Examining the activation of xenobiotic receptors using microbial metabolites and chemical ligands

Date
2024-09-18
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Abstract
The aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) are key xenobiotic receptors involved in regulating chemical metabolism and detoxification. Traditionally, these receptors were known for mediating toxic responses by sensing and responding to chemicals. Recent research shows their role in maintaining gut homeostasis and regulating inflammation. However, the mechanisms by which they induce these responses are not clear. This thesis examines whether the activation of AhR and PXR in epithelial cells by microbial metabolites versus chemical ligands drives unique transcriptional responses and could explain differences in beneficial versus deleterious biological outcomes in the host. PXR and AhR were activated with indole-3-propionic acid (IPA) and indole-3-pyruvic acid (IPyA) as microbial metabolites, and pregnenolone 16α-carbonitrile (PCN) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as chemical ligands, respectively. We compared responses to these ligands, revealing significant gene expression differences. Further analysis showed both IPyA and TCDD activated genes involved in hypoxia-inducible factor (HIF) signaling and metabolism. IPyA upregulated genes for ATP synthesis and purine biosynthesis, while TCDD promoted genes related to cell cycle, cancer, and apoptosis. Given that AhR translocates to the nucleus upon activation, we hypothesized that the differences in transcriptomic responses and gene induction might be attributed to differences in nuclear translocation of AhR, with TCDD potentially inducing greater nuclear translocation compared to IPyA. To test this hypothesis, we established a cellular fractionation protocol for organoids. However, our results revealed no significant difference in AhR nuclear translocation between the two treatments, suggesting that other factors may affect gene expression in the AhR pathway. These findings highlight AhR and PXR's complex roles in gut health and inflammation, suggesting receptor activation can have both adverse and beneficial effects. This research enhances our understanding of AhR and PXR mechanisms and their potential for therapeutic strategies targeting gut disorders and inflammation.
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Xenobiotic receptors, organoids, 3D culture, 2D culture, Aryl Hydrocarbon Receptor (AhR), Pregnane X Receptor (PXR), Xenobiotic Metabolism, Gut microbiota, Transcriptomic Responses, 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), Indole-3-pyruvic Acid (IPyA), Pregnenolone-16α-carbonitrile (PCN), Indole-3-propionic Acid (IPA)
Citation
Shenoda, E. I. G. (2024). Examining the activation of xenobiotic receptors using microbial metabolites and chemical ligands (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.