Abstract
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 γ-chain C-terminal integrin α(IIb)β(3) binding domain in APAP-induced liver injury. METHODS: Mice expressing mutant fibrinogen incapable of engaging integrin α(IIb)β(3) due to a C-terminal fibrinogen γ-chain truncation (mutant fibrinogen-γ(Δ5) [Fibγ(Δ5)] 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 Fibγ(Δ5) mice. This led to the unexpected discovery that fibrinogen γ-chain cross-linking was altered in the livers of APAP-challenged Fibγ(Δ5) mice compared with that in wild-type mice, including absence of γ-γ dimer and accumulation of larger molecular weight cross-linked γ-chain complexes. This finding was not unique to the injured liver because activation of coagulation did not produce γ-γ dimer in plasma from Fibγ(Δ5) mice or purified Fibγ(Δ5) fibrinogen. Sanger sequencing predicted that the fibrinogen-γ(Δ5) γ-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-γ(Δ5) protein. Interestingly, hepatic deposition of this uniquely aberrantly cross-linked fibrin(ogen) in Fibγ(Δ5) mice was associated with exacerbated hepatic injury, an effect not recapitulated by pharmacologic inhibition of integrin α(IIb)β(3). CONCLUSION: The results indicate that fibrinogen-γ(Δ5) lacks critical residues essential to form γ-γ dimer in response to thrombin and suggest that hepatic accumulation of abnormally cross-linked fibrin(ogen) can exacerbate hepatic injury.