title: Deletion of ABCA1 and ABCG1 impairs macrophage migration because of increased Rac1 signaling.
abstract: BACKGROUND
  Reduced plasma cholesterol and increased high-density lipoprotein (HDL) levels promote regression of atherosclerosis, in a process characterized by lipid unloading and emigration of macrophages from lesions. In contrast free cholesterol loading of macrophages leads to imbalanced Rac1/Rho activities and impaired chemotaxis.
  
  
  OBJECTIVE
  To study the role of HDL and the ATP-binding cassette transporters ABCA1 and ABCG1 in modulating the chemotaxis of macrophages.
  
  
  RESULTS
  Abca1(-/-)Abcg1(-/-) mouse macrophages displayed profoundly impaired chemotaxis both in a Transwell chamber assay and in the peritoneal cavity of wild-type (WT) mice. HDL reversed impaired chemotaxis in free cholesterol-loaded WT macrophages but was without effect in Abca1(-/-)Abcg1(-/-) cells, whereas cyclodextrin was effective in both. Abca1(-/-)Abcg1(-/-) macrophages had markedly increased Rac1 activity and increased association of Rac1 with the plasma membrane (PM). Their defective chemotaxis was reversed by a Rac1 inhibitor. To gain a better understanding of the role of transporters in PM cholesterol movement, we measured transbilayer PM sterol distribution. In WT macrophages, the majority of cholesterol was located on the inner leaflet, whereas on upregulation of transporters by liver X receptor activation, PM sterol was shifted to the outer leaflet, where it could be removed by HDL. Abca1(-/-)Abcg1(-/-) macrophages showed increased PM sterol content and defective redistribution of sterol to the outer leaflet.
  
  
  CONCLUSIONS
  Deletion of ABCA1 and ABCG1 causes an increased cholesterol content on the inner leaflet of the PM, associated with increased Rac1 PM localization, activation, and impairment of migration. ABCA1 and ABCG1 facilitate macrophage chemotaxis by promoting PM transbilayer cholesterol movement and may contribute to the ability of HDL to promote regression of atherosclerosis.
authors.affiliation: Division of Molecular Medicine, Department of Medicine, Columbia University, 630 W 168th Street, New York, NY 10032, USA. tamara.pagler@gmail.com
authors.forename: Tamara A
authors.initials: TA
authors.lastname: Pagler
authors.forename: Mi
authors.initials: M
authors.lastname: Wang
authors.forename: Mousumi
authors.initials: M
authors.lastname: Mondal
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Murphy
authors.forename: Marit
authors.initials: M
authors.lastname: Westerterp
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Moore
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Maxfield
authors.forename: Alan R
authors.initials: AR
authors.lastname: Tall
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology*; D002478:Cells, Cultured; D002633:Chemotaxis / Q000502:physiology; D002784:Cholesterol / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008074:Lipoproteins / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D009479:Neuropeptides / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein
chemical_list: C487540:ABCG1 protein, mouse; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D000199:Actins; D008074:Lipoproteins; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D006160:Guanosine Triphosphate; D002784:Cholesterol; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein