Macrophage-specific targeting of LXRs in CVD and NASH

项目摘要 项目1。CVD和NASH中LXR的巨噬细胞特异性靶向 在美国，脂肪肝疾病的发病率迅速增长，据估计， 1亿人患有非酒精性脂肪肝（NAFLD），600万至1600万人患有更严重的 肝病、非酒精性脂肪性肝炎（NASH）。NAFLD是一系列肝脏疾病， 肥胖、胰岛素抵抗、心血管疾病和2型糖尿病。长期前瞻性研究表明， NAFLD的存在和严重程度可独立预测致死性和非致死性CVD事件。发展 NAFLD和CVD的发病率受遗传和环境因素的影响，其中一些是 疾病特异性和影响两种疾病过程的其他因素。在这个项目中，我们将调查中央 假设肝脏中枯否细胞和巨噬细胞中的肝脏X受体功能受损， 动脉壁代表了导致NAFLD和动脉粥样硬化的共同潜在机制， 并且这种机制可以通过用链甾醇模拟物治疗来逆转。的主要限制 靶向LXR治疗动脉粥样硬化的一个重要原因是， 通过诱导肝细胞中SREBP1c的表达来治疗高胆固醇血症。我们对巨噬细胞泡沫 细胞导致发现，桥甾醇，胆固醇生物合成途径中的中间体，是最 内源性LXR激动剂。与选择性结合LXR的常规激动剂不同，桥甾醇 也与SCAP结合，从而抑制SREBP 1和SREBP 2的加工。没想到，我们最近 发现链甾醇和合成链甾醇模拟物不激活LXR或抑制SREBP 肝细胞中的靶基因。用合成的链甾醇模拟物进行的体内研究进一步证实了 Kupffer细胞中LXR靶基因的激活，但整个肝脏中没有。我们的发现揭示了细胞特异性 巨噬细胞和肝细胞中LXR对天然和合成配体反应的差异， 这是预防NASH和动脉粥样硬化的概念性新基础。提出了三个具体目标。 具体目标1将检验库普弗细胞中的LXR活性是正常肝脏所需的假设。 体内平衡和Kupffer细胞特异性LXR缺失导致过度NASH和动脉粥样硬化。 这些研究将开发新的小鼠模型，允许Kupffer细胞特异性缺失LXR。具体目标2 将使用药理学和遗传学方法的组合来测试选择性激活的假设， Kupffer细胞中的LXR与合成的桥甾醇模拟物保护小鼠免受NASH和动脉粥样硬化 与动脉壁内这些配体的作用无关。具体目标3，与 项目4，将测试单核细胞基因表达特征和表观遗传景观的假设， 外周血单核细胞与人类受试者中的CVD表型和纤维化程度相关。的 拟议的研究可能会导致在理解LXR在NASH调节中的作用方面取得质的进展， 动脉粥样硬化和建立链甾醇模拟物的潜力，以进行临床研究。

PROJECT SUMMARY Project 1. Macrophage-specific targeting of LXRs in CVD and NASH Fatty liver diseases account for rapidly growing morbidity in the United States, where it is estimated that 80 to 100 million individuals have non-alcoholic fatty liver disease (NAFLD) and 6 to 16 million have the more severe liver disease, nonalcoholic steatohepatitis (NASH). NAFLD is a spectrum of liver conditions strongly coupled with obesity, insulin resistance, CVD, and type-2 diabetes mellitus. Long term prospective studies indicate that the presence and severity of NAFLD independently predicts fatal and nonfatal CVD events. The development of NAFLD and CVD is influenced by combinations of genetic and environmental factors, some of which are disease-specific and others that affect both disease processes. In this Project, we will investigate the central hypothesis that impaired function of liver X receptors in Kupffer cells in the liver and macrophages within the artery wall represent a common underlying mechanism that contributes to both NAFLD and atherosclerosis, and that this mechanism can be reversed by treatment with desmosterol mimetics. A major limitation in targeting LXRs for treatment of atherosclerosis is that most synthetic agonists cause marked hypertriglyceridemia by inducing the expression of SREBP1c in hepatocytes. Our studies of macrophage foam cells led to the finding that desmosterol, an intermediate in the cholesterol biosynthetic pathway, is the most abundant endogenous LXR agonist. Unlike conventional agonists that selectively bind to LXRs, desmosterol also binds to SCAP, thereby inhibiting processing of SREBP1 and SREBP2. Unexpectedly, we recently discovered that desmosterol and synthetic desmosterol mimetics do not activate LXR or suppress SREBP target genes in hepatocytes. In vivo studies with a synthetic desmosterol mimetic further demonstrated activation of LXR target genes in Kupffer cells but not in the liver as a whole. Our findings reveal cell-specific differences in LXR responses to natural and synthetic ligands in macrophages and hepatocytes that provide a conceptually new basis for prevention of NASH and atherosclerosis. Three Specific Aims are proposed. Specific Aim 1 will test the hypothesis that LXR activity in Kupffer cells is required for normal liver homeostasis and that Kupffer cell-specific deletion of LXRs results in exaggerated NASH and atherosclerosis. These studies will exploit new mouse models allowing Kupffer cell-specific deletion of LXRs. Specific Aim 2 will use a combination of pharmacologic and genetic approaches to test the hypothesis that selective activation of LXRs in Kupffer cells with synthetic desmosterol mimetics protects mice from NASH and atherosclerosis independent of effects of these ligands within the artery wall. Specific Aim 3, performed in collaboration with Project 4, will test the hypothesis that monocyte gene expression signatures and epigenetic landscapes in peripheral blood monocytes correlate with CVD phenotypes and the extent of fibrosis in human subjects. The proposed studies may result in qualitative advances in understanding roles of LXRs in regulation of NASH and atherosclerosis and establish the potential of desmosterol mimetics to be advanced for clinical investigation.