Requirement of glucose metabolism for regulation of glucose transporter type 2 (GLUT2) gene expression in liver.

Previous studies have shown that glucose increases the glucose transporter (GLUT2) mRNA expression in the liver in vivo and in vitro. Here we report an analysis of the effects of glucose metabolism on GLUT2 gene expression. GLUT2 mRNA accumulation by glucose was not due to stabilization of its transcript but rather was a direct effect on gene transcription. A proximal fragment of the 5' regulatory region of the mouse GLUT2 gene linked to a reporter gene was transiently transfected into liver GLUT2-expressing cells. Glucose stimulated reporter gene expression in these cells, suggesting that glucose-responsive elements were included within the proximal region of the promoter. A dose-dependent effect of glucose on GLUT2 expression was observed over 10 mM glucose irrespective of the hexokinase isozyme (glucokinase K(m) 16 mM; hexokinase I K(m) 0.01 mM) present in the cell type used. This suggests that the correlation between extracellular glucose and GLUT2 mRNA concentrations is simply a reflection of an activation of glucose metabolism. The mediators and the mechanism responsible for this response remain to be determined. In conclusion, glucose metabolism is required for the proper induction of the GLUT2 gene in the liver and this effect is transcriptionally regulated.

Deep thiopental anesthesia alters steady-state glucose homeostasis but not the neurochemical profile of rat cortex.

Barbiturates are regularly used as an anesthetic for animal experimentation and clinical procedures and are frequently provided with solubilizing compounds, such as ethanol and propylene glycol, which have been reported to affect brain function and, in the case of (1)H NMR experiments, originate undesired resonances in spectra affecting the quantification. As an alternative, thiopental can be administrated without any solubilizing agents. The aim of the study was to investigate the effect of deep thiopental anesthesia on the neurochemical profile consisting of 19 metabolites and on glucose transport kinetics in vivo in rat cortex compared with alpha-chloralose using localized (1)H NMR spectroscopy. Thiopental was devoid of effects on the neurochemical profile, except for the elevated glucose at a given plasma glucose level resulting from thiopental-induced depression of glucose consumption at isoelectrical condition. Over the entire range of plasma glucose levels, steady-state glucose concentrations were increased on average by 48% +/- 8%, implying that an effect of deep thiopental anesthesia on the transport rate relative to cerebral glucose consumption ratio was increased by 47% +/- 8% compared with light alpha-chloralose-anesthetized rats. We conclude that the thiopental-induced isoelectrical condition in rat cortex significantly affected glucose contents by depressing brain metabolism, which remained substantial at isoelectricity.

Regulation of glucagon secretion by glucose transporter type 2 (glut2) and astrocyte-dependent glucose sensors.

Ripglut1;glut2-/- mice have no endogenous glucose transporter type 2 (glut2) gene expression but rescue glucose-regulated insulin secretion. Control of glucagon plasma levels is, however, abnormal, with fed hyperglucagonemia and insensitivity to physiological hypo- or hyperglycemia, indicating that GLUT2-dependent sensors control glucagon secretion. Here, we evaluated whether these sensors were located centrally and whether GLUT2 was expressed in glial cells or in neurons. We showed that ripglut1;glut2-/- mice failed to increase plasma glucagon levels following glucoprivation induced either by i.p. or intracerebroventricular 2-deoxy-D-glucose injections. This was accompanied by failure of 2-deoxy-D-glucose injections to activate c-Fos-like immunoreactivity in the nucleus of the tractus solitarius and the dorsal motor nucleus of the vagus. When glut2 was expressed by transgenesis in glial cells but not in neurons of ripglut1;glut2-/- mice, stimulated glucagon secretion was restored as was c-Fos-like immunoreactive labeling in the brainstem. When ripglut1;glut2-/- mice were backcrossed into the C57BL/6 genetic background, fed plasma glucagon levels were also elevated due to abnormal autonomic input to the alpha cells; glucagon secretion was, however, stimulated by hypoglycemic stimuli to levels similar to those in control mice. These studies identify the existence of central glucose sensors requiring glut2 expression in glial cells and therefore functional coupling between glial cells and neurons. These sensors may be activated at different glycemic levels depending on the genetic background.

