Activation of the Liver X Receptor Inhibits Th17 and Th1 Responses in Behcet’s Disease and Vogt-Koyanagi-Harada Disease

Regulatory mechanism underlying liver X receptor effects on the tumor microenvironment, inflammation and tumorigenesis

INTRODUCTION

Liver X receptors (LXRs) have emerged as novel targets for tumor treatment. LXRs within the tumor microenvironment show the capacity to impact tumorigenesis and tumor development by regulating the infiltration of immune cells and release of cytokines to moderate inflammation.

AREAS COVERED

In this review, we present a systematic description of recent progress in understanding the impact of LXRs on the tumor microenvironment and tumorigenesis. We also summarize the antitumor effects mediated by LXRs via their regulation of cytokine expression. Additionally, we discuss the limitations of LXR research in tumor studies to date.

EXPERT OPINION

Previous studies have demonstrated abnormal LXR expression in tumor tissues, and activation of LXRs has been shown to inhibit tumorigenesis and promote apoptosis in tumor cells. However, LXRs can also affect tumorigenesis by regulating immune cell functions within the tumor immune microenvironment. By summarizing the impact of LXRs on immune cells, we provide new insights into the multifaceted nature of LXRs as antitumor targets.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRβ, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

LXR directly regulates glycosphingolipid synthesis and affects human CD4+ T cell function

The liver X receptor (LXR) is a key transcriptional regulator of cholesterol, fatty acid, and phospholipid metabolism. Dynamic remodeling of immunometabolic pathways, including lipid metabolism, is a crucial step in T cell activation. Here, we explored the role of LXR-regulated metabolic processes in primary human CD4⁺ T cells and their role in controlling plasma membrane lipids (glycosphingolipids and cholesterol), which strongly influence T cell immune signaling and function. Crucially, we identified the glycosphingolipid biosynthesis enzyme glucosylceramide synthase as a direct transcriptional LXR target. LXR activation by agonist GW3965 or endogenous oxysterol ligands significantly altered the glycosphingolipid:cholesterol balance in the plasma membrane by increasing glycosphingolipid levels and reducing cholesterol. Consequently, LXR activation lowered plasma membrane lipid order (stability), and an LXR antagonist could block this effect. LXR stimulation also reduced lipid order at the immune synapse and accelerated activation of proximal T cell signaling molecules. Ultimately, LXR activation dampened proinflammatory T cell function. Finally, compared with responder T cells, regulatory T cells had a distinct pattern of LXR target gene expression corresponding to reduced lipid order. This suggests LXR-driven lipid metabolism could contribute to functional specialization of these T cell subsets. Overall, we report a mode of action for LXR in T cells involving the regulation of glycosphingolipid and cholesterol metabolism and demonstrate its relevance in modulating T cell function.

Disrupted Lipid Metabolism in Multiple Sclerosis: A Role for Liver X Receptors?

Multiple sclerosis (MS) is a chronic neurological disease driven by autoimmune, inflammatory and neurodegenerative processes leading to neuronal demyelination and subsequent degeneration. Systemic lipid metabolism is disturbed in people with MS, and lipid metabolic pathways are crucial to the protective process of remyelination. The lipid-activated transcription factors liver X receptors (LXRs) are important integrators of lipid metabolism and immunity. Consequently, there is a strong interest in targeting these receptors in a number of metabolic and inflammatory diseases, including MS. We have reviewed the evidence for involvement of LXR-driven lipid metabolism in the dysfunction of peripheral and brain-resident immune cells in MS, focusing on human studies, both the relapsing remitting and progressive phases of the disease are discussed. Finally, we discuss the therapeutic potential of modulating the activity of these receptors with existing pharmacological agents and highlight important areas of future research.

