Icariin Improves The Learning And Memory Function Of APP/PS1 Mice Via Suppressing Endoplasmic Reticulum Stress

Objective:To observe the mechanism of icariin（ICA）against Alzheimer’s disease（AD）through endoplasmic reticulum（ER）stress signaling pathway.Methods:Nine months old male APP/PS1 or wild-type（WT）mice were randomly divided into four groups:WT control,WT+ICA treatment,APP/PS1 control,and APP/PS1+ICA treatment groups.The treated mice were given ICA 60 mg/kg/d and control mice were received the same volume distilled water for consecutive 3 months.Morris water maze and novel object recognition were used to detect animals’behavior.Following behavior assay,animals were subjected to anaesthetization and decapitation,brains were collected.Nissl staining was used to observe the morphology and number of hippocampal neurons.Aβdeposition in hippocampus was observed by immunofluorescence staining.TUNEL staining was used to observe apoptosis in hippocampus.Western blot was used to detect the level of Aβ_1-40-40 and Aβ_1-42;the expression of APP,ADAM10,BACE1;ER stress relative proteins GRP78,ATF6,ATF4 and CHOP protein level,with the phosphorylation level of IRE1,PERK,eIF2α;meanwhile,to test the apoptosis biomarkers Bcl-2 and Bax level,as well as the cleaved Casepase-3,Caspase-9,Caspase-12 fragments.The mRNA level of Trb3,Gadd34 and Ero1αwas measured by RT-qPCR.Results:The behavior performance was deteriorated in APP/PS1 control mice compared with WT mice,which showed that the average escape latency was significantly prolonged and the target quadrant residence time and the number of crossing platforms were significantly reduced,and the new object recognition index was significantly reduced;amount of Aβwas deposited in hippocampus,with increased Aβ_1-40 and Aβ_1-42-42 content;the number of neurons was significantly decreased in hippocampal DG and CA3 areas,with lots of apoptosis cells were found;APP and BACE1 proteins were up-regulated and ADAM10was significantly reduced in hippocampus;Bcl-2/Bax ratio decreased,the activated Caspase-12,Caspase-9,Caspase-3 fragments increased,the protein expression of ER stress relative proteins GRP78,ATF4,CHOP and the phosphorylation of eIF2αand PERK were significantly increased;the mRNA level of Trb3,Gadd34 and Ero1αwas significantly increased;ATF6 protein expression and IRE1αphosphorylation level were not observed significantly changes.However,treatment with ICA significantly improved the learning and memory ability when compared with APP/PS1 control mice,furthermore,partly reversed the abovementioned performance.ICA treatment reduced the deposition and content of Aβin hippocampus;decreased the expression of APP and BACE1 protein,increased the ADAM10 protein expression;reduced neurons loss in hippocampus,suppressed apoptosis,reversed the Bcl-2/Bax ratio,decreased the level of activated Caspase-12,Caspase-9,Caspase-3;inhibited the ER stress with reducing the protein expression of GRP78,ATF4,CHOP and the phosphorylation of eIF2αand PERK,followed by decreased mRNA level of Trb3,Gadd34 and Ero1α.whereas,no significantly differences were found in ATF6 and IRE1α.Conclusion:These results indicate that ICA improves the learning and memory function of APP/PS1 mice and alleviates the characteristic pathological changes of AD,which may be related to the suppression ER stress,specially inhibiting the PERK/eIF2αsignaling pathway in AD mice’s brain.