacology, 1998).

The study

• Authors: A. Barchowsky, R.R. Roussel, R.J. Krieser, B.T. Mossman, M.D. Treadwell
• Journal: Toxicology and Applied Pharmacology
• Published: 1998;152(2):388-96
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

An elongated endothelial cell phenotype, which demonstrated increased ICAM-1-dependent neutrophil adherence, was induced when these cells were exposed to noncytotoxic concentrations of asbestos (Treadwell et al., Toxicol. Appl. Pharmacol. 139, 62-70, 1996). The present study examined mechanisms underlying this phenotypic change by investigating the effects of asbestos on transcription factor activation and expression of urokinase-type plasminogen activator (uPA) and its receptor uPAR. In situ zymography was used to compare the effects of these fibers on the activity of uPA. Cultures incubated with chrysotile or crocidolite asbestos, but not refractory ceramic fiber 1 (RCF-1), demonstrate localized cleavage of plasminogen, which was inhibited by amiloride. Immunocytochemistry showed that chrysotile-stimulated uPA activity was associated with a time-dependent augmentation of uPAR protein levels. RT-PCR analysis was used to investigate molecular mechanisms for these increases. Chrysotile asbestos, but not RCF-1, increased endothelial cell uPA message, relative to changes in beta-actin mRNA. This response to asbestos was not limited to endothelial cells, since both uPA and uPAR mRNA levels increase in human bronchial epithelial BEAS-2B cells exposed to chrysotile fibers. Finally, both types of asbestos, but not RCF-1, increased nuclear levels of nuclear factor-kappaB (NF-kappa B), a transcription factor common to increased expression of ICAM-1 and uPA. These data demonstrate that asbestos caused fiber-specific activation of endothelial and pulmonary epithelial cells, resulting in phenotypes capable of facilitating tissue remodeling.

In plain English

In this laboratory study, the authors exposed cultured pig aortic endothelial cells (cells lining blood vessels) to reference samples of chrysotile and crocidolite asbestos, and compared the effects with those of refractory ceramic fiber 1 (RCF-1). They also exposed a human bronchial epithelial cell line, BEAS-2B, to chrysotile. They measured urokinase (uPA), an enzyme that converts plasminogen into the protein-cutting enzyme plasmin, its receptor (uPAR), and NF-kappaB, a protein that switches on genes. In endothelial cells, 24 hours of chrysotile or crocidolite exposure increased uPA-dependent enzyme activity around the cells, while RCF-1 had no effect. Chrysotile raised uPAR protein after 8 hours but not at 4 hours. It also raised uPA messenger RNA after 24 hours, and RCF-1 did not. In BEAS-2B cells, 3 hours of chrysotile raised both uPA and uPAR messenger RNA. Both asbestos types, but not RCF-1, increased NF-kappaB in endothelial cell nuclei within 30 minutes to 1 hour. The authors concluded that asbestos caused fiber-specific activation of these cells, producing changes capable of facilitating tissue remodeling. They noted that the culture doses are difficult to compare with fiber amounts in inhalation studies.

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) laboratory experiment
• Who was studied: Cultured porcine (pig) aortic endothelial cells and human bronchial epithelial BEAS-2B cells; work done at Dartmouth Medical School and University of Vermont; no humans or animals studied directly
• Exposure: In endothelial cells: NIEHS reference chrysotile and crocidolite asbestos, compared with refractory ceramic fiber 1 (RCF-1). In BEAS-2B cells: chrysotile only. Fiber concentrations were chosen to be maximally effective at activating cells but below levels that affected cell viability. Concentrations are printed as, for example, 10 mg/cm2 chrysotile or RCF-1 and 1 or 5 mg/cm2 crocidolite; see text_problems on units.
• Main results:
  • Endothelial cells exposed to chrysotile or crocidolite for 24 h showed increased protease activity around the cells that required cleavage of plasminogen to plasmin.
  • RCF-1 fibers did not activate endothelial cells and had no effect on this protease activity.
  • In endothelial cells, uPAR protein staining was low in controls and after 4 h of chrysotile, but increased greatly after 8 h of chrysotile exposure.
  • Chrysotile significantly increased uPA messenger RNA in endothelial cells after 24 h; RCF-1 did not affect uPA message levels.
  • In human bronchial epithelial BEAS-2B cells, 3-h exposure to chrysotile (printed as 5 mg/cm2) significantly increased both uPA and uPAR messenger RNA relative to beta-actin.
  • In endothelial cells, chrysotile and crocidolite, but not RCF-1, increased nuclear NF-kappaB (p50/p65); increases began as early as 30 min and were maximal by 1 h.
• The authors' conclusion: The authors concluded that asbestos caused fiber-specific activation of endothelial and pulmonary epithelial cells, resulting in phenotypes capable of facilitating tissue remodeling.
• Limitations the authors state:
  • The doses used in culture are difficult to relate directly to the amount of fibers reaching cells in inhalation studies.
  • In the living body, uPA/uPAR expression may also reflect secondary effects of cytokines from stimulated cells, not only direct fiber effects.
  • Further studies are needed to show causal links between asbestos-triggered signals and the activation of the genes studied.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Crocidolite.

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