E2F1 Drives Endothelial Arterial Programming in Pulmonary Arterial Hypertension

Background: Pulmonary arterial hypertension (PAH) is driven by maladaptive endothelial remodeling, but the transcriptional regulators that couple proliferative stress to arterialized endothelial states remain incompletely defined. E2F transcription factor 1 (E2F1) is classically viewed as a cell-cycle regulator; whether E2F1 functions as a disease-driving node that promotes endothelial arterial programming in PAH remains unknown. Methods: We integrated human PAH lung transcriptomic analyses, deconvolution-based endothelial-state scoring, and complementary mouse and rat PH models with bulk RNA-seq, single-cell RNA-seq, pseudotime analysis, and CellChat inference. E2F1 function was tested using adenoviral E2F1 overexpression, pharmacological pan-E2F inhibition with HLM006474, and E2f1 loss on a tamoxifen-inducible endothelial Egln1-deletion background. Results: In IPAH lungs, E2F1 was increased and arterial endothelial cell (AEC) fraction and expanded arterial program scores were elevated. Similarly, Egln1Tie2Cre lungs showed increased E2F1, induction of arterial remodeling genes, and activation of an E2F target program. Genetic loss of E2f1 reduced RVSP, RV hypertrophy, vascular remodeling, and distal muscularization in Egln1-driven PH mice model. Bulk RNA-seq showed suppression of E2F/G2M, mitotic, EMT, and ECM-remodeling programs. Single-cell RNA-seq showed reduced AEC accumulation, normalized CAP1/CAP2 distribution, and reduced progression along the CAP1-iAEC-AEC trajectory. CellChat analysis identified loss of an arterial communication hub, including reduced ECM, VEGF, and Notch signaling when E2F1 is loss. Conversely, E2F1 overexpression in HLMVECs increased proliferation, activated E2F/cell-cycle and Notch/arterial programs. Pharmacological inhibition of E2F via HLM006474 suppressed VEGF-A- and hypoxia-induced endothelial proliferation and attenuated Egln1-driven and MCT-induced PH, including reversal of established MCT-PH. Conclusions: E2F1 acts as a disease-relevant transcriptional factor linking endothelial cell-cycle activation to arterial programming, matrix and angiogenic communication programs, and pulmonary vascular remodeling. Genetic or pharmacological E2F inhibition mitigates experimental PH, supporting E2F1 as a therapeutic target in PAH.