To investigate the role of bone marrow mesenchymal stem cell (BMSC)-derived exosomes in the repair process of sciatic nerve injury.

Twenty-four SD rats were randomly into three groups: control group, sham group, and exosome group. For inducing sciatic nerve injury, after exposing the sciatic nerve of each rat, the second level strength of microhemostatic forceps was used to clamp the nerve 5 mm above the sciatic nerve bifurcation for 3 times, 10 s for each time, with an interval of 5 s. In the exosome group, 5 μl of exosomes were injected into the subepineurium near the clamp injury. In the control group, 5 μl of PBS was injected in the same site. In the sham group, the nerve was just exposed without any other manipulation. At 4 weeks after surgery, Catwalk was used to detect the recovery of rat motor function. The function of nerve conduction was detected by electrophysiology. Masson staining was used to detect the area of gastrocnemius muscle fiber. The diameter of nerve fibers in each group was detected by transmission electron microscopy. Immunofluorescence staining for GFAP and IBA-1 was applied to demonstrate the positive area of microglia and astrocytes in the lumbar spinal cord segments.

The results of Catwalk showed that the sciatic function index in the exosome group was significantly better than that of the control group (P＜0.05). Electrophysiology showed that both the amplitude of compound muscle action potential and motor nerve conduction velocity were significantly higher than those of the control group (P＜0.05). The area of gastrocnemius muscle fibers detected by Masson staining in the exosome group was significantly larger than that of the control group (P＜0.05). Transmission electron microscopy showed that the cross area of the myelinated nerve fiber of the exosome group was bigger and in better shape than that of the control group (P＜0.05), but smaller than that of the sham group (P＜0.05). The percentages of positive GFAP area and IBA-1 area in the exosome group and control group were significantly larger than that of the sham group (P＜0.05), and they were significantly smaller in the exosome group than in the control group (P＜0.05).

After peripheral nerve injury, BMSC-derived exosomes can promote the functional recovery by promoting axon regeneration and pain relief.