The cancer theory of pulmonary arterial hypertension

Dietary intake and glutamine-serine metabolism control pathologic vascular stiffness

Perivascular collagen deposition by activated fibroblasts promotes vascular stiffening and drives cardiovascular diseases such as pulmonary hypertension (PH). Whether and how vascular fibroblasts rewire their metabolism to sustain collagen biosynthesis remains unknown. Here, we found that inflammation, hypoxia, and mechanical stress converge on activating the transcriptional coactivators YAP and TAZ (WWTR1) in pulmonary arterial adventitial fibroblasts (PAAFs). Consequently, YAP and TAZ drive glutamine and serine catabolism to sustain proline and glycine anabolism and promote collagen biosynthesis. Pharmacologic or dietary intervention on proline and glycine anabolic demand decreases vascular stiffening and improves cardiovascular function in PH rodent models. By identifying the limiting metabolic pathways for vascular collagen biosynthesis, our findings provide guidance for incorporating metabolic and dietary interventions for treating cardiopulmonary vascular disease.

The diverging roles of insulin-like growth factor binding proteins in pulmonary arterial hypertension

Pulmonary hypertension (PH) is a progressive, severe and to date not curable disease of the pulmonary vasculature. Alterations of the insulin-like growth factor 1 (IGF-1) system are known to play a role in vascular pathologies and IGF-binding proteins (IGFBPs) are important regulators of the bioavailability and function of IGFs. In this study, we show that circulating plasma levels of IGFBP-1, IGFBP-2 and IGFBP-3 are increased in idiopathic pulmonary arterial hypertension (IPAH) patients compared to healthy individuals. These binding proteins inhibit the IGF-1 induced IGF-1 receptor (IGF1R) phosphorylation and exhibit diverging effects on the IGF-1 induced signaling pathways in human pulmonary arterial cells (i.e. healthy as well as IPAH-hPASMCs, and healthy hPAECs). Furthermore, IGFBPs are differentially expressed in an experimental mouse model of PH. In hypoxic mouse lungs, IGFBP-1 mRNA expression is decreased whereas the mRNA for IGFBP-2 is increased. In contrast to IGFBP-1, IGFBP-2 shows vaso-constrictive properties in the murine pulmonary vasculature. Our analyses show that IGFBP-1 and IGFBP-2 exhibit diverging effects on IGF-1 signaling and display a unique IGF1R-independent kinase activation pattern in human pulmonary arterial smooth muscle cells (hPASMCs), which represent a major contributor of PAH pathobiology. Furthermore, we could show that IGFBP-2, in contrast to IGFBP-1, induces epidermal growth factor receptor (EGFR) signaling, Stat-3 activation and expression of Stat-3 target genes. Based on our results, we conclude that the IGFBP family, especially IGFBP-1, IGFBP-2 and IGFBP-3, are deregulated in PAH, that they affect IGF signaling and thereby regulate the cellular phenotype in PH.

Metabolic reprogramming and interventions in angiogenesis

BACKGROUND

Endothelial cell (EC) metabolism plays a crucial role in the process of angiogenesis. Intrinsic metabolic events such as glycolysis, fatty acid oxidation, and glutamine metabolism, support secure vascular migration and proliferation, energy and biomass production, as well as redox homeostasis maintenance during vessel formation. Nevertheless, perturbation of EC metabolism instigates vascular dysregulation-associated diseases, especially cancer.

AIM OF REVIEW

In this review, we aim to discuss the metabolic regulation of angiogenesis by EC metabolites and metabolic enzymes, as well as prospect the possible therapeutic opportunities and strategies targeting EC metabolism.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we discuss various aspects of EC metabolism considering normal and diseased vasculature. Of relevance, we highlight that the implications of EC metabolism-targeted intervention (chiefly by metabolic enzymes or metabolites) could be harnessed in orchestrating a spectrum of pathological angiogenesis-associated diseases.

Rieske Iron-Sulfur Protein Mediates Pulmonary Hypertension Following Nicotine/Hypoxia Coexposure

The high mortality rate in patients with chronic obstructive pulmonary disease (COPD) may be due to pulmonary hypertension (PH). These diseases are highly associated with cigarette smoke and its key component nicotine. Here, we created a novel animal model of PH using coexposure to nicotine (or cigarette smoke) and hypoxia. This heretofore unreported model showed significant early-onset pulmonary vasoremodeling and PH. Using newly generated mice with complementary smooth muscle-specific Rieske iron-sulfur protein (RISP) gene knockout and overexpression, we demonstrate that RISP is critically involved in promoting pulmonary vasoremodeling and PH, which are implemented by oxidative ataxia telangiectasia-mutated-mediated DNA damage and NF-κB-dependent inflammation in a reciprocal positive mechanism. Together, our findings establish for the first time an animal model of hypoxia-induced early-onset PH in which mitochondrial RISP-dependent DNA damage and NF-κB inflammation play critical roles in vasoremodeling. Specific therapeutic targets for RISP and related oxidative stress-associated signaling pathways may create unique and effective treatments for PH, chronic obstructive pulmonary disease, and their complications.

Non-Interferon-Dependent Role of STING Signaling in Pulmonary Hypertension

BACKGROUND

Patients with constitutive activation of DNA-sensing pathway through stimulator of IFN (interferon) genes (STING), such as those with STING-associated vasculopathy with onset in infancy, develop pulmonary hypertension (PH). However, the role of STING signaling in general PH patients is heretofore undescribed. Here, we seek to investigate the role of STING in PH development.

METHODS

STING expression in patient lung samples was examined. PH was induced in global STING-deficient mice and global type I IFN receptor 1-deficient mice using bleomycin or chronic hypoxia exposure. PH development was evaluated by right ventricular systolic pressure and Fulton index, with additional histological and flow cytometric analysis. VEGF (vascular endothelial growth factor) expression on murine immune cells was quantified and evaluated with multiplex and flow cytometry. Human myeloid-derived cells were differentiated from peripheral blood mononuclear cells and treated with either STING agonist or STING antagonist for evaluation of VEGF secretion.

RESULTS

Global STING deficiency protects mice from PH development, and STING-associated PH seems independent of type I IFN signaling. Furthermore, a role for STING-VEGF signaling pathway in PH development was demonstrated, with altered VEGF secretion in murine pulmonary infiltrated myeloid cells in a STING-dependent manner. In addition, pharmacological manipulation of STING in human myeloid-derived cells supports in vivo findings. Finally, a potential role of STING-VEGF-mediated apoptosis in disease development and progression was illustrated, providing a roadmap toward potential therapeutic applications.

CONCLUSIONS

Overall, these data provide concrete evidence of STING involvement in PH, establishing biological plausibility for STING-related therapies in PH treatment.

IMPAHCT: A randomized phase 2b/3 study of inhaled imatinib for pulmonary arterial hypertension

AV-101 (imatinib) powder for inhalation, an investigational dry powder inhaled formulation of imatinib designed to target the underlying pathobiology of pulmonary arterial hypertension, was generally well tolerated in healthy adults in a phase 1 single and multiple ascending dose study. Inhaled Imatinib Pulmonary Arterial Hypertension Clinical Trial (IMPAHCT; NCT05036135) is a phase 2b/3, randomized, double-blind, placebo-controlled, dose-ranging, and confirmatory study. IMPAHCT is designed to identify an optimal AV-101 dose (phase 2b primary endpoint: pulmonary vascular resistance) and assess the efficacy (phase 3 primary endpoint: 6-min walk distance), safety, and tolerability of AV-101 dose levels in subjects with pulmonary arterial hypertension using background therapies. The study has an operationally seamless, adaptive design allowing for continuous recruitment. It includes three parts; subjects enrolled in Part 1 (phase 2b dose-response portion) or Part 2 (phase 3 intermediate portion) will be randomized 1:1:1:1 to 10, 35, 70 mg AV-101, or placebo (twice daily), respectively. Subjects enrolled in Part 3 (phase 3 optimal dose portion) will be randomized 1:1 to the optimal dose of AV-101 and placebo (twice daily), respectively. All study parts include a screening period, a 24-week treatment period, and a 30-day safety follow-up period; the total duration is ∼32 weeks. Participation is possible in only one study part. IMPAHCT has the potential to advance therapies for patients with pulmonary arterial hypertension by assessing the efficacy and safety of a novel investigational drug-device combination (AV-101) using an improved study design that has the potential to save 6-12 months of development time. ClinicalTrials.gov Identifier: NCT05036135.

Efficacy of Drpitor1a, a Dynamin-Related Protein 1 inhibitor, in Pulmonary Arterial Hypertension

Rationale

Dynamin-related protein 1 (Drp1), a large GTPase, mediates mitochondrial fission. Increased Drp1-mediated fission permits accelerated mitosis, contributing to hyperproliferation of pulmonary artery smooth muscle cells (PASMC), which characterizes pulmonary arterial hypertension (PAH). We developed a Drp1 inhibitor, Drpitor1a, and tested its ability to regress PAH.

Objectives

Assess Drpitor1a's efficacy and toxicity in: a)normal and PAH human PASMC (hPASMC); b)normal rats versus rats with established monocrotaline (MCT)-induced PAH.

