Human endothelial cells synthesize and release ADAMTS-13

A mutant complement factor H (W1183R) enhances proteolytic cleavage of von Willebrand factor by ADAMTS-13 under shear

BACKGROUND

A loss-of-functional mutation (W1183R) in human complement factor H (CFH) is associated with complement-associated hemolytic uremic syndrome; mice carrying a similar mutation (W1206R) in CFH also develop thrombotic microangiopathy but its plasma von Willebrand factor (VWF) multimer sizes were dramatically reduced. The mechanism underlying such a dramatic change in plasma VWF multimer distribution in these mice is not fully understood.

OBJECTIVES

To determine the VWF and CFH interaction and how CFH proteins affect VWF multimer distribution.

METHODS

We employed recombinant protein expression, purification, and various biochemical and biophysical tools.

RESULTS

Purified recombinant W1183R-CFH but not wild-type (WT) CFH protein enhanced the proteolytic cleavage of both peptidyl and multimeric VWF substrates by recombinant ADAMTS-13 in a concentration-dependent manner. Microscale thermophoresis assay demonstrated that both W1183R-CFH and WT-CFH proteins bound various VWF fragments (eg, AIM-A1, A1-A2-A3, D'D3, D'D3-A1, and D'D3-A1-A2) with high affinities. Optical tweezer experiments further showed a concentration-dependent alteration in the contour length (Lc) and the persistent length (Lp) following pulling VWF-A2 domain in the presence of W1183R-CFH or WT-CFH protein. AlphaFold experiments revealed conformational changes in the VWF-A2, particularly the central region where the cleavage bond resides following addition of W1183R-CFH or WT-CFH protein.

CONCLUSION

These results demonstrate for the first time that W1183R-CFH but not WT-CFH protein enhances the proteolytic cleavage of VWF by ADAMTS-13 under shear. This may be achieved by mechanic-induced conformational changes of the central A2 domain, leading to an enhanced cleavage of Tyr1605-Met1606 bond by ADAMTS-13 under pathophysiological conditions.

Arginine Methylation by PRMT1 Affects ADAMTS13 Secretion and Enzymatic Activity

BACKGROUND

ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, 13), primarily synthesized in hepatic stellate and endothelial cells, plays a pivotal role in regulation of hemostasis by proteolytic cleavage of von Willebrand factor. Severe deficiency of plasma ADAMTS13 activity may result in thrombotic thrombocytopenic purpura, a potentially fatal blood disorder. ADAMTS13 undergoes posttranslational modifications including glycosylation, citrullination, oxidation. The present study determines the impact of arginine methylation by PRMT1 (protein arginine methyltransferase 1) on ADAMTS13 secretion and function.

METHODS

Cell culture, recombinant protein, biochemical analysis, site-directed mutagenesis, and animal models were utilized.

RESULTS

An inhibition of arginine methylation by a type I methyl transferase PRMT inhibitor (MS023) in HEK (human embryonic kidney) 293 cells expressing recombinant ADAMTS13 and in mice results in a significant reduction of ADAMTS13 secretion, but the secreted ADAMTS13 shows an increased specific activity; conversely, an overexpression of PRMT1 in HEK-293 cells and in transgenic mice results in an increase of ADAMTS13 secretion, but the secreted ADAMTS13 exhibits a significantly reduced specific activity. The altered ADAMTS13 activity appeared to be related to its conformational changes. LC-MS/MS (liquid chromatography with tandem mass spectrometry) identified greater than100 arginine methylation events on purified recombinant ADAMTS13. Site-directed mutagenesis performed on 5 highly conserved methylation sites (R193, R498, R692, R1123, and R1206) identifies the critical role of R1206 in ADAMTS13 function. The ADAMTS13 R1206K variant exhibits a 4- to 5-fold increase of specific activity, likely resulting from an alleviation of allosteric inhibition.

CONCLUSIONS

These results demonstrate the crucial role of arginine methylation in ADAMTS13 secretion and function. Our findings may shed new light on the mechanism of allosteric regulation of ADAMTS13, which may have a therapeutic implication.

ADAMTS13 Improves Endothelial Function and Reduces Inflammation in Diabetic Retinopathy

The protease, a disintegrin and metalloproteinase with thrombospondin type 1 motif member 13 (ADAMTS13), known to cleave only the von Willebrand factor (VWF), has powerful regulatory effects on microvascular platelet adhesion, thrombosis, inflammation, and endothelial dysfunction. We study the protection against diabetes-induced retinal injury in experimental rats by supplementation with recombinant ADAMTS13. We compare human epiretinal membranes and vitreous samples from nondiabetic subjects and patients with proliferative diabetic retinopathy (PDR) and extend in vitro analyses with the use of various immunodetection and spectrofluorimetric methods on rat retina and human retinal glial and endothelial cell cultures. Functional studies include the assessment of the blood-retinal barrier (BRB), cell adhesion, and in vitro angiogenesis. In epiretinal membranes, endothelial cells and monocytes/macrophages express ADAMTS13. The levels of VWF, the platelet marker CD41, ADAMTS13, and the biomarkers of endothelial cell injury soluble VE-cadherin and soluble syndecan-1 are increased in PDR vitreous. ADAMTS13 is downregulated in diabetic rat retinas. The intravitreal administration of ADAMTS13 attenuates diabetes-induced BRB breakdown, the downregulation of VE-cadherin and β-catenin, and the upregulation of VWF, CD41, phospho-ERK1/2, HMGB1, VCAM-1, and ICAM-1. In Müller cells, ADAMTS13 attenuates MCP-1, MMP-9, and ROS upregulation induced by diabetic mimetic conditions. In HRMECs, ADAMTS13 attenuates the shedding of the soluble VE-cadherin and soluble syndecan-1 and the levels of phospho-ERK1/2, MCP-1, fractalkine, and ROS induced by diabetic mimetic conditions, the upregulation of ICAM-1 and VCAM-1 elicited by TNF-α, the adherence of monocytes induced by TNF-α, and VEGF-induced migration of human retinal microvascular endothelial cells. Our findings suggest that enhancing ADAMTS13 levels in situ ameliorates diabetes-induced retinal inflammation and vascular dysfunction.

Novel mechanisms of action of emerging therapies of hereditary thrombotic thrombocytopenic purpura

INTRODUCTION

Hereditary thrombotic thrombocytopenic purpura (hTTP) is caused by deficiency of plasma ADAMTS13 activity, resulting from ADAMTS13 mutations. ADAMTS13 cleaves ultra large von Willebrand factor (VWF), thus reducing its multimer sizes. Hereditary deficiency of plasma ADAMTS13 activity leads to the formation of excessive platelet-VWF aggregates in small arterioles and capillaries, resulting in hTTP.

AREAS COVERED

PubMed search from 1956 to 2024 using thrombotic thrombocytopenic purpura and therapy identified 3,675 articles. Only the articles relevant to the topic were selected for discussion, which focuses on pathophysiology, clinical presentations, and mechanisms of action of emerging therapeutics for hTTP. Current therapies include infusion of plasma, or coagulation factor VIII, or recombinant ADAMTS13. Emerging therapies include anti-VWF A1 aptamers or nanobody and gene therapies with adeno-associated viral vector or self-inactivated lentiviral vector or a sleeping beauty transposon system for a long-term expression of a functional ADAMTS13 enzyme.

EXPERT OPINION

Frequent plasma infusion remains to be the standard of care in most parts of the world, while recombinant ADAMTS13 has become the treatment of choice for hTTP in some of the Western countries. The success of gene therapies in preclinical models may hold a promise for future development of these novel approaches for a cure of hTTP.

Endotoxemia and Platelets: 2 Players of Intrahepatic Microthrombosis in NAFLD

Gut dysbiosis-related intestinal barrier dysfunction with increased translocation of bacterial products such as lipopolysaccharide (LPS) into systemic circulation is emerging as pathogenic factor of nonalcoholic fatty liver disease (NAFLD). Experimental and clinical studies suggested a potential role of LPS as a trigger eliciting in situ liver inflammation upon interaction with its receptor toll-like receptor 4. Also, LPS has been reported to prime platelets to respond to the common agonists indicating that it behaves as a prothrombotic molecule. Of note, recent studies suggested platelet-related intrahepatic thrombosis triggered by LPS as a mechanism implicated in the process of liver inflammation. This review describes: 1) the impact of gut barrier dysfunction and endotoxemia in the process of NAFLD; 2) the relationship between endotoxemia and platelet activation in NAFLD; 3) clinical evidence for the use of antiplatelet drugs in NAFLD/nonalcoholic steatohepatitis patients; and 4) the potential therapeutic approach to modulate endotoxemia and eventually platelet activation.

