Endothelial cells from pulmonary endarterectomy specimens possess a high angiogenic potential and express high levels of hepatocyte growth factor

Angiogenesis in Chronic Thromboembolic Pulmonary Hypertension: A Janus-Faced Player?

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare form of pulmonary hypertension characterized by the presence of organized thrombi that obstruct pulmonary arteries, ultimately leading to right heart failure and death. Among others, impaired angiogenesis and inflammatory thrombosis have been shown to contribute to the progression of CTEPH. In this review, we summarize the 2-faced nature of angiogenesis in both thrombus formation and resolution in the context of CTEPH and highlight the dual role of angiogenesis and neovascularization in resolving venous thrombi. Furthermore, we discuss relevant in vitro and in vivo models that support the benefits or drawbacks of angiogenesis in CTEPH progression. We discuss the key pathways involved in modulating angiogenesis, particularly the underexplored role of TGFβ (transforming growth factor-beta) signaling in driving fibrosis as an integral element of CTEPH pathogenesis. We finally explore innovative treatment strategies that target angiogenic pathways. These strategies have the potential to pioneer preventive, inventive, or alternative therapeutic options for patients with CTEPH who may not qualify for surgical interventions. Moreover, they could be used synergistically with established treatments such as pulmonary endarterectomy or balloon pulmonary angioplasty. In summary, this review emphasizes the crucial role of angiogenesis in the development of in fibrothrombotic tissue, a major pathological characteristic of CTEPH.

Single-Cell Analysis Reveals Distinct Immune and Smooth Muscle Cell Populations that Contribute to Chronic Thromboembolic Pulmonary Hypertension

Rationale: Chronic thromboembolic pulmonary hypertension (CTEPH) is a sequela of acute pulmonary embolism (PE) in which the PE remodels into a chronic scar in the pulmonary arteries. This results in vascular obstruction, pulmonary microvasculopathy, and pulmonary hypertension. Objectives: Our current understanding of CTEPH pathobiology is primarily derived from cell-based studies limited by the use of specific cell markers or phenotypic modulation in cell culture. Therefore, our main objective was to identify the multiple cell types that constitute CTEPH thrombusy and to study their dysfunction. Methods: Here we used single-cell RNA sequencing of tissue removed at the time of pulmonary endarterectomy surgery from five patients to identify the multiple cell types. Using in vitro assays, we analyzed differences in phenotype between CTEPH thrombus and healthy pulmonary vascular cells. We studied potential therapeutic targets in cells isolated from CTEPH thrombus. Measurements and Main Results: Single-cell RNA sequencing identified multiple cell types, including macrophages, T cells, and smooth muscle cells (SMCs), that constitute CTEPH thrombus. Notably, multiple macrophage subclusters were identified but broadly split into two categories, with the larger group characterized by an upregulation of inflammatory signaling predicted to promote pulmonary vascular remodeling. CD4+ and CD8+ T cells were identified and likely contribute to chronic inflammation in CTEPH. SMCs were a heterogeneous population, with a cluster of myofibroblasts that express markers of fibrosis and are predicted to arise from other SMC clusters based on pseudotime analysis. Additionally, cultured endothelial, smooth muscle, and myofibroblast cells isolated from CTEPH fibrothrombotic material have distinct phenotypes from control cells with regard to angiogenic potential and rates of proliferation and apoptosis. Last, our analysis identified PAR1 (protease-activated receptor 1) as a potential therapeutic target that links thrombosis to chronic PE in CTEPH, with PAR1 inhibition decreasing SMC and myofibroblast proliferation and migration. Conclusions: These findings suggest a model for CTEPH similar to atherosclerosis, with chronic inflammation promoted by macrophages and T cells driving vascular remodeling through SMC modulation, and suggest new approaches for pharmacologically targeting this disease.

The angiogenic gene profile of pulmonary endarterectomy specimens: Initial study

Objectives

The underlying mechanisms for the development of chronic thromboembolic pulmonary hypertension and prognostic biomarkers are not clear yet. Thus, our aim is to assess and identify new biomarkers for the expression of 84 key genes linked to angiogenesis.

Methods

Patients who had levels more than 1000 dynes·sec·cm^-5 were included in the test group, and the other patients were included in the control group. Twelve specimens were taken from the patients. RT² Profiler PCR Array (Qiagen) was used to quantify the expression of the 84 key genes.

