Vascular Biochemistry of Vitamin B12

描述（由申请人提供）：微量营养素B12（钴胺素，Cbl）在体内大多数（如果不是所有）细胞的同型半胱氨酸代谢中起重要作用。高同型半胱氨酸血症是心血管疾病的主要独立危险因素，也与其他破坏性疾病如神经管缺陷和阿尔茨海默病有关。高同型半胱氨酸血症的决定因素是多因素的，包括遗传和后天条件。心血管细胞和组织的钴胺素转运、加工和辅酶形成是一个被忽视的研究领域。本提案的长期目标是了解1）Cbl在培养的人主动脉内皮细胞和平滑肌细胞中的转运过程，2）Cbl在这些细胞内的加工，以及3）Cbl维生素转化为甲基钴胺素和腺苷钴胺素，分别为细胞溶质甲硫氨酸合酶和线粒体甲基丙二酸单酰辅酶A的辅酶。本研究基于以下假设：1）血管内皮在维持全身Cbl稳态中起重要作用; 2）它通过Cbl结合蛋白transcobalarnin从/尿/（顶/）空间到/尿/（顶/）空间的胞质转运而起作用。（基底外侧）空间，以Cbl作为其货物; 3）如在动脉粥样硬化形成和动脉粥样硬化中发生的内皮细胞损伤可引起Cbl稳态的局部破坏;和4）Cbl缺乏本身是由于角半胱氨酸再甲基化机制的破坏而导致血管细胞功能障碍的原因，其导致高角半胱氨酸血症。本提案的具体目的是：1）建立Cbl在培养的人主动脉内皮细胞和平滑肌细胞中转运和转胞吞的机制; 2）确定Cbl在培养的血管细胞中如何加工以及谷胱甘肽-Cbl在该加工中发挥的作用; 3）阐明Cbl辅酶在培养的人主动脉内皮细胞和平滑肌细胞中形成的机制。

DESCRIPTION (provided by applicant): The micronutrient B12 (cobalamin, Cbl) plays an essential role in homocysteine metabolism in most if not all cells in the body. Hyperhomocysteinemia is a major independent risk factor for cardiovascular disease and is also associated with other devastating conditions such as neural tube defects and Alzheimer's disease. The determinants of hyperhomocysteinemia are multifactorial and include both genetic and acquired conditions. Cobalamin transport, processing and coenzyme formation by cardiovascular cells and tissues is a neglected area of research. The long-term objectives of this proposal are to gain an understanding of 1) Cbl transport processes in cultured human aortic endothelial cells and smooth muscle cells, 2) Cbl processing within these cells, and 3) the conversion of Cbl vitamers to methylcobalamin and adenosylcobalamin, coenzymes for cytosolic methionine synthase and mitochondrial methylmalonyI-CoA mutase, respectively. This study is driven by the hypotheses that 1) the vascular endotheliurn plays an essential role in maintaining Cbl homeostasis throughout the body; 2) it does so by a//owing the Cbl-binding protein transcobalarnin to transcytose from the/urinal/(apical/) space to the ablurninal (basolateral) space with Cbl as its cargo; 3) endothelial ceil injury, as occurs in atherogenesis and atherosclerosis, may cause localized disruption of Cbl homeostasis; and 4) Cbl deficiency itself/f is a cause of vascular ceil dysfunction due to a breakdown of the hornocysteine rernethylation machinery, which leads to hyperhornocysteinernia. The Specific Aims of this proposal are: 1) to establish the mechanisms of Cbl transport and transcytosis in cultured human aortic endothelial and smooth muscle cells; 2) to determine how Cbl is processed in cultured vascular cells and the role that glutathionyl-Cbl plays in this processing; and 3) to elucidate the mechanisms of Cbl coenzyme formation in cultured human aortic endothelial and smooth muscle cells.