APO B TRANSLOCATION AND DEGRADATION

肝脏过度产生载脂蛋白B是一种常见形式的家族性混合性高脂血症，与早产儿心血管疾病相关。我们拟议的小鼠机制研究将使我们能够确定在正常和高脂血症动物和人类中负责调节脂蛋白分泌的因素和过程。为了实现这一目标，我们提出了以下具体目标：1)验证MTP和apo B的相对表达水平有助于确定肝脏组装和分泌含apo B的脂蛋白的最大容量的假设。在这些研究中，我们将使用近交系C57BL/6小鼠，它们改变了MTP和apo B100的表达。2)验证载脂蛋白B过度产生和分泌是家族性混合性高脂血症的基础这一假说。利用一种新的突变小鼠克隆，显示出与人类家族性混合型高脂血症密切相关的基因和表型，我们将确定这种常见高脂血症的分子基础。3)探讨L35细胞MTP启动子失活的分子机制。L35细胞的表型与非脂蛋白血症的肝脏相似(即MTP表达的遗传缺失和不能分泌含载脂蛋白B的脂蛋白)。我们将使用我们已经证明的复制内源性MTP基因转录活性的启动子结构来描述导致L35细胞MTP基因失活的机制。4)验证单个肝细胞MTP、apo B和造脂酶的相对表达水平随着解剖定位和生理营养状态的变化而动态变化的假说。从我们提议的老鼠研究中获得的知识将使我们第一次能够确定从培养细胞模型中提出的假设的生理学意义。从这些拟议的研究中获得的新见解应该有助于设计可能预防人类高脂血症和动脉粥样硬化形成的饮食和药物。

Overproduction of apo B-containing lipoproteins by the liver is responsible for a common form of familial combined hyperlipidemia associated with premature cardiovascular disease. Our proposed mechanistic studies in mice will allow us to identify the factors and processes responsible for regulating the secretion of lipoproteins in normal and hyperlipidemic animals and humans. To achieve this goal, we propose the following Specific Aims: 1) To examine the hypothesis that the relative level of expression of MTP and apo B contribute toward determining the maximal capacity of the liver to assemble and secrete apo B-containing lipoproteins. For these studies we will use inbred C57BL/6 mice which have altered expression of MTP and apo B100. 2) To examine the hypothesis that over-production and secretion of apo B-containing lipoproteins is the basis for familial combined hyperlipidemia. Using a novel mutant mouse clone displaying a genotype and phenotype that closely reflects a human form of familial combined hyperlipidemia, we will determine the molecular basis for this common hyperlipidemic disorder. 3) To define the molecular mechanism responsible for the inactivation of the MTP promoter in L35 cells. L35 cells show a phenotype similar to that of livers from abetalipoproteinemics (i.e. genetic loss of MTP expression and an inability to secrete apo B-containing lipoproteins). We will delineate the mechanism responsible for inactivation of the MTP gene in L35 cells using the promoter constructs that we have shown replicates the transcriptional activity of the endogenous MTP gene. 4) To examine the hypothesis that the relative level of expression of MTP, apo B and lipogenic enzymes displayed by individual liver cells varies dynamically with anatomical localization and changes in physiologic and nutritional state. The knowledge gained from our proposed studies in mice will allow us for the first time to determine the physiologic significance of hypotheses formulated from cultured cell models. New insights gained from these proposed studies should be useful in designing diets and pharmacologic agents that may prevent hyperlipidemia and the formation of atherosclerosis in humans.