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.
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.
Lipid Metabolism Unit, Massachusetts General Hospital (MGH), Center for Computational & Integrative Biology (CCIB), Richard B. Simches Research Center , 185 Cambridge Street, 7th Floor #7150, Boston, Massachusetts 02114, United States.
Norimasa
N
Tamehiro
Lipid Metabolism Unit, Massachusetts General Hospital (MGH), Center for Computational & Integrative Biology (CCIB), Richard B. Simches Research Center , 185 Cambridge Street, 7th Floor #7150, Boston, Massachusetts 02114, United States.
Min Hi
MH
Park
Lipid Metabolism Unit, Massachusetts General Hospital (MGH), Center for Computational & Integrative Biology (CCIB), Richard B. Simches Research Center , 185 Cambridge Street, 7th Floor #7150, Boston, Massachusetts 02114, United States.
Victoria
V
Hawxhurst
Department of Medicine, Division of Infectious Diseases and Immunology, University of Massachusetts Medical School , Worcester, Massachusetts 01605, United States.
Kamalpreet
K
Nagpal
University of Washington , 1705 Northeast Pacific Street, H-418 HSB Campus Box 357290, Seattle, Washington 98195, United States.
Marv E
ME
Adams
Whitaker Cardiovascular Institute, Boston University School of Medicine , 700 Albany Street, W509, Boston, Massachusetts 02118, United States.
Vassilis I
VI
Zannis
Department of Medicine, Division of Infectious Diseases and Immunology, University of Massachusetts Medical School , Worcester, Massachusetts 01605, United States.
Douglas T
DT
Golenbock
Lipid Metabolism Unit, Massachusetts General Hospital (MGH), Center for Computational & Integrative Biology (CCIB), Richard B. Simches Research Center , 185 Cambridge Street, 7th Floor #7150, Boston, Massachusetts 02114, United States.
Michael L
ML
Fitzgerald
D064286:ATP Binding Cassette Transporter 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001693:Biological Transport, Active; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D049029:Dystrophin-Associated Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D050356:Lipid Metabolism; D000071518:Liver X Receptors; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D057093:Orphan Nuclear Receptors / Q000819:agonists*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D015854:Up-Regulation; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D064286:ATP Binding Cassette Transporter 1; D016632:Apolipoprotein A-I; D002135:Calcium-Binding Proteins; D049029:Dystrophin-Associated Proteins; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D009124:Muscle Proteins; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; D013449:Sulfonamides; C577833:Abca1 protein, mouse; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C091824:syntrophin; C091825:syntrophin alpha1