Activation of a HIF1alpha-PPARgamma axis underlies the integration of glycolytic and lipid anabolic pathways in pathologic cardiac hypertrophy.

Development of cardiac hypertrophy and progression to heart failure entails profound changes in myocardial metabolism, characterized by a switch from fatty acid utilization to glycolysis and lipid accumulation. We report that hypoxia-inducible factor (HIF)1alpha and PPARgamma, key mediators of glycolysis and lipid anabolism, respectively, are jointly upregulated in hypertrophic cardiomyopathy and cooperate to mediate key changes in cardiac metabolism. In response to pathologic stress, HIF1alpha activates glycolytic genes and PPARgamma, whose product, in turn, activates fatty acid uptake and glycerolipid biosynthesis genes. These changes result in increased glycolytic flux and glucose-to-lipid conversion via the glycerol-3-phosphate pathway, apoptosis, and contractile dysfunction. Ventricular deletion of Hif1alpha in mice prevents hypertrophy-induced PPARgamma activation, the consequent metabolic reprogramming, and contractile dysfunction. We propose a model in which activation of the HIF1alpha-PPARgamma axis by pathologic stress underlies key changes in cell metabolism that are characteristic of and contribute to common forms of heart disease.

Expression of an uncleavable N-terminal RasGAP fragment in insulin-secreting cells increases their resistance toward apoptotic stimuli without affecting their glucose-induced insulin secretion.

Apoptosis of pancreatic beta cells is implicated in the onset of type 1 and type 2 diabetes. Consequently, strategies aimed at increasing the resistance of beta cells toward apoptosis could be beneficial in the treatment of diabetes. RasGAP, a regulator of Ras and Rho GTPases, is an atypical caspase substrate, since it inhibits, rather than favors, apoptosis when it is partially cleaved by caspase-3 at position 455. The antiapoptotic signal generated by the partial processing of RasGAP is mediated by the N-terminal fragment (fragment N) in a Ras-phosphatidylinositol 3-kinase-Akt-dependent, but NF-kappaB-independent, manner. Further cleavage of fragment N at position 157 abrogates its antiapoptotic properties. Here we demonstrate that an uncleavable form of fragment N activates Akt, represses NF-kappaB activity, and protects the conditionally immortalized pancreatic insulinoma betaTC-tet cell line against various insults, including exposure to genotoxins, trophic support withdrawal, and incubation with inflammatory cytokines. Fragment N also induced Akt activity and protection against cytokine-induced apoptosis in primary pancreatic islet cells. Fragment N did not alter insulin cell content and insulin secretion in response to glucose. These data indicate that fragment N protects beta cells without affecting their function. The pathways regulated by fragment N are therefore promising targets for antidiabetogenic therapy.

Phosphate forms in plant and their internal buffering in five soybean cultivars

Differences among plants in their ability to support nutritional stress periods may be caused by a differential vacuole capacity of ion storage and release and may also depend on the intensity of nutrient re-translocation under such conditions. In five soybean cultivars, submitted to eight days of P deprivation, the dry matter production and the contents of three phosphorus (P) forms - inorganic (Pi), organic (Po), and acid-soluble total (Pts) of different plant organs were determined. Pi release velocity (RSPi) was estimated as the tangent to the equations obtained for Pi f(t) at the point t = 2 days (the mean point in the period of greatest Pi decrease), considering that -deltaPi/deltat expresses the rate of Pi release. The internal Pi buffering capacity (IBCPi) was calculated as the inverse of the RSPi. Cultivars' differences in size of the non-metabolic Pi pool, RSPi, and the ability to transport Pi from less to more actively metabolizing regions were evaluated. The preferential Pi source and sink compartments under limited P absorption conditions were also evaluated. The cultivar Santa Rosa showed the highest Pi storage ability when the external supply was high, and a more intensive release under low P supply conditions than IAC8 and UFV1. The cultivar Uberaba was superior to Doko in its ability to store and use Pi. In all cultivars, upper leaves and roots were the main sink of Pi stored in the middle and lower leaves. Roots and upper leaves showed larger RSPi and lower IBCPi values than middle and lower leaves.

