Glucose regulation of gene transcription

Diabetes mellitus impacts risk of macrovascular invasion in patients undergoing transplantation for hepatocellular carcinoma

Background

Diabetes mellitus (DM) is identified as a negative prognostic indicator in hepatocellular carcinoma (HCC), though the basis for this is unknown.

Methods

This is a retrospective analysis of a prospectively collected database of 191 HCC patients treated at the University of Rochester Medical Center (URMC) with orthotopic liver transplantation between 1998–2008. Clinical characteristics were compared between patients with and without DM prior to liver transplantation and logistic regression analyses were conducted to assess the effect of DM on clinical outcomes including vascular invasion.

Results

Eighty-four of 191 (44%) transplanted patients had DM at time of transplantation. An association of DM with invasive disease was found among transplanted HCC patients where histologically confirmed macrovascular invasion was found in 20.2% (17/84) of diabetics compared to 9.3% of non-diabetics (10/107) (p=0.032). This difference also remained significant when adjusting for tumor size, number of nodules, age, obesity and etiologic risk factors in multivariate logistic regression analysis (OR=3.2, p=0.025).

Conclusions

DM is associated with macrovascular invasion among a cohort of transplanted HCC patients.

Phillyrin attenuates high glucose-induced lipid accumulation in human HepG2 hepatocytes through the activation of LKB1/AMP-activated protein kinase-dependent signalling

Phillyrin, an active constituent found in many medicinal plants and certain functional foods, has anti-obesity activity in vivo. The aim of our study was to provide new data on the molecular mechanism(s) underlying the role of phillyrin in the prevention of high glucose-induced lipid accumulation in human HepG2 hepatocytes. We found that phillyrin suppressed high glucose-induced lipid accumulation in HepG2 cells. Phillyrin strongly inhibited high glucose-induced fatty acid synthase (FAS) expression by modulating sterol regulatory element-binding protein-1c (SREBP-1c) activation. Moreover, use of the pharmacological AMP-activated protein kinase (AMPK) inhibitor compound C revealed that AMPK is essential for suppressing SREBP-1c expression in phillyrin-treated cells. Finally, we found that liver kinase B1 (LKB1) phosphorylation is required for the phillyrin-enhanced activation of AMPK in HepG2 hepatocytes. These results indicate that phillyrin prevents lipid accumulation in HepG2 cells by blocking the expression of SREBP-1c and FAS through LKB1/AMPK activation, suggesting that phillyrin is a novel AMPK activator with a role in the prevention and treatment of obesity.

Effect of glucose availability on glucose transport in bovine mammary epithelial cells

Primary bovine mammary epithelial cells (BMEC) were cultured in media containing varying concentrations of glucose, to determine the effects of glucose availability on glucose transport and its mechanism in bovine mammary gland. The BMEC incubated with 10 and 20 mM glucose had twofold greater glucose uptake than that with 2.5 mM glucose (P < 0.05). Increased glucose availability enhanced the cell proliferation (P < 0.05). As the glucose uptake is mediated by facilitative glucose transporters (GLUTs), the expression of GLUT mRNA was investigated. Compared with the control (2.5 mM), 5 and 10 mM glucose did not influence the abundance of GLUT1 mRNA (P < 0.05), whereas 20 mM glucose decreased the GLUT1 mRNA expression in the BMEC (P < 0.05). The expression of GLUT8 mRNA was not affected by any concentration of glucose (P > 0.05). As GLUTs are coupled with hexokinases (HKs) in regulating glucose uptake, the expression of HKs and their activities were also studied. The HK activity was greater in 5, 10 and 20 mM glucose than that in 2.5 mM glucose (P < 0.05). The expression of HK2 mRNA rather than HK1 mRNA was detected in the BMEC; however, the abundance of HK2 mRNA was not elevated by any concentrations of glucose compared with control (P > 0.05). Furthermore, addition of 3-bromopyruvate (30, 50 or 70 μM), an inhibitor of HK2, resulted in the decrease of glucose uptake and cell proliferation at both 2.5 and 10 mM glucose (P < 0.05). Therefore, the glucose concentrations may affect glucose uptake partly by altering the activity of HKs, and HK2 may play an important role in the regulation of glucose uptake in the BMEC.

Target metabolomics revealed complementary roles of hexose- and pentose-phosphates in the regulation of carbohydrate-dependent gene expression

Carbohydrate response element-binding protein (ChREBP) is a transcription factor that mediates glucose signaling in mammalian liver, leading to the expression of different glycolytic and lipogenic genes, such as pyruvate kinase (L-PK) and fatty acid synthase (FAS). The current model for ChREBP activation in response to sugar phosphates holds that glucose metabolization to xylulose 5-phosphate (X-5-P) triggers the activation of protein phosphatase 2A, which dephosphorylates ChREBP and leads to its nuclear translocation and activation. However, evidence indicates that glucose 6-phosphate (G-6-P) is the most likely signal metabolite for the glucose-induced transcription of these genes. The glucose derivative that is responsible for carbohydrate-dependent gene expression remains to be identified. The difficulties in measuring G-6-P and X-5-P concentrations simultaneously and in changing them independently have hindered such identification. To discriminate between these possibilities, we adapted a liquid chromatography mass spectrometry method to identify and quantify sugar phosphates in human hepatocarcinoma cells (Hep G2) and rat hepatocytes in response to different carbon sources and in the presence/absence of a glucose-6-phosphate dehydrogenase inhibitor. We also used this method to demonstrate that these cells could not metabolize 2-deoxyglucose beyond 2-deoxyglucose-6-phosphate. The simultaneous quantification of sugar phosphates and FAS and L-PK expression levels demonstrated that both X-5-P and G-6-P play a role in the modulation of gene expression. In conclusion, this report presents for the first time a single mechanism that incorporates the effects of X-5-P and G-6-P on the enhancement of the expression of carbohydrate-responsive genes.

Carbon source metabolism and its regulation in cancer cells

Cancer cell proliferation and progression require sufficient supplies of nutrients including carbon sources, nitrogen sources, and molecular oxygen. Particularly, carbon sources and molecular oxygen are critical for the generation of ATP and building blocks, and for the maintenance of intracellular redox status. However, solid tumors frequently outgrow the blood supply, resulting in nutrient insufficiency. Accordingly, cancer cell metabolism shows aberrant biochemical features that are consequences of oncogenic signaling and adaptation. Those adaptive metabolism features, including the Warburg effect and addiction to glutamine, may form the biochemical basis for resistance to chemotherapy and radiation. A better understanding of the regulatory mechanisms that link the signaling pathways to adaptive metabolic reprogramming may identify novel biomarkers for drug development. In this review, we focus on the regulation of carbon source utilization at a cellular level, emphasizing its relevance to proliferative biosynthesis in cancer cells. We summarize the essential needs of proliferating cells and the metabolic features of glucose, lipids, and glutamine, and we review the roles of transcription regulators (i.e., HIF-1, c-Myc, and p53) and two major oncogenic signaling pathways (i.e., PI3K-Akt and MAPK) in regulating the utilization of carbon sources. Finally, the effects of glucose on cell proliferation and perspective from both biochemical and cellular angles are discussed.

