title: Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol.
abstract: We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.
authors.affiliation: Departments of Pathology/Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, NC, USA.
authors.forename: Xuewei
authors.initials: X
authors.lastname: Zhu
authors.forename: John S
authors.initials: JS
authors.lastname: Owen
authors.forename: Martha D
authors.initials: MD
authors.lastname: Wilson
authors.forename: Haitao
authors.initials: H
authors.lastname: Li
authors.forename: Gary L
authors.initials: GL
authors.lastname: Griffiths
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Hiltbold
authors.forename: Michael B
authors.initials: MB
authors.lastname: Fessler
authors.forename: John S
authors.initials: JS
authors.lastname: Parks
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002784:Cholesterol / Q000378:metabolism*; D017353:Gene Deletion; D007249:Inflammation / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000819:agonists / Q000378:metabolism; D051193:Toll-Like Receptors / Q000819:agonists / Q000378:metabolism*
chemical_list: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008070:Lipopolysaccharides; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051197:Toll-Like Receptor 4; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D002784:Cholesterol