Methods

Drpitor1a's effects on recombinant and endogenous Drp1-GTPase activity, mitochondrial fission, and cell proliferation were studied in hPASMCs (normal=3; PAH=5). Drpitor1a's pharmacokinetics and tissue concentrations were measured (n=3 rats/sex). In a pilot study (n=3-4/sex/dose), Drpitor1a (1mg/kg/48-hours, intravenous) reduced adverse PA remodeling only in females. Consequently, we compared Drpitor1a to vehicle in normal (n=6 versus 8) and MCT-PAH (n=9 and 11) females, respectively. Drpitor1a treatment began 17-days post-MCT with echocardiography and cardiac catheterization performed 28-29 days post-MCT.

Results

Drpitor1a inhibited recombinant and endogenous Drp1 GTPase activity, which was increased in PAH hPASMC. Drpitor1a inhibited mitochondrial fission and proliferation and induced apoptosis, in PAH hPASMC but not normal hPASMC. Drpitor1a tissue levels were higher in female versus male RVs. In MCT-PAH females, Drpitor1a regressed PA obstruction, lowered pulmonary vascular resistance, and improved RV function, without hematologic, renal, or hepatic toxicity.

Conclusions

Drpitor1a inhibits Drp1 GTPase, reduces mitochondrial fission, and inhibits cell proliferation in PAH hPASMC. Drpitor1a caused no toxicity in MCT-PAH and had no significant effect on normal rats or hPASMCs. Drpitor1a is a potential PAH therapeutic which displays an interesting therapeutic sexual dimorphism.

Switch-Independent 3A: An Epigenetic Regulator in Cancer with New Implications for Pulmonary Arterial Hypertension

Epigenetic mechanisms, including DNA methylation, histone modifications, and non-coding RNA, play a crucial role in the regulation of gene expression and are pivotal in biological processes like apoptosis, cell proliferation, and differentiation. SIN3a serves as a scaffold protein and facilitates interactions with transcriptional epigenetic partners and specific DNA-binding transcription factors to modulate gene expression by adding or removing epigenetic marks. However, the activation or repression of gene expression depends on the factors that interact with SIN3a, as it can recruit both transcriptional activators and repressors. The role of SIN3a has been extensively investigated in the context of cancer, including melanoma, lung, and breast cancer. Our group is interested in defining the roles of SIN3a and its partners in pulmonary vascular disease. Pulmonary arterial hypertension (PAH) is a multifactorial disease often described as a cancer-like disease and characterized by disrupted cellular metabolism, sustained vascular cell proliferation, and resistance to apoptosis. Molecularly, PAH shares many common signaling pathways with cancer cells, offering the opportunity to further consider therapeutic strategies used for cancer. As a result, many signaling pathways observed in cancer were studied in PAH and have encouraged new research studying SIN3a's role in PAH due to its impact on cancer growth. This comparison offers new therapeutic options. In this review, we delineate the SIN3a-associated epigenetic mechanisms in cancer and PAH cells and highlight their impact on cell survival and proliferation. Furthermore, we explore in detail the role of SIN3a in cancer to provide new insights into its emerging role in PAH pathogenesis.

Comprehensive analyses of m6A RNA methylation patterns and related immune microenvironment in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disease with a poor prognosis and high heritability, characterized by elevated pulmonary vascular resistance (PVR) and pulmonary artery pressure. N6-methyladenosine (m6A) RNA modification influences many RNA metabolism pathways. However, the position of m6A methylation regulators in IPAH remains unknown. Therefore, the study aims to disclose the function m6A regulators exert in the pathological mechanisms of IPAH and the immune microenvironment involved. The GSE117261 dataset was downloaded from the Gene Expression Omnibus (GEO) to screen the differentially expressed genes (DEGs) between normal and IPAH samples. Functional and pathway enrichment analyses of DEGs were then conducted by Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG). We also identified the differentially-expressed m6A (DEm6A) regulators between normal and IPAH samples. Key m6A regulators related to the prediction of IPAH were selected using the random forest model. The results showed that FMR1, RBM15, HNRNPA2B1 and IGFBP3 were upregulated in IPAH. In contrast, LRPPRC was downregulated. The single sample gene set enrichment analysis (ssGSEA) method was then adopted to estimate the immune microenvironment in distinct m6A clusters and m6A phenotype-related genes (PRGs) clusters, respectively. Furthermore, we calculated the m6A score via principal component analysis (PCA), and the Sankey diagram was selected to present the correlation among the m6A clusters, m6A PRGs clusters and m6A score. Finally, quantitative RT-PCR and Western blotting were used to validate the key genes in human pulmonary artery smooth muscle cells (HPASMCs) treated by human platelet-derived growth factor-BB (PDGF-BB). The relative mRNA and protein expression levels of FMR1 were significantly elevated, however, the relative mRNA and protein expression levels of LRPPRC were downregulated. Besides, the relative mRNA level of HNRNPA2B1 was increased. Generally, this bioinformatics analysis might provoke more insights into diagnosing and treating IPAH.

Low-affinity insulin-like growth factor binding protein 7 and its association with pulmonary arterial hypertension severity and survival

Insulin-like growth factor (IGF) binding proteins (IGFBPs) are a family of growth factor modifiers, some of which are known to be independently associated with pulmonary arterial hypertension (PAH) survival. IGF factor binding protein 7 (IGFBP7) is a unique low-affinity IGFBP that, independent of IGF, stimulates prostacyclin production. This study proposed to establish associations between IGFBP7 and PAH severity and survival, using enrollment and longitudinal samples. Serum IGFBP7 levels were significantly elevated in patients with PAH compared to controls. After adjusting for age and sex, logarithmic increases in IGFBP7 were associated with a 20 m shorter six-minute walk distance (6MWD; p < 0.001), a 2-3 mmHg higher mean right atrial pressure (p < 0.001 and 0.02), and a higher likelihood of a greater REVEAL 2.0 risk category placement (p < 0.001). Kaplan-Meier analysis demonstrated significantly decreased survival with IGFBP7 above the median and Cox multivariable analysis adjusted for age and sex, demonstrated higher serum IGFBP7 was an independent predictor of survival. Though the exact mechanism is still unknown, given IGFBP7's role as a prostacyclin stimulant, it has potential use as a therapeutic target for disease modulation.

Purine synthesis suppression reduces the development and progression of pulmonary hypertension in rodent models

AIMS

Proliferation of vascular smooth muscle cells (VSMCs) is a hallmark of pulmonary hypertension (PH). Proliferative cells utilize purine bases from the de novo purine synthesis (DNPS) pathways for nucleotide synthesis; however, it is unclear whether DNPS plays a critical role in VSMC proliferation during development of PH. The last two steps of DNPS are catalysed by the enzyme 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate cyclohydrolase (ATIC). This study investigated whether ATIC-driven DNPS affects the proliferation of pulmonary artery smooth muscle cells (PASMCs) and the development of PH.

METHODS AND RESULTS

Metabolites of DNPS in proliferative PASMCs were measured by liquid chromatography-tandem mass spectrometry. ATIC expression was assessed in platelet-derived growth factor-treated PASMCs and in the lungs of PH rodents and patients with pulmonary arterial hypertension. Mice with global and VSMC-specific knockout of Atic were utilized to investigate the role of ATIC in both hypoxia- and lung interleukin-6/hypoxia-induced murine PH. ATIC-mediated DNPS at the mRNA, protein, and enzymatic activity levels were increased in platelet-derived growth factor-treated PASMCs or PASMCs from PH rodents and patients with pulmonary arterial hypertension. In cultured PASMCs, ATIC knockdown decreased DNPS and nucleic acid DNA/RNA synthesis, and reduced cell proliferation. Global or VSMC-specific knockout of Atic attenuated vascular remodelling and inhibited the development and progression of both hypoxia- and lung IL-6/hypoxia-induced PH in mice.

CONCLUSION

Targeting ATIC-mediated DNPS compromises the availability of purine nucleotides for incorporation into DNA/RNA, reducing PASMC proliferation and pulmonary vascular remodelling and ameliorating the development and progression of PH.

JMJD1C promotes smooth muscle cell proliferation by activating glycolysis in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic disorder characterized by hyperproliferation of pulmonary arterial smooth muscle cells (PASMCs). JMJD1C, a member of the Jumonji domain containing C (JMJC) histone demethylase family, contributes to cardiovascular dysfunction. However, the role of JMJD1C in PAH remains unknown. Mice were exposed to hypoxia to mimic several features associated with PAH clinically. We found that JMJD1C was highly expressed in the lungs of mice after hypoxia exposure. JMJD1C knockdown ameliorated hypoxia-induced right ventricular remodeling and thickening of the pulmonary arterial wall. PASMC hyperproliferation and resistance to apoptosis in mice exposed to hypoxia were suppressed by JMJD1C inhibition. We demonstrated that JMJD1C silencing reduced glycolytic enzymes (HK2, PGK1 and LDHA) and lactate overaccumulation in the lungs of mice exposed to hypoxia. In vitro, hypoxia-induced hyperproliferation and activated glycolytic processes in mouse PASMCs were impaired by JMJD1C knockdown. In addition, the activation of STAT3 signaling by hypoxia was suppressed by JMJD1C silencing both in vivo and in vitro. The overexpression of STAT3 reversed the inhibitory effect of JMJD1C depletion on proliferation and glycolysis in PASMCs under hypoxia. Thus, JMJD1C induces glycolytic processes by activating STAT3 signaling to promote PASMC proliferation and pulmonary vascular remodeling, suggesting the potential role of JMJD1C in regulating the metabolic program and vascular remodeling in PAH.

