Pathobiology of pulmonary arterial hypertension: understanding the roads less travelled

Female Fibroblast Activation Is Estrogen-Mediated in Sex-Specific 3D-Bioprinted Pulmonary Artery Adventitia Models

Pulmonary arterial hypertension (PAH) is a form of pulmonary vascular disease characterized by scarring of the small blood vessels that results in reduced blood flow and increased blood pressure in the lungs. Over time, this increase in blood pressure causes damage to the heart. Idiopathic (IPAH) impacts male and female patients differently, with female patients showing a higher disease susceptibility (4:1 female-to-male ratio) but experiencing longer survival rates postdiagnosis compared to male patients. This complex sex dimorphism is known as the estrogen paradox. Prior studies suggest that estrogen signaling may be pathologic in the pulmonary vasculature and protective in the heart, yet the mechanisms underlying these sex differences in IPAH remain unclear. Many previous studies of PAH relied on male cells or cells of undisclosed origin for in vitro modeling. Here, we present a dynamic, three-dimensional (3D)-bioprinted model incorporating cells and circulating sex hormones from female patients to specifically study how female patients respond to changes in microenvironmental stiffness and sex hormone signaling on the cellular level. Poly(ethylene glycol)-α methacrylate (PEGαMA)-based hydrogels containing female human pulmonary artery adventitia fibroblasts (hPAAFs) from IPAH or control donors were 3D bioprinted to mimic pulmonary artery adventitia. These biomaterials were initially soft, like healthy blood vessels, and then stiffened using light to mimic vessel scarring in PAH. These 3D-bioprinted models showed that stiffening the microenvironment around female IPAH hPAAFs led to hPAAF activation. On both the protein and gene-expression levels, cellular activation markers significantly increased in stiffened samples and were highest in IPAH patient-derived cells. Treatment with a selective estrogen receptor modulator, which is currently in clinical trials for IPAH treatment, reduced the expression of hPAAF activation markers, demonstrating that hPAAF activation is one pathologic response mediated by estrogen signaling in the vasculature. These results showed the utility of sex-specific, 3D-bioprinted pulmonary artery adventitia models for preclinical drug discovery and validation.

Historical milestones and future horizons: exploring the diagnosis and treatment evolution of the pulmonary arterial hypertension in adults

INTRODUCTION

Pulmonary hypertension is a life-threatening condition characterized by elevated mean pulmonary arterial pressure and vascular resistance. Significant advances in diagnosis and treatment have been achieved over the 20th and 21st centuries, yet challenges remain in improving long-term outcomes.

AREAS COVERED

This review discusses the historical milestones in understanding and pharmacotherapy of the pulmonary arterial hypertension (PAH). A comprehensive literature search was conducted to explore the earliest reports of each approved medication for pulmonary hypertension, along with historical papers detailing the pathophysiological and diagnostic development. Additionally, the search aimed to identify novel therapeutic strategies, including repositioned drugs and emerging targets.

EXPERT OPINION

While current therapies, such as prostacyclin analogs and PDE5 inhibitors, improve functional capacity and hemodynamics, they face limitations, including costs, administration, and a predominantly vasodilatory approach. Additionally, the limitations of current clinical trial designs for rare diseases like pulmonary arterial hypertension hinder the evaluation of potentially effective drugs. These challenges underscore the urgent need for translational research to optimize trial methodologies, accelerating the development of new therapies. Innovative approaches, such as drug repositioning and the exploration of novel molecular targets, are critical to overcoming these barriers and ensuring timely, effective, and affordable treatment options for patients with PAH.

Female fibroblast activation is estrogen-mediated in sex-specific 3D-bioprinted pulmonary artery adventitia models

Pulmonary arterial hypertension (PAH) impacts male and female patients in different ways. Female patients exhibit a greater susceptibility to disease (4:1 female-to-male ratio) but live longer after diagnosis than male patients. This complex sexual dimorphism is known as the estrogen paradox. Prior studies suggest that estrogen signaling may be pathologic in the pulmonary vasculature and protective in the heart, yet the mechanisms underlying these sex-differences in PAH remain unclear. PAH is a form of a pulmonary vascular disease that results in scarring of the small blood vessels, leading to impaired blood flow and increased blood pressure. Over time, this increase in blood pressure causes damage to the heart. Many previous studies of PAH relied on male cells or cells of undisclosed origin for in vitro modeling. Here we present a dynamic, 3D-bioprinted model that incorporates cells and circulating sex hormones from female patients to specifically study how female patients respond to changes in microenvironmental stiffness and sex hormone signaling. Poly(ethylene glycol)-alpha methacrylate (PEGαMA)-based hydrogels containing female human pulmonary artery adventitia fibroblasts (hPAAFs) from idiopathic PAH (IPAH) or control donors were 3D bioprinted to mimic pulmonary artery adventitia. These biomaterials were initially soft, like healthy blood vessels, and then stiffened using light to mimic vessel scarring in PAH. These 3D-bioprinted models showed that stiffening the microenvironment around female IPAH hPAAFs led to hPAAF activation. On both the protein and gene-expression levels, cellular activation markers significantly increased in stiffened samples and were highest in IPAH patient-derived cells. Treatment with a selective estrogen receptor modulator reduced expression hPAAF activation markers, demonstrating that hPAAF activation is a one pathologic response mediated by estrogen signaling in the vasculature, validating that drugs currently in clinical trials could be evaluated in sex-specific 3D-bioprinted pulmonary artery adventitia models.

Role of Forkhead box F1 in the Pathobiology of Pulmonary Arterial Hypertension

Rationale

Approximately 80% of patients with non-familial pulmonary arterial hypertension (PAH) lack identifiable pathogenic genetic variants. While most genetic studies of PAH have focused on predicted loss-of-function variants, recent approaches have identified ultra-rare missense variants associated with the disease. FOXF1 encodes a highly conserved transcription factor, essential for angiogenesis and vasculogenesis in human and mouse lungs.

Objectives

We identified a rare FOXF1 missense coding variant in two unrelated probands with PAH. FOXF1 is an evolutionarily conserved transcription factor required for lung vascular development and vascular integrity. Our aims were to determine the frequency of FOXF1 variants in larger PAH cohorts compared to the general population, study FOXF1 expression in explanted lung tissue from PAH patients versus control (failed-donor) lungs, and define potential downstream targets linked to PAH development.

Methods

Three independent, international, multicenter cohorts were analyzed to evaluate the frequency of FOXF1 rare variants. Various composite prediction models assessed the deleteriousness of individual variants. Bulk RNA sequencing datasets from human explanted lung tissues were compared to failed-donor controls to determine FOXF1 expression. Bioinformatic tools identified putative FOXF1 binding targets, which were orthogonally validated using mouse ChIP-seq datasets.

Measurements and Main Results

Seven novel or ultra-rare missense coding variants were identified across three patient cohorts in different regions of the FOXF1 gene, including the DNA binding domain. FOXF1 expression was dysregulated in PAH lungs, correlating with disease severity. Histological analysis showed heterogeneous FOXF1 expression, with the lowest levels in phenotypically abnormal endothelial cells within complex vascular lesions in PAH samples. A hybrid bioinformatic approach identified FOXF1 downstream targets potentially involved in PAH pathogenesis, including BMPR2 .

Conclusions

Large genomic and transcriptomic datasets suggest that decreased FOXF1 expression or predicted dysfunction is associated with PAH.

Phenotypes in pulmonary hypertension

The clinical classification of pulmonary hypertension (PH) has guided diagnosis and treatment of patients with PH for several decades. Discoveries relating to underlying mechanisms, pathobiology and responses to treatments for PH have informed the evolution in this clinical classification to describe the heterogeneity in PH phenotypes. In more recent years, advances in imaging, computational science and multi-omic approaches have yielded new insights into potential phenotypes and sub-phenotypes within the existing clinical classification. Identification of novel phenotypes in pulmonary arterial hypertension (PAH) with unique molecular profiles, for example, could lead to new precision therapies. Recent phenotyping studies have also identified groups of patients with PAH that more closely resemble patients with left heart disease (group 2 PH) and lung disease (group 3 PH), which has important prognostic and therapeutic implications. Within group 2 and group 3 PH, novel phenotypes have emerged that reflect a persistent and severe pulmonary vasculopathy that is associated with worse prognosis but still distinct from PAH. In group 4 PH (chronic thromboembolic pulmonary disease) and sarcoidosis (group 5 PH), the current approach to patient phenotyping integrates clinical, haemodynamic and imaging characteristics to guide treatment but applications of multi-omic approaches to sub-phenotyping in these areas are sparse. The next iterations of the PH clinical classification are likely to reflect several emerging PH phenotypes and improve the next generation of prognostication tools and clinical trial design, and improve treatment selection in clinical practice.

Emerging role of BMPs/BMPR2 signaling pathway in treatment for pulmonary fibrosis

Pulmonary fibrosis is a fatal and chronic lung disease that is characterized by accumulation of thickened scar in the lungs and impairment of gas exchange. The cases with unknown etiology are referred as idiopathic pulmonary fibrosis (IPF). There are currently no effective therapeutics to cure the disease; thus, the investigation of the pathogenesis of IPF is of great importance. Recent studies on bone morphogenic proteins (BMPs) and their receptors have indicated that reduction of BMP signaling in lungs may play a significant role in the development of lung fibrosis. BMPs are members of TGF-β superfamily, and they have been shown to play an anti-fibrotic role in combating TGF-β-mediated pathways. The impact of BMP receptors, in particular BMPR2, on pulmonary fibrosis is growing attraction to researchers. Previous studies on BMPR2 have often focused on pulmonary arterial hypertension (PAH). Given the strong clinical association between PAH and lung fibrosis, understanding BMPs/BMPR2-mediated signaling pathway is important for development of therapeutic strategies to treat IPF. In this review, we comprehensively review recent studies regarding the biological functions of BMPs and their receptors in lungs, especially focusing on their roles in the pathogenesis of pulmonary fibrosis and fibrosis resolution.

Non-invasive imaging techniques for early diagnosis of bilateral cardiac dysfunction in pulmonary hypertension: current crests, future peaks

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease that eventually leads to heart failure (HF) and subsequent fatality if left untreated. Right ventricular (RV) function has proven prognostic values in patients with a variety of heart diseases including PAH. PAH is predominantly a right heart disease; however, given the nature of the continuous circulatory system and the presence of shared septum and pericardial constraints, the interdependence of the right and left ventricles is a factor that requires consideration. Accurate and timely assessment of ventricular function is very important in the management of patients with PAH for disease outcomes and prognosis. Non-invasive modalities such as cardiac magnetic resonance (CMR) and echocardiography (two-dimensional and three-dimensional), and nuclear medicine, positron emission tomography (PET) play a crucial role in the assessment of ventricular function and disease prognosis. Each modality has its own strengths and limitations, hence this review article sheds light on (i) ventricular dysfunction in patients with PAH and RV-LV interdependence in such patients, (ii) the strengths and limitations of all available modalities and parameters for the early assessment of ventricular function, as well as their prognostic value, and (iii) lastly, the challenges faced and the potential future advancement in these modalities for accurate and early diagnosis of ventricular function in PAH.

Charting the cellular landscape of pulmonary arterial hypertension through single-cell omics

This review examines how single-cell omics technologies, particularly single-cell RNA sequencing (scRNAseq), enhance our understanding of pulmonary arterial hypertension (PAH). PAH is a multifaceted disorder marked by pulmonary vascular remodeling, leading to high morbidity and mortality. The cellular pathobiology of this heterogeneous disease, involving various vascular and non-vascular cell types, is not fully understood. Traditional PAH studies have struggled to resolve the complexity of pathogenic cell populations. scRNAseq offers a refined perspective by detailing cellular diversity within PAH, identifying unique cell subsets, gene networks, and molecular pathways that drive the disease. We discuss significant findings from recent literature, summarizing how scRNAseq has shifted our understanding of PAH in human, rat, and mouse models. This review highlights the insights gained into cellular phenotypes, gene expression patterns, and novel molecular targets, and contemplates the challenges and prospective paths for research. We propose ways in which single-cell omics could inform future research and translational efforts to combat PAH.

Pulmonary arterial hypertension: Sex matters

Pulmonary arterial hypertension (PAH) is a complex disease of multifactorial origin. While registries have demonstrated that women are more susceptible to the disease, females with PAH have superior right ventricle (RV) function and a better prognosis than their male counterparts, a phenomenon referred to as the 'estrogen paradox'. Numerous pre-clinical studies have investigated the involvement of sex hormones in PAH pathobiology, often with conflicting results. However, recent advances suggest that abnormal estrogen synthesis, metabolism and signalling underpin the sexual dimorphism of this disease. Other sex hormones, such as progesterone, testosterone and dehydroepiandrosterone may also play a role. Several non-hormonal factor including sex chromosomes and epigenetics have also been implicated. Though the underlying pathophysiological mechanisms are complex, several compounds that modulate sex hormones levels and signalling are under investigation in PAH patients. Further elucidation of the estrogen paradox will set the stage for the identification of additional therapeutic targets for this disease.

Pharmacological Agents and Potential New Therapies in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by an imbalance between vasoactive mediators, which causes vascular remodeling, increased pulmonary vascular resistance, and right ventricular overload, ultimately leading to heart failure and death. A metabolic theory has been suggested to explain the pathophysiology of PAH whereby abnormalities in mitochondrial biogenesis can trigger a hyperproliferative and apoptosis-resistant phenotype in cardiopulmonary and malignant cells, leading to mitochondrial dysfunction, which in turn causes the Warburg effect. This can culminate in the mitophagy of pulmonary vessels and cardiomyocytes. The present narrative review focuses on the pathophysiology of PAH, the pharmacological agents currently available for its treatment, and promising and challenging areas of therapeutic investigation.

NAMPT mediates PDGF-induced pulmonary arterial smooth muscle cell proliferation by TLR4/NF-κB/PLK4 signaling pathway

Nicotinamide phosphoribosyltransferase (NAMPT), a pleiotropic protein, promotes the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), which is associated with the genesis and progression of pulmonary arterial hypertension (PAH). NAMPT is highly increased in PAH patient's plasma and highly relevant to PAH severity. The mRNA and protein levels of NAMPT are elevated in PAH animal models. However, the underlying molecular mechanisms how NAMPT mediated platelet-derived growth factor (PDGF)-induced PASMCs proliferation are still unclear. The present study aimed to address these issues. Primary cultured PASMCs were attained from male Sprague-Dawley (SD) rats. Western blotting, RT-PCR, ELISA, cell transfection, Cell Counting Kit-8 (CCK-8) and EdU incorporation assays were used in the experiments. We showed that PDGF upregulated NAMPT expression through the activation of signal transducers and activators of transcription 5 (STAT5), and elevated extracellular NAMPT further promoted the activation of NF-κB through Toll-like receptor 4 (TLR4), which ultimately upregulated polo-like kinase 4 (PLK4) expression leading to PASMCs proliferation. Knockdown of STAT5, NAMPT or PLK4, and inhibition of TLR4 or NF-κB suppressed PDGF-induced PASMCs proliferation. Our study suggests that NAMPT plays an essential role in PDGF-induced PASMCs proliferation via TLR4/NF-κB/PLK4 pathway, suggesting that targeting NAMPT might be valuable in ameliorating pulmonary arterial hypertension.

Severity of precapillary pulmonary hypertension: Predictive factor

BACKGROUND AND OBJECTIVES

Patients with pulmonary arterial hypertension (PAH) require risk assessments for prognosis and appropriate therapy. These assessments need to be improved by incorporating clinical and laboratory data such as the analysis of the right ventricle. We aim to establish echocardiographic morphometric data of the right ventricle and its relationship with the left ventricle, to estimate the hemodynamic severity of precapillary pulmonary hypertension (PHprecapillary).

METHODS

This cohort, prospective, observational, and cross-sectional study included 41 consecutive patients with PHprecapillary using echocardiographic study and cardiac catheterization.

