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.

Colorectal cancer is the third most common malignancy worldwide and is often linked to obesity, a sedentary lifestyle, carbohydrate- and fat-rich diets and elevated fecal excretion of secondary bile acids. Accumulation of toxic bile acids triggers oxidative damage, mitochondrial dysfunction and tumor progression. Nuclear receptors are transcription factors crucially involved in the regulation of bile acid metabolism and detoxification, and their activation may confer protection from bile acid tumor-promoting activity. In this review, we explore the tangled relationships among bile acids, nuclear receptors and the intestinal epithelium, with particular emphasis on the role of the farnesoid X receptor in colorectal cancer prevention and on novel nuclear receptor-based approaches to expand the portfolio of chemotherapeutic agents

Mouse models that mimic human diseases are invaluable tools to study and discover genetic and pharmacological therapies for human diseases. The protocols described in this article are intended to assess general clinical parameters in the context of the enterohepatic system under both normal and pathological conditions. Methods are presented for characterizing liver and intestinal function with a focus on bile acid and lipid metabolism in the gut-liver axis.

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.

The enzyme stearoyl-coenzyme A desaturase 1 (SCD or SCD1) produces mono-unsaturated fatty acids by introducing double bonds into saturated bonds between carbons 9 and 10, with oleic acid as the main product. SCD1 is present in the intestinal epithelium and fatty acids regulate cell proliferation, so we investigated the effects of SCD1-induced production of oleic acid in enterocytes in mice.

The peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1β (PGC-1 β) coactivator is a master regulator of mitochondrial biogenesis and oxidative metabolism as well as of antioxidant defense. Specifically in the liver PGC-1β also promotes de novo lipogenesis, thus sustaining cellular anabolic processes. Given the relevant pathogenic role of mitochondrial and fatty acid metabolism in hepatocarcinoma (HCC), here we pointed to PGC-1β as a putative novel transcriptional player in the development and progression of HCC. For this purpose, we generated both hepatic-specific PGC-1β overexpressing (LivPGC-1β) and PGC-1β knockout (LivPGC-1βKO) mice, and we challenged them with both chemical and genetic models of hepatic carcinogenesis. Our results demonstrate a pivotal role of PGC-1β in driving liver tumor development. Indeed, whereas mice overexpressing PGC-1β show greater tumor susceptibility, PGC-1β knockout mice are protected from carcinogenesis. High levels of PGC-1β are able to boost ROS scavenger expression, therefore limiting the detrimental ROS accumulation and, consequently, apoptosis. Moreover, it supports tumor anabolism, enhancing the expression of genes involved in fatty acid and triglyceride synthesis. Accordingly, the specific hepatic ablation of PGC-1β promotes the accumulation of ROS-driven macromolecule damage, finally limiting tumor growth . The present data elect hepatic PGC-1β as a transcriptional gatekeeper of mitochondrial function and redox status in HCC, orchestrating different metabolic programs that allow tumor progression. This article is protected by copyright. All rights reserved.

metabolic syndrome is a cluster of cardio-metabolic risk factors associated to atherosclerosis and low-grade inflammation. Using unbiased expression screenings in peripheral blood mononuclear cells, we depict here a novel expression chart of 678 genes and 84 miRNAs controlling inflammatory, immune and metabolic responses. In order to further elucidate the link between inflammation and the HDL cholesterol pathway in metabolic syndrome (MS), we focused on the regulation of the ATP-binding cassette transporter A1 (ABCA1), a key player in cholesterol efflux.

Epicardial adipose tissue (EAT) is an atypical fat depot surrounding the heart with a putative role in the development of atherosclerosis.

The role of the intestine in the maintenance of cholesterol homeostasis increasingly is recognized. Fecal excretion of cholesterol is the last step in the atheroprotective reverse cholesterol transport pathway, to which biliary and transintestinal cholesterol excretion (TICE) contribute. The mechanisms controlling the flux of cholesterol through the TICE pathway, however, are poorly understood. We aimed to identify mechanisms that regulate and stimulate TICE.

