Progress and challenges of selective Farnesoid X Receptor modulation.

Bile acids are amphipathic molecules that were previously known to serve as fat solubilizers in the intestine in postprandial conditions. In the last two decades, bile acids have been recognized as signaling molecules regulating energy metabolism pathways via, amongst others, the farnesoid X receptor (FXR). Upon bile acid activation, FXR controls expression of genes involved in bile acid, lipid, glucose and amino acid metabolism. In addition, FXR activation has been shown to limit the inflammatory response. The central role of FXR in various aspects of metabolism and inflammation makes FXR an attractive drug target for several diseases, such as obesity, metabolic syndrome, non-alcoholic steatohepatitis, cholestasis and chronic inflammatory diseases of the liver and intestine. However, most of the currently available compounds impact on all discovered FXR-mediated functions and may have, on top of beneficial effects, undesired biological actions depending on the disease. Therefore, research efforts are increasingly focused on the development of selective FXR modulators, i.e. selective bile acid receptor modulators (SBARMs), aimed at limiting the potential side-effects of conventional full FXR agonists upon chronic treatment. Here, we review the rationale for the design of SBARMs comprising dissociation between metabolic and inflammatory signaling, gene-selective and tissue-specific targeting. We discuss the potential structural mechanisms underlying the binding properties of dissociating ligands of FXR in light of ongoing efforts on the generation of dissociated ligands for otxher nuclear receptors, as well as their pharmacological and therapeutic potential

Farnesoid X receptor : A "homeostat" for hepatic nutrient metabolism

The Farnesoid X receptor (FXR) is a nuclear receptor activated by bile acids (BAs). BAs are amphipathic molecules that serve as fat solubilizers in the intestine under postprandial conditions. In the post-absorptive state, BAs bind FXR in the hepatocytes, which in turn provides feedback signals on BA synthesis and transport and regulates lipid, glucose and amino acid metabolism. Therefore, FXR acts as a homeostat of all three classes of nutrients, fats, sugars and proteins. Here we re-analyze the function of FXR in the perspective of nutritional metabolism, and discuss the role of FXR in liver energy homeostasis in postprandial, post-absorptive and fasting/starvation states. FXR, by regulating nutritional metabolism, represses autophagy in conditions of nutrient abundance, and controls the metabolic needs of proliferative cells. In addition, FXR regulates inflammation via direct effects and via its impact on nutrient metabolism. These functions indicate that FXR is an attractive therapeutic target for liver diseases

Quantitative liver proteomics identifies FGF19 targets that couple metabolism and proliferation

Fibroblast growth factor 19 (FGF19) is a gut-derived peptide hormone that is produced following activation of Farnesoid X Receptor (FXR). FGF19 is secreted and signals to the liver, where it contributes to the homeostasis of bile acid (BA), lipid and carbohydrate metabolism. FGF19 is a promising therapeutic target for the metabolic syndrome and cholestatic diseases, but enthusiasm for its use has been tempered by FGF19-mediated induction of proliferation and hepatocellular carcinoma. To inform future rational design of FGF19-variants, we have conducted temporal quantitative proteomic and gene expression analyses to identify FGF19-Targets related to metabolism and proliferation. Mice were fasted for 16 hours, and injected with human FGF19 (1 mg/kg body weight) or vehicle. Liver protein extracts (containing light lysine) were mixed 1:1 with a spike-in protein extract from 13C6-lysine metabolically labelled mouse liver (containing heavy lysine) and analysed by LC-MS/MS. Our analyses provide a resource of FGF19 target proteins in the liver. 189 proteins were upregulated (≥ 1.5 folds) and 73 proteins were downregulated (≤ -1.5 folds) by FGF19. FGF19 treatment decreased the expression of proteins involved in fatty acid (FA) synthesis, i.e., Fabp5, Scd1, and Acsl3 and increased the expression of Acox1, involved in FA oxidation. As expected, FGF19 increased the expression of proteins known to drive proliferation (i.e., Tgfbi, Vcam1, Anxa2 and Hdlbp). Importantly, many of the FGF19 targets (i.e., Pdk4, Apoa4, Fas and Stat3) have a dual function in both metabolism and cell proliferation. Therefore, our findings challenge the development of FGF19-variants that fully uncouple metabolic benefit from mitogenic potential

