Effcts Of SOCS3 Ablation On Microglia/macrophage Polarization And Functional Recovery After Spinal Cord Injury In Mice

objective Neuroinflammation after spinal cord injury is a main obstacle to functional recovery. The local microglia and the infiltrated monocytes after injury constitute the major cellular component of the innate immunoreaction. Researches show that Socs3 participate in a variety of inflammatory responses, and can affect functional recovery after spinal cord injury. But the effect of Socs3 on microglia/macrophage activation after spinal cord injury remains unknown. Our research is to estimate the influence of Socs3 conditional ablation on macrophage polarization, axonal growth, remyelination and functional recovery after spinal cord injury in mice, and to discuss the underlying mechanisms.Method (1) To obtain nervous-system-restricted or myeloid-cell-lineage-restricted deletion of Socs3, we generated Socs3f1/f1 Nes cre mice and Socs3fl/fl LysM cre mice, and defined them as knockout group 1(n=40) and knockout group2(n=40). The littermates Socs3f1 mice (n=40) are define as control. Mice underwent spinal cord compressing injury were harvested at 1,3,7 and 14 days respectively. Immunofluorescence staining and qRT-PCR were performed to detect changes of Ml and M2 markers, behavioral experiments were performed for comparisons of functional recovery.(2) Socs3f1/f1 Nes cre mice(n=15) and Socs3fl mice(n=15) were considered as knockout group and control group respectively. After spinal cord injuries, TUNE1 staining was used to detect the cell apoptosis. BDA was injected into the sensorimotor cortex to trace the corticospinal tract. Counterstaining was performed with Glial Fibrillary Acidic Protein (GFAP) staining to determine the lesion core. The CST regenerating and dieback were observed. And the luxol fast blue staining was used to measure the remyelination.Result (1)On the level of genes, the expression of argl, CD206 and Stat3 genes were increased, whereas the expression of CD32 and Socs3 genes were reduced in knockout 1 group, compared with the control group. No significant difference was found between the gene expression in knockout2 group and control group. Similarly, on the protein level, immunofluorescence staining showed that mice in knockout 1 group have a predominance in distribution and population of M2 markers(Arginasel, CD206) positive macrophages but a reduced expression of M1 markers (CD86, D16/32) after spinal cord injury, compared with controls, and no significant difference was found between knockout2 group and control group. The behavioral assessments of the knockout 1 group were superior compared with the knockout2 and control group at 7 and 14 days post-injury.(2) Compared with the control group, the contraction of lesion area was enhanced, the ratio of total labeled sprouts/axons were significantly increased, the ratio of total labeled retraction bulbs/axons were decreased, and the distance of the bundle to lesion border were decreased in knockout group at 14 weeks post-injury. The remyelination detected by Luxol fast blue staining at 14weeks post-injury was greater, and the apoptosis cells at 7 days post-injury was reduced at knockout group, compare with the control group.Conclusion (1) The nervous-system-restricted Socs3 conditional knockout can promote the formation of M2 macrophage after spinal cord injury in mice, corresponding with better functional recovery. The switch of phenotype of macrophages might be a major cause of the improved function.(2) the myeloid-cell-lineage-restricted Socs3 knockout failed to effect the phenotype of macrophages or the functional recovery after spinal cord injury. That may because this type of conditional knockout does not do enough to switch the phenotypes to a significant level, or because the blood-derived monocytes do not serve as a major composition of macrophage activation after injury.(3)The deletion of Socs3 in the nervous system can promote axonal growth, restrict the dieback and restrain the cell apoptosis, as well as improve remyelination. Its effect on functional recovery after spinal cord injury may be a consequence of multimechanisms.