Abstract 530: Impaired Ability of Pulmonary Microvascular, but Not Macrovascular, Endothelial Cells From Patients With Pulmonary Arterial Hypertension to Respond to High Shear Stress

Rationale: We hypothesize that severe pulmonary vascular remodelling in pulmonary arterial hypertension (PAH) results from sustained endothelial injury caused by increased shear stress (SS) in pre-capillary endothelial cells. Therefore we tested whether human pulmonary arterial and microvascular endothelial cells (HPAEC and MVEC resp.) from PAH patients are capable to adapt to high levels of SS. Methods & Results: HPMVEC were isolated from PAH patients and controls (lung tumor patients). Static controls were compared to cells under physiological low (LSS, 2.3 dyn/cm 2 ) and pathological high SS (HSS, up to 25 dyn/cm 2 ). Different flow profiles (laminar, bifurcation-like) were applied and electrical resistance of the monolayers was recorded as a measure of cell proliferation and barrier function. Under static culture conditions, PAH cells showed a decreased and irregular distribution and organization of VE-cadherin and CD31 at the cell periphery, indicating weakened adherens junctions. PAH and control HPMVEC formed similar endothelial barriers with a baseline resistance of 7767 vs. 8102 ohms, and responded to challenge with the hyper-permeability inducer thrombin (1 U/mL) with a specific maximal drop in resistance (to 2109 vs. 2083 ohms). Control HPMVEC re-aligned in flow direction, whereas HPMVEC, but not HPAEC from PAH-patients showed a delayed alignment response. Furthermore, application of HSS to control and PAH HPMVEC caused severe injury when bifurcation-like flow patterns were used. In contrast HPMVEC in laminar flow regions were able to withstand HSS challenge. Known shear-response genes were not affected (normal induction of KLF2, thrombomodulin, eNOS, SMAD6/7 and downregulation of MCP1). Protein analysis showed reduced expression of PECAM1 as part of a shear sensing complex (PECAM1/VEGFR2/VEcadherin) and its downstream signaling molecule Tiam1. Partial depletion of PECAM1 in control HPMEC mimicked the impaired realignment response. Conclusion: HPMVEC, but HPAEC from PAH-patients have defects in the shear sensing complex accompanied by a hampered ability to adapt to pathological HSS, with severe endothelial damage at bifurcations.