A role for Notch signaling in corneal wound healing

To identify the role of the Notch signaling pathway in corneal wound healing, rat corneas receiving either epithelial or stromal wounds were placed in organ culture for up to 3 and 14 days, respectively. Localization of Notch receptors--Notch1, Notch2, and their ligands--Delta1, Jagged1 was determined by immunofluorescence. Wounds were treated with a γ-secretase inhibitor to suppress Notch signaling or recombinant Jagged1 to enhance Notch signaling and morphological changes in the epithelium and stroma were recorded. The expressions of markers of cell proliferation (Ki67) and epithelial differentiation (cytokeratin 3) were assessed by immunohistology. Notch1 and Notch2 were localized to suprabasal epithelial cells in normal corneas. During corneal wound healing, both Notch receptors were detected in suprabasal and superficial epithelial layers. Delta1 and Jagged1 were observed throughout all corneal epithelial cell layers and occasional keratocytes of the stroma in normal and wounded corneas. γ-secretase inhibition of Notch resulted in increased epithelial cell layers, with recombinant Jagged1 activation of Notch leading to a reduction in epithelial cell layers during corneal wound healing. Correspondingly, the activation of Notch resulted in a decreased cytokeratin 3 expression in the corneal epithelium, with no effect on cellular expression of Ki67. Notch signaling pathway suppressed corneal epithelial differentiation during corneal wound healing, but had no effect on epithelial cell proliferation.