ST6Gal I sialyltransferase in hematopoiesis

描述(由申请人提供)：调节造血和维持造血平衡的能力对生物体的福利至关重要，无论是为了满足对抗入侵病原体的额外需求，还是为了在骨髓清除事件后重建造血室。衰老伴随着造血能力的普遍下降，导致对感染和自身免疫性疾病的易感性增加。全面维持造血室的一个关键参数是造血干细胞和造血祖细胞(HSPC)在适当的支持性骨髓壁龛中的驻留。唾液酸化的多聚糖参与多种细胞黏附过程，影响免疫和运输的多个方面；然而，对多聚糖在早期造血过程中所起的作用知之甚少。我们实验室最近发现了唾液酸基转移酶ST6Gal-1在HSPC增殖调控中的一个新的生物学功能。有令人信服的证据表明，细胞外ST6Gal-1可以在不同于经典的ER/高尔基体途径的糖基化途径中重塑HSPC表面。这些数据指出了一种新的概念，即从远端来源产生的胞外糖基转移酶可以作为调节造血的“系统因子”，推测是通过HSPC表面成分的胞外或外源唾液酸化修饰来实现的。有4个具体目标。第一个是通过使用仅表达ST6Gal-1不同的小鼠品系来评估ST6Gal-1在骨髓造血室表达失调的影响。第二个目的是评估ST6Gal-1的外源性和典型的ER/Golgi途径在造血细胞表面唾液酸化中的相对贡献，最终目的是确定外源性ST6Gal-1作用的靶分子。ST6Gal-1调控HSPC的机制将是目标3的重点，通过分析静态和流动条件下HSPC与基质的黏附，以及ST6Gal-1对细胞内信号通路的影响。目的4将评估ST6Gal-1表达异常对造血功能的长期影响。本项目的总体目标是了解ST6Gal-1在维持造血功能中的确切作用和机制，最终得出有效修饰造血功能的葡聚糖工程策略。

DESCRIPTION (provided by applicant): The ability to regulate hematopoiesis and to maintain hematopoietic balance is critical to the welfare of an organism, whether it is to meet additional demands to combat invading pathogens, or to re-establish the hematopoietic compartment subsequent to myelo-ablative events. Aging is accompanied by a general decline in hematopoietic capabilities, contributing to an increasing susceptibility to infections and to autoimmune conditions. A key parameter in the overall maintenance of the hematopoietic compartment is the residency of hematopoietic stem and progenitor cells (HSPCs) in the appropriate supportive marrow niches. Sialylated glycans participate in diverse cellular adhesive processes impacting multiple aspects of immunity and trafficking; however, little is known of the roles glycans play in early hematopoietic processes. Our laboratory has recently uncovered a novel biologic function for the sialyltransferase, ST6Gal-1, in the regulation of HSPC proliferation. There is compelling evidence that HSPC surfaces can be remodeled by extracellular ST6Gal-1, in a glycosylation pathway divergent from the canonical ER/Golgi-based pathway. The data point to the novel concept that extracellular glycosyltransferases generated from distal sources can function as "systemic factors" in regulating hematopoiesis, putatively by the extracellular or extrinsic sialyl-modification of HSPC surface components. There are 4 Specific Aims. The first is to evaluate the impact of dysregulated ST6Gal-1 expression in the bone marrow hematopoietic compartment through the use of mice strains that differ only in the way they express ST6Gal-1. The second aim is to evaluate the relative contributions of the extrinsic and the canonical ER/Golgi-based pathways of ST6Gal-1 in sialylation of hematopoietic cell surfaces, with the ultimate aim of identifying the target molecules of extrinsic ST6Gal-1 action. The mechanism by which HSPCs are regulated by ST6Gal-1 will be the focus of Aim 3, through analysis of HSPC-stroma adhesion under static and flow-sheer conditions, and ST6Gal-1 impact on intracellular signaling pathways. Aim 4 will evaluate the long-term impact of dysregulated ST6Gal-1 expression on hematopoietic capacities. The overall goal of this project is to understand the precise contribution and mechanism of ST6Gal-1 in the maintenance of hematopoietic functions, ultimately to yield glycan engineering strategies for effective modification of hematopoietic function.