Liver X Receptor Agonist GW3965 Research Articles

Protective effect of liver X receptor on cigarette smoke and lipopolysaccharide induced airway inflammation and emphysema in mice

Objective The aim of this study is to assess the impact of Liver X receptors (LXRs) on airway inflammation, airway remodeling, and lipid deposition induced by cigarette smoke and lipopolysaccharide (LPS) exposure in the lung. Methods Wild mice and LXR-deficient mice were exposed to cigarette smoke and LPS to induce airway inflammation and remodeling. In addition, some wild mice received intraperitoneal treatment with the LXR agonist GW3965 before exposure to cigarette smoke and LPS. Lung tissue and bronchoalveolar lavage fluid were collected to evaluate airway inflammation, airway remodeling and lipid deposition. Results Exposure to cigarette smoke and LPS resulted in airway inflammation, emphysema and lipid accumulation in wild mice. These mice also exhibited downregulated LXRα and ABCA1 in the lung. Treatment with GW3965 mitigated inflammation, remodeling and lipid deposition, while the deletion of LXRs exacerbated these effects. Furthermore, GW3965 treatment following exposure to cigarette smoke and LPS increased LXRα and ABCA1 expression and attenuated MyD88 expression in wild mice. Conclusion LXRs demonstrate the potential to mitigate cigarette smoke and LPS- induced airway inflammation, emphysema and lipid disposition in mice.

Enhanced liver X receptor signalling reduces brain injury and promotes tissue regeneration following experimental intracerebral haemorrhage: roles of microglia/macrophages

BackgroundInflammation-exacerbated secondary brain injury and limited tissue regeneration are barriers to favourable prognosis after intracerebral haemorrhage (ICH). As a regulator of inflammation and lipid metabolism, Liver X receptor (LXR) has...

LXR agonist modifies neuronal lipid homeostasis and decreases PGD2 in the dorsal root ganglia in western diet-fed mice

The prevalence of peripheral neuropathy is high in diabetic and overweight populations. Chronic neuropathic pain, a symptom of peripheral neuropathy, is a major disabling symptom that leads to a poor quality of life. Glucose management for diabetic and prediabetic individuals often fail to reduce or improve pain symptoms, therefore, exploring other mechanisms is necessary to identify effective treatments. A large body of evidence suggest that lipid signaling may be a viable target for management of peripheral neuropathy in obese individuals. The nuclear transcription factors, Liver X Receptors (LXR), are known regulators of lipid homeostasis, phospholipid remodeling, and inflammation. Notably, the activation of LXR using the synthetic agonist GW3965, delayed western diet (WD)-induced allodynia in rodents. To further understand the neurobiology underlying the effect of LXR, we used translating ribosome affinity purification and evaluated translatomic changes in the sensory neurons of WD-fed mice treated with the LXR agonist GW3965. We also observed that GW3965 decreased prostaglandin levels and decreased free fatty acid content, while increasing lysophosphatidylcholine, phosphatidylcholine, and cholesterol ester species in the sensory neurons of the dorsal root ganglia (DRG). These data suggest novel downstream interplaying mechanisms that modifies DRG neuronal lipid following GW3965 treatment.

Inhibition of Human Cytomegalovirus Particle Maturation by Activation of Liver X Receptor.

Human cytomegalovirus (HCMV), a herpesvirus family member, is a large, complex enveloped virus. The activation of liver X receptor (LXR) can significantly inhibit the replication of HCMV and weaken the virulence of progeny virus (unpublished data). Our results showed activated LXR affected some important viral protein expression and reduced cholesterol content in HCMV infected cells and virus particles. To further clarify the influence of activated LXR on HCMV replication, HCMV assembly and maturation processes were studied by transmission electron microscopy (TEM) in HCMV infected foreskin fibroblasts treated with LXR agonist GW3965. Results showed that activated LXR could reduce the envelope integrity of maturating virions. The functional stage of activated LXR on viral envelope integrity was mainly at virus assembly compartment (VAC) mediated envelopment but not structurally complete virus nucleocapsid formation and the egress of nucleocapsid from the nucleus to the cytoplasm mediated by nuclear egress complex. Reduced cholesterol synthesis and viral protein expression might interfere with the VAC-mediated envelopment. The nucleocapsid and tegument proteins enter the VAC area for the secondary envelope, which was interfered with and resulted in the defective particle, thereby affecting the amount and infectivity of the mature virus. The results indicate that inhibition of HCMV maturation is one mechanism of activated LXR inhibiting virus replication in infected cells.

