血管内皮細胞における抗凝固性ヘパラン硫酸の局在

抄録

It is thought that anti-thrombotic properties of blood vessels are partially regulated by anticoagulantly active heparin-like compounds on the luminal surface of vascular endothelial cells. Heparan sulfate proteoglycans (HSPG_s) are also known to be located along the abluminal side of the endothelium, that is, basement membrane or extracellular matrix (ECM) of endothelial cells. Does ECM contain HSPG which interact with antithrombin III (ATIII)? If so, how abundant are they, as compared with those on the luminal surface? To answer this question, we have studied the interaction of ¹²⁵I-labeled ATIII with cultured porcine aortic endothelial cells to localize the cellular site of anticoagulantly active HSPG_s. ECM, prepared from endothelial cells cultured on plastic dishes, by removing the cells with nonenzymatic methods, specifically bound ¹²⁵I-ATIII. The amount of ATIII bound to ECM was approximately 40% of that bound to the intact cell. The binding was efficiently displaced by heparan sulfate, and almost completely abolished by pretreatment of ECM with Flavobacterium heparitinase. ECM-associated HSPG_s apparently represented approximately 40% of HSPG_s associated with intact cell, in parallel with the binding experiments. Approximately 15-20% of ECM-associated ³⁵S-glycosaminoglycans was bound to ATIII affinity column with high affinity. ECM accelerated inactivation of thrombin by ATIII. Based upon the above data, we conclude that approximately at least a half of anticoagulantly active HSPG is located in the ECM, that is, abluminal side of cultured aortic endothelial cells. The physiological significance of this finding remains to be determined.