Molecular Dissection of gp130-dependent Pathways in Hepatocytes during Liver Regeneration

Uta Dierssen,Naiara Beraza,Holger H Lutz,Christian Liedtke,Matthias Ernst,Hermann E Wasmuth,Christian Trautwein

doi:10.1074/jbc.m705483200

Abstract

Interleukin-6 (IL-6) via its signal transducer gp130 is an important mediator of liver regeneration involved in protecting from lipopolysaccharide (LPS)-induced liver injury after partial hepatectomy (PH). Here we generated mice either defective (Delta) in hepatocyte-specific gp130-dependent Ras or STAT activation to define their role during liver regeneration. Deletion of gp130-dependent signaling had major impact on acute phase gene (APG) regulation after PH. APG expression was blocked in gp130-DeltaSTAT animals, whereas gp130-DeltaRas mice showed an enhanced APG response and stronger SOCS3 regulation correlating with delayed hepatocyte proliferation. To define the role of SOCS3 during hepatocyte proliferation, primary hepatocytes were co-stimulated with IL-6 and hepatocyte growth factor. Higher SOCS3 expression in gp130-DeltaRas hepatocytes correlated with delayed hepatocyte proliferation. Next, we tested the impact of LPS, mimicking bacterial infection, on liver regeneration. LPS and PH induced SOCS3 and APG in all animal strains and delayed cell cycle progression. Additionally, IL-6/gp130-dependent STAT3 activation in hepatocytes was essential in mediating protection and thus required for maximal proliferation. Unexpectedly, oncostatin M was most strongly induced in gp130-DeltaSTAT animals after PH/LPS-induced stress and was associated with hepatocyte proliferation in this strain. In summary, gp130-dependent STAT3 activation and concomitant SOCS3 during liver regeneration is involved in timing of DNA synthesis and protects hepatocyte proliferation during stress conditions.

Highlights

The liver has the unique capacity to compensate tissue loss after injury through hyperplasia of remaining hepatocytes while keeping its organ-specific functions [1, 2]
In recent years, especially for IL-6, it has been demonstrated that this cytokine does not directly control hepatocyte proliferation after Partial (two-thirds) hepatectomy (PH) but activates signaling pathways that are protective for the progression of regeneration [13]
Phosphorylation of the four distal tyrosines is involved in mediating nuclear translocation of STAT3 and STAT1, whereas phosphorylation of the second most membrane-proximal tyrosine is linked to the Ras/Erk pathway as well as to negative regulation of gp130 signaling [16, 17]

Summary

EXPERIMENTAL PROCEDURES

Generation and Genotyping of gp130-mutated Animals— Hepatocyte-specific AlfpCre gp130LoxP/LoxP; mice were generated by breeding AlfpCre mice with mice expressing LoxPflanked gp130 alleles. Reduced Cyclin A Expression and Cdk Activity after PH and LPS Stimulation in Animals with a Hepatocyte-specific Deleted gp130-STAT Pathway—We analyzed the progression of cell cycle markers in the PH/LPS-treated strains. In AlfpCre gp130LoxP/LoxP animals, no P-STAT3 expression was evident, whereas in AlfpCre gp130⌬STAT/LoxP mice P-STAT3 induction was found 6 h after treatment This regulation was comparable with the changes that were detected in the wt PH only group. At Quantitative real time PCR analysis of RNA derived from total liver extracts was performed for the IL-6 family members OSM, leukemia inhibitor factor, and cardiotrophin 1 This analysis demonstrated higher OSM expression in mice subjected to combined challenge of PH and LPS. After PH only minor OSM regulation compared with PH/LPS-treated animals was found 12 h after PH in AlfpCre gp130⌬STAT/LoxP mice (Fig. 7E), whereas other IL-6 family members remained unaffected (data not shown).

LoxP animals was significantly higher

Findings

DISCUSSION