Control of Treg Homeostasis and Function by the Lipid Phosphatase PTEN

描述（由申请人提供）：我们的实验室对移植和自身免疫中的免疫耐受性有着长期的兴趣，特别关注调节性T细胞（T细胞）。人类和小鼠中的主要TcB群体由X连锁转录因子Foxp 3的表达定义。虽然这些细胞是正常免疫稳态所需的，但越来越多的数据表明这种细胞谱系可能是不稳定的（例如，例如由于IL-2、TCR和CD 28刺激不足，或由于暴露于炎性细胞因子），这意味着TcR可以回复/转化为效应T细胞，从而导致对自身或移植的同种异体移植物的耐受性丧失。 控制淋巴细胞谱系特化和反应性的关键途径之一是磷酸肌醇3-激酶（PI 3 K）途径，其可以通过多种表面受体（最显著地包括CD 28和IL-2 R）活化。虽然该途径对于常规T细胞应答是必不可少的，但它在T细胞中的功能可能有限（如果有的话）。事实上，PI 3 K通路的过度激活显著抑制Treg发育，而STAT 5通路也通过IL-2 R激活，强烈促进Treg发育。T细胞中PI 3 K活性的主要调节剂是脂质磷酸酶PTEN（10号染色体上的磷酸酶和张力蛋白同源物）。该提案的目标是确定TcB中的PTEN如何控制Treg稳态，PI 3 K和STAT 5信号的整合，以及PI 3 K通路的药物靶向是否可以稳定TcB。为了实现这一点，我们通过用Foxp 3-YFP-Cre敲入或BAC转基因动物培育具有PTENfl/fl等位基因的小鼠以产生PTEN-Treg小鼠，来产生在TcB中特异性缺失PTEN的小鼠。令人惊讶的是，尽管这些小鼠具有升高的TcB数量，但这些细胞中的高比例是CD 25-和CD 62 Llo，并且动物发展为严重的多克隆淋巴组织增生性病症。这使我们提出了一个假设，即由于细胞因子受体表达减少、迁移改变和调控能力明显丧失，PTEN缺失破坏了Treg体内平衡。这项研究的目的是确定TGFAP中的PTEN如何控制Treg稳态，PI 3 K和STAT 5信号的整合，以及PI 3 K通路的药物靶向是否可以稳定TGFAP。为此，我们有两个目标。 在目标#1中，采用具有Treg特异性缺失的PTEN的Treg命运作图小鼠，我们将检查在稳态条件下和在自身免疫性疾病模型中，PTEN缺失对天然和适应性Treg稳定性和功能的影响。在目标#2中，我们将剖析CD 25、PI 3 K和STAT 5下游的信号，以确定哪些信号负责我们观察到的Treg表型和功能变化。我们的研究将对Treg信号通路产生新的见解，并为增强免疫耐受提供潜在的治疗策略。

DESCRIPTION (provided by applicant): Our laboratories have a long-standing interest in immune tolerance in transplantation and autoimmunity, with a particular focus on regulatory T cells (Tregs). The primary population of Tregs in humans and mice is defined by expression of the X-linked transcription factor Foxp3. While these cells are required for normal immune homeostasis increasing data suggests that this lineage of cells may be unstable (e.g., as a result for example of inadequate IL-2, TCR and CD28 stimulation, or due to exposure to inflammatory cytokines), meaning that Tregs can revert/convert to effector T cells and thus contribute to loss of tolerance to self or to transplanted allografts. One of the key pathways controlling lymphocyte lineage specification and responsiveness is the phosphoinositide 3-kinase (PI3K) pathway, which can be activated via multiple surface receptors, including, most prominently, CD28 and the IL-2R. While this pathway is essential for conventional T cell responses, it may have limited, if any, function in Tregs. In fact, over activation of the PI3K pathway dramatically inhibits Treg development, while the STAT5 pathway, which is also activated through the IL-2R, strongly promotes Tregs. The primary regulator of PI3K activity in T cells is the lipid phosphatase PTEN (phosphatase and tensin homolog on chromosome 10). The goal of this proposal is to determine how PTEN in Tregs controls Treg homeostasis, the integration of PI3K and STAT5 signals, and whether drug targeting of the PI3K pathway can stabilize Tregs. To accomplish this, we created mice with PTEN deleted specifically in Tregs by breeding mice with a PTENfl/fl allele with Foxp3-YFP-Cre knock-in or BAC transgenic animals to generate PTEN-¿Treg mice. Surprisingly, although these mice have elevated numbers of Tregs, a high proportion of those cells are CD25- and CD62Llo, and the animals develop a severe polyclonal lymphoproliferative disorder. This has led us to formulate the hypothesis that PTEN loss disrupts Treg homeostasis due to reduced cytokine receptor expression, altered migration and apparent loss of regulatory capacity. The goal of this grant is to determine how PTEN in Tregs controls Treg homeostasis, the integration of PI3K and STAT5 signals, and whether drug targeting of the PI3K pathway can stabilize Tregs. To do so, we have two aims. In Aim #1, employing Treg fate mapping mice with Treg specific deletion of PTEN, we will examine the effects of loss of PTEN on natural and adaptive Treg stability and function, both under homeostatic conditions and in a model autoimmune disease. In Aim #2, we will dissect the signals downstream of CD25, PI3K and STAT5 to determine which are responsible for the Treg phenotypic and functional changes we have observed. Our studies will yield new insights into Treg signaling pathways and provide potential therapeutic strategies to enhance immune tolerance.