ChREBP Research Articles

Nrf2-Mediated Antioxidant Defense and Peroxiredoxin 6 Are Linked to Biosynthesis of Palmitic Acid Ester of 9-Hydroxystearic Acid.

Fatty acid esters of hydroxy fatty acids (FAHFAs) are lipid mediators with promising antidiabetic and anti-inflammatory properties that are formed in white adipose tissue (WAT) via de novo lipogenesis, but their biosynthetic enzymes are unknown. Using a combination of lipidomics in WAT, quantitative trait locus mapping, and correlation analyses in rat BXH/HXB recombinant inbred strains, as well as response to oxidative stress in murine models, we elucidated the potential pathway of biosynthesis of several FAHFAs. Comprehensive analysis of WAT samples identified ∼160 regioisomers, documenting the complexity of this lipid class. The linkage analysis highlighted several members of the nuclear factor, erythroid 2 like 2 (Nrf2)-mediated antioxidant defense system (Prdx6, Mgst1, Mgst3), lipid-handling proteins (Cd36, Scd6, Acnat1, Acnat2, Baat), and the family of flavin containing monooxygenases (Fmo) as the positional candidate genes. Transgenic expression of Nrf2 and deletion of Prdx6 genes resulted in reduction of palmitic acid ester of 9-hydroxystearic acid (9-PAHSA) and 11-PAHSA levels, while oxidative stress induced by an inhibitor of glutathione synthesis increased PAHSA levels nonspecifically. Our results indicate that the synthesis of FAHFAs via carbohydrate-responsive element-binding protein-driven de novo lipogenesis depends on the adaptive antioxidant system and suggest that FAHFAs may link activity of this system with insulin sensitivity in peripheral tissues.

Stearoyl-CoA desaturase-1 promotes colorectal cancer metastasis in response to glucose by suppressing PTEN

BackgroundDiabetic patients have a higher risk factor for colorectal cancer (CRC) metastasis. Stearoyl-CoA desaturase 1 (SCD1), the main enzyme responsible for producing monounsaturated fatty acids(MUFA) from saturated fatty acids, is frequently deregulated in both diabetes and CRC. The function and mechanism of SCD1 in metastasis of CRC and its relevance to glucose remains largely unknown.MethodsSCD1 expression levels were analyzed in human CRC tissues and the Cancer Browser database (https://genome-cancer.ucsc.edu/). CRC cell lines stably transfected with SCD1 shRNAs or vector were established to investigate the role of SCD1 in modulating migration and invasion of CRC cells. A glucose concentration gradient was set to investigate regulation of SCD1 in CRC relevant to diabetic conditions.ResultsThe clinical data analysis showed high expression of SCD1 in CRC tissues with a negative correlation with the prognosis of CRC. In vitro experiments revealed that SCD1 increased CRC progression through promoting epithelial–mesenchymal transition (EMT). Lipidomic analysis demonstrated that SCD1 increased MUFA levels and MUFA administration could rescue migration and invasion defect of CRC cells induced by SCD1 knockdown. Furthermore, SCD1-mediated progression of CRC was promoted by carbohydrate response-element binding protein (ChREBP) in response to high glucose. Mechanistically, hyperglycemia-SCD1-MUFA induced CRC cell migration and invasion by regulating PTEN.ConclusionsOur findings show that SCD1 promotes metastasis of CRC cells through MUFA production and suppressing PTEN in response to glucose, which may be a novel mechanism for diabetes-induced CRC metastasis.

ChREBP Rather Than SHP Regulates Hepatic VLDL Secretion.

