Marc F Hoylaerts

KU Leuven | ku leuven · Center for Molecular and Vascular Biology

Alongside their function in primary hemostasis and thrombo-inflammation, platelets are increasingly considered a bridge between mental, immunological and coagulation-related disorders. This review focuses on the link between platelets and the pathophysiology of major depressive disorder (MDD) and its most frequent comorbidities. Platelet-and neuron...

Background Platelet Endothelial Aggregation Receptor 1 (PEAR1) modulates angiogenesis and platelet contact-induced activation, which play a role in the pathogenesis of colorectal cancer. Purpose To study the association of colorectal cancer with genetic and epigenetic variation in PEAR1. Methods Among 2532 randomly recruited participants enrolled...

Pro-thrombotic and inflammatory changes play an important role in cardiovascular morbidity and mortality, resulting from short-term exposure to fine particulate air-pollution. Part of those effects has been attributed to the ultra-fine particles (UFPs) that pass through the lung and directly contact blood-exposed and circulating cells. Despite UFP-...

Various valved conduits and stent-mounted valves are used for right ventricular outflow tract (RVOT) valve replacement in patients with congenital heart disease. When using prosthetic materials however, these grafts are susceptible to bacterial infections and various host responses. Identification of bacterial and host factors that play a vital rol...

Adhesion of Staphylococcus aureus to endothelial cells (ECs) is paramount in infective endocarditis. Bacterial proteins such as clumping factor A (ClfA) and fibronectin binding protein A (FnbpA) mediate adhesion to EC surface molecules and (sub)endothelial matrix proteins including fibrinogen (Fg), fibrin, fibronectin (Fn) and von Willebrand factor...

Background: Staphylococcus aureus(S. aureus) bacteraemia is frequent and carries a high morbidity and mortality. Coagulases secreted byS. aureusinitiate blood coagulation by directly activating prothrombin. This pathogen-activated coagulation is insensitive to most antithrombotic drugs, with the exception of small molecule direct thrombin inhibito...

Chromosomal interactions connect distant enhancers and promoters on the same chromosome, activating or repressing gene expression.PEAR1encodes the Platelet-Endothelial Aggregation Receptor 1, a contact receptor involved in platelet function and megakaryocyte and endothelial cell proliferation.PEAR1expression during megakaryocyte differentiation is...

In this issue of J. Thromb. Haemost., R. Palankar et al. provide a comprehensive model that may contribute to bacterial killing by human platelets [1]. Platelet Factor 4 (PF4) binds to negative polyanionic elements (P) on the surface of Gram‐negative and –positive bacteria. This interaction triggers conformational changes in bound PF4, in turn lead...

Background: Thrombotic thrombocytopenic purpura (TTP) is caused by the absence of ADAMTS13 activity. Thrombocytopenia is presumably related to the formation of microthrombi rich in von Willebrand Factor (VWF) and platelets. Obesity may be a risk factor for TTP; it is associated with abundance of macrophages that may phagocytose platelets. Objecti...

Neuromedin U (NmU) is a pleiotropic hypothalamic neuropeptide involved in the gut–brain axis. It acts via both a Gαq/11-coupled receptor (NMUR1) and a Gαi-coupled receptor (NMUR2) in different cell types. Expression of both receptors was reported in platelets, but their significance for NmU signaling remains elusive. We studied the potential effect...

During the process of endochondral bone formation, chondrocytes and osteoblasts mineralize their extracellular matrix (ECM) by promoting the synthesis of hydroxyapatite (HA) seed crystals in the sheltered interior of membrane-limited matrix vesicles (MVs). Several lipid and proteins present in the membrane of the MVs mediate the interactions of MVs...

Objective Various conduits or stent-mounted valves are used as pulmonary valve graft tissues for Right Ventricular Outflow Tract reconstruction with good hemodynamic results. Valve replacement inherits an increased risk of infective endocarditis (IE). Recent observations rose awareness to IE after transcatheter implantation of a stent-mounted bovin...

Atomic force microscopy (AFM) is one of the most commonly used scanning probe microscopy techniques for nanoscale imaging and characterization of lipid-based particles. However, obtaining images of such particles using AFM is still a challenge. The present study extends the capabilities of AFM to the characterization of proteoliposomes, a special c...

