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Olive oil consumption is beneficial for health as it is associated with a decreased prevalence of cancer and cardiovascular diseases. Oleic acid is, by far, the most abundant component of olive oil. Since it can be made through de novo synthesis in animals, it is not an essential fatty acid. While it has become clear that dietary oleic acid regulates many biological processes, the signaling pathway involved in these regulations remains poorly defined. In this work we tested the impact of an oleic acid-rich diet on hepatic gene expression. We were particularly interested in addressing the contribution of Liver X Receptors (LXR) in the control of genes involved in hepatic lipogenesis, an essential process in whole body energy homeostasis. We used wild-type mice and transgenic mice deficient for both α and β Liver X Receptor isoforms (LXR-/-) fed a control or an oleate enriched diet. We observed that hepatic-lipid accumulation was enhanced as well as the expression of lipogenic genes in the liver of wild-type mice fed the oleate enriched diet. In contrast, none of these changes occurred in the liver of LXR-/- mice. Strikingly, oleate-rich diet reduced cholesterolemia in wild-type mice and induced signs of liver inflammation and damage in LXR-/- mice but not in wild-type mice. This work suggests that dietary oleic acid reduces cholesterolemia while promoting LXR-dependent hepatic lipogenesis without detrimental effects to the liver. [ABSTRACT FROM AUTHOR]

Non-alcoholic fatty liver diseases are the hepatic manifestation of metabolic syndrome. According to the classical pattern of NAFLD progression, de novo fatty acid synthesis has been incriminated in NAFLD progression. However, this hypothesis has been challenged by the re-evaluation of NAFLD development mechanisms together with the description of the role of lipogenic genes in NAFLD and with the recent observation that PGC-1β, a nuclear receptor/transcription factor coactivator involved in the transcriptional regulation of lipogenesis, displays protective effects against NAFLD/NASH progression. In this review, we focus on the implication of lipogenesis and triglycerides synthesis on the development of non-alcoholic fatty liver diseases and discuss the involvement of these pathways in the protective role of PGC-1β toward these hepatic manifestations. [ABSTRACT FROM AUTHOR]

Abstract: Since it is associated to the obesity epidemic, non alcoholic fatty liver disease (NAFLD) has become a major public health issue. NAFLD ranges from benign hepatic steatosis, i.e. abnormally elevated triglyceride accumulation, to non alcoholic steatohepatitis (NASH) that can lead to irreversible liver damages. The search for pharmacological and dietary approaches to treat or prevent NAFLD has pointed at nuclear receptors as sensible targets. Indeed, nuclear receptors are ligand-sensitive transcription factors that play a central role in hepatic lipid metabolism. Among nuclear receptors, the liver X receptor has been identified as an oxysterol receptor. It is involved in the control of various aspects of lipid metabolism that are reviewed in this manuscript. We highlight the role of LXR in the gut–liver axis and the studies that have provided a rationale for strategies specifically targeting the hepatic activity of LXR in NAFLD. [Copyright &y& Elsevier]

Background & Aims: Nutrients influence non-alcoholic fatty liver disease. Essential fatty acids deficiency promotes various syndromes, including hepatic steatosis, through increased de novo lipogenesis. The mechanisms underlying such increased lipogenic response remain unidentified. Methods: We used wild type mice and mice lacking Liver X Receptors to perform a nutrigenomic study that aimed at examining the role of these transcription factors. Results: We showed that, in the absence of Liver X Receptors, essential fatty acids deficiency does not promote steatosis. Consistent with this, Liver X Receptors are required for the elevated expression of genes involved in lipogenesis in response to essential fatty acids deficiency. Conclusions: This work identifies, for the first time, the central role of Liver X Receptors in steatosis induced by essential fatty acids deficiency. [Copyright &y& Elsevier]