Metabolic syndrome (MS) is a cluster of different diseases, namely central obesity, hypertension, hyperglycemia, and dyslipidemia, together with a pro-thrombotic and pro-inflammatory state. These metabolic abnormalities are often associated with an increased risk for cardiovascular disease (CVD) and cancer. Dietary and lifestyle modifications are currently believed more effective than pharmacological therapies in the management of MS patients. Nevertheless, the relatively low grade of compliance of patients to these recommendations, as well as the failure of current therapies, highlights the need for the discovery of new pharmacological and nutraceutic approaches. A deeper knowledge of the patho-physiological events that initiate and support the MS is mandatory. Lipid-sensing nuclear receptors (NRs) are the master transcriptional regulators of lipid and carbohydrate metabolism and inflammatory responses, thus standing as suitable targets. This review focuses on the physiological relevance of the NRs (peroxisome proliferator-activated receptors, liver X receptors, and farnesoid X receptor) in the control of whole-body homeostasis, with a special emphasis on lipid and glucose metabolism, and on the relationships between metabolic unbalances, systemic inflammation, and the onset of CVD. Future perspectives and possible clinical applications are also presented

Reducing post-prandial triglyceridemia may be a promising strategy to lower risk of cardiovascular disorders associated with obesity and type 2 diabetes. In enterocytes, scavenger receptor class B, type 1 (SR-B1, encoded by SCARB1) mediates lipid-micelle sensing to promote assembly and secretion of chylomicrons. The nuclear receptor subfamily 1, group H, members 2 and 3 (also known as liver X receptors or LXRs) regulate genes involved in cholesterol and fatty acid metabolism. We aimed to determine whether intestinal LXRs regulate triglyceride absorption.

BACKGROUND & AIMS: Liver X receptors (LXRs) are transcriptional regulators of cholesterol metabolism, controlling cholesterol flow into cells, catabolism, and efflux. Cholesterol controls cell proliferation; disruptions in cholesterol metabolism have been associated with the development of colon cancer. We investigated whether expression of activated LXR protects against intestinal tumorigenesis in mice. METHODS: We analyzed the development of colon cancer in mice that express a constitutive active form of LXRα only in the intestinal epithelium, under the control of villin promoter (iVP16LXRα). These mice were crossed with adenomatous polyposis coli (Apc)(min/+) mice, or given azoxymethane followed by dextran sodium sulfate, to assess intestinal tumor formation. We also assessed proliferation and apoptosis of a human colorectal cancer cell line (HT29) transfected with an adenoviral vector that expressed Ad VP16hLXRα, compared with cells expressing AdVP16 (control), and their ability to form xenograft tumors in mice. HT29 cells also were incubated with the LXR ligand GW3965. RESULTS: In human colorectal cancer cells, ligand-induced activation of LXR or transfection with Ad VP16hLXRα blocked the G1 phase, increased caspase-dependent apoptosis, and slowed growth of xenograft tumors in mice. iVP16LXRα mice formed fewer, smaller tumors than VP16 (control) mice after administration of azoxymethane and dextran sodium sulfate. APC(min/+)/iVP16LXRα mice also developed fewer, smaller intestinal tumors than APC(min/+)/iVP16 mice. Gene expression analysis indicated that activation of LXRα affected lipid metabolic networks and increased cholesterol efflux in the intestine CONCLUSIONS: Expression of activated LXRα blocks proliferation of human colorectal cancer cells and slows the growth of xenograft tumors in mice. It also reduces intestinal tumor formation after administration of chemical carcinogens, and in Apc(min/+) mice. LXR agonists therefore might be developed as therapeutic treatments for colorectal cancer

Androgens and androgen receptor (AR, NR3C4) clearly play a crucial role in prostate cancer progression. Besides, the link between metabolic disorders and the risk of developing a prostate cancer has been emerging these last years. Interestingly, "lipid" nuclear receptors such as LXRα/NR1H3 and LXRβ/NR1H2 (as well as FXRα/NR1H4 and SHP/NR0B2) have been described to decrease the lipid metabolism, while AR increases it. Moreover, these former orphan nuclear receptors can regulate androgen levels and modulate AR activity. Thus, it is not surprising to find such receptors involved in the physiology of prostate. This review is focused on the roles of liver X receptors (LXRs), farnesoid X receptor (FXR), and small heterodimeric partner (SHP) in prostate physiology and their capabilities to interfere with the androgen-regulated pathways by modulating the levels of active androgen within the prostate. By the use of prostate cancer cell lines, mice deficient for these nuclear receptors and human tissue libraries, several authors have pointed out the putative possibility to pharmacologically target these receptors. These data open a new field of research for the development of new drugs that could overcome the castration resistance in prostate cancer, a usual phenomenon in patients.

