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Cellular mechanisms that mediate steatohepatitis, an increasingly prevalent condition in the Western world for which no therapies are available, are poorly understood. Despite the fact that its synthetic agonists induce fatty liver, the liver X receptor (LXR) transcription factor remains a target of interest because of its anti-atherogenic, cholesterol removal, and anti-inflammatory activities. Here we show that tetratricopeptide repeat domain protein 39B (Ttc39b, C9orf52) (T39), a high-density lipoprotein gene discovered in human genome-wide association studies, promotes the ubiquitination and degradation of LXR. Chow-fed mice lacking T39 (T39(-/-)) display increased high-density lipoprotein cholesterol levels associated with increased enterocyte ATP-binding cassette transporter A1 (Abca1) expression and increased LXR protein without change in LXR messenger RNA. When challenged with a high fat/high cholesterol/bile salt diet, T39(-/-) mice or mice with hepatocyte-specific T39 deficiency show increased hepatic LXR protein and target gene expression, and unexpectedly protection from steatohepatitis and death. Mice fed a Western-type diet and lacking low-density lipoprotein receptor (Ldlr(-/-)T39(-/-)) show decreased fatty liver, increased high-density lipoprotein, decreased low-density lipoprotein, and reduced atherosclerosis. In addition to increasing hepatic Abcg5/8 expression and limiting dietary cholesterol absorption, T39 deficiency inhibits hepatic sterol regulatory element-binding protein 1 (SREBP-1, ADD1) processing. This is explained by an increase in microsomal phospholipids containing polyunsaturated fatty acids, linked to an LXRα-dependent increase in expression of enzymes mediating phosphatidylcholine biosynthesis and incorporation of polyunsaturated fatty acids into phospholipids. The preservation of endogenous LXR protein activates a beneficial profile of gene expression that promotes cholesterol removal and inhibits lipogenesis. T39 inhibition could be an effective strategy for reducing both steatohepatitis and atherosclerosis. Show less

The liver X receptors (LXRs, NR1H2 and NR1H3) and peroxisome proliferator-activated receptor gamma (PPARG, NR1C3) nuclear receptor transcription factors (TFs) are master regulators of energy homeostasis. Intriguingly, recent studies suggest that these metabolic regulators also impact tumor cell proliferation. However, a comprehensive temporal molecular characterization of the LXR and PPARG gene regulatory responses in tumor cells is still lacking. To better define the underlying molecular processes governing the genetic control of cellular growth in response to extracellular metabolic signals, we performed a comprehensive, genome-wide characterization of the temporal regulatory cascades mediated by LXR and PPARG signaling in HT29 colorectal cancer cells. For this analysis, we applied a multi-tiered approach that incorporated cellular phenotypic assays, gene expression profiles, chromatin state dynamics, and nuclear receptor binding patterns. Our results illustrate that the activation of both nuclear receptors inhibited cell proliferation and further decreased glutathione levels, consistent with increased cellular oxidative stress. Despite a common metabolic reprogramming, the gene regulatory network programs initiated by these nuclear receptors were widely distinct. PPARG generated a rapid and short-term response while maintaining a gene activator role. By contrast, LXR signaling was prolonged, with initial, predominantly activating functions that transitioned to repressive gene regulatory activities at late time points. Through the use of a multi-tiered strategy that integrated various genomic datasets, our data illustrate that distinct gene regulatory programs elicit common phenotypic effects, highlighting the complexity of the genome. These results further provide a detailed molecular map of metabolic reprogramming in cancer cells through LXR and PPARG activation. As ligand-inducible TFs, these nuclear receptors can potentially serve as attractive therapeutic targets for the treatment of various cancers. Show less

