Integrins mediation of alveolar epithelial cell migration on fibronectin and type I collagen

Acute lung injury leads to type I alveolar epithelial cell (AEC) death, denudation of the alveolar basement membrane, and formation of an alveolar provisional matrix from fibronectin, fibrinogen, and type I collagen. The provisional matrix provides a scaffold for alveolar repair. To restore normal lung architecture, surviving type II AECs must reepithelialize denuded alveoli. We examined whether AECs migrate on provisional matrix proteins and whether integrins mediate this migration using a Boyden chemotaxis chamber. Cultured AECs migrated on fibronectin-coated filters by haptotaxis (defined as movement on a solid-phase substrate) more than on type I collagen-coated filters, and they did not migrate on fibrinogen-coated filters. Soluble fibronectin augmented migration on type I collagen-coated filters, but not on fibronectin-coated filters. Anti-α(v)β₃-integrin monoclonal antibody (MAb) inhibited migration of substrate-bound fibronectin by 62-77%, whereas anti- β₁-integrin MAb inhibited migration by 48%. Anti-α₂-integrin MAb almost completely inhibited migration on substrate-bound type I collagen, but not on fibronectin. The novel findings in this study are as follows: 1) AECs migrate by haptotaxis more effectively on substrate-bound fibronectin than on type I collagen; 2) α(v)β₃- and β₁-integrins partially mediate AEC haptotaxis on fibronectin; and 3) the α₂β₁-integrin mediates AEC migration on type I collagen. These results support the importance of type II cell migration on provisional matrix proteins during repair of lung injury.