Abstract
Bronchial smooth muscle cell (SMC) hyperplasia is a key feature in the pathology of asthma. Platelet-derived growth factor (PDGF) isoforms are SMC mitogens. We investigated the effect of basic fibroblast growth factor (bFGF), transforming growth factor-beta 1 (TGF-beta 1), interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) on the PDGF receptor system on human bronchial SMC from three different donors. bFGF induced gene expression of the PDGF alpha-receptor (PDGF-R alpha) approximately threefold without altering the PDGF beta-receptor (PDGF-R beta). IL-1 beta and TNF-alpha did not affect the PDGF receptor system. TGF-beta 1 downregulated PDGF-R alpha mRNA approximately 60% without changing PDGF-R beta mRNA levels. Receptor assays showed that bFGF increased the [125I]PDGF-AA binding site approximately twofold, whereas TGF-beta 1 reduced [125I]PDGF-AA binding approximately 60%. TGF-beta 1, but not latent TGF-beta 1, counteracted the bFGF-induced increase in [125I]PDGF-AA binding. PDGF-AA-stimulated tyrosine phosphorylation on the PDGF-R alpha was enhanced after treatment with bFGF, bFGF pretreatment enhanced the mitogenic response of SMC to PDGF-AA and PDGF-AB. These findings suggest that upregulation of the PDGF-R alpha by bFGF could contribute to SMC hyperplasia during chronic airway inflammation in asthma.
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