microRNA-331-3p attenuates neuropathic pain following spinal cord injury via targeting RAP1A.

Neuropathic pain (NP) after spinal cord injury (SCI) leads to compromised physical and cognitive functions in a majority of patients. Aberrant miRNA expression plays vital roles in the pathogenesis of SCI. This study aims to investigate the effect of miR-331-3p in rats following SCI. Microarray assay was performed in SCI- and sham-operated rats to evaluate the expression of miR-331-3p. Assigned SCI rats were treated with miR-331-3p agomiR alone or miR-331-3p agomiR plus RAP1A-expressing lentivirus or control agomiR. Rat locomotor performance was evaluated by BBB locomotor rating scale. Neuronal tissue damage and apoptosis were detected by histological analyses and Western blot. Inflammation in spinal cord was determined by detection of the expression of inflammatory genes with qRT-PCR, and ELISA. Downstream expression of RAP1A was measured by Western blot. The results showed that SCI induced the downregulation of miR-331-3p in the spinal cord of SCI rats. Overexpression of miR-331-3p improved the locomotor performance, reduced tissue damage, neuronal apoptosis and inflammation in rat SCI model. Rap1a (Ras-related protein Rap-1A) was predicted as a downstream target for miR-331-3p, and upregulation of RAP1A impaired the beneficial effect of miR-331-3p post- SCI, which was shown as worse locomotor activity, more severe tissue damage, as well as promoting apoptosis and inflammation in SCI rats. Furthermore, miR-331-3p reduced the activation of RAP1A downstream genes via inhibiting RAP1A expression. These findings indicate a protective role of miR- 331-3p in the development of SCI via the modulation of RAP1A, and may help to develop novel therapy against SCI-induced complications.