A new mechanism for human hypertriglyceridemia and new avenues for investigating intravascular triglyceride metabolism

在过去的5年里，我们一直致力于脂蛋白脂肪酶(LPL)和血管内脂肪分解，重点关注我们最初拨款申请的具体目标。我们的研究一直很有成效，发表了一些论文，描述了对与GPIHBP1相互作用的LPL序列的见解，以及对GPIHBP1介导的LPL跨内皮细胞运输的细胞机制的见解。在这次续签申请中，我们提出了三个新的具体目标。第一个目的与我们的发现有关，即一些人类高甘油三酯血症是由GPIHBP1自身抗体引起的。我们现在需要更好地描述这种新的疾病综合征，并确定其频率。我们的第二个目标与我们的发现有关，即GPIHBP1存在于人血浆中，并且GPIHBP1水平可以用酶联免疫吸附试验定量。我们现在需要确定血浆中的GPIHBP1水平是否是代谢或血管疾病的有用生物标记物。我们的第三个目标是研究LPL-GPIHBP1复合体的持久和根本问题，包括复合体的化学计量比以及它的稳定性和活性如何受到生理变量的影响。我们已经积累了大量的初步数据，以支持我们拟议的研究的可行性。关于第一个特定目标，我们已经在6名高甘油三酯血症患者的血浆样本中记录了GPIHBP1自身抗体。其中一名患者怀孕了，不出所料，自身抗体穿过了胎盘。新生儿的血浆中含有GPIHBP1自身抗体，导致极严重(但短暂的)高甘油三酯血症。GPIHBP1自身抗体导致高甘油三酯血症的发现是一项翻译发现，对医学诊断和治疗具有重大意义。我们现在需要更好地确定GPIHBP1自身抗体的特征，并确定“GPIHBP1自身抗体综合征”的频率。对于第二个特定目的，我们已经开发并鉴定了抗人GPIHBP1的单抗，并使用其中的两种抗体创建了人GPIHBP1的ELISA。我们的酶联免疫吸附试验准确地定量了血浆中的GPIHBP1。我们准备与遗传流行病学研究的领导者合作，测试血浆GPIHBP1水平是否是血管或代谢性疾病的有用生物标记物。关于第三个具体目标，我们在理解LPL-GPIHBP1复合体和制定研究该复合体的实验方法方面取得了实质性进展。我们的研究表明，新分泌的LPL上只有一个GPIHBP1结合位点(尽管LPL被广泛认为是同源二聚体)。相关研究表明，GPIHBP1只与LPL的一个分子结合。我们需要用更多的实验平台来证实这些结果，包括表面等离子体共振研究。我们还需要确定LPL-GPIHBP1相互作用如何受到生理变量的影响，如活性甘油三酯脂解或抑制蛋白(例如，ANGPTL4)。这些研究将大大增加我们对LPL-GPIHBP1相互作用和血管内脂肪分解的生理学的了解。

During the past 5 years, we have pursued our interest in lipoprotein lipase (LPL) and intravascular lipolysis, focusing on the specific aims in our original grant application. Our studies have been productive, yielding papers that describe insights into the LPL sequences that interact with GPIHBP1 and insights into the cellular mechanisms for GPIHBP1-mediated transport of LPL across endothelial cells. In this renewal application, we have proposed three new specific aims. The first aim relates to our discovery that some cases of human hypertriglyceridemia are caused by GPIHBP1 autoantibodies. We now need to better characterize this new disease syndrome and define its frequency. Our second aim relates to our discovery that GPIHBP1 is present in human plasma and that GPIHBP1 levels can be quantified with an ELISA. We now need to determine if GPIHBP1 levels in the plasma are a useful biomarker of metabolic or vascular disease. Our third aim deals with persistent and fundamental questions regarding the LPL–GPIHBP1 complex, including the stoichiometry of the complex and how its stability and activity are influenced by physiologic variables. We have accumulated substantial preliminary data to support the feasibility of our proposed studies. With regard to the first specific aim, we have already documented GPIHBP1 autoantibodies in plasma samples from six patients with hypertriglyceridemia. One of the patients became pregnant and, as expected, the autoantibodies crossed the placenta. The newborn infant’s plasma contained GPIHBP1 autoantibodies, resulting in extremely severe (but transient) hypertriglyceridemia. The discovery that GPIHBP1 autoantibodies cause hypertriglyceridemia is a translational discovery with major implications for medical diagnostics and therapeutics. We now need to better characterize GPIHBP1 autoantibodies and determine the frequency of the “GPIHBP1 autoantibody syndrome.” For the second specific aim, we already developed and characterized monoclonal antibodies against human GPIHBP1 and used two of the antibodies to create an ELISA for human GPIHBP1. Our ELISA accurately quantifies GPIHBP1 in the plasma. We are poised to collaborate with leaders of genetic–epidemiology studies to test whether plasma GPIHBP1 levels are a useful biomarker of vascular or metabolic disease. With regard to the third specific aim, we have made substantial progress in understanding the LPL–GPIHBP1 complex and in developing experimental approaches to study that complex. Our studies suggest that there is only a single binding site for GPIHBP1 on newly secreted LPL (despite the fact that LPL is widely presumed to be a homodimer). Related studies suggest that GPIHBP1 binds only one molecule of LPL. We need to confirm these results with additional experimental platforms, including surface plasmon resonance studies. We also need to determine how LPL–GPIHBP1 interactions are affected by physiologic variables such as active triglyceride lipolysis or inhibitor proteins (e.g., ANGPTL4). These studies will add substantially to our understanding of LPL–GPIHBP1 interactions and the physiology of intravascular lipolysis.