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Biomedical subjects

J Girard

Publications and source records attributed to J Girard.

At least 73 records · Page 4Linked to original sources
PubMed1998

Glucose regulation of gene expression.

Regulation of gene expression by nutrients in mammals is an important mechanism allowing them to adapt to the nutritional environment. In-vivo and in-vitro experiments have demonstrated that the transcription of genes coding for lipogenic and glycolytic enzymes in liver and/or adipose tissue is upregulated by glucose. In order for glucose to act as a gene inducer, it must be metabolized. Recent evidence suggests that glucose-6-phosphate is the signal metabolite in the liver. DNA glucose response elements have been characterized and they have in common the presence of two sequences 5'-CACGTG-3' separated by five nucleotides, which bind in vitro a transcription factor of the basic domain, helix-loop-helix, leucine zipper family called USF/MLTF. Experiments concerning the potential role of USF/MLTF in the glucose response have led to opposite results, suggesting that USF/MLTF might not be the only factor involved. Finally, the glucose effect involves a kinase/phosphatase system. The kinase could be the AMP-activated protein kinase, the mammalian analogue of a yeast kinase, or SNF 1 which is important for the derepression of glucose-inhibited genes.

Animals↗
PubMed1998

Unexpected expression of glucose transporter 4 in villous stromal cells of human placenta.

Glucose transporter 4 (GLUT4) protein expression was characterized in human and rodent term placentas. A 50-kDa protein was detected, by immunoblotting, in term human placenta at levels averaging 25% of those found in white adipose tissue. It was also present, albeit at lower levels, in mouse and rat placentas. The specificity of the 50-kDa signal was established by using skeletal muscle and placental tissues obtained from GLUT4-null mice as controls. Indirect immunohistochemistry, performed in human placentas, showed that intravillous stromal cells were conspicuously labeled by GLUT4 and revealed colocalization of GLUT4 transporters with insulin receptors. This study provides the first evidence that the insulin-responsive GLUT4 glucose transporter is present in human and rodent hemochorial placentas. Placental GLUT4 gene and protein levels were not modified in human pregnancy complicated by insulin-dependent diabetes mellitus. The significance of the high level of GLUT4 protein in human placenta remains to be elucidated, because, so far, this organ was not considered to be insulin-sensitive, with regard to glucose transport.

Animals↗
PubMed1998

Overexpression of placental leptin in diabetic pregnancy: a critical role for insulin.

Leptin, a small peptide produced by adipocytes, is implicated in an increasing number of endocrine regulations, including adiposity, satiety, puberty, and fertility. Although the factors involved in controlling maternal and fetal weight gain during pregnancy have not been fully elucidated, leptin has recently emerged as such a potential factor. In our study, we report the presence of high amounts of leptin mRNA and immunoreactive protein in the human placenta, establishing the placental synthesis of this hormone. A large (three- to fivefold) augmentation in leptin mRNA and protein was found in placentas from insulin-treated diabetic women. This finding was associated with increased concentrations of leptin and insulin in venous cord blood without modification of maternal circulating leptin levels. These data provide evidence that the placenta is a site for regulated leptin production in utero. Insulin is likely to play a critical role in this regulation, thus emphasizing the importance of placental leptin signaling in diabetic pregnancy.

Adult↗
PubMed1998

Development and regulation of glucose-6-phosphatase gene expression in rat liver, intestine, and kidney: in vivo and in vitro studies in cultured fetal hepatocytes.