REVIEWING THE DYSREGULATION OF ADAMTS13 AND VWF IN SEPSIS

ABSTRACT

Sepsis is defined as a life-threatening organ dysfunction caused by excessive host response to infection, and represents the most common cause of in-hospital deaths. Sepsis accounts for 30% of all critically ill patients in the intensive care unit (ICU), and has a global mortality rate of 20%. Activation of blood coagulation during sepsis and septic shock can lead to disseminated intravascular coagulation, which is characterized by microvascular thrombosis. Von Willebrand factor (VWF) and ADAMTS13 are two important regulators of blood coagulation that may be important links between sepsis and mortality in the ICU. Herein we review our current understanding of VWF and ADAMTS13 in sepsis and other critical illnesses and discuss their contribution to disease pathophysiology, their use as markers of severe illness, and potential targets for new therapeutic development.

Von Willebrand factor promotes radiation-induced intestinal injury (RIII) development and its cleavage enzyme rhADAMTS13 protects against RIII by reducing inflammation and oxidative stress

Patients with abdominopelvic cancer undergoing radiotherapy commonly develop radiation-induced intestinal injury (RIII); however, its underlying pathogenesis remains elusive. The von Willebrand factor (vWF)/a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) axis has been implicated in thrombosis, inflammation, and oxidative stress. However, its role in RIII remains unclear. In this study, the effect of radiation on vWF and ADAMTS13 expression was firstly evaluated in patients with cervical cancer undergoing radiotherapy and C57BL/6J mice exposed to different doses of total abdominal irradiation. Then, mice with the specific deletion of vWF in the platelets and endothelium were established to demonstrate the contribution of vWF to RIII. Additionally, the radioprotective effect of recombinant human (rh) ADAMTS13 against RIII was assessed. Results showed that both the patients with cervical cancer undergoing radiotherapy and RIII mouse model exhibited increased vWF levels and decreased ADAMTS13 levels. The knockout of platelet- and endothelium-derived vWF rectified the vWF/ADAMTS13 axis imbalance; improved intestinal structural damage; increased crypt epithelial cell proliferation; and reduced radiation-induced apoptosis, inflammation, and oxidative stress, thereby alleviating RIII. Administration of rhADAMTS13 could equally alleviate RIII. Our results demonstrated that abdominal irradiation affected the balance of the vWF/ADAMTS13 axis. vWF exerted a deleterious role and ADAMTS13 exhibited a protective role in RIII progression. rhADAMTS13 has the potential to be developed into a radioprotective agent.

Dynamic Assessment of Plasma von Willebrand Factor and ADAMTS13 Predicts Mortality in Hospitalized Patients with SARS-CoV-2 Infection

BACKGROUND

Plasma levels of von Willebrand factor (VWF) are significantly elevated in patients with coronavirus disease 2019 (COVID-19). However, dynamic changes and prognostic value of this biomarker in hospitalized patients with COVID-19 have not been determined.

METHODS

A total of 124 patients infected with SARS-CoV-2 were prospectively recruited for the study. Serial blood samples were obtained at the time of admission (D1), 3-4 days following standard-care treatments (D2), and 1-2 days prior to discharge or any time collected prior to death (D3). Plasma VWF antigen, ADAMTS13 antigen, and ADAMTS13 proteolytic activity, as well as the ratio of VWF/ADAMTS13 were determined, followed by various statistical analyses.

RESULTS

On admission, plasma levels of VWF in COVID-19 patients were significantly elevated compared with those in the healthy controls, but no statistical significance was detected among patients with different disease severity. Plasma ADAMTS13 activity but not its antigen levels were significantly lower in patients with severe or critical COVID-19 compared with that in other patient groups. Interestingly, the ratios of plasma VWF antigen to ADAMTS13 antigen were significantly higher in patients with severe or critical COVID-19 than in those with mild to moderate disease. More importantly, plasma levels of VWF and the ratios of VWF/ADAMTS13 were persistently elevated in patients with COVID-19 throughout hospitalization. Kaplan-Meier and Cox proportional hazard regression analyses demonstrated that an increased plasma level of VWF or ratio of VWF/ADAMTS13 at D2 and D3 was associated with an increased mortality rate.

CONCLUSIONS

Persistent endotheliopathy, marked by the elevated levels of plasma VWF or VWF/ADAMTS13 ratio, is present in all hospitalized patients following SARS-CoV-2 infection, which is strongly associated with mortality.

Reduced ADAMTS13 activity and high D-dimer levels are associated with thrombosis in patients with systemic lupus erythematosus

INTRODUCTION

Patients with systemic lupus erythematosus (SLE) have an increased risk of vascular thrombosis compared to the general population. Therefore, biomarkers for predicting the risk of thrombosis in patients with SLE are needed.

METHODS

In the present study, a total of 66 patients with SLE (22 with and 44 without a history of thrombosis) were enrolled. The cases with thrombosis and the controls without thrombosis were matched for age (± 5 years) and sex. We assessed ADAMTS13 activity, D-dimer levels, and antiphospholipid antibodies. Clinical manifestations, SLE disease activity, classical risk factors, and medical history were collected.

RESULTS

ADAMTS13 activity was significantly reduced, and D-dimer levels were significantly increased in patients with SLE with a history of thrombosis compared with those in patients without thrombosis. Receiver operating characteristic curve analysis revealed a good correlation between reduced ADAMTS13 activity and a history of thrombosis. Reduced ADAMTS13 activity was correlated with increased D-dimer levels only in the thrombotic group.

CONCLUSION

Reduced ADAMTS13 activity and high D-dimer levels are associated with thrombosis and may serve as prognostic markers for thrombosis in patients with SLE.

Effect of tranexamic acid on endothelial von Willebrand factor/ADAMTS-13 response to in vitro shock conditions

BACKGROUND

Traumatic/hemorrhagic shock, sepsis and other inflammatory processes lead to endothelial activation and a loss of the endothelial glycocalyx. von Willebrand factor (vWF) is an acute phase reactant that is released from endothelial cells and megakaryocytes. Stimulated but not basal vWF leads to significant formation of ultralarge multimers (ultralarge vWF [ULvWF]) and risk for thrombotic complications. Ultralarge vWF is cleaved by a disintegrin and metalloproteinase with a thrombospondin type motif 13 (ADAMTS 13); alterations in ULvWF/ADAMTS 13 ratio may contribute to trauma-induced coagulopathy. Salutary effects of tranexamic acid (TXA) on trauma-induced coagulopathy have been described. These effects appear apart from antifibrinolytic actions of TXA and include protection of the endothelial glycocalyx. Ultralarge vWF is in part anchored to the glycocalyx layer of the endothelium. Tranexamic acid protected the endothelial glycocalyx layer from degradation using a microfluidic model of the microcirculation subjected to hypoxia-reoxygenation and catecholamine excess. We hypothesized that TXA administration following shock conditions would impact the vWF-ADAMTS-13 axis by protecting the glycocalyx from degradation. This was studied in a endothelial microfluidic flow study.

METHODS

Human umbilical vein endothelial cells were established under flow conditions and subjected to biomimetic shock. Tranexamic acid was added after 90 minutes of perfusion. von Willebrand factor antigen and ADAMTS-13 activity were measured. Western blot analysis was performed for vWF characterization from perfusion media.

RESULTS

Shock conditions increased vWF antigen and decreased ADAMTS 13 activity. Tranexamic acid ameliorated shock induced cleavage in the ADAMTS 13-vWF axis with a reduction of the thrombogenic ULvWF.

CONCLUSION

These results suggest another mechanism whereby administration of TXA early following traumatic/hemorrhagic shock mitigates microvascular perfusion abnormalities and subsequent organ failure. The resultant effects on platelet adhesion and aggregation require further study.

A novel mechanism underlying allosteric regulation of ADAMTS-13 revealed by hydrogen-deuterium exchange plus mass spectrometry

Background

ADAMTS-13, a plasma metalloprotease, cleaves von Willebrand factor. ADAMTS-13 activity appears to be regulated through allosteric inhibition by its distal C-terminus.

Objectives

The objective of this study was to better understand how domain-domain interactions may affect ADAMTS-13 conformations and functions.