Differential impact of nutrition on developmental and metabolic gene expression during fruiting body development in Neurospora crassa

Fungal fruiting body size and form are influenced by the ecology of the species, including diverse environmental stimuli. Accordingly, nutritional resources available to the fungus during development can be vital to successful production of fruiting bodies. To investigate the effect of nutrition, perithecial development of Neurospora crassa was induced on two different media, a chemically sparsely nutritive Synthetic Crossing Medium (SCM) and a natural Carrot Agar (CA). Protoperithecia were collected before crossing, and perithecia were collected at 2, 24, 48, 72, 96, 120, and at full maturity 144 h after crossing. No differences in fruiting body morphology were observed between the two media at any time point. A circuit of microarray hybridizations comparing cDNA from all neighboring stages was performed. For a majority of differentially expressed genes, expression was higher in SCM than in CA, and expression of core metabolic genes was particularly affected. Effects of nutrition were highest in magnitude before crossing, lowering in magnitude during early perithecial development. Interestingly, metabolic effects of the media were also large in magnitude during late perithecial development, at which stage the lower expression in CA presumably reflected the continued intake of diverse complex initial compounds, diminishing the need for expression of anabolic pathways. However, for genes with key regulatory roles in sexual development, including pheromone precursor ccg-4 and poi2, expression patterns were similar between treatments. When possible, a common nutritional environment is ideal for comparing transcriptional profiles between different fungi. Nevertheless, the observed consistency of the developmental program across media, despite considerable metabolic differentiation is reassuring. This result facilitates comparative studies that will require different nutritional resources for sexual development in different fungi.

Elevated transcription factor specificity protein 1 in autistic brains alters the expression of autism candidate genes

BACKGROUND

Profound changes in gene expression can result from abnormalities in the concentrations of sequence-specific transcription factors like specificity protein 1 (Sp1). Specificity protein 1 binding sites have been reported in the promoter regions of several genes implicated in autism. We hypothesize that dysfunction of Sp1 could affect the expression of multiple autism candidate genes, contributing to the heterogeneity of autism.

METHODS

We assessed any alterations in the expression of Sp1 and that of autism candidate genes in the postmortem brain (anterior cingulate gyrus [ACG], motor cortex, and thalamus) of autism patients (n = 8) compared with healthy control subjects (n = 13). Alterations in the expression of candidate genes upon Sp1/DNA binding inhibition with mithramycin and Sp1 silencing by RNAi were studied in SK-N-SH neuronal cells.

RESULTS

We observed elevated expression of Sp1 in ACG of autism patients (p = .010). We also observed altered expression of several autism candidate genes. GABRB3, RELN, and HTR2A showed reduced expression, whereas CD38, ITGB3, MAOA, MECP2, OXTR, and PTEN showed elevated expression in autism. In SK-N-SH cells, OXTR, PTEN, and RELN showed reduced expression upon Sp1/DNA binding inhibition and Sp1 silencing. The RNA integrity number was not available for any of the samples.

CONCLUSIONS

Transcription factor Sp1 is dysfunctional in the ACG of autistic brain. Consequently, the expression of potential autism candidate genes regulated by Sp1, especially OXTR and PTEN, could be affected. The diverse downstream pathways mediated by the Sp1-regulated genes, along with the environmental and intracellular signal-related regulation of Sp1, could explain the complex phenotypes associated with autism.

Proteome changes in the myocardium of experimental chronic diabetes and hypertension: role of PPARα in the associated hypertrophy

Diabetes with or without the presence of hypertension damages the heart. However, there is currently a lack of information about these associated pathologies and the alteration of linked proteins. For these reasons, we were interested in the potential synergistic interaction of diabetes and hypertension in the heart, focusing on the proteome characterization of the pathological phenotypes and the associated hypertrophic response. We treated normotensive and spontaneously hypertensive (SHR) rats with either streptozotocin or vehicle. After 22weeks, type-I diabetic (DM1), SHR, SHR/DM1 and control left-ventricles were studied using proteomic approaches. Proteomics revealed that long-term DM1, SHR and SHR/DM1 rats exhibited 24, 53 and 53 altered proteins in the myocardia, respectively. DM1 myocardium showed over-expression of apoptotic and cytoskeleton proteins, and down-regulation of anti-apoptotic and mitochondrial metabolic enzymes. In both SHR and SHR/DM1 these changes were exacerbated and free fatty-acid (FFA) ß-oxidation enzymes were additionally decreased. Furthermore, SHR/DM1 hearts exhibited a misbalance of specific pro-hypertrophic, anti-apoptotic and mitochondrial ATP-carrier factors, which could cause additional damage. Differential proteins were validated and then clustered into different biological pathways using bioinformatics. These studies suggested the implication of FFA-nuclear receptors and hypertrophic factors in these pathologies. Although key ß-oxidation enzymes were not stimulated in DM1 and hypertensive hearts, peroxisome proliferator-activated receptors-α (PPARα) were potentially activated for other responses. In this regard, PPARα stimulation reduced hypertrophy and pro-hypertrophic factors such as annexin-V in high-glucose and angiotensin-II induced cardiomyocytes. Thus, activation of PPARα could reflect a compensatory response to the metabolic-shifted, apoptotic and hypertrophic status of the hypertensive-diabetic cardiomyopathy.

Glucosensing and glucose homeostasis: from fish to mammals

This review is focused on two topics related to glucose in vertebrates. In a first section devoted to glucose homeostasis we describe how glucose levels fluctuate and are regulated in different classes of vertebrates. The detection of these fluctuations is essential for homeostasis and for other physiological processes such as regulation of food intake. The capacity of that detection is known as glucosensing, and the different mechanisms through which it occurs are known as glucosensors. Different glucosensor mechanisms have been demonstrated in different tissues and organs of rodents and humans whereas the information obtained for other vertebrates is scarce. In the second section of the review we describe the present knowledge regarding glucosensor mechanisms in different groups of vertebrates, with special emphasis in fish.

The function of MoGlk1 in integration of glucose and ammonium utilization in Magnaporthe oryzae

Hexokinases are conserved proteins functioning in glucose sensing and signaling. The rice blast fungus Magnaporthe oryzae contains several hexokinases, including MoHxk1 (hexokinase) and MoGlk1 (glucokinase) encoded respectively by MoHXK1 and MoGLK1 genes. The heterologous expression of MoGlk1 and MoHxk1 in Saccharomyces cerevisiae confirmed their conserved functions. Disruption of MoHXK1 resulted in growth reduction in medium containing fructose as the sole carbon source, whereas disruption of MoGLK1 did not cause the similar defect. However, the ΔMoglk1 mutant displayed decreased proton extrusion and a lower biomass in the presence of ammonium, suggesting a decline in the utilization of ammonium. Additionally, the MoGLK1 allele lacking catalytic activity restored growth to the ΔMoglk1 mutant. Moreover, the expression of MoPMA1 encoding a plasma membrane H⁺-ATPase decreased in the ΔMoglk1 mutant that can be suppressed by glucose and G-6-P. Thus, MoGlk1, but not MoHxk1, regulates ammonium utilization through a mechanism that is independent from its catalytic activity.

Functional characterization of the proximal promoter of the murine pyruvate carboxylase gene in hepatocytes: role of multiple gc boxes

Pyruvate carboxylase (PC) catalyzes the first committed step in gluconeogenesis in the liver. The murine PC gene possesses two promoters, the proximal (P1) and the distal (P2) which mediate production of distinct tissue-specific mRNA isoforms. By comparing the luciferase activities of 5'-nested deletions of the P1-promoter in the AML12 mouse hepatocyte cell line, the critical cis-acting elements required for maintaining basal transcription were located within the 166 nucleotides proximal to the transcription start site. Three GC boxes were identified within this region and shown by gel shift and ChIP assays to bind Sp1/Sp3. Over-expression of Sp1/Sp3 in AML12 and NIH3T3 cells increased P1-promoter activity, with Sp1 being a stronger activator than Sp3. Mutation of any one of the three GC boxes dramatically reduced basal promoter activity by 60-80% suggesting that all three boxes are equally strong regulatory elements. In AML12 cells, over-expression of Sp1/Sp3 restored the transcriptional activity of GC1 and GC2 but not GC3 mutants to levels similar to that of the WT construct, suggesting that GC3 is particularly critical for Sp1/Sp3-mediated induction. In NIH3T3 cells, however, the three boxes were equally important, indicating that the GC boxes differentially contribute to transcriptional regulation of the P1-promoter in the two cell lines. Mutants harboring two disrupted GC boxes showed a further decrease in promoter activity similar to the triple GC box mutant. Neither Sp1 nor Sp3 was able to fully restore the promoter activities of these mutants to that the WT level.

