The Roles of GSK-3ß in Regulation of Retinoid Signaling and Sorafenib Treatment Response in Hepatocellular Carcinoma.

Rationale: Glycogen synthase kinase-3ß (GSK-3ß) plays key roles in metabolism and many cellular processes. It was recently demonstrated that overexpression of GSK-3ß can confer tumor growth. However, the expression and function of GSK-3ß in hepatocellular carcinoma (HCC) remain largely unexplored. This study is aimed at investigating the role and therapeutic target value of GSK-3ß in HCC. Methods: We firstly clarified the expression of GSK-3ß in human HCC samples. Given that deviated retinoid signalling is critical for HCC development, we studied whether GSK-3ß could be involved in the regulation. Since sorafenib is currently used to treat HCC, the involvement of GSK-3ß in sorafenib treatment response was determined. Co-immunoprecipitation, GST pull down, in vitro kinase assay, luciferase reporter and chromatin immunoprecipitation were used to explore the molecular mechanism. The biological readouts were examined with MTT, flow cytometry and animal experiments. Results: We demonstrated that GSK-3ß is highly expressed in HCC and associated with shorter overall survival (OS). Overexpression of GSK-3ß confers HCC cell colony formation and xenograft tumor growth. Tumor-associated GSK-3ß is correlated with reduced expression of retinoic acid receptor-ß (RARß), which is caused by GSK-3ß-mediated phosphorylation and heterodimerization abrogation of retinoid X receptor (RXRα) with RARα on RARß promoter. Overexpression of functional GSK-3ß impairs retinoid response and represses sorafenib anti-HCC effect. Inactivation of GSK-3ß by tideglusib can potentiate 9-cis-RA enhancement of sorafenib sensitivity (tumor inhibition from 48.3% to 93.4%). Efficient induction of RARß by tideglusib/9-cis-RA is required for enhanced therapeutic outcome of sorafenib, which effect is greatly inhibited by knocking down RARß. Conclusions: Our findings demonstrate that GSK-3ß is a disruptor of retinoid signalling and a new resistant factor of sorafenib in HCC. Targeting GSK-3ß may be a promising strategy for HCC treatment in clinic.

Effect of Chemotherapeutic Agents on the Expression of Retinoid Receptors and Markers of Cancer Stem Cells and Epithelial-Mesenchymal Transition.

A large body of evidence suggests that cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT), as well as expression and function of retinoid receptors, are pivotal features of tumor initiation, progression, and chemoresistance. This is also true for pancreatic ductal adenocarcinoma (PDAC), which represents a clinical challenge due to poor prognosis and increasing incidence. Understanding the above features of cancer cells could open new avenues for PDAC treatment strategies. The aim of this study was to investigate the relation between CSCs, EMT, and retinoid receptors in PDAC after treatment with the chemotherapeutic agents - gemcitabine and 5-fluorouracil. First, we demonstrated the difference in the expression levels of CSC and EMT markers and retinoid receptors in the untreated Mia PaCa-2 and Panc1 cells that also differed in the frequency of spontaneous apoptosis and distribution between the cell cycle phases. Chemotherapy reduced the number of cancer cells in the S phase. Gemcitabine and 5-fluorouracil modulated expression of CSC markers, E-cadherin, and RXRß in Panc1 but not in Mia PaCa-2 cells. We suggest that these effects could be attributed to the difference in the basal levels of expression of the investigated genes. The obtained data could be interesting in the context of future preclinical research.

Cellular microRNA miR-c89 inhibits replication of porcine reproductive and respiratory syndrome virus by targeting the host factor porcine retinoid X receptor ß.

