Talens, S.

Novel fibrin clot components : identification, characterization and function (Doctoral Thesis)

2013-03-15T00:00:00Z

The main goal of blood coagulation is to diminish blood loss and to support vessel damage repair. The initial step in primary hemostasis is the adhesion of platelets to the exposed subendothelial extracellular matrix which contains several adhesive macromolecules such as collagen, von Willebrand factor (vWF), laminin, fibronectin and thrombospondin. These adhesive macromolecules are ligands for different platelet-surface receptors. Upon binding, platelets can be activated by different signal transduction pathways. Platelet adhesion and activation is followed by platelet aggregation, which involves fibrinogen binding to an integrin on the surface of the activated platelet. Secondary hemostasis is initiated by exposure of tissue factor (TF) to blood by endothelial damage. TF forms a complex with coagulation factor VII which activates factor IX and factor X. Activated factor X (FXa) forms the prothrombinase complex together with activated factor V (FVa) on a phospholipid membrane surface, which is provided by, for example, activated platelets and microparticles, and which converts prothrombin into thrombin. Thrombin can amplify its own generation by activating FXI, and FXIa activates FIX, that together with activated FVIII forms more FX. Thrombin is an important enzyme that cleaves fibrinogen into fibrin monomer. Fibrin monomers polymerize and the resulting network is stabilized by factor XIIIa-catalyzed cross-linking. This tight fibrin network together with activated platelets occludes the site of vascular injury. After its formation, the clot will retract. The speed and degree of clot retraction are proportional to the number of platelets. Neither the significance of in vivo clot retraction for hemostasis as well as the mechanism of clot retraction are well understood. Retraction may improve the mechanical stability of clots. To maintain a balance, the coagulation pathway is inhibited by several inhibitors. Tissue factor pathway inhibitor (TFPI) inhibits the TF-induced coagulation firstly by binding to FXa. Secondly, this TFPI-FXa complex binds to the TF-FVIIa complex resulting in the formation of an inactive quaternary complex. TFPI can also inhibit the initiation phase of coagulation in one step by binding to activated FX that is not yet released from its complex with TF-FVIIa. Thrombin is directly inhibited by the serine protease inhibitor antithrombin as well as heparin cofactor II. Thrombin can also bind to thrombomodulin and form a complex that activates protein C. Activated protein C (APC), with its cofactor protein S, has anticoagulant properties through proteolytic inactivation of factors Va and VIIIa.

Oxidized high-density lipoprotein reduces blood clot firmness (Article)

2013-03-01T00:00:00Z

Myelin ingestion alters macrophage antigen-presenting function in vitro and in vivo (Article)

2011-07-01T00:00:00Z

During MS, phagocytosing myelin-containing macrophages arise and lie in close proximity to T cells. To date, it has not been addressed whether these myelinladen macrophages have the capacity to present antigens to T cells and whether this contributes to inflammation in disease. We demonstrate that in vitro-generated human and mouse myelin-laden macrophages expressed MHC class I and II and costimulatory molecules and are thus well equipped for antigen presentation.uman myelin-laden macrophages exhibited normal endocytosis of particulate and soluble antigens. In addition, human myelin-laden macrophages elicited active T cell proliferation of nai{dotless}̈ve as well as memory T cells. Furthermore, mouse myelin-laden macrophages induced primary antigen-specific CD4+T cell proliferation in vivo but transiently diminished IFN-γ release. Functionally, MOG peptide-loaded myelin-laden mouse macrophages modestly but significantly reduced the severity of MOG peptide-induced EAE. These data show that myelin uptake results in the induction of a population of macrophages that retains antigen-presenting capacity and limits autoimmune-mediated disease.

Proteomic analysis reveals that apolipoprotein A1 levels are decreased in patients with Budd-Chiari syndrome (Article)

2011-05-01T00:00:00Z

Background & Aims: Budd-Chiari syndrome (BCS) is a rare vascular liver disorder caused by thrombosis of the hepatic veins. In some patients, no known thrombophilic factor can be identified. This study aimed to identify novel factors that might play a role in thrombosis in BCS-patients by using a proteomic approach. Methods: The abundance of plasma clot-bound proteins was compared between nine BCS-patients and nine controls by using two-dimensional difference gel electrophoresis. The protein with the most significant decrease in patients was identified by mass spectrometry. Plasma levels of this protein were measured and the results were validated in a large cohort of BCS-patients. Results: A total of 26 protein spots significantly differed (p <0.001). The spot that decreased with the highest statistical significance in patients was identified by mass spectrometry as apolipoprotein A1 (apo A1). The mean level of apo A1 in the plasma of these BCS-patients (0.74 g/L) was also significantly lower than in controls (1.45 g/L, p = 0.002). This finding was validated in a large cohort of 101 BCS-patients and 101 controls (0.97 g/L vs. 1.32 g/L, p <0.0001). There was no major correlation between plasma levels of apo A1 and various liver function tests. Conclusions: BCS-patients show decreased clot-bound protein abundance and plasma levels of apo A1. Decreased levels of apo A1 may play a role in the etiology of thrombosis in BCS-patients and possibly in other patients with venous thrombosis.