Obesity represents a major public health problem these days. Given the current increase in life expectancy, the prevalence of obesity also raises among aged individuals. This is often accompanied with additional years of susceptibility to chronic diseases associated with obesity in elderly people. Some of these diseases develop in the presence of the low grade inflammation associated with obesity where white adipose tissue macrophages provide chronic levels of inflammatory cytokines such as IL-6 and TWEAK systemically. While this systemic chronic inflammation results in numerous fatal disorders such as the development of insulin resistance, non alcoholic steatohepatitis (NASH) and type 2 diabetes mellitus, it has been proposed that it initially originates from the obesity-associated leaky gut where it spreads to the liver and ultimately to circulation. In the leaky gut, the mucosal immune system is in contact with the commensal microbiota that not only increases systemic endotoxemia but also inflammation (Wunderlich et al., 2018). These increased obesity-induced inflammatory cytokines impair insulin action in metabolic organs and the intestine to ultimately result in the development of insulin resistance (Ostermann et al., 2019). Ultimately, the leaky gut in obesity directly fuels the liver with microbial products to result in NASH. However, the cell type specific consequences of products derived from the gut on signaling cascades in the liver are not well understood. Here, we propose to decipher the cell type specific signaling in hepatocytes and stellate cells that affect NASH progression. We focus on specific TWEAK-induced NIK dependent crosstalk to Growth hormone induced Jak2/Stat5 signaling that we have previously identified as mediator of HCC.
The Wunderlich lab aims at dissecting the link between obesity-induced inflammation and associated disorders such as the development of insulin resistance, NASH and cancer. To this end, we use self generated sophisticated mouse models allowing for cell type specific manipulation of inflammatory and metabolic signaling pathways in disease models. One main focus is NASH and the crosstalk between gut derived factors with stellate cells and hepatocytes. Collectively, our research should shed light on the cellular and molecular mechanisms of NASH to ultimately develop novel therapeutic strategies for patients.
Stellate cell/hepatocyte crosstalk and specific intracellular signaling in NASH
A leaky gut had been proposed as origin of the obesity-induced low grade inflammation where the gut immune system is activated by commensal microbiota to directly fuel the liver with inflammation to ultimately result in NASH. Here, hepatic stellate cells are activated to express TWEAK that binds to Fn14 receptor to turn on NFkB induced kinase (NIK) signaling in hepatocytes. NIK mediates inhibitory Jak2 Serin 633 phosphorylation to specifically impair GH-induced Stat5 required to prevent hepatic lipid accumulation and proliferation. We have developed a dual recombinase system in mice that depends on the well known Cre/loxP and the new Dre/rox systems. We aim at manipulating hepatocyte specific signaling by Cre loxP in combination with stellate cell specific Dre/rox. To this end, the student will generate a stellate cell specific Dre mouse under the control of the Lrat promoter that can be crossed to various rox dependent effector lines in portofolio of our institute. In line with this evidence, we will then be able to trace, activate, inhibit, genetically manipulate as well as determine gene expression in stellate cells in the presence and absence of hepatocyte specific NIK/Stat5 to evaluate the cell type specific consequences. Such mice will be investigated in two NASH mouse model: the fibrosis choline deficient HFD and the metabolic NASH diet. We will examine the specific translatome of stellate cells and hepatocytes under these conditions to identify crosstalks between these cell types. Upon identification of candidate genes, we will genetically manipulate those in a conditional manner by using a novel Cas9 approach. Mice will be phenotyped metabolically, immunologically and histologically. Collectively, the experiments will decipher the crosstalk between stellate cells and hepatocytes that are both critical cell types in NASH development to ultimately define novel targets suitable for therapeutic intervention.
All experiments will be exclusively performed in transgenic mice and tissue culture. Methods include mouse experiments, metabolic experiments (ITT, GTT, Hyperinsulinemic euglycemic CLAMPS, HOMA IR, adiposity etc.), FACS, Western blot, qPCR, ELISA/Multiplex, Immunohistochemistry.
The student should be aware that this project includes in vivo mouse experimentation. A FELSA B course and mouse handling experience would be helpful but can also be acquired/learned during the thesis. Basic immunology, metabolic and molecular biology skills are of advantage but not essentially necessary.