Apo B Translocation and Degradation

描述（由申请方提供）：肝脏产生含载脂蛋白B的脂蛋白在脂质代谢中起着不可或缺的作用。含载脂蛋白B的脂蛋白的产生或其被肝脏去除的不平衡与包括动脉粥样硬化、肥胖和糖尿病在内的几种疾病有关。使用培养的肝细胞和遗传改变的小鼠获得的数据使我们假设，含有脂蛋白的载脂蛋白B的肝脏分泌是转录后调节的。在其翻译过程中，载脂蛋白B有两种代谢命运：在添加脂质以形成脂蛋白颗粒的过程中易位到内质网（ER）的内腔中或通过泛素依赖性蛋白酶体途径降解。微粒体甘油三酯转移蛋白（MTP）和甘油脂（磷脂和甘油三酯）的供应在介导载脂蛋白B易位和组装成脂蛋白颗粒中起着重要作用。基于在上一个资助期内获得的新的和有趣的见解，我们将努力实现以下具体目标： 具体目标1：确定COUP-TFII如何与MTP启动子中的保守DR 1位点相互作用，并改变大鼠肝癌细胞和小鼠肝脏中的基因转录。 具体目标二：研究泛素依赖性蛋白酶体降解在调节载脂蛋白B在小鼠肝脏中的体内代谢命运中的作用。 具体目标3：研究Txnip基因缺失改变碳单位流入脂质和含载脂蛋白B脂蛋白分泌的机制。 显然，MTP介导的易位和脂质转移是改善最严重形式的高胆固醇血症之一的有效靶点（大多数其他药物[例如他汀类药物]对此无效;即，纯合子家族性高胆固醇血症）。我们相信，我们提出的研究将提供新的见解，将进一步证明控制载脂蛋白B加工途径的可行性和推进治疗潜力。

DESCRIPTION (provided by applicant): Hepatic production of apo B-containing lipoproteins plays an integral role in lipid metabolism. Imbalances of the production of apo B-containing lipoproteins or their removal by the liver are associated with several diseases including atherosclerosis, obesity and diabetes. Data obtained using cultured hepatocytes and genetically altered mice have led us to hypothesize that hepatic secretion of apo B containing lipoproteins is regulated post-transcriptionally. During its translation, apo B has two metabolic fates: translocation into the lumen of the endoplasmic reticulum (ER) during the addition of lipid to form a lipoprotein particle or degradation by an ubiquitin-dependent proteasome pathway. Microsomal triglyceride transfer protein (MTP) and the supply of glycerolipids (phospholipids and triglycerides) play an essential role in mediating apo B translocation and assembly into a lipoprotein particle. Based on new and intriguing insights gained during the previous funding period, we will direct our efforts to the following Specific Aims: Specific Aim 1: To define how COUP-TFII interacts with a conserved DR1 site in the MTP promoter and alters gene transcription in rat hepatoma cells and in vivo in the livers of mice. Specific Aim 2: To examine the role of ubiquitin-dependent proteasome degradation in regulating the metabolic fate of apo B in vivo in the livers of mice. Specific Aim 3: To examine the mechanism through which genetic deletion of Txnip alters the flow of carbon units into lipids and secretion of apo B-containing lipoproteins. Clearly, MTP-mediated translocation and lipid transfer is an effective target for ameliorating one of the most severe forms of hypercholesterolemia (for which most other drugs [e.g. statins] are ineffective; i.e., homozygous familial hypercholesterolemia). We are confident that our proposed studies will provide new insights that will add further proof to the feasibility and advance the therapeutic potential of controlling the apo B processing pathway.