Role of Interferon-Gamma / Interleukin-12 Axis in Metabolic Liver Disease

代谢性肝病，包括以胰岛素抵抗为病理生理标志的非酒精性脂肪肝（NAFL）和非酒精性脂肪性肝炎（NASH），是影响美国四分之一成年人的新问题。肥胖的特征是肝脏炎症，周围的巨噬细胞和细胞因子可能在代谢性肝病中起主要作用。我们的长期目标是通过描述巨噬细胞和细胞因子在胰岛素抵抗、NAFL和NASH之间的分子联系，了解肥胖导致代谢性肝病的分子机制。干扰素-γ (IFNγ)是通过启动巨噬细胞来调节先天免疫和适应性免疫的关键因子，在肥胖人群中升高。我们的初步数据表明，在高脂肪饮食后，骨髓细胞中IFNγ信号（Lyz-IFNgR2 KO）条件性丧失的小鼠会发生脂肪肝，但不会发生胰岛素抵抗和肝脏炎症。此外，白细胞介素-12 （IL-12）通过诱导Th1细胞的分化在先天免疫和适应性免疫的桥接中发挥重要作用，IL-12水平在肥胖和NASH肝脏中升高。我们在体内观察到IL-12治疗通过损害肝脏中IRS-1活性导致肝脏胰岛素抵抗。我们还发现IL-12调节肝细胞中IRS-2/FoxO1/FGF21的表达，这可能导致肝星状细胞（hsc）的激活和NAFL向NASH进展过程中的纤维形成。基于这些观察结果，我们假设肥胖介导的巨噬细胞中IFNγ信号的激活，通过释放IL-12，导致代谢性肝病。在Aim 1中，我们将确定ifng - il - 12轴在肥胖介导的肝脏胰岛素抵抗中的作用。代谢，分子和基于细胞的实验将在新创建的Kupffer细胞选择性IFNγ信号传导（Clec4f-IFNgR2 KO）丢失的小鼠中进行。我们还将使用AAV8和遗传缺乏IL-12的小鼠进行慢性和肝脏靶向IL-12治疗，或使用GeRPs通过肝脏选择性IL-12靶向siRNA来验证一个假设，即IL-12激活p38丝裂原激活的蛋白激酶会损害胰岛素信号活性并导致肝脏胰岛素抵抗。目的2将描述ifng - il - 12轴在NAFL向NASH发展过程中调节巨噬细胞、肝细胞和hsc之间的细胞间串扰的作用。我们将使用3d超声和组织学检查致肥性Gubra Amylin NASH饮食对Clec4f-IFNgR2 KO、Lyz-IFNgR2 KO和IL-12功能增加/丧失小鼠的肝脏脂肪变性和纤维化的影响。Kupffer细胞、肝细胞和HSC将从肝脏中分离出来进行分子和细胞实验，以验证IL-12调节肝细胞IRS-2/FoxO1/FGF21通路，导致HSC活化和纤维化的假设。综上所述，这些目标将引入一种新的范式，其中IFNγ信号和IL-12在肝脏胰岛素抵抗和肥胖症中NAFL进展为NASH的过程中，作为巨噬细胞、肝细胞和hsc之间细胞间串扰的关键介质。我们的研究结果将确定IFNγ信号和IL-12作为治疗人类代谢性肝病的潜在治疗靶点。

Metabolic liver disease, encompassing nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) with insulin resistance as the pathophysiological hallmark, is an emerging issue affecting one in four adults in the U.S. Obesity is characterized by inflammation in the liver, and surrounding macrophages and cytokines may play a major role in metabolic liver disease. Our long-term goal is to understand the molecular mechanism by which obesity causes metabolic liver disease by delineating the role of macrophages and cytokines as a molecular link between insulin resistance, NAFL, and NASH. Interferon-γ (IFNγ), a key regulator of innate and adaptive immunity by priming macrophages, is elevated in obese humans. Our preliminary data indicate that mice with conditional loss of IFNγ signaling in myeloid cells (Lyz-IFNgR2 KO) develop fatty liver after a high-fat diet but are protected from insulin resistance and inflammation in the liver. Moreover, interleukin-12 (IL-12) plays a major role in bridging innate and adaptive immunity by inducing differentiation of Th1 cells, and IL-12 levels are elevated in obese humans and NASH liver. We made a novel observation that IL-12 treatment in vivo causes hepatic insulin resistance by impairing IRS-1 activity in the liver. We also found that IL-12 modulates IRS-2/FoxO1/FGF21 expression in hepatocytes, that may lead to the activation of hepatic stellate cells (HSCs) and fibrogenesis during NAFL progression to NASH. Based on these observations, we hypothesize that obesity-mediated activation of IFNγ signaling in macrophages, through the release of IL-12, causes metabolic liver disease. In Aim 1, we will determine the role of the IFNg-IL12 axis in obesity-mediated insulin resistance in the liver. Metabolic, molecular, and cell-based experiments will be performed in newly created mice with Kupffer cell-selective loss of IFNγ signaling (Clec4f-IFNgR2 KO). We will also apply chronic and liver-targeted IL-12 treatment using AAV8 and mice lacking IL-12 genetically or via liver-selective IL-12 targeting siRNA using GeRPs to test a hypothesis that IL-12 activation of p38 mitogen-activated protein kinase impairs insulin signaling activity and causes insulin resistance in the liver. Aim 2 will delineate the role of the IFNg-IL12 axis in regulating intercellular crosstalk between macrophages, hepatocytes, and HSCs during NAFL progression to NASH. We will examine the effects of the obesogenic Gubra Amylin NASH diet on liver steatosis and fibrosis in Clec4f-IFNgR2 KO, Lyz-IFNgR2 KO, and mice with gain/loss-of-function of IL-12 using 3D-ultrasound and histology. Kupffer cells, hepatocytes, and HSCs will be isolated from the liver for molecular and cell-based experiments to test a hypothesis that IL-12 modulates hepatocyte IRS-2/FoxO1/FGF21 pathway, leading to HSC activation and fibrogenesis. Taken together, these aims will introduce a novel paradigm in which IFNγ signaling and IL-12 act as key mediators of intercellular crosstalk between macrophages, hepatocytes, and HSCs in hepatic insulin resistance and during NAFL progression to NASH in obesity. Our findings will identify IFNγ signaling and IL-12 as potential therapeutic targets to treat metabolic liver disease in humans.