The Role Of Abnormal Phosphorylated Tau Protein And Neuroinflammation In The Development Of Acute Cognitive Dysfunction Induced By Laparotomy In Adult Mice

Backgrounds and Aim:Cognitive dysfunction is one kind of neurodegenerative disease,which has been proved to be related to the occurrence and persistence of neuroinflammation along with the reactive gliocyte as well as abnormal phosphorylated tau protein that results in the neurofibrillary tangles and neuron apoptosis.In addition,peripheral inflammation,such as acute pneumonia and urinary tract infection,can trigger central nervous inflammation.Postoperative delirium caused by surgical operations is one of complications that need to be paid high attention after clinical practice.Postoperative delirium is an acute and fluctuating mental state change that occurs after surgery.It is characterized by decreased levels of consciousness and attention.It is usually transient,but may recrudesce sometimes.The incidence increased with the senescence of the brain,and has positive correlations with both short-term and long-term postoperative mortality.Existing studies show that postoperative delirium would increase the length of nursing time or mortality of patients featuring acute cognitive dysfunction,but the symptoms of postoperative delirium was usually imperceptible,now there is short of effective ways on detection of delirium.From our earlier research,in a laparotomy in mice simulating clinical surgery we detected the inflammatory cytokines levels and the pathological progress as well as cognitive function until 14 days after laparotomy,when circulation and central inflammatory factor levels back to normal,but the significant activated gliocyte in the frontal cortex and hippocampus didn’t back,and memory impairment in mice either.At the same time,abnormal phosphorylated tau protein in brain tissue increased significantly,elucidated the pathology of cognitive dysfunction after laparotomy at an relative longer time point.And there is short of research about the characteristics in acute phase of postoperative dysfunction.On this basis,our work studied the cognitive function with levels of peripheral and central inflammation,pathological changes and possible molecular mechanisms beyond the cognitive dysfunction in mice at 4 and 24 hours of postoperative acute period,to provide further understanding and ideas for the prevention and improvement of acute postoperative cognitive dysfunction.Method:Wild C57BL/6J male specific pathogen free mice aged 3 months were randomly divided into three groups:Control(CON),laparotomy at 4hrs and 24hrs(LAP-4hrs,LAP-24hrs),then subjected to laparotomy under sevoflurane anaesthesia.Acute cognitive performance at two time points was evaluated by Open Field test(OFT)and Y-maze test.To evaluate the inflammatory responses induced by laparotomy,we measured m RNA levels and protein expressions of multiple pro-and anti-inflammatory cytokines in the liver and hippocampus.H&E staining were operated to check the neuron damage in brain tissue.Immunofluorescent labeling of Iba1 and GFAP antigen were manipulated on the paraffin section of the mice brain tissue to exhibit the activation of gliacyte in the hippocampi after surgery in LAP-4hrs and LAP-24hrs.Tau protein phosphorylation and related signaling pathways were comparatively determined at postoperative 24h by Western-blot analysis.To explore the relationship between behavioral performance,peripheral and central nervous inflammation,abnormal phosphorylation of tau protein as well as the possible molecular mechanism in each group of mice at 4 h and 24 h after surgery.Results1.Laparotomy induced acute cognitive impairment in adult miceAt 4 and 24 hours after exploratory laparotomy,there was no significant change in the movement ability of the mice referred to CON.At 4 hours after surgery,their grooming time became longer which concerned as the anxious behavior showed in mice.At 24 hours after surgery,the anxious behavior of the mice disappeared,but the memory decreased at both time points.2.Laparotomy induced acute inflammatory response in the peripheral and central nervous systemAt postoperative 4h,the presence of peripheral inflammation induced by laparotomy was showed by obviously increased m RNA levels of proinflammatory cytokines involving IL-1β,IL-6,IL-8,TNF-αand MCP-1 in the liver.Meanwhile,the existence of neuroinflammation was evidenced by the increase of IL-8 m RNA in the hippocampi.However,the inflammatory episode at 24h was different.In the liver,only elevation of inflammatory IL-10 level was significant,but in the hippocampus,pro-inflammatory cytokines like IL-1β,TNF-αand MCP-1 as well as anti-inflammatory cytokine IL-10 decreased at the same time.At both 4h and 24h following laparotomy,the pronounced immunofluorescence of Iba1~+microglia were observed in the entire hippocampus and its sub-regions.Furthermore,the morphology of Iba1~+microglia was increased in the laparotomy groups when compared with the predominately resting microglia seen in the CON group.In addition,notable GFAP~+astrocytes were also detected in the postsurgical hippocampus at both 4h and 24h,whilst the morphology of GFAP~+astrocytes in the surgical mice increased obviously as well.3.Pathological characteristics induced by laparotomyAt 4h and 24h after laparotomy,the neurocellular structure deformity with shrunken cell body and pyknotic nucleus was observed in the hippocampus,especially in CA1 and DG areas.And in the CON,most neurons in the hippocampal sub-regions showed the clear cellular structure with round and pale-stained nuclei.4.Abnormal phosphorylation of tau protein induced by laparotomyAt postoperative 24h,tau phosphorylation at six sites(S396,S404,T205,S199,AT8and AT180)showed a consistent decrease in the hippocampus without affecting total tau protein expression.At 24h following laparotomy,there was massive decrease of p-GSK-3β,On the other hand,laparotomy enhanced the expression of PP2A-C.5.Laparotomy induced changes of related signaling pathways involving Akt,MAPK and JAK2/STAT3In this study,laparotomy induced the down-regulation of major stress kinases such as p-JAK2/p-STAT3,p-ERK,p-JNK and p-Akt at 24h after laparotomy.Conclusions1.The early cognitive impairment after laparotomy may be related to the continuous activation of glial cells and the low phosphorylated tau protein in the brain of mice.2.The low level of tau protein phosphorylation in the process of neuroinflammation may be related to the up-regulation of phosphorylase PP2A-C.3.At 24 hours after laparotomy,abnormal phosphorylation of tau protein may be related to the down-regulation of p-ERK,p-JNK and p-JAK2/p-STAT3.