Id2 Plays An Important Role In Oligodendrocyte Development And Regulated By Fyn Pathway During Remyelination

With the aging populations increased rapidly in our country ,the rate of demyelination are higher in the central nervous system (CNS). Oligodendrocytes are the myelin-forming cells of CNS,and ultimately myelination progress dependent on multiple extracellular and intracellular signals,such as many growth factors, hormone, extracellular matrix, also dependent on intracellular transcription factors,such as Sox10,SCIP,Krox24,and the helix-loop-helix (HLH). Helix-loop-helix(HLH) transcrition factors include basic HLH (bHLH) and inhibitor of DNA binding(Id).Id proteins, including Id1, Id2, Id3, and Id4, are involved in the regulation of the development of T cells, tumour cell proliferation, cell cycle and muscle genesis, neurogenesis and so on.Id2 immunoreactivity was found in the cultured oligodendrocyte precursor cells (OPCs) from the rat optic nerve.Overexpression of Id2 powerfully inhibits oligodendrocyte differentiation, and that absence of Id2 induces premature oligodendrocyte differentiation in vitro.Id2 mRNA is localized in the mouse brain,but in adult rat brain, it is still unknown whether Id2 immunoreactivity mainly exhibits in neuronal, astrocytic and/or oligodendrocyte lineage cells. It is also unclear where and when Id2 immunoreactivity mainly exhibits in oligodendrocyte lineage cells.The present study showed much Id2-immunoreactivity in such brain regions as optic chiasm,the anterior commissure, the fimbria of hippocampus, and the pyramidal tract.It is highly expressed in corpus callosum and cingulum. Ninety percent of Id2 immunoreactivity is in oligdendrocyte lineage cells, These observations suggest that Id2 may be mainly involved interminal maturation of oligodendrocytes and myelination .What role does Id2 play in the development of oligodendrocyte and myelinaton in cingulum?We observe that expression of Id2 in development of oligodendrocyte and myelinaton in cingulum. The rat cingulum was injected by ethidium bromide in the adult CNS.The process that most resembles oligodendrogenesis during development is remyelination.So,what's the difference of Id2 expression in corpus callosum and cingulum of normal and demyelinated rat brain?By what mechanism is Id2 contributing to remyelination?Olig1 and olig2 are necessary for oligodendrocyte lineage development and myelination.During developmental myelination,Olig1 protein is redistributed from a nuclear location in OPCs to a cytoplasmic location in myelinating oligodendrocytes, a position it retains in normal adult white matter in both OLPs and oligodendrocytes. A similar relocalization is present following demyelination:Olig1 is nuclear in OPCs responding to injury, but it appears to relocate to the cytoplasm as the cells begin to differentiate into remyelinating oligodendrocytes. However, since resting OPCs in normal adult white matter have cytoplasmic Olig1 while those contributing to remyelination have nuclear.Olig1 it suggests that subcellular localization is essential for the process by which OPCs become oligodendrocytes.Olig2 are necessary for oligodendrocyte lineage development and myelination.Olig2 is required for development of NG2 progenitor cells, the most prevalent cycling cell in the adult brain and therefore especially susceptible to acquisition of mutations. Functions of Olig1 are more apparent during oligodendrocyte maturation, which is reflected in the redistribution of Olig1 proteins from the nucleus to the cytoplasm.Id proteins function through HLH-mediated heterodimerization of Ids and basic HLH transcription factors such as olig1 and olig2. Id can bind to bHLH class A protein and then interfer the complexes to form.BMP2 and BMP4 promoted dose-dependent astrocyte differentiation of adult OPCs with concurrent suppression of OL differentiation.Treatment of OPCs with BMP2 and BMP4 increased Id4 expression and decreased the expression of olig1 and olig2. Overexpression of olig1 or olig2 blocked the astrocyte differentiation of adult OPCs induced by BMP2 and BMP4. These observations suggest that Id2 may be inhibit olig1/2, and contributing to remyelination.But what can influence the interaction between Id2 and olig1/2? Fyn is a member of the Src family of cytoplasmic nonreceptor protein tyrosine kinase (PTK). Several lines of evidence suggest that Fyn has a role during the initial stages of myelination.The myelin content in brains from fyn -deficient transgenic mice is significantly reduced.Fyn stimulates transcription of the myelin basic protein (MBP) gene for myelination. Fyn can phosphorylate MAPK/ERK,olig2 can be regulated by MAPK/ERK from neural stem cells to OPCs. C/EBP(the CCAAT enhancer binding protein) may be regulated by Fyn PTK. Myelination signaling through Fyn might stimulate C/EBP transcription factors or may regulate