Myocilin Mediates Myelination in the Peripheral Nervous System through ErbB2/3 Signaling

The glaucoma-associated gene, myocilin, is expressed in ocular and non-ocular tissues including the peripheral nervous system, but its functions in these tissues remain poorly understood. We demonstrate that in sciatic nerve, myocilin is expressed in Schwann cells with high concentrations at the nodes of Ranvier. There, myocilin interacts with gliomedin, neurofascin, and NrCAM, which are essential for node formation and function. Treatment of isolated dorsal root ganglion cultures with myocilin stimulates clustering of the nodal proteins neurofascin and sodium channel Nav1.2. Sciatic nerves of myocilin null mice express reduced levels of several myelin-associated and basal membrane proteins compared with those of wild-type littermates. They also demonstrate reduced myelin sheath thickness and partial disorganization of the nodes. Myocilin signaling through ErbB2/3 receptors may contribute to these observed effects. Myocilin binds to ErbB2/ErbB3, activates these receptors, and affects the downstream PI3K-AKT signaling pathway. These data implicate a role for myocilin in the development and/or maintenance of myelination and nodes of Ranvier in sciatic nerve. Background: Myocilin, a secreted glaucoma-associated protein, is detected in the sciatic nerve, but its function there is not clear. Results:Myocilin null mutation leads to defects in the myelination of sciatic nerve acting through the ErbB2/ErbB3 receptor. Conclusion: Myocilin is a novel player in sciatic nerve myelination. Significance: This is the first demonstration of myocilin involvement in myelination.