Hormone-induced thrombosis is mediated through non-canonical fibrin(ogen) aggregation and a novel estrogen target in zebrafish.

Venous thrombosis is a well-known complication of sex hormone therapy, with onset typically within weeks to months after initiation. Worldwide, more than 100 million pre-menopausal women use combined oral contraceptives, with tens to hundreds of thousands developing thrombosis annually, resulting in significant morbidity and mortality. Although it is known that estrogens can alter expression of coagulation factors, the pathways and mechanisms that connect the two systems, as well as the proteins involved in progression to thrombosis, are poorly understood.

The differential formation and composition of leukocyte-platelet aggregates induced by various cellular stimulants.

Background: Leukocyte-platelet aggregates comprise a pathogenic link between hemostasis and immunity, but the prerequisites and mechanisms of their formation remain not understood.

Aims: To quantify the formation, composition, and morphology of leukocyte-platelet aggregates in vitro under the influence of various cellular activators.

Methods: Phorbol-12-myristate-13-acetate (PMA), lipopolysaccharide (LPS), thrombin receptor-activating peptide (TRAP-6), and adenosine diphosphate (ADP) were used as cellular activators.

Mechanics and microstructure of blood plasma clots in shear driven rupture.

Intravascular blood clots are subject to hydrodynamic shear and other forces that cause clot deformation and rupture (embolization). A portion of the ruptured clot can block blood flow in downstream vessels. The mechanical stability of blood clots is determined primarily by the 3D polymeric fibrin network that forms a gel.

Unresolved hemostasis issues in haemophilia.

Despite rapid technological advancement in factor and nonfactor products in the prevention and treatment of bleeding in haemophilia patients, it is imperative that we acknowledge gaps in our understanding of how hemostasis is achieved. The authors will briefly review three unresolved issues in persons with haemophilia (PwH) focusing on the forgotten function that red blood cells play in hemostasis, the critical role of extravascular (outside circulation) FIX in hemostasis in the context of unmodified and extended half-life FIX products and finally on the role that skeletal muscle myosin plays in prothrombinase assembly and subsequent thrombin generation that could mitigate breakthrough muscle hematomas.

Time-dependent ultrastructural changes during venous thrombogenesis and thrombus resolution.

Background: Deep vein thrombosis is a common vascular event that can result in debilitating morbidity and even death due to pulmonary embolism. Clinically, patients with faster resolution of a venous thrombus have improved prognosis, but the detailed structural information regarding changes that occur in a resolving thrombus over time is lacking.

Objectives: To define the spatial-morphologic characteristics of venous thrombus formation, propagation, and resolution at the submicron level over time.

A novel technique to quantify the kinetics of blood clot contraction based on the expulsion of fluorescently labeled albumin into serum.

Background: The platelet-driven contraction or retraction of blood clots has been utilized to obtain blood serum for laboratory studies, but now, in vitro clot contraction assays are used in research laboratories and clinics to assess platelet functionality. The static final extent of clot contraction measured using a clot size or expelled serum volume can be supplemented substantially with a dynamic analysis.

Objectives: To provide a step-by-step protocol for a relatively simple and affordable new automated methodology to follow the kinetics of blood clot contraction, which allows for simultaneous measurements of various samples at a time and requires only a fluorescence plate reader.

Comprehensive Analysis of the Role of Fibrinogen and Thrombin in Clot Formation and Structure for Plasma and Purified Fibrinogen.

Altered properties of fibrin clots have been associated with bleeding and thrombotic disorders, including hemophilia or trauma and heart attack or stroke. Clotting factors, such as thrombin and tissue factor, or blood plasma proteins, such as fibrinogen, play critical roles in fibrin network polymerization. The concentrations and combinations of these proteins affect the structure and stability of clots, which can lead to downstream complications.

Aortic dissection detection and thrombus structure quantification using volumetric ultrasound, histology, and scanning electron microscopy.

Aortic dissection occurs when a weakened portion of the intima tears, and a separation of layers propagates along the aortic wall to form a false lumen filled with active blood flow or intramural thrombus. The unpredictable nature of aortic dissection formation and need for immediate intervention leaves limited serial human image data to study the formation and morphological changes that follow dissection. We used volumetric ultrasound examination, histology, and scanning electron microscopy (SEM) to examine intramural thrombi at well-defined timepoints after dissection occurs in apolipoprotein E-deficient mice infused with angiotensin II (n = 71).

Megakaryocyte-induced contraction of plasma clots: cellular mechanisms and structural mechanobiology.

Nonmuscle cell contractility is an essential feature underlying diverse cellular processes such as motility, morphogenesis, division and genome replication, intracellular transport, and secretion. Blood clot contraction is a well-studied process driven by contracting platelets. Megakaryocytes (MKs), which are the precursors to platelets, can be found in bone marrow and lungs.

Combined computational modeling and experimental study of the biomechanical mechanisms of platelet-driven contraction of fibrin clots.

