Macrophage-specific targeting of LXRs in CVD and NASH

项目总结 项目1.CVD和NASH中LXRs的巨噬细胞特异性靶向 脂肪肝是美国发病率迅速增长的原因，据估计，美国有80%到20%的人患有脂肪肝 1亿人患有非酒精性脂肪性肝病(NAFLD)，600万至1600万人病情更严重 肝脏疾病，非酒精性脂肪性肝炎(NASH)。NAFLD是一种强耦合的肝病谱系 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的存在和严重程度独立地预测致命性和非致命性CVD事件。最新进展 NAFLD和CVD的发病率受到遗传和环境因素的组合影响，其中一些因素是 疾病特有的以及影响这两种疾病过程的其他因素。在这个项目中，我们将调查中央 肝脏枯否细胞和巨噬细胞X受体功能受损的假说 动脉壁是导致NAFLD和动脉粥样硬化的共同潜在机制， 而这一机制可以通过类似于Desmosterol的治疗而逆转。一个主要的限制是 靶向LXRs治疗动脉粥样硬化是大多数合成激动剂引起明显的 诱导肝细胞表达SREBP1c导致高甘油三酯血症。我们对巨噬细胞泡沫的研究 细胞发现，在胆固醇生物合成途径中的中间产物 丰富的内源性LXR激动剂。与选择性结合LXRs的传统激动剂不同，Desmosterol 还与SCAP结合，从而抑制SREBP1和SREBP2的处理。没想到，我们最近 发现Desmosterol和合成的Desmosterol模拟物不能激活LXR或抑制SREBP 肝细胞中的靶基因。体内研究进一步证实了一种合成的Desmosterol模拟物 LXR靶基因在Kupffer细胞中的激活，但不是在整个肝脏中。我们的发现揭示了细胞的特异性 巨噬细胞和肝细胞对天然和合成配体的LXR反应的差异 从概念上为预防NASH和动脉粥样硬化提供了新的依据。提出了三个具体目标。 特定目标1将检验库普弗细胞中的LXR活性是正常肝脏所必需的假设 动态平衡和Kupffer细胞特异性的LXRs缺失会导致NASH和动脉粥样硬化的夸大。 这些研究将开发新的小鼠模型，允许Kupffer细胞特异性删除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LXRs的合成类似物对NASH和动脉粥样硬化小鼠的保护作用 与这些配体在动脉壁内的作用无关。具体目标3，与 项目4，将测试假设单核细胞基因表达签名和表观遗传景观在 受试者外周血单核细胞与CVD表型和纤维化程度相关。这个 拟议的研究可能会在理解LXRs在调节NASH和NASH中的作用方面取得质的进展 并建立了桥粒甾醇类似物在临床研究中的应用潜力。

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.