Open Access

Julia Doller

• In dieser Doktorarbeit konnte in zwei verschiedenen experimentellen Modellen der chronischen Pankreatitis in C57BL/6 Mäusen gezeigt werden, dass die chronische Pankreatitis mit einem Gewichtsverlust und einer Verminderung der muskuloskelettalen Kraft assoziiert sind. Untersuchungen im Kleintier-MRT belegten eine signifikante Verminderung des Durchmessers des Quadrizepsmuskels in beiden Modellen. Auf Proteinebene fanden sich im Skelettmuskel von Mäusen mit chronischer Pankreatitis Expressionssteigerungen von growth differentiation factor 8 (GDF8) und Muscle RING-finger protein-1 (MuRF1). Auf mRNA Ebene konnten wir zeigen, dass Activin A und das transforming growth factor β (TGFβ) in beiden Modellen erhöht waren, wohingegen Follistatin und teilweise auch Inhibin A vermindert waren. Die Anzahl apoptotischer Zellen stieg im Quadrizepsmuskel in beiden Modellen signifikant an, was darauf schließen lässt, dass die Apoptose beim Muskelabbau eine Rolle spielt. Des Weiteren fanden sich in Mäusen mit chronischer Pankreatitis und Sarkopenie Veränderungen des Serummetaboloms und des Stuhlmikrobioms, die jedoch in Abhängigkeit des verwendeten Modells stark variierten. Modellübergreifend war eine Vermehrung von Akkermansia spp. in der chronischen Pankreatitis nachweisbar.
• Chronic pancreatitis is a common gastrointestinal disease that leads to loss of muscle mass and strength and can result in sarcopenia. It is currently not known which molecular mechanisms trigger or influence sarcopenia in chronic pancreatitis. In this PhD thesis, it could be shown by two different experimental models of chronic pancreatitis in C57BL/6 mice that chronic pancreatitis is associated with weight loss and a reduction in skeletal muscle strength. These models are based on the one hand on repetitive bouts of acute pancreatitis induced by the cholecystokinin analogue caerulein and on the other hand on a ligation of the pancreatic duct, which detaches parts of the pancreas. Both models lead to morphological signs of chronic pancreatitis, but a reduction in exocrine and endocrine pancreatic function was only detectable in the caerulein-induced pancreatitis model. We were also able to demonstrate changes in both pro- and anti-inflammatory cytokines in serum, which differed depending on the model. MRI studies showed a significant reduction in the diameter of the quadriceps muscle in both models. At the protein level, an increased expression of growth differentiation factor 8 (GDF8) and muscle RING-finger protein-1 (MuRF1) was found in the skeletal muscle of mice with chronic pancreatitis. We further showed that mRNA expression of activin A and the cytokine transforming growth factor β (TGFβ) were increased in both models, whereas follistatin and inhibin A were decreased. The number of apoptotic cells increased significantly in the quadriceps muscle of mice with chronic pancreatitis, suggesting that apoptosis plays a significant role in muscle breakdown. Furthermore, changes in the serum metabolome and the stool microbiome were found in mice with chronic pancreatitis and sarcopenia, which varied greatly depending on the model used. Multiplication of Akkermansia spp. was detectable in chronic pancreatitis. To further clarify whether the exocrine insufficiency is decisively involved in the development of sarcopenia, the experiments were repeated under a high-fat diet, which the mice received before the induction of chronic pancreatitis. It could be shown that there was also a reduction of body weight and muscle strength over the time course: while the weight loss was less pronounced, the loss of muscle strength remained essentially unchanged. By analogy to the experiments with normal food, there was also a significant reduction in quadriceps diameter and an increase in apoptotic cells in the quadriceps under a fat-enriched diet. We were also able to demonstrate an increase of GDF8 and MuRF1 protein expression as well as changes in activin A, inhibin A, TGFβ, and follistatin mRNA expression. Overall, the results are comparable to those of the standard diet, suggesting that the decrease of muscle size and function on a high-energy diet seem to be independent of exocrine pancreatic function. In summary, it can be concluded that the muscle breakdown in chronic pancreatitis occurs independently of the exocrine pancreatic function and is apparently mediated by members of the TGF-β family, GDF8, and MuRF1.