Bile acids induce CCN2 production through p38 MAP kinase activation in human bronchial epithelial cells: a factor contributing to airway fibrosis

Abstract

Background and objective: Bile acid aspiration occurs in a variety of acute and chronic airway disorders. The consequence of bile acid aspiration and lung disease remains unclear. It was hypothesized that airway epithelium exposure to bile acids would induce fibrosis via production of connective tissue growth factor (CCN2), CCN2 is essential for transforming growth factor-beta (TGFbeta)-induced fibrogenesis and functions as a downstream mediator of TGF-beta action on fibroblasts.

Methods: Human bronchial epithelial cells were grown on air-liquid interface culture inserts. Cells were stimulated with the major components of bile acids, chenodeoxycholic acid (CD) and glycochenodeoxycholic acid (GCD). RT-PCR and real-time quantitative PCR were used to detect mRNA expression. ELISA and western blotting were used to measure protein.

Results: CD-stimulated airway epithelial cells produce CCN2 at both mRNA and protein levels in a dose-dependent manner. GCD failed to increase CCN2 production. CCN2 expression occurred via activation of p38 mitogen-activated protein (MAP) kinase and the downstream transcription factor ATF-2. Dexamethasone and the selective p38 MAP kinase inhibitor SB203580 successfully inhibited p38 MAP kinase, ATF-2 phosphorylation and subsequent CCN2 production. CD induced TGF-beta1 release from airway epithelium via the same signalling pathway. TGF-beta1 therefore enhanced CCN2production in an autocrine manner.

Conclusion: Early intervention to stop these processes may be useful in preventing fibrogenesis in chronic airway diseases associated with bile acid exposure.