Inhibition of proliferation and induction of differentiation of endothelial cells by antithrombin

Anti-angiogenic and anti-tumor activities of latent and cleaved antithrombin has been described, and in vitro, the serpin inhibited proliferation of endothelial cells. We have recently observed that direct cellular effects of antithrombin are mediated by syndecan-4, a heparan sulfate proteoglycan known to bind to the heparin-binding site of antithrombin. Syndecan-4 is known to affect proliferation and differentiation of a variety of cell types. We have, therefore, studied direct effects of intact antithrombin on endothelial cells. Human umbilical vein and calf pulmonary artery endothelial cells were studied in the presence or absence of antithrombin concentrate or monoclonal antibody purified antithrombin with and without concomitant presence of synthetic pentasaccharide. Proliferation was assessed in BrDU incorporation and MTT assays. For testing endothelial cell differentiation, capillary tube formation was investigated in matrigel assays. Proliferation of the two types of endothelial was significantly inhibited by 1–10 U/ml of both antithrombin concentrate and antibody-purified antithrombin. Capillary tube formation induced by matrigel was augmented by the presence of 1–10 U/ml of antithrombin concentrate which was partly reversed with pentasaccharide. Results show that in vitro effects of antithrombin on angiogenesis-related endothelial cell functions may be directly exerted by the intact serpine and can be antagonised by pentasaccharide