Tissue factor in hemophilia

这些研究的总体目标是确定组织因子（TF）在血友病止血中的体内作用。从本项目中拟定的一系列实验中获得的信息将与血友病和抑制剂患者的新疗法（即因子VIIa（FVIIa）突变体）的开发直接相关。高剂量的FVIIa最近已被FDA批准用于治疗患有FVIII抑制剂或FVIII中膜接触位点的FIX修饰的患者所经历的出血-如项目2中所提出的-可能导致开发在以较低剂量（因此成本）治疗出血发作方面上级野生型FVIIa的FVIIa产品。然而，可以想象的是，通过操纵Gla结构域的膜结合位点也会增强不需要的血栓形成性。因此，为了确定这些FVII突变体的作用模式、功效和安全性，了解其必需配体-TF-的体内表达是必要的。为此，本项目将研究人类和血友病动物模型中TF的血管内可用性和激活状态。首先，我们将定义TF“加密”现象的生物化学基础（定义为结合FVII（a）的能力，同时不能表达完全的促凝血活性（PCA））。特别是，膜磷脂酰丝氨酸（PS）的不对称性和TF四级结构在调节TF PCA的表达的作用将被检查。这些实验的结果将指导特异性靶向活性或加密形式的循环TF的抑制分子的设计。这些抑制剂将用作血管内TF功能可用性的探针，将在正常人、血友病患者和获得性血友病兔模型中的两个候选“池”（细胞相关和微粒相关）中进行定量。最后，在与项目2和4紧密吻合的实验中，将使用兔模型来检查TF在生理止血中以及在野生型和突变形式的FVIIa诱导的药理学止血中所起的作用。

The overall goal of these studies is to define the in vivo role of tissue factor (TF) in hemostasis as in pertains to hemophilia. The information gained from the proposed series of experiments in this Project will be directly relevant to the development of new therapies, namely Factor VIIa (FVIIa) mutants, for patients with hemophilia and inhibitors. FVIIa in high doses has recently been approved by t he FDA for the treatment of bleeding experienced by patients who have an inhibitor to FVIII or FIX Modification of the membrane contact site in FVIII-as proposed in Project 2- may lead to the development of FVIIa products that are superior to wild type FVIIa with respect to treatment of bleeding episodes at a lower dose (and therefore cost). However, it is conceivable that unwanted thrombogenicity will also be enhanced by manipulation of the membrane-binding site of the Gla domain. Therefore, in order to define the mode of action, efficacy, and safety of these FVII mutants, an understanding of the in vivo expression of their essential ligand-TF-is essential. To this end, this project will study t he intravascular availability and state of activation of TF in humans, and in an animal model of hemophilia. First, we will define the biochemical basis of the phenomenon of TF 'encryption' (defined as the ability to bind FVII(a) while failing to express full pro-coagulant activity (PCA)). In particular, the roles of membrane phosphatidylserine (PS) asymmetry and TF quaternary structure in modulating the expression of TF PCA will be examined. The results of these experiments will guide the design of inhibitory molecules that specifically target either the active or encrypted forms of circulating TF. These inhibitors will be used as probes of the functional availability of intravascular TF, which will be quantified in two candidate 'pools' (cell-associated and microparticle-associated) in normals, in patients with hemophilia, and in a rabbit model of acquired hemophilia. Finally, in experiments that will dovetail closely with Projects 2 and 4, the rabbit model will be used to examine the role played by TF in physiological hemostasis, and in pharmacological hemostasis induced by wild-type and mutant forms of FVIIa.