Liver X receptor agonist GW3965 protects against sepsis by promoting myeloid derived suppressor cells apoptosis in mice

AimsImmunosuppressive myeloid-derived suppressor cells (MDSCs) continuously expand and lead to poor outcome during sepsis. The activation of liver X receptor (LXR) can mitigate sepsis-induced liver and myocardial damage. This study aims to determine whether LXR plays a protective role in sepsis by regulating MDSCs. Main methodsCecal ligation and puncture(CLP)was used to induce sepsis in mice. The mice were then treated with LXR agonist GW3965 (3 mg/kg) or vehicle 1 h, 6 h, 12 h, 24 h, 48 h, 72 h postoperatively. The effect of LXR on the survival rate and multi-organ injury induced by sepsis was evaluated by survival analysis, histological staining, biochemical analysis and ELISAs. The percentages of MDSCs and T cells were detected using flow cytometry. The mRNA expressions of LXR and ATP-binding cassette transporter A1 (ABCA1) were measured using real-time quantitative PCR (RT-qPCR). ABCA1 protein level was determined using immunofluorescence staining. Key findingsLXR agonist GW3965 treatment improved the survival of septic mice, accompanied by reduced multi-organ injury and a decreased level of inflammatory cytokines. Furthermore, GW3965 treatment decreased MDSCs abundance in spleen by boosting the apoptosis of spleen MDSCs, therefore ameliorating their immunosuppressive activity. Meanwhile, bacteria clearance in tissues was enhanced after the GW3965 administration in septic mice. Mechanistically, GW3965 activated LXRβ and its downstream target ABCA1 to initiate the apoptosis of spleen MDSCs. SignificanceThese findings provide new insights into the relationship between LXR and MDSCs in sepsis, thus revealing a potentially effective approach to target the immunosuppression of sepsis.

Activation of liver X receptors prevents emotional and cognitive dysfunction by suppressing microglial M1-polarization and restoring synaptic plasticity in the hippocampus of mice

Depression is a long-lasting and persistent mood disorder in which the regulatory mechanisms of neuroinflammation are thought to play a contributing role to the physiopathology of the condition. Previous studies have shown that liver X receptors (LXRs) can regulate the activation of microglia and neuroinflammation. However, the role of LXRs in depression remains to be fully understood. In this study, we hypothesized that stress impairs the function of LXRs and that the LXRs agonist GW3965 plays a potential anti-depressive role by inhibiting neuroinflammation. The anti-depressive effects of GW3965 were evaluated in both chronic unpredictable mild stress (CUMS) and lipopolysaccharide (LPS) models. The LXRs antagonist GSK2033 was also employed to block LXRs. Behavioural tests were performed to measure depression-like phenotypes and learning abilities. Electrophysiological recordings and Golgi staining were used to measure the plasticity of the dentate gyrus synapse. The expression of synapse and neuroinflammation related proteins were evaluated by Western blotting and immunofluorescence. The activation of LXRs by GW3965 prevented emotional and cognitive deficits induced by either CUMS or LPS. GW3965 prevented the decreased level of LXR-β induced by CUMS. The activation of LXRs significantly improved the impairment of synaptic plasticity, prevented the up-regulation of inflammatory factors and inhibited NF-κB phosphorylation and microglial M1-polarization in both models. The antidepressive-like effects of GW3965 were blocked by GSK2033 in the CUMS and LPS models. Our data suggest that inhibition of the LXRs signalling pathway may be a key driver in the pathogenesis of neuroinflammation during depression and that LXRs agonists have a high potential in the treatment of depression.

Liver X Receptor Exerts Anti-Inflammatory Effects in Colonic Epithelial Cells via ABCA1 and Its Expression Is Decreased in Human and Experimental Inflammatory Bowel Disease.

Liver X receptor (LXR) exerts anti-inflammatory effects in macrophages. The aim of this study was to explore the expression and function of LXR in the colonic epithelium under inflammatory conditions. The expression of LXR was explored by Western blot and immunohistochemistry in colonic biopsies from patients diagnosed with inflammatory bowel disease (IBD) and control patients. In addition, LXR and its target gene expression were analyzed in the colon from interleukin (IL)-10-deficient (IL-10-/-) and wild-type mice. Caco-2 cells were pretreated with the synthetic LXR agonist GW3965 and further challenged with IL-1β, the expression of IL-8 and chemokine (C-C motif) ligand (CCL)-28 chemokines, the activation of mitogen-activated protein (MAP) kinases, and the nuclear translocation of the p65 subunit of nuclear factor kappa B was evaluated. Glibenclamide was used as an ABCA1 antagonist. We found that LXR expression was downregulated in colonic samples from patients with IBD and IL-10-/- mice. The nuclear positivity of LXR inversely correlated with ulcerative colitis histologic activity. Colonic IL-1β mRNA levels negatively correlated with both LXRα and LXRβ in the colon of IL-10-/- mice, where a decreased mRNA expression of the LXR target genes ABCA1 and FAS was shown. In addition, IL-1β decreased the expression of the LXR target gene ABCA1 in cultured intestinal epithelial cells. The synthetic LXR agonist GW3965 led to a decreased nuclear positivity of the p65 subunit of nuclear factor kappa B, a phosphorylation ratio of the p44-42 MAP kinase, and the expression of CCL-28 and IL-8 in IL-1β-stimulated Caco-2 cells. The pharmacological inhibition of ABCA1 increased the phosphorylation of p44-42 after GW3965 treatment and IL-1β stimulation. The LXR-ABCA1 pathway exerts anti-inflammatory effects in intestinal epithelial cells and is impaired in the colonic mucosa of patients with IBD and IL-10-/- mice.

Regulation of intestinal LDLR by the LXR-IDOL axis

Background and aimsCholesterol metabolism is tightly regulated by transcriptional and post-transcriptional mechanisms. Accordingly, dysregulation of cholesterol metabolism is a major risk factor for the development of coronary artery disease and associated complications. In recent years, it has become apparent that next to the liver, the intestine plays a key role in systemic cholesterol metabolism by governing cholesterol absorption, secretion, and incorporation into lipoprotein particles. We have previously demonstrated that the Liver X receptor (LXR)-regulated E3 ubiquitin ligase inducible degrader of LDLR (IDOL) is a regulator of cholesterol uptake owing to its ability to promote the ubiquitylation of the low-density lipoprotein receptor (LDLR). However, whether the LXR-IDOL-LDLR axis regulates the LDLR in the intestine and whether this influences intestinal cholesterol homeostasis is not known. MethodsIn this study, we evaluated the role of the LXR-IDOL-LDLR axis in enterocyte cell models and in primary enterocytes isolated from Idol(−/−) and wild type mice. Furthermore, we studied the regulation of intestinal LDLR in Idol(−/−) and in wild type mice treated with the LXR agonist GW3965. Finally, we assessed ezetimibe-induced trans-intestinal cholesterol efflux in Idol(−/−) mice. ResultsWe show that in a wide range of intestinal cell lines LXR activation decreases LDLR protein abundance, cell surface occupancy, and LDL uptake in an IDOL-dependent manner. Similarly, we find that pharmacological dosing of C57BL6/N mice with the LXR agonist GW3965 increases Idol expression across the intestine with a concomitant reduction in Ldlr protein. Conversely, primary enterocytes isolated from Idol(−/−) mice have elevated Ldlr. To test whether these changes contribute to trans-intestinal cholesterol efflux, we measured fecal cholesterol in mice following ezetimibe dosing, but found no differences between Idol(−/−) and control mice in this setting. ConclusionsIn conclusion, our study establishes that the LXR-IDOL-LDLR axis is active in the intestine and is part of the molecular circuitry that maintains cholesterol homeostasis in enterocytes.

