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

 描述(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，最终导致ER伴侣、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转录上调。然而，营养流可以在肝脏等代谢组织中引发内质网应激，而UPR又可以调节代谢途径。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流量如何影响ER蛋白质的处理能力是很重要的。这项研究提供的数据表明，肝脏中的内质网应激导致脂肪酸氧化的转录抑制，抑制脂肪酸氧化可以改变内质网的氧化环境，保护肝细胞免受应激的影响。这些发现表明，UPR对脂肪酸氧化的调节是应激反应保护内质网功能的一条新途径。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流量如何影响ER蛋白质的折叠和处理能力。因此，这项工作的目的是了解内质网应激如何调节脂肪酸氧化，脂肪酸氧化如何调节内质网功能，以及这些途径在喂养和禁食过程中如何相互作用。这项建议的工作检验了中心假说，即内质网应激通过UPR调节的转录因子CHOP直接转录抑制脂肪酸氧化，进而改变内质网的氧化蛋白质折叠能力以缓解应激。这一假设将通过三个相辅相成的目标进行检验。第一个目的是阐明UPR调节脂肪酸氧化的基因调控网络。将测试CHOP在这个网络中的作用，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要调节因子的影响。在第二个目标中，当操纵脂肪酸氧化时，将系统地检测内质网有效地输入、折叠、修饰、氧化、运输和降解客户蛋白的能力，并将测试NADPH和谷胱甘肽氧化还原在将脂肪酸氧化与内质网功能联系起来中的作用。第三个目标将确定脂肪酸氧化和内质网蛋白质加工之间的关系如何有助于调节摄食和禁食期间的代谢活动和内质网应激。将测试CHOP在抑制饲喂过程中的脂肪酸氧化和增强其在禁食过程中的作用，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，这些目标将形成一种跨学科的方法，将ER蛋白折叠、UPR信号、脂代谢和氧化还原动态平衡联系起来。

 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.