VWF Activity: Molecular Biology, Ethnic Diversity and Disease Associations

血管性血血病因子（VWF）通过将血小板拴在血管损伤部位而开始止血，并通过保护凝血因子VIII （FVIII）免受蛋白水解降解而参与凝血。低VWF抗原和/或缺乏大的多聚体可导致出血，而高水平和/或超大VWF多聚体的存在与血栓形成有关。这种双向活性表明VWF的表达和粘附活性受到高度调节，以维持主动止血而不促进血栓形成。血浆VWF水平在健康受试者中存在显著差异，并且越来越多的证据表明这种差异存在种族差异。已知环境和遗传因素会导致VWF合成、稳定性、粘附性和清除的变化，但关键问题仍然存在。首先，健康人VWF抗原与黏附活性之间的关系是什么？其次，遗传变异如何与环境因素相互作用，从而改变VWF（一种已知的急性相反应物）的合成和活性？第三，种族和年龄如何影响VWF基因变异与VWF粘附活性和血栓性疾病发展的关联？我们推测：1)VWF基因的变异不仅影响VWF的表达，还影响VWF的粘附活性；2)基因-环境相互作用对VWF黏附活性有很强的影响，这种相互作用通过协变量如种族、年龄和FVIII表现出来；3)与单独模拟VWF抗原相比，评估VWF粘附活性可以改善血栓性疾病的风险评估。我们广泛的、长期的目标是了解VWF的生物活性及其与种族、年龄和FVIII的疾病关联的改变。这项建议有三个具体目标。首先是表征来自社区动脉粥样硬化风险（ARIC）和日本Suita队列的受试者的VWF粘附活性，这些受试者的VWF抗原在25年收集的样本中始终被测量为低（≤50%）或高（≥200%）。VWF的粘附活性、VWF的合成和清除率将被确定，以确定1)VWF水平与粘附活性之间的内在关系，以及2)年龄和种族对这种关系的影响。第二，1)在欧洲裔美国人、非洲裔美国人和日本人三个种族的受试者中鉴定与VWF抗原和粘附活性相关的遗传变异；2)发现这些关联的民族修饰；3)检测调节VWF抗原和粘附活性的遗传上位性和新的分子相互作用。第三是确定1)测量VWF活性和VWF合成清除率是否比单独测量VWF抗原更能提高心肌梗死、缺血性卒中和外周动脉疾病的风险预测；2)低VWF和/或粘附活性的受试者是否免受这些疾病的侵害；3)种族和年龄如何改变风险。该研究与NIH在对抗衰老相关的血栓形成和出血性疾病以改善美国公众健康方面的使命高度相关。

Project Summary von Willebrand factor (VWF) initiates hemostasis by tethering platelets to sites of vascular injury and participates in the coagulation by protecting the coagulation factor VIII (FVIII) against proteolytic degradation. A low VWF antigen and/or lack of large multimers can result in bleeding, whereas high levels and/or the presence of ultra‐large VWF multimers are associated with thrombosis. This bidirectional activity suggests that VWF expression and adhesive activity are highly regulated to maintain active hemostasis without promoting thrombosis. Plasma VWF levels vary significantly among healthy subjects and there is increasing evidence that this variation is ethnically diverse. Environmental and genetic factors are known to contribute to variations in VWF synthesis, stability, adhesiveness, and clearance, but crucial questions remain. First, what is the relationship between VWF antigen and adhesive activity in healthy individuals? Second, how do genetic variations interact with environmental factors to modify the synthesis and activity of VWF, a known acute phase reactant? Third, how do ethnicity and aging influence the association of variants in the VWF gene with VWF adhesive activity and the development of thrombotic diseases? We hypothesize that 1) variation in the VWF gene influences not only VWF expression, but also adhesive activity; 2) there is a strong gene‐ environment interaction that influences VWF adhesive activity and this interaction is manifested through covariates as ethnicity, age and FVIII; and 3) evaluating VWF adhesive activity can improve risk assessments for thrombotic diseases compared to modeling VWF antigen alone. Our broad, long‐term objective is to understand VWF biological activity and its modification of disease associations by ethnicity, aging and FVIII. There are three specific aims in this proposal. First is to characterize VWF adhesive activity in subjects from the Atherosclerosis Risk in Communities (ARIC) and the Japanese Suita cohorts, whose VWF antigen was consistently measured as low (≤ 50%) or high (≥ 200%) in samples collected over 25 years. VWF adhesive activity and rates of VWF synthesis and clearance will be determined to define 1) an intrinsic relationship between VWF levels and adhesive activity and 2) the impact of aging and ethnicity on this relationship. Second is to 1) identify genetic variants associated with VWF antigen and adhesive activity in subjects from three ethnic groups of European American, African Americans, and Japanese; 2) detect ethnic modifications of these associations; and 3) detect the genetic epistasis and novel molecular interactions that regulate the VWF antigen and adhesive activity. Third is to determine 1) if measuring VWF activity and rates of VWF synthesis‐ clearance improve risk predictions for myocardial infarction, ischemic stroke, and peripheral arterial disease than VWF antigen alone; 2) if subjects with low VWF and/or adhesive activity are protected from these diseases; and 3) how ethnicity and aging modify the risk. The research is highly relevant to the mission of NIH in combating aging‐associated thrombotic and bleeding disorders to improve public health in the US.