Contribution of epithelial-derived fibroblasts to bleomycin-induced lung fibrosis

Am J Respir Crit Care Med. 2009 Oct 1;180(7):657-65. doi: 10.1164/rccm.200903-0322OC. Epub 2009 Jun 25.


Rationale: Lung fibroblasts are key mediators of fibrosis resulting in accumulation of excessive interstitial collagen and extracellular matrix, but their origins are not well defined.

Objectives: We aimed to elucidate the contribution of lung epithelium-derived fibroblasts via epithelial-mesenchymal transition (EMT) in the intratracheal bleomycin model.

Methods: Primary type II alveolar epithelial cells were cultured from Immortomice and exposed to transforming growth factor-beta(1) and epidermal growth factor. Cell fate reporter mice that permanently mark cells of lung epithelial lineage with beta-galactosidase were developed to study EMT, and bone marrow chimeras expressing green fluorescent protein under the control of the fibroblast-associated S100A4 promoter were generated to examine bone marrow-derived fibroblasts. Mice were given intratracheal bleomycin (0.08 unit). Immunostaining was performed for S100A4, beta-galactosidase, green fluorescent protein, and alpha-smooth muscle actin.

Measurements and main results: In vitro, primary type II alveolar epithelial cells undergo phenotypic changes of EMT when exposed to transforming growth factor-beta(1) and epidermal growth factor with loss of prosurfactant protein C and E-cadherin and gain of S100A4 and type I procollagen. In vivo, using cell fate reporter mice, approximately one-third of S100A4-positive fibroblasts were derived from lung epithelium 2 weeks after bleomycin administration. From bone marrow chimera studies, one-fifth of S100A4-positive fibroblasts were derived from bone marrow at this same time point. Myofibroblasts rarely derived from EMT or bone marrow progenitors.

Conclusions: Both EMT and bone marrow progenitors contribute to S100A4-positive fibroblasts in bleomycin-induced lung fibrosis. However, neither origin is a principal contributor to lung myofibroblasts.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / administration & dosage*
  • Bleomycin
  • Blotting, Western / methods
  • Cell Culture Techniques
  • Disease Models, Animal
  • Epithelial Cells / metabolism*
  • Epithelium / metabolism
  • Fibroblasts / cytology
  • Fibroblasts / metabolism*
  • Mesoderm / cytology
  • Mesoderm / metabolism
  • Mice
  • Mice, Transgenic
  • Pulmonary Alveoli / metabolism
  • Pulmonary Fibrosis / chemically induced
  • Pulmonary Fibrosis / metabolism*


  • Antibiotics, Antineoplastic
  • Bleomycin