Dexamethasone decreases tissue plasminogen activator activity in trabecular meshwork organ and cell cultures

Previously, we observed that dexamethasone decreased the extracellular activity of some matrix metalloproteinases and tissue plasminogen activator in trabecular meshwork containing organ explants and cell cultures. We have extended these studies to determine whether the decrease in extra-cellular tissue plasminogen activator activity is the result of a decrease in the expression of tissue plasminogen activator, a change in the extracellular level of plasminogen activator inhibitor-1, or a combination of both. We demonstrate that dexamethasone decreases the steady-state levels of tissue plasminogen activator mRNA by 75% in trabecular meshwork cells using Northern blot analysis, and show that this occurs concurrently with a 31% increase in the levels of extracellular plasminogen activator inhibitor-1 as determined by enzyme-linked immunosorbent assay analysis. A 38% increase was also measured in the extracellular plasminogen activator inhibitor-1 levels in trabecular meshwork containing organ explants after treatment. The amount of active, extracellular tissue plasminogen activator decreased by 72% in trabecular meshwork organ explant cultures, and 96% in trabecular meshwork cell cultures after treatment as determined using a parabolic rate assay for tissue plasminogen activator activity. These data suggest that dexamethasone decreases the extracellular activity of tissue plasminogen activator in trabecular meshwork containing organ and cell cultures by decreasing the expression of tissue plasminogen activator and increasing the extracellular levels of plasminogen activator inhibitor-1.