RESULTS

Patients' mean age was 44.0±16.4 years, and 37 were women (90.2%). Idiopathic PAH was diagnosed in 18 patients (43.9%). The World Health Organization/New York Association functional class was III or IV in 31 patients (75.6%). The ratio of the right to left ventricles (RV/LV) echocardiographic diastolic diameters was associated with pulmonary arterial pressures in cardiac catheterization, with the best cutoff per receiver operating characteristic curve being 0.8 for systolic pressure (sensitivity 90.0%, specificity 78.3%, area under the curve [AUC] 0.882) and mean pressure (sensitivity 60.0%, specificity 95.7%, AUC 0.823). Spearman's correlation (R) of RV/LV echocardiographic ratio and the hemodynamic variables was significant for systolic pressure (R = 0.7015, p < 0.0001), mean pressure (R = 0.6332, p < 0.0001), transpulmonary pressure gradient (R = 0.6524, p < 0.0001), pulmonary vascular resistance (R = 0.6076, p = 0.0021), and pulmonary vascular resistance index (R = 0.6229, p = 0.0014).

CONCLUSION

The ratio of RV/LV echocardiographic diastolic diameters contribute to the estimates the hemodynamic severity of precapillary pulmonary hypertension. The best cutoff for this assessment was RV/LV of 0.8.

Seven Additional Patients with SOX17 Related Pulmonary Arterial Hypertension and Review of the Literature

Pulmonary arterial hypertension (PAH) is an infrequent disorder characterized by high blood pressure in the pulmonary arteries. It may lead to premature death or the requirement for lung and/or heart transplantation. Genetics plays an important and increasing role in the diagnosis of PAH. Here, we report seven additional patients with variants in SOX17 and a review of sixty previously described patients in the literature. Patients described in this study suffered with additional conditions including large septal defects, as described by other groups. Collectively, sixty-seven PAH patients have been reported so far with variants in SOX17, including missense and loss-of-function (LoF) variants. The majority of the loss-of-function variants found in SOX17 were detected in the last exon of the gene. Meanwhile, most missense variants were located within exon one, suggesting a probable tolerated change at the amino terminal part of the protein. In addition, we reported two idiopathic PAH patients presenting with the same variant previously detected in five patients by other studies, suggesting a possible hot spot. Research conducted on PAH associated with congenital heart disease (CHD) indicated that variants in SOX17 might be particularly prevalent in this subgroup, as two out of our seven additional patients presented with CHD. Further research is still necessary to clarify the precise association between the biological pathway of SOX17 and the development of PAH.

Emerging biologics for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare pulmonary vascular disorder, wherein mean systemic arterial pressure (mPAP) becomes abnormally high because of aberrant changes in various proliferative and inflammatory signalling pathways of pulmonary arterial cells. Currently used anti-PAH drugs chiefly target the vasodilatory and vasoconstrictive pathways. However, an imbalance between bone morphogenetic protein receptor type II (BMPRII) and transforming growth factor beta (TGF-β) pathways is also implicated in PAH predisposition and pathogenesis. Compared to currently used PAH drugs, various biologics have shown promise as PAH therapeutics that elicit their therapeutic actions akin to endogenous proteins. Biologics that have thus far been explored as PAH therapeutics include monoclonal antibodies, recombinant proteins, engineered cells, and nucleic acids. Because of their similarity with naturally occurring proteins and high binding affinity, biologics are more potent and effective and produce fewer side effects when compared with small molecule drugs. However, biologics also suffer from the limitations of producing immunogenic adverse effects. This review describes various emerging and promising biologics targeting the proliferative/apoptotic and vasodilatory pathways involved in PAH pathogenesis. Here, we have discussed sotatercept, a TGF-β ligand trap, which is reported to reverse vascular remodelling and reduce PVR with an improved 6-minute walk distance (6-MWDT). We also elaborated on other biologics including BMP9 ligand and anti-gremlin1 antibody, anti-OPG antibody, and getagozumab monoclonal antibody and cell-based therapies. Overall, recent literature suggests that biologics hold excellent promise as a safe and effective alternative to currently used PAH therapeutics.

Novel Drugs for the Treatment of Pulmonary Arterial Hypertension: Where Are We Going?

Pulmonary arterial hypertension (PAH) is a progressive disease that despite advances in therapy is associated with a 7-year survival of approximately 50%. Several risk factors are associated with developing PAH, include methamphetamine use, scleroderma, human immunodeficiency virus, portal hypertension, and genetic predisposition. PAH can also be idiopathic. There are traditional pathways underlying the pathophysiology of PAH involving nitric oxide, prostacyclin, thromboxane A2, and endothelin-1, resulting in impaired vasodilation, enhanced vasoconstriction and proliferation in the pulmonary vasculature. Established PAH medications targets these pathways; however, this paper aims to discuss novel drugs for treating PAH by targeting new and alternative pathways.

Early selexipag initiation and long-term outcomes: insights from randomised controlled trials in pulmonary arterial hypertension

Further understanding of when to initiate therapies in pulmonary arterial hypertension (PAH) is important to improve long-term outcomes. Post hoc analyses of GRIPHON (NCT01106014) and exploratory analyses of TRITON (NCT02558231) suggested benefit of early selexipag initiation on long-term outcomes, despite no additional benefit versus initial double combination on haemodynamic and functional parameters in TRITON. Post hoc analyses investigated the effect of early selexipag initiation on disease progression and survival in a large, pooled PAH cohort. Data from newly diagnosed (≤6 months) PAH patients from GRIPHON and TRITON were pooled. Patients on active therapy with selexipag (pooled selexipag group) were compared with those on control therapy with placebo (pooled control group). Disease progression end-points were defined as per the individual studies. Hazard ratios (HR) and 95% CI for time to first disease progression event up to end of double-blind treatment (selexipag/placebo) +7 days and time to all-cause death up to end of study were estimated using Cox regression models. The pooled dataset comprised 649 patients, with 44% on double background therapy. Selexipag reduced the risk of disease progression by 52% versus control (HR: 0.48; 95% CI: 0.35-0.66). HR for risk of all-cause death was 0.70 (95% CI: 0.46-1.10) for the pooled selexipag versus control group. Sensitivity analyses accounting for the impact of PAH background therapy showed consistent results, confirming the appropriateness of data pooling. These post hoc, pooled analyses build on previous insights, further supporting selexipag use within 6 months of diagnosis, including as part of triple therapy, to delay disease progression.

CD39 in the development and progression of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating progressive disease characterised by pulmonary arterial vasoconstriction and vascular remodelling. Endothelial dysfunction has emerged as a contributing factor in the development of PAH. However, despite progress in the understanding of the pathophysiology of this disease, current therapies fail to impact upon long-term outcomes which remain poor in most patients. Recent observations have suggested the disturbances in the balance between ATP and adenosine may be integral to the vascular remodelling seen in PAH. CD39 is an enzyme important in regulating these nucleos(t)ides which may also provide a novel pathway to target for future therapies. This review summarises the role of adenosine signalling in the development and progression of PAH and highlights the therapeutic potential of CD39 for treatment of PAH.

Novel hub genes associated with pulmonary artery remodeling in pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening disease with complex pathogenesis. According to etiology, PH is divided into five major groups in clinical classification. However, pulmonary artery (PA) remodeling is their common feature, in addition to bone morphogenetic protein receptor type 2; it is elusive whether there are other novel common genes and similar underlying mechanisms. To identify novel common hub genes involved in PA remodeling at different PH groups, we analyzed mRNA-Seq data located in the general gene expression profile GSE130391 utilizing bioinformatics technology. This database contains PA samples from different PH groups of hospitalized patients with chronic thromboembolic pulmonary hypertension (CTEPH), idiopathic pulmonary artery hypertension (IPAH), and PA samples from organ donors without known pulmonary vascular diseases as control. We screened 22 hub genes that affect PA remodeling, most of which have not been reported in PH. We verified the top 10 common hub genes in hypoxia with Sugen-induced PAH rat models by qRT-PCR. The three upregulated candidate genes are WASF1, ARHGEF1 and RB1 and the seven downregulated candidate genes are IL1R1, RHOB, DAPK1, TNFAIP6, PKN1, PLOD2, and MYOF. WASF1, ARHGEF1, and RB1 were upregulated significantly in hypoxia with Sugen-induced PAH, while IL1R1, DAPK1, and TNFA1P6 were upregulated significantly in hypoxia with Sugen-induced PAH. The DEGs detected by mRNA-Seq in hospitalized patients with PH are different from those in animal models. This study will provide some novel target genes to further study PH mechanisms and treatment.

