Experimental Study Of Brain White Matter Morphological Change And MBP, MCT1-RNA Abnormal Expression In APP/PS1 Transgenic Mice

Objective:Alzheimer's disease(AD)is characterized by a progressive decline in cognitive function,usually starting with memory complaints.According to World Health Organization and Alzheimer's Disease Association,the incidence of AD rises year by year,and China has become the top country owning the largest number of AD patients.The definitive diagnosis of AD comes from postmortem analysis of the neuropathological changes in the brain.Analyses of both clinical and pathological features have provided important insights into how the pathology correlates with cognitive status.Application of animal models,especially mouse models,have been extremely useful to test mechanistic hypotheses about AD pathophysiology and to predict outcomes from pharmacological interventions.The APP/PS1 mouse model,created on C57BL/6J mouse,overexpressing APPswe(APPswe,K670N/M671L)and lacking Presenilin 1(Presenilin 1,PS1)have been well characterized.Yet,the pathophysiology of AD is still elusive.To date,amyloid ?(A?)plaques and neurofibrillary tangles(NFT)in the brain have been characterized as the most popular pathology of AD.Researches on A ? plaques and NFT have formed amyloid hypothesis.However,clinical trials of high-profile AD antibodies against the aggregation-prone peptide A?,failed to improve clinical outcomes in patients with late onset AD,or the abnormality of A? plaques,NFT or tau phosphorylation in the brain.On the other hand,recent imaging studies confirm previous observations of A? accumulation in a significant proportion of non-demented individuals.Conversely,a sizable proportion of patients clinically diagnosed with AD do not display A? accumulation-even though neurodegeneration is in progress,which means A ?accumulation might occure merely at certain time during the disease.Postmortem and imaging study revealed widespread demyelination in the brain of AD patients.White matter degeneration is an early neuropathological event preceding the presence of over amyloid deposition and tangle formation.Myelin is formed by oligodendrocyte which also maintain long term axonal integrity.Latest research showed that,monocarboxylate transporter 1(MCT1)is highly enriched within oligodendroglia and that disruption of this transporter produces axon damage and neuron loss in animal and cell culture models.During myelin formation,oligodendrocyte express several antigenicity,such as the chondroitin sulfate proteoglycan NG2.Where there is neurodegeneration and myelination is needed,NG2+ cells exhibit enhanced proliferation and accelerated differentiation into oligodendrocytes.Therefore,in this experiment,3 and 6-month APP/PS1 transgenic mice were used as mice model of AD disease,to study the process of demyelination and oligodendrocyte abnormality in the pathogenesis of AD.Methods:1.3-month and 6-month APP/PS1 transgenic mice and C57BL/6J mice were purchased from the animal center of CMU.Morris water maze was used to test the spatial learning and memory of 3-month and 6-month of both APP/PS1 transgenic mice and C57BL/6J mice,in order to test the feasibility of using this mouse model to imitating AD in the following experiment.2.Following Morris water maze,Luxol Fast Blue staining was performed on brain sections of 3-month and 6-month of both APP/PS1 transgenic mice and C57BL/6J mice.Width and the ROD of corpus collosum were measured to study white mater change.In order to further evaluate demyelination,Real-time RT-PCR was performed to test MBP RNA expression in mouse fronto-temporal cortex and immunohistochemistry was used to observe d MBP-positive cells.3.In order to study the involvement of oligodendrycyte in the pathology of AD,immunohistochemistry of NG2 was performed on brain sections and Real-time RT-PCR of MCT1 RNA was applied on fronto-temporal cortex of both 3-month and 6-month of APP/PS1 transgenic mice and C57BL/6J mice.Results:1.The escape latency of APP/PS1 transgenic mice shortened during the learing phase of Morris water maze.2.The time that mice crossing hidden platform and the ratio that the mice swimming in the hidden platform quadrant declined in the memory phase of Morris water maze in 6-month APP/PS1 transgenic mice,while no obvious differences were found 3-month APP/PS1 transgenic mice.3.Luxol Fast Blue staining showed that width and the ROD of corpus collosum declined obviously in 6-month APP/PS1 transgenic mice,while no obvious differences were found in 3-month APP/PS1 transgenic mice.4.Real-time RT-PCR revealed decline in MBP RNA expression at fronto-temporal cortex of both 3-month and 6-month APP/PS1 transgenic mice.5.Immunohistochemistry revealed overexpressing of dMBP+ and NG2+ cells at fronto-temporal cortex of 6-month APP/PS1 transgenic mice,while no differences were found in 3-month APP/PS1 transgenic mice.6.Real-time RT-PCR revealed decline in MCT1 RNA expression at fronto-temporal cortex of 6-month APP/PS1 transgenic mice,while no differences were found in 3-month APP/PS1 transgenic mice.Conclusions: 1.In Morris water maze test,APP/PS1 transgenic mice exibit obvious memory impairment at the age of 6 months,but not at the age of 3 months.2.The shrinkage of corpus callosum,downregulation of MBP mRNA and upregulation of dMBP were observed in APP/PS1 transgenic mice of 3-months,which became more obviously at the age of 6-months.3.NG2 cell reactively overexpressed,and MCT1-RNA down regulated were found in APP/PS1 transgenic mice of 6-months,while no abnormality were found in APP/PS1 transgenic mice of 3-months.