Liver X receptors (LXRs) are members of the nuclear receptor superfamily and are activated by oxysterols and intermediates in the cholesterol synthetic pathway. The pivotal role of LXRs in the metabolic conversion of cholesterol to bile acids has been well established. Furthermore, insulin induces LXRa in hepatocytes, resulting in the suppression of key enzymes in gluconeogenesis, including phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and fructose-1, 6-bisphosphatase (FBPase). LXRs also play an important role in fatty acid metabolism by activating the sterol regulatory element-bing protein 1c gene (SREBP1c). This articles reviews the molecular mechanisms by which LXRs act to influence the lipid and carbohydrate metabolism.
Animals ; Carbohydrate Metabolism ; Humans ; Lipid Metabolism ; Liver X Receptors ; Orphan Nuclear Receptors ; physiology

Nuclear receptor transcription factors are ligand-activated proteins that control various biological events from cell growth and development to lipid metabolism, and energy and glucose homeostasis. Nuclear receptors are important drug targets for metabolic diseases. Liver X receptors (LXRs) are nuclear receptor transcription factors that play essential roles in regulation of cholesterol, triglyceride, fatty acid, and glucose homeostasis. LXR-deficient mice have shown the association of LXR-signaling pathway dysfunction with several human pathologies including atherosclerosis, hyperlipidemia, Alzheimer's disease and cancer. Thus, LXRs are promising pharmacological targets for these diseases. Synthetic LXR agonists may lower cholesterol, but increase triglyceride and induce fatty liver. The naturally occurring LXR ligands, with moderate activity, may serve as nutraceuticals for prevention or treatment of the disorders, while minimizing potential side effects. In this review, recent advances in natural LXR modulators are summarized including agonist, antagonist and the modulator of LXR pathway.
Animals ; Biological Products ; pharmacology ; Humans ; Liver ; metabolism ; physiopathology ; Liver X Receptors ; Orphan Nuclear Receptors ; drug effects ; physiology

OBJECTIVETo explore liver X receptor alpha (LXR alpha) gene changes and their significance in nonalcoholic fatty liver disease (NAFLD) in rats.

METHODSA rat model of nonalcoholic fatty liver disease was produced with a fatty diet regime (feeding group, FG). Rats fed with normal diet served as controls (CG). The mRNA and protein expressions of LXR alpha in liver tissues were detected by reverse transcription and polymerase chain reaction (RT-PCR) and Western blot.

RESULTSThe concentration of free fatty acid (FFA) in the sera of GF rats started to increase to 0.33 mmol/L after 4 weeks of fat diet feeding, while the FFA of the CG was just 0.24+/-0.03 mmol/L, and the difference was significant (P<0.05). The concentration of ALT and AST in sera of the FG rats started to increase to 75.8 U/L and 138.9 U/L at the 8th week, much higher than those of the CG (P<0.01), and at the 12th week they increased further (P<0.01). Meanwhile, the mRNA and protein expressions of LXR alpha at the 2nd week was significantly increased to 0.62 (P>0.01) and its peak was reached at the 12th week (P<0.01). There was a significant positive correlation between the expression of LXR alpha and the degree of NAFLD.

CONCLUSIONThe changes of LXR alpha gene are closely related to the development of nonalcoholic fatty liver disease.

Animals ; Fatty Liver ; etiology ; metabolism ; pathology ; Gene Expression ; Liver ; metabolism ; pathology ; Liver X Receptors ; Male ; Orphan Nuclear Receptors ; genetics ; metabolism ; Rats ; Rats, Wistar

OBJECTIVETo clarify the differential expression of the genes related to the lipid metabolism in the early stage of atherosclerosis in the young LDLR-/- mice of different ages.

METHODSA RT-PCR assay was used to analyse the gene expression patterns in the livers of LDLR-/- mice and wild type (WT) mice from 14 to 90 days. The characteristics of early lipid deposition in intima were evaluated using biochemical and pathological techniques.