The regulation of hepatic very-low-density lipoprotein (VLDL) secretion plays an important role in the pathogenesis of dyslipidemia and fatty liver diseases. VLDL is controlled by hepatic microsomal triglyceride transfer protein (MTTP). Mttp is regulated by carbohydrate response element binding protein (ChREBP) and small heterodimer partner (SHP). However, it is unclear whether both coordinately regulate Mttp expression and VLDL secretion. Here, adenoviral overexpression of ChREBP and SHP in rat primary hepatocytes induced and suppressed Mttp mRNA, respectively. However, Mttp induction by ChREBP was much more potent than suppression by SHP. Promoter assays of Mttp and the liver type pyruvate kinase gene revealed that SHP and ChREBP did not affect the transcriptional activity of each other. Mttp mRNA and protein levels of Shp−/− mice were similar to those of wild-types; however, those of Chrebp−/−Shp−/− and Chrebp−/− mice were significantly much lower. Consistent with this, the VLDL particle number and VLDL secretion rates in Shp−/− mice were similar to wild-types but were much lower in Chrebp−/− and Chrebp−/−Shp−/− mice. These findings suggest that ChREBP, rather than SHP, regulates VLDL secretion under normal conditions and that ChREBP and SHP do not affect the transcriptional activities of each other.

Interplay between ChREBP and SREBP-1c coordinates postprandial glycolysis and lipogenesis in livers of mice

Lipogenesis in liver is highest in the postprandial state; insulin activates SREBP-1c, which transcriptionally activates genes involved in FA synthesis, whereas glucose activates carbohydrate-responsive element-binding protein (ChREBP), which activates both glycolysis and FA synthesis. Whether SREBP-1c and ChREBP act independently of one another is unknown. Here, we characterized mice with liver-specific deletion of ChREBP (L-Chrebp−/− mice). Hepatic ChREBP deficiency resulted in reduced mRNA levels of glycolytic and lipogenic enzymes, particularly in response to sucrose refeeding following fasting, a dietary regimen that elicits maximal lipogenesis. mRNA and protein levels of SREBP-1c, a master transcriptional regulator of lipogenesis, were also reduced in L-Chrebp−/− livers. Adeno-associated virus-mediated restoration of nuclear SREBP-1c in L-Chrebp−/− mice normalized expression of a subset of lipogenic genes, while not affecting glycolytic genes. Conversely, ChREBP overexpression alone failed to support expression of lipogenic genes in the livers of mice lacking active SREBPs as a result of Scap deficiency. Together, these data show that SREBP-1c and ChREBP are both required for coordinated induction of glycolytic and lipogenic mRNAs. Whereas SREBP-1c mediates insulin’s induction of lipogenic genes, ChREBP mediates glucose’s induction of both glycolytic and lipogenic genes. These overlapping, but distinct, actions ensure that the liver synthesizes FAs only when insulin and carbohydrates are both present.

Implication of trans-11,trans-13 conjugated linoleic acid in the development of hepatic steatosis.

ScopeConjugated linoleic acids are linoleic acid isomers found in the diet that can also be produced through bacterial metabolism of polyunsaturated fatty acids. Our objective was to evaluate the contribution of fatty acid metabolites produced from polyunsaturated fatty acids by the gut microbiota in vivo to regulation of hepatic lipid metabolism and steatosis.Methods and resultsIn mice with depleted n-3 polyunsaturated fatty acids, we observed an accumulation of trans-11,trans-13 CLA and cis-9,cis-11 conjugated linoleic acids in the liver tissue that were associated with an increased triglyceride content and expression of lipogenic genes. We used an in vitro model to evaluate the impact of these two conjugated linoleic acids on hepatic lipid metabolism. In HepG2 cells, we observed that only trans-11,trans-13 conjugated linoleic acids recapitulated triglyceride accumulation and increased lipogenic gene expression, which is a phenomenon that may implicate the nuclear factors sterol regulatory element binding protein 1c (SREBP-1c) and carbohydrate-responsive element-binding protein (ChREBP).ConclusionThe trans-11,trans-13 conjugated linoleic acids can stimulate hepatic lipogenesis, which supports the conclusion that gut microbiota and related metabolites should be considered in the treatment of non-alcoholic liver disease.

Vitamin D Deficiency Increases Lipogenesis and Reduces Beta-Oxidation in the Liver of Diet-Induced Obese Mice.

