The Experts below are selected from a list of 3084 Experts worldwide ranked by ideXlab platform
Anath Shalev - One of the best experts on this subject based on the ideXlab platform.
-
Lack of TXNIP protects beta-cells against glucotoxicity.
Biochemical Society transactions, 2020Co-Authors: Anath ShalevAbstract:Glucotoxicity plays a major role in pancreatic beta-cell apoptosis and diabetes progression, but the factors involved have remained largely unknown. Our recent studies have identified TXNIP (thioredoxin-interacting protein) as a novel pro-apoptotic beta-cell factor that is induced by glucose, suggesting that TXNIP may play a role in beta-cell glucotoxicity. Incubation of INS-1 beta-cells and isolated primary mouse and human islets at high glucose levels led to a significant increase in TXNIP as well as in apoptosis. Very similar results were obtained in vivo in islets of diabetic mice. To determine whether TXNIP plays a causative role in glucotoxic beta-cell death, we used TXNIP-deficient islets of HcB-19 mice harbouring a natural nonsense mutation in the TXNIP gene. We incubated islets of HcB-19 and C3H control mice at low and high glucose levels and assessed them for TXNIP expression and apoptosis. Interestingly, whereas in C3H islets, high glucose levels led again to significant elevation of TXNIP and apoptosis levels as measured by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) and cleaved caspase 3, no increase in apoptosis was observed in TXNIP-deficient HcB-19 islets, indicating that TXNIP is required for beta-cell death caused by glucotoxicity. Thus inhibition of TXNIP protects against glucotoxic beta-cell apoptosis and therefore may represent a novel therapeutic approach to halt diabetes progression.
-
Novel Small Molecule TXNIP Inhibitor Protects Against Diabetes
Diabetes, 2018Co-Authors: Lance Thielen, Junqin Chen, Guanlan Xu, Gu Jing, Truman Grayson, Seongho Jo, Anath ShalevAbstract:Loss of functional beta cell mass represents a major factor in the pathogenesis of diabetes. Currently, there are no therapies that halt this process; however, thioredoxin-interacting protein (TXNIP) has recently emerged as a promising therapeutic target. TXNIP was found to be the top glucose-induced gene in a human pancreatic islet microarray, is increased in diabetes, and TXNIP overexpression results in beta cell apoptosis. TXNIP reduction has shown favorable effects in vivo , where whole body TXNIP-deficient and beta cell-specific TXNIP knockout mice have decreased beta cell apoptosis, increased beta cell mass, elevated insulin levels, and are protected from diabetes. We have also shown that pharmacologic TXNIP inhibition, via the anti-hypertensive medication verapamil, was able to mimic the protective effects of genetic TXNIP deletion and reversed overt diabetes in mice. In addition, it has been established that TXNIP downregulation is beneficial in multiple tissues, making it unnecessary and even undesirable to have a beta cell-specific TXNIP inhibitor and suggesting that detrimental off target effects are unlikely. We have since undertaken a high-throughput screen of 300,000 small molecules that has yielded a novel compound, TI-37330, which is more effective than verapamil in inhibiting TXNIP expression. Moreover, TI-37330 protected primary human islets and INS-1 beta cells against glucose- and cytokine-induced TXNIP and beta cell apoptosis. TI-37330 has also shown in vivo potential as it was found to have good pharmacokinetic properties and was well tolerated in healthy mice. In the context of streptozotocin-induced diabetes, oral administration of TI-37330 promoted beta cell survival, prevented diabetes, and even significantly improved overt diabetes. Collectively, these data establish small molecule TXNIP inhibitors, especially TI-37330, as robust candidates for further development. Disclosure L. Thielen: None. J. Chen: None. G. Xu: None. G. Jing: None. T. Grayson: None. S. Jo: None. A. Shalev: None.
-
cytokines regulate β cell thioredoxin interacting protein TXNIP via distinct mechanisms and pathways
Journal of Biological Chemistry, 2016Co-Authors: Kyunghee Hong, Guanlan Xu, Truman Grayson, Anath ShalevAbstract:Abstract Thioredoxin-interacting protein (TXNIP) is a key regulator of diabetic β-cell apoptosis and dysfunction, and TXNIP inhibition prevents diabetes in mouse models of type 1 and type 2 diabetes. Although we have previously shown that TXNIP is strongly induced by glucose, any regulation by the proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interferon γ (IFNγ) has remained largely unexplored. Moreover, even though this three-cytokine mixture is widely used to mimic type 1 diabetes in vitro, the mechanisms involved are not fully understood. Interestingly, we have now found that this cytokine mixture increases β-cell TXNIP expression; however, although TNFα had no effect, IL-1β surprisingly down-regulated TXNIP transcription, whereas IFNγ increased TXNIP levels in INS-1 β-cells and primary islets. Human TXNIP promoter analyses and chromatin immunoprecipitation studies revealed that the IL-1β effect was mediated by inhibition of carbohydrate response element binding protein activity. In contrast, IFNγ increased pro-apoptotic TXNIP post-transcriptionally via induction of endoplasmic reticulum stress, activation of inositol-requiring enzyme 1α (IRE1α), and suppression of miR-17, a microRNA that targets and down-regulates TXNIP. In fact, miR-17 knockdown was able to mimic the IFNγ effects on TXNIP, whereas miR-17 overexpression blunted the cytokine effect. Thus, our results demonstrate for the first time that the proinflammatory cytokines TNFα, IL-1β, and IFNγ each have distinct and in part opposing effects on β-cell TXNIP expression. These findings thereby provide new mechanistic insight into the regulation of TXNIP and β-cell biology and reveal novel links between proinflammatory cytokines, carbohydrate response element binding protein-mediated transcription, and microRNA signaling.
