This snapshot reviews the current state of knowledge on genetic variants of nuclear receptors (NRs) involved in regulating various aspects of liver metabolism. Interindividual differences in responses to diet and other 'in-' and environmental stressors can be caused by variants in components of the NR regulatory gene network. We recapitulate recent evidence for the application of NRs in genetic diagnosis of monogenic liver disease. Genetic analysis of multifactorial liver diseases, such as nonalcoholic fatty liver disease and diabetes mellitus, pinpoints key players in disease predisposition and progression. In particular, NR1H4 variants have been associated with intrahepatic cholestasis of pregnancy and gallstone disease. Other examples include studies of NR1I2 and NR1I3 polymorphisms in patients with drug-induced liver injury and NR5A2 variation in cholangiocarcinoma. Associations of NR gene variants have been identified in patients with dyslipidemia and other metabolic syndrome-associated traits by genome-wide studies. Evidence from these analyses confirms a role for NR variation in common diseases, linking regulatory networks to complex and variable phenotypes. These new insights into the impact of NR variants offer perspectives for their future use in diagnosis and treatment of common diseases.

Background & aims: The nuclear receptor subfamily 1 group H member 4 (NR1H4, also called FXR) is a ligand-activated transcription factor that, upon binding of bile acids, regulates expression of genes involved in bile acid, fat, sugar, and amino acid metabolism. Transcript variants encode the FXR isoforms alpha1, alpha2, alpha3, and alpha4, which activate different genes that regulate metabolism. Little is known about the mechanisms by which the different isoforms regulate specific genes or how expression of these genes affects outcomes of patients given drugs that target FXR.

Methods: We determined genome-wide binding of FXR isoforms in mouse liver organoids that express individual FXR isoforms using chromatin immunoprecipitation, followed by sequencing analysis and DNA motif discovery. We validated regulatory DNA sequences by mobility shift assays and with luciferase reporters using mouse and human FXR isoforms. We analyzed mouse liver organoids and HepG2 cells that expressed the FXR isoforms using chromatin immunoprecipitation, quantitative PCR, and immunoblot assays. Organoids were analyzed for mitochondrial respiration, lipid droplet content, and triglyceride excretion. We used the FXR ligand obeticholic acid to induce FXR activity in organoids, cell lines and mice. We collected data on binding of FXR in mouse liver, and expression levels of FXR isoforms and gene targets in human liver tissue and primary human hepatocytes, from the Gene Expression Omnibus.

Results: In mouse liver cells, 89% of sites that bound FXR were bound by only FXRα2 or FXRα4, via direct interactions with the DNA sequence motif ER-2. Via binding, these isoforms regulated metabolic functions in liver cells, including carbon metabolism and lipogenesis. Incubation with obeticholic acid increased mitochondrial pyruvate transport and reduced insulin-induced lipogenesis in organoids that expressed FXRα2 but not FXRα1. In human liver tissues, levels of FXRα2 varied significantly and correlated with expression of genes predicted to be regulated via an ER-2 motif.

Conclusion: Most metabolic effects regulated by FXR in mouse and human liver cells are regulated by the FXRα2 isoform via specific binding to ER-2 motifs. Expression level of FXRα2 in liver might be used to predict responses of patients to treatment with FXR agonists.

Keywords: NASH; OCA; fatty liver; steatosis.

The cholesteryl ester transfer protein (CETP), a key player in cholesterol metabolism, has been shown to promote the transfer of triglycerides from very low density lipoprotein (VLDL) and low density lipoprotein (LDL) to high density lipoprotein (HDL) in exchange for cholesterol ester. Here we demonstrate that farnesoid X receptor alpha (FXRalpha; NR1H4) down-regulates CETP expression in HepG2 cells. A FXRalpha ligand, chenodeoxycholic acid (CDCA), suppressed basal mRNA levels of the CETP gene in HepG2 cells in a dose-dependent manner. Using gel shift and chromatin immunoprecipitation (ChIP) assays, we found that FXRalpha could bind to the liver X receptor alpha (LXRalpha; NR1H3) binding site (LXRE; DR4RE) located within the CETP 5' promoter region. FXRalpha suppressed LXRalpha-induced DR4RE-luciferase activity and this effect was mediated by a binding competition between FXRalpha and LXRalpha for DR4RE. Furthermore, the addition of CDCA together with a LXRalpha ligand, GW3965, to HepG2 cells was shown to substantially decrease mRNA levels of hepatic CETP gene, which is typically induced by GW3965. Together, our data demonstrate that FXRalpha down-regulates CETP gene expression via binding to the DR4RE sequence within the CETP 5' promoter and this FXRalpha binding is essential for FXRalpha inhibition of LXRalpha-induced CETP expression.

