Plasminogen Activator Inhibitor-1 mRNA Is Localized in the Ciliary Epithelium of the Rodent Eye

To identify in the adult and developing rodent eye cells expressing the gene encoding plasminogen activator inhibitor-1 (PAI-1), an important component of the fibrinolytic system. PAI-1 mRNA was localized in cryostat thin eye sections via in situ hybridization analysis using specific 35S-labeled riboprobes. PAI-1 activity was tested in the aqueous humor using one-phase reverse zymography. In the adult eye, PAI-1 mRNA was detected exclusively in epithelial cells of the ciliary processes, primarily in the apexes. In addition, PAI-1 activity was detected in the aqueous humor. PAI-1 mRNA was first found in the ciliary epithelium in embryonic day 18.5, when the ciliary body has reached an advanced developmental stage. PAI-1 mRNA was also detected in the ganglion cell layer of the retina at postnatal days 1 to 4, when angiogenesis takes place. During development, PAI-1 is likely to be involved in retina vascularization, in agreement with other cases of angiogenesis. Results for the adult eye indicate that the ciliary epithelium is the source for PAI-1 activity found in the aqueous humor. The results suggest that PAI-1 plays a role in balancing fibrinolysis and proteolysis specifically in the anterior segment of the eye, implying that PAI-1 overproduction in the ciliary epithelium could shift the balance against proteolysis and thus may interfere with aqueous outflow.