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Dysmetabolic conditions could drive liver fibrosis in patients with non-alcoholic fatty liver disease (NAFLD), increasing susceptibility to hepatocellular carcinoma (HCC). We therefore aimed to identify novel predictive biomarkers of HCC in patients with and without liver fibrosis.A total of 1,234 patients with putative metabolic conditions and NAFLD were consecutively assessed in our outpatient clinic. Clinical and biochemical data were recorded, and then liver ultrasonography was performed annually for 5 years to detect HCC onset. For the analysis, the population was first divided according to HCC diagnosis; then a further subdivision of those who did not develop HCC was performed based on the presence or absence of liver fibrosis at time 0.Sixteen HCC cases were recorded in 5 years. None of our patients had been diagnosed with cirrhosis before HCC was detected. Compared to patients who did not develop HCC, those who did had higher liver transaminases and fibrosis scores at time 0 (This study identifies HDL-c as aVisceral adiposity and its associated conditions, such as chronic inflammation and insulin resistance, may play a pivotal role in hepatocellular carcinoma development in patients with non-alcoholic fatty liver disease. We provide new insights on the underlying mechanisms of its pathogenesis, shedding light on the involvement of low levels of "good" HDL-cholesterol. We recommend integrating dietary regimens and advice on healthy lifestyles into the clinical management of non-alcoholic fatty liver disease, with the goal of reducing the incidence of hepatocellular carcinoma.

Summary Fibroblast growth factor (FGF) receptor 4 (FGFR4) and its cognate ligand, FGF19, are implicated in a range of cellular processes, including differentiation, metabolism and proliferation. Indeed, their aberrant activation has been associated with the development of hepatic tumours. Despite great advances in early diagnosis and the development of new therapies, liver cancer is still associated with a high mortality rate, owing primarily to high molecular heterogeneity and unclear molecular targeting. The development of FGFR4 inhibitors is a promising tool in patients with concomitant supraphysiological levels of FGF19 and several clinical trials are testing these treatments for patients with advanced hepatocellular carcinoma (HCC). Conversely, using FGF19 analogues to activate FGFR4-KLOTHO β represents a novel therapeutic strategy in patients presenting with cholestatic liver disorders and non-alcoholic steatohepatitis, which could potentially prevent the development of metabolic HCC. Herein, we provide an overview of the currently available therapeutic options for targeting FGFR4 in HCC and other liver diseases, highlighting the need to carefully stratify patients and personalise therapeutic strategies.

Critical regulation of bile acid (BA) pool size and composition occurs via an intensive molecular crosstalk between the liver and gut, orchestrated by the combined actions of the nuclear Farnesoid X receptor (FXR) and the enterokine fibroblast growth factor 19 (FGF19) with the final aim of reducing hepatic BA synthesis in a negative feedback fashion. Disruption of BA homeostasis with increased hepatic BA toxic levels leads to higher incidence of hepatocellular carcinoma (HCC). While native FGF19 has anti-cholestatic and anti-fibrotic activity in the liver, it retains peculiar pro-tumorigenic actions. Thus, novel analogues have been generated to avoid tumorigenic capacity and maintain BA metabolic action. Here, using BA related Abcb4−/− and Fxr−/− mouse models of spontaneous hepatic fibrosis and HCC, we explored the role of a novel engineered variant of FGF19 protein, called FGF19-M52, which fully retains BA regulatory activity but is devoid of the pro-tumoral activity. Expression of the BA synthesis rate-limiting enzyme Cyp7a1 is reduced in FGF19-M52-treated mice compared to the GFP-treated control group with consequent reduction of BA pool and hepatic concentration. Treatment with the non-tumorigenic FGF19-M52 strongly protects Abcb4−/− and Fxr−/− mice from spontaneous hepatic fibrosis, cellular proliferation and HCC formation in terms of tumor number and size, with significant reduction of biochemical parameters of liver damage and reduced expression of several genes driving the proliferative and inflammatory hepatic scenario. Our data bona fide suggest the therapeutic potential of targeting the FXR-FGF19 axis to reduce hepatic BA synthesis in the control of BA-associated risk of fibrosis and hepatocarcinoma development.