Abstract: The Liver X Receptors (LXRs) α and β and the Peroxisome Proliferator-Activated Receptor α (PPARα) are transcription factors that belong to class II nuclear receptors. They drive the expression of genes involved in hepatic lipid homeostasis and therefore are important targets for the prevention and treatment of nonalcoholic fatty liver disease (NAFLD). LXRs and PPARα are regulated by endogenous ligands, oxysterols and fatty acid derived molecules, respectively. In the liver, pharmacological activation of LXRs leads to the over-expression of genes involved in de novo lipogenesis, while PPARα is critical for fatty acid catabolism in nutrient deprivation. Even if these two nuclear receptors seemed to play opposite parts, recent studies have highlighted that PPARα also influence the expression of genes involved in fatty acids synthesis. In this study, we used pharmacological approaches and genetically engineered mice to investigate the cross-talk between LXRs and PPARα in the regulation of genes responsible for lipogenesis. We first investigated the effect of T0901317 and fenofibrate, two synthetic agonists of LXRs and PPARα, respectively. As expected, T0901317 and fenofibrate induce expression of genes involved LXR-dependent and PPARα-dependent lipogenic responses. Considering such overlapping effect, we then tested whether LXR agonist may influence PPARα driven response and vice versa. We show that the lack of PPARα does not influence the effects of T0901317 on lipogenic genes expression. However, PPARα deficiency prevents the up-regulation of genes involved in ω-hydroxylation that are induced by the LXR agonist. In addition, over-expression of lipogenic genes in response to fenofibrate is decreased in LXR knockout mice as well as the expression of PPARα target genes involved in fatty acid oxidation. Altogether, our work provides in vivo evidence for a central interconnection between nuclear receptors that drive hepatic lipid metabolism in response to oxysterol and fatty acids. [Copyright &y& Elsevier]

A study published in the journal Diabetes, Obesity & Metabolism explores the effects of the drug empagliflozin on metabolic dysfunction-associated steatotic liver disease (MASLD) in a mouse model of lipoatrophic diabetes. The researchers found that empagliflozin prevented the development of MASLD in mice and reduced liver steatosis in older mice. The drug achieved these effects by reducing de novo lipogenesis, the process by which the liver produces new fat. The study suggests that empagliflozin could be a potential therapeutic option for managing MASLD associated with lipodystrophies. [Extracted from the article]

The liver plays a central role in the regulation of fatty acid metabolism, which is highly sensitive to transcriptional responses to nutrients and hormones. Transcription factors involved in this process include nuclear hormone receptors. One such receptor, PPARα, which is highly expressed in the liver and activated by a variety of fatty acids, is a critical regulator of hepatic fatty acid catabolism during fasting. The present study compared the influence of dietary fatty acids and fasting on hepatic PPARα-dependent responses. Pparaα-/- male mice and their wild-type controls were fed diets containing different fatty acids for 10 weeks prior to being subjected to fasting or normal feeding. In line with the role of PPARα in sensing dietary fatty acids, changes in chronic dietary fat consumption influenced liver damage during fasting. The changes were particularly marked in mice fed diets lacking essential fatty acids. However, fasting, rather than specific dietary fatty acids, induced acute PPARα activity in the liver. Taken together, the data imply that the potent signalling involved in triggering PPARα activity during fasting does not rely on essential fatty acid-derived ligand. [ABSTRACT FROM AUTHOR]

Abstract: Stearoyl-CoA Desaturase-1 (SCD1) is the rate limiting enzyme catalyzing the synthesis of monounsaturated fatty acids. Variation of SCD1 activity and the ratio of saturated to unsaturated fatty acids have been implicated in a variety of diseases including obesity, type II diabetes and cancers. In liver, many factors regulate SCD1 expression including dietary and hormonal factors such as insulin and leptin. We previously showed in hepatic cells that insulin acts through the PI3K and mTOR pathways to upregulate SCD1 expression. In the present study, using HepG2 cells, we characterized the signaling pathway mediating the leptin inhibitory response on SCD1 gene expression. We showed that leptin inhibits SCD1 at the transcriptional level. Inhibition of the ERK1/2 MAPK pathway with the PD98059 reverses the effect of leptin on SCD1 expression. Our data also demonstrated that the effect of leptin is entirely independent of the effect of insulin. Using the pharmaceutical inhibitors Ag490 and SL0101, we showed that the inhibitory effect of leptin is also mediated by the Janus Kinase 2 (Jak2) and p90RSK. EMSA and transfection experiments suggest a key role for the Sp1 transcription factor, which in turn may compete for the binding of other transcription factors such as AP-1, leading to the inhibition of SCD1 transcription. Taken together, our observations showed that, independently of insulin action, leptin exerts an inhibitory effect on SCD1 transcription via a signaling pathway implicating Jak2, ERK1/2, and p90RSK which probably targets the downstream transcription factor Sp1 on the SCD1 promoter. [Copyright &y& Elsevier]

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,β 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. [ABSTRACT FROM AUTHOR]

