Gene Expression Profiling Reveals that PXR Activation Inhibits Hepatic PPARα Activity and Decreases FGF21 Secretion in Male C57Bl6/J Mice

Abstract

The pregnane X receptor (PXR) is the main nuclear receptor regulating the expression of xenobiotic-metabolizing enzymes and is highly expressed in the liver and intestine. Recent studies have highlighted its additional role in lipid homeostasis, however, the mechanisms of these regulations are not fully elucidated. We investigated the transcriptomic signature of PXR activation in the liver of adult wild-type vs. Pxr^-/- C57Bl6/J male mice treated with the rodent specific ligand pregnenolone 16α-carbonitrile (PCN). PXR activation increased liver triglyceride accumulation and significantly regulated the expression of 1215 genes, mostly xenobiotic-metabolizing enzymes. Among the down-regulated genes, we identified a strong peroxisome proliferator-activated receptor α (PPARα) signature. Comparison of this signature with a list of fasting-induced PPARα target genes confirmed that PXR activation decreased the expression of more than 25 PPARα target genes, among which was the hepatokine fibroblast growth factor 21 (Fgf21). PXR activation abolished plasmatic levels of FGF21. We provide a comprehensive signature of PXR activation in the liver and identify new PXR target genes that might be involved in the steatogenic effect of PXR. Moreover, we show that PXR activation down-regulates hepatic PPARα activity and FGF21 circulation, which could participate in the pleiotropic role of PXR in energy homeostasis.

Keywords: hepatokines; nuclear receptors; transcriptomics.

Figure 1

Effect of pregnenolone 16α-carbonitrile (PCN) treatment on liver parameters (a) and plasma biochemistry (b). Data are shown as mean ± SEM of n = 5–6 per group. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.005 for PCN effect using 2-way ANOVA and Tukey’s post-tests. $ p ≤ 0.05 for genotype effect. ALT: Alanine amino-transferase; FFA: Free fatty acids.

Figure 2

Impact of pregnane X receptor (PXR) activation on the hepatic transcriptome. (a) Principal component analysis (PCA) score plots of the whole transcriptomic dataset. (b) qPCR confirmation on selected genes. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.005 for PCN effect using 2-way ANOVA and Tukey’s post-tests. (c,f) Venn diagram representing the number of genes affected by PCN treatment. (d,g) Gene enrichment analyses of the PXR-target genes. (e,h) The 30 genes with the highest fold-changes upon PCN treatment.

Figure 3

Comparison between PXR and peroxisome proliferator-activated receptor α (PPARα) target genes. (a,d) Venn diagrams representing the number of genes up-(a) or down-(d) regulated upon fasting in Pparα^hep+/+ vs. Pparα^hep-/- mice. (b,e) Venn diagrams representing the number of genes regulated upon PPARα (red) or PXR (blue) activation. (c,f) Fold-changes for the genes that are shared in the previous Venn diagrams.

Figure 4

Impact of PXR activation on hepatic PPARα activity. Gene expression in the liver (a) derived from the microarray and from complementary qPCR experiments. (b) Plasma levels of FGF21. Data are mean ± SEM of n = 5–6 per group. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.005 for PCN effect, # p ≤ 0.05, ## p ≤ 0.01 for genotype effect using 2-way ANOVA and Tukey’s post-tests. UDL: Under the detection limit.