Interleukin-12 and -23 Control Plasticity of CD127(+) Group 1 and Group 3 Innate Lymphoid Cells in the Intestinal Lamina Propria.

Human group 1 ILCs consist of at least three phenotypically distinct subsets, including NK cells, CD127(+) ILC1, and intraepithelial CD103(+) ILC1. In inflamed intestinal tissues from Crohn's disease patients, numbers of CD127(+) ILC1 increased at the cost of ILC3. Here we found that differentiation of ILC3 to CD127(+) ILC1 is reversible in vitro and in vivo. CD127(+) ILC1 differentiated to ILC3 in the presence of interleukin-2 (IL-2), IL-23, and IL-1ß dependent on the transcription factor RORγt, and this process was enhanced in the presence of retinoic acid. Furthermore, we observed in resection specimen from Crohn's disease patients a higher proportion of CD14(+) dendritic cells (DC), which in vitro promoted polarization from ILC3 to CD127(+) ILC1. In contrast, CD14(-) DCs promoted differentiation from CD127(+) ILC1 toward ILC3. These observations suggest that environmental cues determine the composition, function, and phenotype of CD127(+) ILC1 and ILC3 in the gut.

Retinoblastoma, an inside job.

Why are some cell types more prone to transformation than others? In this issue, Xu et al. (2009) show that retinoblastoma cells co-opt several intrinsic features of cone photoreceptors for their survival and growth.

Retinoblastoma has properties of a cone precursor tumor and depends upon cone-specific MDM2 signaling.

Retinoblastomas result from the inactivation of the RB1 gene and the loss of Rb protein, yet the cell type in which Rb suppresses retinoblastoma and the circuitry that underlies the need for Rb are undefined. Here, we show that retinoblastoma cells express markers of postmitotic cone precursors but not markers of other retinal cell types. We also demonstrate that human cone precursors prominently express MDM2 and N-Myc, that retinoblastoma cells require both of these proteins for proliferation and survival, and that MDM2 is needed to suppress ARF-induced apoptosis in cultured retinoblastoma cells. Interestingly, retinoblastoma cell MDM2 expression was regulated by the cone-specific RXRgamma transcription factor and a human-specific RXRgamma consensus binding site, and proliferation required RXRgamma, as well as the cone-specific thyroid hormone receptor-beta2. These findings provide support for a cone precursor origin of retinoblastoma and suggest that human cone-specific signaling circuitry sensitizes to the oncogenic effects of RB1 mutations.

NRL-/- gene edited human embryonic stem cells generate rod-deficient retinal organoids enriched in S-cone-like photoreceptors.

Organoid cultures represent a unique tool to investigate the developmental complexity of tissues like the human retina. NRL is a transcription factor required for the specification and homeostasis of mammalian rod photoreceptors. In Nrl-deficient mice, photoreceptor precursor cells do not differentiate into rods, and instead follow a default photoreceptor specification pathway to generate S-cone-like cells. To investigate whether this genetic switch mechanism is conserved in humans, we used CRISPR/Cas9 gene editing to engineer an NRL-deficient embryonic stem cell (ESC) line (NRL-/- ), and differentiated it into retinal organoids. Retinal organoids self-organize and resemble embryonic optic vesicles (OVs) that recapitulate the natural histogenesis of rods and cone photoreceptors. NRL-/- OVs develop comparably to controls, and exhibit a laminated, organized retinal structure with markers of photoreceptor synaptogenesis. Using immunohistochemistry and quantitative polymerase chain reaction (qPCR), we observed that NRL-/- OVs do not express NRL, or other rod photoreceptor markers directly or indirectly regulated by NRL. On the contrary, they show an abnormal number of photoreceptors positive for S-OPSIN, which define a primordial subtype of cone, and overexpress other cone genes indicating a conserved molecular switch in mammals. This study represents the first evidence in a human in vitro ESC-derived organoid system that NRL is required to define rod identity, and that in its absence S-cone-like cells develop as the default photoreceptor cell type. It shows how gene edited retinal organoids provide a useful system to investigate human photoreceptor specification, relevant for efforts to generate cells for transplantation in retinal degenerative diseases.

