Restoring axonal localization and transport of transmembrane receptors to promote repair within the injured CNS: a critical step in CNS regeneration

Each neuronal subtype is distinct in how it develops, responds to environmental cues, and whether it is capable of mounting a regenerative response following injury. Although the adult central nervous system (CNS) does not regenerate, several experimental interventions have been trialled with successful albeit limited instances of axonal repair. We highlight here some of these approaches including extracellular matrix (ECM) modification, cellular grafting, gene therapy-induced replacement of proteins, as well as application of biomaterials. We also review the recent report demonstrating the failure of axonal localization and transport of growth-promoting receptors within certain classes of mature neurons. More specifically, we discuss an inability of integrin receptors to localize within the axonal compartment of mature motor neurons such as in the corticospinal and rubrospinal tracts, whereas in immature neurons of those pathways and in mature sensory tracts such as in the optic nerve and dorsal column pathways these receptors readily localize within axons. Furthermore we assert that this failure of axonal localization contributes to the intrinsic inability of axonal regeneration. We conclude by highlighting the necessity for both combined therapies as well as a targeted approach specific to both age and neuronal subtype will be required to induce substantial CNS repair.