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Background and purpose: The pro-inflammatory cytokine, interleukin-1β (IL-1β), has been implicated in the pathogenesis of atherosclerosis, potentially via its release from vascular endothelium. Endothelial cells (EC) synthesize IL-1β in response to inflammatory stimuli, but the demonstration and mechanism of release of IL-1 from ECs remains unclear. In activated monocytes, efficient release of bioactive IL-1β occurred via activation of ATP-gated P2X7 receptors (P2X7Rs). Activation of P2X7R in ECs from human umbilical vein (HUVECs) released IL-1 receptor antagonist (IL-1Ra). The purpose of this study was to provide a quantitative investigation of P2XR expression and function, in parallel with IL-1β and IL-1Ra synthesis, processing and release, in HUVECs under pro-inflammatory conditions. Experimental approach: Quantitative RT-PCR, immunoblotting, ELISA, flow cytometry, and whole-cell patch clamp recordings were used to determine protein expression and receptor function. IL-8-luciferase-reporter was used as an IL-1 sensitive bioassay. Key results: HUVECs expressed P2X4R and P2X7R subtypes and both were significantly up-regulated under inflammatory conditions. P2X7R currents were increased 3-fold by inflammatory stimuli, whereas no P2X4R-mediated currents were detected. Caspase-1, but not IL-1β, was present intracellularly under basal conditions; inflammatory stimuli activated the synthesis of intracellular pro-IL-1β and increased caspase-1 levels. Activation of P2X7Rs resulted in low-level release of bioactive IL-1β and simultaneous release of IL-1Ra. The net biological effect of release was anti-inflammatory. Conclusions and implications: Endothelial P2X7Rs induced secretion of both pro- and anti-inflammatory IL-1 receptor ligands, the balance of which may provide a means for altering the inflammatory state of the arterial vessel wall. British Journal of Pharmacology (2007) 151, 96–108. doi:10.1038/sj.bjp.0707213 |
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