The chromatin-modifying enzyme Ezh2 is critical for the maintenance of regulatory T cell identity after activation

Regulatory T cells (Tregs) are essential for maintaining proper immune homeostasis. Extracellular signals (e.g. TCR, CD28, IL-2R) are necessary for the generation and maintenance of Tregs, but how these signals are integrated to control the gene expression patterns of Tregs is less clear. Here we show that the epigenetic regulator, Ezh2, was induced by CD28 costimulation and Ezh2 activity was elevated in Tregs as compared to conventional CD4+ T cells. Deletion of Ezh2 in mouse Tregs led to a progressive autoimmune disease because Tregs were compromised after activation, losing proper control of essential Treg lineage genes and adopting a gene expression pattern similar to Foxp3-deficient 'Tregs.' Lineage-tracing of Ezh2-deficient Tregs in vivo confirmed that the cells were destabilized selectively in activated Treg populations, which led to a significant loss of Tregs in non-lymphoid tissues. These studies reveal an essential role for Ezh2 in the maintenance of Treg "identity" during cellular activation and differentiation. RNAseq of sorted populations of CD62Lhi or CD62Llo Tregs for both Ezh2-HET (Foxp3YFP-Cre/Foxp3WT;Ezh2fl/+ female mice) and Ezh2-KO (Foxp3YFP-Cre/Foxp3WT;Ezh2fl/fl female mice) were generated, in triplicate for each condition, using Illumina HiSeq 2500 single-end 50bp sequencing platform.调节性T细胞（Regulatory T cells，Tregs）是维持机体正常免疫稳态（immune homeostasis）的关键细胞群。细胞外信号（如T细胞受体（T cell receptor，TCR）、CD28、白细胞介素-2受体（Interleukin-2 receptor，IL-2R））是Tregs产生与维持的必要条件，但目前对于这些信号如何协同调控Tregs的基因表达谱仍有待阐明。本研究发现，表观遗传调控因子Ezh2可经CD28共刺激诱导上调，且Tregs中的Ezh2活性显著高于常规CD4阳性T细胞（CD4+ T cells）。在小鼠Tregs中敲除Ezh2会诱发进行性自身免疫病，其机制在于活化后的Tregs功能受损，无法正常维持核心谱系基因的表达，并获得与Foxp3缺陷型"Tregs"相似的转录组特征。对Ezh2缺陷型Tregs的体内谱系示踪实验证实，这些细胞仅在活化的Treg群体中发生稳定性丧失，进而导致非淋巴组织中的Tregs大量流失。本研究揭示了Ezh2在细胞活化与分化过程中维持Treg"身份特性"的核心作用。本研究针对分选得到的CD62L高表达（CD62Lhi）或低表达（CD62Llo）Tregs群体开展了RNA测序（RNA sequencing，RNA-seq），实验对象涵盖Ezh2杂合敲除（Ezh2-HET，即Foxp3YFP-Cre/Foxp3WT;Ezh2fl/+雌性小鼠）与Ezh2基因敲除（Ezh2-KO，即Foxp3YFP-Cre/Foxp3WT;Ezh2fl/fl雌性小鼠）两组，每组设置3次生物学重复，测序采用Illumina HiSeq 2500单端50bp测序平台。