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PAF effects on MCP-1 and IL-6 secretion in U-937 monocytes in comparison with oxLDL and IL-1β effects
Sophia N Verouti1, Elizabeth Fragopoulou, Haralabos C Karantonis
1Faculty of Chemistry, National and Kapodistrian University of Athens, Panepistimioupolis, 15771 Athens, Greece.
Objective:
To study the effects of PAF, in comparison with oxLDL and IL-1β on MCP-1 and IL-6 secretion from U-937 monocytes and to investigate the mechanism of its action.
Methods:
U-937 cell line was cultured in the presence or absence of PAF or oxLDL or IL-1β. Secretion of IL-6 and MCP-1 was measured by ELISA method, mRNA levels of MCP-1 and PAFR was measured using real-time PCR. In order to investigate the mechanism of mediator's action signal transduction appropriate inhibitors was used and oxidant status of cells by measurement the total cellular thiols content and glutathione was determined.
Results And Conclusion:
None of the tested mediators induced the secretion of IL-6. On the other hand PAF and oxLDL caused a short-term while IL-1β caused a long-term secretion and expression of MCP-1. Reduced total thiol levels and GSH/GSSG ratio indicate that the above mediators induce oxidative stress. The signal transduction of all mediators is mediated through G-proteins, protein kinases (PKC, serine-threonine kinase and tyrosine kinase) and NF-κB activation. In addition, PAF, oxLDL, IL-1β activates monocytes leading to increased PAF receptor mRNA levels. These results indicate that PAF and oxLDL, in a different pattern from that of IL-1β, regulate MCP-1 expression via pathways that involve changes in cell redox status.
Insights
Platelet-activating factor (PAF) and oxidized low-density lipoprotein (oxLDL) induce monocyte chemoattractant protein-1 (MCP-1) secretion and expression through oxidative stress pathways. These mediators, along with IL-1β, activate monocytes via G-proteins and NF-κB signaling.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Monocyte chemoattractant protein-1 (MCP-1) is crucial in inflammatory responses.
- Platelet-activating factor (PAF), oxidized low-density lipoprotein (oxLDL), and IL-1β are implicated in monocyte activation and inflammation.
- Understanding the differential effects and mechanisms of these mediators on monocyte function is essential.
Purpose of the Study:
- To compare the effects of PAF, oxLDL, and IL-1β on MCP-1 and IL-6 secretion from U-937 monocytes.
- To elucidate the underlying mechanisms of action, including signal transduction pathways and oxidative stress induction.
Main Methods:
- U-937 monocytes were stimulated with PAF, oxLDL, or IL-1β.
- MCP-1 and IL-6 secretion were quantified using ELISA.
- mRNA levels of MCP-1 and PAF receptor (PAFR) were analyzed by real-time PCR.
- Signal transduction pathways were investigated using specific inhibitors, and cellular oxidant status was assessed by measuring total thiols and glutathione levels.
Main Results:
- None of the mediators induced IL-6 secretion.
- PAF and oxLDL induced short-term MCP-1 secretion and expression, while IL-1β induced long-term effects.
- Mediator-induced reduction in total thiol levels and GSH/GSSG ratio indicated oxidative stress.
- Signal transduction involved G-proteins, protein kinases (PKC, serine-threonine, tyrosine), and NF-κB activation.
- All mediators increased PAFR mRNA levels in activated monocytes.
Conclusions:
- PAF, oxLDL, and IL-1β differentially regulate MCP-1 expression in monocytes.
- These effects are mediated through pathways involving oxidative stress, G-protein signaling, and NF-κB activation.
- PAF and oxLDL, distinct from IL-1β, modulate MCP-1 expression via redox-sensitive pathways.
