Function Of DNA Oxygenase TET1 In Central Nervous System Myelin Development

Myelin is an important structure of the nervous system,which accelerates nerve conduction velocity and exerts nutritional functions by wrapping neuronal axons.The normal function of the nervous system requires a complete myelin sheath structure.Oligodendrocytes(OLs)are myelin-forming cells in the central nervous system(CNS).They are produced by neural stem cells and undergo processes such as oligodendrocytes(OPCs),immature oligodendrocytes(iOLs),and mature oligodendrocytes(OLs),eventually wrapping axons to form myelin sheath.The myelin sheath structure is easily damaged and difficult to regenerate due to its high demand for metabolic energy and susceptibility to external stimuli.A variety of neurological diseases are accompanied by the occurrence of demyelinating symptoms.Therefore,studying the mechanism of central nervous system myelin development and myelin injury repair has important theoretical and practical significance for exploring the treatment of related diseases.Recent studies have shown that the gene transcription regulation mechanism mediated by DNA methylation plays an important role in the function of central nervous system and the development and regeneration of oligodendrocytes.As a newly discovered DNA demethylation modification enzyme,the role of the TET family of dioxygenase molecules in the central nervous system myelination and remyelination is unclear.There are three members of TET family,among which TET1 is highly expressed in the oligodendrocyte progenitor cell phase.Here we focus on the role of TET1 in the process of oligodendrocyte development and its influence on the nervous system function.Objective: In this study,Tet1 conditional knockout(cKO)mice in oligodendrocyte precursor cells(OPC)were constructed to study the effect of Tet1 on oligodendrocytes and myelin sheath formation at the development stage,and to explore the influence of myelin sheath abnormalities on the nervous function of mice.These studies provide experimental basis for further research on the molecular mechanism.Methods: 1)Immunofluorescence was used to observe the number of oligodendrocytes and the expression of myelin in mouse brain and spinal cord from embryonic stage to adult stage.2)The changes of myelin sheath ultrastructure were observed by transmission electron microscope,and counting the number of myelin nerve fibers and myelin sheath thickness.3)Western blot was used to observe the changes in the expression of myelin related proteins in mice,as well as the changes in the expression of specific markers in neurons and astrocytes.4)The proliferation and differentiation of OPC cells was observed by immunofluorescence staining of oligodendrocytes in primary cell culture.The changes of OPC cell cycle were detected by PI staining and flow cytometry.5)The apoptosis of oligodendrocytes was observed by TUNEL and Olig2.6)The electrophysiological methods were used to record the changes of the combined action potential(CAP)of the optic nerve and excitatory postsynaptic potential(both sEPSC and mEPSC)of brain.7)We detected the changes in motor coordination function,anxiety and depression,and learning and memory ability of mice by a series of behavioral methods.Results: 1)The number of oligodendrocytes in the brain of Tet1 cKO mice was reduced after the successful construction of Tet1 cKO mice.2)Tet1 knockout reduced the degree of myelination in the early stage of development,and spontaneous recovery to normal in adult mice.3)Lack of Tet1 did not affect the apoptosis of oligodendrocytes.However,the number of proliferationing OPCs increased,the number of differentiation decreased.And the cell cycle was disturbed.4)Tet1 knockout nither affected the number of other nerve cells or changed the cell fate of OPCs.5)The CAP conduction amplitude and frequency of Tet1 cKO mice decreased,and the synaptic transmission was abnormal.6)The Tet1 cKO mice showed decreased motor coordination ability,anti-anxiety-like behaviors,and impaired spatial memory.Conclusion: The absence of TET1 in oligodendrocytes leads to delayed differentiation and myelin sheath formation during the development stage,which in turn affects the normal functioning of the nervous system.This study provides an important theoretical basis for the design of therapeutic targets for related neurological diseases in the future.