The crypt-villus axis represents the essential unit of the small intestine, which integrity and functions are fundamental to assure tissue and whole-body homeostasis. Disruption of pathways regulating the fine balance between proliferation and differentiation results in diseases development. Nowadays, it is well established that microRNAs (miRNAs) play a crucial role in the homeostasis maintenance and perturbation of their levels may promote tumor development. Here, by using microarray technology, we analysed the miRNAs differentially expressed between the crypt and the villus in mice ileum. The emerged miRNAs were further validated by Real Time qPCR in mouse model (ApcMin/+), human cell lines and human tissue samples (FAP) of colorectal cancer (CRC). Our results indicated that miRNAs more expressed in the villi compartment are negatively regulated in tumor specimens, thus suggesting a close association between these microRNAs and the differentiation process. Particularly, from our analysis let-7e appeared to be a promising target for possible future therapies and a valuable marker for tumor staging, being upregulated in differentiated cells and downregulated in early-stage colonic adenoma samples.

Background: Disruption of bile acid (BA) homeostasis plays a key role in intestinal inflammation. The gut-liver axis is the main site for the regulation of BA synthesis and BA pool size via the combined action of the nuclear Farnesoid X Receptor (FXR) and the enterokine Fibroblast Growth Factor 19 (FGF19). Increasing evidence have linked derangement of BA metabolism with dysbiosis and mucosal inflammation. Thus, here we aimed to investigate the potential action of an FGF19 analogue on intestinal microbiota and inflammation. Methods: A novel engineered non-tumorigenic variant of the FGF19 protein, M52-WO 2016/0168219 was generated. WT and FXRnull mice were injected with AAV-FGF19-M52 or the control AAV-GFP and subjected to Sodium Dextran Sulphate-induced colitis. Findings: FGF19-M52 reduced BA synthesis and pool size, modulated its composition and protected mice from intestinal inflammation. These events were coupled with preservation of the intestinal epithelial barrier integrity, inhibition of inflammatory immune response and modulation of microbiota composition. Interestingly, FGF19-M52-driven systemic and local anti-inflammatory activity was completely abolished in Farnesoid X Receptor (FXR)null mice, thus underscoring the need of FXR to guarantee enterocytes’ fitness and complement FGF19 anti-inflammatory activity. To provide a translational perspective, we also show that circulating FGF19 levels are reduced in patients with Crohn's disease. Interpretation: Reactivation of the FXR-FGF19 axis in a murine model of intestinal inflammation could bona fide provide positive changes in BA metabolism with consequent reduction of intestinal inflammation and modulation of microbiota. These results point to the therapeutic potential of FGF19 in the treatment of intestinal inflammation with concomitant derangement of BA homeostasis. Funding: A. Moschetta is funded by MIUR-PRIN 2017

Diet and lifestyle habits have a profound impact on the pathophysiology of many diseases. Colorectal cancer (CRC) is the third most common cancer worldwide and its etiology is strongly influenced by nutrition and high fat/high carbohydrate Western-style diet. Human epidemiological and animal studies have shown that colonic cancer risk is also related to faecal bile acid concentration. Abnormally high levels of bile acids (BA) trigger the colonic mucosa with a plethora of detrimental effects such as DNA oxidative damage, inflammation and hyperproliferation that highly promote CRC progression in post-initiation phase. The Farnesoid X receptor (FXR) is a nuclear receptor that transcriptionally mediates the signalling activity of BAs. FXR regulates BA metabolism mainly maintaining BA concentrations within a physiological range, thereby preventing BA-induced cytotoxicity. In fact, loss of FXR is associated with higher BA concentrations and with a pro-tumorigenic phenotype. Here we explore the liaison connecting nutrition, intestinal epithelium renewal, BA and their nuclear receptor FXR in CRC. Moreover, we summarize evidence linking BA and CRC, as well as examine current understanding of the protumoral actions of BA and the bona fide antitumoral properties of FXR.

