Normal levels of anticoagulant heparan sulfate are not essential for normal hemostasis

Endothelial cell production of anticoagulant heparan sulfate (HSact) is controlled by the Hs3st1 gene, which encodes the rate-limiting enzyme heparan sulfate 3-O-sulfotransferase-1 (3-OST-1). In vitro, HSact dramatically enhances the neutralization of coagulation proteases by antithrombin. The in vivo role of HSact was evaluated by generating Hs3st1(-/-) knockout mice. Hs3st1(-/-) animals were devoid of 3-OST-1 enzyme activity in plasma and tissue extracts. Nulls showed dramatic reductions in tissue levels of HSact but maintained wild-type levels of tissue fibrin accumulation under both normoxic and hypoxic conditions. Given that vascular HSact predominantly occurs in the subendothelial matrix, mice were subjected to a carotid artery injury assay in which ferric chloride administration induces de-endothelialization and occlusive thrombosis. Hs3st1(-/-) and Hs3st1(+/+) mice yielded indistinguishable occlusion times and comparable levels of thrombin.antithrombin complexes. Thus, Hs3st1(-/-) mice did not show an obvious procoagulant phenotype. Instead, Hs3st1(-/-) mice exhibited genetic background-specific lethality and intrauterine growth retardation, without evidence of a gross coagulopathy. Our results demonstrate that the 3-OST-1 enzyme produces the majority of tissue HSact. Surprisingly, this bulk of HSact is not essential for normal hemostasis in mice. Instead, 3-OST-1-deficient mice exhibited unanticipated phenotypes suggesting that HSact or additional 3-OST-1-derived structures may serve alternate biologic roles.