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