Regulation of VWF (Von Willebrand Factor) in Inflammatory Thrombosis.

Increasing evidence indicates that inflammation promotes thrombosis via a VWF (von Willebrand factor)-mediated mechanism. VWF plays an essential role in maintaining the balance between blood coagulation and bleeding, and inflammation can lead to aberrant regulation. VWF is regulated on a transcriptional and (post-)translational level, and its secretion into the circulation captures platelets upon endothelial activation. The significant progress that has been made in understanding transcriptional and translational regulation of VWF is described in this review. First, we describe how VWF is regulated at the transcriptional and post-translational level with a specific focus on the influence of inflammatory and immune responses. Next, we describe how changes in regulation are linked with various cardiovascular diseases. Recent insights from clinical diseases provide evidence for direct molecular links between inflammation and thrombosis, including atherosclerosis, chronic thromboembolic pulmonary hypertension, and COVID-19. Finally, we will briefly describe clinical implications for antithrombotic treatment.

Epigenetic Modification of the von Willebrand Factor Promoter Drives Platelet Aggregation on the Pulmonary Endothelium in Chronic Thromboembolic Pulmonary Hypertension.

Rationale: von Willebrand factor (vWF) mediates platelet adhesion during thrombosis. While chronic thromboembolic pulmonary hypertension (CTEPH) is associated with increased plasma levels of vWF, the role of this protein in CTEPH has remained enigmatic. Objectives: To identify the role of vWF in CTEPH. Methods: CTEPH-specific patient plasma and pulmonary endarterectomy material from patients with CTEPH were used to study the relationship between inflammation, vWF expression, and pulmonary thrombosis. Cell culture findings were validated in human tissue, and proteomics and chromatin immunoprecipitation were used to investigate the underlying mechanism of CTEPH. Measurements and Main Results: vWF is increased in plasma and the pulmonary endothelium of CTEPH patients. In vitro, the increase in vWF gene expression and the higher release of vWF protein upon endothelial activation resulted in elevated platelet adhesion to CTEPH endothelium. Proteomic analysis revealed that nuclear factor (NF)-κB2 was significantly increased in CTEPH. We demonstrate reduced histone tri-methylation and increased histone acetylation of the vWF promoter in CTEPH endothelium, facilitating binding of NF-κB2 to the vWF promoter and driving vWF transcription. Genetic interference of NFκB2 normalized the high vWF RNA expression levels and reversed the prothrombotic phenotype observed in CTEPH-pulmonary artery endothelial cells. Conclusions: Epigenetic regulation of the vWF promoter contributes to the creation of a local environment that favors in situ thrombosis in the pulmonary arteries. It reveals a direct molecular link between inflammatory pathways and platelet adhesion in the pulmonary vascular wall, emphasizing a possible role of in situ thrombosis in the development or progression of CTEPH.

Bone tissue engineering using 3D silk scaffolds and human dental pulp stromal cells epigenetic reprogrammed with the selective histone deacetylase inhibitor MI192.

Epigenetics plays a critical role in regulating mesenchymal stem cells' (MSCs) fate for tissue repair and regeneration. There is increasing evidence that the inhibition of histone deacetylase (HDAC) isoform 3 can enhance MSC osteogenesis. This study investigated the potential of using a selective HDAC2 and 3 inhibitor, MI192, to promote human dental pulp stromal cells (hDPSCs) bone-like tissue formation in vitro and in vivo within porous Bombyx Mori silk scaffolds. Both 2 and 5 wt% silk scaffolds were fabricated and characterised. The 5 wt% scaffolds possess thicker internal lamellae, reduced scaffold swelling and degradation rates, whilst increased compressive modulus in comparison to the 2 wt% silk scaffold. MI192 pre-treatment of hDPSCs on 5 wt% silk scaffold significantly enhanced hDPSCs alkaline phosphatase activity (ALP). The expression of osteoblast-related genes (RUNX2, ALP, Col1a, OCN) was significantly upregulated in the MI192 pre-treated cells. Histological analysis confirmed that the MI192 pre-treated hDPSCs-silk scaffold constructs promoted bone extracellular matrix (ALP, Col1a, OCN) deposition and mineralisation compared to the untreated group. Following 6 weeks of subcutaneous implantation in nude mice, the MI192 pre-treated hDPSCs-silk scaffold constructs enhanced the vascularisation and extracellular matrix mineralisation compared to untreated control. In conclusion, these findings demonstrate the potential of using epigenetic reprogramming and silk scaffolds to promote hDPSCs bone formation efficacy, which provides evidence for clinical translation of this technology for bone augmentation.

