In order to restore connections interrupted by spinal cord injury, adult neurons must carry out modes of axon extension more typical of developing cells. Many adult neurons, however, are known to be deficient in at least some of the protein components of axonal growth cones, which mediate axon extension and guidance. Successful regeneration appears to require re-expression of these and other proteins, but it is not known which growth cone components are expressed in spinal projection neurons after spinal cord injury. The current proposal is to develop a global gene expression assay that can be used to monitor the activation of a program of gene expression adequate to support axon regeneration and functional repair following spinal cord injury. The first stage of the work will use a large cDNA microarray to compare the changes in neuronal gene expression induced by spinal cord injury and by peripheral nerve damage (which elicits robust axon regeneration and functional recovery).
The second aim i s to determine which of these responses to axon injury reflect the activation of genes involved in axon regeneration, rather than the onset of cell death or stress responses. This analysis will employ two parallel approaches. A correlational cluster analysis of microarray data will be used to identify sets of genes most closely correlated with axon growth, while a """"""""proteomics"""""""" profile of growth cone proteins will be used to determine which genes induced by axotomy represent the expression of proteins directly involved in axon growth. The results will show whether spinal projection neurons ordinarily initiate an effective genetic program for axon regrowth following spinal cord injury, or remain deficient in particular growth cone components. Moreover, they will establish a """"""""molecular profile"""""""" that can be used to distinguish the modes of action of treatments designed to enhance spinal cord repair. We will test the feasibility of using this profile to determine which treatments act by stimulating neuronal genes involved in axon regrowth, and which treatments act by improving the growth-supporting properties of the spinal cord environment. Together, the proposed studies address one of the fundamental hurdles to spinal axon regeneration, and provide a tool for evaluating therapeutic strategies for spinal cord repair.
