Down-regulation Of NgR Receptor By SiRNA Carried By Lentivirus Promotes Functional Recovery In Spinal Cord Injury Rats

ObjectiveTo observe the therapeutic effect of siRNA, which could disturb the expression of NGR, for the regeneration of axon after spinal cord injury (SCI) in Wistar rats, we injected lentivirus carrying siRNA locally during the acute period of SCI, and further to explore its repair mechanisms.Methods60female Wistar rats were randomly divided into four groups:blank control group (group A, n=15), empty vector group (group B, n=15),NGR-scramble group (group C, n=15) and the lentivirus carrying siRNA group (Group D, n=15). NYU Impactor Model-II device was used to induce SCI animal model at the level of Chest10(T10). Group A was injected saline locally after SCI immediately, Group B accepted local injection of lentivirus without siRNA after SCI, Group C accepted local injection of lentivirus with scramble siRNA of NGR after SCI,Group D accepted local injection of lentivirus carrying siRNA of NGR immediately after SCI. Then the hindlimb function behavior score (Basso, Beattie&Bresnahan locomotor rating scale, BBB scale) was analyzed statistically at the time of24h,3rd day,5th day,1st week,2nd week,3rd week,4th week,5th week,6th week,7th week,8th week after SCI. The spinal cord tissue was taken to observe the expression of EGFP under a fluorescence microscope at the time of the8w after SCI, and to observe the local glial scar and axonal regeneration through immunohistochemical staining.ResuItsAt the time of24h,3d,5d,1w,2w after SCI, there was no significant difference among BBB scores of the three groups (P>0.05), and the BBB score of group D was significantly higher than the group A、B and group C at each time point after the3rd week (P<0.05). The BBB scores of all the four groups reach a platform after6w. BBB score of group D increased significantly during the period of2w-6w after SCI, in contrast, the other three groups changed slowly (P<0.05). Lots of Fibrillary Acidic Protein was observed in the gray matter of spinal cord around the syringomyelia under the fluorescence microscope, and there was no significant expression in the proximal and distal spinal cord, lots of astrocytes proliferated arounding the cavities to form glial scar. The corticospinal tracts were disorganized, and only a small amount of nerve tract passes through the injury area. In contrast, while there was no significant difference about the density of astrocytes around the cavities between all the groups. Furthermore, the corticospinal tracts arranged tidily in group D, and there were more intact nerve tract pass through the injury area, immunohistochemical staining of Synaptophysin show there were more functionality synapses than the other groups(P<0.05).ConelusionLocal injection of lentivirus carrying siRNA, which can disturb the expression of NGR, then block the transduction of inhibiting signal from NOGO、MAP、OMGP, and can significantly promote the regeneration of axons after spinal cord injury at last. It was also shown that lentivirus was a safe carrier for gene therapy, and could replicate within the spinal cord tissue for a long time.