The nuclear receptors (NR)-farnesoid X receptor (FXR, NR1H4) and pregnane X receptor (PXR, NR1I2)-have important effects on the expression of genes related to the pharmacokinetics (PKs) of rosuvastatin. This study was designed to investigate whether the genetic variants in drug disposition genes (SLCO1B1 and ABCG2) combined with their upstream regulators (NR1H4 and NR1I2) would affect the PKs of rosuvastatin in a Chinese population. Sixty-one healthy male volunteers were enrolled and the plasma concentrations of rosuvastatin were measured using the liquid chromatographic-tandem mass spectrometry/MS method. All subjects were analyzed and grouped according to the genotypes of NR1H4, NR1I2, SLCO1B1, and ABCG2. The exposure of rosuvastatin was higher in subjects carrying the SLCO1B1 521C or ABCG2 421A allele compared with noncarriers. No association was observed of single-nucleotide polymorphisms in NR1H4 or NR1I2 genes with the PKs of rosuvastatin. After adjusting for the 421C>A and 521T>C variants, the Cmax in subjects with NR1I2 63396TT wild type were about 2-fold of those of NR1I2 mutant type (63396CC and CT) (10.7 vs. 20.4 ng/mL, P = 0.023), whereas no significant differences were observed for other parameters. Polymorphisms investigated in the genes of NR1H4 and NR1I2 seemed to play no significant role in the disposition of rosuvastatin.

The active component-target network and protein-protein interaction network of Compound Anshen essential oil were constructed. The target functions and related pathways were analyzed to explore the mechanism of Compound Anshen essential oil in the treatment of insomnia. GC-MS was used to detect the chemical composition of Compound Anshen essential oil, and the TCMSP, STITCH, TTD, and DrugBank databases were searched to predict and screen the targets of Compound Anshen essential oil in the treatment of insomnia. Cytoscape software was used to construct the network diagrams of the active component-action target and protein-protein interaction networks, ClueGO software was used to analyze the GO enrichment and KEGG pathway of the target, and the systemsDock website database was used for molecular docking. The analysis of the network results showed that the activity of Compound Anshen essential oil mainly involves biological processes such as the phospholipase C-activating G protein-coupled receptor signaling pathway, response to ammonium ions, calcium ion transport into the cytosol, and chloride transport. The results of molecular docking showed that linalool, caryophyllene, dibutyl phthalate, (-)-4-terpineol, and (-)-α-terpineol have good binding activity with ADRB2, DRD2, ESR1, KCNH2, NR1H4, NR1I2, NR1I3, and TRPV1 targets. This study demonstrates the multicomponent, multitarget, and multichannel characteristics of Compound Anshen essential oil and provides a new therapeutic idea and method for further research on the mechanism of Compound Anshen essential oil in the treatment of insomnia.

The bile acid (BA) nuclear receptor, farnesoid X receptor (FXR/NR1H4), maintains metabolic homeostasis by transcriptional control of numerous genes, including an intestinal hormone, fibroblast growth factor-19 (FGF19; FGF15 in mice). Besides activation by BAs, the gene-regulatory function of FXR is also modulated by hormone or nutrient signaling-induced post-translational modifications. Recently, phosphorylation at Tyr-67 by the FGF15/19 signaling-activated nonreceptor tyrosine kinase Src was shown to be important for FXR function in BA homeostasis. Here, we examined the role of this FXR phosphorylation in cholesterol regulation. In both hepatic FXR-knockout and FXR-knockdown mice, reconstitution of FXR expression up-regulated cholesterol transport genes for its biliary excretion, including scavenger receptor class B member 1 (Scarb1) and ABC subfamily G member 8 (Abcg5/8), decreased hepatic and plasma cholesterol levels, and increased biliary and fecal cholesterol levels. Of note, these sterol-lowering effects were blunted by substitution of Phe for Tyr-67 in FXR. Moreover, consistent with Src's role in phosphorylating FXR, Src knockdown impaired cholesterol regulation in mice. In hypercholesterolemic apolipoprotein E-deficient mice, expression of FXR, but not Y67F-FXR, ameliorated atherosclerosis, whereas Src down-regulation exacerbated it. Feeding or treatment with an FXR agonist induced Abcg5/8 and Scarb1 expression in WT, but not FGF15-knockout, mice. Furthermore, FGF19 treatment increased occupancy of FXR at Abcg5/8 and Scarb1, expression of these genes, and cholesterol efflux from hepatocytes. These FGF19-mediated effects were blunted by the Y67F-FXR substitution or Src down-regulation or inhibition. We conclude that phosphorylation of hepatic FXR by FGF15/19-induced Src maintains cholesterol homeostasis and protects against atherosclerosis.

