Inhibition of plasmin-mediated TAFI activation may affect development but not progression of abdominal aortic aneurysms

Identification of heparin interaction sites on thrombin-activatable fibrinolysis inhibitor that modulate plasmin-mediated activation, thermal stability, and antifibrinolytic potential

Background

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a plasma zymogen that provides a molecular link between coagulation and fibrinolysis. Studies have shown that the presence of glycosaminoglycans accelerates TAFI activation by plasmin and stabilizes activated TAFI (TAFIa).

Objectives

We aimed to define the elements of TAFI structure that allow these effects.

Methods

Based on crystallographic studies and homology to heparin-binding proteins, we performed mutagenesis of surface-exposed charged residues on TAFI that putatively constitute heparin-binding sites. We determined heparin binding, kinetics of activation by plasmin in the presence or absence of heparin, thermal stability, and antifibrinolytic potential of each variant.

Results

Mutagenesis of Lys211 and Lys212 did not impair heparin binding but affected the ability of TAFI to be activated by plasmin. Mutagenesis of Lys306 and His308 did not impair heparin binding, but mutation of His308 had a severe negative effect on TAFI/TAFIa function. Mutation of Arg320 and Lys324 in combination markedly decreased heparin binding but had no effect on heparin-mediated acceleration of TAFI activation by plasmin while somewhat decreasing TAFIa stabilization by heparin. Mutagenesis of Lys327 and Arg330 decreased (but did not eliminate) heparin binding while decreasing the ability of heparin to accelerate plasmin-mediated TAFI activation, stabilize TAFIa, and increase the antifibrinolytic ability of TAFIa. A quadruple mutant of Arg320, Lys324, Lys327, and Arg330 completely lost heparin-binding ability and stabilization of the enzyme by heparin.

Conclusion

Basic residues in the dynamic flap of TAFIa define a functionally relevant heparin-binding site, but additional heparin-binding sites may be present on TAFI.

Establishment of a meta-analysis based novel aortic dissection mouse model

Aortic dissection (AD) is a life-threatening disease and the detailed mechanism remains unclear. Thus, proper animal models are urgently required to better understand its pathogenesis. Our current study aims to establish a reliable, time and cost-effective mouse AD model. To conduct the meta-analysis, we searched PubMed for related studies up to 2021 and statistical analysis was conducted using Review Manager 5.4. For the animal experiment, 6-week-old male ApoE^-/- mice were given β-aminopropionitrile (BAPN) at a concentration of 1 g/L for 3 weeks before being infused with saline, 1000 ng/kg/min or 2500 ng/kg/min angiotensin II (AngII) via osmotic mini pumps for 2 or 4 weeks. To determine the presence of AD, we performed B-ultrasonography, hematoxylin and eosin (H&E) staining, and van Gieson staining. The result of the meta-analysis showed that the use of BAPN and more than 2000 ng/kg/min AngII can increase the rate of AD formation, whereas administrating Ang II for more than 28 days has no significant effect on the rate of AD formation when compared with the less than 14 days group. In the present study, mice treated with BAPN combined with 2500 ng/kg/min AngII for 2 weeks (12/20) had a significantly higher AD formation rate than mice treated with BAPN combined with 1000 ng/kg/min Ang II for 4 weeks (2/10), and had a similar model formation rate compared with the mice treated withβ-aminopropionitrile combined with 2500 ng/kg/min AngII for 4 weeks (6/10). There were 3 mice (3/10) and 6 mice (6/20) who died in the group treated with β-aminopropionitrile combined with 2500 ng/kg/min AngII for 4 weeks and 2 weeks respectively, and only one mouse (1/10) died in the group treated with β-aminopropionitrile combined with 1000 ng/kg/min AngII for 4 weeks. In 6-week-old male ApoE^-/- mice that received with 1 g/L BAPN in the drinking water for 3 weeks along with 2500 ng/kg/min AngII infusion via osmotic mini pumps for 2 weeks, the highest model formation rate and relative lower cumulative mortality were noted.

Cell proliferation detected using [18F]FLT PET/CT as an early marker of abdominal aortic aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is a focal aortic dilatation progressing towards rupture. Non-invasive AAA-associated cell proliferation biomarkers are not yet established. We investigated the feasibility of the cell proliferation radiotracer, fluorine-18-fluorothymidine ([18F]FLT) with positron emission tomography/computed tomography (PET/CT) in a progressive pre-clinical AAA model (angiotensin II, AngII infusion).

METHODS AND RESULTS

Fourteen-week-old apolipoprotein E-knockout (ApoE-/-) mice received saline or AngII via osmotic mini-pumps for 14 (n = 7 and 5, respectively) or 28 (n = 3 and 4, respectively) days and underwent 90-minute dynamic [18F]FLT PET/CT. Organs were harvested from independent cohorts for gamma counting, ultrasound scanning, and western blotting. [18F]FLT uptake was significantly greater in 14- (n = 5) and 28-day (n = 3) AAA than in saline control aortae (n = 5) (P < 0.001), which reduced between days 14 and 28. Whole-organ gamma counting confirmed greater [18F]FLT uptake in 14-day AAA (n = 9) compared to saline-infused aortae (n = 4) (P < 0.05), correlating positively with aortic volume (r = 0.71, P < 0.01). Fourteen-day AAA tissue showed increased expression of thymidine kinase-1, equilibrative nucleoside transporter (ENT)-1, ENT-2, concentrative nucleoside transporter (CNT)-1, and CNT-3 than 28-day AAA and saline control tissues (n = 3 each) (all P < 0.001).

CONCLUSIONS

[18F]FLT uptake is increased during the active growth phase of the AAA model compared to saline control mice and late-stage AAA.

Systematic Review and Meta-Analysis of Interventions to Slow Progression of Abdominal Aortic Aneurysm in Mouse Models

[Figure: see text].