-
foxo1 competes with carbohydrate response element binding protein chrebp and inhibits thioredoxin interacting protein TXNIP transcription in pancreatic beta cells
Journal of Biological Chemistry, 2013Co-Authors: Carly R Kibbe, Junqin Chen, Guanlan Xu, Gu Jing, Anath ShalevAbstract:Abstract Thioredoxin-interacting protein (TXNIP) has emerged as an important factor in pancreatic beta cell biology, and tight regulation of TXNIP levels is necessary for beta cell survival. However, the mechanisms regulating TXNIP expression have only started to be elucidated. The forkhead boxO1 transcription factor (FOXO1) has been reported to up-regulate TXNIP expression in neurons and endothelial cells but to down-regulate TXNIP in liver, and the effects on beta cells have remained unknown. We now have found that FOXO1 binds to the TXNIP promoter in vivo in human islets and INS-1 beta cells and significantly decreases TXNIP expression. TXNIP promoter deletion analyses revealed that an E-box motif conferring carbohydrate response element-binding protein (ChREBP)-mediated, glucose-induced TXNIP expression is necessary and sufficient for this effect, and electromobility shift assays confirmed FOXO1 binding to this site. Moreover, FOXO1 blocked glucose-induced TXNIP expression and reduced glucose-induced ChREBP binding at the TXNIP promoter without affecting ChREBP expression or nuclear localization, suggesting that FOXO1 may compete with ChREBP for binding to the TXNIP promoter. In fact, a FOXO1 DNA-binding mutant (FOXO1-H215R) failed to inhibit TXNIP transcription, and the effects were not restricted to TXNIP as FOXO1 also inhibited transcription of other ChREBP target genes such as liver pyruvate kinase. Together, these results demonstrate that FOXO1 inhibits beta cell TXNIP transcription and suggest that FOXO1 confers this inhibition by interfering with ChREBP DNA binding at target gene promoters. Our findings thereby reveal a novel gene regulatory mechanism and a previously unappreciated cross-talk between FOXO1 and ChREBP, two major metabolic signaling pathways.
-
lack of TXNIP protects against mitochondria mediated apoptosis but not against fatty acid induced er stress mediated β cell death
Diabetes, 2010Co-Authors: Junqin Chen, Ghislaine Fontes, Geetu Saxena, Vincent Poitout, Anath ShalevAbstract:OBJECTIVE We have previously shown that lack of thioredoxin-interacting protein (TXNIP) protects against diabetes and glucotoxicity-induced β-cell apoptosis. Because the role of TXNIP in lipotoxicity is unknown, the goal of the present study was to determine whether TXNIP expression is regulated by fatty acids and whether TXNIP deficiency also protects β-cells against lipoapoptosis. RESARCH DESIGN AND METHODS To determine the effects of fatty acids on β-cell TXNIP expression, INS-1 cells and isolated islets were incubated with/without palmitate and rats underwent cyclic infusions of glucose and/or Intralipid prior to islet isolation and analysis by quantitative real-time RT-PCR and immunoblotting. Using primary wild-type and TXNIP-deficient islets, we then assessed the effects of palmitate on apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL]), mitochondrial death pathway (cytochrome c release), and endoplasmic reticulum (ER) stress (binding protein [BiP], C/EBP homologous protein [CHOP]). Effects of TXNIP deficiency were also tested in the context of staurosporine (mitochondrial damage) or thapsigargin (ER stress). RESULTS Glucose elicited a dramatic increase in islet TXNIP expression both in vitro and in vivo, whereas fatty acids had no such effect and, when combined with glucose, even abolished the glucose effect. We also found that TXNIP deficiency does not effectively protect against palmitate or thapsigargin-induced β-cell apoptosis, but specifically prevents staurosporine- or glucose-induced toxicity. CONCLUSIONS Our results demonstrate that unlike glucose, fatty acids do not induce β-cell expression of proapoptotic TXNIP. They further reveal that TXNIP deficiency specifically inhibits the mitochondrial death pathway underlying β-cell glucotoxicity, whereas it has very few protective effects against ER stress–mediated lipoapoptosis.
Faxing Yu - One of the best experts on this subject based on the ideXlab platform.
