Related Experiment Videos
Transforming growth factor beta 1 downregulates the platelet-derived growth factor alpha-receptor subtype on human
J C Bonner1, A Badgett, P M Lindroos
1Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Abstract:
Fibroblasts are the central target cell in pulmonary fibrotic diseases, and their proliferation is mediated largely by platelet-derived growth factor (PDGF) isoforms secreted by activated lung macrophages. Several other macrophage-derived cytokines that are increased during fibrogenesis, including interleukin-1 beta and transforming growth factor-beta 1 (TGF-beta 1), could potentially modulate the mitogenic and chemotactic activity of PDGF by altering the expression of cell-surface PDGF receptors on fibroblasts. The PDGF receptor system on fibroblasts from a variety of tissues shows heterogeneous responses to TGF-beta 1. Lung fibroblasts have not been investigated in this regard. TGF-beta 1 downregulated the gene expression of the 6.5 kb PDGF-alpha receptor (PDGF-R alpha) transcript in normal human lung fibroblasts in a concentration-dependent fashion that was maximal at 3 ng/ml TGF-beta 1; this corresponded with a decrease in cell-surface PDGF-R alpha as measured by radioligand binding assays using [125I]PDGF-AA. The TGF-beta 1-induced down-regulation of the PDGF-R alpha gene was rapid (maximal suppression by 2 h post-treatment) and preceded the decrease in cell-surface alpha-receptor (maximal reduction by 6 h post-treatment). TGF-beta 1 treatment did not alter the rate of PDGF-R alpha mRNA degradation following the inhibition of transcription using actinomycin D, indicating that TGF-beta 1 increases PDGF-R alpha transcription. Scatchard analysis of saturation binding data showed that TGF-beta 1 decreased the number of [125I]PDGF-AA binding sites 5-fold without affecting receptor affinity. [125I]PDGF-AB binding sites were downregulated approximately 25%, and the number of [125I]PDGF-BB binding sites was not changed by TGF-beta 1 treatment, indicating that the PDGF-beta receptor was not affected. TGF-beta 1 reduced the mitogenic and chemotactic response to PDGF-AA by > 90%, whereas these biologic response to PDGF-AB and PDGF-BB were inhibited 50% to 80%. The proliferative and chemotactic responses of fibroblasts during tissue remodeling or during lung fibrosis are likely controlled by a complex network involving PDGF isoforms and cytokines that modify the PDGF receptor system.
Insights
Transforming growth factor-beta 1 (TGF-beta 1) downregulates platelet-derived growth factor-alpha receptor (PDGF-R alpha) gene expression in lung fibroblasts. This reduces fibroblast proliferation and chemotaxis, impacting fibrotic disease progression.
Area of Science:
- Cell Biology
- Pulmonary Medicine
- Molecular Biology
Background:
- Fibroblast proliferation drives pulmonary fibrotic diseases.
- Macrophage-derived factors, including platelet-derived growth factor (PDGF) and transforming growth factor-beta 1 (TGF-beta 1), regulate fibroblast activity.
- The impact of TGF-beta 1 on PDGF receptor expression in lung fibroblasts is not well understood.
Purpose of the Study:
- To investigate the effect of TGF-beta 1 on PDGF receptor expression and function in normal human lung fibroblasts.
- To determine how TGF-beta 1 modulates fibroblast responses to different PDGF isoforms.
Main Methods:
- Normal human lung fibroblasts were treated with varying concentrations of TGF-beta 1.
- Gene expression of PDGF-alpha receptor (PDGF-R alpha) was measured using quantitative assays.
- Cell-surface receptor levels were assessed via radioligand binding assays using [125I]PDGF-AA, [125I]PDGF-AB, and [125I]PDGF-BB.
- Fibroblast mitogenic and chemotactic responses to PDGF isoforms were quantified.
Main Results:
- TGF-beta 1 significantly downregulated PDGF-R alpha gene expression and cell-surface receptor levels in a concentration-dependent manner.
- TGF-beta 1 reduced the number of PDGF-R alpha binding sites without altering receptor affinity, and did not affect the PDGF-beta receptor.
- The study observed a rapid suppression of PDGF-R alpha gene expression preceding the decrease in cell-surface receptors.
- TGF-beta 1 markedly inhibited fibroblast responses to PDGF-AA and partially inhibited responses to PDGF-AB and PDGF-BB.
Conclusions:
- TGF-beta 1 plays a critical role in regulating PDGF receptor expression in lung fibroblasts.
- The downregulation of PDGF-R alpha by TGF-beta 1 significantly impairs fibroblast mitogenic and chemotactic responses to PDGF-AA.
- These findings highlight a complex interplay between PDGF and TGF-beta 1 in controlling fibroblast behavior during fibrotic processes.