It is now well established that a genetic component may contribute to glaucoma, and several glaucoma-associated genes have been identified. The first identified and the most studied gene is MYOCILIN, which is heavily expressed in and secreted by the trabecular meshwork, one of the key components in the aqueous humor outflow system of the eye. This gene is also expressed in non-ocular tissues. The functions of the encoded protein, myocilin, are still not fully understood. We showed that expression of 15-fold higher levels of myocilin in the muscles of transgenic mice led to the elevated association of 1-syntrophin, neuronal nitric oxide synthase, and -dystroglycan with dystrophin-associated protein complex (DAPC) which increased the binding of laminin to -dystroglycan and Akt signaling. Phosphorylation of Akt and Forkhead box O-class 3, key regulators of muscle size, was increased more than 3-fold, while the expression of muscle-specific RING finger protein-1 and atrogin-1, muscle atrophy markers, was decreased by 79% and 88%, respectively, in the muscles of transgenic mice. Consequently, the average size of muscle fibers of the transgenic mice was increased by 34% relative to controls. Myocilin is highly expressed in the tissues of the eye angle including the trabecular meshwork, sclera, iris and ciliary muscle. The state of ciliary muscle and its contractility are important for the architecture of the conventional trabecular meshwork outflow pathway and unconventional uveoscleral outflow pathway. Furthermore, we found that myocilin interacted with the components of DAPC in the eye angle tissues. Our data suggest that the association of myocilin with DAPC in the eye muscles may affect their contractility. This hypothesis is now being tested experimentally. We also demonstrated that myocilin is expressed in Schwann cells and localized at the nodes of Ranvier, where it interacts with gliomedin, neurofascin and NrCAM, which are nodal proteins essential for node formation and function. Addition of myocilin to isolated dorsal root ganglion neurons stimulated clustering of the nodal components, including sodium channel NaV1.1. Sciatic nerves of myocilin null mice showed reduced levels of myelin basic protein, neurofascin and ankyrin G compared with the sciatic nerves of wild-type littermates. This was accompanied by reduced thickness of the myelin sheath, increased frequency of aberrant axons and partial disorganization of the nodes in myocilin null mice compared with wild-type mice. Myocilin signaling through ErbB receptors may contribute to these observed effects. Myocilin binds to ErbB2/ErbB3 and ErbB1 and activates these receptors. Phosphorylation of ErbB2 at Tyr1221 was reduced in the sciatic nerve of myocilin null mice and increased in transgenic mice expressing elevated myocilin levels compared with wild-type mice. These data introduce myocilin as a new player in myelination of the sciatic nerve. Our data demonstrate that myocilin is a multifunctional protein that may play different roles in ocular and non-ocular tissues. A mutation in the Olfactomedin 2 (Olfm2) gene, which leads to an Arg144Gln substitution in the protein sequence is a possible disease-causing mutation in Japanese patients with open-angle glaucoma. We produced Olfm2 knockout mice that are viable and do not demonstrate visible morphological defects. Close examination of Olfm2 null mice indicates that they may have defects in the optic nerve that are currently being analyzed. In addition to studying the pathophysiology of glaucoma, we are also interested in potential treatments for this disease. Glaucoma is associated with impairment in retrograde transport of neurotrophic factors to retinal ganglion cell bodies. Mesenchymal stem cell (MSC) transplantation appears to be protective in a variety of neurodegenerative disorders of the brain and spinal cord, in part via neurotrophic factor secretion. Thus, we have been investigating a potential role of MSC transplantation as a therapy for glaucoma in collaboration with Dr. K. Martin (Cambridge University, Great Britain). We validated an organotypic retinal explant culture system for use as an efficient medium-throughput screening tool to investigate novel retinal ganglion cell (RGC) neuroprotective therapies. We demonstrated that caspase inhibition, BDNF treatment and stem cell transplantation all reduced RGC cell loss in this model. Further screening of potential neuroprotective pharmacological agents demonstrated that betaxolol, losartan, tafluprost and simvastatin all alleviated RGC loss in retinal explants, supporting previous reports. However, treatment with brimonidine did not protect RGC neurons from death in retinal explant cultures. Explants cultured for 4 days ex vivo proved to be the most sensitive for detecting neuroprotection. Our data suggest that an adult organotypic retinal explant culture system could be used for efficient medium-throughput screening of novel neuroprotective therapies for retinal neurodegenerative disease.
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