ApoE production in human monocytes and its regulation by inflammatory cytokines

• Published in: PloS one 2013-11, Vol.8 (11), p.e79908-e79908
• Main Authors: Braesch-Andersen, Sten, Paulie, Staffan, Smedman, Christian, Mia, Sohel, Kumagai-Braesch, Makiko
• Format: Article
• Language: English
• Subjects: Analysis; Apolipoprotein E; Apolipoproteins; Apolipoproteins E - biosynthesis; Apolipoproteins E - immunology; Arteriosclerosis; Atherosclerosis; Biomarkers - metabolism; Bone morphogenetic proteins; CD14 antigen; CD16 antigen; Cloning; Cytokines; Enzyme-linked immunosorbent assay; Etanercept; Fc receptors; Gene Expression; GPI-Linked Proteins - genetics; GPI-Linked Proteins - immunology; Hep G2 Cells; Hepatocytes; Hepatocytes - cytology; Hepatocytes - drug effects; Hepatocytes - immunology; Hepatoma; Humans; Immunoglobulin G - pharmacology; Immunologic Factors - pharmacology; Inflammation; Interferon; Interferon-gamma - pharmacology; Interleukin 12; Interleukin 13; Interleukin 2; Interleukin 23; Interleukin 4; Interleukin 6; Interleukin-1beta - pharmacology; Interleukin-6 - pharmacology; Kinases; Leukocytes (mononuclear); Lipids; Lipopolysaccharide Receptors - genetics; Lipopolysaccharide Receptors - immunology; Lipopolysaccharides; Lipopolysaccharides - pharmacology; Macrophages; Medicin och hälsovetenskap; Mitogens; Monocytes; Monocytes - cytology; Monocytes - drug effects; Monocytes - immunology; Peripheral blood mononuclear cells; Primary Cell Culture; Receptors, IgG - genetics; Receptors, IgG - immunology; Receptors, Tumor Necrosis Factor; Synergism; Transforming Growth Factor beta - pharmacology; Transforming growth factors; Tumor necrosis factor; Tumor Necrosis Factor-alpha - antagonists & inhibitors; Tumor Necrosis Factor-alpha - pharmacology; α-Interferon; γ-Interferon
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0079908

The apoE production by tissue macrophages is crucial for the prevention of atherosclerosis and the aim of this study was to further elucidate how this apolipoprotein is regulated by cytokines present during inflammation. Here we studied apoE production in peripheral blood mononuclear cells (PBMC) and analysis was made with a newly developed apoE ELISpot assay. In PBMC, apoE secretion was restricted to monocytes with classical (CD14(++)CD16(-)) and intermediate (CD14(+)CD16(+)) monocytes being the main producers. As earlier described for macrophages, production was strongly upregulated by TGF-β and downregulated by bacterial lipopolysaccharide (LPS) and the inflammatory cytokines IFN-γ, TNF-α and IL-1β. We could here show that a similar down-regulatory effect was also observed with the type I interferon, IFN-α, while IL-6, often regarded as one of the more prominent inflammatory cytokines, did not affect TGF-β-induced apoE production. The TNF-α inhibitor Enbrel could partly block the down-regulatory effect of IFN-γ, IFN-α and IL-1β, indicating that inhibition of apoE by these cytokines may be dependent on or synergize with TNF-α. Other cytokines tested, IL-2, IL-4, IL-12, IL-13, IL-17A and IL-23, had no inhibitory effect on apoE production. In contrast to the effect on monocytes, apoE production by primary hepatocytes and the hepatoma cell line HepG2 was more or less unaffected by treatment with cytokines or LPS.