Mechanism of Integrative Metabolic Regulation by Iron and Hypoxia

项目摘要 胰岛素抵抗、肝葡萄糖生成过多和胰岛素分泌受损是其标志 2型糖尿病（T2 DM）的发病机制，而组织铁水平对这三种疾病均有显著影响。在小鼠和人类中，我们 已经证明高铁会损害胰岛素分泌并下调瘦素和脂联素。我们的初步 数据进一步表明，铁的这些影响取决于燃料，其中大部分差异是基于较高的 铁水平支持更高水平的脂肪氧化。我们对铁的这些作用的机械研究揭示了 许多途径的参与，包括转录调控（特别是CREB，FoxO 1， PGC 1 α）和营养/代谢物信号（AMPK、sirtuins和mTOR）。因此，铁的作用是复杂的， 多效性，并且不能通过调用单一线性信号转导途径来解释。 最近，我们对铁调节瘦素分泌的机制的研究揭示了一个统一的观点， 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心整合剂 状态，O-连接的N-乙酰葡糖胺（O-GlcNAc）途径。该途径导致O-GlcNAc 大多数转录因子和许多调节代谢的酶的修饰。激活 途径通常是细胞营养通量的直接读出，我们已经证明它足以诱导 胰岛素敏感性、胰岛素分泌和肝脏葡萄糖代谢的变化， 2型糖尿病。对营养和氧化应激都有反应的第二条途径是缺氧感应 通路与O-GlcNAc途径一样，它在两个代谢谱的两端发挥作用-低葡萄糖和低葡萄糖。 氧气以及高葡萄糖和氧化应激。这些通路相互调节，相互作用， 确定肝葡萄糖产生、胰岛素敏感性和胰岛素分泌。重要的是，O- GlcNAc和缺氧通路不仅与病理性铁超载和缺氧有关，而且还调节 在正常生理代谢中，在非常广泛的“正常”铁的范围内，在海平面的个体中。 总之，O-GlcNAc和缺氧途径合作以感知两种糖的可用性或过量。 氧化代谢所需的必需元素，铁和氧。基于上述情况，我们出版的 因此，我们假设这两种途径整合了这些信号， 调节参与T2 DM发病机制的几种代谢途径。O-GlcNAc的调节 铁对多种信号转导途径的影响，导致了广泛的变化， 代谢，在全球范围内改变燃料利用，以赋予适应性反应，无论是缺乏或过量的铁。在 平行地，缺氧途径基于氧可用性或过量氧化剂执行平行功能 应力这两种途径之间的串扰可以放大它们的影响，导致整合和“微调”。 代谢的基础上的营养供应，铁和氧的水平，和氧化应激。测试这些 根据这些假设，我们提出以下具体目标： 1.确定O-GlcNAc介导铁调节瘦素分泌的机制。 2.确定在常氧和缺氧条件下，膳食铁对小鼠β细胞功能的影响。 3.确定铁对O-GlcNAc蛋白修饰的影响机制。 这些研究的意义和影响在于，它们旨在确定组织铁的理想水平， 可能比人类广泛的“正常”范围更窄，并且组织铁很容易通过饮食或血液改变 捐赠。理想的铁水平也可能因氧气状态而异（即在不同居住地的人中 海拔），最终允许对这些个体的糖尿病进行个性化治疗。最后，研究将 我们还发现了治疗糖尿病的新途径：例如，HIF羟化酶可以被抑制， 操纵，并且在对O-GlcNAc途径这样做方面也取得了进展。 !

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. !