Morphological and functional plasticity of olfactory ensheathing cells

Abstract

In the primary olfactory pathway, olfactory ensheathing cells (OECs) extend processes to envelop bundles of olfactory axons as they course towards their termination in the olfactory bulb. The expression of growth-promoting adhesion and extracellular matrix molecules by OECs, and their spatially close association with olfactory axons are consistent with OECs being involved in promoting and guiding olfactory axon growth. Because of this, OECs have been employed as a possible tool for inducing axonal regeneration in the injured adult CNS, resulting in significant functional recovery in some animal models and promising outcomes from early clinical applications. However, fundamental aspects of OEC biology remain unclear. This brief review discusses some of the experimental data that have resulted in conflicting views with regard to the identity of OECs. We present here recent findings which support the notion of OECs as a single but malleable phenotype which demonstrate extensive morphological and functional plasticity depending on the environmental stimuli. The review includes a discussion of the normal functional role of OECs in the developing primary olfactory pathway as well as their interaction with regenerating axons and reactive astrocytes in the novel environment of the injured CNS. The use of OECs to induce repair in the injured nervous system reflects the functional plasticity of these cells. Finally, we will explore the possibility that recent microarray data could point to OECs assuming an innate immune function or playing a role in modulating neuroinflammation.

Migratory properties of cultured olfactory ensheathing cells by single-cell migration assay

“…For example, motile T cells display a polarized morphology with polarized organization of cytoskeletal proteins such as a-tubulin [45]. In this study, we found that Schwann cell-like OECs were more motile than astrocyte-like OECs and astrocyte-like type 1 OECs were more motile than [4,11,25,46]. However, the relationships between the different morphological phenotypes are not clear.…”

“…This remarkable regenerative property of the olfactory system is thought to be in part due to a special type of glia cells [2,3], the olfactory ensheathing cells (OECs), which support and guide the growth of olfactory axons and ensheath the bundles of olfactory nerves that extend from the olfactory epithelium to the olfactory bulb [4]. Owing to these unique roles, OEC transplantation has emerged as a promising experimental therapy for axonal injuries and demyelinating disease [5].…”

“…The elongation of olfactory axons through the lamina propria may be largely attributed to the behavior of the migrating OECs that accompany the nerve fibers [20]. Several studies have reported that distinct OEC subpopulations exist in the olfactory system, based on their morphology and antigenic profiles [4,21,22]. For example, OECs from the lamina propria express unique developmentally important proteins such as NG2, which is not expressed in OECs from the olfactory bulb [22].…”

Olfactory ensheathing cells are attracted to, and can endocytose, bacteria

“…Antimicrobial peptides contain domains of hydrophobic and cationic amino acids that are spatially arranged into an amphipathic design to facilitate their insertion into the bacterial membrane, ultimately resulting in membrane destabilization and bacterial lysis [22][23][24]. Two antimicrobial peptides known to be expressed in OECs are Neuropeptide Y (NPY) and lysozyme [8,25,26]. Neuropeptide Y is expressed in OECs of E15 rat embryos prior to the development of laminae in the olfactory bulb and it persists into adulthood [26].…”

“…Two antimicrobial peptides known to be expressed in OECs are Neuropeptide Y (NPY) and lysozyme [8,25,26]. Neuropeptide Y is expressed in OECs of E15 rat embryos prior to the development of laminae in the olfactory bulb and it persists into adulthood [26]. It has been shown to have antifungal properties, e.g.…”