Scoping out intestinal epithelium differentiation, proliferation, and homeostasis through the lenses of interleukin-10 and aryl hydrocarbon receptor signaling pathways

Abstract

Intestinal epithelial cells (IEC) are crucial for maintaining proper digestion and overall homeostasis of the gut mucosa. IEC proliferation and differentiation are tightly regulated by well described pathways, however, relatively little is known about the influence of interleukin (IL)-10 and aryl hydrocarbon receptor (AHR) signaling pathways on these processes or whether AHR can regulate IL-10R expression in IECs. IL-10 signaling suppresses inflammation. AHR is a ligand activated transcription factor largely known for downstream activation of xenobiotic-metabolizing enzymes but also exerts a diverse range of responses in the host that can be modulated by gut microbe metabolites. Both IL-10 and AHR signaling are shown to promote IEC barrier function, and thus, they may also regulate other critical homeostatic functions like IEC lineage fate and regenerative capacity. These gaps in knowledge were addressed in Chapters 2 and 3. Techniques such as reverse-transcription quantitative polymerase chain reaction (RT-qPCR), western blotting, and histology staining techniques were used to assess changes in expression of target genes and proteins between control and either IL-10R- or AHR-deficient models. Loss of IL-10R or AHR demonstrated substantial impacts exhibiting nearly opposite patterns on lineage fate outcomes and on the proliferative compartment. In Chapter 4, we showed that activation of AHR by microbe-derived tryptophan metabolites increased IL-10R1 expression in IECs, and these metabolites ameliorated disease in a murine model of colitis. Findings from Chapters 2-4 add to a growing body of evidence for the importance of IL-10R and AHR signaling pathways in inflammatory bowel disease (IBD) and gastrointestinal (GI) cancers. Organoid models provide an additional study system to test these gaps in the field and hold great promise for advancing disease research. However, limitations exist for accessing the luminal surface to recapitulate the GI environment. In Chapter 5, we developed the GOFlowChip to solve this problem. This platform applies long-term, steady-state flow through to the organoid and can be modified to serve different research goals. These studies culminate in a deeper understanding of how IEC homeostasis is maintained and how innovative technologies can be developed for advancing this field of research.