Up-regulation of matrix metalloproteinase-1 and interleukin-6 expression in cocultures of corneal fibroblasts and neural cells.

The cornea is the most sensitive tissue in the human body, with the dense nerve endings of the cornea being derived from the first division of the ophthalmic nerve. The existence of such organized nerve fibers reflects the role of neural regulation in corneal homeostasis, with the proper distribution and function of these nerve fibers thus being required for maintenance of a healthy cornea. We recently established an in vitro model, based on the coculture of human corneal epithelial cells and fibroblasts on opposite sides of a collagen vitrigel membrane. We have now examined the role of neural cells in corneal homeostasis with the use of a similar coculture system. Reverse transcription-polymerase chain reaction and immunoblot analyses showed that the presence of neural cells (differentiated PC12 cells) increased the expression of matrix metalloproteinase-1 (MMP-1) in human corneal fibroblasts at both the mRNA and protein levels. The expression of MMP-2 and MMP-9 in corneal fibroblasts was not affected by PC12 cells. Furthermore, a multiplex assay showed that, among various cytokines assayed, only the release of interleukin-6 in cocultures of the two cell types was markedly greater than that in cultures of corneal fibroblasts alone. These results thus suggest that factors released from neural cells may play an important role in regulation of the function of corneal fibroblasts and thereby contribute to the maintenance of corneal structure and function.