Differential Display of Genes in Trabecular Meshwork

Glaucoma is the second leading cause of vision loss worldwide. By the year 2000, an estimated 66.8 million people will have primary glaucoma, and 6.7 million will be bilaterally blind due to this disorder. In the United States, glaucoma is the second leading cause of permanent blindness. Glaucoma is treatable and vision loss can be prevented; once vision loss occurs, it is irreversible. Elevated intraocular pressure (IOP) is a major risk factor for the development of glaucoma, and the mechanism is thought to be due to an increase in outflow resistance through the trabecular meshwork and Schlemm’s canal. Corticosteroids have a variety of effects on cells and tissues. In laboratory studies, exposure to the dexamethasone (DEX) has been shown to inhibit both the migration and proliferation of TM cells. This drug also decreases the expression of mature collagenases, which are necessary for the maintenance and remodeling of the trabecular beams. Exposure of TM cells to DEX can modify the secretion of some glycoproteins, especially a group of sialylated proteins which are postulated to be associated with glaucoma. A variety of genes are affected by steroid treatment. One gene, myocilin (MYOC), also called the Trabecular meshwork Inducible Glucocorticoid Response (TIGR) gene, has been associated with some forms of juvenile and adult glaucoma. Because MYOC is present in the trabecular meshwork of aged normal eyes, the mere presence of MYOC does not cause glaucoma. Glaucoma may be caused by excess amounts of MYOC or its mutant forms, or by an interaction of MYOC with other components in the TM. We suspect that other proteins or gene products may act with MYOC to produce glaucoma. We believe these are most likely related to the basement membrane of Schlemm’s canal. We expect DEX treatment to induce numerous genes, of which several have already been identified. While our goal is to look for the induction of basement membrane products, we will begin by obtaining a total map of the number of genes involved. This will be done at two time periods-after 1 day and after 14 days, looking for a time-dependent induction. Although we do not expect to see much change after 1 day treatment, we consider 1 day as internal control for 14 days’ DEX treatment. Differential display (DD) is a rapid technique for identification and isolation of induced or suppressed genes. We will use DD as a screening method to look for the induction or suppression of genes involved in synthesis of basement membrane after dexamethasone treatment. As previously described, the histological findings of steroid glaucoma suggest excessive basement membrane production.