Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages

Our plain-English summary of Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages, by D.J. Blake, S.A. Wetzel, J.C. Pfau (Toxicology, 2008).

The study

• Authors: D.J. Blake, S.A. Wetzel, J.C. Pfau
• Journal: Toxicology
• Published: 2008;246(2-3):172-9
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos exposure is associated with increased autoimmune responses in humans. For example, in Libby, MT where significant asbestos exposure has occurred due to an asbestos-contaminated vermiculite mine near the community, residents have developed increased autoimmune responses compared to an unexposed population. However, the exact mechanism by which Libby amphibole asbestos generates autoimmune responses is unclear. A murine model of amphibole asbestos-induced autoimmunity was recently established, and one of the targets of the autoantibodies (AAs) was the SSA/Ro52 autoantigen. The purpose of this study was to determine whether the SSA/Ro52 autoantigen is exposed at the surface of cells as a result of asbestos exposure as a possible mechanism leading to antigenicity. Our results indicate that Libby asbestos induces apoptosis in murine macrophages as determined by phosphatidylserine exposure, cleavage of poly(ADP-ribose) polymerase and morphological changes such as nuclear condensation. Moreover, asbestos-induced apoptosis results in the formation of apoptotic cell surface blebs enriched in SSA/Ro52 as determined by confocal microscopy. Most importantly, apoptotic cell surface blebs are recognized by AAs from mice exposed to amphibole asbestos suggesting that these cell surface structures may be antigenic when presented in a pro-inflammatory context. This study supports the hypothesis that the induction of apoptosis plays a key role in environmentally induced autoimmunity through cell surface exposure of a known autoantigen.

In plain English

This was a laboratory study combining cell-culture experiments with serum from mice given fibers by intratracheal instillation. Murine macrophages (RAW264.7 cells) were exposed to Libby amphibole asbestos (a six-location mine sample containing winchite, richterite and tremolite, called "Libby 6-mix") at 62.5 micrograms per square centimetre for up to 72 hours; wollastonite served as a non-cytotoxic control fiber and staurosporine as a positive control for apoptosis. Untreated cells showed a basal apoptosis level of 3-5%, while Libby 6-mix significantly raised apoptotic cells to 10% at 24 hours and 20% at 48 hours (P less than 0.05); wollastonite did not induce apoptosis. Full-length PARP was reduced and the 89 kDa cleavage fragment increased, while the SSA/Ro52 autoantigen itself was not cleaved. Confocal microscopy showed SSA/Ro52 redistributed into surface blebs of apoptotic cells, and serum autoantibodies from mice instilled with Korean tremolite bound these blebs, whereas serum from PBS- or wollastonite-instilled mice did not. The authors concluded this supports a role for apoptosis in asbestos-induced autoimmunity.

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 experimental study in a murine macrophage cell line, using sera from an in vivo mouse fiber-instillation experiment
• Who was studied: RAW264.7 murine macrophage cells in culture, plus sera from 8-week-old C57Bl/6 mice instilled intratracheally and followed for 7 months (University of Montana)
• Exposure: Libby amphibole asbestos ("Libby 6-mix": winchite, richterite and tremolite) at 62.5 micrograms/cm2 in cell culture; mice received two intratracheal doses of 60 micrograms of Korean tremolite, wollastonite or saline
• Main results:
  • In untreated RAW264.7 cells basal apoptosis was 3-5%; Libby 6-mix raised apoptotic cells to 10% at 24 h and 20% at 48 h (P less than 0.05)
  • The control fiber wollastonite did not induce apoptosis in the macrophages
  • With the positive control staurosporine, more than 50% of macrophages were apoptotic after 6 h
  • In Libby 6-mix exposed cells full-length PARP (116 kDa) was reduced after 24 h with an increase in the 89 kDa fragment after 72 h
  • The SSA/Ro52 autoantigen showed no cleavage after 72 h of Libby 6-mix exposure or with staurosporine
  • More than 60% of exposed cells with apoptotic nuclear morphology showed SSA/Ro52 colocalized to membrane blebs
  • Autoantibodies in sera from tremolite-exposed mice colocalized with SSA/Ro52 on apoptotic blebs (Pearson's coefficients 0.612, 0.65 and 0.612 for one image; 0.704, 0.734 and 0.702 for another)
  • Sera from mice exposed to PBS or wollastonite did not recognize apoptotic blebs on exposed cells
• The authors' conclusion: The authors concluded that Libby amphibole asbestos induces apoptosis in murine macrophages, forming cell surface blebs enriched in SSA/Ro52 that are recognized by autoantibodies from asbestos-exposed mice, supporting a role for apoptosis in xenobiotic-induced autoimmune responses
• Limitations the authors state:
  • Cells were not permeabilized before staining yet nuclei stained with propidium iodide, which the authors say may be a fixation artifact raising a concern about membrane leakage
  • The authors state that the role of anti-SSA/Ro52 autoantibodies in asbestos-related disease remains unknown
  • Apoptosis alone is stated by the authors not to be sufficient to elicit autoimmunity; a second pro-inflammatory signal is required

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: Libby amphiboles, Macrophage, Asbestos Exposure, vermiculite, Amphibole Asbestos, Apoptosis.

Related studies

• Libby amphibole-induced mesothelial cell autoantibodies bind to surface plasminogen and alter collagen matrix remodeling — R. Hanson, C. Evilia, et al. (2016)
• Libby amphibole-induced mesothelial cell autoantibodies promote collagen deposition in mice — J. Gilmer, K. Serve, et al. (2016)
• Internalization of Libby amphibole asbestos and induction of oxidative stress in murine macrophages — D.J. Blake, C.M. Bolin, et al. (2007)
• Amphibole, but not chrysotile, asbestos induces anti-nuclear autoantibodies and IL-17 in C57BL/6 mice — A. Ferro, C.N. Zebedeo, et al. (2014)
• Erionite induces production of autoantibodies and IL-17 in C57BL/6 mice — C.N. Zebedeo, C. Davis, et al. (2014)
• Comparative health effects in mice of Libby amphibole asbestos and a fibrous amphibole from Arizona — J.C. Pfau, B. Buck, et al. (2017)

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