The Neuroprotective Effect Of Quercetin On Beta-Amyloid-induced PC12 Cells Injury And Potential Related Mechanism

Alzheimer’s disease（AD）is a common neurodegenerative diseases,which symptoms are mainly progressive cognitive dysfunction and memory deterioration,occurring in the early stage of the elderly and old age.The two significant pathological characteristics of AD is senile plaqueand neurofibrillary tangle in extracellular.So far,the cause of AD is very complex and unclear,owing to the lack of clinical drugs which canreduce the neuron death and delay disease progression.Numerous clinical and epidemiological studies show that women are more likely to develop AD than men.This gender difference in the incidence of ADindicates the lack of estrogen is a risk factor of AD.Recent research has proposed estrogen can be used for the prevention or treatment of AD by reducing the accumulation of amyloid beta protein and increasing neuronal survival.But long term use of estrogen will has side effects,so its clinical trialsislimited to some extent.The researches have shown that the phytoestrogen,which is similar to the chemical structure of estrogen,not only has estrogen-like neuroprotective effects,but also can avoid side effects.Therefore,phytoestrogen is expected to replace estrogen for the prevention and treatment of AD.As a natural flavonoid compounds,quercetin is a kind of phytoestrogenwhich is very similar to estrogenofchemical structure.This small molecule drugcan be extracted from a variety of natural plant or food without obvious toxicity and adverse reactions.Previous studies found that quercetin could promote the proliferation of MCF-7 cells by estrogen receptor alpha,which is showed the estrogen-like effect.And it could play a protective effect on neurons in the hippocampus and cerebral cortex in several ways,including increasing the number of synapses and length,promoting synaptic growth and happen,in order to improve nerve cells growth and survival rate.This study was detected to explore the estrogen-like neuroprotective effects and the related mechanism of quercetin by using PC12 cells induced with Aβ_25-35,provided thought and strategy for the drug therapy of AD.Cells were cultured with Aβ_25-35 for 24hours,17β-estradiol（0.1μmol·L-1）,genistein（50μmol·L-1）and three different concentrations of quercetin（200μmol·L-1,300μmol·L-1,400μmol·L-1）were respectively added after 24 hours.The effects of quercetin on activity of AD model were tested by MTT.Immunohistochemical stain and Western blot were used to detect the expression of estrogen receptors alpha and beta,p-ERK1/2 and apoptosis related proteins.The mechanism of quercetin estrogen-like neuroprotective effects was detected using estrogen receptor antagonist ICI182,780 and MAPKK inhibitor U0126.The results revealed thatthe toxic effects showed in a dose-dependent increase of Aβ_25-35 on PC12 cells.Comparing with the control group,cells injury was observed after cultured with 10μmol·L-1Aβ_25-35for24h（P<0.01）.The MTT results showed that17β-estradiol,genisteinand three different concentrations of quercetin could significantly enhance the cell survival rate compared with the model group（P<0.05）.Compared with model group,Immunofluorescence and Western blot results show that quercetin could improve the estrogen receptor alpha and p-ERK1/2 protein expression（p<0.05）,and the expression of estrogen receptor beta protein is increased without significant difference（p>0.05）.And in the Western blot experiments,the ratio of Bcl-2 and Bax was increased and the expression of Caspase-3 was decreased（P<0.05）.When estrogen receptor inhibition ICI182,780 were reduced,the expression of p-ERK1/2 was decreased（p<0.05）and the ratio of Bcl-2 and Bax was decreased,Caspase-3 protein expression was increased（p<0.05）.In addition,pretreatment of cells with U0126 would reduce Bcl-2/Bax ratio and increase Caspase-3 protein expression increased（p<0.05）.All the results indicate that quercetin protected PC12 cells,which suffered from Aβ_25-35 induced cytotoxicity and exert neuroprotective effects.The estrogen-like neuroprotective effect can reduce the apoptosis in the classic estrogen receptor pathway and MAPK pathway.And quercetin can also active MAPK signaling pathways by the mediation of estrogen receptor alpha.