Shankaran Harish, Alexandridis Paschalis, Neelamegham Sriram
Bioengineering Laboratory, Department of Chemical Engineering, State University of New York at Buffalo, NY 14260, USA.
Blood. 2003 Apr 1;101(7):2637-45. doi: 10.1182/blood-2002-05-1550. Epub 2002 Nov 27.
The binding of plasma von Willebrand factor (VWF) to platelet receptor GpIb under high hydrodynamic shear leads to platelet activation and subsequent shear-induced platelet aggregation (SIPA). We quantitatively examined the aspects of fluid flow that regulate platelet activation by subjecting human blood and isolated platelets to well-defined shear conditions in a cone-plate viscometer. We made the following observations. First, Annexin V binding to phosphatidyl serine expressed on activated cells was detectable within 10 seconds of shear application. Second, fluid shear stress rather than shear rate controls platelet activation, and a threshold shear stress of approximately 80 dyn/cm(2) is necessary to induce significant activation. Under these conditions, individual domains of soluble VWF and platelet GpIb are subjected to similar magnitudes of fluid forces on the order of 0.1 pN, whereas GpIb with bound VWF is subjected to 1 pN. Third, cell-cell collisions and time-varying stresses are not essential for platelet activation. Fourth, the mechanism of platelet activation can be resolved in 2 steps based on the contribution of VWF and fluid forces. Fluid shear and VWF are required during the first step, when GpIb-VWF binding likely occurs. Subsequently, high shear forces alone in the absence of VWF in suspension can induce platelet activation. In other experiments, purified VWF was subjected to shear in the viscometer, and VWF morphology was assessed using light scattering. These studies demonstrate, for the first time, the ability of hydrodynamic forces to induce VWF aggregation in suspension. This VWF self-association may be an additional feature involved in controlling cell adhesion rates in circulation.
在高流体动力剪切力作用下，血浆血管性血友病因子（VWF）与血小板受体糖蛋白Ib（GpIb）结合会导致血小板活化以及随后的剪切诱导血小板聚集（SIPA）。我们通过在锥板粘度计中使人体血液和分离的血小板处于明确的剪切条件下，定量研究了调节血小板活化的流体流动方面。我们有以下发现。首先，在施加剪切力后10秒内即可检测到膜联蛋白V与活化细胞上表达的磷脂酰丝氨酸结合。其次，流体剪切应力而非剪切速率控制血小板活化，诱导显著活化需要约80达因/平方厘米的阈值剪切应力。在这些条件下，可溶性VWF和血小板GpIb的各个结构域受到的流体作用力大小相似，约为0.1皮牛，而结合了VWF的GpIb受到的作用力为1皮牛。第三，细胞间碰撞和随时间变化的应力对于血小板活化并非必不可少。第四，基于VWF和流体作用力的贡献，血小板活化机制可分为两个步骤。第一步需要流体剪切力和VWF，此时可能发生GpIb - VWF结合。随后，在悬浮液中不存在VWF的情况下，仅高剪切力即可诱导血小板活化。在其他实验中，将纯化的VWF置于粘度计中进行剪切，并使用光散射评估VWF形态。这些研究首次证明了流体动力能够在悬浮液中诱导VWF聚集。这种VWF自缔合可能是控制循环中细胞粘附率的一个额外因素。
