Vascular Biochemistry of Vitamin B12

描述（由申请人提供）：微量营养素B12（钴胺素，Cbl）在体内大多数细胞（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，也与神经管缺陷和阿尔茨海默病等其他破坏性疾病有关。高同型半胱氨酸血症的决定因素是多因素的，包括遗传和获得性条件。钴胺素在心血管细胞和组织中的转运、加工和辅酶的形成是一个被忽视的研究领域。本研究的长期目标是了解1)培养的人主动脉内皮细胞和平滑肌细胞中Cbl的转运过程，2)这些细胞中Cbl的加工过程，以及3)Cbl维生素分别转化为甲基钴胺素和腺苷钴胺素，这两种辅酶分别是胞质蛋氨酸合成酶和线粒体甲基丙二酰辅酶a变化酶。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)它通过将钴酸盐结合蛋白转钴胺素从尿囊（顶部）空间转运到尿囊（基底外侧）空间，并将钴酸盐作为货物转运到尿囊（基底外侧）空间；3)内皮细胞损伤，如发生在动脉粥样硬化和动脉粥样硬化中，可能导致局部破坏Cbl稳态；4)由于激素半胱氨酸再甲基化机制的破坏，导致高激素半胱氨酸血症，Cbl缺乏本身是血管天花板功能障碍的一个原因。本课题的具体目的是：1)建立培养的人主动脉内皮细胞和平滑肌细胞中Cbl转运和胞吞作用的机制；2)确定Cbl在培养血管细胞中的加工过程，以及谷胱甘肽-Cbl在这一加工过程中所起的作用；3)阐明体外培养的人主动脉内皮细胞和平滑肌细胞中Cbl辅酶的形成机制。

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.