LXR AGONISM POTENTIATES SORAFENIB ACTIVITY IN HCC BY INDUCING METABOLIC STRESS

Hepatocellular carcinoma (HCC) treatments have low efficacy, as FDA‐approved drugs including sorafenib extend patient survival by three months. We sought to identify novel druggable targets for use in combination with sorafenib to increase its efficacy. We implemented a genetic screening paradigm using an overexpression library of 43 genes. We administered this library in the context of liver injury and treated mice with vehicle or sorafenib and determined the genetic drivers of each tumor. Mice injected with the screening library developed HCC clones containing MYC cDNA plus various other cDNAs. Treatment with sorafenib resulted in sorafenib‐resistant HCCs that were significantly depleted in NR1H3 cDNA, encoding Liver X receptor (LXR), suggesting that LXR activation is incompatible with tumor growth during sorafenib treatment in vivo. Combination treatment using sorafenib and LXR agonist GW3965 in multiple HCC cell lines and a primary cell line led to enhanced cell death as compared to monotherapy, due to reduced expression levels of cell cycle regulators and increased expression of genes linked to apoptosis. Pathway analysis revealed alterations in metabolic pathways, and we observed upregulation of gluconeogenic regulators and downregulation of glycolytic regulators in sorafenib and combination treatment, and increased regulation of fatty acid synthesis genes in GW3965 and combination treatment. When gluconeogenesis and fatty acid synthesis are reduced using siRNA, cells are resistant to combination therapy. We propose that sorafenib upregulates glucose synthesis and downregulates glycolysis, while GW3965 upregulates fatty acid synthesis. In combination, sorafenib and GW3965 deplete cellular resources required for ATP production, subsequently leading to apoptosis.

Differential Role of Liver X Receptor (LXR) α and LXRβ in the Regulation of UDP-Glucuronosyltransferase 1A1 in Humanized UGT1 Mice.

Liver X receptors (LXRs), LXRα and LXRβ, are nuclear receptors that regulate the metabolism of cholesterol and bile acids and are activated by oxysterols. Humanized UGT1 (hUGT1) mice express the 9-human UGT1A genes associated with the UGT1 locus in a Ugt1-null background. The expression of UGT1A1 is developmentally delayed in the liver and intestines, resulting in the accumulation of serum bilirubin during the neonatal period. Induction of UGT1A1 in newborn hUGT1 mice leads to rapid reduction in total serum bilirubin (TSB) levels, a phenotype measurement that allows for an accurate prediction on UGT1A1 expression. When neonatal hUGT1 mice were treated by oral gavage with the LXR agonist T0901317, TSB levels were dramatically reduced. To determine the LXR contribution to the induction of UGT1A1 and the lowering of TSB levels, experiments were conducted in neonatal hUGT1/Lxrα -/- , hUGT1/Lxrβ -/- , and hUGT1/Lxrαβ -/- mice treated with T0901317. Induction of liver UGT1A1 was dependent upon LXRα, with the induction pattern paralleling induction of LXRα-specific stearoyl CoA desaturase 1. However, the actions of T0901317 were also shown to display a lack of specificity for LXR, with the induction of liver UGT1A1 in hUGT1/Lxrαβ -/- mice, a result associated with activation of both pregnane X receptor and constitutive androstane receptor. However, the LXR agonist GW3965 was highly selective toward LXRα, showing no impact on lowering TSB values or inducing UGT1A1 in hUGT1/Lxrα -/- mice. An LXR-specific enhancer site on the UGT1A1 gene was identified, along with convincing evidence that LXRα is crucial in maintaining constitutive expression of UGT1A1 in adult hUGT1 mice. SIGNIFICANCE STATEMENT: It has been established that activation of LXRα, and not LXRβ, is responsible for the induction of liver UGT1A1 and metabolism of serum bilirubin in neonatal hUGT1 mice. Although induction of the human UGT1A1 gene is initiated at a newly characterized LXR enhancer site, allelic deletion of the Lxrα gene drastically reduces the constitutive expression of liver UGT1A1 in adult hUGT1 mice. Combined, these findings indicate that LXRα is critical for the developmental expression of UGT1A1.

