The role of Sonic Hedgehog pathway in the development of spinal cord injury in rat model

Abstract Purpose: The Sonic Hedgehog (Shh) pathway plays an important role in neuroinflammation and neurorepairment after neurological injury, but its role in the development of spinal cord injury (SCI) and related mechanisms are not clear. The purpose of this study was to explore whether and how the Shh signaling pathway exert a neuroprotective effect in SCI. Methods: The SCI model of rat was established by a Allen's weight-drop method. Thirty SPF SD rats were divided into 5 groups as follows: Control, Sham, SCI model, SCI + purmorphamine (Shh activator), and SCI + cyclopamine (Shh inbibitor). Rats in group of Shh activator or Shh inbibitor were administrated with purmorphamine (10 mg/kg) or cyclopamine (10 mg/kg) respectively daily within one week after establishment of SCI model. Scores of Basso, Beattie, Bresnahan (BBB) and Reuter were evaluated at the time-points of 1 st , 3 rd , 5 th and 7 th day after establishment of SCI model. Rats were sacrificed on 7 th day , and the pathological injury, the levels of inflammatory cytokines (IL-1β and TNF-α) and the protein and mRNA expressions of Gli1, Shh and Smoothened in spinal cord tissue were assessed by HE staining, ELISA, Western Blot and RT-qPCR, respectively. Results: Rat treated with purmorphamine exhibited a significant increase in BBB score in comparison with SCI group, whereas there was no significant difference after cyclopamine treatment. Interestingly, purmorphamine treatment declined SCI-induced increases in the levels of inflammatory cytokines (IL-1 β and TNF-α), whereas cyclopamine administration up-regulated their expressions of these inflammatory cytokines. The pyknotic neuronal cells in gray matter area of the spinal cord and the area of cavity in white matter area were reduced in purmorphamine treatment when compared with SCI group, whereas treatment with cyclopamine elicited an opposite changes. When compared with Sham group, the protein and mRNA expressions of Gli1, Shh, Smoothened were up-regulated in SCI group; whereas these SCI-induced expressions were further activated or inhibited by purmorphamine or cyclopamine treatment. Conclusion: We demonstrated that Shh activator plays an important protective role in the development of SCI in rat model, which might provide a new strategy via targeting Shh pathway to prevent or treat SCI in the future.