Histologic and proteomic remodeling of the pulmonary veins and arteries in a porcine model of chronic pulmonary venous hypertension

AIMS

In heart failure (HF), pulmonary venous hypertension (PVH) produces pulmonary hypertension (PH) with remodeling of pulmonary veins (PV) and arteries (PA). In a porcine PVH model, we performed proteomic-based bioinformatics to investigate unique pathophysiologic mechanisms mediating PA and PV remodeling.

METHODS AND RESULTS

Large PV were banded (PVH, n = 10) or not (Sham, n = 9) in piglets. At sacrifice, PV and PA were perfusion labelled for vessel-specific histology and proteomics. The PA and PV were separately sampled with laser-capture micro-dissection for mass spectrometry. Pulmonary vascular resistance [Wood Units; 8.6 (95% confidence interval: 6.3, 12.3) vs. 2.0 (1.7, 2.3)] and PA [19.9 (standard error of mean, 1.1) vs. 10.3 (1.1)] and PV [14.2 (1.2) vs. 7.6 (1.1)] wall thickness/external diameter (%) were increased in PVH (P < 0.05 for all). Similar numbers of proteins were identified in PA (2093) and PV (2085) with 94% overlap, but biological processes differed. There were more differentially expressed proteins (287 vs. 161), altered canonical pathways (17 vs. 3), and predicted upstream regulators (PUSR; 22 vs. 6) in PV than PA. In PA and PV, bioinformatics indicated activation of the integrated stress response and mammalian target of rapamycin signalling with dysregulated growth. In PV, there was also activation of Rho/Rho-kinase signalling with decreased actin cytoskeletal signalling and altered tight and adherens junctions, ephrin B, and caveolae-mediated endocytosis signalling; all indicating disrupted endothelial barrier function. Indeed, protein biomarkers and the top PUSR in PV (transforming growth factor-beta) suggested endothelial to mesenchymal transition in PV. Findings were similar in human autopsy specimens.

CONCLUSION

These findings provide new therapeutic targets to oppose pulmonary vascular remodeling in HF-related PH.

Activation of PPAR-γ prevents TERT-mediated pulmonary vascular remodeling in MCT-induced pulmonary hypertension

Background

It has been demonstrated that elevated telomerase reverse transcriptase (TERT) expression or activity is implicated in pulmonary hypertension (PH). In addition, activation of peroxisome-proliferator-activated receptor γ (PPAR-γ) has been found to prevent PH progression. However, the molecular mechanism responsible for the protective effect of PPAR-γ activation on TERT expression in the pathogenesis of PH remains unknown. This study was performed to address these issues.

Methods

Intraperitoneal injection of monocrotaline (MCT) was used to establish PH. BIBR1532 was applied to inhibit the activity of telomerase. The right ventricular systolic pressure (RVSP) and histological analysis were used to detect the development of PH. The protein levels of p-Akt, t-Akt, c-Myc and TERT were determined by western blotting. Pharmacological inhibition of TERT by BIBR1532 effectively suppressed RVSP, RVHI and the WT% in MCT-induced PH rats.

Results

Pharmacological inhibition of Akt/c-Myc pathway by LY294002 diminished TERT upregulation, RVSP, RVHI and WT% in MCT-PH rats. Activation of PPAR-γ by pioglitazone inhibited p-Akt and c-Myc expressions and further downregulated TERT, thus to reduced RVSP, RVHI and WT% in MCT-treated PH rats.

Conclusions

In conclusion, TERT upregulation contributes to PH development in MCT-treated rats. Activation of PPAR-γ prevents pulmonary arterial remodeling through Akt/c-Myc/TERT axis suppression.

AV-101, a novel inhaled dry-powder formulation of imatinib, in healthy adult participants: a phase 1 single and multiple ascending dose study

Background

Oral imatinib has been shown to be effective, but poorly tolerated, in patients with advanced pulmonary arterial hypertension (PAH). To maintain efficacy while improving tolerability, AV-101, a dry powder inhaled formulation of imatinib, was developed to deliver imatinib directly to the lungs.

Methods

This phase 1, placebo-controlled, randomised single ascending dose (SAD) and multiple ascending dose (MAD) study evaluated the safety/tolerability and pharmacokinetics of AV-101 in healthy adults. The SAD study included five AV-101 cohorts (1 mg, 3 mg, 10 mg, 30 mg, 90 mg) and placebo, and a single-dose oral imatinib 400-mg cohort. The MAD study included three AV-101 cohorts (10 mg, 30 mg, 90 mg) and placebo; dosing occurred twice daily for 7 days.

Results

82 participants (SAD n=48, MAD n=34) were enrolled. For the SAD study, peak plasma concentrations of imatinib occurred within 3 h of dosing with lower systemic exposure compared to oral imatinib (p<0.001). For the MAD study, systemic exposure of imatinib was higher after multiple doses of AV-101 compared to a single dose, but steady-state plasma concentrations were lower for the highest AV-101 cohort (90 mg) compared to simulated steady-state oral imatinib at day 7 (p=0.0002). Across AV-101 MAD dose cohorts, the most common treatment-emergent adverse events were cough (n=7, 27%) and headache (n=4, 15%).

Conclusions

AV-101 was well tolerated in healthy adults, and targeted doses of AV-101 significantly reduced the systemic exposure of imatinib compared with oral imatinib. An ongoing phase 2b/phase 3 study (IMPAHCT; clinicaltrials.gov identifier NCT05036135) will evaluate the safety/tolerability and clinical benefit of AV-101 for PAH.

BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension forms the first and most severe of the 5 categories of pulmonary hypertension. Disease pathogenesis is driven by progressive remodeling of peripheral pulmonary arteries, caused by the excessive proliferation of vascular wall cells, including endothelial cells, smooth muscle cells and fibroblasts, and perivascular inflammation. Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations. Dysfunctional pulmonary arterial endothelial cells lose their ability to produce vasodilatory mediators, together leading to augmented pulmonary arterial smooth muscle cell responses, increased pulmonary vascular pressures and right ventricular afterload, and progressive right ventricular hypertrophy and heart failure. It is recognized that a range of abnormal cellular molecular signatures underpin the pathophysiology of pulmonary arterial hypertension and are enhanced by loss-of-function mutations in the BMPR2 gene, the most common genetic cause of pulmonary arterial hypertension and associated with worse disease prognosis. Widespread metabolic abnormalities are observed in the heart, pulmonary vasculature, and systemic tissues, and may underpin heterogeneity in responsivity to treatment. Metabolic abnormalities include hyperglycolytic reprogramming, mitochondrial dysfunction, aberrant polyamine and sphingosine metabolism, reduced insulin sensitivity, and defective iron handling. This review critically discusses published mechanisms linking metabolic abnormalities with dysfunctional BMPR2 (bone morphogenetic protein receptor 2) signaling; hypothesized mechanistic links requiring further validation; and their relevance to pulmonary arterial hypertension pathogenesis and the development of potential therapeutic strategies.

Lung Cancer Gene Regulatory Network of Transcription Factors Related to the Hallmarks of Cancer

The transcriptomic analysis of microarray and RNA-Seq datasets followed our own bioinformatic pipeline to identify a transcriptional regulatory network of lung cancer. Twenty-six transcription factors are dysregulated and co-expressed in most of the lung cancer and pulmonary arterial hypertension datasets, which makes them the most frequently dysregulated transcription factors. Co-expression, gene regulatory, coregulatory, and transcriptional regulatory networks, along with fibration symmetries, were constructed to identify common connection patterns, alignments, main regulators, and target genes in order to analyze transcription factor complex formation, as well as its synchronized co-expression patterns in every type of lung cancer. The regulatory function of the most frequently dysregulated transcription factors over lung cancer deregulated genes was validated with ChEA3 enrichment analysis. A Kaplan-Meier plotter analysis linked the dysregulation of the top transcription factors with lung cancer patients' survival. Our results indicate that lung cancer has unique and common deregulated genes and transcription factors with pulmonary arterial hypertension, co-expressed and regulated in a coordinated and cooperative manner by the transcriptional regulatory network that might be associated with critical biological processes and signaling pathways related to the acquisition of the hallmarks of cancer, making them potentially relevant tumor biomarkers for lung cancer early diagnosis and targets for the development of personalized therapies against lung cancer.

Specificity Protein 1-Mediated Promotion of CXCL12 Advances Endothelial Cell Metabolism and Proliferation in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a rare yet devastating and incurable disease with few treatment options. The underlying mechanisms of PAH appear to involve substantial cellular proliferation and vascular remodeling, causing right ventricular overload and eventual heart failure. Recent evidence suggests a significant seminal role of the pulmonary endothelium in the initiation and promotion of PAH. Our previous work identified elevated reactive oxygen species (ROS)-producing enzyme NADPH oxidase 1 (NOX1) in human pulmonary artery endothelial cells (HPAECs) of PAH patients promoting endothelial cell proliferation in vitro. In this study, we interrogated chemokine CXCL12's (aka SDF-1) role in EC proliferation under the control of NOX1 and specificity protein 1 (Sp1). We report here that NOX1 can drive hypoxia-induced endothelial CXCL12 expression via the transcription factor Sp1 leading to HPAEC proliferation and migration. Indeed, NOX1 drove hypoxia-induced Sp1 activation, along with an increased capacity of Sp1 to bind cognate promoter regions in the CXCL12 promoter. Sp1 activation induced elevated expression of CXCL12 in hypoxic HPAECs, supporting downstream induction of expression at the CXCL12 promoter via NOX1 activity. Pathological levels of CXCL12 mimicking those reported in human PAH patient serum restored EC proliferation impeded by specific NOX1 inhibitor. The translational relevance of our findings is highlighted by elevated NOX1 activity, Sp1 activation, and CXCL12 expression in explanted lung samples from PAH patients compared to non-PAH controls. Analysis of phosphofructokinase, glucose-6-phosphate dehydrogenase, and glutaminase activity revealed that CXCL12 induces glutamine and glucose metabolism, which are foundational to EC cell proliferation. Indeed, in explanted human PAH lungs, demonstrably higher glutaminase activity was detected compared to healthy controls. Finally, infusion of recombinant CXCL12 into healthy mice amplified pulmonary arterial pressure, right ventricle remodeling, and elevated glucose and glutamine metabolism. Together these data suggest a central role for a novel NOX1-Sp1-CXCL12 pathway in mediating PAH phenotype in the lung endothelium.

