Abstract Number: OC 22.1
Meeting: ISTH 2021 Congress
Background: The fibrinogen αC-region is implicated in promoting fibrin lateral aggregation, enhancing clot stiffness, and regulating fibrinolysis. Genetic variants within the αC-region are often associated with hypofibrinogenemia and/or dysfibrinogenemia.
Aims: To develop a genetic model of αC-region truncation for analysis of the structural, functional, and pathological implications of αC-region truncation in vivo.
Methods: Crispr-Cas9 technology was used to generate Fibrinogen Aα270 (Fga270) mice that carry a stop codon at residue 271 of the Aα-chain, analogous to Fibrinogen Otago. Mice were analyzed for survival and hematological profiles, platelet function, and their response to hemostatic/thrombotic challenge.
Results: Heterozygous crosses of 2 independent lines produced a 22.0% FgaWT/WT, 54.7% FgaWT/270 and 23.3% Fga270/270 genotype distribution at weaning. Fga270/270 adult mice were found to be severely hypofibrinogenemic with plasma levels ~10% relative to FgaWT/WT mice. Reduced plasma fibrinogen was linked to a 90% reduction in hepatic Fga mRNA and analyses of isolated hepatocytes suggested nonsense-mediated decay of the mutant mRNA. Plasma thrombin times, PT, and aPTT were significantly prolonged for Fga270/270. Platelets from FgaWT/WT and Fga270/270 mice displayed comparable initial aggregation following ADP stimulation, but Fga270/270 platelets quickly disaggregated. Fga270/270 platelets contain ~30% of fibrinogen relative to platelets of WT mice. The reduction in platelet fibrinogen in mutant mice was accompanied by a compensatory increase in platelet fibronectin content. Tail bleeding times revealed a time to flow stop of 100.7±14.2 s for FgaWT/WT mice versus 136.4±21.2 s for 5 of 6 Fga270/270 mice. No cessation of bleeding was observed in one Fga270/270 mouse and all Fib-/- mice analyzed. In the IVC stasis venous thrombosis model, FgaWT/WT mice formed large thrombi, while no thrombi formed in Fga270/270 mice within 24 hr.
Conclusions: Collectively, these findings suggest fibrinogen Aα-chain truncation results in profound hypo(dys)fibrinogenemia and reveal synthetic mechanisms requisite for fibrinogen protein expression.
To cite this abstract in AMA style:Hur WS, G Bouck E, S Paul D, Negron O, G Poole L, Cline-Fedewa H, Clark E, Ugarova T, S Wolberg A, Bergmeier W, P Luyendyk J, J Flick M. Genetic Truncation of the Fibrinogen αC-region in Mice Results in Severe Hypofibrinogenemia with Preservation of Hemostasis and Protection from Venous Thrombosis [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/genetic-truncation-of-the-fibrinogen-%ce%b1c-region-in-mice-results-in-severe-hypofibrinogenemia-with-preservation-of-hemostasis-and-protection-from-venous-thrombosis/. Accessed December 3, 2021.
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