Regulatory T cell lineage stability controlled by Foxp3 CNS2

描述（由申请人提供）：调节性T细胞（Regulatory T cell, Treg）在维持免疫系统稳态、预防自身免疫和免疫病理中起关键作用。Treg功能受损与多种自身免疫性疾病有关。Treg细胞谱系的发育和维持依赖于转录因子Foxp3，因为在小鼠和人类中，功能突变的丧失会导致严重的淋巴细胞增生性疾病。因此，了解控制Foxp3诱导和稳定性的机制可能会导致自身免疫性疾病的新疗法。利用比较基因组学方法，郑博士及其同事在Foxp3位点（保守非编码序列（CNS） 1、2和3）上发现了三个进化上保守的内含子顺式元件。为了阐明这些中枢神经系统区域在Treg谱系体内发育中的作用，他们在小鼠中敲除单个Foxp3中枢神经系统区域。这三种CNS基因敲除小鼠的Treg群体都表现出不同的缺陷，表明这些CNS区域在调节Foxp3表达方面发挥着独特的作用。CNS2的独特之处在于它位于Foxp3位点的唯一CpG岛。CNS2的甲基化状态是Tregs与常规T细胞最显著的表观遗传标记之一。CNS2缺失不影响Foxp3的诱导，但Foxp3表达的稳定性受到损害。Treg谱系稳定性的机制不仅是Treg生物学领域的核心问题，而且在Treg细胞为基础的自身免疫性疾病和器官移植患者的治疗中具有实际意义。CNS2 KO小鼠提供了一个独特的机会来探索Treg谱系在体外和体内稳定性的分子和细胞机制。郑博士的团队将研究CNS2在体内长期维持Treg稳定性中的作用，并确定前Treg是否是自身免疫的主要驱动因素（Aim 1）。此外，他们将研究Treg谱系在炎症下是如何维持稳定性的，炎症是自身免疫发展的关键检查点（Aim 2）。他们将剖析炎症条件下保护Tregs的分子途径，这可能会导致稳定Tregs的药物靶点，以达到治疗目的。此外，郑博士的团队将采用最先进的小鼠遗传工具来研究肠道共生诱导的itreg的谱系稳定性（Aim 3）。由于Treg谱系稳定性与基于Treg细胞的多种免疫疾病治疗的安全性直接相关，郑博士对CNS2的研究将提供对保护Treg身份的重要调控回路的见解。

DESCRIPTION (provided by applicant): Regulatory T cell (Treg) plays a critical role in maintaining immune system homeostasis and preventing autoimmunity and immunopathology. Compromised Treg function is linked to multiple autoimmune diseases. The development and maintenance of Treg cell lineage is dependent on transcription factor Foxp3, as loss of function mutations lead to severe lymphoproliferative disease in mice and humans. Thus, understanding the mechanisms that govern Foxp3 induction and stability may lead to novel therapies for autoimmune disease. Using a comparative genomic approach, Dr. Zheng and colleagues identified three evolutionarily conserved intronic cis-elements at the Foxp3 locus (conserved non-coding sequences (CNS) 1, 2 and 3). To elucidate the role of these CNS regions in Treg lineage development in vivo, they proceeded to knockout individual Foxp3 CNS regions in mice. Each of the three CNS knockout mice showed different defects in their Treg population, indicating the unique roles these CNS regions play in regulating Foxp3 expression. CNS2 is unique as it is located in the only CpG island at the Foxp3 locus. The methylation status of CNS2 is one of the most prominent epigenetic markers distinguishing Tregs from conventional T cells. Induction of Foxp3 is not affected by CNS2 deletion, but stabilization of Foxp3 expression is compromised. The mechanism underlying Treg lineage stability is not only a central question in the Treg biology field, but also has practical implications in Treg cell based therapy for autoimmune disease and organ transplant patients. The CNS2 KO mice provide a unique opportunity to explore the molecular and cellular mechanisms of Treg lineage stability in vitro and in vivo. Dr. Zheng's group will study the role of CNS2 in long-term maintenance of Treg stability in vivo, and determine if ex-Tregs are a major driver of autoimmunity (Aim 1). Additionally, they will address how Treg lineage stability is maintained under inflammation, a critical checkpoint for development of autoimmunity (Aim 2). They will dissect the molecular pathways that are involved in safeguarding Tregs under inflammatory conditions, which can potentially lead to drug targets for stabilizing Tregs for therapeutic purpose. Furthermore, Dr. Zheng's group will employ state-of-the-art mouse genetic tools to study the lineage stability of gut commensal induced iTregs (Aim 3). Since Treg lineage stability is directly related to the safety of Treg cell- based therapy for a variety of immune diseases, Dr. Zheng's study on CNS2 will provide insight on an important regulatory circuitry safeguarding Treg identity.