Early administration of tumor necrosis factor-alpha antagonist promotes survival of transplanted neural stem cells and axon myelination after spinal cord injury in rats

Abstract

Neural stem cell (NSC) transplantation has been reported to be a leading strategy to stimulate neuroplasticity, repair neuronal loss and promote the morphologic and functional recovery of spinal cord injury (SCI). However, massive death of transplanted NSCs is still a problem, which is considered to be related to a series of pro-inflammatory cytokines that induce apoptosis, extensive demyelination and axonal destruction. Tumor necrosis factor alpha (TNF-α), as one of the major inflammation initiators, contributes to secondary neural cell death. We previously found that the administration of the TNF-α antagonist etanercept during the acute phase of SCI can reduce the apoptosis of neurons and oligodendrocytes. To investigate whether etanercept can suppress transplanted NSC apoptosis and promote NSC survival, axon myelination and functional recovery, we tested the combination strategy of the early administration of etanercept and NSC transplantation. First we observed that etanercept suppressed the TNF-α expression and apoptosis of transplanted NSCs by Western blot, TUNEL and immunofluorescence staining. The Basso, Beattle and Bresnahan scale and motor-evoked potential were used to evaluate functional recovery. The results suggest significantly better recovery after combination therapy. Further, histopathological alterations were evaluated by hematoxylin and eosin staining and Nissl staining. These procedures showed that the early administration of etanercept improved survival of neurons in the ventral horn, restored neural morphology and produced a smaller cavity area. We observed most abundant NF-positive fibers after the combination treatment, indicating that combination therapy retained and promoted neural regeneration. Finally, the early suppression of TNF-α reduced the occurrence of demyelination, and the combination therapy led to more myelinated axons, as shown by electron microscopy. These data suggest that this strategy significantly protected transplanted NSCs via the anti-inflammation and anti-apoptosis effects of etanercept, promoting re-myelination, neural regeneration and locomotor function.

Keywords: Functional recovery; Neural stem cells; Spinal cord injury; TNF-α.