Hormone-induced thrombosis is mediated through non-canonical fibrin(ogen) aggregation and a novel estrogen target in zebrafish

Venous thrombosis is a well-known complication of estrogen exposure, with nearly every woman at risk across her lifetime through contraception, pregnancy, or hormone therapy. Although estrogens alter expression of coagulation factors, the mechanisms that mediate estrogen-induced thrombosis are poorly understood, partially due to the absence of an animal model. Identification of these mediators is central to understanding of hormone-induced pathophysiology, could ascertain patients at higher risk for thrombosis, and pinpoint future therapeutic targets. The zebrafish is characterized by external development, high fecundity, optical transparency, and hemostasis is highly conserved with humans. Through a transgenic line that generates GFP-tagged fibrinogen, we show rapid onset of thrombosis after exposure to various estrogens, but not progestins or testosterone. Thrombi are localized to the venous system with evidence for clot contraction. Thrombosis is only partially impeded by anticoagulants, occurs in the absence of factor VII, factor X, and prothrombin, but is dependent on tissue factor and fibrin(ogen). Finally, targeting of all known estrogen receptors does not eliminate thrombosis. The inability to completely inhibit thrombosis through genetic/pharmacologic anticoagulation or estrogen receptor disruption suggests mechanisms different from canonical coagulation/thrombosis. These studies suggest that estrogen-induced thrombosis is a unique entity distinct from other forms of venous thrombosis.