Extracellular histones: a unifying mechanism driving platelet-dependent extracellular vesicle release and thrombus formation in COVID-19.

Background: COVID-19 can cause profound inflammation and coagulopathy, and while many mechanisms have been proposed, there is no known common pathway leading to a prothrombotic state.

Objectives: From the beginning of the COVID-19 pandemic, elevated levels of extracellular histones have been found in plasma of patients infected with SARS-CoV-2. We hypothesized that platelet activation triggered by extracellular histones might represent a unifying mechanism leading to increased thrombin generation and thrombosis.

Protein methionine oxidation augments reperfusion injury in acute ischemic stroke.

Reperfusion injury can exacerbate tissue damage in ischemic stroke, but little is known about the mechanisms linking ROS to stroke severity. Here, we tested the hypothesis that protein methionine oxidation potentiates NF-κB activation and contributes to cerebral ischemia/reperfusion injury. We found that overexpression of methionine sulfoxide reductase A (MsrA), an antioxidant enzyme that reverses protein methionine oxidation, attenuated ROS-augmented NF-κB activation in endothelial cells, in part, by protecting against the oxidation of methionine residues in the regulatory domain of calcium/calmodulin-dependent protein kinase II (CaMKII).

Deletion of Methionine Sulfoxide Reductase A Does Not Affect Atherothrombosis but Promotes Neointimal Hyperplasia and Extracellular Signal-Regulated Kinase 1/2 Signaling.

Objective: Emerging evidence suggests that methionine oxidation can directly affect protein function and may be linked to cardiovascular disease. The objective of this study was to define the role of the methionine sulfoxide reductase A (MsrA) in models of vascular disease and identify its signaling pathways.

Approach And Results: MsrA was readily identified in all layers of the vascular wall in human and murine arteries.

Deficiency of superoxide dismutase impairs protein C activation and enhances susceptibility to experimental thrombosis.

Objective: Clinical evidence suggests an association between oxidative stress and vascular disease, and in vitro studies have demonstrated that reactive oxygen species can have prothrombotic effects on vascular and blood cells. It remains unclear, however, whether elevated levels of reactive oxygen species accelerate susceptibility to experimental thrombosis in vivo.

Approach And Results: Using a murine model with genetic deficiency in superoxide dismutase-1 (SOD1), we measured susceptibility to carotid artery thrombosis in response to photochemical injury.

Myeloperoxidase is increased in human cerebral aneurysms and increases formation and rupture of cerebral aneurysms in mice.

Background And Purpose: Cerebral aneurysm (CA) affects 3% of the population and is associated with hemodynamic stress and inflammation. Myeloperoxidase, a major oxidative enzyme associated with inflammation, is increased in patients with CA, but whether myeloperoxidase contributes to CA is not known. We tested the hypotheses that myeloperoxidase is increased within human CA and is critical for formation and rupture of CA in mice.

Smooth Muscle Peroxisome Proliferator-Activated Receptor γ Plays a Critical Role in Formation and Rupture of Cerebral Aneurysms in Mice In Vivo.

Vascular inflammation plays a critical role in the pathogenesis of cerebral aneurysms. Peroxisome proliferator-activated receptor γ (PPARγ) protects against vascular inflammation and atherosclerosis, whereas dominant-negative mutations in PPARγ promote atherosclerosis and vascular dysfunction. We tested the role of PPARγ in aneurysm formation and rupture.

Endothelial PPAR-γ protects against vascular thrombosis by downregulating P-selectin expression.

Objective: We tested the hypothesis that endothelial peroxisome proliferator-activated receptor-γ protects against vascular thrombosis using a transgenic mouse model expressing a peroxisome proliferator-activated receptor-γ mutant (E-V290M) selectively in endothelium.

Approach And Results: The time to occlusive thrombosis of the carotid artery was significantly shortened in E-V290M mice compared with nontransgenic littermates after either chemical injury with ferric chloride (5.1 ± 0.

Hydrogen peroxide promotes aging-related platelet hyperactivation and thrombosis.

Background: The incidence of thrombotic events increases during aging, but the mechanisms are not well understood. To investigate the prothrombotic role of oxidative stress during aging, we tested the hypothesis that aged mice overexpressing the antioxidant enzyme glutathione peroxidase-1 (Gpx1) are protected from experimental thrombosis.

