The protective role of pregnane X receptor in lipopolysaccharide/D-galactosamine-induced acute liver injury.

The pregnane X receptor (PXR) is a nuclear receptor transcription factor regulating drug-metabolizing enzymes and transporters that facilitate xenobiotic and endobiotic detoxification. Recent studies show that PXR is important in abrogating intestinal tissue damage. This study examines the role of PXR in lipopolysaccharide (LPS)/D-galactosamine (GalN)-induced acute liver injury using wild-type and PXR-null mice. LPS/GalN-treated PXR-null mice had greater increases of alanine transaminase (ALT), hepatocyte apoptosis, necrosis, and hemorrhagic liver injury than wild-type mice. LPS/GalN-mediated phosphorylation of JNK1/2 and ERK1/2 was differentially regulated in wild-type and PXR-null mice. Importantly, LPS/GalN-induced hepatic Stat3 survival signaling was impaired and early activation of Jak2 was delayed in PXR-null mice. Expression levels of pro-survival proteins Bcl-xL and heme oxygenase-1 (HO-1), which are downstream of Stat3, were substantially lower in PXR-null than wild-type mouse livers after LPS/GalN treatment. Autophagy is also involved in LPS/GalN-induced liver injury. Lack of PXR resulted in a significant reduction of LC3B-I, -II as well as Beclin-1 protein levels after LPS/GalN treatment. In addition, PXR is implicated in hepatocytes homeostasis. Taken together, PXR is a critical hepatoprotective factor. Increases of LPS/GalN-induced hepatocyte apoptosis and liver injury in PXR-null mice are due to deregulated mitogen-activated protein (MAP) kinase activation as well as delayed Jak2/Stat3 activation, which lead to a compromise in defense mechanisms that involve Bcl-xL-, HO-1, and autophagy-mediated pathways

Microbiota and bile acid profiles in retinoic acid-primed mice that exhibit accelerated liver regeneration.

Background & aimsAll-trans Retinoic acid (RA) regulates hepatic lipid and bile acid homeostasis. Similar to bile acid (BA), RA accelerates partial hepatectomy (PHx)-induced liver regeneration. Because there is a bidirectional regulatory relationship between gut microbiota and BA synthesis, we examined the effect of RA in altering the gut microbial population and BA composition and established their relationship with hepatic biological processes during the active phases of liver regeneration.MethodsC57BL/6 mice were treated with RA orally followed by 2/3 PHx. The roles of RA in shifting gut microbiota and BA profiles as well as hepatocyte metabolism and proliferation were studied.ResultsRA-primed mice exhibited accelerated hepatocyte proliferation revealed by higher numbers of Ki67-positive cells compared to untreated mice. Firmicutes and Bacteroidetes phyla dominated the gut microbial community (>85%) in both control and RA-primed mice after PHx. RA reduced the ratio of Firmicutes to Bacteroidetes, which was associated with a lean phenotype. Consistently, RA-primed mice lacked transient lipid accumulation normally found in regenerating livers. In addition, RA altered BA homeostasis and shifted BA profiles by increasing the ratio of hydrophilic to hydrophobic BAs in regenerating livers. Accordingly, metabolic regulators fibroblast growth factor 21, Sirtuin1, and their downstream targets AMPK and ERK1/2 were more robustly activated in RA-primed than unprimed regenerating livers.ConclusionsPriming mice with RA resulted in a lean microbiota composition and hydrophilic BA profiles, which were associated with facilitated metabolism and enhanced cell proliferation

Inhibition of Carrageenan-Induced Cutaneous Inflammation by PPAR Agonists Is Dependent on Hepatocyte-Specific Retinoid X ReceptorAlpha

It has been proposed that PPAR-dependent, accelerated catabolism of proinflammatory mediators may contribute to the fast resolution of inflammation. Because retinoid X receptors are obligate heterodimer partners of PPARs, we investigated the impact of deleting hepatocyte-specific RXRα on the antiedema effect of PPAR agonists. In wild-type mice (WT), pretreatment with the PPARα agonist perfluorooctanoic acid diminished carrageenan-induced paw edema by 66 ± 10%. This effect was essentially absent (13 ± 8%) in hepatocyte-specific RXRα-deficient mice. Similarly, pretreatment of WT mice with the PPARδ agonist L-783483 or the PPARγ agonist L-805645 caused 54 ± 1% and 38 ± 8% reduction in carrageenan-induced paw edema, respectively. These effects were also significantly diminished or absent in hepatocyte-specific RXRα-deficient mice. In contrast, aspirin reduced carrageenan-induced paw edema equally in WT and hepatocyte-specific RXRα-deficient mice. The identification of RXRα as an important factor involved in the antiedema effect produced by agonists of the three PPAR subtypes is a significant achievement towards the goal of designing novel, effective anti-inflammatory drugs

Function annotation of hepatic retinoid x receptor α based on genome-wide DNA binding and transcriptome profiling.

