Lipopolysaccharide and platelet-activating factor stimulate expression of platelet-activating factor acetylhydrolase via distinct signaling pathways
This study was designed to investigate and characterize the ability of platelet-activating factor (PAF) to induce the expression of platelet-activating factor acetylhydrolase (PAF-AH).
Ribonuclease protection assays and quantitative real-time PCR were used to investigate the ability of lipopolysaccharide (LPS) and PAF to regulate PAF-AH mRNA expression in human monocyte–macrophage 6 (MM6) cells. Pharmacological inhibitors of mitogen activated protein kinases (MAPK) and PAF receptor antagonists were used to investigate the mechanism of regulation of PAF-AH.
PAF-AH mRNA levels were increased upon exposure to LPS or PAF in a dose-dependent manner. LPS elicited a more potent and rapid increase in PAF-AH expression than the PAF-stimulated response. However, when administered concomitantly, PAF augmented the LPS-stimulated response. LPS-stimulated PAF-AH expression was susceptible to partial inhibition by a p38 MAPK inhibitor and PAF receptor antagonists. PAF-induced up-regulation of PAF-AH levels was solely mediated via the PAF receptor and was p38 MAPK-independent.
The proinflammatory mediators, LPS and PAF, increased levels of PAF-AH mRNA via distinct signaling pathways.
KeywordsPAF acetylhydrolase Regulation Lipopolysaccharide Mitogen activated protein kinase PAF receptor
We would like to express our sincere gratitude to Merle S. Olson, University of Texas Health Science Center, who donated much of the equipment to our laboratory to conduct this research. We would like to thank Ziming Cheng for technical help with the RPA assays and Drs. Gillian Galbraith and Barbara St Pierre Schneider for critically reading the manuscript. This work was supported by grants from the National Institutes of Health (HL66130) and the American Heart Association (0465061) to KMH.
Conflict of interest
The authors declare that they have no competing interests.