Results

Eight patients (6 male, 2 female, median age 54.4 ± 13.1 years) who underwent pulmonary endarterectomy were included. Pulmonary vascular resistance improved significantly from 811 ± 390 dyn/s/cm^-5 to 413.3 ± 144.9 dyn/s/cm^-5 (P < .005). A difference was also detected in median mean pulmonary arterial pressure, which decreased from 49.8 ± 9 mm Hg to 32.62 ± 2.50 mm Hg (P > .005) after surgery. Median length of hospital stay was 11.62 ± 2.97 days. The test group had a distinct pattern of impaired angiogenic and antiangiogenic genes. The expression levels of TGFA, TGFB1, THBS2, THBS1, TGFBR1, SERPINE1, SERPINF1, TGFB2, TIMP2, VEGFC, IFNA1, TNF, CXCL10, NOS3, IGF1, and MMP14 were downregulated in the specimens from the patients who had higher pulmonary vascular resistance values, whereas some genes, including PDGFA, showed upregulation that was statistically nonsignificant in the same group.

Conclusions

These results can lead to the development of new markers that could predict adverse outcomes of patients with CTEPH. Identification of new markers that are related to worse outcomes would enable screening patients for early diagnosis and treatment.

Angiopoietin 2 and hsCRP are associated with pulmonary hemodynamics and long-term mortality respectively in CTEPH-Results from a prospective discovery and validation biomarker study

INTRODUCTION

Chronic thromboembolic pulmonary hypertension (CTEPH) is an underdiagnosed disease of uncertain etiology. Altered endothelial homeostasis, defective angiogenesis and inflammation are implicated. Angiopoietin 2 (Ang2) impairs acute thrombus resolution and is associated with vasculopathy in idiopathic pulmonary arterial hypertension.

METHODS

We assessed circulating proteins associated with these processes in serum from patients with CTEPH (n = 71) before and after pulmonary endarterectomy (PEA), chronic thromboembolic pulmonary disease without pulmonary hypertension (CTEPD, n = 9) and healthy controls (n = 20) using Luminex multiplex arrays. Comparisons between groups were made using multivariable rank regression models. Ang2 and high-sensitivity C-reactive protein (hsCRP) were measured in a larger validation dataset (CTEPH = 277, CTEPD = 26). Cox proportional hazards models were used to identify markers predictive of survival.

RESULTS

In CTEPH patients, Ang2, interleukin (IL) 8, tumor necrosis factor α, and hsCRP were elevated compared to controls, while vascular endothelial growth factor (VEGF) c was lower (p < 0.05). Ang2 fell post-PEA (p < 0.05) and was associated with both pre- and post-PEA pulmonary hemodynamic variables and functional assessments (p < 0.05). In the validation dataset, Ang2 was significantly higher in CTEPH compared to CTEPD. Pre-operative hsCRP was an independent predictor of mortality.

CONCLUSIONS

We hypothesize that CTEPH patients have significant distal micro-vasculopathy and consequently high circulating Ang2. Patients with CTEPD without pulmonary hypertension have no discernible distal micro-vasculopathy and therefore have low circulating Ang2. This suggests Ang2 may be critical to CTEPH disease pathogenesis (impaired thrombus organization and disease severity).

Effect of hepatocyte growth factor on mice with hypoxic pulmonary arterial hypertension: a preliminary study

OBJECTIVES

To study the association between hepatocyte growth factor (HGF) and treatment response in mice with hypoxic pulmonary arterial hypertension (HPAH) and the possibility of HGF as a new targeted drug for HPAH.

METHODS

After successful modeling, the HPAH model mice were randomly divided into two groups: HPAH group and HGF treatment group (tail vein injection of recombinant mouse HGF 1 mg/kg), with 10 mice in each group. Ten normal mice were used as the control group. After 5 weeks, echocardiography was used to measure tricuspid peak velocity, right ventricular systolic pressure, right ventricular hypertrophy index, and right ventricular/body weight ratio; the Griess method was used to measure the content of nitric oxide in serum; ELISA was used to measure the serum level of endothelin-1; transmission electron microscopy was used to observe changes in the ultrastructure of pulmonary artery.

RESULTS

Compared with the HGF treatment and normal control groups, the HPAH group had significantly higher tricuspid peak velocity, right ventricular systolic pressure, right ventricular hypertrophy index, and right ventricular/body weight ratio (P<0.05). The transmission electron microscopy showed that the HPAH group had massive destruction of vascular endothelial cells and disordered arrangement of the elastic membrane of arteriolar intima with rupture and loss. The structure of vascular endothelial cells was almost complete and the structure of arterial intima elastic membrane was almost normal in the HGF treatment group. Compared with the normal control and HGF treatment groups, the HPAH group had significantly higher serum levels of nitric oxide and endothelin-1 (P<0.05).

CONCLUSIONS

Increasing serum HGF level can alleviate the impact of HPAH on the cardiovascular system of mice, possibly by repairing endothelial cell injury, improving vascular remodeling, and restoring the normal vasomotor function of pulmonary vessels.