-
a potential mechanism of metformin mediated regulation of glucose homeostasis inhibition of thioredoxin interacting protein TXNIP gene expression
Cellular Signalling, 2012Co-Authors: Tin Fan Chai, Thilo Hagen, Hongpeng He, Shin Yee Hong, Liling Zheng, Faxing YuAbstract:Abstract Metformin (dimethylbiguanide) is widely used among diabetic patients to lower the blood sugar level. Although several mechanisms have been proposed, its mode of action in enhancing peripheral glucose uptake and inhibiting hepatic glucose production is not fully understood. Thioredoxin-interacting protein (TXNIP) is known to play important roles in glucose metabolism by inhibiting cellular glucose uptake and metabolism and promoting hepatic gluconeogenesis. The expression of the gene encoding TXNIP is regulated in a glucose dependent manner via the Mondo:MLX transcription factor complex. In the present study, we report that TXNIP mRNA as well as protein expression in cultured cells is markedly reduced upon metformin administration. The binding of Mondo:MLX to the TXNIP gene promoter is reduced, suggesting that the transcription of the TXNIP gene is repressed by metformin. Moreover, we show that the effect of metformin on TXNIP gene transcription is due to the inhibition of mitochondrial complex I and increased glycolysis, and is partially mediated by the AMP activated kinase (AMPK). These observations prompt us to propose that the novel action of metformin on the TXNIP gene expression may contribute to its therapeutic effects in the treatment of type II diabetes.
-
thioredoxin interacting protein TXNIP gene expression sensing oxidative phosphorylation status and glycolytic rate
Journal of Biological Chemistry, 2010Co-Authors: Faxing Yu, Tin Fan Chai, Hongpeng He, Thilo HagenAbstract:Abstract Thioredoxin-interacting protein (TXNIP) has important functions in regulating cellular metabolism including glucose utilization; the expression of the TXNIP gene is sensitive to the availability of glucose and other fuels. Here, we show that TXNIP expression is down-regulated at the transcriptional level by diverse inhibitors of mitochondrial oxidative phosphorylation (OXPHOS). The effect of these OXPHOS inhibitors is mediated by earlier identified carbohydrate-response elements (ChoREs) on the TXNIP promoter and the ChoRE-associated transcription factors Max-like protein X (MLX) and MondoA (or carbohydrate-response element-binding protein (ChREBP)) involved in glucose-induced TXNIP expression, suggesting that inhibited oxidative phosphorylation compromises glucose-induced effects on TXNIP expression. We also show that the OXPHOS inhibitors repress the TXNIP transcription most likely by inducing the glycolytic rate, and increased glycolytic flux decreases the levels of glycolytic intermediates important for the function of MLX and MondoA (or ChREBP). Our findings suggest that the TXNIP expression is tightly correlated with glycolytic flux, which is regulated by oxidative phosphorylation status. The identified link between the TXNIP expression and glycolytic activity implies a mechanism by which the cellular glucose uptake/homeostasis is regulated in response to various metabolic cues, oxidative phosphorylation status, and other physiological signals, and this may facilitate our efforts toward understanding metabolism in normal or cancer cells.
-
Abstract B100: The expression of thioredoxin‐interacting protein (TXNIP): Modulators, mechanisms and functions
Molecular Cancer Therapeutics, 2009Co-Authors: Faxing YuAbstract:Thioredoxin interacting protein (TXNIP) is a multifunctional protein involved in regulation of cell cycle events and cellular metabolism; the expression of the TXNIP gene is down‐regulated in a large range of cancer cells and up‐regulated in diabetic and pre‐diabetic patients. Therefore, TXNIP might be a link between metabolism and cancer development, and the study of regulatory mechanism(s) that governs TXNIP expression has important clinical relevance. The expression of TXNIP is induced by glucose, which is mediated by an earlier defined carbohydrate response element (ChoRE) on TXNIP promoter and its associated transcription factors, MondoA (or its homolog, ChREBP) and Max‐like protein X (MLX). Here, we show that the transcription of the TXNIP gene is induced by an array of adenosine‐containing molecules, of which an intact adenosine moiety is necessary and sufficient. When cells are treated with adenosine‐containing molecules, the glucose uptake is inhibited and cell cycle progression is retarded, probably attributed to enhanced TXNIP expression. The induction of TXNIP expression by adenosine‐containing molecules is in a glucose‐dependent manner, and MondoA and MLX are known to convey stimulatory signals from extracellular molecules to the TXNIP promoter. Therefore, the regulatory role of adenosine‐containing molecules is exerted via amplifying glucose signaling, hence suggesting that these molecules may modulate the kinetics of glucose homeostasis. To gain more knowledge about the regulation of TXNIP expression, we have also studied the underlying regulatory mechanisms of glucose and adenosine‐containing molecules on TXNIP expression in details. An additional ChoRE on the promoter of TXNIP gene has been identified, and this ChoRE is able to recruit MondoA and MLX in a similar fashion as the previously identified ChoRE in vitro and in vivo. Both ChoREs function cooperatively to mediate optimal TXNIP expression under glucose or adenosine‐containing molecules treatment. However, these two ChoREs are not sufficient to mediate the induction of TXNIP expression by glucose or adenosine‐containing molecules, and two CCAAT boxes, both can recruit nuclear factor Y (NF‐Y) to the TXNIP promoter, are also required for the induction. We also found that the function of ChoREs and associated factors is contingent on tandem CCAAT boxes, in that the occupancy of the TXNIP promoter by the CCAAT box‐associated NF‐Y is a prerequisite for efficacious recruitment of MondoA/MLX to ChoREs under glucose stimulation. Such a strategy suggests a synergy between NF‐Y and MondoA/MLX in enhancing TXNIP expression, which leads us to propose a model for the glucose‐dependent TXNIP expression mediated by dynamic chromatin changes in response to diverse physiological inducers. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B100.
