Shear-induced unfolding triggers adhesion of von Willebrand factor fibers
Shear-induced unfolding triggers adhesion of von Willebrand factor fibers
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DOI：
10.1073/pnas.0608422104
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发表时间：
2007-05-08
影响因子：
11.1
通讯作者：
Schneider, M. F.
中科院分区：
文献类型：
--
作者：
Schneider, S. W.;Nuschele, S.;Schneider, M. F.
血管性血液病因子（VWF）是存在于我们循环系统中的一种蛋白质，对于在小血管中发现的高剪切应力条件下止血是必需的。本文的研究结果有助于揭示流体动力剪切应力的增加如何激活VWF的粘附势，从而导致在强剪切条件下吸附率提高的反直觉现象。使用微流体装置，我们能够模拟大范围的血液流动条件，并直接可视化这种蛋白质在剪切流动下的构象动力学。特别是，我们发现在没有任何吸附表面的情况下，VWF在临界剪切速率下表现出可逆的球-拉伸转变。计算机模拟再现了这种急剧转变，并确定了VWF重复单元的大尺寸是这种独特的流体动力激活的关键之一。在有胶原蛋白底物的情况下，我们发现在相同的临界剪切速率下，蛋白质的吸附量大幅增加，这表明在胶原蛋白底物的情况下，球体的整体展开触发了表面吸附，从而提供了足够的结合位点密度。通过监测多个VWF纤维的吸附过程，我们能够跟踪固定网络的形成，该网络构成了高剪切流下血小板粘附所必需的“粘性”网格。由于高剪切应力区域与机械力对血管壁损伤的可能性较高相吻合，因此我们确定剪切诱导的VWF结合概率的增加是微血管系统的有效自我调节修复机制。
von Willebrand factor (VWF), a protein present in our circulatory system, is necessary to stop bleeding under high shear-stress conditions as found in small blood vessels. The results presented here help unravel how an increase in hydrodynamic shear stress activates VWF's adhesion potential, leading to the counterintuitive phenomena of enhanced adsorption rate under strong shear conditions. Using a microfluidic device, we were able to mimic a wide range of bloodflow conditions and directly visualize the conformational dynamics of this protein under shear flow. in particular, we find that VWF displays a reversible globule-stretch transition at a critical shear rate gamma(crit) in the absence of any adsorbing surface. Computer simulations reproduce this sharp transition and identify the large size of VWF's repeating units as one of the keys for this unique hydrodynamic activation. In the presence of an adsorbing collagen substrate, we find a large increase in the protein adsorption at the same critical shear rate, suggesting that the globule unfolding in bulk triggers the surface adsorption in the case of a collagen substrate, which provides a sufficient density of binding sites. Monitoring the adsorption process of multiple VWF fibers, we were able to follow the formation of an immobilized network that constitutes a "sticky" grid necessary for blood platelet adhesion under high shear flow. Because areas of high shear stress coincide with a higher chance for vessel wall damage by mechanical forces, we identified the shear-induced increase in the binding probability of VWF as an effective self-regulating repair mechanism of our microvascular system.