The role of thrombin-activatable fibrinolysis inhibitor and sex on thrombus stability and pulmonary embolism in murine venous thromboembolism

Abstract

Thrombin-activatable fibrinolysis inhibitor (TAFI) levels correlate with the risk of thrombosis. However, the role of sex or TAFI in venous thromboembolism (VTE) remains uncertain, this study determines the effect of sex and TAFI on thrombus stability using a mouse model of VTE. FeCl3-induced thrombi were formed within femoral veins of male and female wild-type (WT) or TAFI-knockout (Cpb2-/-) mice. Thrombi were imaged at 10- minute intervals over 2-hours using fluorescent intravital videomicroscopy to quantify embolization and thrombus size. Lungs were examined by histology to identify quantity and composition of pulmonary emboli (PE) within pulmonary arteries/tissues. Emboli are considered large when >4 standard deviations above the average. Compared with WT mice, thrombi in Cpb2-/- mice exhibited 3.2-fold and 1.3-fold greater embolization for males and females, respectively. When comparing by sex, female mice embolization events were 7.9- fold and 3.1-fold greater than male WT and Cpb2-/- mice, respectively. Male Cpb2-/- displayed a 10.3-fold greater thrombus size increase compared with male WT mice, while the opposite was true for female mice (5.8-fold greater in WT). Between WT, females had greater thrombus size increase (4.8-fold), while the opposite was true in Cpb2-/- males (12.4-fold). TAFI deficiency led to a 2.2-fold and 2.5-fold increase in PE burden in males and females, respectively, while sex had no influence. Quantitation demonstrated that lungs of female Cpb2-/- mice contained pulmonary emboli with higher fibrin composition compared with WT. Clot lysis times remained similar between male and female WT mice using nascent plasma. Similarly, no differences were observed in circulating TAT concentrations between mice using plasma isolated after imaging. Overall, Sex affects venous thrombus stability, with female mice at increased risk of embolization. Removing TAFI/TAFIa significantly increases PE burden in males and females and increases PE fibrin composition. Inhibition of TAFI may lead to unstable thrombi and increased PE, particularly in females.