title: Regulation of macrophage cholesterol efflux through hydroxymethylglutaryl-CoA reductase inhibition: a role for RhoA in ABCA1-mediated cholesterol efflux.
abstract: The cholesterol biosynthetic pathway produces numerous signaling molecules. Oxysterols through liver X receptor (LXR) activation regulate cholesterol efflux, whereas the non-sterol mevalonate metabolite, geranylgeranyl pyrophosphate (GGPP), was recently demonstrated to inhibit ABCA1 expression directly, through antagonism of LXR and indirectly through enhanced RhoA geranylgeranylation. We used HMG-CoA reductase inhibitors (statins) to test the hypothesis that reduced synthesis of mevalonate metabolites would enhance cholesterol efflux and attenuate foam cell formation. Preincubation of THP-1 macrophages with atorvastatin, dose dependently (1-10 microm) stimulated cholesterol efflux to apolipoprotein AI (apoAI, 10-60%, p < 0.05) and high density lipoprotein (HDL(3)) (2-50%, p < 0.05), despite a significant decrease in cholesterol synthesis (2-90%). Atorvastatin also increased ABCA1 and ABCG1 mRNA abundance (30 and 35%, p < 0.05). Addition of mevalonate, GGPP or farnesyl pyrophosphate completely blocked the statin-induced increase in ABCA1 expression and apoAI-mediated cholesterol efflux. A role for RhoA was established, because two inhibitors of Rho protein activity, a geranylgeranyl transferase inhibitor and C3 exoenzyme, increased cholesterol efflux to apoAI (20-35%, p < 0.05), and macrophage expression of dominant-negative RhoA enhanced cholesterol efflux to apoAI (20%, p < 0.05). In addition, atorvastatin increased the RhoA levels in the cytosol fraction and decreased the membrane localization of RhoA. Atorvastatin treatment activated peroxisome proliferator activated receptor gamma and increased LXR-mediated gene expression suggesting that atorvastatin induces cholesterol efflux through a molecular cascade involving inhibition of RhoA signaling, leading to increased peroxisome proliferator activated receptor gamma activity, enhanced LXR activation, increased ABCA1 expression, and cholesterol efflux. Finally, statin treatment inhibited cholesteryl ester accumulation in macrophages challenged with atherogenic hypertriglyceridemic very low density lipoproteins indicating that statins can regulate foam cell formation.
authors.affiliation: Robarts Research Institute, Vascular Biology Group, and the Departments of Medicine and Biochemistry, the University of Western Ontario, London, Ontario N6A 5K8, Canada.
authors.forename: Carmen A
authors.initials: CA
authors.lastname: Argmann
authors.forename: Jane Y
authors.initials: JY
authors.lastname: Edwards
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Sawyez
authors.forename: Caroline H
authors.initials: CH
authors.lastname: O'Neil
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hegele
authors.forename: J Geoffrey
authors.initials: JG
authors.lastname: Pickering
authors.forename: Murray W
authors.initials: MW
authors.lastname: Huff
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D000069059:Atorvastatin; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D006538:Heptanoic Acids / Q000494:pharmacology; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism*; D008798:Mevalonic Acid / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D047495:PPAR gamma / Q000378:metabolism; D010766:Phosphorylation; D011106:Polyisoprenyl Phosphates / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012717:Sesquiterpenes; D014162:Transfection; D015854:Up-Regulation; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D004224:Diterpenes; D004791:Enzyme Inhibitors; D006538:Heptanoic Acids; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008074:Lipoproteins; D047495:PPAR gamma; D011106:Polyisoprenyl Phosphates; D011758:Pyrroles; D012333:RNA, Messenger; D012717:Sesquiterpenes; C004808:farnesyl pyrophosphate; D002784:Cholesterol; D000069059:Atorvastatin; D006903:Hydroxymethylglutaryl CoA Reductases; D020742:rhoA GTP-Binding Protein; C002963:geranylgeranyl pyrophosphate; D008798:Mevalonic Acid