Enhancement By Voluntary Running Exercise On Myelination And Remyelination Of The Central Nervous System In Adult Mice

The central myelin exhibits a strong plasticity,both during development and adulthood.Studies have shown that social activities,learning and training as well as sensory stimulation can all lead to myelin remodeling in the central nervous system(CNS).However,once pathological demyelination occurs in the CNS,its regeneration and repair are often incomplete,leading to a series of consequences which further initiate and exacerbate axonal degeneration,and ultimately cause a variety of neurological dysfunction such as multiple sclerosis(MS),and severely destroy the patient’s ability to work and live.Exercise is in step with human evolution,and has a lot of impacts on the CNS.Studies have shown that exercise promotes neurogenesis in the hippocampus of rodents,improves learning ability,and regionally increases newborn microglia in the cortex.Exercise also enhances synaptic transmission and plasticity in the hippocampus of rodents,and partially reverses aging related change in neurogenesis and synapse.The existing clinical data suggest that exercise is beneficial for MS patients.It can alleviate fatigue and depression,enhance motor function,and improve life quality of patients.MRI examination has shown that exercise can alleviate white matter damage in MS patients.However,the beneficial effects of exercise have not been paid enough attention in clinical practice due to the lack of sufficient experimental evidence.In this study,we investigated the effects of voluntary running(VR)on the oligodendroglial cells,myelination and remyelination in the motor cortex of adult mice under healthy or demyelination conditions,and analyzed the underlining mechanisms.First,we investigated the effect of VR exercise on the myelination of the CNS in healthy adult male mice.Q-PCR and Western-blotting results showed that the mRNA and protein level of myelin basic protein(MBP)in the motor cortex and hippocampus were significantly increased after 2-week VR exercise.Transmission electron microscopy observation indicated that the rate of myelinated axons and the average thickness of myelin in the motor cortex were significantly increased.Rotarod motor test and suspended wire test showed that VR group mice could stay on the rotating bar and suspended wire for a significantly longer time.These results indicate that VR exercise increases the myelination of motor cortex and thus improves the motor coordination ability.Then,we employed immunofluorescent markers to detect the change in oligodendroglial cells.The results showed that the number of mature oligodendrocytes(OLs)and newborn oligodendrocyte precursor cells(OPCs)increased significantly after 2-week VR exercise,indicating that VR exercise can not only promote the differentiation but also the proliferation of OPCs.Previous studies have shown that Wnt signaling pathway is a regulatory pathway for OPCs differentiation.In order to determine whether Wnt signaling is involved in mediating the effect of VR exercise,we detected the change of key proteins in Wnt signaling pathway.We found that the level of Catenin and Gsk-3β remained unchanged,but the level of p-Catenin increased.Immunohistochemical investigation further confirmed that the numbers of p-Catenin-positive OPCs and mature OLs were increased in the motor cortex upon VR exercise.Since the level of Gsk-3β did not change,we speculated that the level of Wnt ligands changed,leading to the change in the intensity of the signaling pathway.Therefore,we detected the mRNA level of Wnt ligands,and found that the mRNA levels of Wnt3 a and Wnt9 a in the motor cortex were significantly decreased after VR exercise.We then expressed and purified Wnt3 a and Wnt9 a from HEK293 cell lines,added them into the OPCs culture medium in vitro,and found that Wnt3 a and Wnt9 a significantly inhibited the proliferation and differentiation of OPCs.These results suggest that VR exercise promotes the proliferation and differentiation of OPCs at least partially via inhibition of Wnt signaling.Finally,we used cuprizone to induce CNS demyelination in mice to observe the role of VR exercise on remyelination.Healthy adult male mice were fed a diet containing cuprizone for 12 weeks,which resulted in demyelination in the CNS.After termination of cuprizone administration,the mice received VR exercise during the phase of remyelination.The results showed that the level of MBP and the rate of myelinated axons in the motor cortex of VR group mice were significantly increased.The mice walked significantly longer in the open field and moved significantly more quickly,removed the attached glue from their noses with less time,and stayed on the rotating bar and suspended wire for significantly longer time,as compared with controls.The number of newborn OPCs and mature OLs in the motor cortex significantly increased upon VR exercise.These results suggest that VR exercise could promote the proliferation and differentiation of OPCs,which in turn promotes the remyelination of the motor cortex in demyelinated mice.In summary,the present study,through a series of experiments,revealed that VR exercise could promote the differentiation and proliferation of OPCs in the motor cortex in healthy adult mice,improve the level of myelination and enhance the motor coordination ability of the animals.The VR-induced beneficial effect is at least partially mediated via Wnt signaling,with the Wnt ligands subtype 3a and 9a the direct effectors.Furthermore,VR exercise could also promote the differentiation and proliferation of OPCs,accelerate the remyelination in the motor cortex,and enhance the recovery of motor functions in the cuprizone-induced CNS demyelination mice.The present work deepens our understanding of the relationship between motor exercise and myelin plasticity in the CNS,and provides new idea for the intervention and treatment of demyelination diseases in the CNS.