The Constitutive Androstane Receptor (CAR, NR1I3) has been newly described as a regulator of energy metabolism. A relevant number of studies using animal models of obesity suggest that CAR activation could be beneficial on the metabolic balance. However, this remains controversial and the underlying mechanisms are still unknown. This work aimed to investigate the effect of CAR activation on hepatic energy metabolism during physiological conditions, i.e. in mouse models not subjected to metabolic/nutritional stress. Gene expression profiling in the liver of CAR knockout and control mice on chow diet and treated with a CAR agonist highlighted CAR-mediated up-regulations of lipogenic genes, concomitant with neutral lipid accumulation. A strong CAR-mediated up-regulation of the patatin-like phospholipase domain-containing protein 3 ( Pnpla3 ) was demonstrated. Pnpla3 is a gene whose polymorphism is associated with the pathogenesis of nonalcoholic fatty liver disease (NAFLD) development. This observation was confirmed in human hepatocytes treated with the antiepileptic drug and CAR activator, phenobarbital and in immortalized human hepatocytes treated with CITCO. Studying the molecular mechanisms controlling Pnpla3 gene expression, we demonstrated that CAR does not act by a direct regulation of Pnpla3 transcription or via the Liver X Receptor but may rather involve the transcription factor Carbohydrate Responsive Element-binding protein. These data provide new insights into the regulation by CAR of glycolytic and lipogenic genes and on pathogenesis of steatosis. This also raises the question concerning the impact of drugs and environmental contaminants in lipid-associated metabolic diseases. [ABSTRACT FROM AUTHOR]

Background Obesity and the related entity metabolic syndrome are characterized by altered lipid metabolism and associated with increased morbidity risk for cardiovascular disease and cancer. Oxysterols belong to a large family of cholesterol-derived molecules known to play crucial role in many signaling pathways underlying several diseases. Little is known on the potential effect of obesity and metabolic syndrome on oxysterols in human. Objectives In this work, we questioned whether circulating oxysterols might be significantly altered in obese patients and in patients with metabolic syndrome. We also tested the potential correlation between circulating oxysterols and fatty acids. Methods 60 obese patients and 75 patients with metabolic syndrome were enrolled in the study along with 210 age- and sex-matched healthy subjects, used as control group. Plasma oxysterols were analyzed by isotope dilution GC/MS, and plasma fatty acids profiling was assessed by gas chromatography coupled with flame ionization detection. Results We found considerable differences in oxysterols profiling in the two disease groups that were gender-related. Compared to controls, males showed significant differences only in 4α- and 4β-hydroxycholesterol levels in obese and metabolic syndrome patients. In contrast, females showed consistent differences in 7-oxocholesterol, 4α-hydroxycholesterol, 25-hydroxycholesterol and triol. Concerning fatty acids, we found minor differences in the levels of these variables in males of the three groups. Significant changes were observed in plasma fatty acid profile of female patients with obesity or metabolic syndrome. We found significant correlations between various oxysterols and fatty acids. In particular, 4β-hydroxycholesterol, which is reduced in obesity and metabolic syndrome, correlated with a number of saturated and mono-unsaturated fatty acids that are end-products of de novo lipogenesis. Conclusions Our data provide the first evidence that obesity and metabolic syndrome are associated with major, gender-specific, changes in circulating oxysterols and fatty acids. These findings suggest a metabolic link between oxysterols and fatty acids, and that oxysterols may contribute to the epidemic diseases associated with obesity and metabolic syndrome in female. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) is a suspected endocrine disruptor highly prevalent in our environment since it is used as monomer of polycarbonate plastics and epoxy resins. Recent epidemiological and animal studies have suggested that BPA exposure may influence the development of obesity and related pathologies such as type 2 diabetes, and cardiovascular diseases. However, experimental studies have often focused on short-term exposures. In this study, we investigated the effect of several months of BPA exposure on hepatic and plasma metabolic markers in adult mice. Male CD1 mice were exposed during 8 months to five different BPA doses below or equivalent to the current no observed adverse effect level (NOAEL: 5000 μg/kg/day) through drinking water. Plasma lipid profiles and liver transcriptomic analysis were performed in control and BPA-treated animals. We report a specific impact of BPA exposure on glycaemia, glucose tolerance and cholesterolemia. Consistent with the hypercholesterolemia in BPA-treated animals, RT-qPCR performed on hepatic mRNA from same animals demonstrated an overexpression of key genes involved in cholesterol biosynthesis, namely, Mvd , Lss Hmgcr , and Sqle . BPA also induced the expression of the sterol regulatory element-binding proteins 2, a master regulator of hepatic cholesterol biosynthesis. As shown by the plasma lathosterol to cholesterol ratio, a surrogate marker for cholesterol biosynthesis, whole body cholesterol de novo synthesis was also increased in BPA-exposed animals. These original results are consistent with many epidemiological studies reporting on a link between BPA exposure and the onset of cardiovascular diseases. [ABSTRACT FROM AUTHOR]