The Role Of Abnormal Metabolic Pathway Of Cystathionine On Learning And Memory In Alzheimer’s Disease

Background: Alzheimer’s Disease(AD)is an age-related neurodegenerative disease,clinically manifested as progressive learning and memory impairment,which seriously affects the health and quality of life of the elderly.With the aggravation of the aging society,AD also brings a great economic burden to the society,families and individuals.The important pathological features of AD are senile plaques formed by extracellular beta-amyloid(Aβ)aggregation,neurofibrillary tangles(NFTs)formed by intracellular hyperphosphorylated Tau protein,and neuronal loss.Currently,studies on AD mainly focus on the two major pathological features of Aβ and Tau.However,a large number of clinical trials aimed at eliminating Aβ deposition have been not satisfactory,prompting us to reconsider current treatment and research strategies for AD.Metabolism is the general term for various chemical reactions occurring in cells,and brain metabolic disorder is a common pathological feature of AD,which occurs earlier than cognitive impairment,even many years earlier.In recent years,with the rise of metabolomics,more and more studies have shown that metabolic changes may play an important role in the occurrence and development of AD.However,the changes and effects of metabolism on the basis of Tau lesions are still unclear.Objective: To explore the metabolic changes related to Tau pathology in AD,and to improve the learning and memory function in AD through metabolic intervention.Methods: In this experiment,C57/BL6 J mice(hereinafter referred to as C57 mice)and AD model mice rTg4510 were used as experimental research objects.The months of age before and after the onset of rTg4510 mice were identified and verified by literature search and a variety of behavioral tests related to learning and memory.The anxiety state of the mice was detected by the Open Field Test(OFT)and the Elevated Plus Maze(EPM).The learning and memory ability of the mice were tested by the Morris Water Maze(MWM),the Fear Conditioning Test(FCT)and the Barnes Maze Test(BMT).The brain hippocampus tissues of control C57 mice and rTg4510 mice in the same breeding environment and the same month’s age were detected by metabolomics,and the test results were analyzed to screen out important different metabolites and metabolic pathways.Real-time Quantitative polymerase chain reaction(RT-q PCR)was used to detect the changes of enzymes in the metabolic pathway to verify the changes of metabolites and find the significantly altered molecules.Metabolic intervention is performed by intraperitoneal injection of drugs that target metabolic changes.The same behavioral methods described above were used to detect whether the improvement of learning and memory occurred in rTg4510 mice of the same month age after administration.Western Blot(WB)was used to detect the changes of synapse-related proteins in learning and memory,so as to further explore the possible molecular mechanisms in the future.Results: The behavior tests showed that 3.5-month-old rTg4510 mice did not have learning and memory impairment,while 4.5-month-old rTg4510 mice had learning and memory impairment.Metabolomics data analysis of brain hippocampus tissues of 3.5-month-old C57 and rTg4510 mice showed that metabolites such as glycine,serine and cysteine were up-regulated,while metabolites such as glutathione and cystathionine were down-regulated.Further analysis of the data revealed that two metabolic pathways with significant changes are the glycine,serine and threonine metabolic pathway and the glutathione metabolic pathway in KEGG metabolic pathways.The changes of enzymes in the pathway were detected by RT-q PCR to verify the changes of metabolites and metabolic pathways.It was found that the cystathionine-γ-lyase was significantly up-regulated,which was consistent with the significant down-regulation of its substrate cystathionine-γ-lyase.Intraperitoneal administration of DL-propargylglycine(PAG),a commonly used inhibitor of cystathionine-γ-lyase,in 4-month-old C57 mice and rTg4510 mice,and 4.5-month-old mice for testing,showed that PAG had no effect on the cystathionine content of C57 mice,but increased the cystathionine content of rTg4510 mice.And it was found that PAG had no effect on learning and memory in C57 mice,while improved the impairment of learning and memory in rTg4510 mice.The expression levels of synapse-associated proteins were detected by WB,and we found that the expression level of Glutamate receptor 2(Glu A2)was significantly increased in rTg4510 mice treated with PAG.Conclusions: This study showed that the level of cystathionine in the brain hippocampus of 3.5-month-old rTg4510 mice was significantly down-regulated,while cystathionine-γ-lyase was significantly up-regulated.The inhibition of cystathionine-γ-lyase by PAG can increase the content of cystathionine in rTg4510 mice and improve the impairment of learning and memory of rTg4510 mice,suggesting that cystathionine metabolic pathway plays an important role in AD.In addition,administration of PAG reversed the expression level of Glu A2 in rTg4510 mice,suggesting that it may affect the learning and memory of rTg4510 mice by affecting Glu A2.