Brain-Derived Extracellular Vesicles Induce Vasoconstriction and Reduce Cerebral Blood Flow in Mice.

Traumatic brain injury (TBI) impairs cerebrovascular autoregulation and reduces cerebral blood flow (CBF), leading to ischemic secondary injuries. We have shown that injured brains release brain-derived extracellular vesicles (BDEVs) into circulation, where they cause a systemic hypercoagulable state that rapidly turns into consumptive coagulopathy. The BDEVs induce endothelial injury and permeability, leading to the hypothesis that they contribute to TBI-induced cerebrovascular dysregulation. In a study designed to test this hypothesis, we detected circulating BDEVs in C57BL/6J mice subjected to severe TBI, reaching peak levels of 3 × 104/µL at 3 h post-injury (71.2 ± 21.5% of total annexin V-binding EVs). We further showed in an adaptive transfer model that 41.7 ± 5.8% of non-injured mice died within 6 h after being infused with 3 × 104/µL of BDEVs. The BDEVs transmigrated through the vessel walls, induced rapid vasoconstriction by inducing calcium influx in vascular smooth muscle cells, and reduced CBF by 93.8 ± 5.6% within 30 min after infusion. The CBF suppression was persistent in mice that eventually died, but it recovered quickly in surviving mice. It was prevented by the calcium channel blocker nimodipine. When being separated, neither protein nor phospholipid components from the lethal number of BDEVs induced vasoconstriction, reduced CBF, and caused death. These results demonstrate a novel vasoconstrictive activity of BDEVs that depends on the structure of BDEVs and contributes to TBI-induced disseminated cerebral ischemia and sudden death.

Prognostic Biomarkers for Thrombotic Microangiopathy after Acute Graft-versus-Host Disease: A Nested Case-Control Study.

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a complication of allogeneic hematopoietic cell transplantation (HCT) that often occurs following the development of acute graft-versus-host disease (aGVHD). In this study, we aimed to identify early TMA biomarkers among patients with aGVHD. We performed a nested-case-control study from a prospective cohort of allogeneic HCT recipients, matching on the timing and severity of antecedent aGVHD. We identified 13 TMA cases and 25 non-TMA controls from 208 patients in the cohort. Using multivariable conditional logistic regression, the odds ratio for TMA compared with non-TMA was 2.65 (95% confidence interval [CI], 1.00 to 7.04) for every 100 ng/mL increase in terminal complement complex sC5b9 and 2.62 (95% CI, 1.56 to 4.38) for every 1000 pg/mL increase in angiopoietin-2 (ANG2) at the onset of aGVHD. ADAMTS13 and von Willebrand factor (VWF) antigens were not appreciably associated with TMA. Using a Cox regression model incorporating sC5b9 >300 ng/mL and ANG2 >3000 pg/mL at the onset of aGVHD, the adjusted hazard ratio for mortality was 5.33 (95% CI, 1.57 to 18.03) for the high-risk group (both elevated) and 4.40 (95% CI, 1.60 to 12.07) for the intermediate-risk group (one elevated) compared with the low-risk group (neither elevated). In conclusion, we found that elevated sC5b9 and ANG2 levels at the onset of aGVHD were associated with the development of TMA and possibly mortality after accounting for the timing and severity of aGVHD. The results suggest important roles of complement activation and endothelial dysfunction in the pathogenesis of TMA. Measurement of these biomarkers at the onset of aGVHD may inform prognostic enrichment for preventive trials and improve clinical care.

Conformation-dependent blockage of activated VWF improves outcomes of traumatic brain injury in mice.

