CARNITINE TRANSPORTERS: STRUCTURE, FUNCTION & REGULATION

描述：(摘自申请摘要：)当前项目的目标 是研究质膜的结构、功能和调节 负责肉碱动态平衡的转运体和了解 这些转运蛋白与肉碱遗传性疾病的关系 新陈代谢。肉碱是脂肪酸氧化的必需品，因此对 维持心脏和骨骼肌等组织的能量状态。 原发性全身性肉碱缺乏是一种遗传性疾病，与 钠离子依赖的高亲和力肉碱转运体的缺陷。临床 这种疾病的症状主要是心脏和骨骼肌病。 这是由于细胞内肉碱水平下降所致。OCTN2基因编码 对于高亲和力的肉碱转运体。这是一种功能缺失突变 已在原发性全身性肉碱患者中发现基因 缺乏症。有趣的是，OCTN2也是一种药物转运体，与一种 各种药理活性药物。而生理学上的相关性 OCTN2的肉碱转运功能是可以理解的，药物转运 OCTN2的功能仍然是个谜。OCTN2可能在以下方面发挥重要作用 几种治疗剂的生物利用度和药代动力学。 此外，OCTN2的表达受过氧化体激活剂的下调 增殖物激活受体(PPAR)。这表明，长期使用 PPAR配体可能干扰OCTN2的表达并减少细胞内 肉碱水平。这是临床上相关的，因为几个PPAR配体 目前用作治疗剂(如瑞祖林、氯贝特)。在……里面 此外，肉碱具有抗细胞凋亡的活性，有理由 相信OCTN2是这一功能的必备条件。这项研究建议在 这项计划(A)以下列方式描述OCTN2的功能特征 强调其药物转运功能的不同方面以及 肉碱转运功能，(B)调查肉碱的调节方面 心脏、骨骼肌、肾脏、肠道、肝脏和胎盘中的OCTN2 尤其是关于PPAR和底物依赖的作用 调控OCTN_2的表达，(C)阐明OCTN_2的分子机制 肉碱及其酰基酯的抗细胞凋亡作用 OCTN2在这一进程中的作用，(D)确定负责以下工作的运输者 肉碱在极化组织中的载体转移，以及(E)确定 密切相关的转运蛋白OCTN3的功能同一性。这个 克隆的转运体的运输功能将进行以下测量 异源表达在哺乳动物细胞和乳突圆线虫卵母细胞中。这个 规则研究将在完整的动物中进行，使用老鼠作为 模型和人类来源的培养细胞也是如此。

DESCRIPTION: (From the application abstract:) The goals of the current project are to investigate the structure, function, and regulation of plasma membrane transporters responsible for carnitine homeostasis and to understand the relevance of these transporters to the genetic disorders ofcarnitine metabolism. Carnitine is obligatory for fatty acid oxidation and hence for the maintenance of the energy status in tissues such as heart and skeletal muscle. Primary systemic carnitine deficiency is a genetic disorder associated with defectsin the Na+ dependent high-affinity carnitine transporter. Clinical symptoms of the disease consist primarily of cardiac and skeletal myopathy resulting from decreased intracellular carnitine levels. The octn2 gene codes for the high-affinity carnitine transporter. Loss-of-function mutations in this gene have been identified in patients with primary systemic carnitine deficiency. Interestingly, OCTN2 is also a drug transporter with affinity for a variety of pharmacologically active drugs. While the physiological relevance of the carnitine transport function of OCTN2 is understandable, the drug transport function of OCTN2 remains an enigma. OCTN2 may play a significant role in the bioavailability and pharmacokinetics of a number of therapeutic agents. Furthermore, OCTN2 expression is down-regulated by activators of peroxisome proliferator-activated receptors (PPARs). This suggests that chronic use of PPAR ligands may interfere with OCTN2 expression and decrease intracellular carnitine levels. This is clinically relevant because several PPAR ligands are currently in use as therapeutic agents (e.g., Rezulin, clofibrate). In addition, carnitine possesses anti-apoptotic activity and there are reasons to believe that OCTN2 is obligatory for this function. Studies are proposed in this project (a) to delineate the functional characteristics of OCTN2 with emphasis on the differential aspects of its drug transport function and the carnitine transport function, (b) to investigate the regulatory aspects of OCTN2 in the heart, skeletal muscle, kidney, intestine, liver, and placenta particularly with respect to the role of PPARs and substrate-dependent modulation of OCTN2 expression, (c) to delineate the molecular mechanism of the anti-apoptotic function of carnitine and its acyl esters and to analyze the role of OCTN2 in this process, (d) to identify the transporters responsible for vectorial transfer of carnitine in polarized tissues, and (e) to determine the functional identity of the closely related transport protein OCTN3. The transport function of the cloned transporters will be measured following heterologous expression in mammalian cells and in X. laevis oocytes. The regulation studies will be carried out in intact animals using the rat as a model and also in cultured cells of human origin.