Histochemical Analysis of Glaucoma Caused by a Myocilin Mutation in a Human Donor Eye

Mutations in myocilin ( may cause either juvenile open angle glaucoma (JOAG) or adult-onset primary open angle glaucoma (POAG). encodes a glycoprotein that is normally secreted from trabecular meshwork cells that regulate intraocular pressure. Prior transgenic rodent, and organ culture experiments have suggested that abnormal accumulation of MYOC protein within trabecular meshwork cells is a key step in glaucoma pathophysiology. We investigated the pathogenesis of glaucoma by examining a donor eye from a patient with JOAG caused by a Tyr437His mutation. Case-control, immunohistochemical study of a donor eye from a patient with JOAG caused by a Tyr437His mutation and age-matched control donor eyes. An eye from a 59-year-old male with JOAG caused by a Tyr437His mutation and eyes from five donors (ages 51-66) with no known ocular disease were examined. Frozen fixed sections of the iridocorneal angle were prepared from the donor eyes of the glaucoma patient and control eyes. We used antibodies directed against MYOC, collagen IV, and BiP/GRP78 as well as wheat germ agglutinin and concanavalin A lectins to localize MYOC protein in the trabecular meshwork. Qualitative comparison of MYOC protein labeling and localization in the trabecular meshwork of donor eyes from a glaucoma patient with a mutation and from control subjects. Using immunohistochemistry, we detected more abundant MYOC protein within the trabecular meshwork of the glaucoma patient's eye than in control eyes. We further localized MYOC protein within the trabecular meshwork cells of the glaucoma patient's eye by co-labeling with the endoplasmic reticulum (ER) marker GRP78 (BiP). Little to no MYOC was identified within the trabecular meshwork cells of control eyes. Minimal extracellular MYOC was detected in both glaucoma eyes and control eyes. This is the first histopathological analysis of an eye from a glaucoma patient with a mutation. Furthermore, this analysis supports our model of MYOC-associated glaucoma, in which mutations cause abnormal intracellular retention of MYOC within the ER of trabecular meshwork cells as a key step towards development of glaucoma.