The characterization of the olfactory ensheathing cell phenotype by protein analysis

Abstract

Over the recent years, olfactory ensheathing cells (OECs) have gained world-wide attention due to their reputed potential in promoting spinal cord regeneration and repair. In order to isolate, identify, and characterize OECs in vitro and following implantation, researchers have used three OEC markers: p75NTR, GFAP, and S100. The downfall with using these specific proteins is that Schwann cells, which are located within the olfactory system, as well as migrate into the damaged spinal cord, also express these proteins. It is therefore impossible to distinguish OECs from phenotypically similar Schwann cells using these molecular markers. Recently proteomic analyses have revealed that OECs (derived from embryonic rat olfactory bulbs), but not Schwann cells (derived from adult rat sciatic nerves) express a variety of proteins. The main aim of this project is to determine if heat shock protein-27 (Hsp27), carbonic anhydrase-III (CA-III), and annexin-A3 (Anx3) markers label OECs but not Schwann cells, both in vivo and in vitro. Additional analyses were also done to determine if smooth muscle α-actin (SMA) and calponin (two smooth muscle-related markers previously shown to label mucosal OECs of adult rats) label bulbar OECs of adult rats and OECs of adult cats. Using immunohistochemistry we found that SMA labeled olfactory mucosal and bulbar OECs of adult rats and adult cats, Hsp27 labeled olfactory mucosal and bulbar OECs of adult rats and olfactory mucosal OECs of adult cats, while calponin labeled only olfactory mucosal OECs of adult rats. In addition, calponin and SMA did not label Schwann cells (in vivo and in vitro), while Hsp27 labeled this peripheral glial cell. Finally, CA-III did not label OECs of adult rats or adult cats, in vivo or in vitro, and Anx3 did not label OECs in vivo, but showed immunopositive labeling of OECs and Schwann cells in vitro. In conclusion, Hsp27, CA-III, and Anx3 cannot be used as OECs markers either because of their expression in both OECs and Schwann cells or their lack of expression in OECs. Discovering new molecular markers expressed only by OECs is essential in order to determine the properties, fate, and overall potential of OECs in promoting spinal cord regeneration.