Exacerbated inflammatory signaling underlies aberrant response to BMP9 in pulmonary arterial hypertension lung endothelial cells.

Imbalanced transforming growth factor beta (TGFß) and bone morphogenetic protein (BMP) signaling are postulated to favor a pathological pulmonary endothelial cell (EC) phenotype in pulmonary arterial hypertension (PAH). BMP9 is shown to reinstate BMP receptor type-II (BMPR2) levels and thereby mitigate hemodynamic and vascular abnormalities in several animal models of pulmonary hypertension (PH). Yet, responses of the pulmonary endothelium of PAH patients to BMP9 are unknown. Therefore, we treated primary PAH patient-derived and healthy pulmonary ECs with BMP9 and observed that stimulation induces transient transcriptional signaling associated with the process of endothelial-to-mesenchymal transition (EndMT). However, solely PAH pulmonary ECs showed signs of a mesenchymal trans-differentiation characterized by a loss of VE-cadherin, induction of transgelin (SM22α), and reorganization of the cytoskeleton. In the PAH cells, a prolonged EndMT signaling was found accompanied by sustained elevation of pro-inflammatory, pro-hypoxic, and pro-apoptotic signaling. Herein we identified interleukin-6 (IL6)-dependent signaling to be the central mediator required for the BMP9-induced phenotypic change in PAH pulmonary ECs. Furthermore, we were able to target the BMP9-induced EndMT process by an IL6 capturing antibody that normalized autocrine IL6 levels, prevented mesenchymal transformation, and maintained a functional EC phenotype in PAH pulmonary ECs. In conclusion, our results show that the BMP9-induced aberrant EndMT in PAH pulmonary ECs is dependent on exacerbated pro-inflammatory signaling mediated through IL6.

Identification of new drugs to counteract anti-spike IgG-induced hyperinflammation in severe COVID-19.

Previously, we and others have shown that SARS-CoV-2 spike-specific IgG antibodies play a major role in disease severity in COVID-19 by triggering macrophage hyperactivation, disrupting endothelial barrier integrity, and inducing thrombus formation. This hyperinflammation is dependent on high levels of anti-spike IgG with aberrant Fc tail glycosylation, leading to Fcγ receptor hyperactivation. For development of immune-regulatory therapeutics, drug specificity is crucial to counteract excessive inflammation whereas simultaneously minimizing the inhibition of antiviral immunity. We here developed an in vitro activation assay to screen for small molecule drugs that specifically counteract antibody-induced pathology. We identified that anti-spike-induced inflammation is specifically blocked by small molecule inhibitors against SYK and PI3K. We identified SYK inhibitor entospletinib as the most promising candidate drug, which also counteracted anti-spike-induced endothelial dysfunction and thrombus formation. Moreover, entospletinib blocked inflammation by different SARS-CoV-2 variants of concern. Combined, these data identify entospletinib as a promising treatment for severe COVID-19.

Riociguat inhibits ultra-large VWF string formation on pulmonary artery endothelial cells from chronic thromboembolic pulmonary hypertension patients.