Strategizing Drug Therapies in Pulmonary Hypertension for Improved Outcomes

Pulmonary hypertension (PH) is characterized by a resting mean pulmonary artery pressure (PAP) of 20 mmHg or more and is a disease of multiple etiologies. Of the various types of PH, pulmonary arterial hypertension (PAH) is characterized by elevated resistance in the pulmonary arterial tree. It is a rare but deadly disease characterized by vascular remodeling of the distal pulmonary arteries. This paper focuses on PAH diagnosis and management including current and future treatment options. Over the last 15 years, our understanding of this progressive disease has expanded from the concept of vasoconstrictive/vasodilatory mismatch in the pulmonary arterioles to now a better appreciation of the role of genetic determinants, numerous cell signaling pathways, cell proliferation and apoptosis, fibrosis, thrombosis, and metabolic abnormalities. While knowledge of its pathophysiology has expanded, the majority of the treatments available today still modulate the same three vasodilatory pathways that have been targeted for over 30 years (endothelin, nitric oxide, and prostacyclin). While modifying these pathways may help improve symptoms and quality of life, none of these directly modify the underlying disease pathogenesis. However, there are now studies ongoing with new drugs that can prevent or reverse these underlying causes of PAH. This review discusses the evidence base for the current treatment algorithms for PAH, as well as discusses novel therapies in development.

Clinical value of lncRNA SOX2-OT in pulmonary arterial hypertension and its role in pulmonary artery smooth muscle cell proliferation, migration, apoptosis, and inflammatory

BACKGROUND

Non-coding RNA is confirmed to be involved in pulmonary arterial hypertension (PAH).

OBJECTIVES

This study investigated the clinical value and potential mechanisms of the long noncoding RNA (lncRNA) SRY-box transcription factor 2 overlapping transcript (SOX2-OT) in PAH.

METHODS

SOX2-OT levels were measured by quantitative real-time polymerase chain reaction (qRT-PCR) in serum of 82 patients with PAH and 76 healthy controls. Receiver operating characteristic (ROC) analysis was performed to assess the diagnostic value of SOX2-OT. Human pulmonary arterial smooth muscle cells (hPASMCs) were treated by hypoxia to construct PAH cell models. Proliferation, migration, apoptosis, and inflammatory cytokines levels of hPASMCs were examined by CCK-8, Transwell, flow cytometry, and ELISA assay. Dual-luciferase reporter gene assays were performed to verify the target relationships between miR-455-3p and SOX2-OT, as well as small ubiquitin-related modifier 1 (SUMO1).

RESULTS

Serum SOX2-OT was highly expressed in patients with PAH (P < 0.05). And elevated SOX2-OT levels significantly differentiated PAH patients from healthy controls, confirming high diagnostic feasibility. What's more, SOX2-OT was increased in hypoxia-induced hPASMCs in a time-dependent manner. Silencing SOX2-OT could reverse hypoxia-induced proliferation, migration, anti-apoptosis, and inflammation of hPASMCs (P < 0.05). However, rescue experiments showed that this reversal effect of silencing SOX2-OT was attenuated by suppressed miR-455-3p, which was presumably achieved by SUMO1 (P < 0.05).

CONCLUSIONS

Elevated SOX2-OT is a feasible diagnostic marker for PAH, and its silencing may attenuated hypoxia-induced hPASMCs proliferation, migration, anti-apoptosis, and inflammation by modulating the miR-455-3p/SUMO1 axis, preventing vascular remodeling and PAH progression. Our research provided new insights for PAH treatment.

Salt-inducible kinases: new players in pulmonary arterial hypertension?

Salt-inducible kinases (SIKs) are serine/threonine kinases belonging to the AMP-activated protein kinase (AMPK) family. Accumulating evidence indicates that SIKs phosphorylate multiple targets, including histone deacetylases (HDACs) and cAMP response element-binding protein (CREB)-regulated transcriptional coactivators (CRTCs), to coordinate signaling pathways implicated in metabolism, cell growth, proliferation, apoptosis, and inflammation. These pathways downstream of SIKs are altered not only in pathologies like cancer, systemic hypertension, and inflammatory diseases, but also in pulmonary arterial hypertension (PAH), a multifactorial disease characterized by pulmonary vasoconstriction, inflammation and remodeling of pulmonary arteries owing to endothelial dysfunction and aberrant proliferation of smooth muscle cells (SMCs). In this opinion article, we present evidence of SIKs as modulators of key signaling pathways involved in PAH pathophysiology and discuss the potential of SIKs as therapeutic targets for PAH, emphasizing the need for deeper molecular insights on PAH.

Description of Two New Cases of AQP1 Related Pulmonary Arterial Hypertension and Review of the Literature

Pulmonary arterial hypertension (PAH) is a severe clinical condition characterized by an increase in mean pulmonary artery pressure, which leads to a right ventricular hypertrophy and potentially heart failure and death. In the last several years, many genes have been associated with PAH, particularly in idiopathic and heritable forms but also in associated forms. Here we described the identification of two unrelated families in which the AQP1 variant was found from a cohort of 300 patients. The variants were identified by whole exome sequencing (WES). In the first family, the variant was detected in three affected members from a hereditary PAH, and in the second family the proband had PAH associated with scleroderma. In addition, we have reviewed all cases published in the literature thus far of patients with PAH and AQP1 variants. Functional studies have led to some contradictory conclusions, and the evidence of the relationship of AQP1 and PAH is still limited. However, we describe two further families with PAH and variants in AQP1, expanding both the number of cases and the clinically associated phenotype. We provide further evidence of the association of AQP1 and the development of hereditary and associated forms of PAH.

Reduction of BMPR2 mRNA Expression in Peripheral Blood of Pulmonary Arterial Hypertension Patients: A Marker for Disease Severity?

Pulmonary arterial hypertension (PAH) can be caused by pathogenic variants in the gene bone morphogenetic protein receptor 2 (BMPR2). While BMPR2 protein expression levels are known to be reduced in the lung tissue of heritable PAH (HPAH) patients, a systematic study evaluating expression in more easily accessible blood samples and its clinical relevance is lacking. Thus, we analyzed the BMPR2 mRNA expression in idiopathic/HPAH patients and healthy controls in blood by quantitative polymerase chain reaction and protein expression by enzyme-linked immunosorbent assay. Clinical parameters included right heart catherization, echocardiography, six-minute walking test and laboratory tests. BMPR2 variant-carriers (n = 23) showed significantly lower BMPR2 mRNA expression in comparison to non-carriers (n = 56) and healthy controls (n = 30; p < 0.0001). No difference in BMPR2 protein expression was detected. Lower BMPR2 mRNA expression correlated significantly with greater systolic pulmonary artery pressure and pulmonary vascular resistance. Higher BMPR2 mRNA expression correlated with greater glomerular filtration rate, cardiac index and six-minute walking distance. We demonstrated the feasibility to assess BMPR2 expression in blood and, for the first time, that BMPR2 mRNA expression levels are significantly reduced in variant carriers and correlated with clinical parameters. Further studies may evaluate the usefulness of BMPR2 mRNA expression in blood as a new marker for disease severity.