Lipidomic analysis of human primary hepatocytes following LXR activation with GW3965 identifies AGXT2L1 as a main target associated to changes in phosphatidylethanolamine

Liver X receptor (LXR) agonists have the potential to alleviate obesity related diseases, particularly atherosclerosis. However, LXRs are transcriptional regulators that induce de novo lipogenesis and lipid accumulation in hepatocytes which represents a serious adverse effect. In this work, we sought to characterize the LXR agonist GW3965 effects on fatty acid (FA) and phospholipid (PL) remodelling and the correlation with gene expression in order to better understand the underlying effects leading to hepatic pathology upon LXR activation. Human primary hepatocytes treated for 48 h with GW3965 were analysed for changes in lipid metabolism gene expression by qPCR, variations in the FA profile was evaluated by GC-FID and in PL profiles using thin layer chromatography, ESI-MS and MS/MS analysis. Changes in cell membrane biochemical properties were studied using bilayer models generated with CHARMM-GUI. ELOLV6 and SCD1 mRNA increase was consistent with higher C16:1 and C18:1n9 at the expense of C16:0 and C18:0. The reduction of C18:2n6 and increase in C20:2n6 was in agreement with ELOVL5 upregulation. Phosphatydilethanolamine (PE) levels tended to decrease and phosphatidylinositol to increase; although differences did not reach significance, they correlated with changes in AGXT2L1, CDS1 and LPIN1 mRNA levels that were increased. The overall effect of GW3965 on PEs molecular profiles was an increase of long-chain polyunsaturated FA chains and a decrease of C16/C18 saturated and monounsaturated FAs chains. Additionally, PC (32:1) and PC (34:2) were decreased, and PC (36:1) and PC (34:1) were increased. AGXT2L1 is an enzyme with strict substrate specificity for phosphoethanolamine, which is converted into ammonia in GW3965-treated hepatocytes and could explain the PE reduction. In summary, LXR activation by GW3965 targets PE biosynthesis and FA elongation/desaturation, which tends to decrease PE in relation to total PL levels, and remodelling of PC and PE molecular species. We identified the human AGXT2L1 gene as induced by LXR activation by both synthetic and endogenous agonist treatment. The increase in acetaldehyde-induced oxidative stress, and in the lipid species identified have the potential to enhance the inflammatory process and impair membrane function. Future studies should focus on inhibition of AGXT2L1 activity with the aim of reverting the steatosis induced by LXR activation.

Activation of Liver X Receptors by GW3965 Attenuated Deoxycorticosterone Acetate-Salt Hypertension-Induced Cardiac Functional and Structural Changes.

