Nucleolin protects macrophages from oxLDL-induced foam cell formation through up-regulating ABCA1 expression

Biochem Biophys Res Commun. 2017 Apr 29;486(2):364-371. doi: 10.1016/j.bbrc.2017.03.047. Epub 2017 Mar 14.

Abstract

Our recent studies have indicated that nucleolin, as a multifunctional RNA-binding protein, exerts protective effects in the myocardial cells and endothelial cells under the condition of oxidative stress. However, the function of nucleolin and its potential mechanism in macrophage-derived foam cell formation remain largely unexplored. ApoE-/- mice were fed with a high-fat diet (HFD) for 10-24 weeks. Protein expression was measured by western blotting or immunofluorescence, and gene expression at the mRNA level was detected by qRT-PCR. The level of lipid in macrophages was examined by Oil Red O staining, high-performance liquid chromatography (HPLC) and NBD-cholesterol. Actinomycin D (Act D) was used to determine the stability of ABCA1 mRNA in macrophages. The interaction of nucleolin with ABCA1 mRNA was assessed using co-immunoprecipitation (co-IP). The aortas advanced plaques demonstrated significantly lower levels of nucleolin protein compared with early plaques in ApoE-/- mice, in which the macrophage foam cells occupied main body. Nucleolin expression at the mRNA and protein levels in RAW264.7 macrophages was significantly reduced by oxidized low-density lipoprotein (oxLDL) in a dose- and time-dependent manner. Furthermore, nucleolin overexpression markedly attenuated lipid accumulation in oxLDL-challenged macrophages through increasing cholesterol efflux. In addition, nucleolin overexpression significantly increased the expression of ATP-binding cassette transporter A1 (ABCA1) at the mRNA and protein levels without affecting expressions of scavenger receptors (SR)-A, SR-B1, CD36 and ATP-binding cassette transporter G1 (ABCG1) at the mRNA level. Moreover, nucleolin overexpression increased the stability of ABCA1 mRNA in macrophages, whereas nucleolin ablation abrogated the oxLDL-induced up-regulation of ABCA1. The up-regulation of ABCA1 by nucleolin resulted from its protein-RNA interaction. Our data suggested that nucleolin inhibited foam cell formation through enhancing stability of ABCA1 mRNA and subsequently increasing cholesterol efflux.

Keywords: ABCA1; Atherosclerosis; Lipoprotein; Nucleolin; mRNA stability.

MeSH terms

  • ATP Binding Cassette Transporter 1 / genetics*
  • ATP Binding Cassette Transporter 1 / metabolism
  • ATP Binding Cassette Transporter, Subfamily G, Member 1 / genetics
  • ATP Binding Cassette Transporter, Subfamily G, Member 1 / metabolism
  • Animals
  • Apolipoproteins E / deficiency
  • Apolipoproteins E / genetics
  • Atherosclerosis / etiology
  • Atherosclerosis / genetics*
  • Atherosclerosis / metabolism
  • Atherosclerosis / pathology
  • Biological Transport / drug effects
  • CD36 Antigens / genetics
  • CD36 Antigens / metabolism
  • Cell Differentiation
  • Cell Line
  • Cholesterol / metabolism
  • Diet, High-Fat
  • Dose-Response Relationship, Drug
  • Foam Cells / drug effects
  • Foam Cells / metabolism
  • Foam Cells / pathology
  • Gene Expression Regulation
  • Hyperlipidemias / etiology
  • Hyperlipidemias / genetics*
  • Hyperlipidemias / metabolism
  • Hyperlipidemias / pathology
  • Lipoproteins, LDL / pharmacology*
  • Macrophages / drug effects
  • Macrophages / metabolism
  • Macrophages / pathology
  • Male
  • Mice
  • Mice, Knockout
  • Nucleolin
  • Phosphoproteins / genetics*
  • Phosphoproteins / metabolism
  • RNA Stability
  • RNA, Messenger / genetics*
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / genetics*
  • RNA-Binding Proteins / metabolism
  • Scavenger Receptors, Class A / genetics
  • Scavenger Receptors, Class A / metabolism
  • Scavenger Receptors, Class B / genetics
  • Scavenger Receptors, Class B / metabolism
  • Signal Transduction

Substances

  • ABCA1 protein, mouse
  • ABCG1 protein, mouse
  • ATP Binding Cassette Transporter 1
  • ATP Binding Cassette Transporter, Subfamily G, Member 1
  • Apolipoproteins E
  • CD36 Antigens
  • Lipoproteins, LDL
  • Phosphoproteins
  • RNA, Messenger
  • RNA-Binding Proteins
  • Scarb1 protein, mouse
  • Scavenger Receptors, Class A
  • Scavenger Receptors, Class B
  • oxidized low density lipoprotein
  • Cholesterol