The mRNA and the activity of glucose-6-phosphatase (Glc-6-Pase) were present in the liver, kidney, and small intestine of 15-day-old suckling rats, but were absent from the stomach, colon, lung, white and brown adipose tissues, muscle, heart, brain, and spleen. The mRNA encoding Glc-6-Pase was present in the liver of 21-day-old fetal rats and increased markedly immediately after birth. From 5 days after birth to the end of the suckling period, it returned to 50% of the level found in the liver of 48-h starved adult rats. When rats were weaned at 21 days onto a high-carbohydrate, low-fat (HCLF) diet, the concentration of liver Glc-6-Pase mRNA was markedly increased. In the fetal rat jejunum, the activity and mRNA of Glc-6-Pase were very low. It increased during the 5 days after birth and then declined to reach very low levels. Neither mRNA nor activity of Glc-6-Pase was present in the fetal kidney. They appeared and increased slowly during the suckling period to reach maximal levels 15 days after birth and then remained constant. Weaning onto the HCLF diet did not change the Glc-6-Pase gene expression, neither in the jejunum nor in the kidney. The regulation of Glc-6-Pase gene expression by hormones and nutrients was studied in cultured hepatocytes from 20-day-old rat fetuses. Bt2cAMP stimulated the Glc-6-Pase gene expression in a dose-dependent manner. This probably resulted from an increased gene transcription since the half-life of the transcript was not affected by dibutyryl cAMP (Bt2cAMP). The Bt2cAMP-induced Glc-6-Pase mRNA accumulation was antagonized by insulin in a dose-dependent manner. Long-chain fatty acids (LCFAs), but not medium-chain fatty acids, induced the accumulation of Glc-6-Pase mRNA and the stabilization of the transcript. The peroxisome proliferator, clofibrate, induced a threefold increase in Glc-6-Pase mRNA concentration. Both stimulation of Glc-6-Pase mRNA by LCFAs and clofibrate were inhibited by insulin. Increasing concentrations of glucose (from 0 to 20 mmol/l) did not affect the Bt2cAMP-induced Glc-6-Pase gene expression. By contrast, high glucose concentration (25 mmol/l) markedly induced the Glc-6-Pase gene expression in fed adult rat hepatocytes. The difference in the response to glucose between fetal and adult rat hepatocytes is discussed. We conclude that the rapid increase in hepatic Glc-6-Pase mRNA levels that accompanies the fetal-to-neonatal transition in the rat is triggered by the reciprocal change in circulating insulin and LCFA concentrations, coupled to the rise in liver cAMP concentration.

Aging↗
PubMed1998

[Language comprehension by children with profound congenital deafness after cochlear implant].

The consequences of profound deafness on oral language development in children are drastic and well-known. Modern multichannel cochlear implant (CI) has been proven to enhance speech production skills in prelingually deaf children. Speech production skills, however, are known not to be a reliable reflection of oral language competence as a whole. Language is an acquired common code in a specific group, enabling exchange of ideas, feelings and knowledge. In humans, speech is one of the channels conveying language. Assessing language development in CI children is more difficult than simply assessing speech production skills. Many factors may contribute to a poor or an excellent outcome, making it difficult to compare groups of children wearing or not wearing CI. The present study compared receptive language levels in paired matched children from CI and non-CI groups. The main conclusion of this study is that language comprehension scores grow significantly higher over time post-surgery in CI than in paired-matched non-CI children, despite better initial pure tone audiometric thresholds of the latter.

Audiometry, Pure-Tone↗
PubMed1997

Variable expression of hepatic glucokinase in mice is due to a regulational locus that cosegregates with the glucokinase gene.

The Gk activity locus affects expression of hepatic glucokinase (GK) in mice. Analysis of microsatellites within the mouse GK gene locus revealed two major haplotypes in 19 of 22 inbred strains predictive of either high or low hepatic GK gene expression. C3H/HeJ mice, a high-activity strain, and two other wild-derived strains contain less common haplotypes. No coding sequence differences were found in hepatic GK-coding sequences from representative high and low Gk activity strains, thereby excluding kinetic abnormalities as the basis for hepatic GK activity differences. Screening of approximately 10 kb of potential regulatory DNA, including all eight known and three of four newly identified DNase I-hypersensitive sites, by restriction enzyme fingerprinting-single-strand conformation analysis revealed a tetranucleotide microsatellite, the length of which was also predictive of the Gk activity phenotype. This tetranucleotide repeat is located in the first intron of the hepatic transcription unit and lies close to a newly identified liver-specific DNase I-hypersensitive site. These results indicate that the Gk activity alleles are a regulational locus associated with the GK gene locus.