Experimental data indicate that high-fat diet (HFD) may alter proliferative activity and prostate health. However, the consequences of HFD exposure during different periods of ontogenetic development on prostate histophysiology remain to be elucidated. Herein, we compare the influence of obesogenic environment (OE) due to maternal obesity and HFD at different periods of life on proliferative activity and nuclear receptors frequency in the rat ventral prostate and a possible relationship with metabolic and hormonal alterations. Male Wistar rats (19 weeks old), treated with balanced chow (Control group-C; 3% high-fat, 3.5 Kcal/g), were compared with those exposed to HFD (20% high-fat, 4.9 kcal/g) during gestation (G-maternal obesity), gestation and lactation (GL), from post-weaning to adulthood (WA), from lactation to adulthood (LA) and from gestation to adulthood (GA). After the experimental period, the ventral prostate lobes were removed and analyzed with different methods. Metabolic data indicated that G and GL rats became insulin resistant and WA, LA, and GA became insulin resistant and obese. There was a strong inverse correlation between serum testosterone (∼133% lower) and leptin levels (∼467% higher) in WA, LA, and GA groups. Estrogen serum levels increased in GA, and insulin levels increased in all groups, especially in WA (64.8×). OE-groups exhibited prostatic hypertrophy, since prostate weight increased ∼40% in G, GL, LA, and GA and 31% in WA. As indicated by immunohistochemistry, all HFD-groups except G exhibited an increase in epithelial cell proliferation (PCNA-positive) and a decrease in frequency of AR- and ERβ-positive epithelial cells; there was also an increment of ERα-positive stromal cells in comparison with control. Cells containing PPARγ increased in both epithelium and stroma of all OE groups and those expressing LXRα decreased, particularly in groups OE-exposed during gestation (G, GL and GA). OE leads to prostate hypertrophy regardless of the period of development and, except when restricted to gestation, leads to a hyperproliferative status which was correlated to downregulation of AR and LXRα and upregulation of ERα and PPARγ signaling. Show less

The objective of this study was to study how changing the ratio of Lys to Thr, Lys to His, and Lys to Val affects the expression of lipogenic genes and microRNA (miRNA) in bovine mammary epithelial cells. Triplicate cultures with the respective "optimal" amino acid (AA) ratio (OPAA = Lys:Met 2.9:1; Thr:Phe 1.05:1; Lys:Thr 1.8:1; Lys:His 2.38:1; Lys:Val 1.23:1) plus rapamycin (OPAARMC; positive control), OPAA, Lys:Thr 2.1:1 (LT2.1), Lys:Thr 1.3:1 (LT1.3), Lys:His 3.05:1 (LH3.0), or Lys:Val 1.62:1 (LV1.6) were incubated in lactogenic medium for 12 h. The expression of 15 lipogenic genes and 7 miRNA were evaluated. Responses to LT2.1, LT1.3, LH3.0, and LV1.6 relative to the control (OPAARMC) included up-regulated expression of ACSS2, FABP3, ACACA, FASN, SCD, LPIN1, INSIG1, SREBF1, PPARD, and NR1H3 (commonly known as LXR-α). Furthermore, LV1.6 up-regulated expression of ACSL1, DGAT1, and RXRA and down-regulated PPARG expression. Although no effect of OPAA on expression of PPARG was observed, compared with the control, OPAA up-regulated expression of the PPAR targets ACSS2, FABP3, ACACA, FASN, SCD, LPIN1, INSIG1, and SREBF1. Compared with the control, the expression of the anti-lipogenic MIR27AB was down-regulated by OPAA, LT2.1, LT1.3 and LH3.0. In contrast, compared with the control, the expression of the pro-lipogenic MIR21 was up-regulated by LT2.1, LT1.3, LH3.0, and LV1.6. The observed up-regulation of lipogenic gene networks and the changes in expression of key miRNA involved in the control of lipogenic balance are indicative of a potentially important role of EAA ratios and mTOR signaling in the regulation of milk fat synthesis. Show less