The study was conducted to understand better the mechanisms involved in liver changes when there is a combination of diet-induced obesity (DIO) and vitamin D deficiency (VDD). After 8 wk of feeding a control diet (C group) or a high-fat diet (HF), both with vitamin D, and counterpart groups without vitamin D (VitD- groups), we found in plasma: higher alanine aminotransferase, and aspartate aminotransferase in the VitD- groups, and more elevated total cholesterol in the HF group. Compared to their counterparts, HF and HF/VitD- showed hyperinsulinemia and higher hepatic triglycerides and steatosis. The protein expressions of markers linked with the vitamin D action were altered by VDD (vitamin D receptor VDR, 25-hydroxyvitamin D-24-hydroxylase CYP24A1, CYP27B1, and CYP2R1). The hepatic lipogenesis and fatty acid synthesis were enhanced by VDD (peroxisome proliferator-activated receptor PPARγ, sterol regulatory element-binding proteins SREBP1c, carbohydrate-responsive element-binding protein ChREBP, and fatty acid synthase FAS), but markers of beta-oxidation were reduced (PPARα and phosphoenolpyruvate carboxykinase PEPCK). In conclusion, the study provides convincing new evidence that there is an additive and adverse effect on the liver caused by the combination of VDD and DIO. The essence of these changes in the liver is in an increased lipogenesis and a reduced beta-oxidation, which predisposes to the accumulation of fat in the liver, accompanied by IR. The worsening of the pathogenesis of NAFLD may tilt to more severe stages of liver disease.

MondoA Is an Essential Glucose-Responsive Transcription Factor in Human Pancreatic β-Cells.

Although the mechanisms by which glucose regulates insulin secretion from pancreatic β-cells are now well described, the way glucose modulates gene expression in such cells needs more understanding. Here, we demonstrate that MondoA, but not its paralog carbohydrate-responsive element-binding protein, is the predominant glucose-responsive transcription factor in human pancreatic β-EndoC-βH1 cells and in human islets. In high-glucose conditions, MondoA shuttles to the nucleus where it is required for the induction of the glucose-responsive genes arrestin domain-containing protein 4 (ARRDC4) and thioredoxin interacting protein (TXNIP), the latter being a protein strongly linked to β-cell dysfunction and diabetes. Importantly, increasing cAMP signaling in human β-cells, using forskolin or the glucagon-like peptide 1 mimetic Exendin-4, inhibits the shuttling of MondoA and potently inhibits TXNIP and ARRDC4 expression. Furthermore, we demonstrate that silencing MondoA expression improves glucose uptake in EndoC-βH1 cells. These results highlight MondoA as a novel target in β-cells that coordinates transcriptional response to elevated glucose levels.

Intestinal, but not hepatic, ChREBP is required for fructose tolerance.

Increased sugar consumption is a risk factor for the metabolic syndrome including obesity, hypertriglyceridemia, insulin resistance, diabetes, and nonalcoholic fatty liver disease (NAFLD). Carbohydrate responsive element-binding protein (ChREBP) is a transcription factor that responds to sugar consumption to regulate adaptive metabolic programs. Hepatic ChREBP is particularly responsive to fructose and global ChREBP-KO mice are intolerant to diets containing fructose. It has recently been suggested that ChREBP protects the liver from hepatotoxicity following high-fructose diets (HFrDs). We directly tested this hypothesis using tissue-specific ChREBP deletion. HFrD increased adiposity and impaired glucose homeostasis in control mice, responses that were prevented in liver-specific ChREBP-KO (LiChKO) mice. Moreover, LiChKO mice tolerated chronic HFrD without marked weight loss or hepatotoxicity. In contrast, intestine-specific ChREBP-KO (IChKO) mice rapidly lost weight after transition to HFrD, and this was associated with dilation of the small intestine and cecum, suggestive of malabsorption. These findings were associated with downregulation of the intestinal fructose transporter, Slc2a5, which is essential for fructose tolerance. Altogether, these results establish an essential role for intestinal, but not hepatic, ChREBP in fructose tolerance.

