Axon guidance in regeneration of the mature central nervous system: step by step

Unlocking axon regeneration in the injured central nervous system: In adult mammals, central nervous system (CNS) neurons fail to regenerate after a lesion, whether it is traumatic – after spinal cord injury for example – or in the case of neurodegenerative diseases. This causes axons to degenerate and neurons to die, leading to permanent motor and/or cognitive impairment. One of the reasons behind this regeneration failure lies in the mature CNS environment, where a number of growth-inhibitory factors, at the lesion site, contributes to axon regrowth inhibition (He and Jin, 2016). In this context, removing such extrinsic factors should alleviate the growthinhibitory barrier. Yet, surprisingly, no robust regeneration is achieved past the lesion site. These results led researchers to investigate the intrinsic regrowth properties of adult neurons themselves. Indeed, adult CNS neurons lose their capacity to grow an axon, not only because of the switch-off of developmental pro-growth programs during maturation, but also in response to the injury itself (Belin et al., 2015; He and Jin, 2016).