Single-cell transcriptional analysis of human endothelial colony-forming cells from patients with low VWF levels

FLI-1-driven regulation of endothelial cells in human diseases

Endothelial cells (ECs) are widely distributed in the human body and play crucial roles in the circulatory and immune systems. ECs dysfunction contributes to the progression of various chronic cardiovascular, renal, and metabolic diseases. As a key transcription factor in ECs, FLI-1 is involved in the differentiation, migration, proliferation, angiogenesis and blood coagulation of ECs. Imbalanced FLI-1 expression in ECs can lead to various diseases. Low FLI-1 expression leads to systemic sclerosis by promoting fibrosis and vascular lesions, to pulmonary arterial hypertension by promoting a local inflammatory state and vascular lesions, and to tumour metastasis by promoting the EndMT process. High FLI-1 expression leads to lupus nephritis by promoting a local inflammatory state. Therefore, FLI-1 in ECs may be a good target for the treatment of the abovementioned diseases. This comprehensive review provides the first overview of FLI-1-mediated regulation of ECs processes, with a focus on its influence on the abovementioned diseases and existing FLI-1-targeted drugs. A better understanding of the role of FLI-1 in ECs may facilitate the design of more effective targeted therapies for clinical applications, particularly for tumour treatment.

Application of genetic testing for the diagnosis of von Willebrand disease

von Willebrand disease (VWD) is the most frequent inherited bleeding disorder, with an estimated symptomatic prevalence of 1 per 1000 in the general population. VWD is characterized by defects in the quantity, quality, or multimeric structure of von Willebrand factor (VWF), a glycoprotein being hemostatically essential in circulation. VWD is classified into 3 principal types: low VWF/type 1 with partial quantitative deficiency of VWF, type 3 with virtual absence of VWF, and type 2 with functional abnormalities of VWF, being classified as 2A, 2B, 2M, and 2N. A new VWD type has been officially recognized by the ISTH SSC on von Willebrand factor which has also been discussed by the joint ASH/ISTH/NHF/WFH 2021 guidelines (ie, type 1C), indicating patients with quantitative deficiency due to an enhanced VWF clearance. With the advent of next-generation sequencing technologies, the process of genetic diagnosis has substantially changed and improved accuracy. Therefore, nowadays, patients with type 3 and severe type 1 VWD can benefit from genetic testing as much as type 2 VWD. Specifically, genetic testing can be used to confirm or differentiate a VWD diagnosis, as well as to provide genetic counseling. The focus of this manuscript is to discuss the current knowledge on VWD molecular pathophysiology and the application of genetic testing for VWD diagnosis.

Clinical and Laboratory Presentation and Underlying Mechanism in Patients with Low VWF

BACKGROUND

 Low von Willebrand factor (VWF) refers to subjects with plasma levels of 30 to 50 IU/dL. The mechanism of low VWF is poorly understood. We chose to determine the clinical presentation, laboratory phenotype, and underlying mechanisms of low VWF.

MATERIAL AND METHODS

 We included 250 patients characterized with low VWF. The International Society on Thrombosis and Haemostasis Bleeding Assessment Tool (ISTH-BAT) was used to assess clinical symptoms. To determine the underlying mechanisms of low VWF, we used as markers the VWF propeptide (VWFpp) assay and FVIII:C/VWF:Ag ratio for VWF synthesis and the VWFpp/VWF:Ag ratio for VWF clearance. Results were compared with those of 120 healthy controls. Cases with abnormal screening tests were further evaluated for coagulation factor levels and platelet disorders.

RESULTS

 The median age of the cohort was 35 years (range 3-85), 21% were children (n = 53), 34% were adult males (n = 85), and 45% (n = 112) were adult females. According to the ISTH-BAT, abnormal bleeding was found in 35% of children, 47% of males, and 49% of females. No association was found between VWF activity levels and ISTH-BAT. Patients showed an overall decreased VWF synthesis/secretion and an enhanced VWF clearance was identified in 33% of them. In 89 patients (36%), there were other hemostasis-related defects, but there was no difference in the ISTH-BAT between the two groups.