BackgroundRetinoid x receptor α (RXRα) is abundantly expressed in the liver and is essential for the function of other nuclear receptors. Using chromatin immunoprecipitation sequencing and mRNA profiling data generated from wild type and RXRα-null mouse livers, the current study identifies the bona-fide hepatic RXRα targets and biological pathways. In addition, based on binding and motif analysis, the molecular mechanism by which RXRα regulates hepatic genes is elucidated in a high-throughput manner.Principal findingsClose to 80% of hepatic expressed genes were bound by RXRα, while 16% were expressed in an RXRα-dependent manner. Motif analysis predicted direct repeat with a spacer of one nucleotide as the most prevalent RXRα binding site. Many of the 500 strongest binding motifs overlapped with the binding motif of specific protein 1. Biological functional analysis of RXRα-dependent genes revealed that hepatic RXRα deficiency mainly resulted in up-regulation of steroid and cholesterol biosynthesis-related genes and down-regulation of translation- as well as anti-apoptosis-related genes. Furthermore, RXRα bound to many genes that encode nuclear receptors and their cofactors suggesting the central role of RXRα in regulating nuclear receptor-mediated pathways.ConclusionsThis study establishes the relationship between RXRα DNA binding and hepatic gene expression. RXRα binds extensively to the mouse genome. However, DNA binding does not necessarily affect the basal mRNA level. In addition to metabolism, RXRα dictates the expression of genes that regulate RNA processing, translation, and protein folding illustrating the novel roles of hepatic RXRα in post-transcriptional regulation

Fenretinide-induced apoptosis of Huh-7 hepatocellular carcinoma is retinoic acid receptor ß dependent

BACKGROUND:Retinoids are used to treat several types of cancer; however, their effects on liver cancer have not been fully characterized. To investigate the therapeutic potential of retinoids on hepatocellular carcinoma (HCC), the present study evaluates the apoptotic effect of a panel of natural and synthetic retinoids in three human HCC cell lines as well as explores the underlying mechanisms.METHODS:Apoptosis was determined by caspase-3 cleavage using western blot, DNA double-strand breaks using TUNEL assay, and phosphatidylserine translocation using flow cytometry analysis. Gene expression of nuclear receptors was assessed by real-time PCR. Transactivation assay and chromatin immunoprecipitation (ChIP) were conducted to evaluate the activation of RXRa/RARß pathway by fenretinide. Knockdown of RARß mRNA expression was achieved by siRNA transfection.RESULTS:Our data revealed that fenretinide effectively induces apoptosis in Huh-7 and Hep3B cells. Gene expression analysis of nuclear receptors revealed that the basal and inducibility of retinoic acid receptor ß (RARß) expression positively correlate with the susceptibility of HCC cells to fenretinide treatment. Furthermore, fenretinide transactivates the RXRa/RARß-mediated pathway and directly increases the transcriptional activity of RARß. Knockdown of RARß mRNA expression significantly impairs fenretinide-induced apoptosis in Huh-7 cells.CONCLUSION:Our findings reveal that endogenous expression of retinoids receptor RARß gene determines the susceptibility of HCC cells to fenretinide-induced apoptosis. Our results also demonstrate fenretinide directly activates RARß and induces apoptosis in Huh-7 cells in a RARß-dependent manner. These findings suggest a novel role of RARß as a tumor suppressor by mediating the signals of certain chemotherapeutic agents

Long-term, low-dose lead exposure alters the gonadotropin-releasing hormone system in the male rat.

