Neural stem cell-derived exosomes suppress neuronal cell apoptosis by activating autophagy via miR-374-5p/STK-4 axis in spinal cord injury

OBJECTIVES: To evaluate the roles of MicroRNAs (miRNAs) enclosed in the neuron-derived exosomes in the recovery of the spinal cord injury (SCI) and the mechanism. METHODS: The exosomes were isolated from neural stem cells (NSCs) and characterized by transmission electron microscopy (TEM) and NanoSight system (NTA). For in vivo experiments, Basso Mouse Scale, beam walking, and inclined plane tests were used to determine the behavioral symptoms of the SCI mice. For in vitro experiments, H(2)O(2) treated HT22 cells were used to simulate SCI cells and cocultured with exosomes to analyze the cell apoptosis using TUNEL assays and flow cytometry. Apoptosis- and autophagy-related protein expression was detected by western blot and the green fluorescent protein (GFP)-LC3 assay was used to detect the level of autophagy. In addition, luciferase assay was performed to assess the relationship between miR-374-5p and SKT-4. RESULTS: Exosomes from NSCs alleviated spinal cord injury by triggering autophagy flux and suppressing apoptosis. Besides, miR-374-5p was highly expressed in these exosomes and was responsible for the decent in injured neural cell apoptosis by activating autophagy flux. The SKT-4 was the target gene regulated by miR-374-5p in this exosomal protective function to SCI cells. CONCLUSION: The elevated level of miR-374-5p in neuronal exosomes could enhance spinal cord injury recovery by activating autophagy.