Neural stem cell-derived exosomes facilitate spinal cord functional recovery after injury by promoting angiogenesis

Acute traumatic spinal cord injury is a devastating event without effective therapeutic approach. The feeble plasticity of spinal cord microvascular endothelial cells (SCMECs) after trauma is one of the major causes for the exacerbation of spinal cord injury. Therefore, improving the plasticity and regeneration of SCMECs is crucial to promote recovery after spinal cord injury. For the present study, we explored the influence of exosomes derived from neural stem cells (NSCs-Exos) on the spinal cord microvascular regeneration after spinal cord injury and determined the underlying mechanisms. After the primary NSCs and SCMECs were extracted, exosomes were isolated from NSCs conditioned medium and used to co-incubated with the SCMECs in vitro, and then the effect of exosomes on the angiogenic activities of SCMECs was measured. The candidate molecules involved in the NSCs-Exos-mediated angiogenesis were screened using Western blotting. The effect of NSCs-Exos on angiogenesis and spinal cord functional recovery after injury in vivo was analyzed. The results demonstrated that NSCs-Exos could enhance the angiogenic activities of SCMECs, and were highly enriched in VEGF-A. The level of VEGF-A was downregulated in NSCsshVEGF-A-Exos and the pro-angiogenic effects on cocultured SCMECs were inhibited. Furthermore, NSCs-Exos significantly accelerated the microvascular regeneration, reduced the spinal cord cavity, and improved the Basso mouse scale scores in spinal cord injury mice. This work provides the evidence of the underlying mechanism of NSCs-Exos-mediated angiogenesis and suggests a novel therapeutic target for spinal cord injury. Impact statement The feeble plasticity of SCMECs after trauma is one of the major causes for the exacerbation of SCI. Therefore, improving the regeneration ability of SCMECs is crucial to promote spinal cord functional recovery after injury. Our current study uncovered that NSCs-Exos could promote SCMECs migration, tube formation and proliferation in vitro, and further identified that exosomal VEGF-A mediated the pro-angiogenic effect. Furthermore, we observed a remarkable microvascular density increase, spinal cord cavity shrinkage, and motor function recovery in SCI mice treated with NSCs-Exos, which confirmed the therapeutic effects of NSCs-Exos to alleviate SCI. Downregulating VEGF-A partially abolished these effects of NSCs-Exos. This is the first study to reveal that NSCs-Exos has the pro-angiogenic effect on SCMECs by transferring VEGF-A and promote microvascular regeneration and tissue healing, indicating that NSCs-Exos can become a promising therapeutic bioagent for facilitating the functional recovery of SCI.