Interrogating Liver Macrophage LXR Signaling in Health and Non-Alcoholic Fatty Liver Disease

项目摘要： 在体内平衡和疾病中驱动肝巨噬细胞行为的机制很差， 明白肝X受体（LXR）转录因子在肝巨噬细胞中高度表达 和肝细胞。虽然在肝细胞中LXR信号传导控制胆固醇代谢，但巨噬细胞LXR 信号调节胆固醇代谢和炎症，这些过程是胆固醇代谢的核心。 非酒精性脂肪性肝炎（NASH）的发病机制。LXR的激活通过以下方式抑制炎症： 干扰核因子κ B（NFκ B）活化。NFκ B是多种NASH信号传导的下游靶点 途径，包括Toll样受体、白细胞介素-1和肿瘤坏死因子β 该建议的中心假设是，肝脏巨噬细胞中LXR β信号的丢失将阻断LXR 介导的炎症信号传导抑制并恶化NASH进展。Glass之前的研究 实验室已经证明LXR β在枯否细胞（肝脏的常驻巨噬细胞）中高度表达 并且在进入健康和NASH肝脏后在骨髓来源的巨噬细胞中快速上调。 这导致了一种假设，即枯否细胞中LXR β的缺失会使患有NASH的小鼠的NASH表型恶化。 通过增加NFκ B信号传导的代谢疾病。进行了一项初步研究，以检查 NASH中髓系特异性LXR缺失。在这项研究中，缺乏髓样LXR的小鼠被喂食NASH- 20周的模型饮食显示肝纤维化增加，肝脏炎症基因 表情然而，这种效应是否是由于枯否细胞或其他肝巨噬细胞中LXR β的丢失， NASH期间存在的人群未知。 目的1将检测枯否细胞中LXR β信号的缺失是否会增加肝纤维化和肝硬化。 NASH进展。炎症、肝损伤、胆固醇代谢和肝损害的血清标志物 组织病理学将用于评估骨髓特异性或枯否细胞特异性LXR β敲除的作用 在NASH期间。ChIP-seq、ATAC-seq和RNA-seq将用于两种新型小鼠品系， 机制性评估LXR信号传导的丧失是否改变不同肝巨噬细胞中的炎症 NASH期间的人群。目的2将测试肝桥甾醇是否是LXR的天然配体， 枯否细胞。这方面的研究将利用新开发的转基因小鼠来评估 肝桥甾醇耗竭对枯否细胞转录的影响。如果 如果成功，这些研究可以确定一个新的骨髓特异性分子靶点，用于治疗或 预防NASH。

Project Summary: The mechanisms that drive the behavior of hepatic macrophages in homeostasis and disease are poorly understood. The liver X receptor (LXR) transcription factors are highly expressed in hepatic macrophages and hepatocytes. While in hepatocytes LXR signaling controls cholesterol metabolism, macrophage LXR signaling regulates both cholesterol metabolism and inflammation, processes that are central to the pathogenesis of non-alcoholic steatohepatitis (NASH). Activation of LXRs represses inflammation by interfering with nuclear factor κ (NFκ) activation. NFκ is a downstream target of multiple NASH signaling pathways, including toll-like-receptors, interleukin-1, and tumor-necrosis factor  The central hypothesis of this proposal is that loss of LXR signaling in liver macrophages will block LXR mediated inhibition of inflammatory signaling and worsen NASH progression. Prior research by the Glass lab has demonstrated that LXR is highly expressed in Kupffer cells (the resident macrophages of the liver) and rapidly upregulated in bone marrow derived macrophages upon entry into both healthy and NASH livers. This led to the hypothesis that loss of LXR in Kupffer cells would worsen NASH phenotypes in mice with metabolic disease via increased NFκ signaling. A pilot study was performed to examine the effect of myeloid-lineage-specific LXR deletion in NASH. In this study mice lacking myeloid LXR fed a NASH- model diet for 20 weeks demonstrated increased hepatic fibrosis, and hepatic inflammatory gene expression. However, whether this effect is due to loss of LXR in Kupffer cells or other hepatic macrophage populations present during NASH is unknown. Aim 1 will test whether loss of LXR signaling in Kupffer cells increases hepatic fibrosis and worsens NASH progression. Serum markers of inflammation, liver damage, and cholesterol metabolism and hepatic histopathology will be used to assess the effect of myeloid-specific or Kupffer cell-specific LXR knockout during NASH. ChIP-seq, ATAC-seq, and RNA-seq will be used on two novel mouse strains to mechanistically assess whether loss of LXR signaling alters inflammation in different hepatic macrophage populations during NASH. Aim 2 will test whether hepatic desmosterol is the native LXR ligand in Kupffer cells. Studies in this aim will utilize a newly developed transgenic mouse to assess the effects of hepatic desmosterol depletion on Kupffer cell transcription both at homeostasis and during NASH. If successful, these studies could identify a new myeloid specific molecular target for the treatment or prevention of NASH.