PLATELET/HEPARIN INTERACTIONS IN CARDIOVASCULAR SURGERY

50年来，肝素一直是心血管手术和体外循环中的抗凝剂选择，尽管是一个折衷的选择。提供足够常规抗凝作用的肝素剂量可能会通过直接和免疫介导性作用导致血小板的有害激活。大多数心血管手术的失败是由急性的、以血小板为主的血栓形成，或后来由于血管平滑肌细胞的增殖和迁移而导致的内膜增生引起的。然而，很难利用肝素的抗血小板或抗增殖承诺。研究的挑战在于剖析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。这项研究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基于肝素的药物来控制血小板依赖性血栓形成和新生内膜增生。到目前为止，我们已经精制了新型肝素，它通过阻断von Willebrand因子(VWF)来抑制高切下的血小板黏附，但传统的抗凝剂效力较低。我们已经开始定义与这一活动有关的确切的肝素结构。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(进而，肝素调节其他血管整合素)的潜在重要部位。为了推进这项工作，我们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，以及分子建模和生物物理分析正在被用来确定肝素的结构特征，这些结构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用于识别细胞肝素结合部位。我们正在使用异位表达重组整合素和VWF受体(以及突变体)的重组VWF蛋白和细胞系来精确地阐明肝素如何调节整合素依赖的信号和功能，以及VWF黏附功能。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理解，并为开发新型抗血小板和抗增殖肝素药物奠定基础。

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.