Effect of green tea catechins on the postprandial glycemic response to starches differing in amylose content

The effect of tea polyphenols (TPLs), specifically tea catechins, on the postprandial glycemic response to cooked starches differing in amylose contents was investigated. The in vivo test using a mouse model showed a moderate reduction of the postprandial glycemic response to co-cooked normal (containing 27.8% amylose) or waxy corn starch with 10% TPLs (dry weight of starch), while an augmented glycemic response with a delayed blood glucose peak was observed when high amylose corn starch (HAC, containing 79.4% amylose) was used as the starch component. Enzyme kinetics results demonstrated that TPLs noncompetitively inhibit the digestion of waxy or normal corn starch, while the digestion rate of HAC starch was increased in the presence of TPLs, which supports the observed postprandial glycemic responses. Further studies using X-ray powder diffraction showed that the diffraction intensity (area under the diffraction curves) of normal and HAC starch was increased by 45% and 74%, respectively, whereas no change was observed for waxy corn starch. Consistently, dynamic laser light scattering studies using a solution of pure amylose showed an increased hydrodynamic radius of amylose molecules from ∼54 nm to ∼112 nm in the presence of TPLs. These experimental results indicate that there might exist an interaction between TPLs and amylose, which facilitates the association of amylose molecules to form a special nonordered structure that can produce a high and sustained postprandial glycemic response. Thus, a combination of tea polyphenols and specific starches could be used to manipulate postprandial glycemic response for glycemic control and optimal health.

Molecular mechanisms involved in the adaptation to amino acid limitation in mammals

In mammals, metabolic adaptations are required to cope with episodes of protein deprivation and malnutrition. Consequently, mammals have to adjust physiological functions involved in the adaptation to amino acid availability. Part of this regulation involves the modulation of the expression of numerous genes. In particular, it has been shown that amino acids by themselves can modify the expression of target genes. This review describes the regulation of amino acids homeostasis and the their role as signal molecules. The recent advances in the understanding of the molecular mechanisms involved in the control of mammalian gene expression in response to amino acid limitation will be described.

Thyroid hormone responsive Spot 14 increases during differentiation of human adipocytes and its expression is down-regulated in obese subjects

CONTEXT

Very limited information is available regarding the function of human thyroid hormone responsive Spot 14 (human S14, hS14) in adipogenesis and human adiposity.

OBJECTIVE

To evaluate hS14 levels during differentiation of human pre-adipocytes, in human fat depots and isolated fat cells.

DESIGN

This was a cross-sectional study.

SUBJECTS

A total of 161 omental (OM) and 87 subcutaneous (SC) adipose tissue samples obtained during elective surgical procedures from a population who varied widely in terms of obesity.

MEASUREMENTS

hS14 gene expression and protein levels during adipogenesis were assessed by RT-PCR, western blot, and using an automated confocal imaging approach.

RESULTS

hS14 gene expression levels were decreased in OM adipose tissue from overweight (-42.0%) and obese subjects (-56.5%) compared with lean subjects (P<0.05 and P<0.0001, respectively). hS14 mRNA (but not hS14-related) was inversely associated with obesity measures such as body mass index (P=0.001), percent fat mass (P=0.001), waist-to-hip ratio (P=0.020), and systolic blood pressure (P=0.031). hS14 gene expression and protein levels were up-regulated at the early stages of differentiation of human pre-adipocytes as well as for 3T3-L1 cells. That observation was most prominent in those individual cells exhibiting the more marked differentiation features. hS14 gene expression levels increased by approximately 45 000-fold in mature adipocytes. Increased hS14 levels were also found in stromal-vascular cells/pre-adipocytes (3.8-fold, P<0.05) and in adipose tissue samples (1.9-fold, P<0.0001) from SC compared with OM fat depots.

CONCLUSIONS

These results suggest that hS14 is involved in human adipogenesis, but inversely related to obesity and OM fat accumulation.

The role of insulin and glucose in goose primary hepatocyte triglyceride accumulation

In order to obtain some information on how fatty liver arises in geese, we investigated the role of insulin and glucose in triglyceride (TG) accumulation in goose primary hepatocytes. Goose primary hepatocytes were isolated and treated with insulin and glucose. Compared with the control group, 100 and 150 nmol l(-1) insulin increased TG accumulation, acetyl-CoA carboxylase-alpha (ACCalpha) and fatty acid synthase (FAS) activity, and the mRNA levels of sterol regulatory element-binding protein-1 (SREBP-1), FAS and ACCalpha genes. Insulin at 200 nmol l(-1) had an inhibiting effect on TG accumulation and the activity of ACC and FAS, but increased the gene expression of SREBP-1, FAS and ACCalpha. We also found that high glucose (30 mmol l(-1)) increased the TG level, ACC and FAS activity, and the mRNA levels of SREBP-1 and FAS. However, there was no effect of high glucose on ACCalpha mRNA level. In addition, the interaction between insulin and glucose was observed to induce TG accumulation, ACC and FAS activity, and gene expression of SREBP-1, FAS and ACCalpha, and increase SREBP-1 nuclear protein level and binding of nuclear SREBP-1 and the SRE response element of the ACC gene. The result also indicated that the glucose-induced TG accumulation decreased after 96 h when the hepatocytes were cultured with 30 mmol l(-1) glucose. In conclusion, insulin and glucose may affect hepatic lipogenesis by regulating lipogenic gene expression and lipogenic enzyme activity in goose hepatocytes, and SREBP-1 might play an important role in the synergetic activation of lipogenic genes. We propose that the utilization of accumulated TG in hepatocytes is the reason for the reversible phenomenon in goose hepatocellular steatosis.

Emerging roles for the ubiquitin-proteasome system and autophagy in pancreatic beta-cells

Protein degradation in eukaryotic cells is mediated primarily by the ubiquitin-proteasome system and autophagy. Turnover of protein aggregates and other cytoplasmic components, including organelles, is another function attributed to autophagy. The ubiquitin-proteasome system and autophagy are essential for normal cell function but under certain pathological conditions can be overwhelmed, which can lead to adverse effects in cells. In this review we will focus primarily on the insulin-producing pancreatic beta-cell. Pancreatic beta-cells respond to glucose levels by both producing and secreting insulin. The inability of beta-cells to secrete sufficient insulin is a major contributory factor in the development of type 2 diabetes. The aim of this review is to examine some of the crucial roles of the ubiquitin-proteasome system and autophagy in normal pancreatic beta-cell function and how these pathways may become dysfunctional under pathological conditions associated with metabolic syndromes.

Hepatic expression of the SPOT 14 (S14) paralog S14-related (Mid1 interacting protein) is regulated by dietary carbohydrate

The Spot 14 (S14) gene is rapidly up-regulated by signals that induce lipogenesis such as enhanced glucose metabolism and thyroid hormone administration. Previous studies in S14 null mice show that S14 is required for normal lipogenesis in the lactating mammary gland, but not the liver. We speculated that the lack of a hepatic phenotype was due to the expression of a compensatory gene. We recently reported that this gene is likely an S14 paralog that we named S14-Related (S14-R). S14-R is expressed in the liver, but not in the mammary gland. If S14-R compensates for the absence of S14 in the liver, we hypothesized that, like S14, S14-R expression should be glucose responsive. Here, we report that hepatic S14-R mRNA levels increase with high-carbohydrate feeding in mice or within 2 h of treating cultured hepatocytes with elevated glucose. A potential carbohydrate response element (ChoRE) was identified at position -458 of the S14-R promoter. Deletion of or point mutations within the putative S14-R ChoRE led to 50-95% inhibition of the glucose response. Gel-shift analysis revealed that the glucose-activated transcription complex carbohydrate responsive element-binding protein/Max-like protein X (Mlx) binds to the S14-R ChoRE. Finally, S14-R glucose induction is completely blocked when a dominant-negative form of Mlx is overexpressed in primary hepatocytes. In conclusion, our results indicate that the S14-R gene is a glucose-responsive target of carbohydrate responsive element-binding protein/Mlx and suggest that the S14-R protein is a compensatory factor, at least partially responsible for the normal liver lipogenesis observed in the S14 null mouse.