The intestinal epithelium is a multicellular interface in close proximity to a dense microbial milieu that is completely renewed every 3-5 days. Pluripotent stem cells reside at the crypt, giving rise to transient amplifying cells that go through continuous steps of proliferation, differentiation and finally anoikis (a form of programmed cell death) while migrating upwards to the villus tip. During these cellular transitions, intestinal epithelial cells (IECs) possess distinct metabolic identities reflected by changes in mitochondrial activity. Mitochondrial function emerges as a key player in cell fate decisions and in coordinating cellular metabolism, immunity, stress responses and apoptosis. Mediators of mitochondrial signalling include molecules such as ATP and reactive oxygen species and interrelate with pathways such as the mitochondrial unfolded protein response (MT-UPR) and AMP kinase signalling, in turn affecting cell cycle progression and stemness. Alterations in mitochondrial function and MT-UPR activation are integral aspects of pathologies, including IBD and cancer. Mitochondrial signalling and concomitant changes in metabolism contribute to intestinal homeostasis and regulate IEC dedifferentiation-differentiation programmes in the context of diseases, suggesting that mitochondrial function as a cellular checkpoint critically contributes to disease outcome. This Review highlights mitochondrial function and MT-UPR signalling in epithelial cell stemness, differentiation and lineage commitment and illustrates mitochondrial function in intestinal diseases.

BACKGROUND & AIMS: Studies of the transcriptional networks that regulate nuclear receptor-mediated proliferation of quiescent hepatocytes could lead to new information about liver growth and hepatoprotective strategies. METHODS: We used quantitative real-time PCR to analyze expression of neuron-derived orphan receptor 1 (Nor-1) and its target genes during liver regeneration after hepatectomy in mice, and in hepatocellular carcinoma (HCC) samples from patients. We used adenoviral vectors to express Nor-1 in normal liver (Ad/CMV/V5-Nor-1), or reduce its level with small hairpin RNAs (Ad/BLOCK-iT/Nor-1(small hairpin RNA)) after partial hepatectomy. RESULTS: Levels of Nor-1 messenger RNA and protein, and transcription of Nor-1 target genes (Ccnd1 and Vcam-1), increased during the late priming and proliferative phases of liver regeneration after partial hepatectomy. Levels of NOR-1 messenger RNA and transcription of its target gene CCND1 and of the NOR-1 subfamily member NUR-77 also increased in human HCC samples compared with paired HCC-free tissue. Ad-Nor-1(small hairpin RNA) reduced the hepatocyte proliferation after hepatectomy. Overexpression of Nor-1 in normal livers of mice induced proliferation of quiescent hepatocytes independently of interleukin-6 and tumor necrosis factor-α signaling. In gene expression profile analysis, Nor-1 altered expression of genes involved in the cell cycle, proliferation, and tumorigenesis. CONCLUSIONS: In mice, the orphan nuclear receptor Nor-1 activates proliferation of quiescent hepatocytes and is required for hepatocyte proliferation after partial hepatectomy. Nor-1 and its gene targets are also up-regulated in human HCC samples. Nor-1 activates a transcriptional program that induces hepatocyte proliferation independently of inflammatory signaling pathways

The nuclear receptor farnesoid X receptor (FXR) is the master regulator of bile acids (BAs) homeostasis since it transcriptionally drives modulation of BA synthesis, influx, efflux, and detoxification along the enterohepatic axis. Due to its crucial role, FXR alterations are involved in the progression of a plethora of BAs associated inflammatory disorders in the liver and in the gut. The involvement of the FXR pathway in cholestasis development and management has been elucidated so far with a direct role of FXR activating therapy in this condition. However, the recent identification of a new type of genetic progressive familial intrahepatic cholestasis (PFIC) linked to FXR mutations has strengthen also the bona fide beneficial effects of target therapies that by-pass FXR activation, directly promoting the action of its target, namely the enterokine FGF19, in the repression of hepatic BAs synthesis with reduction of total BA levels in the liver and serum, accomplishing one of the major goals in cholestasis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni and Peter Jansen.

