ABCA1/G1 and LXRs in Atherogenesis

 描述（由申请人提供）：血浆HDL水平与冠心病呈反比关系，但最近HDL升高疗法的失败试验以及人类基因组广泛关联研究对这种关系的因果性质提出了质疑。这突出了对HDL和动脉粥样硬化之间关系的更深入的机制理解的需要。由HDL和ABC转运蛋白介导的胆固醇流出途径起抑制炎症和动脉粥样硬化的作用。我们最近的工作已经确定了ABCA 1和ABCG 1介导的胆固醇从细胞流出到ApoA-1和HDL在抑制造血干细胞增殖、骨髓生成、单核细胞增多、巨噬细胞积累和动脉粥样硬化斑块中的炎症基因表达中的作用。我们最近发现ABCA 1/G1在巨噬细胞中起抑制由高胆固醇血症和氧化LDL诱导的炎性小体活化的作用。此外，缺乏ABCA 1/G1的巨噬细胞经历焦变性细胞死亡，这是一种由炎性体引发剂活化的半胱天冬酶-1和炎性体的细胞因子产物（IL-1）诱导的坏死性细胞死亡形式。目的1将评估炎性小体和焦亡对巨噬细胞和巨噬细胞特异性敲除ABCA 1/G1的小鼠中动脉粥样硬化的影响，通过将这些小鼠与缺乏必需炎性小体组分的品系杂交。此外，由于我们在丹吉尔病患者中发现炎性小体产物IL-1和IL-18的血浆水平升高，我们将确定来自这些受试者的单核细胞是否显示炎性小体活化和焦亡的证据，从而评估人类相关性。LXR/RXR转录因子诱导ABCA 1/G1，当用LXR激活剂处理时，这些转运蛋白缺陷的巨噬细胞不能增加胆固醇流出。我们发现，巨噬细胞中ABCA 1/G1缺乏的小鼠在用LXR激活剂治疗时仍然显示出动脉粥样硬化减少，这表明LXR激活剂在巨噬细胞中的新作用不依赖于胆固醇流出或血管效应。在目标2中，我们将寻求在巨噬细胞中鉴定新的LXR抗动脉粥样硬化靶点，例如诱导长链不饱和脂肪酸合成的基因，所述长链不饱和脂肪酸合成导致可促进动脉粥样硬化消退的小促消退脂质介质（SPM）的合成。另一种解释是LXR上调内皮细胞中的ABCA 1/G1，具有抗动脉粥样硬化的结果，这将在这些转运蛋白的内皮特异性缺陷的小鼠中进行测试。总的来说，这些发现可能有助于理解目前在冠心病人体临床试验中涉及HDL输注和LXR激活剂的治疗干预措施，以及确定潜在的新治疗靶点。

 DESCRIPTION (provided by applicant): Plasma HDL levels have an inverse relationship with coronary heart disease, but recent failed trials of HDL raising therapies, as well as human genome wide association studies have called into the question the causal nature of this relationship. This highlights the need for a deeper mechanistic understanding of the relationship between HDL and atherosclerosis. Cholesterol efflux pathways mediated by HDL and ABC transporters act to suppress inflammation and atherosclerosis. Our recent work has defined the role of ABCA1 and ABCG1 which mediate cholesterol efflux from cells to ApoA-1 and HDL in suppressing hematopoietic stem cell proliferation, myelopoiesis, monocytosis, macrophage accumulation and inflammatory gene expression in atherosclerotic plaques. We recently discovered that ABCA1/G1 act in macrophages to suppress inflammasome activation induced by hypercholesterolemia and oxidized LDL. Moreover, macrophages deficient in ABCA1/G1 undergo pyroptotic cell death, a form of necrotic cell death that is induced by inflammasome-initiator activated caspase-1 and cytokine products of the inflammasome (IL-1). Aim 1 will assess the effects of the inflammasome and pyroptosis on atherosclerosis in macrophages and mice with macrophage-specific knockout of ABCA1/G1, by crossing these mice with strains deficient in essential inflammasome components. Also, since we discovered elevated plasma level of inflammasome products IL-1 and IL-18 in patients with Tangier Disease, we will determine if monocytes from these subjects show evidence of inflammasome activation and pyroptosis, thus evaluating human relevance. LXR/RXR transcription factors induce ABCA1/G1 and macrophages deficient in these transporters fail to increase cholesterol efflux when treated with LXR activators. We discovered that mice with deficiency of ABCA1/G1 in macrophages nonetheless show reduced atherosclerosis when treated with LXR activators, suggesting a novel effect of LXR activators in macrophages independent of cholesterol efflux, or a vascular effect. In Aim 2 we will seek to identify novel LXR anti-atherogenic targets in macrophages, such as genes that induce synthesis of long chain unsaturated fatty acids leading to synthesis of small proresolving lipid mediators (SPMs) that may promote resolution of atherosclerosis. An alternative explanation would be that LXRs upregulate ABCA1/G1 in endothelial cells with anti-atherogenic consequences and this will be tested in mice with endothelial-specific deficiency of these transporters. Overall, the findings are likely to contribute to the understanding of therapeutic interventions involving HDL infusions and LXR activators that are currently in human clinical trials for coronary heart disease, as well as to identify potential new therapeutic target.