The apolipoprotein E (APOE) gene is the most highly associated susceptibility locus for late onset Alzheimer's Disease (AD), and augmenting the beneficial physiological functions of apoE is a proposed therapeutic strategy. In a high throughput phenotypic screen for small molecules that enhance apoE secretion from human CCF-STTG1 astrocytoma cells, we show the chrysanthemic ester 82879 robustly increases expressed apoE up to 9.4-fold and secreted apoE up to 6-fold and is associated with increased total cholesterol in conditioned media. Compound 82879 is unique as structural analogues, including pyrethroid esters, show no effect on apoE expression or secretion. 82879 also stimulates liver x receptor (LXR) target genes including ATP binding cassette A1 (ABCA1), LXRα and inducible degrader of low density lipoprotein receptor (IDOL) at both mRNA and protein levels. In particular, the lipid transporter ABCA1 was increased by up to 10.6-fold upon 82879 treatment. The findings from CCF-STTG1 cells were confirmed in primary human astrocytes from three donors, where increased apoE and ABCA1 was observed along with elevated secretion of high-density lipoprotein (HDL)-like apoE particles. Nuclear receptor transactivation assays revealed modest direct LXR agonism by compound 82879, yet 10 μM of 82879 significantly upregulated apoE mRNA in mouse embryonic fibroblasts (MEFs) depleted of both LXRα and LXRβ, demonstrating that 82879 can also induce apoE expression independent of LXR transactivation. By contrast, deletion of LXRs in MEFs completely blocked mRNA changes in ABCA1 even at 10 μM of 82879, indicating the ability of 82879 to stimulate ABCA1 expression is entirely dependent on LXR transactivation. Taken together, compound 82879 is a novel chrysanthemic ester capable of modulating apoE secretion as well as apoE-associated lipid metabolic pathways in astrocytes, which is structurally and mechanistically distinct from known LXR agonists. Show less

The liver X receptor (LXR) functions as a receptor for oxysterols and plays a critical role in the regulation of glucose and lipid metabolism. We recently described a synthetic LXR inverse agonist that displayed efficacy in treatment of hepatic steatosis in a mouse model of non-alcoholic fatty liver disease (NAFLD). This compound, SR9238, was designed to display liver specificity so as to avoid potential detrimental effects on reverse cholesterol transport in peripheral tissues. Here, we examined the effects of a LXR antagonist/inverse agonist, GSK2033, which displays systemic exposure. Although GSK2033 performed as expected in cell-based models as a LXR inverse agonist, it displayed unexpected activity in the mouse NAFLD model. The expression of lipogenic enzyme genes such as fatty acid synthase and sterol regulatory binding protein 1c were induced rather than suppressed and no effect on hepatic steatosis was found. Further characterization of the specificity of GSK2033 revealed that it displayed a significant degree of promiscuity, targeting a number of other nuclear receptors that could clearly alter hepatic gene expression. Show less

A recent study by Wang et al. (2016a) claims that the low-frequency variant NR1H3 p.Arg415Gln is sufficient to cause multiple sclerosis in certain individuals and determines a patient's likelihood of primary progressive disease. We sought to replicate this finding in the International MS Genetics Consortium (IMSGC) patient collection, which is 13-fold larger than the collection of Wang et al. (2016a), but we find no evidence that this variant is associated with either MS or disease subtype. Wang et al. (2016a) also report a common variant association in the region, which we show captures the association the IMSGC reported in 2013. Therefore, we conclude that the reported low-frequency association is a false positive, likely generated by insufficient sample size. The claim of NR1H3 mutations describing a Mendelian form of MS-of which no examples exist-can therefore not be substantiated by data. This Matters Arising paper is in response to Wang et al. (2016a), published in Neuron. See also the related Matters Arising paper by Minikel and MacArthur (2016) and the response by Wang et al. (2016b), published in this issue. Show less

It has recently been reported that an NR1H3 missense variant, R415Q, causes a novel familial form of multiple sclerosis (Wang et al., 2016a). This claim is at odds with publicly available data from the Exome Aggregation Consortium (ExAC; http://exac.broadinstitute.org). The allele frequency of R415Q is not significantly higher in cases (0.024%-0.049%) than in ExAC population controls (0.031%), whereas if R415Q conferred even 50% lifetime risk of developing MS, it would be hundreds of times more common in cases than in controls. The upper bound of the 95% confidence interval of penetrance for R415Q can be estimated at 2.2% for women and 1.2% for men, indicating that even if this variant is disease associated, individuals harboring the variant would have a lifetime risk of developing MS no higher than a few percent. ExAC data should be considered when evaluating claims of variant pathogenicity. This Matters Arising paper is in response to Wang et al. (2016a), published in Neuron. See also the related Matters Arising paper by The International Multiple Sclerosis Genetics Consortium (2016) and the response by Wang et al. (2016b), published in this issue. Show less

