Niemann–Pick C1 like 1 gene expression is down-regulated by LXR activators in the intestine

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Abstract

Niemann–Pick C1 like 1 (NPC1L1) is a protein critical for intestinal cholesterol absorption. The nuclear receptors peroxisome proliferator-activated receptor alpha (PPARα) and liver X receptors (LXRα and LXRβ) are major regulators of cholesterol homeostasis and their activation results in a reduced absorption of intestinal cholesterol. The goal of this study was to define the role of PPARα and LXR nuclear receptors in the regulation of NPC1L1 gene expression. We show that LXR activators down-regulate NPC1L1 mRNA levels in the human enterocyte cell line Caco-2/TC7, whereas PPARα ligands have no effect. Furthermore, NPC1L1 mRNA levels are decreased in vivo, in duodenum of mice treated with the LXR agonist T0901317. In conclusion, the present study identifies NPC1L1 as a novel LXR target gene further supporting a crucial role of LXR in intestinal cholesterol homeostasis.

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Materials and methods

Caco-2/TC7 cell culture. Cell culture reagents were obtained from Invitrogen and microporous PET membrane inserts (23.1 mm, 3 μm pore size) from Becton Dickinson. Caco-2/TC7 cells (kindly provided by Dr. M. Rousset INSERM U505) were routinely grown in plastic flasks (TPP, ATGC) under a humidified atmosphere containing 10% CO2, at 37 °C, in Dulbecco’s modified essential medium containing 25 mM glucose and glutamax, supplemented with penicillin/streptomycin (100 IU/ml and 100 g/ml, respectively), 1%

PPARα ligands do not regulate NPC1L1 gene expression

Treatment with PPARα ligands has been shown to decrease intestinal cholesterol absorption [16]. To test whether PPARα is implicated in NPC1L1 regulation, polarized Caco-2/TC7 cells were treated with different specific PPARα agonists and hNPC1L1 mRNA expression level was determined. Fig. 1A shows that none of the PPARα agonists tested was able to regulate hNPC1L1 gene expression. However, in the same experiment, hPDK4 was highly up-regulated by all the PPARα ligands tested (Fig. 1B). These

Discussion

NPC1L1 has been shown to play a central role in intestinal cholesterol absorption. Given the role of PPARα and LXRα in cholesterol homeostasis, we tested the possibility of a regulation of NPC1L1 gene expression by these nuclear receptors. In this report, we demonstrate that NPC1L1 gene expression is repressed by LXR but not by PPARα agonists both in mice in vivo and in a human enterocyte cell line in vitro.

Previously, it has been reported that LXRα agonists inhibit intestinal cholesterol

Acknowledgments

This work was supported by grants from the Fondation Leducq and the Groupe Lillois de Recherche en Pathologie Vasculaire - Laboratoires Servier (to C.D.). We thank Bruno Derudas for his technical assistance and K. Bertrand (Genfit SA, France) and P. Brown (Glaxo Smith Kline) for providing the T0901317 and GW3965 compounds and the GW7647 compound, respectively.

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