Molecular mechanisms driving the initiation of an inflammatory response in huma lamina propria cells : impact of m TOR pathway activation

Despite the close proximity of intestinal resident lamina propria (LP) cells to bacterial and dietary antigens, these cells normally maintain an immune homeostatic state, in which they possess a hyporesponsive phenotype. Currently, little is known about the molecular mechanisms that initially lead to the onset of an acute inflammatory response in these cells that can under certain conditions lead to the manifestation of chronic inflammatory bowel disease (IBD). This thesis aimed towards a better understanding of these initial mechanisms by utilizing a human ex vivo intestinal organ culture model, the “Loss of Epithelial Layer (LEL)” model. In this model, healthy human colonic mucosa is subjected to EDTA treatment, thereby detaching the epithelial layer from the underlying LP. The thus created barrier defect is associated with the induction of a physiologically relevant global inflammatory response in resident LP cells, as could be shown by global gene expression profiling of microdissected LP and subsequent comparison to published gene expression profiles of biopsies of ulcerative colitis patients. Bioinformatic analysis predicted that the initated inflammatory response in LP cells (as observed in the LEL model) is associated with the upregulation of protein synthesis. This in silico finding was experimentally validated by in situ studies using OPP Click-it® technology. The observed upregulation of protein translation was partially controlled by the activation of the mTOR pathway, as shown by functional studies using the mTOR inhibitor Torin1. Inhibition studies also revealed that mTOR is involved in - and potentially coordinates - multiple aspects of the initial inflammatory response of LP cells such as the recruitment of leukocytes, the induction of inflammasome activation and the restriction of MIF-induced pro-inflammatory processes. These results provide the basis for the future analysis of potential dysregulations of the mTOR pathway in IBD.