Funktionen der IKK-Komplex-Untereinheiten in der Leberentzündung und Hepatokarzinogenese

The rapid increase of severe liver diseases is a major challenge for medical research in both the field of basic research as well as the targeted development of new drugs. Previous studies showed that NF-κB-dependent signalling pathways are relevant in liver disease. The IKK complex consisting of the regulatory subunit NEMO and the catalytic subunits IKK1 and IKK2 plays an important role in this pathway. However, in recent years functions beyond NF-κB-dependent signalling were associated with these subunits. The aim of this thesis was to investigate in detail the functions of the individual subunits and particularly IKK1 in liver disease. For this purpose, LPC-specific "knockout" mouse models were generated, the phenotypic effects analysed and compared.In the first part of this thesis it was analysed in which way the additional deletion of IKK1 inhibits hepatocarcinogenesis in the NEMOLPC-KO mouse model. It was shown that IKK1 favoured the expression of certain mainly inflammatory cytokines and at the same time the recruitment of immune cell populations into the liver tissue of NEMOLPC-KO mice. This inflammatory environment is fostered by oxidative stress and apoptotic cell death of liver cells, with the latter also stimulating proliferation of neighbouring hepatocytes. The additional deletion of IKK1 inhibits the generation of ROS and reduces the apoptosis as well as compensatory proliferation in the livers of the NEMOLPC-KO mice. In the second part of this thesis the phenotype of the IKK1/2LPC-KO mice was analysed, which is characterized by a lethal cholestasis and the presence of necrotic areas. It was shown that the additional deletion of RIPK3 causes a significant reduction of necrotic areas in the liver tissue of these mice. However this had no influence on the development of cholestasis. In contrast, the additional deletion of RIPK1 did not only reduce the formation of necrotic areas in the IKK1/2LPC-KO mice, but led also to a significant improvement of the cholestasis phenotype and the life expectancy of these animals. In addition, it was shown that RIPK1 negatively affects the proliferation of LPCs in the liver tissue of IKK1/2LPC-KO animals independently of its role in cell death. This function might be regulated by the phosphorylation status of RIPK1 in the IKK1/2LPC-KO model. Moreover, the increased proliferation led to tumour formation in the liver tissue of some IKK1/2/RIPK1LPC-KO mice. Interestingly, first examinations of human HCC samples revealed that the expression of IKK1, IKK2 and RIPK1 was remarkably reduced in a certain number of samples. This constitutes an interesting starting point for further investigations of the function of these proteins in hepatocarcinogenesis. In both mouse models (IKK1/2LPC-KO model and NEMOLPC-KO model) Caspase-8-dependent apoptotic cell death represents a major cause for the phenotypes. The different phenotypic characteristics of both models appear to be attributed to an attenuated proliferative response in the IKK1/2LPC-KO mice, which is regulated by RIPK1. In summary, the results of this thesis allow a novel and deeper insight into the functions of the IKK complex subunits and particularly the catalytic subunits in processes such as inflammation, cell death and especially proliferation, which are important for the development of liver cancer as well as cholestatic liver diseases