Transgenic inhibition of astroglial NF-κB leads to increased axonal sparing and sprouting following spinal cord injury

We previously showed that Nuclear Factor kappa B (NF-kappa B) inactivation in astrocytes leads to improved functional recovery following spinal cord injury (SCI). This correlated with reduced expression of pro-inflammatory mediators and chondroitin sulfate proteoglycans, and increased white matter preservation. Hence we hypothesized that inactivation of astrocytic NF-kappa B would create a more permissive environment for axonal sprouting and regeneration. We induced both contusive and complete transection SCI in GFAP-Inhibitor of kappa B-dominant negative (GFAP-I kappa B alpha-dn) and wild-type (WT) mice and performed retrograde [fluorogold (FG)] and anterograde [biotinylated dextran amine (BDA)] tracing 8 weeks after injury. Following contusive SCI, more FG-labeled cells were found in motor cortex, reticular formation, and raphe nuclei of transgenic mice. Spared and sprouting BDA-positive corticospinal axons were found caudal to the lesion in GFAP-I kappa B alpha-dn mice. Higher numbers of FG-labeled neurons were detected immediately rostral to the lesion in GFAP-I kappa B alpha-dn mice, accompanied by increased expression of synaptic and axonal growth-associated molecules. After transection, however, no FG-labeled neurons or BDA-filled axons were found rostral and caudal to the lesion, respectively, in either genotype. These data demonstrated that inhibiting astroglial NF-kappa B resulted in a growth-supporting terrain promoting sparing and sprouting, rather than regeneration, of supraspinal and propriospinal circuitries essential for locomotion, hence contributing to the improved functional recovery observed after SCI in GFAP-I kappa B alpha-dn mice.