Variations in the G6PC2/ABCB11 genomic region are associated with fasting glucose levels

Identifying the genetic variants that regulate fasting glucose concentrations may further our understanding of the pathogenesis of diabetes. We therefore investigated the association of fasting glucose levels with SNPs in 2 genome-wide scans including a total of 5,088 nondiabetic individuals from Finland and Sardinia. We found a significant association between the SNP rs563694 and fasting glucose concentrations (P = 3.5 x 10(-7)). This association was further investigated in an additional 18,436 nondiabetic individuals of mixed European descent from 7 different studies. The combined P value for association in these follow-up samples was 6.9 x 10(-26), and combining results from all studies resulted in an overall P value for association of 6.4 x 10(-33). Across these studies, fasting glucose concentrations increased 0.01-0.16 mM with each copy of the major allele, accounting for approximately 1% of the total variation in fasting glucose. The rs563694 SNP is located between the genes glucose-6-phosphatase catalytic subunit 2 (G6PC2) and ATP-binding cassette, subfamily B (MDR/TAP), member 11 (ABCB11). Our results in combination with data reported in the literature suggest that G6PC2, a glucose-6-phosphatase almost exclusively expressed in pancreatic islet cells, may underlie variation in fasting glucose, though it is possible that ABCB11, which is expressed primarily in liver, may also contribute to such variation.

The transcription factor COUP-TFII is negatively regulated by insulin and glucose via Foxo1- and ChREBP-controlled pathways

COUP-TFII has an important role in regulating metabolism in vivo. We showed this previously by deleting COUP-TFII from pancreatic beta cells in heterozygous mutant mice, which led to abnormal insulin secretion. Here, we report that COUP-TFII expression is reduced in the pancreas and liver of mice refed with a carbohydrate-rich diet and in the pancreas and liver of hyperinsulinemic and hyperglycemic mice. In pancreatic beta cells, COUP-TFII gene expression is repressed by secreted insulin in response to glucose through Foxo1 signaling. Ex vivo COUP-TFII reduces insulin production and secretion. Our results suggest that beta cell insulin secretion is under the control of an autocrine positive feedback loop by alleviating COUP-TFII repression. In hepatocytes, both insulin, through Foxo1, and high glucose concentrations repress COUP-TFII expression. We demonstrate that this negative glucose effect involves ChREBP expression. We propose that COUP-TFII acts in a coordinate fashion to control insulin secretion and glucose metabolism.

The yeast GID complex, a novel ubiquitin ligase (E3) involved in the regulation of carbohydrate metabolism

Glucose-dependent regulation of carbon metabolism is a subject of intensive studies. We have previously shown that the switch from gluconeogenesis to glycolysis is associated with ubiquitin-proteasome linked elimination of the key enzyme fructose-1,6-bisphosphatase. Seven glucose induced degradation deficient (Gid)-proteins found previously in a genomic screen were shown to form a complex that binds FBPase. One of the subunits, Gid2/Rmd5, contains a degenerated RING finger domain. In an in vitro assay, heterologous expression of GST-Gid2 leads to polyubiquitination of proteins. In addition, we show that a mutation in the degenerated RING domain of Gid2/Rmd5 abolishes fructose-1,6-bisphosphatase polyubiquitination and elimination in vivo. Six Gid proteins are present in gluconeogenic cells. A seventh protein, Gid4/Vid24, occurs upon glucose addition to gluconeogenic cells and is afterwards eliminated. Forcing abnormal expression of Gid4/Vid24 in gluconeogenic cells leads to fructose-1,6-bisphosphatase degradation. This suggests that Gid4/Vid24 initiates fructose-1,6-bisphosphatase polyubiquitination by the Gid complex and its subsequent elimination by the proteasome. We also show that an additional gluconeogenic enzyme, phosphoenolpyruvate carboxykinase, is subject to Gid complex-dependent degradation. Our study uncovers a new type of ubiquitin ligase complex composed of novel subunits involved in carbohydrate metabolism and identifies Gid4/Vid24 as a major regulator of this E3.

Glucose activates ChREBP by increasing its rate of nuclear entry and relieving repression of its transcriptional activity

Carbohydrate response element-binding protein (ChREBP) is a glucose-responsive transcription factor that activates genes involved in de novo lipogenesis in mammals. The current model for glucose activation of ChREBP proposes that increased glucose metabolism triggers a cytoplasmic to nuclear translocation of ChREBP that is critical for activation. However, we find that ChREBP actively shuttles between the cytoplasm and nucleus in both low and high glucose in the glucose-sensitive beta cell-derived line, 832/13. Glucose stimulates a 3-fold increase in the rate of ChREBP nuclear entry, but trapping ChREBP in the nucleus by mutagenesis or with a nuclear export inhibitor does not lead to constitutive activation. In fact, mutational studies targeting the nuclear export signal of ChREBP also identified a distinct function essential for glucose-dependent transcriptional activation. From this, we conclude that an additional event independent of nuclear translocation is required for activation. The N-terminal segment of ChREBP (amino acids 1-298) has previously been shown to repress activity under basal conditions. This segment has five highly conserved regions, Mondo conserved regions 1-5 (MCR1 to -5). Based on activating mutations in MCR2 and MCR5, we propose that these two regions act coordinately to repress ChREBP in low glucose. In addition, other mutations in MCR2 and mutations in MCR3 were found to prevent glucose activation. Hence, we conclude that both relief of repression and adoption of an activating form are required for ChREBP activation.

Increased glucose availability activates chicken thymocyte metabolism and survival

Glucose metabolism in mammalian thymocytes is coupled to their development and selection in the thymus. In chickens, thymocytes develop in a low glucose concentration in ovo and a high glucose concentration posthatch. To determine the effect of glucose concentration on thymocyte glucose metabolism, embryonic thymic lobes were cultured in media containing varying glucose concentrations and thymocytes were isolated for analysis. Glucose transporter-1 (Glut-1) and Glut-3 mRNA abundance was at least 2-fold higher in thymocytes incubated with 10 and 20 mmol/L glucose than in those incubated with 0 mmol/L glucose (P < 0.05) and glucose uptake was greatest in thymocytes incubated with 20 mmol/L glucose (P < 0.05). Thymocytes incubated with 0 and 20 mmol/L glucose had 185% greater hexokinase activity than in those incubated with 10 mmol/L glucose (P < 0.05). Consequently, thymocyte glucose utilization was dependent upon glucose availability. Increased glucose utilization resulted in a higher mitochondrial membrane potential in thymocytes incubated with 15 mmol/L glucose than in those incubated with 5 mmol/L glucose (P < 0.05), indicating enhanced thymocyte energy status in response to high glucose concentrations. Additionally, thymocyte viability was lower in thymocytes incubated with 5 mmol/L glucose than in those incubated with 10 and 15 mmol/L glucose (P < 0.05) and rates of thymocyte apoptosis were higher in thymocytes incubated with 5 mmol/L glucose than in those incubated with 15 mmol/L glucose (P < 0.05). Glucose availability induced metabolic changes in thymocytes that altered their energy status and survival. Consequently, these data indicate that glucose availability may influence the development of naïve T cells in the chicken thymus.

