Transforming growth factor-β1 is a potent inhibitor of secretory leukoprotease inhibitor expression in a brochial epithelial cell line

Abstract

Obliterative bronchiolitis (OB) is the major long-term complication following lung and heart-lung transplantation. In bronchoalveolar lavage fluid samples obtained from patients suffering from OB, a marked increase in the number of neutrophils and elevated expression of transforming growth factor (TGF)-β1 had been found. The goal of the study was to evaluate whether TGF-β1 is capable of interfering with the expression of the secretory leukoprotease inhibitor (SLPI), the dominating defence of the conducting airways against neutrophil elastase (NE). The authors analysed the effects of TGF-β1 on gene expression and protein release of SLPI by cultured human bronchial epithelial (BEAS-2B) cells. SLPI protein levels in the supernatants were quantified with a specific enzyme-linked immunosorbent assay; SLPI messenger ribonucleic acid (mRNA) levels were measured by reverse transcriptase polymerase chain reaction. Incubation with TGF-β1 induced a marked decrease in SLPI protein levels (1 ng · mL-1 TGF-β1: stimulation index (SI; protein: relation to SLPI protein release of resting cells) = 0.56; 10 ng · mL-1 TGF-β1: SI = 0.48; 50 ng · mL-1 TGF-β1: SI = 0.37, p<0.01 each) and mRNA expression (1 ng · mL-1 TGF-β1: SI (SI mRNA: relation to SLPI mRNA expression of resting cells) = 0.46; 10 ng · mL-1 TGF-β1: SI= 0.31; 50 ng · mL-1 TGF-β1: SI=0.18, p<0.01 each) in a dose dependent fashion. Simultaneous incubation of BEAS-2B cells with TGF-β1 and NE also caused a significant reduction in SLPI synthesis (10 ng · mL-1 TGF-β1 + 7.5 U · mL-1 NE: mRNA SI = 0.61, p<0.05; protein SI = 0.65, p<0.05; 50 ng · mL-1 TGF-β1 + 7.5 U · mL-1 NE: mRNA SI = 0.52, p<0.05; protein SI = 0.58, p<0.05; 10 ng · mL-1 TGF-β1: mRNA SI = 0.33, p<0.01; protein SI = 0.38, p<0.01). In conclusion, the data suggest that the coincidence of neutrophilia and upregulation of transforming growth factor-β1 in obliterative bronchiolitis may lead to uninhibited neutrophil elastase activity by downregulation of secretory leukoprotease inhibitor, with the consequence of ongoing injury to the epithelium. (C) ERS Journals Ltd 2000.