Previous studies from our laboratory have

Previous studies from our laboratory have demonstrated that CysLT1R mRNA and protein expression can be upregulated by T2-type cytokines (IL-13, IL-4, and IL-5) in monocytes, macrophages, and eosinophilic HL-60 cells., To our knowledge, however, there are no studies on interactions of cytokines (such as TGF-β/IL-13) and cysLTs, in terms of human BSMC proliferation. In the current work, we studied the modulation of CysLT1R expression in human BSMC by TGF-β, IL-13, and IFN-γ and the functional relevance of this modulation in terms of BSMC proliferation in response to LTD. Methods
Results
Discussion Our results demonstrate that TGF-β, IL-13, and IFN-γ can upregulate the expression of CysLT1R protein in BSMC. The effect was time- and concentration-dependent. Interestingly, another prototypic TH2-type cytokine, IL-4, had no effect on CysLT1R expression in human BSMC. Previous results obtained by our laboratory have demonstrated that CysLT1R expression levels are upregulated in eosinophilic HL-60 reboxetine by IL-5 and in monocytes and macrophages by IL-13 and IL-4 but not IFN-γ.18, 19 In these myeloid cells, the increased expression of CysLT1R resulted in an enhanced responsiveness to LTD4 in terms of Ca2+ transients and chemotaxis. In the current study, we showed that TGF-β, IFN-γ, and IL-13 but not IL-4 can also upregulate CysLT1R expression in bronchial smooth muscle, suggesting that CysLT1R expression is regulated differentially in a cell-specific manner. Moreover, a bell-shaped concentration response curve was observed in the cytokine-mediated effect. A bell-shaped isotherm is unusual in cytokine interactions with their receptors, although it is frequently observed with ligand interactions with G-protein–coupled receptors. In the latter, bell-shaped isotherms may be attributed to receptor desensitization at higher ligand concentrations, to different signal transduction systems activated by ligand binding at two independent receptors or to agonist-activated receptor coupling to multiple G proteins, which mediate opposing actions on a downstream effector. It is unclear, however, whether any such mechanisms are operative in our system. The current study is, to our knowledge, the first demonstration that the upregulation of CysLT1R induced by TGF-β and IL-13 increases human BSMC proliferation in response to LTD4. The CysLT1R antagonist Montelukast ablated this effect, suggesting that the proliferation effect was selective for CysLT1R. As previously reported in the literature,10, 23 TGF-β could also induce BSMC proliferation by itself. Recently, Amrani et al reported that IFN-γ could upregulate CysLT1R expression in human airway myocytes and that this upregulation increased their contractile responses to LTD4. This may contribute to the airway hyperreactivity observed in asthma.24, 25 In the Brown Norway rat model, the increase in bronchial responsiveness induced by inhaled antigen was reported to be directly related to an increase in the mass of BSMC, and both increases were blocked by the CysLT1R antagonist MK571. However, in our study, human BSMC pretreated with IFN-γ did not show increased proliferation when exposed to LTD4, although the expression of CysLT1R was augmented by this cytokine. The reason for this discrepancy is not readily evident, and, despite the known inhibitory effects of IFN-γ on cell proliferation and protein synthesis,24, 25, 26 no decrease in basal BSMC proliferation was observed with IFN-γ. It has been demonstrated that a significant increase in the area of airway smooth muscle occurs in chronic asthmatic inflammation. A growing body of evidence suggests that CysLTs may have a role in airway remodeling. Chronic overproduction of relatively low levels of CysLTs by mast cells or eosinophils may have subtle effects on structural cells of the airways, leading to bronchial hyperresponsiveness and possibly influencing pathways involved in airway wall remodeling. Evidence suggests that LTD4 can potentiate the induction of DNA synthesis and proliferation induced by the mitogen epidermal growth factor in human BSMC. In a mouse model, CysLTs appeared to be responsible for the increase in airway smooth muscle after repeated allergen challenge. The allergen-induced increases in airway smooth muscle were significantly reduced by treatment with a CysLT1R antagonist. In Brown Norway rats sensitized to ovalbumin, CysLTs induced airway smooth muscle and epithelial cell DNA synthesis as well as airway smooth muscle thickening after repeated allergen exposure.