Traumatic brain injury-induced coagulopathy (TBI-IC) causes life-threatening secondary intracranial bleeding. Its pathogenesis differs mechanistically from that of coagulopathy arising from extracranial injuries and hemorrhagic shock, but it remains poorly understood. We report results of a study designed to test the hypothesis that von Willebrand factor (VWF) released during acute TBI is intrinsically hyperadhesive because its platelet-binding A1-domain is exposed and contributes to TBI-induced vascular leakage and consumptive coagulopathy. This hyperadhesive VWF can be selectively blocked by a VWF A2-domain protein to prevent TBI-IC and to improve neurological function with a minimal risk of bleeding. We demonstrated that A2 given through intraperitoneal injection or IV infusion reduced TBI-induced death by >50% and significantly improved the neurological function of C57BL/6J male mice subjected to severe lateral fluid percussion injury. A2 protected the endothelium from extracellular vesicle-induced injury, reducing TBI-induced platelet activation and microvesiculation, and preventing a TBI-induced hypercoagulable state. A2 achieved this therapeutic efficacy by specifically blocking the A1 domain exposed on the hyperadhesive VWF released during acute TBI. These results suggest that VWF plays a causal role in the development of TBI-IC and is a therapeutic target for this life-threatening complication of TBI.

Placenta-derived extracellular vesicles induce preeclampsia in mouse models.

Preeclampsia is a pregnancy-induced condition that impairs the mother's health and results in pregnancy termination or premature delivery. Elevated levels of placenta-derived extracellular vesicles (pcEV) in the circulation have been consistently associated with preeclampsia, but whether these vesicles induce preeclampsia or are the product of preeclampsia is not known. Guided by a small cohort study of preeclamptic patients, we examined the impact of pcEV on the pathogenesis of preeclampsia in mouse models. We detected pcEV in pregnant C56BL/6J mice with a peak level of 3.8±0.9×107/mL at 17-18 days post-coitum. However, these pregnant mice developed hypertension and proteinuria only after being infused with vesicles purified from injured placenta. These extracellular vesicles released from injured placenta disrupted endothelial integrity and induced vasoconstriction. Enhancing the clearance of extracellular vesicles prevented the development of the extracellular vesicle-induced preeclampsia in mice. Our results demonstrate a causal role of pcEV in preeclampsia and identify microvesicle clearance as a new therapeutic strategy for the treatment of this pregnancy-associated complication.

Extracellular mitochondria released from traumatized brains induced platelet procoagulant activity.

Coagulopathy often develops soon after acute traumatic brain injury and its cause remains poorly understood. We have shown that injured brains release cellular microvesicles that disrupt the endothelial barrier and induce consumptive coagulopathy. Morphologically intact extracellular mitochondria accounted for 55.2% of these microvesicles, leading to the hypothesis that these extracellular mitochondria are metabolically active and serve as a source of oxidative stress that activates platelets and renders them procoagulant. In testing this hypothesis experimentally, we found that the extracellular mitochondria purified from brain trauma mice and those released from brains subjected to freeze-thaw injury remained metabolically active and produced reactive oxygen species. These extracellular mitochondria bound platelets through the phospholipid-CD36 interaction and induced α-granule secretion, microvesiculation, and procoagulant activity in an oxidant-dependent manner, but failed to induce aggregation. These results define an extracellular mitochondria-induced and redox-dependent intermediate phenotype of platelets that contribute to the pathogenesis of traumatic brain injury-induced coagulopathy and inflammation.

von Willebrand factor enhances microvesicle-induced vascular leakage and coagulopathy in mice with traumatic brain injury.

von Willebrand factor (VWF) is an adhesive ligand, and its activity is proteolytically regulated by the metalloprotease ADAMTS-13 (a disintegrin and metalloprotease with thrombospondin type 1 repeat 13). An elevated level of plasma VWF has been widely considered a marker for endothelial cell activation in trauma and inflammation, but its causal role in these pathological conditions remains poorly defined. Using a fluid percussion injury mouse model, we demonstrated that VWF released during acute traumatic brain injury (TBI) was activated and became microvesicle-bound. The VWF-bound microvesicles promoted vascular leakage and systemic coagulation. Recombinant ADAMTS-13 given either before or after TBI reduced the VWF reactivity with minimal influence on VWF secretion. rADAMTS-13 protected the integrity of endothelial cell barriers and prevented TBI-induced coagulopathy by enhancing VWF cleavage without impairing basal hemostasis. Promoting microvesicle clearance by lactadherin had efficacy similar to that of rADAMTS-13. This study uncovers a novel synergistic action between VWF and cellular microvesicles in TBI-induced vascular leakage and coagulopathy and demonstrates protective effects of rADAMTS-13.