Identification and function of phosphorylation in the glucose-regulated transcription factor ChREBP

In the liver, induction of genes encoding enzymes involved in de novo lipogenesis occurs in response to increased glucose metabolism. ChREBP (carbohydrate-response-element-binding protein) is a basic helix-loop-helix/leucine zipper transcription factor that regulates expression of these genes. To evaluate the potential role of ChREBP phosphorylation in its regulation, we used MS to identify modified residues. In the present paper, we report the detection of multiple phosphorylation sites of ChREBP expressed in hepatocytes, several of which are only observed under high-glucose conditions. Mutation of each of these serine/threonine residues of ChREBP did not alter its ability to respond to glucose. However, mutation of five N-terminal phosphoacceptor sites resulted in a major decrease in activity under high-glucose conditions. These phosphorylated residues are located within a region of ChREBP (amino acids 1-197) that is critical for glucose regulation. Mutation of Ser(56) within this region to an aspartate residue resulted in increased nuclear accumulation and activity under high-glucose conditions. Together, these data suggest that ChREBP activity is regulated by complex multisite phosphorylation patterns involving its N-terminal regulatory region.

Characterization and regulation of monocarboxylate cotransporters Slc16a7 and Slc16a3 in preimplantation mouse embryos

Concurrent with compaction, preimplantation mouse embryos switch from the high pyruvate consumption that prevailed during cleavage stages to glucose consumption against a constant background of pyruvate uptake. However, zygotes exposed to and subsequently deprived of glucose can form blastocysts by increasing pyruvate uptake. This metabolic switch requires cleavage-stage exposure to glucose and is one aspect of metabolic differentiation that normally occurs in vivo. Monocarboxylates, such as pyruvate and lactate, are transported across membranes via the SLC16 family of H(+)-monocarboxylate cotransporter (MCT) proteins. Thus, the increase in pyruvate uptake in embryos developing without glucose must involve changes in activity and localization of MCT. In mouse embryos, continued expression of Slc16a1 (MCT1) requires glucose supply. Messenger RNA for Slc17a7 (MCT2) and Slc16a3 (MCT4) has been detected in mouse preimplantation embryos; however, protein function, localization, and regulation of expression at the basis of these net pyruvate uptake changes remain unclear. The expression and localization of SLC16A7 and SLC16A3 have therefore been examined to clarify their respective roles in embryos derived from the reproductive tract and cultured under varied conditions. SLC16A3 appears localized to the plasma membrane until the morula stage and also maintains a nuclear distribution throughout preimplantation development. However, continued Slc16a3 mRNA expression is dependent on prior exposure to glucose. SLC16A7 localizes to apical cortical regions with punctate, vesicular expression throughout blastomeres, partially colocalizing in peroxisomes with peroxisomal catalase (CAT). In contrast to SLC16A3 and SLC16A1, SLC16A7 and CAT demonstrate upregulation in the absence of glucose. These striking differences between the two isoforms in expression localization and regulation suggest unique roles for each in monocarboxylate transport and pH regulation during preimplantation development, and implicate peroxisomal SLC16A7 as an important redox regulator in the absence of glucose.

Neonatal hyperglycaemia and abnormal development of the pancreas

Transient and permanent neonatal diabetes mellitus (TNDM and PNDM) are rare conditions occurring in around 1 per 300,000 live births. In TNDM, growth-retarded infants develop diabetes in the first few weeks of life, only to go into remission after a few months with possible relapse to permanent diabetes usually around adolescence or in adulthood. In PNDM, insulin secretory failure occurs in the late fetal or early postnatal period. The very recently elucidated mutations in KCNJ11 and ABCC8 genes, encoding the Kir6.2 and SUR1 subunits of the pancreatic K(ATP) channel involved in regulation of insulin secretion, account for a third to a half of the PNDM cases. Molecular analysis of chromosome 6 anomalies and the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1 provides a tool for distinguishing transient from permanent neonatal diabetes mellitus in the neonatal period. Some patients (those with mutations in KCNJ11 and ABCC8) may be transferred from insulin therapy to sulphonylureas.

Sugar sensing by enterocytes combines polarity, membrane bound detectors and sugar metabolism

Sugar consumption and subsequent sugar metabolism are known to regulate the expression of genes involved in intestinal sugar absorption and delivery. Here we investigate the hypothesis that sugar-sensing detectors in membranes facing the intestinal lumen or the bloodstream can also modulate intestinal sugar absorption. We used wild-type and GLUT2-null mice, to show that dietary sugars stimulate the expression of sucrase-isomaltase (SI) and L-pyruvate kinase (L-PK) by GLUT2-dependent mechanisms, whereas the expression of GLUT5 and SGLT1, did not rely on the presence of GLUT2. By providing sugar metabolites, sugar transporters, including GLUT2, fuelled a sensing pathway. In Caco2/TC7 enterocytes, we could disconnect the sensing triggered by detector from that produced by metabolism, and found that GLUT2 generated a metabolism-independent pathway to stimulate the expression of SI and L-PK. In cultured enterocytes, both apical and basolateral fructose could increase the expression of GLUT5, conversely, basolateral sugar administration could stimulate the expression of GLUT2. Finally, we located the sweet-taste receptors T1R3 and T1R2 in plasma membranes, and we measured their cognate G alpha Gustducin mRNA levels. Furthermore, we showed that a T1R3 inhibitor altered the fructose-induced expression of SGLT1, GLUT5, and L-PK. Intestinal gene expression is thus controlled by a combination of at least three sugar-signaling pathways triggered by sugar metabolites and membrane sugar receptors that, according to membrane location, determine sugar-sensing polarity. This provides a rationale for how intestine adapts sugar delivery to blood and dietary sugar provision.

Loss of sugar detection by GLUT2 affects glucose homeostasis in mice

Background

Mammals must sense the amount of sugar available to them and respond appropriately. For many years attention has focused on intracellular glucose sensing derived from glucose metabolism. Here, we studied the detection of extracellular glucose concentrations in vivo by invalidating the transduction pathway downstream from the transporter-detector GLUT2 and measured the physiological impact of this pathway.

Methodology/Principal Findings

We produced mice that ubiquitously express the largest cytoplasmic loop of GLUT2, blocking glucose-mediated gene expression in vitro without affecting glucose metabolism. Impairment of GLUT2-mediated sugar detection transiently protected transgenic mice against starvation and streptozotocin-induced diabetes, suggesting that both low- and high-glucose concentrations were not detected. Transgenic mice favored lipid oxidation, and oral glucose was slowly cleared from blood due to low insulin production, despite massive urinary glucose excretion. Kidney adaptation was characterized by a lower rate of glucose reabsorption, whereas pancreatic adaptation was associated with a larger number of small islets.

Conclusions/Significance

Molecular invalidation of sugar sensing in GLUT2-loop transgenic mice changed multiple aspects of glucose homeostasis, highlighting by a top-down approach, the role of membrane glucose receptors as potential therapeutic targets.

ChREBP, a transcriptional regulator of glucose and lipid metabolism

Dysregulations in hepatic lipid synthesis are often associated with obesity and type 2 diabetes, and therefore a perfect understanding of the regulation of this metabolic pathway appears essential to identify potential therapeutic targets. Recently, the transcription factor ChREBP (carbohydrate-responsive element-binding protein) has emerged as a major mediator of glucose action on lipogenic gene expression and as a key determinant of lipid synthesis in vivo. Indeed, liver-specific inhibition of ChREBP improves hepatic steatosis and insulin resistance in obese ob/ob mice. Since ChREBP cellular localization is a determinant of its functional activity, a better knowledge of the mechanisms involved in regulating its nucleo-cytoplasmic shuttling and/or its post-translational activation is crucial in both physiology and physiopathology. Here, we review some of the studies that have begun to elucidate the regulation and function of this key transcription factor in liver.

