Ephrin-B3 Decreases the Survival of Adult Rat Spinal Cord-Derived Neural Stem/Progenitor Cells In Vitro and After Transplantation into the Injured Rat Spinal Cord

Although transplantation of neural stem/progenitor cells (NSPC) encourages regeneration and repair after spinal cord injury (SCI), the survival of transplanted NSPC is limited. Ephrin-B3 has been shown to reduce the death of endogenous NSPC in the subventricular zone of the mouse brain without inducing uncontrolled proliferation. Due to similarities in the environment of the brain and spinal cord, we hypothesized that ephrin-B3 might reduce the death of both transplanted and endogenous spinal cord-derived NSPC. Both normal and injured (26 g clip compression) spinal cords were examined. Ephrin-B3-Fc was tested, and Fc fragments and phosphate-buffered saline (PBS) were used as controls. We found that EphA4 receptors were expressed by spinal cord-derived NSPC and expressed in the normal and injured rat spinal cord (higher expression in the latter). In vitro, ephrin-B3-Fc did not significantly reduce the survival of NSPC except at 1 mu g/mL (P < 0.05), but Fc fragments alone reduced NSPC survival at all doses in a dose-dependent fashion. In vivo, intrathecal infusion of ephrin-B3-Fc increased the proliferation of endogenous ependymal cells and the proportion of proliferating cells that expressed the glial fibrillary acidic protein astrocytic marker in the injured spinal cord compared with the infusion of PBS (P < 0.05). However, in the injured spinal cord, the infusion of either ephrin-B3-Fc or Fc fragments alone caused a 20-fold reduction in the survival of transplanted NSPC (P < 0.001). Thus, after SCI, ephrin-B3-Fc and Fc fragments are toxic to transplanted NSPC.