Characterization of the Myelin-Associated Glycoprotein Receptor NgR2 in vivo

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DESCRIPTION (provided by applicant): Description: Myelin-associated glycoprotein (MAG) is a bi-functional molecule that has been implicated in stabilizing axon-glial interactions in both the central and peripheral nervous system. In addition, MAG has been identified as a potent inhibitor of neurite outgrowth in vitro. Work from our laboratory identified NgR2 as a high affinity receptor for MAG sufficient to confer MAG responsiveness. The studies outlined in this proposal are aimed at investigating whether NgR2 is a functional MAG receptor in vivo. To study NgR2 function a mouse genetic approach will be pursued. I have generated mice deficient for NgR2 by introducing a GFP reporter cassette into exon III of the NgR2 gene. Similar to MAG mutants, NgR2 null mice are viable into adulthood and thus, will allow us to study the role of NgR2 in the mature central nervous system. A combination of anti-NgR2 and anti-MAG immunofluorescence will be used to map the tempero-spatial expression pattern of NgR2 in direct comparison to MAG expression. In vitro neurite outgrowth assays will be used to test the hypothesis that NgR2 is a MAG receptor necessary for MAG-mediated inhibition of neurite outgrowth and axonal regeneration following optic nerve injury in vivo. Loss of MAG leads to defects in myelin sheaths and the degeneration of axons. To test the hypothesis that NgR2 is a MAG receptor in vivo, electron microscopical studies of myelin sheaths will be performed to examine whether loss of NgR2 leads to defects reminiscent to the ones previously reporter for MAG deficient mice. My preliminary results suggest that NgR2 null mice show myelination defects in the sciatic nerve. As an alternate approach for optic nerve regeneration studies of NgR2 mice in vivo, I propose to use NgR1/NgR2 double mutant mice, as NgR1 might compensate for the loss of NgR2 in NgR2 null mice. Collectively, the experiments proposed are anticipated to provide insights in the role of NgR2 function in MAG mediated growth inhibition and axon-glia interactions in vivo. RELEVANCE TO PUBLIC HEALTH: The damage that occurs in traumatic brain injury (TBI), spinal cord injury or stroke, often leads to permanent neurological deficits. This is primarily due to the lack of spontaneous axonal regeneration and/or remyelination. A complete understanding of the role NgR2 plays in mediating MAG's function, will aid in the development of therapeutic agents that can attentuate MAG inhibition while preserving its protective and stabilizing effects on axons.