Role of IL-6/gp130-dependent signalling pathways in hepatocytes during liver regeneration and inflammation

The signal transducer gp130 initiates cellular events started by induction of JAK kinases resulting in Ras/Erk-mediated signalling and activation of STAT transcription factors, particularly STAT3. Within the present studies the role of the Interleukin-6 (IL-6) receptor gp130 in hepatocytes was investigated in terms of liver regeneration, liver dependent iron homeostasis and gram positive sepsis. Therefore, mice either defective in hepatocyte-specific gp130-dependent Ras/Erk or STAT activation were generated to define the role of these signalling pathways. These mice were used in comparison to conditional gp130 knockout mice having a complete depletion of the gp130 receptor in hepatocytes. After liver resection by partial hepatectomy (PH) the deletion of gp130-dependent signalling had major impact on acute phase gene (APG) regulation. APG expression was blocked in gp130-STAT animals. In contrast, gp130-Ras mice showed an enhanced APG response and a stronger expression of the suppressor of cytokine signalling 3 (SOCS3) combined with delayed hepatocyte proliferation. In order to further elucidate the influence of SOCS3 during hepatocyte proliferation, primary hepatocytes were co-stimulated with IL-6 and HGF. Confirming the in vivo observations, higher SOCS3 expression in primary gp130-Ras hepatocytes also correlated with delayed hepatocyte proliferation. The aim of further studies was to analyze the protective influence of gp130-dependent signalling on inflammatory events during liver regeneration. Therefore mice were additionally challenged with LPS - mimicking bacterial infection. Application of LPS in addition to liver resection resulted in enhanced SOCS3 expression in combination with delayed cell cycle progression. Further investigations provided evidence that IL-6/gp130-dependent STAT3 activation in hepatocytes plays a decisive role in mediating protection as well as this transcription factor is essentially required for maximal hepatocyte proliferation in the liver. In summary, gp130-dependent STAT3 activation and concomitant induction of SOCS3 during liver regeneration controls timing of DNA synthesis and protects hepatocyte proliferation during stress conditions. Engaged in clearing up the molecular mechanisms of gp130-dependent liver iron homeostasis, the second part of the present work deals with the peptide hormone hepcidin. To clarify the molecular pathways involved in hepcidin activation triggered by IL-6, the different gp130-deficient mice strains were stimulated with recombinant IL-6. Additionally, the observations were confirmed by in vitro studies with primary hepatocytes. IL-6 application in vivo resulted in induction of phospho-STAT3 and expression of SOCS3 and APG in livers of wildtype and gp130-Ras mice, whereas this response was completely blunted in gp130-STAT and liver-specific gp130 receptor knockout mice. In wild-type and gp130-Ras animals, significantly higher hepcidin mRNA expression was found after IL-6 stimulation. In contrast, no IL-6-dependent regulation of hepcidin mRNA expression was found in gp130-STAT and gp130 knockout mice. In primary hepatocytes, higher hepcidin mRNA expression after IL-6 stimulation was only observed when gp130-STAT3-dependent signalling was intact. In conclusion, this data demonstrated that both in vivo and in vitro STAT3 is the key transcription factor responsible for IL-6 activation of hepcidin gene expression in the liver. The aim of the third project was to study the hyper inflammatory response in course of gram-positive induced sepsis. Sepsis and septic shock due to gram-positive bacteria have become an increasingly important clinical problem. These processes are accompanied by an overshooting inflammation in which the liver plays a central role as a source and target of inflammatory mediators. Hepatocyte-specific gp130-deficent mice and control mice were infected intravenously with Streptococcus pyogenes and the following parameters were monitored: Mortality, bacterial loads in systemic organs, serum inflammatory cytokines, and organ damage. Interestingly, gp130-deficient mice survived significantly longer, displayed lower bacterial loads in systemic organs, and developed slower pathology than infected control animals. Histopathological examination showed reduced amounts of neutrophil infiltration, apoptosis, and tissue damage in hepatocyte-specific gp130-deficient mice. In terms of this project it was possible to demonstrate, that gp130 triggered signalling cascades in hepatocytes were able to impair inflammation and liver damage during gram-positive sepsis and that blockage of gp130 signalling in these cells might constitute a novel target for adjunctive therapy. In summary, these projects contribute to clarify the physiological function of gp130 in hepatocytes during regeneration and inflammation and provide basic principles of potential new therapeutical approaches.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Dierßen, Uta

Contributors dc:contributor

• Trautwein, Christian

• info:eu-repo/classification/ddc/570
• IL-6
• Streptococcus pyogenes
• Biowissenschaften, Biologie

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112456%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A49888