Department of Immunology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
Pathobiology. 2012;79(4):209-18. doi: 10.1159/000337290. Epub 2012 Apr 16.
A functional methyl group donor is essential for the epigenetic regulation of all biological events due to the importance of DNA methylation and histone methylation as an epigenetic marker. However, the epigenetic alterations in the immune system due to methyl donor deficiency are not well known. In this study, we tried to address this question by studying the lymphocyte development and DNA methylation changes caused by a methyl-deficient diet (MDD). We fed one group of C57BL/6J mice with a methyl-sufficient diet (MSD) and the other group with an MDD for 5 months. Flow cytometry analyses of their immune systems showed a decrease in B220+ IgM+ (immature B) cells and an increase in B220+ IgM- (pro/pre-B) cells in the bone marrow of mice fed an MDD. By means of an in vitro OP9 coculture system, we recognized that this B220+ IgM- cell fraction from the MDD has an intrinsic developmental defect. When we quantitatively measured the mRNA expression levels of transcription factors and recombination machinery related to B cell development in the B220+ IgM- cell fraction of their bone marrow, we found that ADA, EBF1, DNTT and Pax5 mRNA expression levels were significantly downregulated in mice fed with an MDD. In addition, there was a drastic decrease in histone methylation profile H3K4me3 in the Pax5 and EBF1 promoters in these B220+ IgM- B cells. However, CpG-DNA methylation profiles had not changed and this revealed that these two promoters are demethylated even under an MSD condition. We also found changed expression levels of the Polycomb group genes (mel18, bmi1, Pc1, Pc2, Ring1A, Ring1B, Ph1) on semi-quantitative RT-PCR. These results indicate that under an MDD condition, early B cell development in bone marrow is easily affected by epigenetic alterations.
由于 DNA 甲基化和组蛋白甲基化作为表观遗传标记的重要性，一个功能性的甲基供体对于所有生物事件的表观遗传调控都是必不可少的。然而，由于甲基供体缺乏导致的免疫系统的表观遗传改变还不是很清楚。在这项研究中，我们试图通过研究由于甲基缺乏饮食（MDD）引起的淋巴细胞发育和 DNA 甲基化变化来解决这个问题。我们用甲基充足饮食（MSD）喂养一组 C57BL/6J 小鼠，用 MDD 喂养另一组 5 个月。对其免疫系统的流式细胞术分析表明，MDD 喂养的小鼠骨髓中 B220+ IgM+（未成熟 B）细胞减少，B220+ IgM-（前/祖 B）细胞增加。通过体外 OP9 共培养系统，我们发现 MDD 来源的 B220+ IgM-细胞亚群存在内在的发育缺陷。当我们定量测量其骨髓中 B220+ IgM-细胞亚群中与 B 细胞发育相关的转录因子和重组机制的 mRNA 表达水平时，我们发现 ADA、EBF1、DNTT 和 Pax5 的 mRNA 表达水平在 MDD 喂养的小鼠中显著下调。此外，这些 B220+ IgM- B 细胞中 Pax5 和 EBF1 启动子的组蛋白 H3K4me3 甲基化谱也明显减少。然而，CpG-DNA 甲基化谱没有改变，这表明这两个启动子即使在 MSD 条件下也是去甲基化的。我们还发现多梳组基因（mel18、bmi1、Pc1、Pc2、Ring1A、Ring1B、Ph1）的表达水平在半定量 RT-PCR 上发生了变化。这些结果表明，在 MDD 条件下，骨髓中早期 B 细胞发育容易受到表观遗传改变的影响。
