Abstract

The primary olfactory system (POS) is in permanent renewal, especially the primary olfactory neurons (PON) are renewed with a turnover of around four weeks, even in adulthood. The re-growth of these axons is helped by a specific population of glial cells: the olfactory ensheathing cells (OECs). In the POS, OECs constitute an “open-channel” in which the axons of PON cause regrowth from peripheral nervous system (PNS) to central nervous system (CNS). The remarkable role played by OECs into the POS has led scientists to investigate their properties and potential beneficial effects after transplantation in different lesion models of the CNS and PNS. In this review, we will resume and discuss more than thirty years of research regarding OEC studies. Indeed, after discussing the embryonic origins of OECs, we will describe the in vitro and in vivo properties exert at physiological state by these cells. Thereafter, we will present and talk over the effects of the transplantation of OECs after spinal cord injury, peripheral injury and other CNS injury models such as demyelinating diseases or traumatic brain injury. Finally, the mechanisms exerted by OECs in these different CNS and PNS lesion paradigms will be stated and we will conclude by presenting the innovations and future directions which can be considered to improve OECs properties and allow us to envisage their use in the near future in clinical applications.

Highlights

  • Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

  • Thereafter, based on microarray analyses, we have demonstrated that olfactory ensheathing cells (OECs) from OM and OECs from olfactory bulbs (OB), respectively OMOECs and OB-OECs, display distinct gene expression patterns

  • A transcriptomic study confirmed that two subpopulations of OECs, characterized by their differential expression of P75NTR, named P75High and P75Low, are present in cultures obtained from OB [26]

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Summary

Organization of the Olfactory System

The olfactory system is a tissue in which permanent regeneration occurs even in adulthood [1]. PON are selective of specific odorant molecules These neurons constitute several families of cells grouped according to their expression of common olfactory receptors. In the OE and the outer nerve layer (ONL) of the OB, are located the olfactory ensheathing cells (OECs) [8] These cells in the POS exert the same function as the non-myelinating Schwann cells (SCs) in the PNS, they ensheathe the axons without forming myelin in order to protect and guide them. It is thought that these cells do not proliferate in adulthood [10] Their main role would be to constitute an “open-channel” in which the axons of PON could regrowth from PNS to CNS [11]

Origin and Cellular Heterogeneity of the OECs
OECs Properties
A Brief History of the Use of the OECs for Repairing the Nervous System
Transplantation of OECs after Spinal Cord Injury
Transplantation of OECs after Peripheral Nerve Injury
OECs Transplantation in Other CNS Injury Models
Findings
Future Directions
Full Text
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