The role of the miR-99b-5p/mTOR signaling pathway in neuroregeneration in mice following spinal cord injury

The present study aimed to investigate the role of microRNA (miR)-99b-5p in spinal cord injury (SCI). Reverse transcription-quantitative polymerase chain reaction demonstrated that, compared with control mice, the expression levels of miR-99b-5p were upregulated in the mouse spinal cord following SCI. Mechanistic target of rapamycin (mTOR) was predicted to be the possible target of miR-99b-5p according to TargetScan and microrna databases. Dual-luciferase reporter assay verified that miR-99b-5p was able to target mTOR. Furthermore, the results of an apoptosis analysis demonstrated that there were few apoptotic neurons in the control group, whereas SCI induced a significant increase in the number of apoptotic cells. Conversely, apoptosis was inhibited following transfection with a miR-99b-5p inhibitor. The effects of miR-99b-5p on neurite growth were also evaluated. The results of an immunofluorescence analysis indicated that neurite growth was normal in the control group, whereas SCI induced a reduction in neurite growth, which was rescued following transfection with a miR-99b-5p inhibitor. The protein expression levels of mTOR were detected in the three groups by western blotting. The results demonstrated that, compared with the control group, the protein expression levels of mTOR were significantly reduced in SCI neurons, whereas transfection with a miR-99b-5p inhibitor suppressed the SCI-induced reduction of mTOR. In conclusion, treatment with a miR-99b-5p inhibitor may attenuate SCI-induced harmful alterations in spinal cord neurons via the regulation of mTOR expression.