title: PPARγ ligand ciglitazone inhibits TNFα-induced ICAM-1 in human airway smooth muscle cells.
abstract: BACKGROUND
  Modification of human airway smooth muscle (ASM) function by proinflammatory cytokines has been regarded as a potential mechanism underlying bronchial hyperresponsiveness in asthma. Human ASM cells express intercellular adhesion molecule (ICAM)-1 in response to cytokines. Synthetic ligands for peroxisome proliferator-activated receptor (PPAR)γ reportedly possess anti-inflammatory and immunomodulatory properties. In this study, we examined whether ciglitazone, a synthetic PPARγ ligand, can modulate the basal and tumor necrosis factor (TNF)α-induced ICAM1 gene expression in human ASM cells.
  
  
  METHODS
  Human ASM cells were treated with TNFα. ICAM-1 expression was assessed by flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. PPARγ activity was inhibited by target-specific small interfering (si) RNA targeting PPARγ and GW9662, a PPARγ antagonist. Activity of nuclear factor (NF)-κB was assessed by using immunoblot analysis, immune-confocal images, and electrophoretic mobility shift assay (EMSA).
  
  
  RESULTS
  By flow cytometry, ciglitazone alone had no effect on ICAM-1 expression in ASM cells, but inhibited ICAM-1 expression in response to TNFα (10 ng/ml) in a dose-dependent manner (1-10 μM). It also inhibited TNFα-induced ICAM1 gene expression by RT-PCR analysis. Knockdown of PPARγ gene by target-specific siRNA targeting PPARγ enhanced ICAM-1 expression and the inhibitory effect of ciglitazone on TNFα-induced ICAM-1 expression was reversed by PPARγ siRNA and GW9662. SN-50 (10 μg/ml), an inhibitor for nuclear translocation of NF-κB, inhibited TNFα-induced ICAM-1 expression. Ciglitazone did not prevent TNFα-induced degradation of the cytosolic inhibitor of NF-κB (IκB), but inhibited the nuclear translocation of p65 induced by TNFα and suppressed the NF-κB/DNA binding activity.
  
  
  CONCLUSIONS
  These findings suggest that ciglitazone inhibits TNFα-induced ICAM1 gene expression in human ASM cells through the ligand-dependent PPARγ activation and NF-κB-dependent pathway.
authors.affiliation: Department of Thoracic Medicine, Chang Gung Memorial Hospital at Linkou, Chang Gung University College of Medicine, Taoyuan, Taiwan.
authors.forename: Chien-Da
authors.initials: CD
authors.lastname: Huang
authors.forename: Te-Chih
authors.initials: TC
authors.lastname: Hsiung
authors.forename: Shu-Chuan
authors.initials: SC
authors.lastname: Ho
authors.forename: Kang-Yun
authors.initials: KY
authors.lastname: Lee
authors.forename: Yao-Fei
authors.initials: YF
authors.lastname: Chan
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Kuo
authors.forename: Shu-Min
authors.initials: SM
authors.lastname: Lin
authors.forename: Chun-Hua
authors.initials: CH
authors.lastname: Wang
authors.forename: Horng-Chyuan
authors.initials: HC
authors.lastname: Lin
authors.forename: Han-Pin
authors.initials: HP
authors.lastname: Kuo
mesh_terms: D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D047495:PPAR gamma / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D045162:Thiazolidinediones / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D016207:Cytokines; D008024:Ligands; D016328:NF-kappa B; D047495:PPAR gamma; D045162:Thiazolidinediones; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; C039671:ciglitazone