Regulation of Fatty Acid Oxidation during ER stress: mechanisms and consequences

 描述（由申请人提供）：未折叠蛋白反应（UPR）由内质网（ER）中的蛋白质错误折叠应激激活，并在ER伴侣蛋白、降解因子和其他帮助细胞器正确折叠或降解客户蛋白的基因的转录上调中达到高潮。然而，营养流可以引起代谢组织如肝脏中的ER应激，并且UPR可以反过来调节代谢途径。许多疾病都与代谢改变和慢性内质网应激有关，最明显的包括肥胖及其并发症。因此，了解UPR如何调节代谢以及代谢通量如何影响ER蛋白加工能力是很重要的。 该提案中提供的数据表明，肝脏中的ER应激导致脂肪酸氧化的转录抑制，并且脂肪酸氧化的抑制改变了ER的氧化环境并保护肝细胞免受应激。这些发现表明，UPR对脂肪酸氧化的调节代表了一种新的途径，通过这种途径，应激期间的反应保护了ER功能。然而，人们对UPR抑制而不是激活转录的机制知之甚少。也不知道通过代谢途径的通量如何影响ER蛋白的折叠和加工能力。因此，这项工作的目的是了解ER应激如何调节脂肪酸氧化，脂肪酸氧化如何调节ER功能，以及这些途径在进食和禁食期间如何相互作用。本提案中的工作测试了核心假设，即ER应激通过UPR调节的转录因子CHOP导致脂肪酸氧化的直接转录抑制，这反过来又改变了ER的氧化蛋白折叠能力以减轻应激。这一假设将通过三个互补的目标来检验。第一个目标是阐明UPR调控脂肪酸氧化的基因调控网络。将测试CHOP在该网络中的作用，以及CHOP与其他C/EBP家族转录因子的相互作用以及CHOP作用对脂肪酸氧化的主调节因子的影响。在第二个目标中，ER有效地进口，折叠，修改，氧化，运输和降解客户蛋白的能力将被系统地检查时，脂肪酸氧化被操纵，NADPH和谷胱甘肽氧化还原在连接脂肪酸氧化ER功能的作用将被测试。第三个目标将确定脂肪酸氧化和ER蛋白加工之间的关系如何有助于调节进食和禁食期间的代谢活动和ER应激。将测试CHOP对进食期间脂肪酸氧化抑制和禁食期间脂肪酸氧化增强的贡献，以及操纵脂肪酸氧化、NADPH生成和谷胱甘肽氧化对ER功能的影响。总之，这些目标将形成一个跨学科的方法连接ER蛋白折叠，UPR信号，脂质代谢和氧化还原稳态。

 DESCRIPTION (provided by applicant): The unfolded protein response (UPR) is activated by protein misfolding stress in the endoplasmic reticulum (ER), and it culminates in the transcriptional upregulation of ER chaperones, degradation factors, and other genes that help the organelle properly fold or degrade client proteins. However, nutritional flux can elicit ER stress in metabolic tissues such as the liver, and the UPR can in turn regulate metabolic pathways. A number of diseases are associated with both altered metabolism and chronic ER stress, most notably including obesity and its complications. Therefore, it is important to understand how the UPR regulates metabolism and how metabolic flux influences the ER protein processing capacity. Data presented in this proposal show that ER stress in the liver leads to transcriptional suppression of fatty acid oxidation, and that inhibition of fatty acid oxidation alters the oxidizing environment of the ER and protects hepatocytes from stress. These findings suggest that the regulation of fatty acid oxidation by the UPR represents a novel pathway by which the response protects ER function during stress. Yet very little is known about the mechanisms by which the UPR represses rather than activates transcription. Nor is it known how flux through metabolic pathways influences the ER protein folding and processing capacity. Thus, the objective of this work is to understand how ER stress regulates fatty acid oxidation, how fatty acid oxidation regulates ER function, and how these pathways interact during feeding and fasting. The work in this proposal tests the central hypothesis that ER stress leads to direct transcriptional suppression of fatty acid oxidation through the UPR-regulated transcription factor CHOP, and that this in turn alters the oxidative protein folding capacity of the ER to alleviate stress. This hypothesis will be tested by three complementary aims. The first aim will elucidate the gene regulatory network by which the UPR regulates fatty acid oxidation. The role of CHOP in this network will be tested, as will the interactions of CHOP with other C/EBP-family transcription factors and the impact of CHOP action on the master regulators of fatty acid oxidation. In the second aim, the ability of the ER to efficiently import, fold, modify, oxidize, transport, and degrade client proteins will be systematically examined when fatty acid oxidation is manipulated, and the roles of NADPH and glutathione redox in linking fatty acid oxidation to ER function will be tested. The third aim will determine how the relationship between fatty acid oxidation and ER protein processing contributes to the regulation of metabolic activity and ER stress during feeding and fasting. The contribution of CHOP to the suppression of fatty acid oxidation during feeding and its enhancement during fasting will be tested, as will the effects of manipulating fatty acid oxidation, NADPH generation, and glutathione oxidation on ER function. Together, these aims will form a cross-disciplinary approach linking ER protein folding, UPR signaling, lipid metabolism, and redox homeostasis.