MBD3调控造血干细胞自我更新和发育分化的表观遗传机制研究

MBD3 is a subunit of NuRD complex which is indispensable for many physiological processes. NuRD complex functions as chromatin remodeling complex, and contains two major enzymes. One is gene regulation enzyme, histone deacetylase HDAC1 or HDAC2. Another one is histone demethylase LSD1.MBD3 is a methy-CpG binding protein which is essential for the function of NuRD complex. The deletion of MBD3 leads to the suppression of ESC differentiation by activation of stem genes and inhibitory of differentiation genes. In our previous study, we found NuRD is required for iPSC formation. Another report showed that the deficiency of MBD3 increases the efficiency of iPSC formation, indicating that MBD3 is important for the expression of differentiation genes and inhibition of stem genes. However, the function of MBD3 in hematopoietic stem cells (HSC) is unknown, and the mechanism of MBD3 regulating HSC development and differentiation has not been reported. During our study, we found that the expression of MBD3 is low in HSCs, but remarkably increased in CLPs and CMPs. The function and differentiation of HSC cells with silenced MBD3 was impaired. In this project, we are going to verify the function of MBD3 in HSCs by using MBD3 conditional knockout mice, and finding out the mechanism of MBD3 regulating HSC development and differentiation.

MBD3是NuRD重塑复合物的重要组分，该重塑复合物在多种重要生命活动调控中作用至关重要。MBD3缺失导致早期胚胎死亡，并显著提高iPS细胞的重编程效率。我们前期发现NuRD重塑复合物对于iPS形成亦具有调控作用，表明MBD3在细胞重编程过程中发挥重要作用。但MBD3对于造血干细胞（HSC）的调控尚未见报道。我们近期发现MBD3在HSC中的表达量低，在CLP和CMP细胞中表达显著升高。MBD3敲低表达的HSC细胞重建血液系统的功能和诱导血液细胞分化受到影响，血液谱系分化基因表达受到抑制。在此基础上，本课题将利用MBD3条件基因敲除小鼠，探究MBD3在造血干细胞自我更新和发育分化的作用及其表观遗传调控机制，阐明MBD3调控造血干细胞发育分化的分子基础。

MBD3是NuRD染色质重塑复合物的重要组成成分，NuRD复合物和MBD3参与了多种重要的生理和病理过程。我们在前期研究中发现NuRD复合物参与了体细胞重编程过程，并且进一步发现MBD3在造血干细胞中低表达，在下游分化的细胞CLP和CMP中表达量升高，并且敲低MBD3以后，造血干细胞向下游分化能力受到影响。我们在项目中制备了造血干细胞特异敲除MBD3的小鼠，MBD3缺失以后小鼠出现贫血的症状，造血干细胞增多，外周血液细胞明显减少，造血干细胞分化和重建能力降低，说明MBD3对造血干细胞的分化有着重要的调控作用。进一步的机制研究发现，在造血干细胞分化过程中，MBD3能够与结合到Irf2基因的启动子区域，抑制Irf2基因表达，从而关闭了干性基因，启动了分化基因表达。我们在研究中还发现环状非编码RNA-circIrf2表达受到MBD3蛋白调控，进一步调控了下游分化基因的开放，相关研究成果正在Cell Stem Cell杂志修稿中。我们在研究造血干细胞调控过程中还发现环状非编码RNA对于造血干细胞的自我更新和分化有着重要调控作用。在造血干细胞中高表达的环状RNA-ciacGAS能够结合细胞核内的cGAS避免造血干细胞由于cGAS活化引起的耗竭，相关研究成果发表在Immunity（2018）杂志上。本项目支持的研究还发表在Nat Immunol，J Exp Med，Nat Commun等杂志上面。