Mutant myocilin nonsecretion in vivo is not sufficient to cause glaucoma

Glaucoma is a leading cause of blindness, affecting over 70 million people worldwide. Vision loss is the result of death of the retinal ganglion cells. The best-known risk factor for glaucoma is an elevated intraocular pressure (IOP); however, factors leading to IOP elevation are poorly understood. Mutations in the MYOC gene are an important cause of open-angle glaucoma. Over 70 MYOC mutations have been identified, and they lead to approximately 5% of all primary open-angle glaucoma cases. Nevertheless, the pathogenic mechanisms by which these mutations elevate IOP are presently unclear. Data suggest that a dominant interfering effect of misfolded mutant MYOC molecules may be pathogenic. To test this hypothesis, we have generated mice carrying a mutant allele of Myoc that is analogous to a human mutation that leads to aggressive glaucoma in patients. We show that mutant MYOC is not secreted into the aqueous humor. Instead of being secreted, mutant MYOC accumulates within the iridocorneal angle of the eye, consistent with the behavior of abnormally folded protein. Surprisingly, the accumulated mutant protein does not activate the unfolded protein response and lead to elevated intraocular pressure or glaucoma in aged mice of different strains. These data suggest that production, apparent misfolding, and nonsecretion of mutant MYOC are not, by themselves, sufficient to cause glaucoma in vivo.