Methods

We performed deuterium-hydrogen exchange plus mass spectrometry to assess the number and rate of deuterium incorporation into various peptides of full-length ADAMTS-13 and its truncated variants.

Results

Under physiological conditions, a bimodal distribution of deuterium incorporation was detected in the peptides from metalloprotease (217-230 and 282-304), cysteine-rich (446-482), and CUB (for complement C1r/C1s, Uegf, Bmp1) domains (1185-1214, 1313-1330, 1341-1347, 1358-1378, and 1393-1407) of full-length recombinant ADAMTS-13, but not of truncated variants. These results suggest that the full-length ADAMTS-13 undergoes conformational changes. On removal of the middle and distal C-terminal domains, the number and rate of deuterium incorporation were increased in the peptides from cysteine-rich (445-467, 467-482, and 495-503) and spacer domains (621-642 and 655-654) but decreased in the peptides from metalloprotease (115-124, 217-230, and 274-281). Moreover, most peptides, except for 217-230 and 1357-1376, exhibited a pD-dependent deuterium incorporation in the full-length ADAMTS-13, but not in the truncated variant (eg, MDTCS or T5C). These results further suggest that the bimodal deuterium incorporation observed in the peptides from the full-length ADAMTS-13 is the result of potential impact from the middle to distal C-terminal domains. Surface plasmon resonance revealed the direct binding interactions between the distal and proximal domains of ADAMTS-13.

Conclusion

Our results provide novel insight on how intramolecular interactions may affect conformations of ADAMTS-13, thus regulating its proteolytic functions.

Mechanisms of ADAMTS13 regulation

Recombinant ADAMTS13 is currently undergoing clinical trials as a treatment for hereditary thrombotic thrombocytopenic purpura, a lethal microvascular condition resulting from ADAMTS13 deficiency. Preclinical studies have also demonstrated its efficacy in treating arterial thrombosis and inflammation without causing bleeding, suggesting that recombinant ADAMTS13 may have broad applicability as an antithrombotic agent. Despite this progress, we currently do not understand the mechanisms that regulate ADAMTS13 activity in vivo. ADAMTS13 evades canonical means of protease regulation because it is secreted as an active enzyme and has a long half-life in circulation, suggesting that it is not inhibited by natural protease inhibitors. Although shear can spatially and temporally activate von Willebrand factor to capture circulating platelets, it is also required for cleavage by ADAMTS13. Therefore, spatial and temporal regulation of ADAMTS13 activity may be required to stabilize von Willebrand factor-platelet strings at sites of vascular injury. This review outlines potential mechanisms that regulate ADAMTS13 in vivo including shear-dependency, local inactivation, and biochemical and structural regulation of substrate binding. Recently published structural data of ADAMTS13 is discussed, which may help to generate novel hypotheses for future research.

ADAMTS13 protease or lack of von Willebrand factor protects irradiation and melanoma-induced thrombotic microangiopathy in zebrafish

BACKGROUND

Severe deficiency of plasma ADAMTS13 activity may result in potentially fatal thrombotic thrombocytopenic purpura and relative deficiency of plasma ADAMTS13 activity may be associated with adverse outcomes of certain malignancies. Here, we report the role of ADAMTS13 or lack of von Willebrand factor (VWF) in reducing irradiation and melanoma-induced thrombotic microangiopathy (TMA) and mortality in zebrafish.

METHODS

Zebrafish melanoma cell line (ZMEL) was injected subcutaneously into wild-type (wt), adamts13-/- (a13-/- ), von Willebrand factor (vwf-/- ), and a13-/- vwf-/- zebrafish following total body irradiation; the tumor growth, its gene expression pattern, the resulting thrombocytopenia, and the mortality were determined.

RESULTS

Total body irradiation at 30 Gy alone resulted in a transient thrombocytopenia in both wt and a13-/- zebrafish. However, thrombocytopenia occurred earlier and more profound in a13-/- than in wt zebrafish, which was resolved 2 weeks following irradiation alone. An inoculation of ZMEL following the irradiation resulted in more severe and persistent thrombocytopenia, as well as earlier death in a13-/- than in wt zebrafish. The vwf-/- or a13-/- vwf-/- zebrafish were protected from developing severe thrombocytopenia following the same maneuvers. RNA-sequencing revealed significant differentially expressed genes associated with oxidation-reduction, metabolism, lipid, fatty acid and cholesterol metabolic processes, steroid synthesis, and phospholipid efflux in the melanoma explanted from a13-/- zebrafish compared with that from the wt controls.

CONCLUSIONS

Our results indicated that plasma ADAMTS13 or lack of VWF may offer a significant protection against the development of irradiation- and/or melanoma-induced TMA. Such a microenvironment may directly affect melanoma cell phenotypes via alternation in the oxidation-reduction and lipid metabolic pathways.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Diabetes mellitus and diabetic nephropathy: a review of the literature on hemostatic changes in coagulation and thrombosis

Vascular complications lead to morbidity and mortality in patients with diabetes. Diabetic nephropathy (DN) is one of the main life-threatening problems for these patients, as it is the main cause of end-stage renal disease. This study aimed to measure the clinical effects of diabetes in patients with diabetes and in patients with diabetic nephropathy. Improved hypoglycemic control in patients with diabetes could impressively reduce platelet hyperreactivity, and oxidative stress alters the levels of many coagulation and thrombosis factors, resulting in an abnormal hemostasis and impaired levels of numerous serum markers. Most studies have revealed that coagulation factor levels are high in patients with diabetes and nephrodiabetes. Serum inflammatory factors, and coagulation and endothelial functions are good predictors of diabetic nephropathy. This literature review was conducted with access to scholarly databases and Google Scholar through Qassim University, and it analyzes studies from early 2010 until November 2020. Many studies have inferred that diabetes severely affects hemostasis and increases the risk of cardiovascular disease.

COVID-19 microthrombosis: unusually large VWF multimers are a platform for activation of the alternative complement pathway under cytokine storm

ADAMTS13, a metalloproteinase, specifically cleaves unusually large multimers of von Willebrand factor (VWF), newly released from vascular endothelial cells. The ratio of ADAMTS13 activity to VWF antigen (ADAMTS13/VWF) and indicators of the alternative complement pathway (C3a and sC5b-9) are both related to the severity of COVID-19. The ADAMTS13/VWF ratio is generally moderately decreased (0.18–0.35) in patients with severe COVID-19. When these patients experience cytokine storms, both interleukin-8 and TNFα stimulate VWF release from vascular endothelial cells, while interleukin-6 inhibits both production of ADAMTS13 and its interaction with VWF, resulting in localized severe deficiency of ADAMTS13 activity. Platelet factor 4 and thrombospondin-1, both released upon platelet activation, bind to the VWF-A2 domain and enhance the blockade of ADAMTS13 function. Thus, the released unusually-large VWF multimers remain associated with the vascular endothelial cell surface, via anchoring with syndecan-1 in the glycocalyx. Unfolding of the VWF-A2 domain, which has high sequence homology with complement factor B, allows the domain to bind to activated complement C3b, providing a platform for complement activation of the alternative pathway. The resultant C3a and C5a generate tissue factor-rich neutrophil extracellular traps (NETs), which induce the mixed immunothrombosis, fibrin clots and platelet aggregates typically seen in patients with severe COVID-19.

Advances in ADAMTS biomarkers

A Disintegrin and Metalloproteinase with Thrombospondin motifs (ADAMTS) are major mediators in extracellular matrix (ECM) turnover and have gained increasing interest over the last years as major players in ECM remodeling during tissue homeostasis and the development of diseases. Although, ADAMTSs are recognized in playing important roles during tissue remodeling, and loss of function in various member of the ADAMTS family could be associated with the development of numerous diseases, limited knowledge is available about their specific substrates and mechanism of action. In this chapter, we will review current knowledge about ADAMTSs and their use as disease biomarkers.

Reduced ADAMTS13 Activity in Correlation with Pathophysiology, Severity, and Outcome of COVID-19: A Retrospective Observational Study

BACKGROUND

Low ADAMTS13 activity has been suggested to be an interplaying factor in the pathogenesis of COVID-19, considering that it is a thromboinflammatory disease with high risk of microthrombosis.

OBJECTIVES

The study aimed to explore the correlation between ADAMTS13 activity and the pathophysiological pathway of COVID-19.

METHODS

We carried out a retrospective observational study of 87 patients with COVID-19 in NMC Royal Hospital, Abu Dhabi, UAE. ADAMTS13 activity was measured and compared with patients' characteristics and clinical outcomes.

