Liver receptor homolog-1 is critical for adequate up-regulation of Cyp7a1 gene transcription and bile salt synthesis during bile salt sequestration

Yellow tea polysaccharides protect against non-alcoholic fatty liver disease via regulation of gut microbiota and bile acid metabolism in mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a major clinical and global public health issue, with no specific pharmacological treatment available. Currently, there is a lack of approved drugs for the clinical treatment of NAFLD. Large-leaf yellow tea polysaccharides (YTP) is a natural biomacromolecule with excellent prebiotic properties and significant therapeutic effects on multiple metabolic diseases. However, the specific mechanisms by which YTP regulates NAFLD remain unclear.

PURPOSE

This study aims to explore the prebiotic effects of YTP and the potential mechanisms by which it inhibits hepatic cholesterol accumulation in NAFLD mice.

METHODS

The effects of YTP on lipid accumulation were evaluated in NAFLD mice through obesity trait analysis and bile acids (BAs) metabolism assessment. Additionally, fecal microbiota transplantation (FMT) was performed, and high-throughput sequencing was employed to investigate the mechanisms underlying YTP's regulatory effects on gut microbiota and BA metabolism.

RESULTS

Our study demonstrated that YTP altered the constitution of colonic BA, particularly increasing the levels of conjugated BA and non-12OH BA, which suppressed ileum FXR receptors and hepatic BA reabsorption, facilitated BA synthesis, and fecal BA excretion. The modifications were characterized by a decrease in the levels of FXR, FGF15, FGFR4, and ASBT proteins, and an increase in the levels of Cyp7a1 and Cyp27a1 proteins. YTP might affect enterohepatic circulation and by the activated the hepatic FXR-SHP pathway. Meanwhile, YTP reshaped the intestinal microbiome structure by decreasing BSH-producing genera and increasing taurine metabolism genera. The correlation analysis implied that Muribaculaceae, Pseudomonas, acterium_coprostanoligenes_group, Clostridiales, Lachnospiraceae_NK4A136_group, Delftia, Dubosiella, and Romboutsia were strongly correlated with specific BA monomers.

CONCLUSIONS

YTP modulates bile salt hydrolase-related microbial genera to activate alternative bile acid synthesis pathways, thereby inhibiting NAFLD progression. These results suggest that YTP may serve as a potential probiotic formulation, offering a feasible dietary intervention for NAFLD.

The nuclear receptor LRH-1 discriminates between ligands using distinct allosteric signaling circuits

Nuclear receptors (NRs) are transcription factors that regulate essential biological processes in response to cognate ligands. An important part of NR function involves ligand-induced conformational changes that recruit coregulator proteins to the activation function surface (AFS), ~15 Å away from the ligand-binding pocket. Ligands must communicate with the AFS to recruit appropriate coregulators and elicit different transcriptional outcomes, but this communication is poorly understood. These studies illuminate allosteric communication networks underlying activation of liver receptor homolog-1 (LRH-1), a NR that regulates development, metabolism, cancer progression, and intestinal inflammation. Using >100 μs of all-atom molecular dynamics simulations involving 74 LRH-1 complexes, we identify distinct signaling circuits used by active and inactive ligands for AFS communication. Inactive ligands communicate via strong, coordinated motions along paths through the receptor to the AFS. Activating ligands disrupt the "inactive" circuit and induce connectivity with a second allosteric site. Ligand-contacting residues in helix 7 help mediate the switch between circuits, suggesting new avenues for developing LRH-1-targeted therapeutics. We also elucidate aspects of coregulator signaling, showing that localized, destabilizing fluctuations are induced by inappropriate ligand-coregulator pairings. These studies have uncovered novel features of LRH-1 allostery, and the quantitative approach used to analyze many simulations provides a framework to study allosteric signaling in other receptors.

Multi‑omics‑based analysis of the regulatory mechanism of gypenosides on bile acids in hypercholesterolemic mice

Gynostemma pentaphyllum is a traditional medicine used by ethnic minorities in southwest China and gypenosides are currently recognized as essential components of the pharmacological substances of Gynostemma pentaphyllum, which are effective in regulating metabolic syndrome, especially in improving hepatic metabolic disorders. The present study randomly divided C57BL/6J male mice into the normal diet control group (ND), high-fat diet modeling group (HFD) and gypenosides group (GP). Liquid chromatography-mass spectrometry (UPLC-MS) was applied to quantify bile acids in the liver, bile and serum of mice in ND, HFD and GP groups. Liver proteins were extracted for trypsin hydrolysis and analyzed quantitatively using UPLC-MS + MS/MS (timsTOF Pro 2). Total mouse liver RNA was extracted from ND, HFD and GP groups respectively, cDNA sequencing libraries constructed and sequenced using BGISEQ-500 sequencing platform. The expression of key genes Fxr, Shp, Cyp7a1, Cyp8b1, and Abab11 was detected by RT-qPCR. The results showed that gypenosides accelerated free bile acid synthesis by promoting the expression of bile acid synthase CYP7A1 and CYP8B1 genes and proteins and accelerating the secretion of conjugated bile acids from the liver to the bile ducts. GP inhibited the bile acid transporters solute carrier organic anion transporter family member (SLCO) 1A1 and SLCO1A4, reducing the reabsorption of free bile acids and accelerating the excretion of free bile acids from the blood to the kidneys. It also promoted the metabolic enzyme CYP3A11, which accelerated the metabolism and clearance of bile acids, thus maintaining the balance of the bile acid internal environment.

The nuclear receptor LRH-1 discriminates between ligands using distinct allosteric signaling circuits

Nuclear receptors (NRs) are transcription factors that regulate essential biological processes in response to cognate ligands. An important part of NR function involves ligand-induced conformational changes that recruit coregulator proteins to the activation function surface (AFS), ~15 Å away from the ligand binding pocket. Ligands must communicate with the AFS to recruit appropriate coregulators and elicit different transcriptional outcomes, but this communication is poorly understood. These studies illuminate allosteric communication networks underlying activation of liver receptor homolog-1 (LRH-1), a NR that regulates development, metabolism, cancer progression and intestinal inflammation. Using >100 microseconds of all-atom molecular dynamics simulations involving 69 LRH-1 complexes, we identify distinct signaling circuits used by active and inactive ligands for AFS communication. Inactive ligands communicate via strong, coordinated motions along paths through the receptor to the AFS. Activating ligands disrupt the "inactive" circuit by inducing connectivity elsewhere. Ligand-contacting residues in helix 7 help mediate the switch between circuits, suggesting new avenues for developing LRH-1-targeted therapeutics. We also elucidate aspects of coregulator signaling, showing that localized, destabilizing fluctuations are induced by inappropriate ligand-coregulator pairings. These studies have uncovered novel features of LRH-1 allostery, and the quantitative approach used to analyze many simulations provides a framework to study allosteric signaling in other receptors.

