EXPRESSION AND DISTRIBUTION OF ADHESION MOLECULE CD44 IN HEALING CORNEAL EPITHELIA

PURPOSE. TO study isoform expression and cellular distribution of CD44 , a cell surface glycoprotein thought to be an adhesion molecule in ce ll-cell and cell-substratum interactions, during corneal epithelial wo und healing. METHODS. Reverse transcription-polymerase chain reaction was performed to determine alternatively spliced rat CD44 isoforms. In situ hybridization was carried out on frozen sections of the mt corne as obtained at different time points after epithelial debridement. S-3 5-Labeled sense and antisense cRNA that recognizes rat CD44 standard f orm was used as a probe. Immunofluorescence was used to assess express ion and localization of CD44 in the rat corneas during reepithelializa tion. RESULTS. Corneal epithelia contained several alternatively splic ed CD44 variants. Four large CD44 variants with inserts V1 through V10 , V2 through V10, V3 through V10, and V4 through V10 were differential ly expressed in migratory epithelia. The silver grains, indicating CD4 4 transcripts, started to increase in the epithelial cells surrounding the wound margin 3 hours after wounding and peaked at 18 hours in the basal epithelial cell layers, at which time the epithelia were active ly migrating. As the cells began proliferation after wounding, the den sity of CD44 mRNA label declined but was still significantly higher th an that in control specimens. The label returned to basal level as epi thelial cells reverted to their normal phenotype. The location of CD44 on cell surfaces during corneal reepithelialization was consistent wi th the pattern of mRNA production. In the corneas at 18 hours after wo unding, CD44 immunoreactivity was elevated in the entire epithelium, f rom the leading edge to the limbal-corneal border. As happened for the mRNA, the cell surface CD44 declined as cells differentiated to reest ablish the multilayered epithelium. CONCLUSIONS. The expression of CD4 4 correlates with corneal reepithelialization, suggesting that CD44 ma y be involved in cell-cell interactions that provide adhesive strength for the much stressed epithelial sheet and in the cell-substratum int eractions that mediate cell migration during reepithelialization.