HSPGs as remnant receptors: critical role in diabetic postprandial dyslipidemia

描述（由申请方提供）：动脉粥样硬化性心血管疾病仍然是1型和2型糖尿病（T1 DM、T2 DM）患者的主要死亡原因。动脉粥样硬化是由富含胆固醇的含载脂蛋白B（apoB）的脂蛋白滞留在血管壁内引起的。重要的是，糖尿病患者患有心血管风险的一个独特且通常被忽视的方面，即，每餐后血浆中存在显著持久性的来自母体的apoB-脂蛋白，称为“残余物”。原因是肝脏对这些有害颗粒的清除存在缺陷。这方面的一个主要障碍是我们对残留物进入肝脏的途径的无知。超过四分之一个世纪前，肝脏对残余物的摄取被证明不依赖于LDL受体。这一认识启动了对责任分子的长期而艰难的搜索。在1991-1992年，我们实验室的开创性工作涉及硫酸乙酰肝素蛋白聚糖（HSPGs）在残余脂蛋白摄取。每个HSPG分子由一条蛋白链组成，细胞在其上组装糖聚合物，称为硫酸乙酰肝素，我们发现它可以捕获脂蛋白。尽管存在大约50个直接参与肝脏HSPG组装和分解的基因，但到目前为止，我们的研究结果表明，糖尿病患者中只有其中两个基因失调。此外，T1 DM和T2 DM诱导不同的分子紊乱。首先，我们确定了Ndst 1，硫酸乙酰肝素组装中的关键酶，在体内T1 DM肝脏中特异性抑制。其次，在最近的一项重大突破中，我们发现T2 DM在肝脏中诱导了一种新的HSPG降解酶。因此，我们的中心假设是，T1 DM和T2 DM的致动脉粥样硬化、餐后血脂异常均由数量少得令人惊讶的直接影响肝脏HSPG结构的关键分子的失调引起。目的1将使用特异性基因转移来检验Ndst 1抑制是T1 DM中残基清除受损的原因的假设。由于Ndst 1缺陷可以掩盖其他HSPG组装酶的缺陷，我们将全面表征T1 DM中肝脏HSPG的结构、分子生物学和作为体内残余受体的功能，无论是否存在Ndst 1基因转移。目的2将使用体内特异性敲低来检验过表达的降解酶损害T2 DM中残留物清除的假设。为了确保一个全面的调查，我们将描述肝脏HSPG的精细结构，分子生物学，和餐后血脂异常的T2 DM，没有和敲低。总之，这些提出的目标将定义HSPG组装中的结构和分子紊乱，这些结构和分子紊乱是糖尿病餐后血脂异常的原因。这项工作将扩大我们对糖尿病过度心血管疾病的理解，并提供新的治疗靶点。 公共卫生相关性：1型和2型糖尿病患者患有致命和致残的动脉粥样硬化性心血管疾病，部分原因是每餐后血浆中有害的来源于母体的脂蛋白（称为“残余物”）的惊人持久性。基于我们的开创性工作，硫酸乙酰肝素蛋白聚糖（HSPG）在肝脏对残余脂蛋白的快速、健康处置中起着至关重要的作用，我们现在试图描述T1 DM和T2 DM中导致肝脏HSPG功能受损的结构和分子紊乱。通过扩大我们对糖尿病餐后血脂异常的病理生理学的理解，我们可能能够避免糖尿病心血管疾病的巨大过度负担。

DESCRIPTION (provided by applicant): Atherosclerotic cardiovascular disease remains the major cause of death in patients with type 1 and type 2 diabetes mellitus (T1DM, T2DM). Atherosclerosis arises from the retention of cholesterol-rich, apolipoprotein-B (apoB)-containing lipoproteins within the vessel wall. Importantly, diabetic patients suffer from a unique and typically neglected aspect of cardiovascular risk, namely, the striking persistence of intestinally derived apoB-lipoproteins, called 'remnants,' in their plasma after each meal. The cause is a defect in hepatic clearance of these harmful particles. A major impediment in this area has been our ignorance regarding pathways for remnant uptake into liver. Over a quarter century ago, hepatic uptake of remnants was shown to be independent of LDL receptors. This realization launched a long, difficult search for the responsible molecules. In 1991-1992, seminal work from our laboratory implicated heparan sulfate proteoglycans (HSPGs) in remnant lipoprotein uptake. Each HSPG molecule consists of a protein strand onto which the cell assembles sugar polymers, called heparan sulfate, that we showed could capture lipoproteins. Despite the existence of roughly 50 genes that are directly involved in hepatic HSPG assembly and disassembly, our results so far indicate dysregulation of only two of them in diabetes. Moreover, T1DM and T2DM induce distinct molecular derangements. First, we identified Ndst1, a key enzyme in heparan sulfate assembly, as specifically suppressed in T1DM liver in vivo. Second, in a major, recent breakthrough, we found that T2DM induces a novel HSPG degradative enzyme in liver. Thus, our central hypothesis is that the atherogenic, postprandial dyslipidemias of T1DM and T2DM each arise from dysregulation of a surprisingly small number of key molecules that directly affect hepatic HSPG structure. Aim 1 will use specific gene transfer to test the hypothesis that Ndst1 suppression is responsible for impaired remnant clearance in T1DM. Because Ndst1 deficiency can mask defects in other HSPG assembly enzymes, we will compre- hensively characterize hepatic HSPG structure, molecular biology, and function as remnant recep- tors in vivo in T1DM, without and with Ndst1 gene transfer. Aim 2 will use a specific knock-down in vivo to test the hypothesis that the overexpressed degradative enzyme impairs remnant clearance in T2DM. To ensure a comprehensive survey, we will characterize hepatic HSPG fine structure, molecular biology, and postprandial dyslipidemia in T2DM, without and with the knock-down. Overall, these proposed Aims will define the structural and molecular derangements in HSPG assembly that are responsible for diabetic postprandial dyslipidemias. The work will expand our understanding of excess cardiovascular disease in diabetes and provide novel therapeutic targets. PUBLIC HEALTH RELEVANCE: Project relevance to public health Patients with type 1 and type 2 diabetes mellitus suffer from fatal and disabling atherosclerotic cardiovascular disease that results in part from the striking persistence of harmful intestinally derived lipoproteins, called 'remnants,' in their plasma after each meal. Based on our seminal work implicating a crucial role for heparan sulfate proteoglycans (HSPGs) in the rapid, healthy disposal of remnant lipoproteins by the liver, we now seek to characterize the structural and molecular derangements responsible for impaired hepatic HSPG function in T1DM and T2DM. By expanding our understanding of the pathophysiology of diabetic postprandial dyslipidemias, we may be able to avert the tremendous excess burden of cardiovascular disease in diabetes.