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

Abstract

PurposeTo understand the role and further dissect pathways downstream of tissue plasminogen activator (tPA) and the fibrinolytic pathway in modulating outflow facility.MethodsOutflow 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.ResultsPlat 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.ConclusionstPA 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.

ID1 and ID3 are Negative Regulators of TGFβ2-Induced Ocular Hypertension and Compromised Aqueous Humor Outflow Facility in Mice

“…[64][65][66] TGFβ2 also increases PAI-1 expression, which inhibits plasmin activation and thereby negatively regulates activation of MMPs. 15,67 By contrast, inhibition of PAI-1 in TM cells will rescue MMP activity and lower IOP, even while in the presence of elevated levels of TGFβ2. This increase in PAI-1 expression in response to overexpression of active TGFβ2 has also been confirmed in the TGFβ2 ocular hypertensive mouse model.…”

“…ID1 is known to suppress PAI-1 and uPA expression and thereby control MMP2, MMP3, MMP9, and MMP14 activities. 29 , 30 , 67 , 69 , 71 In addition, ID1 also suppresses expression of the fibrotic proteins thrombospondin-1, LOX, βV-integrin, inhibin betaA, and FN expression in murine fibroblasts. 48 , 50 Recent reports suggest that ID3 plays a critical role in regulating corneal fibrosis by blocking α-smooth muscle actin expression.…”

Acute Effects of Intraocular Pressure-Induced Changes in Schlemm's Canal Morphology on Outflow Facility in Healthy Human Eyes

“…Although outflow facility measurement is not adopted in routine clinical practice, it is an important research tool for revealing the physiological properties of the eye and the different mechanisms of antiglaucoma medications and surgeries. 3 , 4 Electronic Schitøz tonometry 5 and pneumatonography 6 have been used to measure the outflow facility in numerous studies. Outflow facility was calculated from the pressure decay curves, and then the C value was estimated using the Langham's pressure-volume relationship tables and a polynomial fitted to the decay curve.…”

Factors Affecting Predominantly Peripheral Lesion Identification and Grading

“…Previous studies have relied on a standard qualitative technique to assess DR lesions within and outside the ETDRS fields. 1 , 2 , 6 , 7 Grading takes into account both number and extent of the lesion being graded within the field. If PPL is assessed to be present in any of the peripheral fields, the eye has been considered to have PPL.…”

“…Prior studies have shown that hemorrhages and microaneurysms (H/Mas) are by far the most frequent lesions in PPL (75–95%) and therefore could be used alone as a surrogate marker for PPL presence and severity. 1 , 2 , 6 , 7 PPLs might also be determined automatically by applying the same principles and definitions as global grading to the automated H/Ma counts. 1 , 2 , 6 , 7 This ability would be particularly important given the increased interest in developing rapid automated H/Ma counting techniques for UWF images and its potential use in clinical trials and research studies.…”