SOX17 Prevents Endothelial-Mesenchymal Transition of Pulmonary Arterial Endothelial Cells in Pulmonary Hypertension through Mediating TGF-β/Smad2/3 Signaling

Endothelial to mesenchymal transition (EndMT) has been reported to cause pulmonary vascular remodeling of pulmonary hypertension (PH). We have demonstrated that SOX17, a member of the SRY-Box (SOX) transcription factor family, affects pulmonary artery vascular homeostasis through exosomes in an autocrine and paracrine manner. However, the role of SOX17 in mediating EndMT of pulmonary arterial endothelial cells (PAECs) in PH and its underlying intracellular mechanisms are not yet clarified. Here, we show that in the remodeling pulmonary vascular of idiopathic PH patients and Sugen 5416/hypoxia (Sugen/hypoxia)-induced PH rats, the downregulation of SOX17 expression was accompanied by a significant pulmonary arterial EndMT and TGF-β/Smad2/3 signaling activation. In primary HPAECs, the expression of SOX17 was inhibited by canonical TGF-β signaling. SOX17 overexpression reversed TGF-β- and hypoxia-induced EndMT. It is suggested that SOX17 is required for HPAECs to acquire TGF-β-mediated EndMT. Mechanistically, SOX17 prevented TGF-β-induced EndMT of PAECs through trans-suppressing ROCK1 expression by binding to the specific promoter region of ROCK1, thereby inhibiting the phosphorylation of MYPT1 and MLC. Further, we found that Tie2-Cre rats with endothelial cell-specific SOX17 overexpression were prevented from Sugen/hypoxia-induced EndMT and pulmonary vascular remodeling. In keeping with the in vitro data, compared with the Tie2-Cre rats treated by Sugen/hypoxia, the rats with SOX17 overexpression showed decreased expression of ROCK1 as well as the MYPT1 and MLC phosphorylation. Overall, our studies demonstrate a novel TGF-β/SOX17/ROCK1 pathway regulating EndMT of PAECs and propose SOX17 as a potential target for exploring therapeutics to alleviate pulmonary vascular remodeling in PH.