title: Liver X receptor agonists suppress vascular smooth muscle cell proliferation and inhibit neointima formation in balloon-injured rat carotid arteries.
abstract: The liver X receptors alpha and beta (LXRalpha and LXRbeta) are important regulators of cholesterol homeostasis in liver and macrophages. Synthetic LXR ligands prevent the development of atherosclerosis in murine models; however, the potential functional relevance of LXRs in vascular smooth muscle cells (VSMCs) has not been investigated. In the present study, we demonstrate that LXRs are expressed and functional in primary human coronary artery VSMCs (CASMCs). LXR ligands inhibited mitogen-induced VSMC proliferation and G1-->S phase progression of the cell cycle. Inhibition of G1 exit by LXR ligands was accompanied by a dose-dependent inhibition of retinoblastoma protein (Rb) phosphorylation, which functions as the key switch for G1-->S cell cycle progression. LXR ligands suppressed mitogen-induced degradation of the cyclin-dependent kinase inhibitor p27Kip1, attenuated cyclin D1 and cyclin A expression, and inhibited the expression of S phase-regulatory minichromosome maintenance protein 6. Stabilization of p27kip1 by LXR ligands was mediated by supressing the transcriptional activation of the S phase kinase-associated protein 2 (Skp2), an F-box protein that targets p27Kip1 for degradation. Inhibition of Rb phosphorylation and G1-->S cell cycle progression by LXR ligands was reversed in VSMCs overexpressing Skp2, indicating that Skp2 as an upstream regulator of p27Kip1 degradation plays a central role in LXR ligand-mediated inhibition of VSMC proliferation. Furthermore, adenovirus-mediated overexpression of the S phase transcription factor E2F, which is released after Rb phosphorylation, reversed the inhibitory effect of LXR ligands on VSMC proliferation and S phase gene expression, suggesting that the primary mechanisms by which LXR ligands inhibit VSMC proliferation occur upstream of Rb phosphorylation. Finally, neointima formation in a model of rat carotid artery balloon injury was significantly attenuated after treatment with the LXR ligand T1317 compared with vehicle-treated animals. These data demonstrate that LXR ligands inhibit VSMC proliferation and neointima formation after balloon injury and suggest that LXR ligands may constitute a novel therapy for proliferative vascular diseases. The full text of this article is available online at http://circres.ahajournals.org.
authors.affiliation: Division of Endocrinology, Diabetes, and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, USA.
authors.forename: Florian
authors.initials: F
authors.lastname: Blaschke
authors.forename: Olli
authors.initials: O
authors.lastname: Leppanen
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Takata
authors.forename: Evren
authors.initials: E
authors.lastname: Caglayan
authors.forename: Joey
authors.initials: J
authors.lastname: Liu
authors.forename: Michael C
authors.initials: MC
authors.lastname: Fishbein
authors.forename: Kai
authors.initials: K
authors.lastname: Kappert
authors.forename: Keiichi I
authors.initials: KI
authors.lastname: Nakayama
authors.forename: Alan R
authors.initials: AR
authors.lastname: Collins
authors.forename: Eckart
authors.initials: E
authors.lastname: Fleck
authors.forename: Willa A
authors.initials: WA
authors.lastname: Hsueh
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Law
authors.forename: Dennis
authors.initials: D
authors.lastname: Bruemmer
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D020212:Carotid Artery Injuries / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D003331:Coronary Vessels / Q000166:cytology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004268:DNA-Binding Proteins / Q000819:agonists / Q000502:physiology*; D016193:G1 Phase / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D006845:Hydrocarbons, Fluorinated; D006965:Hyperplasia; D007328:Insulin / Q000494:pharmacology; D008024:Ligands; D000071518:Liver X Receptors; D064151:Minichromosome Maintenance Complex Component 6; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism; D057093:Orphan Nuclear Receptors; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D016160:Retinoblastoma Protein / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D013449:Sulfonamides; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D017539:Tunica Intima / Q000187:drug effects / Q000473:pathology*; D017540:Tunica Media / Q000187:drug effects / Q000473:pathology*; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
chemical_list: D000924:Anticholesteremic Agents; D001565:Benzoates; D001596:Benzylamines; D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004268:DNA-Binding Proteins; D006845:Hydrocarbons, Fluorinated; D007328:Insulin; D008024:Ligands; D000071518:Liver X Receptors; D064151:Minichromosome Maintenance Complex Component 6; D057093:Orphan Nuclear Receptors; D010982:Platelet-Derived Growth Factor; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D044786:S-Phase Kinase-Associated Proteins; D013449:Sulfonamides; D025521:Tumor Suppressor Proteins; C493962:Cdkn1b protein, rat; C473027:GW 3965; C000605213:NR1H3 protein, human; C000605215:Nr1h3 protein, rat; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides; C103258:MCM6 protein, human