PBMSCs transplantation facilitates functional recovery after spinal cord injury by regulating microglia/macrophages plasticity

Background: Stem cell therapy has been proven as one of the promising strategies for treating spinal cord injury (SCI). However, the role of peripheral blood-derived mesenchymal stem cells (PBMSCs) in animal models of SCI has not been fully uncovered. This study aimed to investigate whether transplanted PBMSCs could inhibit neuroinflammation and then promote the functional recovery by shifting the microglia/macrophages phenotype from M1 to M2 at the site of injury after SCI. Methods: PBMSCs harvested from peripheral blood were analyzed by morphology and phenotype. Rat models of SCI were administrated with PBMSCs 1 week after injury. Inclined plane test and Basso-Beattie-Bresnahan (BBB) scores were used for assessing the functional recovery. Enzyme-linked immunosorbent assay (ELISA), reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and flow cytometry (FCM) were performed on days 3, 7, 14, 28 and 56 after PBMSCs transplantation. Results: PBMSCs were plastic-adherent and fibroblast-like with positive expression of cluster of differentiation (CD)29, CD90 and CD44. ELISA and RT-qPCR both showed a lower expression of pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha while a higher expression of anti-inflammatory cytokines IL 10 and transforming growth factor (TGF)-beta 1 after PBMSCs transplantation. This was associated with increased numbers of M2 microglia/macrophages and decreased numbers of M1 microglia/macrophages. These changes taken together were associated with the functional recovery in PBMSCs groups. Conclusions: Administration of PBMSCs following SCI may provide an anti-inflammatory and reparative micro environment for locomotive recovery by shifting microglia/macrophages phenotype from M1 towards M2.