Potentiation by cyclic AMP of the stimulatory effect of epidermal growth factor on corneal epithelial migration.

Abstract

To provide insight into the mechanism by which epidermal growth factor (EGF) stimulates corneal epithelial migration, we investigated the possible interaction between EGF and cyclic AMP (cAMP) signaling pathways during epithelial migration with an organ culture system for the rabbit cornea. Rabbit corneal blocks were cultured in the absence or presence of various agents for 24 hours and were then fixed, dehydrated, embedded in paraffin, sectioned, and stained with hematoxylin-eosin. The path length of epithelial migration was measured on light micrographs of the stained sections. Epidermal growth factor alone stimulated corneal epithelial migration in a dose-dependent manner. In contrast, neither of two cell-permeable cAMP analogs, dibutyryl cAMP and 8-bromo cAMP, affected epithelial migration at concentrations up to 1 mM. In the presence of EGF (10 ng/mL), however, each of the two cAMP derivatives increased the extent of epithelial migration in a concentration-dependent manner. Neither the adenylate cyclase activator forskolin nor the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine alone affected epithelial migration. However, each of these two agents potentiated the stimulatory effect of EGF on this process. The stimulatory effects of fibronectin, hyaluronan, and interleukin-6 on corneal epithelial migration were not modified by either dibutyryl cAMP or 3-isobutyl-1-methylxanthine. These results demonstrate that cAMP potentiates the stimulation of corneal epithelial migration by EGF in vitro, suggesting that endogenous cAMP might function as a modulator of epithelial wound healing promoted by this growth factor in vivo.