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Submitted on May 1, 2008
Accepted on June 10, 2008
gene transcription by Liver X Receptors
Institut Pasteur de Lille, Département d'Athérosclérose, Lille, F-59019, Inserm, U545, Lille, F59019, Faculté des Sciences Pharmaceutiques et Biologiques, Université de Lille 2, Lille, France F-59006; GlaxoSmithKline, Cardiovascular & Urogenital Center of Excellence for Drug Discovery, 25 Avenue du Québec, 91951 Les Ulis, France; CNRS UMR6247 - GReD; Centre de Recherche en Nutrition Humaine d'Auvergne; Clermont Université 24 avenue des Landais, 63177 Aubière, France
* To whom correspondence should be addressed. E-mail: philippe.delerive{at}genfit.com.
LXR
and LXR
(Liver X Receptor) are ligand-activated transcription factors belonging to the nuclear receptor super-family. They have been identified as key players in cholesterol homeostasis, lipid and glucose metabolism as well as immune and inflammatory responses. In the small intestine, LXRs have been shown to regulate cholesterol absorption and excretion but also to promote HDL biogenesis via the ABCA1 signaling pathway. Here, using gene expression assays, we identified PPAR
as an intestine-specific LXR target gene. Chronic administration of LXR synthetic agonists led to a significant increase of PPAR
mRNA levels in the small intestine but not in the liver. In addition, this specific PPAR
gene up-regulation occurred in the duodenum, jejunum and ileum in a dose-dependent manner and translated at the protein level as demonstrated by western blot analysis. Furthermore, PPAR
gene induction was completely abolished in LXR-deficient mice. Finally, the physiological relevance of LXR-mediated PPAR
up-regulation in the small intestine was assessed in PPAR
-deficient mice. Administration of a synthetic LXR agonist to wild type mice led to the induction of several PPAR
target genes including PDK4 and CPT1. Those effects were completely abolished in PPAR
-deficient mice demonstrating the biological relevance of this LXR-PPAR
transcriptional cascade. Taken together, these results demonstrate that PPAR
is an intestine-specific LXR target gene and suggest the existence of a transcriptional cross talk between those members of the nuclear receptor super-family.
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