Inflammatory bowel disease (IBD) is a chronic multifactorial inflammatory disorder characterized by periods of activation and remission of intestinal inflammation, with potentially severe complications, that can lead to mortality. Experimental animal models of intestinal inflammation are crucial for understanding the pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC), the two major human IBD phenotypes. Animal models have been instrumental in unveiling the molecular background of IBD, and although a single model is not able to capture the complexity of this disease, each of them provided valuable insight into its different aspects. Chemically induced models of intestinal inflammation, mainly dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis, are widely used. This article describes DSS- and TNBS-induced colitis models and their relevance to IBD pathophysiology and pre-clinical therapeutic management. © 2017 by John Wiley & Sons, Inc.

The endocrine fibroblast growth factors (FGFs), FGF19, FGF21, and FGF23, play a key role in whole-body homeostasis. In particular, FGF19 is a postprandial hormone regulating glucose homeostasis, glycogen and protein synthesis, and primary bile acid (BA) metabolism. In the ileum, BA-dependent farnesoid X receptor (FXR) activation induces the production of FGF19, which reaches the liver through the portal system where it represses the expression of CYP7A1, the rate-limiting enzyme of hepatic de novo BAs synthesis. Dysregulation of BA levels associated with alteration in FGF19 level has been depicted in different pathological conditions of the gut-liver axis. Furthermore, FGF19 exploits strong anti-cholestatic and anti-fibrotic activities in the liver. However, native FGF19 seems to retain peculiar hepatic pro-tumorigenic actions. Recently engineered FGF19 analogues have been recently synthetized, with fully retained BA regulatory activity but without intrinsic pro-tumoral action, thus opening bona fide novel pharmacological strategy for the treatment of gut-liver axis diseases.

Inflammatory bowel disease (IBD) represents a group of progressive disorders characterized by recurrent chronic inflammation of the gut. Ulcerative colitis and Crohn′s disease are the major manifestations of IBD. While our understanding of IBD has progressed in recent years, its etiology is far from being fully understood, resulting in suboptimal treatment options. Complementing other biological endpoints, bioanalytical “omics” methods that quantify many biomolecules simultaneously have great potential in the dissection of the complex pathogenesis of IBD. In this review, we focus on the rapidly evolving proteomics and lipidomics technologies and their broad applicability to IBD studies; these range from investigations of immune-regulatory mechanisms and biomarker discovery to studies dissecting host–microbiome interactions and the role of intestinal epithelial cells. Future studies can leverage recent advances, including improved analytical methodologies, additional relevant sample types, and integrative multi-omics analyses. Proteomics and lipidomics could effectively accelerate the development of novel targeted treatments and the discovery of complementary biomarkers, enabling continuous monitoring of the treatment response of individual patients; this may allow further refinement of treatment and, ultimately, facilitate a personalized medicine approach to IBD.

While aberrant cancer cell growth is frequently associated with altered biochemical metabolism, normal mitochondrial functions are usually preserved and necessary for full malignant transformation. The transcription factor FoxO3A is a key determinant of cancer cell homeostasis, playing a dual role in survival/death response to metabolic stress and cancer therapeutics. We recently described a novel mitochondrial arm of the AMPK-FoxO3A axis in normal cells upon nutrient shortage. Here, we show that in metabolically stressed cancer cells, FoxO3A is recruited to the mitochondria through activation of MEK/ERK and AMPK, which phosphorylate serine 12 and 30, respectively, on FoxO3A N-terminal domain. Subsequently, FoxO3A is imported and cleaved to reach mitochondrial DNA, where it activates expression of the mitochondrial genome to support mitochondrial metabolism. Using FoxO3A−/− cancer cells generated with the CRISPR/Cas9 genome editing system and reconstituted with FoxO3A mutants being impaired in their nuclear or mitochondrial subcellular localization, we show that mitochondrial FoxO3A promotes survival in response to metabolic stress. In cancer cells treated with chemotherapeutic agents, accumulation of FoxO3A into the mitochondria promoted survival in a MEK/ERK-dependent manner, while mitochondrial FoxO3A was required for apoptosis induction by metformin. Elucidation of FoxO3A mitochondrial vs. nuclear functions in cancer cell homeostasis might help devise novel therapeutic strategies to selectively disable FoxO3A prosurvival activity.

