ABSTRACT
Connective tissue growth factor (CTGF) is a newly described 38-kDa peptide mitogen for fibroblasts and a promoter of connective tissue deposition in the skin. The CTGF gene promotor contains a transforming growth factor-beta1 (TGF-beta1) response element. Because TGF-beta1 expression is upregulated in several models of fibroproliferative lung disease, we asked whether CTGF is also upregulated in a murine lung fibrosis model and whether CTGF could mediate some of the fibrogenic effects associated with TGF-beta1. A portion of the rat CTGF gene was cloned and used to show that primary isolates of both murine and human lung fibroblasts express CTGF mRNA in vitro. There was a greater than twofold increase in CTGF expression in both human and murine lung fibroblasts 2, 4, and 24 h after the addition of TGF-beta1 in vitro. A bleomycin-sensitive mouse strain (C57BL/6) and a bleomycin-resistant mouse strain (BALB/c) were given bleomycin, a known lung fibrogenic agent. CTGF mRNA expression was upregulated in the sensitive, but not in the resistant, mouse strain after administration of bleomycin. In vivo differences in the CTGF expression between the two mouse strains were not due to an inherent inability of BALB/c lung fibroblasts to respond to TGF-beta1 because fibroblasts from untreated BALB/c mouse lung upregulated their CTGF message when treated with TGF-beta1 in vitro. These data demonstrate that CTGF is expressed in lung fibroblasts and may play a role in the pathogenesis of lung fibrosis.
Subject(s)
Bleomycin/toxicity , Cytokines/pharmacology , Gene Expression Regulation/drug effects , Growth Substances/genetics , Immediate-Early Proteins , Intercellular Signaling Peptides and Proteins , Lung/metabolism , Pulmonary Fibrosis/metabolism , Transcription, Genetic/drug effects , Transforming Growth Factor beta/pharmacology , Animals , Base Sequence , Cloning, Molecular , Connective Tissue Growth Factor , DNA, Complementary , Fibroblasts/metabolism , Growth Substances/biosynthesis , Humans , Lung/drug effects , Lung/pathology , Male , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mitogens/genetics , Pulmonary Fibrosis/chemically induced , Pulmonary Fibrosis/pathology , RNA, Messenger/biosynthesis , Rats , Rats, Sprague-Dawley , Recombinant Fusion Proteins/biosynthesis , Sequence Alignment , Sequence Homology, Nucleic Acid , Time Factors , Transforming Growth Factor beta/biosynthesis , Transforming Growth Factor beta/geneticsABSTRACT
Platelet-derived growth factor-AA (PDGF-AA) and its matching alpha receptor (PDGF-R alpha) are upregulated in rat lung fibroblasts (RLFs) after exposure to chrysotile asbestos fibers in vitro, which results in asbestos-induced RLF proliferation. We now report our in vivo observations, which show an increase in the expression of PDGF-R alpha mRNA, but not PDGF-beta receptor mRNA, in asbestos-exposed rat lungs when compared with RNA from air-exposed (sham) and iron-exposed lungs. Western analysis of membrane preparations confirmed the observations on mRNA expression by demonstrating an increase in PDGF-R alpha peptide expression in the asbestos-exposed rat lungs, compared with that in the air-exposed lungs. Immunohistochemistry for the PDGF-R alpha was performed on air- and asbestos-exposed rat lungs and revealed a clear increase in staining within interstitial and subepithelial compartments in the exposed animals. These observations, along with our previous report demonstrating an increase in the PDGF-AA isoform expression immediately after asbestos-exposure, suggest a scenario in which a potent lung mesenchymal cell mitogen, PDGF-AA, and its alpha-receptor are upregulated prior to the development of a fibroproliferative lung lesion, and thus may play a central role in the pathogenesis of asbestos-induced lung fibrosis.
