Down-regulation of Notch signaling during corneal epithelial proliferation.

PURPOSE: We evaluated the expression and activation of Notch pathway genes in the adult human and murine corneal epithelium during proliferation.

METHODS: The expression of Notch pathway genes in the limbal and central human corneal epithelium was compared by reverse transcription polymerase chain reaction (RT-PCR). Their expression pattern was examined by immunofluorescence and in situ hybridization. The temporal expression of Notch1 during murine wound healing was assessed by RT-PCR. Notch activity was determined using western blot for the Notch intracellular domain (NotchIC). The expression of Hes1 was evaluated in cell culture.

RESULTS: The expression of Notch1 and Jagged1 was higher in the human limbal epithelium while the expression of Hes1 and Hes5 was higher in the central cornea. Expression of Notch1, Jagged1, and Hes1 was found predominantly in the basal and immediate suprabasal cells. During neonatal corneal development, NotchIC was detected in occasional cells at P10 while at P15 and P90, it was found in the basal and early suprabasal layers. NotchIC was found to be lower in the limbal compared to central corneal epithelium. The expression of Notch1 was lower at 24 h post-wounding but was completely restored in six days. The levels of NotchIC were decreased at 24 h post-wounding and after application of topical phorbol myristate. In vitro, the expression of Hes1 was higher in confluent cells maintained under high calcium conditions.

CONCLUSIONS: The inverse correlation between Notch signaling and the proliferative status of the corneal epithelium is consistent with the idea that Notch plays a role in corneal epithelial differentiation.