Inhaled seralutinib exhibits potent efficacy in models of pulmonary arterial hypertension

BACKGROUND

Signalling through platelet-derived growth factor receptor (PDGFR), colony-stimulating factor 1 receptor (CSF1R) and mast/stem cell growth factor receptor kit (c-KIT) plays a critical role in pulmonary arterial hypertension (PAH). We examined the preclinical efficacy of inhaled seralutinib, a unique small-molecule PDGFR/CSF1R/c-KIT kinase inhibitor in clinical development for PAH, in comparison to a proof-of-concept kinase inhibitor, imatinib.

METHODS

Seralutinib and imatinib potency and selectivity were compared. Inhaled seralutinib pharmacokinetics/pharmacodynamics were studied in healthy rats. Efficacy was evaluated in two rat models of PAH: SU5416/Hypoxia (SU5416/H) and monocrotaline pneumonectomy (MCTPN). Effects on inflammatory/cytokine signalling were examined. PDGFR, CSF1R and c-KIT immunohistochemistry in rat and human PAH lung samples and microRNA (miRNA) analysis in the SU5416/H model were performed.

RESULTS

Seralutinib potently inhibited PDGFRα/β, CSF1R and c-KIT. Inhaled seralutinib demonstrated dose-dependent inhibition of lung PDGFR and c-KIT signalling and increased bone morphogenetic protein receptor type 2 (BMPR2). Seralutinib improved cardiopulmonary haemodynamic parameters and reduced small pulmonary artery muscularisation and right ventricle hypertrophy in both models. In the SU5416/H model, seralutinib improved cardiopulmonary haemodynamic parameters, restored lung BMPR2 protein levels and decreased N-terminal pro-brain natriuretic peptide (NT-proBNP), more than imatinib. Quantitative immunohistochemistry in human lung PAH samples demonstrated increased PDGFR, CSF1R and c-KIT. miRNA analysis revealed candidates that could mediate seralutinib effects on BMPR2.

CONCLUSIONS

Inhaled seralutinib was an effective treatment of severe PAH in two animal models, with improved cardiopulmonary haemodynamic parameters, a reduction in NT-proBNP, reverse remodelling of pulmonary vascular pathology and improvement in inflammatory biomarkers. Seralutinib showed greater efficacy compared to imatinib in a preclinical study.

Metabolic reprogramming: A novel metabolic model for pulmonary hypertension

Pulmonary arterial hypertension, or PAH, is a condition that is characterized by pulmonary artery pressures above 20 mmHg (at rest). In the treatment of PAH, the pulmonary vascular system is regulated to ensure a diastolic and contraction balance; nevertheless, this treatment does not prevent or reverse pulmonary vascular remodeling and still causes pulmonary hypertension to progress. According to Warburg, the link between metabolism and proliferation in PAH is similar to that of cancer, with a common aerobic glycolytic phenotype. By activating HIF, aerobic glycolysis is enhanced and cell proliferation is triggered. Aside from glutamine metabolism, the Randle cycle is also present in PAH. Enhanced glutamine metabolism replenishes carbon intermediates used by glycolysis and provides energy to over-proliferating and anti-apoptotic pulmonary vascular cells. By activating the Randle cycle, aerobic oxidation is enhanced, ATP is increased, and myocardial injury is reduced. PAH is predisposed by epigenetic dysregulation of DNA methylation, histone acetylation, and microRNA. This article discusses the abnormal metabolism of PAH and how metabolic therapy can be used to combat remodeling.

Evolving Concepts in Endothelial Pathobiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a deadly disease, characterized by increased vascular resistance, pulmonary arteriolar loss, and occlusive arterial remodeling, leading to eventual right heart failure. Evidence increasingly points to the pulmonary endothelium as a central actor in PAH. Endothelial cell apoptosis can result directly in distal lung arteriolar pruning and indirectly in the formation of complex and occlusive arterial lesions, reflecting an imbalance between endothelial injury and repair in the development and progression of PAH. Many of the mutations implicated in PAH are in genes, which are predominantly, or solely, expressed in endothelial cells, and the endothelium is a major target for therapeutic interventions to restore BMP signaling. We explore how arterial pruning can promote the emergence of occlusive arterial remodeling mediated by ongoing endothelial injury secondary to hemodynamic perturbation and pathological increases in luminal shear stress. The emerging role of endothelial cell senescence is discussed in the transition from reversible to irreversible arterial remodeling in advanced PAH, and we review the sometimes conflicting evidence that female sex hormones can both protect or promote vascular changes in disease. Finally, we explore the contribution of the endothelium to metabolic changes and the altered inflammatory and immune state in the PAH lung, focusing on the role of excessive TGFβ signaling. Given the complexity of the endothelial pathobiology of PAH, we anticipate that emerging technologies that allow the study of molecular events at a single cell level will provide answers to many of the questions raised in this review.

Identifying General Tumor and Specific Lung Cancer Biomarkers by Transcriptomic Analysis

The bioinformatic pipeline previously developed in our research laboratory is used to identify potential general and specific deregulated tumor genes and transcription factors related to the establishment and progression of tumoral diseases, now comparing lung cancer with other two types of cancer. Twenty microarray datasets were selected and analyzed separately to identify hub differentiated expressed genes and compared to identify all the deregulated genes and transcription factors in common between the three types of cancer and those unique to lung cancer. The winning DEGs analysis allowed to identify an important number of TFs deregulated in the majority of microarray datasets, which can become key biomarkers of general tumors and specific to lung cancer. A coexpression network was constructed for every dataset with all deregulated genes associated with lung cancer, according to DAVID’s tool enrichment analysis, and transcription factors capable of regulating them, according to oPOSSUM´s tool. Several genes and transcription factors are coexpressed in the networks, suggesting that they could be related to the establishment or progression of the tumoral pathology in any tissue and specifically in the lung. The comparison of the coexpression networks of lung cancer and other types of cancer allowed the identification of common connectivity patterns with deregulated genes and transcription factors correlated to important tumoral processes and signaling pathways that have not been studied yet to experimentally validate their role in lung cancer. The Kaplan–Meier estimator determined the association of thirteen deregulated top winning transcription factors with the survival of lung cancer patients. The coregulatory analysis identified two top winning transcription factors networks related to the regulatory control of gene expression in lung and breast cancer. Our transcriptomic analysis suggests that cancer has an important coregulatory network of transcription factors related to the acquisition of the hallmarks of cancer. Moreover, lung cancer has a group of genes and transcription factors unique to pulmonary tissue that are coexpressed during tumorigenesis and must be studied experimentally to fully understand their role in the pathogenesis within its very complex transcriptomic scenario. Therefore, the downstream bioinformatic analysis developed was able to identify a coregulatory metafirm of cancer in general and specific to lung cancer taking into account the great heterogeneity of the tumoral process at cellular and population levels.

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.

The Potential Application and Promising Role of Targeted Therapy in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare yet serious progressive disorder that is currently incurable. This female-predominant disease unfolds as a pan-vasculopathy that affects all layers of the vessel wall. Five classes of pharmacological agents currently exist to target the three major cellular signaling pathways identified in PAH but are incapable of effectively reversing the disease progression. While several targets have been identified for therapy, none of the current PAH specific therapies are curative and cost-effective as they fail to reverse vascular remodeling and do not address the cancer-like features of PAH. Our purpose is to review the current literature on the therapeutic management of PAH, as well as the molecular targets under consideration for therapy so as to shed light on the potential role and future promise of novel strategies in treating this high-mortality disease. This review study summarizes and discusses the potential therapeutic targets to be employed against PAH. In addition to the three major conventional pathways already used in PAH therapy, targeting PDGF/PDGFR signaling, regulators in glycolytic metabolism, PI3K/AKT pathways, mitochondrial heat shock protein 90 (HSP90), high-mobility group box-1 (HMGB1), and bromodomain and extra-terminal (BET) proteins by using their specific inhibitors, or a pharmacological induction of the p53 expression, could be attractive strategies for treating PAH.