-
adenosine containing molecules amplify glucose signaling and enhance TXNIP expression
Molecular Endocrinology, 2009Co-Authors: Faxing YuAbstract:Eukaryotic cells sense extracellular glucose concentrations via diverse mechanisms to regulate the expression of genes involved in metabolic control. One such example is the tight correlation between the expression of thioredoxin-interacting protein (TXNIP) and extracellular glucose levels. In this report, we show that the transcription of the TXNIP gene is induced by adenosine-containing molecules, of which an intact adenosine moiety is necessary and sufficient. TXNIP promoter contains a carbohydrate response element, which mediates the induction of TXNIP expression by these molecules in a glucose-dependent manner. Max-like protein X and MondoA are transcription factors previously shown to stimulate glucose-dependent TXNIP expression and are shown here to convey stimulatory signals from extracellular adenosine-containing molecules to the TXNIP promoter. The regulatory role of these molecules may be exerted via amplifying glucose signaling. Hence, this revelation may pave the way for interventions aimed t...
Thilo Hagen - One of the best experts on this subject based on the ideXlab platform.
-
2 deoxyglucose induces the expression of thioredoxin interacting protein TXNIP by increasing o glcnacylation implications for targeting the warburg effect in cancer cells
Biochemical and Biophysical Research Communications, 2015Co-Authors: Shin Yee Hong, Thilo HagenAbstract:The high proliferation rate of cancer cells and the microenvironment in the tumor tissue require the reprogramming of tumor cell metabolism. The major mechanism of metabolic reprogramming in cancer cells is the Warburg effect, defined as the preferential utilization of glucose via glycolysis even in the presence of oxygen. Targeting the Warburg effect is considered as a promising therapeutic strategy in cancer therapy. In this regard, the glycolytic inhibitor 2-deoxyglucose (2DG) has been evaluated clinically. 2DG exerts its effect by directly inhibiting glycolysis at the level of hexokinase and phosphoglucoisomerase. In addition, 2DG is also known to induce the expression of thioredoxin interacting protein (TXNIP), a tumor suppressor protein and an important negative regulator of cellular glucose uptake. Hence, characterization of the mechanism through which 2DG regulates TXNIP expression may reveal novel approaches to target the Warburg effect in cancer cells. Therefore, in this study we sought to test various hypotheses for the mechanistic basis of the 2DG dependent TXNIP regulation. We have shown that 2DG induced TXNIP expression is independent of carbohydrate response element mediated transcription. Furthermore, the induction of TXNIP is neither dependent on the ability of 2DG to deplete cellular ATP nor to cause endoplasmic reticulum stress. We found that the 2DG induced TXNIP expression is at least in part dependent on the inhibition of the O-GlcNAcase enzyme and the accumulation of O-GlcNAc modified proteins. These results have implications for the identification of therapeutic targets to increase TXNIP expression in cancer.
-
Mechanistic target of rapamycin (mTOR) dependent regulation of thioredoxin interacting protein (TXNIP) transcription in hypoxia
Biochemical and Biophysical Research Communications, 2013Co-Authors: Regina Wan Ju Wong, Thilo HagenAbstract:Abstract Thioredoxin interacting protein (TXNIP), first identified as an inhibitor of thioredoxin, is also a tumor suppressor as well as an inhibitor of lipogenesis. TXNIP is known to be transcriptionally regulated in response to nutrients such as glucose and stress signals, including endoplasmic reticulum stress and lactic acidosis. In this study, we characterized the transcriptional regulation of TXNIP in response to hypoxia. Using a hepatocellular carcinoma cell line, we have found that TXNIP mRNA expression is regulated in a biphasic manner in hypoxia whereby TXNIP expression showed an initial rapid decrease, followed by an increase under prolonged hypoxia. Interestingly, we have shown that TXNIP induction in prolonged hypoxia is independent of the Hypoxia-Inducible Factor (HIF) transcription factor. The effect of hypoxia on TXNIP expression is mediated via the inhibition of the 4E-BP1/eIF4E axis of mechanistic target of rapamycin (mTORC1). Thus, we found that inhibiting mTORC1-dependent 4E-BP1 phosphorylation mimics the effect of hypoxia on TXNIP expression. Furthermore, overexpressing eIF4E prevents the induction of TXNIP in hypoxia. Our results suggest that mTORC1 may be an important regulator of hypoxia-dependent gene expression.