RESULTS

Low ADAMTS13 activity was associated with pneumonia (p = 0.007), severity of COVID-19 (p <0.001), and mechanical ventilation rates (p = 0.018). Death was more frequently observed among patients (5 patients) with low ADAMTS13 activity compared with normal activity (1 patient), as well as inflammatory markers. Decreased ADAMTS13 activity increased with the risk of pneumonia, severity of COVID-19, need for mechanical ventilation, and use of anticoagulants ([OR = 4.75, 95% CI 1.54-18.02, p = 0.011], [OR = 6.50, 95% CI 2.57-17.74; p <0.001], [OR = 4.10, 95% CI 1.29-15.82; p = 0.024], [OR = 8.00, 95% CI 3.13-22.16; p <0.001], respectively). The low ADAMTS13 activity group had a slightly longer time to viral clearance than the normal ADAMTS13 activity group, but it was not statistically significant (20 days, 95% CI 16-27 days vs 17 days, 95% CI 13-22 days; p = 0.08; Log rank = 3.1).

CONCLUSIONS

Low ADAMTS13 activity has been linked to pneumonia, COVID-19 severity, use of anticoagulants, and need for mechanical ventilation but not to mortality. We propose rADAMTS13 as a novel treatment for severe COVID-19.

Involvement of von Willebrand factor and botrocetin in the thrombocytopenia induced by Bothrops jararaca snake venom

Patients bitten by snakes consistently manifest a bleeding tendency, in which thrombocytopenia, consumption coagulopathy, mucous bleeding, and, more rarely, thrombotic microangiopathy, are observed. Von Willebrand factor (VWF) is required for primary hemostasis, and some venom proteins, such as botrocetin (a C-type lectin-like protein) and snake venom metalloproteinases (SVMP), disturb the normal interaction between platelets and VWF, possibly contributing to snakebite-induced bleedings. To understand the relationship among plasma VWF, platelets, botrocetin and SVMP from Bothrops jararaca snake venom (BjV) in the development of thrombocytopenia, we used (a) Wistar rats injected s.c. with BjV preincubated with anti-botrocetin antibodies (ABA) and/or Na2-EDTA (a SVMP inhibitor), and (b) VWF knockout mice (Vwf-/-) injected with BjV. Under all conditions, BjV induced a rapid and intense thrombocytopenia. In rats, BjV alone reduced the levels of VWF:Ag, VWF:CB, high molecular weight multimers of VWF, ADAMTS13 activity, and factor VIII. Moreover, VWF:Ag levels in rats that received BjV preincubated with Na2-EDTA and/or ABA tended to recover faster. In mice, BjV caused thrombocytopenia in both Vwf-/- and C57BL/6 (background control) strains, and VWF:Ag levels tended to decrease in C57BL/6, demonstrating that thrombocytopenia was independent of the presence of plasma VWF. These findings showed that botrocetin present in BjV failed to affect the extent or the time course of thrombocytopenia induced by envenomation, but it contributed to decrease the levels and function of plasma VWF. Thus, VWF alterations during B. jararaca envenomation are an ancillary event, and not the main mechanism leading to decreased platelet counts.

ADAMTS-13-VWF axis in sickle cell disease patients

Sickle cell disease (SCD) comprises a group of genetic disorders characterized by the presence of the hemoglobin (Hb) S in homozygosis or in heterozygosis with some other Hb variant or in interaction with thalassemia. SCD is characterized by a very complex pathophysiology, which determines a wide variability of clinical manifestations, including a chronic state of hypercoagulability responsible for the increased risk of thromboembolic events. ADAMTS13 and von Willebrand factor (VWF) play an important role in arterial and venous thrombosis. Thus, the aim of this study was to understand how the ADAMTS13-VWF axis behaves in sickle cell disease, as well as whether there is an association of these markers with the use of hydroxyurea (HU). This is a cross-sectional study conducted with 40 patients diagnosed with SCD and 40 healthy individuals. The analysis of the ADAMTS13-VWF axis was comparatively performed between groups of patients and controls and, afterwards, between patients with SCD who were users and non-users of HU. ADAMTS13 activity, ADAMTS13 activity/VWF:Ag, and ADAMTS13:Ag/VWF:Ag ratios were significantly lower and VWF:Ag levels significantly higher in SCD patients when compared to the controls. There was no statistically significant difference in ADAMTS13:Ag and VWF collagen binding (VWF:CB) levels between the groups evaluated. Among the categories of HU use, there was no statistically significant difference in any of the evaluated markers. As a conclusion, we could observe that the ADAMTS13-VWF axis is altered in SCD when compared to healthy individuals and that there is no association between these markers and the use of HU.

Thrombocytopenia-Associated Multiple Organ Failure

Thrombocytopenia-associated multiple organ failure is a clinical phenotype encompassing a spectrum of syndromes associated with disseminated microvascular thromboses. Autopsies performed in patients that died with thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, or disseminated intravascular coagulation reveal specific findings that can differentiate these 3 entities. Significant advancements have been made in our understanding of the pathologic mechanisms of these syndromes. Von Willebrand factor and ADAMTS-13 play a central role in thrombotic thrombocytopenic purpura. Shiga toxins and the complement pathway drive the hemolytic uremic syndrome pathology. Tissue factor activity is vital in the development of disseminated intravascular coagulation.

Diverse activities of von Willebrand factor in traumatic brain injury and associated coagulopathy

Traumatic brain injury (TBI) is a leading cause of death and disability. Patients with isolated TBI lose a limited amount of blood to primary injury, but they often develop secondary coagulopathy, resulting in delayed or recurrent intracranial and intracerebral hematoma. TBI-induced coagulopathy is closely associated with poor outcomes for these patients, including death. This secondary coagulopathy is consumptive in nature, involving not only brain-derived molecules, coagulation factors, and platelets, but also endothelial cells in a complex process now called blood failture. A key question is how a localized injury to the brain is rapidly disseminated to affect systemic hemostasis that is not directly affected the way it is in trauma to the body and limbs, especially with hemorrhagic shock. Increasing evidence suggests that the adhesive ligand von Willebrand factor (VWF), which is synthesized in and released from endothelial cells, plays a paradoxical role in both facilitating local hemostasis at the site of injury and also propagating TBI-induced endotheliopathy and coagulopathy systemically. This review discusses recent progress in understanding these diverse activities of VWF and the knowledge gaps in defining their roles in TBI and associated coagulopathy.

Von Willebrand factor:antigen and ADAMTS-13 level, but not soluble P-selectin, are risk factors for the first asymptomatic deep vein thrombosis in cancer patients undergoing chemotherapy

Background

There is a high incidence of deep vein thrombosis (DVT) among cancer patients undergoing chemotherapy. Chemotherapy-induced vascular endothelial cell activation (VECA) is characterized by increased plasma levels of von Willebrand factor (vWF) and soluble P-selectin (sP-selectin), leading to the activation of endothelial cells and signaling cascades. The biological role of a disintegrin-like and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS-13) is to control the activity of vWF and consequently the risk of thrombosis. The objective of this study was to investigate the roles of sP-selectin, vWF, and ADAMTS-13 as risk factors for the first episode of DVT in cancer patients undergoing chemotherapy.

Methods

This prospective cohort study was conducted at Dr. Kariadi Hospital, Indonesia, on 40 cancer patients. Prechemotherapy (baseline) and postchemotherapy sP-selectin, vWF antigen (vWF:Ag), and ADAMTS-13 plasma levels were determined with ELISAs before and 3 months after chemotherapy. The clinical characteristics of the patients, cancer type, cancer stage, chemotherapy regimen, ABO blood type, D-dimer level and Khorana risk score were also analyzed using logistic regression. Patients were observed for the possibility of developing DVT during chemotherapy.

Results

DVT was confirmed in 5 patients (12.5%) after a period of 3 months. In patients with DVT, sP-selectin and vWF were significantly higher while ADAMTS-13 was lower than in their counterparts. The levels of baseline vWF:Ag and ADAMTS-13, with cut-off points ≥ 2.35 IU/mL and ≤ 1.03 IU/mL, respectively, were found to independently predict the incidence of DVT. In the multivariate logistic regression analysis, the relative risk (RR) for DVT in patients with high vWF:Ag was 3.80 (95% CI 1.15–12.48, p = 0.028), and that for patients with low ADAMTS-13 was 2.67 (95% CI 1.22–23.82, p = 0.005). The vWF:Ag/ADAMTS-13 ratio and both vWF:Ag and ADAMTS-13 dynamics during treatment were also able to differentiate those with prospective DVT. However, sP-selectin and other covariates showed no statistical significance.