MDM2-Mediated Ubiquitination of RXRβ Contributes to Mitochondrial Damage and Related Inflammation in Atherosclerosis

A novel function of retinoid X receptor beta (RXRβ) in endothelial cells has been reported by us during the formation of atherosclerosis. Here, we extended the study to explore the cellular mechanisms of RXRβ protein stability regulation. In this study, we discovered that murine double minute-2 (MDM2) acts as an E3 ubiquitin ligase to target RXRβ for degradation. The result showed that MDM2 directly interacted with and regulated RXRβ protein stability. MDM2 promoted RXRβ poly-ubiquitination and degradation by proteasomes. Moreover, mutated MDM2 RING domain (C464A) or treatment with an MDM2 inhibitor targeting the RING domain of MDM2 lost the ability of MDM2 to regulate RXRβ protein expression and ubiquitination. Furthermore, treatment with MDM2 inhibitor alleviated oxidized low-density lipoprotein-induced mitochondrial damage, activation of TLR9/NF-κB and NLRP3/caspase-1 pathway and production of pro-inflammatory cytokines in endothelial cells. However, all these beneficial effects were reduced by the transfection of RXRβ siRNA. Moreover, pharmacological inhibition of MDM2 attenuated the development of atherosclerosis and reversed mitochondrial damage and related inflammation in the atherosclerotic process in LDLr^-/- mice, along with the increased RXRβ protein expression in the aorta. Therefore, our study uncovers a previously unknown ubiquitination pathway and suggests MDM2-mediated RXRβ ubiquitination as a new therapeutic target in atherosclerosis.

Glucose-6-phosphate dehydrogenase and MEG3 controls hypoxia-induced expression of serum response factor (SRF) and SRF-dependent genes in pulmonary smooth muscle cell

Although hypoxia induces aberrant gene expression and dedifferentiation of smooth muscle cells (SMCs), mechanisms that alter dedifferentiation gene expression by hypoxia remain unclear. Therefore, we aimed to gain insight into the hypoxia-controlled gene expression in SMCs. We conducted studies using SMCs cultured in 3% oxygen (hypoxia) and the lungs of mice exposed to 10% oxygen (hypoxia). Our results suggest hypoxia upregulated expression of transcription factor CP2-like protein1, krüppel-like factor 4, and E2f transcription factor 1 enriched genes including basonuclin 2 (Bcn2), serum response factor (Srf), polycomb 3 (Cbx8), homeobox D9 (Hoxd9), lysine demethylase 1A (Kdm1a), etc. Additionally, we found that silencing glucose-6-phosphate dehydrogenase (G6PD) expression and inhibiting G6PD activity downregulated Srf transcript and hypomethylation of SMC genes (Myocd, Myh11, and Cnn1) and concomitantly increased their expression in the lungs of hypoxic mice. Furthermore, G6PD inhibition hypomethylated MEG3, a long non-coding RNA, gene and upregulated MEG3 expression in the lungs of hypoxic mice and in hypoxic SMCs. Silencing MEG3 expression in SMC mitigated the hypoxia-induced transcription of SRF. These findings collectively demonstrate that MEG3 and G6PD codependently regulate Srf expression in hypoxic SMCs. Moreover, G6PD inhibition upregulated SRF-MYOCD-driven gene expression, determinant of a differentiated SMC phenotype.

Inhibition of KIF23 Alleviates IPAH by Targeting Pyroptosis and Proliferation of PASMCs

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive vascular disease with high mortality and heritability. Pyroptosis is a novel form of programmed cell death, and it is closely associated with IPAH. However, the roles of pyroptosis-related genes (PRGs) in IPAH are still largely unknown. In this study, we identified KIF23 as the most relevant gene for IPAH and pyroptosis, and its expression was significantly increased in pulmonary arterial smooth muscle cells (PASMCs) of IPAH. Besides, the pyroptosis level of PASMCs was also considerably upregulated in IPAH. Knockdown of KIF23 in PASMCs could significantly suppress the PASMCs’ pyroptosis and proliferation and then alleviate the increase in pulmonary arterial pressure, right ventricular hypertrophy, and pulmonary vascular resistance in IPAH. KIF23 regulated the expression of Caspase3, NLRP3, and HMGB1, and they were all involved in the PI3K/AKT and MAPK pathways, indicating that PI3K/AKT and MAPK pathways might participate in regulating PASMCs pyroptosis by KIF23. In conclusion, our study suggests that KIF23 may be a new therapeutic target for IPAH, which can alleviate the symptoms of IPAH by inhibiting the pyroptosis and proliferation of PASMCs.

Proteasome Inhibitors Decrease the Viability of Pulmonary Arterial Smooth Muscle Cells by Restoring Mitofusin-2 Expression under Hypoxic Conditions

Pulmonary hypertension (PH) is a severe progressive disease, and the uncontrolled proliferation of pulmonary artery smooth muscle cells (PASMCs) is one of the main causes. Mitofusin-2 (MFN2) profoundly inhibits cell growth and proliferation in a variety of tumor cell lines and rat vascular smooth muscle cells. Down-regulation of MFN2 is known to contribute to PH. Proteasome inhibitors have been shown to inhibit the proliferation of PASMCs; however, there is no study on the regulation of proteasome inhibitors through MFN-2 in the proliferation of PASMCs, a main pathophysiology of PH. In this study, PASMCs were exposed to hypoxic conditions and the expression of MFN2 and cleaved-PARP1 were detected by Western blotting. The effects of hypoxia and proteasome inhibitors on the cell viability of PASMC cells were detected by CCK8 assay. The results indicated that hypoxia increases the viability and reduces the expression of MFN2 in a PASMCs model. MFN2 overexpression inhibits the hypoxia-induced proliferation of PASMCs. In addition, proteasome inhibitors, bortezomib and marizomib, restored the decreased expression of MFN2 under hypoxic conditions, inhibited hypoxia-induced proliferation and induced the expression of cleaved-PARP1. These results suggest that bortezomib and marizomib have the potential to improve the hypoxia-induced proliferation of PASMCs by restoring MFN2 expression.

The Impact of Sex Chromosomes in the Sexual Dimorphism of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a sex-biased disease with a poorly understood female prevalence. Emerging research suggests that nonhormonal factors, such as the XX or XY sex chromosome complement and sex bias in gene expression, may also lead to sex-based differences in PAH incidence, penetrance, and progression. Typically, one of females' two X chromosomes is epigenetically silenced to offer a gender-balanced gene expression. Recent data demonstrate that the long noncoding RNA X-inactive specific transcript, essential for X chromosome inactivation and dosage compensation of X-linked gene expression, shows elevated levels in female PAH lung specimens compared with controls. This molecular event leads to incomplete inactivation of the females' second X chromosome, abnormal expression of X-linked gene(s) involved in PAH pathophysiology, and a pulmonary artery endothelial cell (PAEC) proliferative phenotype. Moreover, the pathogenic proliferative p38 mitogen-activated protein kinase/ETS transcription factor ELK1 (Elk1)/cFos signaling is mechanistically linked to the sexually dimorphic proliferative response of PAECs in PAH. Apprehending the complicated relationship between long noncoding RNA X-inactive specific transcript and X-linked genes and how this relationship integrates into a sexually dimorphic proliferation of PAECs and PAH sex paradox remain challenging. We highlight herein new findings related to how the sex chromosome complement and sex-differentiated epigenetic mechanisms to control gene expression are decisive players in the sexual dimorphism of PAH. Pharmacologic interventions in the light of the newly elucidated mechanisms are discussed.

Endothelial Senescence: A New Age in Pulmonary Hypertension

Pulmonary hypertension is an enigmatic, deleterious disease driven by multiple heterogeneous causes with a burgeoning proportion of older patients with complex, chronic comorbidities without adequate treatment options. The underlying endothelial pathophenotypes that direct vasoconstriction and panvascular remodeling remain both controversial and incompletely defined. This review discusses emerging concepts centered on endothelial senescence in pulmonary vascular disease. This principle proposes a more heterogeneous, dynamic pulmonary endothelium in disease; it provides a potentially unifying feature of endothelial dysfunction in pulmonary hypertension irrespective of cause; and it supports a clinically relevant link between aging and pulmonary hypertension like other chronic illnesses. Thus, taking cues from studies on aging and age-related diseases, we present possible opportunities and barriers to diagnostic and therapeutic targeting of senescence in pulmonary hypertension.

LncPTSR Triggers Vascular Remodeling in Pulmonary Hypertension by Regulating [Ca2+]i in Pulmonary Arterial Smooth Muscle Cells

Pulmonary hypertension (PH) is characterized by vascular remodeling and sustained increase in right ventricular systolic pressure (RVSP). The molecular mechanisms behind PH development remain unclear. Here, a long non-coding RNA (lncRNA) attenuated by platelet-derived growth factor BB (PDGF-BB) was identified and its functional roles were investigated in vitro and in vivo. Using RNA-seq data and rapid amplification of cDNA ends, a lncRNA neighboring the locus of plasma membrane calcium transporting ATPase 4 (PMCA4) was identified and named lncPTSR. It is a highly-conserved nuclear lncRNA, and was downregulated in pulmonary arterial smooth muscle cells (PASMCs) with PDGF-BB stimulation or hypoxia induction. Gene interruption/overexpression assays revealed that lncPTSR negatively regulates rat PASMCs proliferation, apoptosis, and migration. LncPTSR interruption in Sprague Dawley (SD) rats using adenovirus associated virus type 9 (AAV9)-mediated short-hairpin RNA (shRNA) resulted in a significant increase in RVSP and vascular remodeling in normoxic condition. LncPTSR knockdown also suppressed PMCA4 expression and attenuated the intracellular Ca2+ efflux of PASMCs in vitro and in vivo. Further studies suggest a complex cross-talk between lncPTSR and mitogen-activated protein kinase (MAPK) pathway: inhibition of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) abolishes the PDGF-BB-mediated lncPTSR downregulation, and lncPTSR plays a feedback regulation for MAPK signaling molecules. The present study suggests that lncPTSR participates in pulmonary artery (PA) remodeling via modulating the expression of PMCA4 and intracellular Ca2+ homeostasis downstream of PDGF-BB driven MEK/ERK signaling. These results suggest lncPTSR may be a promising therapeutic target in PH treatment.