MicroRNAs (miRNAs) play critical roles in the complex networks of virus-host interactions. Our previous research showed that porcine reproductive and respiratory syndrome virus (PRRSV) infection markedly upregulates miR-c89 expression, suggesting that miR-c89 may play an important role in PRRSV infection. The present study sought to determine the function of miR-c89 and its molecular mechanism during PRRSV infection. Using quantitative reverse transcription PCR (RT-qPCR) verification, we demonstrated that both highly pathogenic PRRSV and low-pathogenic PRRSV infection induced miR-c89 expression. The overexpression of miR-c89 significantly suppressed the replication of a variety of PRRSV strains, regardless of the timing of infection. Further, miR-c89 can directly target the 3'UTR of porcine retinoid X receptor ß (RXRB) mRNA in a sequence-specific manner. Knockdown affected RXRB expression, as siRNA can suppress the replication of a variety of PRRSV strains. This work not only provides new insights into PRRSV-cell interactions, but also highlights the potential for the use of miR-c89 in the development of new antiviral strategies to combat PRRSV infection.

Lycopene inhibits hepatic stellate cell activation and modulates cellular lipid storage and signaling.

Hepatic stellate cells are liver-specific perivascular cells, identified as the major source of collagen in liver fibrosis, following their activation and conversion to myofibroblast-like cells. Lycopene is a carotenoid with biological activities and protective effects described in different pathologies, but little is known about its role in liver protection. We evaluated the influence of lycopene on the cell cycle and lipid metabolism and monitored the possible pathways involved in lycopene inhibition of stellate cell activation. Lycopene induced expression of the lipocyte phenotype, with an accumulation of fat droplets in cytoplasm, with high synthesis and turnover of phospholipids and triglycerides. Cell proliferation analysis showed that lycopene reduced the growth of GRX cells. Lycopene induced an arrest in the G0/G1 phase, followed by a decrease of cells in the G2/M phase, regardless of the concentration of lycopene used. Lycopene modulated relevant signaling pathways related to cholesterol metabolism, cellular proliferation, and lipid metabolism. Also, lycopene treatment increased the expression of RXR-α, RXR-ß, and PPARγ, important biomarkers of liver regeneration. These results show that lycopene was able to negatively modulate events related to the activation of hepatic stellate cells through mechanisms that involve changes in expression of cellular lipid metabolism factors, and suggest that this compound might provide a novel pharmacological approach for the prevention and treatment of fibrotic liver diseases.

Maternal Supplementation with ß-Carotene During Pregnancy Disturbs Lipid Metabolism and Glucose Homoeostasis in F1 Female Mice.

SCOPE: ß-Carotene (BC), a substitute for vitamin A, is widely used for its benefits. The present study investigates whether in-utero BC administration can alter lipid and glucose homoeostasis in offspring. METHODS AND RESULTS: Pregnant mice are supplemented with BC (1 mg kg-1 weight) by oral gavage once every 3 days, for a total of six doses. Increased visceral fat may be caused by up-regulated PPARγ (peroxisome proliferator-activated receptor gamma) and RXRα/ß (retinoid X receptors) in liver and adipose tissue, and glucose intolerance is observed in F1 adult females prenatally supplemented with BC, while F1 males do not exhibit these symptoms. In females, increased serum leptin, resistin, and IL-6 and reduced adiponectin, caused by visceral obesity, may result in downregulated insulin receptor signaling in muscle and further account for glucose intolerance. Increased pancreatic ß-cell mass might compensate for the downregulated insulin gene (ins2). Increased glucagon and α-cell mass, accompanied by upregulated glucagon gene (gcg), might also be risk factors for the development of diabetes. CONCLUSIONS: Maternal supplementation with BC disturbs lipid metabolism and induces glucose intolerance in F1 female mice, suggesting that BC supplementation during pregnancy should be used with caution.

Nuclear RXRα and RXRß receptors exert distinct and opposite effects on RA-mediated neuroblastoma differentiation.