Serum Metabolomic Profiling of Patients with Non-Infectious Uveitis

The activities of various metabolic pathways can influence the pathogeneses of autoimmune diseases, and intrinsic metabolites can potentially be used to diagnose diseases. However, the metabolomic analysis of patients with uveitis has not yet been conducted. Here, we profiled the serum metabolomes of patients with three major forms of uveitis (Behҫet's disease (BD), sarcoidosis, and Vogt-Koyanagi-Harada disease (VKH)) to identify potential biomarkers. This study included 19 BD, 20 sarcoidosis, and 15 VKH patients alongside 16 healthy control subjects. The metabolite concentrations in their sera were quantified using liquid chromatography with time-of-flight mass spectrometry. The discriminative abilities of quantified metabolites were evaluated by four comparisons: control vs. three diseases, and each disease vs. the other two diseases (such as sarcoidosis vs. BD + VKH). Among 78 quantified metabolites, 24 kinds of metabolites showed significant differences in these comparisons. Four multiple logistic regression models were developed and validated. The area under the receiver operating characteristic (ROC) curve (AUC) in the model to discriminate disease groups from control was 0.72. The AUC of the other models to discriminate sarcoidosis, BD, and VKH from the other two diseases were 0.84, 0.83, and 0.73, respectively. This study provides potential diagnostic abilities of sarcoidosis, BD, and VKH using routinely available serum samples that can be collected with minimal invasiveness.

Disabled-2 (DAB2) Overexpression Inhibits Monocyte-Derived Dendritic Cells' Function in Vogt-Koyanagi-Harada Disease

Purpose

Recent studies reported that the tumor suppressor disabled-2 (DAB2) is a negative regulator of immune function. In this study, we investigated the role of DAB2 in monocyte-derived dendritic cells (DCs) from Vogt-Koyanagi-Harada disease (VKH) patients.

Methods

The mRNA and protein levels of DAB2 were quantified by quantitative real-time PCR and Western blot. The Sequenom MassARRAY system was used to detect the promoter methylation level. An adenovirus carrying the DAB2 gene was transduced into immature DCs, isolated, and induced from active VKH patients. The surface markers of DCs, the frequency of T helper (Th) type 1 (Th1) and Th17 cells in CD4+T cells, which were cocultured with DCs, were tested by flow cytometry. ELISA was used to analyze the inflammatory cytokines produced by DC and CD4+T cell cocultures.

Results

The mRNA and protein expression levels of DAB2 in DCs obtained from active VKH patients were decreased, while the DAB2 promoter methylation level was marginally increased when compared with inactive VKH patients and normal controls. The expression of CD86 on DCs was significantly downregulated by DAB2 overexpression. The DC-related inflammatory factors IL-6 and TNF-α were also decreased. The frequency of Th1 and Th17 cells and their related cytokines were reduced significantly after coculture with DAB2 overexpressing DCs. DAB2 overexpression did not affect autophagy in DCs from VKH patients.

Conclusions

These results suggest that the decreased expression of DAB2 in DCs plays a role in the pathogenesis of VKH disease. DAB2 overexpression inhibits DC function, but this is not mediated via autophagy.

Th lymphocyte subsets in patients with Vogt-Koyanagi-Harada disease

AIM

To assess helper T (Th) lymphocyte subset balance in patients with Vogt-Koyanagi-Harada (VKH) disease.

METHODS

Sixty-eight active VKH patients and seventy-two inactive VKH patients were included in this study. One hundred healthy individuals served as controls. Peripheral blood was obtained from VKH patients and healthy controls. Th lymphocyte subsets were analyzed by flow cytometry. Plasma concentration of interleukin (IL)-17, IL-10, transforming growth factor (TGF)-β, IL-23 and IL-6 was examined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

VKH patients with active uveitis had significantly higher percentages of both Th1 and Th17 cells and lower percentages of regulatory T (Treg) cells as compared with inactive VKH patients and healthy controls. Th1/Th2 and Th17/Treg ratios were also significantly elevated in active VKH patients. The percentages of Th1, Th17 and Treg cells and the Th1/Th2, Th17/Treg ratio did not differ between inactive VKH patients and healthy controls. There was no difference concerning the percentage of Th2 cells among all the groups. VKH patients with active uveitis showed an elevated level of peripheral Th17 related cytokines levels (TGF-β, IL-6, IL-23, and IL-17) and a decreased level of Treg related cytokines (IL-10) compared with inactive VKH patients and healthy controls. Inactive VKH patients showed no differences in peripheral Th17 related cytokines (TGF-β, IL-6, IL-23, and IL-17) and Treg related cytokines (IL-10) levels compared with healthy controls.

