Sialyl transferase function in vascular biology

将唾液酸转化为糖蛋白和糖脂的酶称为唾液酸转移酶。唾液酸加成通常终止进一步的低聚糖生物合成，从而可以产生并掩盖与生物相关的糖链结构。在脊椎动物中，存在一个高度保守的唾液酸基转移酶基因家族，至少包含18个成员。这些基因的表达谱通常是发育受限的，细胞或 特定于组织类型。从有限的研究到目前为止，唾液酸链已经被发现调节细胞的运输，黏附，血浆中的糖蛋白半衰期，以及涉及多亚单位受体复合体的信号转导。在体内确定唾液酸基转移酶基因功能时，在胚胎干细胞和成年小鼠中使用Cre-loxP定点重组产生小鼠生殖系突变。随后，通过使用本计划项目拨款提供的特定表型核心设施来评估生理参数。通过这种方式，我们以前的发现已经为特定的唾液酸基转移酶基因确立了关键的止血和免疫学作用。例如，ST3Gal-I和ST3Gal-IV促进血小板动态平衡，而ST3Gal-IV缺乏特异性地导致小鼠常染色体显性Yon Willebrand病样综合征。这个项目的目标是进一步阐明血管和 唾液酸基转移酶ST3Gal-I、ST3Gal-IV和新近发现的ST3Gal-VI的天然免疫功能。他们在掩蔽特定的去唾液酸糖蛋白受体配体中的作用，以及ST3Gal-IV作为人类VWD修饰剂的可能参与。我们对ST3Gal唾液酸转移酶突变体的研究进一步得出了这样的假设，即ST3Gal-VI对于选择素配体的形成是必不可少的，从而在炎症过程中发挥先天免疫功能。这一假说将通过产生ST3Gal-VI基因功能缺陷的小鼠并使用PPG Core设备进行表型分析来进行研究，这些分析涉及确定血管和先天免疫参数以及选择素配体的形成和 基于选择素的生理反应。这些ST3Gal唾液酸转移酶的血管和先天免疫功能也被认为影响伤口愈合和细菌入侵。这些假定的ST3Gal-I、ST3Gal-IV和ST3Gal-VI的保护作用将通过PPG核心设施进行研究。这些研究将确定α2-3连接唾液酸在调节血管和免疫系统中的作用机制，并可能建立重要的作用，可能导致对人类疾病的新见解。

Enzymes that transfer sialic acids to glycoproteins and glycolipids are termed sialyltransferases. Sialic acid addition generally terminates further oligosaccharide biosynthesis and thereby can generate as well as mask biologically relevant glycan structures. Among vertebrates, a highly conserved sialyltransferase gene family exists that contains at least eighteen members. These genes exhibit expression profiles that are commonly developmentally restricted and cell- or tissue-type specific. From limited studies thus far, sialic acid linkages have been found to regulate cell trafficking, adhesion, glycoprotein half-life in plasma, and signal transduction involving multi-subunit receptor complexes. In determining sialyltransferase gene function in vivo, mouse germline mutations are produced using Cre-loxP site-directed recombination in embryonic stem cells and adult mice. Subsequently, physiologic parameters are assessed by the use of specific phenotyping Core facilities provided by this Program Project Grant. In this manner, our previous findings have established critical hemostatic and immunologic roles for specific sialyltransferase genes. For example, ST3Gal-I and ST3Gal-IV promote platelet homeostasis, while ST3Gal-IV deficiency specifically results in an autosomal dominant yon Willebrand disease-like syndrome in mice. The goal of this project is to further elucidate the vascular and innate immune functions of sialyltransferases ST3Gal-I, ST3Gal-IV, and the recently identified ST3Gal-VI. Their roles in masking specific asialoglycoprotein receptor ligands, and the possible involvement of ST3Gal-IV as a modifier of human VWD will be explored. Our studies of ST3Gal sialyltransferase mutants have further resulted in the hypothesis that ST3Gal-VI will be found essential for selectin ligand formation and thus innate immune function during inflammation. This hypothesis will be investigated by generating mice deficient in ST3Gal-VI gene function and subjecting them to phenotypic analyses with PPG Core facilities, that involve determining vascular and innate immune parameters as well as selectin ligand formation and selectin-based physiologic responses. The vascular and innate immune functions of these ST3Gal sialyltransferases are also hypothesized to affect wound healing and bacterial invasion. These putative protective roles of ST3Gal-I, ST3Gal-IV and ST3Gal-VI will be investigated with the PPG Core facility. These studies will define the mechanisms by which alpha2-3 linked sialic acids function in modulating vascular and immune systems, and will likely establish important roles that may lead to new insights in human disease.