Post‐transcriptional regulation of VEGF expression by oxidised LDL in human macrophages

Abstract

Accumulation of oxidised low density lipoproteins (oxLDL) in macrophages and their subsequent transformation into lipid-filled foam cells is generally considered an early event in atherosclerosis. Vascular Endothelial Growth Factor (VEGF) may contribute to atherogenesis through increased vascular permeability, chemoattraction towards monocytes and intraplaque vessel formation. In this study we investigate the effect and regulation of VEGF expression in human macrophages stimulated with oxLDL. Vascular Endothelial Growth Factor mRNA and protein expression was assayed using RT-PCR and ELISA, respectively. The activity of mitogen-activated protein kinases (MAPKs) was investigated using Western blots. In human monocyte-derived macrophages, oxLDL significantly increased VEGF mRNA expression and subsequent protein secretion in a concentration-dependent manner after 6 h and 18 h, respectively. Using an in vitro mRNA decay assay, we show that this oxLDL-induced VEGF expression partly is regulated through increased stability of the VEGF mRNA. Involvement of MAPKs has previously been implicated in the stabilisation of VEGF mRNA. Activity of the p38 MAPK, but not the c-jun-N-terminal kinase (JNK), increased in macrophages stimulated with oxLDL (50 micro g mL-1) for 5-15 min. Preincubation with SB202190 (20 micro M), a specific inhibitor of p38 MAPK, significantly decreased the oxLDL-induced VEGF mRNA expression by 40%. The prolonged half-life of VEGF mRNA, induced by oxLDL, was not inhibited by SB202190. OxLDL increases VEGF expression and p38 MAPK activity in human macrophages. The increased VEGF mRNA expression by oxLDL is mediated through at least two intracellular pathways, one involving p38 MAPK and another that independently of p38 MAPK activity increases VEGF mRNA stability.