RXRγ attenuates cerebral ischemia-reperfusion induced ferroptosis in neurons in mice through transcriptionally promoting the expression of GPX4.

Cerebral ischemia is a common cerebrovascular disease with high mortality and disability rate. Exploring its mechanism is essential for developing effective treatment for cerebral ischemia. Therefore, this study aims to explore the regulatory effect and mechanism of retinoid X receptor γ (RXRγ) on cerebral ischemia-reperfusion (I/R) injury. A mouse intraluminal middle cerebral artery occlusion model was established, and PC12 cells were exposed to anaerobic/reoxygenation (A/R) as an in vitro model in this study. Cerebral I/R surgery or A/R treatment induced ferroptosis, downregulated RXRγ and GPX4 (glutathione peroxidase 4) levels, upregulated cyclooxygenase-2 (COX-2) level and increased ROS (reactive oxygen species) level in A/R induced cells or I/R brain tissues in vivo or PC12 cells in vitro. Knockdown of RXRγ downregulated GPX4 and increased COX-2 and ROS levels in A/R induced cells. RXRγ overexpression has the opposite effect. GPX4 knockdown reversed the improvement of RXRγ overexpression on COX-2 downregulation, GPX4 upregulation and ferroptosis in PC12 cells. Furthermore, chromatin immunoprecipitation (ChIP) and luciferase reporter gene assays revealed that RXRγ bound to GPX4 promoter region and activated its transcription. Overexpression of RXRγ or GPX4 alleviated brain damage and inhibited ferroptosis in I/R mice. In conclusion, RXRγ-mediated transcriptional activation of GPX4 might inhibit ferroptosis during I/R-induced brain injury.

Retinoid X receptor gamma (RXRG) is an independent prognostic biomarker in ER-positive invasive breast cancer.

BACKGROUND: Retinoid X Receptor Gamma (RXRG) is a member of the nuclear receptor superfamily and plays a role in tumour suppression. This study aims to explore the prognostic significance of RXRG in breast cancer. METHODS: Primary breast cancer tissue microarrays (n = 923) were immuno-stained for RXRG protein and correlated with clinicopathological features, and patient outcome. RESULTS: Nuclear RXRG expression was significantly associated with smaller tumour size (p = 0.036), lower grade (p < 0.001), lobular histology (p = 0.016), lower Nottingham Prognostic Index (p = 0.04) and longer breast cancer-specific survival (p < 0.001), and longer time to distant metastasis (p = 0.002). RXRG expression showed positive association with oestrogen receptor (ER)-related biomarkers: GATA3, FOXA1, STAT3 and MED7 (all p < 0.001) and a negative correlation with the Ki67 proliferation marker. Multivariate analysis demonstrated RXRG protein as an independent predictor of longer breast cancer-specific survival and distant metastasis-free survival. In the external validation cohorts, RXRG expression was associated with improved patients' outcome (p = 0.025). In ER-positive tumours, high expression of RXRG was associated with better patient outcome regardless of adjuvant systemic therapy. ER signalling pathway was the top predicted master regulator of RXRG protein expression (p = 0.005). CONCLUSION: This study provides evidence for the prognostic value of RXRG in breast cancer particularly the ER-positive tumours.

Cone Genesis Tracing by the Chrnb4-EGFP Mouse Line: Evidences of Cellular Material Fusion after Cone Precursor Transplantation.

The cone function is essential to mediate high visual acuity, color vision, and daylight vision. Inherited cone dystrophies and age-related macular degeneration affect a substantial percentage of the world population. To identify and isolate the most competent cells for transplantation and integration into the retina, cone tracing during development would be an important added value. To that aim, the Chrnb4-EGFP mouse line was characterized throughout retinogenesis. It revealed a sub-population of early retinal progenitors expressing the reporter gene that is progressively restricted to mature cones during retina development. The presence of the native CHRNB4 protein was confirmed in EGFP-positive cells, and it presents a similar pattern in the human retina. Sub-retinal transplantations of distinct subpopulations of Chrnb4-EGFP-expressing cells revealed the embryonic day 15.5 high-EGFP population the most efficient cells to interact with host retinas to provoke the appearance of EGFP-positive cones in the photoreceptor layer. Importantly, transplantations into the DsRed retinas revealed material exchanges between donor and host retinas, as >80% of transplanted EGFP-positive cones also were DsRed positive. Whether this cell material fusion is of significant therapeutic advantage requires further thorough investigations. The Chrnb4-EGFP mouse line definitely opens new research perspectives in cone genesis and retina repair.

