Combination strategies for repair, plasticity, and regeneration using regulation of gene expression during the chronic phase after spinal cord injury

Abstract

Although recovery after spinal cord injury (SCI) is rare in humans, recent literature indicates that some patients do recover sensorimotor function years after the trauma. This study seeks to elucidate the genetic underpinnings of SCI repair through the investigation of neurodegenerative and regenerative associated genes involved in the response to SCI during the chronic phase in adult rats. Intervention on the level of gene regulation focused on enhancing naturally attempting SCI regenerative genes has the potential to promote SCI repair. Our aim was to analyze gene expression characteristics of candidate genes involved in the neuro-degenerative and -regenerative processes following various animal models of SCI. We compiled data showing gene expression changes after SCI in adult rats and created a chronological time-line of candidate genes differentially expressed during the chronic phase of SCI. Compiled data showed that SCI induced a transient upregulation of endogenous neuro-regenerative genes not only within a few hours but also within a few days, weeks, and months after SCI. For example, gene controlling growth-associated protein-43 (GAP-43), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and others, showed significant changes in mRNA accumulation in SCI animals, from 48 hours to 12 weeks after SCI. Similarly, inhibitory genes, such as RhoA, LINGO-1, and others, were upregulated as late as 4 to 14 days after injury. This indicates that gene specific regulation changes, corresponding to repair and regenerative attempts, are naturally orchestrated over time after injury. These delayed changes after SCI give ample time for therapeutic gene modulation through upregulation or silencing of specific genes responsible for the synthesis of the corresponding biogenic proteins. By following the examination of differential gene regulation during the chronic phase, we have determined times, successions, co-activations, interferences, and dosages for potential therapeutic synchronized interventions. Finally, local cellular specificities and their neuropathophysiologies have been taken into account in the elaboration of the combination treatment strategy we propose. The interventions we propose suggest the delivery of exogenous therapeutic agents to upregulate or downregulate chosen genes or the expression of the downstream proteins to revert the post-traumatic stage of SCI during the chronic phase. The proposed combination and schedule of local cell-specific treatment should enhance intrinsic regenerative machinery and provide a promising strategy for treating patients sustaining chronic SCI.