Osteoprotegerin upregulates endothelial cell adhesion molecule response to tumor necrosis factor-alpha associated with induction of angiopoietin-2.
OBJECTIVE
Osteoprotegerin (OPG) and osteopontin (OPN) have been identified within unstable atherosclerosis and circulating concentrates have been linked to cardiovascular events. We studied the influence of OPG and OPN on endothelial adhesion molecule expression and monocyte binding.


METHODS
Resting or tumor necrosis factor (TNF-alpha) activated human endothelial cells were incubated with OPG (0, 0.5, 5, and 10 ng/mL) or OPN (0, 2.5, 10 and 50 nmol/L). The expression of endothelial genes and proteins was investigated with the Oligo GEArray microarray series, multiplexed gene expression analysis, flow cytometry, ELISA and immunohistochemistry. Monocyte-binding studies were carried out using fluorescently labeled THP-1 cells and analysed by flow cytometry.


RESULTS
OPG but not OPN stimulated a dose-dependent increase in the expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin by endothelial cells in the presence of TNF-alpha (p<or=0.05) which was reflected by enhanced binding of THP-1 monocytes. In the absence of TNF-alpha, OPG had no significant effect on adhesion molecule expression but upregulated angiopoietin-2. When the induction of angiopoietin-2 was inhibited using interfering RNA the ability of OPG to upregulate adhesion molecules in the presence of TNF-alpha was abolished. OPN did not effect adhesion molecule expression by resting or activated endothelial cells.


CONCLUSIONS
OPG upregulates angiopoietin-2 in human endothelial cells sensitizing them to the effects of TNF-alpha. These findings suggest a mechanism by which OPG may stimulate inflammation in atheroma and thereby promote the progression and complications of atherosclerosis.
Mangan
Simone H
SH
Vascular Biology Unit, Department of Surgery, School of Medicine, James Cook University, Townsville, 4811 Australia.
Van Campenhout
Ann
A
Rush
Catherine
C
Golledge
Jonathan
J
D042702:Angiopoietin-2 / Q000378:metabolism*; D002478:Cells, Cultured; D019040:E-Selectin / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D009000:Monocytes / Q000187:drug effects; D020411:Oligonucleotide Array Sequence Analysis; D053495:Osteopontin / Q000502:physiology; D053244:Osteoprotegerin / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014471:Umbilical Veins / Q000166:cytology / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism*
D042702:Angiopoietin-2; D019040:E-Selectin; D053244:Osteoprotegerin; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1; D053495:Osteopontin; D018799:Intercellular Adhesion Molecule-1
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