-
a potential mechanism of metformin mediated regulation of glucose homeostasis inhibition of thioredoxin interacting protein TXNIP gene expression
Cellular Signalling, 2012Co-Authors: Tin Fan Chai, Thilo Hagen, Hongpeng He, Shin Yee Hong, Liling Zheng, Faxing YuAbstract:Abstract Metformin (dimethylbiguanide) is widely used among diabetic patients to lower the blood sugar level. Although several mechanisms have been proposed, its mode of action in enhancing peripheral glucose uptake and inhibiting hepatic glucose production is not fully understood. Thioredoxin-interacting protein (TXNIP) is known to play important roles in glucose metabolism by inhibiting cellular glucose uptake and metabolism and promoting hepatic gluconeogenesis. The expression of the gene encoding TXNIP is regulated in a glucose dependent manner via the Mondo:MLX transcription factor complex. In the present study, we report that TXNIP mRNA as well as protein expression in cultured cells is markedly reduced upon metformin administration. The binding of Mondo:MLX to the TXNIP gene promoter is reduced, suggesting that the transcription of the TXNIP gene is repressed by metformin. Moreover, we show that the effect of metformin on TXNIP gene transcription is due to the inhibition of mitochondrial complex I and increased glycolysis, and is partially mediated by the AMP activated kinase (AMPK). These observations prompt us to propose that the novel action of metformin on the TXNIP gene expression may contribute to its therapeutic effects in the treatment of type II diabetes.
-
thioredoxin interacting protein TXNIP gene expression sensing oxidative phosphorylation status and glycolytic rate
Journal of Biological Chemistry, 2010Co-Authors: Faxing Yu, Tin Fan Chai, Hongpeng He, Thilo HagenAbstract:Abstract Thioredoxin-interacting protein (TXNIP) has important functions in regulating cellular metabolism including glucose utilization; the expression of the TXNIP gene is sensitive to the availability of glucose and other fuels. Here, we show that TXNIP expression is down-regulated at the transcriptional level by diverse inhibitors of mitochondrial oxidative phosphorylation (OXPHOS). The effect of these OXPHOS inhibitors is mediated by earlier identified carbohydrate-response elements (ChoREs) on the TXNIP promoter and the ChoRE-associated transcription factors Max-like protein X (MLX) and MondoA (or carbohydrate-response element-binding protein (ChREBP)) involved in glucose-induced TXNIP expression, suggesting that inhibited oxidative phosphorylation compromises glucose-induced effects on TXNIP expression. We also show that the OXPHOS inhibitors repress the TXNIP transcription most likely by inducing the glycolytic rate, and increased glycolytic flux decreases the levels of glycolytic intermediates important for the function of MLX and MondoA (or ChREBP). Our findings suggest that the TXNIP expression is tightly correlated with glycolytic flux, which is regulated by oxidative phosphorylation status. The identified link between the TXNIP expression and glycolytic activity implies a mechanism by which the cellular glucose uptake/homeostasis is regulated in response to various metabolic cues, oxidative phosphorylation status, and other physiological signals, and this may facilitate our efforts toward understanding metabolism in normal or cancer cells.
Lalit P Singh - One of the best experts on this subject based on the ideXlab platform.
-
TXNIP regulates mitophagy in retinal muller cells under high glucose conditions implications for diabetic retinopathy
Cell Death and Disease, 2017Co-Authors: Takhellambam S Devi, Mallika Somayajulu, Renu A Kowluru, Lalit P SinghAbstract:Thioredoxin-interacting protein (TXNIP) is involved in oxidative stress and apoptosis in diabetic retinopathy. However, the role of TXNIP in the removal of damaged mitochondria (MT) via mitophagy, a process of macroautophagy, remains unexplored. Here we investigate the associated cellular and molecular mechanisms underlying mitophagy in retinal cells under diabetic conditions. For this, we maintained a rat Muller cell line (rMC1) under high-glucose (25 mM, HG) or low-glucose (5.5 mM, LG) condition for 5 days. Our data reveal that HG upregulates TXNIP in the cytosol as well as in the MT. Moreover, mitochondrial oxidative stress and membrane depolarization occur under prolonged hyperglycemia leading to fragmentation. These damaged MT are targeted to lysosome for mitophagic degradation, as is evident by co-localization of mitochondrial protein COXIV, a subunit of cytochrome c oxidase, with autophagosome marker LC3BII and the lysosomal membrane protein LAMP2A. In addition, under HG conditions, there is an accumulation of dynamin-related fission protein Drp1 and E3 ubiquitin ligase Parkin in damaged MT, suggesting their roles in mitochondrial fragmentation and ubiquitination, respectively, which is absent in LG conditions. Subsequently, ubiquitin receptors, optineurin and p62/sequestrome 1, bind to the damaged MT and target them to LC3BII autophagosomes. Conversely, TXNIP knockout via CRISPR/Cas9 and TXNIP gRNA prevents the HG-induced mitochondrial damage and mitophagy in rMC1. Last, TXNIP level is also significantly upregulated in the diabetic rat retina in vivo and induces radial glial fibrillary acidic protein expression, a marker for Muller glia activation, and the formation of LC3BII puncta, which are prevented by intravitreal injection of TXNIP siRNA. Therefore, TXNIP represents a potential target for preventing ocular complications of diabetes.