The nuclear Farnesoid X Receptor (FXR) is a transcription factor critically involved in metabolic homeostasis in the gut-liver axis. FXR activity is mediated by hormonal and dietary signals and driven by bile acids (BAs), which are the natural FXR ligands. Given the great physiological importance in BA homeostasis, as well as in the regulation of glucose and lipid metabolism, FXR plays a pivotal role in the pathogenesis of a wide range of disease of the liver, biliary tract and intestine, including hepatic and colorectal cancer. In the last years several studies have shown the relative FXR tissue-specific importance, highlighting synergism and additive effects in the liver and intestine. Gain- and loss-of-FXR-function mouse models have been generated in order to identify the biological processes and the molecular FXR targets. Taking advantage of the knowledge on the structure-activity relationship of BAs for FXR, semi-synthetic and synthetic molecules have been generated to obtain more selective and powerful FXR activators than BAs. This article is part of a Special Issue entitled: Linking transcription to physiology in lipodomics.

Nat. Genet.; 10.1038/ng.3773; corrected online 31 January 2017 In the version of this article initially published online, the names of authors Hermannus Kempe and Pernette J. Verschure were spelled incorrectly. These errors have been corrected in the print, PDF and HTML versions of this article.

Tumor evolution is shaped by many variables, potentially involving external selective pressures induced by therapies1. After surgery, estrogen receptor (ERα) positive breast cancer (BCa) patients are treated with adjuvant endocrine therapy2 including selective estrogen receptor modulators (SERMs) and/or aromatase inhibitors (AIs)3. However, over 20% of patients relapse within 10 years and eventually progress to incurable metastatic disease4. Here we demonstrate that the choice of therapy has a fundamental influence on the genetic landscape of relapsed diseases: in this study, 21.5% of AI-treated, relapsed patients had acquired CYP19A1 gene (aromatase) amplification (CYP19A1amp). Relapsed patients also developed numerous mutations targeting key breast cancer genes including ESR1 and CYP19A1. Strikingly, CYP19A1amp cells also emerge in vitro but only in AI resistant models. CYP19A1 amplification causes increased aromatase activity and estrogen-independent ERα binding to target genes resulting in CYP19A1amp cells displaying decreased sensitivity to AI treatment. Collectively these data suggest that AI treatment itself selects for acquired CYP19A1 amplification and promotes local autocrine estrogen signalling in AI resistant metastatic patients.

The nuclear receptor (NR) family comprises 48 transcription factors (TFs) with essential and diverse roles in development, metabolism and disease. Differently from other TFs, NRs engage with well-defined DNA-regulatory elements, mostly after ligand-induced structural changes. However, NR binding is not stochastic, and only a fraction of the cognate regulatory elements within the genome actively engage with NRs. In this review, we summarize recent advances in the understanding of the interactions between NRs and DNA. We discuss how chromatin accessibility and epigenetic modifications contribute to the recruitment and transactivation of NRs. Lastly, we present novel evidence of the interplay between non-coding RNA and NRs in the mediation of the assembly of the transcriptional machinery.

