Pulmonary arterial hypertension (PAH) is a rare, complex, and progressive disease that is characterized by the abnormal remodeling of the pulmonary arteries that leads to right ventricular failure and death. Although our understanding of the causes for abnormal vascular remodeling in PAH is limited, accumulating evidence indicates that endothelial cell (EC) dysfunction is one of the first triggers initiating this process. EC dysfunction leads to the activation of several cellular signalling pathways in the endothelium, resulting in the uncontrolled proliferation of ECs, pulmonary artery smooth muscle cells, and fibroblasts, and eventually leads to vascular remodelling and the occlusion of the pulmonary blood vessels. Other factors that are related to EC dysfunction in PAH are an increase in endothelial to mesenchymal transition, inflammation, apoptosis, and thrombus formation. In this review, we outline the latest advances on the role of EC dysfunction in PAH and other forms of pulmonary hypertension. We also elaborate on the molecular signals that orchestrate EC dysfunction in PAH. Understanding the role and mechanisms of EC dysfunction will unravel the therapeutic potential of targeting this process in PAH.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension characterized by the presence of fibrotic intraluminal thrombi and causing obliteration of the pulmonary arteries. Although both endothelial cell (EC) dysfunction and inflammation are linked to CTEPH pathogenesis, regulation of the basal inflammatory response of ECs in CTEPH is not fully understood. Therefore, in the present study, we investigated the role of the nuclear factor (NF)-κB pro-inflammatory signaling pathway in ECs in CTEPH under basal conditions. Basal mRNA levels of interleukin (IL)-8, IL-1β, monocyte chemoattractant protein-1 (MCP-1), C-C motif chemokine ligand 5 (CCL5), and vascular cell adhesion molecule-1 (VCAM-1) were upregulated in CTEPH-ECs compared to the control cells. To assess the involvement of NF-κB signaling in basal inflammatory activation, CTEPH-ECs were incubated with the NF-κB inhibitor Bay 11-7085. The increase in pro-inflammatory cytokines was abolished when cells were incubated with the NF-κB inhibitor. To determine if NF-κB was indeed activated, we stained pulmonary endarterectomy (PEA) specimens from CTEPH patients and ECs isolated from PEA specimens for phospho-NF-κB-P65 and found that especially the vessels within the thrombus and CTEPH-ECs are positive for phospho-NF-κB-P65. In summary, we show that CTEPH-ECs have a pro-inflammatory status under basal conditions, and blocking NF-κB signaling reduces the production of inflammatory factors in CTEPH-ECs. Therefore, our results show that the increased basal pro-inflammatory status of CTEPH-ECs is, at least partially, regulated through activation of NF-κB signaling and potentially contributes to the pathophysiology and progression of CTEPH.

Background: Chronic thromboembolic pulmonary hypertension (CTEPH) is caused by non-resolution of thrombi that obstruct main pulmonary arteries and secondary cause vascular remodeling of the pulmonary vasculature. Endothelial cells (EC) lining the vascular wall are an important component in vascular disease development. We speculated that metabolic dysregulation of EC contribute to cellular changes that promote vascular remodeling in CTEPH. Methods: This study used endothelial cells (EC-CTEPH, n=12) isolated from specimen extracted at pulmonary endarterectomy. Expression levels of metabolic enzymes were studied at mRNA and protein level by RT-PCR and western blot, respectively. Glucose consumption and lactate production was measured in the supernatant overlying EC-CTEPH and HPAE using BGEM test cards. Results: EC-CTEPH showed significantly lower mRNA levels of all glycolytic enzymes analyzed compared to HPAE. Additionally, protein levels of HK2, PFKFB3 and LDH-A were reduced in EC-CTEPH compared to HPAE. Transcript levels of PDK1, inhibitor of PDHA1, and GLUD1, involved in glutamine metabolism, were also downregulated. Fatty acid and pentose phosphate metabolism did not present significant differences between EC-CTEPH and HPAE. A lower glycolytic flux in EC-CTEPH, when compared to HPAE, was observed in terms of glucose consumption and lactate production. Conclusion: Our results showed that EC in human CTEPH present a reduced glycolytic metabolism compared to healthy EC. TCA and glutamine metabolism were also downregulated in EC-CTEPH. Other metabolic pathways such as FAO and PPP did not show a compensatory upregulation. More studies need to be performed to determine the role of our findings in EC-CTEPH pathogenesis.