Simvastatin mobilizes bone marrow stromal cells migrating to injured areas and promotes functional recovery after spinal cord injury in the rat

► Simvastatin treatment was given by subarachnoid injection immediately after SCI. ► Locomotive functional recovery significantly improved by simvastatin treatment. ► Bone marrow stromal cells migrated to the injured site enhanced by simvastatin. ► Simvastatin increased the expression of BDNF and VEGF in injured rats. This study investigated the therapeutic effects of simvastatin administered by subarachnoid injection after spinal cord injury (SCI) in rats; explored the underlying mechanism from the perspective of mobilization, migration and homing of bone marrow stromal cells (BMSCs) to the injured area induced by simvastatin. Green fluorescence protein labeled-bone marrow stromal cells (GFP-BMSCs) were transplanted into rats through the tail vein for stem cell tracing. Twenty-four hours after transplantation, spinal cord injury (SCI) was produced using weight-drop method (10g4cm) at the T10 level. Simvastatin (5mg/kg) or vehicle was administered by subarachnoid injection at lumbar level 4 after SCI. Locomotor functional recovery was assessed in the 4 weeks following surgery using the open-field test and inclined-plane test. At the end of the study, MRI was used to evaluate the reparation of the injured spinal cord. Animals were then euthanized, histological evaluation was used to measure lesion cavity volumes. Immunofluorescence for GFP and cell lineage markers (NeuN and GFAP) was used to evaluate simvastatin-mediated mobilization and differentiation of transplanted BMSCs. Western blot and immunohistochemistry were used to assess the expression of vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF). Simvastatin-treated animals showed significantly better locomotor recovery, less signal abnormality in MRI and a smaller cavity volume compared to the control group. Immunofluorescence revealed that simvastatin increased the number of GFP-positive cells in the injured spinal cord, and the number of cells double positive for GFP/NeuN or GFP/GFAP was larger in the simvastatin treated group than the control group. Western blot and immunohistochemistry showed higher expression of BDNF and VEGF in the simvastatin treated group than the control group. In conclusion, simvastatin can help to repair spinal cord injury in rat, where the underlying mechanism appears to involve the mobilization of bone marrow stromal cells to the injured area and higher expression of BNDF and VEGF.