The Endogenous Dual Retinoid Receptor Agonist Alitretinoin Exhibits Immunoregulatory Functions on Antigen-Presenting Cells.

Retinoids are a frequently used class of drugs in the treatment of inflammatory as well as malignant skin diseases. Retinoids have differential affinity for the retinoic acid receptor (RAR) and/or the retinoid X receptor (RXR). The endogenous dual RAR and RXR agonist alitretinoin (9-cis retinoic acid) demonstrated remarkable efficacy in the treatment of chronic hand eczema (CHE) patients; however, detailed information on the mechanisms of action remains elusive. Here, we used CHE as a model disease to unravel immunomodulatory pathways following retinoid receptor signaling. Transcriptome analyses of skin specimens from alitretinoin-responder CHE patients identified 231 significantly regulated genes. Bioinformatic analyses indicated keratinocytes as well as antigen presenting cells as cellular targets of alitretinoin. In keratinocytes, alitretinoin interfered with inflammation-associated barrier gene dysregulation as well as antimicrobial peptide induction while markedly inducing hyaluronan synthases without affecting hyaluronidase expression. In monocyte-derived dendritic cells, alitretinoin induced distinct morphological and phenotypic characteristics with low co-stimulatory molecule expression (CD80 and CD86), the increased secretion of IL-10 and the upregulation of the ecto-5'-nucleotidase CD73 mimicking immunomodulatory or tolerogenic dendritic cells. Indeed, alitretinoin-treated dendritic cells demonstrated a significantly reduced capacity to activate T cells in mixed leukocyte reactions. In a direct comparison, alitretinoin-mediated effects were significantly stronger than those observed for the RAR agonist acitretin. Moreover, longitudinal monitoring of alitretinoin-responder CHE patients could confirm in vitro findings. Taken together, we demonstrate that the dual RAR and RXR agonist alitretinoin targets epidermal dysregulation and demonstrates strong immunomodulatory effects on antigen presenting cell functions.

Retinoid X receptor ligand regulates RXRα/Nur77-dependent apoptosis via modulating its nuclear export and mitochondrial targeting.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder disease in elderly. It is characterized by the formation of amyloid plaques and nerve cells apoptosis in the brain. This study focuses on the association between nerve cells apoptosis and nuclear receptors within AD. Thus, we detected the changes of the expression and subcellular localization of RXRα/Nur77 and the apoptotic rate of neuroblastoma cells, SH-SY5Y cells and nerve cells in C57BL/6 mouse hippocampus in Alzheimer's disease pathologic condition, and investigated the effect of RXRα exporting inhibition caused by 9-cis-RA on the apoptosis of neurons. We demonstrated that Aß peptide and H2O2 treatment could result in the translocation of RXRα and Nur77 from the nucleus to the mitochondria, and the ligand of RXR, 9-cis-RA, treatment can block the above phenomenon. More importantly, 9-cis-RA treatment could reduce the apoptotic rate of neurons caused by H2O2 or Aß stimulation via enhancing the expression level of Bcl-2 protein. Therefore, our studies revealed a critical role of RXRα/Nur77 in 9-cis-RA-mediated anti-apoptosis in nerve cells and provided novel information for better management of AD.

Genetic dissection of retinoid esterification and accumulation in the liver and adipose tissue.

Approximately 80-90% of all retinoids in the body are stored as retinyl esters (REs) in the liver. Adipose tissue also contributes significantly to RE storage. The present studies, employing genetic and nutritional interventions, explored factors that are responsible for regulating RE accumulation in the liver and adipose tissue and how these influence levels of retinoic acid (RA) and RA-responsive gene expression. Our data establish that acyl-CoA:retinol acyltransferase (ARAT) activity is not involved in RE synthesis in the liver, even when mice are nutritionally stressed by feeding a 25-fold excess retinol diet or upon ablation of cellular retinol-binding protein type I (CRBPI), which is proposed to limit retinol availability to ARATs. Unlike the liver, where lecithin:retinol acyltransferase (LRAT) is responsible for all RE synthesis, this is not true for adipose tissue where Lrat-deficient mice display significantly elevated RE concentrations. However, when CrbpI is also absent, RE levels resemble wild-type levels, suggesting a role for CrbpI in RE accumulation in adipose tissue. Although expression of several RA-responsive genes is elevated in Lrat-deficient liver, employing a sensitive liquid chromatography tandem mass spectrometry protocol and contrary to what has been assumed for many years, we did not detect elevated concentrations of all-trans-RA. The elevated RA-responsive gene expression was associated with elevated hepatic triglyceride levels and decreased expression of Pparδ and its downstream Pdk4 target, suggesting a role for RA in these processes in vivo.

Antagonistic effect of the inflammasome on thymic stromal lymphopoietin expression in the skin.

