Release of biologically active TGF-beta1 by alveolar epithelial cells results in pulmonary fibrosis

Am J Physiol Lung Cell Mol Physiol. 2003 Sep;285(3):L527-39. doi: 10.1152/ajplung.00298.2002. Epub 2003 Feb 21.


Idiopathic pulmonary fibrosis (IPF) is a progressive fatal fibrotic lung disease. Transforming growth factor (TGF)-beta1 is present in a biologically active conformation in the epithelial cells lining lesions with advanced IPF. To determine the role of aberrant expression of biologically active TGF-beta1 by alveolar epithelial cells (AECs), the AECs of explanted normal rat lungs were transfected with the TGF-beta1 gene using the retrovirus pMX-L-s223,225-TGF-beta1. In situ hybridization using a digoxigenin-labeled cDNA of the puromycin resistance gene contained in the pMX demonstrated that pMX-L-s233,225-TGF-beta1 was selectively transfected into AECs of the explants. Conditioned media overlying explants obtained 7 days after being treated with pMX-L-s223,225-TGF-beta1 contained 14.5 +/- 3.15 pg/ml of active TGF-beta1. With the use of Masson's trichrome staining of explant sections obtained 14 days after transfection, there were lesions similar to those in IPF, characterized by type II AEC hyperplasia, interstitial thickening, extensive increase in interstitial and subepithelial collagen, an increase in the number of fibroblasts, and areas resembling fibroblast buds. Collagens I, III, IV, and V and fibronectin were increased in explants treated with pMX-L-s223,225-TGF-beta1. The findings in the current study suggest that IPF may be a disorder of epithelial cells and not inflammatory cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cells, Cultured
  • Collagen Type I / metabolism
  • Collagen Type III / metabolism
  • Collagen Type IV / metabolism
  • Collagen Type V / metabolism
  • Connective Tissue Growth Factor
  • Culture Media, Conditioned / pharmacology
  • DNA-Binding Proteins / metabolism
  • Female
  • Fibroblasts / immunology
  • Fibroblasts / metabolism
  • Fibroblasts / pathology
  • Fibronectins / metabolism
  • Immediate-Early Proteins / metabolism
  • Intercellular Signaling Peptides and Proteins / metabolism
  • Phosphorylation
  • Pulmonary Alveoli / immunology
  • Pulmonary Alveoli / metabolism*
  • Pulmonary Alveoli / pathology
  • Pulmonary Fibrosis / immunology*
  • Pulmonary Fibrosis / metabolism*
  • Pulmonary Fibrosis / pathology
  • Rats
  • Rats, Sprague-Dawley
  • Respiratory Mucosa / immunology
  • Respiratory Mucosa / metabolism*
  • Respiratory Mucosa / pathology
  • Smad2 Protein
  • Trans-Activators / metabolism
  • Transfection
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / immunology
  • Transforming Growth Factor beta / metabolism*
  • Transforming Growth Factor beta1


  • CCN2 protein, rat
  • Collagen Type I
  • Collagen Type III
  • Collagen Type IV
  • Collagen Type V
  • Culture Media, Conditioned
  • DNA-Binding Proteins
  • Fibronectins
  • Immediate-Early Proteins
  • Intercellular Signaling Peptides and Proteins
  • Smad2 Protein
  • Smad2 protein, rat
  • Tgfb1 protein, rat
  • Trans-Activators
  • Transforming Growth Factor beta
  • Transforming Growth Factor beta1
  • Connective Tissue Growth Factor