Xanthophylls increased HDLC level and nuclear factor PPARγ, RXRγ and RARα expression in hens and chicks.

This study was designed to investigate effects of xanthophylls on serum lipid profile (triglyceride, TG; cholesterol, CHO; high-density lipoprotein cholesterol, HDLC; and low-density lipoprotein cholesterol, LDLC) and nuclear factor (peroxisome proliferator-activated receptor gamma, PPARγ; PPAR gamma coactivator 1 alpha, PGC1α; retinoid X receptor gamma, RXRγ; and retinoic acid receptor alpha, RARα) gene expression of breeding hens and chicks. In experiment 1, 432 hens were divided into three groups and fed diets supplemented with 0 (as control group), 20 or 40 mg/kg xanthophylls. Blood was sampled at 7, 14, 21, 28 and 35 days of trial. Liver, duodenum, jejunum and ileum were sampled at 35 days of trial. Results showed that serum HDLC level of hens was increased after dietary 40 mg/kg xanthophyll addition for 21, 28 and 35 days, while serum TG, CHO and LDLC were not affected. Xanthophyll addition also increased PPARγ expression in jejunum, RXRγ expression in duodenum and jejunum, and RARα expression in liver and duodenum. Experiment 2 was a 2 × 2 factorial design. Male chicks hatched from 0 or 40 mg/kg xanthophyll diet of hens were fed diet containing either 0 or 40 mg/kg xanthophylls. Liver, duodenum, jejunum and ileum were sampled at 0, 7, 14 and 21 days after hatching. Blood samples were also collected at 21 days. Results showed that in ovo xanthophylls elevated PPARγ in duodenum and jejunum, and RXRγ and RARα in liver of chicks mainly within 1 week after hatching, while dietary xanthophylls increased serum HDLC level and PPARγ and RXRγ in liver from 2 weeks onwards. In conclusion, our research suggested xanthophylls can regulate serum lipid profile and nuclear factor expression in hens and chicks.

Selective ligand activity at Nur/retinoid X receptor complexes revealed by dimer-specific bioluminescence resonance energy transfer-based sensors.

Retinoid X receptors (RXRs) play a role as master regulators because of their capacity to form heterodimers with other nuclear receptors (NRs). Accordingly, retinoid signaling is involved in multiple biologic processes, including development, cell differentiation, metabolism, and cell death. However, the role and function of RXRs in different heterodimer complexes remain unidentified, mainly because most RXR drugs (called rexinoids) are not selective of specific heterodimer complexes. The lack of selectivity strongly limits the use of rexinoids for specific therapeutic approaches. To better characterize rexinoids at specific NR complexes, we have developed and optimized luciferase (Luc) protein complementation(PCA)-based bioluminescence resonance energy transfer (BRET) assays that can directly measure recruitment of a coactivator (CoA) motif fused to yellow fluorescent protein (YFP) by specific NR dimers. To validate the assays, we compared rexinoid modulation of CoA recruitment by the RXR homodimer and by the heterodimers Nur77/RXR and Nurr1/RXR. Results revealed that some rexinoids display selective CoA recruitment activities with homo- or heterodimer complexes. In particular, SR11237 (BMS649) has stronger potency for recruitment of CoA motif and transcriptional activity with the heterodimer Nur77/RXR than other complexes. This technology should be useful in identifying new compounds with specificity for individual dimeric species formed by NRs.

Regulation of Retinoic Acid Receptor Beta by Interleukin-15 in the Lung during Cigarette Smoking and Influenza Virus Infection.

