Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro

Our plain-English summary of Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro, by K.M. Serve, B. Black, J. Szeinuk, et al (Inhalation Toxicology, 2013).

The study

• Authors: K.M. Serve, B. Black, J. Szeinuk, J.C. Pfau
• Journal: Inhalation Toxicology
• Published: 2013;25(14):774-84
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Fibrosis, characterized by excessive collagen protein deposition, is a progressive disease that can fatally inhibit organ function. Prolonged exposure to pathogens or environmental toxicants such as asbestos can lead to chronic inflammatory responses associated with fibrosis. Significant exposure to amphibole asbestos has been reported in and around Libby, Montana due to local mining of asbestos-contaminated vermiculite. These exposures have been implicated in a unique disease etiology characterized predominantly by pleural disorders, including fibrosis. We recently reported the discovery of mesothelial cell autoantibodies (MCAAs) in the sera of Libby residents and demonstrated a positive and significant correlation with pleural disease; however, a mechanistic link was not determined. Here we demonstrate that MCAAs induce pleural mesothelial cells to produce a collagen matrix but do not affect production of the pro-inflammatory cytokine tumor growth factor-β. While autoantibodies commonly induce a pro-fibrotic state by inducing epithelial-mesenchymal transition (EMT) of target cells, we found no evidence supporting EMT in cells exposed to MCAA positive human sera. Although implicated in other models of pulmonary fibrosis, activity of the protein SPARC (secreted protein, acidic and rich in cysteine) did not affect MCAA-induced collagen deposition. However, matrix formation was dependent on matrix metalloproteinase (MMP) activity, and we noted increased expression of MMP-8 and -9 in supernatants of mesothelial cells incubated with MCAA positive sera compared to control. These data suggest a mechanism by which MCAA binding leads to increased collagen deposition through altering MMP expression and provides an important mechanistic link between MCAAs and asbestos-related, autoimmune-induced pleural fibrosis.

In plain English

This was an in vitro study in which cultured human pleural mesothelial cells (MeT-5A) were incubated for four days with pooled sera collected in Libby, Montana, previously classified as mesothelial cell autoantibody (MCAA) positive or negative, with normal human serum and IgG-cleared serum as controls. MCAA positive sera bound mesothelial cells significantly more than MCAA negative sera or normal serum (p less than 0.001), and binding was lost when IgG was removed. Cells exposed to MCAA positive sera deposited significantly more type I collagen (p less than 0.001), while IgG clearance returned collagen to background. Smooth muscle alpha-actin did not differ significantly between MCAA positive and MCAA negative sera, although sera from asbestos-exposed subjects raised it above normal human serum, so the authors saw no evidence of an MCAA-induced mesenchymal transition; MCAA positive sera did not increase TGF-beta, and SPARC inhibition did not significantly alter collagen deposition. The MMP inhibitor EDTA significantly reduced collagen in MCAA positive cultures (p equals 0.018), and MMP-8 was significantly increased compared with normal serum. The authors concluded that MCAAs may contribute to asbestos-associated pleural 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 laboratory experiment using a cultured human mesothelial cell line exposed to pooled human sera
• Who was studied: Cultured human pleural mesothelial cells (MeT-5A) treated with pooled sera collected in Libby, Montana, previously classified as MCAA positive or negative, plus normal human serum from a donor with no known asbestos exposure and IgG-cleared serum
• Exposure: Human sera containing mesothelial cell autoantibodies from people exposed to Libby amphibole asbestos, applied to cells at 1:50 dilution for 4 days; comparisons with IgG-cleared sera, normal human sera and TGF-beta as a positive control
• Main results:
  • MCAA positive sera bound mesothelial cells significantly more than MCAA negative sera and normal human sera (p less than 0.001)
  • Binding was lost after IgG removal, indicating MCAAs are IgG antibodies
  • Type I collagen detection was significantly increased in cells exposed to MCAA positive sera versus MCAA negative sera or normal human sera (p less than 0.001), and fell to background after IgG clearance
  • No significant difference in smooth muscle alpha-actin expression between cells given MCAA positive and MCAA negative sera; the TGF-beta positive control did increase expression
  • Sera from asbestos-exposed subjects (both MCAA positive and negative) did increase smooth muscle alpha-actin expression compared with normal human sera, but less than the TGF-beta positive control
  • About 35 ng/ml TGF-beta was measured in the pooled MCAA positive and negative sera, with no statistical difference between them
  • About 0.7 ng/ml TGF-beta was measured in cell supernatants, which the authors attributed to the added serum rather than the cells
  • Soluble (newly synthesised) collagen in supernatants did not differ between sera exposures
  • Endogenous SPARC protein levels did not change with MCAA positive or negative sera
  • SPARC detection by cell-based ELISA increased significantly in cells exposed to MCAA positive sera
  • Inhibiting SPARC did not significantly affect collagen deposition
  • The MMP inhibitor EDTA (5 mM) significantly reduced collagen deposition in cells exposed to MCAA positive sera (p = 0.018) but not in cells given normal human sera (p = 0.28) or MCAA negative sera (p = 0.32)
  • Zymography showed a double band at 98 and 92 kDa, corresponding to pro and active MMP-9
  • Zymography also showed a band at 58 kDa, corresponding to active MMP-8
  • Immunoblot densitometry showed significantly more MMP-8 with MCAA positive sera than with normal human sera
  • MCAA negative sera also increased MMP-8, but not significantly (p = 0.085)
• The authors' conclusion: The authors concluded that MCAA binding induces extracellular type I collagen deposition without a mesenchymal transition, suggesting a potential role for these autoantibodies in the development of asbestos-associated pleural fibrosis
• Limitations the authors state:
  • Attempts to detect MMP-9 by immunoblot did not succeed
  • MMP inhibition did not bring collagen down to background, so the authors suggest another collagenolytic protein or mechanism also contributes
  • The authors note that detecting TGF-beta in the sera does not rule out another serum component being responsible for the slight increase in collagen synthesis
  • The authors state the MMP-9 activity observed is unlikely to be an MCAA-specific mechanism

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

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

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)
• Mesothelial cell autoantibodies upregulate transcription factors associated with fibrosis — J. Gilmer, T. Harding, et al. (2017)
• Alteration of fibroblast phenotype by asbestos-induced autoantibodies — J.C. Pfau, S. Li, et al. (2011)
• Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages — D.J. Blake, S.A. Wetzel, et al. (2008)
• A protective role for T lymphocytes in asbestos-induced pulmonary inflammation and collagen deposition — E. Corsini, M.I. Luster, et al. (1994)

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