Oxidised LDL decreases VEGFR-1 expression in human monocyte-derived macrophages

Monocyte infiltration followed by differentiation into macrophages and accumulation of oxidised LDL (oxLDL) comprise early stages of atherosclerosis. Vascular endothelial growth factor (VEGF), which is upregulated by oxLDL, may contribute to atherogenesis through monocyte recruitment, increased vascular permeability and promotion of intraplaque vessels. The VEGF receptor-1 (VEGFR-1/Flt-1) mediates monocyte migration towards VEGF and regulates the levels of available VEGF through ligand-entrapment. In this study we investigated the effect of oxLDL on VEGFR-1 expression in human monocyte-derived macrophages. mRNA expression was estimated using RT-PCR, protein secretion was measured with ELISA and the amount of membrane-bound VEGFR-1 was analysed using flow cytometry analysis. Binding of transcription factors to the promoter was studied with EMSA. Incubation with oxLDL decreased VEGFR-1 mRNA expression in a time- and dose-dependent manner, followed by a subsequent decrease in protein secretion of VEGFR-1 and a reduction of the amount of receptor expressed on the cell surface. Furthermore, the PPARgamma agonists 9-hydroxy-(S)-10,12-octadecadienoic acid (9-HODE) and darglitazone also decreased VEGFR-1 mRNA expression. Incubation of macrophages with oxLDL or 9-HODE decreased binding of the transcription factor AP-1 (c-jun/ATF-2) to the VEGFR-1 promoter. Together, these data suggest that oxLDL decreases VEGFR-1 expression in macrophages, probably through a PPARgamma-dependent reduction in the AP-1 transcriptional activity. This implies that oxLDL has effects on the biological availability of VEGF, besides its direct effect on VEGF expression.