Lead is a male reproductive toxicant. Data suggest that rats dosed with relatively high levels of lead acetate for short periods of time induced changes in the hypothalamic gonadotropin-releasing hormone (GnRH) at the molecular level, but these changes were attenuated with increased concentration of exposure. The current study evaluated whether exposure to low levels of lead acetate over longer periods of time would produce a similar pattern of adaptation to toxicity at the molecular and biologic levels. Adult 100-day-old Sprague-Dawley male rats were dosed with 0, 0.025, 0.05, 0.1, and 0.3% lead acetate in water. Animals were killed after 1, 4, 8, and 16 weeks of treatment. Luteinzing hormone (LH) and GnRH levels were measured in serum, and lead levels were quantified in whole blood. Hypothalamic GnRH mRNA levels were also quantified. We found no significant differences in serum LH and GnRH among the groups of animals treated within each time period. A significant dose-related increase of GnRH mRNA concentrations with lead dosing occurred in animals treated for 1 week. Animals treated for more than 1 week also exhibited a significant increase in GnRH mRNA, but with an attenuation of the increase at the higher concentrations of lead with increased duration of exposure. We conclude that the signals within and between the hypothalamus and pituitary gland appear to be disrupted by long-term, low-dose lead exposure

Pharmacogenomic strategy for individualizing antidepressant therapy

Despite remarkable progress, pharmacotherapy in general, including that for the treatment of depressive conditions, has often ignored the magnitude and clinical significance of the huge interindividual variations in pharmacokinetics and pharmacodynamics, resulting in poor compliance, suboptimal therapeutic effects, and treatment resistance. Advances in pharmacogenomics and computer modeling technologies hold promise for achieving the goals of “individualized” (“personalized”) medicine. However, the challenges for realizing such goals remain substantial. These include the packaging and interpretation of genotyping results, changes in medical practice (innovation diffusion), and infrasiructural, financing, ethical, and organizational issues related to the use of new information

Hepatocyte RXRalpha deficiency in matured and aged mice: impact on the expression of cancer-related hepatic genes in a gender-specific manner

<p>Abstract</p> <p>Background</p> <p>The occurrence of liver cancer is higher in males than in females, and the incidence increases during aging. Signaling pathways regulated by retinoid × receptor α (RXRα) are involved in hepatocellular carcinogenesis. The phenotype of hepatocyte RXRα deficient mice is different between genders. To explore the impact of hepatocyte RXRα deficiency on gender-dependent hepatic gene expression, we compared the expression profiles of cancer-related genes in 6 and 24 month old male and female mice.</p> <p>Results</p> <p>In 6 month old mice, male mutant mice showed more cancer-related genes with alteration in mRNA levels than females did (195 vs. 60). In aged mice (24 month), female mutant mice showed greater deviation in mRNA expression levels of cancer-related genes than their male counterparts (149 vs. 82). The genes were classified into five categories according to their role in carcinogenesis: apoptosis, metastasis, cell growth, stress, and immune respnse. In each category, dependent upon age and gender, the genes as well as the number of genes with altered mRNA levels due to RXRα deficiency varies.</p> <p>Conclusion</p> <p>The change in hepatic cancer-related gene expression profiles due to RXRα deficiency was gender- and age-dependent. The alteration of mRNA levels of cancer-related genes implied that aberrant RXRα signaling could potentially increase the risk of liver cancer and that retinoid signaling might contribute to gender- and age-associated liver cancer incidence.</p

Function Annotation of Hepatic Retinoid x Receptor α Based on Genome-Wide DNA Binding and Transcriptome Profiling

Background Retinoid x receptor α (RXRα) is abundantly expressed in the liver and is essential for the function of other nuclear receptors. Using chromatin immunoprecipitation sequencing and mRNA profiling data generated from wild type and RXRα-null mouse livers, the current study identifies the bona-fide hepatic RXRα targets and biological pathways. In addition, based on binding and motif analysis, the molecular mechanism by which RXRα regulates hepatic genes is elucidated in a high-throughput manner. Principal Findings Close to 80% of hepatic expressed genes were bound by RXRα, while 16% were expressed in an RXRα-dependent manner. Motif analysis predicted direct repeat with a spacer of one nucleotide as the most prevalent RXRα binding site. Many of the 500 strongest binding motifs overlapped with the binding motif of specific protein 1. Biological functional analysis of RXRα-dependent genes revealed that hepatic RXRα deficiency mainly resulted in up-regulation of steroid and cholesterol biosynthesis-related genes and down-regulation of translation- as well as anti-apoptosis-related genes. Furthermore, RXRα bound to many genes that encode nuclear receptors and their cofactors suggesting the central role of RXRα in regulating nuclear receptor-mediated pathways. Conclusions This study establishes the relationship between RXRα DNA binding and hepatic gene expression. RXRα binds extensively to the mouse genome. However, DNA binding does not necessarily affect the basal mRNA level. In addition to metabolism, RXRα dictates the expression of genes that regulate RNA processing, translation, and protein folding illustrating the novel roles of hepatic RXRα in post-transcriptional regulation.This work was supported by the National Institutes of Health (DK092100 and CA053596 to YYW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript