| White matter occupies about 60% of adult brain volume,whose main component is the myelinated axons.Myelin is a segmental multilayer membrane structure formed mature oligodendrocytes(OLs)in the central nervous system(CNS).The exposed axon membrane between the segmental myelin is rich in ion channels,called Ranvier’s node.Action potentials can conduct alone the axons leaping between Ranvier’s node,so myelin accelerates the conduction of electrical signals along axons.Therefore,OL that forms the myelin provides metabolic nutrients such as lactic acid and acetylase SIRT2 to support the axons.Our previous study has found that myelin formation during early stages could regulate synaptic development and thus affects long-term neurological function.Myelination in the CNS relies on the differentiation and maturation of oligodendrocyte precursor cells(OPCs).Myelin development begins in embryonic 28 day and experiences a rapid development stage from birth to adolescence in human brain.Similarly,myelin development in mice begins 3 days after birth and is in a stage of rapid development by 1 month of age.Recent studies have found that there is still a large amount of newly-formed myelin in adult and even elderly mice,and myelination in adults plays an important role in cognitive functions,such as motor skill learning,consolidation of fear memory and spatial memory.OPCs are distributed into the whole brain from the early stage of development,which could differentiate into mature OLs under the regulation of much internal and external factors.And then the OLs wrap axons to form myelin.However,myelination would be retarded in some hereditary diseases or diseases induced by external pathogenic factors such as ischemia and hypoxia,then damaging long-term neurological function.For example,mutations of gene encoding myelin protein PLP1 mutations could cause Pelizaeus-Merzbacher disease(PMD).previous studies had demonstrated that immature OPC is more sensitive to adverse factors such as hypoxia,so premature infants or birth extrusion could cause myelin dysplasia,leading to neonatal white matter injury and multiple types neurofunction impairments.Although myelin remains stable for a long time after formed,demyelination occurred in the autoimmune disease multiple sclerosis(MS)or some other neurodegenerative diseases.MS patients experienced neurological impairment related to the area and extent of myelin damage,which were caused by attraction of autoimmune cells.In addition,evidence from our and other reseachers showed diffused myelin degeneration in a Alzheimer’s disease(AD)mice model,and promoting myelin formation and increasing the total amount of myelin can improve the cognitive dysfunction in AD mice.When demyelinating lesions occur,OPC near the injured area can migrate to the injured area,proliferate and differentiate to envelop axons to form myelin,known as remyelination,but remyelination is not efficient to compensate for myelin loss in patients.Therefore,exploring potential targets and effective compounds to regulate OPC differentiation and myelination is of great significance for the treatment of neurological damage caused by myelin dysplasia or demyelination.In the early stage,our laboratory found two types of compounds that can promote OPC differentiation through the established high-throughput drug screening system,type 1muscarinic(M1)receptor blocker and kappa opioid receptor agonist.We found that the M1 receptor antagonist,clemastine,can improve the myelin development and neurological functions in WMI mice.Thereafter,clemastine increased myelin formation in aged or AD mice.The drug has completed phase Ⅲ clinical trials recently.Further,our laboratory found a series of new compounds,tamoxifen,ospemifene,clomifene and other compounds have the effect of promoting OPC differentiation through the BIMA system,which are also called selective estrogen receptor modulators(SERMs)-It was demonstrated that the myelinationpromoting effect of SERM is not mediated by classical estrogen receptors Eα or Eβ.Therefore,we wanted to further explore the role of SERM in myelin dysplasia and demyelinating lesions,and explore their potential targets.Among the SERMs,clomifene has the most pronounced OPC-promoting differentiation effect,and it has been approved by FDA for inducing ovulation in assisted reproduction processes,so we chose this compound as the research object.We usded chronic hypoxia induced WMI model,focal or diffuse demyelinating lesions induced by lysolethesin or cuprizone to explore the effects of clomifene in myelin development and remyelination with immunofluorescence staining,ex vivo OPC cell culture,behavioral experiments,etc..We explored the effects of clomifene in regulating myelination and improving neurological dysfunction from the following four aspects:(1)the effect of clomifene on myelin development and long-term neurological damage in the WMI model;(2)the effect of clomifene treatment on remyelination in focal demyelinating model mice induced by lysolecithin;(3)the effect of clomifene on remyelination in cuprizone-induced diffuse demyelinating model mice;(4)the effect and potential targets of clomifene on promoting OPC differentiation.The following results are obtained:1.In the neonatal white matter injury model induced by chronic hypoxia,clomifene treatment can increase the number of CC1-positive mature OLs and the expression of myelin proteins MBP and PLP in the brains of mice,but does not affect NF200-positive axonal and glial cell activation,and improves the long-term motor coordination function of mice.2.In the LPC-induced focal demyelinating model,clomifene treatment can increase the expression of MBP in the injuried area,and clomifene treatment also increased mGFP positive newly-formed myelin in the lesions using a transgenic mouse line.3.In CPZ-induced diffuse demyelinating model mice,clomifene treatment could promote OPC differentiation and remyelination,but has no significant effect on the activation of microglia and astrocytes;4.In ex vivo culture OPC experiments,the results showed that clomifene treatment could significantly increase the number of MBP-positive cells,indicating that it had the effect of promoting the differentiation of OPC into OL.we also culture OPCs from GPR30 knockout mice,and clomifene treatment showed reduced differentiation efficiency,suggesting that the pro-OPCs differentiation effect of clomifene was partially mediated by GPR30.In summary,selective estrogen receptor modulators represented by clomifene may regulate OPC differentiation and myelination through G protein-coupled estrogen receptor 1(GPER1,also known as GPR30),and the discovery of this class of compounds can provide new potential effective drugs for the treatment of neurological dysfunction caused by myelin dysplasia or demyelinating diseases. |
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