Conclusion

We found that prechemotherapy plasma levels of vWF:Ag ≥ 2.35 IU/mL and ADAMTS-13 ≤ 1.03 IU/mL are independent risk factors for DVT incidence among cancer patients.

Tryptophan 387 and 390 residues in ADAMTS13 are crucial to the ability of vascular tube formation and cell migration of endothelial cells

A disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13) was mainly generated and secreted from endothelial cells (ECs). Our previous study showed that tryptophan (Trp) residues at 387 and 390 in ADAMTS13 are required for its secretion and enzymatic activity. However, the effects on its host cell as well as the potential mechanism have not been clear. The aim of the study was to examine the effects of Trp residues 387 and 390 of ADAMTS13 on the biological processes of ECs. Herein, Trp was substituted with alanine in ADAMTS13 to generate ADAMTS13 mutants at 387 (W387A), 390 (W390A), and double mutants at 387 and 390 (2WA), respectively. We found that substitution mutation impaired vascular endothelial growth factor (VEGF) secretion and the downstream JAK1/STAT3 activation, the binding ability to Von Willebrand factor, cell proliferation, migration, and vascular tube formation. Overall, our study concluded that Trp387 and Trp390 of ADAMTS13 play vital roles in the biological function of ECs.

Apolipoprotein B100/Low-Density Lipoprotein Regulates Proteolysis and Functions of von Willebrand Factor under Arterial Shear

BACKGROUND

 Proteolytic cleavage of von Willebrand factor (VWF) by a plasma a disintegrin and metalloproteinase with a thrombospondin type 1 motifs, member 13 (ADAMTS13) is regulated by shear stress and binding of coagulation factor VIII, platelets or platelet glycoprotein 1b, and ristocetin to VWF.

OBJECTIVE

 Current study aims to identify novel VWF binding partners that may modulate VWF functions under physiological conditions.

METHODS

 A deoxyribonucleic acid aptamer-based affinity purification of VWF, followed by tandem mass spectrometry, functional, and binding assays was employed.

RESULTS

 Apolipoprotein B100/low-density lipoprotein (apoB100/LDL) was identified as a novel VWF-binding partner. Purified apoB100/LDL was able to accelerate the proteolytic cleavage of VWF by ADAMTS13 under shear in a concentration-dependent manner. This rate-enhancing activity was dramatically reduced when apoB100/LDL was oxidized. More interestingly, the oxidized apoB100/LDL appeared to compete with native apoB100/LDL for its enhancing activity on VWF proteolysis under shear. As a control, a purified apoA1/high-density lipoprotein (apoA1/HDL) or apoB48 exhibited a minimal or no activity enhancing VWF proteolysis by ADAMTS13 under the same conditions. Both VWF and ADAMTS13 were able to bind native or oxidized apoB100/LDL with high affinities. No binding interaction was detected between VWF (or ADAMTS13) and apoA1/HDL (or apoB48). Moreover, apoB100/LDL but not its oxidized products inhibited the adhesion of platelets to ultra large VWF released from endothelial cells under flow. Finally, significantly reduced ratios of high to low molecular weight of VWF multimers with increased levels of plasma VWF antigen were detected in LDLR-/- mice fed with high cholesterol diet.

CONCLUSION

 These results indicate that apoB100/LDL may be a novel physiological regulator for ADAMTS13-VWF functions.

The role of ADAMTS13 testing in the diagnosis and management of thrombotic microangiopathies and thrombosis

ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, 13) is a metalloprotease responsible for cleavage of ultra-large von Willebrand factor (VWF) multimers. Severely deficient activity of the protease can trigger an acute episode of thrombotic thrombocytopenic purpura (TTP). Our understanding of the pathophysiology of TTP has allowed us to grasp the important role of ADAMTS13 in other thrombotic microangiopathies (TMAs) and thrombotic disorders, such as ischemic stroke and coronary artery disease. Through its action on VWF, ADAMTS13 can have prothrombotic and proinflammatory properties, not only when its activity is severely deficient, but also when it is only moderately low. Here, we will discuss the biology of ADAMTS13 and the different assays developed to evaluate its function in the context of TTP, in the acute setting and during follow-up. We will also discuss the latest evidence regarding the role of ADAMTS13 in other TMAs, stroke, and cardiovascular disease. This information will be useful for clinicians not only when evaluating patients who present with microangiopathic hemolytic anemia and thrombocytopenia, but also when making clinical decisions regarding the follow-up of patients with TTP.

Inflammation, von Willebrand factor, and ADAMTS13

Increasing evidence indicates that inflammation can cause thrombosis by a von Willebrand factor (VWF)-mediated mechanism that includes endothelial activation, secretion of VWF, assembly of hyperadhesive VWF strings and fibers, cleavage by ADAMTS13, and adhesion and deposition of VWF-platelet thrombi in the vasculature. This mechanism appears to contribute to thrombosis not only in small vessels, but also in large vessels. Inflammation and VWF contribute to atherogenesis and may contribute to arterial and venous thrombosis as well as stroke. Elucidation of the mechanism will hopefully identify new targets and suggest new approaches for prevention and intervention.

Usefulness of ADAMTS13 to predict response to recanalization therapies in acute ischemic stroke

OBJECTIVE

We aimed to analyze ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) in relation to arterial recanalization in patients treated with IV tissue plasminogen activator (tPA) and in relation to futile recanalization in patients treated with mechanical thrombectomy.

METHODS

Acute ischemic stroke patients (n = 108) with documented arterial occlusions treated with IV-tPA were selected. ADAMTS13 activity was measured by ELISA in samples collected before treatment. Recanalization was assessed at 2 hours by transcranial Doppler. In 78 consecutive patients treated with endovascular thrombectomy, ADAMTS13 antigen was measured by ELISA and futile recanalization was defined as complete recanalization plus modified Rankin Scale score >2 at 3 months. Independent predictors of recanalization and futile recanalization were determined by logistic regression, adjusted by age, NIH Stroke Scale score, and time from stroke onset.

RESULTS

Patients who achieved tPA-induced recanalization had higher baseline ADAMTS13 activity (78.1% [68%-88%] vs 70.1% [61%-79%], p = 0.021). In logistic regression analysis, ADAMTS13 activity >75% was an independent predictor of recanalization (odds ratio = 6.76 [1.52-30.02], p = 0.012), together with absence of early ischemic signs and Oxfordshire Community Stroke Project classification. Regarding endovascular therapies, a reduced ADAMTS13 concentration (<982 ng/mL) was an independent predictor of futile recanalization (odds ratio = 67.4 [1.4-3,282.1], p = 0.034), together with age and diabetes mellitus. The addition of ADAMTS13 to clinical predictors of tPA-induced recanalization and futile recanalization improved discrimination and reclassification (integrated discrimination improvement = 10.06% and 28.4%, net reclassification improvement = 61.0% and 107.4%, respectively).

CONCLUSIONS

A reduced ADAMTS13 was associated with poor response to recanalization therapies. If confirmed in future prospective studies, a panel of blood biomarkers including ADAMTS13 might be a useful tool to guide reperfusion therapies.

Mutations in Coagulation Factor VIII Are Associated with More Favorable Outcome in Patients with Cutaneous Melanoma

Coagulation factor VIII (FVIII), von Willebrand factor (VWF), and ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats 13) play an important role in the regulation of normal hemostasis. However, little is known about their roles in patients with malignancy, particularly with cutaneous melanoma. Whole genome sequencing data are available for 25,719 cases in 126 cancer genomic studies for analysis. All sequencing data and corresponding pathology findings were obtained from The Cancer Genome Atlas. The cBioPortal bioinformatics tools were used for the data analysis. Our results demonstrated that mutations in genes encoding FVIII , VWF , and ADAMTS13 were reported in 92 of 126 cancer genomic studies, and high mutation rates in these three genes were observed in patients with cutaneous melanoma from three independent studies. Moreover, high mutation rates in FVIII , VWF , and ADAMTS13 were also found in patients with diffuse large B cell lymphoma (22.9%), lung small cell carcinoma (20.7%), and colon adenocarcinoma (19.4%). Among 366 melanoma cases from TCGA provisional, the somatic mutation rates of FVIII , VWF , and ADAMTS13 in tumor cells were 15, 14, and 5%, respectively. There was a strong tendency for coexisting mutations of FVIII , VWF , and ADAMTS13 . Kaplan–Meier survival analysis demonstrated that melanoma patients with FVIII mutations had a more favorable overall survival rate than those without FVIII mutations ( p  = 0.02). These findings suggest, for the first time, that the FVIII mutation burden may have a prognostic value for patients with cutaneous melanoma. Further studies are warranted to delineate the molecular mechanisms underlying the favorable prognosis associated with FVIII mutations.

