Identification of the fibrogenic cells in the liver

Abstract

The liver is an important multitasking organ with diverse functions to maintain body homeostasis. Adjustment of glucose level, detoxification, secretion of blood proteins, and synthesis of bile acids are the among these crucial functions. The fibrosis is one of the most common liver injury types. Although liver has a high capacity for regeneration via the proliferation of cells, this regeneration ability is directly dependent on the severity of fibrosis. One of the proliferative cells during fibrosis is cholangiocytes located around the portal triad. The cholangiocytes contain a primary cilium, a non-motile, ciliated organelle. The response of primary cilium to fibrosis is not well understood. The aim of this thesis was to characterize responses of cholangiocytes to liver fibrosis. For this purpose, TAA induced fibrosis model was generated for different weeks of samples, 16 weeks, 20 weeks, and 24 weeks in mice. IHC stainings and data collection from confocal microscopy were performed. According to our study, we observed that around the portal vein, big cell masses are formed and these cells are migrating between portal veins by following a path upon fibrosis. Moreover, several cells are escaping from this path and expanding through the central vein. The main contributors of these giant cell masses are cholangiocytes which keep their primary cilia under fibrotic conditions. Furthermore, we identified a new subpopulation of Arl13b+ cholangiocytes which are undergoing partial EMT by expressing mesenchymal markers such as Vimentin, CD34, and Pdgfra in these cell masses. During this process, they gain novel mesenchymal features at the same time they maintain their epithelial character. As a following goal, we wanted to identify components of these big cell masses, so niche components of partial EMT undergoing Arl13b+ cholangiocytes. We identified that Vimentin, CD34, and Pdgfra mesenchymal cells and Thy1+ portal fibroblasts (minority) are components of these massive cells in addition to homeostatic and partial EMT undergoing Arl13b+ cholangiocytes. As a final objective, we identified novel, possible markers for partial EMT undergoing Arl13b+ cholangiocytes and their niche components. To conclude, the novelties of this thesis were the demonstration of the primary cilium response against fibrosis, the identification of a new Arl13b+ cholangiocyte subpopulation undergoing partial EMT, and the characterization of components of the migratory big cell masses under fibrotic conditions.