Retinoic acid (RA) promotes differentiation in multiple neurogenic cell types by promoting gene reprogramming through retinoid receptors and also by inducing cytosolic signaling events. The nuclear RXR receptors are one of the main mediators of RA cellular effects, classically by joining the direct receptors of RA, the nuclear RAR receptors, in RAR/RXR dimers which act as transcription factors. Distinct RXR genes lead to RXRα, RXRß and RXRγ subtypes, but their specific roles in neuronal differentiation remain unclear. We firstly investigated both RXRs and RARs expression profiles during RA-mediated neuronal differentiation of human neuroblastoma cell line SH-SY5Y, and found varying levels of retinoid receptors transcript and protein contents along the process. In order to understand the roles of the expression of distinct RXR subtypes to RA signal transduction, we performed siRNA-mediated silencing of RXRα and RXRß during the first stages of SH-SY5Y differentiation. Our results showed that RXRα is required for RA-induced neuronal differentiation of SH-SY5Y cells, since its silencing compromised cell cycle arrest and prevented the upregulation of neuronal markers and the adoption of neuronal morphology. Besides, silencing of RXRα affected the phosphorylation of ERK1/2. By contrast, silencing of RXRß improved neurite extension and led to increased expression of tau and synaptophysin, suggesting that RXRß may negatively regulate neuronal parameters related to neurite outgrowth and function. Our results indicate distinct functions for RXR subtypes during RA-dependent neuronal differentiation and reveal new perspectives for studying such receptors as clinical targets in therapies aiming at restoring neuronal function.

PGC1ß regulates multiple myeloma tumor growth through LDHA-mediated glycolytic metabolism.

Multiple myeloma (MM) is an incurable hematologic malignancy due to inevitable relapse and chemoresistance development. Our preliminary data show that MM cells express high levels of PGC1ß and LDHA. In this study, we investigated the mechanism behind PGC1ß-mediated LDHA expression and its contribution to tumorigenesis, to aid in the development of novel therapeutic approaches for MM. Real-time PCR and western blotting were first used to evaluate gene expression of PGC1ß and LDHA in different MM cells, and then, luciferase reporter assay, chromatin immunoprecipitation, LDHA deletion report vectors, and siRNA techniques were used to investigate the mechanism underlying PGC1ß-induced LDHA expression. Furthermore, knockdown cell lines and lines stably overexpressing PGC1ß or LDHA lentivirus were established to evaluate in vitro glycolysis metabolism, mitochondrial function, reactive oxygen species (ROS) formation, and cell proliferation. In addition, in vivo xenograft tumor development studies were performed to investigate the effect of PGC1ß or LDHA expression on tumor growth and mouse survival. We found that PGC1ß and LDHA are highly expressed in different MM cells and LDHA is upregulated by PGC1ß through the PGC1ß/RXRß axis acting on the LDHA promoter. Overexpression of PGC1ß or LDHA significantly potentiated glycolysis metabolism with increased cell proliferation and tumor growth. On the other hand, knockdown of PGC1ß or LDHA largely suppressed glycolysis metabolism with increased ROS formation and apoptosis rate, in addition to suppressing tumor growth and enhancing mouse survival. This is the first time the mechanism underlying PGC1ß-mediated LDHA expression in multiple myeloma has been identified. We conclude that PGC1ß regulates multiple myeloma tumor growth through LDHA-mediated glycolytic metabolism. Targeting the PGC1ß/LDHA pathway may be a novel therapeutic strategy for multiple myeloma treatment.

Fundamental studies of adrenal retinoid-X-receptor: Protein isoform, tissue expression, subcellular distribution, and ligand availability.

Adrenal gland reportedly expresses many nuclear receptors that are known to heterodimerize with retinoid-X-receptor (RXR) for functions, but the information regarding the glandular RXR is not adequate. Studies of rat adrenal homogenate by Western blotting revealed three RXR proteins: RXRα (55kDa), RXRß (47kDa) and RXR (56kDa). RXRγ was not detectable. After fractionation, RXRα was almost exclusively localized in the nuclear fraction. In comparison, substantial portions of RXRß and RXR were found in both nuclear and post-nuclear particle fractions, suggesting genomic and non-genomic functions. Cells immunostained for RXRα were primarily localized in zona fasciculata (ZF) and medulla, although some stained cells were found in zona glomerulosa (ZG) and zona reticularis (ZR). In contrast, cells immunostained for RXRß were concentrated principally in ZG, although some stained cells were seen in ZR, ZF, and medulla (in descending order, qualitatively). Analysis of adrenal lipid extracts by LC/MS did not detect 9-cis-retinoic acid (a potent RXR-ligand) but identified all-trans retinoic acid. Since C20 and C22 polyunsaturated fatty acids (PUFAs) can also activate RXR, subcellular availabilities of unesterified fatty acids were investigated by GC/MS. As results, arachidonic acid (C20:4), adrenic acid (C22:4), docosapentaenoic acid (C22:5), and cervonic acid (C22:6) were detected in the lipids extracted from each subcellular fraction. Thus, the RXR-agonizing PUFAs are available in all the main subcellular compartments considerably. The present findings not only shed light on the adrenal network of RXRs but also provide baseline information for further investigations of RXR heterodimers in the regulation of adrenal steroidogenesis.