Dihydroartemisinin promoted FXR expression independent of YAP1 in hepatocellular carcinoma

Loss of FXR, one of bile acid receptors, enlarged livers. Yes-associated protein 1 (YAP1), a dominant oncogene, promotes hepatocellular carcinoma (HCC). However, the relationship between FXR and YAP1 was unspecified in bile acid homeostasis in HCC. Here, we used TIMER2.0, the Cancer Genome Atlas (TCGA) Database, and Kaplan-Meier Plotter Database and discovered that FXR was positively correlated with better prognosis in liver cancer patients. Our previous research showed that dihydroartemisinin (DHA) inhibited cell proliferation in HepG2 and HepG22215 cells. However, the relationship of YAP1 and the bile acid receptor FXR remains elusive during DHA treatment. Furthermore, we showed that DHA improved FXR and reduced YAP1 in the liver cancer cells and mice. Additionally, the expression of nucleus protein FXR was enhanced in Yap1^LKO mice with liver cancer. DHA promoted the expression level of whole and nuclear protein FXR independent of YAP1 in Yap1^LKO mice with liver cancer. DHA declined cholesterol 7α-hydroxylase, but not sterol 27-hydroxylase, and depressed cholic acid and chenodeoxycholic acid of liver tissue in Yap1^LKO mice with liver cancer. Generally, our results suggested that DHA improved FXR and declined YAP1 to suppress bile acid metabolism. Thus, we suggested that FXR acted as a potential therapeutic target in HCC.

Regulatory mechanisms of the bile salt export pump (BSEP/ABCB11) and its role in related diseases

The bile salt export pump (BSEP/ABCB11) is located on the apical membrane and mediates the secretion of bile salts from hepatocytes into the bile. BSEP-mediated bile salt efflux is the rate-limiting step of bile salt secretion and the main driving force of bile flow. BSEP drives and maintains the enterohepatic circulation of bile salts. In recent years, research efforts have been focused on understanding the physiological and pathological functions and regulatory mechanisms of BSEP. These studies elucidated the roles of farnesoid X receptor (FXR), AMP-activated protein kinase (AMPK), liver receptor homolog-1(LRH-1) and nuclear factor erythroid 2-related factor 2 (Nrf-2) in BSEP expression and discovered some regulatory factors which participate in its post-transcriptional regulation. A series of liver diseases have also been shown to be related to BSEP expression and dysfunction, such as cholestasis, drug-induced liver injury, and gallstones. Here, we systematically review and summarize recent literature on BSEP structure, physiological functions, regulatory mechanisms, and related diseases.

Nuclear receptor subfamily 5 group A member 2 (NR5A2): role in health and diseases

Nuclear receptors are the regulatory molecules that mediate cellular signals as they interact with specific DNA sequences. NR5A2 is a member of NR5A subfamily having four members (Nr5a1-Nr5a4). NR5A2 shows involvement in diverse biological processes like reverse cholesterol transport, embryonic stem cell pluripotency, steroidogenesis, development and differentiation of embryo, and adult homeostasis. NR5A2 haploinsufficiency has been seen associated with chronic pancreatitis, pancreatic and gastrointestinal cancer. There is a close relationship between the progression of pancreatic cancer from chronic pancreatitis, NR5A2 serving a common link. NR5A2 activity is regulated by intracellular phospholipids, transcriptional coregulators and post-translational modifications. The specific ligand of NR5A2 is unknown hence called an orphan receptor, but specific phospholipids such as dilauroyl phosphatidylcholine and diundecanoyl phosphatidylcholine act as a ligand and they are established drug targets in various diseases. This review will focus on the NR5A2 structure, regulation of its activity, and role in biological processes and diseases. In future, need more emphasis on discovering small molecule agonists and antagonist, which act as a drug target for therapeutic applications.

Nuclear receptor NR5A2 negatively regulates cell proliferation and tumor growth in nervous system malignancies

Nervous system malignancies are characterized by rapid progression and poor survival rates. These clinical observations underscore the need for novel therapeutic insights and pharmacological targets. To this end, here, we identify the orphan nuclear receptor NR5A2/LRH1 as a negative regulator of cancer cell proliferation and promising pharmacological target for nervous system-related tumors. In particular, clinical data from publicly available databases suggest that high expression levels of NR5A2 are associated with favorable prognosis in patients with glioblastoma and neuroblastoma tumors. Consistently, we experimentally show that NR5A2 is sufficient to strongly suppress proliferation of both human and mouse glioblastoma and neuroblastoma cells without inducing apoptosis. Moreover, short hairpin RNA-mediated knockdown of the basal expression levels of NR5A2 in glioblastoma cells promotes their cell cycle progression. The antiproliferative effect of NR5A2 is mediated by the transcriptional induction of negative regulators of the cell cycle, CDKN1A (encoding for p21cip1), CDKN1B (encoding for p27kip1) and Prox1 Interestingly, two well-established agonists of NR5A2, dilauroyl phosphatidylcholine (DLPC) and diundecanoyl phosphatidylcholine, are able to mimic the antiproliferative action of NR5A2 in human glioblastoma cells via the induction of the same critical genes. Most importantly, treatment with DLPC inhibits glioblastoma tumor growth in vivo in heterotopic and orthotopic xenograft mouse models. These data indicate a tumor suppressor role of NR5A2 in the nervous system and render this nuclear receptor a potential pharmacological target for the treatment of nervous tissue-related tumors.

Limb expression 1-like (LIX1L) protein promotes cholestatic liver injury by regulating bile acid metabolism

BACKGROUND & AIMS

Cholestatic liver diseases comprise a variety of disorders of bile formation and/or flow which generally result in progressive hepatobiliary injury. Regulation of bile acid (BA) synthesis and homeostasis is a promising strategy for the treatment of cholestatic liver disease. Limb expression 1-like protein (LIX1L) plays an important role in post-transcriptional gene regulation, yet its role in cholestatic liver injury remains unclear.

METHODS

LIX1L expression was studied in patients with primary sclerosing cholangitis (PSC) or primary biliary cholangitis (PBC), and 3 murine models of cholestasis (bile duct ligation [BDL], Mdr2 knockout [Mdr2^-/-], and cholic acid [CA] feeding). Lix1l knockout mice were employed to investigate the function of LIX1L in cholestatic liver diseases. Chromatin immunoprecipitation assays were performed to determine whether Egr-1 bound to the Lix1l promoter. MiRNA expression profiling was analyzed by microarray. An adeno-associated virus (AAV)-mediated hepatic delivery system was used to identify the function of miR-191-3p in vivo.

RESULTS

LIX1L expression was increased in the livers of patients with PSC and PBC, and in the 3 murine models, as well as in BA-stimulated primary mouse hepatocytes. BA-induced Lix1l upregulation was dependent on Egr-1, which served as a transcriptional activator. LIX1L deficiency attenuated cholestatic liver injury in BDL and Mdr2^-/- mice. MiR-191-3p was the most reduced miRNA in livers of WT-BDL mice, while it was restored in Lix1l^-/--BDL mice. MiR-191-3p targets and downregulates Lrh-1, thereby inhibiting Cyp7a1 and Cyp8b1 expression. AAV-mediated hepatic delivery of miR-191-3p significantly attenuated cholestatic liver injury in Mdr2^-/- mice.

CONCLUSIONS

LIX1L deficiency alleviates cholestatic liver injury by inhibiting BA synthesis. LIX1L functions as a nexus linking BA/Egr-1 and miR-191-3p/LRH-1 signaling. LIX1L and miR-191-3p may be promising targets for the treatment of BA-associated hepatobiliary diseases.

