Abstract Body (Do not enter title and authors here): Introduction: Pulmonary hypertension (PH) is a progressive and life-threatening disease. Pulmonary vascular remodeling partially due to the increased lung vascular endothelial cell (EC) proliferation is a major cause for the elevated pulmonary arterial pressure in patients with PH. Endothelial-to-mesenchymal transition (EndMT) is biological process that converts EC into mesenchymal cells with the increased proliferative capacity. Signal transducer and activator of transcription 3 (STAT3) is an important for EC homeostasis but its role in the development of EndMT and PH is unknown. We hypothesized that STAT3 induces EndMT and vascular permeability to contribute to EC dysfunction in PH.
Methods: Human lung EC were exposed to normoxia (21% O2) or hypoxia (3% O2) for 72 hours to induce EndMT. C57BL/6J wild-type or EC-specific STAT3-KO mice were exposed to normal air (21% O2) or hypoxia (10% O2) for 6 weeks to induce PH. EndMT profile was measured by expression of specific EC markers or mesenchymal markers using qPCR, Western blotting, and immunostaining. Vascular permeability was determined by FITC-dextran assay in vitro or in vivo. PH phenotype was assessed by hemodynamic measurements, right ventricular hypertrophy and morphological analysis of H&E-stained lung tissues. Normal EC were transfected with STAT3 siRNA followed by exposure to hypoxia or normoxia. In addition, EndMT and STAT3 signaling were estimated in lung tissues from healthy donors and patients with hypoxia-associated Group 3 PH.
Results: Mice with hypoxia-induced PH exhibit enhanced pulmonary vascular remodeling, EndMT and vascular permeability. Upregulated SNAI1/2 and enhanced EndMT are correlated with activated STAT3 signaling in hypoxic human lung EC or hypoxic mice. Hypoxia also increased EC survival and monolayer permeability, while disrupting cell-cell junctions. Knockdown of STAT3 abolished hypoxia-induced EndMT and restored EC barrier function in vitro. EC-specific STAT3 deletion significantly improved PH phenotype, reduced vascular leakage, EndMT, and right ventricular hypertrophy in mice under hypoxic conditions. Immunostaining of lung tissues from Group 3 PH patients showed increased expression of SNAI1-mediated EndMT and p-STAT3 compared with controls.
Conclusions: STAT3 induces EC dysfunction, vascular leakage, and pulmonary vascular remodeling through SNAI-mediated EndMT in hypoxia-induced PH. Targeting this pathway may offer a novel therapeutic strategy to treat PH patients.