Objective: Restoration of patency is a natural target of vascular remodeling after venous thrombosis that involves vascular endothelial cells and smooth muscle cells, as well as leukocytes. Acute pulmonary emboli usually resolve <6 months. However, in some instances, thrombi transform into fibrous vascular obstructions, resulting in occlusion of the deep veins, or in chronic thromboembolic pulmonary hypertension (CTEPH). We proposed that dysregulated thrombus angiogenesis may contribute to thrombus persistence.
Approach and results: Mice with an endothelial cell-specific conditional deletion of vascular endothelial growth factor receptor 2/kinase insert domain protein receptor were used in a model of stagnant flow venous thrombosis closely resembling human deep vein thrombosis. Biochemical and functional analyses were performed on pulmonary endarterectomy specimens from patients with CTEPH, a human model of nonresolving venous thromboembolism. Endothelial cell-specific deletion of kinase insert domain protein receptor and subsequent ablation of thrombus vascularization delayed thrombus resolution. In accordance with these findings, organized human CTEPH thrombi were largely devoid of vascular structures. Several vessel-specific genes, such as kinase insert domain protein receptor, vascular endothelial cadherin, and podoplanin, were expressed at lower levels in white CTEPH thrombi than in organizing deep vein thrombi and organizing thrombi from aortic aneurysms. In addition, red CTEPH thrombi attenuated the angiogenic response induced by vascular endothelial growth factor.
Conclusions: In the present work, we propose a mechanism of thrombus nonresolution demonstrating that endothelial cell-specific deletion of kinase insert domain protein receptor abates thrombus vessel formation, misguiding thrombus resolution. Medical conditions associated with the development of CTEPH may be compromising early thrombus angiogenesis.
Keywords: endothelium; thrombosis; vascular endothelial growth factor receptor-2.