Let-7 participates in the regulation of inflammatory response in spinal cord injury through PI3K/Akt signaling pathway

OBJECTIVE: To study the potential mechanism of let-7 in participating in the regulation of inflammatory response in spinal cord injury (SCI). MATERIALS AND METHODS: A total of 40 male Sprague-Dawley rats were randomly divided into four groups: group A (Sham, n=10). group B (SCI+NC, n=10), group C (SCI+antagomir, n=10), and group D (SCI+mimics, n=10). The SCI model was established via operation in all groups. After successful modeling, let-7-antagomir negative control (80 mg/kg) was intraperitoneally injected in SCI+NC group at 5 d, an equal amount of let-7-antagomir was intraperitoneally injected in SCI+antagomir group at 5 d, and an equal amount of let-7-mimics was intraperitoneally injected in SCI+mimics group at 5 d. The inflammatory cells in experimental groups and control group were observed via hematoxylin-eosin (HE) staining. At the same time, the expression of let-7 in the four groups was detected via Reverse Transcription-Polymerase Chain Reaction (RT-PCR), the expressions of phosphatidylinositol 3-hydroxy kinase (PI3K) and protein kinase B (Akt) in all groups were detected via Western blotting, and the inflammatory index levels in each group were detected via enzyme-linked immunosorbent assay (ELISA). RESULTS: In Sham group, it was observed via HE staining that there were only a few bleeding or inflammatory cells. In SCI+NC group, bleeding and inflammatory cells basically tended to be stable. There were a large number of inflammatory cells in SCI+mimics group. while there were some inflammatory cells in SCI+antagomir group, but showing a decreasing trend compared with SCI+NC group. It was found in the RT-PCR detection of let-7 expression level in all groups that the expression of let-7 significantly declined in SCI+antangomir group compared with that in Sham group and SCI+NC group, and there were significant differences (p<0.01). The expression of let-7 was significantly increased in SCI+mimics group compared with that in Sham group and SCI+NC group, and there were significant differences (p<0.01). The results of Western blotting revealed that the PI3K and Akt protein expressions were significantly decreased in SCI+mimics group compared with those in in SCI+antagomir group, SCI+NC group, and Sham group (p<0.05). The ELISA results showed that the levels of inflammatory factors in SCI+mimics group, SCI+antagomir group, and SCI+NC group were significantly higher than those in Sham group. In SCI+mimics group, the levels of inflammatory factors were abnormally high and reached extremely significant levels (p<0.05). indicating that let-7 promotes the inflammatory response after SCI. CONCLUSIONS: Let-7 participates in the regulation of inflammatory response in SCI through the PI3K/Akt signaling pathway.