JNK mediates differential protection in hepatocytes and non-parenchymal cells during cholestasis

Background Chronic cholestasis triggers severe liver injury, inflammation and subsequently liver fibrosis associated with c-Jun N-terminal kinases (JNK) activation. However, the JNK specific role during cholestasis in parenchymal and non-parenchymal cells (NPCs) has not been defined yet. Previously, we demonstrated that Jnk1 in hepatocytes has no impact on chronic hepatic injury during experimental fibrosis. Here, we investigated the relevance of Jnk2 but also Jnk1 and Jnk2 specifically in hepatocytes and NPCs for cholestatic liver fibrosis.

Methods JNK activation was investigated in patients with cholestatic liver disease namely primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) (n = 27). Wildtype (WT), hepatocyte-specific knockout mice for Jnk2 (Jnk2^Δhepa ) or Jnk1 and Jnk2 (Jnk1^Δhepa/2^Δhepa ) were generated. Additionally, Jnk2 knockout (Jnk2^-/- ), Jnk1^Δhepa/2^-/- and Mdr2 knockout mice were included. Mice were subjected to bile duct ligation (BDL) for 28 days. Hepatic damage, cell death, proliferation, inflammation and fibrosis were assessed by immunostainings, Western Blot and qRT-PCR. Additionally, microarray analysis and bone marrow transplantation (BMT) were performed.

Results Protein expression of pJNK was significantly increased in human PSC and PBC samples and correlated with disease activity. Furthermore, mice with surgically- or genetically-induced cholestasis (BDL and Mdr2^-/- ) showed increased pJNK expression. After BDL, Jnk2^∆hepa livers showed no significant differences in hepatic injury, inflammation and fibrosis compared to WT controls. In contrast, Jnk1^Δhepa/2^Δhepa livers exhibited exacerbated liver damage and immunostainings of liver sections revealed increased cell death, proliferation, inflammation and fibrogenesis demonstrating a combined protective role of Jnk genes in hepatocytes during cholestasis. Moreover, Jnk2^-/- and Jnk1^Δhepa/2^-/- mice displayed increased liver injury and fibrosis compared to Jnk2^Δhepa and Jnk1^Δhepa/2^Δhepa mice, respectively. Finally, BMT experiments demonstrated the involvement of Jnk2 in NPCs but not in BM-derived cells in controlling BDL-dependent disease progression.

Conclusion Combined but not individual function of Jnk1 and Jnk2 in hepatocytes is essential to protect against BDL-induced liver fibrosis. Jnk2 in NPCs but not BM-derived cells confers additional protection during cholestasis. Hence JNKs have a differential and cell-type specific protective role during cholestasis.

Publication History

Article published online:
04 January 2021