An Overview of Different Techniques for Improving the Treatment of Pulmonary Hypertension Secondary in Systemic Sclerosis Patients

In systemic sclerosis (SSc) mortality is mainly linked to lung involvement which is characterized by interstitial lung disease (ILD) and pulmonary hypertension (PH). In SSc, PH may be due to different etiologies, including ILD, chronic thromboembolic disease, pulmonary veno-occlusive disease, and pulmonary arterial hypertension (PAH). The main tool to screen PAH is transthoracic echocardiography (TTE), which has a sensitivity of 90%, even if definitive diagnosis should be confirmed by right heart catheterization (RHC). The radiological evaluation (i.e., HRTC) plays an important role in defining the possible causes and in monitoring the evolution of lung damage. For PAH, identifying individuals who have borderline elevation of pulmonary arterial pressure needs to be appropriately managed and followed. In the past few years, the strategy for the management of PAH has significantly evolved and new trials are underway to test other therapies. This review provides an overview of the tools to evaluate PAH in SSc patients and on treatment options for these patients.

hsa_circWDR37_016 Regulates Hypoxia-Induced Proliferation of Pulmonary Arterial Smooth Muscle Cells

Pulmonary arterial hypertension (PAH) is characterized by abnormal remodeling of pulmonary vessel walls caused by excessive pulmonary arterial smooth muscle cell (PASMC) proliferation. Our previous clinical studies have demonstrated the importance of the downregulated circRNA in PAH. However, the role of upregulated circRNAs is still elusive. Here, we identified the upregulated circRNA in PAH patients, hsa_circWDR37_016 (circWDR37), as a key regulator of hypoxic proliferative disorder of pulmonary arterial smooth muscle cells (PASMCs). Quantitative real-time PCR (qRT-PCR) analysis validated that exposure to hypoxia markedly increased the circWDR37 level in cultured human PASMCs. As evidenced by flow cytometry, 5-ethynyl-2′-deoxyuridine (EdU) incorporation, wound healing, and Tunel assay, silencing of endogenous circWDR37 attenuated proliferation and cell-cycle progression in hypoxia-exposed human PASMCs in vitro. Furthermore, bioinformatics and Luciferase assay showed that circWDR37 directly sponged hsa-miR-138-5p (miR-138) and was involved in the immunoregulatory and inflammatory processes of PAH. Together, these studies suggested new insights into circRNA regulated the pathology of PAH, providing a new potential therapeutic target for PAH treatment.

The MFF-SIRT1/3 axis, regulated by miR-340-5p, restores mitochondrial homeostasis of hypoxia-induced pulmonary artery smooth muscle cells

Mitochondrial dynamics and quality control play a central role in the maintenance of the proliferation-apoptosis balance, which is closely related to the progression of pulmonary arterial hypertension (PAH). However, the exact mechanism of this balance remains unknown. Pulmonary artery smooth muscle cells (PASMCs) were cultured in hypoxia condition for constructing a PAH model in vitro. The expression of genes and proteins were determined by qRT-PCR and western bolt assays. Cell proliferation-apoptosis balance were tested by MTT, EdU and TUNEL assays. The mitochondrial functions were assessed by flow cytometry, JC-1, Mito tracker red staining, and corresponding kits. Besides, the molecular interaction was validated by dual-luciferase reporter assay. MFF was overexpressed in hypoxia-treated PAMSCs. Knockdown of MFF significantly repressed the excessive proliferation but enhanced cell apoptosis in hypoxia-treated PAMSCs. Moreover, MFF silencing improved mitochondrial function of hypoxia-treated PAMSCs by increasing ATP production and decreasing ROS release and mitochondrial fission. Mechanistically, MFF was a directly target of miR-340-5p, and could negatively regulate SIRT1/3 expression. Subsequently, functional rescue assays showed that the biological effects of MFF in hypoxia-treated PAMSCs were negatively regulated by miR-340-5p and depended on the regulation on SIRT1/3 pathway. These results provided evidences that miR-340-5p regulated MFF-SIRT1/3 axis to improve mitochondrial homeostasis and proliferation-apoptosis imbalance of hypoxia-treated PAMSCs, which provided a theoretical basis for the prevention and treatment of PAH.

Upregulation of Aquaporin 1 Mediates Increased Migration and Proliferation in Pulmonary Vascular Cells From the Rat SU5416/Hypoxia Model of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disorder characterized by exuberant vascular remodeling leading to elevated pulmonary arterial pressure, maladaptive right ventricular remodeling, and eventual death. The factors controlling pulmonary arterial smooth muscle cell (PASMC) and endothelial cell hyperplasia and migration, hallmark features of the vascular remodeling observed in PAH, remain poorly understood. We previously demonstrated that hypoxia upregulates the expression of aquaporin 1 (AQP1), a water channel, in PASMCs, and that this upregulation was required for hypoxia-induced migration and proliferation. However, whether the same is true in a model of severe PAH and in pulmonary microvascular endothelial cells (MVECs) is unknown. In this study, we used the SU5416 plus hypoxia (SuHx) rat model of severe pulmonary hypertension, which mimics many of the features of human PAH, to determine whether AQP1 levels were altered in PASMCs and MVECs and contributed to a hyperproliferative/hypermigratory phenotype. Rats received a single injection of SU5416 (20 mg/kg) and then were placed in 10% O2 for 3 weeks, followed by a return to normoxic conditions for an additional 2 weeks. We found that AQP1 protein levels were increased in both PASMCs and MVECs from SuHx rats, even in the absence of sustained hypoxic exposure, and that in MVECs, the increase in protein expression was associated with upregulation of AQP1 mRNA levels. Silencing of AQP1 had no significant effect on PASMCs from control animals but normalized enhanced migration and proliferation observed in cells from SuHx rats. Loss of AQP1 also reduced migration and proliferation in MVECs from SuHx rats. Finally, augmenting AQP1 levels in MVECs from control rats using forced expression was sufficient to increase migration and proliferation. These results demonstrate a key role for enhanced AQP1 expression in mediating abnormal migration and proliferation in pulmonary vascular cells from a rodent model that reflects many of the features of human PAH.

Topic-Based, Recent Literature Review on Pulmonary Hypertension

Pulmonary hypertension is a complex condition but a relatively common manifestation of severe cardiopulmonary disease. By contrast, pulmonary arterial hypertension is uncommon and is more prevalent in young women. To better categorize patients and to guide clinical decision-making, 5 diagnostic groups and associated subgroups characterize the spectrum of disease. A multidisciplinary approach to evaluation and treatment is recommended by published guidelines and often entails referral to a designated pulmonary hypertension center. Several key publications during the last couple of years merit review. The PubMed database was searched for English-language studies and guidelines relating to pulmonary hypertension. The following terms were searched, alone and in combination: pulmonary hypertension, pulmonary arterial hypertension, portopulmonary hypertension, and chronic thromboembolic pulmonary hypertension. The focus was on those publications with new information on evaluation and management of pulmonary hypertension between January 1, 2019, and January 31, 2021. Of the subgroups, 2 were of particular interest for this review: portopulmonary hypertension and chronic thromboembolic pulmonary hypertension. Last, available data on the impact of the coronavirus disease 2019 pandemic and newer treatment agents in early trials were selectively reviewed. The review is therefore intended to serve as a practical, focused review of important topics germane to those clinicians caring for patients with pulmonary hypertension.

TORREY, a Phase 2 study to evaluate the efficacy and safety of inhaled seralutinib for the treatment of pulmonary arterial hypertension

Aberrant kinase signaling that involves platelet-derived growth factor receptor (PDGFR) α/β, colony stimulating factor 1 receptor (CSF1R), and stem cell factor receptor (c-KIT) pathways may be responsible for vascular remodeling in pulmonary arterial hypertension. Targeting these specific pathways may potentially reverse the pathological inflammation, cellular proliferation, and fibrosis associated with pulmonary arterial hypertension progression. Seralutinib (formerly known as GB002) is a novel, potent, clinical stage inhibitor of PDGFRα/β, CSF1R, and c-KIT delivered via inhalation that is being developed for patients with pulmonary arterial hypertension. Here, we report on an ongoing Phase 2 randomized, double-blind, placebo-controlled trial (NCT04456998) evaluating the efficacy and safety of seralutinib in subjects with World Health Organization Group 1 Pulmonary Hypertension who are classified as Functional Class II or III. A total of 80 subjects will be enrolled and randomized to receive either study drug or placebo for 24 weeks followed by an optional 72-week open-label extension study. The primary endpoint is the change from baseline to Week 24 in pulmonary vascular resistance by right heart catheterization. The secondary endpoint is the change in distance from baseline to Week 24 achieved in the 6-min walk test. A computerized tomography sub-study will examine the effect of seralutinib on pulmonary vascular remodelling. A separate heart rate monitoring sub-study will examine the effect of seralutinib on cardiac effort during the 6-min walk test.

Three- Versus Two-Drug Therapy for Patients With Newly Diagnosed Pulmonary Arterial Hypertension

BACKGROUND

In pulmonary arterial hypertension (PAH), there are no data comparing initial triple oral therapy with initial double oral therapy.

OBJECTIVES

TRITON (The Efficacy and Safety of Initial Triple Versus Initial Dual Oral Combination Therapy in Patients With Newly Diagnosed Pulmonary Arterial Hypertension; NCT02558231), a multicenter, double-blind, randomized phase 3b study, evaluated initial triple (macitentan, tadalafil, and selexipag) versus initial double (macitentan, tadalafil, and placebo) oral therapy in newly diagnosed, treatment-naive patients with PAH.