Identifying rare genetic variants that drive the onset of disease is challenging, even before considering the additional genetic and environmental influences that likely exist in complex diseases. We recently published a study proposing a rare variant in the NR1H3 gene (p.R415Q, rs61731956) as responsible for the onset of multiple sclerosis (MS) in two multi-incident families (Wang et al., 2016). This publication has generated much discussion, and fortunately the possibility to validate a finding or prove it spurious can occur rapidly in genetic studies. All novel discoveries must be replicated, and best efforts should be made to ensure that these replications use the appropriate samples and approach, and provide the correct interpretation of the results. This Matters Arising Response paper addresses the Minikel and MacArthur (2016) and The International Multiple Sclerosis Genetics Consortium (2016) Matters Arising papers, published concurrently in Neuron. Show less

Nonalcoholic fatty liver disease (NAFLD) is a rapidly emerging global health-problem. NAFLD encompasses a range of conditions associated with hepatic steatosis, aberrant accumulation of fat in hepatocytes. Although obesity and metabolic syndrome are considered to have a strong association with NAFLD, genetic factors that predispose liver to NAFLD and molecular mechanisms by which excess hepatic lipid develops remain largely unknown. We report that the transcription cofactor CRTC1 confers broad spectrum protection against hepatic steatosis development. CRTC1 directly interferes with the expression of genes regulated by lipogenic transcription factors, most prominently liver x receptor α (LXRα). Accordingly, Crtc1 deficient mice develop spontaneous hepatic steatosis in young age. As a cyclic AMP effector, CRTC1 mediates anti-steatotic effects of calorie restriction (CR). Notably, CRTC1 also mediates anti-lipogenic effects of bile acid signaling, whereas it is negatively regulated by miR-34a, a pathogenic microRNA upregulated in a broad spectrum of NAFLD. These patterns of gene function and regulation of CRTC1 are distinct from other CR-responsive proteins, highlighting critical protective roles that CRTC1 selectively plays against NAFLD development, which in turn provides novel opportunities for selectively targeting beneficial therapeutic effects of CR. Show less

Nuclear hormone receptor liver X receptor-alpha (LXRα) has a vital role in cholesterol homeostasis and is reported to have a role in adipose function and obesity although this is controversial. Conversely, mesenchymal stem cells (MSCs) are suggested to be a major source of adipocyte generation. Accordingly, we examined the role of LXRα in adipogenesis of MSCs. Adult murine MSCs (mMSCs) were isolated from wild-type (WT) and LXR-null mice. Using WT mMSCs, we further generated cell lines stably overexpressing GFP-LXRα (mMSC/LXRα/GFP) or GFP alone (mMSC/GFP) by retroviral infection. Confluent mMSCs were differentiated into adipocytes by the established protocol. Compared with MSCs isolated from WT mice, MSCs from LXR-null mice showed significantly increased adipogenesis, as determined by lipid droplet accumulation and adipogenesis-related gene expression. Moreover, mMSCs stably overexpressing GFP-LXRα (mMSC/LXRα/GFP) exhibited significantly decreased adipogenesis compared with mMSCs overexpressing GFP alone (mMSC/GFP). Since Wnt/beta-catenin signaling is reported to inhibit adipogenesis, we further examined it. The LXR-null group showed significantly decreased Wnt expression accompanied by a decrease of cellular beta-catenin (vs WT). The mMSC/LXRα/GFP group exhibited significantly increased Wnt expression accompanied by an increase of cellular beta-catenin (vs mMSC/GFP). These data demonstrate that LXRα has an inhibitory effect on adipogenic differentiation in mMSCs with Wnt/beta-catenin signaling. These results provide important insights into the pathophysiology of obesity and obesity-related consequences such as metabolic syndrome and may identify potential therapeutic targets. Show less

