Mechanism of Integrative Metabolic Regulation by Iron and Hypoxia

项目总结 胰岛素抵抗、肝脏葡萄糖分泌过多和胰岛素分泌受损是其特征。 2型糖尿病(T2 DM)的发病率和组织铁水平对这三种疾病都有显著影响。在老鼠和人类身上，我们 研究表明，高铁会损害胰岛素的分泌，并下调瘦素和脂联素的水平。我们的预赛 数据进一步表明，铁的这些影响是依赖于燃料的，这种差异很大程度上是基于较高的 铁的水平支持更高水平的脂肪氧化。我们对铁的这些效应所做的机械研究揭示了 许多途径的参与，包括转录调控(特别是通过CREB、FoxO1和 α)和营养/代谢物信号转导(AMPK、sirtuins和mTOR)。因此，铁的影响是复杂的， 多效性，不能用单一的线性信号转导途径来解释。 最近，我们关于铁调节瘦素分泌的机制的研究揭示了一个统一的 这些多效性效应的概念：高组织铁下调营养和氧化还原的中央整合因子 O-连接N-乙酰氨基葡萄糖(O-GlcNAc)途径。这一途径导致O-GlcNAc 修饰大多数转录因子和许多调节新陈代谢的酶。激活 途径通常是细胞营养通量的直接读数，我们已经证明它足以诱导 总而言之，胰岛素敏感性、胰岛素分泌和肝脏葡萄糖代谢的变化 T2 DM。同时对营养和氧化应激作出反应的第二条途径是低氧感知。 路径。与O-GlcNAc途径一样，它在两个代谢谱的两端发挥作用--低糖和低糖 氧气以及高糖和氧化应激。这些途径相互调节，并在 测定肝脏葡萄糖产量、胰岛素敏感性和胰岛素分泌。重要的是，O- GlcNAc和低氧途径不仅与病理性铁超载和低氧有关，而且还调节 正常生理中的代谢，跨越非常广泛的“正常”铁的范围，以及在海平面上的个体。 总而言之，O-GlcNAc和低氧途径共同作用来感知两种物质的可用性或过剩 氧化代谢所需的基本元素，铁和氧。基于以上原因，我们出版了 工作和初步数据，因此我们假设这两条通路将这些信号整合到 调节参与T2 DM发病机制的几个代谢途径。O-GlcNAc的调制 铁途径影响许多信号转导途径，导致广泛的基础改变 在全球范围内改变燃料利用的新陈代谢，以对缺铁或过多做出适应性反应。在……里面 与之平行的是，缺氧途径基于氧气的可用性或过量的氧化剂来执行平行的功能 压力。两条通路之间的串扰可以放大它们的影响，导致整合和“微调” 基于营养可获得性、铁和氧水平以及氧化应激的新陈代谢。为了测试这些 根据假设，我们提出了以下具体目标： 1.确定O-GlcNAc介导铁调节瘦素分泌的机制。 2.明确膳食铁在常氧和低氧条件下对小鼠β-细胞功能的影响。 3.确定铁对O-GlcNAc蛋白修饰的作用机制。 这些研究的意义和影响是，他们的目标是定义理想的组织铁水平， 可能比人类的正常范围窄，而且组织铁很容易被饮食或血液改变。 捐款。理想的铁水平也可能因氧气状况而有所不同(即居住环境不同的人 海拔)，最终允许对这些人进行个性化的糖尿病治疗。最后，这些研究将 还要确定治疗糖尿病的新途径：例如，HIF羟基酶可以在药理上 被操纵，而且在为O-GlcNAc途径这样做方面也取得了进展。 好了！

PROJECT SUMMARY Insulin resistance, excess hepatic glucose production, and impaired insulin secretion are the hallmarks of type 2 diabetes mellitus (T2DM), and tissue iron levels significantly affect all three. In mice and humans, we have shown that high iron impairs insulin secretion and down regulates leptin and adiponectin. Our preliminary data show further that these effects of iron are fuel-dependent, with much of this difference based on higher iron levels supporting higher levels of fat oxidation. Our mechanistic work on these effects of iron has revealed the involvement of numerous pathways, including transcriptional regulation (notably by CREB, FoxO1, and PGC1α) and nutrient/metabolite signaling (AMPK, sirtuins, and mTOR). Thus, the effects of iron are complex, pleiotropic, and cannot be explained by invoking a single linear signal transduction pathway. Recently our work on the mechanism by which iron regulates leptin secretion has revealed a unifying concept for these pleiotropic effects: High tissue iron down-regulates a central integrator of nutrient and redox status, the O-linked N-acetyl glucosamine (O-GlcNAc) pathway. This pathway results in the O-GlcNAc modification of most transcription factors and numerous enzymes that regulate metabolism. Activation of the pathway is often a direct readout of cellular nutrient fluxes, and we have shown it to be sufficient to induce changes in insulin sensitivity, insulin secretion, and hepatic glucose metabolism in ways that recapitulate T2DM. A second pathway that responds to both nutrient and oxidative stresses is the hypoxia-sensing pathway. Like the O-GlcNAc pathway, it functions at both ends of two metabolic spectra—low glucose and low oxygen as well as high glucose and oxidative stress. The pathways regulate one another and interact in determining hepatic glucose production, insulin sensitivity, and insulin secretion. Importantly, both the O- GlcNAc and hypoxia pathways are not only relevant to pathologic iron overload and hypoxia, but regulate metabolism in normal physiology, across the very broad range of “normal” iron and in individuals at sea level. In sum, the O-GlcNAc and hypoxia pathways cooperate to sense the availability or excess of two essential elements required for oxidative metabolism, iron and oxygen. Based on the above, our published work, and Preliminary Data, we therefore hypothesize that these two pathways integrate these signals to regulate several metabolic pathways involved in the pathogenesis of T2DM. Modulation of the O-GlcNAc pathway by iron affects numerous signal transduction pathways, leading to broad-based changes in metabolism that globally alter fuel utilization to confer adaptive responses to either a lack or excess of iron. In parallel, the hypoxia pathway performs a parallel function based on oxygen availability or excess oxidant stress. Crosstalk between the two pathways can amplify their effects, resulting in integration and a “fine-tuning” of metabolism based on nutrient availability, iron and oxygen levels, and oxidant stress. To test these hypotheses, we propose the following Specific Aims: 1. Determine the mechanism by which O-GlcNAc mediates the regulation of leptin secretion by iron. 2. Define the effects of dietary iron on β-cell function in mice, in normoxia and hypoxia. 3. Determine the mechanism for the effects of iron on O-GlcNAc protein modification. The significance and impact of these studies is that they aim to define ideal levels of tissue iron that may be narrower than the broad “normal” range in humans, and tissue iron is easily modifiable by diet or blood donation. Ideal iron levels may also differ based on oxygen status (i.e. in those with different habitation altitudes), ultimately allowing personalized therapy for diabetes in those individuals. Finally, the studies will also identify new pathways to treat diabetes: For example, the HIF hydroxylases can be pharmacologically manipulated, and advances are also being made in doing so for the O-GlcNAc pathway. !