Neural stem cells grafts decrease neural apoptosis associated with caspase-7 downregulation and BDNF upregulation in rats following spinal cord hemisection

Abstract

Transplantation of neural stem cells (NSCs) into lesioned spinal cord demonstrated a beneficial effect for neural repair, the underlying mechanism, however, remains to be elusive. Here, we showed that NSCs, possessing the capacity to differentiate toward into neurons and astrocytes, exhibit a neuroprotective effect by anti-apoptosis mechanism in spinal cord hemi-transected rats despite it did not improve behavior. Intravenous NSCs injection substantially upregulated the level of BDNF mRNA but not its receptor TrkB in hemisected spinal cord, while caspase-7, a downstream apoptosis gene of caspase-3, has been largely down-regulated. TUNEL staining showed that the number of apoptosis cells in injured spinal cord decreased significantly, compared with seen in rats with no NSCs administration. The present finding therefore provided crucial evidence to explain neuroprotective effect of NSCs grafts in hemisected spinal cord, which is associated with BDNF upregulation and caspase-7 downregulation.

Fig. 1

Morphology and identification of NSC. The second passaged neurosphere emits green fluorescence, shown in a. Nestin immunohistochemical staining was performed to confirm NSC, shown in b. Scale bar 50 μm (Color figure online)

Fig. 2

The fate of transplanted NSC in host spinal cord after hSCT. A few NSC with green fluorescence was found in host spinal cord surrounding epicenter (a), and the number of NSC gradually decrease when the distance is far away epicenter (b). Scale bar 50 μm

Fig. 3

Identification of differentiation on NSC in host spinal cord. To identify the differentiation of NSC in the spinal cord, enzyme-linked immunohistochemical staining was performed. Engrafted NSC emitting green fluorescence were shown in a, c, simultaneously expressed NeuN marker (b), and GFAP marker (d), respectively. These confirmed NSC differentiation toward neuronal-like cells and GFAP-like cells. Scale bar 50 μm (Color figure online)

Fig. 4

NSC grafts decreased the neural apoptosis. The picture a showed the normal morphology without apoptosis in sham group comparatively, there were a few apoptotic cells in spinal cord after hSCT (b), and the number of apoptotic cells decreased significantly after NSC grafts (c). The statistic analysis was shown in d. Scale bar 50 μm

Fig. 5

Expression of BDNF and TrkB in the spinal cord. Quantitative PCR showed that the level of BDNF mRNA was significantly decreased after hSCT, whereas it was significantly increased after NSC transplantation. Comparatively, the mRNA level of trkB, a receptor of BDNF, is not changed

Fig. 6

Changes of caspase-7 in the spinal cord. Q-PCR showed that NSCs transplantation could downregulate the mRNA level of caspase-7 (a), while protein level of caspase-7 was also decreased in NSC administrated rats than that of rats only subjected to hSCT (b)

Fig. 7

BBB scores of hind limbs in each group. Records of BBB score in different time point (1, 7, 14, 21 dpo) in injured side of different groups with or without NSCs transplantation. NSCs transplantation did not exhibited a significant improvement on the hind limbs locomotor function in rats with hSCT