Neuropeptides released from trigeminal neurons promote the stratification of human corneal epithelial cells.

PURPOSE To examine the effects of neural cells on the stratification of and junctional protein expression by corneal epithelial cells with a coculture system. METHODS PC12 cells induced to undergo neuronal differentiation or rat trigeminal nerve cells were cultured together with simian virus 40-transformed human corneal epithelial (HCE) cells on opposite sides of a collagen vitrigel membrane. Stratification of HCE cells was examined by immunofluorescence analysis with antibodies to zonula occludens-1. Expression of junctional proteins in HCE cells was assessed by RT-PCR and immunoblot analyses. RESULTS The presence of neural cells (PC12 cells or trigeminal neurons) markedly promoted the stratification of HCE cells as well as increased the amounts of N-cadherin mRNA and protein in these cells. These effects of the neural cells were mimicked by conditioned medium prepared from differentiating PC12 cells or by the neuropeptides substance P and calcitonin gene-related peptide (CGRP). Furthermore, the stimulatory effects of trigeminal neurons on the stratification of and N-cadherin expression by HCE cells were inhibited by antagonists of substance P or of CGRP. CONCLUSIONS These results suggest that trigeminal neurons play an important role in the differentiation of corneal epithelial cells. Neuropeptides released from these neurons may thus regulate adhesion between corneal epithelial cells and thereby contribute to the establishment and maintenance of corneal structure and function.