Virus-induced exacerbations often lead to further impairment of lung function in chronic obstructive pulmonary disease. IL-15 is critical in antiviral immune responses. Retinoic acid (RA) signaling plays an important role in tissue maintenance and repair, particularly in the lung. We studied RA signaling and its relation to IL-15 in the lung during cigarette smoke (CS) exposure and influenza virus infection. In vivo studies show that RA signaling is diminished by long-term CS exposure or influenza virus infection alone, which is further attenuated during infection after CS exposure. RA receptor ß (RARß) is specifically decreased in the lung of IL-15 transgenic (overexpression; IL-15Tg) mice, and a greater reduction in RARß is found in these mice compared with wild-type (WT) mice after infection. RARß is increased in IL-15 knockout (IL-15KO) mice compared with WT mice after infection, and the additive effect of CS and virus on RARß down-regulation is diminished in IL-15KO mice. IL-15 receptor α (IL-15Rα) is increased and RARß is significantly decreased in lung interstitial macrophages from IL-15Tg mice compared with WT mice. In vitro studies show that IL-15 down-regulates RARß in macrophages via IL-15Rα signaling during influenza virus infection. These studies suggest that RA signaling is significantly diminished in the lung by CS exposure and influenza virus infection. IL-15 specifically down-regulates RARß expression, and RARß may play a protective role in lung injury caused by CS exposure and viral infections.

Neuroendocrine factors regulate retinoic acid receptors in normal and hypoplastic lung development.

KEY POINTS: Retinoic acid (RA) and ghrelin levels are altered in human hypoplastic lungs when compared to healthy lungs. Although considerable data have been obtained about RA, ghrelin and bombesin in the congenital diaphragmatic hernia (CDH) rat model, neuroendocrine factors have never been associated with the RA signalling pathway in this animal model. In this study, the interaction between neuroendocrine factors and RA was explored in the CDH rat model. The authors found that normal fetal lung explants treated with RA, bombesin and ghrelin showed an increase in lung growth. Hypoplastic lungs presented higher expression levels of the RA receptors α and γ. Moreover bombesin and ghrelin supplementation, in vitro, to normal lungs increased RA receptor α/γ expression whereas administration of bombesin and ghrelin antagonists to normal and hypoplastic lungs decreased it. These data reveal for the first time that there is a link between neuroendocrine factors and RA, and that neuroendocrine factors sensitise the lung to the RA action through RA receptor modulation. ABSTRACT: Congenital diaphragmatic hernia (CDH) is characterised by a spectrum of lung hypoplasia and consequent pulmonary hypertension, leading to high morbidity and mortality rates. Moreover, CDH has been associated with an increase in the levels of pulmonary neuroendocrine factors, such as bombesin and ghrelin, and a decrease in the action of retinoic acid (RA). The present study aimed to elucidate the interaction between neuroendocrine factors and RA. In vitro analyses were performed on Sprague-Dawley rat embryos. Normal lung explants were treated with bombesin, ghrelin, a bombesin antagonist, a ghrelin antagonist, dimethylsulfoxide (DMSO), RA dissolved in DMSO, bombesin plus RA and ghrelin plus RA. Hypoplastic lung explants (nitrofen model) were cultured with bombesin, ghrelin, bombesin antagonist or ghrelin antagonist. The lung explants were analysed morphometrically, and retinoic acid receptor (RAR) α, ß and γ expression levels were assessed via Western blotting. Immunohistochemistry analysis of RAR was performed in normal and hypoplastic lungs 17.5 days post-conception (dpc). Compared with the controls, hypoplastic lungs exhibited significantly higher RARα/γ expression levels. Furthermore considering hypoplastic lungs, bombesin and ghrelin antagonists decreased RARα/γ expression. Normal lung explants (13.5 dpc) treated with RA, bombesin plus RA, ghrelin plus RA, bombesin or ghrelin exhibited increased lung growth. Moreover, bombesin and ghrelin increased RARα/γ expression levels, whereas the bombesin and ghrelin antagonists decreased RARα/γ expression. This study demonstrates for the first time that neuroendocrine factors function as lung growth regulators, sensitising the lung to the action of RA through up-regulation of RARα and RARγ.

Regulation of retinoid X receptor gamma expression by fed state in mouse liver.

