Vessel wall-dependent metabolic pat hways of the

The integrity of the vessel wall under quiescent conditions as well as its appropriate responsiveness under conditions of stimulation, inflammation or vascular injury is controlled by a number of adhesive interactions involving distinct cellular receptor systems and various multifunctional adhesive ligands. While a number of these extracellular matrix components of the vessel wall are endogenously produced, secreted and deposited, exogenous adhesion proteins may become translocated from the intra- to the extravascular space by virtue of endothelial cell-specific transport systems. Two prominent examples for each metabolic pathway are discussed. Endothelial cellspecific biosynthesis and secretion as well as deposition of multimeric von-Willebrand-factor within intracellular granules (Weibel-Palade bodies) relates to the first possibility of processing, whereas binding of reactive forms of circulating vitronectin to diverse cellular receptors with subsequent extravasation and deposition into the extracellular matrix appears to be characteristic for the second case. In this review the known features of the metabolic routes of both adhesion proteins are discussed and set in perspective to their functional properties. Their localized mode of action in the vessel wall appears to be crucial for balanced haemostasis and immune systems, two major defence mechanisms of the organism

Domain structure of the endothelial cell receptor thrombomodulin as deduced from modulation of its anticoagulant functions. Evidence for a glycosaminoglycan-dependent secondary binding site for thrombin.

Rabbit thrombomodulin (TM) influences blood coagulation by serving as a cofactor for thrombin-induced protein C activation (activity a), by directly affecting the procoagulant activity of thrombin (activity b) and by accelerating the inhibition of thrombin by antithrombin III (AT III) (activity c). Although high molecular weight cationic compounds, such as poly-L-lysine and the ionophore-releasate from human platelets, only partly affected activity a in a concentration-dependent manner, activities b and c, however, were almost totally inhibited by these cationic compounds. Likewise, a heparin- and dermatan sulfate-binding peptide which represents a portion of the glycosaminoglycan-binding domain of vitronectin (VN) selectively inhibited activities b and c, indicating the presence of clustered acidic domain(s) in TM responsible for these activities. While heparinase or heparitinase did not affect rabbit TM function at all, digestion of rabbit TM with chondroitin ABC-lyase abolished activities b and c, whereas activity a remained unaffected. Modification of rabbit TM with chondroitin ABC-lyase was associated with a decrease in molecular mass of the receptor by about 10 kDa and a 2- to 3-fold decrease in affinity to thrombin as deduced from direct binding studies. These results suggest that at least two acidic thrombin binding domains are present in rabbit TM, whereby a dermatan sulfate-like glycosaminoglycan moiety constitutes the secondary binding domain for thrombin, eliciting both the direct as well as the AT III-dependent anticoagulant function of rabbit TM (activities b and c) but not protein C activation (activity a). In contrast to rabbit TM, human TM isolated from placenta only showed weak activities b and c. These differences in reactivity of TM from different sources appeared to be due to the masking (or absence) of the proposed secondary thrombin binding site in human TM, since VN could be identified as a major contamination in the human TM preparation as revealed by enzyme-linked immunosorbent assay and Western blot analysis. In addition, the major part of human TM could be immunoprecipitated by monospecific antibodies to VN. These findings indicate a possible modulatory function for VN in the human thrombin-TM system

Thrombin Promotes Macrophage Polarization into M1-Like Phenotype to Induce Inflammatory Responses

© 2020 Georg Thieme Verlag. All rights reserved. Despite strong evidence supporting the cellular interplay between haemostasis and innate immunity, humoral connections between blood coagulation and the behavior of inflammatory macrophages are not well understood. In this study, we investigated changes in gene expression of selected cytokines and chemokines and their secretion profiles following thrombin stimulation of murine macrophages. Thrombin promoted differentiation of macrophages into an M1-like phenotype that was associated with the expression of classical pro-inflammatory markers. The cellular actions of thrombin on macrophages were mediated in part by protease-activated receptor-1 (PAR-1) and were dependent on phosphoinositide 3-kinase/AKT and nuclear factor-κB. Moreover, heat-denatured thrombin stimulated the secretion of some pro-inflammatory mediators to the same magnitude indicating that different receptors transmit cellular signals of enzymatically active thrombin and nonactive thrombin, the latter remaining so far undefined. Finally, pretreatment of macrophages with thrombin resulted in tolerance against secondary stimulation by lipopolysaccharide with regard to expression of tumor necrosis factor-α. These results provide new insights into the molecular link between the key enzyme of haemostasis and innate immunity responses

Plasminogen activator inhibitor type 1 inhibits smooth muscle cell proliferation in pulmonary arterial hypertension

RATIONALE: Pulmonary arterial smooth muscle cells (PASMCs) in the medial layer of the vessel wall are responsible for vessel homeostasis, but also for pathologic vascular remodelling in diseases, such as idiopathic pulmonary arterial hypertension (IPAH). Vascular remodelling in IPAH results in vessel stiffness, occlusion, and increased vascular resistance, but its underlying mechanisms remain to be fully elucidated. In this study, we investigated the expression and function of plasminogen activator inhibitor (PAI)-1, an inhibitor of the plasminogen activator system and target gene of the transforming growth factor (TGF)-beta1 signalling cascade, in PASMC in IPAH. METHODS AND RESULTS: RNA and protein analysis from lung tissues of donors and patients with IPAH (n=7 each) revealed a significant downregulation of PAI-1 in IPAH lungs. Immunohistochemical analysis localised PAI-1 to the bronchial and alveolar epithelium, as well as to vascular and airway smooth muscle cells. PAI-1 was also downregulated in primary PASMC derived from IPAH lungs as compared with donor-derived PASMC. In order to elucidate PAI-1 function, primary PASMC were stimulated with active recombinant (r)PAI-1, or transfected with PAI-1-specific siRNA. Stimulation with rPAI-1 led to decreased PASMC proliferation and adhesion to vitronectin, and increased PASMC migration. In contrast, PAI-1 knock-down with siRNA increased PASMC proliferation and decreased PASMC migration. CONCLUSIONS: PAI-1 is significantly downregulated in PASMC in IPAH, on the mRNA and protein level. PAI-1 negatively regulates PASMC proliferation, while it increases PASMC migration. Thus, its loss in IPAH may therefore contribute to pathologic vascular remodelling in IPAH

Aufbau von automatisierten molekularen Screening-Systemen zur Auffindung neuer biomedizinisch wirksamer Naturstoffe. Teilprojekt: Klonierung, Expression und Strukturanalyse von Adhaesivrezeptor-Liganden Schlussbericht

The aim of this project was the cloning, expression and characterization of structure-function relationship of integrin ligands, in particular fragments of vitronectin. Recombinant site-direct mutants of the adhesion protein should be made available for receptor binding studies with the possibility to investigate these isolated ligand receptor systems for screening assays of integrin inhibitors. We have successfully generated stable recombinant fragments of vitronectin that contain the relevant integrin binding sites. These recombinant fragments are very similar in their structural and functional properties to the natural adhesion protein and were successfully included in screening systems for integrin inhibitors. Furthermore, high density cellular expression systems yielded sufficient recombinant material that is available for direct structural analysis in order to obtain molecular information for subsequent rational drug design. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(76,38) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman