Hepatic retinaldehyde deficiency is involved in diabetes deterioration by enhancing PCK1- and G6PC-mediated gluconeogenesis

Type 2 diabetes (T2D) is often accompanied with an induction of retinaldehyde dehydrogenase 1 (RALDH1 or ALDH1A1) expression and a consequent decrease in hepatic retinaldehyde (Rald) levels. However, the role of hepatic Rald deficiency in T2D progression remains unclear. In this study, we demonstrated that reversing T2D-mediated hepatic Rald deficiency by Rald or citral treatments, or liver-specific Raldh1 silencing substantially lowered fasting glycemia levels, inhibited hepatic glucogenesis, and downregulated phosphoenolpyruvate carboxykinase 1 (PCK1) and glucose-6-phosphatase (G6PC) expression in diabetic db/db mice. Fasting glycemia and Pck1/G6pc mRNA expression levels were strongly negatively correlated with hepatic Rald levels, indicating the involvement of hepatic Rald depletion in T2D deterioration. A similar result that liver-specific Raldh1 silencing improved glucose metabolism was also observed in high-fat diet-fed mice. In primary human hepatocytes and oleic acid-treated HepG2 cells, Rald or Rald + RALDH1 silencing resulted in decreased glucose production and downregulated PCK1/G6PC mRNA and protein expression. Mechanistically, Rald downregulated direct repeat 1-mediated PCK1 and G6PC expression by antagonizing retinoid X receptor α, as confirmed by luciferase reporter assays and molecular docking. These results highlight the link between hepatic Rald deficiency, glucose dyshomeostasis, and the progression of T2D, whilst also suggesting RALDH1 as a potential therapeutic target for T2D.

Retinoid X receptor agonist inhibits TGF-β1-induced collagen synthesis in cardiac fibroblasts by repressing Smad2 activation / 中国病理生理杂志

AIM:To investigate the effect of activation of retinoid X receptor (RXR) on transforming growth factor β1 (TGF-β1) induced collagen synthesis under hypoxic environment in rat cardiac fibroblasts (CFs) and underlying molecular mechanisms .METHODS: CFs were cultured using myocardial tissue with dry method .Hypoxic environment was established for CFs by continuous nitrogen supplement .Type I and type III collagens in supernatants were detected by ELISA.Nuclear and cytoplasmic extractions were prepared using NE-PER nuclear and cytoplasmic extraction reagents .The protein levels of Smad2 and p-Smad2 were determined by Western blot and immunocytochemical staining .RESULTS:Un-der hypoxic condition , TGF-β1 (0.01~10 μg/L) increased the synthesis of type I and type III collagens in a dose-de-pendent manner in the CFs .At the concentration of 5μg/L, the synthesis of collagen I and III was significantly increased as compared with control group (P<0.01).RXR agonist 9-cis-retinoic acid (9-cis-RA;10 -9 ~10 -6 mol/L) decreased TGF-β1 (5μg/L)-induced synthesis of type I and III collagens in a dose-dependent manner in the CFs under hypoxic con-dition.The synthesis of type I and type III collagens was significantly inhibited by 9-cis-RA (P<0.01).Smad2 inhibitor ( 20 nmol/L) showed similar inhibitory effect on the synthesis of type I and III collagens induced by TGF -β1 under hypoxic condition.Compared with TGF-β1 intervention group, the cytoplasmic level of p-Smad2 in the CFs was significantly in-creased in TGF-β1+9-cis-RA group, but the nuclear p-Smad2 level was significantly decreased (P<0.05).CONCLU-SION:Retinoid X receptor agonist 9-cis-RA inhibits TGF-β1-induced synthesis of type I and type III collagens in the CFs by repressing p-Smad2 nuclear translocation under hypoxic condition .

Retinoid X receptor signaling pathway in leukemia / 器官移植

Retinoid X receptor (RXR) acts as ligand-dependent transcription factors playing an important role in regulating a serial of physiological processes,such as embryo development and organ homeostasis.At the molecular level,RXRs exert their functions by inter-activating with multiple signal pathways to regulate target gene expression which control cell growth,differentiation,survival and death.The interference in the network of RXR and other signal pathways has turned RXR into an attractive drug target.

