HSPGs as remnant receptors: critical role in diabetic postprandial dyslipidemia

描述（由申请人提供）：动脉粥样硬化性心血管疾病仍然是1型和2型糖尿病（T1DM、T2DM）患者死亡的主要原因。动脉粥样硬化是由于富含胆固醇、含载脂蛋白b （apoB）的脂蛋白滞留在血管壁内而引起的。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，即每次饭后血浆中存在肠道来源的载脂蛋白，称为“残留物”。原因是肝脏对这些有害颗粒的清除有缺陷。这个领域的一个主要障碍是我们对残体进入肝脏的途径的无知。超过25年前，肝脏对残体的摄取被证明是独立于LDL受体的。这一认识开启了对相关分子的漫长而艰难的探索。在1991-1992年，我们实验室的开创性工作表明硫酸肝素蛋白聚糖（HSPGs）与残余脂蛋白摄取有关。每个HSPG分子由一条蛋白质链组成，细胞在其上组装称为硫酸肝素的糖聚合物，我们证明了它可以捕获脂蛋白。尽管存在大约50个基因直接参与肝脏HSPG的组装和拆卸，但我们的研究结果迄今为止表明糖尿病中只有两个基因失调。此外，T1DM和T2DM诱导不同的分子紊乱。首先，我们发现Ndst1是硫酸肝素组装的关键酶，在T1DM肝脏中被特异性抑制。其次，在最近的一项重大突破中，我们发现T2DM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，T1DM和T2DM的动脉粥样硬化、餐后血脂异常都是由直接影响肝脏HSPG结构的少数关键分子的失调引起的。目的1将使用特定的基因转移来验证Ndst1抑制是导致T1DM残体清除受损的原因。由于Ndst1的缺乏可以掩盖其他HSPG组装酶的缺陷，我们将全面表征肝脏HSPG的结构、分子生物学以及在T1DM中作为残余受体的功能，无论Ndst1基因是否转移。目的2将在体内使用特异性敲除来验证过表达的降解酶损害T2DM残体清除的假设。为了确保全面的调查，我们将描述T2DM患者肝脏HSPG精细结构、分子生物学和餐后血脂异常，有无敲除。总的来说，这些拟议的目标将确定HSPG组装的结构和分子紊乱，这些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。

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.