CONCLUSION

 Our findings indicate that reduced VWF synthesis/secretion and enhanced VWF clearance are major mechanisms of low VWF levels. Patients with low VWF have significant bleeding manifestations. While other hemostasis defects occurred together with low VWF, this combination did not exacerbate clinical symptoms.

Recent advances in endothelial colony-forming cells: from the transcriptomic perspective

Endothelial colony-forming cells (ECFCs) are progenitors of endothelial cells with significant proliferative and angiogenic ability. ECFCs are a promising treatment option for various diseases, such as ischemic heart disease and peripheral artery disease. However, some barriers hinder the clinical application of ECFC therapeutics. One of the current obstacles is that ECFCs are dysfunctional due to the underlying disease states. ECFCs exhibit dysfunctional phenotypes in pathologic states, which include but are not limited to the following: premature neonates and pregnancy-related diseases, diabetes mellitus, cancers, haematological system diseases, hypoxia, pulmonary arterial hypertension, coronary artery diseases, and other vascular diseases. Besides, ECFCs are heterogeneous among donors, tissue sources, and within cell subpopulations. Therefore, it is important to elucidate the underlying mechanisms of ECFC dysfunction and characterize their heterogeneity to enable clinical application. In this review, we summarize the current and potential application of transcriptomic analysis in the field of ECFC biology. Transcriptomic analysis is a powerful tool for exploring the key molecules and pathways involved in health and disease and can be used to characterize ECFC heterogeneity.

Origins and functional differences of blood endothelial cells

The interests in blood endothelial cells arise from their therapeutic potential in vascular repair and regeneration. Our understanding of blood endothelial cells that exist in the circulation has been evolving significantly from the original concept of endothelial progenitor cells. Many studies have uncovered heterogeneities of blood endothelial subtypes where some cells express both endothelial and hematopoietic antigens, and others possess either mature or immature endothelial markers. Due to the lack of definitive cell marker identities, there have been momentums in the field to adopt a technical-oriented labeling system based on the cells' involvement in postnatal neovascularization and cell culture derivatives. Our review streamlines nomenclatures for blood endothelial subtypes and standardizes understanding of their functional differences. Broadly, we will discuss about myeloid angiogenic cells (MACs), endothelial colony-forming cells (ECFCs), blood outgrowth endothelial cells (BOECs) and circulating endothelial cells (CECs). The strategic location of blood endothelial cells confers them essential roles in supporting physiological processes. MACs exert angiogenic effects through paracrine mechanisms, while ECFCs are recruited to sites of vascular injury to participate directly in new vessel formation. BOECs are an in vitro derivative of ECFCs. CECs are shed into the bloodstream from damaged vessels, hence reflective of endothelial dysfunction. With clarity on the functional attributes of blood endothelial subtypes, we present recent advances in their applications in disease modelling, along with serving as biomarkers of vascular tissue homeostasis.

Clusterin knockdown has effects on intracellular and secreted von Willebrand factor in human umbilical vein endothelial cells

Alterations in von Willebrand factor (VWF) have an important role in human health and disease. Deficiency of VWF is associated with symptoms of bleeding and excesses of VWF are associated with thrombotic outcomes. Understanding the mechanisms that drive VWF regulation can lead to a better understanding of modulation of VWF levels in humans. We identified clusterin (CLU) as a potential candidate regulator of VWF based on a single cell RNA sequencing (scRNA-seq) analysis in control endothelial cells (ECs) and von Willebrand disease (VWD) endothelial colony-forming-cells (ECFCs). We found that patients with deficiencies of VWF (von Willebrand disease, VWD) had decreased CLU expression and ECs with low VWF expression also had low CLU expression. Based on these findings, we sought to evaluate the role of CLU in the regulation of VWF, specifically as it relates to VWD. As CLU is primarily thought to be a golgi protein involved in protein chaperoning, we hypothesized that knockdown of CLU would lead to decreases in VWF and alterations in Weibel-Palade bodies (WPBs). We used both siRNA- and CRISPR-Cas9-based approaches to modulate CLU in human umbilical vein endothelial cells (HUVECs) and evaluated VWF protein levels, VWF mRNA copy number, and WPB quantity and size. We demonstrated that siRNA-based knockdown of CLU resulted in decreases in VWF content in cellular lysates and supernatants, but no significant change in WPB quantity or size. A CRISPR-Cas9-based knockdown of CLU demonstrated similar findings of decreases in intracellular VWF content but no significant change in WPB quantity or size. Our data suggests that CLU knockdown is associated with decreases in cellular VWF content but does not affect VWF mRNA levels or WPB quantity or size.