Histone deacetylases (HDACs) can enzymatically transferred acetyl functional group from protein or lysine residues of histone, so they can regulate the expression of lots of genes. Now HDACs are used as drug targets and many HDAC inhibitors (HDACis) were approved for cancer therapy or in clinical trials. However, the physiological mechanisms and regulatory processes of HDACi anti-cancer effects are largely unexplored and uncompleted. Here we use the virtual screening workflow obtained 25 hit compounds and ZINC24469384 can significantly inhibit HDAC activity while arrest cell cycle at G1/S phase and significantly induced HepG2 cell apoptosis, time-course RNA-seq demonstrate that HepG2 cells transcriptionally respond to ZINC24469384. Pathway analysis of DEGs and DASGs reveal that NR1H4 may play an important role in ZINC24469384-induced anti-proliferation effect and is dramatically alleviated by down-regulating the SOCS2 expression and promoting STAT3 phosphorylation in knockdown NR1H4 HepG2 cells. Analysis based on TCGA database indicated that NR1H4 and SOCS2 were downregulated in liver cancer, this suggest NR1H4 and SOCS2 may play an important role in tumorigenesis. These results indicated that ZINC24469384 is a novel benzamine lead compound of HDACi and provides a novel mechanism for HDACi to inhibit cancer.

Nucleoside diphosphate kinase 7, non-metastatic cells 7 (NME7) is an acknowledged member of ciliome and is involved in the biogenesis or function of cilia. As obesity and diabetes are common in several ciliopathies, we aimed to analyze changes of gene expression within Nme7 interactome in genetically designed rat models of metabolic syndrome. We assessed the liver transcriptome by Affymetrix microarrays in adult males of 14 PXO recombinant inbred rat strains and their two progenitor strains, SHR-Lx and BXH2. In the strains with the lowest expression of Nme7, we have identified significant enrichment of transcripts belonging to Nme7 interactome. In the subsequent network analysis, we have identified three major upstream regulators - Hnf4a, Ppara and Nr1h4 and liver steatosis (p=0.0001) and liver necrosis/cell death (apoptosis of liver cells, p=0.0003) among the most enriched Tox categories. The mechanistic network reaching the top score showed substantial overlap with Assembly of non-motile cilium and Glucose metabolism disorder gene lists. In summary, we show in a genetic model of metabolic syndrome that rat strains with the lowest expression of Nme7 present gene expression shifts of Nme7 interactome that are perturbing networks relevant for carbohydrate and lipid metabolism as well as ciliogenesis.

