ADAMTS13 deficiency in mice does not affect adipose tissue development

Quantitative Methods to Assess Adipose Vasculature

Adipose tissue depots are invested with an extensive capillary network that is closely associated with maintenance of adipose functions and enables healthy tissue expansion. The capillary network displays a high level of plasticity, demonstrating either growth (angiogenesis) or regression (rarefaction) under various physiological/pathological conditions, which has significant consequences for cardiometabolic health. Thus, the visualization and quantification of adipose vascular networks is an important aspect of studying factors that regulate adipose tissue health. This chapter provides an overview of several methods to quantify adipose vascularization. In-depth protocols are provided for the visualization of vascular structures by staining and imaging of whole-mount adipose tissues or paraffin-embedded adipose tissue sections, together with the quantitative analysis of vascularization from these images.

Targeting von Willebrand factor in liver diseases: A novel therapeutic strategy?

Acute and chronic liver disease are associated with substantial alterations in the hemostatic system. Evidence from both experimental and clinical studies suggests that anticoagulants slow the progression of liver disease. Efficacy of those anticoagulant drugs is, in part, attributed to a reduction of microthrombi formation within the liver. Although anticoagulant drugs show promising results, bleeding risk associated with these drugs is an obvious drawback, particularly in patients with a complex coagulopathy driven by decreased liver function. Identifying therapies that reduce intrahepatic thrombosis with minimal bleeding risk would significantly advance the field. Among the hemostatic alterations observed in patients are substantially increased levels of the platelet-adhesive protein von Willebrand factor (VWF). In contrast, levels of A Disintegrin and Metalloproteinase with Thrombospondin motifs, the enzyme that regulates VWF activity, are significantly reduced in patients with liver disease. Highly elevated VWF levels are proposed to accelerate intrahepatic thrombus formation and thus be a driver of disease progression. Strong clinical evidence suggesting a link between liver disease and changes in VWF is now being matched by emerging mechanistic data showing a detrimental role for VWF in the progression of liver disease. This review focuses on clinical and experimental evidence supporting a connection between VWF function and the progression of acute and chronic liver diseases. Furthermore, with the recent anticipated approval of several novel therapies targeting VWF, we discuss potential strategies and benefits of targeting VWF as an innovative therapy for patients with liver disease.

Platelet rescue by macrophage depletion in obese ADAMTS-13-deficient mice at risk of thrombotic thrombocytopenic purpura

Essentials Obesity is a potential risk factor for development of thrombotic thrombocytopenic purpura (TTP). Obese ADAMTS-13-deficient mice were triggered with von Willebrand factor (VWF). Depletion of hepatic and splenic macrophages protects against thrombocytopenia in this model. VWF enhances phagocytosis of platelets by macrophages, dose-dependently.

SUMMARY

Background Thrombotic thrombocytopenic purpura (TTP) is caused by the absence of ADAMTS-13 activity. Thrombocytopenia is presumably related to the formation of microthrombi rich in von Willebrand factor (VWF) and platelets. Obesity may be a risk factor for TTP; it is associated with abundance of macrophages that may phagocytose platelets. Objectives To evaluate the role of obesity and ADAMTS-13 deficiency in TTP, and to establish whether macrophages contribute to thrombocytopenia. Methods Lean or obese ADAMTS-13-deficient (Adamts-13-/- ) and wild-type (WT) mice were injected with 250 U kg-1 of recombinant human VWF (rVWF), and TTP characteristics were evaluated 24 h later. In separate experiments, macrophages were depleted in the liver and spleen of lean and obese WT or Adamts-13-/- mice by injection of clodronate-liposomes, 48 h before injection of rVWF. Results Obese Adamts-13-/- mice had a lower platelet count than their lean counterparts, suggesting that they might be more susceptible to TTP development. Lean Adamts-13-/- mice triggered with a threshold dose of rVWF did not develop TTP, whereas typical TTP symptoms developed in obese Adamts-13-/- mice, including severe thrombocytopenia and higher lactate dehydrogenase (LDH) levels. Removal of hepatic and splenic macrophages by clodronate injection in obese Adamts-13-/- mice before treatment with rVWF preserved the platelet counts measured 24 h after the trigger. In vitro experiments with cultured macrophages confirmed a VWF dose-dependent increase of platelet phagocytosis. Conclusions Obese Adamts-13-/- mice are more susceptible to the induction of TTP-related thrombocytopenia than lean mice. Phagocytosis of platelets by macrophages contributes to thrombocytopenia after rVWF injection in this model.