Animals↗
PubMed1997

Evidence for a direct interaction between insulin receptor substrate-1 and Shc.

Insulin receptor substrate-1 (IRS-1) and Shc are two proteins implicated in intracellular signal transduction. They are activated by an increasing number of extracellular signals, mediated by receptor tyrosine kinases, cytokine receptors, and G protein-coupled receptors. In this study we demonstrate that Shc interacts directly with IRS-1, using the yeast two-hybrid system and an in vitro interaction assay. Deletion analysis of the proteins to map the domains implicated in this interaction shows that the phosphotyrosine binding domain of Shc binds to the region of IRS-1 comprising amino acids 583-661. An in vitro association assay, performed with or without activation of tyrosine kinases, gives evidence that tyrosine phosphorylation of IRS-1 and Shc drastically improves the interaction. Site-directed mutagenesis on IRS-1 583-693 shows that the asparagine, but not the tyrosine residue of the N625GDY628motif domain, is implicated in the IRS-1-Shc-phosphotyrosine binding interaction. Mutation of another tyrosine residue, Tyr608, also induced a 40% decrease in the interaction. This study, describing a phosphotyrosine-dependent interaction between IRS-1 and Shc, suggests that this association might be important in signal transduction.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Effects of triiodothyronine and retinoic acid on glucokinase gene expression in neonatal rat hepatocytes.

Glucokinase (EC 2.7.1.2) first appears in rat liver two weeks after birth and increases rapidly after weaning on to a high-carbohydrate diet. We investigated the role of triiodothyronine and retinoic acid in the absence of insulin on the first expression of the glucokinase gene in primary cultures of hepatocytes from 10 day-old rats. These two hormones were able to induce a rapid accumulation of liver glucokinase mRNA, secondarily to a stimulation of gene transcription during the first 24 h of culture. Moreover, the effects of individual hormones were not additive. Finally, glucokinase mRNA stability was not modified by these hormones. This suggests that triiodothyronine and retinoic acid act on glucokinase gene at the transcriptional.

Animals↗
PubMed1997

Identification and localization of a skeletal muscle secrotonin 5-HT2A receptor coupled to the Jak/STAT pathway.

The neurotransmitter serotonin mediates a wide variety of peripheral and central physiological effects through the binding to multiple receptor subtypes (Wilkinson, L. O., and Dourish, C. T. (1991) in Serotonin Receptor Subtypes: Basic and Clinical Aspects (Peroutka, S. J., ed) Vol. 15, pp.147-210, Wiley-Liss, New York). Among them, serotonin 5-HT2A receptors are known to activate the phospholipase C-beta second messenger pathway (Peroutka, S. J. (1995) Trends Neurosci. 18, 68-69). We identified and localized in rat skeletal muscle myoblasts a functional serotonin 5-HT2A receptor. This receptor was detected on the plasma membrane, in myoblasts, and at the level of T-tubules in contracting myotubes. Binding of serotonin to its receptor increases the expression of genes involved in myogenic differentiation. Unexpectedly, the 5-HT2A receptor is able to activate another signaling pathway; it triggers a rapid and transient tyrosine phosphorylation of Jak2 kinase in response to serotonin. Jak2 auto-phosphorylation is followed by the tyrosine phosphorylation of STAT3 (signal transducers and activators of transcription) and its translocation into the nucleus. We also find that the 5-HT2A receptor and STAT3 co-precipitate with Jak2, indicating that they are physically associated. We conclude that the serotonin 5-HT2A receptor identified in skeletal muscle myoblasts is able to activate the intracellular phosphorylation pathway used by cytokines. The presence of serotonin receptors in T-tubules suggests a role for serotonin in excitation-contraction coupling and (or) an effect in skeletal muscle fiber repairing.

Animals↗
PubMed1997

cAMP prevents the glucose-mediated stimulation of GLUT2 gene transcription in hepatocytes.

