Human bronchial fibroblasts express the 5-lipoxygenase pathway

Background: Fibroblasts are implicated in sub-epithelial fibrosis in remodeled asthmatic airways and contribute to airway inflammation by releasing cytokines and other mediators. Fibroblast activity is influenced by members of the leukotriene family of bronchoconstrictor and inflammatory mediators, but it is not known whether human bronchial fibroblasts can synthesize leukotrienes. Methods: The expression of leukotriene biosynthetic enzymes and receptors was investigated in primary fibroblasts from the bronchi of normal and asthmatic adult subjects using RT-PCR, Western blotting, immunocytochemistry and flow cytometry. Results: These techniques revealed that human bronchial fibroblasts from both subject groups constitutively express 5-lipoxygenase, its activating protein FLAP, the terminal enzymes leukotriene A(4) hydrolase and leukotriene C-4 synthase, and receptors for leukotriene B-4 (BLT1) and cysteinyl-leukotrienes (CysLT(1)). Human bronchial fibroblasts generated immunoreactive leukotriene B4 and cysteinyl-leukotrienes spontaneously and in increased amounts after calcium-dependent activation. Flow cytometry showed that human bronchial fibroblasts transformed to a myofibroblast-like phenotype by culture with transforming growth factor-beta(1) expressed 320 - 400% more immunofluorescence for leukotriene C-4 synthase and CysLT(1) receptors, with 60 - 80% reductions in leukotriene A(4) hydrolase and BLT1 receptors. Conclusion: These results indicate that human bronchial fibroblasts may not only respond to exogenous leukotrienes but also generate leukotrienes implicated in narrowing, inflammation and remodeling of the asthmatic airway.