GM-CSF-Mediated Amplification of Airway Fibrosis

Problem 1. To determine if GM-CSF (granulocyte macrophage-colony stimulating factor) protects against fibrosis using an experimental animal model of tracheal injury. 2. To determine if GM-CSF prevents cytokine-induced expression of fibrotic markers in human bronchial epithelial cells in vitro. Methods Tracheae from GM-CSF (20ng) or vehicle (PBS) treated Sprague-Dawley donor rats were heterotopically transplanted into Fischer 344 recipients. Recipients were treated daily with either GM-CSF or vehicle for seven days. Allografts were harvested on days 14 or 21 post-transplantation and analyzed for luminal collagen deposition and the presence of intact epithelium. In parallel, human bronchial epithelial cells (Beas2B) were treated with pro-fibrotic cytokines (TGFbeta1, IL-13) with or without GM-CSF. Treated cells were harvested and processed for RT-PCR or immunocytochemical analyses for expression of fibrotic markers (alpha smooth muscle actin, fibroblast-specific protein 1). Results Tracheal allografts treated with GM-CSF demonstrated a significant increase in luminal collagen deposition compared to vehicle-treated allografts. GM-CSF- treatment was associated with destruction of airway epithelium, contributing to amplification of fibrosis. Beas2B cells treated with the same concentration of GM-CSF demonstrated increased expression of markers of tissue remodeling and fibrosis as well as decreased epithelial markers. Conclusion We hypothesized that GM-CSF-mediated protection of the tracheal epithelium may prevent fibrosis of the airway. We show here that GM-CSF increases luminal fibrosis and decreases epithelial viability in vivo. In addition, treatment of Beas2B cells with GM-CSF in vitro increases expression of pro-fibrotic markers. These data emphasize the critical role of the epithelium in preventing luminal fibrosis after tracheal injury. Significance Various mediators have been considered in the etiology of tracheal stenosis. Previous studies in our lab have demonstrated the presence of GM-CSF receptors in tracheal epithelium. Our hypothesis was that protection of this epithelium could prevent airway fibrosis. The current study demonstrates that airway fibrosis correlates with a loss in epithelium induced by GM-CSF.