In this study, the effect of liver X receptor (LXR) activation on hypertension-induced cardiac structural and functional alterations was investigated. Hypertension was induced by deoxycorticosterone acetate (DOCA)-salt administration in uninephrectomized rats for 6 weeks. LXR agonist GW3965 (3-{3-[(2-chloro-3-trifluoromethyl-benzyl)-(2,2-diphenyl-ethyl)-amino]-propoxy}-phenyl)-acetic acid was given for the past week. Rhythmic activity and contractions of the isolated heart tissues were recorded. Biochemical parameters were assessed in ventricular tissue and plasma samples. Cardiac expressions of various proteins were examined, and histopathological evaluation was performed in the left ventricle and liver. GW3965 reduced systolic blood pressure and enhanced noradrenaline-stimulated papillary muscle contraction induced by DOCA-salt + uninephrectomy. Plasma and tissue total antioxidant capacity (TAC) increased and tissue 4-hydroxynonenal (4-HNE) levels decreased in the DOCA-salt group. GW3965 elevated plasma and tissue TAC levels in both of groups. Glucose-regulated protein-78 (GRP78), phospho-dsRNA-activated-protein kinase-like ER kinase (p-PERK), matrix metalloproteinase-2 (MMP-2), and nuclear factor-κB p65 (NF-κB p65) expression was augmented, and inhibitor-κB-α (IκB-α) expression was reduced in hypertensive hearts. The altered levels of all these markers were reversed by GW3965. Also, GW3965 ameliorated DOCA-salt + uninephrectomy-induced cardiac and hepatic inflammation and fibrosis. However, GW3965 unchanged the plasma lipid levels and hepatic balloon degeneration score. These results demonstrated that LXR activation may improve hypertension-induced cardiac changes without undesired effects.

Liver X receptor-α activation enhances cholesterol secretion in lactating mammary epithelium.

Liver X receptors (LXRs) are ligand-dependent transcription factors activated by cholesterol metabolites. These receptors induce a suite of target genes required for de novo synthesis of triglycerides and cholesterol transport in many tissues. Two different isoforms, LXRα and LXRβ, have been well characterized in liver, adipocytes, macrophages, and intestinal epithelium among others, but their contribution to cholesterol and fatty acid efflux in the lactating mammary epithelium is poorly understood. We hypothesize that LXR regulates lipogenesis during milk fat production in lactation. Global mRNA analysis of mouse mammary epithelial cells (MECs) revealed multiple LXR/RXR targets upregulated sharply early in lactation compared with midpregnancy. LXRα is the primary isoform, and its protein levels increase throughout lactation in MECs. The LXR agonist GW3965 markedly induced several genes involved in cholesterol transport and lipogenesis and enhanced cytoplasmic lipid droplet accumulation in the HC11 MEC cell line. Importantly, in vivo pharmacological activation of LXR increased the milk cholesterol percentage and induced sterol regulatory element-binding protein 1c (Srebp1c) and ATP-binding cassette transporter a7 (Abca7) expression in MECs. Cumulatively, our findings identify LXRα as an important regulator of cholesterol incorporation into the milk through key nodes of de novo lipogenesis, suggesting a potential therapeutic target in women with difficulty initiating lactation.

The impact of 27-hydroxycholesterol on endometrial cancer proliferation.

Endometrial cancer (EC) is the most common gynaecological malignancy. Obesity is a major risk factor for EC and is associated with elevated cholesterol. 27-hydroxycholesterol (27HC) is a cholesterol metabolite that functions as an endogenous agonist for Liver X receptor (LXR) and a selective oestrogen receptor modulator (SERM). Exposure to oestrogenic ligands increases risk of developing EC; however, the impact of 27HC on EC is unknown. Samples of stage 1 EC (n = 126) were collected from postmenopausal women undergoing hysterectomy. Expression of LXRs (NR1H3, LXRα; NR1H2, LXRβ) and enzymes required for the synthesis (CYP27A1) or breakdown (CYP7B1) of 27HC were detected in all grades of EC. Cell lines originating from well-, moderate- and poorly-differentiated ECs (Ishikawa, RL95, MFE 280 respectively) were used to assess the impact of 27HC or the LXR agonist GW3965 on proliferation or expression of a luciferase reporter gene under the control of LXR- or ER-dependent promoters (LXRE, ERE). Incubation with 27HC or GW3965 increased transcription via LXRE in Ishikawa, RL95 and MFE 280 cells (P < 0.01). 27HC selectively activated ER-dependent transcription (P < 0.001) in Ishikawa cells and promoted proliferation of both Ishikawa and RL95 cells (P < 0.001). In MFE 280 cells, 27HC did not alter proliferation but selective targeting of LXR with GW3965 significantly reduced cell proliferation (P < 0.0001). These novel results suggest that 27HC can contribute to risk of EC by promoting proliferation of endometrial cancer epithelial cells and highlight LXR as a potential therapeutic target in the treatment of advanced disease.