Background Platelet Endothelial Aggregation Receptor 1 (PEAR1), a membrane protein highly expressed in platelets and endothelial cells, plays a role in platelet contact-induced activation, sustained platelet aggregation and endothelial function. Previous reports implicate PEAR1 rs12041331 as a variant influencing risk in patients with coronary hear...

Mineralization of the skeleton starts within cell-derived matrix vesicles (MVs); then, minerals propagate to the extracellular collagenous matrix. Tissue-nonspecific alkaline phosphatase (TNAP) degrades inorganic pyrophosphate (PPi), a potent inhibitor of mineralization, and contributes Pi (Phosphate) from ATP to initiate mineralization. Compared t...

Objective: When establishing endovascular infections, Staphylococcus aureus (S. aureus) overcomes shear forces of flowing blood by binding to von Willebrand factor (VWF). Staphylococcal VWF-binding protein (vWbp) interacts with VWF, but it is unknown how this secreted protein binds to the bacterial cell wall. We hypothesized that vWbp interacts wi...

Key Points Active MMP-2 enhances platelet activation by cleaving PAR1 at an extracellular site different from the thrombin cleavage site. The novel PAR1-tethered ligand exposed by MMP-2 selectively stimulates PAR1-dependent Gq and G12/13 pathway activation.

ADAMTS13 cleaves ultralarge multimeric von Willebrand Factor (VWF), thereby preventing formation of platelet-rich microthrombi. ADAMTS13 is mainly produced by hepatic stellate cells, and numerous studies have suggested a functional role of ADAMTS13 in the pathogenesis of liver diseases. The aim of our study was to investigate a potential role of AD...

Background: Platelet Endothelial Aggregation Receptor-1 (PEAR1) is a transmembrane platelet receptor that amplifies the activation of the platelet fibrinogen receptor (αIIbβ3) during platelet aggregation. In man, Pear1 polymorphisms are associated with changes in platelet aggregability. In this report, we characterized Pear1 expression and functio...

Key Points Rs12041331 is the first functional CpG-SNP related to platelet function whose regulatory mechanism depends on DNA methylation. Rs12041331 marks allele-specific methylation at the CpG island encompassing the first untranslated exon during megakaryopoiesis.

Unlabelled: Dextran sulfate (DxS; Mr 500 kD) induces fibrinogen receptor (αIIbβ3) activation via CLEC-2/Syk signaling and via a Syk-independent SFK/PI3K/Akt-dependent tyrosine kinase pathway in human and murine platelets. The platelet surface receptor, responsible for the DxS-induced Syk-independent Akt-activation, has hitherto not been identified...

Ziel: Untersuchung der Thrombinproduktion im Fruchtwasser wahrend fetoskopischer Eingriffe. Des Weiteren die Untersuchung von Thrombinproduktion und Aktivierung von Matrix-Metalloproteinasen (MMPs) an punktierten fetalen Membranen in vitro, so wie die Lokalisierung des Thrombin Rezeptors PAR-1. Methodik: In vivo Studie: Fruchtwasser Proben wurden a...

Objective: We first aimed to investigate in vivo thrombin generation induced by fetoscopy, and second we used term membrane explants for measurement of thrombin generation, thrombin receptor location and induction of selected matrix metalloproteinases (MMPs) in tissue culture. Materials and methods: In vivo study (37 cases): samples of amniotic...

Tissue-nonspecific alkaline phosphatase (TNAP) plays a crucial role during skeletal mineralization, and TNAP deficiency leads to the soft bone disease hypophosphatasia. TNAP is anchored to the external surface of the plasma membranes by means of a GPI (glycosylphosphatidylinositol) anchor. Membrane-anchored and solubilized TNAP displays different k...

We describe the production of stable DPPC and DPPC:DPPS-proteoliposomes harboring annexin V (AnxA5) and tissue-nonspecific alkaline phosphatase (TNAP) and their use to investigate whether the presence of AnxA5 impacts the kinetic parameters for hydrolysis of TNAP substrates at physiological pH. The best catalytic efficiency was achieved in DPPS 10%...