Renal fibrosis is the common pathway of chronic kidney disease progression. The nuclear receptor farnesoid X receptor [FXR, NR1H4 (nuclear receptor subfamily 1 group member 4)], a multifunctional transcription factor, plays a pivotal role in protecting against fibrosis. However, the mechanisms underlying these antifibrotic actions of FXR in kidney disease are largely unknown. Here, we show that agonist GW4064-mediated FXR activation inhibits the activity of the nonreceptor tyrosine kinase Src (proto-oncogene tyrosine-protein kinase), which is critical for regulation of yes-associated protein (YAP) phosphorylation and nuclear localization in renal fibrosis. Activation of FXR suppressed renal fibrosis and Tyr416-Src phosphorylation in TGF-β-treated human renal proximal tubule epithelial (HK2) cells. Moreover, GW4064 treatment in HK2 cells increased Ser127 phosphorylation, cytosolic accumulation of YAP, and interaction of the hippo core kinases (Ste20-like kinase 1, large tumor suppressor kinase 1, and salvador homolog 1). Inhibition of Src using PP2 (Src kinase inhibitor) prevented renal fibrosis and increased Ser127 phosphorylation and cytosolic accumulation of YAP. The expression of fibrosis markers, inflammatory genes, and YAP target genes was increased in the kidneys of FXR knockout mice compared with those of wild-type mice. In addition, GW4064 or WAY-362450 (turofexorate isopropyl) treatment protected against unilateral ureteral obstruction-induced renal fibrosis. Collectively, our data support the novel conclusion that Src-mediated crosstalk between FXR and YAP protects against renal fibrosis, making this pathway a possible therapeutic target for chronic kidney disease.-Kim, D.-H., Choi, H.-I., Park, J. S., Kim, C. S., Bae, E. H., Ma, S. K., Kim, S. W. Src-mediated crosstalk between FXR and YAP protects against renal fibrosis.

Farnesoid X receptor (FXR, encoded by NR1H4), a bile acid-activated nuclear receptor, is widely implicated in human tumorigenesis. The FXR agonist obeticholic acid (OCA) has preliminarily displayed tumour suppressor potential. However, the anticancer effects of this agent on colorectal cancer (CRC) remain unclear. In this study, the treatment of colon cancer cells with OCA inhibited cell proliferation and invasion in vitro, retarded tumour growth in vivo and prevented the G₀ /G₁ to S phase transition. Moreover, the expression of active caspase-3, p21 and E-cadherin was up-regulated and the expression of cyclin D1, c-Myc, vimentin, N-cadherin and MMP9 was down-regulated in OCA-treated colon cancer cells. Mechanistic studies indicated that OCA treatment suppressed the activity of JAK2/STAT3 pathway by up-regulating SOCS3 expression. Colivelin, an agonist of JAK2/STAT3 pathway, antagonized the tumour-suppressive effect of OCA on colon cancer cells. Dual-luciferase reporter and quantitative chromatin immunoprecipitation (qChIP) assays further confirmed that OCA promoted SOCS3 transcription by enhancing the binding of FXR to the FXRE/IR9 of the SOCS3 promoter. In conclusion, our study demonstrates that targeting FXR and improving its function might be a promising strategy for CRC treatment.

Keywords: Farnesoid X receptor; JAK2/STAT3 signalling; SOCS3; colorectal cancer; obeticholic acid.

Rats of the adenomatous polyposis coli (Apc)-mutated female polyposis in rat (PIRC) (F344/NTac-Apc^am1137) model exhibit a low level of intestinal tumorigenesis and are thus potentially exploitable as a model for identifying substances increasing colorectal cancer (CRC).

To test this possibility, we treated such rats with the bile acid (BA) cholic acid (CA) (0.3% w/w in the diet), known to promote CRC, and assessed tumorigenesis.Precancerous colonic lesions (mucin-depleted foci) and intestinal tumors were dramatically increased in CA-treated rats compared to controls (p<0.01). Colon mucosa proliferation was higher and apoptosis lower than those in controls. Expression of nuclear receptor 1h4 (Nr1h4) gene [encoding for BA receptor farnesoid X receptor (FXR)], organic solute transporter beta (Ostb) and fatty acid-binding protein 6 (Fabp6), FXR-dependent BA transporters, were dramatically down-regulated in CA-treated rats.CA-increased tumorigenesis in female PIRC rats, with mechanisms involving increased proliferation, reduced apoptosis and marked down-regulation of genes controlling BA homeostasis. Since BAs have been implicated in CRC, we suggest that female PIRC rats can be used to identify CRC-promoting agents.