-
critical role of TXNIP in oxidative stress dna damage and retinal pericyte apoptosis under high glucose implications for diabetic retinopathy
Experimental Cell Research, 2013Co-Authors: Takhellambam S Devi, Kenichi Hosoya, Tetsuya Terasaki, Lalit P SinghAbstract:Abstract Diabetic retinopathy (DR) is characterized by early loss of retinal capillary pericytes and microvascular dysfunction. We recently showed that pro-oxidative stress and pro-apoptotic thioredoxin interacting protein (TXNIP) is significantly up-regulated in rat retinas in experimental diabetes and mediates inflammation and apoptosis. Therefore, we hypothesize here that TXNIP up-regulation in pericyte plays a causative role in oxidative stress and apoptosis under sustained high glucose exposure in culture. We maintained a rat retinal capillary pericyte cell line (TR-rPCT1) for 5 days under low glucose (LG, 5.5 mM) or high glucose (HG, 25 mM) with or without anti-oxidant N-acetylcysteine (5 mM, NAC), Azaseine (2 μM, AzaS), an inhibitor of TXNIP, and TXNIP siRNA (siTXNIP3, 20 nM). The results show that HG increases TXNIP expression in TR-rPCT1, which correlates positively with ROS generation, protein S-nitrosylation, and pro-apoptotic caspase-3 activation. Furthermore, pericyte apoptosis is demonstrated by DNA fragmentation (alkaline comet assay) and a reduction in MTT survival assay. Treatment of TR-rPCT1 with NAC or an inhibition of TXNIP by AzaS or siTXNIP3 each reduces HG-induced ROS, caspase-3 activation and DNA damage demonstrating that TXNIP up-regulation under chronic hyperglycemia is critically involved in cellular oxidative stress, DNA damage and retinal pericyte apoptosis. Thus, TXNIP represents a novel gene and drug target to prevent pericyte loss and progression of DR.
-
TXNIP links innate host defense mechanisms to oxidative stress and inflammation in retinal muller glia under chronic hyperglycemia implications for diabetic retinopathy
Experimental Diabetes Research, 2012Co-Authors: Takhellambam S Devi, Maik Huttemann, Ashok Kumar, Kwaku D Nantwi, Lalit P SinghAbstract:Thioredoxin Interacting Protein (TXNIP) mediates retinal inflammation, gliosis, and apoptosis in experimental diabetes. Here, we investigate the temporal response of Muller glia to high glucose (HG) and TXNIP expression using a rat Muller cell line (rMC1) in culture. We examined if HG-induced TXNIP expression evokes host defense mechanisms in rMC1 in response to metabolic abnormalities. HG causes sustained up-regulation of TXNIP (2 h to 5 days), ROS generation, ATP depletion, ER stress, and inflammation. Various cellular defense mechanisms are activated by HG: (i) NLRP3 inflammasome, (ii) ER stress response (sXBP1), (iii) hypoxic-like HIF-1α induction, (iv) autophagy/mitophagy, and (v) apoptosis. We also found in vivo that streptozocin-induced diabetic rats have higher retinal TXNIP and innate immune response gene expression than normal rats. Knock down of TXNIP by intravitreal siRNA reduces inflammation (IL-1β) and gliosis (GFAP) in the diabetic retina. TXNIP ablation in vitro prevents ROS generation, restores ATP level and autophagic LC3B induction in rMC1. Thus, our results show that HG sustains TXNIP up-regulation in Muller glia and evokes a program of cellular defense/survival mechanisms that ultimately lead to oxidative stress, ER stress/inflammation, autophagy and apoptosis. TXNIP is a potential target to ameliorate blinding ocular complications of diabetic retinopathy.
-
inhibition of TXNIP expression in vivo blocks early pathologies of diabetic retinopathy
Cell Death and Disease, 2010Co-Authors: Lorena Perrone, Takhellambam S Devi, Kenichi Hosoya, Tetsuya Terasaki, Lalit P SinghAbstract:Evidence is mounting that proinflammatory and proapoptotic thioredoxin-interacting protein (TXNIP) has a causative role in the development of diabetes. However, there are no studies investigating the role of TXNIP in diabetic retinopathy (DR). Here, we show that, in diabetic rats, TXNIP expression and hexosamine biosynthesis pathway (HBP) flux, which regulates TXNIP, are elevated in the retina and correlates well with the induction of inflammatory cyclooxygenase 2 (Cox-2) and sclerotic fibronectin (FN). We blocked the expression of TXNIP in diabetic rat retinas by: (i) inhibiting HBP flux; (ii) inducing post-transcriptional gene silencing (PTGS) for TXNIP mRNA; and (iii) performing an in vivo transcriptional gene silencing (TGS) approach for TXNIP knockdown by promoter-targeted small interfering RNAs and cell-penetrating peptides as RNA interference (RNAi) transducers. Each of these methods is efficient in downregulating TXNIP expression, resulting in blockade of its target genes, Cox-2 and FN, demonstrating that TXNIP has a causative role in aberrant gene induction in early DR. RNAi TGS of TXNIP abolishes diabetes-induced retinal gliosis and ganglion injury. Thus, TXNIP has a critical role in inflammation and retinal injury in early stages of DR. The successful employment of TXNIP TGS and amelioration of its pathological effects open the way for novel therapeutic strategies aimed to block disease onset and progression of DR.