Flavopiridol Mitigates the Progression of Monocrotaline-Induced Pulmonary Hypertension in Rats by Targeting Cyclin-Dependent Kinase 9

PURPOSE

To investigate the role of cyclin-dependent kinase 9 (CDK9) and the therapeutic potential of a CDK9 inhibitor (flavopiridol) in monocrotaline (MCT)-induced pulmonary hypertension (PH).

METHODS

For the in vivo experiments, rats with PH were established by a single intraperitoneal injection of MCT (60 mg/kg). After 2 weeks of MCT injection, rats were then treated with flavopiridol (5 mg/kg, i.p., twice a week) or vehicle for 2 weeks. For the in vitro experiments, human pulmonary artery smooth muscle cells (HPASMCs) were treated with flavopiridol (0.025-1 μM) or vehicle under hypoxic conditions. Hemodynamic recording, right ventricle histology, lung histology, and pulmonary arterial tissue isolation were performed. The expression levels of CDK9, RNA polymerase II, c-Myc, Mcl-1, and survivin were determined by qRT-PCR and western blotting, and the proliferation and apoptosis of rat pulmonary arterial tissues and/or HPASMCs were also assayed.

RESULTS

Compared to the control group, CDK9 was upregulated in pulmonary arterial tissues from MCT-induced PH rats and hypoxic cultured HPASMCs. Upregulation of CDK9 was associated with enhanced phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (RNA pol II) at serine-2 (Ser-2), promoting the expression of prosurvival and antiapoptotic proteins (c-Myc, Mcl-1, and survivin). Furthermore, treatment with flavopiridol (5 mg/kg) significantly alleviated pulmonary artery remodeling and partially reversed the progression of MCT-induced PH. Consistently, flavopiridol (0.5 μM) treatment decreased the proliferation and induced the apoptosis of cultured HPASMCs under hypoxic conditions. As a result of CDK9 inhibition and subsequent inhibition of RNA pol II CTD phosphorylation at Ser-2, flavopiridol decreased c-Myc, Mcl-1, and survivin expression in isolated pulmonary small arteries, leading to cell growth inhibition and apoptosis.

CONCLUSION

Flavopiridol mitigates the progression of MCT-induced PH in rats by targeting CDK9.

The Transition From Ambrisentan to Macitentan in Patients With Pulmonary Arterial Hypertension: A Real-word Prospective Study

Background: In a long-term event-driven trial, macitentan has demonstrated beneficial time to clinical worsening in patients with pulmonary arterial hypertension (PAH) and reduced PAH-related hospitalization rates compared with placebo. Macitentan is the most recently approved endothelin receptor antagonist (ERA) and is the first ERA that has shown efficacy for morbidity and mortality in PAH patients; therefore, patients and physicians may consider converting treatment from ambrisentan to macitentan. Our study evaluated the safety, efficacy, and quality of life in PAH patients transitioning from ambrisentan to macitentan. Methods: This was a real-world, prospective study with a 12-month follow-up. PAH patients who had received stable doses of ambrisentan for over 3 months, were within the World Health Organization Functional Class II/III, and 6-min walk distance ≥ of 250 m were enrolled. The study included a screening period, followed by a transition phase, after which patients entered the long-term follow-up. Clinical data and treatment satisfaction outcomes were collected to assess and monitor the safety and efficacy of the transition. The trial was registered at the Chinese Clinical Trial Registry (www.chictr.org.cn; No. ChiCTR2000034898). Results: One hundred and fifty-seven enrolled PAH patients completed the transition. All criteria for continuous treatment transition were met by 145 patients (92.4%). Results showed improvements in exercise capacity, cardiac function, and hemodynamics compared with baseline. During the process, 4 patients discontinued macitentan due to adverse events. There was no statistical difference in the overall incidence of adverse events before and after the transition. Conclusion: Transition to macitentan from ambrisentan was successful and well-tolerated by PAH patients, and was associated with greater efficacy and satisfaction.

The Transition From Ambrisentan to Macitentan in Patients With Pulmonary Arterial Hypertension: A Real-word Prospective Study

Background: In a long-term event-driven trial, macitentan has demonstrated beneficial time to clinical worsening in patients with pulmonary arterial hypertension (PAH) and reduced PAH-related hospitalization rates compared with placebo. Macitentan is the most recently approved endothelin receptor antagonist (ERA) and is the first ERA that has shown efficacy for morbidity and mortality in PAH patients; therefore, patients and physicians may consider converting treatment from ambrisentan to macitentan. Our study evaluated the safety, efficacy, and quality of life in PAH patients transitioning from ambrisentan to macitentan.

Methods: This was a real-world, prospective study with a 12-month follow-up. PAH patients who had received stable doses of ambrisentan for over 3 months, were within the World Health Organization Functional Class II/III, and 6-min walk distance ≥ of 250 m were enrolled. The study included a screening period, followed by a transition phase, after which patients entered the long-term follow-up. Clinical data and treatment satisfaction outcomes were collected to assess and monitor the safety and efficacy of the transition. The trial was registered at the Chinese Clinical Trial Registry (www.chictr.org.cn; No. ChiCTR2000034898).

Results: One hundred and fifty-seven enrolled PAH patients completed the transition. All criteria for continuous treatment transition were met by 145 patients (92.4%). Results showed improvements in exercise capacity, cardiac function, and hemodynamics compared with baseline. During the process, 4 patients discontinued macitentan due to adverse events. There was no statistical difference in the overall incidence of adverse events before and after the transition.

Conclusion: Transition to macitentan from ambrisentan was successful and well-tolerated by PAH patients, and was associated with greater efficacy and satisfaction.

Pulmonary Arterial Hypertension: Emerging Principles of Precision Medicine across Basic Science to Clinical Practice

Pulmonary arterial hypertension (PAH) is an enigmatic and deadly vascular disease with no known cure. Recent years have seen rapid advances in our understanding of the molecular underpinnings of PAH, with an expanding knowledge of the molecular, cellular, and systems-level drivers of disease that are being translated into novel therapeutic modalities. Simultaneous advances in clinical technology have led to a growing list of tools with potential application to diagnosis and phenotyping. Guided by fundamental biology, these developments hold the potential to usher in a new era of personalized medicine in PAH with broad implications for patient management and great promise for improved outcomes.

Utilizing Network Pharmacology and Molecular Docking Integrated Surface Plasmon Resonance Technology to Investigate the Potential Targets and Mechanisms of Tripterygium wilfordii against Pulmonary Artery Hypertension

BACKGROUND

Pulmonary artery hypertension (PAH) is a rare, life-limiting cardiopulmonary disorder characterized by the progressive and remodeling of pulmonary vasculature. Although the development of the technology brings us many approaches for the treatment of PAH, the effect of treatment is unsatisfactory. Tripterygium wilfordii (TW), as a traditional Chinese medicine (TCM), has been widely used in anti-inflammation, anticancer, and other fields. However, the potential of TW in treating PAH is currently unclear.

METHODS

Active ingredients and their corresponding genes were harvested from the Traditional Chinese Medicine Database and Analysis Platform (TCMSP), CTD, and STITCH. Meanwhile, genes associated with PAH were adopted from OMIM and GeneCards databases. Through Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analyses, potential targeting KEGG pathways and functions were further collected. Then, STRING was used to generate the protein-protein interaction (PPI) network. The "ingredients-targets-pathway" network was built by Cystoscope. Finally, the binding between active ingredients of TW and corresponding targets of PAH was identified via molecular docking technology and surface plasmon resonance (SPR) experiments.

RESULTS

The network pharmacology analysis revealed 36 active ingredients in TW and 150 potential targets related to the treatment of PAH with TW. Moreover, GO enrichment analysis showed that the key function in molecular function (MF) was related to enzyme binding, the key function in biological process (BP) was related to cellular response to organic substance, and the key function in cellular component (CC) was related to KEGG enrichment analysis and found that it was closely related to the IL-17 signaling pathway, TNF signaling pathway, Toll-like receptor signaling pathway, and apoptosis. At last, molecular docking results revealed that the main active ingredients of TW had a strong binding ability with the PAH target protein. In addition, the SPR experiment revealed that kaempferol was combined with the CASP3 protein rather than PARP1, while triptolide was combined with PARP1 rather than the CASP3 protein.

CONCLUSION

TW may have therapeutic effects on PAH through multitargets and multimethods, which provide a scientific basis for further elaborating the mechanism of Tripterygium wilfordii in the treatment of PAH.

Plasma tumour and metabolism related biomarkers AMBP, LPL and Glyoxalase I differentiate heart failure with preserved ejection fraction with pulmonary hypertension from pulmonary arterial hypertension

BACKGROUND

Discrimination of heart failure with preserved ejection fraction with pulmonary hypertension (HFpEF-PH) from pulmonary arterial hypertension (PAH) is crucial for clinical management but may be challenging due to similarities in clinical and comorbid characteristics. We aimed to investigate tumour and metabolism related proteins in differentiating HFpEF-PH from PAH.

METHODS

Sixty-nine tumour and metabolism plasma proteins were analysed with proximity extension assay in heathy controls (n = 20), patients with PAH (n = 48) and LHF-PH (n = 67) [HFpEF-PH (n = 31) and HF reduced EF-PH (n = 36)]. Haemodynamics were assessed with right heart catheterization.

