Hypoxia-Inducible Factors in Liver Metabolism

描述(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中，代表了一种临床组织病理学实体，其组织学特征类似于酒精诱导的肝损伤。我们已经在肝细胞中使用条件基因打靶来灭活pVHL-E3-泛素连接酶，该连接酶以缺氧诱导因子(HIF)为靶点，在常氧下降解。我们发现，HIF活性增加会改变脂肪酸代谢，导致小鼠发生非酒精性脂肪性肝病。低氧诱导因子-1和低氧诱导因子-2(HIF-1和HIF-2)是异源二聚体碱性环螺旋转录因子，是细胞适应低氧供应的关键介质。我们的发现表明，HIF信号，特别是通过HIF-2的信号，与脂肪肝的发展有关。在这项拨款申请中，我们建议进行体内和体外研究，利用条件基因打靶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，还建议进行体外研究，特别集中在选定的HIF靶基因上，以研究它们在低氧下脂代谢中的作用。在目标1中，我们对VHL突变小鼠进行了功能研究，在目标2中，我们研究了HIF激活在成人pVHL急性失活后脂肪变性发生中的作用，目标3和4研究了HIF-2在野生型遗传背景中的作用，重点是与脂肪变性发生相关的HIF-2靶基因。这些研究不仅对我们理解HIF在脂质代谢中的基本功能具有重要意义，更重要的是具有直接的临床意义。我们提供了低氧损伤和脂肪肝发展之间的直接分子联系，并为HIF通路在NAFLD发病机制中的新作用奠定了基础。

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.