Exercise protects against spinal cord injury through miR-21-mediated suppression of PDCD4

Spinal cord injury (SCI) can lead to different levels of paraplegia. Studies have shown that exercise exerts wide protective effects against various diseases, and microRNAs (miRNAs) are involved in its beneficial effects. However, the specific role of miRNAs in the protective effects of exercise against SCI remains unclear. Here, we showed that exercise exerted protective effects against SCI as evidenced by increased locomotor activity and spinal cord cell survival in rats with SCI. Exercise upregulated circulating miR-21, detected by miRNA microarray, in rats with SCI. Treating SCI rats with agomiR-21 upregulated circulating miR-21 and exerted protective effects against SCI. Additionally, downregulating miR-21 using antagomir-21 abolished the protective effects of exercise on SCI. Programmed cell death protein 4 (PDCD4) was found to be the target of miR-21. These results suggested that exercise protects against SCI, at least partly, through miR-21-mediated suppression of PDCD4.