Brown Adipogenic Reprogramming Induced by a Small Molecule.

Brown adipose tissue (BAT) has attracted considerable research interest because of its therapeutic potential to treat obesity and associated metabolic diseases. Augmentation of brown fat mass and/or its function may represent an attractive strategy to enhance energy expenditure. Using high-throughput phenotypic screening to induce brown adipocyte reprogramming in committed myoblasts, we identified a retinoid X receptor (RXR) agonist, bexarotene (Bex), that efficiently converted myoblasts into brown adipocyte-like cells. Bex-treated mice exhibited enlarged BAT mass, enhanced BAT function, and a modest browning effect in subcutaneous white adipose tissue (WAT). Expression analysis showed that Bex initiated several "browning" pathways at an early stage during brown adipocyte reprogramming. Our findings suggest RXRs as new master regulators that control brown and beige fat development and activation, unlike the common adipogenic regulator PPARγ. Moreover, we demonstrated that selective RXR activation may potentially offer a therapeutic approach to manipulate brown/beige fat function in vivo.

Retinoic acid-pretreated Wharton's jelly mesenchymal stem cells in combination with triiodothyronine improve expression of neurotrophic factors in the subventricular zone of the rat ischemic brain injury.

Stroke is the consequence of limited blood flow to the brain with no established treatment to reduce the neurological deficits. Focusing on therapeutic protocols in targeting subventricular zone (SVZ) neurogenesis has been investigated recently. This study was designed to evaluate the effects of retinoic acid (RA)-pretreated Wharton's jelly mesenchymal stem cells (WJ-MSCs) in combination with triiodothyronine (T3) in the ischemia stroke model. Male Wistar rats were used to induce focal cerebral ischemia by middle cerebral artery occlusion (MCAO). There were seven groups of six animals: Sham, Ischemic, WJ-MSCs, RA-pretreated WJ-MSCs, T3, WJ-MSCs +T3, and RA-pretreated WJ-MSCs + T3. The treatment was performed at 24 h after ischemia, and animals were sacrificed one week later for assessments of retinoid X receptor ß (RXRß), brain-derived neurotrophic factor (BDNF), Sox2 and nestin in the SVZ. Pro-inflammatory cytokines in sera were measured at days four and seven after ischemia. RXRß, BDNF, Sox2 and nestin had the significant expressions in gene and protein levels in the treatment groups, compared with the ischemic group, which were more vivid in the RA-pretreated WJ-MSCs + T3 (p ≤ 0.05). The same trend was also resulted for the levels of TNF-α and IL-6 at four days after ischemia (p ≤ 0.05). In conclusion, application of RA-pretreated WJ-MSCs + T3 could be beneficial in exerting better neurotrophic function probably via modulation of pro-inflammatory cytokines.

Expression of retinoic acid-binding proteins and retinoic acid receptors in sebaceous cell carcinoma of the eyelids.

