Asbestos modulates thioredoxin-thioredoxin interacting protein interaction to regulate inflammasome activation

Our plain-English summary of Asbestos modulates thioredoxin-thioredoxin interacting protein interaction to regulate inflammasome activation, by J.K. Thompson, C.M. Westbom, M.B. MacPherson, et al (Particle and Fibre Toxicology, 2014).

The study

• Authors: J.K. Thompson, C.M. Westbom, M.B. MacPherson, B.T. Mossman, N.H. Heintz, P. Spiess, A. Shukla
• Journal: Particle and Fibre Toxicology
• Published: 2014;11:24
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Asbestos exposure is related to various diseases including asbestosis and malignant mesothelioma (MM). Among the pathogenic mechanisms proposed by which asbestos can cause diseases involving epithelial and mesothelial cells, the most widely accepted one is the generation of reactive oxygen species and/or depletion of antioxidants like glutathione. It has also been demonstrated that asbestos can induce inflammation, perhaps due to activation of inflammasomes.

Methods: The oxidation state of thioredoxin was analyzed by redox Western blot analysis and ROS generation was assessed spectrophotometrically as a read-out of solubilized formazan produced by the reduction of nitrotetrazolium blue (NTB) by superoxide. Quantitative real time PCR was used to assess changes in gene transcription.

Results: Here we demonstrate that crocidolite asbestos fibers oxidize the pool of the antioxidant, Thioredoxin-1 (Trx1), which results in release of Thioredoxin Interacting Protein (TXNIP) and subsequent activation of inflammasomes in human mesothelial cells. Exposure to crocidolite asbestos resulted in the depletion of reduced Trx1 in human peritoneal mesothelial (LP9/hTERT) cells. Pretreatment with the antioxidant dehydroascorbic acid (a reactive oxygen species (ROS) scavenger) reduced the level of crocidolite asbestos-induced Trx1 oxidation as well as the depletion of reduced Trx1. Increasing Trx1 expression levels using a Trx1 over-expression vector, reduced the extent of Trx1 oxidation and generation of ROS by crocidolite asbestos, and increased cell survival. In addition, knockdown of TXNIP expression by siRNA attenuated crocidolite asbestos-induced activation of the inflammasome.

Conclusion: Our novel findings suggest that extensive Trx1 oxidation and TXNIP dissociation may be one of the mechanisms by which crocidolite asbestos activates the inflammasome and helps in development of MM.

In plain English

This was a laboratory study on human cells grown in dishes, not on people. The researchers exposed human peritoneal mesothelial cells (LP9/hTERT) to crocidolite asbestos, chrysotile asbestos, or glass beads used as a harmless control. Crocidolite oxidized thioredoxin-1 (Trx1), a protective antioxidant protein, which sharply lowered the amount of its active, reduced form. Chrysotile and glass beads did not change the oxidation state of Trx1 at 8 and 24 hours. Crocidolite raised Trx1 gene activity 1.6-fold at 24 hours, lowered total Trx1 protein by about 67%, and increased reactive oxygen species. Cells made to produce extra Trx1 showed a non-significant trend toward lower oxygen species and a trend toward better survival. Lowering the partner protein TXNIP reduced activation of caspase-1, a marker that the inflammasome had switched on. The inflammasome is a protein complex involved in inflammation. In asbestos-exposed cells, blocking caspase-1 beforehand raised cell viability by 18% compared with asbestos alone. The authors concluded that asbestos activates the inflammasome partly through TXNIP, as a consequence of changes in Trx1. They said the caspase-1 cell-death finding still needs confirmation.

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 (in vitro) cell culture experiment
• Who was studied: An immortalized human peritoneal mesothelial cell line (LP9/hTERT), obtained from Brigham and Women's Hospital, Boston. Some experiments also used a human mesothelioma cell line (HMESO) in which the protein ERK2 had been knocked down. No people or animals were studied.
• Exposure: Crocidolite asbestos (NIEHS reference sample), mainly at 75 × 10 to the 6th square micrometres per square centimetre (5 micrograms per square centimetre), sometimes also at 15 × 10 to the 6th (1 microgram per square centimetre). Chrysotile asbestos (NIEHS reference sample) was used for comparison. Glass beads served as a non-pathogenic control. Exposures lasted from 2 to 48 hours.
• Main results:
  • In crocidolite-exposed cells, Trx1 mRNA rose 1.6-fold at 24 hours compared with controls (p less than 0.05).
  • In asbestos-exposed cells, total Trx1 protein fell by about 67% after 24 hours.
  • In asbestos-exposed cells, Trx1 became irreversibly oxidized and levels of reduced Trx1 fell sharply compared with control cells.
  • In cells exposed to chrysotile or glass beads, levels of reduced and semi-oxidized Trx1 stayed the same at 8 and 24 hours.
  • Pretreatment with dehydroascorbic acid slightly increased reduced Trx1 in asbestos-exposed cells. The increase was not significant compared with controls or with asbestos alone.
  • In cells exposed to asbestos for 24 hours, reactive oxygen species were significantly higher than in controls.
  • In cells over-expressing Trx1, reactive oxygen species after 2 hours of asbestos showed a downward trend. The trend was not statistically significant.
  • In cells over-expressing Trx1, cell survival after asbestos exposure increased moderately, as a trend.
  • In cells pretreated with the antioxidant N-acetylcysteine, active caspase-1 released after asbestos exposure was significantly reduced.
  • In cells where TXNIP was knocked down (by about 50%), active caspase-1 after asbestos exposure was lower than in control-transfected cells.
  • In asbestos-exposed cells pretreated with a caspase-1 inhibitor, cell viability was 18% higher than in cells exposed to asbestos alone.
• The authors' conclusion: The authors concluded that asbestos activates the inflammasome partly through TXNIP, as a consequence of changes in the redox state of Trx1 in the cell.
• Limitations the authors state:
  • The finding that part of asbestos-induced cell death was caspase-1-dependent (pyroptosis) needs confirmation in future studies.
  • The reduction in reactive oxygen species with Trx1 over-expression was not statistically significant.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Malignant Mesothelioma, Mesothelial Cells, Reactive Oxygen Species (ROS), Glutathione (GSH), Inflammation, Superoxide, Crocidolite.

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