| Objective:Alzheimer's disease(AD)is an aging-related neuropathy,which is a common cause of dementia.The etiology of AD is complex and diverse,and the abnormal accumulation of ?-amyloid protein(A?)in the brain is considered to be an important factor in the development of AD.The deposition of A? can induce neuroinflammation,however,some studies have shown that neuroinflammation can aggravate A? deposition.Anti-inflammatory treatment can reduce the accumulation of A? in the brain and decrease the risk of AD.Therefore,reducing the inflammatory response and the accumulation of A? in the brain may become an effective way to prevent and treat AD.Activation of astrocytes and microglia play a supporting role under normal conditions,and damage to astrocytes and microglia can be caused by damage to the central nervous system.Activated astrocytes become reactive astrocytes and mainly secrets interleukin-1?(IL-1?),tumor necrosis factor(TNF-?).There are two subtypes of activated microglia: one is the classical activation type(M1 type),and the other is the selective activation type(M2 type).M1 cells secrete IL-1?,TNF-? and other pro-inflammatory cytokines.M2 The type of cells secrete anti-inflammatory cytokines such as interleukin-4 and interleukin-10.This study found that the number of reactive astrocytes and activated microglia in AD brain increased significantly,and microglia could change from M2 to M1 with the aggravation of AD.In the pathogenesis of AD model mice,IL-1? expression in the brain continues to increase,while TNF-? expression decreases first and then increases.Therefore,reducing M1-type activation in reactive astrocytes and microglia may reduce the inflammatory response in AD brain.Toll-like receptor-2(TLR2)is one of the congenital receptors on the surface of astrocytes and microglia,the deficiency of TLR2 can significantly reduce A?-triggered astrocytes and Microglia M1 type activation.Nuclear factor ?B(NF-?B)is a transcription factor downstream of TLR2.It is normally present in non-activated form in glial cells;when glial cells are activated,it can be involved in the regulation of proinflammatory cytokine expression.NF-?Bp65,a subtype of the NF-?B protein family,is recognized as a key factor in the regulation of inflammatory responses.It is suggested that down-regulation of TLR2 can inhibit the activation of NF-?Bp65 and reduce the expression of pro-inflammatory factors,thereby reducing the neuroinflammatory response.Prebiotics are oligosaccharides,polysaccharides,and polyhydric alcohols that are difficult to be digested,mainly include galactooligosaccharide(GOS),milk sucrose,etc,which can exert anti-inflammatory effects through various ways such as anti-inflammatory and anti-oxidation.GOS is a functional oligosaccharide with natural properties,which has anti-neuroinflammatory and anxiolytic effects.It has been reported in the literature that lactose can reduce the expression of TLR2 in the colon of mice.However,whether GOS can down-regulate the expression of TLR2 in AD brain has not been reported.In this study,We used the transgenic mice with APPswe/PS1dE9 double transgenic mice as AD models to explore whether GOS decreases activation of reactive astrocytes and M1 type microglia,reduces NF-?Bp65 and IL-1?,alleviates A? deposition,improves cognitive function by down-regulating the expression of TLR2,and then plays a significant role in antagonising AD.Methods:Five-month-old APPswe/PS1dE9 double transgenic mice were selected and divided into AD model group(AD)and AD intervention group(AD+GOS).Besides,C57/BL6 mice were assignedto wild intervention group(WT+GOS)and wild controls group(WT).The wild intervention group and the AD intervention group were fed a diet containing 5% GOS;the WT and the AD model group received a normal pellet feed.The treatment was continued for 6 months,and the Morris water maze test was used for neurobehavioral examination at the end of the experiment.The deposition of A? in the brain tissue was detected by thioflavin T staining.Reactive astrocytesand M1 type microglia markers GFAP,CD86,and TLR2,IL-1? tested by using quantitative real-timepolymerase chain reaction.The expression levels of GFAP,CD86,TLR2,NF-?Bp65 and IL-1? protein in cerebral cortex were detected by Western Blotting.Statistical analysis of experimental data was performed using SPSS 20.0.Results:1.The escape latency was shortened accompany toincrease the number of training days.Compared with the wild control mice,there were prolonging of the escape latency in the AD model group,and the difference was statistically significant on the third and fourth days(P<0.05,P<0.01),moreover,there were significantly decreasing in the staying time and the times of cross platform(P<0.05);compared to the group of AD model,the avoidance latency of the AD intervention group showed a shortening trend,and the difference between the third and fourth days was statistically significant(P<0.05),the staying time as well as the times of cross platform were augmented(P<0.05).2.Compared withWT,the numbers of A? plaques were raised in brain tissue of AD model group and GOS compared group(P<0.01,P<0.05).Besides,there were significant decrease of the numbers of A? plaques in feeding GOS compared to AD model group(P<0.01).3.Compared with the wild control mice,the relative expression levels of GFAP,CD86,IL-1? mRNA and protein in the cerebral cortex of the AD model group were significantly increased(P<0.01),and the expression levels of GFAP and CD86 mRNA and protein were significantly increased(P<0.05)of the AD intervention group;Compared with the AD model group,the GFAP,CD86,IL-1? mRNA and protein in the cerebral cortex of the AD intervention group were decreased(P<0.01,P<0.05).4.Compared with wild control mice,the relative expression levels of TLR2 mRNA and protein and NF-?Bp65 protein in the brain of AD model group were remarkably increased;compared with AD model group mice,the relative expression levels of TLR2 mRNA and protein and NF-?Bp65 protein in the cerebral cortex of the AD intervention group were significantly decreased(P<0.01,P<0.05).Conclusion:GOS can reduce reactive astrocytes and M1 type microglia,decrease the expression of NF-?Bp65 and IL-1?,alleviate A? deposition,by down-regulating the expression of TLR2.Moreover,it can improve cognitive impairment in the double transgenic mice of APPswe/PS1dE9. |
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