METHODS

Efficacy was assessed until the last patient randomized completed week 26 (end of main observation period). The primary endpoint was change in pulmonary vascular resistance (PVR) at week 26.

RESULTS

Patients were assigned to initial triple (n = 123) or initial double therapy (n = 124). At week 26, both treatment strategies reduced PVR compared with baseline (by 54% and 52%), with no significant difference between groups (ratio of geometric means: 0.96; 95% confidence interval: 0.86-1.07; P = 0.42). Six-minute walk distance and N-terminal pro-brain natriuretic peptide improved by week 26, with no difference between groups. Risk for disease progression (to end of main observation period) was reduced with initial triple versus initial double therapy (hazard ratio: 0.59; 95% confidence interval: 0.32-1.09). Most common adverse events with initial triple therapy included headache, diarrhea, and nausea. By the end of the main observation period, 2 patients in the initial triple and 9 in the initial double therapy groups had died.

CONCLUSIONS

In patients with newly diagnosed PAH, both treatment strategies markedly reduced PVR by week 26, with no significant difference between groups (primary endpoint not met). Exploratory analyses suggested a possible signal for improved long-term outcomes with initial triple versus initial double oral therapy.

Extracellular Vesicle TGF-β1 Is Linked to Cardiopulmonary Dysfunction in Human Immunodeficiency Virus

Extracellular vesicles (EVs) have emerged as important mediators in cell-cell communication; however, their relevance in pulmonary hypertension (PH) secondary to human immunodeficiency virus (HIV) infection is yet to be explored. Considering that circulating monocytes are the source of the increased number of perivascular macrophages surrounding the remodeled vessels in PH, this study aimed to identify the role of circulating small EVs and EVs released by HIV-infected human monocyte-derived macrophages in the development of PH. We report significantly higher numbers of plasma-derived EVs carrying higher levels of TGF-β1 (transforming growth factor-β1) in HIV-positive individuals with PH compared with individuals without PH. Importantly, levels of these TGF-β1-loaded, plasma-derived EVs correlated with pulmonary arterial systolic pressures and CD4 counts but did not correlate with the Dl CO or viral load. Correspondingly, enhanced TGF-β1-dependent pulmonary endothelial injury and smooth muscle hyperplasia were observed. HIV-1 infection of monocyte-derived macrophages in the presence of cocaine resulted in an increased number of TGF-β1-high EVs, and intravenous injection of these EVs in rats led to increased right ventricle systolic pressure accompanied by myocardial injury and increased levels of serum ET-1 (endothelin-1), TNF-α, and cardiac troponin-I. Conversely, pretreatment of rats with TGF-β receptor 1 inhibitor prevented these EV-mediated changes. Findings define the ability of macrophage-derived small EVs to cause pulmonary vascular modeling and PH via modulation of TGF-β signaling and suggest clinical implications of circulating TGF-β-high EVs as a potential biomarker of HIV-associated PH.

Cellular mechanosignaling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by sustained elevated pulmonary arterial pressures in which the pulmonary vasculature undergoes significant structural and functional remodeling. To better understand disease mechanisms, in this review article we highlight recent insights into the regulation of pulmonary arterial cells by mechanical cues associated with PAH. Specifically, the mechanobiology of pulmonary arterial endothelial cells (PAECs), smooth muscle cells (PASMCs) and adventitial fibroblasts (PAAFs) has been investigated in vivo, in vitro, and in silico. Increased pulmonary arterial pressure increases vessel wall stress and strain and endothelial fluid shear stress. These mechanical cues promote vasoconstriction and fibrosis that contribute further to hypertension and alter the mechanical milieu and regulation of pulmonary arterial cells.

Novel Treatment Pathways in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe and progressive vascular disease characterized by pulmonary vascular remodeling, proliferation, and inflammation. Despite the availability of effective treatments, PAH may culminate in right ventricular failure and death. Currently approved medications act through three well-characterized pathways: the nitric oxide, endothelin, and prostacyclin pathways. Ongoing research efforts continue to expand our understanding of the molecular pathogenesis of this complex and multifactorial disease. Based on recent discoveries in the pathobiology of PAH, several new treatments are being developed and tested with the goal of modifying the disease process and ultimately improving the long-term prognosis.

The Prostacyclin Analogue, Treprostinil, Used in the Treatment of Pulmonary Arterial Hypertension, is a Potent Antagonist of TREK-1 and TREK-2 Potassium Channels

Pulmonary arterial hypertension (PAH) is an aggressive vascular remodeling disease that carries a high morbidity and mortality rate. Treprostinil (Remodulin) is a stable prostacyclin analogue with potent vasodilatory and anti-proliferative activity, approved by the FDA and WHO as a treatment for PAH. A limitation of this therapy is the severe subcutaneous site pain and other forms of pain experienced by some patients, which can lead to significant non-compliance. TWIK-related potassium channels (TREK-1 and TREK-2) are highly expressed in sensory neurons, where they play a role in regulating sensory neuron excitability. Downregulation, inhibition or mutation of these channels leads to enhanced pain sensitivity. Using whole-cell patch-clamp electrophysiological recordings, we show, for the first time, that treprostinil is a potent antagonist of human TREK-1 and TREK-2 channels but not of TASK-1 channels. An increase in TASK-1 channel current was observed with prolonged incubation, consistent with its therapeutic role in PAH. To investigate treprostinil-induced inhibition of TREK, site-directed mutagenesis of a number of amino acids, identified as important for the action of other regulatory compounds, was carried out. We found that a gain of function mutation of TREK-1 (Y284A) attenuated treprostinil inhibition, while a selective activator of TREK channels, BL-1249, overcame the inhibitory effect of treprostinil. Our data suggests that subcutaneous site pain experienced during treprostinil therapy may result from inhibition of TREK channels near the injection site and that pre-activation of these channels prior to treatment has the potential to alleviate this nociceptive activity.

Significance of BMPR2 mutations in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a debilitating disease that results from progressive remodeling and inflammation of pulmonary arteries. PAH develops gradually, is difficult to diagnose, and has a high mortality rate. Although mutation in the bone morphogenetic protein receptor 2 (BMPR2) gene has been identified as the main genetic cause of PAH, the underlying pathways involving the pathophysiology of PAH are complex and still not fully understood. Endothelial dysfunction has been observed in PAH development that results in a multitude of disturbances in the cellular processes in pulmonary vessels. Changes in the pulmonary vasculature caused by the disruption of BMPR2 signaling are observed in three main vascular components; endothelial cells, smooth muscle cells, and fibroblasts. BMPR2 also has a prominent role in maintenance of the immune system. The disruption of BMPR2 signaling pathway causes an increased degree of inflammation and decreases the ability of the immune system to resolve it. Inflammatory processes and changes in pulmonary vasculature interact with one another, resulting in the progression of chronic PAH. In this review, we highlight the various components of vascular remodeling and immune response that are caused by disruption of BMPR2 signaling, including the clinical evidence and the prospects of these components as a potential target for PAH therapy. Indeed, development of drugs to target the pathogenic pathways involved in PAH may complement existing treatment regimens and improve patient prognosis.

S1P induces proliferation of pulmonary artery smooth muscle cells by promoting YAP-induced Notch3 expression and activation

Sphingosine-1-phosphate (S1P), a natural multifunctional phospholipid, is highly increased in plasma from patients with pulmonary arterial hypertension and mediates proliferation of pulmonary artery smooth muscle cells (PASMCs) by activating the Notch3 signaling pathway. However, the mechanisms underpinning S1P-mediated induction of PASMCs proliferation remain unclear. In this study, using biochemical and molecular biology approaches, RNA interference and gene expression analyses, 5'-ethynyl-2'-deoxyuridine incorporation assay, and 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, we demonstrated that S1P promoted the activation of signal transducers and activators of transcription 3 (STAT3) through sphingosine-1-phosphate receptor 2 (S1PR2), and subsequently upregulated the expression of the microRNA miR-135b, which further reduced the expression of E3 ubiquitin ligase β-transduction repeat-containing protein and led to a reduction in yes-associated protein (YAP) ubiquitinated degradation in PASMCs. YAP is the core effector of the Hippo pathway and mediates the expression of particular genes. The accumulation of YAP further increased the expression and activation of Notch3 and ultimately promoted the proliferation of PASMCs. In addition, we showed that preblocking S1PR2, prior silencing of STAT3, miR-135b, or YAP, and prior inhibition of Notch3 all attenuated S1P-induced PASMCs proliferation. Taken together, our study indicates that S1P stimulates PASMCs proliferation by activation of the S1PR2/STAT3/miR-135b/β-transduction repeat-containing protein/YAP/Notch3 pathway, and our data suggest that targeting this cascade might have potential value in ameliorating PASMCs hyperproliferation and benefit pulmonary arterial hypertension.

