EFFECT OF ELASTASE ON THE DIRECTIONAL MIGRATION OF LUNG FIBROBLASTS WITHIN A 3-DIMENSIONAL COLLAGEN MATRIX

Interactions between airway epithelial cells and bronchial fibroblasts often require close proximity between these cells. Previous studies h ave demonstrated that airway epithelial cells direct the migration of lung fibroblasts, but the factors that regulate this process during ai rway injury are not clear. We hypothesized that exposure of culture su bstrates to proteolytic enzymes, like those present in the inflamed ai rway, would increase fibroblast recruitment. We also postulated that e lastase might affect the epithelium's ability to attract fibroblasts. We used an in vitro model with fibroblasts embedded between two layers of collagen gel to investigate their migration. Embedded fibroblasts exposed to culture medium alone (baseline) had a slight downward migra tion (migration directed to the upper gel layer expressed as a percent age of total migration was -2.8 +/- 1.4), but medium supplemented with porcine pancreatic elastase (PPE) resulted in a slight upward migrati on (2.0 +/- 1.4). When airway epithelial cells were cultured on the up per gel surface, the index of directed migration toward them was 15.9 +/- 1.3. Addition of PPE to the culture medium resulted in a significa nt increase to 22.3 +/- 1.5 (p < .05). Human neutrophil elastase (HNE) produced similar results, and these effects were inhibited by alpha 1 -proteinase inhibitor. Similarly, total fibroblasts per 20 high-powere d fields were counted In all conditions, suggesting that mitogenic int eractions were not important in this system. The percentage of the tot al fibroblasts migrating at least 5 mu m in any direction was also sim ilar in all groups, suggesting chemokinetic mechanisms were not involv ed. These data suggest that elastase exposure in a model of the human airway increases directed fibroblast migration through the extracellul ar matrix. This phenomenon may play a role in the development of subep ithelial fibrosis seen in inflammatory airway diseases like asthma.