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by elevated pulmonary arterial pressure and organized thrombi within pulmonary arteries. Riociguat is a soluble guanylate cyclase stimulator and is approved for patients with inoperable CTEPH or residual pulmonary hypertension after pulmonary endarterectomy (PEA). Previous work suggested that riociguat treatment is associated with an increased risk of bleeding, although the mechanism is unclear. The aim of this study is to assess how riociguat affects primary hemostasis by studying its effect on the interaction between platelets and endothelial cells derived from CTEPH patients. Pulmonary artery endothelial cells (PAECs) were isolated from thrombus-free regions of PEA material. Purified PAECs were cultured in flow chambers and were stimulated with 0.1 and 1 µM riociguat for 24 h before flow experiments. After stimulation with histamine, PAECs were exposed to platelets under shear stress. Platelet adhesion and expression of von Willebrand Factor (VWF) were evaluated to assess the role of riociguat in hemostasis. Under dynamic conditions, 0.1 and 1.0 µM of riociguat suppressed platelet adhesion on the surface of PAECs. Although riociguat did not affect intracellular expression and secretion of VWF, PAECs stimulated with riociguat produced fewer VWF strings than unstimulated PAECs. Flow cytometry suggested that decreased VWF string formation upon riociguat treatment may be associated with suppressed cell surface expression of P-selectin, a protein that stabilizes VWF anchoring on the endothelial surface. In conclusion, Riociguat inhibits VWF string elongation and platelet adhesion on the surface of CTEPH-PAECs, possibly by reduced P-selectin cell surface expression.

C/EBPδ Suppresses Motility-Associated Gene Signatures and Reduces PDAC Cell Migration.

Pancreatic Ductal Adenocarcinoma (PDAC) is among the most aggressive human cancers and occurs globally at an increasing incidence. Metastases are the primary cause of cancer-related death and, in the majority of cases, PDAC is accompanied by metastatic disease at the time of diagnosis, making it a particularly lethal cancer. Regrettably, to date, no curative treatment has been developed for patients with metastatic disease, resulting in a 5-year survival rate of only 11%. We previously found that the protein expression of the transcription factor CCAAT/Enhancer-Binding Protein Delta (C/EBPδ) negatively correlates with lymph node involvement in PDAC patients. To better comprehend the etiology of metastatic PDAC, we explored the role of C/EBPδ at different steps of the metastatic cascade, using established in vitro models. We found that C/EBPδ has a major impact on cell motility, an important prerequisite for tumor cells to leave the primary tumor and to reach distant sites. Our data suggest that C/EBPδ induces downstream pathways that modulate actin cytoskeleton dynamics to reduce cell migration and to induce a more epithelial-like cellular phenotype. Understanding the mechanisms dictating epithelial and mesenchymal features holds great promise for improving the treatment of PDAC.

Development of a 3-Dimensional Model to Study Right Heart Dysfunction in Pulmonary Arterial Hypertension: First Observations.

Pulmonary arterial hypertension (PAH) patients eventually die of right heart failure (RHF). Currently, there is no suitable pre-clinical model to study PAH. Therefore, we aim to develop a right heart dysfunction (RHD) model using the 3-dimensional engineered heart tissue (EHT) approach and cardiomyocytes derived from patient-induced pluripotent stem cells (iPSCs) to unravel the mechanisms that determine the fate of a pressure-overloaded right ventricle. iPSCs from PAH and healthy control subjects were differentiated into cardiomyocytes (iPSC-CMs), incorporated into the EHT, and maintained for 28 days. In comparison with control iPSC-CMs, PAH-derived iPSC-CMs exhibited decreased beating frequency and increased contraction and relaxation times. iPSC-CM alignment within the EHT was observed. PAH-derived EHTs exhibited higher force, and contraction and relaxation times compared with control EHTs. Increased afterload was induced using 2× stiffer posts from day 0. Due to high variability, there were no functional differences between normal and stiffer EHTs, and no differences in the hypertrophic gene expression. In conclusion, under baseline spontaneous conditions, PAH-derived iPSC-CMs and EHTs show prolonged contraction compared with controls, as observed clinically in PAH patients. Further optimization of the hypertrophic model and profound characterization may provide a platform for disease modelling and drug screening.

High titers and low fucosylation of early human anti-SARS-CoV-2 IgG promote inflammation by alveolar macrophages.

