Epithelial-mesenchymal transition involved in pulmonary fibrosis induced by multi-walled carbon nanotubes via TGF-beta/Smad signaling pathway

Our plain-English summary of Epithelial-mesenchymal transition involved in pulmonary fibrosis induced by multi-walled carbon nanotubes via TGF-beta/Smad signaling pathway, by T. Chen, H. Nie, X. Gao, et al (Toxicology Letters, 2014).

The study

• Authors: T. Chen, H. Nie, X. Gao, J. Yang, J. Pu, Z. Chen, X. Cui, Y. Wang, H. Wang, G. Jia
• Journal: Toxicology Letters
• Published: 2014;226(2):150-62
• Cited by: 91 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Multi-walled carbon nanotubes (MWCNT) are a typical nanomaterial with a wide spectrum of commercial applications. Inhalation exposure to MWCNT has been linked with lung fibrosis and mesothelioma-like lesions commonly seen with asbestos. In this study, we examined the pulmonary fibrosis response to different length of MWCNT including short MWCNT (S-MWCNT, length=350-700nm) and long MWCNT (L-MWCNT, length=5-15μm) and investigated whether the epithelial-mesenchymal transition (EMT) occurred during MWCNT-induced pulmonary fibrosis. C57Bl/6J male mice were intratracheally instilled with S-MWCNT or L-WCNT by a single dose of 60μg per mouse, and the progress of pulmonary fibrosis was evaluated at 7, 28 and 56 days post-exposure. The in vivo data showed that only L-MWCNT increased collagen deposition and pulmonary fibrosis significantly, and approximately 20% of pro-surfactant protein-C positive epithelial cells transdifferentiated to fibroblasts at 56 days, suggesting the occurrence of EMT. In order to understand the mechanism, we used human pulmonary epithelial cell line A549 to investigate the role of TGF-β/p-Smad2 signaling pathway in EMT. Our results showed that L-MWCNT downregulated E-cadherin and upregulated α-smooth muscle actin (α-SMA) protein expression in A549 cells. Taken together, both in vivo and in vitro study demonstrated that respiratory exposure to MWCNT induced length dependent pulmonary fibrosis and epithelial-derived fibroblasts via TGF-β/Smad pathway.

Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

In plain English

This was an animal experiment combined with cell-culture work on multi-walled carbon nanotubes (MWCNT), which the authors introduced as fibre-shaped materials that may act like asbestos. Male C57Bl/6J mice received a single intratracheal instillation of 60 micrograms of short MWCNT (350-700 nm) or long MWCNT (5-15 micrometres), with PBS as control and silicon dioxide as positive control, and were examined 7, 28 and 56 days later. Only long MWCNT raised TGF-beta1 in bronchoalveolar lavage fluid (significant at 7 and 28 days, not significant at 56 days) and increased lung collagen; short MWCNT showed no fibrogenic ability. By flow cytometry, 10.93 percent and 19.97 percent of SP-C-staining lung cells were also positive for alpha-SMA at 28 and 56 days in the long MWCNT group, and 18.88 percent and 22.48 percent were positive for vimentin. In human A549 lung epithelial cells, long MWCNT lowered E-cadherin and raised alpha-SMA; the TGF-beta receptor inhibitor SB431542 blocked this, though not completely.

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: animal experiment (mouse intratracheal instillation) combined with in vitro cell-culture experiments
• Who was studied: Male C57Bl/6J mice (18-22 g), killed at 7, 28 and 56 days after a single instillation, plus the human pulmonary epithelial cell line A549; work done in Beijing, China
• Exposure: Single intratracheal instillation of 60 micrograms per mouse of short MWCNT (350-700 nm) or long MWCNT (5-15 micrometres), with PBS control and silicon dioxide positive control; A549 cells exposed to 1, 4 and 16 micrograms per square centimetre for 72 h
• Main results:
  • In mice, TGF-beta1 in BAL fluid rose significantly with long MWCNT at 7 and 28 days, but the rise at 56 days was not statistically significant
  • Short MWCNT produced no increase in TGF-beta1 or lung collagen
  • In the long MWCNT group, 10.93% and 19.97% of SP-C-staining lung cells were positive for alpha-SMA at 28 and 56 days
  • In the long MWCNT group, 18.88% and 22.48% of SP-C-staining cells were positive for vimentin at 28 and 56 days
  • In A549 cells, long MWCNT reduced E-cadherin and raised alpha-SMA; short MWCNT produced no significant change
  • Inflammatory cytokines in BAL fluid: significant TNF-alpha increase only in the silicon dioxide group; long MWCNT raised TNF-alpha without statistical significance
  • The TGF-beta receptor kinase inhibitor SB431542 blocked the EMT response of A549 cells to long MWCNT
• The authors' conclusion: The authors concluded that the fibrotic effect of MWCNT depends on tube length, and that long MWCNT exposure causes pulmonary injury and fibrosis promoted by epithelial-mesenchymal transition and the TGF-beta/Smad2 signalling pathway
• Limitations the authors state:
  • The authors state the role of length still needs further investigation
  • The authors note the differing metal content of the two tube preparations may have contributed to the greater toxicity of long MWCNT
  • The authors note the TGF-beta receptor inhibitor did not block the response completely, suggesting other pathways
  • The authors state that lifetime, repeated low-concentration inhalation studies are still needed

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Fibrosis, Mesothelioma, Collagen, Deposition, Fibroblast, A549 Cells.

Related studies

• Multi-walled carbon nanotubes directly induce epithelial-mesenchymal transition in human bronchial epithelial cells via the TGF-β-mediated Akt/GSK-3β/SNAIL-1 signalling pathway — M. Polimeni, G.R. Gulino, et al. (2016)
• A single intratracheal instillation of single-walled carbon nanotubes induced early lung fibrosis and subchronic tissue damage in mice — E.J. Park, J. Roh, et al. (2011)
• Distinct autophagy-apoptosis related pathways activated by Multi-walled (NM 400) and Single-walled carbon nanotubes (NIST-SRM2483) in human bronchial epithelial (16HBE14o-) cells — M. Ghosh, S. Murugadoss, et al. (2020)
• Similar and Differential Canonical Pathways and Biological Processes Associated With Multiwalled Carbon Nanotube and Asbestos-Induced Pulmonary Fibrosis: A 1-Year Postexposure Study — J.M. Dymacek, B.N. Snyder-Talkington, et al. (2018)
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• Blockage of epithelial to mesenchymal transition and upregulation of let 7b are critically involved in ursolic acid induced apoptosis in malignant mesothelioma cell — E.J. Sohn, G. Won, et al. (2016)

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