Platelet Endothelial Aggregation Receptor-1 (PEAR1) is a cell membrane protein, expressed on platelets and endothelial cells (ECs). PEAR1 sustains αIIbβ3-activation in aggregating platelets and attenuates megakaryopoiesis via controlling the degree of Akt-phosphorylation. Its role in EC biology is unknown. The aim of this study was to determine the...

The conserved active site of alkaline phosphatases (AP) contains catalytically important Zn2+ (M1 and M2) and Mg2+-sites (M3) and a fourth peripheral Ca2+ site (M4) of unknown significance. We have studied Ca2+ binding to M1-4 of tissue-nonspecific AP (TNAP), an enzyme crucial for skeletal mineralization, using recombinant TNAP and a series of M4 m...

Genome-wide association studies to identify loci responsible for platelet function and cardiovascular disease susceptibility have repeatedly identified polymorphisms linked to a gene encoding Platelet endothelium aggregation receptor 1 (PEAR1), an ″orphan″ cell surface receptor that is activated to stabilize platelet aggregates. To investigate how...

Inflammatory bowel disease (IBD) is recognized as an independent risk factor for thrombosis. First, we investigate whether the concentration of fibrinolysis inhibitors is increased in patients with IBD. Second, we investigate the effect of infliximab induction therapy on the hemostatic profile. This prospective study included 103 patients with IBD...

Background: Staphylococcus lugdunensis (S. lugdunensis) is an emerging cause of endocarditis. To cause endovascular infections S. lugdunensis requires mechanisms to overcome shear stress. We investigated whether platelets and von Willebrand factor (VWF) mediate bacterial adhesion to the vessel wall and the cardiac valves under flow. Methods: S....

Staphylococcus aureus (S. aureus) is a frequent cause of skin and soft tissue infections. A unique feature of S. aureus is the combined presence of coagulases that trigger fibrin formation and of the plasminogen activator staphylokinase (SAK). Whereas the importance of fibrin generation for S. aureus virulence has been established, the role of SAK...

Air pollution has wide-ranging and deleterious effects on human health and is a major issue for the global community. The Global Burden of Disease study has described the worldwide impact of air pollution with as many as 3.1 million of 52.8 million all-cause and all-age deaths being attributable to ambient air pollution in the year 2010.1 Moreover,...

Background Pulmonary exposure to nanoparticles (NPs) may affect, in addition to pulmonary toxicity, the cardiovascular system such as procoagulant effects, vascular dysfunction and progression of atherosclerosis. However, only few studies have investigated hemostatic effects after pulmonary exposure.Methods We used Bmal1 (brain and muscle ARNT-like...

PHOSPHO1 and tissue-nonspecific alkaline phosphatase (TNAP) have non-redundant functions during skeletal mineralization. While TNAP deficiency (Alpl(-/-) mice) leads to hypophosphatasia, caused by accumulation of the mineralization inhibitor inorganic pyrophosphate (PPi ), comparably elevated levels of PPi in Phospho1(-/-) mice do not explain their...

Medial vascular calcification (MVC) is a pathological phenomenon common to a variety of conditions, including aging, chronic kidney disease, diabetes, obesity, and a variety of rare genetic diseases, that causes vascular stiffening and can lead to heart failure. These conditions share the common feature of tissue-nonspecific alkaline phosphatase (T...

Background: Both activated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and active Plasminogen Activator Inhibitor-1 (PAI-1) attenuate fibrinolysis and may therefore contribute to the pathophysiology of Venous ThromboEmbolism (VTE). Whether increased TAFI and/or PAI-1 concentrations are associated with VTE is unclear. Objective: To study a...

Adhesion of Staphylococcus aureus to blood vessels under shear stress requires von Willebrand factor (VWF). Several bacterial factors have been proposed to interact with VWF, including VWF-binding protein (vWbp), a secreted coagulase that activates the host's prothrombin to generate fibrin. We measured the adhesion of S aureus Newman and a vWbp-def...

The Calibrated Automated Thrombogram (CAT) assay that measures thrombin generation (TG) in platelet-poor and -rich plasma, is increasingly being recognised as a more sensitive tool to determine the overall function of the haemostatic system. We developed a method enabling the measurement of TG in a small aliquot of blood. The objective was to valid...

