Injured axons in the mature central nervous system (CNS), including the optic nerve, cannot regenerate spontaneously. This inability to regenerate causes permanent disability after CNS injuries. A better understanding of the impediments to axon regeneration, and novel approaches towards overcoming them, are necessary for the development of new drugs and procedures that may improve the fate of patients with nervous system injury in the future. Our goal is to enable CNS axon regeneration by elevating intrinsic growth signaling. The RAF kinase is known to drive fast axon growth in embryonic sensory neurons; we therefore will now activate this kinase in the retina.
Our first aim i s to promote regeneration in the injured optic nerve using a conditional B-RAF gain-of-function mouse model. We will then test the roles of signaling molecules downstream of RAF signaling - the MEKs, ERKs and RNDs - for their contributions to B-RAF-driven retinal axon regeneration (Aim 2). Next, we plan to combine activation of B-RAF with activation of PI3-kinase signaling (using a knock-out of the PI3-kinase antagonist PTEN) to see whether this combination will further boost regenerative optic nerve axon growth in vivo (Aim 3). If we can observe regeneration into any of the optic tract nuclei, we will test the mice for any recovery of visual function; such functional recovery being the ultimate goal of all axon regeneration studies. The proposed study will define the roles of RAF signaling and its downstream effectors in the context of optic nerve regeneration, laying groundwork for translational research and for the identification of novel drug targets.
The inability of injured mature axons to regenerate is a major obstacle preventing recovery from traumatic CNS injuries. Axonal damage and regeneration failure in optic nerve are salient features of trauma, glaucoma and other CNS injuries. The proposed study is relevant to public health because it aims to identify a novel and comprehensive means to promote long- distance axon growth and functional recovery following optic nerve injury.
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