Abstract 10270: High Shear Stress Decreases ERG Causing Endothelial to Mesenchymal Transition and Pulmonary Arterial Hypertension

Introduction: Computational modeling studies indicated that pathological high shear stress (HSS) of 100 dynes/cm 2 is generated in pulmonary arteries (PA) (100-500μM) in patients with a ventricular septal defect or idiopathic pulmonary arterial hypertension (PAH) and occlusive vascular remodeling. Endothelial-to-mesenchymal transition (EndMT) is a feature of PAH. Hypothesis: Pathological HSS induces EndMT, which contributes to the initiation and progression of PAH. Methods: We apply the Ibidi perfusion system to human PA endothelial cells (EC), to determine whether HSS (100 dynes/cm 2 ) induces EndMT, when compared to normal laminar shear stress (LSS) (15 dynes/cm 2 ). We assessed the mechanism and targeted it to prevent PAH in a mouse with HSS resulting from an aortocaval (AV) shunt. Results: HSS induced EndMT, as assessed by an increase in transcription factors, SNAI1 and SNAI2, reduced BMPR2 (previously shown to inhibit EndMT), decreased EC markers PECAM1 and CDH5, and increased mesenchymal markers, ACTA2 and FSP-1. While the flow-induced transcription factors, KLF2 and KLF4 were similar in LSS and HSS, the co-transcription factor ERG was reduced with HSS. Indeed ERG siRNA under LSS caused EndMT whereas under HSS, transfection of ERG prevented EndMT. To address the significance of our observations in an animal model we created an AV shunt in mice and compared PAH in those sham operated vs transfected with an adeno-associated viral (AAV2- ESGHGYF) vector selectively targeting PAEC with a luciferase (control) or an ERG expressing construct (N=10 per group). Eight weeks after AV shunt, right ventricular systolic pressures was 21.9 ±0.6 mmHg in sham, 37.2±1.0 mmHg in AV shunt with luciferase vector (p<0.01 vs sham) and 29.2±0.8 mmHg in ERG-vector (p<0.01 vs both sham and luciferase). Muscularization of peripheral PA was similarly reduced in ERG-vector (p<0.01 vs luciferase) but not normalized (p<0.01 vs sham) as was immunohistochemical evidence of EndMT (p<0.01 vs luciferase). Conclusions: Our study is the first to document pathological HSS as an inducer of EndMT and PAH and to show that this results from reduced PAEC ERG. Agents that upregulate ERG could reverse HSS mediated PAH and occlusive vascular remodeling as a consequence of high flow or narrowed PAs.