Low von Willebrand Disease: A Bleeding Disorder of Unknown Cause?

von Willebrand disease (VWD) represents the most common inherited bleeding disorder. The majority of VWD cases are characterized by partial quantitative reductions in plasma von Willebrand factor (VWF) levels. Management of patients with mild to moderate VWF reductions in the range of 30 to 50 IU/dL poses a common clinical challenge. Some of these low VWF patients present with significant bleeding problems. In particular, heavy menstrual bleeding and postpartum hemorrhage can cause significant morbidity. Conversely, however, many individuals with mild plasma VWF:Ag reductions do not have any bleeding sequelae. In contrast to type 1 VWD, most patients with low VWF do not have detectable pathogenic VWF sequence variants, and bleeding phenotype correlates poorly with residual VWF levels. These observations suggest that low VWF is a complex disorder caused by variants in other genes beyond VWF. With respect to low VWF pathobiology, recent studies have shown that reduced VWF biosynthesis within endothelial cells likely plays a key role. However, pathological enhanced VWF clearance from plasma has also been described in approximately 20% of low VWF cases. For low VWF patients who require hemostatic treatment prior to elective procedures, tranexamic acid and desmopressin have both been shown to be efficacious. In this article, we review the current state of the art regarding low VWF. In addition, we consider how low VWF represents an entity that appears to fall between type 1 VWD on the one hand and bleeding disorders of unknown cause on the other.

Quantitative analysis of Weibel-Palade bodies

Weibel Palade bodies (WPBs) are vesicles found in endothelial cells which carry the multimeric protein von Willebrand factor (VWF). As cellular confluency has been shown to influence the number of WPBs in endothelial cells, we propose to test two methods of attaining endothelial cell confluence to inform on the relevancy of cellular culture methods when analyzing endothelial WPBs. We test these cellular culture methods in two endothelial cell types, human umbilical vein endothelial cells (HUVECs) and endothelial colony forming cells (ECFCs). One method maintains a constant incubation time of 96 hrs. while varying the seeding density. The second method maintains a constant seeding density of 30,000 cells/cm2 while varying incubation time. In comparing these two methods, we evaluate the nuclei count, total WPB count, and WPB/nuclei count for each. Our results show that there is a trend of increasing nuclei count, total WPB count, and WPB/nuclei count as incubation time and seeding density increases. However, there is no difference in WPB/nuclei quantification whether confluency is reached via a constant seeding density or a constant incubation time. In addition, we show that confluency plays a major role in WPB/nuclei generation as we demonstrate higher WPB/nuclei counts in confluent cultures compared to sub-confluent cultures.

Inferring bona fide Differentially Expressed Genes and Their Variants Associated with Vitamin K Deficiency Using a Systems Genetics Approach

Systems genetics is key for integrating a large number of variants associated with diseases. Vitamin K (VK) is one of the scarcely studied disease conditions. In this work, we ascertained the differentially expressed genes (DEGs) and variants associated with individual subpopulations of VK disease phenotypes, viz., myocardial infarction, renal failure and prostate cancer. We sought to ask whether or not any DEGs harbor pathogenic variants common in these conditions, attempt to bridge the gap in finding characteristic biomarkers and discuss the role of long noncoding RNAs (lncRNAs) in the biogenesis of VK deficiencies.