Proposed regulation of gene expression by glucose in rodent heart

Background

During pressure overload-induced hypertrophy, unloading-induced atrophy, and diabetes mellitus, the heart induces ‘fetal’ genes (e.g. myosin heavy chain β; mhcβ).

Hypothesis

We propose that altered glucose homeostasis within the cardiomyocyte acts as a central mechanism for the regulation of gene expression in response to environmental stresses. The evidence is as follows.

Methods and Results

Forced glucose uptake both ex vivo and in vivo results in mhc isoform switching. Restricting dietary glucose prevents mhc isoform switching in hearts of both GLUT1-Tg mice and rats subjected to pressure overload-induced hypertrophy. Thus, glucose availability correlates with mhc isoform switching under all conditions investigated. A potential mechanism by which glucose affects gene expression is through O-linked glycosylation of specific transcription factors. Glutamine:fructose-6-phosphate amidotransferase (GFAT) catalyzes the flux generating step in UDP-N-acetylglucosamine biosynthesis, the rate determining metabolite in protein glycosylation. Ascending aortic constriction increased intracellular levels of UDP-N-acetylglucosamine, and the expression of gfat2, but not gfat1, in the rat heart.

Conclusions

Collectively, the results strongly suggest glucose-regulated gene expression in the heart, and the involvement of glucose metabolites in isoform switching of sarcomeric proteins characteristic for the fetal gene program.

[Neonatal diabetes: a disease linked to multiple mechanisms]

Transient (TNDM) and Permanent (PNDM) Neonatal Diabetes Mellitus are rare conditions occurring in about 1: 300,000 live births. In TNDM growth retarded infants develop diabetes in the first few weeks of life only to go into remission in a few months with possible relapse to a permanent diabetes state usually around adolescence or as adults. We believe that pancreatic dysfunction in this condition is maintained throughout life with relapse initiated at times of metabolic stress such as puberty or pregnancy. In PNDM, insulin secretory failure occurs in the late fetal or early postnatal period. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular levels. Among those, the very recently elucidated mutations in KCNJ11 and ABCC8 gene, encoding the Kir6.2 and SUR1 subunit of the pancreatic K(ATP) channel involved in regulation of insulin secretion accounts for one third to a half of the PNDM cases. Patients with TNDM are more likely to have intrauterine growth retardation and less likely to develop ketoacidosis than patients with PNDM. In TNDM, patients are younger at the diagnosis of diabetes and have lower initial insulin requirements. Considerable overlap occurs between the two groups, so that TNDM cannot be distinguished from PNDM based on clinical features. Very early onset diabetes mellitus seems to be unrelated to autoimmunity in most instances. Recurrent diabetes is common in patients with "transient" neonatal diabetes mellitus and, consequently, prolonged follow-up is imperative. Molecular analysis of chromosome 6 anomalies, the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1 provide a tool to identify transient from permanent neonatal diabetes mellitus in the neonatal period. This analysis also has potentially important therapeutic consequences leading to transfer some patients, those with mutations in KCNJ11 and ABCC8 from insulin therapy to sulfonylureas. Realizing how difficult it is to take care of a child of this age with diabetes mellitus should prompt clinicians to transfer these children to specialized centers. Insulin therapy and high caloric intake are the basis of the treatment. Insulin pump may offer an interesting therapeutic tool in this age group in experienced hands.

Sp1 expression is disrupted in schizophrenia; a possible mechanism for the abnormal expression of mitochondrial complex I genes, NDUFV1 and NDUFV2

BACKGROUND

The prevailing hypothesis regards schizophrenia as a polygenic disease, in which multiple genes combine with each other and with environmental stimuli to produce the variance of its clinical symptoms. We investigated whether the ubiquitous transcription factor Sp1 is abnormally expressed in schizophrenia, and consequently can affect the expression of genes implicated in this disorder.

METHODOLOGY/PRINCIPAL FINDINGS

mRNA of Sp1 and of mitochondrial complex I subunits (NDUFV1, NDUFV2) was analyzed in three postmortem brain regions obtained from the Stanley Foundation Brain Collection, and in lymphocytes of schizophrenic patients and controls. Sp1 role in the transcription of these genes was studied as well. Sp1 was abnormally expressed in schizophrenia in both brain and periphery. Its mRNA alteration pattern paralleled that of NDUFV1 and NDUFV2, decreasing in the prefrontal cortex and the striatum, while increasing in the parieto-occipital cortex and in lymphocytes of schizophrenic patients as compared with controls. Moreover, a high and significant correlation between these genes existed in normal subjects, but was distorted in patients. Sp1 role in the regulation of complex I subunits, was demonstrated by the ability of the Sp1/DNA binding inhibitor, mithramycin, to inhibit the transcription of NDUFV1 and NDUFV2, in neuroblastoma cells. In addition, Sp1 activated NDUFV2 promoter by binding to its three GC-boxes. Both activation and binding were inhibited by mithramycin.

CONCLUSIONS/SIGNIFICANCE

These findings suggest that abnormality in Sp1, which can be the main activator/repressor or act in combination with additional transcription factors and is subjected to environmental stimuli, can contribute to the polygenic and clinically heterogeneous nature of schizophrenia.

c-Myc and ChREBP regulate glucose-mediated expression of the L-type pyruvate kinase gene in INS-1-derived 832/13 cells

Increased glucose flux generates metabolic signals that control transcriptional programs through poorly understood mechanisms. Previously, we demonstrated a necessity in hepatocytes for c-Myc in the regulation of a prototypical glucose-responsive gene, L-type pyruvate kinase (L-PK) (Collier JJ, Doan TT, Daniels MC, Schurr JR, Kolls JK, Scott DK. J Biol Chem 278: 6588-6595, 2003). Pancreatic beta-cells have many features in common with hepatocytes with respect to glucose-regulated gene expression, and in the present study we determined whether c-Myc was required for the L-PK glucose response in insulin-secreting (INS-1)-derived 832/13 cells. Glucose increased c-Myc abundance and association with its heterodimer partner, Max. Manipulations that prevented the formation of a functional c-Myc/Max heterodimer reduced the expression of the L-PK gene. In addition, glucose augmented the binding of carbohydrate response element binding protein (ChREBP), c-Myc, and Max to the promoter of the L-PK gene in situ. The transactivation of ChREBP, but not of c-Myc, was dependent on high glucose concentrations in the contexts of either the L-PK promoter or a heterologous promoter. The glucose-mediated transactivation of ChREBP was independent of mutations that alter phosphorylation sites thought to regulate the cellular location of ChREBP. We conclude that maximal glucose-induced expression of the L-PK gene in INS-1-derived 832/13 cells involves increased c-Myc abundance, recruitment of c-Myc, Max, and ChREBP to the promoter, and a glucose-stimulated increase in ChREBP transactivation.

