Effects Of Aβ And ApoE4 On Hippocampal CA1 Synaptophysin And ChAT In Rat

Alzheimer's disease(AD),as the most frequent dementia type,is a central nervous system degenerative disease characterized by chronic progressing inreversible failure of memory, cognitive handicap and personality change,of which the incidence is climbing with the world population ageing.Heavily influencing patient's physical and mental health as well as quality of life,Alzheimer's disease has become a tough problem that is drawing more and more attention.The distinctive hallmarks of AD are extracellular senile plaque(SP)and intracellular neurofibrillary tangles(NFTs).The core of SP mainly comprise of fibriform aggregated beta-amyloid protein.Emerging evidence showed that apolipoprotein E4(ApoE4)plays an important role in the pathogenesis of AD.ApoE is produced mainly in liver,and secondly in brain(astrocyte and microglia).ApoE in the brain is considered of having the abilities to repair neurons,develop dendrite,and maintain synaptic plasticity.APOE gene has polymorphism,the three common alleles areε2,ε3 andε4.Genotypeε4 is a main risk factor for familial late onset AD and sporadic AD.The protein apoE4 corresponding toε4 has avid affinity with Aβ,and the binding ofapoE4 to Aβmay promote the occurrence of AD.The study at cellular level by Guo indicated that apoE4 exerted synergistic action in the neurotoxicity of beta-amyloid,the same conclution was drawed from transgenic animal. Coinjection of Aβand apoE4 to hippocampus in vivo to identify their relationship has never been reported.Synaptic loss,one of the significant histomorphologic changes of AD,parallels to dementia severity of AD patients,and is known as the base of cognition descending.Synaptophysin (SYN),as a specifc marker of presynaptic terminal,can be used to detect density and distribution of Synapse.Cholinergic system damage is related to AD.Choline acetyl transferase(CHAT),a rate-limiting enzyme of acetylcholine(Ach)synthesis in central nervous system,is the specific marker of cholinergic neuron.Among animal models of AD,injection of Aβinto hippocampus has been used to mimic some pathological features.Here,we coinject Aβand ApoE4 into rat hippocampus for the first time to reproduce multiple pathological features of AD and investigate the synergistic effect of Aβand ApoE4 through detecting the changes of synaptophysin and CHAT in hippocampus. PartⅠEffects of Aβand apoE4 on hippocampal CA1 synaptophysin in rat Objective:To investigate the effects of Aβand apoE4 on synaptophysin in hippocarnpus and clarify if Aβand apoE4 have synergistic effect.Methods:Healthy male wistar rats were used in this experiment,and divided into four groups: control group,Aβgroup,apoE4 group and Aβ+apoE4 group.After 6 weeks of D-galactose (50mg/kg/d)intraperitoneal injection,rats in different group received bilateral hippocampus CA1 regions injection of normal saline,Aβ_1-40,apoE4 and Aβ+apoE4 respectively under the control of a brain stereotaxic apparatus.Two weeks later,the hippocampuses were fixed, paraffin imbedded,cut coronally in slices,and the expression of synaptophysin in hippocampus CA1 regions was detected by immunohistochemistry method.Results:The synaptophysin immunoreaction positive product of CA1 in control group rats, being granule or punctiform,appeared lamellar distribution mainly in the neuropil.The neuron cytoplasm was slightly dyed,the gliocyte,blood vessel and white matter were absolutely undyed.Optical density values of synaptophysin were significantly lower in the Aβgroup and apoE4 group than in the contral group(P＜0.01),Aβgroup more lower than apoE4 group(P＜0.05).Aβand apoE4 had interaction in lowering optical density value of synaptophysin(P＜0.05).Conclusions:1.Aβand apoE4 all induced injury to hippocampal synapse formation,Aβmore serious than apoE4;2.Aβand apoE4 had synergistic effect in this injury course.PartⅡEffects of Aβand apoE4 on hippocampal CA1 ChATmRNA in ratObjective:To investigate the effects of Aβand apoE4 on ChATmRNA in hippocampus and clarify if Aβand apoE4 have synergistic effect.Methods:Methods:Animal selecting,grouping and interventing methods are same as part one. The ChAT mRNA level in hippocampus CA1 regions was detected by hybridization method.Results:There were many Cha T hybridization in situ dyeing positive neurons in control group rat CA1,which appeared brown colour,spherical or oval shape,clear layer,compact arrangement, relatively big cell body,with projection in some neurons.ChATmRNA PU values were significantly lower in the Aβgroup and apoE4 group than in the contral group(P＜0.01),Aβgroup more lower than apoE4 group(P＜0.05).Aβand apoE4 had interaction in lowering ChATmRNA level(P＜0.05).Conclusions:1.Aβand apoE4 all induced injury to hippocampal cholinergic system,Aβmore serious than apoE4;2.Aβand apoE4 had synergistic effect in this injury course.