Harm Jan Bogaard

SOX17 is an embryonic transcription factor implicated in arterial endothelial differentiation, but its function in the adult vasculature remains incompletely defined. Because genetic variation in SOX17 is associated with pulmonary arterial hypertension (PAH), a fatal disease marked by pulmonary vascular remodeling, we investigated whether SOX17 regulates endothelial mechanoadaptation. We show that SOX17 is enriched in pulmonary artery endothelial cells and is induced by laminar shear stress. Loss of SOX17 impaired shear-induced cell elongation, promoted intercellular gap formation, and compromised endothelial barrier function and regenerative capacity. SOX17 depletion reduced VE-cadherin and β-catenin abundance and disrupted adherens junction architecture in both two-dimensional and three-dimensional models. Transcriptomic profiling identified Semaphorin 3G (SEMA3G) as a downstream effector of SOX17, and CUT&RUN analysis revealed shear-dependent binding of SOX17 at regulatory regions of CDH5, ESAM and SEMA3G. Recombinant SEMA3G restored endothelial junction integrity following SOX17 depletion in vitro , and rescued vascular injury in endothelial-specific Sox17-knockout mice. Together, these findings identify SOX17 as a key regulator of endothelial barrier homeostasis under shear, and suggest that SOX17 deficiency sensitizes the arterial endothelium to injury.

Background: Sodium glucose cotransporter 2 inhibitors may improve mitochondrial biogenesis and attenuate pulmonary vascular remodeling in pulmonary arterial hypertension (PAH). We investigated the impact of empagliflozin in PAH. Methods: Microvascular endothelial cells (MVECs) were collected from the lungs of control patients and patients with PAH, and the effects of empagliflozin on MVECs were evaluated. Subsequently, treatment effects of empagliflozin (300 mg/kg chow, n=12) or placebo (n=12) were evaluated in experimental PAH rats (SU5416 injection followed by 3 weeks of hypoxia). In addition, we conducted a phase IIa proof‐of‐concept trial, EMPHOWER PoC (Feasibility Study of Empagliflozin as Treatment for Idiopathic Pulmonary Arterial Hypertension), to assess the feasibility of 12 weeks of empagliflozin treatment in patients with PAH. Results: In comparison to control MVECs, PAH MVECs showed increased protein expression of sodium glucose cotransporter 2. Empagliflozin enhanced expression of mitochondrial‐encoded genes and respiration, while attenuating oxidative stress and proliferation of PAH MVECs. In SU5416 and hypoxia rats, chronic empagliflozin treatment reduced pulmonary vascular resistance and thickening of the intima of small pulmonary arteries. Finally, 8 patients diagnosed with idiopathic and heritable PAH were enrolled in EMPHOWER PoC. No discontinuation of empagliflozin during the study period or treatment‐associated serious adverse events were observed. There were no changes in N‐terminal pro‐B‐type natriuretic peptide, World Health Organization functional class, 6‐minute walk distance, or emPHasis score; however, right ventricular ejection fraction slightly worsened (from 45%±10% to 38%±12%, P =0.031). Conclusions: Empagliflozin attenuates proliferation of PAH MVECs. Empagliflozin reduces pulmonary vascular remodeling in experimental PAH. While 12 weeks of empagliflozin treatment was feasible in patients with idiopathic or hereditary PAH, we observed signs of right ventricular deterioration. Registration: URL: https://www.clinicaltrials.gov ; Unique identifiers: NCT05493371.

Background: Chronic thromboembolic pulmonary disease (CTEPD) is a long-term complication of pulmonary embolism (PE) and can occur with pulmonary hypertension. Inflammation is implicated but its causal role remains unclear.Objectives: Investigate whether local immune activation modifies haemodynamic, inflammatory, and thromboembolic responses after repetitive PE.Methods: In a 30-day prospective study, six pigs underwent repetitive autologous PE containing cyclic GMP–AMP (cGAMP) to induce local immune activation and were compared with six pigs receiving repetitive PE and tranexamic acid-mediated inhibition of endogenous fibrinolysis (TXA). Animals underwent haemodynamic assessment, blood sampling, computed tomography pulmonary angiography (CTPA), lung tissue cytokine quantification, and histological analysis.Results: Repetitive embolization induced acute transient increases in mean pulmonary arterial pressure in both groups, but no animals developed pulmonary hypertension at follow-up (18±3 mmHg in cGAMP-group and 16±2 mmHg in TXA-group, p=0.20). CTPA demonstrated persistent vascular obstruction in both groups, with comparable obstruction percentages (85 [75–87] % vs. 72 [50–80] %, p=0.29). Systemic leukocyte, neutrophil, and lymphocyte counts remained within porcine reference intervals. groups. Lung tissue CXCL10 levels were higher in the cGAMP-group than in the TXA-group (9120±5027 vs. 3763±1904 pg/g, p=0.035), whereas IL-1β, TNF-α, and IL-8 did not differ. Immunohistochemistry demonstrated CXCL10–positive inflammatory cell infiltration within organised thrombi.Conclusions: In this porcine model, repetitive PE combined with local cGAMP exposure increased lung tissue CXCL10 without inducing pulmonary hypertension over 30 days, suggesting that selective activation of the immune system at clot level alone is insufficient to drive a more advanced chronic thromboembolic phenotype.

