Mechanisms of ER stress - induced fatty liver

描述（由申请人提供）：脂肪肝（FLD）有多种原因，包括慢性饮酒、肥胖、病毒感染、营养不良和急性肝毒素暴露。FLD可以从单纯的脂肪变性发展为损害肝功能的脂肪性肝炎，导致炎症、纤维化、肝硬化，最终导致肝功能衰竭。虽然FLD很可能反映了脂质合成、储存、氧化和/或分泌之间的不平衡，但这种不平衡的潜在分子原因仅部分被理解。由于酒精性和非酒精性的FLD非常常见，因此确定其病因（可能多种多样）将为预防肝功能衰竭提供治疗途径。这项研究计划基于强有力的初步数据，这些数据表明内质网（ER）应激导致参与维持脂质稳态的基因的转录抑制；内质网应激感应蛋白ATF61基因缺陷的小鼠无法克服内质网应激，并在挑战时变得严重脂肪变性。这些在未受伤状态下正常的动物，为解剖内质网应激和肝脏脂质代谢之间的联系提供了有价值的工具。这项工作的长期目标是了解内质网紊乱如何导致脂肪肝疾病。这一目标将通过三个互补的调查领域来实现。第一个目的是了解内质网应激反应是如何在转录水平上与脂质稳态机制相关的。基因调控事件将根据atf61缺失小鼠体内关键代谢转录因子过表达部分或完全挽救脂肪变性的能力进行分级。同时，内质网应激调节转录因子对基因的直接调控将通过无偏倚和靶向染色质免疫沉淀来探索。最后，将确定将代谢转录调控与未解决的内质网应激联系起来的机制。第二个目的是确定内质网应激反应对脂质代谢的调节如何反过来影响内质网功能。这一目标将通过确定内质网应激期间导致脂肪变性的脂质代谢途径，并测试内质网折叠和加工客户蛋白的能力（即“内质网功能”）在这些途径被操纵独立于内质网应激时是如何改变的来实现。第三个目的是确定慢性内质网应激如何导致病理性脂肪变性，特别是酒精性脂肪性肝病。我们将使用atf61缺失小鼠来测试内质网功能损伤是否会使小鼠在慢性酒精消耗过程中对脂肪变性敏感。我们还将确定慢性乙醇消耗如何通过内质网应激调节的基因表达变化改变细胞稳态。这项工作提供了几个独立的途径来解决脂肪变性发展的一个方面，目前知之甚少，并将确定新的关键调控途径，可能代表未来治疗干预的有吸引力的目标，以防止肝功能衰竭。公共卫生相关性：脂肪变性或脂肪肝是西方国家最常见的肝脏疾病，约有25%的美国成年人患有脂肪肝；它可发展为脂肪性肝炎、纤维化、肝硬化和肝功能衰竭。脂肪变性发展的原因尚不清楚，必须了解有效的治疗方法。内质网应激是脂肪变性的一个促进因素，这表明本文提出的工作将增强我们对脂肪变性分子基础的理解，并提出治疗方法。

DESCRIPTION (provided by applicant): Fatty liver disease (FLD) has a variety of causes including chronic alcohol consumption, obesity, viral infection, malnutrition, and acute exposure to hepatotoxins. FLD can progress from simple steatosis to steatohepatitis that compromises liver function, leading to inflammation, fibrosis, cirrhosis, and ultimately liver failure. While FLD most likely reflects an imbalance between lipid synthesis, storage, oxidation, and/or secretion, the underlying molecular causes of this imbalance are only partially understood. As FLD of both alcoholic and nonalcoholic origins is very common, identifying its etiologies, which are likely varied, will suggest avenues of treatment to prevent liver failure. This research proposal is based upon strong preliminary data demonstrating that endoplasmic reticulum (ER) stress leads to transcriptional suppression of genes involved in maintaining lipid homeostasis; mice genetically deficient in the ER stress-sensing protein ATF61 fail to overcome ER stress, and become profoundly steatotic upon challenge. These animals, which are otherwise normal in the uninjured state, provide a valuable tool for dissecting the connections between ER stress and liver lipid metabolism. The long-term objective of this work is to understand how ER perturbation contributes to fatty liver disease. This goal will be achieved by three complementary areas of investigation. The first aim is to understand how the ER stress response is mechanistically connected to lipid homeostasis at the level of transcription. Gene regulatory events will be placed into a hierarchy based on the ability of in vivo overexpression of key metabolic transcription factors to partially or fully rescue steatosis in Atf61-null mice. In parallel, direct regulation of genes by ER stress-regulated transcription factors will be probed by both unbiased and targeted chromatin immunoprecipitation. Finally, the mechanism that ties metabolic transcriptional regulation to unresolved ER stress will be determined. The second aim is to determine how the regulation of lipid metabolism by the ER stress response in turn impacts ER function. This aim will be achieved by pinpointing the pathways of lipid metabolism that contribute to steatosis during ER stress, and testing how the ability of the ER to fold and process client proteins (i.e., "ER function") is altered when these pathways are manipulated independent of ER stress. The third aim is to determine how chronic ER stress contributes to pathological steatosis, in particular alcoholic fatty liver disease. We will use Atf61-null mice to test whether impairment of ER function sensitizes mice to steatosis during chronic ethanol consumption. We will also determine how chronic ethanol consumption alters cellular homeostasis through ER stress-regulated changes in gene expression. This work provides several independent avenues to address an aspect of the development of steatosis that is currently poorly understood, and will identify novel key regulatory pathways that might represent attractive targets for future therapeutic intervention to prevent liver failure. PUBLIC HEALTH RELEVANCE: Public Health Relevance Steatosis, or fatty liver disease, is the most common liver disease in Western countries, being present in approximately 25 percent of American adults; it can progress to steatohepatitis, fibrosis, cirrhosis, and liver failure. The causes underlying the development of steatosis are not clear, and must be understood for effective therapies to be developed. The identification of endoplasmic reticulum stress as a contributing factor to steatosis suggests that the work proposed here will enhance our understanding of molecular basis for steatosis and suggest means of therapeutically treating it.