Characteristics and outcomes of patients developing pulmonary hypertension associated with proteasome inhibitors.

RATIONALE: Pulmonary arterial hypertension (PAH) has been described in patients treated with proteasome inhibitors (PI). OBJECTIVES: To evaluate the association between PI and PAH. METHODS: Characteristics of incident PAH cases previously treated with Carfilzomib or Bortezomib were analyzed from the French PH Registry and the VIGIAPATH program from 2004 to 2023, concurrently with a pharmacovigilance disproportionality analysis using the WHO's global database, and a meta-analysis of randomized controlled trials. RESULTS: Eleven incident cases of PI associated PAH were identified (6 with Carfilzomib and 5 with Bortezomib) with a female: male ratio of 2.7:1, a median age of 61 years, and a median delay between PI first exposure and PAH of 6 months. Four patients died (2 from right heart failure, 1 from respiratory distress, and 1 from an unknown cause). At diagnosis, 6 were in NYHA-Fc III/IV with severe hemodynamic impairment (median mean pulmonary artery pressure of 39 mmHg, cardiac index 2.45 L/min·m-2, and pulmonary vascular resistance of 7.2 WU). In the WHO pharmacovigilance database, 166 cases of PH associated with PI were reported since 2013 with significant statistics of disproportionate reporting (SDR) for Carfilzomib, regardless of the definition of cases or control group. However, SDR for Bortezomib was inconsistent. The systematic review identified 17 clinical trials, and Carfilzomib was associated with a significantly higher risk of dyspnea, severe dyspnea and PH compared to Bortezomib. CONCLUSION: PI may induce PAH in patients undergoing treatment, with Carfilzomib emitting a stronger signal than Bortezomib, and these patients should be monitored closely.

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.

A correlated light and electron microscopy approach to study the subcellular localization of phosphorylated vimentin in human lung tissue.

Correlative microscopy is an important approach for bridging the resolution gap between fluorescence light and electron microscopy. Here, we describe a fast and simple method for correlative immunofluorescence and immunogold labeling on the same section to elucidate the localization of phosphorylated vimentin (P-Vim), a robust feature of pulmonary vascular remodeling in cells of human lung small arteries. The lung is a complex, soft and difficult tissue to prepare for transmission electron microscopy (TEM). Detailing the molecular composition of small pulmonary arteries (<500µm) would be of great significance for research and diagnostics. Using the classical methods of immunochemistry (either hydrophilic resin or thin cryosections), is difficult to locate small arteries for analysis by TEM. To address this problem and to observe the same structures by both light and electron microscopy, correlative microscopy is a reliable approach. Immunofluorescence enables us to know the distribution of P-Vim in cells but does not provide ultrastructural detail on its localization. Labeled structures selected by fluorescence microscope can be identified and further analyzed by TEM at high resolution. With our method, the morphology of the arteries is well preserved, enabling the localization of P-Vim inside pulmonary endothelial cells. By applying this approach, fluorescent signals can be directly correlated to the corresponding subcellular structures in areas of interest.

Differential responses of pulmonary vascular cells from PAH patients and controls to TNFα and the effect of the BET inhibitor JQ1.

BACKGROUND: Pulmonary arterial hypertension (PAH) encompasses a group of diseases characterized by raised pulmonary vascular resistance, resulting from vascular remodelling and inflammation. Bromodomain and extra-terminal (BET) proteins are required for the expression of a subset of NF-κB-induced inflammatory genes which can be inhibited by the BET mimic JQ1+. We hypothesised that JQ+ would supress TNFα-driven inflammatory responses in human pulmonary vascular cells from PAH patients. METHODS: Immunohistochemical staining of human peripheral lung tissue (N = 14 PAH and N = 12 non-PAH) was performed for the BET proteins BRD2 and 4. Human pulmonary microvascular endothelial cells (HPMEC) and pulmonary artery smooth muscle cells (HPASMC) from PAH patients (N = 4) and non-PAH controls (N = 4) were stimulated with TNFα in presence or absence of JQ1+ or its inactive isomer JQ1-. IL-6 and -8 mRNA was measured by RT-qPCR and protein levels by ELISA. Chromatin immunoprecipitation analysis was performed using EZ-ChIP™ and NF-κB p65 activation determined using a TransAm kit. MTT assay was used to measure cell viability. RESULTS: Nuclear staining of BRD2 and BRD4 was significantly (p < 0.0001) increased in the lung vascular endothelial and smooth muscle cells from PAH patients compared to controls with normal lung function. TNFα-driven IL-6 release from both HPMECs and HPASMCs was greater in PAH cells than control cells. Levels of CXCL8/IL-8 protein release was higher in PAH HPASMCs than in control cells with similar release observed in HPMECs. TNFα-induced recruitment of activated NF-κB p65 to the IL-6 and CXCL8/IL-8 promoters were similar in both cell types and between subject groups. JQ1+ suppressed TNFα-induced IL-6 and CXCL8/IL-8 release and mRNA expression to a comparable extent in control and PAH HPMECs and HPASMCs. JQ1 had a greater efficacy on IL-6 release in HPMEC and on CXCL8/IL-8 release in HPASMC. CONCLUSION: BET inhibition decreases TNFα driven inflammation in primary pulmonary vascular cells. The anti-inflammatory actions of JQ1 suggests distinct cell-specific regulatory control of these genes. BET proteins could be a target for future therapies for PAH.

