Pre-ischemic Treadmill Training Induces Tolerance To Brain Ischemia By Up-regulating GLT-1

Objective:Transient slight ischemia has protection on the severe ischemiaoccurred after slight ischemic, and this phenomenon is called brain ischemictolerance. The transient slight ischemic before severe ischemic is calledischemic preconditioning. In recent years, scholars found that manyinterventions including intermittent hypoxemia, anoxia, remote ischemia,medicine, acupuncture, oxidative stress could cause tolerance for subsequentserious damage. Due to the consideration of security, exercise pretreatment iswidely studied. Pre-ischemic exercise training induces tolerance for thesubsequent severe brain damage. But the mechanism still remainsunclear.Previous studies had shown that pre-ischemic exercise might alleviatebrain damage caused by ischemic by glutamate system. The neural protectionmechanism of pre-ischemic exercise,involving glutamate system, should befurther clarified.Glutamate is one of the primary small molecule neurotransmittersresponsible for fast excitatory signaling in the central nervous system. Overrelease of glutamate has severe nerve toxicity.Reducing the glutamateconcentration of extracellular fluid is very important for alleviating braindamage.The glutamate transporters distributed in both glial cells and neurons arethe only method to uptake glutamate from extracellular space tointracellular．To date，five types of cell membrane glutamate transporters havebeen cloned，which include EAAT1(GLAST)，EAAT2(also named as glialglutamate transporter-1，GLT-1)，EAAT3(EAAC1)，EAAT4and EAAT5．Ithas been shown that GLT-1plays a dominant role for the long termmaintenance of low and non-toxic concentrations of glutamate in extracellularspace. The aim of our study is to investigate whether exercise preconditioning reduces the concentrations of glutamate to alleviate brain damage via thepathway regulated by GLT-1.Watanabe et al have demonstrated mitoKATPplays an important role in thebrain ischemic tolerance through two animal models of cerebral ischemia anda model of cell oxygen deprivation of sugar.Domestic scholar Wang and Yangshowed that mito KATP,acting on glutamate system,played a neuroprotectionrole by inducing brain ischemic tolerance.A recent study showed thatinhibition of mitoKATPmay eliminate anti-arrhythmic effects caused byexercise training.In conclusion,exercise training,acting on glutamate system,play a role of neuroprotective by mitoKATPsignaling pathways.In regard to MitoKATP downstream pathways, an experiment reportedwortmannin,an inhabitor of PI3K could eliminate the neural protective effectcaused by mitoKATPagonist against glutamic acid system. It was indicated thatPI3K played a vital role in the glutamate mediated cerebral ischemia tolerancemechanism Matejíková’s study proved that PI3-K/AKT participated in Cardiacischemic tolerance mechanism induced by mitoKATPagonist.Li’s researchshowed that PI3K can adjust expression of GLT-1in glial cells.The purpose ofour study is to illuminate whether exercise conditioning strengthen glial cellsglutamate uptake ability by PI3K via GLT-1.Method:54male rats were randomly divided into threegroups(n=18/group):sham surgery,MCAO without exercise and MCAO withexercise.After treadmill training for three weeks,Ischemic stroke was inducedby occluding the MCA for2.0hours,followed by reperfusion.24hours afterreperfusion, six rats in each group were evaluated for neurological deficits andthen decapitated to calculate the infarct volume. Six rats in each group weresacrificed to detect the level of PI3K,p-PKB and total-PKB.Six rats in eachgroup were sacrificed to detect the level of GLT-1by westernblot.Neurological deficit scores and infarct volume between ischemic rats withand without pre-ischemic exercise group were compared by an independentt-test.The rest of the inspection items among three groups were analyzed byone-way analysis of variance(ANOVA). Result: For behavioral scores: In the sham surgery group, the ratsdemonstrated no neurological symptoms, and the scores is0.In contrast, therewas a significant difference of behavior scores between MCAO withoutexercise and MCAO with exercise group (P<0.05).Infarct volume: The rats in the sham surgery group showed no ischemicareas.In contrast,the rats in the MCAO with exercise group showed asignificantly reduced ischemic area in the brain relative to those in the MCAOwithout exercise group(P<0.05).Expression of GLT-1: There was significant difference of GLT-1expression among the three groups(P<0.05).The rats in the MCAO withexercise group showed a higher GLT-1expression in the brain relative to thosein the MCAO without exercise group(P<0.05).Expression of PI3K: There was significant difference of PI3K expressionamong the three groups (P<0.05).The rats in the MCAO with exercise groupshowed a higher PI3K expression in the brain relative to those in the MCAOwithout exercise group(P<0.05).The rats in the MCAO without exercise groupshowed a higher PI3K expression in the brain relative to those in the shamsurgery (P<0.05).Expression of PI3K,P-PKB: There was significant difference of PI3K、P-PKB expression among the three groups(P<0.05).The rats in the MCAOwith exercise group showed a higher PI3K,P-PKB expression in the brainrelative to those in the MCAO without exercise group(P<0.05).Conclusion: In summary, the results in this study indicated that treadmilltraining exercise prior to MCAO/Reperfusion enhanced glutamate intake ofGLT-1by increasing the expression level of PI3K and P-PKB in thebrain.Therefore,the pre-ischemic exercise alleviated brain damage and reducedmotor dysfunction after MCAO.This result could be beneficial for developingrational program of prevention and treat meat for ischemic stroke.