Vascular dermatan sulfate regulates the antithrombotic activity of heparin cofactor II

Abstract

Heparin cofactor II (HCII)-deficient mice form occlusive thrombi more rapidly than do wild-type mice following injury to the carotid arterial endothelium. Dermatan sulfate (DS) and heparan sulfate (HS) increase the rate of inhibition of thrombin by HCII in vitro, but it is unknown whether vascular glycosaminoglycans play a role in the antithrombotic effect of HCII in vivo. In this study, we found that intravenous injection of either wild-type recombinant HCII or a variant with low affinity for HS (K173H) corrected the abnormally short thrombosis time of HCII-deficient mice, while a variant with low affinity for DS (R189H) had no effect. When HCII was incubated with frozen sections of the mouse carotid artery, it bound specifically to DS in the adventitia. HCII was undetectable in the wall of the uninjured carotid artery, but it became concentrated in the adventitia following endothelial injury. These results support the hypothesis that HCII interacts with DS in the vessel wall after disruption of the endothelium and that this interaction regulates thrombus formation in vivo. IntroductionVascular injury allows circulating coagulation factor VIIa to interact with tissue factor. 1 This interaction triggers a series of zymogen activation reactions, which lead to generation of the proteolytic enzyme thrombin. Thrombin promotes clot formation by converting fibrinogen to fibrin, by stimulating platelet aggregation and secretion, and by activating certain proteins (factors V, VIII, and XI) upstream in the coagulation cascade. Thrombin also has multiple effects on vascular endothelial cells, smooth muscle cells, and monocytes/macrophages that may be important in tissue repair or in the development of atherosclerotic or neointimal lesions. 2 Thrombin can be inhibited by 2 serpins, antithrombin (AT) and heparin cofactor II (HCII), which are produced by the liver and circulate at micromolar concentrations in plasma. 3 Both of these serpins inhibit thrombin at least 1000 times faster upon interaction with certain glycosaminoglycans. AT is activated by heparin or by heparan sulfate (HS) proteoglycans synthesized by vascular endothelial cells and is thought to produce an antithrombotic effect at the blood-endothelial interface. 4 Patients with partial AT deficiency have an increased incidence of venous thromboembolism, 5 and homozygous AT-deficient mice die in late gestation with evidence of fibrin deposition and a consumptive coagulopathy. 6 Heparin and HS also bind and activate HCII, although with much lower affinity in comparison with AT. 7 By contrast, purified dermatan sulfate (DS), 7 as well as DS proteoglycans synthesized by fibroblasts, 8,9 stimulate thrombin inhibition by HCII but not by AT; these findings support the hypothesis that HCII inhibits thrombin in the vessel wall after disruption of the endothelium. Patients with low plasma concentrations of HCII do not appear to be at increased risk for venous thrombosis, 10 but they may be predisposed to development of atherosclerosis 11 or neointima formation following...

A mouse model of spontaneous preterm birth based on the genetic ablation of biglycan and decorin

“…The placentae of infants with in utero growth restriction display decreased biglycan and decorin as well as thrombosis (Murthi et al 2010, Swan et al 2010, Fuke et al 1994), while the glycosaminoglycan chains on biglycan and decorin display anticoagulant activity (He et al 2008). Thus, the absence of biglycan and decorin in the placenta may lead to thrombosis and fibrosis of the placenta with subsequent in utero growth restriction.…”

Exosite Determinants of Serpin Specificity

“…Similarly, whereas antithrombin-heparin can inhibit fIXa and fXa as well as IIa, a separate serpin, HCII, has been designed to inhibit only IIa by down-regulating all RCL interactions with these Arg-specific proteinases and allowing only exosite-based up-regulation for the IIa interaction. Here, dermatan sulfate in the subendothelium, where it is abundant, may regulate IIa activity after vascular injury (24). Such deliberate down-regulation except when additional exosite interactions overcompensate is thus critical to achieve serpin specificity and is likely to hold for most inhibitory serpins involved in complex proteolytic cascades.…”

Characterization of Glycosaminoglycans by15N NMR Spectroscopy and in Vivo Isotopic Labeling

“…These glycans are commonly attached to a membrane protein core to form the cell surface proteoglycans found virtually in all mammalian cells 4. As a part of the ECM they influence numerous physiological processes, including organogenesis/growth control,5, 6 cell adhesion,7 angiogenesis,8 wound healing,9, 10 tumorigenesis,10, 11 morphogenesis,12, 13 inflammation,14–16 haemostasis,17, 18 and neural development/regeneration 19–22. GAGs also participate as receptors of various pathogens during the process of infection,23 and they have found applications in the treatment of diseases,24–26 for example, in the use of heparins for the treatment of acute coronary conditions 27–30.…”