Hypoxia-Inducible Factors in Liver Metabolism

描述（由申请人提供）：非酒精性脂肪性肝病（NAFLD）发生在没有大量饮酒的患者身上，是一种具有类似酒精性肝损伤组织学特征的临床-组织病理学实体。我们在肝细胞中使用条件基因靶向使pvhl - e3泛素连接酶失活，pvhl - e3泛素连接酶靶向缺氧诱导因子（HIF）在常氧条件下降解。我们发现HIF活性的增加改变了脂肪酸代谢，导致小鼠非酒精性脂肪性肝病的发展。缺氧诱导因子-1和-2 （HIF-1和HIF-2）是异二聚体碱基环螺旋转录因子，是细胞适应缺氧供应的关键介质。我们的发现暗示了HIF信号，特别是通过HIF-2的信号，在脂肪肝疾病的发展中。在这项拨款申请中，我们提出了体内和体外研究，利用条件基因靶向技术和转基因来研究HIF信号在脂肪酸摄取、合成、β -氧化和分泌调节中的作用。此外，还提出了进一步的体外研究，专门针对选定的HIF靶基因，研究它们在缺氧条件下脂质代谢中的作用。在Aims 1中，我们对VHL突变小鼠进行了功能研究，在Aims 2中，我们研究了HIF激活在成年pVHL急性失活后早期脂肪变性发展中的作用，Aims 3和Aims 4研究了HIF-2在野生型遗传背景中的作用，重点研究了与脂肪变性发展相关的HIF-2靶基因。提出的研究不仅对我们了解HIF在脂质代谢中的基本功能很重要，更重要的是具有直接的临床意义。我们提供了缺氧损伤和脂肪肝发展之间的直接分子联系，并建立了HIF通路在NAFLD发病机制中的新作用。公共卫生相关性：本资助申请研究了低氧和缺氧诱导因子（HIF）信号在调节肝脏脂肪酸代谢中的作用。该建议适用于所有患有非酒精性脂肪性肝病、肥胖症、糖尿病和那些患有导致长期低血氧水平的心肺疾病的患者。

DESCRIPTION (provided by applicant): Nonalcoholic fatty liver disease (NAFLD) occurs in patients without significant alcohol consumption and represents a clinico-histopathological entity with histological features that resemble alcohol-induced liver injury. We have used conditional gene targeting in hepatocytes to inactivate the pVHL-E3-ubiquitin ligase, which targets Hypoxia-Inducible-Factor (HIF) for degradation under normoxia. We have discovered that increased HIF activity alters fatty acid metabolism and results in the development of non-alcoholic fatty liver disease in mice. Hypoxia-Inducible Factor-1 and -2 (HIF-1 and HIF-2) are heterodimeric basic-loop-helix transcription factors and are key mediators of cellular adaptation to diminished oxygen supply. Our findings implicate HIF signaling, in particular signaling through HIF-2, in the development of fatty liver disease. In this grant application we propose in vivo and in vitro studies that make use of conditional gene targeting technology and transgenesis to investigate the role of HIF signaling in the regulation of fatty acid uptake, synthesis, beta-oxidation and secretion. Additional in vitro studies are proposed that specifically focus on selected HIF target genes to study their role in lipid metabolism under hypoxia. In Aim 1 we carry out functional studies in VHL mutant mice, in Aim 2 we investigate the role of HIF activation early in the development of steatosis following acute inactivation of pVHL in the adult, and Aims 3 and 4 investigate the role of HIF-2 in a wild type genetic background with a focus on HIF-2 target genes relevant for the development of steatosis. The proposed studies are not only important for our understanding of basic HIF functions in lipid metabolism, but more importantly have direct clinical relevance. We provide a direct molecular link between hypoxic injury and fatty liver development and establish a novel role for the HIF pathway in the pathogenesis of NAFLD. PUBLIC HEALTH RELEVANCE: This grant application examines the role of low oxygen and signaling through Hypoxia-Inducible Factor (HIF) in the regulation of hepatic fatty acid metabolism. The proposal has relevance for all patients with non-alcoholic fatty liver disease, obesity, diabetes and those that suffer from cardio-pulmonary conditions resulting in chronically low blood oxygen levels.