ISRIB Prevents Synaptic Plasticity Disruption And Cognitive Deficits In Rat Model Of Alzheimer’s Disease

BackgroundAlzheimer’s disease（AD）is the most common disease that causes dementia,and its main feature is that it can cause progressive and irreversible cognitive damage.At present,the number of dementia patients in China has reached 9.5 million,which has become a heavy social burden.Thus,it is particularly urgent to study the pathogenesis of AD and find effective treatment methods.Previously,we reported that that amyloid-β-protein（Aβ）facilitates metabotropic glutamate receptor（m Glu R）dependent LTD in rat hippocampus.The downstream phosphorylation pathway of eukaryotic initiation factor 2α-subunit（e IF2α）regulates the translation of protein synthesis.And increasing e IF2αphosphorylation facilitates m Glu R-LTD and suppressing its phosphorylation has the opposite effect.While,it has not been reported whether the phosphorylation of e IF2αand its downstream pathway can regulate the Aβ-mediated m Glu R dependent LTD by regulating the phosphorylation level of e IF2αthrough the use of exogenous Aβ.ISRIB,a small molecule inhibitor of the integrated stress response（ISR）,can restore protein synthesis by activating the activity of the nucleotide exchange factor e IF2B,thus restoring downstream translation without affecting the expression of phosphorylated e IF2α.ISRIB has shown good therapeutic effects in various animal models of neurodegenerative diseases,its role in animal models of its therapeutic effect on AD remains unclear.Therefore,in view of the research focus above,we established AD rat models by injecting Aβinto the lateral ventricle.In vivo electrophysiological induction of m Glu R-LTD was used as a model to study the effect of ISRIB on Aβfacilitated m Glu R-LTD;Morris water maze was used to detect the effect of Aβon spatial learning and memory ability of rats,and the therapeutic effect of ISRIB on spatial learning and memory impairment of AD rats.Methods1.Explore the effect of ISRIB on Aβ-facilitated m Glu R dependent LTD.Aβ-mediated m Glu R dependent LTD was recorded in the rat hippocampus by electrophysiological recording in vivo.The effects of Emetine,a protein synthesis inhibitor,and ISRIB,a small molecule inhibitor of ISR,on Aβ-facilitated hippocampal LTD were examined.2.Explore the therapeutic effect of ISRIB on cognitive impairment of Aβinjected rats.Synthetic Aβ_1-42 was injected into the lateral ventricle,after two weeks repairing,the spatial memory ability of AD rats was detected by Morris water maze test.Then AD rats were treated with ISRIB to test the therapeutic effect of ISRIB on spatial memory impairment in AD rats.3.Explore the molecular mechanism of the therapeutic effect of injecting Aβinto the lateral ventricle of ISRIB in rats.Western blot was used to detect the expression of p-e IF2α,ATF4,e IF2B and p-e IF2B in AD rat models.And changes in the expression levels of the above proteins after treatment with ISRIB.Results1.ISRIB blocks Aβ-facilitated hippocampal LTD in vivo.Rats were selected randomly,then Emetine,a protein synthesis inhibitor,was injected into the lateral ventricle to detect its effect on the hippocampal LTD in vivo of na（?）ve rats.The results showe that Emetine can block the hippocampal LTD of the CA3-CA1 synapse in the na（?）ve rats（*P<0.05,one-way ANOVA）,so we further used Emetine to act on the acute lateral ventricle AD-Aβmodel,and the results showed that Emetine did not affect the AD-Aβfacilitated LTD of CA3-CA1 synapses.Therefore,we selected ISRIB,a small-molecule inhibitor of the ISR,to test its effect on hippocampal LTD.The results showed that both the control group and the ISRIB group could produce robust and stable LTD（*P<0.05,paired t）,ISRIB did not affect the LTD of the CA3-CA1 synapses in the control group.Furthermore,we used ISRIB to AD-Aβinjected rats into the lateral ventricle.The results showed that compared with the control group,ISRIB can significantly block the Aβ-facilitated LTD（*P<0.05,unpaired t）,it means that ISRIB restored Aβ-facilitated hippocampus LTD of CA3-CA1 synapses.2.ISRIB abrogates spatial memory deficits in Aβ-injected rats.Behavioral texts show that,in the standard training protocol,compared with sham+vehicle group,Aβ_1-42-injected rats group The escape latency was significantly higher from day 3（P<0.05,two-way ANOVA）;and ISRIB treatment consistently significantly shortened escape latencies in Aβ_1-42-injected rats（P<0.05,two-way ANOVA）;Aβ_1-42+vehicle group crossed the platform area much less compared with sham surgery rats and the Aβ_42-1 injected group when the platform was removed 24 h after the last training trial（*P<0.05,one-way ANOVA）.Compared with the Aβ_1-42+vehicle group,the percentage of stay time in the target quadrant and the number of crossing platforms in the Aβ_1-42+ISRIB group were significantly increased,it is means ISRIB significantly reversed the memory deficit caused by Aβ_1-42 injection（*P<0.05,one-way ANOVA）.In the weak protocol,consisting of one swimming trial per day,the results show that in the escape latency and the number of times crossing the platform,the Aβ_1-42group showed obvious spatial cognitive deficits,and ISRIB can significantly reverse this cognitive disfunction,but the treat of ISRIB to the control group did not show memory enhancement.3.ISRIB restores the expression of ATF4 without affecting the expression of p-e IF2αin Aβ-injected rats.The results show that,compare with the control group,the levels of p-e IF2αand ATF4 in the Aβ_1-42+vehicle group were abnormally increased,and the addition of ISRIB had no effect on the expression of p-e IF2α,while the expression of ATF4 was significantly reduced（*P<0.05,**P<0.01,***P<0.001,one-way ANOVA）.The results show that ISRIB can restore the expression of ATF4 without affecting the abnormal phosphorylation of e IF2α.p-e IF2Bεand e IF2Bεshowe no significant difference among all groups（P>0.05,One-way ANOVA）.Conclusions1.ISRIB,a small-molecule inhibitor of the ISR,provides well protective effect on our Aβfacilitated LTD model and Aβ-induced spatial learning and memory deficit.2.The beneficial action of ISRIB may be mediated by its ability to abrogate Aβinduced ATF4 elevation in the hippocampus.3.Targeting the integrated stress response by suppressing the p-e IF2αdownstream with ISRIB may provide protective effects in the early stage of sporadic AD.