In vivo stimulation of vascular plasminogen activator inhibitor-1 production by very low-density lipoprotein involves transcription factor binding toa VLDL-responsive element

High plasma levels of plasminogen activator inhibitor-1 (PAI-1) are associa ted with an increased risk of cardiovascular disease. There is also a close relation between high plasma levels of PAI-1 and hypertriglyceridemia. Cel l culture studies have shown that very low density lipoprotein (VLDL) incre ases the production and secretion of PAI-1 in endothelial cells and hepatoc ytes, suggesting a possible mechanism for this association. To determine wh ether VLDL stimulates PAI-1 production in vascular cells also in vivo, Spra gue-Dawley rats were injected intravenously with 6 mg/kg of VLDL (derived f rom human subjects with type IV hyperlipidemia). Previous studies have demo nstrated that this results in an accumulation of human VLDL in the aorta an d other arteries followed by increased nuclear factor-kappa B (NF-kappa B) activation. Endothelial, but not smooth muscle cells, showed a basal PAI-1 mRNA and protein expression as assessed by in situ hybridization and immuno histochemistry, respectively. Six to twenty-four hours after the VLDL injec tion, lipoprotein particle accumulation was seen in the aortic wall, which was accompanied by increasing PAI-1 mRNA and protein expression in endothel ial and smooth muscle cells. Within the rat PAI-1 promoter we identified a sequence located at -589 to -571 with 74% homology with the recently descri bed VLDL responsive element in the human PAI-1 promoter and located adjacen t to a 4-guanosine motif presumably corresponding to the human 4G/5G polymo rphism. Transient transfection studies showed that VLDL exerts its stimulat ory effects on rat PAI-1 gene expression in vascular cells by interaction w ith promoter sequences located within bp-656 and -505. Electrophoretic mobi lity shift assays showed that VLDL increases the binding of as yet incomple tely characterized factors to this response element. Taken together these o bservations support a direct influence of VLDL on vascular PAI-1 gene expre ssion in vivo. This stimulation is exerted on the level of PAI-1 gene trans cription, and involves transcription factor binding to a VLDL responsive el ement adjacent to a 4G motif within the PAI-1 promoter.