Olfactory Ensheathing Glia: Drivers of Axonal Regeneration in the Central Nervous System?

Abstract

Olfactory ensheathing glia (OEG) accompany olfactory growing axons in their entry to the adult mammalian central nervous system (CNS). Due to this special characteristic, considerable attention has been focused on the possibility of using OEG for CNS regeneration. OEG present a large heterogeneity in culture with respect to their cellular morphology and expressed molecules. The specific characteristics of OEG responsible for their regenerative properties have to be defined. These properties probably result from the combination of several factors: molecular composition of the membrane (expressing adhesion molecules as PSA-NCAM, L1 and/or others) combined with their ability to reduce glial scarring and to accompany new growing axons into the host CNS. Their capacity to produce some neurotrophic factors might also account for their ability to produce CNS regeneration.

Figure 1

Neuron-OEG cross talk. OEG and extending axons of olfactory sensory neurons interact through membrane adhesion molecules (represented by the Y symbols). OEG also bear receptors to neuregulins and possibly to other chemotactic factors produced by the developing neurons (solid arrows) and/or other cells. Furthermore, OEG produce and secrete neurotrophic factors and neuritogenic extracellular matrix proteins which interact with developing neurons (dashed arrows). The characteristics of OEG together with their influence on glial scarring and their ability to migrate within the CNS might be responsible for their axonal-regenerative properties in CNS injuries. OEG permit CNS axonal regeneration by acting as a vehicle, ensheathing, driving, and nurturing growing axons through a hostile territory.