Deficiency of TRAIL or overexpression of human-MCL1 attenuates liver injury in the bile duct ligated Mouse

ALISAN KAHRAMAN; FERNANDO J BARREYRO; STEVEN F BRONK; NATHAN W. WERNEBURG; JUSTIN L. MOTT; KAREN BRALEY; RUTH W. CRAIG; GREGORY J GORES

Boston, USA

Congreso; 58th Annual Meeting of the American Association for the Study of Liver Diseases (AASLD). 2007; 2007

American Association for the Study of Liver Diseases

Hepatocellular apoptosis is a key mechanism of liver injury during cholestasis. Apoptosis during cholestasis is triggered by hepatic retention of toxic bile acids. Although we have reported that toxic bile acids increase hepatocyte expression of tumor necrosis factor-related apoptosis inducing ligand (TRAIL) death receptor 5 (DR5), the contribution of TRAIL and its opponent myeloid cell leukemia sequence-1 (Mcl-1) to cholestatic liver injury have not been explored. Thus, our AIM was to ascertain if genetic deficiency of TRAIL or overexpression of human Mcl- 1 (hMcl-1) attenuates liver injury in the bile duct ligated (BDL) mouse. METHODS: C57/BL6 wild-type (wt), TRAIL knockout (TRAIL-/-) and hMcl-1 transgenic (TG) mice were used for these studies. Real-time polymerase chain reaction (PCR) was used to measure mRNA transcripts for TRAIL. Hepatocyte apoptosis was quantified by the TUNEL assay and immunofluorescence for activated caspases 3/7. Liver injury was assessed by histopathology, quantification of bile infarcts and serum ALT determinations. Hepatic fibrosis was assessed by Sirius red staining and quantitative morphometry. RESULTS: Following 7 days of BDL, hepatic TRAIL mRNA was 6-fold greater in BDL vs. sham-operated wild-type animals (p < 0.01). As compared to sham-operated wild-type mice, BDL mice displayed a 13-fold increase in TUNEL and an 11-fold increase in caspase 3/7 positive hepatocytes (p < 0.01). The number of TUNEL and caspase 3/7 positive cells was reduced by > 80% in BDL TRAIL knockout and hMcl-1 TG animals (p < 0.01). Consistent with the apoptosis data, histologic examination of TRAIL knockout and hMcl-1 TG BDL livers also demonstrated a 50% reduction in the number of bile infarcts as compared to wild-type BDL mice. Serum ALT values, which were increased 200-fold in wildtype BDL vs. sham-operated animals, were also reduced by > 80% in TRAIL knockout or hMcl-1 TG BDL mice. These differences could not be ascribed to differences in cholestasis as serum total bilirubin concentrations were nearly identical in wt, TRAIL knockout and hMcl-1 TG BDL mice (12-15 mg/dl). Finally, hepatic fibrosis was 3-fold increased in wt as compared to hMcl-1 TG animals following 14 days of BDL. In CONCLUSION: The present study demonstrates that in the BDL mouse, hepatocyte apoptosis, liver injury and hepatic fibrosis are attenuated in the TRAIL-deficient or hMcl-1 TG mouse. In conclusion, these observations support a pivotal role for TRAIL-mediated liver injury that can be inhibited by Mcl-1 and further define conditions under which TRAIL is hepatotoxic.