Cellular Basis of Steroid Glaucoma

Glaucoma is a blinding disease affecting millions of Americans. This disease causes blindness because the eye pressure becomes elevated and destroys the optic nerve without which one cannot see. Treatment of the eye with steroid eye drops can result in an increase in pressure inside the eye, and in some individuals steroids can actually cause glaucoma, and loss of vision. The purpose of the research outlined in this grant proposal is to discover the reasons that steroid treatment causes increased pressure, and to use this knowledge to develop potential means to prevent and treat this type of glaucoma. It is even likely that these new treatment approaches will help us develop new medications for other types of glaucoma. There are two layers of cells through which the clear fluid in the eye, or aqueous humor, must pass as it drains from the eye and returns to the circulation. Normally, the aqueous flows through small spaces which lie between the cells in these layers. By studying human cells kept alive and growing in a healthy state, we are seeking to understand how the passage of fluid across these cells is regulated. Early results indicate that steroid treatment narrows the channels between cells and reduces the now. We have also discovered that this reduction in flow is caused by the fact that steroids appear to increase formation of zipper-like structures. It is these “zippers” which hold the cells close together so that the fluid cannot pass through those barriers as easily. If this goes on in the eyes of patients with steroid glaucoma, then we would expect to identify many more “zippers” in the drainage system of the eye. Similarly, if we can learn how to prevent the formation of such structures, it may be possible to allow the fluid to get out of the eye more rapidly thus reducing the eye pressure to normal levels. Our studies indicate that steroid treatment narrows the channels between cells and reduces the flow several-fold. We have also discovered that this reduction in flow is accompanied by an increase in specialized cell “junctions” which “zip” the cells together more tightly. Finally, we found that a particular protein, which is associated with these cell junctions, increases dramatically with steroid treatment. To test the relationship of this protein to fluid flow we have selectively blocked its production with a molecule designed to “lock” onto its cellular message. Blocking expression of this protein results in increased now across cell monolayers. During the first year of this project, we have developed a new technique for rapid measurement of the steroid effect which we can apply to our future studies in which we will determine whether the effects of the steroid are directly related to the dose of the drug, by measurement of changes in fluid now through the cells and alterations in the cell junctions and their associated proteins. Once we understand the mechanisms by which steroids act on the cell barriers, we can begin to evaluate potential medical treatments to block these specific effects. To this end, we will conduct similar investigations in experimental animals, with the ultimate goal of designing a specific therapy to prevent steroid glaucoma.