RESULTSIn LDLR-/- mice, when compared to WT mice, the mRNA level of the apolipoprotein A IV (apoA IV), fatty acid translocase (Fat/CD36) and carnitine palmitoyl transferase I (CPT I) changed prominently at the age of 14-days (P < 0.05). At 30 days, the mRNA level of apolipoprotein A I (apoA I) was up regulated, but apolipoprotein F (apoF), CD36 and CPT I were down regulated (P < 0.05). At 60 days, the mRNA levels of apoA I, CPT I and liver X receptor alpha (LXRalpha) were up regulated, but apoA IV was down regulated (P < 0.05). At 90 days, the level of the apoA I was higher, but the expression of the apoA IV, apoF and acyl-coenzymeA oxidase 1 (ACOX1) were down regulated (P < 0.05), whereas the expression of apolipoprotein A V (apoA V), apolipoprotein E (apoE), peroxidase proliferator-activated receptor alpha (PPARalpha) and angiopoietin-like protein 3 (angptl 3) had no significant changes (P > 0.05). The serum levels of TC (P < 0.05), TG (P < 0.05) and LDLC (P < 0.05) in LDLR-/- mice were significantly higher than those in wild type mice with the same age.

CONCLUSIONSThe mRNA levels of the apoA I, apoA IV, apoF, FAT/CD36, CPT I, ACOX1 and LXRalpha of the LDLR-/- mice were significantly changed compared to the WT mice. The genes may be of some relevance to the complicated lipid metabolism network, and have effect in the early stage of atherogenesis.

Animals ; Apolipoprotein A-I ; genetics ; metabolism ; Apolipoproteins A ; genetics ; metabolism ; Apolipoproteins E ; genetics ; metabolism ; Gene Expression ; Lipid Metabolism ; Liver ; metabolism ; Liver X Receptors ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Knockout ; Orphan Nuclear Receptors ; genetics ; metabolism ; RNA, Messenger ; metabolism ; Receptors, LDL ; deficiency

OBJECTIVE: To explore whether oxidized low-density lipoprotein (ox-LDL) can stimulate the cholesterol efflux in fully differentiated 3T3-L1 cells and the possible mechanism. METHODS: Fully differentiated 3T3-L1 cells were incubated in the medium containing various concentrations of ox-LDL ( 0 to 50 microg/mL) for 8 or 24 hours. 22(R)-Hydroxycholesterol (10 micromol/L) was exposed to preconditioned adipocytes with 25 microg/mL ox-LDL for 24 hours. Reverse transcription polymerase chain reaction (RT-PCR) was used to evaluate ATP binding cassette transporter A1 (ABCA1), scavenger receptor class B type I (SR-BI), and liver X receptor alpha (LXRalpha) mRNA expression. Cholesterol efflux mediated by apolipoprotein A-I (apoA-I) was determined using liquid scintillator. RESULTS: Low levels (12.5-25 microg/mL) of ox-LDL could increase cholesterol efflux via the enhancement of ABCA1 pathway and SR-BI expression, whereas the higher concentration (50 microg/mL) could not. In adipocytes preincubated with 25 microg/mL ox-LDL for 24 hours, 22(R)-hydroxycholesterol could increase ABCA1 and LXRalpha mRNA and apoA-I-mediated cholesterol efflux, but had no effect on the SR-BI mRNA expression. CONCLUSION Low levels of ox-LDL may enhance the LXRalpha-ABCA1-apoA-I pathway in adipocytes, up-regulate SR-BI mRNA expression, and then increase the cholesterol efflux. This new effect of ox-LDL will not only make contribution to cholesterol homeostasis in adipocytes, but also be potentially atheroprotective.
3T3-L1 Cells ; ATP Binding Cassette Transporter 1 ; metabolism ; Adipocytes ; drug effects ; metabolism ; Animals ; Cholesterol ; metabolism ; Lipid Metabolism ; Lipoproteins, LDL ; pharmacology ; Liver X Receptors ; Mice ; Orphan Nuclear Receptors ; metabolism ; Scavenger Receptors, Class B ; metabolism

OBJECTIVETo investigate the effect of Hepatitis B Virus X Protein (HBx) on the expression of lipid metabolism-related genes and its role in pathogenesis of hepatocyte fatty degeneration.