Liver X receptor (LXR) is a member of the nuclear receptor superfamily, and it regulates various biologic processes, including de novo lipogenesis, cholesterol metabolism, and inflammation. Selective inhibition of LXR may aid the treatment of nonalcoholic fatty liver diseases. In the present study, we evaluated the effects of three cinnamamide derivatives on ligand-induced LXRα activation and explored whether these derivatives could attenuate steatosis in mice. N-(4-trifluoromethylphenyl) 3,4-dimethoxycinnamamide (TFCA) decreased the luciferase activity in LXRE-tk-Luc-transfected cells and also suppressed ligand-induced lipid accumulation and expression of the lipogenic genes in murine hepatocytes. Furthermore, it significantly attenuated hepatic neutral lipid accumulation in a ligand-induced fatty liver mouse system. Modeling study indicated that TFCA inhibited activation of the LXRα ligand-binding domain by hydrogen bonding to Arg305 in the H5 region of that domain. It regulated the transcriptional control exerted by LXRα by influencing coregulator exchange; this process involves dissociation of the thyroid hormone receptor-associated proteins (TRAP)/DRIP coactivator and recruitment of the nuclear receptor corepressor. These results show that TFCA has the potential to attenuate ligand-induced lipogenesis and fatty liver by selectively inhibiting LXRα in the liver. Show less

The liver X receptors (LXRs) are important regulators of lipid, cholesterol, and glucose homeostasis by transcriptional regulation of many key genes in these processes, and the transcriptional activities of LXRs are finely controlled by cooperating with retinoid X receptors and many other coregulators. Here, we report that the LIM protein Ajuba binds to the hinge and the ligand binding domains of LXRα via its C-terminal tandem LIM motifs and enhances LXR target gene expression in liver cells. Depletion of Ajuba in HepG2 cells and in mouse primary hepatocytes decreases LXR target gene expression, whereas stable expression of Ajuba in HepG2 cells results in increased expression of these genes. Mechanistic investigations found that Ajuba selectively interacts with LXRα/retinoid X receptor-γ heterodimer to form a ternary complex, which displays a higher transactivation activity to LXR target genes. Moreover, Ajuba and LXR mutually affect their DNA binding activity at endogenous target chromatins and the cooperation between Ajuba and LXRα is dependent on the functional LXR response elements located in the target promoters. Together, our studies demonstrate that Ajuba is a novel coactivator for LXRs and may play important role in lipid and glucose metabolism. Show less

Liver X receptors (LXRs) contribute not only to maintain cholesterol homeostasis but also to control cell growth. However, the molecular mechanisms behind the LXR-mediated anti-proliferative effects are largely unknown. Here we show, by immunohistochemistry, that LXRα and LXRβ are differentially distributed in oral stratified squamous epithelia. By immunohistochemical and Western blot analyses, we also reveal that LXRα is abundantly expressed in human oral squamous cell carcinoma (HOSCC) tissues and cell lines. Cell counting, BrdU labeling and cell cycle assay indicated that LXR stimulation led to significant reduction of proliferation in HOSCC cells. Importantly, our study highlights, by using RNA interference, that the ATP-binding cassette transporter A1 (ABCA1)-accelerated cholesterol efflux is critical for the growth inhibitory action of LXRs in HOSCC cells. Moreover, we demonstrate that LXR activation reduces the growth of xenograft tumour of HOSCC cells in mice accompanied by the upregulation of ABCA1 expression and the decline of cholesterol levels in the tumour. These findings strongly suggested that targeting the LXR-regulated cholesterol transport, yielding in lowering intracellular cholesterol levels, could be a promising therapeutic option for certain types of cancers. Show less

Here, we investigated the role of LXRα in capsaicin mediated anti-inflammatory effects. Results revealed that capsaicin inhibits LPS-induced IL-1β, IL-6 and TNF-α production in a time- and dose-dependent manner. Moreover, capsaicin increases LXRα expression through PPARγ pathway. Inhibition of LXRα activation by siRNA diminished the inhibitory action of capsaicin on LPS-induced IL-1β, IL-6 and TNF-α production. Additionally, LXRα siRNA abrogated the inhibitory action of capsaicin on p65 NF-κB protein expression. Thus, we propose that the anti-inflammatory effects of capsaicin are LXRα dependent, and LXRα may potentially link the capsaicin mediated PPARγ activation and NF-κB inhibition in LPS-induced inflammatory response. Show less