Role of calcium in regulating the intra- and extracellular cleavage of von Willebrand factor by the protease ADAMTS13

von Willebrand factor (VWF) and the metalloprotease a disintegrin and metalloprotease with thrombospondin type 1 motif 13 (ADAMTS13) are present both within endothelial cells (ECs) and in peripheral blood. Calcium concentrations are lower in intracellular compartments (80-400 μM) compared with the extracellular milieu (∼1.25 mM). Because low calcium favors VWF A2-domain proteolysis by ADAMTS13, the dependence of proteolysis rates on calcium was assayed both within ECs and in blood. Confocal microscopy studies demonstrate partial perinuclear colocalization of VWF with ADAMTS13 in human umbilical vein ECs (HUVECs). Consequently, low levels (5%-10%) of VWF cleavage products were detected in HUVEC lysates and also culture-supernatant following EC stimulation. This proteolysis occurred before disulfide bond formation. Compared with wild-type VWF A2-domain, calcium-binding mutants including the common von Willebrand disease (VWD) type 2A R1597W mutant were expressed in an open conformation in ECs and were highly susceptible to intracellular proteolysis. Fluorescence resonance energy transfer measurements demonstrate strong calcium-dependent VWF-A2 conformation changes at concentrations <500 μM, with unfolding rates being fourfold higher for monomeric VWF A2-domain compared with multimeric, full-length VWF. Under shear, physiological levels of ADAMTS13 did not cleave VWF strings on HUVECs, unless platelets were attached to stretch these strings under flow. Further, VWF-platelet string cleavage under shear proceeded with equal efficiency in the absence and presence of calcium at shear stress ≥1 dyn/cm². Overall, low calcium levels may promote intracellular VWF proteolysis particularly during VWD type 2A disease. Calcium has a negligible effect on VWF-platelet string proteolysis under physiologically relevant fluid shear.

Expression of ADAMTS13 in Normal and Abnormal Placentae and Its Potential Role in Angiogenesis and Placenta Development

OBJECTIVE

ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 repeats, member 13) is primarily synthesized in liver. The biosynthesis of ADAMTS13 and its physiological role in placenta are not known.

APPROACH AND RESULTS

We used real-time polymerase chain reaction, immunohistochemistry, and Western blotting analyses, as well as proteolytic cleavage of FRETS (fluorescent resonance energy transfers)-VWF73, to determine ADAMTS13 expression in placenta and trophoblasts obtained from individuals with normal pregnancy and patients with severe preeclampsia. We also determined the role of ADAMTS13 in extravillous trophoblasts using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, wound scratch assay, transwell migration assay, tube formation assay, and tissue outgrowth assays. We showed that full-length and proteolytically active ADAMTS13 was expressed in normal human placenta, primarily in the trophoblasts and villous core fetal vessel endothelium during pregnancy. Placental expression of ADAMTS13 mRNA, protein, and proteolytic activity was at the highest levels during the first trimester and significantly reduced at the term of gestation. Additionally, significantly reduced levels of placental ADAMTS13 expression was detected under hypoxic conditions and in patients with preeclampsia. In addition, recombinant ADAMTS13 protease stimulated proliferation, migration, invasion, and network formation of trophoblastic cells in culture. Finally, knockdown of ADAMTS13 expression attenuated the ability of tube formation in trophoblast (HTR-8/SVNEO) cells and the extravillous trophoblast outgrowth in placental explants.

CONCLUSIONS

Our results demonstrate for the first time the expression of ADAMTS13 mRNA and protein in normal and abnormal placental tissues and its role in promoting angiogenesis and trophoblastic cell development. The findings support the potential role of the ADAMTS13-von Willebrand factor pathway in normal pregnancy and pathogenesis of preeclampsia.

siRNA-knockdown of ADAMTS-13 modulates endothelial cell angiogenesis

ADAMTS-13, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13, is a zinc-containing metalloprotease that cleaves von Willebrand factor (vWf). Previous publications by our laboratory have shown that ADAMTS-13 may also be involved in angiogenesis. For this study, we report the successful transient knockdown of endogenous ADAMTS-13 in human umbilical vein endothelial cells (HUVEC) via siRNA and the effects of reduced endogenous ADAMTS-13 on HUVEC angiogenesis functions. 15nM of ADAMTS-13 siRNA reduced HUVEC ADAMTS-13 protein levels by 90% after 24h incubation, whereas control siRNA did not affect endogenous ADAMTS-13 levels. Furthermore, this transfection did not affect the HUVEC endogenous protein level of ADAMTS-1, a related family member of ADAMTS-13 indicating the specificity of the siRNA. Transfection of HUVEC with 15nM of ADAMTS-13 siRNA resulted in a 21% decrease in proliferation after 24h incubation. The effects of ADAMTS-13 knockdown on migration of HUVEC across a scratch wound were also evaluated. 24h after transfection with control siRNA, there was increased cell migration across the scratch wound. This dramatic migration did not occur with ADAMTS-13 knockdown cells. Decreased protein levels of endogenous ADAMTS-13 also affected angiogenesis as measured by endothelial cell tube formation using a Matrigel matrix method. The tube lengths, sizes and junction numbers of the ADAMTS-13 knockdown cells were all significantly lower compared to control cells by about 40%. The protein level of vascular endothelial growth factor (VEGF), a well-known regulator of angiogenesis, was significantly decreased by 45% upon knockdown of ADAMTS-13. Moreover, activity of the AKT pathway, one of the VEGF angiogenesis downstream signaling pathways was down-regulated by ADAMTS-13 siRNA. These data indicate that in cultured endothelial cells, one role of endogenous ADAMTS-13 is regulation of angiogenesis, mediated through VEGF and AKT signaling pathway. Overall, our data suggest an additional model of endogenous ADAMTS-13 functionality, beyond that of cleaving von Willebrand factor.

ADAMTS13 Retards Progression of Diabetic Nephropathy by Inhibiting Intrarenal Thrombosis in Mice

OBJECTIVE

ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type I repeats-13) prevents microvascular thrombosis by cleaving prothrombogenic ultralarge von Willebrand factor (VWF) multimers. Clinical studies have found association between reduced ADAMTS13-specific activity, ultralarge VWF multimers, and thrombotic angiopathy in patients with diabetic nephropathy. It remains unknown, however, whether ADAMTS13 deficiency or ultralarge VWF multimers have a causative effect in diabetic nephropathy.

APPROACH AND RESULTS

The extent of renal injury was evaluated in wild-type (WT), Adamts13^-/- and Adamts13^-/-Vwf^-/- mice after 26 weeks of streptozotocin-induced diabetic nephropathy. We found that WT diabetic mice exhibited low plasma ADAMTS13-specific activity and increased VWF levels (P<0.05 versus WT nondiabetic mice). Adamts13^-/- diabetic mice exhibited deterioration of kidney function (increased albuminuria, plasma creatinine, and urea; P<0.05 versus WT diabetic mice), independent of hyperglycemia and hypertension. Deterioration of kidney function in Adamts13^-/- diabetic mice was concomitant with aggravated intrarenal thrombosis (assessed by plasminogen activator inhibitor, VWF, fibrin(ogen), and CD41-positive microthrombi), increased mesangial cell expansion, and extracellular matrix deposition (P<0.05 versus WT diabetic mice). Genetic deletion of VWF in Adamts13^-/- diabetic mice improved kidney function, inhibited intrarenal thrombosis, and alleviated histological changes in glomeruli, suggesting that exacerbation of diabetic nephropathy in the setting of ADAMTS13 deficiency is VWF dependent.

CONCLUSIONS

ADAMTS13 retards progression of diabetic nephropathy, most likely by inhibiting VWF-dependent intrarenal thrombosis. Alteration in ADAMTS13-VWF balance may be one of the key pathophysiological mechanisms of thrombotic angiopathy in diabetes mellitus.

Thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP; also known as Moschcowitz disease) is characterized by the concomitant occurrence of often severe thrombocytopenia, microangiopathic haemolytic anaemia and a variable degree of ischaemic organ damage, particularly affecting the brain, heart and kidneys. Acute TTP was almost universally fatal until the introduction of plasma therapy, which improved survival from <10% to 80-90%. However, patients who survive an acute episode are at high risk of relapse and of long-term morbidity. A timely diagnosis is vital but challenging, as TTP shares symptoms and clinical presentation with numerous conditions, including, for example, haemolytic uraemic syndrome and other thrombotic microangiopathies. The underlying pathophysiology is a severe deficiency of the activity of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13), the protease that cleaves von Willebrand factor (vWF) multimeric strings. Ultra-large vWF strings remain uncleaved after endothelial cell secretion and anchorage, bind to platelets and form microthrombi, leading to the clinical manifestations of TTP. Congenital TTP (Upshaw-Schulman syndrome) is the result of homozygous or compound heterozygous mutations in ADAMTS13, whereas acquired TTP is an autoimmune disorder caused by circulating anti-ADAMTS13 autoantibodies, which inhibit the enzyme or increase its clearance. Consequently, immunosuppressive drugs, such as corticosteroids and often rituximab, supplement plasma exchange therapy in patients with acquired TTP.

The expression of ADAMTS13 in human microvascular endothelial cells

ADAMTS13, as a specific von Willebrand factor (VWF)-cleaving protease, prevents microvascular thrombosis of VWF/platelet thrombi. It has been reported that human vascular endothelial cells could also synthesize and secrete ADAMTS13, and these reports were focused in human umbilical vascular endothelial cells. Considering the particularity of its huge quantity and structure of human microvascular endothelial cells (HMECs) in the body, whether ADAMTS13 is expressed in HMECs also needs to be confirmed. To investigate whether ADAMTS13 is expressed in HMECs. Real-time PCR (RT-PCR) amplification detected ADAMTS13 mRNA in HMEC-1 cell line. The expression and distribution of ADAMTS13 protein and VWF were detected by fluorescence immunoassay and western blot. We observed the expression and distribution of ADAMTS13 in HMECs. We confirmed the expression of ADAMTS13 mRNA in HMEC-1, and found that there were some partly common distributions of ADAMTS13 protein and VWF. This study provides the evidence that HMECs also express ADAMTS13. HMECs might also be a primary source for human plasma ADAMTS13. The overlap region for the distribution of ADAMTS13 and VWF suggests that ADAMTS13 might have a potential regulation role for VWF inside cells.

Role of fluid shear stress in regulating VWF structure, function and related blood disorders

Von Willebrand factor (VWF) is the largest glycoprotein in blood. It plays a crucial role in primary hemostasis via its binding interaction with platelet and endothelial cell surface receptors, other blood proteins and extra-cellular matrix components. This protein is found as a series of repeat units that are disulfide bonded to form multimeric structures. Once in blood, the protein multimer distribution is dynamically regulated by fluid shear stress which has two opposing effects: it promotes the aggregation or self-association of multiple VWF units, and it simultaneously reduces multimer size by facilitating the force-dependent cleavage of the protein by various proteases, most notably ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type repeats, motif 1 type 13). In addition to these effects, fluid shear also controls the solution and substrate-immobilized structure of VWF, the nature of contact between blood platelets and substrates, and the biomechanics of the GpIbα–VWF bond. These features together regulate different physiological and pathological processes including normal hemostasis, arterial and venous thrombosis, von Willebrand disease, thrombotic thrombocytopenic purpura and acquired von Willebrand syndrome. This article discusses current knowledge of VWF structure–function relationships with emphasis on the effects of hydrodynamic shear, including rapid methods to estimate the nature and magnitude of these forces in selected conditions. It shows that observations made by many investigators using solution and substrate-based shearing devices can be reconciled upon considering the physical size of VWF and the applied mechanical force in these different geometries.

ADAMTS13 and von Willebrand factor interactions

PURPOSE OF REVIEW

ADAMTS13 is a zinc-containing metalloprotease that cleaves von Willebrand factor (VWF). Deficiency of plasma ADAMTS13 activity is accountable for a potentially fatal blood disorder thrombotic thrombocytopenic purpura (TTP). Understanding of ADAMTS13-VWF interaction is essential for developing novel treatments to this disorder.

RECENT FINDINGS

Despite the proteolytic activity of ADAMTS13 being restricted to the metalloprotease domain, the ancillary proximal C-terminal domains including the disintegrin domain, first TSP-1 repeat, cysteine-rich region, and spacer domain are all required for cleavage of VWF and its analogs. Recent studies have added to our understandings of the role of the specific regions in the disintegrin domain, the cysteine-rich domain, and the spacer domain responsible for its interaction with VWF. Additionally, regulative functions of the distal portion of ADAMTS13 including the TSP-1 2-8 repeats and the CUB domains have been proposed. Finally, fine mapping of anti-ADAMTS13 antibody epitopes have provided further insight into the essential structural elements in ADAMTS13 for VWF binding and the mechanism of autoantibody-mediated TTP.

SUMMARY

Significant progress has been made in our understandings of the structure-function relationship of ADAMTS13 in the past decade. To further investigate ADAMTS13-VWF interactions for medical applications, these interactions must be studied under physiological conditions in vivo.

Tissue factor: A potent stimulator of Von Willebrand factor synthesis by human umbilical vein endothelial cells

Inflammation and dysfunction of endothelial cells are thought to be triggers for the secretion of Von Willebrand factor. The aim of this study was to examine the effects of the inflammatory cytokines interleukin-6 (IL-6), interleukin-8 (IL-8) and tumour necrosis factor-alpha (TNF-α) and the coagulation factors, tissue factor and thrombin on the release and cleavage potential of ultra-large von Willebrand factor (ULVWF) and its cleavage protease by cultured human umbilical vein endothelial cells (HUVEC). HUVEC were treated with IL-6, IL-8, and TNF-α, tissue factor (TF) and thrombin, and combinations thereof for 24 hours under static conditions. The cells were then exposed to shear stress after which the VWF-propeptide levels and the VWF cleavage protease, ADAMTS13 content were measured. All treatments and their combinations, excluding IL-6, significantly stimulated the secretion of VWF from HUVEC. The VWF secretion from the HUVEC was stimulated most by the combination of TF with TNF-α. Slightly lower levels of ADAMTS13 secretion were found with all treatments. This may explain the thrombogenicity of patients with inflammation where extremely high VWF levels and slightly lower ADAMTS13 levels are present.

Endothelial cell control of thrombosis

Hemostasis encompasses a set of tightly regulated processes that govern blood clotting, platelet activation, and vascular repair. Upon vascular injury, the hemostatic system initiates a series of vascular events and activates extravascular receptors that act in concert to seal off the damage. Blood clotting is subsequently attenuated by a plethora of inhibitors that prevent excessive clot formation and eventual thrombosis. The endothelium which resides at the interface between the blood and surrounding tissues, serves an integral role in the hemostatic system. Depending on specific tissue needs and local stresses, endothelial cells are capable of evoking either antithrombotic or prothrombotic events. Healthy endothelial cells express antiplatelet and anticoagulant agents that prevent platelet aggregation and fibrin formation, respectively. In the face of endothelial dysfunction, endothelial cells trigger fibrin formation, as well as platelet adhesion and aggregation. Finally, endothelial cells release pro-fibrinolytic agents that initiate fibrinolysis to degrade the clot. Taken together, a functional endothelium is essential to maintain hemostasis and prevent thrombosis. Thus, a greater understanding into the role of the endothelium can provide new avenues for exploration and novel therapies for the management of thromboembolisms.

Thrombocytopenia-Associated Multiple Organ Failure and Acute Kidney Injury

Thrombocytopenia-associated multiple organ failure (TAMOF) is a clinical phenotype that encompasses a spectrum of syndromes associated with disseminated microvascular thromboses, such as the thrombotic microangiopathies thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) and disseminated intravascular coagulation (DIC). Autopsies findings in TTP, HUS, or DIC reveal specific findings that can differentiate these 3 entities. Von Willebrand factor and ADAMTS-13 play a central role in TTP. Shiga toxins and the complement pathway are vital in the development of HUS. Tissue factor is the major protease that drives the pathology of DIC. Acute kidney injury (AKI) is a common feature in patients with TAMOF.

