# 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

## TL;DR

Removing a liver protein called Bsep reduces liver scarring in mice by blocking harmful cell signals and reducing inflammation.

## Contribution

This study shows that Bsep loss prevents liver fibrosis by suppressing JNK signaling and HSC activation.

## Key findings

- Bsep-/- mice showed reduced liver inflammation and fibrosis after toxin exposure compared to wild-type mice.
- THBAs suppressed JNK activation in hepatocytes and reduced HSC activation markers in vitro.
- Loss of Bsep altered bile acid profiles, which protected against toxin-induced liver damage.

## Abstract

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.

Wild-type (WT) and Bsep-/- mice were exposed to carbon tetrachloride (CCl4) 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.

In contrast to WT mice, serum transaminases were not elevated in Bsep-/- mice after CCl4 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 CCl4 or TAA. Mechanistically, hepatic protein expression of pJNK (a known mediator of CCl4-induced liver fibrosis) was reduced in Bsep-/- CCl4 mice in comparison to CCl4-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.

Loss of Bsep protects mice from toxin-induced liver fibrosis via suppression of hepatocellular pJNK signaling and attenuation of HSC activation.