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Modulation of bFGF in lung fibroblasts by TGF-beta and PDGF
K T Goldsmith1, R B Gammon, R I Garver
1Department of Medicine, University of Alabama School of Medicine, Birmingham 35294.
Abstract:
Growth factors produced by alveolar macrophages are thought to promote the fibroblast proliferation within interstitial spaces of fibrotic lungs. This study investigated the possibility that the macrophage-produced growth factors might modulate the expression of basic fibroblast growth factor (bFGF) by lung fibroblasts. To evaluate this question, bFGF gene expression and protein production were evaluated in normal adult human lung fibroblast cell lines. Under normal culture conditions, the fibroblasts expressed the bFGF gene as two major transcripts (7.1, 3.7 kb). The addition of fetal calf serum (FCS) to serum-starved fibroblasts caused a 5- to 10-fold increase in bFGF expression. Steady-state bFGF expression was increased 108% by platelet-derived growth factor (PDGF) and 602% by transforming growth factor-beta (TGF-beta). Insulin-like growth factor-1 had no significant effect on bFGF expression. Nuclear runoff studies demonstrated that both PDGF and TGF-beta increased the relative rates of bFGF transcription in the fibroblasts. Western blot analysis of lysates from fibroblasts treated with either PDGF or TGF-beta had no detectable increase in bFGF protein above unstimulated controls. However, the simultaneous addition of PDGF and TGF-beta, or FCS, produced a marked increase in bFGF. These experiments show that two growth factors present in the alveolar airspace compartment of fibrotic lungs can promote the expression of bFGF within lung fibroblasts.
Insights
Growth factors from alveolar macrophages may influence lung fibrosis by affecting basic fibroblast growth factor (bFGF) expression in lung fibroblasts. This study shows specific growth factors can increase bFGF gene and protein levels, potentially driving fibrotic processes.
Area of Science:
- Pulmonary Medicine
- Cell Biology
- Fibrosis Research
Background:
- Alveolar macrophages produce growth factors implicated in lung fibrosis.
- These factors are hypothesized to stimulate fibroblast proliferation and extracellular matrix deposition.
- The precise mechanisms by which macrophages influence fibroblast behavior in fibrotic lungs require further elucidation.
Purpose of the Study:
- To investigate if macrophage-derived growth factors modulate basic fibroblast growth factor (bFGF) expression in lung fibroblasts.
- To determine the effects of specific growth factors on bFGF gene and protein production.
- To understand the role of bFGF in the context of lung fibrotic diseases.
Main Methods:
- Utilized normal adult human lung fibroblast cell lines.
- Assessed bFGF gene expression via transcript analysis (Northern blot implied).
- Quantified bFGF protein levels using Western blot analysis.
- Investigated the impact of fetal calf serum (FCS), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta) on bFGF expression.
- Employed nuclear runoff assays to evaluate bFGF transcriptional rates.
Main Results:
- Fibroblasts constitutively express bFGF gene at basal levels.
- Fetal calf serum (FCS) significantly increased bFGF expression (5- to 10-fold).
- Platelet-derived growth factor (PDGF) increased steady-state bFGF expression by 108%.
- Transforming growth factor-beta (TGF-beta) markedly increased steady-state bFGF expression by 602%.
- PDGF and TGF-beta increased the relative rates of bFGF gene transcription.
- Neither PDGF nor TGF-beta alone increased detectable bFGF protein levels.
- Simultaneous addition of PDGF and TGF-beta, or FCS, led to a marked increase in bFGF protein.
Conclusions:
- Specific growth factors, namely PDGF and TGF-beta, found in fibrotic lung environments can significantly enhance bFGF gene expression in lung fibroblasts.
- While these factors increase bFGF transcription, protein levels are only markedly elevated under conditions of combined stimulation or FCS exposure.
- These findings suggest a complex regulatory mechanism where macrophage-derived factors contribute to the fibrotic process by modulating bFGF expression in lung fibroblasts.