LAY SUMMARY

Bile acid homeostasis can be impaired in cholestatic liver diseases. Our study identified a novel mechanism of positive feedback regulation in cholestasis. LIX1L and miR-191-3p represent potential therapeutic targets for cholestatic liver diseases.

Emerging functions of the nuclear receptor LRH-1 in liver physiology and pathology

Nuclear receptors play pleiotropic roles in cell differentiation, development, proliferation, and metabolic processes to govern liver physiology and pathology. The nuclear receptor, liver receptor homolog-1 (LRH-1, NR5A2), originally identified in the liver as a regulator of bile acid and cholesterol homeostasis, was recently recognized to coordinate a multitude of other hepatic metabolic processes, including glucose and lipid processing, methyl group sensing, and cellular stress responses. In this review, we summarize the physiological and pathophysiological functions of LRH-1 in the liver, as well as the molecular mechanisms underlying these processes. This review also focuses on the recent advances highlighting LRH-1 as an attractive target for liver-associated diseases, such as non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC).

Inflammation-induced cholestasis in cancer cachexia

BACKGROUND

Cancer cachexia is a debilitating metabolic syndrome contributing to cancer death. Organs other than the muscle may contribute to the pathogenesis of cancer cachexia. This work explores new mechanisms underlying hepatic alterations in cancer cachexia.

METHODS

We used transcriptomics to reveal the hepatic gene expression profile in the colon carcinoma 26 cachectic mouse model. We performed bile acid, tissue mRNA, histological, biochemical, and western blot analyses. Two interventional studies were performed using a neutralizing interleukin 6 antibody and a bile acid sequestrant, cholestyramine. Our findings were evaluated in a cohort of 94 colorectal cancer patients with or without cachexia (43/51).

RESULTS

In colon carcinoma 26 cachectic mice, we discovered alterations in five inflammatory pathways as well as in other pathways, including bile acid metabolism, fatty acid metabolism, and xenobiotic metabolism (normalized enrichment scores of -1.97, -2.16, and -1.34, respectively; all Padj < 0.05). The hepatobiliary transport system was deeply impaired in cachectic mice, leading to increased systemic and hepatic bile acid levels (+1512 ± 511.6 pmol/mg, P = 0.01) and increased hepatic inflammatory cytokines and neutrophil recruitment to the liver of cachectic mice (+43.36 ± 16.01 neutrophils per square millimetre, P = 0.001). Adaptive mechanisms were set up to counteract this bile acid accumulation by repressing bile acid synthesis and by enhancing alternative routes of basolateral bile acid efflux. Targeting bile acids using cholestyramine reduced hepatic inflammation, without affecting the hepatobiliary transporters (e.g. tumour necrosis factor α signalling via NFκB and inflammatory response pathways, normalized enrichment scores of -1.44 and -1.36, all Padj < 0.05). Reducing interleukin 6 levels counteracted the change in expression of genes involved in the hepatobiliary transport, bile acid synthesis, and inflammation. Serum bile acid levels were increased in cachectic vs. non-cachectic cancer patients (e.g. total bile acids, +5.409 ± 1.834 μM, P = 0.026) and were strongly correlated to systemic inflammation (taurochenodeoxycholic acid and C-reactive protein: ρ = 0.36, Padj = 0.017).

CONCLUSIONS

We show alterations in bile acid metabolism and hepatobiliary secretion in cancer cachexia. In this context, we demonstrate the contribution of systemic inflammation to the impairment of the hepatobiliary transport system and the role played by bile acids in the hepatic inflammation. This work paves the way to a better understanding of the role of the liver in cancer cachexia.

Effects of Schizochytrium and micro-minerals on immune, antioxidant, inflammatory and lipid-metabolism status of Micropterus salmoides fed high- and low-fishmeal diets

A 12-week factorial experiment was conducted to investigate the interactive effects of dietary algal meal (Schizochytrium sp., AM) and micro-minerals (MM, either organic [OM] or inorganic [IM]) on the immune and antioxidant status, and the expression of hepatic genes involved in the regulation of antioxidants, inflammatory cytokines, lipid metabolism, and organ growth of largemouth bass (LMB; Micropterus salmoides) fed high-and low-fishmeal (FM) diets. For this purpose, two sets of six iso-nitrogenous (42% crude protein) and iso-lipidic (12% lipid) diets, such as high (35%) and low (10%) FM diets were formulated. Within each FM level, AM was used to replace 50% or 100% of fish oil (FO), or without AM (FO control) and supplemented with either OM or IM (Fe, Zn, Mn, Cu, and Se). Diets were fed to juvenile LMB (initial weight, 25.87 ± 0.08 g) to near satiation twice daily. The results indicated that FO replacement by dietary AM did not change the levels of most biochemical (ALB, AMY, TP and GLOB), antioxidants (SOD, GPx and GSH), and immune (IgM and lysozyme) parameters in LMB, except ALP and CAT. MM affected only hepatic GSH, with lower values in fish fed the OM diets. FM influenced the levels of ALP, AMY, GLOB, IgM, and MDA (P < 0.05). A three-way interactive effect (P = 0.016) was found on IgM only, with lower levels in fish fed diet 12 (low-FM, AM100, OM). Subsequently, the relative expressions of hepatic antioxidants (Cu/Zn-SOD and GPx-4), inflammatory cytokines (TNF-α and TGF-β1), lipid metabolism (FASN and CYP7A1), and organ growth (IGF-I) related genes were affected by the dietary treatments, with interactions being present in Cu/Zn-SOD, TNF-α, TGF-β1, FASN and IGF-I. Overall, dietary AM could be used as an alternative to FO in low-FM diets without compromising the health of LMB, especially when it is supplemented with MM.

Theabrownin from Pu-erh tea attenuates hypercholesterolemia via modulation of gut microbiota and bile acid metabolism

Pu-erh tea displays cholesterol-lowering properties, but the underlying mechanism has not been elucidated. Theabrownin is one of the most active and abundant pigments in Pu-erh tea. Here, we show that theabrownin alters the gut microbiota in mice and humans, predominantly suppressing microbes associated with bile-salt hydrolase (BSH) activity. Theabrownin increases the levels of ileal conjugated bile acids (BAs) which, in turn, inhibit the intestinal FXR-FGF15 signaling pathway, resulting in increased hepatic production and fecal excretion of BAs, reduced hepatic cholesterol, and decreased lipogenesis. The inhibition of intestinal FXR-FGF15 signaling is accompanied by increased gene expression of enzymes in the alternative BA synthetic pathway, production of hepatic chenodeoxycholic acid, activation of hepatic FXR, and hepatic lipolysis. Our results shed light into the mechanisms behind the cholesterol- and lipid-lowering effects of Pu-erh tea, and suggest that decreased intestinal BSH microbes and/or decreased FXR-FGF15 signaling may be potential anti-hypercholesterolemia and anti-hyperlipidemia therapies.

