CELLULAR AND MOLECULAR STRATEGIES IN SPINAL CORD REPAIR

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The devastating effects of spinal cord injury are due to the death of neurons and to the failure of the axons of surviving neurons to regenerate through the inhospitable environment created by the injury. The proposed experiments will test whether novel cellular and molecular strategies of repair will promote regeneration leading to locomotor and sensory recovery in well-characterized models of spinal cord injury in adult rats. In preliminary studies we have prepared retrovirus and recombinant adenovirus constructs of neurotrophins and shown that intraspinal transplants of fibroblasts genetically modified to express BDNF promote regeneration of rubrospinal axons that contribute to locomotor recovery. We have also used intraspinal injections of plasmid constructs and recombinant adenovirus to administer genes to spinal and supraspinal neurons that can enhance their survival and regeneration after axotomy. In the present experiments we will use as transplants multipotential neural stem cells isolated from embryonic rat spinal cord. These cells are very promising because of their capacities for self- renewal, differentiation into neurons and glia and genetic modification. We will genetically modify these cells to express neurotrophin factors BDNF and NT3 or adhesion protein L1, and in addition deliver the antiapoptotic gene Bcl-2 by plasmid injections or adenovirus. We propose that this combination of treatments will enhance neuron survival and axon regeneration and promote the recovery of locomotor and sensory function as measured by quantitative tests. In the first series of experiments we will test the idea that engineered neural stem cells transplanted into a unilateral cervical hemisection lesion will integrate with the injured host and supply factors that will rescue axotomized spinal and supraspinal neurons, promote regeneration of their axons and enhance recovery. In the second series of experiments we will test the idea that the best strategy of combined treatments will stimulate regeneration of descending pathways and recovery of hindlimb function after spinal cord transection, a model for complete spinal cord injury in humans in which results of anatomical and behavioral studies are unambiguous. The results of these experiments will contribute to developing an effective strategy for promoting neuron survival and axon regeneration that will enhance functional recovery after spinal cord injury.