Epigenetic reprogramming of lung fibroblasts drives pulmonary hypertension in obesity-related HFpEF

Background Obesity-related HFpEF (obHFpEF) is often complicated by pulmonary hypertension (PH-obHFpEF), a major contributor to morbidity and mortality. Lung fibroblasts drive vascular and tissue remodeling through inflammatory and profibrotic signals, but the epigenetic mechanisms remain poorly understood, and effective therapies are limited. BET proteins, key regulators of inflammation and fibrosis, represent a promising target. The selective BET inhibitor apabetalone (APA) has been linked to reduced heart failure hospitalizations, suggesting potential for treating PH-obHFpEF. Purpose To investigate how lung fibroblasts contribute to PH in obHFpEF and whether BET inhibition with apabetalone (APA) can reverse pro-inflammatory fibroblast activation. Methods Mice were subjected to high-fat diet feeding and L-NAME treatment for 15 weeks to induce PH-obHFpEF and were treated with the BET inhibitor APA (150mg/kg/day) or vehicle for 21 days. Cardiopulmonary function was evaluated by high-resolution ultrasound imaging (Vevo3100), and treadmill testing was used to assess exercise tolerance. Lung snRNA-seq was performed on ND and PH-obHFpEF samples. Primary lung fibroblasts (mFs) were isolated, exposed to APA for 48 h, and analyzed by proteomics, secretome profiling, Seahorse bioenergetics, and immunoblotting. Results obHFpEF mice developed pulmonary hypertension, characterized by elevated pulmonary artery pressure and resistance, right ventricular hypertrophy, and reduced pulmonary artery acceleration time, while in vivo treatment with APA markedly improved these parameters. snRNA-seq identified fibroblasts as key transcriptional hubs associated with PH severity, while interactome analyses revealed that mFs are the main source of intercellular signals targeting endothelial cells and macrophages in PH-obHFpEF lungs. Primary pulmonary PH-obHFpEF mFs displayed a myofibroblast phenotype and bioenergetic profile, with upregulated inflammatory and profibrotic gene expression. Proteomic profiling of fibroblasts and their secretome confirmed upregulation of inflammatory mediators (CSF2, NTF3, TNFRSF11B, and ACVRL1) and matrix regulators, consistent with a myofibroblast-like phenotype. Notably, CSF2 and NTF3 signal to immune and endothelial cells, promoting paracrine macrophage polarization, modulating nitric oxide production, and potentially driving endothelial activation and dysfunction. APA treatment normalized both transcriptional and secreted protein profiles in mFs, markedly reducing their expression and secretion, restoring mitochondrial bioenergetics, and reversing the myofibroblast phenotype. Conclusions Fibroblasts in PH-obHFpEF acquire a pathogenic, epigenetically reprogrammed phenotype that amplifies inflammation, endothelial dysfunction, and fibrotic remodeling. BET inhibition with apabetalone re-establishes fibroblast quiescence, dampens pathological intercellular signaling, and mitigates pulmonary hypertension development.APA1APA2