Protective role of retinoid X receptor in H9c2 cardiomyocytes from hypoxia/reoxygenation injury in rats / 世界急诊医学杂志（英文）

BACKGROUND:Retinoid X receptor (RXR) plays a central role in the regulation of intracellular receptor signaling pathways. The activation of RXR has protective effect on H2O2-induced apoptosis of H9c2 ventricular cells in rats. But the protective effect and mechanism of activating RXR in cardiomyocytes against hypoxia/reoxygenation (H/R)-induced oxidative iniury are stillunclear. METHODS:The model of H/R injury was established through hypoxia for 2 hours and reoxygenation for 4 hours in H9c2 cardiomyocytes of rats. 9-cis-retinoic acid (9-cis RA) was obtained as an RXR agonist, and HX531 as an RXR antagonist. Cultured cardiomyocytes were randomly divided into four groups:sham group, H/R group, H/R+9-cis RA -pretreated group (100 nmol/L 9-cis RA), and H/R+9-cis RA+HX531-pretreated group (2.5 μmol/L HX531). The cellviability was measured by MTT, apoptosis rate of cardiomyocytes by flow cytometry analysis, and mitochondrial membrane potential (ΔΨm) by JC-1 fluorescent probe, and protein expressions of Bcl-2, Bax and cleaved caspase-9 with Western blotting. Allmeasurement data were expressed as mean±standard deviation, and analyzed using one-way ANOVA and the Dunnett test. Differences were considered significant whenP was <0.05. RESULTS:Pretreatment with RXR agonist enhanced cellviability, reduced apoptosis ratio, and stabled ΔΨm. Dot blotting experiments showed that under H/R stress conditions, Bcl-2 protein level decreased, while Bax and cleaved caspase-9 were increased. 9-cis RA administration before H/R stress prevented these effects, but the protective effects of activating RXR on cardiomyocytes against H/R induced oxidative injury were abolished when pretreated with RXR pan-antagonist HX531. CONCLUSION:The activation of RXR has protective effects against H/R injury in H9c2 cardiomyocytes of rats through attenuating signaling pathway of mitochondria apoptosis.

Atorvastatin inhibits atherogenesis by RXRα-mediated depressing oxida-tive stress in STZ-induced diabetic ApoE-/-mice with fat-rich diet / 中国病理生理杂志

AIM:To explore the effects of atorvastatin (Atorv) on atherosclerosis in streptozotocin (STZ)-in-duced diabetic apolipoprotein E knockout ( ApoE-/-) mice with fat-rich diet and the possible mechanism .METHODS:C57 mice served as control.ApoE-/-mice (n=34) fed with high-fat diet were randomly divided into ApoE-/-group, STZ-ApoE-/-group and STZ-ApoE-/-+Atorv group.Intraperitoneal injection of streptozotocin was performed to create di-abetic animal model .Blood glucose was determined by glucose oxidase method .Blood lipid levels were detected by enzymic method or selective homogeneous method .The plaque area in the thoracic aorta was measured by HE staining .The protein level of nicotinamide-adenine dinucleotide phosphate ( NADPH) oxidase subunit gp91phox in the thoracic aorta was deter-mined by Western blotting .The levels of reactive oxygen species ( ROS) in blood and thoracic aorta homogenates were de-tected by Fenton reaction and Griess reagent .Human umbilical vein endothelial cells ( HUVECs ) were isolated from healthy umbilical cords by collagenase I and cultured .ROS production was detected by flow cytometry .NADPH oxidase ac-tivity was measured using lucigenin assay .Effects of retinoid X receptor α( RXRα) on inhibition of oxidative stress by ator-vastatin were evaluated by RNA interference and plasmid transfection .RESULTS: (1) Compared with C57 group, the plaque areas of the thoracic aorta in ApoE-/-group were increased .No difference of the fasting glucose between the 2 groups was observed.The levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), thoracic aorta gp91phox protein and ROS in blood and thoracic aorta homogenates were higher in ApoE-/-group than those in C57 group.(2) Compared with ApoE-/-group, the plaque areas of the thoracic aorta in STZ-ApoE-/-group were further enlarged [(314.13 ±35.72) μm2 vs (215.88 ±34.19) μm2, P<0.05].The levels of blood glucose, TG, TC and LDL-C, thoracic aorta gp91phox protein and ROS in blood and thoracic aorta homogenates were higher in STZ-ApoE-/-group than those in ApoE-/-group (P<0.05).(3) Compared with STZ-ApoE-/-group, the plaque areas of the thoracic aorta in STZ-ApoE-/-+Atorv group were reduced [(217.47 ±24.56) μm2 vs (314.13 ±35.72) μm2, P<0.05].The levels of blood glucose , LDL-C, TC, HDL-C and TG showed no significant difference between the 2 groups.Thoracic aorta gp91phox protein level and ROS production in blood and thoracic aorta homogenates were lower in STZ -ApoE-/-+Atorv group than those in STZ-ApoE-/-group (P<0.05).(4) High glucose-induced increases in NADPH oxidase activity and gp91phox expression were significantly inhibited by atorvastatin (10-6 mol/L) in HUVECs.The inhibitory effects of atorvasta-tin on high glucose-induced ROS production and NADPH oxidase activation were largely impaired when the cells were trans -fected with RXRαsiRNA.However , the effect of atorvastatin was significantly strengthened when RXRαwas over-expressed in the HUVECs transfected with RXRαplasmid.CONCLUSION: Atorvastatin inhibits atherogenesis by depressing high glucose-induced oxidative stress in diabetic ApoE-/-mice with fat-rich diet.The anti-oxidative stress effect of atorvastatin is mediated by RXRα.

