2009 Southern Regional Meeting Abstracts

Purpose of Study: Idiopathic Pulmonary Fibrosis (IPF) is a chronic, progressive interstitial lung disease with an unknown cause. Patients with IPF often suffer from some form of gastroesophageal reflux disease (GERD), which can range from esophageal reflux to aspiration into the lung. Although GERD has been implicated in the pathogenesis of IPF, its role is controversial and the mechanisms involved in this association remain largely unexplored. Studies suggest that injury to lung epithelial cells might promote lung fibrosis. This process includes the transformation of epithelial cells into mesenchymal-type smooth muscle-like cells with augmented capacity for matrix remodeling and tissue contraction. Because of the perceived importance of this process, termed epithelial-mesenchymal transformation (EMT), we explored the relationship between GERD and EMT in vitro.
Methods Used: We tested the hypothesis that specific components of gastric fluid could stimulate EMT. Specifically, we explored the effects of gastric fluid (HCl with and without pepsin, pH 2.0) versus pepsin (a protein-degrading enzyme) alone on rat lung epithelial type II cells. We incorporated techniques that involved cell culture, western blot analysis for protein production, RT-PCR for RNA analysis, and zymography for detection of enzyme activity.
Summary of Results: We found that exposure to pepsin stimulated the expression of α-smooth muscle actin (αSMA), a marker of EMT. Interestingly, gastric fluid (pH 2.0) in the absence of pepsin failed to stimulate αSMA expression. Of note, pepsin-induced EMT was also associated with increased expression of fibronectin, an extracellular matrix glycoprotein implicated in injury and repair. Furthermore, we determined that pepsin induced the expression of gelatinolytic activity related to matrix metalloproteinase-9 (MMP-9) and matrix metalloproteinase-7 (MMP-7).
Conclusions: Together, these in vitro observations suggest that pepsin stimulates lung epithelial cells to undergo EMT characterized by increased expression of αSMA, matrix glycoproteins, and matrix-degrading proteases, thereby providing a cellular mechanism by which chronic GERD can promote the progression of IPF, and unveiling potential targets for therapy.