Early changes in matrix metalloproteinases and inhibitors after in vitro laser treatment to the trabecular meshwork

Extracellular matrix turnover in the trabecular meshwork may play a role in regulating aqueous humor outflow. Laser trabeculoplasty is a common treatment for open-angle glaucoma. The mechanism of this treatment is not understood. We investigated changes in the levels and expression of the matrix metalloproteinases and their tissue inhibitors (TIMPs) in this tissue using cultured human anterior segment explants and standard clinical-parameter laser treatment. Medium gelatinase A activity levels are relatively high for sham-treated controls and are not changed dramatically following laser treatment. Medium gelatinase B and stromelysin activity levels are low in sham-treated explants and increase significantly by 24 h after treatment. TIMP1 levels, as assessed by immunoblots of Western transfers, are initially low. However, by 24 h TIMP1 levels have increased significantly. Using semi-quantitative reverse transcription and the polymerase chain reaction, mRNA levels of stromelysin, gelatinase B and TIMP1 are shown to increase after laser treatment, while gelatinase A and TIMP2 remain relatively constant. The increases in trabecular stromelysin and gelatinase B in response to laser trabeculoplasty may have important implications for the mechanism of action of this treatment for open-angle glaucoma.