Impairment of Angiogenesis-Driven Clot Resolution Is a Key Event in the Progression to Chronic Thromboembolic Pulmonary Hypertension: Validation in a Novel Rabbit Model.

BACKGROUND: Chronic thromboembolic pulmonary hypertension (CTEPH) is a life-threatening condition and rare complication of acute pulmonary embolism. Mechanisms underlying impaired clot resolution and in sustained fibrothrombotic obstruction of the pulmonary arterial bed remain poorly understood. Since defective angiogenesis correlated to defective clot resolution based on observations in surgical material from patients with CTEPH, we aimed to validate its crucial pathogenic role by intrathrombus inhibition of angiogenesis in a novel CTEPH rabbit model. METHODS: We aimed to compare whether intrathrombus administration of an antifibrinolytic agent, tranexamic acid, or an inhibitor of angiogenesis, SU5416, would contribute to CTEPH progression. Both products were administered on a weekly basis by autologous clot embolization in rabbits. Right ventricular pressure was monitored by telemetry, right ventricular function by transthoracic echocardiography, and a complete pulmonary hemodynamic evaluation was obtained through right heart catheterization. Markers of inflammation, endothelial dysfunction, heart failure, and fibrinolysis were measured in plasma. Pulmonary vessel remodeling was analyzed by immunohistochemistry. RESULTS: Impairing intrathrombus angiogenesis by repeatedly embolizing autologous blood clots containing SU5416 resulted in elevated mean pulmonary arterial pressure (38 mm Hg), increased indexed pulmonary vascular resistance, and enhanced right ventricular hypertrophy (80%, 1.9-fold, 36%, respectively, compared with rabbits embolized with clots containing an antifibrinolytic agent). This was caused by both obstruction of large pulmonary arteries with fibrothrombotic material and muscularization of pulmonary microvessels, and accompanied by inflammatory cell infiltration and increased circulating endothelin-1. CONCLUSIONS: The key role of angiogenesis-driven clot resolution was validated in a reliable small-animal model reproducing the major pathophysiological hallmarks of CTEPH.

[Physiopathology and treatment of pulmonary arterial hypertension]. / Physiopathologie et traitements de l'hypertension artérielle pulmonaire.

Pulmonary arterial hypertension (PAH) is a rare disease affecting mainly the pre-capillary pulmonary vascular bed. However, some forms of the disease have venous/capillary involvement. It is an obstructive remodelling of the pulmonary arterioles coupled with vascular pruning, increasing right ventricular afterload and leading to right heart failure. PAH has a complex pathogeny that is detailed in this review. Current specific treatments target endothelial dysfunction, and primarily aim at vasodilatation. Promising innovative treatments targeting the pulmonary artery remodelling are under development.

Title: Physiopathologie et traitements de l'hypertension artérielle pulmonaire. Abstract: L'hypertension artérielle pulmonaire (HTAP) est une maladie rare affectant principalement le lit vasculaire pulmonaire pré-capillaire. Certaines formes de la maladie présentent néanmoins une atteinte veinulaire/capillaire. Il s'agit d'un remodelage obstructif des artérioles pulmonaires couplé à une raréfaction vasculaire, augmentant la post-charge ventriculaire1 droite et conduisant à une insuffisance cardiaque droite. La physiopathologie de l'HTAP est complexe. Les traitements spécifiques actuels ciblent la dysfonction endothéliale, avec une action essentiellement vasodilatatrice. Des traitements innovants prometteurs ciblant le remodelage vasculaire pulmonaire sont en cours de développement.

