Regulation of endothelial lipase and systemic HDL cholesterol levels by SREBPs and VEGF-A
2012
Kivelä, Annukka M. | Dijkstra, Marike H. | Heinonen, Suvi E. | Gurzeler, Erika | Jauhiainen, Suvi | Levonen, Anna-Liisa | Ylä-Herttuala, Seppo
OBJECTIVE: Endothelial lipase (EL) regulates HDL cholesterol levels and in inflammatory states, like atherosclerosis, EL expression is increased contributing to low HDL cholesterol. The regulation of EL expression is poorly understood and has mainly been attributed to inflammatory stimuli. As sterol regulatory element binding proteins (SREBPs) are regulators of genes involved in lipid metabolism, we hypothesized that EL is regulated by SREBPs and that EL expression is modified by the SREBP activator vascular endothelial growth factor A (VEGF-A). METHODS: and results: Quantitative PCR and Western blot results demonstrated that starvation increased EL expression in human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs). Also, 25-hydroxycholesterol (25HC), an inhibitor of SREBP activation inhibited EL expression. With siRNA-mediated inhibition of SREBPs the effect of starvation was shown to be SREBP-2 dependent. VEGF-A decreased EL expression in both endothelial cell lines used, most likely via inhibition of SREBP-2 binding determined by chromatin immunoprecipitation (ChIP). Furthermore, in atherosclerosis prone LDLR⁻/⁻ApoB¹⁰⁰/¹⁰⁰ mice, systemic adenoviral gene transfer with human VEGF-A decreased EL mRNA in peripheral tissues and increased plasma HDL cholesterol. CONCLUSIONS: These results identify SREBPs as novel regulators of EL expression. VEGF-A as an endogenous EL inhibitor could be therapeutically relevant in atherosclerosis by increasing systemic HDL cholesterol levels.
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