Mesothelial cell autoantibodies upregulate transcription factors associated with fibrosis

Our plain-English summary of Mesothelial cell autoantibodies upregulate transcription factors associated with fibrosis, by J. Gilmer, T. Harding, L. Woods, et al (Inhalation Toxicology, 2017).

The study

• Authors: J. Gilmer, T. Harding, L. Woods, B. Black, R. Flores, J. Pfau
• Journal: Inhalation Toxicology
• Published: 2017;29(1):10-17
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Amphibole asbestos exposure is associated with the production of mesothelial cell autoantibodies (MCAA). These MCAA have been linked with pleural fibrotic disease in the asbestos exposed community of Libby, Montana, and induce collagen deposition by cultured mesothelial cells. However, the exact intracellular mechanism by which these autoantibodies cause an increase in collagen deposition remains unknown. This study sought to gain insight into the transcription factors involved in the collagen production after human mesothelial cells are exposed to MCAA. In this study, transcription factor activation profiles were generated from human mesothelial cells (Met5A) treated with serum from Libby subjects, and were compared to cells treated with serum cleared of IgG, and therefore containing no MCAA. Analysis of those profiles indicated C/EBP-beta and hypoxia inducible factor 1 alpha (HIF-1α) are significantly increased in the nucleus, indicating activation, due to MCAA exposure compared to controls. Inhibition of either of these transcription factors significantly reduced collagen 1 deposition by these cells following exposure to MCAA. These data suggest autoantibodies are directly involved in type I collagen deposition and may elucidate potential therapeutic targets for autoantibody mediated fibrosis.

In plain English

This was a laboratory study of human mesothelial cells (MeT-5A line). The cells were treated with pooled serum from Libby, Montana, subjects previously found to carry mesothelial cell autoantibodies (MCAA). Control cells got the same serum minus its IgG antibodies. In a screen of 48 transcription factors (proteins that switch genes on), 11 differed more than twofold with MCAA serum. Two of them, C/EBP-beta and HIF-1a, were confirmed as significantly more active (three samples per group, p less than 0.05). Cells given MCAA serum laid down significantly more collagen than cells given cleared serum. Blocking either factor significantly reduced this collagen, though not back to control levels. Of 83 fibrosis-related genes tested, 56 were detected; 22 of these differed between treatments by more than one PCR threshold cycle. The authors concluded these factors play a key role in the collagen increase in cultured cells and therefore may be associated with Libby Amphibole-induced pleural fibrosis. They noted that the C/EBP-beta blocker acts broadly, that only 48 factors and 83 genes were examined, and that any link to pleural fibrosis remains to be determined.

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 a cultured human mesothelial cell line (not a study of patients)
• Who was studied: Human mesothelial cells of the MeT-5A line, treated with pooled serum from subjects previously identified as MCAA-positive. The serum was collected by the Center for Asbestos Related Disease (CARD) in Libby, Montana, USA. The article does not state how many people contributed serum.
• Exposure: The cells were treated with serum containing mesothelial cell autoantibodies (MCAA) from Libby Amphibole-exposed subjects. The comparison treatment was the same serum cleared of IgG antibodies. No asbestos fibers were applied to the cells in these experiments.
• Main results:
  • In the screening array, cells treated with MCAA serum showed more than twofold differences in activation in 11 of the 48 transcription factors examined, compared with cells treated with cleared serum.
  • In the screening array (Table 2), activated C/EBP was 16.166-fold higher and HIF was 9.016-fold higher in MCAA-treated cells than in cells given cleared serum.
  • In follow-up tests, mesothelial cells treated with MCAA serum had significantly more active C/EBP-beta and HIF-1a than cells treated with cleared serum (N = 3, p less than 0.05).
  • Cells that received MCAA-positive serum produced significantly more collagen than cells that received serum cleared of IgG.
  • Blocking C/EBP-beta (with ALLN) or HIF-1a (with an HIF-1a inhibitor) significantly reduced collagen from MCAA-induced levels (p less than 0.05). The levels did not return to those of the negative control or the cleared serum.
  • Of 83 fibrosis-associated genes analyzed, 56 were detected. Of these, 22 differed between MCAA-treated and cleared-serum-treated cells by more than 1 threshold cycle, and 8 by 2 or more.
  • More than twofold differences in MCAA-treated cells were seen for C/EBP-beta, LOX, PDGFA, TGFBR2, TIMP1 and STAT6.
  • With MCAA treatment, mRNAs for the matrix metalloproteinases MMP1, MMP14, MMP2 and MMP9 were all slightly decreased.
  • The authors observed no significant changes in activation of Smads, NF-kB or p53.
• The authors' conclusion: The authors concluded that C/EBP-beta and HIF-1a play a key role in the increased collagen deposition seen in vitro. They concluded these factors therefore may be associated with Libby Amphibole-induced pleural fibrosis.
• Limitations the authors state:
  • ALLN, the drug used to block C/EBP-beta, broadly inhibits cellular cysteine proteases and may affect collagen output through other pathways.
  • The collagen assay measures only collagen, but fibrosis involves more than collagen production.
  • An increase in transcription factor mRNA does not confirm that the transcription factors are activated.
  • Only 48 transcription factors and 83 mRNAs were examined. More molecules are likely involved.
  • Whether MCAA-induced collagen deposition is connected with fibrosis in the pleural cavity remains to be determined.
  • The decrease in MMP mRNA conflicts with an earlier study by Serve et al., which found increased MMP-8 and MMP-9 protein and activity. Protein levels still need to be measured.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Fibrosis, Amphibole Asbestos, Collagen, Deposition, Hypoxia.

Related studies

• Libby amphibole-induced mesothelial cell autoantibodies promote collagen deposition in mice — J. Gilmer, K. Serve, et al. (2016)
• Libby amphibole-induced mesothelial cell autoantibodies bind to surface plasminogen and alter collagen matrix remodeling — R. Hanson, C. Evilia, et al. (2016)
• Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro — K.M. Serve, B. Black, et al. (2013)
• Asbestos upregulates expression of the urokinase-type plasminogen activator receptor on mesothelial cells — R.C. Perkins, V.C. Broaddus, et al. (1999)
• Hypoxia Inducible Factor-1α Inhibition in Von Hippel Lindau-mutant Malignant Pleural Mesothelioma Cells — T. Shukuya, J. Oyanagi, et al. (2020)
• Increased expression of epidermal growth factor receptor in rat pleural mesothelial cells correlates with carcinogenicity of mineral fibres — S.P. Faux, C.E. Houghton, et al. (2000)

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