Phosphatidyl inositol 3-kinase signaling in hypothalamic proopiomelanocortin neurons contributes to the regulation of glucose homeostasis.

Recent studies demonstrated a role for hypothalamic insulin and leptin action in the regulation of glucose homeostasis. This regulation involves proopiomelanocortin (POMC) neurons because suppression of phosphatidyl inositol 3-kinase (PI3K) signaling in these neurons blunts the acute effects of insulin and leptin on POMC neuronal activity. In the current study, we investigated whether disruption of PI3K signaling in POMC neurons alters normal glucose homeostasis using mouse models designed to both increase and decrease PI3K-mediated signaling in these neurons. We found that deleting p85alpha alone induced resistance to diet-induced obesity. In contrast, deletion of the p110alpha catalytic subunit of PI3K led to increased weight gain and adipose tissue along with reduced energy expenditure. Independent of these effects, increased PI3K activity in POMC neurons improved insulin sensitivity, whereas decreased PI3K signaling resulted in impaired glucose regulation. These studies show that activity of the PI3K pathway in POMC neurons is involved in not only normal energy regulation but also glucose homeostasis.

Glomerular hyperfiltration and increased proximal sodium reabsorption in subjects with type 2 diabetes or impaired fasting glucose in a population of the African region.

BACKGROUND. Glomerular hyperfiltration (GHF) is a well-recognized early renal alteration in diabetic patients. As the prevalence of GHF is largely unknown in populations in the African region with respect to normal fasting glucose (NFG), impaired fasting glucose (IFG) and type 2 diabetes [diabetes mellitus (DM)], we conducted a cross-sectional study in the Seychelles islands among families including at least one member with hypertension. METHODS. The glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and proximal tubular sodium reabsorption were measured using inulin, p-aminohippurate (PAH) and endogenous lithium clearance, respectively. Twenty-four-hour urine was collected on the preceding day. RESULTS. Of the 363 participants (mean age 44.7 years), 6.6% had IFG, 9.9% had DM and 63.3% had hypertension. The prevalence of GHF, defined as a GFR >140 ml/min, was 17.2%, 29.2% and 52.8% in NFG, IFG and DM, respectively (P trend <0.001). Compared to NFG, the adjusted odds ratio for GHF was 1.99 [95% confidence interval (CI) 0.73-5.44] for IFG and 5.88 (2.39-14.45) for DM. Lithium clearance and fractional excretion of lithium were lower in DM and IFG than NFG (P < 0.001). CONCLUSION. In this population of African descent, subjects with impaired fasting glucose or type 2 diabetes had a high prevalence of GHF and enhanced proximal sodium reabsorption. These findings provide further insight on the elevated incidence of nephropathy reported among African diabetic individuals.

Evidence that extrapancreatic GLUT2-dependent glucose sensors control glucagon secretion.

