Effects And Mechanisms Of Tubulin Post-translational Modification In The Repair Of Cauda Equina Lesions

BackgroundDorsal root ganglion?DRG?neuron is pseudo-unipolar neuron.Its cell body settled in DRG,but two branches of axon are extended to cornu dorsal or periphery sensors each.Posterior ramus of lumbar spinal nerves consist of peripheral axon branches of DRG neurons,which can readily regenerate after injury caused by lumbar disc herniation.Lower limb pain and numbness can be significantly relieved after lumbar decompression surgery.In contrast,the sensory branches of cauda equine consist of central axon branches of DRG neurons.The consequences of cauda equine syndrome?CES?,such as sensory disturbance of perineal region,is hard to recover after injury caused by central lumbar disc herniation.However,the central axon branches,critical components of cauda equine,do not easily regenerate after DRG neurons injury.Such differences between the peripheral and central branches of DRG have not been fully elucidated.Microtubules are a component of the cytoskeleton,which is important in a broad range of cellular processes,such as organelle movement,macromolecular assemblies,and chromosome separation.Moreover,extensive investigations of the neuronal microtubules reveal that they play critical roles in the axon growth,dendritic arborization,and neuron migration to their destinations.In the current study,we explored the expression patter of tubulin post-translational enzymes?acetylase and deacetylase?in the damaged peripheral and central branch of DRG neurons in the rat models of spinal nerve injury and cauda equine injury.ObjectiveThe differences between the peripheral and central branches of dorsal root ganglion?DRG?have not been fully elucidated.This study aimed to differential expression of tubulin post-translational modifications?acetylation and deacetylation?between the damaged peripheral and central branch of DRG neurons.And we define the effect of target PTM enzyme on axonal regeneration of DRG neurons and functional recovery of cauda equine injury in vivo.MethodsThe 50 Sprague-Dawley rats were randomly assigned to five groups with 10 in each group.These five groups consisted of SNL at 24h and 48h,and CEC at 24h and48h,and a sham group.Spinal nerve ligation?SNL?injury in rats was induced by ligating L5 and L6 spinal nerves with 1-0 silk thread outboard the DRGs.Cauda equina compression?CEC?injury in rats was induced by a piece of silicone?10×1×1mm?placed under the laminae of the L_5-6 vertebra.Sham-operated rats underwent a simple laminectomy in L₄,but silicone was not implanted.The expression profile of acetylase and deacetylase was examined by real time PCR,western blot,and immunohistochemistry.According to the result of HDAC6 gradually decreased in DRG neurons following peripheral axonal injury compared to central axonal injury,we designed that the 30Sprague-Dawley rats were randomly allocated into three groups with 10 in each group.These three groups consisted of cauda equina compression group,Tubastatin A?HDAC6 inhibitor?group,and a sham group.The experimental group was treated with Tubastatin A?4%DMSO+30%PEG300+66%pure water?intraperitoneally?10mg/kg body weight?once a day for a week,whereas the compression and sham groups received equal volumes of solvent.The content of HDAC6 in DRG neurons was detected by Western blot and immunofluorescence.TUNEL staining was used to detect the apoptosis of DRG neurons.The tail-flick test was performed to assess whether Tubastatin A improved sensory function.ResultsIn the experimental groups,rats presented increased expression of acetylase?NAT1 and MEC-17?and decreased deacetylase?Sirt2 and HDAC6?levels.Additionally,the expression of NAT1 and MEC-17 was gradually increased in DRG neurons following peripheral axonal injury compared to central axonal injury in a time-dependent manner.Conversely,the expression of Sirt2 and HDAC6 was gradually decreased in DRG neurons following peripheral axonal injury compared to central axonal injury in a time-dependent manner.Western blot and immunofluorescence showed that the expression of HDAC6 of DRG in the experimental group was significantly lower than that of the compression group at seventh day after operation.TUNEL staining showed that the DRG apoptosis rate in the experimental group was significantly lower than that in the compression group.Significant differences in the tail-flick test results were detected at seventh day between the experimental group and the compression group.ConclusionOur study indicates that insufficiency of acetylase and up-regulation of deacetylase in DRG neurons after central axonal injury may contribute to the pathogenesis of cauda equine syndrome.HDAC6 inhibitor?Tubastatin A?can effectively reduce the content of HDAC6 in the DRG neurons of rats after cauda equina injury,reduce the apoptosis of nerve cells and the changes of cauda equina demyelination,and restore some nerve function.