Nitric oxide induces angiogenesis and upregulates alpha(v)beta(3) integrinexpression on endothelial cells

Nitric oxide (NO) has been implicated as a mediator of angiogenesis. Howeve r, its precise role in angiogenesis and its mechanism of action have not be en established. We performed in vivo and in vitro angiogenesis assays using NO donor S-nitroso-N-acetylpenicillamine (SNAP) and NO synthase inhibitor N-iminoethyl-(L)-ornithine (L- NIO). SNAP significantly increased and L-NIO significantly suppressed capillary ingrowth into subcutaneously implanted Matrigel plugs in mice. For the in vitro angiogenesis assay, human umbilica l vein endothelial cells (HUVECs) (4 x 10(4) cells/well) were treated with placebo, SNAP (100 muM), or L-NIO (100 muM) and cultured on Matrigel for 18 h. The typical capillary networks formed on Matrigel by HUVECs as a result of cell migration and differentiation were quantified by computer-assisted image analysis as a measure of angiogenesis. Treatment of HUVECs with SNAP significantly increased the capillary network area compared with control, 8701 +/- 693 vs 6258 +/- 622 area units (P < 0.05), whereas L-NIO) signific antly decreased the capillary area (4540 +/- 342, P < 0.05). Furthermore, w e have shown with a blocking monoclonal antibody that formation of capillar y networks works on Matrigel is mediated by the functional expression of th e alpha (v)beta (3) integrin, which plays a role in facilitating endothelia l cell adhesion to basement membrane matrix and endothelial cell migration. After an 18-h culture, flow cytometry revealed that SNAP significantly upr egulated and L-NIO significantly downregulated in a concentration-dependent manner alpha (v)beta (3) integrin expression on endothelial cells. In conc lusion, NO induces angiogenesis in vivo and in vitro by promoting endotheli al cell migration and differentiation into capillaries. One possible mechan ism might involve the upregulation of alpha (v)beta (3) integrin on endothe lial cells, a critical mediator of cell-matrix adhesion and migration. (C) 2000 Academic Press.