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Endotoxin-induced migration of monocytes and PECAM-1 phosphorylation are abrogated by PAF receptor antagonists
1Department of Biochemistry, Childrens Hospital Los Angeles, University of Southern California School of Medicine, Los Angeles, California 90033, USA.
Abstract:
The trafficking of monocytes across the endothelial lining of the blood vessel increases in response to bacterial infection at sites of inflammation. However, the molecular events involved in the diapedesis of monocytes in response to endotoxin are not completely understood. Our studies revealed that signaling by lipopolysaccharide (LPS) in human umbilical vein endothelial cells (HUVEC) resulted in a threefold increase in the transendothelial migration of monocyte-like HL-60 cells and a sevenfold increase in the phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1). The transmigration induced by LPS was inhibited by an antibody to PECAM-1. Both the phosphorylation of PECAM-1 and transendothelial migration of monocytes were inhibited by a platelet-activating factor (PAF) receptor antagonist, indicating the autocrine effect of PAF in these events. Treatment of HUVEC with LPS caused a fourfold increase in PAF receptor mRNA expression that was completely blocked by the PAF receptor antagonist. We conclude that PAF, generated by HUVEC in response to LPS or gram-negative bacterial infection, acts in an autocrine manner, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.
Insights
Lipopolysaccharide (LPS) triggers monocyte migration via platelet-activating factor (PAF) and PECAM-1 phosphorylation in endothelial cells. This study elucidates key molecular events in monocyte diapedesis during bacterial infections.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Monocyte trafficking across blood vessels is crucial for inflammatory responses during bacterial infections.
- The precise molecular mechanisms of monocyte diapedesis induced by endotoxin remain incompletely understood.
Purpose of the Study:
- To investigate the molecular events underlying monocyte transendothelial migration stimulated by lipopolysaccharide (LPS).
- To elucidate the role of platelet-activating factor (PAF) and PECAM-1 in LPS-induced monocyte diapedesis.
Main Methods:
- Utilized human umbilical vein endothelial cells (HUVEC) and monocyte-like HL-60 cells.
- Assessed transendothelial migration and PECAM-1 phosphorylation.
- Employed PAF receptor antagonist and anti-PECAM-1 antibody for inhibition studies.
- Quantified PAF receptor mRNA expression using RT-PCR.
Main Results:
- LPS significantly increased HL-60 cell migration and PECAM-1 phosphorylation in HUVEC.
- Anti-PECAM-1 antibody inhibited LPS-induced transmigration.
- PAF receptor antagonist blocked both PECAM-1 phosphorylation and monocyte migration, suggesting an autocrine PAF effect.
- LPS upregulated PAF receptor mRNA expression in HUVEC.
Conclusions:
- Platelet-activating factor (PAF) is generated by HUVEC in response to LPS, acting in an autocrine manner.
- PAF signaling leads to PECAM-1 phosphorylation, facilitating monocyte transendothelial migration.
- These findings reveal a critical pathway for monocyte recruitment during endotoxin exposure and bacterial infections.
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