Platelets abundantly express the membrane receptor CD36 and store its ligand thrombospondin-1 (TSP1) in the α-granules. We investigated whether released TSP1 can support platelet adhesion and thrombus formation via interaction with CD36. Mouse platelets deficient in CD36 showed reduced adhesion to TSP1 and subsequent phosphatidylserine expression....

Recombinant alkaline phosphatases are becoming promising protein therapeutics to prevent skeletal mineralization defects, inflammatory bowel diseases, and treat acute kidney injury. By substituting the flexible crown domain of human intestinal alkaline phosphatase (IAP) with that of the human placental isozyme (PLAP) we generated a chimeric enzyme...

During endochondral bone formation, chondrocytes and osteoblasts synthesize and mineralize the extracellular matrix through a process that initiates within matrix vesicles (MVs) and ends with bone mineral propagation onto the collagenous scaffold. pH gradients have been identified in the growth plate of long bones, but how pH changes affect the ini...

Arterial ageing may be associated with a reduction in vasodilation due to increased reactive oxygen species (ROS) production, whereas endothelial cell activation induces procoagulant changes. However, little is known on the effect of ageing on expression of anticoagulant endothelial markers such as endothelial protein C receptor (EPCR). To study ag...

Background: Platelet endothelial aggregation receptor-1 (PEAR1), a type I transmembrane receptor, is expressed on platelets and endothelial cells (ECs) but its contribution to EC function is unknown. We aim to unravel its (patho)physiological role in ECs. Methods and results: PEAR1 expression was analyzed in cultured human endothelial progenitors (...

Platelet endothelial aggregation receptor-1 (PEAR1) participates in platelet aggregation via sustaining αIIbβ3 activation. To investigate the role of PEAR1 in platelet formation, we monitored and manipulated PEAR1 expression in vitro in differentiating human CD34(+) hematopoietic stem cells and in vivo in zebrafish embryos. PEAR1 expression rose du...

Staphylococcus aureus (S. aureus) is a frequent cause of catheter-related infections. S. aureus secretes the coagulases staphylocoagulase and von Willebrand factor–binding protein, both of which form a staphylothrombin complex upon binding to prothrombin. Although fibrinogen and fibrin facilitate the adhesion of S. aureus to catheters, the contribu...

Antagonizing Bcl-2 proteins by BH3 mimetics is a promising anti-cancer strategy. Yet, this has been associated with thrombocytopenia. Dysregulation of the intracellular Ca(2+) homeostasis in platelets by ABT-737 has been implicated in this phenomenon, but the underlying mechanism is a highly controversial issue. It is important to establish whether...

Objectives: We aimed to demonstrate local thrombin generation by fetal membranes, as well as its ability to generate fibrin from fibrinogen concentrate. Furthermore, we aimed to investigate the efficacy of collagen plugs, soaked with plasma and fibrinogen, to seal iatrogenic fetal membrane defects. Methods: Thrombin generation by homogenized fet...

Medial vascular calcification (MVC) is common in patients with chronic kidney disease, obesity, and aging. MVC is an actively regulated process that resembles skeletal mineralization, resulting from chondro-osteogenic transformation of vascular smooth muscle cells (VSMCs). Here, we used mineralizing murine VSMCsto study the expression of PHOSPHO1,...

Alkaline phosphatase (AP) isozymes are present in a wide range of species from bacteria to man and are capable of dephosphorylation and transphosphorylation of a wide spectrum of substrates in vitro. In humans, four AP isozymes have been identified—one tissue-nonspecific (TNAP) and three tissue-specific—named according to the tissue of their predom...

Background: Mice with single gene deficiency of thrombin-activatable fibrinolysis inhibitor (TAFI) or plasminogen activator inhibitor-1 (PAI-1) have an enhanced fibrinolytic capacity. Objectives: To unravel the function and relevance of both antifibrinolytic proteins through the generation and characterization of mice with combined TAFI and PAI-...

Medial vascular calcification (MVC) is common in patients with chronic kidney disease, type II diabetes, obesity, and aging. MVC is an actively regulated process that resembles skeletal mineralization, resulting from chondro-osteogenic transformation of vascular smooth muscle cells (VSMCs), including the production of mineralization-competent matri...