BACKGROUND: Nuclear receptors are a class of 48 ligand-activated transcription factors identified as key players of metabolic and developmental processes. Most of these receptors are potential targets for pharmacological strategies in the Metabolic Syndrome. In the present study, we analyzed changes in the mRNA expression of nuclear receptors in the peripheral blood mononuclear cells of patients with Metabolic Syndrome, in order to identify novel biomarkers of disease and candidate targets for putative therapeutical approaches. METHODS AND RESULTS: We enrolled thirty healthy controls (14 M:16 F) and thirty naïve patients (16 M: 14 F; >3 criteria for Metabolic Syndrome upon Adult Treatment Panel III) without organ damage. Using quantitative real-time PCR, we assessed the expression patterns of nuclear receptors in peripheral blood mononuclear cells. 33/48 nuclear receptors were expressed in peripheral blood mononuclear cells. In patients with Metabolic Syndrome, we found a significant down-regulation of the entire PPAR, NR4A and RAR families, together with a repression of RXRα, VDR, and Rev-Erbα. Furthermore, we performed a novel statistical analysis with classification trees, which allowed us to depict a predictive core of nuclear receptor expression patterns characterizing subjects with Metabolic Syndrome. Random Forest Analysis identified NOR1 and PPARδ, which were both reduced in peripheral blood mononuclear cells and specifically in CD14(+) cells (mostly monocytes), as classifiers of Metabolic Syndrome, with high specificity and sensitivity. CONCLUSIONS: Our results point to the use of PPAR and NR4A mRNA levels in the overall peripheral blood mononuclear cells as biomarkers of Metabolic Syndrome and bona fide putative targets of pharmacological therapy

A comprehensive understanding of the pathways underlying hepatocyte turnover and liver regeneration is essential for the development of innovative and effective therapies in the management of chronic liver disease, and the prevention of hepatocellular carcinoma (HCC) in cirrhosis. Nuclear receptors (NRs) are master transcriptional regulators of liver development, differentiation and function. NRs have been implicated in the modulation of hepatocyte priming and proliferation in regenerating liver, chronic hepatitis and HCC development. In this review, we focus on NRs and their pathways regulating hepatocyte proliferation and liver regeneration, with a perspective view on NRs as candidate biomarkers and novel pharmacological targets in the management of liver disease and HCC

Background -The pericardial adipose tissue (AT) contains a high density of lymphoid clusters. Is unknown whether these clusters play a role in post-myocardial infarction (MI) inflammatory responses and cardiac outcome. Methods -Lymphoid clusters were examined in epicardial AT of humans with or without coronary artery disease (CAD). Murine pericardial lymphoid clusters were visualized in mice subjected to coronary artery ligation. To study the relevance of pericardial clusters during inflammatory responses after MI, we surgically removed the pericardial AT, performed B cell depletion and GM-CSF blockade. Leukocytes in murine hearts, pericardial AT, spleen, mediastinal lymph nodes, and bone marrow were quantified by flow cytometry. Cannabinoid receptor CB2 (CB2-/-) mice were used as a model for enhanced B cell responses. The effect of impaired dendritic cell (DC) trafficking on pericardial AT inflammatory responses was tested in CCR7-/- mice subjected to MI. Cardiac fibrosis and ventricular function were assessed by histology and echocardiography. Results -We identified larger B cell clusters in epicardial AT of human CAD patients compared to controls without CAD. Infarcted mice also had larger pericardial clusters and 3-fold upregulated numbers of GM-CSF-producing B cells within pericardial AT, but not spleen or lymph nodes. This was associated with higher DC and T cell counts in pericardial AT, which outnumbered DCs and T cells in lymph nodes. Analysis of DC maturation markers, tracking experiments with fluorescently labelled cells and use of CCR7-deficient mice suggested that activated DCs migrate from infarcts into pericardial AT via CCR7. B cell depletion or GM-CSF neutralization inhibited DC and T cell expansion within pericardial AT, and translated into reduced bone marrow granulopoiesis and cardiac neutrophil infiltration 3 days after MI. The relevance of the pericardial AT in mediating all these effects was confirmed by removal of pericardial AT andex vivococulture with pericardial AT and granulocyte progenitors. Finally, enhanced fibrosis and worsened ejection fraction in CB2-/- mice was limited by pericardial AT removal. Conclusions -Our findings unveil a new mechanism by which the pericardial AT coordinates immune cell activation, granulopoiesis and outcome after MI.

