Caspase 8 differentially controls hepatocytes and non-parenchymal liver cells during chronic cholestatic liver injury in mice

Abstract

Background & aims: Receptor mediated cell death through the activation of caspases has been identified as an important mechanism to control life and death in various tissues and is thus crucial for the maintenance of liver tissue homeostasis. Here we investigated how caspase 8 (Casp8) differentially regulates immune-mediated liver injury and regeneration in distinct liver cell types during chronic liver injury.

Methods: Conditional knockout mice with hepatocellular (Casp8(Δhepa)) and ubiquitous deletion of Casp8 (Casp8(ΔMx)) were used in models of cholestatic hepatitis [(DDC (3,5-diethoxycarbonyl-1,4-dihydrocollidine) treatment, bile duct ligation (BDL) and choline deficient diet with ethionine supplementation (CDE)].

Results: Mice with a hepatocellular deletion of Casp8 (Casp8(Δhepa)) were protected after DDC-treatment. Animals with a ubiquitous conditional Casp8 knockout (Casp8(ΔMx)) displayed a significantly enhanced liver injury in various models of cholestatic liver injury. This was associated with higher transaminases, bilirubin levels and finally more liver fibrosis. However, caspase 3 (Casp3) activity was reduced in both knockout strains, suggesting additionally mechanisms contributing to the phenotype. Casp8(ΔMx) mice displayed a stronger infiltration of mononuclear immune cells and more proliferation of liver-parenchymal cells in periportal areas. Further analysis confirmed that these infiltrating immune cells are resistant against extrinsic apoptosis. Bone-marrow-transplantation (BMT) experiments demonstrated that Casp8-deficient bone marrow derived cells are responsible for increased liver injury in DDC fed mice.

Conclusions: Our results demonstrate that cell-type specific differences in apoptosis resistance mediated by Casp8 deletion are of significant relevance for the outcome of chronic liver injury.

Keywords: 3,5-diethoxycarbonyl-1,4-dihydrocollidine; 4weeks; 4wk; 5-bromo-2-deoxyuridine; ALT; Apoptosis resistance; BM; BMT; BrdU; Casp; Casp8 knockout allele; Casp8 knockout mice; Casp8(loxP/loxP); Casp8(ΔMx); Casp8(Δhepa); Caspase; Caspase-8; DDC; Hepatic immune cells; LPC; Mx1; NPCs; PCR; Progenitor cells; RT; SD; Secondary sclerosing cholangitis; TUNEL; WT; alanine-aminotransferase; bone marrow; bone marrow transplantation; i.p.; intraperitoneally; liver progenitor cell; myxovirus resistance-1; non-parenchymal cells; pIpC; polymerase chain reaction; polyriboinosinic-polyribocytidylic; real-time; standard deviation; terminal deoxynucleotidyltransferase-mediated nick end labelling; ubiquitous deletion of Casp8; weight; wild type; wt.