Effect Of Treadmill Exercise On Hippocampal SUMOylation In APP/PS1 Transgenic Mice

Background Alzheimer’s disease(AD),one of the most common neurodegenerative diseases,undermines the happiness of patients and their families.The etiological hallmarks of AD are mainly extracellular senile plaque deposition,intracellular nerve fiber tangles and excessive neuronal apoptosis.Small ubiquitin-like modifier(SUMO)is involved in the post-translational modification of protein,and the process that combined with substrate protein calls SUMOylation.Previous studies have shown that SUMOylation were dysfunctional in AD brain,which participated in the processes of senile plaque deposition,nerve fiber tangles and neuronal apoptosis.Appropriate physical exercise has been proved to improve people’s cognitive and memory abilities.In fields related to exercise and AD,it has been found that exercise alleviate the learning and memory ability,reduce the deposition of senile plaques,nerve fiber tangles and neuronal apoptosis.However,in AD brain,whether SUMO related to the beneficial effect of exercise,and whether exercise improve the abnormal SUMOylation still remain unknown.Objective In our research,we used APP/PS1 transgenic mice and subjected a three-month treadmill exercise as intervention.Firstly,we aim to investigate the effect of exercise on learning and memory abilities and whether exercise attenuate Aβ deposition in hippocampus.Secondly,we expect to explore the SUMO-related protein expression and protein SUMOylation levels in hippocampus of APP/PS1 mice.Finally,we try to identify the effect of exercise on protein SUMOylation.Methods In the current experiment,3-month-old C57BL/6 male wild-type mice were randomly divided into wild-type control group(WC,n=12),wild-type exercise group(WE,n=12).And 3-month-old APP/PS1 male transgenic mice were randomly divided into APP/PS1 control group(AC,n=12)and APP/PS1 exercise group(AE,n=12)respectively.Mice in exercise group(WE,AE)were subjected to 3-month treadmill exercise,while mice in the control group(WC,AC)were reared for three months normally.After exercise intervention,the Morris water maze experiment was used to test the learning and memory ability of the mice.Then six mice in each group were executed by heart perfusion to make frozen slices.Thioflavin S staining was used to detect the aggregation of Aβ.The rest of six mice in each group were sacrificed by neck dissection and bilateral hippocampus were isolated.Western blotting was used to detect the expression of SUMO-related proteins;RT-PCR was used to detect the m RNA expression of SUMO-related genes.Results(1)The learning and memory abilities of 6-month-old APP/PS1 mice were impaired,3-month exercise improved the learning and memory abilities of APP/PS1 mice: Morris water maze results showed that in the positioning sailing experiment on day 1-5,compared with WC group,the escape latency and the total swimming distance of AC group mice were significantly increased(P ＜ 0.01),but the target quadrant time of AC group was significantly reduced(P＜0.05).However,compared with AC group,the escape latency and the total swimming distance of AE group mice were significantly decreased(P ＜ 0.01),but the target quadrant time of AE group was significantly enhanced(P＜0.05).In the space exploration experiment on the sixth day,compared with WC group,the number of platform crossing and the target quadrant time percentage of AC group were significantly reduced(P＜0.05),but the total swimming distance of AC group was insignificantly changed(P ＞ 0.05);However,compared with AC group,the number of platform crossing and the target quadrant time percentage of AE group were both increased significantly(P＜0.05),but the total swimming distance of AE group was insignificantly changed(P ＞ 0.05).(2)Aβ aggregations in the hippocampus of 6-month-old APP/PS1 mice were significantly increased,3-month exercise reduced Aβ aggregation in the hippocampus of APP/PS1 mice: Thioflavin S staining results showed that compared with WC group,Aβ plaque deposition of AC group was significantly increased(P ＜ 0.01);but compared with AC group,Aβ plaque deposition of AE group was significantly reduced(P ＜ 0.01).(3)Exercise reduced SUMO1 modification level in the hippocampus of 6-month-old APP/PS1 mice: WB results showed that,compared with WC group,SUMOylation in the hippocampus of AC group have no significant changes(P ＞ 0.05);but compared with the AC group,the SUMO1 modification level at 30 k Da and 52 k Da(P ＜ 0.01)in the hippocampus of AE group was significantly reduced,while the expression of SUMO2/3 and Ubc9 had insignificant changes(P ＞ 0.05).(4)SUMO-related genes in the hippocampus of 6-month-old APP/PS1 mice were increased,3-month exercise reduced m RNA expressions of SUMO-related genes: RTPCR results showed that compared with the WC group,the m RNA expression of SUMO1 and SENP1 of AC group were significantly increased(P＜0.05);but compared with the AC group,the m RNA expression of SUMO1 and SENP1 of AE group were significantly decreased(P＜0.05).However,compared with WC group,there was insignificant change in SUMO2 and Ubc9 m RNA expression(P ＞ 0.05)of AC group;compared with AC group,there was no significant change in SUMO2 and Ubc9 m RNA expression(P ＞ 0.05)of AE group.Conclusion The impaired of learning and memory abilities and aggregations of Aβ in hippocampus of 6-month-old APP/PS1 mice were related to the increase of SUMO1 m RNA expression.Treadmill exercise improves APP/PS1 mice’s learning and memory ability,and reduces Aβ deposition in the brain,which were associated with the decrease of SUMO1 modification,whereas unassociated with SUMO2/3 modification.