Investigations on the Role of the Fibrinolytic Pathway on Outflow Facility Regulation

PURPOSE: To understand the role and further dissect pathways downstream of tissue plasminogen activator (tPA) and the fibrinolytic pathway in modulating outflow facility. METHODS: Outflow facility of tissue plasminogen activator (Plat) knockout (KO) mice was determined and compared to that of wild-type (WT) littermates. Gene expression of urokinase plasminogen activator (Plau), plasminogen activator inhibitor (Pai-1), plasminogen (Plg), and matrix metalloproteinases (Mmp-2, -9, and -13) was measured in angle tissues. Expression of the same genes and outflow facility were measured in KO and WT mice treated with triamcinolone acetonide (TA). Amiloride was used to inhibit urokinase plasminogen activator (uPA) in Plat KO mice, and outflow facility was measured. RESULTS: Plat deletion resulted in outflow facility reduction and decreased Mmp-9 expression in angle tissues. Plasminogen expression was undetectable in both KO and WT mice. TA led to further reduction in outflow facility and decreases in expression of Plau and Mmp-13 in plat KO mice. Amiloride inhibition of uPA activity prevented the TA-induced outflow facility reduction in Plat KO mice. CONCLUSIONS: tPA deficiency reduced outflow facility in mice and was associated with reduced MMP expression. The mechanism of action of tPA is unlikely to involve plasminogen activation. tPA is not the only mediator of TA-induced outflow facility change, as TA caused reduction in outflow facility of Plat KO mice. uPA did not substitute for tPA in outflow facility regulation but abrogated the effect of TA in the absence of tPA, suggesting a complex role of components of the fibrinolytic system in outflow regulation.