Summary Background The coagulation cascade has been shown to participate in chronic liver injury and fibrosis, but the contribution of various thrombin targets, such as protease activated receptors (PARs) and fibrin(ogen), has not been fully described. Emerging evidence suggests that in some experimental settings of chronic liver injury, platelets can promote liver repair and inhibit liver fibrosis. However, the precise mechanisms linking coagulation and platelet function to hepatic tissue changes following injury remain poorly defined. Objectives To determine the role of PAR-4, a key thrombin receptor on mouse platelets, and fibrin(ogen) engagement of the platelet αIIbβ3 integrin in a model of cholestatic liver injury and fibrosis. Methods Biliary and hepatic injury was characterized following 4 week administration of the bile duct toxicant α-naphthylisothiocyanate (ANIT) (0.025%) in PAR-4-deficient mice (PAR-4−/− mice), mice expressing a mutant form of fibrin(ogen) incapable of binding integrin αIIbβ3 (FibγΔ5), and wild-type mice. Results Elevated plasma thrombin-antithrombin and serotonin levels, hepatic fibrin deposition and platelet accumulation in liver accompanied hepatocellular injury and fibrosis in ANIT-treated wild-type mice. PAR-4 deficiency reduced plasma serotonin levels, increased serum bile acid concentration, and exacerbated ANIT-induced hepatocellular injury and peribiliary fibrosis. Compared to PAR-4-deficient mice, ANIT-treated FibγΔ5 mice displayed more widespread hepatocellular necrosis accompanied by marked inflammation, robust fibroblast activation and extensive liver fibrosis. Conclusions Collectively, the results indicate that PAR-4 and fibrin-αIIbβ3 integrin engagement, pathways coupling coagulation to platelet activation, each exert hepatoprotective effects during chronic cholestasis.
Background & aims Acetaminophen (APAP)-induced liver injury is coupled to activation of the blood coagulation cascade and fibrin(ogen) accumulation within APAP-injured livers of experimental mice. We sought to define the precise role of fibrin(ogen) deposition in APAP-induced liver injury and repair. Methods Fasted mice were injected with 300 mg/kg APAP i.p. and evaluated various times later. Results In wild-type mice APAP overdose increased intrahepatic levels of high molecular weight cross-linked fibrin(ogen). Anticoagulation reduced early APAP hepatotoxicity (6 hours), but surprisingly, increased hepatic injury at 24 hours, implying a protective role for coagulation at the onset of repair. Complete fibrin(ogen) deficiency delayed liver repair after APAP overdose, evidenced by a reduction of proliferating hepatocytes (24 hours) and unresolved hepatocellular necrosis (48 and 72 hours). Mutant mice with fibrin(ogen) incapable of binding leukocyte αMβ2 integrin (Fibγ390-396A mice) had decreased hepatocyte proliferation and increases in multiple indices of liver injury, suggesting a mechanism related to fibrin(ogen)-leukocyte interaction. Induction of the macrophage-associated gene, matrix metalloproteinase 12 (Mmp12), was dramatically reduced in APAP-treated Fibγ390-396A mice, and mice lacking Mmp12 displayed exacerbated APAP-induced liver injury, resembling Fibγ390-396A mice. In contrast, administration of the αMβ2 integrin allosteric agonist leukadherin-1 enhanced hepatic MMP12 mRNA and reduced necrosis in APAP-treated mice. Further, administration of recombinant MMP12 protein to APAP-treated Fibγ390-396A mice restored hepatocyte proliferation. Conclusions Collectively, these studies highlight an entirely novel pathway of liver repair after APAP overdose, mediated by fibrin(ogen)-αMβ2 integrin engagement and demonstrate for the first time a protective role of Mmp12 expression after APAP overdose.
Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Key Points Fibrin engagement of leukocyte integrin-αMβ2 restricts bile duct hyperplasia and inhibits periductal fibrosis. Periductal fibrosis following bile duct injury is inhibited by leukadherin-1, an allosteric activator of integrin-αMβ2 fibrin binding.
Introduction: Intravascular fibrin clots and extravascular fibrin deposits are often implicated in the progression of liver fibrosis. However, evidence supporting a pathological role of fibrin in hepatic fibrosis is indirect and based largely on studies using anticoagulant drugs that inhibit activation of the coagulation protease thrombin, which has other downstream targets that promote fibrosis. Therefore, the goal of this study was to determine the precise role of fibrin deposits in experimental hepatic fibrosis. Methods: Liver fibrosis was induced in mice expressing mutant fibrinogen insensitive to thrombin-mediated proteolysis (i.e., locked in the monomeric form), termed FibAEK mice, and Factor XIII A2 subunit-deficient mice (FXIII−/−). Female wild-type mice, FXIII−/− mice, and homozygous FibAEK mice were challenged with carbon tetrachloride (CCl4), twice weekly for 4 or 6 weeks (1 ml/kg, ip). Results: Hepatic injury and fibrosis induced by CCl4 challenge were unaffected by FXIII deficiency or inhibition of thrombin-catalyzed fibrin polymer formation (in FibAEK mice). Surprisingly, hepatic deposition of cross-linked fibrin(ogen) was not reduced in CCl4-challenged FXIII−/− mice or FibAEK mice compared to wild-type mice. Rather, deposition of cross-linked hepatic fibrin(ogen) following CCl4 challenge was dramatically reduced in tissue transglutaminase-deficient mice (TGM2−/− mice). However, the reduction in cross-linked fibrin(ogen) in TGM2−/− mice did not affect CCl4-induced liver fibrosis. Conclusions: These results indicate that neither traditional fibrin clots, formed by the thrombin:FXIIIa pathway, nor atypical TGM2-cross-linked fibrin(ogen) contribute to experimental CCl4-induced liver fibrosis. Collectively, the results indicate that liver fibrosis occurs independently of intrahepatic fibrin(ogen) deposition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.