Loss of Bile Salt Export Pump (Bsep/Abcb11) Ameliorates Toxin-induced Hepatic Fibrosis via Suppression of Hepatocellular Jun Amino-terminal Kinase Signaling and Hepatic Stellate Cell Activation.

BACKGROUND & AIMS: Loss of Bsep/Abcb11 results in a hydrophilic bile acid (BA) pool consisting of tetrahydroxylated BAs (THBAs) reducing cholestasis-induced liver injury. In this study, we investigated whether loss of Bsep may protect mice from development of toxin-induced liver fibrosis by directly impacting on hepatic stellate cell (HSC) activation. METHODS: Wild-type (WT) and Bsep(-/-) mice were exposed to carbon tetrachloride (CCl(4)) or thioacetamide (TAA) for 4 weeks (3 injections per week) as models of toxin-induced liver fibrosis. In vitro, the human HSC line LX2 and immortalized human hepatocytes (IHHs) were challenged with TGFβ or 12S-HETE (arachonidonic acid derivate) with or without THBA treatment. Liver immunohistochemistry (IHC), immunofluorescence (IF), gene and protein expression, intrahepatic BA profile, luciferase activity, and 12S-HETE assays were performed. RESULTS: In contrast to WT mice, serum transaminases were not elevated in Bsep(-/-) mice after CCl(4) or TAA injection. Accordingly, IHC accompanied by gene expression profiling and measurement of hepatic hydroxyproline levels reduced hepatic inflammation and fibrosis in Bsep(-/-) mice challenged with CCl(4) or TAA. Mechanistically, hepatic protein expression of pJNK (a known mediator of CCl(4)-induced liver fibrosis) was reduced in Bsep(-/-) CCl(4) mice in comparison to CCl(4)-exposed WT mice. In vitro, activation of JNK was suppressed by THBA in IHH cells. LX2 cell activation was attenuated by treatment with THBA as reflected by reduced AP1-luciferase activity and by restoring gene expression levels of p62 and Nrf2 as well as by significant reduction of αSma, Tgfβ, and Mcp-1 gene expression. CONCLUSIONS: Loss of Bsep protects mice from toxin-induced liver fibrosis via suppression of hepatocellular pJNK signaling and attenuation of HSC activation.