Molecular targets to promote central nervous system regeneration

Trauma in the adult mammalian central nervous system (CNS) results in devastating clinical consequences due to the failure of injured axons to spontaneously regenerate. This regenerative failure can be attributed to both a lack of positive cues and to the presence of inhibitory cues that actively prevent regeneration. Substantial progress has been made in elucidating the molecular identity of negative cues present at the CNS injury site following injury. In the past several years, multiple myelin-associated inhibitors including Nogo, Myelin-associated glycoprotein and Oligodendrocyte-myelin glycoprotein have been characterized. Furthermore a neuronal receptor complex and several intracellular substrates leading to outgrowth inhibition have been identified. Rapid progress has also been made in identifying the role of neurotrophins and other positive cues in promoting axonal regrowth. The most recent advances in our understanding of positive stimuli for axon regeneration come from transplantation studies at the CNS lesion site. A number of artificial substrates, tissues, and cells including fetal cells, neural stem cells, Schwann cells and olfactory-ensheathing cells have been tested in animal models of CNS injury. Based on our expanded knowledge of inhibitory influences and on the positive characteristics of various transplants, a number of interventions have been tested to promote recovery in models of CNS trauma. These advances represent the first steps in developing a viable therapy to promote axon regeneration following CNS trauma.