Molecular changes during TGF β‐mediated lung fibroblast‐myofibroblast differentiation: implication for glucocorticoid resistance

Abstract

Airway remodeling is an important process in response to repetitive inflammatory‐mediated airway wall injuries. This is characterized by profound changes and reorganizations at the cellular and molecular levels of the lung tissue. It is of particular importance to understand the mechanisms involved in airway remodeling, as this is strongly associated with severe asthma leading to devastating airway dysfunction. In this study, we have investigated the transforming growth factor‐ β ( TGF β, a proinflammatory mediator)‐activated fibroblast to myofibroblast transdifferentiation pathway, which plays a key role in asthma‐related airway remodeling. We show that TGF β induces fibroblast to myofibroblast transdifferentiation by the expression of α SMA, a specific myofibroblast marker. Furthermore, Smad2/Smad3 gene and protein expression patterns are different between fibroblasts and myofibroblasts. Such a change in expression patterns reveals an important role of these proteins in the cellular phenotype as well as their regulation by TGF β during cellular transdifferentiation. Interestingly, our data show a myofibroblastic TGF β‐mediated increase in glucocorticoid receptor ( GR) expression and a preferential localization of GR in the nucleus, compared to in fibroblasts. Furthermore, the GR β (nonfunctional GR isoform) is increased relative to GR α (functional isoform) in myofibroblasts. These results are interesting as they support the idea of a GR β‐mediated glucocorticoid resistance observed in the severe asthmatic population. All together, we provide evidence that key players are involved in the TGF β‐mediated fibroblast to myofibroblast transdifferentiation pathway in a human lung fibroblast cell line. These players could be the targets of new treatments to limit airway remodeling and reverse glucocorticoid resistance in severe asthma.