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

红细胞（RBC）影响流变学，并释放ADP、ATP和一氧化氮，表明RBC在止血和血栓形成中的作用。最近，我们已经表明，血小板和红细胞之间的直接细胞相互作用通过Fas配体（FasL）-FasR（CD 95）途径诱导磷脂酰丝氨酸（PS）的外化，从而在红细胞膜上形成促凝血表面。FasL或FasL的抑制或基因缺失导致RBC和血小板的PS暴露减少，凝血酶生成减少，体外血栓形成减少，体内动脉和静脉血栓形成保护。在血栓切除术后患者的手术标本中，证实了血小板和RBC通过FasL-FasR的直接细胞接触。 在新的初步研究中，我们能够提供血小板整合素αIIbβ3（纤维蛋白原受体）作为红细胞膜上FasR的潜在配体的初步证据。此外，我们确定了一个潜在的新机制，通过CD 36调节PS暴露在红细胞膜可能通过结合血小板释放的血小板反应蛋白-1（TSP-1）。早期的实验提供了证据表明，除了对静脉和动脉血栓形成的影响外，血小板-RBC相互作用对腹主动脉瘤（AAA）也有影响。AAA通常以腔内血栓（ILT）的形成为特征，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，血小板和红细胞迁移到实验性AAA小鼠的腹主动脉壁中，血小板耗竭小鼠的AAA进展减缓。此外，增强PS暴露在血小板和红细胞膜AAA患者。迄今为止，连接血小板活化和凝血酶生成细胞外基质（ECM）降解和AAA进展的途径和蛋白质在很大程度上是未知的。此外，我们认为，不同的机制，血小板-红细胞相互作用是负责凝血酶生成血管疾病血栓并发症。我们假设红细胞通过不同的信号通路调节动脉血栓形成和AAA中的血小板活化和血栓形成，根据氧的可用性。因此，我们希望实验性地遵循当前提案中的三个主要目标。首先，我们要确定和表征在常氧和缺氧条件下止血和血栓形成中血小板-RBC相互作用的新细胞机制。其次，我们想验证实验小鼠血管疾病（包括动脉血栓形成和AAA）中血小板-RBC相互作用的相关性。第三，我们将分析AAA患者血小板-RBC相互作用的机制作为第一个转化方法。

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.