In vivo magnetic resonance tracking of olfactory ensheathing glia grafted into the rat spinal cord

Engraftment of olfactory ensheathing cells (OEC), a unique type of glia required for olfactory nerve growth throughout life, has been shown to foster axonal regeneration in different types of CNS and PNS injuries. However, a lack of suitable markers of OEC has hindered studies assessing survival and function of OEC grafts following transplantation. The aim of this study was to examine the possible usefulness of superparamagnetic iron oxide nanoparticles (magnetodendrimers) as a label to allow in vivo tracking of grafted OEC by MR imaging and to determine temporal and spatial migration of OEC in normal and injured rat spinal cords, including the possibility of such cells to cross a complete spinal cord injury zone. We found that labeled OEC were readily detectable in vivo by MR imaging for at least 2 months. Labeled OEC migrated extensively in normal spinal cord as shown by MRI and histological markers. In contrast, OEC showed limited migration in transected spinal cord and were not able to cross the transection gap. Furthermore, iron-containing hemorrhage products confounded interpretation of MR contrast patterns in the injured spinal cord. We conclude that (1) MR imaging is useful for noninvasive observation of cell migration dynamics after grafting in vivo, although interpretation in severe injuries should be cautious, and that (2) OEC migratory and thus regeneration-enhancing ability is limited when confronted with the glial scar of a transected spinal cord.