Effect of icariin on ubiquitination of amyloid precur-sor protein in Alzheimer's disease mice / 中国药理学与毒理学杂志

ABSTRACT

OBJECTIVE To investigate the effect of icariin(ICA)on the ubiquitination modification of β-amy-loid precursor protein(APP)in Alzheimer's disease mice.METHODS In vitro,① HEK 293 cells stably overex-pressing human APP695(OE-hAPP)were treated with different concentrations of ICA(10-100 μmol·L-1)for 24 h and the cell viability was detected by MTT assay.②CHX(50 mg·L-1)was used to block protein synthesis and MG132(20 μmol·L-1)inhibits proteasome activity,then the level of APP in different time(0,0.5,1,2,3 and 4 h)and the ubiquitination were tested by Western blotting.③ E3 ubiquitin ligases HMG-CoA reductase degradation pro-tein 1(HRD1)protein expression in OE-hAPP was tested by Western blotting,as well as the level and ubiquitination of APP were tested under HRD1 silent condition by Co-IP and Western blotting.In vivo,① male APP/PS1 mice and wild type(WT)mice were randomly divided into 5 groups:WT,WT+ICA,APP/PS1,APP/PS1+ICA,and APP/PS1+donepezil(DPZ)groups.ICA(60 mg·kg-1·d-1)and DPZ(1 mg·kg-1·d-1)were treated for 3 months by gavage from 6 months of age,and WT mice were given equal volume of distilled water.②Morris water maze and Y-maze experiments were used to detect the alteration of spatial learning memory function.③ After then,the brain tissues were collected,total proteins were extracted,APP antibodies were subjected to Co-IP,and total ubiqui-tination(Ub),K48-linked polyubiquitination(UbK48)and K63-linked polyubiquitination of APP level,APP and HRD1 proteins were detected by Western blotting.RESULTS In vitro results showed that ICA significantly enhanced APP degradation(vs control,P＜0.01),up-reg-ulated HRD1 expression(vs control,P＜0.05;vs OE-hAPP,P＜0.05),elevated the level Ub and UbK48 of APP,as well as increased APP degradation.Moreover,silenced HRD1 gene abolished abovementioned effects of ICA(vs control-siRNA,P＜0.05;vs HRD1-siRNA,P＜0.05).In vivo results showed that ICA improved the spa-tial learning and memory function APP/PS1 mice by Mor-ris water maze and Y-maze tests,increased HRD1 expres-sion(vs APP/PS1 + vehicle,P＜0.05),enhanced APP ubiquitination and reduced APP protein level(vs APP/PS1 + vehicle,P＜0.01).CONCLUSION ICA promotes the ubiquitination and proteasome-dependent degrada-tion of APP by up-regulating HRD1,thereby improving the spatial learning and memory function of Alzheimer disease mice.