Lactadherin promotes microvesicle clearance to prevent coagulopathy and improves survival of severe TBI mice.

Coagulopathy is common in patients with traumatic brain injury (TBI) and predicts poor clinical outcomes. We have shown that brain-derived extracellular microvesicles, including extracellular mitochondria, play a key role in the development of TBI-induced coagulopathy. Here, we further show in mouse models that the apoptotic cell-scavenging factor lactadherin, given at a single dose of 400 µg/kg 30 minutes before (preconditioning) or 30 minutes after cerebral fluid percussion injury, prevented coagulopathy as defined by clotting time, fibrinolysis, intravascular fibrin deposition, and microvascular bleeding of the lungs. Lactadherin also reduced cerebral edema, improved neurological function, and increased survival. It achieved these protective effects by enhancing the clearance of circulating microvesicles through phosphatidylserine-mediated phagocytosis. Together, these results identify the scavenging system for apoptotic cells as a potential therapeutic target to prevent TBI-induced coagulopathy and improve the outcome of TBI.

Quantification of Von Willebrand Factor Cleavage by adamts-13 in Patients Supported by Left Ventricular Assist Devices.

Patients supported by left ventricular assist devices (LVADs) often present with the loss of large von Willebrand factor (VWF) multimers. This VWF deficiency is believed to contribute to the bleeding diathesis of patients on LVAD support and is caused by excessive VWF cleavage by the metalloprotease ADAMTS-13 under high shear stress. However, only a small percentage of patients who have suffered the loss of large VWF multimers bleed. The actual rates of VWF cleavage in these patients have not been reported, primarily because of the lack of reliable detection methods. We have developed and validated a selected reaction monitoring (SRM) mass spectrometry method to quantify VWF cleavage as the ratio of the ADAMTS-13-cleaved peptide MVTGNPASDEIK to the ILAGPAGDSNVVK peptide. The rate of VWF cleavage was found to be 1.26% ± 0.36% in normal plasma. It varied significantly in patient samples, ranging from 0.23% to 2.5% of total VWF antigen, even though all patients had the loss of large VWF multimers. Von Willebrand factor cleavage was greater in post-LVAD samples from patients in whom bleeding had developed, but was mostly reduced in patients in whom thrombosis had developed. This SRM method is reliable to quantify the rate of VWF cleavage in patients on LVAD support.

Cardiolipin-mediated procoagulant activity of mitochondria contributes to traumatic brain injury-associated coagulopathy in mice.

Cardiolipin (CL) is an anionic phospholipid located exclusively in the mitochondrial inner membrane. Its presence in blood indicates mitochondrial damage and release from injured cells. Here, we report the detection of CL-exposed brain-derived mitochondrial microparticles (mtMPs) at 17 547 ± 2677/µL in the peripheral blood of mice subjected to fluid percussion injury to the brain. These mtMPs accounted for 55.2% ± 12.6% of all plasma annexin V-binding microparticles found in the acute phase of injury. They were also released from cultured neuronal and glial cells undergoing apoptosis. The mtMPs synergized with platelets to facilitate vascular leakage by disrupting the endothelial barrier. The disrupted endothelial barrier allowed the release of mtMPs into the systemic circulation to promote coagulation in both traumatically injured and mtMP- or CL-injected mice, leading to enhanced fibrinolysis, vascular fibrin deposition, and thrombosis. This mtMP-induced coagulation was mediated by CL transported from the inner to the outer mitochondrial membrane and was blocked by the scavenging molecule lactadherin. The mtMP-bound CL was ∼1600 times as active as purified CL in promoting coagulation. This study uncovered a novel procoagulant activity of CL and CL-exposed mitochondria that may contribute to traumatic brain injury-associated coagulopathy and identified potential pathways to block this activity.