The fibrinogen γA/γ′ isoform does not promote acute arterial thrombosis in mice

Summary Background Elevated plasma fibrinogen is associated with arterial thrombosis in humans and promotes thrombosis in mice by increasing fibrin formation and thrombus fibrin content. Fibrinogen is composed of six polypeptide chains: (Aα, Bβ, and γ)2. Alternative splicing of the γ chain leads to a dominant form (γA/γA) and a minor species (γA/γ′). Epidemiological studies have detected elevated γA/γ′ fibrinogen in patients with arterial thrombosis, suggesting that this isoform promotes thrombosis. However, in vitro data show that γA/γ′ is anticoagulant due to its ability to sequester thrombin and suggest its expression is upregulated in response to inflammatory processes. Objective To determine whether γA/γ′ fibrinogen is prothrombotic in vivo. Methods We separated γA/γA and γA/γ′ fibrinogen from human plasma‐purified fibrinogen and determined the effects on in vitro plasma clot formation and on in vivo thrombus formation and circulating thrombin–antithrombin complexes in mice. Results and Conclusions Both γA/γA and γA/γ′ fibrinogen were cleaved by murine and human thrombin and were incorporated into murine and human clots. When γA/γA or γA/γ′ was spiked into plasma, γA/γA increased the fibrin formation rate to a greater extent than γA/γ′. In mice, compared to controls, γA/γA infusion shortened the time to carotid artery occlusion, whereas γA/γ′ infusion did not. Additionally, γA/γ′ infusion led to lower levels of plasma thrombin–antithrombin complexes following arterial injury, whereas γA/γA infusion did not. These data suggest that γA/γ′ binds thrombin in vivo and decreases prothrombotic activity. Together, these findings indicate that elevated levels of γA/γA fibrinogen promote arterial thrombosis in vivo, whereas γA/γ′ does not.