Molecular Cloning and Mrna Expression Analysis of Sichuan White Goose (Anser Cygnoides) Chrebp Gene

ABSTRACT The carbohydrate response element-binding protein (ChREBP) is an important nuclear factor that regulates glycolysis and de novo lipogenesis. However, the role of ChREBP in fatty liver development in geese remains unclear. In order to understand the function of ChREBP in lipid metabolism of geese, we first cloned the complete cDNA of the ChREBP of the Sichuan White goose (Anser cygnoides) using RT-PCR, 5’ RACE and 3’ RACE, and analyzed goose ChREBP expression in nine different tissues using real-time PCR technology. The results showed that the goose ChREBP CDS consists of 945bp nucleotides that encode 314 amino acids, and the sequence has high similarities with the swan goose (Anser cygnoides domesticus) and duck (Anas platyrhynchos) sequences, both at the nucleotide and amino acid levels. The predicted ChREBP protein had a molecular mass of 35.64 kDa with pI value of 5.36. The phylogenetic analysis indicated its evolutionary relationships with corresponding orthologous sequences in swan geese and ducks. The qPCR assays revealed that ChREBP is highly expressed in liver in the Sichuan White goose. Together, these results indicate that goose ChREBP may play an important role in the development of hepatic steatosis.

Antiobesity effect of Lactobacillus reuteri 263 associated with energy metabolism remodeling of white adipose tissue in high-energy-diet-fed rats

Obesity is a serious and costly issue to the medical welfare worldwide. Probiotics have been suggested as one of the candidates to resolve the obesity-associated problems, but how they combat obesity is not fully understood. Herein, we investigated the effects of Lactobacillus reuteri 263 (L. reuteri 263) on antiobesity using four groups of Sprague–Dawley rats (n=10/group), namely, C (normal diet with vehicle treatment), HE [high-energy diet (HED) with vehicle treatment], 1X (HED with 2.1×109 CFU/kg/day of L. reuteri 263) and 5X (HED with 1.05×1010 CFU/kg/day of L. reuteri 263), for 8 weeks. L. reuteri 263 improved the phenomenon of obesity, serum levels of proinflammatory factors and antioxidant enzymes. More importantly, L. reuteri 263 increased oxygen consumption in white adipose tissue (WAT). The mRNA expressions of thermogenesis genes uncoupling protein-1, uncoupling protein-3, carnitine palmitoyltransferase-1 and cell death-inducing DFFA-like effector-a were up-regulated in WAT of the 5X group. Moreover, L. reuteri 263 might induce browning of WAT due to the higher mRNA levels of browning-related genes peroxisome proliferator-activated receptor-γ, PR domain containing-16, Pparγ coactivator-1α, bone morphogenetic protein-7 and fibroblast growth factor-21 in the 1X and 5X groups compared to the HE group. Finally, L. reuteri 263 altered the expressions of genes involved in glucose and lipid metabolisms in WAT, including increasing the levels of glucose transporter type 4 and carbohydrate-responsive element-binding protein and decreasing the expression of Acetyl-CoA carboxylase-1. The results suggest that L. reuteri 263 may treat obesity through energy metabolism remodeling of WAT in the high-energy-diet-induced obese rats.

Sugar-sweetened beverage intake associations with fasting glucose and insulin concentrations are not modified by selected genetic variants in a ChREBP-FGF21 pathway: a meta-analysis.

