Olfactory ensheathing cells proliferate from stem cells after injury

Olfactory ensheathing cells (OECs) support the regeneration of olfactory sensory neurons throughout life. However, it remains unclear how OECs respond to a major injury and whether stem cells give rise to new OECs in those conditions. Purpose: To identify where OECs proliferate in the olfactory pathway and the regions to whic they migrate. Methods: We examined the proliferation and migration of OECs by surgically removing an olfactory bulb from neonatal mice. The outer layer of the olfactory bulb, the nerve fibre layer, is rich with OECs and thus bulbectomy removed the OECs of the olfactory bulb. The peripheral region of the olfactory nerve within the nasal cavity and the olfactory epithelium where the stem cells are located remained untouched. Proliferating cells were labelled by the thymidine analogue, ethynyl deoxyuridine (EdU) at different days after surgery (days 0-14) and animals (n=3 at each time point) were harvested either 4 hr later or up to 14 days later. Results: In the unilateral bulbectomy model, there was a large stimulation of OEC proliferation throughout the olfactory nerve up to 14 days after bulbectomy. Tracking cells that had proliferated revealed that stem cells lining the basal layer of the olfactory epithelium also gave rise to OECs that subsequently migrated along the length of the olfactory nerve. Conclusion: These results demonstrate that OECs actively respond to widespread degeneration of olfactory axons and that both local proliferation of OECs as well as stem cells give rise to new OECs that migrate along the olfactory nerve to the regions of need.