METHODSHepatitis B Virus X gene eukaryon expression vector pIRES2-eGFP-HBx was transfected into HepG2 cells to establish HepG2/HBx cell model for HBx expression. HepG2 cells transfected with pIRES2-eGFP (HepG2/pIRES2 cell) and non-transfected were used as controls. At 24, 48 and 72 hours after transfection, the expression of green fluorescent protein (GFP) was observed by fluorescence microscope and the triglyceride(TG) content was detected. RT-PCR and Western blot were applied to detect the levels of sterol regulatory element binding protein-1 (SREBP-1), liver x receptor alpha (LXRalpha) mRNA and the levels of HBx, LXRalpha and fatty acid synthase (FAS) protein. At 24, 48 and 72 hours after transfection, the expression of GFP was found in HepG2/HBx and HepG2/pIRES2 cells, and increased gradually. The expression of HBx was detected only in HepG2/HBx cells, and was increased with time after transfection (F = 32.21, P less than 0.01). These suggested successful obtaining of HepG2-HBx cell model for HBx expression.

RESULTSAt 24h, 48h and 72h after transfection, the expression levels of LXRalpha mRNA (0.386+/-0.055, 0.505+/-0.071, 0.649+/-0.058 ) and SREBP-1 mRNA (0.395+/-0.055, 0.548+/-0.047, 0.795+/-0.058), as well as the levels of LXRalpha protein(0.178+/-0.036, 0.263+/-0.047, 0.347+/-0.058) and FAS protein(0.436+/-0.055, 0.608+/-0.053, 0.827+/-0.046) in HepG2-HBx group were dramatically higher than those in the controls at the same time points (all P less than 0.05/0.01), and were gradually increased with time (all P less than 0.05/0.01). A positive correlationship was observed between HBX protein level and the LXRalpha, SREbP-1 mRNA and LXRalpha, FAS protein levels. The difference of TG content between HepG2/HBx group and control groups was not statistically significant (P more than 0.05).

CONCLUSIONSHBx-LXRalpha-SREBP-1/FAS pathway suggested regulating transcription and expression of lipid metabolism-related genes, which might be one of the important molecular mechanism causing hepatocyte fatty degeneration.

Carcinoma, Hepatocellular ; metabolism ; Fatty Acid Synthase, Type I ; metabolism ; Hep G2 Cells ; Humans ; Lipid Metabolism ; genetics ; Liver Neoplasms ; metabolism ; Liver X Receptors ; Orphan Nuclear Receptors ; metabolism ; Sterol Regulatory Element Binding Protein 1 ; metabolism ; Trans-Activators ; genetics ; Transfection

