[The role of myocilin in the pathogenesis of primary open-angle glaucoma]

Mutations in myocilin are responsible for autosomal-dominant inherited juvenile open-angle glaucoma and some subgroups of adult-onset glaucoma (POAG). Myocilin is a secreted glycoprotein with a molecular weight of approximately 55-57 kDa that forms dimers and multimers. Structural motives are domains that have similarities with myosin and olfactomedin, a signalling sequence as well as a leucine zipper at the N-terminus of myocilin. Most mutations that were identified in patients with POAG are localized in the olfactomedin domain which is highly conserved between species. In the eye, myocilin is highly expressed in the trabecular meshwork (TM), the sclera, the ciliary body and the iris, lower amounts are seen in the retina and the optic nerve. In addition, secreted myocilin is detected in the aqueous humor. In the chamber angle, myocilin is associated with fibrillar components of the extracellular matrix in the cribriform portion of the TM. Myocilin binds specifically to the HepII domain of fibronectin. In organ cultures of perfused anterior eye segments, recombinant myocilin increases outflow resistance. In cultured TM cells, myocilin is induced by treatment with dexamethasone in a similar time course as observed in steroid-induced glaucoma. Myocilin is also induced by transforming growth factor-beta (TGF-beta) and mechanical stress. Mice with a targeted disruption of the myocilin gene do not express a phenotype. Experimental data indicate that mutated myocilin is not secreted and accumulates in cells which might critically impair the function of the TM.