Injury to the spinal cord results in paralysis below the level of the injury, which results from cell death and limited regeneration. Although spinal cord neurons have the innate capacity to regenerate, they are limited by an insufficient supply of factors to promote regeneration, and an abundant supply of factors that inhibit regeneration. Our long-term goal is to develop a combination therapy based on biomaterials that bridge the injury site to control the microenvironment. The bridge microstructure will direct axonal outgrowth and localized drug delivery will provide factors that stimulate regeneration yet limit the factors that inhibit axonal outgrowth. Bridges capable of localized DMA delivery will transfect cells locally, whereas protein delivery will degrade inhibitors to regeneration. This bridge releasing DMA encoding for neurotrophic factors will be employed to test the hypothesis that the transfection profile will initiate axonal elongation into the bridge, across the injury site, and facilitate re-entry into the host tissue. This hypothesis is based on the observations that i) DMA delivery can induce sustained, localized transgene expression in vivo, ii) neurotrophin delivery to the injury site can promote axonal elongation into a synthetic bridge, iii) cell transplantation or osmotic pump implantation does not provide a controllable concentration of neurotrophins for promoting regeneration, iv) axonal re-entry into the host is encouraged by reducing the growth promoting stimuli within the bridge to levels comparable to host tissue, and degrading inhibitors in the scar adjacent to the bridge. Based on these observations, the experimental focus is on designing bridges for efficient gene transfer and applying them in a spinal cord model of regeneration.
Specific Aim 1 : Investigate transgene expression (quantity, duration) and transfection (cell number, distribution, and identity) in the spinal cord by sustained release from the multiple channel bridge.
Specific Aim 2 : Investigate axonal elongation with the transfection profile using an in vitro model.
Specific Aim 3 : Investigate the dependence of axonal growth through the bridge in vivo on the transfection profile to maximize the number of axons crossing the bridge.
Specific Aim 4 : Investigate dual delivery of neurorophin-encoding plasmid and chondroitinase to enable axons crossing the bridge, the focus of Aim 3, to re-enter the host tissue. ? ? ?
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