5-羟甲基胞嘧啶（5-hmc）表观遗传调控髓鞘相关基因表达和少突胶质细胞分化成熟的分子机制研究

Demyelination in the central nervous system (CNS) is associated with demyelinating disorders and nervous system injury. Oligodendrocyte (OL) is the myelinating cell in the CNS and the failure of OL remyelination impairs rapid propagation of action potentials alone axons and leads to nerve degeneration. Epigenetic modification has been identified as an important player in the regulation of OL differentiation and we have observed the stage-specific appearance of 5-hydroxymethylcytosine (5-hmc) during OL differentiation, which assumes that 5-hmc might be involved in the turning on of certain myelin associated genes and thus the maturation of OL. In this project, we plan to study the loss-of-function and gain-of-function of TET dioxygenase in OL differentiation, which mediates the formation of 5-hmc. To elucidate the mechanism, we will map the genomic distribution of 5-hmc, especially in the promoter region of genes associated with OL differentiation, by performing 5hmc-ChIP-Seq. Using 5-hmc labeled genes as target genes, we will study the possibility of 5-hmc as a marker in DNA cis-regulatory elements for recruiting transcription factors, either repressors or activators onto different target genes that promote or inhibit the differentiation of OL. This study reveals a new epigenetic category in our understanding of OL differentiation and can be applied in further study on the promoting of remyelination in CNS related diseases.

中枢神经系统（CNS）脱髓鞘将大大损伤神经元快速传导神经冲动的功能，是多种神经系统疾病的重要病理特征。研究CNS髓鞘形成细胞-少突胶质细胞（OL）的分化成熟机制对于促进损伤后成功的再髓鞘化非常重要。近年来表观遗传修饰被证明在OL的分化成熟过程中发挥重要作用。我们在预实验中观察到，一种新的表观遗传修饰-DNA羟甲基胞嘧啶（5-hmc）在OL分化起始阶段瞬时升高。因此我们推测5-hmc标记可能调控OL髓鞘基因的表达并发挥促进OL分化的功能。本研究计划从催化5-hmc产生的双氧合酶TET蛋白入手，研究5-hmc对OL分化的作用；进而验证5-hmc作为重要的DNA顺式调控元件标记物，在不同的靶基因位置上，分别募集转录负调控因子和正调控因子与之结合，调控相关靶基因的表达。本研究为全面认识OL分化的调控机制提供了崭新的思路，同时为促进相关神经系统疾病中髓鞘缺失后的再髓鞘化提供了重要的实验依据。

少突胶质细胞的分化与成熟是由转录与表观遗传调控共同相互作用驱动进行的。由Tet氧合酶催化的DNA羟甲基化修饰主要在哺乳动物的胚胎干细胞和神经元中存在，其在少突胶质细胞中的生物功能仍不清楚。在本研究中，我们发现Tet1分子在调节少突前体细胞增殖和成熟过程中发挥重要作用。少突胶质细胞中条件性缺失Tet1的小鼠表现出髓鞘化不足的表型，同时伴有运动协调能力变差、抗焦虑样行为，以及记忆力下降。通过将Tet1条件性敲除小鼠的少突前体细胞做mRNA表达水平与羟甲基化谱的高通量分析，我们发现了一系列羟甲基化水平与mRNA水平同时表达下调的基因。这些基因参与了少突胶质细胞的功能，特别是钙信号调控。这些结果提示，Tet1分子调控的DNA羟甲基化修饰在少突胶质细胞发育过程中发挥重要的作用。