Effect of SDF-1/CXCR4 axis on the migration of transplanted bone mesenchymal stem cells mobilized by erythropoietin toward lesion sites following spinal cord injury

Accumulating evidence has indicated that the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis plays a crucial role in the recruitment of bone marrow-derived mesenchymal stem cells (BMSCs) into lesion sites in animal models. The aim of this study was to investigate the effects of the SDF-1/CXCR4 axis on the migration of transplanted BMSCs mobilized by erythropoietin (EPO) toward the lesion site following spinal cord injury (SCI). A model of SCI was established in rats using the modified Allen's test. In the EPO group, EPO was administered at a distance of 2 mm cranially and then 2 mm caudally from the site of injury. In the BMSC group, 10 µl of BMSC suspension was administered in the same manner. In the BMSC + EPO group, both BMSCs and EPO were administered as described above. In the BMSC + EPO + AMD3100 group, in addition to the injection of BMSCs and EPO, AMD3100 (a chemokine receptor antagonist) was administered. The Basso-Beattie-Bresnahan (BBB) Locomotor Rating Scale and a grid walk test were used to estimate the neurological recovery following SCI. Enzyme-linked immunosorbent assay (ELISA) was performed to assess the tumor necrosis factor-α (TNF-α) and SDF-1 expression levels. An immunofluorescence assay was performed to identify the distribution of the BMSCs in the injured spinal cord. A Transwell migration assay was performed to examine BMSC migration. A terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was performed to detect the apoptotic index (AI). Western blot analysis was performed to measure the expression levels of erythropoietin receptor (EPOR) and CXCR4. Significant improvements in locomotor function were detected in the BMSC + EPO group compared with the BMSC group (P<0.05). GFP-labeled BMSCs were observed and were located at the lesion sites. Additionally, EPO significantly decreased the TNF-α levels and increased the SDF-1 levels in the injured spinal cord (P<0.05).The AI in the BMSC + EPO group was significantly lower compared with that in the other groups (P<0.05). Furthermore, EPO significantly upregulated the protein expression of CXCR4 in the BMSCs and promoted the migration of the BMSCs, whereas these effects were markedly inhibited when the BMSCs were co-transplanted with AMD3100. The findings of the present study confirm that EPO mobilizes BMSCs to the lesion site following SCI and enhances the anti-apoptotic effects of the BMSCs by upregulating the expression of SDF-1/CXCR4 axis.