Role of Mitochondria in the Regulation of Iron metabolism by Alcohol

描述(由申请人提供)：线粒体在铁代谢中起关键作用，并在酒精诱导的肝损伤中发挥作用。酒精会改变线粒体的功能，导致氧化应激。我们已经证明，酒精诱导的氧化应激下调了海普西丁的转录，而不会引起肝脏组织学的变化或甘油三酯的增加。海普西丁是一种在肝脏合成的循环肽。它通过调节肠道和网状内皮铁的运输，在铁的动态平衡中发挥核心作用。因此，酒精处理的动物表现出十二指肠中铁转运蛋白和肝脏中铁储存蛋白铁蛋白的表达增加。酒精还使肝脏中的海普西丁合成对体内铁水平不敏感。值得注意的是，海普西丁通过抑制铁的运输来保护身体免受铁超载的影响。因此，酒精可能会破坏海普西丁的这种保护机制，这可能与酒精性肝病(ALD)有关。值得注意的是，ALD患者和ALD动物模型显示铁超载，但其潜在机制尚不清楚。我们的研究结果表明，肝脏中海普西丁合成的失控可能是ALD铁超载的潜在机制之一。用抗氧化剂处理可消除酒精对海普西丁表达的影响。酒精诱导的氧化应激通过多种途径发挥作用，包括Kupffer细胞的激活、CYP2E1酶的激活和线粒体功能的改变。我们的初步结果排除了库普弗细胞、肿瘤坏死因子α细胞因子和细胞色素P450 1在酒精介导的肝脏氧化应激调节海普西丁表达中的作用。线粒体也参与了酒精介导的氧化应激。酒精导致电子传递链蛋白质的损伤，并减少线粒体中的ATP/ADP转位和ATP合成。我们的初步结果表明，线粒体在海普西丁的表达调节中起作用。抑制线粒体中DNA和蛋白质的合成导致平面HepG2肝癌细胞中海普西丁的表达显著降低。线粒体在细胞凋亡中起着关键作用，酒精对线粒体的影响可诱导细胞凋亡。然而，细胞凋亡在海普西丁表达调控中的作用尚不清楚。我们的初步研究结果表明，Fas介导的细胞凋亡下调了肝脏中海普西丁的表达。本应用的目的是确定线粒体通过酒精调节肝脏海普西丁表达和铁代谢的分子机制。我们的中心假设是乙醇诱导的线粒体结构和功能的改变在酒精对海普西丁转录的调控中起着关键作用。我们将使用线粒体抗氧化酶、腺嘌呤核苷酸转运、细胞色素c氧化酶活性或低氧诱导转录因子二聚体缺陷的转基因小鼠模型来研究酒精介导的氧化应激对海普西丁转录的调节。从这些研究中获得的知识，表征了线粒体的关键作用，将使我们能够确定ALD患者由铁和酒精引起的肝损伤的机制。

DESCRIPTION (provided by applicant): Mitochondria are critical in iron metabolism and play a role in alcohol-induced liver injury. Alcohol alters mitochondrial function and leads to oxidative stress. We have demonstrated that alcohol-induced oxidative stress down-regulates hepcidin transcription without causing changes in liver histology or an increase in triglycerides. Hepcidin is a circulatory peptide synthesized in the liver. It plays a central role in iron homeostasis by regulating both intestinal and reticulo-endothelial iron transport. Accordingly, alcohol-treated animals exhibited an increase in the expression of iron transporters in the duodenum and the iron storage protein, ferritin in the liver. Alcohol also rendered hepcidin synthesis in the liver insensitive to body iron levels. It is noteworthy, that hepcidin protects the body from iron overload by inhibiting iron transport. Thus, alcohol may compromise this protective mechanism of hepcidin, which may have implications for alcoholic liver disease (ALD). Of note, ALD patients and animal models of ALD display iron overload but the underlying mechanisms are unclear. Our findings suggest that the deregulation of hepcidin synthesis in the liver may be one of the underlying mechanisms of iron overload observed in ALD. Treatment with antioxidants abolished the effect of alcohol on hepcidin expression. Multiple pathways play a role in alcohol-induced oxidative stress, including activation of Kupffer cells, CYP2E1 enzyme and changes to mitochondrial function. Our preliminary results exclude a role for Kupffer cells, TNF alpha cytokine and CYP2E1 in the regulation of hepcidin expression by alcohol-mediated oxidative stress in the liver. Mitochondria also are involved in alcohol-mediated oxidative stress. Alcohol induces lesions in the proteins of the electron transport chain, and reduces ATP/ADP translocation and ATP synthesis in the mitochondria. Our preliminary results suggest a role for mitochondria in the regulation of hepcidin expression. Inhibition of DNA and protein synthesis in the mitochondria caused a significant decrease in hepcidin expression in plain HepG2 hepatoma cells. Mitochondria play a key role in apoptosis and alcohol-mediated changes in mitochondria induce apoptotic stimuli. However, the role of apoptosis in the regulation of hepcidin expression is unknown. Our preliminary findings demonstrate that Fas-mediated apoptosis down-regulates hepcidin expression in the liver. The objective of this application is to identify the molecular mechanisms whereby mitochondria regulate liver hepcidin expression and iron metabolism by alcohol. Our central hypothesis is that ethanol-induced modifications of mitochondrial structure and function play a key role in the regulation of hepcidin transcription by alcohol. We will employ transgenic mouse models deficient in mitochondrial antioxidant enzymes, adenine nucleotide transport, cytochrome c oxidase activity or the dimerization of hypoxia-inducible transcription factors to study the regulation of hepcidin transcription by alcohol-mediated oxidative stress. The knowledge obtained from these studies, characterizing the pivotal role of mitochondria, will enable us to determine the mechanisms of liver injury caused by iron and alcohol in patients with ALD.