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Defective angiogenesis, incomplete thrombus revascularisation and fibrosis are considered critical pathomechanisms of chronic thromboembolic pulmonary hypertension (CTEPH) after pulmonary embolism (PE). Angiopoietin-2 (ANGPT2) has been shown to regulate angiogenesis, but its importance for thrombus resolution and remodelling is unknown.ANGPT2 plasma concentrations were measured in patients with CTEPH (n=68) and acute PE (n=84). Tissue removed during pulmonary endarterectomy (PEA) for CTEPH was analysed (immuno)histologically. A mouse model of inferior vena cava ligation was used to study the kinetics of venous thrombus resolution in wild-type mice receiving recombinant ANGPT2 via osmotic pumps, and in transgenic mice overexpressing ANGPT2 in endothelial cells.Circulating ANGPT2 levels were higher in CTEPH patients compared to patients with idiopathic pulmonary arterial hypertension and healthy controls, and decreased after PEA. Plasma ANGPT2 levels were also elevated in patients with PE and diagnosis of CTEPH during follow-up. Histological analysis of PEA specimens confirmed increased ANGPT2 expression, and low levels of phosphorylated TIE2 were observed in regions with early-organised pulmonary thrombi, myofibroblasts and fibrosis. Microarray and high-resolution microscopy analysis could localise ANGPT2 overexpression to endothelial cells, and hypoxia and TGF-β1 were identified as potential stimuli. Gain-of-function experiments in mice demonstrated that exogenous ANGPT2 administration and transgenic endothelial ANGPT2 overexpression resulted in delayed venous thrombus resolution, and thrombi were characterised by lower TIE2 phosphorylation and fewer microvessels.Our findings suggest that ANGPT2 delays venous thrombus resolution and that overexpression of ANGPT2 contributes to thrombofibrosis and may thus support the transition from PE to CTEPH.

Background Inflammation and incomplete thrombus resolution leading to obstructive fibrotic remodelling are considered critical mechanisms for the development of chronic thromboembolic pulmonary hypertension (CTEPH) after pulmonary embolism (PE). Osteopontin (OPN) is involved in a variety of biological processes including inflammation and tissue fibrosis. Methods OPN plasma concentrations were measured in 70 CTEPH and 119 PE patients. Tissue material from 6 CTEPH patients removed during pulmonary endarterectomy and murine venous thrombi induced by subtotal ligation of the inferior vena cava in C57BL/6 mice were analysed by (immuno)histochemistry. Results CTEPH patients had higher OPN plasma concentrations (median, 106.9 [interquartile range, 75.6–155.9]) compared to PE patients (90.4 [53.3–123.9] ng/mL, p = 0.001). OPN- and matrix metalloproteinase (MMP)-9-positive cells were predominantly present in myofibroblast-rich and profibrotic areas of CTEPH tissue material. Early stages of murine thrombus resolution were characterised by high numbers of OPN- and MMP-2-positive cells while OPN was almost absent in fresh thrombi of CTEPH tissue material. PE patients with OPN plasma concentrations of < 55 ng/mL had a 15.2-fold (95% confidence interval, 1.7–135.5, p = 0.015) increased risk for a diagnosis of CTEPH during follow-up. Conclusion The results of the present observational translational study point to a possible involvement of OPN in the pathogenesis of CTEPH by affecting early inflammatory and late fibrotic processes.

Introduction: Although a number of risk factors for chronic thromboembolic pulmonary hypertension (CTEPH) have been reported, the exact prevalence is controversial and varies between published cohorts. The aim of the present study was to investigate the prevalence of risk factors in operable CTEPH patients with special emphasis on thyroid disease and function. Material and methods: Overall, 228 CTEPH patients (47.7% female; median age 63 [IQR 52-72] years) scheduled for pulmonary endarterectomy between 01/2014 and 12/2015 were studied. Prevalence of risk factors was assessed, and patients were classified according to their thyroid function based on laboratory measurements. Results: As many as 86.0% of patients reported a history of pulmonary embolism (PE; of those, 24.5% were diagnosed with "acute" PE less than six months before the diagnosis of CTEPH), 80.7% of patients had a blood group non-0 and 24.1% of patients had known thyroid disease (of those, 78.2% hypothyroidism). Laboratory measurements revealed thyroid dysfunction in 10.5% of patients (of those, 54.8% had no known thyroid disease). Patients with hypothyroid function had higher WHO functional classes, NT-proBNP levels and a lower cardiac index compared to patients with euthyroid function. Conclusions: The prevalence of a history of PE and blood group non-0 was higher than previously reported. However, a relevant proportion of patients might have suffered from pre-existing CTEPH rather than acute PE. Thyroid disease and dysfunction were frequent and hypothyroid function associated with more severe disease.