| Background and objective: Traumatic spinal cord injury(TSCI)is a catastrophic event that usually results in paraplegia or quadriplegia,causing permanent sensory and motor dysfunction.Currently,there is no effective treatment strategy.Dexmedetomidine(Dex)has neuroprotective effects,but whether it can inhibit apoptosis induced by endoplasmic reticulum stress after TSCI is unknown.In this study,the protective effect of Dex on rats with spinal cord injury was investigated by establishing a TSCI model,and whether the mechanism was related to the inhibition of endoplasmic reticulum stress-dependent apoptosis was determined.Methods: Sixty SD rats were divided into five groups randomly(n = 12),that is sham operation group(Sham group),traumatic spinal cord injury group(SCI group),Dex intervention group(Dex group),Tunicamycin intervention group(TM group),and Tunicamycin and Dex intervention group(TM + Dex group).Incised skin along the posterior midline of the rat,separated the T9-T11 spinous processes,and then the laminectomy was performed at the T10 vertebra,exposed the spinal cord without damaging dura mater.A contusion injury was induced by weight compression.The rats in TM group and TM + Dex group were injected intraperitoneally with TM(100μg/kg body weight)immediately after operation,and the other groups were given the same amount of 5% DMSO solution.The rats in Dex group and TM + Dex group were intraperitoneally injected with Dex(10μg/kg body weight),once a day and for 3 consecutive days,the other groups were given the same dose of normal saline.At 1,3,and 7 days after operation,the locomotor activity of the hind limbs of all rats were evaluated by using BBB scoring system.At 7 days after injury,T9-T11 segmental of every rat were removed,and 6 specimens in each group were embedded in paraffin and sectioned for HE staining,Nissl staining,and TUNEL staining.The remaining 6 were subjected to detect the expression level of anti-apoptotic proteins Bcl-2,apoptotic proteins Bax and Cle-Caspase3,as well as endoplasmic reticulum stress-related proteins GRP78,PERK,ATF4,CHOP and Caspase12 by western blot.Results: After injury,the locomotor activity of hindlimb of the rats was impaired severely.The BBB scores of rats that subjected to contusion were 0 at the first day after operation.At 3 day after injury,the locomotor was recovered to some degree,but there was no significant difference between the SCI and Dex groups.At 7 days following operation,the score of Dex group was higher than that of SCI group(8.17±1.89 vs 5.54±1.29,P<0.001),and the scores of TM group and TM + Dex group were both lower than that of Dex group.HE staining showed that the degree of injury in spinal cord was severe in the SCI group,and cavities formation at the injury site.The average percentage of the damage area in the Dex groupwas lower than that of SCI group(0.23±0.03 vs 0.33±0.02,P<0.001).The degree of injury in the TM + Dex group was more severe compared with the Dex group.Nissl staining revealed a large number,normal and clear Nissl bodiesin the Sham group,while the Nissl bodies were markedly reduced as well as blurred or absent.Compared to SCIgroup,treatment with Dex retained more Nissl bodies,and the morphology was relatively normal,the difference was significant(22.72±1.39 vs19.56±1.63,P=0.01).The numbers of normal neurons in the spinal cord in the TM and TM+Dex groups were notably lower than that of in the Dex group.TUNEL staining results indicated that there was a large number of apoptotic cells in the SCI group,while the number of TUNEL-positive cell in Dex group was reduced compared to SCI group(47.33±3.37 vs 75.17±2.91,P<0.001).The apoptotic cells in the TM + Dex group was more than that in the Dex group(P<0.05).Western blot results showed that,the expression of anti-apoptotic protein Bcl-2 was at a high level while the apoptotic proteins Bax and Cle-Caspase3 were both at a low level in Sham group.However,the content of Bcl-2 was markedly decreased,and Bax as well as Cle-Caspase3 were significantly increased in the SCI group.Compared with the SCI group,treatment with Dex promoted the expression of Bcl-2(1.01±0.19 vs 0.57±0.05,P<0.001)but reduced the content of Bax and Cle-Caspase3(0.62±0.13 vs 0.95±0.20,P=0.003,0.82±0.07 vs 1.09±0.16,P=0.003,respectively).The levels of Bax and Cle-Caspase3 in TM + Dex group were significantly higher than those in Dex group,while the content of Bcl-2was markedly lower.In addition,the expression of endoplasmic reticulum stress-related proteins was low in the Sham group,but the content of GRP78,PERK,ATF4,CHOP and Caspase12 in the SCI group were significantly increased.Treatment with Dex reduced the expression levels of all the above proteins,while the content of these proteins in the TM + Dex group were significantly increased compared with the Dex group.Conclusion: The results of this study indicate that,treatment with Dex can improve locomotor activity of rats with traumatic spinal cord injury,as well as reduce neuron injury and apoptosis in spinal cord,andthe mechanism is related to the inhibition of apoptosis induced by endoplasmic reticulum stress response. |
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