Exosomes derived from bone marrow mesenchymal stem cells overexpressing microRNA-25 protect spinal cords against transient ischemia.

OBJECTIVE

We investigated the neuroprotection of exosomes derived from bone marrow mesenchymal stem cells overexpressing microRNA-25 on ischemic spinal cords.

METHODS

Cultured mesenchymal stem cells were transfected with lentivirus vectors containing pre-microRNA-25 or control vectors. Exosomes were isolated and harvested by centrifugation. Spinal cord ischemia was induced in rats by crossclamping the descending aorta just distal to the left subclavian artery for 15 minutes. Exosomes from mesenchymal stem cells, mesenchymal stem cells transfected with control vector, or pre-microRNA-25 were administered by intrathecal injection before ischemia. Hind-limb motor function was assessed with the motor deficit index. Contents of interleukin-1β, tumor necrosis factor-α, malondialdehyde, and superoxide dismutase activity were measured using commercial kits. Expressions of NADPH oxidase 2, NADPH oxidase 4, and microRNA-25 were detected by Western blot and quantitative reverse transcription polymerase chain reaction. Lumbar spinal cords were harvested for histologic examination.

RESULTS

Transfection of pre-microRNA-25 significantly enhanced microRNA-25 levels in mesenchymal stem cells and their exosomes (P < .001). All exosome-pretreating groups exhibited lower levels of interleukin-1β and tumor necrosis factor-α (P < .001), more intact motor neurons (P < .001), and lower motor deficit index scores (P < .005) than those of controls. Compared with exosomes, microRNA-25-enriched exosomes markedly enhanced microRNA-25 level (P < .001), inhibited NADPH oxidase 4 expression (P = .012), but not NADPH oxidase 2 expression, decreased malondialdehyde content (P = .022), increased superoxide dismutase activity (P < .001) in spinal cords, and had additional neuroprotective effects as evidenced by lower motor deficit index scores (P < .005) and more survival neurons (P = .002).

CONCLUSIONS

The neuroprotection of exosomes from mesenchymal stem cells on ischemic spinal cords can be enhanced by genetic modification of the exosomes to contain elevated microRNA-25.