Aryl hydrocarbon receptor nuclear translocator and upstream stimulatory factor regulate Cytochrome P450 2a5 transcription through a common E-box site

The aryl hydrocarbon receptor nuclear translocator (ARNT) belongs to the basic-helix-loop-helix (bHLH) transcription factors and regulates several genes as heterodimers with other bHLH proteins. ARNT is also able to homodimerize, but no mammalian target genes for the homodimer have been shown. We identified a palindromic E-box element in the 5' regulatory region of the murine cytochrome P450 (Cyp) 2a5 gene that was found to be important for Cyp2a5 transcription in primary hepatocytes, and was found by chromatin immunoprecipitation assays to interact with ARNT. Electrophoretic mobility-shift assay experiments with in vitro translated ARNT showed binding without heterodimerization partner, indicating binding as a homodimer. Transfection studies in wild-type and ARNT-deficient Hepa-1 cells revealed that ARNT expression is necessary for full activity of the Cyp2a5 promoter. In the liver-specific Arnt-null mouse line, the level of hepatic CYP2A5 mRNA was decreased significantly. Co-transfection studies with an ARNT expression vector lacking the transactivation domain (TAD) demonstrated that the ARNT TAD is needed for Cyp2a5 activation, which suggests that ARNT transactivates Cyp2a5 as a homodimer. In primary hepatocytes, the mRNA levels of both CYP2A5 and ARNT splice variant 1 were increased during cultivation. Upstream stimulatory factors 1 and 2a were also able to bind to the same E-box as ARNT, indicating that there may be competition for DNA binding between these factors. Indeed, the upstream stimulatory factors activated the Cyp2a5 promoter through the E-box only in the presence of hepatocyte nuclear factor-4alpha, while ARNT transactivation was independent of hepatocyte nuclear factor-4alpha. In conclusion, these results indicate that ARNT controls Cyp2a5 transcription and thus, for the first time, suggest active involvement of the ARNT homodimer in mammalian gene regulation.

Glucose is necessary for embryonic pancreatic endocrine cell differentiation

Mature pancreatic cells develop during embryonic life from endodermal progenitors, and this developmental process depends on activation of a hierarchy of transcription factors. While information is available on mesodermal signals controlling pancreas development, little is known about environmental factors, such as the levels of nutrients including glucose, that may control this process. Here, we studied the effects of glucose on pancreatic cells development. We used an in vitro model where both endocrine and acinar cells develop from early pancreatic and duodenal homeobox-1 (PDX1)-positive embryonic pancreatic progenitors. We first showed that glucose does not have a major effect on global pancreatic cell proliferation, survival, and acinar cell development. On the other hand, glucose controlled both alpha and beta cell development. Specifically, the surface occupied by insulin-positive cells was 20-fold higher in pancreases cultured in presence than in absence of glucose, and this effect was dose-dependent over the range 0.5-10 mm. Glucose did not appear to control beta cell development by activating the proliferation of early progenitors or beta cells themselves but instead tightly regulated cell differentiation. Thus, glucose did not modify the pattern of expression of Neurogenin3, the earliest marker of endocrine progenitor cells, but was necessary for the expression of the transcription factor NeuroD, a direct target of Neurogenin3 known to be important for proper pancreatic endocrine cell development. We conclude that glucose interferes with the pancreatic endocrine cells development by regulating the transition between Ngn3 and upstream NeuroD.

Neonatal diabetes mellitus: a disease linked to multiple mechanisms

Transient (TNDM) and Permanent (PNDM) Neonatal Diabetes Mellitus are rare conditions occurring in 1:300,000-400,000 live births. TNDM infants develop diabetes in the first few weeks of life but go into remission in a few months, with possible relapse to a permanent diabetes state usually around adolescence or as adults. The pancreatic dysfunction in this condition may be maintained throughout life, with relapse initiated at times of metabolic stress such as puberty or pregnancy. In PNDM, insulin secretory failure occurs in the late fetal or early post-natal period and does not go into remission. Patients with TNDM are more likely to have intrauterine growth retardation and less likely to develop ketoacidosis than patients with PNDM. In TNDM, patients are younger at the diagnosis of diabetes and have lower initial insulin requirements. Considerable overlap occurs between the two groups, so that TNDM cannot be distinguished from PNDM based on clinical features. Very early onset diabetes mellitus seems to be unrelated to autoimmunity in most instances. A number of conditions are associated with PNDM, some of which have been elucidated at the molecular level. Among these, the very recently elucidated mutations in the KCNJ11 and ABCC8 genes, encoding the Kir6.2 and SUR1 subunit of the pancreatic KATP channel involved in regulation of insulin secretion, account for one third to half of the PNDM cases. Molecular analysis of chromosome 6 anomalies (found in more than 60% in TNDM), and the KCNJ11 and ABCC8 genes encoding Kir6.2 and SUR1, provides a tool to identify TNDM from PNDM in the neonatal period. This analysis also has potentially important therapeutic consequences leading to transfer some patients, those with mutations in KCNJ11 and ABCC8 genes, from insulin therapy to sulfonylureas. Recurrent diabetes is common in patients with "transient" neonatal diabetes mellitus and, consequently, prolonged follow-up is imperative. Realizing how difficult it is to take care of a child of this age with diabetes mellitus should prompt clinicians to transfer these children to specialized centers. Insulin therapy and high caloric intake are the basis of the treatment. Insulin pump may offer an interesting therapeutic tool in this age group in experienced hands.

Neonatal diabetes mellitus: A rare but important diagnosis in the critically ill infant

Diabetes mellitus is a heterogeneous disorder that may occur at any age. Neonatal diabetes mellitus, defined as hyperglycaemia presenting within the first 6 weeks of life in term infants, is a rare disorder that may result in permanent or transient diabetes mellitus. Although reported in paediatric diabetes literature, there are no reports of this condition in emergency medicine journals and these children may present to emergency departments with a picture mimicking sepsis. We report the case of a 5-week-old infant with diabetes mellitus who presented with diabetic ketoacidosis and review the literature surrounding this rare condition.

Identification of a protein hydrolysate responsive G protein-coupled receptor in enterocytes

G protein-coupled receptors (GPCRs) have the potential to play a role as molecular sensors responsive to luminal dietary contents. Although such a role for GPCRs has been implicated in the intestinal response to protein hydrolysate, no GPCR directly involved in this process has been previously identified. In the present study, for the first time, we identified GPR93 expression in enterocytes and demonstrated its activation in these cells by protein hydrolysate with EC50 of 10.6 mg/ml as determined by the induction of intracellular free Ca2+. In enterocytes, GPR93 was synergistically activated by protein hydrolysate in combination with an agonist, oleoyl-l-alpha-lysophosphatidic acid (LPA), which activated the receptor in these enterocytes with EC50 of 7.9 nM. The increased intracellular Ca2+ by GPR93 activation was observed without the addition of a promiscuous Galpha protein and was pertussis toxin sensitive, which suggests Galpha(q)- and Galpha(i)-mediated pathways. Activated GPR93 also induced pertussis toxin-sensitive ERK1/2 phosphorylation. Both nuclear factor of activated T cells and 12-O-tetradecanoylphorbol 13-acetate responsive elements reporter activities were induced by protein hydrolysate in cells exogenously expressing GPR93. The peptidomimetic cefaclor by itself did not activate GPR93 but potentiated the protein hydrolysate response and further amplified the synergistic enhancement of GPR93 activation by protein hydrolysate and LPA. These data suggest that, physiologically, the composition of stimuli might determine GPR93 activity or its sensitivity toward a given activator and suggest a new mechanism of the regulation of mucosal cell proliferation and differentiation and hormonal secretion by dietary products in the lumen.

A critical role for the loop region of the basic helix-loop-helix/leucine zipper protein Mlx in DNA binding and glucose-regulated transcription

The carbohydrate response element (ChoRE) is a cis-acting sequence found in the promoters of genes induced transcriptionally by glucose. The ChoRE is composed of two E box-like motifs that are separated by 5 bp and is recognized by two basic helix–loop–helix/leucine zipper (bHLH/LZ) proteins, ChREBP and Mlx, which heterodimerize to bind DNA. In this study, we demonstrate that two ChREBP/Mlx heterodimers interact to stabilize binding to the tandem E box-like motifs in the ChoRE. Based on a model structure that we generated of ChREBP/Mlx bound to the ChoRE, we hypothesized that intermolecular interactions between residues within the Mlx loop regions of adjacent heterodimers are responsible for stabilizing the complex. We tested this hypothesis by preparing Mlx variants in which the loop region was replaced with that of another family member or mutated at several key residues. These Mlx variants retained their ability to bind to a single perfect E-box motif as a heterodimer with ChREBP, but no longer bound to the ChoRE nor supported glucose responsive activity. In summary, our results support a model in which the loop regions of Mlx play an important functional role in mediating the coordinate binding of ChREBP/Mlx heterodimers to the ChoRE.

