HGF,c-Met and IL-6,gp130 mediated signalling pathways in a model of acute and chronic cholestatic liver injury in mice

Hepatocyte growth factor (HGF), its receptor c-Met and Interleukin-6 (IL-6) together with its signalling transducer gp130 are important mediators of liver regeneration and mediate hepatoprotective effects. C-Met and HGF are essential for liver development during embryogenesis and it was shown that HGF/c-Met mediated signalling is essential for the regeneration of the liver after an injury. IL-6/gp130 mediated signalling is important for the regulation of the acute phase response after an acute liver injury, the modulation of liver regeneration and immune cell homeostasis. The aim of this thesis is to define the effects of HGF/c-Met and IL-6/gp130 dependent signalling in the model of bile duct ligation (BDL) that induces a chronic cholestatic liver injury, which leads to liver fibrosis. In this thesis, wildtype-mice (c-Met/gp130loxP/loxP), conditional c-Met knockout mice (c-Met Delta hepa), conditional gp130-deficient mice (gp130 Delta hepa) and conditional c-Met/gp130-double-deficient mice (c-Met/gp130 Delta hepa) were subjected to BDL for up to 4 weeks. The conditional knockout-mice where generated by using the cre-loxP-system under the control of a hepatocyte-specific albumin-promoter. The first efforts to generate hepatocyte specific c-Met knockouts with a pre-natal activated albumin promoter resulted in embryonic lethality. The change to a post-natal, hepatocyte-specific albumin promoter allowed the generation of viable offspring carrying a hepatocyte specific c-Met deficiency. It was shown that depletion of c-Met results in a higher grade of liver injury, which is ascribed to a greater sensitivity to FAS-induced apoptosis by lack of c-Met mediated anti-apoptotic gene-expression. In concordance with the liver injury, c-Met-deficient mice displayed a stronger liver inflammation compared to c-Met/gp130loxP/loxp-mice. This together with the lack in anti-apoptotic gene expression finally results in a higher degree of liver fibrosis. A further part of this thesis investigates the contribution of HGF/c-Met and IL-6/gp130 to the regulation of the acute phase response. After BDL gp130 and c-Met/gp130 Delta hepa displayed a high mortality rate during the first 7d after BDL, in contrast to this, c-Met Delta hepa and wildtype-mice survived without a case of death. The reason for enhanced mortality was linked to a bacterial induced sepsis, and comparative signalling pathway analysis and gene expression studies revealed a lack of acute phase response and antibacterial signalling in gp130 Delta hepa and c-Met/gp130 Delta hepa mice strains. In contrast to this, c-Met Delta hepa-mice had a reduced, but still present acute phase response. Both, c-Met and gp130, do contribute to liver protection and play an important role for the regulation and modulation of the acute phase response as well. They participate in specific signalling pathways like anti-apoptotic signalling in the case of c-Met and anti-bacterial signalling in the case of gp130 in pathway and ligand specific manner. These findings lead to a further and more detailed understanding of the signalling specific effects mediated by c-Met and gp130 during chronic cholestatic liver disease. Those findings can support the eforts to find a cure against fibrosis and helps to improve the treatment of bacterial induced sepsis

HGF,c-Met and IL-6,gp130 mediated signalling pathways in a model of acute and chronic cholestatic liver injury in mice

Hepatocyte growth factor (HGF), its receptor c-Met and Interleukin-6 (IL-6) together with its signalling transducer gp130 are important mediators of liver regeneration and mediate hepatoprotective effects. C-Met and HGF are essential for liver development during embryogenesis and it was shown that HGF/c-Met mediated signalling is essential for the regeneration of the liver after an injury. IL-6/gp130 mediated signalling is important for the regulation of the acute phase response after an acute liver injury, the modulation of liver regeneration and immune cell homeostasis. The aim of this thesis is to define the effects of HGF/c-Met and IL-6/gp130 dependent signalling in the model of bile duct ligation (BDL) that induces a chronic cholestatic liver injury, which leads to liver fibrosis. In this thesis, wildtype-mice (c-Met/gp130loxP/loxP), conditional c-Met knockout mice (c-Met Delta hepa), conditional gp130-deficient mice (gp130 Delta hepa) and conditional c-Met/gp130-double-deficient mice (c-Met/gp130 Delta hepa) were subjected to BDL for up to 4 weeks. The conditional knockout-mice where generated by using the cre-loxP-system under the control of a hepatocyte-specific albumin-promoter. The first efforts to generate hepatocyte specific c-Met knockouts with a pre-natal activated albumin promoter resulted in embryonic lethality. The change to a post-natal, hepatocyte-specific albumin promoter allowed the generation of viable offspring carrying a hepatocyte specific c-Met deficiency. It was shown that depletion of c-Met results in a higher grade of liver injury, which is ascribed to a greater sensitivity to FAS-induced apoptosis by lack of c-Met mediated anti-apoptotic gene-expression. In concordance with the liver injury, c-Met-deficient mice displayed a stronger liver inflammation compared to c-Met/gp130loxP/loxp-mice. This together with the lack in anti-apoptotic gene expression finally results in a higher degree of liver fibrosis. A further part of this thesis investigates the contribution of HGF/c-Met and IL-6/gp130 to the regulation of the acute phase response. After BDL gp130 and c-Met/gp130 Delta hepa displayed a high mortality rate during the first 7d after BDL, in contrast to this, c-Met Delta hepa and wildtype-mice survived without a case of death. The reason for enhanced mortality was linked to a bacterial induced sepsis, and comparative signalling pathway analysis and gene expression studies revealed a lack of acute phase response and antibacterial signalling in gp130 Delta hepa and c-Met/gp130 Delta hepa mice strains. In contrast to this, c-Met Delta hepa-mice had a reduced, but still present acute phase response. Both, c-Met and gp130, do contribute to liver protection and play an important role for the regulation and modulation of the acute phase response as well. They participate in specific signalling pathways like anti-apoptotic signalling in the case of c-Met and anti-bacterial signalling in the case of gp130 in pathway and ligand specific manner. These findings lead to a further and more detailed understanding of the signalling specific effects mediated by c-Met and gp130 during chronic cholestatic liver disease. Those findings can support the eforts to find a cure against fibrosis and helps to improve the treatment of bacterial induced sepsis