The Correlation Between Microglia Polarization And Remyelination In Cuprizone-induced Acute/Chronic Demyelination

Background:Multiple sclerosis(MS)is an autoimmune disease which is characterized by demyelination in white matter of the central nervous system(CNS).According to the mechanisms of demyelination,MS can be divided into four pathological types:I macrophage-mediated demyelination,?antibody-mediated demyelination,? distal of oligodendrocyte injury demyelination,IVprimary oligodendrocyte injury demyelination.Recently more reseachers have begun to use cuprizone-induced demyelination as the animal model to mimic type ? MS.The process of demyalination induced by cuprizone treatment can be easily controlled by diet or withdraw,and for its reproducibility,controllability and concordance futures,Cuprzione-induced demyeliantion model has been widely used to study demyelinaton disease.Acute and chronic demyelination model can be established by controlling the duration of cuprizone diet.In acute model demyelination generally is companied by remyelination,however,in chronic model no remyelination occur even though cupriozne withdraw.Thus this model can be used to investigate the mechanisms of both demyelination and remyelination.Microglia is the crucial immune cell in CNS which is involved in process of demyelination by activation,accumulation in the demyelinatibn lesion and secrete cytokines.Besides that,microglia can also clean myelin sheath debris and promote remyelination.This "double-edged sword" effect of microglia is related to their polarization states.Activated microglia can be polarized into two phenotypes;classically activated(M1)and alternatively activated(M2).Ml phenotype microglia are important for promoting inflammation,whereas M2 cells are characterized by anti-inflammation and tissue remodeling through secrete anti-inflammation cytokines and neurotrophic factor.However,the polarization status of microglia and the relationship between microglia polarization and remyelination in cuprizone-induced acute and chronic demyelination model are still unclear.Objective:Investigate the polarization status of microglia in acute and chronic demyelinating process,clarify the correlation between microglia polarization and remyelination in cuprizone-induced acute and chronic demyelination modelMethods:C57BL/6 mice were fed with 0.2%cuprizone for 6 weeks and 16weeks to establish CNS acute/chronic demyelinating model,respectively.After cuprizone administrated 6 weeks,cuprizone was withdrawed and fed mice normal food to build a convalescent period model.Immunohistochemical staining was used to detect the activation of microglia(Iba-1 positive),the number of oligodendrocyte(CC1 positive)and the expression of myelin basic protein(MBP).Real time PCR was used to detect the expression of cytokines(IL-1?,TNF-a)mRNAs and the marker mRNAs of Ml(IL-1?,TNF-?,CD86,CD32,CD16),M2(Arg-1? mrc-1,Chil-3,Tgfb-1)microglia in CNS.Image J was used for image analysis.The data were evaluated for statistical significance with one-way ANOVA.P<0.05 was considered significant differences.Results:1.The results showed severe demyelination in corpus callosum and cerebral cortex,significantly decreased in MBP expression and reduced CC1 positive cells in both cuprizone-induced acute/chronic demyelination.After cuprizone was withdrawed the number of CC1 positive cells was increased significantly which implied remyelination occuring.2.Activated and accumulation of microglia significantly increased in acute demyelination.The number of activated microglia was decreased after cuprizone withdrawing which compared to that in acute demyelination period.There is less activated microglia in chronic demyelination model than that in acute demyelination.3.The expression of IL-1? and TNF-a mRNAs were increased significantly in acute demyelination,but gradually decreased after cupriozne withdrawing.The expression of IL-1? and TNF-a mRNAs had no significance between chronic demyelinating mice and control mice.4.Both M1 and M2 microglia marker mRNA were found highly expressed in acute model,but significantly decreased after cupriozne withdraw.In chronic model the expression of M1 and M2 microglia marker mRNA had no significant difference compared with that in control mice.Conclusions:1.Microglia is activated obviously in cuprizone-induced acute demyelination model,and the activated microglia can be polarizated to M1 and M2 microgliapheno types.2.In chronic demyelination model,even though the microglia were still activated,but there is no polarization of microglia,implying the paralysis of microglial function may be the reason of failure remyelinaiton.