Glucose homoeostasis necessitates the presence in the liver of the high Km glucose transporter GLUT2. In hepatocytes, we and others have demonstrated that glucose stimulates GLUT2 gene expression in vivo and in vitro. This effect is transcriptionally regulated and requires glucose metabolism within the hepatocytes. In this report, we further characterized the cis-elements of the murine GLUT2 promoter, which confers glucose responsiveness on a reporter gene coding the chloramphenicol acetyl transferase (CAT) gene. 5'-Deletions of the murine GLUT2 promoter linked to the CAT reporter gene were transfected into a GLUT2 expressing hepatoma cell line (mhAT3F) and into primary cultured rat hepatocytes, and subsequently incubated at low and high glucose concentrations. Glucose stimulates gene transcription in a manner similar to that observed for the endogenous GLUT2 mRNA in both cell types; the -1308 to -212 bp region of the promoter contains the glucose-responsive elements. Furthermore, the -1308 to -338 bp region of the promoter contains repressor elements when tested in an heterologous thymidine kinase promoter. The glucose-induced GLUT2 mRNA accumulation was decreased by dibutyryl-cAMP both in mhAT3F cells and in primary hepatocytes. A putative cAMP-responsive element (CRE) is localized at the -1074/-1068 bp region of the promoter. The inhibitory effect of cAMP on GLUT2 gene expression was observed in hepatocytes transfected with constructs containing this CRE (-1308/+49 bp fragment), as well as with constructs not containing the consensus CRE (-312/+49 bp fragment). This suggests that the inhibitory effect of cAMP is not mediated by the putative binding site located in the repressor fragment of the GLUT2 promoter. Taken together, these data demonstrate that the elements conferring glucose and cAMP responsiveness on the GLUT2 gene are located within the -312/+49 region of the promoter.

Animals↗
PubMed1997

Comparative chemical analyses of drug samples: general approach and application to heroin.

The methodology used for the comparative chemical analyses of illicit drug seizures, and its application to a heroin comparison case, is described. The illicit drug sample is subjected to a three-step procedure. The first is the qualitative and quantitative analysis of each sample, i.e. identification and quantitation of major and minor constituents. The second is the analysis of trace level impurities contained in each sample, after isolation from the drug matrix. The last step is the isotopic analysis of each sample, i.e. the determination of the isotopic enrichment of the major constituents. That analytical procedure, applied to heroin, allowed the determination of common batch samples with a high degree of certainty.

Drug Contamination↗
PubMed1997

The role of non-esterified fatty acids in the deterioration of glucose tolerance in Caucasian subjects: results of the Paris Prospective Study.

Although an increased plasma non-esterified fatty acid (NEFA) concentration has been shown to increase insulin resistance (Randle cycle), decrease insulin secretion and increase hepatic gluconeogenesis, the effect of NEFA on the deterioration of glucose tolerance has not been studied prospectively in Caucasian subjects. Therefore, we investigated whether plasma NEFA may be regarded as predictors of deterioration of glucose tolerance in subjects with normal (NGT, n = 3671) or impaired (IGT, n = 418) glucose tolerance who were participants in the Paris Prospective study. The subjects were first examined between 1967 and 1972 and underwent two 75-g oral glucose tolerance tests 2 years apart with measurements of plasma glucose, insulin and NEFA concentrations. Glucose tolerance deteriorated from NGT to IGT or non-insulin-dependent diabetes (NIDDM) in 177 subjects and from IGT to NIDDM in 32 subjects. In multivariate analysis, high fasting plasma NEFA in NGT subjects and high 2-h plasma NEFA and low 2-h plasma insulin concentrations in IGT subjects were significant independent predictors of deterioration along with older age, high fasting and 2-h plasma glucose concentrations and high iliac to thigh ratio. When subjects were divided by tertiles of plasma NEFA concentration at baseline, there was an increase in 2-h glucose concentration with increasing NEFA in the subjects who did not deteriorate, but no effect of plasma NEFA in those who deteriorated. In subjects with IGT who deteriorated compared with those who did not 2-h plasma insulin concentration was lower but there was no evidence that this resulted from an effect of plasma NEFA. Our data suggest that a high plasma NEFA concentration is a risk marker for deterioration of glucose tolerance independent of the insulin resistance or the insulin secretion defect that characterize subjects at risk for NIDDM.

