Nanoparticle and epothilone D combinatorial intervention improves motor performance and regeneration in chronic cervical spinal cord injury

Spinal cord injury (SCI) causes the loss of motor function below the site of injury due to neuron loss and the severing of spinal tracts. The injury leads to the recruitment of circulating myeloid cells that create an inflammatory microenvironment and exacerbate cell death, with subsequent migration of fibroblasts and astrocytes that contribute to scar tissue that inhibits regeneration. Herein, we investigated a combinatorial treatment in a chronic cervical hemisection model involving cargo-less nanoparticles (NPs) administered acutely, and a multichannel bridge and microtubule stabilizer delivered chronically. NPs administration acutely for one-week post-injury contributed to improved paw placement on a ladder beam relative to vehicle control. Four weeks after injury, damaged tissue was resected, and a microporous, multichannel PLG bridge was inserted to reduce scar tissue and provide a substrate for axon regrowth. Epothilone D (epoD), a microtubule stabilizer, was also administered to further decrease fibrotic scar formation and improve axon elongation. Mice receiving a scaffold with NP treatment or epoD treatment had improved motor performance, but the combination of NP and epoD maximally improved function. In conjunction with this improved performance, mice that received NPs or epoD exhibited increased neuromuscular junction innervation, robust axon growth into the bridge, and both oligodendrocyte and Schwann-cell myelination of regenerating axons. Collectively, these results suggest that a combinatorial treatment plan targeting inflammation and scarring, a substrate for growth, and growth-promoting factors can improve motor performance following SCI.