Leukotriene D4‐induced, epithelial cell‐derived transforming growth factor β1 in human bronchial smooth muscle cell proliferation

Abstract

Cysteinyl-leukotrienes (cys-LTs) orchestrate many pathognomonic features of asthma in animal models of allergic airway inflammation, including bronchial smooth muscle cell (BSMC) hyperplasia. However, because cys-LTs alone do not induce mitogenesis in monocultures of human BSMC, the effect observed in vivo seemingly involves indirect mechanisms, which are still undefined. This study aims to investigate the regulatory role of leukotriene (LT)D(4) on TGF-beta1 expression in airway epithelial cells and the consequence of this interplay on BSMC proliferation. HEK293 cells stably transfected with cys-LT receptor 1 (CysLT1) (293LT1) were stimulated with LTD(4) and TGF-beta1 mRNA and protein expression was measured using Northern blot and ELISA, respectively. Conditioned medium (CM) harvested from LTD(4)-treated cells was then assayed for its proliferative effect on primary human BSMC. TGF-beta1 mRNA expression was also determined in tumoural type II pneumocytes A549 and in normal human bronchial epithelial cells (NHBE) following LTD(4) stimulation. The results demonstrated that LTD(4)-induced TGF-beta1 mRNA production in a time- and concentration-dependent manner in 293LT1. TGF-beta1 secretion was also up-regulated and CM from LTD(4)-treated 293LT1 was shown to increase BSMC proliferation in a TGF-beta1-dependent manner. The increased expression of TGF-beta1 mRNA by LTD(4) also occured in A549 and NHBE cells via a CysLT1-dependent mechanism. In conclusion, elevated expression of cys-LTs in asthmatic airways might contribute to BSMC hyperplasia and concomitant clinical features of asthma such as airway hyperresponsiveness via a paracrine loop involving TGF-beta1 production by airway epithelial cells.