Evidence for thrombin binding to dermatan sulphate sites in the rabbit aorta subendothelium in vitro

The proposal that thrombin binds to dermatan sulphate chains of extracellular proteoglycans has been examined directly using the subendothelium of the rabbit aorta. Freshly excised aortas were de-endothelialized by balloon catheter in vitro and then incubated with 125I-thrombin to allow adsorption of 20-30 fmol of thrombin/cm2. Pretreatment of the subendothelium with FPR-thrombin or chondroitinase ABC partially inhibited thrombin binding, each by approximately 40-45%. The addition of dermatan sulphate inhibited, competitively, up to 50% of thrombin from binding to the subendothelium whereas chondroitin-4 or -6 sulphates had little or no effect. By contrast, protamine inhibited 90% of FPR-thrombin binding. Of subendothelium-bound thrombin, chondroitinase ABC released only a small proportion (3-12%) of bound thrombin but up to 44% of bound FPR-thrombin. It is concluded that, when 125I-thrombin is bound in vitro at a concentration of < 30 fmol/cm2 of aorta intima-media, approximately 50% of subendothelial 125I-thrombin is bound to dermatan sulphate chains of proteoglycan in the extracellular matrix. The possibility is discussed that dermatan sulphate chains may function as thrombin-binding loci to control or augment thrombin activity in the ECM of the injured vascular wall in vivo.