Glucose metabolism is balanced by glycolysis and gluconeogenesis with precise control in the liver. The expression of genes related to glucose metabolism is regulated primarily by glucose and insulin at transcriptional level. Nuclear receptors play important roles in regulating the gene expression of glucose metabolism at transcriptional level. Some of these nuclear receptors form heterodimers with RXRs to bind to their specific regulatory elements on the target promoters. To date, three isotypes of RXRs have been identified; RXRα, RXRß and RXRγ. However, their involvement in the interactions with other nuclear receptors in the liver remains unclear. In this study, we found RXRγ is rapidly induced after feeding in the mouse liver, indicating a potential role of RXRγ in controlling glucose or lipid metabolism in the fasting-feeding cycle. In addition, RXRγ expression was upregulated by glucose in primary hepatocytes. This implies that glucose metabolism governed by RXRγ in conjunction with other nuclear receptors. The luciferase reporter assay showed that RXRγ as well as RXRα increased SREBP-1c promoter activity in hepatocytes. These results suggest that RXRγ may play an important role in tight control of glucose metabolism in the fasting-feeding cycle.

Daily rhythms of catalase and glutathione peroxidase expression and activity are endogenously driven in the hippocampus and are modified by a vitamin A-free diet.

OBJECTIVES: Alterations in enzymatic antioxidant defense systems lead to a deficit of cognitive functions and altered hippocampal synaptic plasticity. The objectives of this study were to investigate endogenous rhythms of catalase (CAT) and glutathione peroxidase (GPx) expression and activity, as well as CREB1 mRNA, in the rat hippocampus, and to evaluate to which extent the vitamin A deficiency could affect those temporal patterns. METHODS: Rats from control and vitamin A-deficient (VAD) groups received a diet containing 4000 IU of vitamin A/kg diet, or the same diet devoid of vitamin A, respectively, during 3 months. Rats were maintained under 12-hour-dark conditions, during 10 days before the sacrifice. Circadian rhythms of CAT, GPx, RXRγ, and CREB1 mRNA levels were determined by reverse transcriptrase polymerase chain reaction in hippocampus samples isolated every 4 hours during a 24-hour period. CAT and GPx enzymatic activities were also determined by kinetic assays. Regulatory regions of clock and antioxidant enzymes genes were scanned for E-box, RXRE, and CRE sites. RESULTS: E-box, RXRE, and CRE sites were found on regulatory regions of GPx and CAT genes, which display a circadian expression in the rat hippocampus. VAD phase shifted CAT, GPx, and RXRγ endogenous rhythms without affecting circadian expression of CREB1. DISCUSSION: CAT and GPx expression and enzymatic activity are circadian in the rat hippocampus. The VAD affected the temporal patterns antioxidant genes expression, probably by altering circadian rhythms of its RXR receptors and clock factors; thus, it would impair the temporal orchestration of hippocampal daily cognitive performance.

Phthalates efficiently bind to human peroxisome proliferator activated receptor and retinoid X receptor α, ß, γ subtypes: an in silico approach.

This exhaustive in silico study looks into the molecular interactions of phthalates and their metabolites with human peroxisome proliferator-activated receptor (hPPAR) and retinoid X receptor (hRXR) α, ß and γ subtypes--the nuclear receptor proteins function as transcription factors by regulating the expression of downstream genes. Apart from the much discussed plasticizer bisphenol A, we examined the binding affinities of 15 common diphthalates and their monophthalates, natural (linoleic acid, conjugated linoleic acid) and synthetic (bezafibrate, pioglitazone, GW 50156) ligands with hPPARs. In addition to these phthalates, specific natural (retinoic and phytanic acids) and synthetic (bexarotene, rosiglitazone) ligands were examined with hRXRs. The Maestro, Schrödinger Suite 2012 was used for the molecular docking study. In general, natural ligands of hPPAR showed less binding efficiencies than phthalic acid esters and drugs. The diphthalate di-iso-decyl phthalate showed the highest G score (-9.99) with hPPAR (γ), while its monophthalate (mono-iso-decyl phthalate) showed a comparatively less G score (-9.56). Though the PPAR modulator GW 50156 showed strong affinity with all hPPAR subtypes, its highest G score (-12.43) was with hPPARß. Hazardous di(2-ethylhexyl)phthalate generally showed a greater preference to hRXRs than hPPARs, but its highest G score (-10.87) was with hRXRα; while its monophthalate (Mono(2-ethylhexyl)phthalate) showed a lesser G score (-8.59). The drug bexarotene showed the highest G score (-13.32) with hRXRß. Moreover, bisphenol A showed more affinity towards hRXR. Briefly, this study gives an overview on the preference of phthalic acid esters, natural and synthetic ligands on to hPPAR and hRXR subtypes, which would lead to further in vitro mechanistic as well as in vivo preclinical and clinical studies.

