APO B TRANSLOCATION AND DEGRADATION

肝脏过量产生含载脂蛋白b的脂蛋白是一种常见的家族性合并高脂血症与过早心血管疾病相关的原因。我们在小鼠中提出的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，我们提出以下具体目标：1)检验MTP和载脂蛋白B的相对表达水平有助于确定肝脏组装和分泌载脂蛋白B的最大能力的假设。在这些研究中，我们将使用改变了MTP和apo B100表达的近交系C57BL/6小鼠。2)探讨家族性合并高脂血症的基础是过量产生和分泌含载脂蛋白b的脂蛋白。利用一种新的突变小鼠克隆，其基因型和表型与人类家族性合并高脂血症的基因型和表型密切相关，我们将确定这种常见高脂血症的分子基础。3)明确L35细胞中MTP启动子失活的分子机制。L35细胞表现出类似于非高脂蛋白血症肝脏的表型（即遗传性MTP表达缺失和无法分泌载脂蛋白b）。我们将描述L35细胞中MTP基因失活的机制，使用我们已经展示的复制内源性MTP基因转录活性的启动子结构。4)探讨肝细胞中MTP、载脂蛋白B和脂肪生成酶的相对表达水平随解剖定位和生理营养状态的变化而动态变化的假说。从我们提出的小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制定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.