Derivation and characterisation of endothelial cells from patients with chronic thromboembolic pulmonary hypertension

Pulmonary endarterectomy (PEA) resected material offers a unique opportunity to develop an in vitro endothelial cell model of chronic thromboembolic pulmonary hypertension (CTEPH). We aimed to comprehensively analyze the endothelial function, molecular signature, and mitochondrial profile of CTEPH-derived endothelial cells to better understand the pathophysiological mechanisms of endothelial dysfunction behind CTEPH, and to identify potential novel targets for the prevention and treatment of the disease. Isolated cells from specimens obtained at PEA (CTEPH-EC), were characterized based on morphology, phenotype, and functional analyses (in vitro and in vivo tubule formation, proliferation, apoptosis, and migration). Mitochondrial content, morphology, and dynamics, as well as high-resolution respirometry and oxidative stress, were also studied. CTEPH-EC displayed a hyperproliferative phenotype with an increase expression of adhesion molecules and a decreased apoptosis, eNOS activity, migration capacity and reduced angiogenic capacity in vitro and in vivo compared to healthy endothelial cells. CTEPH-EC presented altered mitochondrial dynamics, increased mitochondrial respiration and an unbalanced production of reactive oxygen species and antioxidants. Our study is the foremost comprehensive investigation of CTEPH-EC. Modulation of redox, mitochondrial homeostasis and adhesion molecule overexpression arise as novel targets and biomarkers in CTEPH.

Chronic Thromboembolic Pulmonary Hypertension: the Bench

PURPOSE OF REVIEW

Chronic thromboembolic pulmonary hypertension (CTEPH) is an uncommon complication of acute pulmonary embolism (PE), in which the red, platelet-rich thrombus does not resolve but forms into an organized yellow, fibrotic scar-like obstruction in the pulmonary vasculature. Here we review the pathobiology of CTEPH.

RECENT FINDINGS

Our current knowledge has predominantly been informed by studies of human samples and animal models that are inherently limited in their ability to recapitulate all aspects of the disease. These studies have identified alterations in platelet biology and inflammation in the formation of a scar-like thrombus that comprised endothelial cells, myofibroblasts, and immune cells, along with a small vessel pulmonary arterial hypertension-like vasculopathy. The development of CTEPH-specific therapies is currently hindered by a limited knowledge of its pathobiology. The development of new CTEPH medical therapies will require new insights into its pathobiology that bridge the gap from bench to bedside.

Endothelial Dysfunction in Pulmonary Hypertension: Cause or Consequence?

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.

Activated Endothelial TGFβ1 Signaling Promotes Venous Thrombus Nonresolution in Mice Via Endothelin-1: Potential Role for Chronic Thromboembolic Pulmonary Hypertension

RATIONALE

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by defective thrombus resolution, pulmonary artery obstruction, and vasculopathy. TGFβ (transforming growth factor-β) signaling mutations have been implicated in pulmonary arterial hypertension, whereas the role of TGFβ in the pathophysiology of CTEPH is unknown.

OBJECTIVE

To determine whether defective TGFβ signaling in endothelial cells contributes to thrombus nonresolution and fibrosis.

METHODS AND RESULTS

Venous thrombosis was induced by inferior vena cava ligation in mice with genetic deletion of TGFβ1 in platelets (Plt.TGFβ-KO) or TGFβ type II receptors in endothelial cells (End.TGFβRII-KO). Pulmonary endarterectomy specimens from CTEPH patients were analyzed using immunohistochemistry. Primary human and mouse endothelial cells were studied using confocal microscopy, quantitative polymerase chain reaction, and Western blot. Absence of TGFβ1 in platelets did not alter platelet number or function but was associated with faster venous thrombus resolution, whereas endothelial TGFβRII deletion resulted in larger, more fibrotic and higher vascularized venous thrombi. Increased circulating active TGFβ1 levels, endothelial TGFβRI/ALK1 (activin receptor-like kinase), and TGFβRI/ALK5 expression were detected in End.TGFβRII-KO mice, and activated TGFβ signaling was present in vessel-rich areas of CTEPH specimens. CTEPH-endothelial cells and murine endothelial cells lacking TGFβRII simultaneously expressed endothelial and mesenchymal markers and transcription factors regulating endothelial-to-mesenchymal transition, similar to TGFβ1-stimulated endothelial cells. Mechanistically, increased endothelin-1 levels were detected in TGFβRII-KO endothelial cells, murine venous thrombi, or endarterectomy specimens and plasma of CTEPH patients, and endothelin-1 overexpression was prevented by inhibition of ALK5, and to a lesser extent of ALK1. ALK5 inhibition and endothelin receptor antagonization inhibited mesenchymal lineage conversion in TGFβ1-exposed human and murine endothelial cells and improved venous thrombus resolution and pulmonary vaso-occlusions in End.TGFβRII-KO mice.

CONCLUSIONS

Endothelial TGFβ1 signaling via type I receptors and endothelin-1 contribute to mesenchymal lineage transition and thrombofibrosis, which were prevented by blocking endothelin receptors. Our findings may have relevant implications for the prevention and management of CTEPH.