RXRγ gene variants are associated with HIV lipodystrophy.

HIV lipodystrophy (HIVLD), associated with combination antiretroviral therapy (cART), leads to metabolic and cardiovascular diseases. Nuclear receptors play a central role in lipid homoeostasis and drug disposition; their genetic variants may predispose an individual to the development of HIVLD. DNA samples obtained from cART-treated HIV-positive patients with (HIVLD+; 124) and without (HIVLD-; 56) HIVLD were genotyped for 77 single nucleotide polymorphisms in nine nuclear receptor genes. Statistical analysis was carried out using Haploview software and by logistic regression. Three single nucleotide polymorphisms in RXRγ (rs2134095, rs113471, rs2194899) and its haplotypes (HIVLD+, 54%; HIVLD-, 40.6%; P=0.02) showed significant association with HIVLD. Multivariate analysis identified time since diagnosis (P=0.001) and carriage of the RXRγ haplotype (P=0.02) to be independently associated with HIVLD. Genetic variation in RXRγ, a common binding partner of nuclear receptors that modulate lipid homoeostasis and drug disposition, may contribute to the development of HIVLD in cART-treated HIV patients. These results need replication in other cohorts.

The nuclear receptor hepatocyte nuclear factor 4alpha acts as a morphogen to induce the formation of microvilli.

Microvilli are actin-based organelles found on apical plasma membranes that are involved in nutrient uptake and signal transduction. Numerous components, including ezrin/radixin/moesin (ERM) proteins, have been identified that link filamentous actins to transmembrane proteins, but the signals driving microvillus biogenesis are not known. In this study, we show that the conditional and/or ectopic expression of a nuclear receptor, hepatocyte nuclear factor 4alpha (HNF4alpha), triggers microvillus morphogenesis. We also demonstrate that HNF4alpha expression induces ERM-binding phosphoprotein 50 (EBP50) expression and that attenuation of EBP50 using RNA interference inhibits microvillus development. We conclude that HNF4alpha acts as a morphogen to trigger microvillus formation.

Retinoid X receptor γ up-regulation is correlated with dedifferentiation of tumor cells and lymph node metastasis in papillary thyroid carcinoma.

The expression of retinoid X receptor γ (RXRγ) and the clinicopathological parameters of total 69 patients with papillary thyroid carcinoma (PTC) larger than 1 cm were examined. The PTCs were classified into two groups according to the presence of loss of cellular polarity/cohesiveness (LOP/C). The expression of RXRγ mRNA was examined by reverse transcriptase polymerase chain reaction and quantitative real-time PCR. The RXRγ mRNA up-regulation was found to be positively correlated with extrathyroid invasion (r = 0.293, P = 0.019), advanced tumor stage (r = 0.318, P = 0.016) and lymph node metastasis (LNM) (r = 0.338, P = 0.005), as well as LOP/C (r = 0.345, P = 0.004), which was proposed as a histological characteristic of poor cellular differentiation. The RXRγ mRNA expression, as well as extrathyroid invasion, LOP/C and advanced tumor stage, was further confirmed to be one of the independent predictive factors (Odds ratio: 6.545; 95% confidence interval: 1.575-27.208) of LNM using multivariate analysis. These results suggest that RXRγ may play a role in the dedifferentiation and metastasis of PTC.

Loss of retinoid X receptor gamma subunit impairs group 1 mGluR mediated electrophysiological responses and group 1 mGluR dependent behaviors.

