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Hypoxia induces PECAM-1 phosphorylation and transendothelial migration of monocytes
1Department of Biochemistry and Molecular Biology, University of Southern California School of Medicine, Los Angeles 90033, USA.
Abstract:
Polymorphonuclear neutrophils (PMN) adhere to the vascular endothelium under hypoxic conditions, causing microvascular injury. The molecular mechanism of hypoxia-induced adhesion of PMN to and diapedesis through the vascular endothelium is poorly understood. We examined the effects of hypoxia on the transendothelial migration of monocytes. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in Transwell chambers under low oxygen tension (3% O2 compared with 21% O2) resulted in an increased rate of migration of both monocyte-like HL-60 cells and human peripheral blood monocytes. Migration was inhibited by addition of an antibody to platelet endothelial cell adhesion molecule-1 (PECAM-1), a protein kinase C (PKC) inhibitor, or a platelet-activating factor (PAF)-receptor antagonist. In HUVEC, hypoxic conditions (1, 3, 5, and 14% O2) increased the phosphorylation of PECAM-1. The extent of phosphorylation of PECAM-1 was inversely related to the concentration of oxygen to which HUVEC were exposed. Hypoxia-induced phosphorylation of PECAM-1 was inhibited by either a PKC inhibitor or a PAF-receptor antagonist, indicating the involvement of hypoxia-induced release of PAF in both PKC activation and the concomitant phosphorylation of PECAM-1. These results were substantiated by the findings that treatment of HUVEC with 100 nM PAF under normoxic conditions augmented 11.8-fold the phosphorylation of PECAM-1 and twofold increase in the transendothelial migration of monocyte-like HL-60 cells. We conclude that PAF, produced by cultured endothelial cells in response to hypoxia, acts in an autocrine fashion to activate PKC, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.
Insights
Hypoxia increases monocyte migration across endothelial cells by triggering platelet-activating factor (PAF) release. This PAF activates protein kinase C (PKC), leading to PECAM-1 phosphorylation and enhanced cell transmigration.
Area of Science:
- Endothelial cell biology
- Immunology
- Cellular physiology
Background:
- Polymorphonuclear neutrophils (PMN) adhere to endothelium under hypoxia, causing microvascular injury.
- The molecular mechanisms of hypoxia-induced PMN adhesion and diapedesis are not fully understood.
Purpose of the Study:
- To investigate the effects of hypoxia on monocyte transendothelial migration.
- To elucidate the molecular pathways involved in hypoxia-induced monocyte migration.
Main Methods:
- Human umbilical vein endothelial cells (HUVEC) and monocyte-like HL-60 cells were used.
- Cells were exposed to varying oxygen tensions (hypoxic vs. normoxic conditions).
- Migration rates, PECAM-1 phosphorylation, and involvement of PKC and PAF were assessed using specific inhibitors and antibodies.
Main Results:
- Hypoxia significantly increased monocyte migration through HUVEC.
- Hypoxia induced phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1) in HUVEC.
- This phosphorylation was dependent on hypoxia-induced platelet-activating factor (PAF) release and protein kinase C (PKC) activation.
Conclusions:
- Hypoxia stimulates endothelial cells to release PAF.
- PAF acts in an autocrine manner to activate PKC, leading to PECAM-1 phosphorylation.
- This process facilitates monocyte transendothelial migration, contributing to microvascular injury.