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）和血管内脂解的研究，专注于我们最初的资助申请中的具体目标。我们的研究是富有成效的，产生的论文，描述了与GPIHBP 1相互作用的LPL序列的见解和GPIHBP 1介导的LPL跨内皮细胞转运的细胞机制的见解。在这次更新申请中，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，即人类高胆红素血症的一些病例是由GPIHBP 1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。我们的第二个目的涉及我们发现GPIHBP 1存在于人血浆中，并且GPIHBP 1水平可以用ELISA定量。我们现在需要确定血浆中GPIHBP 1水平是否是代谢或血管疾病的有用生物标志物。我们的第三个目标是处理关于LPL-GPIHBP 1复合物的持久性和根本性问题，包括复合物的化学计量以及其稳定性和活性如何受到生理变量的影响。我们已累积了大量初步数据，以支持我们建议的研究的可行性。关于第一个具体的目标，我们已经记录了GPIHBP 1自身抗体的血浆样本中的6例高脂血症。其中一名患者怀孕了，正如预期的那样，自身抗体穿过了胎盘。新生儿血浆中含有GPIHBP 1自身抗体，导致极严重（但短暂）的高血糖症。GPIHBP 1自身抗体导致高脂血症的发现是一个转化发现，对医学诊断和治疗有重大意义。我们现在需要更好地表征GPIHBP 1自身抗体并确定“GPIHBP 1自身抗体综合征”的频率。对于第二个具体目标，我们已经开发并表征了针对人GPIHBP 1的单克隆抗体，并使用其中两种抗体来创建针对人GPIHBP 1的ELISA。我们的ELISA准确定量血浆中的GPIHBP 1。我们准备与遗传流行病学研究的领导者合作，以测试血浆GPIHBP 1水平是否是血管或代谢疾病的有用生物标志物。关于第三个具体目标，我们在了解LPL-GPIHBP 1复合物和开发研究该复合物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GPIHBP 1结合位点（尽管LPL被广泛认为是同源二聚体）。相关研究表明，GPIHBP 1仅结合LPL的一个分子。我们需要用额外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-GPIHBP 1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-GPIHBP 1相互作用和血管内脂解生理学的理解。

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.