Sugar-sweetened beverages (SSBs) are a major dietary contributor to fructose intake. A molecular pathway involving the carbohydrate responsive element-binding protein (ChREBP) and the metabolic hormone fibroblast growth factor 21 (FGF21) may influence sugar metabolism and, thereby, contribute to fructose-induced metabolic disease. We hypothesise that common variants in 11 genes involved in fructose metabolism and the ChREBP-FGF21 pathway may interact with SSB intake to exacerbate positive associations between higher SSB intake and glycaemic traits. Data from 11 cohorts (six discovery and five replication) in the CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) Consortium provided association and interaction results from 34,748 adults of European descent. SSB intake (soft drinks, fruit punches, lemonades or other fruit drinks) was derived from food-frequency questionnaires and food diaries. In fixed-effects meta-analyses, we quantified: (1) the associations between SSBs and glycaemic traits (fasting glucose and fasting insulin); and (2) the interactions between SSBs and 18 independent SNPs related to the ChREBP-FGF21 pathway. In our combined meta-analyses of discovery and replication cohorts, after adjustment for age, sex, energy intake, BMI and other dietary covariates, each additional serving of SSB intake was associated with higher fasting glucose (β±SE 0.014±0.004 [mmol/l], p=1.5×10-3) and higher fasting insulin (0.030±0.005 [log e pmol/l], p=2.0×10-10). No significant interactions on glycaemic traits were observed between SSB intake and selected SNPs. While a suggestive interaction was observed in the discovery cohorts with a SNP (rs1542423) in the β-Klotho (KLB) locus on fasting insulin (0.030±0.011 log e pmol/l, uncorrected p=0.006), results in the replication cohorts and combined meta-analyses were non-significant. In this large meta-analysis, we observed that SSB intake was associated with higher fasting glucose and insulin. Although a suggestive interaction with a genetic variant in the ChREBP-FGF21 pathway was observed in the discovery cohorts, this observation was not confirmed in the replication analysis. Trials related to this study were registered at clinicaltrials.gov as NCT00005131 (Atherosclerosis Risk in Communities), NCT00005133 (Cardiovascular Health Study), NCT00005121 (Framingham Offspring Study), NCT00005487 (Multi-Ethnic Study of Atherosclerosis) and NCT00005152 (Nurses' Health Study).

Hepatocellular glycogenotic foci after combined intraportal pancreatic islet transplantation and knockout of the carbohydrate responsive element binding protein in diabetic mice

AimsThe intraportal pancreatic islet transplantation (IPIT) model of diabetic rats is an insulin mediated model of hepatocarcinogenesis characterized by the induction of clear cell foci (CCF) of altered hepatocytes, which are pre-neoplastic lesions excessively storing glycogen (glycogenosis) and exhibiting activation of the AKT/mTOR protooncogenic pathway. In this study, we transferred the IPIT model to the mouse and combined it with the knockout of the transcription factor carbohydrate responsive element binding protein (chREBP).MethodsC57BL/6J Wild-type (WT) and chREBP-knockout (chREBP-KO) mice (n = 297) were matched to 16 groups (WT/ chREBP-KO, experimental/control, streptozotocine-induced diabetic/not diabetic, one/four weeks). Experimental groups received the intraportal transplantation of 70 pancreatic islets. Liver and pancreatic tissue was examined using histology, morphometry, enzyme- and immunohistochemistry and electron microscopy.ResultsCCF emerged in the liver acini downstream of the transplanted islets. In comparison to WT lesions, CCF of chREBP-KO mice displayed more glycogen accumulation, reduced activity of the gluconeogenic enzyme glucose-6-phosphatase, decreased glycolysis, lipogenesis and reduced levels of the AKT/mTOR cascade members. Proliferative activity of CCF was ∼two folds higher in WT mice than in chREBP-KO mice.ConclusionsThe IPIT model is applicable to mice, as murine CCF resemble preneoplastic liver lesions from this hepatocarcinogenesis model in the rat in terms of morphological, metabolic and molecular alterations and proliferative activity, which is diminished after chREBP knockout. chREBP appears to be an essential component of AKT/mTOR mediated cell proliferation and the metabolic switch from a glycogenotic to lipogenic phenotype in precursor lesions of hepatocarcinogenesis.

Aralia elata (Miq) Seem Extract Decreases O-GlcNAc Transferase Expression and Retinal Cell Death in Diabetic Mice.

