Deciphering the function of CREB in regulatory T cells - regulator for type one versus type two immune-responses?

调节性T(Treg)细胞是预防自身免疫性疾病、维持免疫动态平衡的重要细胞之一。促进Treg细胞分化的潜在机制具有极其重要的治疗意义，因此是一个深入研究的问题。以往的研究表明，转录激活剂CREB通过直接转录机制诱导Treg细胞的生成并促进其维持。与目前的范式相反，我们发现在体内耗尽Foxp3阳性细胞中的CREB可以增强Treg细胞的频率和功能。这还包括诱导转录因子CREM的表达，该转录因子与系统性红斑狼疮(SLE)相关，与CREB具有相同的结合位点。特别是，Foxp3特异性的CREB缺失可诱导Tregs中IL-10、IL-13和ST-2的表达，从而防止实验性转移性结肠炎模型中炎症的发生，同时它还诱导了具有高IgE水平的活化B细胞的自发发生。因此，我们假设CREB描述了未知的Foxp3调节机制，并将从三个特定的目的来揭示CREB对Treg的表达和功能的作用：1.CREB如何调节Treg的表达和功能？2.CREM和CREB的相互作用对Treg细胞的数量和功能是否至关重要？3.CREB在人的Treg中的表达是如何调节的，这是否具有转录和功能上的后果？我们将利用实验性转移性结肠炎模型，详细研究CREB占据哪些CRE基序，以及DNA甲基化是否影响稳态和炎症中调节性T细胞的DNA甲基化。我们将使用OVA诱导的哮喘模型来描述CREB缺陷的Tregs是否倾向于Th2，CREM和CREB的相互作用是否对使用Cre-lox系统的Tregs的IL-10调节至关重要，以及CREB缺陷小鼠的Tregs的高功能是否依赖于IL-10。最后，我们将研究SLE患者、过敏性哮喘患者和炎症性肠病患者以及对照组的CREB/pCREB表达和随后的功能后果。对这些机制的深入了解可能有助于阐明自身免疫性疾病T细胞耐受性下降的原因，也可能为提高自身免疫性疾病中Treg细胞的功能和/或数量提供新的治疗策略。

Regulatory T (Treg) cells are one of the most important players to prevent autoimmune disease and maintain immune homeostasis. The underlying mechanisms, which promote differentiation of Treg cells, are of utmost therapeutic importance and therefore a matter of intensive research. Previous studies describe that the transcriptional activator CREB induces generation and promotes maintenance of Treg cells by direct transcriptional mechanisms. In contrast to the current paradigm, we found that in vivo- depletion of CREB in Foxp3 positive cells enhances Treg cell frequencies and function. This furthermore involved induction of CREM expression, a transcription factor, which is associated with systemic lupus erythematosus (SLE) and shares the same binding site with CREB. In particular, Foxp3 specific deletion of CREB induced IL-10 as well as IL-13 and ST-2 in Tregs, which prevented the occurrence of inflammation in a model of experimental transfer colitis, while it induced spontaneous occurrence of activated B cells with elevated IgE levels. We thus hypothesize that CREB depicts unknown mechanisms of Foxp3 regulation and will unravel the role of CREB for expression and function of Tregs in 3 specific aims: 1. How does CREB regulate expression and function of Tregs?2. Is the interaction of CREM and CREB critical for Treg cell number and function?3. How is the expression of CREB regulated in human Tregs and does this have transcriptional and functional consequences?In detail we will investigate which CRE motifs are occupied by CREB and whether DNA methylation is affected in regulatory T cells in steady state and in inflammation using a model of experimental transfer colitis, we will delineate whether CREB deficient Tregs are Th2 prone using an OVA-induced Asthma model, whether the interaction of CREM and CREB is critical for the IL-10 regulation in Tregs using the CRE-lox system and whether the higher functionality of Tregs in CREB deficient mice is dependent on IL-10. Finally we will investigate Tregs of SLE patients, of patients with allergic asthma and of patients with inflammatory bowel disease as well as controls with regard to CREB/pCREB expression and subsequent functional consequences. A deeper understanding of these mechanisms might help to elucidate the reasons for the breakdown of T cell tolerance in autoimmune diseases but might also provide new treatment strategies to enhance function and/or numbers of Treg cells in autoimmune diseases.