Pulmonary arterial hypertension in systemic sclerosis

Pulmonary arterial hypertension (PAH) is a frequent and severe complication of systemic sclerosis (SSc) due to combined vasculopathy and fibrogenesis. Early diagnosis and treatment are highly challenging in SSc-PAH and require referral to an expert PAH centre. Diagnostic algorithms evolved in the last decade. Novel therapeutic options notably targeting pulmonary vascular remodeling are needed.

Carcinoembryonic antigen levels are increased with pulmonary output in pulmonary hypertension due to congenital heart disease

OBJECTIVE

Pulmonary artery hypertension (PAH) is a severe complication of congenital heart disease (CHD). Monitoring of pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) is essential during follow-up. This retrospective study aimed to examine carcinoembryonic antigen (CEA) as an additional marker for evaluation by investigating the correlation between CEA levels and hemodynamics in CHD-PAH.

METHODS

Seventy-six patients with CHD-PAH (mean PAP [mPAP] >25 mmHg and PVR >3 Wood units, group A), 71 patients with CHD and pulmonary hypertension (CHD-PH, mPAP >25 mmHg and PVR ≤3 Wood units, group B), and 102 patients with CHD without PH (mPAP ≤25 mmHg, group C) were enrolled. Serum CEA levels and the relationships between CEA levels and hemodynamic data were assessed.

RESULTS

Mean serum CEA levels were 1.99±1.61, 2.44±1.82, and 1.58±1.07 ng/mL, mPAP was 58.66±20.21, 30.2±4.83, and 17.31±4.51 mmHg, and PVR was 10.12±7.01, 2.19±0.56, and 2.2±1.1 Wood units in groups A, B, and C, respectively. Mean pulmonary output (PO) was 7.24±3.07, 15.79±5.49, 10.18±4.72 L/minute, respectively. CEA levels were positively correlated with PO and negatively correlated with PVR in all of the patients.

CONCLUSION

CEA levels are increased with PO and decreased with PVR in CHD-PH.

Necrosis-Released HMGB1 (High Mobility Group Box 1) in the Progressive Pulmonary Arterial Hypertension Associated With Male Sex

Damage-associated molecular patterns, such as HMGB1 (high mobility group box 1), play a well-recognized role in the development of pulmonary arterial hypertension (PAH), a progressive fatal disease of the pulmonary vasculature. However, the contribution of the particular type of vascular cells, type of cell death, or the form of released HMGB1 in PAH remains unclear. Moreover, although male patients with PAH show a higher level of circulating HMGB1, its involvement in the severe PAH phenotype reported in males is unknown. In this study, we aimed to investigate the sources and active forms of HMGB1 released from damaged vascular cells and their contribution to the progressive type of PAH in males. Our results showed that HMGB1 is released by either pulmonary artery human endothelial cells or human pulmonary artery smooth muscle cells that underwent necrotic cell death, although only human pulmonary artery smooth muscle cells produce HMGB1 during apoptosis. Moreover, only human pulmonary artery smooth muscle cell death induced a release of dimeric HMGB1, found to be mitochondrial reactive oxygen species dependent, and TLR4 (toll-like receptor 4) activation. The modified Sugen/Hypoxia rat model replicates the human sexual dimorphism in PAH severity (right ventricle systolic pressure in males versus females 54.7±2.3 versus 44.6±2 mm Hg). By using this model, we confirmed that necroptosis and necrosis are the primary sources of circulating HMGB1 in the male rats, although only necrosis increased circulation of HMGB1 dimers. Attenuation of necrosis but not apoptosis or necroptosis prevented TLR4 activation in males and blunted the sex differences in PAH severity. We conclude that necrosis, through the release of HMGB1 dimers, predisposes males to a progressive form of PAH.

Implication of Potassium Channels in the Pathophysiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare and severe cardiopulmonary disease without curative treatments. PAH is a multifactorial disease that involves genetic predisposition, epigenetic factors, and environmental factors (drugs, toxins, viruses, hypoxia, and inflammation), which contribute to the initiation or development of irreversible remodeling of the pulmonary vessels. The recent identification of loss-of-function mutations in KCNK3 (KCNK3 or TASK-1) and ABCC8 (SUR1), or gain-of-function mutations in ABCC9 (SUR2), as well as polymorphisms in KCNA5 (Kv1.5), which encode two potassium (K⁺) channels and two K⁺ channel regulatory subunits, has revived the interest of ion channels in PAH. This review focuses on KCNK3, SUR1, SUR2, and Kv1.5 channels in pulmonary vasculature and discusses their pathophysiological contribution to and therapeutic potential in PAH.

Prediction of haemodynamics after interatrial shunt for heart failure using the generalized circulatory equilibrium

Aims

Interatrial shunting (IAS) reduces left atrial pressure in patients with heart failure. Several clinical trials reported that IAS improved the New York Heart Association score and exercise capacity. However, its effects on haemodynamics vary depending on shunt size, cardiovascular properties, and stressed blood volume. To maximize the benefit of IAS, quantitative prediction of haemodynamics under IAS in individual patients is essential. The generalized circulatory equilibrium framework determines circulatory equilibrium as the intersection of the cardiac output curve and the venous return surface. By incorporating IAS into the framework, we predict the impact of IAS on haemodynamics.

Methods and results

In seven mongrel dogs, we ligated the left anterior descending artery and created impaired cardiac function with elevated left atrial pressure (baseline: 7.8 ± 1.0 vs. impaired: 11.9 ± 3.2 mmHg). We established extracorporeal left‐to‐right atrial shunting with a centrifugal pump. After recording pre‐IAS haemodynamics, we changed IAS flow stepwise to various levels and measured haemodynamics under IAS. To predict the impact of IAS on haemodynamics, we modelled the fluid mechanics of IAS by Newton's second law and incorporated IAS into the generalized circulatory equilibrium framework. Using pre‐IAS haemodynamic data obtained from the dogs, we predicted the impact of IAS flow on haemodynamics under IAS condition using a set of equations. We compared the predicted haemodynamic data with those measured. The predicted pulmonary flow [r² = 0.88, root mean squared error (RMSE) 11.4 mL/min/kg, P < 0.001), systemic flow (r² = 0.92, RMSE 11.2 mL/min/kg, P < 0.001), right atrial pressure (r² = 0.92, RMSE 0.71 mmHg, P < 0.001), and left atrial pressure (r² = 0.83, RMSE 0.95 mmHg, P < 0.001) matched well with those measured under normal and impaired cardiac function. Using this framework, we further performed a simulation study to examine the haemodynamic benefit of IAS in heart failure with preserved ejection fraction. We simulated the IAS haemodynamics under volume loading and exercise conditions. Volume loading and exercise markedly increased left atrial pressure. IAS size‐dependently attenuated the increase in left atrial pressure in both volume loading and exercise. These results indicate that IAS improves volume and exercise intolerance.

Conclusions

The framework developed in this study quantitatively predicts the haemodynamic impact of IAS. Simulation study elucidates how IAS improve haemodynamics under volume loading and exercise conditions. Quantitative prediction of IAS haemodynamics would contribute to maximizing the benefit of IAS in patients with heart failure.

