The protective role of liver X receptor (LXR) during fumonisin B1-induced hepatotoxicity.

Fumonisin B1 (FB1), a congener of fumonisins produced by Fusarium species, is the most abundant and most toxicologically active fumonisin. FB1 causes severe mycotoxicosis in animals, including nephrotoxicity, hepatotoxicity, and disruption of the intestinal barrier. However, mechanisms associated with FB1 toxicity are still unclear. Preliminary studies have highlighted the role of liver X receptors (LXRs) during FB1 exposure. LXRs belong to the nuclear receptor family and control the expression of genes involved in cholesterol and lipid homeostasis. In this context, the toxicity of FB1 was compared in female wild-type (LXR+/+) and LXRα,ß double knockout (LXR-/-) mice in the absence or presence of FB1 (10 mg/kg body weight/day) for 28 days. Exposure to FB1 supplemented in the mice's drinking water resulted in more pronounced hepatotoxicity in LXR-/- mice compared to LXR+/+ mice, as indicated by hepatic transaminase levels (ALT, AST) and hepatic inflammatory and fibrotic lesions. Next, the effect of FB1 exposure on the liver transcriptome was investigated. FB1 exposure led to a specific transcriptional response in LXR-/- mice that included altered cholesterol and bile acid homeostasis. ELISA showed that these effects were associated with an elevated FB1 concentration in the plasma of LXR-/- mice, suggesting that LXRs participate in intestinal absorption and/or clearance of the toxin. In summary, this study demonstrates an important role of LXRs in protecting the liver against FB1-induced toxicity, suggesting an alternative mechanism not related to the inhibition of sphingolipid synthesis for mycotoxin toxicity.

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

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.

The pregnane X receptor drives sexually dimorphic hepatic changes in lipid and xenobiotic metabolism in response to gut microbiota in mice.

BACKGROUND: The gut microbiota-intestine-liver relationship is emerging as an important factor in multiple hepatic pathologies, but the hepatic sensors and effectors of microbial signals are not well defined. RESULTS: By comparing publicly available liver transcriptomics data from conventional vs. germ-free mice, we identified pregnane X receptor (PXR, NR1I2) transcriptional activity as strongly affected by the absence of gut microbes. Microbiota depletion using antibiotics in Pxr+/+ vs Pxr-/- C57BL/6J littermate mice followed by hepatic transcriptomics revealed that most microbiota-sensitive genes were PXR-dependent in the liver in males, but not in females. Pathway enrichment analysis suggested that microbiota-PXR interaction controlled fatty acid and xenobiotic metabolism. We confirmed that antibiotic treatment reduced liver triglyceride content and hampered xenobiotic metabolism in the liver from Pxr+/+ but not Pxr-/- male mice. CONCLUSIONS: These findings identify PXR as a hepatic effector of microbiota-derived signals that regulate the host's sexually dimorphic lipid and xenobiotic metabolisms in the liver. Thus, our results reveal a potential new mechanism for unexpected drug-drug or food-drug interactions. Video abstract.

Hepatocyte-specific deletion of Pparα promotes NAFLD in the context of obesity.

Peroxisome proliferator activated receptor α (PPARα) acts as a fatty acid sensor to orchestrate the transcription of genes coding for rate-limiting enzymes required for lipid oxidation in hepatocytes. Mice only lacking Pparα in hepatocytes spontaneously develop steatosis without obesity in aging. Steatosis can develop into non alcoholic steatohepatitis (NASH), which may progress to irreversible damage, such as fibrosis and hepatocarcinoma. While NASH appears as a major public health concern worldwide, it remains an unmet medical need. In the current study, we investigated the role of hepatocyte PPARα in a preclinical model of steatosis. For this, we used High Fat Diet (HFD) feeding as a model of obesity in C57BL/6 J male Wild-Type mice (WT), in whole-body Pparα- deficient mice (Pparα-/-) and in mice lacking Pparα only in hepatocytes (Pparαhep-/-). We provide evidence that Pparα deletion in hepatocytes promotes NAFLD and liver inflammation in mice fed a HFD. This enhanced NAFLD susceptibility occurs without development of glucose intolerance. Moreover, our data reveal that non-hepatocytic PPARα activity predominantly contributes to the metabolic response to HFD. Taken together, our data support hepatocyte PPARα as being essential to the prevention of NAFLD and that extra-hepatocyte PPARα activity contributes to whole-body lipid homeostasis.