Helper T effector cytokines implicated in asthma modulate the contractility of human airway smooth muscle (HASM) cells. We have reported recently that a profibrotic cytokine, transforming growth factor (TGF)-β1, induces HASM cell shortening and airway hyperresponsiveness. Here, we assessed whether TGF-β1 affects the ability of HASM cells to relax in response to β2-agonists, a mainstay treatment for airway hyperresponsiveness in asthma. Overnight TGF-β1 treatment significantly impaired isoproterenol (ISO)-induced relaxation of carbachol-stimulated, isolated HASM cells. This single-cell mechanical hyporesponsiveness to ISO was corroborated by sustained increases in myosin light chain phosphorylation. In TGF-β1–treated HASM cells, ISO evoked markedly lower levels of intracellular cAMP. These attenuated cAMP levels were, in turn, restored with pharmacological and siRNA inhibition of phosphodiesterase 4 and Smad3, respectively. Most strikingly, TGF-β1 selectively induced phosphodiesterase 4D gene expression in HASM cells in a Smad2/3-dependent manner. Together, these data suggest that TGF-β1 decreases HASM cell β2-agonist relaxation responses by modulating intracellular cAMP levels via a Smad2/3-dependent mechanism. Our findings further define the mechanisms underlying β2-agonist hyporesponsiveness in asthma, and suggest TGF-β1 as a potential therapeutic target to decrease asthma exacerbations in severe and treatment-resistant asthma.
Ojiaku CA, Chung E, Parikh V, et al. Transforming growth factor-β1 decreases β2-agonist–induced relaxation in human airway smooth muscle. Am J Respir Cell Mol Biol. 2019;61(2):2019-2018. https://doi.org/10.1165/rcmb.2018-0301OC
American Thoracic Society
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