Aralia elata (Miq) Seem (AES) is a medicinal plant used in traditional Chinese and Korean medicine for the treatment of several diseases, including diabetes. This study aimed to investigate the neuroprotective effect of AES extract against high glucose-induced retinal injury in diabetic mice. AES extract (20 and 100 mg/kg body weight) was orally administered to control mice or mice with streptozotocin-induced diabetes. Protein levels of O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT), carbohydrate-responsive element-binding protein (ChREBP), sterol regulatory element-binding protein (SREBP)-1, thioredoxin-interacting protein (TXNIP), fatty acid synthase (FAS), and acetyl CoA carboxylase (ACC) were analyzed by western blotting. Colocalization of terminal deoxynucleotide transferase-mediated dUTP nicked-end labeling (TUNEL)-positive ganglion cells and OGT, ChREBP, or TXNIP were monitored using double immunofluorescence analysis. Interaction between ChREBP and OGT was assessed using coimmunoprecipitation analysis. AES extract protected the retinas from neuronal injury and decreased levels of OGT, ChREBP, TXNIP, SREBP-1, FAS, and ACC in the diabetic retinas. AES extract reduced colocalization of TUNEL-positive ganglion cells and OGT, ChREBP, or TXNIP in the diabetic retinas. Coimmunoprecipitation analysis indicated that AES extract reduced interaction between ChREBP and OGT and attenuated ganglion cell death in diabetic retinas. Moreover, the ChREBP that colocalized with OGT or the TUNEL signal was significantly decreased in diabetic mice treated with AES extract. These findings show that AES extract can alleviate OGT-, ChREBP-, TXNIP-, or SREBP-1-related retinal injury in diabetic retinopathy.

A Specific ChREBP and PPARα Cross-Talk Is Required for the Glucose-Mediated FGF21 Response

SummaryWhile the physiological benefits of the fibroblast growth factor 21 (FGF21) hepatokine are documented in response to fasting, little information is available on Fgf21 regulation in a glucose-overload context. We report that peroxisome-proliferator-activated receptor α (PPARα), a nuclear receptor of the fasting response, is required with the carbohydrate-sensitive transcription factor carbohydrate-responsive element-binding protein (ChREBP) to balance FGF21 glucose response. Microarray analysis indicated that only a few hepatic genes respond to fasting and glucose similarly to Fgf21. Glucose-challenged Chrebp−/− mice exhibit a marked reduction in FGF21 production, a decrease that was rescued by re-expression of an active ChREBP isoform in the liver of Chrebp−/− mice. Unexpectedly, carbohydrate challenge of hepatic Pparα knockout mice also demonstrated a PPARα-dependent glucose response for Fgf21 that was associated with an increased sucrose preference. This blunted response was due to decreased Fgf21 promoter accessibility and diminished ChREBP binding onto Fgf21 carbohydrate-responsive element (ChoRE) in hepatocytes lacking PPARα. Our study reports that PPARα is required for the ChREBP-induced glucose response of FGF21.

Absence of Carbohydrate Response Element Binding Protein in Adipocytes Causes Systemic Insulin Resistance and Impairs Glucose Transport

Lower adipose-ChREBP and de novo lipogenesis (DNL) are associated with insulin resistance in humans. Here, we generated adipose-specific ChREBP knockout (AdChREBP KO) mice with negligible sucrose-induced DNL in adipose tissue (AT). Chow-fed AdChREBP KO mice are insulin resistant with impaired insulin action in the liver, muscle, andAT and increased AT inflammation. HFD-fed AdChREBP KO mice are also more insulin resistantthan controls. Surprisingly, adipocytes lacking ChREBP display a cell-autonomous reduction in insulin-stimulated glucose transport that is mediated by impaired Glut4 translocation and exocytosis, not lower Glut4 levels. AdChREBP KO mice have lower levels of palmitic acid esters of hydroxy stearic acids (PAHSAs) in serum, and AT. 9-PAHSA supplementation completely rescues their insulin resistance and AT inflammation. 9-PAHSA also normalizes impaired glucose transport and Glut4 exocytosis in ChREBP KO adipocytes. Thus, lossof adipose-ChREBP is sufficient to cause insulin resistance, potentially by regulating AT glucose transport and flux through specific lipogenic pathways.