Rationale: While therapeutic advances have improved survival in Group 1 Pulmonary Arterial Hypertension (PAH), patients with Group 1.5 “PAH with features of venous/capillary involvement” (formerly Pulmonary Veno-Occlusive Disease or Pulmonary Capillary Hemangiomatosis, now collectively termed PVOD/PCH) remain underrecognized, develop serious complications from usual PAH therapy titrations, and suffer high mortality awaiting necessary lung transplant. Identifying PVOD/PCH early before therapy initiation could aid management and expedite transplant referral. Objective: We aimed to develop a likelihood score distinguishing PVOD/PCH from other forms of PAH using clinical variables. Methods: Due to low PVOD/PCH prevalence and no dedicated registries, we leveraged published case control/series studies to assess the ability of several clinical variables to discriminate PVOD/PCH from PAH. From pooled literature-derived data, we performed Sensitivity/Specificity and simulation-based Receiver Operator Characteristic (ROC) analyses to estimate variable performance. Top-performing variables formed a PVOD/PCH Likelihood score, which had its accuracy tested for distinguishing histopathology-confirmed PVOD/PCH cases (n = 37) from PAH controls (n = 60) in three cohorts of transplant-eligible patients from the United States, Spain, and the Netherlands. Measurements and Main Results: DLCO, six-minute walk desaturation, PaO2, sex, smoking history, CT septal line thickening, and CT lymphadenopathy had the highest sensitivity and specificity performance and were incorporated into the PVOD score. Across test cohorts, the score achieved a ROC area under the curve of 0.97 (95% CI 0.93-1.00) for discriminating PVOD/PCH and it retained accuracy when data were missing. Conclusions: This score could facilitate early PVOD/PCH identification in incident PAH, potentially helping expedite transplant referral and informing therapy initiation/titration decisions.

Background: Chronic thromboembolic pulmonary hypertension (CTEPH) is associated with elevated right ventricular (RV) afterload and progressive RV remodeling. Balloon pulmonary angioplasty (BPA) has emerged as an established and increasingly used alternative to pulmonary endarterectomy (PEA). This study aimed to evaluate hemodynamic, functional and structural cardiac responses to PEA and BPA, with specific focus on RV reverse remodeling. Methods: In this prospective, multicenter cohort study, 93 patients with CTEPH (PEA; n=50, BPA; n=43) from the Netherlands and Denmark underwent cardiac magnetic resonance imaging, right heart catheterization, exercise testing and biomarker assessment at baseline and 6-months post-intervention. Longitudinal changes were assessed with repeated-measures ANOVA. A subgroup underwent analysis at 18 months. Results: BPA patients were older (68.9±10.1 versus 62.4±11.1 years, p = 0.004), and used more PH medication. PEA-treated patients had higher RV mass index at baseline (40.1±13.5 versus 32.9±12.2 g·m ⁻² ; p=0.017), and consistently higher relative RV wall thickness at baseline and follow-up (both 0.4±0.1 versus 0.3±0.1; p p versus 92.2±20.2 mL·m ⁻² ; p versus 49.0±18.8 mL·m ⁻² ; p=0.014). Conclusions: In this multicenter European study, both therapies resulted in significant RV reverse remodeling. PEA was associated with larger absolute reductions in indexed RV mass and volumes than BPA. However, remodeling sensitivity to unloading appeared broadly similar across treatments. Despite favorable outcomes following both treatments, our findings emphasize the need for randomized controlled studies, to optimize treatment strategies for operable and inoperable patients.

BACKGROUND: Pulmonary arterial hypertension (PAH) is a progressive disorder involving disrupted BMP (bone morphogenetic protein) signaling, pulmonary inflammation, and endothelial-to-mesenchymal transition (EndMT). We hypothesized that IL (interleukin)-33 signaling contributes to PAH progression by inducing EndMT and interacting with BMP9, a key modulator of inflammation and vascular remodeling. METHODS: IL-33 expression was assessed in lung tissues from Sugen/hypoxia and control mice, as well as in pulmonary arterial endothelial cells (PAECs) and lung tissues from patients with PAH and healthy donors. EndMT and signaling pathways were analyzed in PAECs and microvascular endothelial cells (MVECs) exposed to IL-33, BMP9, and sST2 (soluble supression of tumorigenicity 2) using quantitative polymerase chain reaction, Western blotting, ELISA, and immunostaining. Plasma BMP9 and sST2 levels were quantified in patients with PAH. RESULTS: Immunofluorescent analysis revealed elevated IL-33 expression in pulmonary endothelial cells of Sugen/hypoxia mice compared with controls, consistent with findings in PAECs from patients with PAH. BMP9 significantly upregulated sST2 expression in human PAEC and microvascular endothelial cells, inhibited IL-33 target gene expression, and effectively suppressed IL-33-induced EndMT. Notably, BMP9 demonstrated greater efficacy in preventing EndMT compared with rsST2 (recombinant soluble ST2) or ST2L-neutralizing antibodies. Circulating BMP9 and sST2 levels in the plasma of patients with PAH were positively correlated in specific patient groups stratified by sex, age, and New York Heart Association functional class, suggesting a protective role of BMP9 in modulating IL-33-induced EndMT. CONCLUSIONS: BMP9 plays a protective role against IL-33-induced EndMT in PAECs by upregulating sST2 expression and neutralizing IL-33, suggesting that targeting the IL-33 signaling pathway may represent a promising therapeutic strategy to mitigate EndMT in PAH.

Pulmonary arterial hypertension (PAH) is characterised by increased pulmonary vascular resistance and afterload on the right heart. The degree of right ventricular (RV) adaptation determines exercise capacity and prognosis [1]. RV dilatation and RV–pulmonary artery coupling parameters show prognostic value in addition to current risk stratification tools [2]. Right atrial (RA) function also contributes to PAH risk assessment since RA pressure and volume are associated with mortality [3, 4].