OBJECTIVES: The liver X receptors (LXRs) are members of the nuclear hormone receptor superfamily, and LXR-β is an important receptor for cholesterol content in brain cells. LXR-β/retinoic X receptor (RXR-α)/ATP binding cassette transporter A1 (ABCA1) cholesterol transmembrane transport system is closely related to the occurrence and development of Alzheimer's disease (AD). LXR agonist TO901317 can affect the accumulation of β- amyloid protein in the brain tissue of APP/PS1 double transgenic AD mice. However, the molecular mechanism is not clarified in detail. This study aims to evaluate the effects of LXR agonist TO901317 on the cognitive function of AD mice fed with high cholesterol diet, and to explore its possible mechanism from the perspective of cholesterol metabolism. METHODS: Twenty four male 6-month-old APP/PS1 double transgenic AD mice were randomly divided into 4 groups, 6 mice in each group: a control group (fed with normal diet), a cholesterol rich diet (CRD) group, a TO901317 group (fed with CRD combined with TO901317), and a GSK2033 group (fed with CRD combined with TO901317 and LXR antagonist GSK2033). The mice were fed with pellet feed made of high cholesterol feed, mixed with lard, egg yolk powder, and cod liver oil twice a day. TO901317 and GSK2033 were dissolved and diluted to a final concentration at 0.03%. The drugs were given to the mice daily through gastric tube according to their body weight. Meanwhile, the mice in the drug group were fed with high cholesterol diet . After feeding for 3 months, Morris water maze was used to observe the changes of spatial exploration and memory ability of AD mice in each group. The contents of TC, LDL, and HDL in serum of mice in each group were detected by cholesterol enzyme colorimetry, and the differences among the groups were compared. The expression of Aβ₄₂ in the brain of AD mice was detected by ELISA. Western blotting was used to detect the protein levels of LXR-β, RXR-α, ABCA1, and Caveolin-1 in the brain of each group. RESULTS: Morris water maze results showed that the times, distance and the duration of mice crossing the platform in the CRD group were significantly decreased compared with the control group (all P<0.05), while these three figures in TO901317 group were significantly increased compared with the CRD group (all P<0.05). Compared with the TO901317 group, there was a decrease of these figures in the GSK2033 group (all P<0.05). The serum TC and LDL levels in the CRD group were significantly higher than those in the control group, while HDL levels were significantly lower (all P<0.001). The figures of the TC and LDL contents level in the TO901317 group were lower than those in the CRD group, while HDL levels were higher (all P<0.001). Compared with TO901317 group, the contents of the TC and LDL in GSK2033 group were significantly increased, while HDL content was significantly decreased (all P<0.001). ELISA results showed that the production of Aβ₄₂ peptides in the brain of CRD group was the highest while the content in the TO901317 group was significantly decreased (P<0.001), which was the lowest among the groups. The figure in the control group was close to the GSK2033 group. Western blotting results showed that the protein levels of LXR-β, RXR-α, and ABCA1 in the CRD group were significantly decreased compared with the control group, but the protein level of Caveolin-1 was increased (all P<0.01). After TO901317 treatment, the protein levels of LXR-β, RXR-α and ABCA1 were significantly increased, while the protein level of Caveolin-1 was decreased partially (all P<0.001). In the GSK2033 group, the effect of TO901317 on AD mice was partially reversed by GSK2033. Compared to TO901317 group, the protein levels of LXR-β, RXR-α, and ABCA1 showed a decrease trend, while the protein level of Caveolin-1 showed an increase state (all P<0.05). CONCLUSIONS High cholesterol diet leads to severer spatial exploration, learning and memory impairment in transgenic AD mice, while the LXR agonist TO901317 attenuates this effect. The mechanism may be that TO901317 promotes cholesterol efflux by activating LXR-β/RXR-α/ABCA1 transmembrane transport system, reduces the expression of Caveolin-1, improves the composition of lipid raft, and ultimately reduces the production of Aβ₄₂ in the brain.
Male ; Animals ; Mice ; Liver X Receptors/metabolism* ; Mice, Transgenic ; Alzheimer Disease/genetics* ; Caveolin 1/metabolism* ; Hydrocarbons, Fluorinated/pharmacology* ; Cognition ; Amyloid beta-Peptides/metabolism* ; Cholesterol

OBJECTIVETo investigate the relationship of NOR-1 with the inhibition of inflammatory reaction in mice Kupffer cells (KCs) induced by lipopolysaccharide (LPS) via liver X receptor alpha (LXR alpha).

METHODSKCs from male KM mice were isolated by density gradient centrifugation, incubated and then randomly assigned to three groups: control group, LPS treated group and LPS+T0901317 treated group.

RESULTSThe mRNA and protein expressions of LXR alpha and NOR-1 in each group were determined by RT-PCR, immunofluorescent assay and western blot, respectively. The densities of TNF alpha and IL-10 in supernatants were evaluated by enzyme linked immunosorbent assay (ELISA). The mRNA and protein expression levels of LXR alpha in LPS + T0901317 group were the highest as compared to the other two groups (0.748+/-0.072 and 1.217+/-0.133 respectively), The mRNA and protein expression levels of NOR-1 in LPS+ T0901317 group were the highest as compared to the other two groups (2.726+/-0.065 and 0.842+/-0.058 respectively). The densities of supernatant TNF alpha in LPS group and IL-10 in LPS+T0901317 group were the highest [(450.89+/-78.52) ng/L and (537.41+/-36.41) ng/L respectively].

CONCLUSIONSPromoting the expression of LXR alpha in KCs can elevate the NOR-1 expression and then inhibit inflammatory reaction.

