Thrombin-activatable fibrinolysis inhibitor (TAFI) deficiency is compatible with murine life

Abstract

To investigate the consequence of deficiency in thrombin-activatable fibrinolysis inhibitor (TAFI), we generated homozygous TAFI-deficient mice by targeted gene disruption. Intercrossing of heterozygous TAFI mice produced offspring in the expected Mendelian ratio, indicating that transmission of the mutant TAFI allele did not lead to embryonic lethality. TAFI-deficient mice developed normally, reached adulthood, and were fertile. No gross physical abnormalities were observed up to 24 months of age. Hematological analysis of TAFI-deficient mice did not show any major differences including plasma fibrinogen level, prothrombin time, and activated partial thromboplastin time. TAFI-deficient mice did not suffer from excess bleeding as determined by blood loss following tail transection, although their plasma failed to prolong clot lysis time in vitro. In vivo, TAFI deficiency did not influence occlusion time in either an arterial or a venous injury model. TAFI deficiency did not improve survival rate compared with the wild-type in thrombin-induced thromboembolism, factor X coagulant protein–induced thrombosis, and endotoxin-induced disseminated intravascular coagulation. Furthermore, TAFI deficiency did not alter kaolin-induced writhing response, implying that TAFI does not play a major role in bradykinin catabolism. The current study demonstrates that TAFI deficiency does not change normal responses to acute challenges

Ambivalent roles of carboxypeptidase B in the lytic susceptibility of fibrin

“…One hypothesis for this phenomenon is the removal of lysine 452 of α 2 -plasmin inhibitor by carboxypeptidases [21] , but this is difficult to reconcile with the findings that the C-terminal lysine in the inhibitor is not essential for its interaction with plasmin [22] . The completely normal phenotype of TAFI knock-out mice (including hemostasis at basal state or if challenged by a variety of prothrombotic stimuli) [23] also raises the possibility for subtle TAFI effects in vivo beyond the known mechanism of action. Thus, the details of TAFI function still require further elaboration despite its well-documented anti-fibrinolytic action in vitro .…”

TAFI deficiency causes maladaptive vascular remodeling after hemophilic joint bleeding

“…In TAFI-KO mice, PD signals were increased in all age groups (3, 9, and 18 months), showing markedly altered vascularity patterns ( Figure 3D), reminiscent of those seen in FVIII-KO mice after severe joint bleeding. To exclude the possibility that the increased PD signals in this TAFI-KO line (44) were due to potential off-target effects as the result of genetic drift, results were confirmed in an independently generated and maintained TAFI-KO strain (45). Indeed, increased PD signals were also observed in this TAFI-KO line in both younger (<6 months) and aged (>6 months) mice compared with their respective age-matched WT controls (Supplemental Figure 8).…”

“…The development of vascular abnormalities in the joint was also confirmed in aging TAFI-KO mice in 2 independently generated and maintained strains (44,45). In general, mice exhibited spontaneously increased vessel diameters with aging that may be a result of aging-associated chronic and low-grade inflammation.…”

“…FVIII-KO mice on a BALB/c background (64) were a gift of David Lillicrap (Queens University, Ontario, Canada), and WT-BALB/c were obtained from The Scripps Research Institute internal breeding facility. TAFI-KO mice on a C57Bl/6J background were a gift of Joost Meijers (Sanquin Research Amsterdam, The Netherlands) (44,45) and were backcrossed 5 generations to C57Bl/6J obtained from The Scripps Research Institute internal breeding facility to confirm key findings. A second, independently generated TAFI-KO strain on a C57Bl/6J background was maintained at Stanford University School of Medicine (45).…”

“…TAFI-KO mice on a C57Bl/6J background were a gift of Joost Meijers (Sanquin Research Amsterdam, The Netherlands) (44,45) and were backcrossed 5 generations to C57Bl/6J obtained from The Scripps Research Institute internal breeding facility to confirm key findings. A second, independently generated TAFI-KO strain on a C57Bl/6J background was maintained at Stanford University School of Medicine (45). Skeletally mature mice (age 12-16 weeks) of both sexes were used for joint injury studies.…”