Bronchial Epithelial Cells Respond to Insulin and Insulin-like Growth Factor-I as a Chemoattractant

Abstract

Abstract Migration of epithelial cells to cover areas of injury is thought to be important in the repair process following airway insult. Insulin is reported to be a growth factor for bronchial epithelial cells, and growth factors have been known to be chemotactic for many types of cells. Thus, we hypothesized that insulin may be a chemoattractant for bronchial epithelial cells. To evaluate this, we prepared bronchial epithelial cells and measured their chemotactic activity toward insulin. Bronchial epithelial cells were isolated by overnight digestion with bacterial protease, filtered through 100-µm nitex mesh, and then cultured at 1 × 106 cells/ml in tissue culture dishes in medium 199 supplemented with transferrin, insulin, epidermal growth factor, hydrocortisone, antibiotics, and 10% FCS for 3 d. The cultured cells were rinsed twice to remove supplements, trypsinized and resuspended at 1 × 106 cells/ml in medium 199 without supplements, and used as the cell source for Chemotaxis. Chemotactic activity of bronchial epithelial cells was measured by the blind well chamber technique using 8-µm Nuclepore filter membranes coated with 0.1% gelatin. The cells were added to the top wells in a 48-multiwell chamber with insulin in the bottom wells and incubated for 6 h at 37° C, 5% CO2. Bronchial epithelial cells migrated in response to insulin in a dose-dependent manner up to an optimal dose of insulin, 100 µg/ml, and decreased at higher concentrations. The number of migrated cells per 10 high power fields was 33.7 ± 1.9 at the optimum and 3.7 ± 0.7 without insulin (P < 0.01). “Checkerboard” analysis demonstrated that the migration was both chemokinetic and chemotactic. Insulin-like growth factor-I (IGF-I) was tested similarly and found to be both chemoattractant for bronchial epithelial cells and more potent than insulin. Multiple stimulating activity (MSA, insulin-like growth factor-II of mouse) had no chemotactic activity. These data suggest the possible binding of insulin to IGF type I receptor to stimulate Chemotaxis. The release of IGF-I-like peptides at sites of inflammation and airway injury could, therefore, be a mechanism to mediate early stages of airway repair.