Background and objective: Connective tissue growth factor (CTGF) is up-regulated in the lungs of patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke and repeated bacterial infections, both of which are rich sources of LPS, are major causes of COPD. The high levels of LPS in lung epithelial lining fluid also suggest that it may have a considerable impact on the airway epithelium, in terms of cytokine and growth factor production. The aim of this study was to clarify the mechanism of LPS-induced CTGF expression in bronchial epithelial cells.
Methods: The expression and transcriptional regulation of the CTGF gene were assessed using the cultured human bronchial epithelial cell line, BEAS-2B.
Results: LPS significantly up-regulated CTGF mRNA expression in a dose-dependent fashion, with 100 microg/mL LPS causing a twofold increase after 2 h. CTGF protein expression was also up-regulated by LPS after 8 h. Transforming growth factor-beta1 mRNA expression was not changed by LPS treatment. A pharmacological inhibitor of nuclear factor (NF)-kappaB, MG132, inhibited LPS-induced CTGF mRNA expression. Furthermore, luciferase assays demonstrated that deletion of base pairs -253 to -53 from the CTGF promoter, where the Smad and proximal NF-kappaB binding sites are located, decreased the induction of CTGF by LPS. After stimulation with LPS, the p65 subunit of NF-kappaB was shown to be bound to the CTGF promoter in vitro and in situ.
Conclusions: LPS directly induced CTGF expression in bronchial epithelial cells, independently of transforming growth factor-beta1, suggesting a possible mechanism for airway remodelling in COPD that is induced by smoking and repeated bacterial infections.