Abstract
Transforming growth factor-beta(1) (TGF-beta(1)) is a central mediator in tissue remodeling processes, including fibrosis and airway smooth muscle (ASM) hyperplasia, as observed in asthma. The mechanisms underlying this response, however, remain unclear because TGF-beta(1) exerts only weak mitogenic effects on ASM cells. In this study, we hypothesized that the mitogenic effect of TGF-beta(1) on ASM is indirect and requires prolonged exposure to allow for extracellular matrix (ECM) deposition. To address this hypothesis, we investigated the effects of acute and prolonged treatment with TGF-beta(1), alone and in combination with the muscarinic receptor agonist methacholine, on human ASM cell proliferation. Acutely, TGF-beta(1) exerted no mitogenic effect. However, prolonged treatment (for 7 d) with TGF-beta(1) increased ASM cell proliferation and potentiated the platelet-derived growth factor-induced mitogenic response. Muscarinic receptor stimulation with methacholine synergistically enhanced the effect of TGF-beta(1). Interestingly, the integrin-blocking peptide Arg-Gly-Asp-Ser, as well as integrin alpha 5 beta(1) function-blocking antibodies, inhibited the effects of TGF-beta(1) and its combination with methacholine on cell proliferation. Accordingly, prolonged treatment with TGF-beta(1) increased fibronectin expression, which was also synergistically enhanced by methacholine. The synergistic effects of methacholine on TGF-beta(1)-induced proliferation were reduced by the long-acting muscarinic receptor antagonist tiotropium and the M-2 receptor subtype-selective antagonist gallamine, but not the M-3-selective antagonist DAU5884. In line with these findings, the irreversible G(i) protein inhibitor pertussis toxin also prevented the potentiation of TGF-beta(1)-induced proliferation by methacholine. We conclude that prolonged exposure to TGF-beta(1) enhances ASM cell proliferation, which is mediated by extracellular matrix-integrin interactions, and which can be enhanced by muscarinic M-2 receptor stimulation.
Original language | English |
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Pages (from-to) | 18-27 |
Number of pages | 10 |
Journal | American Journal of Respiratory Cell and Molecular Biology |
Volume | 49 |
Issue number | 1 |
DOIs | |
Publication status | Published - Jul-2013 |
Keywords
- airway smooth muscle cell proliferation
- TGF-beta(1)
- collagen Type I
- fibronectin
- muscarinic receptor
- EXTRACELLULAR-MATRIX PROTEINS
- NONNEURONAL CHOLINERGIC SYSTEM
- HUMAN LUNG FIBROBLAST
- GUINEA-PIG MODEL
- TGF-BETA
- MEDIATE STIMULATION
- CELL PROLIFERATION
- PULMONARY-FIBROSIS
- TIOTROPIUM BROMIDE
- ASTHMA