Pulmonary vascular heterogeneity: microvascular vs. arterial generation of angiopoietin-2 (IRC5P.633)

Endothelial cell (EC) growth factors, Angiopoietin (Ang)-1 and Ang-2, are important mediators of EC function. Bound to a shared receptor, Tie2, expressed on ECs, they have opposing effects on EC activation. Ang-1/Tie2 promotes a quiescent while Ang-2/Tie2 promotes an activated phenotype and increased vascular permeability. Ang-2, stored preformed in EC Weibel Palade bodies (WPbs), is rapidly released from activated ECs. We have reported increased Ang-2 in the blood of trauma patients with ARDS, representing a potential therapeutic target. To assess lung EC activation and release of Ang-2, we used human pulmonary arterial ECs (hPAECs) and microvascular ECs (hPMECs) grown on electric cell-substrate impedance sensing arrays. These arrays measure changes in EC monolayer integrity in response to inflammatory stimulus. We show that, in response to TNF-a stimulation, hPMECs exhibited increased loss of barrier function compared to hPAECs. Also, Ang-2 in culture supernatant increased in both hPAECs and hPMECs compared to untreated controls. While ECs in larger vessels (arteries), contain WPbs, they are not observed in microvascular ECs (<10um diam). To further investigate, we inhibited WPb vesicle exocytosis. Our findings show that inhibition of WPb release decreased Ang-2 in supernatant from hPAECs, but not significantly from hPMECs, suggesting that the microvascular is a region with distinct responses potentially associated with their location and anatomic structure.