HEPATIC METABOLISM OF DIET DERIVED LIPOPROTEINS

这是一个长期项目的持续资金的要求， 饮食来源的胆固醇如何代谢并影响整体 胆固醇稳态多年来，该计划一直是一个 主要焦点，研究肝切除的机制， 乳糜微粒残留。在上一个资助期内， 细胞膜、肝细胞和完整的小鼠， 有三种方法可以去除残留物的主要决定因素 在正常动物中最后一个被摄取的是LDL受体。新 发现LRP对这些颗粒的亲和力较低， LDL受体的备份机制，但数量较少 在正常动物中很重要。此外，完整的肝脏可能 在迪斯空间隔离残余物，我们称之为， 筛分.这将构成第三种途径，可以起到清除 甚至是apoE缺陷颗粒。肝脂肪酶，载脂蛋白E， 糖胺聚糖，可能介导的筛选，似乎是旁分泌 加速LDL吸收的因素。在接下来的时间里，我们 建议研究继续测试这些途径，并评估其 在不同国家的数量。脉冲追踪肝脏灌注 然后进行细胞分离研究，以精确测量 筛分的贡献。LDL受体的竞争性抑制剂， LRP已经准备好，并将准备好，以及它们对残留物清除的影响， 将研究离体肝脏和体内。脂蛋白摄取 分泌apoE、肝脂酶和/或表达锚定形式的细胞 肝脂肪酶的活性。细胞内脂蛋白摄取 培养，并在体内将其与其他相同的细胞进行比较 不分泌这些蛋白质。一旦体外系统提供了 对清除残余物的各种因素的一般了解 途径，将评估它们在体内的相对重要性。这将是 使用表达多种基因工程的完整小鼠， 系统各组成部分的缺陷。待研究的小鼠 包括apoE缺陷和肝脂酶缺陷小鼠，以及 在肝外部位过度表达LDL受体， 肝脂肪酶位于肝脏。通过这些研究，我们将获得 对残留物吸收机制的组成部分有全面的了解 以及改变和缺陷如何影响整个系统。

This is a request for continued funding for a long term program to learn how diet derived cholesterol is metabolized and affects overall cholesterol homeostasis. For a number of years, the program has had as a major focus, investigation of the mechanism of hepatic removal of chylomicron remnants. During the last grant period, studies with liver cell membranes, hepatocytes, and intact mice has led to the hypothesis that there are three pathways for remnant removal. The major determinant of remnant uptake in the normal animal is the LDL receptor. The newly discovered LRP has a lower affinity for these particles and serves as a backup mechanism for the LDL receptor, but is quantitatively less important in the normal animal. In addition, the intact liver may sequester remnants in the space of Disse, a process we have termed, sieving. This would constitute a third pathway and could function to clear even apoE deficient particles. Hepatic lipase, apoE, and glycosaminoglycans, may mediate the sieving, and seem to be paracrine factors that accelerate the uptake of LDL. During the next period, we propose studies to continue to test these pathways and assess their quantitative significance in various states. Pulse chase liver perfusion followed by cell isolation studies are proposed to precisely measure the contribution of sieving. Competitive inhibitors of the LDL receptor and the LRP have, and will be prepared, and their effect on remnant removal in the isolated liver and in vivo will be studied. Lipoprotein uptake by cells that secrete apoE, hepatic lipase, and/or express an anchored form of hepatic lipase, have been prepared. Lipoprotein uptake, both in cell culture, and in vivo will be compared to that of otherwise identical cells that do not secrete these proteins. Once the in vitro systems provide a general understanding of the various contributors to the remnant removal pathways, their relative importance in vivo will be assessed. This will be done using intact mice expressing a variety of genetically engineered defects in the various components of the system. The mice to be studied include apoE deficient and hepatic lipase deficient, as well as mice that over-express LDL receptors in an extra-hepatic site, and mice that express hepatic lipase localized to the liver. From these studies, we will obtain a complete understanding of the components of the remnant uptake mechanism and how alterations and deficiencies affect the entire system.