Role of apoE in HDL-mediated enhanced survival of human regulatory T-cells

摘要 调节性T细胞(Tregs)介导抗炎功能，并与自身最相关 免疫和自身免疫性疾病。然而，考虑到亚临床或持续性低水平的潜在作用 炎症在代谢和心血管疾病中的作用，最近人们的注意力集中在 Tregs在控制这些病理过程中的促炎环境。特雷格的一个子集，效应器内存 树人是最压抑的，但也是最短暂的。我们做了一个惊人的观察- 密度脂蛋白(HDL)，而不是其他脂蛋白，显著提高了Treg的存活率。这些发现提供了 解释了我们发现高密度脂蛋白胆固醇和Treg丰度之间的正相关关系。我们的 初步数据显示，高密度脂蛋白优先结合并被Treg记忆亚集内化，特别是通过 效应器记忆树，通过减少效应器caspase的激活来促进它们的存活。从机械上讲，我们的 新的数据还表明，这种高密度脂蛋白促进生存的作用可能是通过激活AKT信号通路来实现的， 这会促进从头合成脂肪酸，降低线粒体的氧化应激。由于高密度脂蛋白 是一类具有复杂脂质和蛋白质混合物的相关颗粒，我们开始探索哪种高密度脂蛋白 亚种或成分可刺激Treg存活。我们发现这种促进生存的作用是通过 高密度脂蛋白成分，特别是相对次要的高密度脂蛋白成分，载脂蛋白(APO)E， 和/或共存在于含APOE的高密度脂蛋白上的其他蛋白质。相比之下，主要的高密度脂蛋白支架蛋白来自 载脂蛋白A家族并没有发挥主要作用。我们的主要假设是富含载脂蛋白的高密度脂蛋白 用Tregs来触发限制caspase依赖的细胞凋亡的通路。目标1将识别细胞内 高密度脂蛋白介导的Treg存活的信号通路，特别是参与高密度脂蛋白结合的受体(S) 记忆树的内化以及高密度脂蛋白促进Treg存活的机制。我们还将 确定高密度脂蛋白对Treg抑制的影响。目标2将确定特定的高密度脂蛋白亚种和蛋白质 促进Treg存活的成分。我们还将进行缺失和定点突变 识别载脂蛋白E关键区域(S)的实验，为探索能够模拟的合成肽提供信息 APOE对记忆树的促存活作用。目标3将评估富含载脂蛋白的高密度脂蛋白在Treg中的参与 活体内存活。我们将利用辛辛那提儿童糖尿病和肥胖中心队列，探索 Treg亚群的绝对数及其功能特征与高密度脂蛋白亚种之间的关系， 减肥手术前后。手术前后采集的高密度脂蛋白亚类的能力 促进记忆和效应器记忆Treg存活将被研究。通过识别特定的细胞通路和 负责Treg生存效应的特定脂蛋白物种，我们将开辟潜在的新途径 旨在调节自身免疫和慢性代谢宿主Treg功能的治疗干预 疾病。

Abstract Regulatory T cells (Tregs) mediate anti-inflammatory functions and have been most associated with self- immunity and autoimmune diseases. However, given the underlying role of subclinical or persistent low-level inflammation in metabolic and cardiovascular diseases, attention has recently focused on the potential role of Tregs in controlling the proinflammatory milieu in these pathologies. A subset of Tregs, the effector memory Tregs, are the most suppressive, but are also the most transient. We made the striking observation that high- density lipoproteins (HDL), but not other lipoproteins, significantly improved Treg survival. These findings offer an explanation for the positive correlation we found between HDL cholesterol and Treg abundance. Our preliminary data show that HDL preferentially bind and are internalized by Treg memory subsets, particularly by effector memory Tregs, promoting their survival by reducing effector caspase activation. Mechanistically, our new data also suggest that this HDL pro-survival effect may occur via activation of the AKT signaling pathway, which results in enhanced de novo fatty acid synthesis and reduced mitochondrial oxidative stress. Since HDL is a family of related particles with complex mixtures of lipids and proteins, we started exploring which HDL subspecies or components stimulate Treg survival. We found that the pro-survival effect was mediated by the HDL protein component, and particularly the relatively minor HDL protein constituent, apolipoprotein (APO)E, and/or other proteins that co-reside on APOE-containing HDL. In contrast, the major HDL scaffold proteins from the APOA family did not play a major role. Our overarching hypothesis is that APOE-rich HDL specifically interact with Tregs to trigger pathways that limit caspase-dependent apoptosis. Aim 1 will identify the intracellular signaling pathways involved in HDL-mediated survival of Treg, notably the receptor(s) involved in HDL binding/ internalization by memory Tregs and the mechanisms by which HDL promote Treg survival. We will also determine the effect of HDL on Treg suppression. Aim 2 will identify specific HDL subspecies and protein components that promote Treg survival. We will also perform deletional and site-directed mutagenesis experiments to identify the critical region(s) of APOE, to inform explorations of synthetic peptides that can mimic APOE’s pro-survival effects on memory Tregs. Aim 3 will assess the involvement of APOE-rich HDL in Treg survival in vivo. We will leverage the Cincinnati Pediatric Diabetes and Obesity Center cohort and probe the association between absolute numbers of Treg subsets, their functional characteristics, and HDL subspecies, before and after weight reduction surgery. The ability of HDL subspecies collected before and after surgery to promote memory and effector memory Treg survival will be studied. By identifying specific cellular pathways and specific lipoprotein species responsible for the Treg survival effects, we will open new avenues for potential therapeutic intervention aimed at modulating Treg function in a host of auto-immune and chronic metabolic diseases.