Upon mild liver injury, pre-existing hepatocytes replicate. However, if hepatocyte proliferation is compromised, such as in chronic liver diseases, biliary epithelial cells (BECs) contribute to hepatocytes through liver progenitor cells (LPCs), thereby restoring hepatic mass and function. Recently, augmenting innate BEC-driven liver regeneration has garnered attention as an alternative to liver transplantation, the only reliable treatment for patients with end-stage liver diseases. Despite this attention, the molecular basis of BEC-driven liver regeneration remains poorly understood. By performing a chemical screen with the zebrafish hepatocyte ablation model, in which BECs robustly contribute to hepatocytes, we identified farnesoid X receptor (FXR) agonists as inhibitors of BEC-driven liver regeneration. Here we show that FXR activation blocks the process via the FXR-PTEN-PI3K-AKT-mTOR axis. We found that FXR activation blocked LPC-to-hepatocyte differentiation, but not BEC-to-LPC dedifferentiation. FXR activation also suppressed LPC proliferation and increased its death. These defects were rescued by suppressing PTEN activity with its chemical inhibitor and ptena/b mutants, indicating PTEN as a critical downstream mediator of FXR signaling in BEC-driven liver regeneration. Consistent with the role of PTEN in inhibiting the PI3K-AKT-mTOR pathway, FXR activation reduced the expression of pS6, a marker of mTORC1 activation, in LPCs of regenerating livers. Importantly, suppressing PI3K and mTORC1 activities with their chemical inhibitors blocked BEC-driven liver regeneration, as did FXR activation. Conclusion: FXR activation impairs BEC-driven liver regeneration by enhancing PTEN activity; the PI3K-AKT-mTOR pathway controls the regeneration process. Given clinical trials and usage of FXR agonists for multiple liver diseases due to their beneficial effects on steatosis and fibrosis, the detrimental effects of FXR activation on LPCs suggest a rather personalized use of the agonists in the clinic.

Keywords: FXR; GW4064; Nr1h4; biliary epithelial cells.

OBJECTIVE

To examine expression profile of gallbladder using microarray and to investigate the role of gallbladder in lipid homeostasis.

METHODS

33P-labelled cDNA derived from total RNA of gallbladder tissue was hybridized to a cDNA array representing 17,000 cDNA clusters. Genes with intensities>> or =2 and variation <0.33 between two samples were considered as positive signals with subtraction of background chosen from an area where no cDNA was spotted. The average gray level of two gallbladders was adopted to analyze its bioinformatics. Identified target genes were confirmed by touch-down polymerase chain reaction and sequencing.

RESULTS

A total of 11 047 genes expressed in normal gallbladder, which was more than that predicted by another author, and the first 10 genes highly expressed (high gray level in hybridization image), e.g. ARPC5 (2 225.88+/-90.46), LOC55972 (2 220.32+/-446.51) and SLC20A2 (1 865.21+/-98.02), were related to the function of smooth muscle contraction and material transport. Meanwhile, 149 lipid-related genes were expressed in the gallbladder, 89 of which were first identified (with gray level in hybridization image), e.g. FASN (11.42+/-2.62), APOD (92.61+/-8.90) and CYP21A2 (246.11+/-42.36), and they were involved in each step of lipid metabolism pathway. In addition, 19 of those 149 genes were gallstone candidate susceptibility genes (with gray level in hybridization image), e.g. HMGCR (10.98+/-0.31), NPC1 (34.88+/-12.12) and NR1H4 (16.8+/-0.65), which were previously thought to be expressed in the liver and/or intestine tissue only.

CONCLUSIONS

Gallbladder expresses 11 047 genes and takes part in lipid homeostasis.

Cholesterol levels are strictly regulated to maintain its homeostasis; therefore, if it is not absorbed with the diet, the cholesterol biosynthetic pathway is enhanced and vice versa. Nowadays, the commonly prescribed therapeutic treatments for hypocholesterolemic patients are targeted toward the reduction of both cholesterol intestinal absorption and/or its endogenous biosynthesis. But, when hypercholesterolemia is still moderate the consumption of food products with cholesterol-lowering capacities is more desirable than using drugs. Marketed foods supplemented with hypocholesterolemic compounds are only inhibiting mechanisms for cholesterol absorption (i.e. phytosterols and cereal β-glucans). However, certain fungal extracts obtained from edible mushrooms might be able to modulate cholesterol levels by both strategies, pharmaceutical drugs and functional foods. In vitro and in vivo studies indicated that fungal sterols down-regulated genes involved in cholesterol homeostasis (such as Srebf2 and Nr1h4 (FXR)) and other specific mushroom extracts (β-glucans and other water-soluble compounds) also stimulated transcriptional profiles similar to simvastatin or ezetimibe (two hypocholesterolemic drugs). These and other observations suggested that the hypocholesterolemic effect of mushroom extracts could be due to transcriptional and post-transcriptional modulations besides other indirect effects.