As a continuation of previous efforts in mapping functional hot spots on the bile acid scaffold, we here demonstrate that the introduction of a hydroxy group at the C11β position affords high selectivity for FXR. In particular, the synthesis and FXR/TGR5 activity of novel bile acids bearing different hydroxylation patterns at the C ring are reported and discussed from a structure-activity standpoint. The results obtained led us to discover the first bile acid derivative endowed with high potency and selectivity at the FXR receptor, 3α,7α,11β-trihydroxy-6α-ethyl-5β-cholan-24-oic acid (TC-100, 7) which also shows a remarkable physicochemical and pharmacological profile. Compound 7 combines the excellent physicochemical properties of hydrophilic bile acids such as ursodeoxycholic acid, with the distinct ability to specifically bind and regulate FXR activity in vivo, thus providing a bona fide novel therapeutic agent to treat enterohepatic disorders such as cholestasis, NASH, and inflammatory bowel disease.

Background & aims Inflammatory bowel disease (IBD) is characterised by chronic intestinal inflammation, resulting from dysregulation of the mucosal immune system and compromised intestinal epithelial barrier function. The bile salt, nuclear farnesoid X receptor (FXR), was recently implicated in intestinal antibacterial defence and barrier function. The aim of this study was to investigate the therapeutic potential of FXR agonists in the treatment of intestinal inflammation in complementary in vivo and in vitro models. Methods Colitis was induced in wild-type (WT) and Fxr-null mice using dextran sodium sulfate, and in WT mice using trinitrobenzenesulfonic acid. Mice were treated with vehicle or the FXR agonist INT-747, and colitis symptoms were assessed daily. Epithelial permeability assays and cytokine expression analysis were conducted in mouse colon and enterocyte-like cells (Caco-2/HT29) treated with medium or INT-747. Inflammatory cytokine secretion was determined by ELISA in various human immune cell types. Results INT-747-treated WT mice are protected from DSS- and TNBS-induced colitis, as shown by significant reduction of body weight loss, epithelial permeability, rectal bleeding, colonic shortening, ulceration, inflammatory cell infiltration and goblet cell loss. Furthermore, Fxr activation in intestines of WT mice and differentiated enterocyte-like cells downregulates expression of key proinflammatory cytokines and preserves epithelial barrier function. INT-747 significantly decreases tumour necrosis factor a secretion in activated human peripheral blood mononuclear cells, purified CD14 monocytes and dendritic cells, as well as in lamina propria mononuclear cells from patients with IBD. Conclusions FXR activation prevents chemically induced intestinal inflammation, with improvement of colitis symptoms, inhibition of epithelial permeability, and reduced goblet cell loss. Furthermore, FXR activation inhibits proinflammatory cytokine production in vivo in the mouse colonic mucosa, and ex vivo in different immune cell populations. The findings provide a rationale to explore FXR agonists as a novel therapeutic strategy for IBD. RI van Mil, Saskia/C-3751-2009

Resistance to aromatase inhibitors (AI) involves extensive transcriptional reprogramming to overcome drug-mediated cell cycle arrest. Chromatin accessibility and epigenetic modifications play a crucial role in regulating gene expression in normal development and contribute to aberrant transcription commonly found in malignant cells. In this chapter we will discuss the latest research findings linking AI resistance to epigenetics. Initially we will examine the epigenetic regulation of the aromatase gene. The estrogen receptor activity is significantly influenced by the chromatin template and we will present evidence on how the estrogen receptor-chromatin crosstalk can contribute to the development of resistance. Next we will consider alternative survival pathways and how they are epigenetically regulated in response to AI treatment. Afterward, we will review the current state of epigenetic-based medicine in the context of endocrine therapies. Finally, we will offer some insights on future challenges and possible breakthroughs.

The nuclear receptor Farnesoid X Receptor (FXR) critically regulates nascent bile formation and bile acid enterohepatic circulation. Bile acids and FXR play a pivotal role in regulating hepatic inflammation and regeneration as well as in regulating extent of inflammatory responses, barrier function and prevention of bacterial translocation in the intestinal tract. Recent evidence suggests, that the bile acid-FXR interaction is involved in the pathophysiology of a wide range of diseases of the liver, biliary and gastrointestinal tract, such as cholestatic and inflammatory liver diseases and hepatocellular carcinoma, inflammatory bowel disease and inflammation-associated cancer of the colon and esophagus. In this review we discuss current knowledge of the role the bile acid-FXR interaction has in (patho)physiology of the liver, biliary and gastrointestinal tract, and proposed underlying mechanisms, based on in vitro data and experimental animal models. Given the availability of highly potent synthetic FXR agonists, we focus particularly on potential relevance for human disease.