While blood clot formation has been relatively well studied, little is known about the mechanisms underlying the subsequent structural and mechanical clot remodeling called contraction or retraction. Impairment of the clot contraction process is associated with both life-threatening bleeding and thrombotic conditions, such as ischemic stroke, venous thromboembolism, and others. Recently, blood clot contraction was observed to be hindered in patients with COVID-19.

Biomechanics, Energetics, and Structural Basis of Rupture of Fibrin Networks.

Fibrin provides the main structural integrity and mechanical strength to blood clots. Failure of fibrin clots can result in life-threating complications, such as stroke or pulmonary embolism. The dependence of rupture resistance of fibrin networks (uncracked and cracked) on fibrin(ogen) concentrations in the (patho)physiological 1-5 g L range is explored by performing the ultrastructural studies and theoretical analysis of the experimental stress-strain profiles available from mechanical tensile loading assays.

Activation of Piezo1 channels in compressed red blood cells augments platelet-driven contraction of blood clots.

Background: Piezo1 is a mechanosensitive cationic channel that boosts intracellular [Ca]. Compression of red blood cells (RBCs) during platelet-driven contraction of blood clots may cause the activation of Piezo1.

Objectives: To establish relationships between Piezo1 activity and blood clot contraction.

Role of red blood cells in clinically relevant bleeding tendencies and complications.

The multiple roles of red blood cells (RBCs) are often neglected as contributors in hemostasis and thrombosis. Proactive opportunities to increase RBC numbers, either acutely or subacutely in the case of iron deficiency, are critical as RBCs are the cellular elements that initiate hemostasis together with platelets and stabilize fibrin and clot structure. RBCs also possess several functional properties to assist hemostasis: releasing platelet agonists, promoting shear force-induced von Willebrand factor unfolding, procoagulant capacity, and binding to fibrin.

Blood clot contraction: Mechanisms, pathophysiology, and disease.

A State of the Art lecture titled "Blood Clot Contraction: Mechanisms, Pathophysiology, and Disease" was presented at the International Society on Thrombosis and Haemostasis (ISTH) Congress in 2022. This was a systematic description of blood clot contraction or retraction, driven by activated platelets and causing compaction of the fibrin network along with compression of the embedded erythrocytes. The consequences of clot contraction include redistribution of the fibrin-platelet meshwork toward the periphery of the clot and condensation of erythrocytes in the core, followed by their deformation from the biconcave shape into polyhedral cells (polyhedrocytes).

Fracture toughness of fibrin gels as a function of protein volume fraction: Mechanical origins.

The mechanical stability of blood clots necessary for their functions is provided by fibrin, a fibrous gel. Rupture of clots leads to life-threatening thrombotic embolization, which is little understood. Here, we combine experiments and simulations to determine the toughness of plasma clots as a function of fibrin content and correlate toughness with fibrin network structure characterized by confocal and scanning electron microscopy.

A familial case of MYH9 gene mutation associated with multiple functional and structural platelet abnormalities.

Mutations in the MYH9 gene result in macrothrombocytopenia often associated with hemorrhages. Here, we studied the function and structure of platelets in three family members with a heterozygous mutation R1933X in the MYH9 gene, characteristic of closely related disorders known as the May-Hegglin anomaly and Sebastian syndrome. The examination included complete blood count, blood smear microscopy, platelet flow cytometry (expression of P-selectin and active integrin αIIbβ3 before and after activation), the kinetics of platelet-driven contraction (retraction) of blood clots, as well as scanning/transmission electron microscopy of platelets.

Effects of clot contraction on clot degradation: A mathematical and experimental approach.

Thrombosis, resulting in occlusive blood clots, blocks blood flow to downstream organs and causes life-threatening conditions such as heart attacks and strokes. The administration of tissue plasminogen activator (t-PA), which drives the enzymatic degradation (fibrinolysis) of these blood clots, is a treatment for thrombotic conditions, but the use of these therapeutics is often limited due to the time-dependent nature of treatment and their limited success. We have shown that clot contraction, which is altered in prothrombotic conditions, influences the efficacy of fibrinolysis.

Contribution of septins to human platelet structure and function.

Although septins have been well-studied in nucleated cells, their role in anucleate blood platelets remains obscure. Here, we elucidate the contribution of septins to human platelet structure and functionality. We show that Septin-2 and Septin-9 are predominantly distributed at the periphery of resting platelets and co-localize strongly with microtubules.

Chronic Immune Platelet Activation Is Followed by Platelet Refractoriness and Impaired Contractility.

Autoimmune diseases, including systemic lupus erythematosus (SLE), have a high risk of thrombotic and hemorrhagic complications associated with altered platelet functionality. We studied platelets from the blood of SLE patients and their reactivity. The surface expression of phosphatidylserine, P-selectin, and active integrin αIIbβ3 were measured using flow cytometry before and after platelet stimulation.

Biomechanical origins of inherent tension in fibrin networks.

Blood clots form at the site of vascular injury to seal the wound and prevent bleeding. Clots are in tension as they perform their biological functions and withstand hydrodynamic forces of blood flow, vessel wall fluctuations, extravascular muscle contraction and other forces. There are several mechanisms that generate tension in a blood clot, of which the most well-known is the contraction/retraction caused by activated platelets.