Failures of nerve regeneration caused by aging or chronic denervation are rescued by restoring Schwann cell c-Jun

After nerve injury, myelin and Remak Schwann cells reprogram to repair cells specialized for regeneration. Normally providing strong regenerative support, these cells fail in aging animals, and during the chronic denervation that results from slow axon growth. This impairs axonal regeneration and causes a significant clinical problem. We find that aging and chronically denervated repair cells express reduced c-Jun protein and the regenerative support provided by these cells is also reduced. In both cases, genetically restoring Schwann cell c-Jun levels restores regeneration to that in controls. We identify potential gene candidates mediating this effect and implicate Shh in the control of Schwann cell c-Jun levels. These experiments reveal that a common mechanism, reduced c-Jun in repair cells, underlies two major reasons for regeneration failure in the PNS. They underscore the central importance of Schwann cell c-Jun as a regulator of nerve repair, and point to molecular pathways that can be manipulated for improving the clinical outcome of nerve injuries.