Monitoring of Hemodynamics With Right Heart Catheterization in Children With Pulmonary Arterial Hypertension.

Background Right heart catheterization (RHC) is a high-risk procedure in children with pulmonary arterial hypertension without clear guidelines for the indications and targets of invasive reassessment. Our objectives are to define the aims of repeated RHC and evaluate the correlation between noninvasive criteria and hemodynamic parameters. Methods and Results Clinical and hemodynamic characteristics from 71 incident treatment-naïve children (median age 6.2 years) with pulmonary arterial hypertension who had a baseline and reevaluation RHC were analyzed. Correlations between noninvasive predictors and hemodynamic parameters were tested. Adverse outcomes were defined as death, lung transplantation, or Potts shunt. At baseline, pulmonary vascular resistance index (hazard ratio [HR] 1.07 per 1 WU·m2 increase [95% CI, 1.02-1.12], P=0.002), stroke volume index (HR 0.95 per 1 L·min-1·m-2 increase [95% CI, 0.91-0.99], P=0.012), pulmonary artery compliance index (HR 0.16 per 1 mL·mm Hg-1·m-2 increase [95% CI, 0.051-0.52], P=0.002), and right atrial pressure (HR, 1.31 per 1 mm Hg increase [95% CI, 1.01-1.71], P=0.043) were associated with adverse outcomes. Pulmonary vascular resistance index, pulmonary artery compliance index, and right atrial pressure were still associated with a worse outcome at second RHC. Noninvasive criteria accurately predicted hemodynamic evolution; however, 70% of the patients who had improved based on noninvasive criteria still presented at least 1 "at risk" hemodynamics at second RHC. Conclusions Pulmonary vascular resistance index, pulmonary artery compliance index, and right atrial pressure are solid predictors of adverse outcomes in pediatric pulmonary arterial hypertension and potential therapeutic targets. Noninvasive criteria accurately predict the evolution of hemodynamic parameters, but insufficiently. Repeated RHC are helpful to identify children with persistent higher risk after treatment introduction.

T-cell dysregulation and inflammatory process in Gcn2 (Eif2ak4-/-)-deficient rats in basal and stress conditions.

Hereditary pulmonary veno-occlusive disease (hPVOD) is a severe form of autosomal recessive pulmonary hypertension and is due to biallelic loss of function of the EIF2AK4 gene (alias GCN2) coding for GCN2. GCN2 is a stress kinase that belongs to the integrated stress response pathway (ISR). Three rat lines carrying biallelic Gcn2 mutation were generated and found phenotypically normal and did not spontaneously develop a PVOD-related disease. We submitted these rats to amino acid deprivation to document the molecular and cellular response of the lungs and to identify phenotypic changes that could be involved in PVOD pathophysiology. Gcn2-/- rat lungs were analyzed under basal conditions and 3 days after a single administration of PEG-asparaginase (ASNase). Lung mRNAs were analyzed by RNAseq and single-cell RNAseq (scRNA-seq), flow cytometry, tissue imaging, and Western blots. The ISR was not activated after ASNase treatment in Gcn2-/- rat lungs, and apoptosis was increased. Several proinflammatory and innate immunity genes were overexpressed, and inflammatory cells infiltration was also observed in the perivascular area. Under basal conditions, scRNA-seq analysis of Gcn2-/- rat lungs revealed increases in two T-cell populations, a LAG3+ T-cell population and a proliferative T-cell population. Following ASNase administration, we observed an increase in calprotectin expression involved in TLR pathway activation and neutrophil infiltration. In conclusion, under basal and asparagine and glutamine deprivation induced by asparaginase administration, Gcn2-/- rats display molecular and cellular signatures in the lungs that may indicate a role for Gcn2 in immune homeostasis and provide further clues to the mechanisms of hPVOD development.

Bleomycin-induced lung injury: Revisiting an old tool to model group III PH associated with pulmonary fibrosis.

Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation that often associates with other respiratory diseases (i.e., group III PH), leading to worsened symptoms and prognosis, notably when combined with interstitial lung diseases such as pulmonary fibrosis (PF). PH may lead to right ventricular (RV) failure, which accounts for a substantial part of the mortality in chronic lung disease patients. The disappointing results of pulmonary arterial hypertension (PAH)-related therapies in patients with PF emphasize the need to better understand the pathophysiologic mechanisms that drive PH development and progression in this specific setting. In this work, we validated an animal model of group III PH associated with PF (PH-PF), by using bleomycin (BM) intratracheal instillation and characterizing the nature of induced lung and vascular remodeling, including the influence on RV structure and function. To our knowledge, this is the first work describing this dose of BM in Sprague Dawley rats and the effects upon the heart and lungs, using different techniques such as echocardiography, heart catheterization, and histology. Our data shows the successful implementation of a rat model that mimics combined PF-PH, with most features seen in the equivalent human disease, such as lung and arterial remodeling, increased mPAP and RV dysfunction.

Disruption of GCN2 Pathway Aggravates Vascular and Parenchymal Remodeling during Pulmonary Fibrosis.

Pulmonary fibrosis (PF) and pulmonary hypertension (PH) are chronic diseases of the pulmonary parenchyma and circulation, respectively, which may coexist, but underlying mechanisms remain elusive. Mutations in the GCN2 (general control nonderepressible 2) gene (EIF2AK4 [eukaryotic translation initiation factor 2 alpha kinase 4]) were recently associated with pulmonary veno-occlusive disease. The aim of this study is to explore the involvement of the GCN2/eIF2α (eukaryotic initiation factor 2α) pathway in the development of PH during PF, in both human disease and in a laboratory animal model. Lung tissue from patients with PF with or without PH was collected at the time of lung transplantation, and control tissue was obtained from tumor resection surgery. Experimental lung disease was induced in either male wild-type or EIF2AK4-mutated Sprague-Dawley rats, randomly receiving a single intratracheal instillation of bleomycin or saline. Hemodynamic studies and organ collection were performed 3 weeks after instillation. Only significant results (P < 0.05) are presented. In PF lung tissue, GCN2 protein expression was decreased compared with control tissue. GCN2 expression was reduced in CD31+ endothelial cells. In line with human data, GCN2 protein expression was decreased in the lung of bleomycin rats compared with saline. EIF2AK4-mutated rats treated with bleomycin showed increased parenchymal fibrosis (hydroxyproline concentrations) and vascular remodeling (media wall thickness) as well as increased right ventricular systolic pressure compared with wild-type animals. Our data show that GCN2 is dysregulated in both humans and in an animal model of combined PF and PH. The possibility of a causative implication of GCN2 dysregulation in PF and/or PH development should be further studied.

Molecular Function and Contribution of TBX4 in Development and Disease.

Over the past decade, recognition of the profound impact of the TBX4 (T-box 4) gene, which encodes a member of the evolutionarily conserved family of T-box-containing transcription factors, on respiratory diseases has emerged. The developmental importance of TBX4 is emphasized by the association of TBX4 variants with congenital disorders involving respiratory and skeletal structures; however, the exact role of TBX4 in human development remains incompletely understood. Here, we discuss the developmental, tissue-specific, and pathological TBX4 functions identified through human and animal studies and review the published TBX4 variants resulting in variable disease phenotypes. We also outline future research directions to fill the gaps in our understanding of TBX4 function and of how TBX4 disruption affects development.

Lipidomic Profile Analysis of Lung Tissues Revealed Lipointoxication in Pulmonary Veno-Occlusive Disease.

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary arterial hypertension (PAH) occurring in a heritable form (hPVOD) due to biallelic inactivating mutations of EIF2AK4 (encoding GCN2, general control nonderepressible 2) or in a sporadic form in older age (sPVOD), following exposure to chemotherapy or organic solvents. In contrast to PAH, PVOD is characterized by a particular remodeling of the pulmonary venous system and the obliteration of small pulmonary veins by fibrous intimal thickening and patchy capillary proliferation. The pathobiological knowledge of PVOD is poor, explaining the absence of medical therapy for PVOD. Lung transplantation remains the only therapy for eligible PVOD patients. As we recently demonstrated, respiratory diseases, chronic obstructive pulmonary disease, or cystic fibrosis exhibit lipointoxication signatures characterized by excessive levels of saturated phospholipids contributing to the pathological features of these diseases, including endoplasmic reticulum stress, pro-inflammatory cytokines production, and bronchoconstriction. In this study, we investigated and compared the clinical data and lung lipid signature of control (10 patients), idiopathic PAH (7 patients), heritable PAH (9 BMPR2 mutations carriers), hPVOD (10 EIF2AK4 mutation carriers), and sPVOD (6 non-carriers) subjects. Mass spectrometry analyses demonstrated lung lipointoxication only in hPVOD patients, characterized by an increased abundance of saturated phosphatidylcholine (PC) at the expense of the polyunsaturated species in the lungs of hPVOD patients. The present data suggest that lipointoxication could be a potential player in the etiology of PVOD.