Liver disease is the second most common cause of mortality in HIV-infected persons. Exactly how HIV infection per se affects liver disease progression is unknown. Here we have investigated mRNA expression of 49 nuclear hormone receptors (NRs) and 35 transcriptional coregulators in HepG2 cells upon stimulation with the HIV matrix protein p17. This viral protein regulated mRNA expression of some NRs among which LXRα and its transcriptional co-activator MED1 were highly induced at mRNA level. Dissection of p17 downstream intracellular pathway demonstrated that p17 mediated activation of Jak/STAT signaling is responsible for the promoter dependent activation of LXR. The treatment of both HepG2 as well as primary hepatocytes with HIV p17 results in the transcriptional activation of LXR target genes (SREBP1c and FAS) and lipid accumulation. These effects are lost in HepG2 cells pre-incubated with a serum from HIV positive person who underwent a vaccination with a p17 peptide as well as in HepG2 cells pre-incubated with the natural LXR antagonist gymnestrogenin. These results suggest that HIV p17 affects NRs and their related signal transduction thus contributing to the progression of liver disease in HIV infected patients. Show less

The schweinfurthins have potent antiproliferative activity in multiple glioblastoma multiforme (GBM) cell lines; however, the mechanism by which growth is impeded is not fully understood. Previously, we demonstrated that the schweinfurthins reduce the level of key isoprenoid intermediates in the cholesterol biosynthetic pathway. Herein, we describe the effects of the schweinfurthins on cholesterol homeostasis. Intracellular cholesterol levels are greatly reduced in cells incubated with 3-deoxyschweinfurthin B (3dSB), an analog of the natural product schweinfurthin B. Decreased cholesterol levels are due to decreased cholesterol synthesis and increased cholesterol efflux; both of these cellular actions can be influenced by liver X-receptor (LXR) activation. The effects of 3dSB on ATP-binding cassette transporter 1 levels and other LXR targets are similar to that of 25-hydroxycholesterol, an LXR agonist. Unlike 25-hydroxycholesterol, 3dSB does not act as a direct agonist for LXR α or β. These data suggest that cholesterol homeostasis plays a significant role in the growth inhibitory activity of the schweinfurthins and may elucidate a mechanism that can be targeted in human cancers such as GBM. Show less

The expression of the epidermal growth factor receptor (EGFR) is highly regulated in normal cells, whereas some cancer cells have high constitutive levels. Understanding naturally-occurring ways of downregulating EGFR in cancer cells was investigated. Phosphatidic acid (PA) or Nuclear Receptors (NR) PPARα/RXRα/LXRα, enhance EGFR expression, mediated by the promoter region -856(A) to -226(T). Unexpectedly, the combination of NRs and PA caused repression. PA induces a conformational change in the nuclear receptor PPARα (increase of alpha-helices at the expense of decreasing beta-sheets), as evidenced by circular dichroism. This represses the naturally-enhancing capability of PPARα on EGFR transcription. PPARα-overexpressing cells in the presence of PA > 300 nM or the enzyme that produces it, phospholipase D (PLD), downregulate EGFR expression. The reasons are two-fold. First, PA displaces PPARα binding to the EGFR promoter at those concentrations. Second, NR heterodimer-dependent promoter activity is weakened in the presence of PA in vivo. Since other genes considered (β-catenin, cyclin D3, PLD2 and ACOX-1) are also downregulated with a PA + PPARα combination, the transrepression appears to be a global phenomenon. Lastly, the reported effect is greater in MCF-7 than in MDA-MB-231 breast cancer cells, which could provide a novel basis for regulating excessive expression of EGFR in luminal cancer cells. Show less

