Leukotriene D4 stimulates collagen production from myofibroblasts transformed by TGF-β

Background: Airway remodeling has an important role in the pathogenesis of bronchial asthma. Many mediators that influence the pathophysiology of bronchial asthma, especially cysteinyl leukotrienes (CysLTs) and TGF-beta(1), are involved in airway remodeling. Objective: To know whether TGF-beta(1) alters fibroblast responsiveness to CysLTs, we examined the effects of leukotriene (LT) D-4 on collagen production from fibroblasts and from myofibroblasts transformed by TGF-beta(1). We also examined whether TGF-beta(1) upregulates CysLT1 receptor (CysLT1R) expression in fibroblasts. Methods: Concentrations of procollagen in the human fetal lung fibroblast (HFL) 1 cell supernatant were measured by using an enzyme immunoassay kit in the presence or absence of various concentrations of LTD4, TGF-beta(1), CysLT1R antagonist, or some combination of these. The mRNA expression of CysLT1R and alpha-smooth muscle actin as a marker of myofibroblasts was measured by means of real-time PCR. Furthermore, protein expression of CysLTIR on fibroblasts was measured by means of flow cytometric analysis. Results: TGF-beta(1) stimulated collagen production from HFL-1 cells, but LTD4 alone did not. LTD4 in combination with TGF-beta(1) increased collagen production compared with TGF-beta(1) alone. Real-time PCR showed that stimulation with TGF-beta(1) significantly upregulated CysLTIR and alpha-smooth muscle actin mRNA expression in HFL-1 cells. Conclusions: LTD4 increased collagen production by upregulating CysLT1R induced by TGF-beta(1). In the TGF-beta-rich milieu, activated myolibroblasts expressing CysLT1R can respond to CysLTs and produce large amounts of extracellular matrix, thereby contributing to airway remodeling. These data suggest that treatment with leukotriene receptor antagonists might prevent airway remodeling in patients with asthma.