Single Prolonged Stress Induced PTSD Leads To Tau Hyperphosphorylation

Background:Post-traumatic stress disorder(PTSD)is a mental health problem that some people develop after experiencing or witnessing a life-threatening event,and it severely impairs the quality of our life.Some previous studies have shown that people with PTSD are especially vulnerable to cognitive disorder.And the risk of developing Alzheimer's disease in old age has more than twice,which suggested that there is a close association between PTSD and AD.AD is a very common neurodegenerative disease and it has two major pathologies,one is senile plaques(SPs)consist of amyloid-beta,and another is neurofibrillary tangles(NFTs)made of hyperphosphorylated tau.And the number of NFTs has positive correlation with dementia degree.Therefore,NFTs induced by abnormal aggregation of hyperphosphorylated tau is considered as a key to AD.Previous studies have reported that tau hyperphosphorylation was found in the brain of PTSD patients.However,the mechanisms underlying that PTSD induces tau hyperphosphorylation and then accelerate AD remain unknown.Objective: To study tau hyperphosphorylation induced by PTSD and its mechanism.Methods: Single prolonged stress(SPS)was employed to create a PTSD model in the present study.After observing animal for seven days,open field test and high plus maze were carried out for behavior test.Rat corticosterone ELISA kit was employed to measure rats CORT concentrations in hippocampus.Then western blotting and immunochemistry were performed to detect the level of total tau,p-tau(AT8(Ser202/Thr205),p S199,p S396,p S404),the level of A?1-40 and A?1-42 were also detected by ELISA kits.In this study,we used Western blotting to detect the levels of GSK3 ?,SGK1,AKT,Ca MKII and PP2 A,which are most important tau related protein kinase and protein phosphatase.Q-PCR technique was used to detect the stress-related key protein phosphokinase SGK1 m RNA level.In order to investigate the loss and damage of neurons in the early stage of PTSD,we used Nissl staining and WB to detect the number of neurons and the level of synapticassociated proteins(PSD95,synapsin1,synaptophysin).Results: Open field test and high plus maze displayed a PTSD like anxiety in SPS rats.The ELISA result showed a higher CORT in hippocampus compared with control.WB showed that tau was hyperphosphorylated at Ser202/Thr205(AT8)and Ser404 in hippocampus of SPS rats,but no change of tau phosphorylation at Ser199 and Ser396.And the level of A?1-40 and A?1-42 were no significant difference among each group at this stage.WB showed that the level of PP2 Ac and PP2Ac-Y307 was similar with control group,indicating that the activity of PP2 A was no change and PP2 A does not participate in tau hyperphosphorylation in PTSD.Compared with control,the phosphorylation of GSK-3? at Ser9(inactive form)was markedly decreased,while the phosphorylation of GSK-3? at Tyr216(active form)was markedly increased,supporting that PTSD induces GSK-3? activation.However,the level of SGK1 protein and m RNA,which is the upstream kinase of GSK3?,was notably decreased compared to control.The level of p-AKT were decreased in SPS rats.Interestingly,the level of p-ERK1/2(a tau related kinase)was decreased in hippocampus of SPS rats,while the level of Ca MKII was no change.Nissl staining showed that the number of nerve cell was no change,and WB results showed that PSD95,synapsin1 and synaptophysin in SPS rats didn't have difference with control.In cortex,all above indicators had no change.Conclusion: SPS-induced PTSD upregulates AKT/GSK3? pathway,which leads to tau hyperphosphorylation at Ser202/Thr205(AT8)and Ser404.Meanwhile,down-regulation of SGK1/ERK1/2 pathway in SPS rats counteracted tau hyperphosphorylation at Ser199 and Ser396.Tau hyperphosphorylation in SPS-induced PTSD is regulated by AKT/GSK3? and SGK1/ERK1/2 pathway.