Toll-like receptor 4 signalling is neither sufficient nor required for oxidised phospholipid mediated induction of interleukin-8 expression.
OBJECTIVE
Toll-like receptor (TLR)-4 signalling has been shown to accelerate atherosclerosis. As oxidised phospholipids are present in atherosclerotic plaque and have been shown to modulate TLR4 signalling, we investigated the role of oxidised 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (OxPAPC) in the regulation of TLR 1, 2, 4 and 6 signalling.


RESULTS
Unlike established TLR agonists, OxPAPC did not induce NF-kappaB-dependent gene expression in monocytic THP-1 cells, human aortic endothelial cells or TLR-deficient HEK-293 cells transfected with TLRs 1, 2, 4 or 6. OxPAPC induction of IL-8 was not blocked by the TLR4 specific antagonist Rhodobacter sphaeroides LPS in human aortic endothelial cells, though OxPAPC potently inhibited TLR4 mediated IL-8 induction in these cells. OxPAPC upregulated IL-8 production in TLR4 deficient HEK-293 cells and this was not increased following TLR4 overexpression. Lipids extracted from carotid atherectomy samples did not stimulate TLR 1, 2, 4 or 6 signalling in a HEK-293 transfection assay.


CONCLUSIONS
TLR4 signalling does not contribute to OxPAPC induced IL-8 expression in human epithelial HEK-293, monocytic THP-1 or aortic endothelial cells. As lipids extracted from diseased human artery also induced no TLR signalling, it is likely that the TLR-activating materials contributing to atherosclerosis are not of endogenous lipid origin.
Erridge
Clett
C
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 204 George Street, Glasgow G1 1XW, UK. clett.erridge@strath.ac.uk
Webb
David J
DJ
Spickett
Corinne M
CM
D050197:Atherosclerosis / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics; D008055:Lipids / Q000302:isolation & purification / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D010713:Phosphatidylcholines / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D017931:DNA Primers; D016209:Interleukin-8; D008055:Lipids; D016328:NF-kappa B; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; C472349:oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine