Traumatic brain injury is commonly associated with the inability of blood to clot (coagulopathy), resulting in secondary or delayed systemic and intracranial bleeding. Substantial blood loss, hemodilution due to fluid resuscitation, and hypothermia are the most common causes of coagulopathy associated with trauma to the body and limbs and hemorrhagic shock. We have recently demonstrated that an injured brain releases extracellular vesicles (EVs) into circulation. These brain?derived EVs induce a hypercoagulable state that quickly evolves into consumptive coagulopathy. Extracellular mitochondria (exMTs) are also released into circulation and promote coagulation through the surface?exposed mitochondrial phospholipid cardiolipin. ExMts also maintain the respiratory activity to generate reactive oxygen species that activate platelets and endothelial cells. These findings demonstrate that TBI induces consumptive coagulopathy that is mechanistically distinct from deficient and dilutional coagulopathy associated with extracranial trauma and hemorrhagic shock. Our recent study further implicates the adhesive ligand von Willebrand factor (VWF) for mediating EV?induced vascular injury and for activating platelets to propagate coagulopathy in mouse models of traumatic brain injury. These recently findings led us to hypothesize that: 1) brain?derived EVs released from injured brains stimulate endothelial cells to release hyper?adhesive VWF multimers that are not timely and sufficiently cleaved by the enzyme ADAMTS13, 2) these hyper?adhesive VWF multimers facilitate EV? induced vascular leakage and propagate EV?induced coagulopathy, and 3) the hyper?adhesive activity of VWF can be selectively blocked in acute brain injury without reducing the hemostatic activity of VWF. Here, we propose testing these hypotheses in two specific aims. The first is to study ADAMTS?13 variants, the VWF A2 domain, and the apoptotic cell?scavenging molecule Del?1 for blocking the TBI?induced hyper?adhesive activity of VWF to protect mice from developing traumatic brain injury?induced coagulopathy, and to define the underlying mechanisms of their actions in mouse models. The second is to conduct a cohort study of 120 patients with TBI and trauma controls to determine the clinical relevance of findings from the mouse study. We will analyze patient samples to quantify VWF activity and ADAMTS?13 cleavage as primary variables and to define platelet activation, plasma levels of EVs and clinical coagulopathy as outcome variables. We will associate primary variables to outcome variables through multivariate analyses to define a causal role of hyper?adhesive VWF in traumatic brain injury?induced coagulopathy and to develop new markers for predicting the coagulopathy with focus on VWF hyper?reactivity and EV clearance. This study is an integral part of our long?term goal to define the systemic impact of traumatic brain injury and to study a role of the traumatic brain injury?induced systemic changes in propagating secondary cerebral injury.
This study is designed to examine synergistic effects of von Willebrand factor and brain?derived microvesicles on systemic coagulation that becomes deficient in patients with severe traumatic brain injury. We will conduct complementary studies of patients with TBI, mice subjected to TBI, combined with in vitro experiments to investigate the cause of traumatic brain injury?induced bleeding and to find more accurate predictive biomarkers and effective therapeutics for this severe and life?threatening complication of traumatic brain injury.
