Researchers are making inroads into understanding and manipulating mechanisms of nerve regrowth so as to improve the outcome following injury:
The researchers were interested in understanding how axons in the peripheral nervous system (PNS) make a vigorous effort to grow back when they are damaged, whereas central nervous system (CNS) axons mount little or no effort. If damage occurs in the peripheral nervous system, which controls areas outside of the brain and spinal cord, about 30% of the nerves grow back and there is often recovery of movement and function. The researchers wanted to explore whether it was possible to generate a similar response in the CNS.
To investigate the differences between how the two systems respond to damage, the researchers looked at mouse models and cells in culture. They compared the responses to PNS damage and CNS damage in a type of neuron called a dorsal root ganglion, which connects to both the CNS and the PNS.
When nerves are damaged in the PNS, the damaged nerves send 'retrograde' signals back to the cell body to switch on an epigenetic program to initiate nerve growth. Very little was previously known about the mechanism which allows this 'switching on' to occur. The researchers identified the sequence of chemical events that lead to the 'switching on' of the program to initiate nerve regrowth and pinpointed the protein PCAF as being central to the process. Furthermore when they injected PCAF into mice with damage to their central nervous system, there was a significant increase in the number of nerve fibres that grew back.