Hepatocyte Clock Genes in Alcohol and High Fat Diet - Induced Liver Injury

描述（由申请人提供）：轮班工作、肥胖、暴食和衰老导致的昼夜节律紊乱对受影响个体的健康和福祉有不利影响。在过去的10年里，我们对特定转录因子（即时钟基因）如何调节和协调中枢神经系统和外周组织的昼夜节律的理解有了深刻的提高。下丘脑前部的视交叉上核（SCN）驱动许多生理昼夜节律，如运动活动、核心体温和激素产生。SCN通过一系列连锁的转录和翻译反馈回路产生这些节律信号，这些反馈回路涉及6个主要的核心基因和蛋白质。这些时钟基因已被证明在包括肝脏在内的外周器官的细胞中存在并起作用。然而，它们对这些器官局部昼夜节律控制的贡献尚未明确。利用遗传方法，研究人员已经证明，小鼠大脑和外周组织中昼夜节律振荡器的整体破坏会对代谢、肿瘤抑制和药物诱导的器官毒性产生不利影响。例如，一只全球突变的小鼠在长期摄入酒精后，会出现脂肪肝肿大。然而，在这些模型中，全球时钟基因敲除或转基因小鼠不能解决肝细胞内的外周时钟本身是否调节酒精诱导的损伤和纤维化。我们的主要假设是：(1)评估参与酒精代谢和损伤的肝脏基因的昼夜节律调节将增强我们对这种药物的肝毒性作用的理解；(2)肝细胞生物钟的丧失将加剧酒精或高脂肪单独或联合引起的肝损伤和纤维化。在这个项目中，我们将使用新发现的肝细胞特异性缺失Bmal 1的小鼠模型，Bmal 1是一种重要的时钟成分。这种缺失破坏了肝细胞中的一些（但不是全部）昼夜节律，部分原因是这些细胞仍然对SCN或其他器官（如肾上腺和消化道）发出的神经或激素昼夜节律信号，甚至是来自肝脏非实质细胞的旁分泌信号有反应。我们将使用该模型来研究内在生物钟是否在乙醇-高脂肪肝损伤和纤维化模型中调节生物钟基因、酒精代谢和损伤相关基因以及纤维化基因的表达水平。该项目将使我们更好地了解肝细胞时钟基因在介导酒精和高脂肪的各种肝毒性以及肝脏对慢性损伤的反应中所起的作用。

DESCRIPTION (provided by applicant): Disruption of circadian rhythms by shift work, obesity, binge feeding, and aging has adverse effects on the health and well-being of the affected individuals. Within the last 10 years, there has been a profound increase in our understanding of how specific transcriptional factors, known as clock genes, regulate and coordinate circadian rhythms within the central nervous system as well as peripheral tissues. The suprachiasmatic nuclei (SCN) in the anterior hypothalamus drive many physiological circadian rhythms such as motor activity, core body temperature, and hormone production. The SCN generates these rhythmic signals through a set of interlocking transcriptional and translational feedback loops that involve six main core genes and proteins. These clock genes have been shown to be present and operational in cells within peripheral organs, including the liver, as well. However, their contribution to the control of local circadian rhythms in these organs is not well-defined. Using genetic methods, investigators have shown that the global disruption of the circadian oscillators in the brain and in peripheral tissues of mice adversely affects metabolism, tumor suppression, and drug-induced organ toxicities. For example, a global CLOCK mutant mouse develops an enlarged fatty liver after chronic ingestion of alcohol. However, global clock gene knockouts or transgenic mice can not address whether the peripheral clocks in hepatocytes themselves modulate alcohol-induced injury and fibrosis in these models. Our central hypotheses are that (1) an evaluation of the circadian regulation of hepatic genes involved in alcohol metabolism and injury will enhance our understanding of the hepatotoxic effects of this agent and (2) the loss of the circadian clock in hepatocytes will exacerbate the liver injury and fibrosis caused by alcohol or high fat alone or in combination. In this project, we will use the newly-characterized murine model of a hepatocyte-specific deletion of Bmal 1, an essential clock component. This deletion disrupts some, but not all, circadian rhythms in the hepatocytes, in part because these cells are still responsive to neural or hormonal circadian signals emanating from the SCN or other organs, such as the adrenal gland and digestive tract, or even paracrine signals, from non-parenchymal cells in the liver. We will use this model to investigate whether the intrinsic circadian clock modulates the expression levels of clock genes, genes involved in alcohol metabolism and injury and fibrogenic genes in the ethanol-high fat model of liver injury and fibrosis. This project will lead to a greater understanding of the role played by hepatocyte clock genes in mediating the various hepatic toxicities of alcohol and high fat as well as the hepatic response to chronic injury.