-
thioredoxin interacting protein TXNIP induces inflammation through chromatin modification in retinal capillary endothelial cells under diabetic conditions
Journal of Cellular Physiology, 2009Co-Authors: Lorena Perrone, Takhellambam S Devi, Kenichi Hosoya, Tetsuya Terasaki, Lalit P SinghAbstract:Chronic hyperglycemia and activation of receptor for advanced glycation end products (RAGE) are known risk factors for microvascular disease development in diabetic retinopathy. Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of antioxidant thioredoxin (TRX), plays a causative role in diabetes and its vascular complications. Herein we investigate whether HG and RAGE induce inflammation in rat retinal endothelial cells (EC) under diabetic conditions in culture through TXNIP activation and whether epigenetic mechanisms play a role in inflammatory gene expression. We show that RAGE activation by its ligand S100B or HG treatment of retinal EC induces the expression of TXNIP and inflammatory genes such as Cox2, VEGF-A, and ICAM1. TXNIP silencing by siRNA impedes RAGE and HG effects while stable over-expression of a cDNA for human TXNIP in EC elevates inflammation. p38 MAPK-NF-κB signaling pathway and histone H3 lysine (K) nine modifications are involved in TXNIP-induced inflammation. Chromatin immunoprecipitation (ChIP) assays reveal that TXNIP over-expression in EC abolishes H3K9 tri-methylation, a marker for gene inactivation, and increases H3K9 acetylation, an indicator of gene induction, at proximal Cox2 promoter bearing the NF-κB-binding site. These findings have important implications toward understanding the molecular mechanisms of ocular inflammation and endothelial dysfunction in diabetic retinopathy. J. Cell. Physiol. 221: 262–272, 2009. © 2009 Wiley-Liss, Inc
Junqin Chen - One of the best experts on this subject based on the ideXlab platform.
-
Novel Small Molecule TXNIP Inhibitor Protects Against Diabetes
Diabetes, 2018Co-Authors: Lance Thielen, Junqin Chen, Guanlan Xu, Gu Jing, Truman Grayson, Seongho Jo, Anath ShalevAbstract:Loss of functional beta cell mass represents a major factor in the pathogenesis of diabetes. Currently, there are no therapies that halt this process; however, thioredoxin-interacting protein (TXNIP) has recently emerged as a promising therapeutic target. TXNIP was found to be the top glucose-induced gene in a human pancreatic islet microarray, is increased in diabetes, and TXNIP overexpression results in beta cell apoptosis. TXNIP reduction has shown favorable effects in vivo , where whole body TXNIP-deficient and beta cell-specific TXNIP knockout mice have decreased beta cell apoptosis, increased beta cell mass, elevated insulin levels, and are protected from diabetes. We have also shown that pharmacologic TXNIP inhibition, via the anti-hypertensive medication verapamil, was able to mimic the protective effects of genetic TXNIP deletion and reversed overt diabetes in mice. In addition, it has been established that TXNIP downregulation is beneficial in multiple tissues, making it unnecessary and even undesirable to have a beta cell-specific TXNIP inhibitor and suggesting that detrimental off target effects are unlikely. We have since undertaken a high-throughput screen of 300,000 small molecules that has yielded a novel compound, TI-37330, which is more effective than verapamil in inhibiting TXNIP expression. Moreover, TI-37330 protected primary human islets and INS-1 beta cells against glucose- and cytokine-induced TXNIP and beta cell apoptosis. TI-37330 has also shown in vivo potential as it was found to have good pharmacokinetic properties and was well tolerated in healthy mice. In the context of streptozotocin-induced diabetes, oral administration of TI-37330 promoted beta cell survival, prevented diabetes, and even significantly improved overt diabetes. Collectively, these data establish small molecule TXNIP inhibitors, especially TI-37330, as robust candidates for further development. Disclosure L. Thielen: None. J. Chen: None. G. Xu: None. G. Jing: None. T. Grayson: None. S. Jo: None. A. Shalev: None.
