TGF-β causes up-regulation of prepro-endothelin-1 in bronchial epithelial cells, an effect opposed by insulin

Prof. Dr. Racké, Kurt1, Dr. Warnken, Mareille1, Holtin, Stefan Michael1, Reitzenstein, Ulrich1, Prof. Dr. Juergens, Uwe R.2, Dr. Mayer, Peter3. 1Univ. Bonn Depart. Pharmacol, Reuterstr. 2b, D-53113 Bonn, Germany ; 2Univ. Hospital Med. Clinic II, Sigmund-Freud-Str. 25, 53105 Bonn, Germany ; 3Federal Inst. for Drugs and Medical Devices, Kurt-Georg-Kiesinger Allee 3, 53175 Bonn, Germany.

There is increasing evidence that endothelin may be involved in the pathogenesis of pulmonary hypertension and various fibrotic remodelling processes associated with chronic inflammatory airway diseases. TGF-β is a cytokine of particular importance for the initiation and maintenance of fibrotic processes. In the lung TGF-β can trigger epithelial-mesenchymal transition (EMT), a process which may result in the generation of activated pulmonary fibroblasts. The present study aimed to explore whether TGF-β–induced EMT of bronchial epithelial cells is associated with altered expression of endothelin and/or endothelin receptors.

Human bronchial epithelial (H-292) cells were cultured for 1 week in presence of 1 % FCS and absence or presence of 5 ng/ml TGF-β. Expression of mRNA encoding N-cadherin (a mesenchymal marker), prepro-endothelin-1 and endothelin (ET-A and ET-B) receptors was determined by quantitative real time PCR.

After one week exposure to TGF-β, H-292 cells lost their typical epithelial shape and showed a fibroblast-like appearance, changes associated with a marked increase in the expression of N-cadherin mRNA (by 2186±90%, n=13). Mesenchymal transition of H-292 cells results in a marked up-regulation of prepro-endothelin-1 mRNA which was increased by 1258±90% (n=4) after one week exposure to TGF-β. ET-A, but no ET-B receptor mRNA was found to be expressed in H-292 cells cultured under control conditions and TGF-β exposure resulted in 80% reduction of the ET-A receptor transcript. Most interestingly, insulin (1 µM) present together with TGF-β markedly opposed the TGF-β-induced EMT and the up-regulation of prepro-endothelin-1 mRNA.

Human bronchial epithelial cells are potential source of pulmonary endothelin-1. The marked up-regulation of endothelin-1 by TGF-β suggests a role of endothelin in fibrotic lung processes. The mechanisms by which insulin opposes epithelial-mesenchymal transition and the up-regulation of endothelin-1 remain to be determined.