Impact of platelet-red blood cell interactions on thrombosis and abdominal aortic aneurysm formation: Mechanisms and consequences

红细胞影响血液流变学，释放ADP、ATP和一氧化氮，提示红细胞在止血和血栓形成中发挥作用。最近，我们发现，通过Fas配体(FasL)-FasR(CD95)途径，血小板与红细胞之间的直接细胞相互作用诱导磷脂酰丝氨酸(PS)外化，从而在红细胞膜上形成促凝血剂表面。抑制或基因缺失FasL或FasR可减少红细胞和血小板的PS暴露，减少凝血酶的生成，减少体外血栓的形成，并对体内动静脉血栓形成具有保护作用。在血栓切除患者的手术标本中，显示了血小板与红细胞通过FasL-Fasr直接细胞接触。在新的初步研究中，我们能够提供初步证据，证明血小板整合素αIIbβ3(纤维蛋白原受体)是红细胞膜FasR的潜在配体。此外，我们通过CD36确定了一个潜在的新机制，可能是通过与血小板释放的凝血酶敏感蛋白-1(TSP-1)结合来调节红细胞膜上PS的暴露。早期实验提供的证据表明，除了对静脉和动脉血栓形成的影响外，血小板-红细胞相互作用对腹主动脉瘤(AAA)也有影响。腹主动脉硬化常以腔内血栓(ILT)的形成为特征，并伴有主动脉壁内缺氧和高凝血酶血浆水平。我们实验室的数据显示，实验性AAA小鼠的血小板和红细胞迁移到腹主动脉壁，并减缓了血小板耗竭小鼠的AAA进展。此外，AAA患者的血小板和红细胞膜上PS暴露增加，到目前为止，将血小板激活和凝血酶生成与细胞外基质(ECM)降解和AAA进展联系起来的途径和蛋白很大程度上是未知的。此外，我们认为不同的血小板-红细胞相互作用机制导致血栓并发症的血管疾病中凝血酶的产生。我们假设，在动脉血栓形成和AAA中，红细胞通过不同的信号通路调节血小板的激活和血栓的形成，根据氧气的可获得性。因此，我们希望试验性地遵循当前提案中的三个主要目标。首先，我们想要确定和表征在常氧和低氧条件下，血小板-红细胞相互作用在止血和血栓形成中的新的细胞机制。其次，我们想要验证血小板-红细胞相互作用在实验性小鼠血管疾病中的相关性，包括动脉血栓形成和AAA。第三，我们将分析AAA患者的血小板-红细胞相互作用的机制，作为第一个翻译方法。

Red blood cells (RBCs) influence rheology, and release ADP, ATP and nitric oxide suggesting a role for RBCs in hemostasis and thrombosis. Recently, we have shown that a direct cell interaction between platelets and RBCs via the Fas ligand (FasL)-FasR (CD95) pathway induces the externalization of phosphatidylserine (PS) and thus the formation of a pro-coagulant surface at the RBC membrane. Inhibition or genetic deletion of either FasL or FasR resulted in reduced PS exposure of RBCs and platelets, decreased thrombin generation and reduced thrombus formation in vitro and protection against arterial and venous thrombosis in vivo. In surgical specimens of patients after thrombectomy, direct cell contacts of platelets and RBCs via FasL-FasR were demonstrated. In new preliminary studies, we were able to provide initial evidence that the platelet integrin αIIbβ3 (fibrinogen receptor) serves as a potential ligand for FasR at the RBC membrane. Furthermore, we identified a potential new mechanism via CD36 that regulates PS exposure at the RBC membrane probably via binding to platelet released thrombospondin-1 (TSP-1). Early experiments provide evidence for an impact of platelet-RBC interactions in abdominal aortic aneurysm (AAA) in addition to effects on venous and arterial thrombosis. AAA is frequently characterized by the formation of an intraluminal thrombus (ILT) accompanied by hypoxia within the aortic wall and high thrombin plasma levels. Data from our lab showed migration of platelets and RBCs into the abdominal aortic wall of mice with experimental AAA and reduced progression of AAA in platelet-depleted mice. Moreover, enhanced PS exposure at the platelet and RBC membrane was measured in patients with AAA.To date, the pathways and proteins that link platelet activation and thrombin generation to extracellular matrix (ECM) degradation and AAA progression are largely unknown. Moreover, we believe that different mechanisms of platelet-RBC interactions are responsible for thrombin generation in vascular diseases with thrombotic complications. We hypothesize that RBCs modulate platelet activation and thrombus formation in arterial thrombosis and AAA via different signaling pathways according to the availability of oxygen. Therefore we want to experimentally follow three major objectives in the current proposal. First, we want to identify and characterize new cellular mechanisms of platelet-RBC interactions in hemostasis and thrombosis under normoxia and hypoxia. Second, we want to validate the relevance of platelet-RBC interactions in vascular diseases in experimental mice including arterial thrombosis and AAA. Third, we will analyze the mechanisms of platelet-RBC interactions in patients with AAA as a first translational approach.