Insulin modulation of bronchial epithelial cell fibronectin in vitro

Fibronectin (Fn) is involved in the migration of epithelial cells in re- epithelialization of wounds. Epithelial cell-derived Fn is particularly potent as a chemotactic factor for bronchia/epithelial cells (BECs) in vitro. Thus modulation of airway epithelial cell Fn may be a key aspect of airway repair. Insulin is both an important growth factor and known chemotactic factor for cultured BECs. We postulated that insulin may modulate Fn production of cultured BECs. We examined this hypothesis utilizing bovine BECs in culture with serum-free media with and without insulin. BECs grown in media without insulin released more Fn into culture supernatants and contained more Fn in cell layers than cells grown with insulin. Labeling of cells with [³⁵S]methionine demonstrated an increase in new protein production and Fn mRNA expression was increased. Increased Fn in BEC cultures without insulin was associated with an increase in active transforming growth factor-β (TGF-β) release as measured by a standard bioassay. Increased BEC Fn in cultures without insulin was partially inhibited by exposure of cultures to TGF-β antibody. Thus insulin appears to modulate BEC Fn production in vitro in part through a TGF-β-dependent mechanism. Insulin may be involved in airway repair mechanisms through modulation of epithelial cell Fn production.