Effects of TGF-beta and budesonide on MAPK phosphorylation, IL-6/IL-11 secretion, and cell proliferation in human lung fibroblasts

Transforming growth factor-beta (TGF-beta) is crucially involved in the fibrotic events characterizing interstitial lung diseases, as well as in the airway remodeling process typical of asthma. Within such a context, the aim of our study was to investigate, in primary cultures of normal human lung fibroblasts, the effects of TGF-beta1 on mitogen activated protein kinase (MAPK) phosphorylation, cell proliferation and production of interleukins 6 (IL-6) and 11 (IL-11), in the presence or absence of a pretreatment with either budesonide or MAPK inhibitors. MAPK phosphorylation was detected by Western blotting, using specific monoclonal antibodies against the phosphorylated, active forms of these enzymes. Cell count was performed by Trypan blue staining, and the release of IL-6 and IL-11 into cell culture supernatants was assessed by ELISA. TGF-beta1 (10 ng/mL) significantly stimulated MAPK phosphorylation (p<0.01), and also enhanced cell numbers as well as the secretion of both IL-6 and IL-11 (p<0.01), which reached the highest increases at the 72nd hour of cell exposure to this growth factor. All such effects were prevented by budesonide (10-8 M) and, with the exception of IL-6 release, also by a mixture of MAPK inhibitors. Therefore, our findings suggest that the fibrotic action exerted by TGF-beta1 in both airways and lung parenchyma is mediated at least in part by MAPK activation and by an increased synthesis of the profibrogenic cytokines IL-6 and IL-11; these effects seem to be prevented by glucocorticoids via inhibition of MAPK phosphorylation.