Anticoagulant heparan sulfate proteoglycans bind and activate antithrombin by virtue of a specific 3-O-sulfated pentasaccharide. They not only occur in the vascular wall but also in extravascular tissues, such as the ovary, where their functions remain unknown. The rupture of the ovarian follicle at ovulation is one of the most striking examples of tissue remodeling in adult mammals. It involves tightly controlled inflammation, proteolysis, and fibrin deposition. We hypothesized that ovarian heparan sulfates may modulate these processes through interactions with effector proteins. Our previous work has shown that anticoagulant heparan sulfates are synthesized by rodent ovarian granulosa cells, and we now have set out to characterize heparan sulfates from human follicular fluid. Here we report the first anticoagulant heparan sulfate purified from a natural human extravascular source. Heparan sulfate chains were fractionated according to their affinity for antithrombin, and their structure was analyzed by 1 H NMR and MS/MS. We find that human follicular fluid is a rich source of anticoagulant heparan sulfate, comprising 50.4% of total heparan sulfate. These antithrombin-binding chains contain more than 6% 3-Osulfated glucosamine residues, convey an anticoagulant activity of 2.5 IU/ml to human follicular fluid, and have an anti-Factor Xa specific activity of 167 IU/mg. The heparan sulfate chains that do not bind antithrombin surprisingly exhibit an extremely high content in 3-O-sulfated glucosamine residues, which suggest that they may exhibit biological activities through interactions with other proteins.Follicular fluid contains components of the coagulation cascade and subsequent to ovulation undergoes clotting within the ruptured follicle. Yet the timing of this process must be tightly regulated as a liquid state must initially be maintained for the oocyte to be successfully delivered to the oviduct. Given the complexity of coagulation, there are likely multiple mechanisms to regulate clotting of follicular fluid. One such mechanism could involve heparan sulfate proteoglycans (HSPGs).
2HSPGs are ubiquitously distributed on the surface of animal cells and are secreted into the extracellular environment. They have numerous important biological activities mediated through interactions with diverse proteins. HSPGs are composed of a core protein with covalently attached HS chains formed by repetitive sulfated disaccharides of uronic acid and glucosamine. The different length and variable sequence of sulfated disaccharides generate the structural diversity required to form specific oligosaccharide-binding sites for proteins such as growth factors, protease inhibitors, or cell adhesion molecules. The reactivity of proteins is affected by their binding to HS. This principle is exemplified by heparin and anticoagulant HS (aHS), which bind to antithrombin (AT) and thereby accelerate the rate at which AT inhibits serine proteases in the bloodclotting cascade.The AT-binding pentasaccharide of heparin and aHS proteoglycans ...