Patients diagnosed with coronavirus disease 2019 (COVID-19) become critically ill primarily around the time of activation of the adaptive immune response. Here, we provide evidence that antibodies play a role in the worsening of disease at the time of seroconversion. We show that early-phase severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) spike protein-specific immunoglobulin G (IgG) in serum of critically ill COVID-19 patients induces excessive inflammatory responses by human alveolar macrophages. We identified that this excessive inflammatory response is dependent on two antibody features that are specific for patients with severe COVID-19. First, inflammation is driven by high titers of anti-spike IgG, a hallmark of severe disease. Second, we found that anti-spike IgG from patients with severe COVID-19 is intrinsically more proinflammatory because of different glycosylation, particularly low fucosylation, of the antibody Fc tail. Low fucosylation of anti-spike IgG was normalized in a few weeks after initial infection with SARS-CoV-2, indicating that the increased antibody-dependent inflammation mainly occurs at the time of seroconversion. We identified Fcγ receptor (FcγR) IIa and FcγRIII as the two primary IgG receptors that are responsible for the induction of key COVID-19-associated cytokines such as interleukin-6 and tumor necrosis factor. In addition, we show that anti-spike IgG-activated human macrophages can subsequently break pulmonary endothelial barrier integrity and induce microvascular thrombosis in vitro. Last, we demonstrate that the inflammatory response induced by anti-spike IgG can be specifically counteracted by fostamatinib, an FDA- and EMA-approved therapeutic small-molecule inhibitor of Syk kinase.

Microchannels Are an Architectural Cue That Promotes Integration and Vascularization of Silk Biomaterials in Vivo.

Functional integration of implanted biomaterials and bioengineered tissues in vivo requires effective and timely vascular ingrowth. While many vascularization strategies rely on delivery of angiogenic growth factors or endothelial cells to promote vascular ingrowth, the effect of physical and architectural features of biomaterials on the vascularization process is less well understood. Microchannels are a simple, accessible architectural feature frequently engineered into 3D biomaterials to promote mass transfer. In this study, the effect of microchannels on the integration and vascularization of 3D porous silk scaffolds was explored over a 14 week period. An array of 508 µm diameter microchannels spanning the length of critically sized, porous silk scaffolds significantly improved tissue ingrowth into the constructs. At week 6, all silk scaffolds (n = 8) with microchannels showed complete tissue infiltration throughout the construct, while only one of eight (12.5%) did so in the absence of microchannels. The presence of microchannels improved silk scaffold vascularization with significantly more vessels per unit area in the presence of microchannels. The vessel size distribution was similar in both scaffold types, but a shift in distribution toward smaller vessels was observed in the presence of microchannels. The blood vessels in silk scaffolds were perfused, functional and connected to the animal's cardiovascular system, as demonstrated by the presence of red blood cells in the vessel lumens, and effective delivery of a contrast agent the vessels inside the scaffold. This study demonstrates the utility of microchannels as a simple architectural feature that significantly improves vascularization and integration of implanted biomaterials.

In Vitro Microfluidic Disease Model to Study Whole Blood-Endothelial Interactions and Blood Clot Dynamics in Real-Time.

The formation of blood clots involves complex interactions between endothelial cells, their underlying matrix, various blood cells, and proteins. The endothelium is the primary source of many of the major hemostatic molecules that control platelet aggregation, coagulation, and fibrinolysis. Although the mechanism of thrombosis has been investigated for decades, in vitro studies mainly focus on situations of vascular damage where the subendothelial matrix gets exposed, or on interactions between cells with single blood components. Our method allows studying interactions between whole blood and an intact, confluent vascular cell network. By utilizing primary human endothelial cells, this protocol provides the unique opportunity to study the influence of endothelial cells on thrombus dynamics and gives valuable insights into the pathophysiology of thrombotic disease. The use of custom-made microfluidic flow channels allows application of disease-specific vascular geometries and model specific morphological vascular changes. The development of a thrombus is recorded in real-time and quantitatively characterized by platelet adhesion and fibrin deposition. The effect of endothelial function in altered thrombus dynamics is determined by postanalysis through immunofluorescence staining of specific molecules. The representative results describe the experimental setup, data collection, and data analysis. Depending on the research question, parameters for every section can be adjusted including cell type, shear rates, channel geometry, drug therapy, and postanalysis procedures. The protocol is validated by quantifying thrombus formation on the pulmonary artery endothelium of patients with chronic thromboembolic disease.