Olfactory ensheathing cells promote corticospinal axonal outgrowth by a L1 CAM-dependent mechanism

Olfactory ensheathing cells (OECs) support the ability of the olfactory neuraxis to continually retarget within the mature central nervous system. This has led many groups to transplant OECS into the lesioned rodent spinal cord (SCd) in vivo, with variable degrees of anatomical, physiological, and behavioral success. Some of the most conflicting results in OEC transplantation have come from the corticospinal tract (CST) which has shown a relatively poor regeneration response. Although spinal neurite sprouting occurs in response to OECs in vivo and in vitro, we do not know if OECs possess the molecular machinery to stimulate outgrowth of functionally important motor tracts like the CST. Here, we assay cultured postnatal day 8 mouse CST neurons expressing yellow fluorescent protein (YFP) for their ability to extend axons and dendrites in response to different glia, and show that CST axons elongate in response to proteins in OEC plasma membrane (PM). In contrast, CST dendritic branching preferentially occurs in response to factors secreted by both OECs and astrocytes. We identify the L1-neural cell adhesion molecule (L1-NCAM) as a major component of OEC-induced corticospinal axon elongation, and have determined that OEC PM factors (including L1), can stimulate CST outgrowth even when inhibition is induced by myelin associated glycoprotein. Together, these results suggest that in the right context, OEC-derived PM factors could enhance CST axonal regeneration, and potentially contribute to approaches to ameliorate recovery from SCd injury.