New Avenues in GPIHBP1 Research

项目摘要/摘要 这项建议的目的是确定GPIHBP1是否对脂类分解特别重要 含apo-B48的脂蛋白的加工，以了解Gpihbp1缺陷的动脉粥样硬化 (Gpihbp1-/-)小鼠，并为自然发生的GPIHBP1建立和分析敲入小鼠模型 人类的突变。 我们最近发现Gpihbp1-/-小鼠有乳糜粒微粒血症，即使在饮食中也是如此，并伴有血浆甘油三酯。 胆固醇水平高达8000毫克/分升，血浆胆固醇水平高达800毫克/分升。因为GPIHBP1是 位于“脂解组织”(如心脏、肌肉、脂肪)的毛细血管的管腔表面，因为 GPIHBP1结合脂蛋白脂酶(LPL)和乳糜粒，我们怀疑GPIHBP1是一种 富含甘油三酯的脂蛋白代谢处理平台。值得注意的是，GPIHBP1包含一个强烈的 带负电荷的氨基末端结构域，对结合脂蛋白和脂蛋白很重要。 Gpihbp1-/-小鼠血浆中含有apo-B48的脂蛋白水平升高，但正常水平 含有载脂蛋白B100的脂蛋白。我推测GPIHBP1可能在 含载脂蛋白B48的脂蛋白的加工。为了探索这一假设，我将研究 ApoB中“仅apo-B100”或“apo-B48-only”突变为纯合子的Gpihbp1-/-小鼠。 大的脂蛋白，如乳糜粒，通常被认为不会导致动脉粥样硬化，但我有 研究表明，喂食Gpihbp1-/-小鼠会出现自发性动脉粥样硬化病变。以确定是否 Gpihbp1-/-小鼠的动脉粥样硬化是由富含甘油三酯的脂蛋白的胆固醇含量驱动的，即 将研究ezetimibe和NPC1L1缺乏对Gpihbp1-/-小鼠易感性的影响 动脉硬化。 最近，GPIHBP1基因G56R和Q115P纯合子突变在慢性阻塞性肺疾病患者中被发现。 乳糜体微粒血症。这两种突变都发生在高度保守的残基中。我发现Q115P突变 取消了GPIHBP1与LPL或乳糜粒结合的能力，但G56R突变没有检测到 效果--通过体外试验来判断。这些发现给我留下了不确定性，即试管内的 GPIHBP1检测是体内GPIHBP1功能的可靠指标。为了探讨这个问题，我将 建立和鉴定G56R和Q115P突变的敲入小鼠模型。 这项建议的三个具体目标是：(1)确定GPIHBP1是否对 清除含apo-B48的脂蛋白；(2)确定喂食Gpihbp1的动脉粥样硬化病变是否- /-小鼠是由富含甘油三酯的脂蛋白的胆固醇含量驱动的；和(3)创造敲入小鼠 GPIHBP1的G56R和Q115P突变模型。与公共卫生的相关性 了解脂蛋白代谢很重要，因为血浆脂蛋白将甘油三酯燃料输送到 因为脂蛋白是动脉粥样硬化形成的致病因素。该项目的一个关键目标是 了解GPIHBP1在脂蛋白脂肪酶介导的富含甘油三酯的脂蛋白加工中的作用。 这项拟议的研究可能会提供有关脂肪营养如何输送到重要组织的新信息； 我的实验还将探索Gpihbp1缺乏和动脉粥样硬化的机制 确定特定的人类GPIHBP1错义突变在体内的相关性。

PROJECT SUMMARY/ABSTRACT The objectives of this proposal are to determine if GPIHBP1 is particularly important for the lipolytic processing of apo-B48-containing lipoproteins, to understand the atherosclerosis in Gpihbp1-deficient (Gpihbp1-/-) mice, and to create and analyze knock-in mouse models for naturally occurring GPIHBP1 mutations in humans. We recently found that Gpihbp1-/- mice have chylomicronemia, even on chow diet, with plasma triglyceride levels as high as 8000 mg/dl and plasma cholesterol levels as high as 800 mg/dl. Because GPIHBP1 is located on the luminal surface of capillaries of "lipolytic tissues" (e.g., heart, muscle, fat) and because GPIHBP1 binds both lipoprotein lipase (LPL) and chylomicrons, we suspect that GPIHBP1 serves as a platform for the metabolic processing of triglyceride-rich lipoproteins. Of note, GPIHBP1 contains a strongly negatively charged amino-terminal domain that is important for binding both LPL and lipoproteins. Gpihbp1-/- mice have elevated levels of apo-B48-containing lipoproteins in their plasma, but normal levels of apo-B100-containing lipoproteins. I hypothesize that GPIHBP1 may have a particularly important role in the processing of apo-B48-containing liporoteins. To explore this hypothesis, I will examine the phenotypes of Gpihbp1-/- mice that are homozygous for the "apo-B100-only" or "apo-B48-only" mutations in Apob. Large lipoproteins such as chylomicrons are generally assumed to be nonatherogenic, but I have demonstrated that chow-fed Gpihbp1-/- mice develop spontaneous atheroscerotic lesions. To determine if the atherosclerosis in Gpihbp1-/- mice is driven by the cholesterol content of the "triglyceride-rich" lipoproteins, I will examine the impact of ezetimibe and Npc1l1 deficiency on the susceptibility of Gpihbp1-/- mice to atherosclerosis. Recently, homozygous G56R and Q115P mutations in GPIHBP1 were identified in patients with chylomicronemia. Both mutations occurred in highly conserved residues. I found that the Q115P mutation abolishes the ability of GPIHBP1 to bind to LPL or chylomicrons, but the G56R mutation had no detectable effect-as judged by in vitro assays. These findings left me with uncertainty regarding whether the in vitro assays of GPIHBP1 were truly reliable indicators of GPIHBP1 function in vivo. To explore this issue, I will generate and characterize knock-in mouse models for the G56R and the Q115P mutations. The three specific aims of this proposal are: (1) to determine if GPIHBP1 is particularly important for the clearance of apo-B48-containing lipoproteins; (2) to determine if atherosclerotic lesions in chow-fed Gpihbp1- /- mice are driven by the cholesterol content of "triglyceride-rich" lipoproteins; and (3) to create knock-in mouse models for the G56R and Q115P mutations in GPIHBP1. RELEVANCE TO PUBLIC HEALTH Understanding lipoprotein metabolism is important because plasma lipoproteins deliver triglyceride fuel to vital tissues and because lipoproteins are causal factors in atherogenesis. A key goal of this project is to understand the role of GPIHBP1 in the lipoprotein lipase-mediated processing of triglyceride-rich lipoproteins. The proposed studies are likely to provide new information on how lipid nutrients are delivered to vital tissues; my experiments will also explore mechanisms for atherosclerosis in the setting of Gpihbp1 deficiency and define the in vivo relevance of specific human GPIHBP1 missense mutations.