Liver X Receptor Agonist GW3965 Regulates Synaptic Function upon Amyloid Beta Exposure in Hippocampal Neurons.

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by beta-amyloid (Aβ) accumulation and neurofibrillary tangles formation in the brain which are associated to synaptic deficits and dementia. Liver X receptor (LXR) agonists have been demonstrated to revert of pathologic and cognitive defects in murine models of AD through the regulation of Apolipoprotein E, ATP-Binding Cassette A1 (ABCA1), by dampening neuroinflammation and also by reducing the levels of amyloid-β (Aβ) accumulation in the brain. However, the role of LXR with regard to the regulation of synaptic function remains relatively understudied. In the present paper, we analyzed the in-vitro effect of the LXR agonist GW3965 on synaptic function upon exposure of primary hippocampal cultures to oligomeric amyloid-β (oAβ(1-42)). We showed that oAβ(1-42) exposure significantly decreased the density of mature (mushroom shaped) dendritic spines density and synaptic contacts number. oAβ(1-42) also modulates the expression of pre- (VGlut1, SYT1, SV2A) and post-synaptic (SHANK2, NMDA) proteins, it decreases the expression of PINK1, and increases ROCKII, and activates of caspase-3; these changes were prevented by the pre-treating neuronal cultures with GW3965. These results show further support the role of the LXR agonist GW3965 in synaptic physiology and highlight its potential as an alternative pharmacological strategy for AD.

Liver X Receptors Activation Attenuates Ischemia Reperfusion Injury of Liver Graft in Rats

ABSTRACTPurpose: Suppression of the Toll like receptor 4 (TLR4)-nuclear factor-κB (NF-κB) signaling was critical in protection against liver IRI. Previous studies revealed that Liver X receptors (LXRs) activation could antagonize TLR4-NF-κB signaling. The purpose of this study is to determine whether LXRs agonist GW3965 can suppress the TLR4-NF-κB signaling during liver transplantation and protect ischemia-reperfusion injury (IRI). Materials and Methods: Sprague Dawley (SD) rats were used to perform orthotropic liver transplantation. Donors were pretreatment with GW3965 (0.3 mg/kg) through caudal vein injection 30 min before the surgery. The followings were analyzed after transplantation: alanine aminotransferase (ALT), interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) level in serum, ATP binding cassette transporter A1 (Abca1) expression, NF-κB transcriptional activity, apoptosis and histological injury. Results: GW3965 pretreatment significantly ameliorated the degree of IRI associated with the effects of upregulating Abca1 expression, inhibiting NF-κB transcriptional activity, and downregulating TNF-α and IL-6 level. Conclusion: LXRs activation attenuated hepatic IRI by preventing TLR4–NF-κB signaling.

Liver X receptor activation promotes differentiation of regulatory T cells.

The nuclear receptor Liver X Receptor (LXR) is a ligand-activated transcription factor that has been implicated in control of chronic inflammation by downregulating pro-inflammatory T cell responses. An impaired function of regulatory T cells, a subset of CD4+ T cells with a crucial role in maintaining lymphocytes homeostasis and immune regulation, is frequently observed in chronic inflammatory diseases. We observed that pharmacological activation of LXR in T cells not only resulted in a thorough suppression of Th1 and Th17 polarization in vitro, but also significantly induced regulatory T cells (Treg) cell differentiation in a receptor-specific fashion. In line with this, systemic LXR activation by oral treatment of mice with the LXR agonist GW3965 induced gut-associated regulatory T cells in vivo. Importantly, such LXR-activated Tregs had a higher suppressive capacity in functional in vitro coculture assays with effector T cells. Our data thus point towards a dual role of LXR-mediated control of inflammation by suppression of pro-inflammatory T cells and reciprocal induction of regulatory T cells.

Targeted Nanotherapeutics Encapsulating Liver X Receptor Agonist GW3965 Enhance Antiatherogenic Effects without Adverse Effects on Hepatic Lipid Metabolism in Ldlr-/- Mice.