Peroxisome proliferator-activated receptor-γ coactivator 1-α (PGC1α) is a transcriptional coactivator able to up-regulate mitochondrial biogenesis, respiratory capacity, oxidative phosphorylation, and fatty acid β-oxidation with the final aim of providing a more efficient pathway for aerobic energy production. In the continuously renewed intestinal epithelium, proliferative cells in the crypts migrate along the villus axis and differentiate into mature enterocytes, increasing their respiratory capacity and finally undergoing apoptosis. Here we show that in the intestinal epithelial surface, PGC1α drives mitochondrial biogenesis and respiration in the presence of reduced antioxidant enzyme activities, thus determining the accumulation of reactive oxygen species and fostering the fate of enterocytes toward apoptosis. Combining gain- and loss-of-function genetic approaches in human cells and mouse models of intestinal cancer, we present an intriguing scenario whereby PGC1α regulates enterocyte cell fate and protects against tumorigenesis.

BACKGROUND & AIMS: Cholestasis is a liver disorder characterized by impaired bile flow, reduction of bile acids (BAs) in the intestine, and retention of BAs in the liver. The farnesoid X receptor (FXR) is the transcriptional regulator of BA homeostasis. Activation of FXR by BAs reduces circulating BA levels in a feedback mechanism, repressing hepatic cholesterol 7α-hydroxylase (Cyp7a1), the rate-limiting enzyme for the conversion of cholesterol to BAs. This mechanism involves the hepatic nuclear receptor small heterodimer partner and the intestinal fibroblast growth factor (FGF) 19 and 15. We investigated the role of activation of intestine-specific FXR in reducing hepatic levels of BAs and protecting the liver from cholestasis in mice. METHODS: We generated transgenic mice that express a constitutively active FXR in the intestine. Using FXR gain- and loss-of-function models, we studied the roles of intestinal FXR in mice with intrahepatic and extrahepatic cholestasis. RESULTS: Selective activation of intestinal FXR induced FGF15 and repressed hepatic Cyp7a1, reducing the pool size of BAs and changing the BA pool composition. Activation of intestinal FXR protected mice from obstructive extrahepatic cholestasis after bile duct ligation or administration of α-naphthylisothiocyanate. In Mdr2(-/-) mice, transgenic expression of activated FXR in the intestine protected against liver damage, whereas absence of FXR promoted progression of liver disease. CONCLUSIONS: Activation of FXR transcription in the intestine protects the liver from cholestasis in mice by inducing FGF15 expression and reducing the hepatic pool of BA; this approach might be developed to reverse cholestasis in patients

Elevated bile acid (BA) concentrations in the liver is associated with severe disease, including cholestasis and hepatocellular carcinoma. The nuclear Farnesoid X Receptor (FXR) is the master regulator of BAs homeostasis. In the ileum, BA-dependent FXR activation induces the production of the fibroblast growth factor FGF19, a hormone that reaches the liver through the portal system where it represses the expression of CYP7A1, the rate limiting enzyme in the process of hepatic BAs synthesis. This gut-liver FXR-FGF19 dual action is the paradigm of physiological BA regulation and it is currently targeted in the clinical practice for liver disease such as primary cholangitis. At a variance of FXR activation, native FGF19 has strong anti-cholestatic and anti-fibrotic activity in the liver but it retains peculiar pro-tumorigenic actions. Thus, novel analogues have been generated to avoid tumorigenic capacity while maintaining BA metabolic action. Here we present a novel and intriguing view on the putative possibility to target the FXR-FGF19 duo in order to offer a bona fide promising therapeutic approach to bile acid promoted hepatocarcinoma.

The endocrine fibroblast growth factors (FGFs), FGF19, FGF21 and FGF23, are critical for maintaining whole-body homeostasis, with roles in bile acid, glucose and lipid metabolism, modulation of vitamin D and phosphate homeostasis and metabolic adaptation during fasting. Given these functions, the endocrine FGFs have therapeutic potential in a wide array of chronic human diseases, including obesity, type 2 diabetes, cancer, and kidney and cardiovascular disease. However, the safety and feasibility of chronic endocrine FGF administration has been challenged, and FGF analogues and mimetics are now being investigated. Here, we discuss current knowledge of the complex biology of the endocrine FGFs and assess how this may be harnessed therapeutically.