Membrane Phospholipids: The Key Regulators of Tissue Factor Encryption/Decryption

在血管损伤时，血浆凝血因子VII（FVII）沿着有痕量的活化FVII（FVIIa）进入血管内。 与辅助因子组织因子（TF）接触，TF在血管壁内的细胞中组成型表达。 FVIIa与TF的复合物形成导致FVIIa的催化活性显著增强， 触发TF介导的血液凝固。某些疾病条件诱导TF在循环血液中表达 细胞和血管内皮细胞，从而允许循环血液和TF之间的直接接触， 血栓形成虽然TF介导的血液凝固对于维持止血是必不可少的，但是异常的凝血因子依赖性凝血因子受体。 TF介导的血液凝固的激活导致血栓形成，这是急性心肌梗死中的促发事件。 梗塞、缺血性中风和败血症。因此，TF表达和活性的适当调节是 不仅对于维持止血平衡而且对于一般健康都是至关重要的。通常，大多数 的TF在细胞中表达保持加密，具有非常少的促凝血活性，这足以实现 止血，但不引起血管内凝血。细胞损伤增强TF促凝活性 而不改变TF抗原水平，即，将隐藏的TF转化为血栓前TF。TF促凝剂 细胞中的活性受多种翻译后机制的动态控制。我们最近的研究 揭示了质膜外叶中的鞘磷脂（SM）负责维持 TF处于加密状态，SM的水解激活TF并释放TF+微泡（MV）。SM 代谢在许多疾病环境中改变，包括动脉粥样硬化、糖尿病、败血症和癌症， 相同的疾病环境诱导TF的异常激活。目前的建议是建立在上述小说 研究结果和建议，以调查病理生理相关的SM代谢调节TF- 介导的止血、血栓形成和炎症。目的1侧重于阐明SM 代谢调节TF促凝血活性，而目的2研究SM代谢是否 影响止血和血栓形成。目标3中提出的实验将检验以下假设： 炎症诱导的SM代谢的改变在TF激活和TF介导的 凝血病目的4着重于研究SM代谢的改变是否通过以下途径导致炎症： TF活性的调节。在拟议的研究中，我们将操纵巨噬细胞中的SM水平， 内皮细胞和其它细胞类型通过各种相关酶的过表达或下调而表达 在SM代谢中或使用这些酶的特定药理学抑制剂。我们将采用各种 SM代谢改变的基因敲除小鼠和止血和血栓形成的小鼠模型，以研究 新发现机制的病理生理学相关性。我们提出的研究将导致 我们对TF介导的凝血在各种疾病环境中如何被激活的理解发生了范式转变。 它们还可能导致开发新的、有针对性的干预措施来预防血栓形成。

Upon vascular injury, plasma clotting factor VII (FVII) along with traces of activated FVII (FVIIa) come into contact with the cofactor tissue factor (TF), which is expressed constitutively in cells within the vessel wall. Complex formation of FVIIa with TF results in a marked enhancement of the catalytic activity of FVIIa and triggers TF-mediated blood coagulation. Certain disease conditions induce TF expression in circulating blood cells and vascular endothelial cells and thus allow direct contact between circulating blood and TF that leads to thrombosis. While TF-mediated blood coagulation is essential to maintain hemostasis, the aberrant activation of TF-mediated blood coagulation leads to thrombosis, the precipitating event in acute myocardial infarction, ischemic stroke, and sepsis. Therefore, the proper regulation of TF expression and the activity is critical for not only to the maintenance of the hemostatic balance but also for health in general. Typically, most of the TF expressed in cells stays encrypted with very little procoagulant activity that is sufficient to achieve hemostasis but not to cause intravascular coagulation. Cellular injury enhances TF procoagulant activity greatly without altering TF antigen levels, i.e., transforming cryptic TF to prothrombotic TF. TF procoagulant activity in cells is controlled dynamically by a variety of post-translational mechanisms. Our recent studies revealed that sphingomyelin (SM) in the outer leaflet of the plasma membrane is responsible for maintaining TF in an encrypted state and that hydrolysis of SM activates TF and releases TF+ microvesicles (MVs). SM metabolism is altered in many disease settings, including atherosclerosis, diabetes, sepsis, and cancer, the same disease settings that induce aberrant activation of TF. The current proposal is built on the above novel findings and proposes to investigate the pathophysiologic relevance of SM metabolism in regulation of TF- mediated hemostasis, thrombosis, and inflammation. Aim 1 focuses on elucidating mechanisms by which SM metabolism regulates TF procoagulant activity, whereas Aim 2 investigates whether SM metabolism influences hemostasis and thrombosis. Experiments proposed in Aim 3 will test the hypothesis that acute inflammation-induced alterations in SM metabolism play a key role in TF activation and TF-mediated coagulopathy. Aim 4 focuses on investigating whether altered SM metabolism contributes to inflammation via the regulation of TF activity. In the proposed studies, we will manipulate SM levels in macrophages, endothelial cells, and other cell types by the overexpression or down regulation of various enzymes involved in the SM metabolism or using specific pharmacological inhibitors of these enzymes. We will employ various knock-out mice with altered SM metabolism and murine models of hemostasis and thrombosis to investigate the pathophysiologic relevance of the newly identified mechanism. Our proposed studies will lead to a paradigm shift in our understanding of how TF-mediated coagulation is activated in various disease settings. They may also lead to the development of novel, targeted interventions to prevent thrombosis.