BACKGROUND: Sebaceous cell carcinoma of the eyelid is a malignant tumor. However, the pathoetiology of sebaceous cell carcinoma is not clear. Retinoic acid (RA) signaling is essential for skin epidermal differentiation including the eyelids. In this study, we investigate the expression of ß-catenin, RA-binding proteins and RA receptors in sebaceous cell carcinoma of the eyelid and try to estimate their influence on its pathoetiology. METHODS: Retrospective, noncomparative, consecutive interventional case series. Sixteen cases of eyelid sebaceous gland carcinoma who received tumor excision at our hospital between 2001 and 2011 were included. Immunohistochemical staining for ß-catenin, cellular retinoic acid binding protein 1 (CRABP1), cellular retinoic acid binding protein 2 (CRABP2), fatty acid-binding protein 5 (FABP5), retinoic acid receptors (RAR-α, -ß, -γ), and retinoid X receptors (RXR-α, -ß, -γ) was performed on tissue samples obtained from tumor excision. RESULTS: Of the 16 sebaceous cell carcinoma cases reviewed, six were male and 10 female. The mean follow-up period was 6.7 ± 3.66 years (range, 0.3-13 years). Of these 16 cases, the expression of ß-catenin was significantly increased in sebaceous cell carcinoma cases. CRABP1 was similarly expressed in the sebaceous cell carcinoma and control groups. CRABP2 and FABP5 were expressed in hair follicles of lid skin in both groups, whereas the CRABP2 and FABP5 were aberrantly expressed in the tumor cells of the sebaceous glands. Notably, the expression of retinoic acid receptor (RAR-ß) and retinoid X receptors (RXR-ß, -γ) was significantly upregulated in sebaceous cell carcinoma of the eyelids. CONCLUSIONS: Our findings indicate that retinoic acid signaling is related to the pathogenesis of sebaceous cell carcinoma of the eyelids.

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.

Abnormal retinoid and TrkB signaling in the prefrontal cortex in mood disorders.

The prefrontal cortex shows structural and functional alterations in mood disorders. Retinoid signaling, brain-derived neurotrophic factor (BDNF), and its receptor TrkB are reported to be involved in depression. Here, we found that mRNA levels of key elements of retinoid signaling were significantly reduced in the postmortem dorsolateral prefrontal cortex/anterior cingulate cortex (ACC) from elderly depressed patients who did not die from suicide. Decreased mRNA levels of BDNF and TrkB isoforms were also found. Similar alterations were observed in rats subjected to chronic unpredictable mild stress. Along with neurons immunopositive for both retinoic acid receptor-α (RARα) and TrkB, a positive correlation between mRNA levels of the 2 receptors was found in the ACC of control subjects but not of depressed patients. In vitro studies showed that RARα was able to bind to and transactivate the TrkB promoter via a putative RA response element within the TrkB promoter. In conclusion, the retinoid and BDNF-TrkB signaling in the prefrontal cortex are compromised in mood disorders, and the transcriptional upregulation of TrkB by RARα provide a possible mechanism for their interaction. The retinoid signaling pathway that may activate TrkB expression will be an alternative novel target for BDNF-based antidepressant treatment.

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.

Targeting of histone deacetylases to reactivate tumour suppressor genes and its therapeutic potential in a human cervical cancer xenograft model.

Aberrant histone acetylation plays an essential role in the neoplastic process via the epigenetic silencing of tumour suppressor genes (TSGs); therefore, the inhibition of histone deacetylases (HDAC) has become a promising target in cancer therapeutics. To investigate the correlation of histone acetylation with clinicopathological features and TSG expression, we examined the expression of acetylated H3 (AcH3), RARß2, E-cadherin, and ß-catenin by immunohistochemistry in 65 cervical squamous cell carcinoma patients. The results revealed that the absence of AcH3 was directly associated with poor histological differentiation and nodal metastasis as well as reduced/negative expression of RARß2, E-cadherin, and ß-catenin in clinical tumour samples. We further demonstrated that the clinically available HDAC inhibitors valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA), in combination with all-trans retinoic acid (ATRA), can overcome the epigenetic barriers to transcription of RARß2 in human cervical cancer cells. Chromatin immunoprecipitation analysis showed that the combination treatment increased the enrichment of acetylated histone in the RARß2-RARE promoter region. In view of these findings, we evaluated the antitumor effects induced by combined VPA and ATRA treatment in a xenograft model implanted with poorly differentiated human squamous cell carcinoma. Notably, VPA restored RARß2 expression via epigenetic modulation. Additive antitumour effects were produced in tumour xenografts by combining VPA with ATRA treatment. Mechanistically, the combination treatment reactivated the expression of TSGs RARß2, E-cadherin, P21 (CIP1) , and P53 and reduced the level of p-Stat3. Sequentially, upregulation of involucrin and loricrin, which indicate terminal differentiation, strongly contributed to tumour growth inhibition along with partial apoptosis. In conclusion, targeted therapy with HDAC inhibitors and RARß2 agonists may represent a novel therapeutic approach for patients with cervical squamous cell carcinoma.

