Molecular Mechanisms Of Glaucoma

National Eye Institute

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Abstract

It is now well established that mutations in the myocilin (MYOC) gene are associated with juvenile open angle glaucoma, often showing high IOP. Moreover, between 2.6% and 4.3% of sporadic primary open angle glaucoma cases are associated with mutations in this gene. Animal models may provide a very useful tool to study the molecular mechanisms involved in IOP elevation after expression of mutated Myoc in eye tissues. Since it has not been know whether mutations in the olfactomedin domain of Myoc, in species other than humans, will affect secretion of these proteins, we compared properties of wild-type and mutated mouse and human Myocilin (Myoc) proteins. Tyr423His and Ile463Ser mutations were introduced into the mouse Myoc protein by in vitro mutagenesis. Similar to human MYOC, wild-type and mutated mouse Myoc demonstrated vesicular staining in transfected cells. However, while wild-type human and mouse Myoc were preferentially located in both the endoplasmic reticulum and Golgi, mutated human and mouse Myoc were located mainly in the endoplasmic reticulum and were excluded from Golgi. Similar to mutations in human MYOC, mutations in mouse Myoc dramatically reduced its secretion from transfected cells. The presence of mutated human MYOC prevented secretion of wild-type mouse Myoc but did not dramatically effect secretion of alkaline phosphatase, thrombospondin, TIMP-3 or olfactomedin-1. This suggests that the presence of mutated mouse or human Myoc does not block a general secretory pathway. We concluded that properties of the mouse Myoc protein are similar to those of the human MYOC. We continue to study properties of a novel olfactomedin domain-containing protein, optimedin, which we previously identified. We demonstrated that the optimedin-expressing PC12 cells were more strongly attached to collagen I or collagen IV extracellular matrix compared with control cells. mRNA levels of about 100 genes were changed by >2 fold in optimedin-expressing cells versus control cells 6 hrs after nerve growth factor treatment. We demonstrated (in collaboration with Dr. A. Surguchov, VAMC and Department of Neurology, Kansas University Medical Center, Kansas City, MO) that myocilin may interact with gamma-synuclein. gamma-Synuclein is a small (14.5 kDa) soluble centrosome-associated protein expressed in the retina and optic nerve head, as well as in other tissues. We suggested that interaction of myocilin and gamma-synuclein may play an important role in glaucoma.