Well-understood functions for "traditional" platelet receptors are described, but "newer" receptors are equally discussed. Receptors are described biochemically (structure, ligand(s), protein partners, and function) and whenever possible, their clinical importance (mutations, polymorphisms, syndrome) are highlighted.

Epidemiological studies indicate that elderly persons are particularly susceptible to the cardiovascular health complications of air pollution, but pathophysiological mechanisms behind the increased susceptibility remain unclear. Therefore, we investigated how continuous traffic-related air pollution exposure affects haemostasis parameters in young...

TB-402 is a partially inhibiting antibody of factor VIII that is under development as a long-acting anticoagulant. The reversibility of FVIII inhibition by TB-402 was evaluated in vitro after spiking with recombinant human FVIII (rhFVIII), human plasma-derived FVIII (hpdFVIII), recombinant activated human FVII (rhFVIIa), FVIII inhibitor bypassing a...

Interactions of Staphylococcus aureus (S. aureus) and platelets play an important role in the pathogenesis of intravascular infections such as infective endocarditis (IE). A typical feature of S. aureus is the ability to generate thrombin activity through the secretion of two prothrombin activating molecules, staphylocoagulase and von Willebrand fa...

To evaluate the effect of aging on adipose tissue development, subcutaneous (SC) and gonadal (GON) white and peri-aortic brown adipose tissues were analyzed of 10 and 30 week old mice deficient in the clock gene Bmal1 (brain and muscle arnt like protein 1) (Bmal1(-/-)) and wild-type littermates (Bmal1(+/+)) kept on a standard fat diet. At both ages...

Because single nucleotide polymorphisms (SNPs) in platelet endothelial aggregation receptor 1 (PEAR1) are associated with differential functional platelet responses in healthy subjects, we studied the function of PEAR1 in human platelets. During platelet aggregation by various agonists, the membrane expression of PEAR1 and its tyrosine phosphorylat...

The effect of ageing on the morphology of veins, venous valves and arteries was investigated in male wild-type mice using an adapted procedure with injection of a silicone polymer Microfil(®) that preserves morphology of the vasculature. Throughout the hind limb the arterial, but not the venous, lumen area and wall thickness were significantly grea...

Visceral obesity is associated with the rising incidence of type 2 diabetes and metabolic syndrome. Low-grade chronic inflammation and oxidative stress synergize in obesity and obesity-induced disorders. We searched a cluster of molecules that support interactions between these stress conditions in monocytes. RNA expressions in blood monocytes of t...

Gene expression profile of obese women with and without T2DM. Gene expression of key molecules in the TLR2/NFκB inflammatory pathway in blood monocytes of 25 lean controls, 40 obese women without T2DM and 62 obese women with T2DM. Data are expressed as means. *P<0.05, **P<0.01 and ***P<0.001 obese compared with lean controls; $P<0.05 obese with T2D...

Primers used in qRT-PCR. (DOC)

We previously showed that the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and its receptor VPAC1 are negative regulators of megakaryopoiesis and platelet function, but their downstream signaling pathway that inhibits this process still remained unknown. A combined proteomic, transcriptomic, and bioinformatic approach was here used to...

Ambient environmental air pollutants include gaseous and particulate components. In polluted air, especially particulate matter seems responsible for cardiovascular complications: It consists of a heterogeneous mixture of solid and liquid particles with different diameters ranging from large thoracic to ultrafine particles, with a diameter < 100 nm...

Staphylocoagulase and von Willebrand binding protein (VWbp) bind to prothrombin to form the staphylothrombin complex that converts fibrinogen into fibrin. To study the role of staphylothrombin and its inhibition by dabigatran on Staphylococcus aureus virulence. We studied the effect of staphylothrombin inhibition on bacterial attachment to polystyr...

Epidemiological studies suggest an association between exposure to particulate matter (PM) in air pollution and the risk of venous thromboembolism (VTE). To investigate the underlying pathophysiological pathways linking PM exposure and VTE. We assessed potential associations between PM exposure and coagulation and inflammation parameters, including...

Background: Epidemiological studies suggest an association between exposure to particulate matter (PM) in air pollution and the risk of venous thromboembolism (VTE). Objectives: To investigae the underlying pathophysiological pathways linking PM exposure and VTE. Patients and methods: We assessed potential associations between PM exposure and coagu...