DIFFERENTIAL INTRASTROMAL INVASION BY NORMAL OCULAR SURFACE EPITHELIAIS MEDIATED BY DIFFERENT FIBROBLASTS

For most mucosal epithelia including the ocular surface, it is general ly believed that wound healing is executed by epithelial migration on the plane of erosion or ulceration. In explant cultures, we incidental ly observed the phenomenon of intrastromal invasion by corneal, limbal and conjunctival epithelial cells even when cell migration on plastic s was promoted. Homotypic and heterotypic tissue recombinants between corneal and conjunctival epithelial cells and their stroma revealed th at this phenomena was dependent on viable mesenchymal cells and was mo re active in conjunctival stroma than corneal stroma. Using organotypi c cultures in which 3T3 fibroblasts were incorporated in collagen gel, we noted that this phenomenon was fibroblast-dependent and up-regulat ed by lifting the culture to the air-fluid interphase. The extent of i ntrastromal invasion was decreased if 3T3 fibroblasts were treated wit h increasing concentrations of mitomycin C. The invading epithelial is lands retained the same basal and suprabasal epithelial phenotypes as those of the surface epithelial layers using several anti-keratin mono clonal antibodies. Using 5-fluorouracil (5-FU) to eliminate the rapid- cycling, i.e. transient amplifying progenitor basal cells, we further noted that this phenomenon could still be produced by 5-FU-resistant s low-cycling progenitor cells of corneal, limbal and conjunctival expla nts. In organotypic cultures, conjunctival fibroblasts were more activ e than corneal fibroblasts in inducing corneal or conjunctival epithel ial invasion. As such intrastromal invasion can experimentally be prod uced by normal non-transformed adult epithelial cells and mediated by fibroblasts, this in vitro phenomenon may be useful for studying the e pithelial-mesenchymal interactions operating during embryonic developm ent and post-natal wound healing. (C) 1995 Academic Press Limited