Effects Of β-amyloid Protein 1-40 And Apolipoprotein E4 On The Learning-memory Ability, Hippocampus Neuron Ultrastructures And The Phosphorylation Of Tau In Rats

Objectives:①To build up an animal model suitable for AD by co-injection ofβ-amyloid protein 1-40(Aβ_1-40)and apolipoprotein E4(apoE4)into hippocampus of D-gal induced aging rats.②To investigate the synergistic action between apoE4 and Aβ_1-40in the pathogenesis of AD.Methods:1.Animal selecting and grouping:A total of 32 healthy and smart adult male Wistar rats aged 4 months were selected and randomly divided into 4 groups(n=8):control group,Aβgroup,apoE4 group and Aβ+apoE4 group.2.Intevention method:Each animal was injected intraperitoneally with D-gal(50mg/kg/d)for 6 weeks.At the 7th week,for the Aβ+apoE4 group, 2μl mixed liquor of A[3 and apoE4 was injected into the hippocampus CA1 regions bilaterally under the control of a stereotaxic apparatus.For the control group,Aβgroup and apoE4 group,same quantity of normal saline,Aβ_1-40and apoE4 was injected into same regions respectively.3.Indexes observed:Two weeks later,the escape latency and the times of passing platform,representing learning and memory ability was measured by Morris water maze test; the CA1 hippocampus neuron morophology and ultrastructure were observed using optical microscope and electron microscope;the phosphorylation of Tau was detected by immunohisochemistry staining.4.Statistic processing:Measurement data was expressed in mean±SEM((?)+S),and 2×2 factorial design ANOVA was employed through Statistical Package for Social Sciences 13.0 and Statistical Analysis System 8.0. Results:1.The effects of Aβ_1-40and apoE4 on the learning-memory ability in rats:Through 5 days of trainging all animals appeared learning-memory ability with the escape latency shortened gradually,but ingection of Aβ_1-40and apoE4 all induced learning-memory damage,because the the escape latency at fifth day were significantly prolonged(P＜0.01)and the times of passing platform were obviously decreased(P＜0.01),both in Aβand apoE4 group than in control group,furthermore,Aβmore than apoE4(P＜0.01).An interaction between Aβand apoE4 also was observed,with the escape latency further prolonged and the times of passing platform further decreased(P＜0.01).2.The effects of Aβ_1-40and apoE4 on the CA1 hippocampus neuron's morophology and ultrastructure in rats:Under the optical microscope,for the control group,the neurons of hippocampus CA1 region disposed regularly,the nuclear were big and nucleolus were clear in control group.For the Aβgroup,neurons disposed irregularly,cell boundary was not very clear and the cell belt was incomplete,some of cell bodies were reduced and karyopyknosis appeared. For the apoE4 group,the neuron arrangement was not very close and some of nuclei shrinked slightly.For the Aβ+apoE4 group,the neurons disposed disorderly and were lost seriously,the cell belt was not clear and the karyopyknosis was obvious.Under the electronmicroscope,for the control group,the chondriosomes's apparence was regular.For the Aβgroup,the chondriosomes swelled and vacuolized,rough endoplasmic reticulum expanded and ribosome shed.For the apoE4 group,chondriosomes were gently damaged,rough endoplasmic reticulum and free ribosome disposed irregularly.For the Aβ+apoE4 group,the karyopyknosis was severe, the perinuclear cisterna expanded,even the karyotheca structure was unclear,the nuclear shape was extremely irregular and the nucleolus was dissymmetry,chondriosomes apparently swelled, crista was broken and became empty bubble,the chromatin condensed and gathered to side,the nuclear matrix and basic cytoplasm were compacted and many lipofuscin deposited in the hippocampus neurons.3.The effects of Aβ_1-40and apoE4 on the phosphorylated of tau in rats:Injection of Aβ_1-40and apoE4 all induced enhancement of phosphorylation of tan,with the gray values significantly decreased(P＜0.01)both in Aβand apoE4 group than in control group,furthermore,Aβmore than apoE4(P＜0.01).An interaction between Aβand apoE4 also was observed,with the gray values further decreased(P＜0.01).Conclusions:1.A new AD model builded up by co-injection of Aβ_1-40and apoE4 into the hippocampus of D-galactose induced aging rat perfectly reproduced the charictristics of AD in behaviorial, morphological and molecular pathologic aspects,accordingly is a model more suitable and representative for AD.2.ApoE4 exerts a synergistic action in the pathogenesis of AD together with Aβ.