November 1, 2004

Brain Star Award (biweekly award to trainees)

Recipient:

Gordon Boyd - Biosketch
Post-doctoral fellow/MD
Queen's University

Article:

Boyd, JG., Lee, J., Skihar, V., Doucette, R., and Kawaja, M. D. (2004). " LacZ-expressing olfactory ensheathing cells do not associate with myelinated axons after implantation into the compressed spinal cord."  PNAS 101: 2162-2166.

Significance of Research:

Olfactory axons convey the sensation of smell from the nose to the brain. These axons are the only axons in the CNS that continually regenerate throughout the lifetime of adult mammals. This ability is attributed to their associated support cell-the olfactory ensheathing cell (OEC). This ability to promote axon regeneration within the CNS has generated much excitement in the field of spinal cord injury research, and for over a decade many reports have demonstrated the beneficial effects of OEC transplantation in animal models of spinal cord injury. In addition, several studies have provided evidence to suggest that OECs "morph" once transplanted into the spinal cord. Specifically, they contact axons and synthesize myelin in a manner similar to Schwann cells, the principle support cell of the PNS. Our study used OECs genetically modified to enable tracking and identification of the cells at the ultrastructural level. We demonstrated a dramatic increase in axon growth following intraspinal implantation of OECs. Importantly, when examined using electron microscopy, OECs were NOT observed making direct contact with axons or synthesizing myelin. However, they formed unique "tunnels" in the damaged spinal cord. In these tunnels, unlabeled Schwann cells (from the host animal) were found associating with axons and synthesizing myelin. Our results provide unequivocal evidence that OECs do NOT "morph" following implantation, and many of the features attributed to OECs (eg myelination, axon association) are in fact Schwann cells that have migrated into the damaged spinal cord. These data suggest that much of the ultrastructural data describing the behaviour of OECs in the damaged spinal cord has been misinterpreted for the past decade. This misunderstanding of the fundamental biology of olfactory ensheathing cells is especially concerning in light of the fact that several recent international clinical trials outside of North America have begun using OECs in humans with spinal cord injury.