Regeneration of rabbit cornea following excimer laser photorefractive keratectomy: A study on gap junctions, epithelial junctions and epidermal growth factor receptor expression in correlation with cell proliferation

Corneal wound repair was investigated in rabbits following excimer laser ab lation of a 6 mm diameter and 90 mum deep disc. In the healing process part icular attention was focused on the epithelium where gap junction expressio n and the rearrangement of desmosomes and hemidesmosomes were correlated wi th cell proliferation and epidermal growth factor receptor expression. Immu nofluorescence-based confocal laser scanning microscopy, semithin resin sec tion morphology and electron microscopy were utilized. In resting cornea tw o isotypes of gap junctions, confined to different regions in the same basa l epithelial cells, were detected. Particulate connexin43 (alpha1) immunost aining was concentrated on the apical while the connexin26 type (beta2) in the baso-latheral cell membranes. This is the first report of connexin26 in the cornea. Connexin43 was found also in corneal keratocytes and endotheli al cell. Since the two connexins do not form functioning heteromeric channe ls and have selective permeabilities they may serve alternative pathways fo r direct cell-cell communication in the basal cell layer. During regenerati on both connexins were expressed throughout the corneal epithelium includin g the migrating cells. They also showed transient up-regulation 24 hr after wounding in the form of overlapping relocation to the upper cell layers. A t this time, basal epithelial cells at the limbal region, adjacent to the w ound and those migrating over the wounded area all expressed membrane bound epidermal growth factor receptor and they were highly proliferating. In co nclusion, like in other stratified epithelia connexin26 is also expressed i n the cornea. Transient up-regulation and relocation of connexins within th e regenerating epithelium may reflect the involvement of direct cell-cell c ommunication in corneal wound healing, Mitotic activity in the migrating co rneal epithelial cells is also a novel finding which is probably the sign o f the excessive demand for new epithelial cells in larger wounds not met al one by the proliferating limbal stock. (C) 2001 Academic Press.