Originally called retinoid X receptor interacting protein 14 (RIP14), the farnesoid X receptor (FXR) was renamed after the ability of its rat form to bind supra-physiological concentrations of farnesol. In 1999 FXR was de-orphanized since primary bile acids were identified as natural ligands. Strongly expressed in the liver and intestine, FXR has been shown to be the master transcriptional regulator of several entero-hepatic metabolic pathways with relevance to the pathophysiology of conditions such as cholestasis, fatty liver disease, cholesterol gallstone disease, intestinal inflammation and tumors. Furthermore, given the importance of FXR in the gut-liver axis feedbacks regulating lipid and glucose homeostasis, FXR modulation appears to have great input in diseases such as metabolic syndrome and diabetes. Exciting results from several cellular and animal models have provided the impetus to develop synthetic FXR ligands as novel pharmacological agents. Fourteen years from its discovery, FXR has gone from bench to bedside; a novel nuclear receptor ligand is going into clinical use.

Background The bile acid-activated nuclear receptor Farnesoid X Receptor (FXR) is critical in maintaining intestinal barrier integrity and preventing bacterial overgrowth. Patients with Crohn's colitis (CC) exhibit reduced ileal FXR target gene expression. FXR agonists have been shown to ameliorate inflammation in murine colitis models. We here explore the feasibility of pharmacological FXR activation in CC. Methods Nine patients with quiescent CC and 12 disease controls were treated with the FXR ligand chenodeoxycholic acid (CDCA; 15 mg/kg/day) for 8 days. Ileal FXR activation was assessed in the fasting state during 6 hrs after the first CDCA dose and on day 8, by quantification of serum levels of fibroblast growth factor (FGF) 19. Since FGF19 induces gallbladder (GB) refilling in murine models, we also determined concurrent GB volumes by ultrasound. On day 8 ileal and cecal biopsies were obtained and FXR target gene expression was determined. Results At baseline, FGF19 levels were not different between CC and disease controls. After the first CDCA dose, there were progressive increases of FGF19 levels and GB volumes during the next 6 hours in CC patients and disease controls (FGF19: 576 resp. 537% of basal; GB volumes: 190 resp. 178% of basal) without differences between both groups, and a further increase at day 8. In comparison with a separate untreated control group, CDCA affected FXR target gene expression in both CC and disease controls, without differences between both groups. Conclusions Pharmacological activation of FXR is feasible in patients with CC. These data provide a rationale to explore the anti-inflammatory properties of pharmacological activation of FXR in these patients. Trial Registration TrialRegister.nl NTR2009

A Functional Variant of the Farnesoid X Receptor (FXR) Predisposes to Ileocolonic Localization of Crohn's Disease Rian M. Nijmeijer, Raffaella Maria Gadaleta, Karel J. Van Erpecum, Adriaan A. van Bodegraven, J. Bart A. Crusius, Gerard Dijkstra, Daniel W. Hommes, Dirk J. De Jong, Cyriel Ponsioen, Hein W. Verspaget, Rinse K. Weersma, Christien J. van der Woude, Marguerite E. Schipper, Cisca Wijmenga, Saskia W. van Mil, Bas Oldenburg