Regulation of liver receptor homologue-1 by DDB2 E3 ligase activity is critical for hepatic glucose metabolism

Liver receptor homologue-1 (LRH-1) plays a critical role in hepatic metabolism and disease. Here we show that LRH-1 protein stability is regulated by the cullin 4 (CUL4) E3 ubiquitin ligase complex. We found that DNA damage-binding protein 2 (DDB2) directly interacts with LRH-1 and functions as a substrate recognition component of CUL4-DDB1 to promote LRH-1 ubiquitination and proteasomal degradation. In human hepatoma (HepG2) cells, we observed that protein levels of endogenous LRH-1 are increased by insulin without a change in mRNA levels of LRH-1. However, overexpression of DDB2 impaired the insulin-stimulated increase in LRH-1 levels. In addition, DDB2 overexpression decreased LRH-1 transcriptional activation and expression of target genes, such as glucokinase, whereas knockdown of DDB2 increased the expression of glucokinase. Finally, we demonstrated that DDB2 knockdown increases glucose uptake and intracellular levels of glucose-6-phosphate in HepG2 cells. Our study reveals a novel regulatory mechanism of LRH-1 activity and suggests a role for DDB2 in hepatic glucose metabolism.

LRH1-driven transcription factor circuitry for hepatocyte identity: Super-enhancer cistromic analysis

BACKGROUND

The injured liver loses normal function, with concomitant decrease of key identity genes. Super-enhancers contribute to mammalian cell identity. Here, we identified core transcription factors (TFs) that are active in hepatocytes, using genome-wide analysis and hierarchical ordering of super-enhancer distribution.

METHODS

Expression of core TFs was assessed in a cohort of patients with hepatitis or cirrhosis and animal models. Quantitative PCR, chromatin immunoprecipitation assays, and hydrodynamic gene delivery methods were used to assess gene regulation and hepatocyte viability. RNA-sequencing data were generated to investigate the role of LRH1 in hepatocyte protection from injury.

RESULTS

Network analysis of super-enhancer-associated gene interactions and expression arrays for cohorts of patients with hepatitis and cirrhosis enabled us to identify a super-enhancer-associated network, and LRH1, HNF4α, PPARα, and RXRα as core TFs. In mouse models, expression of core TFs was robustly inhibited by single and multiple challenge(s) with liver toxicant. RNA-seq analysis revealed changes in expression in the super-enhancer-associated genes sensitively biased toward repression by intoxication. LRH1 gene delivery prevented the loss of hepatic super-enhancer-associated signaling circuitry in toxicant-challenged mice, and protected the liver from injury, indicating the role of LRH1 in hepatocyte identity and viability. In hepatocytes, overexpression of each core TF promoted induction of other TFs.

CONCLUSION

Overall, this study identified LRH1-driven pathway as a circuitry responsible for hepatocyte identity by using cistromic analysis, improving our understanding of liver pathophysiology and identifying novel therapeutic targets.

Liver receptor homologue 1, a novel prognostic marker in colon cancer patients

Liver receptor homologue 1 (LRH-1) is an orphan nuclear receptor that is highly expressed in a variety of cancer tissues, promotes tumor cell proliferation and metastasis, and is involved in the tumor cell cycle and apoptosis. The aim of the present study was to assess the association between the expression of LRH-1 and the prognosis of patients with colon cancer. Immunohistochemistry was used to detect the expression of LRH1 in 128 cases of colon cancer and adjacent tissues. The 5-year survival rate was obtained from telephone follow-up data, outpatient review and through access to medical records. Positive expression of LRH-1 was found in 108/128 colon cancer samples, compared with 17/128 normal tissues. Statistical analysis showed that positive LRH-1 expression was significantly associated with clinical pathological stage, depth of invasion and lymph node metastasis. The overall survival (OS) rate of patients with positive LRH-1 expression was significantly lower than that of patients with low expression. Multivariate analysis showed that LRH-1 expression could be used as an independent predictor of OS. In conclusion, the present findings suggest that LRH-1 may serve an important role in the development and progression of colon cancer, with potential value as a prognostic molecular marker that could be used to assist in the diagnosis and evaluation of colon cancer. LRH-1 may become a target for novel therapies for patients with colon cancer.

Prenatal Exposure to a Maternal High Fat Diet Increases Hepatic Cholesterol Accumulation in Intrauterine Growth Restricted Rats in Part Through MicroRNA-122 Inhibition of Cyp7a1

Intrauterine growth restriction (IUGR) and consumption of a high saturated fat diet (HFD) increase the risk of hypercholesterolemia, a leading cause of morbidity and mortality. The mechanism through which the cumulative impact of IUGR and in utero exposure to a maternal HFD increase cholesterol levels remains unknown. Cholesterol 7α hydroxylase (Cyp7a1) initiates catabolism of cholesterol to bile acids for elimination from the body, and is regulated by microRNA-122 (miR-122). We hypothesized that IUGR rats exposed to a maternal HFD would have increased cholesterol and decreased Cyp7a1 protein levels in juvenile rats, findings which would be normalized by administration of a miR-122 inhibitor. To test our hypothesis we used a rat model of surgically induced IUGR and fed the dams a regular diet or a HFD from prior to conception through lactation. At the time of weaning, IUGR female rats exposed to a maternal HFD had increased hepatic cholesterol, decreased hepatic Cyp7a1 protein and hepatic bile acids, and increased hepatic miR-122 compared to non-IUGR rats exposed to the same HFD. In vivo inhibition of miR-122 increased hepatic Cyp7a1 protein and decreased hepatic cholesterol. Our findings suggest that IUGR combined with a maternal HFD decreased cholesterol catabolism to bile acids, in part, via miR-122 inhibition of Cyp7a1.

Animal models to study bile acid metabolism

The use of animal models, particularly genetically modified mice, continues to play a critical role in studying the relationship between bile acid metabolism and human liver disease. Over the past 20 years, these studies have been instrumental in elucidating the major pathways responsible for bile acid biosynthesis and enterohepatic cycling, and the molecular mechanisms regulating those pathways. This work also revealed bile acid differences between species, particularly in the composition, physicochemical properties, and signaling potential of the bile acid pool. These species differences may limit the ability to translate findings regarding bile acid-related disease processes from mice to humans. In this review, we focus primarily on mouse models and also briefly discuss dietary or surgical models commonly used to study the basic mechanisms underlying bile acid metabolism. Important phenotypic species differences in bile acid metabolism between mice and humans are highlighted.

REV-ERBα Regulates CYP7A1 Through Repression of Liver Receptor Homolog-1

Nuclear heme receptor reverse erythroblastosis virus (REV-ERB) α (a transcriptional repressor) is known to regulate cholesterol 7α-hydroxylase (CYP7A1) and bile acid synthesis. However, the mechanism for REV-ERBα regulation of CYP7A1 remains elusive. Here, we investigate the role of LRH-1 in REV-ERBα regulation of CYP7A1 and cholesterol metabolism. We first characterized the tertiary amine N-(4-chloro-2-methylbenzyl)-N-(4-chlorobenzyl)-1-(5-nitrothiophen-2-yl)methanamine (GSK2945) as a highly specific Rev-erbα/REV-ERBα antagonist using cell-based assays and confirmed expression of Rev-erbα in mouse liver. GSK2945 treatment increased hepatic mouse cholesterol 7α-hydroxylase (Cyp7a1) level and lowered plasma cholesterol in wild-type mice. Likewise, the compound increased the expression and microsomal activity of Cyp7a1 in hypercholesterolemic mice. This coincided with reduced plasma and liver cholesterol and enhanced production of bile acids. Increased levels of Cyp7a1/CYP7A1 were also found in mouse and human primary hepatocytes after GSK2945 treatment. In these experiments, we observed parallel increases in Lrh-1/LRH-1 (a known hepatic activator of Cyp7a1/CYP7A1) mRNA and protein. Luciferase reporter, mobility shift, and chromatin immunoprecipitation assays revealed that Lrh-1/LRH-1 was a direct Rev-erbα/REV-ERBα target gene. Furthermore, conditional deletion of Lrh-1 in the liver abrogated the regulatory effects of Rev-erbα on Cyp7a1 and cholesterol metabolism in mice. In conclusion, Rev-erbα regulates Cyp7a1 and cholesterol metabolism through its repression of the Lrh-1 receptor. Targeting the REV-ERBα/LRH-1 axis may represent a novel approach for management of cholesterol-related diseases.