Synergistic growth inhibition by acyclic retinoid and phosphatidylinositol 3-kinase inhibitor in human hepatoma cells.

BACKGROUND: A malfunction of RXRα due to phosphorylation is associated with liver carcinogenesis, and acyclic retinoid (ACR), which targets RXRα, can prevent the development of hepatocellular carcinoma (HCC). Activation of PI3K/Akt signaling plays a critical role in the proliferation and survival of HCC cells. The present study examined the possible combined effects of ACR and LY294002, a PI3K inhibitor, on the growth of human HCC cells. METHODS: This study examined the effects of the combination of ACR plus LY294002 on the growth of HLF human HCC cells. RESULTS: ACR and LY294002 preferentially inhibited the growth of HLF cells in comparison with Hc normal hepatocytes. The combination of 1 µM ACR and 5 µM LY294002, in which the concentrations used are less than the IC50 values of these agents, synergistically inhibited the growth of HLF, Hep3B, and Huh7 human HCC cells. These agents when administered in combination acted cooperatively to induce apoptosis in HLF cells. The phosphorylation of RXRα, Akt, and ERK proteins in HLF cells were markedly inhibited by treatment with ACR plus LY294002. Moreover, this combination also increased RXRE promoter activity and the cellular levels of RARß and p21(CIP1), while decreasing the levels of cyclin D1. CONCLUSION: ACR and LY294002 cooperatively increase the expression of RARß, while inhibiting the phosphorylation of RXRα, and that these effects are associated with the induction of apoptosis and the inhibition of cell growth in human HCC cells. This combination might therefore be effective for the chemoprevention and chemotherapy of HCC.

Retinoic X receptor subtypes exert differential effects on the regulation of Trh transcription.

How Retinoid X receptors (RXR) and thyroid hormone receptors (TR) interact on negative TREs and whether RXR subtype specificity is determinant in such regulations is unknown. In a set of functional studies, we analyzed RXR subtype effects in T3-dependent repression of hypothalamic thyrotropin-releasing hormone (Trh). Two-hybrid screening of a hypothalamic paraventricular nucleus cDNA bank revealed specific, T3-dependent interaction of TRs with RXRß. In vivo chromatin immuno-precipitation showed recruitment of RXRs to the TRE-site 4 region of the Trh promoter in the absence of T3. In vivo overexpression of RXRα in the mouse hypothalamus heightened T3-independent Trh transcription, whereas RXRß overexpression abrogated this activity. Loss of function of RXRα and ß by shRNAs induced inverse regulations. Thus, RXRα and RXRß display specific roles in modulating T3-dependent regulation of Trh. These results provide insight into the actions of these different TR heterodimerization partners within the context of a negatively regulated gene.

High-fructose diet downregulates long-chain acyl-CoA synthetase 3 expression in liver of hamsters via impairing LXR/RXR signaling pathway.

Long-chain acyl-CoA synthetases (ACSL) play key roles in fatty acid metabolism in liver and other metabolic tissues in an isozyme-specific manner. In this study, we examined the effects of a fructose-enriched diet on expressions of ACSL isoforms in the liver of hamsters. We showed that the fructose diet markedly reduced the mRNA and protein expressions of ACSL3 in hamster liver without significant effects on other ACSLs. The decrease in ACSL3 abundance was accompanied by a reduction in ACSL-catalyzed synthesis of arachidonyl-CoA and oleoyl-CoA in liver homogenates of hamsters fed the fructose diet as opposed to normal diet. We further showed that fructose diet specifically reduced expressions of three key components of the LXR signaling pathway, namely, liver X receptor (LXR)α, LXRß, and retinoid X receptor (RXR)ß. Exogenous expression and activation of LXRα/ß increased hamster ACSL3 promoter activities in a LXR-responsive element (LXRE)-dependent fashion. Finally, we showed that treating hamsters with LXR agonist GW3965 increased hepatic ACSL3 expression without affecting other ACSL isoforms. Furthermore, the ligand-induced increases of ACSL3 expression were accompanied with the reduction of hepatic triglyceride levels in GW3965-treated hamster liver. Altogether, our studies demonstrate that fructose diet has a negative impact on LXR signaling pathway in liver tissue and reduction of ACSL3 expression/activity could be a causal factor for fructose-induced hepatic steatosis.