DNA-dependent protein kinase (DNA-PK) is required for the repair of double strand DNA breaks by nonhomologous DNA end joining. The catalytic subunit of DNA-PK, PRKDC, may also be involved in repair-related or separate cell signaling pathways. To learn more about the cellular function of DNA-PK under normal physiological conditions, we identified genes that are differentially expressed between an immortalized wild-type mouse fibroblast cell line and its DNA-PK-deficient counterpart (Prkdc -/-). The proto-oncogene Mdm2 and the farnesoid X receptor gene Nrlh4 were overexpressed in the DNA-PK-deficient cell line. We show that in the DNA-PK-deficient cell line the genes for both Mdm2 and Nrlh4 are amplified to a degree that could account for most, if not all, of their increased expression. Other genes were strongly downregulated in the DNA-PK-deficient cell line, but this opposite expression pattern was not due to gene amplification in the wild-type cells. None of these genes was differentially expressed in DNA-PK-containing and DNA-PK-deficient primary mouse embryo fibroblasts. Our results suggest a model in which DNA-PK indirectly affects the cellular gene expression profile through its caretaker role and by preventing gene amplification.

Nuclear receptor liver receptor homolog-1 (LRH-1; NR5A2) plays a crucial role in the homeostasis of bile acids and cholesterol by controlling the expression of genes central to bile acid synthesis and efflux, reverse cholesterol transport, and high density lipoprotein-remodeling. However, the molecular mechanisms that modulate the transactivation activity of LRH-1 remain unclear. It is proposed that LRH-1's activity is regulated by post-modifications, the binding of small heterodimer partner (SHP), or the binding of coregulators. To search for cofactors that regulate the transactivation activity of LRH-1, we performed a pull-down assay using glutathione S-transferase (GST) fused to the N-terminal portion of LRH-1 and nuclear extracts from HeLa cells, and identified Ku proteins as interacting proteins with LRH-1. We also found that Ku proteins associate with LRH-1 through its DNA-binding domain and hinge region. Luciferase reporter assays revealed that Ku proteins repressed the SHP promoter activity mediated by LRH-1. Furthermore, Ku proteins suppressed the coactivating effect of peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1alpha (PGC-1alpha), an LRH-1 coactivator, on the LRH-1-mediated SHP promoter activity. Previously, we showed that Ku proteins interacted with nuclear receptor farnesoid X receptor (FXR; NR1H4) and decreased the expression of its target gene. In this study, we demonstrated that Ku proteins also interacted with not only LRH-1 but various nuclear receptors, such as the estrogen receptor, PPAR, and Rev-erb. Ku proteins may function as corepressors for various nuclear receptors including LRH-1.

Experimental studies suggest that maternal hypercholesterolemia may be relevant for the early onset of cardiovascular disease in offspring. We investigated the effect of perinatal hypercholesterolemia on the atherosclerosis development in the offspring of apolipoprotein E-deficient mice and the underlying mechanism.

Atherosclerosis and related parameters were studied in adult male or female apolipoprotein E-deficient mice offspring from either normocholesterolemic or hypercholesterolemic mothers and normocholesterolemic fathers. Female born to hypercholesterolemic mothers had more aortic root lesions than female born to normocholesterolemic mothers. Lesions in whole aorta did not differ between groups. Higher trimethylamine-N-oxide levels and Fmo3 hepatic gene expression were higher in female born to hypercholesterolemic mothers offspring compared with female born to normocholesterolemic mothers and male. Trimethylamine-N-oxide levels were correlated with the size of atherosclerotic root lesions. Levels of hepatic cholesterol and gallbladder bile acid were greater in male born to hypercholesterolemic mothers compared with male born to normocholesterolemic mothers. At 18 weeks of age, female born to hypercholesterolemic mothers showed lower hepatic Scarb1 and Cyp7a1 but higher Nr1h4 gene expression compared with female born to normocholesterolemic mothers. Male born to hypercholesterolemic mothers showed an increase in Scarb1 and Ldlr gene expression compared with male born to normocholesterolemic mothers. At 25 weeks of age, female born to hypercholesterolemic mothers had lower Cyp7a1 gene expression compared with female born to normocholesterolemic mothers. DNA methylation of Fmo3, Scarb1, and Ldlr promoter regions was slightly modified and may explain the mRNA expression modulation.

