The failure of axon regeneration in the injured spinal cord results in partial or complete loss of function distal to the injury. To restore the function, severed axons must regrow and functionally reconnect to appropriate targets below the injury site. We have shown previously that forced overexpression of pro-regenerative transcription factors including Sox11 and KLF7 promotes axon growth in corticospinal tracts (CST) neurons. Moreover, using optogenetic stimulation to specifically stimulate CST axon terminals, we have shown that newly sprouted, genetically stimulated axons are able to form functional synaptic connections with spinal neurons. However, these experiments were performed in models of partial spinal injury, and growing CST axons were observed mainly in trajectories that circumvented injuries, taking advantage of spared tissue. Here we tested the ability of Sox11 or KLF7-stimulated axons to regenerate through more complete spinal injuries. Adult mice were subjected to complete thoracic crush injuries or severe cervical injuries in which 1mm of tissue was unilaterally removed. Cortical neurons were treated with AAV-Sox11 or AAV-VP16-KLF7 along with AAV-EGFP tracer. CST axons were not observed to traverse these sites of injury. Combined, these data suggest that KLF7- and Sox11-based interventions enhance innate growth ability while maintaining the capacity for synaptic integration, but do not confer the ability to extend into sites of spinal injury. Recent reports indicate that transplanted stem cells can serve as a substrate for CST growth in the injured spinal cord. Accordingly, in current experiments we are combining transcriptional manipulation of injured cortical neurons with transplantation of embryonic and induced pluripotent stem cells into C5 unilateral injury sites. Preliminary data confirm integration of the transplanted cells and fiber outgrowth into host tissue. Ongoing assessment of CST growth into and beyond the grafts will assess the utility of combined stem cells treatment and gene therapy to re-establish lost synaptic connection following spinal cord injury.
*N. JAYAPRAKASH, Z. WANG, N. KRUEGER, A. KRAMER, M. BLACKMORE;
Marquette Univ., Milwaukee, WI
N. Jayaprakash: None. Z. Wang: None. N. Krueger: None. A. Kramer: None. M. Blackmore: None.