The inflammatory bowel diseases, ulcerative colitis and Crohn's disease are characterised by spontaneously relapsing and remitting inflammation, associated with increased mucosal levels of the inflammatory cytokine, interleukin-1 (IL-1)β. IL-1β processing and release is mediated by ATP stimulation of the purine receptor, P2X7. P2X7 is a membrane ion channel highly expressed in immune cells. Signal transduction occurs via rapid cation exchange, plasma membrane depolarisation and increased intracellular calcium. Additionally, prolonged or repeated P2X7 stimulation leads to formation of a non-selective membrane pore permeable to small molecules, and ultimately to cell death. The aim of this project was to investigate the properties of the P2X7 receptor in mononuclear cells, to show that it is associated with IL-1β release in the colon, and that this release can be modified by P2X7 antagonists. Studies of ethidium bromide uptake, a functional assay, showed that P2X7 receptors are present on LPMCs and displayed properties similar to those of PBMCs and THP-1 cells. P2X7 receptor-stimulation released mature IL-1β from LPMCs in a dose-dependent manner that, in IBD patients, matched the severity of their inflammation, and could be markedly reduced by P2X7 antagonists. P2X7 stimulation also results in increased exposure of phosphatidylserine on the outer cell membrane (PS flip), often considered to be a marker of apoptotic cell death. P2X7-stimulated PS flip however is reversible and is not associated with cell death following brief stimulation times. Cell death caused by longer stimulation did not have features of apoptosis, was more evident in monocytes than lymphocytes, with LPMCs being less susceptible than PBMCs and THP-1 cells. These studies have shown that the P2X7 receptor is intimately involved in the release of IL-1β from human colonic mononuclear cells, that the release is greater in cells from IBD tissue and can be markedly inhibited by P2X7 antagonists.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:581982 |
| Date | January 2008 |
| Creators | Stevenson, Diane J. |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/28897/ |
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