Activation of PPARα decreases bile acids in livers of female mice while maintaining bile flow and biliary bile acid excretion

Fibrates are hypolipidemic drugs that act as activators of peroxisome proliferator-activated receptor α (PPARα). In both humans and rodents, females were reported to be less responsive to fibrates than males. Previous studies on fibrates and PPARα usually involved male mice, but little has been done in females. The present study aimed to provide the first comprehensive analysis of the effects of clofibrate (CLOF) and PPARα on bile acid (BA) homeostasis in female mice. Study in WT male mice showed that a 4-day CLOF treatment increased liver weight, bile flow, and biliary BA excretion, but decreased total BAs in both serum and liver. In contrast, WT female mice were less susceptible to these CLOF-mediated responses observed in males. In WT female mice, CLOF decreased total BAs in the liver, but had little effect on the mRNAs of hepatic BA-related genes. Next, a comparative analysis between WT and PPARα-null female mice showed that lack of PPARα in female mice decreased total BAs in serum, but had little effect on total BAs in liver or bile. However, lack of PPARα in female mice increased mRNAs of BA synthetic enzymes (Cyp7a1, Cyp8b1, Cyp27a1, and Cyp7b1) and transporters (Ntcp, Oatp1a1, Oatp1b2, and Mrp3). Furthermore, the increase of Cyp7a1 in PPARα-null female mice was associated with an increase in liver Fxr-Shp-Lrh-1 signaling. In conclusion, female mice are resistant to CLOF-mediated effects on BA metabolism observed in males, which could be attributed to PPARα-mediated suppression in females on genes involved in BA synthesis and transport.

LRH-1-dependent programming of mitochondrial glutamine processing drives liver cancer

Xu et al. identify the nuclear receptor liver receptor homolog 1 (LRH-1) as a key regulator in the process of hepatic tumorigenesis through the coordination of a noncanonical glutamine pathway that is reliant on the mitochondrial and cytosolic transaminases glutamate pyruvate transaminase 2 (GPT2) and glutamate oxaloacetate transaminase 1 (GOT1), which fuel anabolic metabolism.

Various tumors develop addiction to glutamine to support uncontrolled cell proliferation. Here we identify the nuclear receptor liver receptor homolog 1 (LRH-1) as a key regulator in the process of hepatic tumorigenesis through the coordination of a noncanonical glutamine pathway that is reliant on the mitochondrial and cytosolic transaminases glutamate pyruvate transaminase 2 (GPT2) and glutamate oxaloacetate transaminase 1 (GOT1), which fuel anabolic metabolism. In particular, we show that gain and loss of function of hepatic LRH-1 modulate the expression and activity of mitochondrial glutaminase 2 (GLS2), the first and rate-limiting step of this pathway. Acute and chronic deletion of hepatic LRH-1 blunts the deamination of glutamine and reduces glutamine-dependent anaplerosis. The robust reduction in glutaminolysis and the limiting availability of α-ketoglutarate in turn inhibit mTORC1 signaling to eventually block cell growth and proliferation. Collectively, these studies highlight the importance of LRH-1 in coordinating glutamine-induced metabolism and signaling to promote hepatocellular carcinogenesis.

Prostaglandin E2 promotes hepatic bile acid synthesis by an E prostanoid receptor 3-mediated hepatocyte nuclear receptor 4α/cholesterol 7α-hydroxylase pathway in mice

Prostaglandin E₂ (PGE₂ ) is an important lipid mediator of inflammation. However, whether and how PGE₂ regulates hepatic cholesterol metabolism remains unknown. We found that expression of the PGE₂ receptor, E prostanoid receptor 3 (EP3) expression is remarkably increased in hepatocytes in response to hyperlipidemic stress. Hepatocyte-specific deletion of EP3 receptor (EP3^hep-/- ) results in hypercholesterolemia and augments diet-induced atherosclerosis in low-density lipoprotein receptor knockout (Ldlr^-/- ) mice. Cholesterol 7α-hydroxylase (CYP7A1) is down-regulated in livers of EP3^hep-/- Ldlr^-/- mice, leading to suppressed hepatic bile acid (BA) biosynthesis. Mechanistically, hepatic-EP3 deficiency suppresses CYP7A1 expression by elevating protein kinase A (PKA)-dependent Ser143 phosphorylation of hepatocyte nuclear receptor 4α (HNF4α). Disruption of the PKA-HNF4α interaction and BA sequestration rescue impaired BA excretion and ameliorated atherosclerosis in EP3^hep-/- Ldlr^-/- mice.

CONCLUSION

Our results demonstrated an unexpected role of proinflammatory mediator PGE₂ in improving hepatic cholesterol metabolism through activation of the EP3-mediated PKA/HNF4α/CYP7A1 pathway, indicating that inhibition of this pathway may be a novel therapeutic strategy for dyslipidemia and atherosclerosis. (Hepatology 2017;65:999-1014).

Induction of farnesoid X receptor signaling in germ-free mice colonized with a human microbiota

The gut microbiota influences the development and progression of metabolic diseases partly by metabolism of bile acids (BAs) and modified signaling through the farnesoid X receptor (FXR). In this study, we aimed to determine how the human gut microbiota metabolizes murine BAs and affects FXR signaling in colonized mice. We colonized germ-free mice with cecal content from a mouse donor or feces from a human donor and euthanized the mice after short-term (2 weeks) or long-term (15 weeks) colonization. We analyzed the gut microbiota and BA composition and expression of FXR target genes in ileum and liver. We found that cecal microbiota composition differed between mice colonized with mouse and human microbiota and was stable over time. Human and mouse microbiota reduced total BA levels similarly, but the humanized mice produced less secondary BAs. The human microbiota was able to reduce the levels of tauro-β-muricholic acid and induce expression of FXR target genes Fgf15 and Shp in ileum after long-term colonization. We show that a human microbiota can change BA composition and induce FXR signaling in colonized mice, but the levels of secondary BAs produced are lower than in mice colonized with a mouse microbiota.