Splenic dendritic cell involvement in FXR-mediated amelioration of DSS colitis

Inflammatory Bowel Disease (IBD) is a multifactorial disorder involving dysregulation of the immune response and bacterial translocation through the intestinal mucosal barrier. Previously, we have shown that activation of the bile acid sensor Farnesoid X Receptor (FXR), which belongs to the family of nuclear receptors, improves experimental intestinal inflammation, decreasing expression of pro-inflammatory cytokines and protecting the intestinal barrier.Here, we aimed to investigate the immunological mechanisms that ameliorate colitis when FXR is activated. We analyzed by FACS immune cell populations in mesenteric lymph nodes (MLN) and in the spleen to understand whether FXR activation alters the systemic immune response. We show that FXR activation by obeticholic acid (OCA) has systemic anti-inflammatory effects that include increased levels of plasma IL-10, inhibition of both DSS-colitis associated decrease in splenic dendritic cells (DCs) and increase in Tregs. Impact of OCA on DC relative abundance was seen in spleen but not MLN, possibly related to the increased FXR expression in splenic DCs compared to MLN DCs. Moreover, FXR activation modulates the chemotactic environment in the colonic site of inflammation, as Madcam1 expression is decreased, while Ccl25 is upregulated. Together, our data suggest that OCA treatment elicits an anti-inflammatory immune status including retention of DCs in the spleen, which is associated with decreased colonic inflammation. Pharmacological FXR activation is therefore an attractive new drug target for treatment of IBD

FGF19 elicits expression changes in target genes of tumorigenic regulators.

<p>(A) Ingenuity upstream regulator analysis applied to protein changes observed upon FGF19 treatment for 12h. Prediction of upstream regulators is based on the overlap between the dataset proteins and the genes that are regulated by a transcription factor/hormone/compound, based on the knowledge included in Ingenuity database (overlap p-value <0.01). Green bars, upstream regulators with positive activation z-score; grey bars, upstream regulators with negative activation z-score.</p

FGF19 modulates expression of proteins involved in metabolism and cell survival.

<p>(A) IPA of pathways enriched in mice treated with FGF19 for 12h compared to vehicle control. For the analysis, proteins with fold change ≥1.3 FGF19 over vehicle were included. Pathways related to physiology or disease that were significantly enriched (p-value < 0.01) are ranked in function of their activation z-score and grouped into functional classes. (B) Venn Diagram representation of proteins changed upon FGF19 treatment that are involved in metabolism and cell survival/cancer, inferred from the metabolic (#) and cell survival (*) pathways depicted in panel A. Fold change upon FGF19 treatment for proteins classified in metabolism, cell survival/cancer pathways or both is shown.</p

FGF19 regulates Stat3 expression and phosphorylation at Tyr705.

<p>Western blot analyses of Stat3 protein (A) and phospho-Stat3 (Tyr705) (B) at 0h, 15 min, 1h, 2h and 12h after FGF19 treatment. Quantification for Stat3 is shown as relative protein signal normalized to tubulin. Data are expressed as mean ± SD. Each lane represents one mouse liver.</p

FGF19-mediated regulation of liver protein expression resolved by quantitative proteomics.

<p>(A) Schematic representation of the experimental outline to determine the hepatic proteomic profile of mice treated with FGF19 or Veh for 12 h. (n = 3) (B) Frequency plot of proteins identified in vehicle-treated Wt mice based on their total log2 heavy/light normalized ratio. The plot is representative of mean Wt untreated condition to show the basal efficiency of the heavy spike-in added to the light samples. Percentage of proteins with a log2 heavy/light normalized ratio included in interval (-1,+1) is shown. (C) Protein ranking based on changes of the log2 light/heavy normalized ratio induced by FGF19 when comparing FGF19 treatment for 12h to vehicle control. Number of proteins, of which expression was decreased (≤ -1.5 fold), unchanged or increased (≥1.5 fold) are indicated. (C) Volcano plot depicting the protein changes induced by FGF19 after 12h treatment. Plots are accompanied by tables listing the significant upregulated or downregulated proteins with fold change >1.5 (n = 3; p<0.05).</p

FGF19 stimulation affects mRNA expression of genes involved in metabolism and cell survival.

<p>(A) Schematic representation of the experimental outline to determine gene expression changes occurring upon FGF19 treatment for 0, 15 min, 1h, 2h, 4h and 12h. (B) Hepatic expression of genes involved in metabolism (Cyp7a1, Acox1, Acsl3), proliferation (Egfr, c-Fos, Hdlbp, Anxa2) or both (Stat3, Apoa4, Apoe, Fas, Gtpbp4) was determined by Real Time qPCR. (n = 5–6). Data are normalized to Gapdh expression and expressed as mean ± SEM.</p

TGFB1 targets regulated by FGF19.

<p>TGFB1 targets regulated by FGF19.</p