Role of sialoglycan binding in the pathogenesis of streptococcal endocarditis

项目摘要 口腔链球菌是感染性心内膜炎（IE）的主要原因。其中一些物种表达Siglec- 例如，富含丝氨酸的重复序列（SRR）粘附素，其结合人糖蛋白上的多种O-连接的唾液酸聚糖， 细胞戈登链球菌M99的SRR粘附素GspB的表达导致其毒力增加， IE动物模型这种增强的致病性被认为是由于GspB与病原体的相互作用。 三糖唾液酸-T抗原（sTa，核心1唾液酸聚糖）对血小板受体GPIb γ，导致增加 血液中的细菌附着在心脏瓣膜表面和赘生物形成。等基因 表达优先结合核心2唾液酸聚糖的GspB变体的M99突变体（例如，唾液酸乳糖胺） 与WT菌株相比，毒性较低。这些发现表明，不同类型的 唾液酸聚糖结合（“选择性”）影响生物体启动和繁殖内分泌的能力 感染，一些相互作用增强发病机制，而其他相互作用减少疾病。我们 假设在体内，血流中的链球菌与血小板或心脏表面上的sTa的结合 有助于引发感染，并且这种结合通过高剪切流产生的血液动力学效应而增强。 相反，与血细胞上的核心2唾液酸聚糖结合可导致细菌清除增加，从而 减弱毒性。瓣膜上细菌与核心1和核心2唾液酸聚糖的后续相互作用 可能通过对血小板活化、凝血或内皮愈合的不同影响来影响疾病进展。 为了进一步阐明唾液酸聚糖结合选择性在IE发病机制中的作用，我们将通过流式细胞术比较 上述同基因菌株在体外与血小板、RBC和WBC的结合。我们还将研究 这些菌株结合的血小板GPIb唾液酸聚糖含量不同， 结构影响血小板活化。此外，我们将评估选择性如何影响 细菌到受损的心脏表面，如由衬有固定血小板的微流体腔室所模拟的， 血管性血友病因子、胶原或活化的人血管内皮细胞，以及血液动力学的影响 约束力。我们还将通过评估应变来探索选择性对植被形成的影响。 触发血小板收缩性的差异和对血小板依赖性内皮愈合的影响。我们还将 比较这些菌株在体内产生的赘生物与毒力相关的关键特征，包括共同 与血小板和生物膜的生产定位。 这些研究将提供关于唾液酸聚糖选择性和血流动力学力如何影响 内分泌物感染起始和传播。通过定义这些事件的机制，本研究 将重新定义我们对链球菌IE发病机制中关键步骤的理解。这些概念和 研究结果将广泛适用于其他血管内病原体，并将提供新的见解， 微生物与宿主聚糖的相互作用。

PROJECT SUMMARY The oral streptococci are a major cause of infective endocarditis (IE). Several of these species express Siglec- like, serine-rich repeat (SRR) adhesins that bind a variety of O-linked sialoglycans on human glycoproteins and cells. Expression of the SRR adhesin GspB of Streptococcus gordonii M99 results in increased virulence in animal models of IE. This enhanced pathogenicity is thought to be due the interaction of GspB with the trisaccharide sialyl-T antigen (sTa, a core 1 sialoglycan) on the platelet receptor GPIb, leading to increased attachment of bacteria in the blood stream to cardiac valve surfaces and vegetation formation. Isogenic mutants of M99 expressing GspB variants that preferentially bind core 2 sialoglycans,(e.g., sialyl-lactosamine) are less virulent, as compared with the WT strain. These findings indicate that differences in the type of sialoglycan bound ("selectivity") affect the ability of organisms to both initiate and propagate endocardial infection, with some interactions enhancing pathogenesis, while other interactions reducing disease. We hypothesize that in vivo, the binding of streptococci in the bloodstream to sTa on platelets or cardiac surfaces helps initiate infection, and that this binding is enhanced by hemodynamic effects created by high shear flow. In contrast, binding to core 2 sialoglycans on blood cells may lead to increased bacterial clearance, thereby attenuating virulence. Subsequent interactions of bacteria on valves with core 1 versus core 2 sialoglycans may affect disease progression via different effects on platelet activation, clotting, or endothelial healing. To further address the roles of sialoglycan binding selectivity in the pathogenesis of IE, we will compare by flow the above isogenic strains for their binding to platelets, RBCs and WBCs in vitro. We will also examine whether these strains bind platelets that differ in GPIb sialoglycan content, and whether binding to sTa versus core 2 structures affects platelet activation. In addition, we will assess how selectivity impacts the attachment of bacteria to damaged cardiac surfaces, as modeled by microfluidic chambers lined with immobilized platelets, von Willebrand Factor, collagen or activated human vascular endothelial cells, and the effect of hemodynamic forces on binding. We will also explore the impact of selectivity on vegetation formation by assessing strain differences in triggering platelet contractility and effects on platelet-dependent endothelial healing. We will also compare vegetations produced in vivo by these strains for key features linked to virulence, including co- localization with platelet and biofilm production. These studies will provide novel insights as to how sialoglycan selectivity and hemodynamic forces affect the initiation and propagation of endocardial infection. By defining the mechanisms for these events, this research will redefine our understanding of the key steps in the pathogenesis of streptococcal IE. These concepts and findings will be broadly applicable to other endovascular pathogens, and will provide novel insights into microbial interactions with host glycans.