title: Apolipoprotein A-I stimulates cholesteryl ester transfer protein and apolipoprotein E secretion from lipid-loaded macrophages; the role of NF-κB and PKA signaling pathways.
abstract: Cholesteryl ester transfer protein (CETP) and apolipoprotein E (apoE) are secreted by macrophages. Apolipoprotein A-I (apoA-I) is a potent inducer of apoE secretion from lipid-loaded macrophages, but its effect on CETP is not known. We aimed to identify the signaling pathways involved in apoA-I and HDL-mediated regulation of CETP and apoE secretion from lipid-loaded macrophages. THP-1 macrophages were loaded with lipids by incubation with human copper-oxidized LDL. The cells were subsequently exposed to human purified apoA-I or HDL(3) with/without inhibitors of NF-κB (TPCK) or PKA (H89). CETP and apoE in the cultured cells and media were quantified by real-time PCR and Western blot. Results showed that in lipid-loaded macrophages: (i) CETP and apoE gene expression and secretion were increased in the presence of apoA-I, and further increased by inhibition of NF-kB with TPCK; (ii) CETP and apoE gene expression and secretion were reduced by the inhibition of PKA with H89; (iii) PKA-gamma subunit was activated by oxidized LDL and moreover by apoA-I. We also showed that: (i) siRNA-mediated CETP gene silencing diminished apoE secretion from both non-loaded and lipid-loaded macrophages; (ii) addition of apoA-I partially restored apoE secretion from lipid-loaded macrophages with the silenced CETP gene. In conclusion, our data suggest a new mechanism by which apoA-I stimulates CETP secretion, in addition to apoE, from lipid loaded macrophages, a process involving NF-κB inhibition and/or PKA pathway activation.
authors: Department of Lipoproteins and Atherosclerosis, Institute of Cellular Biology and Pathology Nicolae Simionescu, Bucharest, Romania.
authors: Loredan S
authors: LS
authors: Niculescu
authors: Marius R
authors: MR
authors: Robciuc
authors: Gabriela M
authors: GM
authors: Sanda
authors: Anca V
authors: AV
authors: Sima
mesh_terms: D016632:Apolipoprotein A-I / Q000378:metabolism* / Q000494:pharmacology; D001057:Apolipoproteins E / Q000378:metabolism*; D053480:Cholesterol Ester Transfer Proteins / Q000235:genetics / Q000378:metabolism*; D008076:Cholesterol, HDL / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D015870:Gene Expression; D020868:Gene Silencing; D006801:Humans; D050356:Lipid Metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction
chemical_list: D016632:Apolipoprotein A-I; D001057:Apolipoproteins E; D053480:Cholesterol Ester Transfer Proteins; D008076:Cholesterol, HDL; D016328:NF-kappa B; D034741:RNA, Small Interfering; D017868:Cyclic AMP-Dependent Protein Kinases