An Overview of Circulating Pulmonary Arterial Hypertension Biomarkers.

Pulmonary arterial hypertension (PAH), also known as Group 1 Pulmonary Hypertension (PH), is a PH subset characterized by pulmonary vascular remodeling and pulmonary arterial obstruction. PAH has an estimated incidence of 15-50 people per million in the United States and Europe, and is associated with high mortality and morbidity, with patients' survival time after diagnosis being only 2.8 years. According to current guidelines, right heart catheterization is the gold standard for diagnostic and prognostic evaluation of PAH patients. However, this technique is highly invasive, so it is not used in routine clinical practice or patient follow-up. Thereby, it is essential to find new non-invasive strategies for evaluating disease progression. Biomarkers can be an effective solution for determining PAH patient prognosis and response to therapy, and aiding in diagnostic efforts, so long as their detection is non-invasive, easy, and objective. This review aims to clarify and describe some of the potential new candidates as circulating biomarkers of PAH.

An emerging phenotype of pulmonary arterial hypertension patients carrying SOX17 variants.

BACKGROUND: The phenotype of pulmonary arterial hypertension (PAH) patients carrying SOX17 pathogenic variants remains mostly unknown. METHODS: We report the genetic analysis findings, characteristics and outcomes of patients with heritable PAH carrying SOX17 variants from the French Pulmonary Hypertension Network. RESULTS: 20 patients and eight unaffected relatives were identified. The median (range) age at diagnosis was 17 (2-53) years, with a female:male ratio of 1.5. At diagnosis, most of the patients (74%) were in New York Heart Association Functional Class III or IV with severe haemodynamic compromise, including a median pulmonary vascular resistance of 14.0 (4.2-31.5) WU. An associated congenital heart disease (CHD) was found in seven PAH patients (35%). Patients with CHD-associated PAH were significantly younger at diagnosis than PAH patients without CHD. Four patients (20%) suffered from recurrent haemoptysis requiring repeated arterial embolisations. 13 out of 16 patients (81%) for whom imaging was available displayed chest computed tomography abnormalities, including dilated, tortuous pulmonary vessels, ground-glass opacities as well as anomalies of the bronchial and nonbronchial arteries. After a median (range) follow-up of 47 (1-591) months, 10 patients underwent lung transplantation and one patient benefited from a heart-lung transplantation due to associated CHD. Histopathological analysis of lung explants showed a congested lung architecture with severe pulmonary arterial remodelling, subpleural vessel dilation and numerous haemorrhagic foci. CONCLUSIONS: PAH due to SOX17 pathogenic variants is a severe phenotype, frequently associated with CHD, haemoptysis and radiological abnormalities. Pathological assessment reveals severe pulmonary arterial remodelling and malformations affecting pulmonary vessels and thoracic systemic arteries.

Pulsatile pulmonary artery pressure in a large animal model of chronic thromboembolic pulmonary hypertension: Similarities and differences with human data.

A striking feature of the human pulmonary circulation is that mean (mPAP) and systolic (sPAP) pulmonary artery pressures (PAPs) are strongly related and, thus, are essentially redundant. According to the empirical formula documented under normotensive and hypertensive conditions (mPAP = 0.61 sPAP + 2 mmHg), sPAP matches ~160%mPAP on average. This attests to the high pulsatility of PAP, as also witnessed by the near equality of PA pulse pressure and mPAP. Our prospective study tested if pressure redundancy and high pulsatility also apply in a piglet model of chronic thromboembolic pulmonary hypertension (CTEPH). At baseline (Week-0, W0), Sham (n = 8) and CTEPH (n = 27) had similar mPAP and stroke volume. At W6, mPAP increased in CTEPH only, with a two- to three-fold increase in PA stiffness and total pulmonary resistance. Seven CTEPH piglets were also studied at W16 at baseline, after volume loading, and after acute pulmonary embolism associated with dobutamine infusion. There was a strong linear relationship between sPAP and mPAP (1) at W0 and W6 (n = 70 data points, r² = 0.95); (2) in the subgroup studied at W16 (n = 21, r² = 0.97); and (3) when all data were pooled (n = 91, r² = 0.97, sPAP range 9-112 mmHg). The PA pulsatility was lower than that expected based on observations in humans: sPAP matched ~120%mPAP only and PA pulse pressure was markedly lower than mPAP. In conclusion, the redundancy between mPAP and sPAP seems a characteristic of the pulmonary circulation independent of the species. However, it is suggested that the sPAP thresholds used to define PH in animals are species- and/or model-dependent and thus must be validated.