BACKGROUND: Innate immune sensors control key cytokines that regulate T-cell priming and T-cell fate. This is particularly evident in allergic reactions, which represent ideal systems to study the interplay of innate and adaptive immunity. In patients with contact dermatitis, inflammasome-mediated IL-1 activation is responsible for a TH1 immune response. Surprisingly, the IL-1 signaling pathway was also proposed to control the activation of thymic stromal lymphopoietin (TSLP), a cytokine implicated in development of the T(H)2 response in patients with atopic dermatitis (AD) and asthma. OBJECTIVES: We sought to assess the effect of the inflammasome on TSLP expression levels and the development of AD. METHODS: We studied the effect of the inflammasome activator 2,4-dinitrofluorobenzene, and IL-1ß on TSLP mRNA expression levels in mouse and human cell lines (in vitro assays), as well as in live mice and on human skin transplants. We also assessed the effect of 2,4-dinitrofluorobenzene on TSLP and the TH2 response in mice in which the inflammasome and IL-1 signaling pathways were blocked, either genetically or pharmacologically, in 2 models of AD. RESULTS: We provide in vitro and in vivo evidence that inflammasome activation has an inhibitory role on TSLP mRNA expression and T(H)2 cell fate in the skin. We also show that solvents influence the activation of TSLP and IL-1ß and direct the T-cell fate to a given hapten. CONCLUSION: Our observations strongly suggest that the TH1 versus TH2 cell fate decision is regulated at multiple levels and starts with innate immune events occurring within peripheral epithelial tissues.

Macrophages engulfing apoptotic thymocytes produce retinoids to promote selection, differentiation, removal and replacement of double positive thymocytes.

The thymus provides the microenvironment in which thymocytes develop into mature T-cells, and interactions with thymic stromal cells are thought to provide the necessary signals for thymocyte maturation. Recognition of self-MHC by T-cells is a basic requirement for mature T-cell functions, and those thymocytes that do not recognize or respond too strongly to the peptide-loaded self-MHC molecules found in the thymus undergo apoptosis. As a result, 95% of the thymocytes produced will die and be subsequently cleared by macrophages. This review describes a complex crosstalk between developing thymocytes and engulfing macrophages which is mediated by retinoids produced by engulfing macrophages. The interaction results in the harmonization of the rate of cell death of dying double positive cells with their clearance and replacement, and in promotion of the differentiation of the selected cells in the thymus.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology.

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

Synergistic effects of Herceptin and 9-cis-RA on MDA-MB-453 breast cancer cells / 第三军医大学学报

Objective To investigate the synergistic effects of Herceptin and 9-cis-RA on the proliferation, cell cycle and apoptosis of HER2-positive breast cancer cells. Methods MDA-MB-453 breast cancer cells were treated with 5 ?g/ml Herceptin or 1 ?mol/L 9-cis-RA or both for 24, 48 or 72 h. The proliferation of MDA-MB-453 breast cancer cells was determined by MTT, the pro-apoptotic effects were detected by TUNEL, the cell cycle phase was detected by FCM. Results As compared with control group, Herceptin and 9-cis-RA synergistically inhibited the proliferation of MDA-MB-453 breast cancer cells, and the percentage of G_ 0 /G_ 1 cells increased after treatment with Herceptin and 9-cis-RA for 72 h. Simultaneously, Herceptin and 9-cis-RA synergistically induced the apoptosis of MDA-MB-453 cells. Conclusion Herceptin and 9-cis-RA could synergistically and effectively inhibit MDA-MB-453 breast cancer cells by blocking their cell cycle progression and inducing their apoptosis.

THE SYNERGISTIC EFFECTS OF HERCEPTIN AND 9-CIS-RETINOIC ACID ON HER2/NEU POSITIVE BREAST CANCER CELLS IN VIVO / 营养学报

Objective To observe the synergistic effects of Herceptin(HER)and 9-cis-retinoic acid (9-cis-RA) on HER2/neu positive breast cancer cells in vivo. Method MCF-7 breast cancer cells transfected with exogenous HER2 gene were inoculated into athymic nude mice. Four weeks after tumor inoculation,mice bearing a tumor of 200 mm3 in volume approximately were selected to be treated with HER and/or 9-cis-RA(SC) for 20d. After that tumor volume was precisely measured,concurrently the HE staining and Ki-67 immunohistochemical (IHC) assay were performed to detect the anti-proliferative effect of HER in combination with 9-cis-RA in vivo. Results After 3 w of treatment,HER and 9-cis-RA synergistically decreased the tumor volume as compared with control group. IHC results showed that Ki-67 expression was significantly inhibited by co-treatment of HER and 9-cis-RA,which means the arrest of cell cycle progression. Conclusion Herceptin and 9-cis-RA could synergistically inhibit the proliferation of HER2 positive breast cancer cells in vivo.