Glaucoma is a heterogeneous eye disease that is the second leading cause of bilateral blindness worldwide. The prevalence of open angle glaucoma (OAG), the most common form of the disease, is increasing in the United States because of an aging population. Myocilin is the first gene to be conclusively associated with inherited OAG, but the mechanism(s) by which heterozygous myocilin mutations cause a dominant glaucoma phenotype is not known. In work accomplished during the last funding period, we found that mutant myocilin proteins are misfolded and accumulate as aggregates within the endoplasmic reticulum (ER) of cells. Prolonged expression of mutant myocilin resulted in death of cultured human trabecular meshwork (HTM) cells. Culturing cells at a lower temperature, a condition known to promote protein folding, increased secretion of the mutant protein and ameliorated its deleterious effects on HTM cells. Testing of a variety of mutant myocilins showed that temperature sensitive secretion is a general property and that there is a correlation between the biochemical properties of particular mutant myocilins and the severity of their associated glaucoma phenotypes. Our findings indicate that myocilin-associated glaucoma is a protein conformational disease, and suggest a progression of events in which chronic expression of misfolded, non- secreted myocilin leads to prolonged ER-stress, HTM cell dysfunction and death, and, ultimately, a dominant glaucoma phenotype. We now seek to identify the factors that influence HTM cell susceptibility to mutant myocilin expression. We will exploit differences among myocilin mutants, HTM cell lines, and culture temperature conditions to identify critical stress-induced consequences of mutant myocilin expression in cells. Knowledge of these pathways will be used to test defined hypotheses regarding manipulations that may protect HTM cells from the deleterious effects of mutant myocilin. Success of this project will indicate points for therapeutic intervention for myocilin-associated glaucoma, and may uncover aspects of HTM cell physiology that are relevant to a wider spectrum of this blinding, neurodegenerative disease.
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