In the adult mammalian brain and spinal cord, neuronal injury results in failed regeneration, in part due to the upregulation of chondroitin sulfate proteoglycans (CSPGs). The majority of CSPGs originate from reactive astrocytes of the glial scar surrounding the lesion. The glial scar is beneficial for the recovering nervous system and should not be """"""""excised"""""""", but axonal growth could be promoted if the expression of specific inhibitory portions of CSPGs could be targeted selectively. Our previous data indicate that neuronal inhibition is due to specific CSPG microheterogeneities and to the specific configurations of CSPGs predicted by their structure and by the molecules to which they bind. Our goal is to identify the most significant of the CSPG motifs with respect to neurite inhibition and regeneration, and specifically, to manipulate these moieties to promote regeneration. To this end, we and our collaborators have engineered 1) an array of CSPG isoforms and mutants we call """"""""Designer PCs"""""""", 2) a variety of unique bioassays to express CSPGs, including a novel model of the glial scar in vitro, and 3) imaging methods to measure subtle features of nerve responses to CSPGs. The hypothesis of this proposal is: Identification and manipulation of specific inhibitory CSPG motifs using designer PGs and novel models of the glial scar will promote plasticity and regeneration in vitro and in vivo. We propose three Specific Aims that represent independent but interrelated studies to test this hypothesis. One, we will determine the expression and relative abundance of specific, inhibitory CSPG types and posttranslational modifications or core protein domains by reactive astrocytes in vitro. Two, we will determine the inhibitory potential for specific CSPG posttranslational modifications or core protein domains by establishing an inhibitory quotient to evaluate the responses of adult neurons in vitro. Three, we will manipulate specific inhibitory moieties of CSPGs to promote neuronal regeneration of adult neurons in vivo. The long term goal of this study is to identify the mechanism(s) of CSPG-induced inhibition following brain and spinal cord injury. The significance of the studies lies in the tremendous potential for translational application through the manipulation of specific CSPG motifs in injured patients, providing a therapeutic avenue to stimulate neuronal plasticity, facilitate reconnectivity of injured neurons, and accomplish restoration of function.
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