Our findings suggest that maternal hypercholesterolemia may exacerbate the development of atherosclerosis in female offspring by affecting metabolism of trimethylamine-N-oxide and bile acids. These data could be explained by epigenetic alterations.

OBJECTIVE

This study aimed to investigate whether genetic polymorphisms of the organic anion transporting polypeptides influence hepatic enhancement in gadoxetic acid-enhanced MRI.

METHODS

We analyzed the genotypes of SLCO1B1 388A>G, SLCO1B1 521T>C, SLCO1B3 334T>G and NR1H4 -1G>T and calculated the mean quantitative liver-spleen contrast ratio, as an index of liver parenchymal enhancement, in 226 patients with liver disease.

RESULTS

Multiple linear regression analysis using the mean quantitative liver-spleen contrast ratio as the dependent variable revealed that not only Child-Pugh score, but also SLCO1B1*1b haplotype (β = 0.12; p = 0.04), were significant predictors of liver parenchymal enhancement. In addition, SLCO1B3 334T>G (β = -0.18; p = 0.03) was a significant predictor when the data were analyzed in a subgroup of 117 patients, excluding the carriers of NR1H4 -1G>T, who reportedly exhibit reduced transcriptional activity of SLCO1B3.

CONCLUSIONS

These genetic variants, as well as hepatic function, may contribute to individual differences in hepatic enhancement with gadoxetic acid.

The nuclear receptor farnesoid-X-receptor (FXR; NR1H4) is expressed not only in the liver, gut, kidney and adipose tissue but also in the immune cells. FXR has been shown to confer protection in several animal models of inflammation, including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). FXR agonists are currently tested in clinical trials for treatment of human metabolic diseases. The beneficial effect of FXR agonists in EAE suggests that FXR might represent a potential target in inflammatory-demyelinating CNS diseases, such as MS. In MS, oligodendrocytes not only undergo cell death but also contribute to remyelination. This repair mechanism is impaired due to a differentiation block of oligodendroglial progenitor cells. Activation of other nuclear receptors that heterodimerize with FXR promote oligodendroglial differentiation. Therefore, we wanted to address the functional relevance of FXR for glial cells, especially for oligodendroglial differentiation.

We isolated primary murine oligodendrocytes from FXR-deficient (FXR Ko) and wild-type (WT) mice and determined the effect of FXR deficiency and activation on oligodendroglial differentiation by analysing markers of oligodendroglial progenitor cells (OPCs) and mature oligodendrocytes (OLs) using qRT-PCR and immunocytochemistry. Additionally, we determined whether FXR activation modulates the pro-inflammatory profile of astrocytes or microglia and whether this may subsequently modulate oligodendroglial differentiation. These in vitro studies were complemented by histological analyses of oligodendrocytes in FXR Ko mice.

FXR is expressed by OPCs and mature oligodendrocytes. However, lack of FXR did not affect oligodendroglial differentiation in vitro or in vivo. Furthermore, activation of FXR using the synthetic agonist GW4064 did not affect oligodendroglial differentiation, remyelination in an ex vivo model or the expression of pro-inflammatory molecules in astrocytes or microglia. Concordantly, no effects of supernatants from macrophages cultured in the presence of GW4064 were observed regarding a possible indirect impact on oligodendroglial differentiation.

Our data suggest that FXR is dispensable for oligodendroglial differentiation and that FXR agonists, such as GW4064, represent a potential therapeutic approach for MS which specifically targets peripheral immune cells including macrophages but not brain-resident cells, such as oligodendrocytes, astrocytes or microglia.