The pharmacological manipulation of liver X receptors (LXRs) has been an attractive therapeutic strategy for atherosclerosis treatment as they control reverse cholesterol transport and inflammatory response. This study presents the development and efficacy of nanoparticles (NPs) incorporating the synthetic LXR agonist GW3965 (GW) in targeting atherosclerotic lesions. Collagen IV (Col IV) targeting ligands are employed to functionalize the NPs to improve targeting to the atherosclerotic plaque, and formulation parameters such as the length of the polyethylene glycol (PEG) coating molecules are systematically optimized. In vitro studies indicate that the GW-encapsulated NPs upregulate the LXR target genes and downregulate proinflammatory mediator in macrophages. The Col IV-targeted NPs encapsulating GW (Col IV-GW-NPs) successfully reaches atherosclerotic lesions when administered for 5 weeks to mice with preexisting lesions, substantially reducing macrophage content (≈30%) compared to the PBS group, which is with greater efficacy versus nontargeting NPs encapsulating GW (GW-NPs) (≈18%). In addition, mice administered the Col IV-GW-NPs do not demonstrate increased hepatic lipid biosynthesis or hyperlipidemia during the treatment period, unlike mice injected with the free GW. These findings suggest a new form of LXR-based therapeutics capable of enhanced delivery of the LXR agonist to atherosclerotic lesions without altering hepatic lipid metabolism.

LXR agonists promote the proliferation of neural progenitor cells through MEK-ERK pathway

The liver X receptors (LXRs) are transcriptional regulators of lipid homeostasis and may be critical for neurodegeneration and neurogenesis in vivo. However, it remains largely unknown about the role of LXRs and its agonists in the in vitro proliferation of neural progenitor cells (NPCs). Here we revealed for the first time that LXRs were markedly expressed in mouse NPCs and were critical for the in vitro proliferation. LXR agonists GW3965 and LXR623 promoted the proliferation of wildtype NPCs, but not NPCs from LXR double-knockout mice. Mechanistically, phosphorylation of MEK1/2 and ERK1/2 in NPCs was enhanced upon LXR agonist treatment, while abrogation of MEK/ERK phosphorylation by the inhibitors PD98059 and U0126 impaired the proliferation of wildtype NPCs in the presence or absence of LXR agonists. Collectively, our findings suggest that LXR agonists GW3965 and LXR623 can stimulate the NPC proliferation in LXR- and MEK/ERK-dependent manner.

Activation of Liver X Receptor Attenuates Oleic Acid–Induced Acute Respiratory Distress Syndrome

Liver X receptors (LXRs) were identified as receptors that sense oxidized cholesterol derivatives. LXRs are best known for their hepatic functions in regulating cholesterol metabolism and triglyceride synthesis, but whether and how LXRs play a role in the lung diseases is less understood. To study the function of LXRs in acute respiratory distress syndrome (ARDS), we applied the oleic acid (OA) model of ARDS to mice whose LXR was genetically or pharmacologically activated. The VP-LXRα knock-in (LXR-KI) mice, in which a constitutively activated LXRα (VP-LXRα) was inserted into the mouse LXRα locus, were used as the genetic gain-of-function model. We showed that the OA-induced lung damages, including the cytokine levels and total cell numbers and neutrophil numbers in the bronchoalveolar lavage fluid, the wet/dry weight ratio, and morphological abnormalities were reduced in the LXR-KI mice and wild-type mice treated with the LXR agonist GW3965. The pulmonoprotective effect of GW3965 was abolished in the LXR-null mice. Consistent with the pulmonoprotective effect of LXR and the induction of antioxidant enzymes by LXR, the OA-induced suppression of superoxide dismutase and catalase was attenuated in LXR-KI mice and GW3965-treated wild-type mice. Taken together, our results demonstrate that activation of LXRs can alleviate OA-induced ARDS by attenuating the inflammatory response and enhancing antioxidant capacity.