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Plasminogen Activator Inhibitor Type 2 in Human Corneal Epithelium

¹ From the Departments of Dermatology and ³ Ophthalmology, University of Pennsylvania School of Medicine, Philadelphia; the ² Department of Biological Sciences, University of Wollongong, Australia; and the ⁴ Gynaecological Cancer Research Centre, Royal Women’s Hospital, Carlton, Victoria, Australia.

PURPOSE. To examine normal human corneal epithelium in vivo and in vitro for expression and status of plasminogen activator inhibitor type 2 (PAI-2).

METHODS. Normal human corneas were prepared for frozen sections and for culture of corneal keratinocytes. PAI-2 was analyzed by immunohistochemistry and 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 presence of PAI-2 in its relaxed (i.e., cleaved) conformation. In vivo, the staining 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 superficial cells. In vitro, the staining pattern indicated a cytoplasmic localization 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 considered as a differentiation product. At least in vitro, all detectable PAI-2 is cell associated, with a cytoplasmic distribution. A subpopulation of keratinocytes also contains PAI-2 in its relaxed (i.e., cleaved) conformation. Cleavage by an as yet unidentified cytoplasmic proteinase may constitute a crucial aspect of the function of corneal epithelial PAI-2, which may be relevant to terminal differentiation and death of the corneal keratinocyte.

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