Altered fibrinogen & gamma;-chain cross-linking in mutant fibrinogen-& gamma;& UDelta;5 mice drives acute liver injury

Background: Hepatic deposition of cross-linked fibrin(ogen) occurs alongside platelet accumulation as a hallmark of acetaminophen (APAP)-induced liver injury. Objectives: We sought to define the precise role of the fibrinogen & gamma;-chain C-terminal integrin & alpha;IIb & beta;3 binding domain in APAP-induced liver injury. Methods: Mice expressing mutant fibrinogen incapable of engaging integrin & alpha;IIb & beta;3 due to a C-terminal fibrinogen & gamma;-chain truncation (mutant fibrinogen-& gamma;& UDelta;5 [Fib & gamma;& UDelta;5] mice) and wild-type mice were challenged with APAP (300 mg/kg, intraperitoneally). Results: We observed an altered pattern of fibrin(ogen) deposition in the livers of APAP-challenged Fib & gamma;& UDelta;5 mice. This led to the unexpected discovery that fibrinogen & gamma;-chain cross-linking was altered in the livers of APAP-challenged Fib & gamma;& UDelta;5 mice compared with that in wild-type mice, including absence of & gamma;-& gamma; dimer and accumulation of larger molecular weight cross-linked & gamma;-chain complexes. This finding was not unique to the injured liver because activation of coagulation did not produce & gamma;-& gamma; dimer in plasma from Fib & gamma;& UDelta;5 mice or purified Fib & gamma;& UDelta;5 fibrinogen. Sanger sequencing predicted that the fibrinogen-& gamma;& UDelta;5 & gamma;-polypeptide would terminate at lysine residue 406, but liquid chromatography tandem mass spectrometry analysis revealed that this critical lysine residue was absent in purified fibrinogen-& gamma;& UDelta;5 protein. Interestingly, hepatic deposition of this uniquely aberrantly cross-linked fibrin(ogen) in Fib & gamma;& UDelta;5 mice was associated with exacerbated hepatic injury, an effect not recapitulated by pharmacologic inhibition of integrin & alpha;IIb & beta;3. Conclusion: The results indicate that fibrinogen-& gamma;& UDelta;5 lacks critical residues essential to form & gamma;-& gamma; dimer in response to thrombin and suggest that hepatic accumulation of abnormally cross-linked fibrin(ogen) can exacerbate hepatic injury.