Targeting peptidyl-prolyl isomerase 1 in experimental pulmonary arterial hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) is a progressive disease characterised by pro-proliferative and anti-apoptotic phenotype in vascular cells, leading to pulmonary vascular remodelling and right heart failure. Peptidyl-prolyl cis/trans isomerase, NIMA interacting 1 (Pin1), a highly conserved enzyme, which binds to and catalyses the isomerisation of specific phosphorylated Ser/Thr-Pro motifs, acts as a molecular switch in multiple coordinated cellular processes. We hypothesised that Pin1 plays a substantial role in PAH, and its inhibition with a natural organic compound, Juglone, would reverse experimental pulmonary hypertension. RESULTS: We demonstrated that the expression of Pin1 was markedly elevated in experimental pulmonary hypertension (i.e. hypoxia-induced mouse and Sugen/hypoxia-induced rat models) and pulmonary arterial smooth muscle cells of patients with clinical PAH. In vitro Pin1 inhibition by either Juglone treatment or short interfering RNA knockdown resulted in an induction of apoptosis and decrease in proliferation of human pulmonary vascular cells. Stimulation with growth factors induced Pin1 expression, while its inhibition reduced the activity of numerous PAH-related transcription factors, such as hypoxia-inducible factor (HIF)-α and signal transducer and activator of transcription (STAT). Juglone administration lowered pulmonary vascular resistance, enhanced right ventribular function, improved pulmonary vascular and cardiac remodelling in the Sugen/hypoxia rat model of PAH and the chronic hypoxia-induced pulmonary hypertension model in mice. CONCLUSION: Our study demonstrates that targeting of Pin1 with small molecule inhibitor, Juglone, might be an attractive future therapeutic strategy for PAH and right heart disease secondary to PAH.

Single-cell RNA sequencing reveals that BMPR2 mutation regulates right ventricular function via ID genes.

BACKGROUND: Mutations in bone morphogenetic protein type II receptor (BMPR2) have been found in patients with congenital heart disease-associated pulmonary arterial hypertension (CHD-PAH). Our study aimed to clarify whether deficient BMPR2 signalling acts through downstream effectors, inhibitors of DNA-binding proteins (IDs) during heart development to contribute to the progress of PAH in CHD patients. METHODS: To confirm that IDs are downstream effectors of BMPR2 signalling in cardiac mesoderm progenitors (CMPs) and contribute to PAH, we generated cardiomyocyte-specific Id 1/3 knockout mice (Ids cDKO), and 12 out of 25 developed mild PAH with altered haemodynamic indices and pulmonary vascular remodelling. Moreover, we generated ID1 and ID3 double-knockout (IDs KO) human embryonic stem cells that recapitulated the BMPR2 signalling deficiency of CHD-PAH induced pluripotent stem cells (iPSCs). RESULTS: Cardiomyocytes differentiated from iPSCs derived from CHD-PAH patients with BMP receptor mutations exhibited dysfunctional cardiac differentiation and reduced calcium (Ca2+) transients, as evidenced by confocal microscopy experiments. Smad1/5 phosphorylation and ID1 and ID3 expression were reduced in CHD-PAH iPSCs and in Bmpr2 +/- rat right ventricles. Moreover, ultrasound revealed that 33% of Ids cDKO mice had detectable defects in their ventricular septum and pulmonary regurgitation. Cardiomyocytes isolated from mouse right ventricles also showed reduced Ca2+ transients and shortened sarcomeres. Single-cell RNA sequencing analysis revealed impaired differentiation of CMPs and downregulated USP9X expression in IDs KO cells compared with wild-type cells. CONCLUSION: We found that BMPR2 signals through IDs and USP9X to regulate cardiac differentiation, and the loss of ID1 and ID3 expression contributes to cardiomyocyte dysfunction in CHD-PAH patients with BMPR2 mutations.