Control of Treg Homeostasis and Function by the Lipid Phosphatase PTEN

描述(申请人提供)：我们的实验室长期以来一直对移植和自身免疫中的免疫耐受感兴趣，特别关注调节性T细胞(Tregs)。Tregs在人类和小鼠中的初级种群是由X连锁转录因子Foxp3的表达决定的。虽然这些细胞是正常免疫稳态所必需的，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，由于IL-2、TCR和CD28刺激不足，或由于暴露于炎性细胞因子)，这意味着Treg可以回复/转换为效应性T细胞，从而导致对自身或移植的耐受性丧失。控制淋巴细胞谱系特异性和反应性的关键途径之一是磷脂酰肌醇3-激酶(PI3K)途径，该途径可通过多种表面受体激活，其中最突出的是CD28和IL-2R。虽然这一途径对传统的T细胞反应是必不可少的，但它在Treg中的功能可能有限(如果有的话)。事实上，PI3K通路的过度激活极大地抑制了Treg的发育，而同样通过IL-2R激活的STAT5通路则强烈促进Treg的发育。T细胞中PI3K活性的主要调节因子是脂肪磷酸酶PTEN(10号染色体上的磷酸酶和张力蛋白同源物)。这项研究的目的是确定Tregs中的PTEN如何控制Treg的稳态，PI3K和STAT5信号的整合，以及PI3K通路的药物靶向是否可以稳定Treg。为了做到这一点，我们通过培育带有PTENf1/fl等位基因的带有Foxp3-YFP-Cre敲入的小鼠或BAC转基因动物来产生PTEN-Treg小鼠，从而创建了在Tregs中特异缺失的PTEN小鼠。令人惊讶的是，尽管这些小鼠的Treg细胞数量增加，但这些细胞中有很高比例是CD25-和CD62Llo，并且这些动物患上了严重的多克隆淋巴增生性疾病。这导致我们提出了一种假设，即PTEN的缺失破坏了Treg的动态平衡，这是由于细胞因子受体表达减少、迁移改变和明显的调节能力丧失所致。这项资助的目标是确定Tregs中的PTEN如何控制Treg动态平衡，PI3K和STAT5信号的整合，以及PI3K途径的药物靶向是否可以稳定Treg。为此，我们有两个目标。在目标1中，利用带有PTEN的Treg特异性缺失的Treg命运图谱，我们将研究PTEN的缺失对自然和适应性Treg的稳定性和功能的影响，无论是在体内平衡条件下还是在自身免疫性疾病的模型中。在目标2中，我们将剖析CD25、PI3K和STAT5下游的信号，以确定哪些信号是我们观察到的Treg表型和功能变化的原因。我们的研究将对Treg信号通路产生新的见解，并提供潜在的治疗策略来增强免疫耐受性。

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.