The Effects Of Tau Hyperphosphorylation On Olfactory Bulb In Alzheimer's Desease Model Mice

BackgroundAlzheimer's disease(AD)is the progressive,irreversible neurodegenerative disease,whose etiology is not yet clear.Olfactory dysfunction is the early clinical manifestation of AD,followed by a series of pathological changes in the central nervous system.With the increasing aging of global population,the incidence of AD is increasing year by year.This will definitely bring great pressure to the society and seriously affect the quality of life of human beings.AD has become one of the most difficult diseases to be solved.Currently,the clinical drugs treatment focused on amyloid deposition is only temporary and effective,and does not delay the progression of the disease.Therefore,the exploration of olfactory dysfunction in the early stage of AD has become an important direction and breakthrough.A number of studies found that hyperphosphorylated Tau(p-tau)is present in brain tissue in many neurodegenerative diseases,while a series of neurodegeneration still occurred in the absence of amyloid pathology.Therefore,hyperphosphorylated Tau protein plays a key role in the course of AD.In the past 40 years,the mechanism of overphosphorylated Tau protein in learning and memory impairment of AD has made more progresses,but there are few studies related to overphosphorylation of Tau in the olfactory bulb of AD.Therefore,this study focused on the functional changes of Tau hyperphosphorylation to olfactory bulb system in Alzheimer's disease model mice.Olfactory system is an important component of sensory nervous system,and in olfactory system,olfactory bulb is the second station that olfactory information transmits to senior central,playing an extremely important role in the coding olfactory signal transmission.However,in the P301S model mice with the gene mutation of Tau overexpression,the overphosphorylated Tau protein mainly induced early olfactory dysfunction by affecting which kinds of neurons?And how overphosphorylated Tau protein is involved in olfactory signaling and encoding olfactory information?Answering the above questions is crucial to further elucidating the mechanism of hyperphosphorylation of Tau in early olfactory dysfunction.This topic will be discussed.Objectives1.Observe the expression and distribution of phosphorylated Tau in the olfactory bulb of AD patients and normal ageings.2.Observe the time of olfactory dysfunction and cognitive impairment in P301S transgenic mice.3.Observe the expression and distribution characteristics of phosphorylated Tau protein in the olfactory bulb.4.Observe the changes of morphological and functional changes of olfactory bulb mitrial cells effected by phosphorylated Tau.5.Observe the structional and functional changes of dendro-dentric synaptics in the EPL of olfactory bulb.Methods1.Using paraffin immunohistochemistry to observe the expression and distribution of phosphorylated Tau in olfactory bulb of AD patients.2.Olfactory and cognitive behavior in P301S transgenic mice was determined by buried food test,Y maze and passive avoidance test.3.Western Blot was used to detect the Tau-5 and P-Tau protein expression of mouse olfactory bulb.4.Immunofluorescence staining was used to observe the expression and distribution of phosphorylated Tau in the olfactory bulb.5.The number and morphology of mitral cells in the olfactory bulb of P301S transgenic mice were observed by Nissl staining.6.Using the microelectrode array(MEA)recording system of isolated brain slices,the discharge frequency of the mitral layer in the olfactory bulb of P301S transgenic mice was recorded.7.Western Blot method was used to detect the expression of synaptic-related proteins in the olfactory bulb of P301S transgenic mice.8.Using Golgi staining technique to observe the dendritic spines of granule cells in P301S transgenic mice.9.Transmission electron microscopy was used to observe the dendro-dendric synaptic structure between granule cells and mitral cells in the olfactory bulb of P301S mice.10.Using the microelectrode array(MEA)recording system of isolated brain slices,record the change of Gamma oscillation and low Gamma in the EPL of the olfactory bulb of P301S transgenic mice.Results1.Compared with the normal group,the phosphorylation of Tau in the olfactory bulb of AD patients was largely expressed in each layer,and mainly located in the MCL and the EPL.2.Olfactory dysfunction occurred from 2 months old,but spatial working memory disorder began to appear at 5 months old.3.The protein expression levels of Tau-5 and phosphorylated Tau in the olfactory bulb of P301S transgenic mice were significantly increased.4.Phosphorylated tau expression was observed in all lamellar structures in the olfactory bulb of P301S mice,but MCs in the OB of P301S mice were the susceptible neurons to P-tau.5.The dorsal and ventral mitral cells of the olfactory bulb of P301S mice showed a significant decrease in the number from 5 months old.6.The firing frequencies of mitral cells were significantly decreased at 2 M and 9 M P301S mice.7.At 2 months of age,no significant differences were observed,but within both the 5 M and 9 M P301S mice were significantly decreased,compared with aged-matched WT mice.8.At 5 months of age,excitatory synaptic and inhibitory structures in the olfactory bulb of P301S mice were altered.9.At 2 M.Gamma and low Gamma showed no significantly difference between P301S mice and WT mice,but at 9 M,both Gamma and low Gamma were significantly increased.Conclusions1.The expression of phosphorylated Tau in the olfactory bulbs of AD patients is mainly distributed in the EPL and the MCL.2.the olfaction dysfunction of P301S mice occurred earlier than cognitive impairment,indicating that P301S mice well mimicked the AD-like pathological features.3.Given the expression of P-tau in MC,the functional changes of MC and the changes in olfactory behavior occurred simultaneously in 2 M,we speculated that the olfaction behavioral dysfunction in P301S mice may be related to the accumulation of P-tau in MCs.4.In the olfactory bulb of P301S transgenic mice,p-tau could affect the dendro-dendric synapse structure and lead to abnormal enhancement of Gamma oscillations in EPL of olfactory bulb.5.Early MC firing frequency reduction is not the results of MCs loss and GCs suppression.