The Effect Of Stilbene Glycoside On The Endoplamic Reticulum Stress And The Mechanism In AD Model

Background:Much attention has been focused on the role ofβ-amyloid pepetide(Aβ),the major component of senile plaques,which is a prominenthistopathological feature of AD.β-amyloid pepetide's neuro-toxicity is the key risk factor of the development and formation of AD,which is related to the development of the Aβpeptide.aggregation. Aβis a peptide formed by 39-43 amino acids and derived from the amyloid precurs protein(APP).The secondary structure of Aβis theα-Helix,aggregation is weak.And protease can hydrolize it.Various kinds of factor cause space conformation misfolded,transform the secondary structure of Aβtoβ-sheet,the protein will be aggregated and accumulation of misfolded or aggregation prone proteins may damage the cell.So,in the molecular level,the nature of AD is a protein conformational disease,which is involved in protein misfolding and aggregation and cellular toxicity.The Amyloid cytotoxicity can damage cytomembrane.When massive Ca²⁺influx into cells,overloaded-calcicum is a toxic environmental contaminant,exerts adverse effects on different cellular pathways such as cell proliferation,DNA damage,and apoptosis.In particular,the modulation of Ca²⁺homeostasis seems to be an important role.Aβinduced Ca²⁺release from the ER is mediated by ryanodine receptors(RyR),The ER is an essential intracellular organelle involved in calcium homeostasis,and in the folding and processing of proteins.In response to several stimuli that perturb the normal ER function,protein misfolding occurs and unfolded proteins accumulate in the ER.activating the unfolded protein response(UPR).UPR can up-regulate some ER chaperones(Grp78).These proteins counteract the accumulation of misfolded proteins during unbalance on condition of cailcium overload and ER stress,thus trying to promote cell survival.Under conditions of severe or prolonged ER stress,UPR can trigger the expression of caspase-12,which is an endoplasmic reticulum-specific protein which could induce apoptotic cell death.Objective.In this present work we have extended our previous observations.to study the effects of Stilbene glucoside(TSG),the main component of Polygonum multiflorum-Tetrahydroxy,on model rats of AD,and investigate the molecular mechanisms of AD related to unfolded protein response,GRP78 and apoptosis pathway.Methods:Rats were randomly divied into three group:control group AD model group(Aβ1-42 injection into the rat of hippocampus),TSG group (treated with TSG group.following Aβ1-42 injection into the rat of hippocampus)to observe the effect of TSG on the learning and memory by Y-electric-maze and changes of ultramicro-structure observed by electron microscope.Relative concentration of intracellular calcium were monitored by means of immunofluorescence under laser scanning confocal microscope;mRNA expression of RyR3 utilized reverse transcriptase PCR(RT-PCR);The expression of GRP78 and Caspase-12 expression were detected by RT-PCR and Western blot. ERAB location of hippocampal structure were detected in rat brain by immunohistochemistry measure.The in situ end-labeled DNA(Tunel)was used to analyze neurocyte apoptosis.Result:Compared with the control group,the times of successful. avoidance of electric-stimulus significantly decreased in model rats(P＜0.05);Electron microscope results showed that the neurons in the hippocampus of rats injected with Aβ1-42 showed such ultrastructural pathological changes as cellular edema,endoplasmic reticulum dilatationand chromatin agglomeration;Calcium overload were confirmed by means of immunofluorescence under laser scanning confocal microscope;the expressions of ERAB,GRP78 and Caspase-12 were increased;the rate of neurons apoptosis rised.(P＜0.05).Compared with the model group there were significant differences in TSG group:result showed that TSG can improve the learning and memory capacity,the pathological changes were alleviated and the decrease of intracellular calcium was found(P＜0.05).The expression of RyR3 had no significant difference(P＞0.05)the expressions of ERAB,GRP78 and Caspase-12 were down regulated and the rate of hippocampal neurons apoptosis was reduced(P＜0.05).Conclusion:1.β-Amyloid neurotoxicity cause the disorder of intracellular calcium ho meostasis.it's not be the pathway of CICR induced by RyR3,but the changes of the permeability of the cytomembrane.2.The accumulation of theβ-Amyloid misfolded resulted in the increase of the expression of GRP78 in response to endoplasmic reticulum stress,which can protect neuron from the danmage.In the reaction to over-stress,An endoplasmic reticulum-specific stress.activated caspase-12 is implicated in the mechanism of AD.3.TSG can improve the learning and memory capacity of model rats. This is made by lowering the relative concentration of calcium and the extend of endoplamic reticulum stress,and depressing the apoptotic pathways related endoplasmic reticulum,which play a role of the protection from amyloid neurotoxicity on nerves cells.