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

Toxicol Lett. 2014 Apr 21;226(2):150-62. doi: 10.1016/j.toxlet.2014.02.004. Epub 2014 Feb 12.


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.

Keywords: Epithelial–mesenchymal transition; MWCNT; Pulmonary fibrosis; Smad; TGF-β.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Animals
  • Antigens, CD
  • Biomarkers / metabolism
  • Cadherins / metabolism
  • Cell Line, Tumor
  • Collagen / metabolism
  • Disease Models, Animal
  • Epithelial Cells / metabolism
  • Epithelial Cells / pathology
  • Epithelial-Mesenchymal Transition*
  • Fibroblasts / metabolism
  • Fibroblasts / pathology
  • Humans
  • Lung / metabolism*
  • Lung / pathology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Nanotubes, Carbon*
  • Particle Size
  • Phosphorylation
  • Pulmonary Fibrosis / chemically induced
  • Pulmonary Fibrosis / metabolism*
  • Pulmonary Fibrosis / pathology
  • Signal Transduction*
  • Smad2 Protein / metabolism*
  • Time Factors
  • Transforming Growth Factor beta1 / metabolism*


  • ACTA2 protein, human
  • Actins
  • Antigens, CD
  • Biomarkers
  • CDH1 protein, human
  • Cadherins
  • Nanotubes, Carbon
  • SMAD2 protein, human
  • Smad2 Protein
  • Smad2 protein, rat
  • TGFB1 protein, human
  • Tgfb1 protein, rat
  • Transforming Growth Factor beta1
  • Collagen