Activating retinoid X receptor protected rat cardiomyocytes H9c2 from hypoxia/reoxygenation injury / 中华急诊医学杂志

Objective To determine the protective effects and potential mechanism of activating retinoid X receptor (RXR) on rat cardiomyocytes H9c2 against hypoxia/reoxygenation (H/R) induced oxidative injury.Methods The model of H-/R injury was established with hypoxia for 2 hours and reoxygenation for 4 hours in cardiomyocytes of H9c2,and 9-cis-retinoic acid (c-RA) was obtained as RXR agonist,and HX531 as RXR antagonist.Cultured cardiomyocytes were randomly (random number) divided into four groups:sham group,H/R group,H/R + c-RA-pretreated group (100 nmol/L c-RA) and H/R +c-RA + HX531-pretreated group (2.5 μmol/L HX531).We measured the cell viability by MTT (methyl thiazolyl tetrazolium),apoptosis rate of cardiomyocytes by using flow cytometry,and mitochondrial membrane potential by JC-1 fluorescent probe,protein levels of Bcl-2,Bax and cleaved Caspase-9 with Western blot.All measurement data were expressed as (-x ± s),and statistically analyzed using One-way ANOVA and Dunnett-t test.Differences were considered significant when P ＜ 0.05.Results Pretreatment with RXR agonist enhanced cell viability,reduced apoptosis ratio,stabilized mitochondrial membrane potential.Dot blotting experiments demonstrated that under H/R stress conditions,Bcl-2 protein level decreased,while Bax and cleaved Caspase-9 increased.The c-RA administration prior to H/R stress prevented these effects,however,overall protective effects of activating RXR on rat cardiomyocytes against H/R induced oxidative injury were abolished when pretreated with RXR pan-antagonist HX531.Conclusions Activating RXR has the protective effects against H/R injury in rat cardiomyocytes H9c2 through attenuation of mitochondria apoptosis signaling pathway.

Beta-amyloid affects retinoid receptor-α exporting into cytoplasm / 中华神经科杂志

Objective To investigate the effect of Alzheimer' s beta-amyloid (Aβ) on the production and the translocation in cytoplasm of retinoid receptor-α (RXRα). MethodsN2awt cells were treated with Aβ peptide or amyloid protein precursor(APP695) transfection. The nucleus were separated from the cytoplasm by kit. The quantity of RXRα in the nucleus and cytoplasm was detected by Westernblot. The translocation of RXRα in the nucleus and cytoplasm of above N2awt cells or of the cortex cells in the brains of Alzheimer' s disease (AD) patients and their normal control groups was observed by immune fluorescence. ResultsIn N2awt cells, the increasing APP or Aβ had no significant effect on the production of RXRα but resulted in RXRα exporting into cytoplasm, the ratio of RXRα in cytoplasm increased from 3.2％ (in control group) to 17.6％ (in APP+ group) and from 3.8％ (in control group) to 14.3％ (in Aβ + group) respectively; compared with normal cortex cells, the translocation of RXRα in the cytoplasm of the cortex cells in the brains of AD increased significantly. ConclusionAβ may affect RXRα exporting into cytoplasm.

