Association between neurodegeneration and tissue plasminogen activator and plasminogen activator inhibitors in spinal cord after sciatic nerve transection

Abstract

Objective To investigate whether tissue plasminogen activator(tPA),type Ⅰ plasminogen activator inhibitor(PAI-1)and neuroserpin(NSP)are involved in neurodegeneration following sciatic nerve transection in rats.Methods Fifty-six male Sprague Dawley rats were randomly divided into normal group and sciatic nerve transection group.Spinal cord from level L4 to L6 was removed at several time points after sciatic nerve transection for Nissl staining and transmission electron microscopy to evaluate neurodegenerative changes and neuronal death.The dynamic expression of tPA,NSP and PAI-1 were examined by immunohistochemical staining and semi-quantitative reverse transcription-polymerase chain reaction(RT-PCR).Results Statistically significant neuron loss in spinal anterior horn of the injured side was found 7 days following sciatic nerve transection.The neuron survival rate at 21 days after the operation was 61.6％.Furthermore transmission electron microscopy showed a considerable number of apoptotic neurons and glia cells at various phases in the anterior horn from 7 days postoperatively.Furthermore,a few apoptotic cells could be detected in the posterior horn at 14 days after the operation as well.The results of immunohistochemistry showed that tPA was up-regulated in laminae Ⅴ to Ⅸ of the injury side by 1 day post-lesion(P ＜ 0.05)and peaked at 7 days.After that,tPA protein was down-regulated.But until the time point of 21 days,the level of tPA had not returned to the normal level(P ＞ 0.05).However,PAI-1 could be detected in neither normal nor experimental spinal cord.Semi RT-PCR revealed a change tendency of tPA mRNA that was similar to tPA protein but just a little earlier than the latter.Meanwhile,NSP mRNA was up-regulated by 1 day and stayed at a higher level for two weeks.It returned to normal level at 21 days.Conclusion The 50％ motor neuron loss in the ipsilateral spinal cord anterior horn after sciatic nerve transection was related to the upregulation of synthesis and release of tPA from neurons and microglia in the grey matter.Meanwhile the axotomy stimulated upregulation of tPA inhibitor NSP which may play a neuroprotective role. Key words: Sciatic nerve; Spinal cord; Neurons; Degeneration; Tissue plasminogen activator