Oxidized Lipoproteins Enhance the in Vitro Tube Formation by Endothelial Cells Cultured on Matrigel
When U937 monocyte-like cells were pretreated with oxidized low density lipoproteins (LDL) or oxidized lipoprotein (a) [Lp(a)] and subsequently the U937 cells were co-cultured with human microvascular endothelial cells (HMVECs), or human umbilical vascular endothelial cells (HUVECs) seeded on Matrigel, angiogenic differentiation and formation of microtubules were enhanced. The effect was depended on the concentration of the oxidized lipoproteins and it was negligible when U937 was treated with native lipoproteins. Under optimum conditions, 250 ug LDL or 200 ug oxidized lipoprotein(a) [Lp(a)], respectively, preincubated with 106 U937 cells per ml of media, for 24 hours, followed by 24 hours of co-culture with endothelial cells (EC) seeded on Matrigel (50,000 cells per 300 uL Matrigel), gave similar results with the average capillary length of the microtubules increasing from 160±25 to 400±40um. When potentially active components of oxidized LDL, like malondialdehyde, hexanal, 4-hydroxynonenal and lysophospholipids were pre-incubated with U937 cells prior to co-culturing them with HMVECs and HUVECs on Matrigel, only malondialdehyde and lysophospholipids, gave an effect similar in size to the oxidized lipoproteins. Antibodies (moAb Mac-1) directed against the CD1 lb/CD18 epitopes inhibited adhesion of U937 cells to EC and formation of microtubes when used in conjunction with moAbs towards ICAM-1(CD54). Blockage of tube formation by antibodies to Mac-1 and ICAM-1 seems to suggest that there is a link between the formation of a complex between adhesion molecule CD lib/CD 18 and adhesion molecules CD54 from ICAM-1 and tube formation as observed in co-cultures of activated U937 and HMVECs or HUVECs grown on Matrigel.
KeywordsU937 Cell Tube Formation Human Microvascular Endothelial Cell Human Umbilical Vascular Endothelial Cell Endothelial Cell Tube Formation
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