ObjectiveTo investigate the effect of granulocyte colony-stimulating factor (G-CSF) mobilizing the bone marrow mesenchymal stem cells (BMSCs) homing to the spinal cord injury sites in rats, and to evaluate the feasibility of G-CSF mobilizing the BMSCs home to the injured spinal cord. MethodsTwenty-four healthy adult female Sprague Dawley rats were injected with 1 mL green fluorescence protein labeled BMSCs (GFP-BMSCs, 1×106 cells/mL) into tail vein at 12 hours before operation. They were randomly divided into sham operation group (group A), sham operation+G-CSF group (group B), spinal cord injury group (group C), and spinal cord injury+G-CSF group (group D), with 6 rats in each group. In groups C and D, spinal cord injury model was established by T10 level spinal cord hemisection. In groups A and B, only laminectomy was performed without injury to the spinal cord. Groups B and D were injected with G-CSF (10 μg/kg·d) at 1 hour after operation for 3 consecutive days, and groups A and C were injected with the same amount of saline. The Basso-Beattie-Bresnahan (BBB) score was used to estimate the neurological function of rats and the expressions of tumor necrosis factor α (TNF-α) and stromal-derived factor 1 (SDF-1) were detected by ELISA method at 1, 3, 7, 14, 21, and 28 days after operation. The spinal cord samples of rats were sacrificed at 28 days after operation for immunohistochemical staining to observe the expression of cytokines, including SDF-1, brain derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and TNF-α, and immunofluorescence staining to observe GFP-BMSCs positive cells, double-stained fluorescent yellow GFP/neuronal nuclear antigen (NeuN) positive neurons, and GFP/glial fibrillary acidic protein (GFAP) positive neurons. The number of glial cells and apoptosis were detected by TUNEL method. ResultsThe BBB score of groups A and B had no significant change at each time point after operation. At 1 day after operation, the BBB score of groups C and D decreased to the lowest level, and then gradually increased. The BBB score of group D was significantly higher than that of group C at all time points except 1 day after operation (P<0.05). At 3, 7, 14, 21, 28 days after operation, the levels of TNF-α and SDF-1 in groups C and D were significantly higher than those in groups A and B (P<0.05), but the levels of TNF-α in group D were significantly lower than those in group C at each time point, and the levels of SDF-1 were significantly higher than those in group C (P<0.05). Immunohistochemical staining showed that the expressions of SDF-1, BDNF, VEGF, and TNF-α in groups C and D were significantly higher than those in groups A and B (P<0.05); the expressions of SDF-1, BDNF, and VEGF in group D were significantly higher than those in group C, and the expression of TNF-α was significantly lower than that in group C (P<0.05). Immunofluorescence staining showed that the number of GFP-BMSCs, GFP/NeuN, and GFP/GFAP positive cells in groups C and D were significantly higher than those in groups A and B, and in group D than in group C (P<0.05). TUNEL assay showed that the number of apoptotic cells in groups C and D was significantly lower than that in groups A and B, and in group D than in group C (P<0.05). ConclusionG-CSF can mobilize BMSCs to the spinal cord injury site and promote repair effect by down-regulating TNF-α to promote the anti-apoptosis function and up-regulating SDF-1, BDNF, VEGF to promote BMSCs migration.