The regulation and role of carbohydrate response element-binding protein in metabolic homeostasis and disease.

The transcription factor carbohydrate response element-binding protein (ChREBP) is a member of the basic helix-loop-helix leucine zipper transcription factor family. Under high-glucose conditions, it has a role in regulating the expression of key genes involved in various pathways, including glycolysis, gluconeogenesis and lipogenesis. It does this by forming a tetrameric complex made up of two ChREBP/Mlx heterodimers, which enables it to bind to the carbohydrate response element (ChoRE) in the promoter region of its target genes to regulate transcription. Because ChREBP plays a key role in glucose signalling and metabolism, and aberrations in glucose homeostasis are often present in metabolic diseases, this transcription factor presents itself as an enticing target with respect to further understanding metabolic disease mechanisms and potentially uncovering new therapeutic targets.

Insights into the Hexose Liver Metabolism-Glucose versus Fructose.

High-fructose intake in healthy men is associated with characteristics of metabolic syndrome. Extensive knowledge exists about the differences between hepatic fructose and glucose metabolism and fructose-specific mechanisms favoring the development of metabolic disturbances. Nevertheless, the causal relationship between fructose consumption and metabolic alterations is still debated. Multiple effects of fructose on hepatic metabolism are attributed to the fact that the liver represents the major sink of fructose. Fructose, as a lipogenic substrate and potent inducer of lipogenic enzyme expression, enhances fatty acid synthesis. Consequently, increased hepatic diacylglycerols (DAG) are thought to directly interfere with insulin signaling. However, independently of this effect, fructose may also counteract insulin-mediated effects on liver metabolism by a range of mechanisms. It may drive gluconeogenesis not only as a gluconeogenic substrate, but also as a potent inducer of carbohydrate responsive element binding protein (ChREBP), which induces the expression of lipogenic enzymes as well as gluconeogenic enzymes. It remains a challenge to determine the relative contributions of the impact of fructose on hepatic transcriptome, proteome and allosterome changes and consequently on the regulation of plasma glucose metabolism/homeostasis. Mathematical models exist modeling hepatic glucose metabolism. Future models should not only consider the hepatic adjustments of enzyme abundances and activities in response to changing plasma glucose and insulin/glucagon concentrations, but also to varying fructose concentrations for defining the role of fructose in the hepatic control of plasma glucose homeostasis.

Both 3,5-Diiodo-L-Thyronine and 3,5,3'-Triiodo-L-Thyronine Prevent Short-term Hepatic Lipid Accumulation via Distinct Mechanisms in Rats Being Fed a High-Fat Diet.

3,3′,5-triiodo-L-thyronine (T3) improves hepatic lipid accumulation by increasing lipid catabolism but it also increases lipogenesis, which at first glance appears contradictory. Recent studies have shown that 3,5-diiodothyronine (T2), a natural thyroid hormone derivative, also has the capacity to stimulate hepatic lipid catabolism, however, little is known about its possible effects on lipogenic gene expression. Because genes classically involved in hepatic lipogenesis such as SPOT14, acetyl-CoA-carboxylase (ACC), and fatty acid synthase (FAS) contain thyroid hormone response elements (TREs), we studied their transcriptional regulation, focusing on TRE-mediated effects of T3 compared to T2 in rats receiving high-fat diet (HFD) for 1 week. HFD rats showed a marked lipid accumulation in the liver, which was significantly reduced upon simultaneous administration of either T3 or T2 with the diet. When administered to HFD rats, T2, in contrast with T3, markedly downregulated the expression of the above-mentioned genes. T2 downregulated expression of the transcription factors carbohydrate-response element-binding protein (ChREBP) and sterol regulatory element binding protein-1c (SREBP-1c) involved in activation of transcription of these genes, which explains the suppressed expression of their target genes involved in lipogenesis. T3, however, did not repress expression of the TRE-containing ChREBP gene but repressed SREBP-1c expression. Despite suppression of SREBP-1c expression by T3 (which can be explained by the presence of nTRE in its promoter), the target genes were not suppressed, but normalized to HFD reference levels or even upregulated (ACC), partly due to the presence of TREs on the promoters of these genes and partly to the lack of suppression of ChREBP. Thus, T2 and T3 probably act by different molecular mechanisms to achieve inhibition of hepatic lipid accumulation.

