Stem Cells and Ensheathing Cells from the Nasal Olfactory Mucosa: a Tool for the Repair of the Damaged Spinal Cord

Abstract

The olfactory mucosa has been shown to be a site where continual regeneration takes place throughout adulthood, making this system relatively unique with great potential in respect to autologous cell graft therapies. The olfactory mucosa is readily accessible with no deleterious effects on olfaction if biopsied. The presence of olfactory ensheathing cells (OECs), as well as a stem cell to facilitate the regeneration of this tissue, has been previously described. The first aim of this study was to further characterise olfactory ensheathing cells in rat and human and to gain some insights into their biology in vitro and in vivo, with the hope of applying this knowledge to clinical therapies employing autologous cell grafts. The second aim was to isolate stem cells in the form of neurospheres from the adult olfactory lamina propria, to elucidate their differentiation potential into both neural and non neural lineages, and to subsequently graft these cells into animal models of spinal cord injury to assess their behaviour in vivo in regards to survival, proliferation, and integration into the host spinal cord. Recovery of locomotor function due to axon regeneration across the lesion site following grafting was also assessed. Glial cells isolated from the adult olfactory lamina propria were identified as OECs in vitro and in vivo using the immunological markers GFAP, S100, and p75NTR. Neurotrophin growth factors were shown to promote their proliferation and purification in vitro from both rat and human. Immunocytochemistry and PCR were used to confirm the expression of neurotrophin trk receptors A, B, and C, as well as NT3, NGF and BDNF by OECs in rat and human. NT3 was shown to purify adult human OECs in vitro. Through the use of EGF and FGF2, it was shown that the olfactory lamina was capable of generating neurospheres consisting of a heterogeneous cell population, containing fully differentiated cells, progenitor cells, as well as undifferentiated stem cells indentified by the markers nestin and c-kit. Using growth factors, single or in combination, as well as tissue conditioned medium, olfactory stem cells within these neurospheres were induced to differentiate into the neural lineage, namely neurons, astrocytes, and oligodendrocytes. Non neural differentiation into liver, skeletal muscle, and cardiac cells was induced in vitro by cell-cell contact between neurospheres and frozen rat tissue sections.