RESULTS

The plasma levels of alpha-1-microglobulin/bikunin precursor (AMBP) and lipoprotein lipase (LPL), were higher in HFpEF-PH compared to healthy controls (p < 0.01), HFrEF-PH (p < 0.05), and PAH (p < 0.001). Glyoxalase I levels were higher in HFpEF-PH and HFrEF-PH compared to controls (p < 0.001) and PAH (p < 0.001). Each of plasma AMBP, LPL, and glyoxalase I, adjusted for age and sex in multivariable logistic regression models, could differentiate HFpEF-PH from PAH, with areas under the receiver operating characteristic curve (AUC) of 0.81, 0.84 and 0.79, respectively. The combination of AMBP, LPL and glyoxalse I yielded the largest AUC of 0.87 [95% confidence interval (0.79-0.95)] in discriminating HFpEF-PH from PAH, with a sensitivity of 87.1% and a specificity of 85.4%. In HFpEF-PH, the plasma levels of AMBP correlated with pulmonary arterial wedge pressure (r_s = -0.42, p = 0.018).

CONCLUSIONS

Plasma AMBP, LPL and glyoxalase I may facilitate the distinction of HFpEF-PH from PAH. Larger clinical studies are encouraged to confirm and validate our findings.

Innovative Anti-Inflammatory and Pro-resolving Strategies for Pulmonary Hypertension: High Blood Pressure Research Council of Australia Award 2019

Pulmonary hypertension is a rare, ostensibly incurable, and etiologically diverse disease with an unacceptably high 5-year mortality rate (≈50%), worse than many cancers. Irrespective of pathogenic origin, dysregulated immune processes underlie pulmonary hypertension pathobiology, particularly pertaining to pulmonary vascular remodeling. As such, a variety of proinflammatory pathways have been mooted as novel therapeutic targets. One such pathway involves the family of innate immune regulators known as inflammasomes. In addition, a new and emerging concept is differentiating between anti-inflammatory approaches versus those that promote pro-resolving pathways. This review will briefly introduce inflammasomes and examine recent literature concerning their role in pulmonary hypertension. Moreover, it will explore the difference between inflammation-suppressing and pro-resolution approaches and how this links to inflammasomes. Finally, we will investigate new avenues for targeting inflammation in pulmonary hypertension via more targeted anti-inflammatory or inflammation resolving strategies.

Transcriptomic profile of cationic channels in human pulmonary arterial hypertension

The dysregulation of K⁺ channels is a hallmark of pulmonary arterial hypertension (PAH). Herein, the channelome was analyzed in lungs of patients with PAH in a public transcriptomic database. Sixty six (46%) mRNA encoding cationic channels were dysregulated in PAH with most of them downregulated (83%). The principal component analysis indicated that dysregulated cationic channel expression is a signature of the disease. Changes were very similar in idiopathic, connective tissue disease and congenital heart disease associated PAH. This analysis 1) is in agreement with the widely recognized pathophysiological role of TASK1 and K_V1.5, 2) supports previous preliminary reports pointing to the dysregulation of several K⁺ channels including the downregulation of K_V1.1, K_V1.4, K_V1.6, K_V7.1, K_V7.4, K_V9.3 and TWIK2 and the upregulation of K_Ca1.1 and 3) points to other cationic channels dysregulated such as Kv7.3, TALK2, Ca_V1 and TRPV4 which might play a pathophysiological role in PAH. The significance of other changes found in Na⁺ and TRP channels remains to be investigated.

Critical role of VGLL4 in the regulation of chronic normobaric hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension (PH), a rare but deadly cardiopulmonary disorder, is characterized by extensive remodeling of pulmonary arteries resulting from enhancement of pulmonary artery smooth muscle cell proliferation and suppressed apoptosis; however, the underlying pathophysiological mechanisms remain largely unknown. Recently, epigenetics has gained increasing prominence in the development of PH. We aimed to investigate the role of vestigial-like family member 4 (VGLL4) in chronic normobaric hypoxia (CNH)-induced PH and to address whether it is associated with epigenetic regulation. The rodent model of PH was established by CNH treatment (10% O₂ , 23 hours/day). Western blot, quantitative reverse transcription polymerase chain reaction, immunofluorescence, immunoprecipitation, and adeno-associated virus tests were performed to explore the potential mechanisms involved in CNH-induced PH in mice. VGLL4 expression was upregulated and correlated with CNH in PH mouse lung tissues in a time-dependent manner. VGLL4 colocalized with α-smooth muscle actin in cultured pulmonary arterial smooth muscle cells (PASMCs), and VGLL4 immunoactivity was increased in PASMCs following hypoxia exposure in vitro. VGLL4 knockdown attenuated CNH-induced PH and pulmonary artery remodeling by blunting signal transducer and activator of transcription 3 (STAT3) signaling; conversely, VGLL4 overexpression exacerbated the development of PH. CNH enhanced the acetylation of VGLL4 and increased the interaction of ac-H3K9/VGLL4 and ac-H3K9/STAT3 in the lung tissues, and levels of ac-H3K9, p-STAT3/STAT3, and proliferation-associated protein levels were markedly up-regulated, whereas apoptosis-related protein levels were significantly downregulated, in the lung tissues of mice with CNH-induced PH. Notably, abrogation of VGLL4 acetylation reversed CNH-induced PH and pulmonary artery remodeling and suppressed STAT3 signaling. Finally, STAT3 knockdown alleviated CNH-induced PH. In conclusion, VGLL4 acetylation upregulation could contribute to CNH-induced PH and pulmonary artery remodeling via STAT3 signaling, and abrogation of VGLL4 acetylation reversed CNH-induced PH. Pharmacological or genetic deletion of VGLL4 might be a potential target for therapeutic interventions in CNH-induced PH.

Emodin inhibits viability, proliferation and promotes apoptosis of hypoxic human pulmonary artery smooth muscle cells via targeting miR-244-5p/DEGS1 axis

OBJECTIVE

This study aimed to determine the effects of emodin on the viability, proliferation and apoptosis of human pulmonary artery smooth muscle cells (PASMCs) under hypoxia and to explore the underling molecular mechanisms.

METHODS

PASMCs were cultured in a hypoxic environment (1% oxygen) and then treated with emodin. Cell viability, proliferation and apoptosis were evaluated using CCK-8 assay, EdU staining assay, western blot and Mito-tracker red CMXRos and Annexin V-FITC apoptosis detection assay. The microRNA (miRNA)/mRNA and protein expression levels were assessed by quantitative real-time PCR and western blotting, respectively. Based on transcriptomics and proteomics were used to identify potential signaling pathways. Luciferase reporter assay was utilized to examine the interaction between miR-244-5p and DEGS1.

RESULTS

Emodin at 40 and 160 µM concentration-dependently suppressed cell viability, proliferation and migration, but enhanced cell apoptosis of PASMCs under hypoxia. Transcriptomic and proteomic analysis revealed that emodin could attenuate the activity of PI3K/Akt signaling in PASMCs under hypoxia. In addition, delta 4-desaturase, sphingolipid 1 (DEGS1) was found to be a direct target of miR-244-5p. Emodin could significantly up-regulated miR-244-5p expression and down-regulated DEGS1 expression in PASMCs under hypoxia. Furthermore, emodin-mediated effects on cell viability, migration, apoptosis and PI3K/Akt signaling activity of PASMCs under hypoxia were significantly attenuated by miR-244-5p knockdown.

CONCLUSIONS

Our results indicated that emodin suppressed cell viability, proliferation and migration, promoted cell apoptosis of PASMCs under hypoxia via modulating miR-244-5p-mediated DEGS1/PI3K/Akt signaling pathway. MiR-244-5p/DEGS1 axis was initially investigated in this current study, which is expected to further the understanding of the etiology of pulmonary arterial hypertension.

Role of Long Non-Coding RNAs in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a debilitating condition of the pulmonary circulatory system that occurs in patients of all ages and if untreated, eventually leads to right heart failure and death. Despite existing medical treatment options that improve survival and quality of life, the disease remains incurable. Thus, there is an urgent need to develop novel therapies to treat this disease. Emerging evidence suggests that long non-coding RNAs (lncRNAs) play critical roles in pulmonary vascular remodeling and PAH. LncRNAs are implicated in pulmonary arterial endothelial dysfunction by modulating endothelial cell proliferation, angiogenesis, endothelial mesenchymal transition, and metabolism. LncRNAs are also involved in inducing different pulmonary arterial vascular smooth muscle cell phenotypes, such as cell proliferation, apoptosis, migration, regulation of the phenotypic switching, and cell cycle. LncRNAs are essential regulators of gene expression that affect various diseases at the chromatin, transcriptional, post-translational, and even post-translational levels. Here, we focus on the role of LncRNAs and their molecular mechanisms in the pathogenesis of PAH. We also discuss the current research challenge and potential biomarker and therapeutic potentials of lncRNAs in PAH.

