Inactivation of caspase 8 in liver parenchymal cells confers protection against murine obstructive cholestasis

Abstract

Background & aims: Caspase 8 (CASP8) is the apical initiator caspase in death receptor-mediated apoptosis. Strong evidence for a link between death receptor signaling pathways and cholestasis has recently emerged. Herein, we investigated the role of CASP8-dependent and independent pathways during experimental cholestasis.

Methods: Liver injury was characterized in a cohort of human sera (n = 28) and biopsies from patients with stage IV primary biliary cholangitis. In parallel, mice with either specific deletion of Casp8 in liver parenchymal cells (Casp8^Δhepa) or hepatocytes (Casp8^Δhep), and mice with constitutive Ripk3 (Ripk3^-/-) deletion, were subjected to surgical ligation of the common bile duct (BDL) from 2 to 28 days. Floxed (Casp8^fl/fl) and Ripk3^+/+ mice were used as controls. Moreover, the pan-caspase inhibitor IDN-7314 was used, and cell death mechanisms were studied in primary isolated hepatocytes.

Results: Overexpression of activated caspase 3, CASP8 and RIPK3 was characteristic of liver explants from patients with primary biliary cholangitis. Twenty-eight days after BDL, Casp8^Δhepamice showed decreased necrotic foci, serum aminotransferase levels and apoptosis along with diminished compensatory proliferation and ductular reaction. These results correlated with a decreased inflammatory profile and ameliorated liver fibrogenesis. A similar phenotype was observed in Ripk3^-/- mice. IDN-7314 treatment decreased CASP8 levels but failed to prevent BDL-induced cholestasis, independently of CASP8 in hepatocytes.

Conclusion: These findings show that intervention against CASP8 in liver parenchymal cells - specifically in cholangiocytes - might be a beneficial option for treating obstructive cholestasis, while broad pan-caspase inhibition might trigger undesirable side effects.

Lay summary: Loss of caspase 8 - a protein involved in programmed cell death - in liver parenchymal cells protects against experimental cholestasis. Therefore, specific pharmacological intervention against caspase 8 might be a valid alternative for the treatment of obstructive cholestasis in the clinic, whereas broad pan-caspase inhibiting drugs might trigger undesirable side effects.

Keywords: BDL; Caspase 8; Cholangiocytes; Cholestasis; Hepatocytes; PBC.