them through MAP kinase or PKC.Id2 is a direct target of C/EBP.FcRγ/Fyn-Rho (Rac1)-MAPK (P38 MAPK)-p-MBPs pathway plays an important role in cuprizone induced demyelinated brain.So, fyn may directly regulated Id2 or regulated olig1/2 through MAPK.Id2 can inhibit olig1/2 function. Interaction of Id2 and olig1/2 can be effedcted by fyn during remyelination.So,we have observed:(1) Where does Id2 immunoreactivity exhibit in high expression by immunofluorescent staining?Whether Id2 immunoreactivity mainly exhibits in neuronal, astrocytic and/or oligodendrocyte lineage cells. When Id2 immunoreactivity mainly exhibits in oligodendrocyte lineage cells. (2) We observed that the temporal and spatial expression patterns of Id2 and olig1/2 in the development of oligodendrocyte and myelinaton in normal cingulum,then we observed the expression changes of Id2,olig1/2 and fyn in demyelinated cingulum injected by ethidium bromide. We also observed that the co-localization of Id2 and olig1/2,and expression changes of fyn in order to offer some data for the interaction between Id2 and olig1/2 regulated by fyn. (3) We observed the effect of PP1, a Fyn tyrosine kinase inhibitor on oligodendrocyte differentiation from neural stem cells in vitro and whether the interaction between Id2 and olig1/2 is regulated by fyn tyrosine kinase inhibitor.The results are as follows:1. The present study showed high expression of Id2-immunoreactivity in optic chiasm, the anterior commissure, the fimbria of hippocampus, and the pyramidal tract etc,higest in the corpus callosum and cingulum.5% of Id2 immunoreactivity was observed inβ-tubulin III-positive neurons such as in the superior vestibular nucleus(sv), mature Purkinje cells. Five percent of Id2 immunoreactivity was observed to be localized to astrocytes in some regions such as the cortex ,the cingulum.Ninety percent of Id2 immunoreactivity is expressed in oligdendrocyte lineage cells, some in olig1+,olig2+ and PDGFaR+ OPCs,seventy percent in CC-1+ oligodendrocytes.Id2 may be play a role in development of neuron and astrocyte, mainly involved in terminal maturation of oligodendrocytes and myelinaton.2. We observed that it is demyelinated obviously in rat cingulum which injected by ethidium bromide,but not induced by cuprizone. Expression of Id2 increase gradually from in P0 to in adult,but Olig1and Olig2 exhibit in high expression at birth.Olig1 protein is redistributed from a cytoplasmic location to a nuclear location in OPCs in myelinating and remyelinating oligodendrocytes. A localization of Id2 is opposite to olig1 in normal and demyelination: some of Id2 is in cytoplasm in embryo and two weeks after birth, but it appears to locate to the nuclear in adult. Id2 is in cytoplasm in OPCs responding to injury, but it appears to relocate to the cytoplasm as the cells begin to differentiate into remyelinating oligodendrocytes. Id2 is co-localizated in nuclear with olig1 in cingulum injected by ethidium bromide after seven days, in cytoplasm with olig1 after 10 days. Id2 may be interacts olig1/2 and mediate remyelination. Expression of fyn and Id2 reduce, while Olig1and Olig2 increase,this may be coincidenced that Id2 can inhibit olig1/2 function.,interaction between Id2 and olig1/2 can be effedcted by fyn during remyelination.3. We observed that OPCs are small and round, having monopole or dipolar processes,stained by PDGFα-R in mixed cultured cells from neural stem cells at eleven day. Id2 is co-localizated in nuclear with Olig1 in early differentiated OPCs, in cytoplasm in oligodendrocytes. Olig1 is only expressed in oligdendrocyte lineage cells,while Olig2 is also expressed in astrocytes. 1μM PP1,a fyn tyrosine kinase inhibitor inhibit on oligodendrocyte differentiation from neural stem cells in vitro, expression of Id2 reduce, while Olig1 increase. Olig1 is still in cytoplasm,while Id2 in nuclear in Olig1 positive cells. Id2, olig1/2 and interaction of them may be effedcted by fyn in vitro.In summary, we have observed the expression of Id2 in adult rat brain and whether Id2 immunoreactivity mainly exhibits in neuronal, astrocytic and/or oligodendrocyte lineage cells,also observed that where and when Id2 immunoreactivity mainly exhibits in oligodendrocyte lineage cells.We observed the expression patterns of Id2,olig1/2 and fyn in normal and demyelinated cingulum,and the co-localization of Id2 and olig1/2. We observed the effect of a Fyn tyrosine kinase inhibitor on oligodendrocyte differentiation and the interaction between Id2 and olig1/2. These observations suggest that Id2 may be mainly involved in terminal maturation of oligodendrocytes and myelinaton. Id2 can inhibit olig1/2 function..Interaction between Id2 and olig1/2 can be effedcted by fyn during remyelination.So, Id2 plays an important role in oligodendrocyte development and may be regulated by Fyn-Olig1/2 pathway during remyelination.