Thioredoxin-interacting protein promotes high-glucose-induced macrovascular endothelial dysfunction

Thioredoxin-interacting protein (TXNIP) emerges as a central regulator for glucose homeostasis, which goes awry in diabetic subjects. Endothelial dysfunction is considered the earliest detectable stage of cardiovascular disease (CVD), a major complication of diabetes. Here, we hypothesize that TXNIP may promote endothelial dysfunction seen in Type 1 diabetes mellitus (T1D). Using a T1D-like rat model, we found that diabetic rats showed significantly higher TXNIP mRNA and protein levels in peripheral blood, compared to their non-diabetic counterparts. Those changes were accompanied by decreased production of nitric oxide (NO) and vascular endothelial growth factor (VEGF), concurrent with increased expression of reactive oxygen species (ROS) and vascular cell adhesion molecule 1 (VCAM-1) in the aortic endothelium. In addition, TXNIP overexpression in primary human aortic endothelial cells (HAECs) induced by either high glucose or overexpression of carbohydrate response element binding protein (ChREBP), a major transcriptional activator of TXNIP, promoted early apoptosis and impaired NO bioactivity. The correlation between TXNIP expression levels and endothelial dysfunction suggests that TXNIP may be a potential biomarker for vascular complications in T1D patients.

OP.8B.06] SACCHARIN INCREASES FASTING BLOOD GLUCOSE BUT NOT LIVER INSULIN RESISTANCE IN COMPARISON TO HIGH FRUCTOSE FED RAT MODEL

Objective: The prevalence of obesity, metabolic syndrome (MS) and diabetes is increasing steadily, in part due to the high caloric- high fructose content of the western diet. The use of low caloric artificial sweeteners (AS) is recommended as a strategy fighting this pandemic. However, recent data indicate that AS may have deleterious effect on glucose metabolism. The aim of this study is to assess the metabolic effects of AS on glucose absorption and insulin resistance (IR) in comparison to the effect of a high fructose diet (HFrD) in Sprague-Dawley (SD) rats. Design and method: Thirty SD male rats (8 weeks old) were divided into 3 groups (n = 10): 1. Control- fed regular chow. 2. Fed regular chow and saccharin (0.1 mg/ml) in the water. 3. Fed HFrD for 6 weeks. Fasting blood glucose, insulin and Triglycerides (Tg) levels were measured at the end of the study. HOMA-IR index was used to determine insulin resistance. Liver was stained for detection sign of fatty liver. Hepatic mRNA expression of glucose metabolism regulation genes SREBP-1c (sterol regulatory element binding protein) and chREB (carbohydrate response element binding protein) was measured as IR markers. Results: Adding saccharin to normal chaw fed rats increased significantly the fasting blood glucose to the same level as in the HFrD fed rats (137 ± 6 and 140 ± 5 vs. 118 ± 2.6 mg/dL in the control group). Saccharin administration didn’t affect Insulin secretion nor Tg levels. Fructose but not saccharin increased HOMA-IR index compare to the control group (3.4 ± 0.4 in the HFrD group vs. 2.3 ± 0.3 and 2.13 ± 0.3 in the regular chow groups). There were no sign for fatty liver in the regular chow groups. SREBP-1c and chREB mRNA expression was significantly high (2.6 and 1.55 time fold higher than in the contol, respectively) in the fructose but not in the saccharin fed rats. Conclusions: Saccharin may increase fasting blood glucose but induces no liver insulin resistance.