Metabolism-independent sugar effects on gene transcription: the role of 3-O-methylglucose

Glucose effects on cellular functions such as gene expression require, in general, glucose metabolism at least to glucose-6-phosphate (G-6-P). However, the example of thioredoxin-interacting protein (TXNIP), a glucose-regulated gene involved in the cellular redox state and pancreatic beta cell apoptosis, demonstrates that this rule may not always apply. We found that aside form glucose, the nonmetabolizable sugars 2-deoxyglucose, which is still converted to G-6-P as well as 3-O-methylglucose (3-MG), which cannot be phosphorylated by glucokinase, stimulate TXNIP expression. In contrast, incubation of INS-1 beta cells with equimolar amounts (25 mM) of l-glucose or mannitol had no effect on TXNIP expression as measured by real-time RT-PCR, eliminating the possibility of an osmotic effect. Also, glucose uptake into the cell is critical because phloretin, an inhibitor of glucose transporter 2, blunted the glucose effects. Moreover, the 3-MG effect was not restricted to a cell line and was observed in 293 cells and primary human islets. Incubation of INS-1 cells with 30mM mannoheptulose, an inhibitor of glucose metabolism, blunted all glucose-induced gene expression but left the 3-MG effects unaltered. Using transient transfection studies and deletion constructs of the human TXNIP promoter, we found that the effects of glucose and 3-MG were dependent on the same region of the TXNIP promoter containing an E-box repeat carbohydrate response element (ChoRE). Thus, these findings provide the first evidence for regulation of gene expression by 3-MG, which is independent of glucose metabolism and suggest that glucose and 3-MG regulate transcription by two distinct pathways converging at a common ChoRE.

Deficiency of carbohydrate-activated transcription factor ChREBP prevents obesity and improves plasma glucose control in leptin-deficient (ob/ob) mice

The transcription factor carbohydrate response element-binding protein (ChREBP) mediates insulin-independent, glucose-stimulated gene expression of multiple liver enzymes responsible for converting excess carbohydrate to fatty acids for long-term storage. To investigate ChREBP's role in the development of obesity and obesity-associated metabolic dysregulation, ChREBP-deficient mice were intercrossed with ob/ob mice. As a result of deficient leptin expression, ob/ob mice overeat, become obese and resistant to insulin, and display marked elevations in hepatic lipogenesis, gluconeogenesis, and plasma glucose and triglycerides. mRNA expression of all hepatic lipogenic enzymes was significantly lower in ob/ob-ChREBP-/- than in ob/ob mice, resulting in decreased hepatic fatty acid synthesis and normalization of plasma free fatty acid and triglyceride levels. Overall weight gain in addition to adiposity was reduced in the doubly deficient mice. The former was largely attributable to decreased food intake and may result from decreased hypothalamic expression of the appetite-stimulating neuropeptide agouti-related protein. mRNA expression and activity of gluconeogenic enzymes also was lower in the doubly deficient mice, contributing to significantly lower blood glucose levels. The results of this study suggest that inactivation of ChREBP expression not only reduces fat synthesis and obesity in ob/ob mice but also results in improved glucose tolerance and appetite control.

Carbohydrate response element binding protein, ChREBP, a transcription factor coupling hepatic glucose utilization and lipid synthesis

The ability of an organism to sense and store nutrients is vital to survival. The liver is the major organ responsible for converting excess dietary carbohydrate to lipid for storage. An elegant molecular pathway has evolved that allows increased glucose flux into hepatocytes to generate a signaling molecule, xylulose 5-phosphate, that triggers rapid changes in glycolytic enzyme activities and nuclear import of a transcription factor, ChREBP, which coordinates the transcriptional regulation of enzymes that channel the glycolytic end-products into lipogenesis. Further understanding of this metabolic cascade should provide insights on conditions such as fatty liver, obesity, and the metabolic syndrome.

Signalling mechanisms linking hepatic glucose and lipid metabolism

Fatty liver and hepatic triglyceride accumulation are strongly associated with obesity, insulin resistance and type 2 diabetes, and are subject to nutritional influences. Hepatic regulation of glucose and lipid homeostasis is influenced by a complex system of hormones, hormonally regulated signalling pathways and transcription factors. Recently, considerable progress has been made in elucidating molecular pathways and potential factors that are affected in insulin-resistant states. In this review we discuss some of the key factors that are involved in both the regulation of glucose and lipid metabolism in the liver. Understanding the molecular network that links hepatic lipid accumulation and impaired glucose metabolism may provide targets for dietary or pharmacological interventions.

Hexose transporters GLUT1 and GLUT3 are colocalized with hexokinase I in caveolae microdomains of rat spermatogenic cells

Postmeiotic spermatogenic cells, but not meiotic spermatogenic cells respond differentially with glucose-induced changes in [Ca2+]i indicating a differential transport of glucose via facilitative hexose transporters (GLUTs) specifically distributed in the plasma membrane. Several studies have indicated that plasma membrane in mammalian cells is not homogeneously organized, but contains specific microdomains known as detergent-resistant membrane domains (DRMDs), lipid rafts or caveolae. The association of these domains and GLUTs isoforms has not been characterized in spermatogenic cells. We analyzed the expression and function of GLUT1 and GLUT3 in isolated spermatocytes and spermatids. The results showed that spermatogenic cells express both glucose transporters, with spermatids exhibiting a higher affinity glucose transport system. In addition, spermatogenic cells express caveolin-1, and glucose transporters colocalize with caveolin-1 in caveolin-enriched membrane fractions. Experiments in which the integrity of caveolae was disrupted by pretreatment with methyl-beta-cyclodextrin, indicated that the involvement of cholesterol-enriched plasma membrane microdomains were involved in the localization of GLUTs and uptake of 2-deoxyglucose. We also observed cofractionation of GLUT3 and caveolin-1 in low-buoyant density membranes together with their shift to higher densities after methyl-beta-cyclodextrin treatment. GLUT1 was found in all fractions isolated. Immunofluorescent studies indicated that caveolin-1, GLUT1, and hexokinase I colocalize in spermatocytes while caveolin-1, GLUT3, and hexokinase I colocalize in spermatids. These findings suggest the presence of hexose transporters in DRMDs, and further support a role for intact caveolae or cholesterol-enriched membrane microdomains in relation to glucose uptake and glucose phosphorylation. The results would also explain the different glucose-induced changes in [Ca2+]i in both cells.

Transcriptional regulation of metabolism

Our understanding of metabolism is undergoing a dramatic shift. Indeed, the efforts made towards elucidating the mechanisms controlling the major regulatory pathways are now being rewarded. At the molecular level, the crucial role of transcription factors is particularly well-illustrated by the link between alterations of their functions and the occurrence of major metabolic diseases. In addition, the possibility of manipulating the ligand-dependent activity of some of these transcription factors makes them attractive as therapeutic targets. The aim of this review is to summarize recent knowledge on the transcriptional control of metabolic homeostasis. We first review data on the transcriptional regulation of the intermediary metabolism, i.e., glucose, amino acid, lipid, and cholesterol metabolism. Then, we analyze how transcription factors integrate signals from various pathways to ensure homeostasis. One example of this coordination is the daily adaptation to the circadian fasting and feeding rhythm. This section also discusses the dysregulations causing the metabolic syndrome, which reveals the intricate nature of glucose and lipid metabolism and the role of the transcription factor PPARgamma in orchestrating this association. Finally, we discuss the molecular mechanisms underlying metabolic regulations, which provide new opportunities for treating complex metabolic disorders.