Hepatic Aryl Hydrocarbon Receptor Regulation of Obesity: Mechanisms of Action

项目总结/摘要 芳香烃受体（Aryl Hydrocarbon Receptor，AhR）是真核生物中Per-ARNT-Sim（PAS）结构域蛋白的一员 调节对多种化学污染物的适应性和毒性反应的家族，包括多环 芳烃和多氯二恶英，最显著的是2，3，7，8-四氯二苯并对二恶英（TCDD）。 我们最近发现，雌性，而不是雄性肝脏特异性AhR条件性敲除小鼠， 高脂肪饮食诱导的肥胖症，并表现出改善的代谢稳态。两性异形 表型的增加归因于雌性中成纤维细胞生长因子21（FGF 21）的肝表达增加。 FGF 21是一种循环肝细胞因子，影响碳水化合物和脂质代谢，并诱导产热 在白色和棕色脂肪沉积物中，通过将线粒体呼吸与电子传递链解偶联。 这些特性促使人们研究开发基于FGF 21的治疗方法，以对抗 代谢紊乱和肥胖症，但迄今为止收效甚微。因此，了解AhR活性如何 对照Fgf 21表达可能为临床干预的发展指明新的策略或靶点。 肝脏Fgf 21表达也受性类固醇控制，并受昼夜节律影响。的 后一个观察值得注意，因为AhR及其伴侣蛋白AhR核转位蛋白 （ARNT），属于与几种昼夜节律（时钟）蛋白相同的PAS蛋白家族，包括 脑和肌肉ARNT样1（BMAL 1）。肝脏AhR表达呈现24小时周期性， BMAL 1振荡，提示这些蛋白质的共同调节。此外，ARNT还分享了大量 与BMAL 1的序列相似性，并且已经报道了AhR-BMAL 1相互作用，这意味着相互作用 昼夜节律和AhR信号之间是相互的和重要的。这个问题的核心前提是 应用是，肝Fgf 21表达代表了一种联系，其中AhR信号传导和分子事件 潜在的两性异形和昼夜节律，结合。我们假设一个全面的 需要评估这些生理上不同的信号传导过程是如何整合的， 了解AhR调节Fgf 21表达及其对饮食诱导的肥胖的影响。为了验证这个假设， 我们提出了实验策略，保留生理背景和基因组环境。具体目标1 我们将从AhR、ARNT和BMAL 1活性的角度研究Fgf 21启动子的功能， 昼夜节律的影响。Specific Aim 2将使用单细胞转录组学来识别肝脏中的昼夜变化 由于AhR、ARNT和BMAL 1活性导致的基因表达。具体目标3将询问性二态性 fgf 21表达与雌激素活性的关系。具体目标构成了独特而又综合的努力 为了机械地理解AhR如何调节肝脏中Fgf 21的表达，在实验条件下， 保持负责两性异形和昼夜节律的生理过程的条件 在保持正常染色质结构的天然基因组环境的背景下，

PROJECT SUMMARY/ABSTRACT The Aryl Hydrocarbon Receptor (AhR) is a member of the eukaryotic Per-ARNT-Sim (PAS) domain protein family that regulates adaptive and toxic responses to a variety of chemical pollutants, including polycyclic aromatic hydrocarbons and polychlorinated dioxins, most notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We recently showed that female, but not male liver-specific AhR conditional knockout mice are protected from high fat diet-induced obesity and exhibited improved metabolic homeostasis. The sexually dimorphic phenotype was attributed to increased hepatic expression of fibroblast growth factor 21 (FGF21) in females. FGF21 is a circulating hepatokine that affects carbohydrate and lipid metabolism, and induces thermogenesis in white and brown fat deposits by uncoupling mitochondrial respiration from the electron transport chain. These properties have motivated research into the development of FGF21-based therapeutics to combat metabolic disorders and obesity, but with little success to date. Hence, understanding how AhR activity controls Fgf21 expression may point to novel strategies or targets for the development of clinical interventions. Hepatic Fgf21 expression is also under the control of sex steroids and is subject to circadian rhythms. The latter observation is of note because both the AhR and its partner protein, the AhR Nuclear Translocator (ARNT), belong to the same PAS protein family as several of the circadian rhythm (clock) proteins, including brain and muscle ARNT-like 1 (BMAL1). Hepatic AhR expression exhibits a 24 h periodicity in phase with BMAL1 oscillations, suggestive of co-regulation of these proteins. Moreover, ARNT shares considerable sequence similarity to BMAL1, and an AhR-BMAL1 interaction has been reported, implying that interactions between circadian rhythmicity and AhR signaling are reciprocal and significant. The central premise of this application is, that hepatic Fgf21 expression represents a nexus where AhR signaling and the molecular events underlying sexual dimorphism and circadian rhythmicity, coalesce. We hypothesize that a comprehensive assessment of how these physiologically disparate signaling processes are integrated is required to fully understand AhR regulated Fgf21 expression, and its impact on diet-induced obesity. To test the hypothesis, we propose experimental strategies that preserve the physiological context and genomic milieu. Specific Aim 1 will examine Fgf21 promoter functionality from the standpoint of AhR, ARNT, and BMAL1 activity as a function of circadian rhythmicity. Specific Aim 2 will use single-cell transcriptomics to identify diurnal changes in liver gene expression due to AhR, ARNT, and BMAL1 activity. Specific Aim 3 will interrogate sexually dimorphic Fgf21 expression as a function of estrogenicity. The Specific Aims constitute distinct yet integrated endeavors to mechanistically understand how the AhR regulates Fgf21 expression in the liver, under experimental conditions that preserve the physiological processes responsible for the sexual dimorphism and circadian rhythmicity in the context of a native genomic milieu that retains normal chromatin architecture.