Effects And Potential Mechanisms Of Tau Protein In Hippocampus In The Development Of Cognitive Impairment After Traumatic Brain Injury

Background Traumatic brain injury often occurs in traffic accidents,sports,fights,accidents and other events.It has been reported that traumatic brain injury ranks first in all types of trauma in the world.Although the survival rate of patients with traumatic brain injury has been significantly improved with the improvement of medical conditions,many patients often have different degrees of irreversible physical and/or mental symptoms due to the degree of injury,even leading to long-term Alzheimer’s disease-like lesion such as learning and memory damage.This has become a public problem that plagues families and society.Tau protein is a microtubule-associated protein mainly expressed in neurons of the central nervous system.It has the function of maintaining neuronal integrity and axonal transportation.Hyperphosphorylation or other modification of tau plays a crucial role in AD disease.With the deep research on tau protein in recent years,it has been found that there is an AD-like pathological basis in brain injury.Studies showed that some genes and their products in hippocampus have changed after traumatic brain injury,and several micro RNAs which regulate tau protein have been found.Therefore,to explore the changes of tau protein in brain injury,and to detect the expression of upstream proteins or regulatory genes,will be significant for establishing the mechanism of cognitive dysfunction after traumatic brain injury as well as for prevention and treatment of it.Objective1.To establish a rat model of severe traumatic brain injury and then observe the cognitive impairment of rats,the histomorphological changes of hippocampal neurons and detect the expression of tau protein in rat hippocampus after brain injury.2.To investigate the effects of drug intervention on the expression of tau protein and its upstream regulatory proteins and micro RNAs after brain injury.3.To construct a mechanism pathway for tau protein mediated cognitive dysfunction after traumatic brain injury.4.To explore the treatment strategy of cognitive dysfunction after traumatic brain injury.Methods 1.Determine the occurrence point of tauopathy by detecting tau protein levels in human hippocampus.2.A model of severe traumatic brain injury in SD rats was established by CCI.Rats were randomly divided into normal control group,sham operation group,TBI group of 1d,7d,14 d and 28 d,and drug intervention group.3.Each group of rats underwent objects recognition test at the corresponding time points after brain injury to evaluate the cognitive impairment status.4.H&E staining and silver staining were used to observe the morphological changes and neurofibrillary tangles in hippocampal CA1 area of each group after perfusion.5.The expression of tau protein and its upstream regulatory proteins and micro RNAs were detected by qRT-PCR and Western Blot.Results 1.The expression of phosphorylated tau protein in human hippocampus increased after 3 months of injury,and it was significantly expressed in the half year or more after injury.2.Rats in the normal control group and the sham-operated group spent more time exploring the new object than the old object.All the TBI group spent similar time exploring the two objects,which had no significant differences.DI of TBI group had significant differences compared to control group.The rats in the intervention group prolonged the exploration of new object after 7 days of drug intervention.The exploration time of new objects after 28 days of intervention was significantly longer than that of the old one.DI was not statistically different from the control group.3.H&E staining showed that the neurons in the hippocampal CA1 area of the control group and the sham group were arranged neatly and the cell morphology was regular.The morphology of neurons in the hippocampal CA1 area changed in TBI 1d and 7d group,and degeneration and necrosis appeared.The form gradually recovered.Silver staining showed that a small amount of neurofibrillary tangles appeared in the hippocampal CA1 area 1d after injury.The number of neurofibrillary tangles increased 7d after injury,and reached a peak at TBI 14 d.NFTs in intervention group decreased a lot,but still higher than the control group.4.qRT-PCR showed that the expression of mi R-132 was lower in the control group,sham group and TBI 1d group,and the expression was significantly up-regulated at TBI 7d,14 d and 28 d.The expression of mi R-132 in intervention group recovered.The expression of mi R-144 at TBI 1d,7d,14 d and 28 d was lower than it at the control and sham group.And the expression of mi R-144 in the intervention group had no statistical difference compared to TBI 28 d.5.Western blot results(1)REST expression was down-regulated at TBI 1d,and was up-regulated at TBI 7d and 14 d.It recovered at TBI 28 d.REST expression in the intervention group and the control group had no statistical difference.(2)Nrf2 protein was up-regulated at TBI 1d,7d,14 d and 28 d.The expression of Nrf2 in the intervention group recovered compared to TBI 28 d.(3)The expression of PTBP2 was down-regulated at TBI 1d,and it was slightly increased at TBI 7d,14 d and 28 d.The expression of PTBP2 in the intervention group was lower compared to TBI 28 d.(4)Total tau protein was down-regulated at TBI 1d and gradually recovered from TBI 7d.The total tau protein expression in the intervention group had no statistical difference to the control group.(5)P-tau Ser-404 was up-regulated at TBI 1d,7d,14 d and 28 d,and the expression in the intervention group was significantly lower than that at TBI 28 d.There was no significant change in AT-8(Ser 202/Thr 205)expression at TBI 1d and 7d.The expression was up-regulated at TBI 14 d and 28 d,and it in the intervention group was significantly lower than that in TBI 28 d.Conclusions 1.Severe TBI can lead to changes in the structure and function of tau.This change is a process of gradualization over a longer period of time that will affect the prognosis of patients with traumatic brain injury.2.Histomorphology shows neuronal degeneration,necrosis and neurofibrillary tangles,which constitute the morphological basis of cognitive dysfunction in rats.At the same time,the object recognition test confirm that traumatic brain injury can lead to learning,memory and other cognitive impairment in rats,especially in the middle and late stages of brain injury.3.Tau as the core of AD-like lesions have a complex regulatory network after traumatic brain injury.First,after injury,oxidative stress reaction caused ROS to increase rapidly.The oxidative stress-related protein REST positively regulates mi R-132,and mi R-132 turns from down-regulated to up-regulated with the prolongation of injury time,leading the downstream PTBP2 protein expression increased.Thus,the ratio of 4Rtau/3Rtau may change.At the same time,mi R-144 can reverse-regulate the target gene Nrf2,so that Nrf2 can initiate the Nrf2-ARE pathway in the early stage of injury and resist oxidative stress.However,as the injury prolongs,the Nrf2-ARE pathway is inhibited,resulting in the hyperphosphorylation of tau protein.The two regulatory pathways interact with each other and ultimately leading to abnormalities and functional impairment of tau protein.4.A specific form of tau inhibitor that interfere with abnormal aggregation or phosphorylation of tau protein can prevent cognitive dysfunction caused by abnormal structure and function of tau protein to a certain extent.