Medizinische Universität Graz - Research portal
Selected Publication:
Zaufel, A.
The role of bile acids in lipid and energy metabolism in health and disease
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medizinische Universität Graz; 2022. pp.
- Authors Med Uni Graz:
- Advisor:
- Fickert Peter
- Madl Tobias
- Moustafa Tarek
- Altmetrics:
- Abstract:
- Introduction: The lysosome acts as a central hub in cellular homeostasis by controlling nutrient availability and energy metabolism. It provides a signaling platform for the mTOR pathway, which detects diverse environmental cues to regulate the balance between catabolic and anabolic processes within eukaryotes. Nonetheless, we have little knowledge regarding the role of lysosome-associated signaling pathways in enterohepatic physiology, cholesterol and bile acid metabolism. Methods: We studied three different conditional knockout mouse models with altered mTORC1 activity and lysosomal homeostasis: Lamtor2fl/fl (Ltor2-LKO), Raptorfl/fl (Rptor-LKO) and Tsc1fl/fl (Tsc1-LKO) mice. Gene knockout was achieved by crossbreeding the mice with Alb-Cre mice (chronic loss-of-function; during development; hepatoblast-specific) or by injecting AAV8-TBG-Cre (acute loss-of-function; adult animals; hepatocyte-specific). Mice were challenged with diets enriched in bile acids. tdTomato-reporter mice were used to visualize Cre-mediated recombination. Results: Loss of Lamtor2 in hepatoblasts (Alb-Cre) disrupts normal hepatic architecture. Livers of Ltor2-LKO mice showed clearly visible patches of hepatocytes with small/condensed nuclei and a clear/glycogenated cytoplasm. In contrast to areas of normal appearing patches/clusters of hepatocytes, these smaller cells were negative for pS6 (readout for mTORC1 activity). Tracing of cells with Cre-mediated recombination (by crossbreeding mice with tdTomato-reporter mice) confirmed gene knockout in all hepatocytes. Systemic handling of glucose and bile acids was altered in Ltor2-LKO, showing features of both Rptor-LKO (reduced mTORC1 activity) and Tsc1-LKO (constitutively active mTORC1) mice. Acute loss of Lamtor2 in adult hepatocytes resulted in a severe phenotype with hepatic accumulation of glycogen and a humanized bile acid pool (similar but less pronounced changes after acute loss of Raptor). qPCR, WB and IF revealed a significant downregulation of classical hepatocellular marker genes/proteins and an upregulation of progenitor/cholangiocyte-like markers in the livers of those mice. Conclusions: Our data demonstrate that the Ragulator/mTORC1 complex is indispensable to maintain hepatocellular glucose as well as cholesterol/bile acid metabolism. Furthermore, we show that the Ragulator/mTORC1 pathway plays a critical role in preserving cell differentiation in adult hepatocytes in vivo.