GLUT2-/- mice reexpressing GLUT1 or GLUT2 in their beta-cells (RIPGLUT1 x GLUT2-/- or RIPGLUT2 x GLUT2-/- mice) have nearly normal glucose-stimulated insulin secretion but show high glucagonemia in the fed state. Because this suggested impaired control of glucagon secretion, we set out to directly evaluate the control of glucagonemia by variations in blood glucose concentrations. Using fasted RIPGLUT1 x GLUT2-/- mice, we showed that glucagonemia was no longer increased by hypoglycemic (2.5 mmol/l glucose) clamps or suppressed by hyperglycemic (10 and 20 mmol/l glucose) clamps. However, an increase in plasma glucagon levels was detected when glycemia was decreased to &lt; or =1 mmol/l, indicating preserved glucagon secretory ability, but of reduced sensitivity to glucopenia. To evaluate whether the high-fed glucagonemia could be due to an abnormally increased tone of the autonomic nervous system, fed mutant mice were injected with the ganglionic blockers hexamethonium and chlorisondamine. Both drugs lead to a rapid return of glucagonemia to the levels found in control fed mice. We conclude that 1) in the absence of GLUT2, there is an impaired control of glucagon secretion by low or high glucose; 2) this impaired glucagon secretory activity cannot be due to absence of GLUT2 from alpha-cells because these cells do not normally express this transporter; 3) this dysregulation may be due to inactivation of GLUT2-dependent glucose sensors located outside the endocrine pancreas and controlling glucagon secretion; and 4) because fed hyperglucagonemia is rapidly reversed by ganglionic blockers, this suggests that in the absence of GLUT2, there is an increased activity of the autonomic nervous system stimulating glucagon secretion during the fed state.

Genetic Variants of Serum Uric Acid and Gout: An Analysis of > 170,000 Individuals

Background/Purpose: Gout is a common and excruciatingly painful inflammatory arthritis caused by hyperuricemia. In addition to various lifestyle risk factors, a substantial genetic predisposition to gout has long been recognized. The Global Urate Genetics Consortium (GUGC) has aimed to comprehensively investigate the genetics of serum uric acid and gout using data from _ 140,000 individuals of European-ancestry, 8,340 individuals of Indian ancestry, 5,820 African-Americans, and 15,286 Japanese. Methods: We performed discovery GWAS meta-analyses of serum urate levels (n_110,347 individuals) followed by replication analyses (n_32,813 different individuals). Our gout analysis involved 3,151 cases and 68,350 controls, including 1,036 incident gout cases that met the American College of Rheumatology Criteria. We also examined the association of gout with fractional excretion of uric acid (n_6,799). A weighted genetic urate score was constructed based on the number of risk alleles across urate-associated loci, and their association with the risk of gout was evaluated. Furthermore, we examined implicated transcript expression in cis (expression quantitative trait loci databases) for potential insights into the gene underlying the association signal. Finally, in order to further identify urate-associated genomic regions, we performed functional network analyses that incorporated prior knowledge on molecular interactions in which the gene products of implicated genes operate. Results: We identified and replicated 28 genome-wide significant loci in association with serum urate (P 5_10_8), including all previously-reported loci as well as 18 novel genetic loci. Unlike the majority of previouslyidentified loci, none of the novel loci appeared to be obvious candidates for urate transport. Rather, they were mapped to genes that encode for purine production, transcription, or growth factors with broad downstream responses. Besides SLC2A9 and ABCG2, no additional regions contained SNPs that differed significantly (P _ 5_10_8) between sexes. Urateincreasing alleles were associated with an increased risk of gout for all loci. The urate genetic risk score (ranging from 10 to 45) was significantly associated with an increased odds of prevalent gout (OR per unit increase, 1.11; 95% CI, 1.09-1.14) and incident gout (OR, 1.10; 95% CI, 1.08-1.13). Associations for many of the loci were of similar magnitude in individuals of non-European ancestry. Detailed characterization of the loci revealed associations with transcript expression and the fractional excretion of urate. Network analyses implicated the inhibins-activins signaling pathways and glucose metabolism in systemic urate control. Conclusion: The novel genetic candidates identified in this urate/gout consortium study, the largest to date, highlight the importance of metabolic control of urate production and urate excretion. The modulation by signaling processes that influence metabolic pathways such as glycolysis and the pentose phosphate pathway appear to be central mechanisms underpinned by the novel GWAS candidates. These findings may have implications for further research into urate-lowering drugs to treat and prevent gout.

Glucose sensing and the pathogenesis of obesity and type 2 diabetes.