Retinoid X receptors are members of the nuclear receptor family that regulate gene expression in response to retinoic acid and related ligands. Group 1 metabotropic glutamate receptors are G-protein coupled transmembrane receptors that activate intracellular signaling cascades in response to the neurotransmitter, glutamate. These two classes of molecules have been studied independently and found to play important roles in regulating neuronal physiology with potential clinical implications for disorders such as depression, schizophrenia, Parkinson's and Alzheimer's disease. Here we show that mice lacking the retinoid X receptor subunit, RXRγ, exhibit impairments in group 1 mGluR-mediated electrophysiological responses at hippocampal Schaffer collateral-CA1 pyramidal cell synapses, including impaired group 1 mGluR-dependent long-term synaptic depression (LTD), reduced group 1 mGluR-induced calcium release, and loss of group 1 mGluR-activated voltage-sensitive currents. These animals also exhibit impairments in a subset of group 1 mGluR-dependent behaviors, including motor performance, spatial object recognition, and prepulse inhibition. Together, these observations demonstrate convergence between the RXRγ and group 1 mGluR signaling pathways that may function to coordinate their regulation of neuronal activity. They also identify RXRγ as a potential target for the treatment of disorders in which group 1 mGluR signaling has been implicated.

Pre-activation of retinoid signaling facilitates neuronal differentiation of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) can differentiate into neurons in an appropriate cellular environment. Retinoid signaling pathway is required in neural development. However, the effect and mechanism through retinoid signaling regulates neuronal differentiation of MSCs are still poorly understood. Here, we report that all-trans-retinoic acid (ATRA) pre-induction improved neuronal differentiation of rat MSCs. We found that, when MSCs were exposed to different concentrations of ATRA (0.01-100 micromol/L) for 24 h and then cultured with modified neuronal induction medium (MNM), 1 micromol/L ATRA pre-induction significantly improved neuronal differentiation efficiency and neural-cell survival. Compared with MNM alone induced neural-like cells, ATRA/MNM induced cells expressed higher levels of Nestin, neuron specific enolase (NSE), microtubule-associated protein-2 (MAP-2), but lower levels of CD68, glial fibrillary acidic protein (GFAP), and glial cell line-derived neurotrophic factor(GDNF), also exhibited higher resting membrane potential and intracellular calcium concentration, supporting that ATRA pre-induction promotes maturation and function of derived neurons but not neuroglia cells from MSCs. Endogenous retinoid X receptors (RXR) RXRalpha and RXRgamma (and to a lesser extent, RXRbeta) were weakly expressed in MSCs. But the expression of RARalpha and RARgamma was readily detectable, whereas RARbeta was undetectable. However, at 24 h after ATRA treatment, the expression of RARbeta, not RARalpha or RARgamma, increased significantly. We further found the subnuclear redistribution of RARbeta in differentiated neurons, suggesting that RARbeta may function as a major mediator of retinoid signaling during neuronal differentiation from MSCs. ATRA treatment upregulated the expression of Vimentin and Stra13, while it downregulated the expression of Brachyury in MSCs. Thus, our results demonstrate that pre-activation of retinoid signaling by ATRA facilitates neuronal differentiation of MSCs.

PPARgamma and RXRgamma ligands act synergistically as potent antineoplastic agents in vitro and in vivo glioma models.

Glioblastoma represent the most common primary brain tumor in adults and are currently considered incurable. We investigated antiproliferative and anti-invasive mechanisms of 6-OH-11-O-hydroxyfenantrene (IIF), a retinoid X receptor ligand, and pioglitazone (PGZ), a peroxisome proliferator-activated receptor gamma activator, in three different glioblastoma cell lines. A dose-dependent reduction of tumor invasion and strong decrease of matrix metalloproteinases 2 and 9 expression was observed, especially when a combination therapy of IIF and PGZ was administered. Combined treatment also markedly reduced proliferation and induced apoptosis in all glioma cell lines tested. This was in particular accompanied by decrease of antiapoptotic proteins Bcl2 and p53, while simultaneously pro-apoptotic cytochrome c, cleaved caspase 3, Bax and Bad levels increased. These in vitro findings were further substantiated in a murine glioma model in vivo, where oral administration of PGZ and IIF resulted in significantly reduced tumor volume and proliferation. Of note, treatment with nuclear receptor ligands was not only effective when the treatment was initiated shortly after the intraparenchymal seeding of the glioma cells, but even when initiated in the last third of the observation period. Collectively, our results demonstrate the effectiveness of a combined treatment of ligands of proliferator-activated receptor and retinoid X receptor against glioblastoma.