Low-density lipoprotein in hypercholesterolemic human plasma induces vascular endothelial cell apoptosis by inhibiting fibroblast growth factor 2 transcription

Background - Apoptosis of vascular endothelial cells (ECs) can be induced in vitro by experimentally modified LDL. Description of proapoptotic circulating lipoproteins may significantly enhance understanding of atherothrombosis pathophysiology. Methods and Results - Fast protein liquid chromatography of LDL samples from 7 asymptomatic, hypercholesterolemic patients yielded subfractions L₁-L₅, in increasing electronegativity. L₄ and L₅ were not detectable or collectible in normolipidemic samples. In bovine aortic EC cultures, L₅ induced marked apoptosis and L₄ had a mild effect, whereas hypercholesterolemic or normolipidemic L₁-L₃ had negligible effects. Compared with copper-oxidized LDL, L₅ was only mildly oxidized, although its propensity to form conjugated dienes in response to copper exceeded that of other subfractions. L₅-induced apoptosis was associated with suppressed fibroblast growth factor 2 (FGF-2) transcription, as assessed by nuclear run-on analysis. Degrading platelet-activating factor (PAF)-like lipids in L₅by a recombinant PAF acetylhydrolase prevented both FGF-2 downregulation and apoptosis. Furthermore, the ability of L₅ lipid extract to induce calcium influx into neutrophils was lost after pretreatment of the extract with PAF acetylhydrolase. FGF-2 supplementation, PAF receptor (PAFR) blockade with WEB-2086, and inactivation of PAFR-coupled G_i protein with pertussis toxin all effectively attenuated L₅-induced apoptosis. Conclusions - Our findings indicate that a highly electronegative, mildly oxidized LDL subfraction present in human hypercholesterolemic but not normolipidemic plasma can induce apoptosis in cultured ECs. The evidence that a freshly isolated LDL species modulates transcription of FGF-2 may provide a physiological insight into the mechanism of vascular EC apoptosis in hypercholesterolemia.