Plasminogen activator inhibitor type 2 in human corneal epithelium

PURPOSE. To examine normal human corneal epithelium in vivo and in vitro fo r expression and status of plasminogen activator inhibitor type 2 (PAI-2). METHODS. Normal human corneas were prepared for frozen sections and for cul ture of corneal keratinocytes. PAI-2 was analyzed by immunohistochemistry a nd western blot analysis using antibodies that recognize all forms of PAI-2 . RESULTS. In vivo and in vitro, PAI-2 was immunohistochemically localized to the superficial corneal keratinocytes. Immunostaining also revealed the pr esence of PAI-2 in its relaxed (i.e., cleaved) conformation. In vivo, the s taining pattern of the relaxed form was identical with that of total PAI-2, but in vitro the relaxed form was detected in a smaller subpopulation of s uperficial cells, in vitro, the staining pattern indicated a cytoplasmic lo calization for PAI-2. Western blot analysis revealed that most of the PAI-2 was cell associated and functionally active. CONCLUSIONS. The present results are the first to show that PAI-2 is found in normal human corneal epithelium in vivo and in vitro, where it can be co nsidered as a differentiation product. At least in vitro, all detectable PA I-2 is cell associated, with a cytoplasmic distribution. A subpopulation of keratinocytes also contains PAI-2 in its relaxed (i.e., cleaved) conformat ion. Cleavage by an as yet unidentified cytoplasmic proteinase may constitu te a crucial aspect of the function of corneal epithelial PAI-2, which may be relevant to terminal differentiation and death of the corneal keratinocy te.