Regulation and function of plasma lipid transfer proteins

低HDL水平是一个主要的动脉粥样硬化危险因素，目前尚无专门的治疗方法。血浆液体转移蛋白胆固醇酯转移蛋白（CETP）和磷脂转移蛋白（PLTP）在HDL稳态中起重要作用。CETP将高密度脂蛋白CE转化为富含甘油三酯的脂蛋白，然后被肝脏吸收，这是一个逆向胆固醇或内源性高胆固醇血症的过程。我们使用天然侧翼区CETP转基因（Tg）小鼠和报告基因构建来定位CETP对基因近端启动子中的新元件的反应，我们已经证明这种积极反应是由核受体LXR在体外介导的。由于已知lxrα可以介导胆固醇转化为胆盐的限速酶cyp7a的上调，我们的研究结果表明，LXRs可能有助于协调多种参与体内胆固醇去除的基因的反应。在Aim 1中，我们将使用lxrα和β敲除小鼠来评估LXRs在体内脂质转移蛋白基因调控中的作用，并探索这些转录因子在调节参与胆固醇逆向转运的基因中的总体作用；这些小鼠也将杂交到动脉粥样硬化易感的背景，以评估它们在动脉粥样硬化发生中的作用。目的2：我们将使用最近开发的PLTP敲除（plt0）小鼠来探索PLTP在脂蛋白代谢和动脉粥样硬化中的作用。我们将通过将CETP交叉到LTP0背景中来研究CETP和PLTP活动的可能冗余。plt0小鼠也将与载脂蛋白Tg小鼠杂交并进行动脉粥样硬化研究。这些研究将评估在高脂肪饮食的plt0小鼠中积累的磷脂/apoA-IV/apoE囊泡可能通过向新生HDL添加磷脂而具有抗动脉粥样硬化的PLTP的假设。该项目可能为甾醇调节脂质转移蛋白的分子机制提供明确的信息。它还将测试新的假设，即LXRs协调一个具有抗动脉粥样硬化后果的逆向胆固醇运输程序。最后，本文将评价PLTP缺乏作为抗动脉粥样硬化状态的新观点。该项目将与项目4有很强的相互作用，研究高密度脂蛋白介导的巨噬细胞胆固醇外排的机制，并将提供LXRs调控的新基因和途径的信息，这可能与项目1和项目2的研究相关。

Low HDL levels are a major atherogenic risk factor for which no specific treatment is yet available. The plasma liquid transfer proteins, cholestryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), play a an important part in HDL homeostasis. CETP transfers HDL CE to triglyceride-rich lipoproteins which are then taken up in the liver, in a process of reverse cholesterol or endogenous hypercholesterolemia. We have used natural flanking region CETP transgenic (Tg) mice, and reporter gene constructs, to localize the CETP response to a novel element in the gene proximal promoter, and we have shown that this positive response is mediated in vitro by the nuclear receptor, LXR. Since LXRalpha is known to mediate sterol up-regulation of cyp7a, the rate- limiting enzyme in the conversion of cholesterol into bile salts, our findings suggest that LXRs may help to coordinate the response of a variety of genes involved in cholesterol removal from the body. In Aim 1 we will use LXRalpha and beta knock-out mice to evaluate the role of LXRs in lipid transfer protein gene regulation in vivo and to explore the overall role of these transcription factors in regulating genes involved in reverse cholesterol transport; these mice will also be crossed onto atherosclerosis-susceptible backgrounds in order to evaluate their role in atherogenesis. Aim 2 we will use recently developed PLTP knockout-out (PLTP0) mice to explore the role of PLTP in lipoprotein metabolism and atherogenesis. We will investigate possible redundancy of CETP and PLTP activities by crossing CETP into the LTP0 background. PLTP0 mice will also be crossed with apoB Tg mice and atherosclerosis studies performed. These studies will evaluated the hypothesis that phospholipid/apoA-IV/apoE vesicles accumulating in PLTP0 mice on a high fat diet may have anti-atherogenic PLTP in adding phospholipids to nascent HDL. This project is likely to provide definitive information on the molecular mechanism of lipid transfer protein regulation by sterols. It will also test the novel hypothesis that LXRs coordinate a program of reverse cholesterol transport with anti-atherogenic consequences. Finally, it will evaluate a new idea concerning PLTP deficiency as an anti- atherogenic state. This project will have strong interactions with Project 4, investigating mechanisms of HDL-mediated cholesterol efflux from macrophages, and will provide information on novel genes and pathways regulated by LXRs, which may be relevant to studies in Projects 1 and 2.