The control of body weight and of blood glucose concentrations depends on the exquisite coordination of the function of several organs and tissues, in particular the liver, muscle and fat. These organs and tissues have major roles in the use and storage of nutrients in the form of glycogen or triglycerides and in the release of glucose or free fatty acids into the blood, in periods of metabolic needs. These mechanisms are tightly regulated by hormonal and nervous signals, which are generated by specialized cells that detect variations in blood glucose or lipid concentrations. The hormones insulin and glucagon not only regulate glycemic levels through their action on these organs and the sympathetic and parasympathetic branches of the autonomic nervous system, which are activated by glucose or lipid sensors, but also modulate pancreatic hormone secretion and liver, muscle and fat glucose and lipid metabolism. Other signaling molecules, such as the adipocyte hormones leptin and adiponectin, have circulating plasma concentrations that reflect the level of fat stored in adipocytes. These signals are integrated at the level of the hypothalamus by the melanocortin pathway, which produces orexigenic and anorexigenic neuropeptides to control feeding behavior, energy expenditure and glucose homeostasis. Work from several laboratories, including ours, has explored the physiological role of glucose as a signal that regulates these homeostatic processes and has tested the hypothesis that the mechanism of glucose sensing that controls insulin secretion by the pancreatic beta-cells is also used by other cell types. I discuss here evidence for these mechanisms, how they integrate signals from other nutrients such as lipids and how their deregulation may initiate metabolic diseases.

Macrophage migration inhibitory factor deficiency leads to age-dependent impairment of glucose homeostasis in mice.

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine produced by many cells and tissues including pancreatic beta-cells, liver, skeletal muscle, and adipocytes. This study investigates the potential role of MIF in carbohydrate homeostasis in a physiological setting outside of severe inflammation, utilizing Mif knockout (MIF-/-) mice. Compared with wild-type (WT) mice, MIF-/- mice had a lower body weight, from birth until 4 months of age, but subsequently gained weight faster, resulting in a higher body weight at 12 months of age. The lower weight in young mice was related to a higher energy expenditure, and the higher weight in older mice was related to an increased food intake and a higher fat mass. Fasting blood insulin level was higher in MIF-/- mice compared with WT mice at any age. After i.p. glucose injection, the elevation of blood insulin level was higher in MIF-/- mice compared with WT mice, at 2 months of age, but was lower in 12-month-old MIF-/- mice. As a result, the glucose clearance during intraperitoneal glucose tolerance tests was higher in MIF-/- mice compared with WT mice until 4 months of age, and was lower in 12-month-old MIF-/- mice. Insulin resistance was estimated (euglycemic-hyperinsulinemic clamp tests), and the phosphorylation activity of AKT was similar in MIF-/- mice and WT mice. In conclusion, this mouse model provides evidence for the role of MIF in the control of glucose homeostasis.

Fluoxetine regulates the expression of neurotrophic/growth factors and glucose metabolism in astrocytes.

Rationale The pharmacological actions of most antidepressants are ascribed to the modulation of serotonergic and/or noradrenergic transmission in the brain. During therapeutic treatment for major depression, fluoxetine, one of the most commonly prescribed selective serotonin reuptake inhibitor (SSRI) antidepressants, accumulates in the brain, suggesting that fluoxetine may interact with additional targets. In this context, there is increasing evidence that astrocytes are involved in the pathophysiology of major depression.Objectives The aim of this study was to examine the effects of fluoxetine on the expression of neurotrophic/growth factors that have antidepressant properties and on glucose metabolism in cultured cortical astrocytes.Results Treatment of astrocytes with fluoxetine and paroxetine, another SSRI antidepressant, upregulated brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and VGF mRNA expression. In contrast, the tricyclic antidepressants desipramine and imipramine did not affect the expression of these neurotrophic/growth factors. Analysis of the effects of fluoxetine on glucose metabolism revealed that fluoxetine reduces glycogen levels and increases glucose utilization and lactate release by astrocytes. Similar data were obtained with paroxetine, whereas imipramine and desipramine did not regulate glucose metabolism in this glial cell population. Our results also indicate that the effects of fluoxetine and paroxetine on glucose utilization, lactate release, and expression of BDNF, VEGF, and VGF are not mediated by serotonin-dependent mechanisms.Conclusions These data suggest that, by increasing the expression of specific astrocyte-derived neurotrophic factors and lactate release from astrocytes, fluoxetine may contribute to normalize the trophic and metabolic support to neurons in major depression.