Retinoic acid receptors move in time with the clock in the hippocampus. Effect of a vitamin-A-deficient diet.

An endogenous time-keeping mechanism controls circadian biological rhythms in mammals. Previously, we showed that vitamin A deficiency modifies clock BMAL1 and PER1 as well as BDNF and neurogranin daily rhythmicity in the rat hippocampus when animals are maintained under 12-h-light:12-h-dark conditions. Retinoic acid nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), have been detected in the same brain area. Our objectives were (a) to analyze whether RARα, RARß and RXRß exhibit a circadian variation in the rat hippocampus and (b) to investigate the effect of a vitamin-A-deficient diet on the circadian expression of BMAL1, PER1 and retinoic acid receptors (RARs and RXRß) genes. Holtzman male rats from control and vitamin-A-deficient groups were maintained under 12-h-light:12-h-dark or 12-h-dark:12-h-dark conditions during the last week of treatment. RARα, RARß, RXRß, BMAL1 and PER1 transcript and protein levels were determined in hippocampus samples isolated every 4 h in a 24-h period. Regulatory regions of RARs and RXRß genes were scanned for clock-responsive sites, while BMAL1 and PER1 promoters were analyzed for retinoic acid responsive elements and retinoid X responsive elements. E-box and retinoid-related orphan receptor responsive element sites were found on regulatory regions of retinoid receptors genes, which display an endogenously controlled circadian expression in the rat hippocampus. Those temporal profiles were modified when animals were fed with a vitamin-A-deficient diet. Similarly, the nutritional vitamin A deficiency phase shifted BMAL1 and abolished PER1 circadian expression at both mRNA and protein levels. Our data suggest that vitamin A deficiency may affect the circadian expression in the hippocampus by modifying the rhythmic profiles of retinoic acid receptors.

A new methodological sequence to expand and transdifferentiate human umbilical cord blood derived CD133+ cells into a cardiomyocyte-like phenotype.

Transplantation of antigenic-separated stem cells for human cardiovascular diseases such as myocardial infarction needs to be supported by experimental studies that allow refinement of the procedure. In this study we investigated optimising a protocol for the expansion and subsequent differentiation of human umbilical cord blood (HUCB) derived CD133(+) stem cells into a cardiomyocyte-like lineage. CD133(+) cells from HUCB were selected first by immunomagnetic separation and their purity was confirmed by flow cytometry analysis. For expansion and differentiation we developed a novel culture medium recipe that involves sequential signalling factors. Briefly, CD133(+) cells were expanded for 6 days under optimal serum-free conditions in combination with fibronectin and assessed by microscopy and AlamarBlue proliferation assay. Expanded CD133(+) cells were then plated in a cardiac differentiation promoting medium and cultured up to 4 weeks. With this protocol HUCB-CD133(+) cells can be regularly expanded in serum-free medium to obtain recovery and growth in vitro up to 6 folds. The addition of recombinant human thrombopoietin to the remaining factors of the expanding medium was associated with larger cell expansion. Expanded UCB CD133(+) cells showed a cardiomyocyte-like phenotype following differentiation in vitro through expressing intracellular cardiac specific markers including cardiac-specific α-actin, myosin heavy chain and troponin I. This change in phenotype was associated with the expression of cardiac-specific transcription factors Gata-4 and MEF2C. In addition, the change in phenotype was associated with an upregulation of nuclear receptor transcription factors including PPAR α, PPARγ, RXR α and RXRß. We believe our protocol represents a significant advancement and overcome the technical hurdle of deriving cardiomyogenic-like cells from HUCB CD133(+) stem cells. In addition, it has the required attributes of simplicity and consistency. This will permit more robust manipulation of these cells towards better engraftment and repair in patients with myocardial infarction.