Adequate intake of dietary fibers has proven metabolic and cardiovascular benefits, molecular mechanisms remain still limited. This study was aimed to investigate the effects of cereal dietary fiber on obesity-related liver lipotoxicity in C57BL/6J mice fed a high-fat/cholesterol (HFC) diet and underlying mechanism. Forty-eight adult male C57BL/6J mice were randomly given a reference chow diet, or a high fat/cholesterol (HFC) diet supplemented with or without oat fiber or wheat bran fiber for 24 weeks. Our results showed mice fed oat or wheat bran fiber exhibited lower weight gain, lipid profiles and insulin resistance, compared with HFC diet. The two cereal dietary fibers potently decreased protein expressions of sterol regulatory element binding protein-1 and key factors involved in lipogenesis, including fatty acid synthase and acetyl-CoA carboxylase in target tissues. At molecular level, the two cereal dietary fibers augmented protein expressions of peroxisome proliferator-activated receptor alpha and gamma, liver X receptor alpha, and ATP-binding cassette transporter A1 in target tissues. Our findings indicated that cereal dietary fiber supplementation abrogated obesity-related liver lipotoxicity and dyslipidemia in C57BL/6J mice fed a HFC diet. In addition, the efficacy of oat fiber is greater than wheat bran fiber in normalizing these metabolic disorders and pathological profiles. Show less

It has been suggested that retinoic acid (RA) has a potential role in the prevention of atherosclerotic CVD. In the present study, we used J774A.1 cell lines and primary peritoneal macrophages to investigate the protective effects of RA on foam cell formation and atherogenesis in apoE-deficient (apoE- / -) mice. A total of twenty male apoE- / - mice (n 10 animals per group), aged 8 weeks, were fed on a high-fat diet (HFD) and treated with vehicle or 9-cis-RA for 8 weeks. The atherosclerotic plaque area in the aortic sinus of mice in the 9-cis-RA group was 40·7 % less than that of mice in the control group (P< 0·01). Mouse peritoneal macrophages from the 9-cis-RA group had higher protein expression levels of ATP-binding cassette transporter A1 (ABCA1) and G1 (ABCG1) than those from the control group. Serum total and LDL-cholesterol concentrations were lower in the 9-cis-RA group than in the control group (P< 0·05). In vitro studies showed that incubation of cholesterol-loaded J774A.1 macrophages with 9-cis-RA (0·1, 1 and 10 μmol/l) induced cholesterol efflux in a dose-dependent manner. The 9-cis-RA treatment markedly attenuated lipid accumulation in macrophages exposed to oxidised LDL. Moreover, treatment with 9-cis-RA significantly increased the protein expression levels of ABCA1 and ABCG1 in J774A.1 macrophages in a dose-dependent manner. Furthermore, 9-cis-RA dose-dependently enhanced the protein expression level of liver X receptor-α (LXRα), the upstream regulator of ABCA1 and ABCG1. Taken together, the present results show that 9-cis-RA suppresses foam cell formation and prevents HFD-induced atherogenesis via the LXRα-dependent up-regulation of ABCA1 and ABCG1. Show less

The liver X receptors (LXRs), LXRα and LXRβ, are transcription factors with well-established roles in the regulation of lipid metabolism and cholesterol homeostasis. In addition, LXRs influence innate and adaptive immunity, including responses to inflammatory stimuli, proliferation and differentiation, migration, apoptosis and survival. However, the majority of work describing the role of LXRs in immune cells has been carried out in mouse models, and there are a number of known species-specific differences concerning LXR function. Here we review what is known about the role of LXRs in human immune cells, demonstrating the importance of these receptors in the integration of lipid metabolism and immune function, but also highlighting the need for a better understanding of the species, isoform, and cell-type specific effects of LXR activation. Show less