Mastoparan, a novel mitogen for Swiss 3T3 cells, stimulates pertussis toxin-sensitive arachidonic acid release without inositol phosphate accumulation

Mastoparan, a basic tetradecapeptide isolated from wasp venom, is a novel mitogen for Swiss 3T3 cells. This peptide induced DNA synthesis in synergy with insulin in a concentration-dependent manner; half-maximum and maximum responses were achieved at 14 and 17 microM, respectively. Mastoparan also stimulated DNA synthesis in the presence of other growth promoting factors including bombesin, insulin-like growth factor-1, and platelet-derived growth factor. The synergistic mitogenic stimulation by mastoparan can be dissociated from activation of phospholipase C. Mastoparan did not stimulate phosphoinositide breakdown, Ca2+ mobilization or protein kinase C-mediated phosphorylation of a major cellular substrate or transmodulation of the epidermal growth factor receptor. In contrast, mastoparan stimulated arachidonic acid release, prostaglandin E2 production, and enhanced cAMP accumulation in the presence of forskolin. These responses were inhibited by prior treatment with pertussis toxin. Hence, mastoparan stimulates arachidonic acid release via a pertussis toxin-sensitive G protein in Swiss 3T3 cells. Arachidonic acid, like mastoparan, stimulated DNA synthesis in the presence of insulin. The ability of mastoparan to stimulate mitogenesis was reduced by pertussis toxin treatment. These results demonstrate, for the first time, that mastoparan stimulates reinitiation of DNA synthesis in Swiss 3T3 cells and indicate that this peptide may be a useful probe to elucidate signal transduction mechanisms in mitogenesis.

Blood flow, flow reserve, and glucose utilization in viable and nonviable myocardium in patients with ischemic cardiomyopathy.

PURPOSE: The aim of the study was to determine whether glucose uptake in viable myocardium of ischemic cardiomyopathy patients depends on rest myocardial blood flow (MBF) and the residual myocardial flow reserve (MFR). METHODS: Thirty-six patients with ischemic cardiomyopathy (left ventricular ejection fraction 25 ± 10 %) were studied with N-ammonia and F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Twenty age-matched normals served as controls. Regional MBF was determined at rest and during dipyridamole hyperemia and regional FDG extraction was estimated from regional FDG to N-ammonia activity ratios. RESULTS: Rest MBF was reduced in viable (0.42 ± 0.18 ml/min per g) and nonviable regions (0.32 ± 0.09 ml/min per g) relative to remote regions (0.68 ± 0.23 ml/min per g, p < 0.001) and to normals (0.63 ± 0.13 ml/min per g). Dipyridamole raised MBFs in controls, remote, viable, and nonviable regions. MBFs at rest (p < 0.05) and stress (p < 0.05) in viable regions were significantly higher than that in nonviable regions, while MFRs did not differ significantly (p > 0.05). Compared to MFR in remote myocardium, MFRs in viable regions were similar (1.39 ± 0.56 vs 1.70 ± 0.45, p > 0.05) but were significantly lower in nonviable regions (1.23 ± 0.43, p < 0.001). Moreover, the FDG and thus glucose extraction was higher in viable than in remote (1.40 ± 0.14 vs 0.90 ± 0.20, p < 0.001) and in nonviable regions (1.13 ± 0.21, p < 0.001). The extraction of FDG in viable regions was independent of rest MBF but correlated inversely with MFRs (r =-0.424, p < 0.05). No correlation between the FDG extraction and MFR was observed in nonviable regions. CONCLUSION: As in the animal model, decreasing MFRs in viable myocardium are associated with increasing glucose extraction that likely reflects a metabolic adaptation of remodeling hibernating myocytes.