Abstract 13304: Sox17 Deficiency Induces Pulmonary Hypertension Through E2F1/BRD4 Signaling

Introduction: Pulmonary arterial hypertension (PAH) is a disaster disease characterized by obliterative vascular remodeling and persistent increase of vascular resistance, leading to right heart failure and premature death. Understanding the cellular and molecular mechanisms will help develop novel therapeutic approaches for PAH patients. Hypothesis: Genetic SOX17 mutations are associated with PAH. We hypothesized that endothelial SOX17 mutations or loss of function contributes to endothelial dysfunction and the pathogenesis of PAH. Methods: Endothelial-specific deletion of Sox17 ( Sox17iCKO ) mice were generated. Sox17iCKO and Sox17f/f (WT) mice after tamoxifen injection were incubated without or with hypoxia (10% O 2 ) for 3 weeks to induce PH. EC proliferation, apoptosis, cell junction assay, Western blotting, QRT-PCR, RNA-sequencing analysis, and luciferase assays were performed to understand the molecular mechanisms of SOX17 deficiency and mutation in ECs. siRNA and inhibitors were used to determine the involvement of E2F1/BRD4 signaling in SOX17 deficiency ECs. Results: Sox17iCKO mice developed spontaneous mild PH and exaggerated hypoxia-induced PH evidenced by the increase of RVSP and RV hypertrophy compared to WT mice. SOX17 knockdown in human PVECs induced cell proliferation, anti-apoptosis, and impaired cell integrity. SOX17 knockdown reduced BMPR2 signaling. SOX17 knockdown and mutations at the HMG domain lost transcriptional activities and its ability to repress -catenin. RNA-seq analysis demonstrated enrichment of cell cycle pathway after the loss of SOX17 in PVECs. iRegulon analysis revealed the involvement of transcriptional factor E2F1. siRNA-mediated E2F1 knockdown normalized SOX17 deficiency-induced PVECs dysfunction. Knockdown SOX17 significantly upregulated E2F1 promoter activity, which was dependent on the binding site in the E2F1 promoter by luciferase and mutagenesis assay. E2F1 or BRD4 inhibitors attenuated SOX17 deficiency-induced PH in mice. Conclusions: Our study demonstrated that endothelial loss of SOX17 induces PH in mice. Pharmacological inhibition of E2F1/BRD4 signaling attenuated PH development in Sox17iCKO mice.