Liver X receptors (LXRs) are key regulators of lipid homeostasis and are involved in multiple testicular functions. The Lxrα(-/-);Lxrβ(-/-) mice have illuminated the roles of both isoforms in maintenance of the epithelium in the seminiferous tubules, spermatogenesis, and T production. The requirement for LXRβ in Sertoli cells have been emphasized by early abnormal cholesteryl ester accumulation in the Lxrβ(-/-) and Lxrα(-/-);Lxrβ(-/-) mice. Other phenotypes, such as germ cell loss and hypogonadism, occur later in life in the Lxrα(-/-);Lxrβ(-/-) mice. Thus, LXRβ expression in Sertoli cells seems to be essential for normal testicular physiology. To decipher the roles of LXRβ within the Sertoli cells, we generated Lxrα(-/-);Lxrβ(-/-):AMH-Lxrβ transgenic mice, which reexpress Lxrβ in Sertoli cells in the context of Lxrα(-/-);Lxrβ(-/-) mice. In addition to lipid homeostasis, LXRβ is necessary for maintaining the blood-testis barrier and the integrity of the germ cell epithelium. LXRβ is also implicated in the paracrine action of Sertoli cells on Leydig cells to modulate T synthesis. The Lxrα(-/-);Lxrβ(-/-) and Lxrα(-/-);Lxrβ(-/-):AMH-Lxrβ mice exhibit lipid accumulation in germ cells after the Abcg8 down-regulation, suggesting an intricate LXRβ-dependent cooperation between the Sertoli cells and germ cells to ensure spermiogenesis. Further analysis revealed also peritubular smooth muscle defects (abnormal lipid accumulation and disorganized smooth muscle actin) and spermatozoa stagnation in the seminiferous tubules. Together the present work elucidates specific roles of LXRβ in Sertoli cell physiology in vivo beyond lipid homeostasis. Show less

A promising treatment for obesity involves the use of therapeutic agents that increase the level of the glucagon-like peptide (GLP-1) which reduces appetite and food intake. Native GLP-1 is rapidly metabolized by the dipeptidyl peptidase-4 (DPP-4) enzyme and, as such, GLP-1 mimetics or DPP-4 inhibitors represent promising treatment approaches. Interestingly, obese patient receiving such medications showed improved lipid profiles and cholesterol homeostasis, however the mechanism(s) involved are not known. Members of the ATP-binding cassette (ABC) transporters, including ABCA1 and ABCG1, play essential roles in reverse cholesterol transport and in high density lipoprotein (HDL) formation. These transporters are under the transcriptional regulation of liver X receptor alpha (LXR-α). We hypothesize that GLP-1 mimetics and/or DPP-4 inhibitors modulate ABCA1/ABCG1 expression in adipocytes through an LXR-α mediated process and thus affecting cholesterol homeostasis. 3T3-L1 adipocytes were treated with the DPP-4 inhibitor vildagliptin (2 nM) or the GLP-1 mimetic exendin-4 (5 nM). Gene and protein expression of ABCA1, ABCG1 and LXR-α were determined and correlated with cholesterol efflux. Expression levels of interleukin-6 (IL-6), leptin and the glucose transporter-4 (GLUT-4) were also determined. Treatment with both medications significantly increased the expression of ABCA1, ABCG1, LXR-α and GLUT-4, decreased IL-6 and leptin, and improved cholesterol efflux from adipocytes (P < 0.05). Our data suggest that GLP-1-based therapy modulate ABCA1/ABCG1 expression in adipocytes potentially through an LXR-α mediated process. Show less

The accumulation of cholesterol in macrophages could induce the formation of foam cells and increase the risk of developing atherosclerosis. We wonder if quercetin, one of flavonoids with anti-inflammation functions in different cell types, could elevate the development of foam cells formation in atherosclerosis. We treated foam cells derived from oxLDL induced THP-1 cells with quercetin, and evaluated the foam cells formation, cholesterol content and apoptosis of the cells. We found that quercetin induced the expression of ABCA1 in differentiated THP-1 cells, and increased the cholesterol efflux from THP-1 cell derived foam cells. Eventually, cholesterol level and the formation of foam cell derived from THP-1 cells decreased after quercetin treatment. In addition, quercetin activated PPARγ-LXRα pathway to upregulate ABCA1 expression through increasing protein level of PPARγ and its transcriptional activity. Inhibition of PPARγ activity by siRNA knockdown or the addition of chemical inhibitor, GW9662, abolished quercetin induced ABCA1 expression and cholesterol efflux in THP-1 derived macrophages. Our data demonstrated that quercetin increased cholesterol efflux from macrophages through upregulating the expressions of PPARγ and ABCA1. Taken together, increasing uptake of quercetin or quercetin-rich foods would be an effective way to lower the risk of atherosclerosis. Show less