title: Mode of peroxisome proliferator-activated receptor γ activation by luteolin.
abstract: The peroxisome proliferator-activated receptor γ (PPARγ) is a target for treatment of type II diabetes and other conditions. PPARγ full agonists, such as thiazolidinediones (TZDs), are effective insulin sensitizers and anti-inflammatory agents, but their use is limited by adverse side effects. Luteolin is a flavonoid with anti-inflammatory actions that binds PPARγ but, unlike TZDs, does not promote adipocyte differentiation. However, previous reports suggested variously that luteolin is a PPARγ agonist or an antagonist. We show that luteolin exhibits weak partial agonist/antagonist activity in transfections, inhibits several PPARγ target genes in 3T3-L1 cells (LPL, ORL1, and CEBPα) and PPARγ-dependent adipogenesis, but activates GLUT4 to a similar degree as rosiglitazone, implying gene-specific partial agonism. The crystal structure of the PPARγ ligand-binding domain (LBD) reveals that luteolin occupies a buried ligand-binding pocket (LBP) but binds an inactive PPARγ LBD conformer and occupies a space near the β-sheet region far from the activation helix (H12), consistent with partial agonist/antagonist actions. A single myristic acid molecule simultaneously binds the LBP, suggesting that luteolin may cooperate with other ligands to bind PPARγ, and molecular dynamics simulations show that luteolin and myristic acid cooperate to stabilize the Ω-loop among H2', H3, and the β-sheet region. It is noteworthy that luteolin strongly suppresses hypertonicity-induced release of the pro-inflammatory interleukin-8 from human corneal epithelial cells and reverses reductions in transepithelial electrical resistance. This effect is PPARγ-dependent. We propose that activities of luteolin are related to its singular binding mode, that anti-inflammatory activity does not require H12 stabilization, and that our structure can be useful in developing safe selective PPARγ modulators.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP, Brazil.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Puhl
authors.forename: Amanda
authors.initials: A
authors.lastname: Bernardes
authors.forename: Rodrigo L
authors.initials: RL
authors.lastname: Silveira
authors.forename: Jing
authors.initials: J
authors.lastname: Yuan
authors.forename: Jéssica L O
authors.initials: JL
authors.lastname: Campos
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Saidemberg
authors.forename: Mario S
authors.initials: MS
authors.lastname: Palma
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Cvoro
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Ayers
authors.forename: Paul
authors.initials: P
authors.lastname: Webb
authors.forename: Peter S
authors.initials: PS
authors.lastname: Reinach
authors.forename: Munir S
authors.initials: MS
authors.lastname: Skaf
authors.forename: Igor
authors.initials: I
authors.lastname: Polikarpov
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D047311:Luteolin / Q000737:chemistry / Q000494:pharmacology*; D051379:Mice; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D019814:Myristic Acid / Q000737:chemistry; D047495:PPAR gamma / Q000819:agonists* / Q000737:chemistry / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000037:antagonists & inhibitors / Q000494:pharmacology
chemical_list: D017931:DNA Primers; D047495:PPAR gamma; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D019814:Myristic Acid; D047311:Luteolin