The characterization of an intestine-like genomic signature maintained during Barrett's-associated adenocarcinogenesis reveals an NR5A2-mediated promotion of cancer cell survival

Barrett’s oesophagus (BO), an intestinal-type metaplasia (IM), typically arising in conjunction with gastro-oesophageal reflux disease, is a prominent risk factor for the development of oesophageal adenocarcinoma (OAC). The molecular similarities between IM and normal intestinal tissues are ill-defined. Consequently, the contribution of intestine-enriched factors expressed within BO to oncogenesis is unclear. Herein, using transcriptomics we define the intestine-enriched genes expressed in meta-profiles of BO and OAC. Interestingly, 77% of the genes differentially expressed in a meta-profile of BO were similarly expressed in intestinal tissues. Furthermore, 85% of this intestine-like signature was maintained upon transition to OAC. Gene networking analysis of transcription factors within this signature revealed a network centred upon NR5A2, GATA6 and FOXA2, whose over-expression was determined in a cohort of BO and OAC patients. Simulated acid reflux was observed to induce the expression of both NR5A2 and GATA6. Using siRNA-mediated silencing and an NR5A2 antagonist we demonstrate that NR5A2-mediated cancer cell survival is facilitated through augmentation of GATA6 and anti-apoptotic factor BCL-XL levels. Abrogation of NR5A2-GATA6 expression in conjunction with BCL-XL co-silencing resulted in synergistically increased sensitivity to chemotherapeutics and photo-dynamic therapeutics. These findings characterize the intestine-like signature associated with IM which may have important consequences to adenocarcinogenesis.

Transcriptional regulation of Niemann-Pick C1-like 1 gene by liver receptor homolog-1

Factors that modulate cholesterol levels have major impacts on cardiovascular disease. Niemann-Pick C1-like 1 (NPC1L1) functions as a sterol transporter mediating intestinal cholesterol absorption and counter-balancing hepatobiliary cholesterol excretion. The liver receptor homolog 1 (LRH-1) had been shown to regulate genes involved in hepatic lipid metabolism and reverse cholesterol transport. To study whether human NPC1L1 gene is regulated transcriptionally by LRH-1, we have analyzed evolutionary conserved regions (ECRs) in HepG2 cells. One ECR was found to be responsive to the LRH-1. Through deletion studies, LRH-1 response element was identified and the binding of LRH-1 was demonstrated by EMSA and ChIP assays. When SREBP2, one of several transcription factors which had been shown to regulate NPC1L1 gene, was co-expressed with LRH-1, synergistic transcriptional activation resulted. In conclusion, we have identified LRH-1 response elements in NPC1L1 gene and propose that LRH-1 and SREBP may play important roles in regulating NPC1L1 gene. [BMB Reports 2015; 48(9): 513-518]

Resveratrol Attenuates Trimethylamine-N-Oxide (TMAO)-Induced Atherosclerosis by Regulating TMAO Synthesis and Bile Acid Metabolism via Remodeling of the Gut Microbiota

The gut microbiota is found to be strongly associated with atherosclerosis (AS). Resveratrol (RSV) is a natural phytoalexin with anti-AS effects; however, its mechanisms of action remain unclear. Therefore, we sought to determine whether the anti-AS effects of RSV were related to changes in the gut microbiota. We found that RSV attenuated trimethylamine-N-oxide (TMAO)-induced AS in ApoE^−/− mice. Meanwhile, RSV decreased TMAO levels by inhibiting commensal microbial trimethylamine (TMA) production via gut microbiota remodeling in mice. Moreover, RSV increased levels of the genera Lactobacillus and Bifidobacterium, which increased the bile salt hydrolase activity, thereby enhancing bile acid (BA) deconjugation and fecal excretion in C57BL/6J and ApoE^−/− mice. This was associated with a decrease in ileal BA content, repression of the enterohepatic farnesoid X receptor (FXR)-fibroblast growth factor 15 (FGF15) axis, and increased cholesterol 7a-hydroxylase (CYP7A1) expression and hepatic BA neosynthesis. An FXR antagonist had the same effect on FGF15 and CYP7A1 expression as RSV, while an FXR agonist abolished RSV-induced alterations in FGF15 and CYP7A1 expression. In mice treated with antibiotics, RSV neither decreased TMAO levels nor increased hepatic BA synthesis. Additionally, RSV-induced inhibition of TMAO-caused AS was also markedly abolished by antibiotics. In conclusion, RSV attenuated TMAO-induced AS by decreasing TMAO levels and increasing hepatic BA neosynthesis via gut microbiota remodeling, and the BA neosynthesis was partially mediated through the enterohepatic FXR-FGF15 axis.

Recently, trimethylamine-N-oxide (TMAO) has been identified as a novel and independent risk factor for promoting atherosclerosis (AS) partially through inhibiting hepatic bile acid (BA) synthesis. The gut microbiota plays a key role in the pathophysiology of TMAO-induced AS. Resveratrol (RSV) is a natural phytoalexin with prebiotic benefits. A growing body of evidence supports the hypothesis that phenolic phytochemicals with poor bioavailability are possibly acting primarily through remodeling of the gut microbiota. The current study showed that RSV attenuated TMAO-induced AS by decreasing TMAO levels and increasing hepatic BA neosynthesis via gut microbiota remodeling. And RSV-induced hepatic BA neosynthesis was partially mediated through downregulating the enterohepatic farnesoid X receptor-fibroblast growth factor 15 axis. These results offer new insights into the mechanisms responsible for RSV’s anti-AS effects and indicate that the gut microbiota may become an interesting target for pharmacological or dietary interventions to decrease the risk of developing cardiovascular diseases.

Structures and regulation of non-X orphan nuclear receptors: A retinoid hypothesis

Nuclear receptors are defined as a family of ligand regulated transcription factors [1-6]. While this definition reflects that ligand binding is a key property of nuclear receptors, it is still a heated subject of debate if all the nuclear receptors (48 human members) can bind ligands (ligands referred here to both physiological and synthetic ligands). Recent studies in nuclear receptor structure biology and pharmacology have undoubtedly increased our knowledge of nuclear receptor functions and their regulation. As a result, they point to new avenues for the discovery and development of nuclear receptor regulators, including nuclear receptor ligands. Here we review the recent literature on orphan nuclear receptor structural analysis and ligand identification, particularly on the orphan nuclear receptors that do not heterodimerize with retinoid X receptors, which we term as non-X orphan receptors. We also propose a speculative "retinoid hypothesis" for a subset of non-X orphan nuclear receptors, which we hope to help shed light on orphan nuclear receptor biology and drug discovery. This article is part of a Special Issue entitled 'Orphan Nuclear Receptors'.

Suppression of liver receptor homolog-1 by microRNA-451 represses the proliferation of osteosarcoma cells

Liver receptor homolog-1 (LRH-1) plays an important role in the onset and progression of many cancer types. However, the role of LRH-1 in osteosarcoma has not been well investigated. In this study, the critical role of LRH-1 in osteosarcoma cells was described. Quantitative polymerase chain reaction and Western blot analysis results revealed that LRH-1 was highly overexpressed in osteosarcoma cells. LRH-1 was knocked down by small interfering RNA (siRNA), and this phenomenon significantly inhibited osteosarcoma cell proliferation. Bioinformatics analysis results showed that LRH-1 contained putative binding sites of microRNA-451 (miR-451); this result was further validated through a dual-luciferase activity reporter assay. miR-451 was overexpressed in osteosarcoma cells through transfection of miR-451 mimics; miR-451 overexpression then significantly inhibited LRH-1 expression and cell proliferation. The loss of LRH-1 by siRNA or miR-451 mimics significantly impaired Wnt/β-catenin activity, leading to G0/G1 cell cycle arrest. Results showed that LRH-1 is implicated in osteosarcoma. Therefore, miR-451-induced suppression of LRH-1 can be a novel therapy to treat osteosarcoma.

Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational

HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.

SUMOylation-dependent LRH-1/PROX1 interaction promotes atherosclerosis by decreasing hepatic reverse cholesterol transport

Reverse cholesterol transport (RCT) is an antiatherogenic process in which excessive cholesterol from peripheral tissues is transported to the liver and finally excreted from the body via the bile. The nuclear receptor liver receptor homolog 1 (LRH-1) drives expression of genes regulating RCT, and its activity can be modified by different posttranslational modifications. Here, we show that atherosclerosis-prone mice carrying a mutation that abolishes SUMOylation of LRH-1 on K289R develop less aortic plaques than control littermates when exposed to a high-cholesterol diet. The mechanism underlying this atheroprotection involves an increase in RCT and its associated hepatic genes and is secondary to a compromised interaction of LRH-1 K289R with the corepressor prospero homeobox protein 1 (PROX1). Our study reveals that the SUMOylation status of a single nuclear receptor lysine residue can impact the development of a complex metabolic disease such as atherosclerosis.

The adipokine Retnla modulates cholesterol homeostasis in hyperlipidemic mice

Hyperlipidemia is a well-recognized risk factor for atherosclerosis and can be regulated by adipokines. Expression of the adipokine resistin-like molecule alpha (Retnla) is regulated by food intake; whether Retnla has a role in the pathogenesis of hyperlipidemia and atherosclerosis is unknown. Here we report that Retnla has a cholesterol-lowering effect and protects against atherosclerosis in low-density lipoprotein receptor-deficient mice. On a high-fat diet, Retnla deficiency promotes hypercholesterolaemia and atherosclerosis, whereas Retnla overexpression reverses these effects and improves the serum lipoprotein profile, with decreased cholesterol in the very low-density lipoprotein fraction concomitant with reduced serum apolipoprotein B levels. We show that Retnla upregulates cholesterol-7-α-hydroxylase, a key hepatic enzyme in the cholesterol catabolic pathway, through induction of its transcriptional activator liver receptor homologue-1, leading to increased excretion of cholesterol in the form of bile acids. These findings define Retnla as a novel therapeutic target for treating hypercholesterolaemia and atherosclerosis.

Identification of transcription factors and single nucleotide polymorphisms of Lrh1 and its homologous genes in Lrh1-knockout pancreas of mice

BACKGROUND

To identify transcription factors (TFs) and single nucleotide polymorphisms (SNPs) of Lrh1 (also named Nr5a2) and its homologous genes in Lrh1-knockout pancreas of mice.

METHODS

The RNA-Seq data GSE34030 were downloaded from Gene Expression Omnibus (GEO) database, including 2 Lrh1 pancreas knockout samples and 2 wild type samples. All reads were processed through TopHat and Cufflinks package to calculate gene-expression level. Then, the differentially expressed genes (DEGs) were identified via non-parametric algorithm (NOISeq) methods in R package, of which the homology genes of Lrh1 were identified via BLASTN analysis. Furthermore, the TFs of Lrh1 and its homologous genes were selected based on TRANSFAC database. Additionally, the SNPs were analyzed via SAM tool to record the locations of mutant sites.

RESULTS

Total 15683 DEGs were identified, of which 23 was Lrh1 homology genes (3 up-regulated and 20 down-regulated). Fetoprotein TF (FTF) was the only TF of Lrh1 identified and the promoter-binding factor of FTF was CYP7A. The SNP annotations of Lrh1 homologous genes showed that 92% of the mutation sites were occurred in intron and upstream. Three SNPs of Lrh1 were located in intron, while 1819 SNPs of Phkb were located in intron and 1343 SNPs were located in the upstream region.

CONCLUSION

FTF combined with CYP7A might play an important role in Lrh1 regulated pancreas-specific transcriptional network. Furthermore, the SNPs analysis of Lrh1 and its homology genes provided the candidate mutant sites that might affect the Lrh1-related production and secretion of pancreatic fluid.

Cross-talk between liver and intestine in control of cholesterol and energy homeostasis

A major hurdle for organisms to dispose of cholesterol is the inability to degrade the sterol nucleus which constitutes the central part of the molecule. Synthesis of the sterol nucleus requires a complex, energy costly, metabolic pathway but also generates a diverse array of intermediates serving crucial roles in cellular energy metabolism and signal transduction. This may be the reason why this complex pathway has survived evolutionary pressure. The only way to get rid of substantial amounts of cholesterol is conversion into bile acid or direct excretion of the sterol in the feces. The lack of versatility in disposal mechanisms causes a lack of flexibility to regulate cholesterol homeostasis which may underlie the considerable human pathology linked to cholesterol removal from the body. Export of cholesterol from the body requires an intricate communication between intestine and the liver. The last decade this inter-organ cross talk has been focus of intense research leading to considerable new insight. This novel information on particular the cross-talk between liver and intestine and role of bile acids as signal transducing molecules forms the focus of this review.

Human FXR regulates SHP expression through direct binding to an LRH-1 binding site, independent of an IR-1 and LRH-1

Background

Farnesoid X receptor/retinoid X receptor-alpha (FXR/RXRα) is the master transcriptional regulator of bile salt synthesis and transport in liver and intestine. FXR is activated by bile acids, RXRα by the vitamin A–derivative 9-cis retinoic acid (9cRA). Remarkably, 9cRA inhibits binding of FXR/RXRα to its response element, an inverted repeat-1 (IR-1). Still, most FXR/RXRα target genes are maximally expressed in the presence of both ligands, including the small heterodimer partner (SHP). Here, we revisited the FXR/RXRα-mediated regulation of human SHP.

Methods

A 579-bp hSHP promoter element was analyzed to locate FXR/chenodeoxycholic acid (CDCA)- and RXRα/9cRA-responsive elements. hSHP promoter constructs were analyzed in FXR/RXRα-transfected DLD-1, HEK293 and HepG2 cells exposed to CDCA, GW4064 (synthetic FXR ligand) and/or 9cRA. FXR-DNA interactions were analyzed by in vitro pull down assays.

Results

hSHP promoter elements lacking the previously identified IR-1 (−291/−279) largely maintained their activation by FXR/CDCA, but were unresponsive to 9cRA. FXR-mediated activation of the hSHP promoter was primarily dependent on the −122/−69 region. Pull down assays revealed a direct binding of FXR to the −122/−69 sequence, which was abrogated by site-specific mutations in a binding site for the liver receptor homolog-1 (LRH-1) at −78/−70. These mutations strongly impaired the FXR/CDCA-mediated activation, even in the context of a hSHP promoter containing the IR-1. LRH-1 did not increase FXR/RXRα-mediated activation of hSHP promoter activity.

Conclusion

FXR/CDCA-activated expression of SHP is primarily mediated through direct binding to an LRH-1 binding site, which is not modulated by LRH-1 and unresponsive to 9cRA. 9cRA-induced expression of SHP requires the IR-1 that overlaps with a direct repeat-2 (DR-2) and DR-4. This establishes for the first time a co-stimulatory, but independent, action of FXR and RXRα agonists.

