PLATELET/HEPARIN INTERACTIONS IN CARDIOVASCULAR SURGERY

50年来，肝素一直是心血管手术和体外循环的首选抗凝剂，尽管是一种折衷的选择。提供足够常规抗凝的肝素剂量可能通过直接和免疫介导的作用引起血小板的有害活化。大多数心血管手术失败是由于急性血小板占主导地位的血栓形成，或后来由于血管平滑肌细胞增殖和迁移引起的内膜增生。然而，利用肝素抗血小板或抗增殖的潜力一直很困难。研究的挑战是解剖肝素的不同生物学效应，特别是考虑到肝素的结构异质性，以及它与细胞和蛋白质相互作用的多样性。本研究计划的主要目的是了解肝素与血管细胞和蛋白质相互作用的基本结构-功能关系和基本机制。我们的长期目标是设计新的以肝素为基础的药物来控制血小板依赖性血栓形成和新生内膜增生。迄今为止，我们已经提炼出新的肝素，通过阻断血管性血液病因子（vWf）来抑制高剪切下血小板粘附，但传统的抗凝效力较低。我们已经开始确定负责这种活动的精确肝素结构。我们已经确定血小板整合素alphaIIb/beta3是肝素直接调节血小板功能的一个潜在的重要位点（进一步说，肝素调节其他血管整合素）。为了进一步开展这项工作，我们已经开发或组装了关键工具。精确定义的合成寡糖和多聚体结构，以及分子模型和生物物理分析被用来确定肝素的结构特征，这些特征决定了它与血小板和血管平滑肌细胞的结合。独特的肝素交联剂和探针被用于识别细胞肝素结合位点。我们利用重组vWf蛋白和异位表达重组整合素和vWf受体（和突变体）的细胞系来精确阐明肝素如何调节整合素依赖的信号和功能，以及vWf的粘附功能。这些研究将促进我们对肝素如何调节止血、血管生成和血管修复的基本认识，并为开发新型抗血小板和抗增殖肝素类药物奠定基础。

For 50 years, heparin has been the anticoagulant of choice in cardiovascular surgery and extracorporeal circulation, albeit a compromise choice. The doses of heparin that provide adequate conventional anticoagulation may cause harmful activation of platelets through direct and immune-mediated effects. Most failures in cardiovascular surgery are caused by acute, platelet- dominated thrombosis, or later intimal hyperplasia due to vascular smooth muscle cell proliferation and migration. Yet it has been difficult to capitalize on heparin's anti-platelet or antiproliferative promise. The investigative challenge has been dissecting the different biological effects of heparin from each other, especially considering the structural heterogeneity of heparins, and the multiplicity of its interactions with cells and proteins. The Chief Aim of this research proposal is to understand the fundamental structure-function relations and basic mechanisms of heparin interaction with vascular cells and proteins. Our long- term goals are to devise novel heparin-based drugs to control platelet dependent thrombosis and neointimal hyperplasia. To date we have refined novel heparins that inhibit platelet adhesion under high shear, by blocking von Willebrand factor (vWf), but have low conventional anticoagulant potency. We have begun to define the precise heparin structure responsible for this activity. We have identified the platelet integrin alphaIIb/beta3 as a potentially important site for heparin's direct modulation of platelet function (and by extension, heparin modulation of other vascular integrins). To further this work, we have developed or assembled critical tools. Precisely defined synthetic oligosaccharides and multimeric constructs, as well as molecular modeling and biophysical analyses are being used to identify the structural features of heparin that dictate its binding to platelets and vascular smooth muscle cells. Unique heparin crosslinkers and probes are engaged to identify cellular heparin binding sites. And we are employing recombinant vWf proteins and cell lines that ectopically express recombinant integrin and vWf receptors (and mutants) to elucidate precisely how heparin modulates integrin-dependent signalling and function, and vWf adhesive function. These studies will advance our fundamental understandings of how heparins modulate hemostasis, angiogenesis, and vascular repair, and lay the foundations for the development of novel anti-platelet and anti-proliferative heparin-based drugs.