LXR Agonism Upregulates the Macrophage ABCA1/Syntrophin Protein Complex That Can Bind ApoA-I and Stabilized ABCA1 Protein, but Complex Loss Does Not Inhibit Lipid Efflux

Biochemistry. 2015 Nov 24;54(46):6931-41. doi: 10.1021/acs.biochem.5b00894. Epub 2015 Nov 9.

Abstract

Macrophage ABCA1 effluxes lipid and has anti-inflammatory activity. The syntrophins, which are cytoplasmic PDZ protein scaffolding factors, can bind ABCA1 and modulate its activity. However, many of the data assessing the function of the ABCA1-syntrophin interaction are based on overexpression in nonmacrophage cells. To assess endogenous complex function in macrophages, we derived immortalized macrophages from Abca1(+/+) and Abca1(-/-) mice and show their phenotype recapitulates primary macrophages. Abca1(+/+) lines express the CD11B and F4/80 macrophage markers and markedly upregulate cholesterol efflux in response to LXR nuclear hormone agonists. In contrast, immortalized Abca1(-/-) macrophages show no efflux to apoA-I. In response to LPS, Abca1(-/-) macrophages display pro-inflammatory changes, including an increased level of expression of cell surface CD14, and 11-26-fold higher levels of IL-6 and IL-12 mRNA. Given recapitulation of phenotype, we show with these lines that the ABCA1-syntrophin protein complex is upregulated by LXR agonists and can bind apoA-I. Moreover, in immortalized macrophages, combined α1/β2-syntrophin loss modulated ABCA1 cell surface levels and induced pro-inflammatory gene expression. However, loss of all three syntrophin isoforms known to bind ABCA1 did not impair lipid efflux in immortalized or primary macrophages. Thus, the ABCA1-syntrophin protein complex is not essential for ABCA1 macrophage lipid efflux but does directly interact with apoA-I and can modulate the pool of cell surface ABCA1 stabilized by apoA-I.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter 1 / deficiency
  • ATP Binding Cassette Transporter 1 / genetics
  • ATP Binding Cassette Transporter 1 / metabolism*
  • Animals
  • Apolipoprotein A-I / metabolism*
  • Biological Transport, Active
  • Calcium-Binding Proteins / deficiency
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism
  • Cell Line
  • Dystrophin-Associated Proteins / deficiency
  • Dystrophin-Associated Proteins / genetics
  • Dystrophin-Associated Proteins / metabolism*
  • Hydrocarbons, Fluorinated / pharmacology
  • Lipid Metabolism
  • Liver X Receptors
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Membrane Proteins / deficiency
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred DBA
  • Mice, Knockout
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / metabolism
  • Muscle Proteins / deficiency
  • Muscle Proteins / genetics
  • Muscle Proteins / metabolism
  • Orphan Nuclear Receptors / agonists*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Stability
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Sulfonamides / pharmacology
  • Up-Regulation

Substances

  • ABCA1 protein, mouse
  • ATP Binding Cassette Transporter 1
  • Apolipoprotein A-I
  • Calcium-Binding Proteins
  • Dystrophin-Associated Proteins
  • Hydrocarbons, Fluorinated
  • Liver X Receptors
  • Membrane Proteins
  • Multiprotein Complexes
  • Muscle Proteins
  • Orphan Nuclear Receptors
  • RNA, Messenger
  • Sulfonamides
  • T0901317
  • syntrophin
  • syntrophin alpha1