Neuroprotective Effects Of Long-Term Exercise Training On Alzheimer’s Disease And The Related Mechanisms

Background:Alzheimer’s disease(AD)is the most common neurodegenerative disease,and its main clinical manifestation is progressive cognitive and behavior impairment,which can cause disability in the elderly.The main pathological alterations of AD include senile plaques formed by extracellular depsitions ofβ-amyloid protein(Aβ),neurofibrillary tangles(NFT)formed by intracellular aggregations of Tau protein,synaptic dysfunction,neuronal loss and gliosis.Due to the complicated pathological mechanisms,there is still no effective strategy on controlling or reversing AD pathology at present.Neumerous studies have indicated that the pathogenesis of AD is closely related to inhealthy lifestyles in the elderly,such as the lack of physical exercise.Moreover,largescale clinical trials have demonstrated that physical exercise can effectively prevent cognitive decline in the elderly,and exercise can improve spatial memory and learning ablity,as well as decresing Aβ load of AD model mice.Nevertheless,the specific mechanisms of physical exercise are still confliting.In this study,we aimed to explore the effect of long-term treadmill exercise on Aβ burdens,neuronal density,gliosis and Aβ metabolism in APP/PS1 transgenic mouse.Methods:Experimental design Five-month old APP/PS1 transgenic mice and their wild-type littermates were randomly divided into 4 groups(n = 6),including sedentary wild-type control mice(SED-Con),exercise-trained wild-type control mice(EXE-Con),sedentary APP/PS1 transgenic mice(SED-APP/PS1)and exercise-trained APP/PS1 transgenic mice(EXE-APP/PS1).Treadmill exercise protocols After adaptive trainings for 2 days,the mice in exercise-trained groups were subjected to treadmill exercise for 30 minutes,and the training velocities gradually elevated from 5m/min to 11m/min,6 days one week.The exercise training lasted for a total of 5 months.Immunostaining After deparaffinization,antigens retrieval and serum blockage,the paraffin sections were incubated with primary antibodies of Aβ,NeuN,GFAP and Ibal,followed by incubations of Alexa Fluor secondary antibodies for immunofluorescence staining.The acquired graphs were analyzed using ImageJ software.Western blotting Different kinds of neuronal biomarkers and Aβmetabolism-associated enzymes or proteins were detected by Western blotting.The neocortical proteins of mice were extracted with RIPA buffer solution,followed by SDS-PAGE gelelectrophoresis and transferring onto mambranes.Thereafter,the mambranes were incubated with corresponding primary antibodies and perioxidase-conjugated secondary antibodies.The graphs were collected and analyzed by ImageJ software.Results:1)Long-term treadmill exercise markedly attenuated Aβ burdens in APP/PS1 transgenic mice.Compared with SED-APP/PS1 mice,the number and area fraction of Aβ plaques in hippocampus and neocortex were significantly decresed in EXE-APP/PS1 mice(P<0.01),Furthermore,the size of Aβ plaques in hippocampus was also decresed in EXE-APP/PS1 mice in comparison with SED-APP/PS1 mice(P<0.05),while not for neocortex(P>0.05).2)Long-term treadmill exercise elevated neuronal density in the hippocampus and neocortex of APP/PS1 transgenic mice.As indicated by immunofluorescence stainings,5-month treadmill exercise elevated neuronal density in the hippocampus and neocortex of APP/PS1 transgenic mice(P<0.05).These phenomena were further validated by Western blotting analysis(P<0.01).3)Long-term treadmill exercise suppressed activation of astrocytes in the hippocampus and neocortex of APP/PS1 transgenic mice.Compared with wild-type mice,the astrocytes were conspicuously activated in APP/PS1 transgenic mice(P<0.001).However,long-term treadmill exercise evidently inhibited the expression of GFAP(P<0.001,P<0.05),together with significantly inhibiting Aβ-associated astrocytosis surrounding senile plaques(P<0.001).Although microgliosis was also observed in the hippocampus and neocortex of APP/PS1 transgenic mice(P<0.05),it was not affected by exercise intervention(P>0.05).The recruitment and activation of microglia around Aβ plaques were not ameliorated either(P>0.05).4)Long-term treadmill exercise altered the metabolism of Aβ in APP/PS1 transgenic mice.Long-term treadmill exercise reduced the expression levels of APP,inhibited itsβ-clevage and y-clevage,while simultaneously enhanced a-clevage.More specifically,compared with SED-APP/PS1 mice,the expression levels of APP、BACE1 and PS 1 were reduced in EXE-APP/PS1 mice(P<0.01,P<0.01,P<0.05).By contrast,the expression level of ADAM 10 was elevated(P<0.05).Moreover,long-term treadmill exercise downregulated the expressions of Aβ degrading enzymes(such as CD 10 and IDE(P<0.01,P<0.05))and blood-brain barrier transportation molecules(like RAGE(P<0.05)).Conclusions:Long-term treadmill execise could delay the progression of pathology in APP/PS1 transgenic mice via altering the metabolism of Aβ,elevating neuronal density,suppressing activation of astrocytes.The abovementioned results suggested that appropriate long-term exercise intervention might interfere with multiple pathological alterations of AD,thus making it a promising and effective strategy for AD treatment.