EGCG Attenuates Chronic Unpredictable Mild Stress-induced Memory Impairment In Rat By Restoring The Autophagy-lysosome Pathway In The Hippocampus

Objective:To investigate the influence of stress on Aβ1–42accumulation andautophagy in CA1, and the effects and potential mechanisms of EGCG onattenuating CUMS-induced memory impairment.Methods:50male rats were randomly divided into five groups of ten individuals:non-stressed (control) group; chronic unpredictable mild stress (CUMS) group;EGCG+CUMS (EGCG) group; CQ+EGCG+CUMS (CQ) and vehicle+CUMS (Vehicle) group. In addition to the control groud, the rest of groud weretreated with chronic stress. From the first of day of chronic stress, EGCG wasinjected intracerebroventricularly in2μl volume at a dose of20μg/kg, CQgroud was treated with2μl EGCG and2ul CQ. Vehicle groud was treated with2μl volume of vehicle, The speed of injection drugs control in0.4ul/min, and thetime of injection drugs contiued four weeks. All groud of rats were treated withchronic stress at four weeks for performing Morris water maze experiment.After the completion of Water maze experiment, all rats were docked tail forblood and then beheaded for hippocampal CA1area organization.Theexpression level of plasma corticosterone is determined by Radioimmunoassaymethod.the histomorphology of hippocampal CA1area was observed byhematoxylin-eosin staining (HE). the apoptosis of hippocampal CA1area was observed by TUNEL. the number of autophagosome of hippocampal CA1areawas observed by transmission electron microscope. The expression of LC3、P62、Beclin1、mTORCI and P70（P70S6K） were measured by Western-Blotrespectively, the expression of Aβ1-42were measured by immunohistochemistry.Results:(1) CUMS caused a significantly greater elevation in blood corticosteronelevels in the CUMS group than in the control group. There were no significantdifferences between the EGCG treatment and CUMS groups with regard toplasma corticosterone levels (p>0.05).(2) Compared with the control group, the escape latency in CUMS groupwas prolonged, and the learning and memory ability of CUMS group declined.But, after EGCG treatment, the escape latency of rats was significantly shorten andthe learning and memory ability of rats elevated.Compared with the EGCGgroup, the escape latency in CQ group was prolonged, and the learning andmemory ability of CQ group declined.(3) In the CUMS group, the CA1cells were irregularly arranged, and theedge of many cells was unclear., the nucleus and nucleolus of many Cellsbecame ambiguous,that was observed by hematoxylin-eosin staining (HE).For the number of cells in the CA1area, Post-hoc comparisons indicated that theCUMS group showed a significantly smaller number of CA1cells comparedwith the control and EGCG groups.The total number of the apoptosis of cellswas obviously increased in the CUMS rats. Compared with the CUMS group,EGCG treatment significantly decreased the number of the apoptosis of cellsin the CA1. Compared with the EGCG groud,the total number of the apoptosisof cells was obviously increased in the CQ rats. The number of mitochondrialswelling and autophagosome in hippocampus CA1region of CUMS group washigher compared with control group, EGCG treatment significantly increasedthe number of mitochondrial swelling and autophagosome in the CA1.Compared with EGCG group, the number of mitochondrial swelling andautophagosome significantly increased in the CQ rats.(4) Results of Western-Blot: Compared with the control group, theexpression of LC3、P62、P-mTOR and P-P70（P-P70S6K) in CUMS groupwere significantly higher, the difference was statistically significant(p<0.05).Compared with the CUMS group, the expression of LC3、P62、P-mTOR and P-P70（P70S6K) in EGCG group were significantly declined, thedifference was statistically significant (p<0.05). No significant changes in theexpression of Beclin-1were observed in the CA1between control and CUMSrats.Compared with EGCG group, the expression of LC3、P62、P-mTOR andP-P70in CQ group were significantly higher, the difference was statisticallysignificant (p<0.05).(5) Results of immunohistochemistry: compared with the control group, theexpression of Aβ1–42was markedly increased in the CA1region of CUMS rats,the difference was statistically significant (p<0.05).However, the expression ofAβ1–42in the EGCG treated rats was reduced compared with the CUMS group.Compared with the EGCG group, the expression of Aβ1–42in the CQ rats wasmarkedly increased,the difference was statistically significant (p<0.05).Conclusion:(1) CUMS resulted in increased intracellular Aβ-amyloid accumulation andautophagic influx impairment in CA1of rats(2) EGCG-treatment efficiently ameliorated learning and memory deficitsand attenuated impairment of autophagic influx induced by CUMS，Which maybe through restoration of dysregulated mTOR signaling pathway.