Methods And Results: Susceptibility to carotid artery thrombosis was first examined in wild-type C57BL/6J mice.

Human thrombomodulin knock-in mice reveal differential effects of human thrombomodulin on thrombosis and atherosclerosis.

Objective: We sought to develop a murine model to examine the antithrombotic and antiinflammatory functions of human thrombomodulin in vivo.

Methods And Results: Knock-in mice that express human thrombomodulin from the murine thrombomodulin gene locus were generated. Compared with wild-type mice, human thrombomodulin knock-in mice exhibited decreased protein C activation in the aorta (P<0.

Overexpression of dimethylarginine dimethylaminohydrolase protects against cerebral vascular effects of hyperhomocysteinemia.

Rationale: Hyperhomocysteinemia is a cardiovascular risk factor that is associated with elevation of the nitric oxide synthase inhibitor asymmetrical dimethylarginine (ADMA).

Objective: Using mice transgenic for overexpression of the ADMA-hydrolyzing enzyme dimethylarginine dimethylaminohydrolase-1 (DDAH1), we tested the hypothesis that overexpression of DDAH1 protects from adverse structural and functional changes in cerebral arterioles in hyperhomocysteinemia.

Methods And Results: Hyperhomocysteinemia was induced in DDAH1 transgenic (DDAH1 Tg) mice and wild-type littermates using a high methionine/low folate (HM/LF) diet.

Critical role for the mitochondrial permeability transition pore and cyclophilin D in platelet activation and thrombosis.

Many of the cellular responses that occur in activated platelets resemble events that take place following activation of cell-death pathways in nucleated cells. We tested the hypothesis that formation of the mitochondrial permeability transition pore (MPTP), a key signaling event during cell death, also plays a critical role in platelet activation. Stimulation of murine platelets with thrombin plus the glycoprotein VI agonist convulxin resulted in a rapid loss of mitochondrial transmembrane potential (Deltapsi(m)) in a subpopulation of activated platelets.

Prothrombotic effects of hyperhomocysteinemia and hypercholesterolemia in ApoE-deficient mice.

Objective: We tested the hypothesis that hyperhomocysteinemia and hypercholesterolemia promote arterial thrombosis in mice.

Methods And Results: Male apolipoprotein E (Apoe)-deficient mice were fed one of four diets: control, hyperhomocysteinemic (HH), high fat (HF), or high fat/hyperhomocysteinemic (HF/HH). Total cholesterol was elevated 2-fold with the HF or HF/HH diets compared with the control or HH diets (P<0.

Enhanced susceptibility to arterial thrombosis in a murine model of hyperhomocysteinemia.

Hyperhomocysteinemia is a risk factor for thrombosis, but the mechanisms are not well defined. We tested the hypothesis that hyperhomocysteinemia accelerates arterial thrombosis in mice. Mice heterozygous for a targeted disruption of the cystathionine beta-synthase gene (Cbs+/-) and wild-type littermates (Cbs+/+) were fed either a control diet or a high methionine/low folate (HM/LF) diet for 6 to 8 months to produce graded hyperhomocysteinemia.

Mechanisms of the atherogenic effects of elevated homocysteine in experimental models.

Hyperhomocysteinemia is a risk factor for cardiovascular disease and stroke. During the last decade, considerable progress in delineating the mechanisms that underlie the atherogenic effects of hyperhomocysteinemia has been achieved through the use of experimental animal models. Among the most informative animal models are those that use genetic and dietary approaches to produce hyperhomocysteinemia in mice.

Genetic analysis of four novel peroxisome proliferator activated receptor-gamma splice variants in monkey macrophages.

Peroxisome proliferator activated receptor-gamma (PPAR-gamma) is abundantly expressed in atherosclerotic lesions and is implicated in atherogenesis. The existence of three splice variants, PPAR-gamma 1, PPAR-gamma 2, and PPAR-gamma 3 has been established. Using monocyte-derived macrophages from cynomolgus monkeys, we demonstrate here the identification of two new PPAR-gamma exons, exon C and exon D, which splice together with already established exons A1, A2, and B in the 5(') terminal region to generate four novel PPAR-gamma subtypes, PPAR-gamma 4, -gamma 5, -gamma 6, and -gamma 7.