Labeling of cycling corneal endothelial cells during healing with a monoclonal antibody to the Ki67 antigen (MIB-1)

Purpose. To assess the efficacy of labeling actively cycling corneal endothelial cells by using a monoclonal antibody to the Ki67 antigen (MIB-1) and to determine what changes in f-actin and ZO-1 organization are associated with entry into the cell cycle during wound healing under different culture conditions. Methods. Three corneal buttons (6 mm diameter) were punched from each cornea of 15 cats. After a mechanical scrape injury (2 mm diameter) was made, buttons were cultured for 24, 48, or 72 h in serum-free media (SFM), SFM plus 10% fetal calf serum, or SFM plus basic fibroblast growth factor (bFGF). Buttons were single and double labeled by using phalloidin, anti-ZO- 1, and MIB-1. Counts of Ki67-positive cells were used to determine the number of actively cycling endothelial cells. Results. After culture in SFM, wounds healed by cell spreading with maintenance of normal apical f-actin and ZO-1 organization; Ki67-positive cells were detected near the leading edge in some areas. A significant increase in the number of cycling cells was measured after 48 h of culture in bFGF as compared with SFM (p < 0.05); serum increased the number of cycling cells more than both SFM and bFGF (p < 0.05). In all cases, positive MIB-1 staining was not observed until 48 h after injury, was limited to cells actively spreading over the wound area, and was diminished after wound closure (72 h). Double labeling demonstrated that endothelial cells exhibited a fibroblastic phenotype in some central areas of cell proliferation after culture in serum or bFGF, but, in general, apical cell border-associated f-actin and ZO-1 organization was partially maintained in most Ki67-positive cells. Conclusion. The data suggest that spreading corneal endothelial cells are capable of proliferating and can respond to growth factors, but that dedifferentiation or fibroblastic transformation is not required before entry into the cell cycle. Overall, the MIB-1 antibody appears to be ideally suited to the study of corneal endothelial proliferation during wound healing.