Sciatic nerve conditioning injury induces microRNA-182 down-regulation in rats with dorsal column lesion and further up-regulates cyclic adenosine monophosphate-response element binding protein expression

Abstract

Objective To explore the repairment mechanism of dorsal column lesion which is promoted by sciatic nerve conditioning injury on the basis of microRNA genomics to find the key therapeutic target. Methods Forty-eight healthy female Wistar rats were randomly divided into sciatic nerve conditioning injury group (n=15), simple dorsal column lesion group (n=15), simple sciatic nerve injury group (n=15) and control group (n=3). Sciatic neurotomy was performed 7 d before giving dorsal column lesion in rats from the sciatic nerve conditioning injury group and simple dorsal column lesion group; and then, rats from the four groups were sacrificed and excised the bilateral dorsal root ganglions (DRGs) connected with bilateral sciatic nerves 4 h, and 1, 3 and 7 d after giving dorsal column lesion. Microarray was used to investigate microRNA expression profiles, real time-quantitative PCR was applied to detect the expression of miR-182, ELISA was employed to detect the cyclic adenosine monophosphate (cAMP) level, and Western blotting was used to detect the protein expressions of cAMP-response element binding (CREB) and phosphorylating-CREB (p-CREB). The injured spinal cord segments (10th thoracic spinal cord segments) were obtained 14 d after giving dorsal column lesion, Hematoxylin and eosin (HE) stainning was used to observe the morphology of nerve fiber bundles, and immunohistochemistry was used to investigate the expression of neurofilament protein NF-200 in dorsal column. Results As compared with control group, there were 681 changed miRNAs at different check points in the sciatic nerve conditioning injury group and simple dorsal column lesion group. As compared with that in the simple dorsal column lesion group, miR-182 level in the sciatic nerve conditioning injury group was down-regulated 3 and 7 d after giving dorsal column lesion (P 0.05), whereas the protein expressions of CREB and p-CREB 3 and 7 d after giving dorsal column lesion and the cAMP level 4 h, and 1, 3 and 7 d after giving dorsal column lesion were significantly increased in the DRGs from sciatic conditioning injury group (P<0.05). HE staining showed that shape of nerve fiber bundle was more regular in caudal lesion site of sciatic nerve conditioning injury group as compared with that in the simple dorsal column lesion group. Immunohistochemical staining indicated that NF-200 expression in caudal of dorsal column lesion center from the sciatic nerve conditioning injury group was significantly increased than that in the simple dorsal column lesion group (P<0.05). Conclusion The sciatic nerve conditioning injury can promote the repair of dorsal column lesion, which might be related to the down-regulation of miR-182 and elevation of cAMP levels. Key words: Sciatic nerve conditioning injury; MicroRNA; Dorsal column lesion; Cyclic adenosine monophosphate-response element binding