Role of ADAMTS13 in diet-induced liver steatosis

Previous studies, predominantly based on increased or decreased plasma levels, have reported conflicting data on a potential functional role of ADAMTS13 in the pathogenesis of liver diseases, including non‑alcoholic steatohepatitis (NASH). The aim of the current study was to evaluate whether ADAMTS13 deficiency affects development of NASH. Therefore, male wild‑type (WT) and Adamts13 deficient (Adamts13‑/‑) mice were kept on a steatosis‑inducing diet devoid of methionine and choline (MCD) or a control diet (MCC) for 4 weeks. Induction of NASH did not affect plasma ADAMTS13 antigen levels of WT mice. MCD as compared with MCC feeding resulted in reduced body and liver weight with no differences between the genotypes. Plasma levels of the liver enzymes AST and ALT were significantly higher for MCD vs. MCC fed Adamts13‑/‑ and WT mice, however were not different between the genotypes. Liver triglyceride levels were also higher after MCD feeding, but were not different between WT and Adamts13‑/‑ mice. Adamts13‑/‑ mice on the two diets exhibited higher insulin sensitivity when compared with WT mice. On the MCC diet, the genotype did not show clear histological abnormalities in the liver, whereas severe steatosis and fibrosis were observed on MCD diet, however were comparable for both genotypes. This was supported by comparably enhanced hepatic expression in the two genotypes on MCD diet of the steatosis marker CD36 and of the fibrosis marker tissue inhibitor of metalloproteinase 1. Thus, the results of the current study do not support a functional role of ADAMTS13 in this murine model of NASH.

ADAMTS13 deficiency promotes microthrombosis in a murine model of diet-induced liver steatosis

ADAMTS13 cleaves ultralarge multimeric von Willebrand Factor (VWF), thereby preventing formation of platelet-rich microthrombi. ADAMTS13 is mainly produced by hepatic stellate cells, and numerous studies have suggested a functional role of ADAMTS13 in the pathogenesis of liver diseases. The aim of our study was to investigate a potential role of ADAMTS13 in formation of hepatic microthrombi and development of non-alcoholic steatohepatitis (NASH), and furthermore to evaluate whether plasmin can compensate for the absence of ADAMTS13 in removal of thrombi. Therefore, we used a model of high-fat diet-induced steatosis in Adamts13 deficient (Adamts13^-/-) and wild-type (WT) control mice. Microthrombi were more abundant in the liver of obese Adamts13^-/- as compared to obese WT or to lean Adamts13^-/- mice. Obese Adamts13^-/- mice displayed lower platelet counts and higher prevalence of ultra-large VWF multimers. Hepatic plasmin-α2-antiplasmin complex levels were comparable for obese WT and Adamts13^-/- mice and were lower for lean Adamts13^-/- than WT mice, not supporting marked activation of the fibrinolytic system. High fat diet feeding, as compared to normal chow, resulted in enhanced liver triglyceride levels for both genotypes (p < 0.0001) and steatosis (p < 0.0001 for WT mice, p = 0.002 for Adamts13^-/- mice) without differences between the genotypes. Expression of markers of inflammation, oxidative stress, steatosis and fibrosis was affected by diet, but not by genotype. Thus, our data confirm that obesity promotes NASH, but do not support a detrimental role of ADAMTS13 in its development. However, Adamts13 deficiency in obese mice promotes hepatic microthrombosis, whereas a compensatory role of plasmin in removal of microthrombi in the absence of ADAMTS13 could not be demonstrated.