Liver X Receptor Agonists Suppress Vascular Smooth Muscle Cell Proliferation and Inhibit Neointima Formation in Balloon-Injured Rat Carotid Arteries

Abstract

Abstract-The liver X receptors ␣ and ␤ (LXR␣ and LXR␤) 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 G 1 3 S phase progression of the cell cycle. Inhibition of G 1 exit by LXR ligands was accompanied by a dose-dependent inhibition of retinoblastoma protein (Rb) phosphorylation, which functions as the key switch for G 1 3 S cell cycle progression. LXR ligands suppressed mitogen-induced degradation of the cyclin-dependent kinase inhibitor p27 Kip1 , attenuated cyclin D1 and cyclin A expression, and inhibited the expression of S phase-regulatory minichromosome maintenance protein 6. Stabilization of p27 kip1 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 G 1 3 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. (Circ Res. 2004;95:e110-e123.) Key Words: vascular smooth muscle cell Ⅲ liver X receptor Ⅲ arterial injury C ardiovascular disease is the leading cause of mortality in industrialized nations, accounting for nearly 50% of all deaths. 1 Vascular smooth muscle cell (VSMC) activation, migration, and proliferation in response to injury play not only a decisive role for development of atherosclerosis but are also the primary pathophysiologic mechanism resulting in the failure of procedures used to treat occlusive proliferative atherosclerotic diseases, such as postangioplasty restenosis, transplant vasculopathy, and vein bypass graft failure. 2,3 Although much effort has been devoted to targeting VSMC activation and proliferation, effective t...

The liver X receptor agonist T0901317 acts as androgen receptor antagonist in human prostate cancer cells

“…In spite of its undesirable side effects, T0901317 is still a popular reagent for LXR signaling-related research. Administration of the LXR agonist T0901317 in mouse disease models was reported to be effective for treatment of atherosclerosis, diabetes, Alzheimer's disease, and cancer [9][10][11][12][13][14][15]. The concentration of T0901317 to exhibit these therapeutic effects in vitro range between 1-10 μM [10][11][12][13][14][15].…”

“…T0901317 is the most commonly used LXR agonist for investigating physiological roles of the LXRs. Treatment with T0901317 has been reported to improve several disease murine models, including lowering of serum and liver cholesterol level, inhibition of atherosclerosis development, stimulation of insulin secretion, improvement of glucose tolerance, activation of anti-inflammatory effects, and reduction of amyloid beta production related to Alzheimer's disease [9][10][11][12][13][14]. Recently, we reported that T0901317 suppressed growth of prostate tumors in athymic mice [15].…”

Activation of liver X receptors inhibits pancreatic islet beta cell proliferation through cell cycle arrest

“…Furthermore, GW3965 exerted an effect similar to T1317 (results not shown). It has been reported that LXR agonists suppress proliferation of different cell types [17,18]. To further examine the effects of LXR activation on pancreatic beta cell growth, two different methods were used.…”

“…Previous studies have reported that levels of LXRα and LXRβ are elevated in the pancreatic beta cells of rodent models of type 2 diabetes and these receptors have been implicated as important regulators of glucose and insulin metabolism [14][15][16]. In addition, it has been recently reported that activation of LXRs by T0901317 (T1317), a synthetic agonist, inhibits the proliferation of cancer cells [17] and vascular smooth muscle cells [18], partially through p27 protein level upregulation. However, the role of LXRs in the regulation of pancreatic beta cell proliferation is not clear.…”

A Nuclear Receptor Corepressor–Dependent Pathway Mediates Suppression of Cytokine-Induced C-Reactive Protein Gene Expression by Liver X Receptor

“…39 Human CRP cDNA was obtained from Dr Alok Agrawal (East Tennessee State University, Johnson City). Blots were cohybridized with human GAPDH cDNA (SigmaAldrich) to assess equal loading of samples.…”