CONCLUSION

Th1 and Th17 cells are significantly increased and Treg cells significantly decreased in active VKH compared with inactive VKH or healthy controls. Therefore, Th lymphocyte subset analysis may serve as a disease biomarker for VKH.

Liver X receptors agonist GW3965 re-sensitizes gefitinib-resistant human non-small cell lung cancer cell to gefitinib treatment by inhibiting NF-κB in vitro

The recent research shows that the inhibition of the nuclear factor-κB (NF-κB) pathway is a promising therapeutic option for patients who progress after treatment with the novel mutant-selective EGFR-TKIs. For propose to find a nontoxic drug to reverse the acquired gefitinib resistance, we examined whether the Liver X Receptors agonist GW3965 affect gefitinib resistance of HCC827/GR-8-2 cells. Cell viability was measured by CCK-8 assay. Levels of NF-κB, p-AKT and caspases were detected by Western blot analysis. Immunocytochemical analysis was used to detect the expression of NF-κB, p-AKT intracellularly. Induction of apoptosis and cell cycle arrest was measured by Flow cytometry assay. And results revealed that more than 90% of HCC827/GR-8-2 cells lived upon treatment with gefitinib at a dose of 5μM for 48h. However, when under the combine treatment of GW3965 (5μM) & gefitinib(5μM), cell death rate was increased observably. Co-administration of gefitinib & GW3965 induced cell apoptosis and cell cycle arrest. Additionally, we observed a dose-dependent- down-regulation of NF-κB in HCC827/GR-8-2 cells treated with gefitinib & GW3965. GW3965 and gefitinib synergistically decreased cell proliferation and induced apoptosis by inhibiting NF-κB signaling pathway in gefitinib resistant cells. These findings support our hypothesis that GW3965 could act as a useful drug to reverse the gefitinib resistance.

Vogt-Koyanagi-Harada disease: Novel insights into pathophysiology, diagnosis and treatment

Vogt-Koyanagi-Harada (VKH) disease is one of the major vision-threatening diseases in certain populations, such as Asians, native Americans, Hispanics and Middle Easterners. It is characterized by bilateral uveitis that is frequently associated with neurological (meningeal), auditory, and integumentary manifestations. Although the etiology and pathogenesis of VKH disease need to be further elucidated, it is widely accepted that the clinical manifestations are caused by an autoimmune response directed against melanin associated antigens in the target organs, i.e. the eye, inner ear, meninges and skin. In the past decades, accumulating evidence has shown that genetic factors, including VKH disease specific risk factors (HLA-DR4) and general risk factors for immune mediated diseases (IL-23R), dysfunction of immune responses, including the innate and adaptive immune system and environmental triggering factors are all involved in the development of VKH disease. Clinically, the criteria of diagnosis for VKH disease have been further improved by the employment of novel imaging techniques for the eye. For the treatment, early and adequate corticosteroids are still the mainstream regime for the disease. However, immunosuppressive and biological agents have shown benefit for the treatment of VKH disease, especially for those patients not responding to corticosteroids. This review is focused on our current knowledge of VKH disease, especially for the diagnosis, pathogenesis (genetic factors and immune mechanisms), ancillary tests and treatment. A better understanding of the role of microbiome composition, genetic basis and ongoing immune processes along with the development of novel biomarkers and objective quantitative assays to monitor intraocular inflammation are needed to improve current management of VKH patients.

Liver X receptors in immune cell function in humans

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.