Sonic hedgehog expression and role in healing corneal epithelium

To examine the expression pattern and roles of Sonic hedgehog (Shh) in healing corneal epithelium.

Immunofluorescent staining and Western blot analysis were used to detect Shh, patched 1 (Ptc 1) receptors, and Gli transcription factors in corneal epithelium of Wistar rats (n = 44) at various intervals after an epithelial defect. Effects of exogenous Shh on cell proliferation and cyclin D1 expression were determined in healing corneal epithelium of organ-cultured mouse eyes.

Uninjured rat corneal epithelium was not labeled by anti-Shh antibody, but weakly positive for Ptc 1. Basal cells of limbal and conjunctival epithelia were labeled by antibodies against Shh and Ptc 1. Shh protein was transiently upregulated in limbal epithelium in 2 hours and was also transiently expressed in the migrating corneal epithelium with its peak at 12 hours postdebridement. Such upregulation of Shh expression was associated with a transient nuclear translocation of Gli-3 without lifting the suppression of cell proliferation in migrating epithelium postdebridement in vivo. However, an addition of Shh protein to culture medium resulted in nuclear accumulation of cyclin D1 and marked acceleration of epithelial cell proliferation in migrating corneal epithelium of an organ-cultured mouse eye.

Corneal epithelial debridement causes a transient upregulation of Shh expression and activation of Shh/Gli-3 signaling cascade in healing corneal and limbal epithelia. Although exogenous Shh promotes epithelial cell proliferation in corneal organ culture, its expression in migrating epithelium in vivo does not counteract the suppression of cell proliferation at the early healing phase of epithelium debridement.