ApoE production in human monocytes and its regulation by inflammatory cytokines

PLoS One. 2013 Nov 14;8(11):e79908. doi: 10.1371/journal.pone.0079908. eCollection 2013.

Abstract

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.

MeSH terms

  • Apolipoproteins E / biosynthesis*
  • Apolipoproteins E / immunology
  • Biomarkers / metabolism
  • Etanercept
  • GPI-Linked Proteins / genetics
  • GPI-Linked Proteins / immunology
  • Gene Expression
  • Hep G2 Cells
  • Hepatocytes / cytology
  • Hepatocytes / drug effects
  • Hepatocytes / immunology
  • Humans
  • Immunoglobulin G / pharmacology
  • Immunologic Factors / pharmacology
  • Interferon-gamma / pharmacology*
  • Interleukin-1beta / pharmacology*
  • Interleukin-6 / pharmacology
  • Lipopolysaccharide Receptors / genetics
  • Lipopolysaccharide Receptors / immunology
  • Lipopolysaccharides / pharmacology
  • Monocytes / cytology
  • Monocytes / drug effects*
  • Monocytes / immunology
  • Primary Cell Culture
  • Receptors, IgG / genetics
  • Receptors, IgG / immunology
  • Receptors, Tumor Necrosis Factor
  • Transforming Growth Factor beta / pharmacology
  • Tumor Necrosis Factor-alpha / antagonists & inhibitors
  • Tumor Necrosis Factor-alpha / pharmacology*

Substances

  • Apolipoproteins E
  • Biomarkers
  • FCGR3B protein, human
  • GPI-Linked Proteins
  • IL6 protein, human
  • Immunoglobulin G
  • Immunologic Factors
  • Interleukin-1beta
  • Interleukin-6
  • Lipopolysaccharide Receptors
  • Lipopolysaccharides
  • Receptors, IgG
  • Receptors, Tumor Necrosis Factor
  • Transforming Growth Factor beta
  • Tumor Necrosis Factor-alpha
  • Interferon-gamma
  • Etanercept

Grants and funding

The authors have no support or funding to report.