Hepatocyte apoptosis after bile duct ligation in the mouse involves Fas

Background & Aims: Cholestatic liver injury results from the intrahepatic accumulation of toxic bile salts. Toxic bile salt-induced hepatocyte apoptosis in vitro is Fas dependent. The aim of this study was to ascertain if hepatocyte apoptosis in vivo during cholestasis is Fas dependent. Methods: Studies were performed in bile duct-ligated (BDL) Fas-deficient Ipr (lymphoproliferation) and wild-type mice. Results: Hepatocyte apoptosis was the predominant mechanism of cell death as determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and trypan blue assays to quantitate apoptosis and necrosis. The mechanisms of hepatocyte apoptosis were dependent on the presence or absence of the Fas receptor and the duration of BDL. After BDL of 3 days' duration, increased hepatocyte apoptosis occurred only in wild-type but not Ipr mice, indicating the apoptosis was Fas dependent. In contrast, after BDL of greater than or equal to 7 days, hepatocyte apoptosis also occurred in Ipr animals consistent with a Fas-independent mechanism of apoptosis. Hepatocyte apoptosis in BDL Ipr mice was associated with an increase in Bax expression and Bax association with mitochondria. Conclusions: During extrahepatic cholestasis, hepatocyte apoptosis is mediated by Fas. However, in the absence of the Fas receptor, additional mechanisms of hepatocyte apoptosis occur. Inhibition of multiple apoptotic pathways is necessary to attenuate chronic cholestatic liver injury.