Inhibitory Effect of RXRγ and RARβ on Growth of Human Gastric Carcinoma Cell Line SGC7901 Treated by 9-cis-RA / 天津医药

Objective:To investigate the inhibitory effect of RXRγ and RARβ on the growth of human gastric carcinoma cell line SGC7901 treated by RXR agonist(9-cis-RA). Methods:The human gastric carcinoma cell line SGC7901 was treated with 9-cis-RA, and then the morphological changes were observed by H-E staining. The cell growth was detected by MTT assay. The apoptosis and the cell cycle progression were analyzed by flow cytometry. The expressions of RXRγ and RARβ were detected by immunocytochemistry staining and western-blot assay. Results: HE stain showed that the SGC7901 cells were sparser with the increasing concentration of 9-cis-RA. The growth of SGC7901 cell was inhibited by 9-cis-RA at the concentration of 20 μmol/L in time and dose depended manner. The apoptotic rate of the tumor cells increased after 72 hours at the concentration of 20 μmol/L 9-cis-RA and the tumor cells were arrested in G0/G1 phase. Immunocytochemistry and Western-blot assay showed that the expressions of RXRγ and RARβ increased after 72 hours, compared with those of negative control group. Conclusion: RXR agonist 9-cis-RA can inhibit the growth of SGC7901 cells via inducing cell apoptosis through upgrading the expressions of RXRγ and RARβ.

The effect of activating retinoid X receptor inhibiting hydrogen peroxide-induced apoptosis in cultured rat neonatal cardiomyocytes / 中华急诊医学杂志

Objective To investigate the effect of 9-cis retinoid acid(c-RA),a retinoid X receptor(RXR)agonist,on hydrogen peroxide(H2O2)induced apoptosis in cultured rat neonatal cardiomyoeytes,and to explore the mechanism.Method Cultured cardiomyocpes were randomly divided into three groups:normal group treated with vehicle(N group),H2O2 group treated with 100 μmol/L H2O2(H group),and c-RA group pretreated with 100nmol/L c-RA(H+R group).Cell viability was detected by MTT.Morphological changes of apoptotic cardiomyocytes were observed by Hoechst 33258 staining under fluorescence microscope.The apoptotic rate was determined by flow cytometry.Mitochondrial membrane potential(△(ψ)m)was measured by JC-1 dye.Cellular reactive oxygen species(ROS)production was detected by CM-H2DCFDA fluorescent probe.All measurement data wIe expressed as(x±s),and statistically analyzed using one-way ANOVA analysis and Dunnett test.Differences were considered significant when P was＜0.05.Results Treatment with c-RA significantly enhanced cell viability,reduced apoptosis ratio,stabled mitoehondrial membrane potential and reduced level of cellular reactive oxygen species.Conclusions RXR agonist c-RA inhibits H2O2-induced myocyte apoptosis in cultured rat neonatal cardiomyocytes,which may be related to alleviate oxidative stress injury.

EFFECTS OF IGFBP-3/RXR? OR STAT-1 SIGNALING PATHWAY ON A?_(1-42) INDUCED APOPTOSIS IN RAT HIPPOCAMPUS NEURONS / 解剖学报

Objective To investigate the effects of IGFBP-3,RXR? and STAT-1 on A?_ 1-42 induced apoptosis in rat hippocampus neurons.Methods Apoptosis was induced by fibrillar A?_ 1-42.The percentage of neurons apoptosis was evaluated by microscopy after staining with TUNEL/DAPI.IGFBP-3 and RXR? positive neurons were observed by immunofluorescence.The expression of RXR? and STAT-1 protein were detected by Western blotting.Results After treatment with 20?mol/L A?_ 1-42 for 24 hours,the apoptotic hippocampus neurons were shown by TUNEL/DAPI assay.The percentage of apoptotic neurons was increased in a time-dependent manner.During the development of apoptosis,both the percentage of IGFBP-3/RXR? positive neurons and the expression of RXR? protein increased markedly after 3-6hours(P

