Strategies for nerve regeneration after CNS injury

It was traditionally thought that the central nerve system (CNS) defects the regenerated ability, following the injury. However, the peripheral nerve system (PNS) possesses an ability of regeneration after injury. Also it was found that the axon in CNS might extend into the graft, as soon as the peripheral nerve tissue was transplanted into the injured part of CNS. Therefore, it implied that the axons in CNS also possess the regeneration ability, and the regeneration of axon in CNS just depended on the microenvironment around them. The microenvironment of CNS doesn’t adapt to the nerve regeneration after damage. The different microenvironment between CNS and PNS mainly results from the different types of glial cells--the oligodendrocytes in CNS play an inhibit role, while the Schwann cells in PNS play an active role in the repairing process following the nerve injury. When CNS damaged, the injured myelin sheath that composed from oligodendrocytes released a lot of inhibitors for axon-regeneration. On the other hand, glial scar inhibited the axon regeneration by space obstruction proteoglycan inhibition (e.g. chondroitin sulfate proteoglycans, CSPGs).Therefore, the repair strategies for nerve regeneration of CNS were just as “Seeds Substitution and Soil Amendment”, following injury. For example, Soil Improvement was performed by weakening the inhibitors of obstructing the CNS regeneration, removing the glial scar, supplying the advantageous factors, transplanting the endothelial progenitor cells (EPCs) in order to re-establish the microvascular, and repairing the injured myelin. Seed Substitution was done by transplanting the nerve stem cells (NSCs), and applying the bio-macromolecules as the cellular bridges during the CNS regeneration. Finally, the injured CNS can be repaired.