Overexpression of steroidogenic acute regulatory protein increases macrophage cholesterol efflux to apolipoprotein AI.
OBJECTIVE
In this study, we investigated the impact of enhancing cholesterol delivery to mitochondrial sterol 27-hydroxylase, via steroidogenic acute regulatory protein (StAR), on the expression of genes involved in macrophage cholesterol homeostasis and efflux of cholesterol to apolipoprotein (apo) AI.


RESULTS
Stably transfected, murine (RAW 264.7) macrophages were used to investigate the role of StAR in cholesterol homeostasis. Cellular responses were analysed using quantitative PCR, immunoblotting, and an LXRE reporter plasmid; [3H]cholesterol efflux was measured in the presence or absence of apoAI. Macrophage overexpression of mitochondrial cholesterol trafficking protein, StAR, activates and induces expression of liver X receptors (LXRs), and significantly alters expression of genes involved in cholesterol homeostasis, decreasing Fdps, Hmgcr, Mvk, Ldlr, and Scap, and markedly increasing Abca1 mRNA and protein. Overexpression of StAR, but not mutated 'loss-of-function' (R181L) StAR, enhanced efflux of [3H]cholesterol to apoAI, and this effect was maintained in macrophages pretreated with LDL or acetylated LDL. The effect of StAR overexpression on apoAI-dependent [3H]cholesterol efflux was mimicked by non-sterol agonist, T901317, and 27-hydroxycholesterol, and blocked by LXR inhibitor, geranylgeranyl pyrophosphate, sterol 27-hydroxylase inhibitor, GW273297x, and probucol, inhibitor of ATP binding cassette transporter A1 (ABCA1). Importantly, all observed effects of StAR overexpression were dependent upon cyclic AMP (cAMP analogue, dibutyryl cAMP), which is required for the full activity of the StAR protein to be manifested.


CONCLUSIONS
Macrophage overexpression of StAR significantly enhances LXR-dependent apoAI- and ABCA1-dependent cholesterol efflux, by which disposal of excess arterial cholesterol deposits and atheroma regression can be achieved.
Taylor
Janice M W
JM
Vascular Biology Group, Glasgow Caledonian University, Cowcaddens Road, Glasgow, UK.
Borthwick
Faye
F
Bartholomew
Chris
C
Graham
Annette
A
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D001692:Biological Transport; D002460:Cell Line; D053493:Cholestanetriol 26-Monooxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D003563:Cyclic CMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006706:Homeostasis; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D006888:Hydroxycholesterols / Q000378:metabolism; D015151:Immunoblotting; D050356:Lipid Metabolism / Q000235:genetics; D008077:Lipoproteins, LDL / Q000378:metabolism; D000071518:Liver X Receptors; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D057093:Orphan Nuclear Receptors / Q000819:agonists / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011106:Polyisoprenyl Phosphates / Q000494:pharmacology; D011341:Probucol / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013449:Sulfonamides / Q000494:pharmacology; D014162:Transfection; D014280:Triglycerides / Q000378:metabolism; D015854:Up-Regulation; D000098682:Steroidogenic Acute Regulatory Protein; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D053493:Cholestanetriol 26-Monooxygenase; D002784:Cholesterol; D003563:Cyclic CMP; D004791:Enzyme Inhibitors; D006845:Hydrocarbons, Fluorinated; D006888:Hydroxycholesterols; D008077:Lipoproteins, LDL; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D010750:Phosphoproteins; D011106:Polyisoprenyl Phosphates; D011341:Probucol; D012333:RNA, Messenger; D013449:Sulfonamides; D014280:Triglycerides; D000098682:Steroidogenic Acute Regulatory Protein; C577836:ABCA1 protein, human; C505693:APOA1 protein, human; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C032629:acetyl-LDL; C053441:dibutyryl cyclic-3',5'-cytidine monophosphate; C076996:27-hydroxycholesterol; C002963:geranylgeranyl pyrophosphate