Prevention of liver cancer: basic and clinical aspects

Cancer prevention is a challenging project both in the basic and clinical medicine. In particular, prevention of liver cancer is the most urgent task in countries where the incidence of hepatitis virus-related liver cancer is rising. As reviewed in this article, liver cancer is going to be the first cancer that will be actually prevented by primary and secondary interventions. Even the improvement of absolute survival of the patients can be expected by successful prevention, as already demonstrated in a few clinical trials. Thus, prevention of liver cancer is promising to provide not only cost-effectiveness by morbidity reduction but also cost-benefit by mortality improvement.

Expression and significance of PPAR? and RXR? in gastric carcinoma / 中华消化杂志

Objective To investigate the significance of expression of peroxisome proliferator activated receptor ?(PPAR?) and retinoid X receptor ?(RXR?) in chronic gastritis, gastric mucosal dysplasia and gastric carcinoma and to identify the correlation between PPAR? and RXR?. Methods Avidin biotin peroxidase complex immunohistochemical methods were adopted to examine the expression of PPAR? and RXR? in 53 patients with gastric carcinoma, and 18 with gastric mucosal dysplasia, 31 with chronic non atrophic gastritis and 30 with chronic atrophic gastritis were served as controls. Results The positive rates of PPAR? and RXR? were 41.5% and 54.7% in gastric carcinoma respectively, 27.8% and 38.9% in gastric mucosal dysplasia, 10.0% and 20.0% in chronic atrophic gastritis, 6.5% and 16.1% in chronic non atrophic gastritis. From chronic non atrophic gastritis, chronic atrophic gastritis to gastric carcinoma, expressions of PPAR? and RXR? showed an ascending tendency. Compared with those in chronic gastritis, expressions of PPAR? and RXR? in gastric mucosal dysplasia and gastric carcinoma were significantly enhanced ( P0.05). There was a significant correlation between expressions of PPAR? and RXR? in gastric carcinoma ( r =0.54). Conclusion PPAR? and RXR? protein overexpression is a relatively early event in gastric carcinogenesis, and it may play both an independent and synergetic role in progression of gastric carcionma.

Growth Regulation of Ovarian Cancer Cells through the Inactivation of AP-1 by Retinoid Derivatives / 대한암학회지

PURPOSE: The growth regulatory effect of retinoid derivatives could be mediated by the transcriptional inactivation of AP-1 oncogenic transcription factor. By using ovarian cancer cell lines we were to investigate the cross-regulation mechanism between retinoids and AP-1. MATERIALS AND METHODS: Cell proliferation assays were performed in 4 ovarian cancer cells (A2774, PA-1, OVCAR-3, SKOV-3) by increasing the concentrations of all-trans retinoic acid (ATRA), 9-cis retinoic acid (9RA), 13-cis RA (13RA), 4-hydroxyphenyl retinamide (4-HPR). Transient transfection and CAT ELISA were done to determine the selective activity of each retinoid on the RAR (alpha, beta, gamma), RXR (alpha, beta, gamma). and the negative activity on AP-1 (c-Jun). RESULTS: Antiproliferative effect of 4-HPR (IC50; 0.7~2.7 micrometer) was more potent than those of other retinoid derivatives (IC50; 2.7~9.0 micrometer). To assess the anticancer mechanism, we examined the effect of 4-HPR on the transriptional activity of retinoic acid receptors (RAR/RXR) and of c-jun. Contrary to other retinoid derivatives that are active for RAR and RXR with some different levels, 4-HPR showed weak activity only for RARgamma. However, 4-HPR exerted the strongest suppression on AP-1 (c-Jun) activity. CONCLUSION: Based on our results showing much 4-HPR's potent antiproliferative activity coupled with the most effectively inhibiting activity on AP-1 and minimum activity on RA receptor (selective for RARgamma) than other retinoid derivatives, we suggest that 4-HPR may be a novel, and very effective anticancer drugs for ovarian cancer.