Application of [18F]FLT-PET in pulmonary arterial hypertension: a clinical study in pulmonary arterial hypertension patients and unaffected bone morphogenetic protein receptor type 2 mutation carriers

Pulmonary arterial hypertension is a heterogeneous group of diseases characterized by vascular cell proliferation leading to pulmonary vascular remodelling and ultimately right heart failure. Previous data indicated that 3'-deoxy-3'-[18F]-fluorothymidine (18FLT) positron emission tomography (PET) scanning was increased in pulmonary arterial hypertension patients, hence providing a possible biomarker for pulmonary arterial hypertension as it reflects vascular cell hyperproliferation in the lung. This study sought to validate 18FLT-PET in an expanded cohort of pulmonary arterial hypertension patients in comparison to matched healthy controls and unaffected bone morphogenetic protein receptor type 2 mutation carriers. 18FLT-PET scanning was performed in 21 pulmonary arterial hypertension patients (15 hereditary pulmonary arterial hypertension and 6 idiopathic pulmonary arterial hypertension), 11 unaffected mutation carriers and 9 healthy control subjects. In-depth kinetic analysis indicated that there were no differences in lung 18FLT k3 phosphorylation among pulmonary arterial hypertension patients, unaffected bone morphogenetic protein receptor type 2 mutation carriers and healthy controls. Lung 18FLT uptake did not correlate with haemodynamic or clinical parameters in pulmonary arterial hypertension patients. Sequential 18FLT-PET scanning in three patients demonstrated uneven regional distribution in 18FLT uptake by 3D parametric mapping of the lung, although this did not follow the clinical course of the patient. We did not detect significantly increased lung 18FLT uptake in pulmonary arterial hypertension patients, nor in the unaffected bone morphogenetic protein receptor type 2 mutation carriers, as compared to healthy subjects. The conflicting results with our preliminary human 18FLT report may be explained by a small sample size previously and we observed large variation of lung 18FLT signals between patients, challenging the application of 18FLT-PET as a biomarker in the pulmonary arterial hypertension clinic.

ROCK Inhibition as Potential Target for Treatment of Pulmonary Hypertension

Pulmonary hypertension (PH) is a cardiovascular disease caused by extensive vascular remodeling in the lungs, which ultimately leads to death in consequence of right ventricle (RV) failure. While current drugs for PH therapy address the sustained vasoconstriction, no agent effectively targets vascular cell proliferation and tissue inflammation. Rho-associated protein kinases (ROCKs) emerged in the last few decades as promising targets for PH therapy, since ROCK inhibitors demonstrated significant anti-remodeling and anti-inflammatory effects. In this review, current aspects of ROCK inhibition therapy are discussed in relation to the treatment of PH and RV dysfunction, from cell biology to preclinical and clinical studies.

CDC2 Is an Important Driver of Vascular Smooth Muscle Cell Proliferation via FOXM1 and PLK1 in Pulmonary Arterial Hypertension

A key feature of pulmonary arterial hypertension (PAH) is the hyperplastic proliferation exhibited by the vascular smooth muscle cells from patients (HPASMC). The growth inducers FOXM1 and PLK1 are highly upregulated in these cells. The mechanism by which these two proteins direct aberrant growth in these cells is not clear. Herein, we identify cyclin-dependent kinase 1 (CDK1), also termed cell division cycle protein 2 (CDC2), as having a primary role in promoting progress of the cell cycle leading to proliferation in HPASMC. HPASMC obtained from PAH patients and pulmonary arteries from Sugen/hypoxia rats were investigated for their expression of CDC2. Protein levels of CDC2 were much higher in PAH than in cells from normal donors. Knocking down FOXM1 or PLK1 protein expression with siRNA or pharmacological inhibitors lowered the cellular expression of CDC2 considerably. However, knockdown of CDC2 with siRNA or inhibiting its activity with RO-3306 did not reduce the protein expression of FOXM1 or PLK1. Expression of CDC2 and FOXM1 reached its maximum at G1/S, while PLK1 reached its maximum at G2/M phase of the cell cycle. The expression of other CDKs such as CDK2, CDK4, CDK6, CDK7, and CDK9 did not change in PAH HPASMC. Moreover, inhibition via Wee1 inhibitor adavosertib or siRNAs targeting Wee1, Myt1, CDC25A, CDC25B, or CDC25C led to dramatic decreases in CDC2 protein expression. Lastly, we found CDC2 expression at the RNA and protein level to be upregulated in pulmonary arteries during disease progression Sugen/hypoxia rats. In sum, our present results illustrate that the increased expression of FOXM1 and PLK1 in PAH leads directly to increased expression of CDC2 resulting in potentiated growth hyperactivity of PASMC from patients with pulmonary hypertension. Our results further suggest that the regulation of CDC2, or associated regulatory proteins, will prove beneficial in the treatment of this disease.

Fetal Gene Reactivation in Pulmonary Arterial Hypertension: GOOD, BAD, or BOTH?

Pulmonary arterial hypertension is a debilitating chronic disorder marked by the progressive obliteration of the pre-capillary arterioles. This imposes a pressure overload on the right ventricle (RV) pushing the latter to undergo structural and mechanical adaptations that inexorably culminate in RV failure and death. Thanks to the advances in molecular biology, it has been proposed that some aspects of the RV and pulmonary vascular remodeling processes are orchestrated by a subversion of developmental regulatory mechanisms with an upregulation of a suite of genes responsible for the embryo's early growth and normally repressed in adults. In this review, we present relevant background regarding the close relationship between overactivation of fetal genes and cardiopulmonary remodeling, exploring whether the reawakening of developmental factors plays a causative role or constitutes a protective mechanism in the setting of PAH.

Inhibition of Glucose-6-Phosphate Dehydrogenase Activity Attenuates Right Ventricle Pressure and Hypertrophy Elicited by VEGFR Inhibitor + Hypoxia

Pulmonary hypertension (PH) is a disease of hyperplasia of pulmonary vascular cells. The pentose phosphate pathway (PPP)-a fundamental glucose metabolism pathway-is vital for cell growth. Because treatment of PH is inadequate, our goal was to determine whether inhibition of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP, prevents maladaptive gene expression that promotes smooth muscle cell (SMC) growth, reduces pulmonary artery remodeling, and normalizes hemodynamics in experimental models of PH. PH was induced in mice by exposure to 10% oxygen (Hx) or weekly injection of vascular endothelial growth factor receptor blocker [Sugen5416 (SU); 20 mg kg-1] during exposure to hypoxia (Hx + SU). A novel G6PD inhibitor (N-[(3β,5α)-17-oxoandrostan-3-yl]sulfamide; 1.5 mg kg-1) was injected daily during exposure to Hx. We measured right ventricle (RV) pressure and left ventricle pressure-volume relationships and gene expression in lungs of normoxic, Hx, and Hx + SU and G6PD inhibitor-treated mice. RV systolic and end-diastolic pressures were higher in Hx and Hx + SU than normoxic control mice. Hx and Hx + SU decreased expression of epigenetic modifiers (writers and erasers), increased hypomethylation of the DNA, and induced aberrant gene expression in lungs. G6PD inhibition decreased maladaptive expression of genes and SMC growth, reduced pulmonary vascular remodeling, and decreased right ventricle pressures compared with untreated PH groups. Pharmacologic inhibition of G6PD activity, by normalizing activity of epigenetic modifiers and DNA methylation, efficaciously reduces RV pressure overload in Hx and Hx + SU mice and preclinical models of PH and appears to be a safe pharmacotherapeutic strategy. SIGNIFICANCE STATEMENT: The results of this study demonstrated that inhibition of a metabolic enzyme efficaciously reduces pulmonary hypertension. For the first time, this study shows that a novel inhibitor of glucose-6-phosphate dehydrogenase, the rate-limiting enzyme in the fundamental pentose phosphate pathway, modulates DNA methylation and alleviates pulmonary artery remodeling and dilates pulmonary artery to reduce pulmonary hypertension.

Novel TNIP2 and TRAF2 Variants Are Implicated in the Pathogenesis of Pulmonary Arterial Hypertension

Background: Pulmonary arterial hypertension (PAH) is a rare disease characterized by pulmonary vascular remodeling and right heart failure. Specific genetic variants increase the incidence of PAH in carriers with a family history of PAH, those who suffer from certain medical conditions, and even those with no apparent risk factors. Inflammation and immune dysregulation are related to vascular remodeling in PAH, but whether genetic susceptibility modifies the PAH immune response is unclear. TNIP2 and TRAF2 encode for immunomodulatory proteins that regulate NF-κB activation, a transcription factor complex associated with inflammation and vascular remodeling in PAH. Methods: Two unrelated families with PAH cases underwent whole-exome sequencing (WES). A custom pipeline for variant prioritization was carried out to obtain candidate variants. To determine the impact of TNIP2 and TRAF2 in cell proliferation, we performed an MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay on healthy lung pericytes transfected with siRNA specific for each gene. To measure the effect of loss of TNIP2 and TRAF2 on NF-kappa-beta (NF-κB) activity, we measured levels of Phospho-p65-NF-κB in siRNA-transfected pericytes using western immunoblotting. Results: We discovered a novel missense variant in the TNIP2 gene in two affected individuals from the same family. The two patients had a complex form of PAH with interatrial communication and scleroderma. In the second family, WES of the proband with PAH and primary biliary cirrhosis revealed a de novo protein-truncating variant in the TRAF2. The knockdown of TNIP2 and TRAF2 increased NF-κB activity in healthy lung pericytes, which correlated with a significant increase in proliferation over 24 h. Conclusions: We have identified two rare novel variants in TNIP2 and TRAF2 using WES. We speculate that loss of function in these genes promotes pulmonary vascular remodeling by allowing overactivation of the NF-κB signaling activity. Our findings support a role for WES in helping identify novel genetic variants associated with dysfunctional immune response in PAH.