| Objective:1.To investigate the effect of chronic unpredictable mild stress(CUMS) onautophagy and HMGB1/TLR4signaling pathway in rat hippocampus.2.To study therelationship between autophagy, HMGB1/TLR4signaling pathway and the decline inlearning-memory ability.3.To explore the possible mechanism of learning andmemory ability decline in depression rat modle.Methods:60male wistar rats were randomly divided into control group and chronicunpredictable mild stress(CUMS) group,30rats in each group. Chronic unpredictablemild stress was used to the rats of CUMS group to develope the depression modles,while the rats of control group without any stimulation. Before CUMS and everyweek after CUMS, the performance of all rats was measured through open field test:sucrose preference test and morris water maze test. The rats of each group weresacrificed after they received the stress for0,1and4weeks (10rats in each group atone time point). Brain tissue which contain the hippocampus CA1region wascollected, the histomorphology was observed by hematoxylin-eosin staining (HE), theapoptosis was observed by TUNEL, the number of autophagosome was observed bytransmission electron microscope. The expression of HMGB1, TLR4, Myd88andBeclin1were measured by Western-Blot respectively, and the expression of TLR4andLC3Ⅱwere measured by immunohistochemistry. Results:(1) After4weeks of stress compared with the control group, the scores inopen-field test and the sucrose preference test in CUMS group were lower, but theescape latency in CUMS group was prolonged. The learning and memory ability ofCUMS group declined.(2) Many cells disappeared in CUMS group after4weeks of stress, that wasobserved by hematoxylin-eosin staining (HE). A few apoptotic cells in CUMS groupappeared after1week of stress, but4weeks latter the number of apoptotic cells wassignificantly higher then before. After1week of stress, the number of autophagosomein hippocampus CA1region of CUMS group was higher compared with control group,after4weeks of stress, the number of autophagosome futher increased.(3)Results of Western-Blot: After4weeks of stress compared with the controlgroup, the expression of HMBG1, TLR4and Myd88in CUMS group weresignificantly higher, the difference was statistically significant (1.08±0.12VS0.51±0.08, P<0.05),(1.13±0.14VS0.52±0.04, P<0.05) and (1.18±0.11VS0.53±0.09, P<0.05). After1week of stress, the expression of beclin1in CUMS group wasmarkedly higher compared with control group (0.90±0.13VS0.47±0.06, P<0.05).(4) Results of immunohistochemistry:4weeks after the stress, the expression ofTLR4in CUMS group was higher than control group (1.31±0.21VS0.63±0.08,P<0.05). After1week of the stress, the expression of LC3Ⅱin CUMS group washigher compared with control group (12.45±3.21VS4.05±2.13, P<0.05）,4weekslatter he expression of LC3Ⅱin CUMS group further increased and was significantlyhigher compared with the control group (25.41±5.43VS5.08±1.50, P<0.05）.Conclusion:(1) CUMS can activate the HMGB1/TLR4signaling pathway in hippocampusCA1region of rats.(2) The excessive autophagy of neuronal cells in hippocampus CA1region ofrats may be relation to activation of HMGB1/TLR4signaling pathway.(3) The memory ability decline in depression rat modle may be relation to neuronal apoptosis resulted by excessive autophagy in hippocampus CA1region ofrats. |
