LXRs; Oxysterol-activated nuclear receptors that regulate genes controlling lipid homeostasis
VASCULAR PHARMACOLOGY
Authors: Edwards, PA; Kennedy, MA; Mak, PA
Abstract
The Liver X Receptors (LXRalpha, NR1H3; LXRbeta, NR1H2) encode highly homologous transcription factors that are members of the nuclear receptor superfainily of proteins. Both LXRalpha and LXRbeta form heterodimers with the obligate partner 9-cis retinoic acid receptor alpha (RYRalpha; NR2B1). LXR/RXR heterodimers function as sensors for cellular oxysterols and, when activated by these agonists, increase the expression of genes that control sterol and fatty acid metabolism/homeostasis. These conclusions are based on studies that: (i) identified oxysterols as the natural ligands for both LXRalpha and LXRbeta; (ii) identified target genes that are activated by LXR/RXR; (iii) generated mice that were deficient in LXRalpha, LXRbeta or both LXRalpha and LXRbeta; (iv) identified synthetic LXR ligands that were extremely potent in vivo; and (v) demonstrated significant alterations in cholesterol and fatty acid homeostasis in animals in which LXR had been either activated or deleted. These findings suggest that synthetic LXR ligands may prove useful in the treatment of certain dyslipidemias. In this review, we summarize the current status of this rapidly moving area with a special emphasis on the potential for pharrnacological intervention. (C) 2002 Elsevier Science Inc. All rights reserved.
Ablation of Liver X receptors alpha and beta leads to spontaneous peripheral squamous cell lung cancer in mice
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Authors: Dai, Yu-bing; Miao, Yi-fei; Wu, Wan-fu; Li, Yu; D'Errico, Francesca; Su, Wen; Burns, Alan R.; Huang, Bo; Maneix, Laure; Warner, Margaret; Gustafsson, Jan-Ake
Abstract
The etiology of peripheral squamous cell lung cancer (PSCCa) remains unknown. Here, we show that this condition spontaneously develops in mice in which the genes for two oxysterol receptors, Liver X Receptor (LXR) alpha (Nr1h3) and beta (Nr1h2), are inactivated. By 1 y of age, most of these mice have to be euthanized because of severe dyspnea. Starting at 3 mo, the lungs of LXR alpha,beta(Dko) mice, but not of LXR alpha or LXR beta single knockout mice, progressively accumulate foam cells, so that by 1 y, the lungs are covered by a "golden coat." There is infiltration of inflammatory cells and progressive accumulation of lipid in the alveolar wall, type 2 pneumocytes, and macrophages. By 14 mo, there are three histological lesions: one resembling adenomatous hyperplasia, one squamous metaplasia, and one squamous cell carcinoma characterized by expression of transformation-related protein (p63), sex determining region Y-box 2 (Sox2), cytokeratin 14 (CK14), and cytokeratin 13 (CK13) and absence of thyroid transcription factor 1 (TTF1), and prosurfactant protein C (pro-SPC). RNA sequencing analysis at 12 mo confirmed a massive increase in markers of M1 macrophages and lymphocytes. The data suggest a previously unidentified etiology of PSCCa: cholesterol dysregulation and M1 macrophage-predominant lung inflammation combined with damage to, and aberrant repair of, lung tissue, particularly the peripheral parenchyma. The results raise the possibility that components of the LXR signaling may be useful targets in the treatment of PSCCa.