Abstract
Abstract: :
Purpose:To examine the kinetics of activation of Smad and of MAP kinase (MAPK) in healing, injured, corneal epithelium. TGFß signals via Smads and MAPK signaling pathway play pivotal roles in modulating wound healing. Methods:Central corneal epithelium was scraped in one eye of 35 C57Bl6 mice and was allowed to heal up to 24 hr. The animals were sacrificed after i.p. BrdU labeling . The eye was subjected to immunostaining for Smads, Erk-1, TG-interacting factor (TGIF), vimentin, lumican, and BrdU. Effects of intraocular administration of neutralizing antibodies against each TGFß on Smad4 localization and BrdU incorporation were also examined. Results:Uneven immunoreactivity of Smad3/4 was seen in nuclei of uninjured corneal epithelium. Migrating epithelial cells at 6 and 12 hr were negative for nuclear Smads3/4, whereas the cells outside the defect were positive. The migrating epithelium was BrdU-negative, and transiently expressed vimentin and lumican. At 18 and 24 h, Smad3/4 can be detected in many nuclei of the regenerated epithelium. Smad7 protein expression was up-regulated in migrating cells and returned to normal after resurfacing. Erk-1 and TGIF were located in cell cytoplasm in normal central corneal epithelium, whereas they were translocated to nuclei throughout the healing up to 24 hr. TGFß1- or ß2-neutralizing antibody induced an increment of BrdU-positive epithelial cells and a decrease of Smad4-positive nuclei and of Smad7 protein expression. Conclusion:Migrating epithelium has characteristics of mesenchymal cells. Migrating corneal epithelial cells lack nuclear Smads3/4 and transiently up-regulate Smad7, signifying Smad signal transduction in corneal epithelial wound healing. TGFß via Smad signal in migrating epithelial cells might involve epithelial-mesenchymal transition. Activation of MAPK cascade may involve cell proliferation in regenerated epithelium.
Keywords: 372 cornea: epithelium • 631 wound healing • 580 signal transduction