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De novo phosphatidylcholine synthesis in intestinal lipid metabolism and disease
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- Author / Creator
- Kennelly, John
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Phosphatidylcholine (PC), the most abundant phospholipid in eukaryotic cells, is an important component of cellular membranes and lipoprotein particles. The enzyme CTP: phosphocholine cytidylyltransferase (CT) regulates de novo PC synthesis in response to changes in membrane lipid composition in all nucleated mammalian cells. The aim of this thesis was to determine the role that CTα plays in metabolic function and immune function in the murine intestinal epithelium. Mice with intestinal epithelial cell-specific deletion of CTα (CTαIKO mice) were generated. When fed a chow diet, CTαIKO mice showed normal lipid absorption after an oil gavage despite a ~30% decrease in small intestinal PC concentrations relative to control mice. These data suggest that biliary PC can fully support chylomicron output under these conditions. However, when acutely fed a high-fat diet, CTαIKO mice showed impaired intestinal fatty acid and cholesterol uptake from the intestinal lumen into enterocytes, resulting in lower postprandial plasma triglyceride concentrations. Impaired intestinal fatty acid uptake in CTαIKO mice was linked to disruption of intestinal membrane lipid transporters (Cd36, Slc27a4 and Npc1l1) and higher postprandial plasma Glucagon-like Peptide 1 and Peptide YY. Unexpectedly, there was a shift in expression of bile acid transporters to the proximal small intestine of CTαIKO mice, which was associated with enhanced biliary bile acid, PC and cholesterol output relative to control mice. Gene expression profiling of small intestinal epithelial cells showed induction of transcripts linked to cellular proliferation and inflammation in CTαIKO mice relative to control mice. Colonic inflammation after loss of intestinal epithelial cell CTα was linked to increased intestinal permeability (as assessed by Fluorescein Isothiocyanate-Dextran gavage), invasion of the intestinal epithelium by microbes, and enhanced inflammatory cytokine secretion. Impaired intestinal barrier function in CTαIKO mice was mechanistically linked to induction of endoplasmic reticulum stress and depletion of goblet cells. Antibiotics and 4-phenylbutyric acid both partially ameliorated inflammatory cytokine secretion in CTαIKO mice, suggesting that microbes and endoplasmic reticulum stress are key drivers of the inflammatory phenotype in CTαIKO mice. In further support of a role for de novo PC synthesis in colonic barrier function, feeding C57BL/6J mice a choline-deficient diet increased their susceptibility to Citrobacter rodentium-induced colitis relative to mice fed sufficient dietary choline.In conclusion, de novo PC synthesis in the small intestinal epithelium is required for dietary lipid absorption under certain dietary conditions, and the re-acylation of biliary lyso-PC cannot compensate for loss of CTα under these conditions. Furthermore, CTα activity prevents invasion of the intestinal epithelium by microbes. Accordingly, disruption of CTα in intestinal epithelial cells induces spontaneous colitis in mice. Finally, an adequate supply of dietary choline, the essential nutritional substrate for CTα, is an important factor in protecting the colon from Citrobacter rodentium -induced inflammation.
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- Subjects / Keywords
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- Graduation date
- Spring 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.