Urokinase and its receptor in follicular and inflammatory cysts of the jaws

Objective: Proteases are considered critical in peri-cystic tissue degradation required in jaw cyst expansion. We studied the expression of the plasminogen activation system (plasminogen activators; their inhibitor type-1, PAI-1; the receptor for the urokinase-type plasminogen activator, uPAR) in follicular and inflammatory cysts of the jaw, to identify a possible role of this system in jaw cyst enlargement. Materials and Methods: Jaw cysts were collected by therapeutic enucleation. ELISA and casein zymography were used to measure and characterize plasminogen activators in cyst fluid. By immunohistochemistry we examined the presence of uPAR in cyst walls and inflammatory cells, and by Western blotting the molecular forms of uPAR within the cyst fluid. Results: Inflammatory cysts fluid contained higher amounts of plasminogen activators of the urinary-type (uPA), and lower amounts of PAI-1, when compared to follicular cysts fluid. Epithelial layers of both types of cysts and inflammatory cells expressed uPAR. Native 3-domain uPAR was scarcely detectable within cysts, where its cleavage was accounted for by uPA. Conclusion: These data suggest a plasminogen activation-dependent mechanism of cyst enlargement, where only the outward uPAR expressed on epithelial cells and on inflammatory cells direct the peri-cystic protease cascade, in a way similar to tumor enlargement within tissues.