Role of GPIba Receptor Shedding in Platelet Dysfunction Following Trauma

描述（由申请人提供）：创伤性损伤是美国第三大死亡原因，其中约40%的死亡是由出血引起的。四分之一的创伤患者由于凝血功能受损（凝血功能障碍）而经历长期出血。这些病人遭受与他们的伤害不成比例的大量出血，人们对这种现象知之甚少。在受伤后实现止血对控制失血至关重要，而血小板是这一过程的关键调节因子。血小板粘附受损的内皮细胞是由血管性血友病因子（vWF）与活化血小板上的GPIb受体结合介导的。初步数据显示，损伤后血小板对vWF的粘附明显降低。此外，这些患者显示血小板GPIb¿受体表达减少，GPIb¿在血浆中的脱落增加，这可能是血小板- vwf粘附缺陷的机制。长期目标是了解血小板受体脱落对创伤患者血小板功能障碍和出血的影响。

DESCRIPTION (provided by applicant): Traumatic injury is the third leading cause of death in the US and about 40% of these deaths are due to hemorrhage. One quarter of all trauma patients experience prolonged hemorrhage due to impaired blood clotting (coagulopathy). These patients suffer from excessive bleeding disproportionate to their injuries, a phenomenon that is poorly understood. Achieving hemostasis following injury is crucial to controlling blood loss and platelets are critical regulators of this process. Platelet adhesion to damaged endothelium is mediated by von Willebrand factor (vWF) binding to the GPIb¿ receptor on activated platelets. Preliminary data show that platelet adhesion to vWF was significantly reduced following injury. In addition, these patients displayed reduced platelet GPIb¿ receptor expression and increased shedding of GPIb¿ into the plasma, suggesting a possible mechanism behind defective platelet-vWF adhesion. The long-term goal is to understand the contribution of platelet receptor shedding to platelet dysfunction and bleeding in trauma patients. Shedding of GPIb¿ is proteolytically regulated by tumor necrosis factor-¿ converting enzyme (TACE), which modulates platelet-vWF adhesion through cleavage of GPIb¿. Preliminary clinical results show a substantial increase in TACE expression on platelets following injury. Therefore, the objective of this application is to determine the contribution of TACE-mediated GPIb¿ receptor shedding to the defective platelet-vWF adhesion observed following traumatic injury. The central hypotheses are: 1) Excessive hemorrhage in trauma patients results from defective platelet-vWF adhesion due to inappropriate shedding of GPIb¿; 2) This shedding is mediated by elevated TACE, and can be corrected through TACE inhibition. The rationale for this research is that understanding the effects of injury on platelet-vWF binding will allow identification of the mechanisms behind life-threatening hemorrhage and develop pharmacologic interventions to alleviate bleeding. These hypotheses will be tested by pursuing two specific aims: 1) Identify the mechanisms behind defective platelet-vWF adhesion following traumatic injury; and 2) Characterize the effect of TACE absence and inhibition on platelet GPIb¿ receptor expression and hemostasis in a mouse model of trauma and hemorrhage. Under the first aim, serial blood samples will be collected from severely injured patients to measure effects of injury and resuscitation fluids on expression of platelet GPIb¿ and TACE by flow cytometry and shedding of GPIb¿ by ELISA. Under the second aim, TACE absence and inhibition will be tested in a mouse model using both platelet-specific TACE knock-out mice and TACE inhibitors in wild-type mice to determine the effects of TACE absence and inhibition on preserving GPIb¿ receptor expression. This approach is innovative because it utilizes both human and animal subjects and a unique patient population rarely studied in the lab setting. The proposed research is significant because the results will identify strategies to facilitate more effective platelet- vWF binding, which could subsequently improve primary hemostasis in hemorrhaging trauma patients.