LRH-1 heterozygous knockout mice are prone to mild obesity

Obesity is a global health problem that increases the risk of several common diseases. Liver receptor homologue-1 (LRH-1) has an important role in steroid hormone metabolism, which influences body weight. Whether LRH-1 gene deletion causes obesity is yet to be clarified. In this study using LRH-1 heterozygous knockout (LRH-1(+/-)) mice, we investigated the role of LRH-1 on body weight gain and glucose and lipid metabolism. LRH-1(+/-) mice showed mild but significant body weight gains compared with wild-type littermate mice after being fed a high-fat diet. We performed glucose tolerance tests and insulin tolerance tests and did not find any significant differences between wild-type and LRH-1(+/-) mice. To clarify how LRH-1 gene deletion affects body weight gain, we measured food intake, oxygen consumption, respiratory quotient, spontaneous activity and rectal temperature, and found no significant differences between wild-type and LRH-1(+/-) mice fed a normal diet and a high-fat diet. The results suggest that heterozygous gene deletion of LRH-1 causes body weight gains without any apparent worsening of glucose and lipid metabolism. Identifying the effects of LRH-1 on body weight will aid in understanding the pathogenesis of obesity.

Reversible infertility in a liver receptor homologue-1 (LRH-1)-knockdown mouse model

Liver receptor homologue-1 (LRH-1) is an orphan nuclear receptor that has been implicated in steroid hormone biosynthesis and fertility. Herein we describe a transgenic inducible short hairpin (sh) RNA mouse model that was used to study the effect of transient LRH-1 knockdown in vivo. Induction of expression of the shRNA directed against LRH-1 for 2–6 weeks resulted in 80% knockdown of LRH-1 protein in the ovary and complete infertility. Gonadotropin hyperstimulation could not rescue the observed defects in ovulation and corpus luteum formation in LRH-1-knockdown mice. The infertility phenotype was fully reversible because LRH-1-knockdown females became pregnant and delivered normal size litters and healthy pups after cessation of LRH-1 shRNA expression. Timed ovarian microarray analysis showed that, in line with the observed decrease in plasma progesterone levels, key steroid biosynthesis genes, namely Star, Cyp11a1, Hsd3b and Scarb1, were downregulated in LRH-1-knockdown ovaries. In contrast with what has been described previously, no clear effect was observed on oestrogenic activity in LRH-1-knockdown mice. Only Sult1e1 and, surprisingly, Hsd17b7 expression was modulated with potentially opposite effects on oestradiol bioavailability. In conclusion, the fully reversible infertility phenotype of LRH-1-knockdown mice shows the feasibility of an LRH-1 antagonist as new contraceptive therapy with a mechanism of action that most prominently affects cholesterol availability and progesterone production.

Nuclear receptor LRH-1 induces the reproductive neuropeptide kisspeptin in the hypothalamus

The differential expression and secretion of the neuropeptide kisspeptin from neurons in the arcuate (Arc) and anteroventral periventricular (AVPV) nuclei of the hypothalamus coordinate the temporal release of pituitary gonadotropins that control the female reproductive cycle. However, the molecular basis for this differential regulation is incompletely understood. Here, we report that liver receptor homolog-1 (LRH-1), a member of the nuclear receptor superfamily, is expressed in kisspeptin neurons in the Arc but not in the AVPV in female mice. LRH-1 binds directly to the kisspeptin (Kiss1) promoter and stimulates Kiss1 transcription. Deletion of LRH-1 from kisspeptin neurons in mice decreased Kiss1 expression in the Arc, leading to reduced plasma FSH levels, dysregulated follicle maturation, and prolongation of the estrous cycle. Conversely, overexpression of LRH-1 in kisspeptin neurons increased Arc Kiss1 expression and plasma FSH concentrations. These studies provide a molecular basis for the differential regulation of basal kisspeptin expression in Arc and AVPV neurons and reveal a prominent role for LRH-1 in hypothalamus in regulating the female reproductive axis.

Colesevelam hydrochloride: evidence for its use in the treatment of hypercholesterolemia and type 2 diabetes mellitus with insights into mechanism of action

Colesevelam hydrochloride is a molecularly engineered, second-generation bile acid sequestrant demonstrating enhanced specificity for bile acids which has been approved for use as adjunctive therapy to diet and exercise as monotherapy or in combination with a β-hydroxymethylglutaryl-coenzyme A reductase inhibitor for the reduction of elevated low-density lipoprotein cholesterol in patients with primary hypercholesterolemia. It is also the only lipid-lowering agent currently available in the United States which has been approved for use as adjunctive therapy in patients with type 2 diabetes mellitus whose glycemia remains inadequately controlled on therapy with metformin, sulfonylurea, or insulin. With the recent emphasis upon drug safety by the Food and Drug Administration and various consumer agencies, it is fitting that the role of nonsystemic lipid-lowering therapies such as bile acid sequestrants – with nearly 90 years of in-class, clinically safe experience – should be reexamined. This paper presents information on the major pharmacologic effects of colesevelam, including a discussion of recent data derived from both in vitro and in vivo rodent and human studies, which shed light on the putative mechanisms involved.

LRH-1-dependent glucose sensing determines intermediary metabolism in liver

Liver receptor homolog 1 (LRH-1), an established regulator of cholesterol and bile acid homeostasis, has recently emerged as a potential drug target for liver disease. Although LRH-1 activation may protect the liver against diet-induced steatosis and insulin resistance, little is known about how LRH-1 controls hepatic glucose and fatty acid metabolism under physiological conditions. We therefore assessed the role of LRH-1 in hepatic intermediary metabolism. In mice with conditional deletion of Lrh1 in liver, analysis of hepatic glucose fluxes revealed reduced glucokinase (GCK) and glycogen synthase fluxes as compared with those of wild-type littermates. These changes were attributed to direct transcriptional regulation of Gck by LRH-1. Impaired glucokinase-mediated glucose phosphorylation in LRH-1-deficient livers was also associated with reduced glycogen synthesis, glycolysis, and de novo lipogenesis in response to acute and prolonged glucose exposure. Accordingly, hepatic carbohydrate response element-binding protein activity was reduced in these animals. Cumulatively, these data identify LRH-1 as a key regulatory component of the hepatic glucose-sensing system required for proper integration of postprandial glucose and lipid metabolism.

Bile acid sequestrants: more than simple resins

PURPOSE OF REVIEW

Bile acid sequestrants (BAS) have been used for more than 50 years in the treatment of hypercholesterolemia. The last decade, bile acids are emerging as integrated regulators of metabolism via induction of various signal transduction pathways. Consequently, BAS treatment may exert unexpected side-effects. We discuss a selection of recently published studies that evaluated BAS in several metabolic diseases.

RECENT FINDINGS

Recently, an increasing body of evidence has shown that BAS in addition to ameliorating hypercholesterolemia are also effective in improving glycemic control in patients with type 2 diabetes, although the mechanism is not completely understood. Furthermore, some reports suggested using these compounds to modulate energy expenditure. Many of these effects have been related to the local effects of BAS in the intestine by directly binding bile acids in the intestine or indirectly by interfering with signaling processes.

SUMMARY

A substantial effort is being made by researchers to fully define the mechanism by which BAS improve glycemic control in type 2 diabetic patients. A new challenge will be to confirm in clinical trials the recent discoveries coming from animal experiments suggesting a role for bile acids in energy metabolism.