All-trans retinoic acid modulates the balance of ADAMTS13 and VWF in human microvascular endothelial cells

PURPOSE

To better understand the antithrombotic property of All-trans retinoic acid (ATRA), we investigated whether ATRA may affect the balance between ADAMTS13 and von Willebrand factor (VWF) in human microvascular endothelial cell.

METHODS

Compared to tumor necrosis factor-alpha (TNF-α), we observed the effects of ATRA on the expression of ADAMTS13 and VWF. ADAMTS13mRNA in human microvascular endothelial cell (HMEC-1 cell line) were detected by real-time polymerase chain reaction amplification (RT-PCR). The levels of ADAMTS13 and VWF antigen were detected by western blot or enzyme-linked immunosorbent assay (ELISA), and the proteolytic activity of ADAMTS13 was also determined by using GST-VWF73-His peptide as a specific substrate.

RESULTS

ATRA significantly upregulated the expression of ADAMTS13mRNA in HMEC-1, while TNF-α inhibited ADAMTS13mRNA expression. ATRA could reverse the inhibition expression of ADAMTS13 by TNF-α. The results were confirmed from the levels of ADAMTS13 protein and its activity, while ATRA had no significant affection on triggering release of VWF.

CONCLUSIONS

This study provides the evidence that ATRA modulates the balance of ADAMTS13 and VWF in human microvascular endothelial cell, which might be a very relevant compartment for the antithrombotic property of ATRA.

Reduced ADAMTS13 activity is associated with thrombotic risk in systemic lupus erythematosus

BACKGROUND

Severe deficiency of ADAMTS13 activity leads to von Willebrand factor (VWF) ultralarge multimers with high affinity for platelets, causing thrombotic thrombocytopenic purpura. Other pathological conditions with moderate ADAMTS13 activity exhibit a thrombotic risk. We examined the ADAMTS13 activity in systemic lupus erythematosus (SLE) and its value as a thrombotic biomarker.

METHODS

ADAMTS13 activity, VWF antigen and multimeric structure, and vascular cell adhesion molecule 1 (VCAM-1) were measured in plasma samples from 50 SLE patients and 50 healthy donors. Disease activity (systemic lupus erythematosus disease activity index; SLEDAI) and organ damage (systemic lupus international collaborating clinics) scores, thrombotic events, antiphospholipid syndrome (APS) and antiphospholipid antibodies (aPLs) were registered.

RESULTS

SLE patients showed decreased ADAMTS13 activity and high VWF levels compared with controls (66 ± 27% vs. 101 ± 8%, P < 0.01, and 325 ± 151% vs. 81 ± 14%, P < 0.001). VCAM-1 levels were higher in SLE patients (P < 0.05). Considering three groups of SLE patients depending on ADAMTS13 activity (>60%, 60-40% and <40%), comparative analysis showed significant association between ADAMTS13 activity and SLEDAI (P < 0.05), presence of aPLs (P < 0.001), APS (P < 0.01) and thrombotic events (P < 0.01). Reduced ADAMTS13 activity together with increased VWF levels were especially notable in patients with active disease and with aPLs.

CONCLUSION

ADAMTS13 activity, in combination with other laboratory parameters, could constitute a potential prognostic biomarker of thrombotic risk in SLE.

ADAMTS13 and its variants promote angiogenesis via upregulation of VEGF and VEGFR2

Severe plasma ADAMTS13 deficiency results in the clinical disorder thrombotic thrombocytopenic purpura. However, other potential pathophysiological roles of ADAMTS13 in endothelial cell biology remain unexplored. The goals of this study were to understand the angiogenic pathways ADAMTS13 activates and to identify the important structural components of ADAMTS13 that stimulate angiogenesis. Incubation of human umbilical vein endothelial cells (HUVEC) with 150 ng/mL (1 nM) of recombinant human ADAMTS13 induced VEGF expression by 53 % and increased VEGF mRNA by over sixfold, both within 10 min; the measured VEGF levels steadily decreased over 2 h, as shown by Western blot and ELISA. Phosphorylation of VEGFR2 was significantly enhanced in HUVEC after incubation with ADAMTS13 (1 nM). Structure-function analysis showed that an ADAMTS13 variant containing thrombospondin type 1 (TSP1) 2-8 repeats (TSP1 2-8), TSP1 2-8 plus CUB domains (TSP1 2-8 plus CUB), or TSP1 5-8 repeats plus CUB domains (TSP1 5-8 plus CUB) increased HUVEC proliferation by 41-54 % as compared to the EBM-2 controls. Chemotaxis assays further demonstrated that the TSP1 domains of ADAMTS13 increased HUVEC migration by 2.65-fold. Incubation of HUVEC with both ADAMTS13 variants containing TSP1 repeats and anti-VEGF IgG abrogated the enhanced effect of ADAMTS13 on proliferation, migration, and VEGFR2 phosphorylation. In conclusion, ADAMTS13-induced endothelial cell angiogenesis occurs via the upregulation of VEGF and phosphorylation of VEGFR2. This angiogenic activity depends on the C-terminal TSP1 repeats of ADAMTS13.

Clinical utility of ADAMTS-13 testing in suspected thrombotic microangiopathy: an audit of ADAMTS-13 activity assay requests in routine practice from a tertiary hospital

AIMS

Differentiation between thrombotic thrombocytopenic purpura (TTP) and other microangiopathic haemolytic anaemia (MAHA) processes can be difficult. Since the documentation of ADAMTS-13 deficiency in TTP, several ADAMTS-13 activity assays have been developed for use in the diagnosis of TTP and/or other microangiopathic disorders. We reviewed the clinical utility of ADAMTS-13 activity testing in suspected TTP, as used in routine clinical practice in a tertiary referral hospital.

METHODS

All requests for ADAMTS-13 activity levels performed at our institution after introduction of the assay were retrospectively audited with respect to clinical diagnosis and results.

RESULTS

In total 57 individual patients were tested, of whom only 46% had a MAHA process. Severe ADAMTS-13 deficiency was present in five TTP patients and in one patient with fulminant hepatic failure.

CONCLUSIONS

Our experience suggests that severely reduced levels are relatively specific for TTP, but may also occur in fulminant hepatic failure. Patients without MAHA may have reduced ADAMTS-13 activity and there is significant overlap in the range of ADAMTS-13 activity seen in non-TTP MAHA diagnoses. This supports the observation that outside the diagnosis and (possible) follow-up of suspected idiopathic TTP, the ADAMTS-13 activity assay has limited clinical utility. Further education about the role of ADAMTS-13 activity testing is needed.

THE SENSITIVITY OF VASCULAR ENDOTHELIUM AND ITS PREDICTORS IN PATIENTS WITH CARDIOVASCULAR PATHOLOGY

Aim.To estimate the role of endogenous metabolic factors in formation of vascular endothelium reactivity in patients with different genesis cardiovascular regulation disorders.

Materials and methods.The research included 30 patients with ischemic heart disease (IHD) with stable form of exertional angina (EA) of II–III severity class, 30 patients with I–II stage and 1st–2nd degree essential hypertension (EH), and 15 clinically healthy volunteers. We researched the signs of functional state of vascular endothelium before and after occlusion test. The parameters investigated included: adhesion of thrombocytes, spontaneous aggregation, prostacyclin activity of blood plasma, levels of antithrombine-III, of von Willebrand factor, contents of malonic aldehyde, of nitrites, of endothelin-1, of membrane-connected haemoglobin, of methaemoglobin in erythrocytes, activity of angiotensineconverting enzyme, level of sorption on the membrane of erythrocytes of nucleotides. Research of hemorheology was performed by viscosimetry method.

Results.In healthy volunteers high probability of endothelium sensitivity to transverse strain decrease (in 82%) was determined and 25% increase of activity of peroxide oxidation of lipids. In patients with exertional angina influence of dynamic changes of blood flow on endothelium occurred by 2% decrease of viscosity and more than 120% increase of production von Willebrand factor (in 87%). It was concluded that as higher the production of prostacyclin in response to mechanic stimuli (more than 50%) is, the higher is probability of blood flow dynamic changes influence on endothelium. In patients with essential hypertension 30% increase of level of antithrombine-III in 100% of cases caused increase of sensibility of vascular endothelium to transverse strain.

Conclusion.The most significant factors linked with sensibility of endothelium of vascular wall to dynamic blood flow changes in examined groups of patients were determined. In patients with exertional angina vascular reaction was mostly linked with rheological qualities and adhesive-aggregation characteristics of blood. In patients with essential hypertension the sensitivity of vascular endothelium was implied to be concordant with anticoagulant activity of blood plasma.