Animals ; Cells, Cultured ; DNA-Binding Proteins ; metabolism ; Inflammation ; metabolism ; Interleukin-10 ; metabolism ; Kupffer Cells ; metabolism ; Liver X Receptors ; Male ; Mice ; Mice, Inbred Strains ; Nerve Tissue Proteins ; metabolism ; Orphan Nuclear Receptors ; metabolism ; Receptors, Steroid ; metabolism ; Receptors, Thyroid Hormone ; metabolism ; Tumor Necrosis Factor-alpha ; metabolism

OBJECTIVETo explore the possible mechanism of the inhibitory effect of liver X receptor alpha (LXRalpha) on lipopolysaccharide (LPS)-induced inflammation in mouse Kupffer cells (KCs).

METHODSThe KCs isolated from the liver of male KM mice and cultured in RPMI 1640 containing 20% FBS for 24 h were divided into control, LPS, T0901317, and LPS+T0901317 groups with corresponding treatments. The expressions of LXRalpha, interferon regulatory factor 3 (IRF3) and glucocorticoid receptor interacting protein 1 (GRIP1) in the KCs were detected by Western blotting. The levels of interferon beta (IFNbeta), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in the supernatant were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTSThe level of LXRalpha protein was highest in T0901317 group and lowest in LPS group, and was significantly higher in LPS+T0901317 group than in LPS group but lower than in T0901317 group (P<0.05). The levels of IRF3 and GRIP1 protein were the highest in LPS group, and significantly lowered by T0901317 treatment (P<0.05). The expression of IRF3 and GRIP1 proteins in LPS group and LPS+ T0901317 group were significantly higher than those in the control and T0901317 groups (P<0.05). The concentration of IFN-beta was significantly higher in LPS group than in the control and T0901317 group (P<0.05), and decreased in LPS+T0901317 group in comparison with that in LPS group (P<0.05). IFN-beta was the lowest in T0901317 group. The levels of TNF-alpha and IL-1beta were the highest in LPS group (P<0.05), and comparable between the other 3 groups (P>0.05).

CONCLUSIONPre-treatment with T0901317 before LPS stimulation can suppress the expressions of IRF3 and GRIP1 to inhibit the inflammation and hence Kupffer cell activation.

Animals ; Cells, Cultured ; Hydrocarbons, Fluorinated ; pharmacology ; Inflammation ; chemically induced ; Interferon Regulatory Factor-3 ; metabolism ; Kupffer Cells ; cytology ; metabolism ; Lipopolysaccharides ; pharmacology ; Liver X Receptors ; Male ; Mice ; Nuclear Receptor Coactivator 2 ; metabolism ; Orphan Nuclear Receptors ; physiology ; Sulfonamides ; pharmacology

AIMTo investigate the liver X receptors agonists T0901317's effect on expression of FAT/CD36 gene mRNA in adult human skeletal muscle cell.

METHODSMyotubes from humans were exposed to different T0901317 concentrations (0, 0.5, and 1.0 micromol/L) for 24 hours before experiments were performed. Then the expression of FAT/CD36 mRNA in skeletal muscle cell of each experimental group was detected by SYBR Green I real-time quantitative polymerase chain reaction. The relative data were compared among groups by 2-delta delta Ct method.

RESULTS(1) The Ct mean of control group, T0901317 (0.5 micromol/L) group, T0901317 (1 micromol/L) group were analyzed and there was significant difference (P < 0.01). (2) The expression of FAT/CD36 mRNA with liver X receptors agonists T0901317 in human skeletal muscle cell in the T0901317 (0.5 micromol/L) group and T0901317 (1 micromol/L) group were 2.91 times and 3.03 times than the control group.

CONCLUSIONThe expression of FAT/CD36 mRNA in human skeletal muscle cell afer the treatment of liver X receptors agonists T0901317 is increased, so we may propose that T0901317 may increase the risk of resistance in adult human skeletal muscle.

Adult ; CD36 Antigens ; genetics ; metabolism ; Cells, Cultured ; Female ; Humans ; Hydrocarbons, Fluorinated ; pharmacology ; Liver X Receptors ; Male ; Muscle, Skeletal ; cytology ; metabolism ; Orphan Nuclear Receptors ; agonists ; RNA, Messenger ; genetics ; metabolism ; Sulfonamides ; pharmacology