SOX17 and RUNX1: Unraveling Their Roles in Endothelial Dysfunction and PAH

RATIONALE: SOX17 (SRY-box transcription factor 17) is a critical transcription factor involved in the development of the pulmonary vasculature and endothelial regeneration following injury and its loss-of-function mutations are associated with severe, early-onset pulmonary arterial hypertension (PAH). Importantly, SOX17 directly suppresses RUNX1 expression by binding to its promoter. RUNX1, a key regulator of myeloid differentiation and aberrant angiogenesis, has been implicated in PAH. Previous studies have demonstrated that inhibiting RUNX1 expression or activity can prevent and reverse PAH in animal models. In this study we aim to clarify the role of impaired SOX17/RUNX1 axis in the development and progression of PAH and we hypothesize that the loss of SOX17 contributes to PAH by enabling RUNX1 to disrupt endothelial function and angiogenesis. Methods: We developed stable Human Pulmonary Arterial Endothelial Cell (HPAEC) lines using a lentiviral system to overexpress RUNX1 or knock out SOX17 with CRISPR-Cas9. Changes in endothelial cell marker expression were analyzed using RT-PCR arrays and western blot techniques. Functional assays, such as tube formation, migration, and proliferation tests, were performed to assess cellular behavior. In vivo studies evaluated the effects of pharmacological RUNX1 inhibition and the endothelial-specific deletion of RUNX1 in Sugen/hypoxia-induced PAH models. These experiments were conducted in transgenic SOX17 enhancer-knockout (SOX17eKO) mice as well as in wild-type (WT) mice. Both groups received a low dose of Sugen 5416 (5 mg/kg) and were exposed to 3 weeks of mild hypoxia (12% O 2 ). The severity of PAH was assessed by measuring right ventricular systolic pressure (RVSP) and the right ventricle-to-left ventricle plus septum (RV/LV+S) ratio. Results: In HPAECs, RUNX1 overexpression and SOX17 downregulation resulted in significant changes in gene expression and cellular characteristics, leading to a loss of the typical endothelial cell identity, as evidenced by a marked reduction in endothelial-specific markers. Functionally, these changes were associated with abnormal tube formation, increased cellular proliferation, and enhanced migratory capabilities, all of which are hallmarks of pathological endothelial remodeling. RUNX1 expression was notably elevated in SOX17-downregulated cells treated with M2-macrophage conditioned media, representative of the inflammatory microenvironment observed in chronic PAH, underscoring the critical regulatory role of SOX17 in modulating RUNX1 levels under stress conditions. In vivo studies showed that SOX17 eKO mice are more susceptible to PAH induced by low dose sugen and mild hypoxia. Pharmacological RUNX1 inhibition or inducible deletion of RUNX1 in endothelial cells prevented the development of PAH in SOX17eKO mice, supporting the hypothesis that excessive RUNX1 activity drives the disease process in the absence of adequate SOX17 function. Conclusion: These findings highlight the pivotal role of the SOX17/RUNX1 axis in maintaining endothelial cell identity and preventing vascular remodeling in PAH. Low RUNX1 levels are crucial for preserving endothelial functionality, suggesting that targeting the SOX17/RUNX1 axis could serve as a promising therapeutic strategy for PAH. This work is supported by NIH/NHLBI R01-HL158841, AHA 18TPA34110329 and Cardiovascular Surgery Research Training Grant (T32 HL160517-02). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.