Vascular Homeostasis and Inflammation in Health and Disease-Lessons from Single Cell Technologies

The vascular system is critical infrastructure that transports oxygen and nutrients around the body, and dynamically adapts its function to an array of environmental changes. To fulfil the demands of diverse organs, each with unique functions and requirements, the vascular system displays vast regional heterogeneity as well as specialized cell types. Our understanding of the heterogeneity of vascular cells and the molecular mechanisms that regulate their function is beginning to benefit greatly from the rapid development of single cell technologies. Recent studies have started to analyze and map vascular beds in a range of organs in healthy and diseased states at single cell resolution. The current review focuses on recent biological insights on the vascular system garnered from single cell analyses. We cover the themes of vascular heterogeneity, phenotypic plasticity of vascular cells in pathologies such as atherosclerosis and cardiovascular disease, as well as the contribution of defective microvasculature to the development of neurodegenerative disorders such as Alzheimer's disease. Further adaptation of single cell technologies to study the vascular system will be pivotal in uncovering the mechanisms that drive the array of diseases underpinned by vascular dysfunction.

Pulmonary hypertension in Saudi Arabia: First data from the SAUDIPH registry with a focus on pulmonary arterial hypertension

BACKGROUND AND OBJECTIVE

This study presents the first results of 'SAUDIPH' registry, aiming to assess patient characteristics, treatment approach and clinical and survival outcomes in patients with PAH.

METHODS

The registry enrolled patients with Group 1 and Group 4 PH under clinical management in a specialized tertiary care centre from 2004 to 2018. Changes from baseline to last follow-up visit were assessed.

RESULTS

A total of 222 patients were enrolled, and Group 1 PH was the most frequent aetiology (57.7%). Mean age at diagnosis was 32 years. mPAP was 55.0 mm Hg and was higher for Group 1 PH (59.0 mm Hg, P < 0.001). At the last visit, most patients were on specific therapy (83.7%) and 30% shifted from FC III/IV to FC I/II. NT-proBNP improved by 29.2% in the overall population. The 1-, 3- and 5-year cumulative probabilities of survival were 95.6% (95% CI: 91.5-99.9%), 89.2% (95% CI: 82.1-96.9%) and 74.6% (95% CI: 59.4-93.7%), respectively. CHD-PAH demonstrated the best survival among Group 1 PAH with 1-, 3- and 5-year cumulative probability of 100%, 100%, and 75.0% (95% CI: 42.6-100), respectively.

CONCLUSION

PAH was the most frequent aetiology and patients were younger at diagnosis compared to other cohorts. Most patients showed improvement in FC and NT-proBNP. The estimated 1-year survival was better than previous studies, possibly reflecting wider use of combination therapy and the high prevalence of CHD-PAH.

Quantification of uncertainty in a new network model of pulmonary arterial adventitial fibroblast pro-fibrotic signalling

Here, we present a novel network model of the pulmonary arterial adventitial fibroblast (PAAF) that represents seven signalling pathways, confirmed to be important in pulmonary arterial fibrosis, as 92 reactions and 64 state variables. Without optimizing parameters, the model correctly predicted 80% of 39 results of input-output and inhibition experiments reported in 20 independent papers not used to formulate the original network. Parameter uncertainty quantification (UQ) showed that this measure of model accuracy is robust to changes in input weights and half-maximal activation levels (EC50), but is more affected by uncertainty in the Hill coefficient (n), which governs the biochemical cooperativity or steepness of the sigmoidal activation function of each state variable. Epistemic uncertainty in model structure, due to the reliance of some network components and interactions on experiments using non-PAAF cell types, suggested that this source of uncertainty had a smaller impact on model accuracy than the alternative of reducing the network to only those interactions reported in PAAFs. UQ highlighted model parameters that can be optimized to improve prediction accuracy and network modules where there is the greatest need for new experiments. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.

Effects of Different Types of Exercise Training on Pulmonary Arterial Hypertension: A Systematic Review

Pulmonary arterial hypertension (PAH) represents a chronic progressive disease characterized by high blood pressure in the pulmonary arteries leading to right heart failure. The disease has been a focus of medical research for many years due to its worse prognosis and limited treatment options. The aim of this study was to systematically assess the effects of different types of exercise interventions on PAH. Electronic databases were searched until July 2019. MEDLINE database was used as the predominant source for this paper. Studies with regards to chronic physical activity in adult PAH patients are compared on retrieving evidence on cellular, physiological, and psychological alterations in the PAH setting. Twenty human studies and 12 rat trials were identified. Amongst all studies, a total of 628 human subjects and 614 rats were examined. Regular physical activity affects the production of nitric oxygen and attenuates right ventricular hypertrophy. A combination of aerobic, anaerobic, and respiratory muscle training induces the strongest improvement in functional capacity indicated by an increase of 6 MWD and VO₂peak. In human studies, an increase of quality of life was found. Exercise training has an overall positive effect on the physiological and psychological components of PAH. Consequently, PAH patients should be encouraged to take part in regular exercise training programs.

3D in vitro Model of Vascular Medial Thickening in Pulmonary Arterial Hypertension

In pulmonary arterial hypertension (PAH), excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) causes vascular medial thickening. Medial thickening is a histopathological hallmark of pulmonary vascular remodeling, the central disease process driving PAH progression. Pulmonary vascular remodeling causes stenosis and/or obstruction of small pulmonary arteries. This leads to increased pulmonary vascular resistance, elevated pulmonary arterial pressure, and ultimately right heart failure. To improve the survival of PAH patients, which remains at approximately 60% at 3 years after diagnosis, the development of novel PAH-targeted drugs is desired. To this end, a detailed understanding of the mechanisms underlying excessive PASMC proliferation and the medial thickening that ensues is necessary. However, a lack of in vitro models that recapitulate medial thickening impedes our deeper understanding of the pathogenetic mechanisms involved. In the present study, we applied 3-dimensional (3D) cell culture technology to develop a novel in vitro model of the pulmonary artery medial layer using human PAH patient-derived PASMCs. The addition of platelet-derived growth factor (PDGF)-BB, a mitogen known to promote excessive PASMC proliferation in PAH, resulted in increased thickness of the 3D-PAH media tissues. Conversely, administration of the PDGF receptor inhibitor imatinib or other clinical PAH drugs inhibited this medial thickening-inducing effect of PDGF-BB. Altogether, by using 3D cell culture technology, we report the generation of an in vitro model of medial thickening in PAH, which had hitherto not been successfully modeled in vitro. This model is potentially useful for assessing the ability of candidate PAH drugs to suppress medial thickening.

Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension

Despite recent improvements in management of idiopathic pulmonary arterial hypertension, mortality remains high. Understanding the alterations in the transcriptome–phenotype of the key lung cells involved could provide insight into the drivers of pathogenesis. In this study, we examined differential gene expression of cell types implicated in idiopathic pulmonary arterial hypertension from lung explants of patients with idiopathic pulmonary arterial hypertension compared to control lungs. After tissue digestion, we analyzed all cells from three idiopathic pulmonary arterial hypertension and six control lungs using droplet-based single cell RNA-sequencing. After dimensional reduction by t-stochastic neighbor embedding, we compared the transcriptomes of endothelial cells, pericyte/smooth muscle cells, fibroblasts, and macrophage clusters, examining differential gene expression and pathways implicated by analysis of Gene Ontology Enrichment. We found that endothelial cells and pericyte/smooth muscle cells had the most differentially expressed gene profile compared to other cell types. Top differentially upregulated genes in endothelial cells included novel genes: ROBO4, APCDD1, NDST1, MMRN2, NOTCH4, and DOCK6, as well as previously reported genes: ENG, ORAI2, TFDP1, KDR, AMOTL2, PDGFB, FGFR1, EDN1, and NOTCH1. Several transcription factors were also found to be upregulated in idiopathic pulmonary arterial hypertension endothelial cells including SOX18, STRA13, LYL1, and ELK, which have known roles in regulating endothelial cell phenotype. In particular, SOX18 was implicated through bioinformatics analyses in regulating the idiopathic pulmonary arterial hypertension endothelial cell transcriptome. Furthermore, idiopathic pulmonary arterial hypertension endothelial cells upregulated expression of FAM60A and HDAC7, potentially affecting epigenetic changes in idiopathic pulmonary arterial hypertension endothelial cells. Pericyte/smooth muscle cells expressed genes implicated in regulation of cellular apoptosis and extracellular matrix organization, and several ligands for genes showing increased expression in endothelial cells. In conclusion, our study represents the first detailed look at the transcriptomic landscape across idiopathic pulmonary arterial hypertension lung cells and provides robust insight into alterations that occur in vivo in idiopathic pulmonary arterial hypertension lungs.