Farnesoid X receptor (FXR, NR1H4) is a member of the nuclear receptor superfamily of ligand-activated transcription factors. Since the role of FXR in osteoclast differentiation remains ill-defined, we investigated the biological function of FXR on osteoclastogenesis, using FXR-deficient mice. We demonstrated that FXR deficiency increases osteoclast formation in vitro and in vivo. First, FXR deficiency was found to accelerate osteoclast formation via down-regulation of c-Jun N-terminal kinase (JNK) 1/2 expression. Increased expression of peroxisome proliferator-activated receptor (PPAR)γ and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1)β seems to mediate the pro-osteoclastogenic effect of FXR deficiency via the JNK pathway. In addition, we found that FXR deficiency downregulated the expression of interferon-β (IFN-β), a strong inhibitor of osteoclastogenesis, via receptor activator of nuclear factor-kappaB ligand (RANKL). We further suggested that interference of IFN-β expression by FXR deficiency impaired the downstream JAK3-STAT1 signaling pathways, which in turn increased osteoclast formation. Finally, FXR deficiency accelerated unloading- or ovariectomy-induced bone loss in vivo. Thus, our findings demonstrate that FXR is a negative modulator in osteoclast differentiation and identify FXR as a potential therapeutic target for postmenopausal osteoporosis and unloading-induced bone loss.

Farnesoid X receptor (FXR, NR1H4) protects the liver from insults of various etiologies. A role of FXR in drug-induced liver injury (DILI) has also been hypothesized, yet only marginally investigated. The aim of this study was to assess the effect of FXR activation on gene expression and phenotype of the liver of mice treated with valproic acid- (2-propylpentanoic acid, VPA), a prototypical hepatotoxic drug. Obeticholic acid (OCA) was used to activate FXR both in mice and in human hepatocellular carcinoma (Huh-7) cells. Next generation sequencing of mouse liver tissues was performed from control, VPA and VPA+OCA-treated mice. Pathway analysis validation was performed using real time RT-PCR, western blotting, immunohistochemistry and fluorometric assays. FXR activation induced antioxidative pathways, confirmed by a marked reduction in VPA-induced lipid peroxidation and endoplasmic reticulum (ER) stress. In vitro, VPA-induced oxidative stress was independent of lipid accumulation, stemmed from the cytoplasm and was mitigated by OCA. In the liver of the mice treated with OCA, the levels of cytochrome P450 potentially involved in VPA metabolism were increased. The hepatic lipid lowering effect observed in animals co-treated with VPA and OCA in comparison to that of animals treated with VPA was associated with regulation of the genes involved in the steatogenic nuclear receptor peroxisome proliferator-activated γ (PPARγ) pathway. In conclusion, pronounced antioxidant activity, repression of the PPARγ pathway and higher expression of CYP450 enzymes involved in VPA metabolism may underlie the hepatoprotective of FXR activation during VPA treatment. SIGNIFICANCE STATEMENT: Valproic acid-induced oxidative stress occurs in absence of lipid accumulation and is not of mitochondrial origin. Valproic acid exposure induces the expression of the steatogenic nuclear receptor peroxisome proliferator-activated γ (PPARγ) and its downstream target genes. Constitutive activation of the farnesoid X receptor reduces PPARγ hepatic expression and induces hepatic antioxidant activity. The variability in FXR expression level/activity, for instance in individuals carrying loss-of-function genetic variants of the FXR gene, could contribute to valproic acid pharmacokinetic and toxicokinetic profile.

A detailed understanding of the gene-regulatory network in ankylosing spondylitis (AS) is vital for elucidating the mechanisms of AS pathogenesis. Assaying transposase-accessible chromatin in single cell sequencing (scATAC-seq) is a suitable method for revealing such networks. Thus, scATAC-seq was applied to define the landscape of active regulatory DNA in AS. As a result, there was a significant change in the percent of CD8+ T cells in PBMCs, and 37 differentially accessible transcription factor (TF) motifs were identified. T cells, monocytes-1 and dendritic cells were found to be crucial for the IL-17 signaling pathway and TNF signaling pathway, since they had 73 potential target genes regulated by 8 TF motifs with decreased accessibility in AS. Moreover, natural killer cells were involved in AS by increasing the accessibility to TF motifs TEAD1 and JUN to induce cytokine-cytokine receptor interactions. In addition, CD4+ T cells and CD8+ T cells may be vital for altering host immune functions through increasing the accessibility of TF motifs NR1H4 and OLIG (OLIGI and OLIG2), respectively. These results explain clear gene regulatory variation in PBMCs from AS patients, providing a foundational framework for the study of personal regulomes and delivering insights into epigenetic therapy.