-
foxo1 competes with carbohydrate response element binding protein chrebp and inhibits thioredoxin interacting protein TXNIP transcription in pancreatic beta cells
Journal of Biological Chemistry, 2013Co-Authors: Carly R Kibbe, Junqin Chen, Guanlan Xu, Gu Jing, Anath ShalevAbstract:Abstract Thioredoxin-interacting protein (TXNIP) has emerged as an important factor in pancreatic beta cell biology, and tight regulation of TXNIP levels is necessary for beta cell survival. However, the mechanisms regulating TXNIP expression have only started to be elucidated. The forkhead boxO1 transcription factor (FOXO1) has been reported to up-regulate TXNIP expression in neurons and endothelial cells but to down-regulate TXNIP in liver, and the effects on beta cells have remained unknown. We now have found that FOXO1 binds to the TXNIP promoter in vivo in human islets and INS-1 beta cells and significantly decreases TXNIP expression. TXNIP promoter deletion analyses revealed that an E-box motif conferring carbohydrate response element-binding protein (ChREBP)-mediated, glucose-induced TXNIP expression is necessary and sufficient for this effect, and electromobility shift assays confirmed FOXO1 binding to this site. Moreover, FOXO1 blocked glucose-induced TXNIP expression and reduced glucose-induced ChREBP binding at the TXNIP promoter without affecting ChREBP expression or nuclear localization, suggesting that FOXO1 may compete with ChREBP for binding to the TXNIP promoter. In fact, a FOXO1 DNA-binding mutant (FOXO1-H215R) failed to inhibit TXNIP transcription, and the effects were not restricted to TXNIP as FOXO1 also inhibited transcription of other ChREBP target genes such as liver pyruvate kinase. Together, these results demonstrate that FOXO1 inhibits beta cell TXNIP transcription and suggest that FOXO1 confers this inhibition by interfering with ChREBP DNA binding at target gene promoters. Our findings thereby reveal a novel gene regulatory mechanism and a previously unappreciated cross-talk between FOXO1 and ChREBP, two major metabolic signaling pathways.
-
lack of TXNIP protects against mitochondria mediated apoptosis but not against fatty acid induced er stress mediated β cell death
Diabetes, 2010Co-Authors: Junqin Chen, Ghislaine Fontes, Geetu Saxena, Vincent Poitout, Anath ShalevAbstract:OBJECTIVE We have previously shown that lack of thioredoxin-interacting protein (TXNIP) protects against diabetes and glucotoxicity-induced β-cell apoptosis. Because the role of TXNIP in lipotoxicity is unknown, the goal of the present study was to determine whether TXNIP expression is regulated by fatty acids and whether TXNIP deficiency also protects β-cells against lipoapoptosis. RESARCH DESIGN AND METHODS To determine the effects of fatty acids on β-cell TXNIP expression, INS-1 cells and isolated islets were incubated with/without palmitate and rats underwent cyclic infusions of glucose and/or Intralipid prior to islet isolation and analysis by quantitative real-time RT-PCR and immunoblotting. Using primary wild-type and TXNIP-deficient islets, we then assessed the effects of palmitate on apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL]), mitochondrial death pathway (cytochrome c release), and endoplasmic reticulum (ER) stress (binding protein [BiP], C/EBP homologous protein [CHOP]). Effects of TXNIP deficiency were also tested in the context of staurosporine (mitochondrial damage) or thapsigargin (ER stress). RESULTS Glucose elicited a dramatic increase in islet TXNIP expression both in vitro and in vivo, whereas fatty acids had no such effect and, when combined with glucose, even abolished the glucose effect. We also found that TXNIP deficiency does not effectively protect against palmitate or thapsigargin-induced β-cell apoptosis, but specifically prevents staurosporine- or glucose-induced toxicity. CONCLUSIONS Our results demonstrate that unlike glucose, fatty acids do not induce β-cell expression of proapoptotic TXNIP. They further reveal that TXNIP deficiency specifically inhibits the mitochondrial death pathway underlying β-cell glucotoxicity, whereas it has very few protective effects against ER stress–mediated lipoapoptosis.
-
glucose stimulated expression of TXNIP is mediated by carbohydrate response element binding protein p300 and histone h4 acetylation in pancreatic beta cells
Journal of Biological Chemistry, 2009Co-Authors: Hyunjoo Chamolstad, Junqin Chen, Geetu Saxena, Anath ShalevAbstract:Recently, we identified TXNIP (thioredoxin-interacting protein) as a mediator of glucotoxic beta cell death and discovered that lack of TXNIP protects against streptozotocin- and obesity-induced diabetes by preventing beta cell apoptosis and preserving endogenous beta cell mass. TXNIP has therefore become an attractive target for diabetes therapy, but although we have found that TXNIP transcription is highly induced by glucose through a unique carbohydrate response element, the factors controlling this effect have remained unknown. Using transient transfection experiments, we now show that overexpression of the carbohydrate response element-binding protein (ChREBP) transactivates the TXNIP promoter, whereas ChREBP knockdown by small interfering RNA completely blunts glucose-induced TXNIP transcription. Moreover, chromatin immunoprecipitation demonstrated that glucose leads to a dose- and time-dependent recruitment of ChREBP to the TXNIP promoter in vivo in INS-1 beta cells as well as human islets. Furthermore, we found that the co-activator and histone acetyltransferase p300 co-immunoprecipitates with ChREBP and also binds to the TXNIP promoter in response to glucose. Interestingly, this is associated with specific acetylation of histone H4 and recruitment of RNA polymerase II as measured by chromatin immunoprecipitation. Thus, with this study we have identified ChREBP as the transcription factor that mediates glucose-induced TXNIP expression in human islets and INS-1 beta cells and have characterized the chromatin modification associated with glucose-induced TXNIP transcription. In addition, the results reveal for the first time that ChREBP interacts with p300. This may explain how ChREBP induces H4 acetylation and sheds new light on glucose-mediated regulation of chromatin structure and transcription.
