Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy

Our plain-English summary of Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy, by J. Xue, S. Patergnani, C. Giorgi, et al (Proceedings of the National Academy of Sciences of the United States of America, 2020).

The study

• Authors: J. Xue, S. Patergnani, C. Giorgi, J. Suarez, K. Goto, A. Bononi, M. Tanji, F. Novelli, S. Pastorino, R. Xu, N. Caroccia, A.U. Dogan, H.I. Pass, M. Tognon, P. Pinton, G. Gaudino, T.W. Mak, M. Carbone, H. Yang
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2020;117(41):25543-25552
• Cited by: 68 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos causes malignant transformation of primary human mesothelial cells (HM), leading to mesothelioma. The mechanisms of asbestos carcinogenesis remain enigmatic, as exposure to asbestos induces HM death. However, some asbestos-exposed HM escape cell death, accumulate DNA damage, and may become transformed. We previously demonstrated that, upon asbestos exposure, HM and reactive macrophages releases the high mobility group box 1 (HMGB1) protein that becomes detectable in the tissues near asbestos deposits where HMGB1 triggers chronic inflammation. HMGB1 is also detectable in the sera of asbestos-exposed individuals and mice. Searching for additional biomarkers, we found higher levels of the autophagy marker ATG5 in sera from asbestos-exposed individuals compared to unexposed controls. As we investigated the mechanisms underlying this finding, we discovered that the release of HMGB1 upon asbestos exposure promoted autophagy, allowing a higher fraction of HM to survive asbestos exposure. HMGB1 silencing inhibited autophagy and increased asbestos-induced HM death, thereby decreasing asbestos-induced HM transformation. We demonstrate that autophagy was induced by the cytoplasmic and extracellular fractions of HMGB1 via the engagement of the RAGE receptor and Beclin 1 pathway, while nuclear HMGB1 did not participate in this process. We validated our findings in a novel unique mesothelial conditional HMGB1-knockout (HMGB1-cKO) mouse model. Compared to HMGB1 wild-type mice, mesothelial cells from HMGB1-cKO mice showed significantly reduced autophagy and increased cell death. Autophagy inhibitors chloroquine and desmethylclomipramine increased cell death and reduced asbestos-driven foci formation. In summary, HMGB1 released upon asbestos exposure induces autophagy, promoting HM survival and malignant transformation.

In plain English

This laboratory study examined whether autophagy contributes to asbestos-induced transformation of primary human mesothelial cells (HM). Serum levels of the autophagy marker ATG5 were compared in 29 workers with histories of occupational asbestos exposure and 30 unexposed individuals, and were higher in the exposed group (45.11 ± 12.14 ng/mL versus 28.29 ± 9.4 ng/mL, ANOVA P less than 0.0001). In culture, carcinogenic fibers increased LC3-I to LC3-II conversion; asbestos-exposed cells showed a more than twofold increase in autophagy by flow cytometry, and crocidolite-induced autophagy increased with fiber density, becoming detectable at 2 micrograms per square centimetre and increasing up to 8; noncarcinogenic glass fibers increased neither autophagy, DNA damage (gamma-H2AX) nor cell death. Silencing HMGB1 reduced asbestos-induced autophagy and increased apoptosis and necrosis markers; the reduction in LC3-II was reversed by cytoplasmic but not nuclear HMGB1 constructs. Mesothelial cells from conditional HMGB1-knockout mice showed reduced autophagy and increased cell death, and peritoneal tissue from these mice showed minimal ATG5 staining. Chloroquine and desmethylclomipramine increased asbestos-induced cell death and significantly reduced foci formation. The authors concluded that HMGB1 released upon asbestos exposure induces autophagy, promoting HM survival and malignant transformation.

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: Experimental laboratory study: in vitro work on primary human mesothelial cells, a conditional knockout mouse model, and a comparison of serum marker levels between exposed and unexposed people
• Who was studied: Sera from 29 asbestos-exposed workers and 30 unexposed controls (all male, from a collection approved by the County Ethics Committee of the University of Ferrara); primary human mesothelial cells from pleural fluids of de-identified donors; 10 mesothelial HMGB1-cKO mice and 10 HMGB1 wild-type mice
• Exposure: Occupational asbestos exposure (serum study); in vitro exposure of human mesothelial cells to crocidolite and other carcinogenic fibers at 4 micrograms per square centimetre (5 for foci formation), with noncarcinogenic glass fibers as comparison; intraperitoneal crocidolite in mice
• Main results:
  • Serum ATG5 was higher in the 29 asbestos-exposed individuals than in the 30 unexposed individuals
  • Flow cytometry showed a more than twofold increase in autophagy in asbestos-exposed human mesothelial cells compared with unexposed cells
  • The dose-response experiment used crocidolite: autophagy (LC3-II) became detectable at 2 micrograms per square centimetre and increased up to 8
  • Noncarcinogenic glass fibers produced neither autophagy nor cell death in human mesothelial cells, and no increase in the DNA damage marker gamma-H2AX
  • Silencing HMGB1 in human mesothelial cells reduced asbestos-induced autophagy and increased apoptosis and necrosis
  • In the rescue experiment, the reduction of LC3-II caused by HMGB1 silencing was reversed by recombinant or cytoplasmic HMGB1, but not by nuclear HMGB1
  • Blocking RAGE or HMGB1 with antibodies partially reduced autophagy, while the HMGB1 antagonist BoxA suppressed it completely
  • In mice given a total of 5 mg crocidolite intraperitoneally, ATG5 was strongly expressed in mesothelial cells of wild-type mice but minimal or absent in HMGB1-cKO mice, where p62, TUNEL and p-RIP staining were elevated
  • Chloroquine and desmethylclomipramine increased asbestos-induced cell death and reduced three-dimensional foci formation in asbestos-exposed human mesothelial cells
• The authors' conclusion: The authors concluded that asbestos-released HMGB1 (cytoplasmic and extracellular) induces autophagy, which allows DNA-damaged mesothelial cells to survive and become transformed, and that inhibiting autophagy reduces asbestos-driven transformation in tissue culture
• Limitations the authors state:
  • The authors state that the possible use of ATG5 as a biomarker of asbestos exposure requires validation in larger studies
  • HMGB1 silencing was incomplete (about 50% reduction), so the mTOR-ULK pathway could not be fully inhibited
  • The authors state that the transformation findings were obtained in tissue culture and that the hypothesis still has to be tested in vivo

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, High Mobility Group Box 1 (HMGB1), Malignant Transformation, Mesothelioma, Carcinogenesis, Asbestos Exposure, Macrophage, Chronic Inflammation.

Related studies

• Continuous exposure to chrysotile asbestos can cause transformation of human mesothelial cells via HMGB1 and TNF-α signaling — F. Qi, G. Okimoto, et al. (2013)
• BAP1 forms a trimer with HMGB1 and HDAC1 that modulates gene × environment interaction with asbestos — F. Novelli, A. Bononi, et al. (2021)
• HMGB1 released by mesothelial cells drives the development of asbestos-induced mesothelioma — J.S. Suarez, F. Novelli, et al. (2023)
• BAP1 regulates IP3R3-mediated Ca2+ flux to mitochondria suppressing cell transformation — A. Bononi, C. Giorgi, et al. (2017)
• HMGB1 targeting by ethyl pyruvate suppresses malignant phenotype of human mesothelioma — L. Pellegrini, J. Xue, et al. (2017)
• Autophagy facilitates the release of immunogenic signals following chemotherapy in 3D models of mesothelioma — C. Follo, Y. Cheng, et al. (2019)

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