Molecular Mechanisms Of Glaucoma

National Eye Institute

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Abstract

It is now well established that a genetic component may contribute to glaucoma, and several glaucoma-associated genes have been identified. The first identified and the most studied gene is Myocilin, which is heavily expressed in and secreted by the trabecular meshwork, one of the key components of the eye aqueous humor outflow system. The myocilin protein belongs to a family of glycosylated proteins containing a C-terminal olfactomedin domain. Dominant mutations in Myocilin are found in 3-4% of patients with primary open angle glaucoma and most of these glaucoma-causing mutations are located in the olfactomedin domain. The function of wild-type Myocilin is not clear. To study functions of human myocilin, wild-type and mutated myocilin were expressed in HEK293 cells under inducible promoter. Conditioned medium from myocilin-expressing cells as well as purified myocilin induced formation of stress fibers in primary cultures of human trabecular meshwork or NIH3T3 cells. Stress fiber-inducing activity of myocilin was blocked by antibodies against myocilin as well as secreted inhibitors of Wnt-signaling, sFRP1 or sFRP3. Interaction of myocilin with sFRP3 and several frizzled receptors was confirmed by immunoprecipitation experiments and by binding of myocilin to the surface of cells expressing cysteine-rich domains of different sFRPs and Frizzled proteins. Treatment of NIH3T3 cells with myocilin and its proteolytic fragments induced intracellular re-distribution of -catenin and its accumulation on the cellular membrane but did not induce nuclear accumulation of -catenin. Overexpression of myocilin in the eye angle tissues of transgenic mice stimulated accumulation of -catenin in these tissues. Myocilin and Wnt proteins may perform redundant functions in the mammalian eye, as myocilin modulates Wnt signaling by interacting with components of this signaling pathway.