title: Pioglitazone enhances cholesterol efflux from macrophages by increasing ABCA1/ABCG1 expressions via PPARγ/LXRα pathway: findings from in vitro and ex vivo studies.
abstract: OBJECTIVE
  Pioglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) agonist, reportedly reduces cardiovascular events in diabetic patients. ATP cassette binding transporters (ABC) A1 and G1 are pivotal molecules for cholesterol efflux (ChE) from macrophages and high density-lipoprotein biogenesis, and the A1 transporter is regulated by a PPARγ-liver receptor X (LXR) pathway. Also, pioglitazone induces ABCG1 expression, though the exact mechanism remains unclear. We therefore investigated the effects of pioglitazone on ABCA1/G1 expression in vitro and ex vivo.
  
  
  METHODS
  The effects of pioglitazone on ChE and ABCA1/G1 expressions in macrophages were assessed. Then, mRNA was quantified in macrophages when PPARγ/LXR inhibition by siRNA or overexpression of oxysterol sulfotransferase was performed. ABCA1/G1 promoter activity with mutated LXR-responsive elements was also measured. As an ex vivo study, 15 type 2 diabetic patients were administered pioglitazone or placebo, and ChE assays and protein expressions were determined using macrophages cultured with the corresponding sera.
  
  
  RESULTS
  Pioglitazone increased LXRα/ABCA1/G1 expressions, which enhanced ChE from macrophages. Inhibition of PPARγ/LXR pathways revealed that LXR was primarily involved in pioglitazone's transactivation of ABCA1 but only partially involved for ABCG1. Promoter assays showed that ABCG1 was regulated more by the promoter in intron 4 than that upstream of exon 1 but both promoters were responsive to LXR activation. Sera obtained after pioglitazone treatment promoted ChE and ABCA1/G1 expressions in macrophages.
  
  
  CONCLUSIONS
  Pioglitazone enhanced ChE from macrophages by increasing ABCA1/G1 in LXR-dependent and -independent manners. Our comparable in vitro and ex vivo results shed new light on pioglitazone's novel anti-atherogenic property.
authors.affiliation: Division of Anti-aging, Department of Internal Medicine, National Defense Medical College, 3-2 Namiki, Tokorozawa 359-8513, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Ozasa
authors.forename: Makoto
authors.initials: M
authors.lastname: Ayaori
authors.forename: Maki
authors.initials: M
authors.lastname: Iizuka
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Terao
authors.forename: Harumi
authors.initials: H
authors.lastname: Uto-Kondo
authors.forename: Emi
authors.initials: E
authors.lastname: Yakushiji
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takiguchi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nakaya
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hisada
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Uehara
authors.forename: Masatsune
authors.initials: M
authors.lastname: Ogura
authors.forename: Makoto
authors.initials: M
authors.lastname: Sasaki
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Komatsu
authors.forename: Shunpei
authors.initials: S
authors.lastname: Horii
authors.forename: Seibu
authors.initials: S
authors.lastname: Mochizuki
authors.forename: Michihiro
authors.initials: M
authors.lastname: Yoshimura
authors.forename: Katsunori
authors.initials: K
authors.lastname: Ikewaki
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis*; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D000071518:Liver X Receptors; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D057093:Orphan Nuclear Receptors / Q000096:biosynthesis*; D047495:PPAR gamma / Q000378:metabolism*; D000077205:Pioglitazone; D034622:RNA Interference; D045162:Thiazolidinediones / Q000494:pharmacology*
chemical_list: C577836:ABCA1 protein, human; C419353:ABCG1 protein, human; D064286:ATP Binding Cassette Transporter 1; D000070998:ATP Binding Cassette Transporter, Subfamily G, Member 1; D018528:ATP-Binding Cassette Transporters; D007004:Hypoglycemic Agents; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; D057093:Orphan Nuclear Receptors; D047495:PPAR gamma; D045162:Thiazolidinediones; D002784:Cholesterol; D000077205:Pioglitazone