The bile salt nuclear receptor Farnesoid X Receptor (FXR) was recently implicated in intestinal antibacterial defense and barrier function. We aimed to study its role in pathogenesis of inflammatory bowel diseasE. colitis was induced in Wild Type (WT) and FXR knock-out (ko) mice (n=8 to 10 for each group) by Dextran Sodium Sulphate (DSS: 2.5% in drinking water, 10 days) with or without synthetic FXR ligand 6-Ethyl Chenodeoxycholic Acid (6ECDCA: 5 mg/kg/day, 13 days, starting 3 days before DSS). Colitis symptoms were checked daily and intestinal permeability (FITC-dextran assay), bile salt composition (HPLC), histology and colonic inflammatory gene expression (Q-PCR) determined. mRNA expression of FXR and target genes was determined in IBD patient biopsies. Underlying mechanisms were explored in complementary In Vitro experiments. 6ECDCA-treated WT but not FXR ko mice were protected from DSS-induced colitis, as shown by highly significant reduction of body weight loss, rectal bleeding, colonic shortening, normalization of intestinal permeability, 49% reduction in blinded histological score and 55% reduction in goblet cell loss. Only in 6ECDCA-treated WT mice, mRNA levels of pro-inflammatory genes (IL-1β, IL-6, IL10 and MCP-1) were strongly down-regulated while antibacterial defense gene iNOS was upregulated. 6ECDCA was enriched in bile of both WT and FXR ko mice (9.8% and 5.3% of total bile salts, respectively). However intestinal expression of FXR target genes FGF15 and SHP was increased 4.5and 19-fold with 6ECDCA treatment only in WT. In patients with quiescent Crohn colitis (n=17), mRNA expression of FXR and SHP was significantly altered compared to patients with ulcerative colitis (n=16) or healthy controls (n=17). In differentiated CaCo2 cells grown on trans-well plates, FXR activation by GW4064 prevented DSS-dependent loss of integrity of the monolayer. In differentiated HT29 cells, TNFαinduced 20-fold increase of IL-1β expression was abolished by GW4064-dependent FXR activation. In reporter assays, the FXR agonist GW4064 prevented TNFα-induced NF-κB activity in HEK293 cells transfected with WT FXR, but no effect was achieved with FXR mutant W469A (defective in Ligand Binding Domain), indicating FXR-mediated inhibition of NF-κB signalling. In conclusion, FXR activation protects against experimental murine colitis, supposedly by preserving the intestinal barrier and inhibitingNF-κB activity. Currently available potent synthetic FXR agonists may offer new therapeutic strategies for inflammatory bowel disease.

Hyperactivation of NF-κB is a key factor in the pathophysiology of inflammatory bowel disease (IBD). We previously showed that the bile salt nuclear Farnesoid X Receptor (FXR) counter-regulates intestinal inflammation, possibly via repression of NF-κB. Here, we examine whether mutual antagonism between NF-κB and FXR exists. FXR and its target genes IBABP and FGF15/19 expression were determined in HT29 colon carcinoma cells and ex vivo in intestinal specimens of wild type (WT) and Fxr -ko mice, treated with/without FXR ligands (GW4064/INT-747) and inflammatory stimuli (TNFα/IL-1β). In addition, FXR activation was studied in vivo in WT and Fxr -ko mice with DSS-colitis. The involvement of NF-κB in decreasing FXR activity was investigated by reporter assays and Glutathione S-transferase pulldown assays. FXR target gene expression was highly reduced by inflammatory stimuli in all model systems, while FXR mRNA expression was unaffected. In line with these results, reporter assays showed reduced FXR transcriptional activity upon TNFα/IL-1β stimulation. We show that this reduction in FXR activity is probably mediated by NF-κB, since overexpression of NF-κB subunits p50 and/or p65 also lead to inhibition of FXR activity. Finally, we report that p65 and p50 physically interact with FXR in vitro . Conclusions : Together, these results indicate that intestinal inflammation strongly reduces FXR activation, probably via NF-κB-dependent tethering of FXR. Therefore, FXR not only inhibits inflammation, but also is targeted by the inflammatory response itself. This could result in a vicious cycle where reduced FXR activity results in less repression of inflammation, contributing to development of chronic intestinal inflammation. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.