Basal Metabolism↗
PubMed1997

Phenotype of transgenic mice overexpressing GLUT4 and hexokinase II in muscle.

To optimize glucose utilization, double transgenic mice were created by crossing mice overexpressing glucose transporter GLUT4 with mice overexpressing hexokinase (HKII) in muscle. Transgenic mice overexpressing GLUT4 alone have exhibited improvements in glucose tolerance and insulin action. In vitro studies of hexose uptake in soleus muscle from transgenic mice suggested that GLUT4 was limiting the glucose flux except at high glucose concentration, where hexokinase became the limiting step. In vivo, glucose tolerance was similar in GLUT4 and GLUT4/HKII mice, although stimulated plasma insulin values were significantly lower in the latter group. Insulin tolerance tests performed in diabetic GLUT4 vs. diabetic GLUT4/HKII transgenic mice yielded identical results. Again, endogenous insulin in GLUT4/HKII mice during a mild hyperglycemic clamp was stimulated by only two- vs. fourfold in GLUT4 mice. Although the overexpression of HKII alone resulted in increased glucose utilization in several muscles, the overexpression of GLUT4 plus HKII did not augment basal or stimulated in vivo glucose utilization compared to GLUT4 overexpression. In conclusion, GLUT4 is rate limiting for muscle glucose utilization but HKII might be important under hyperglycemia. The addition of HKII to GLUT4 overexpression is not sufficient to further augment glucose tolerance or insulin action. In GLUT4/HKII double transgenic mice, glucose clearance is tempered by a low insulin stimulated level.

Animals↗
PubMed1997

Mechanisms by which carbohydrates regulate expression of genes for glycolytic and lipogenic enzymes.

Regulation of gene expression by nutrients is an important mechanism in the adaptation of mammals to their nutritional environment. This is especially true for enzymes involved in the storage of energy, such as the lipogenic and glycolytic enzymes in liver and adipose tissue. Transcription of the genes for lipogenic and glycolytic enzymes is stimulated by glucose in adipose tissue, liver, and pancreatic beta-cells. Several lines of evidence suggest that glucose must be metabolized to glucose-6-phosphate to stimulate gene transcription. In adipose tissue, insulin increases the expression of lipogenic enzymes indirectly by stimulating glucose uptake. In the liver, insulin also acts indirectly by stimulating the expression of glucokinase and, hence, by increasing glucose metabolism. Glucose response elements have been characterized for the L-pyruvate kinase and S14 genes. They have in common the presence of a sequence 5'-CACGTG-3', which binds a transcription factor called USF (upstream stimulatory factor). Another glucose response element, which uses a transcription factor named Sp1, has been characterized in the gene for the acetyl-coenzyme A carboxylase. The mechanisms linking glucose-6-phosphate to the glucose-responsive transcription complex are largely unknown.

Acetyl-CoA Carboxylase↗
PubMed1997

Effects of insulin-like growth factor I combined with growth hormone on glucocorticoid-induced whole-body protein catabolism in man.

Treatment with insulin-like growth factor I (IGF-I) alone failed to affect glucocorticoid-induced protein catabolism in a previous study from our laboratory. To assess the effects of the combination of IGF-I and GH in a similar protocol, 24 normal subjects received (in a double-blind, randomized, placebo-controlled manner) s.c. injections of either GH alone (0.3 IU/kg.day), the combination of IGF-I (80 micrograms/kg.day) and GH (0.3 IU/kg.day), or placebo for a period of 6 days during which they were treated with methylprednisolone (0.5 mg/kg.day). Whole-body protein kinetics measured, using the [1-13C]-leucine infusion technique, demonstrated that leucine flux (a parameter of protein breakdown) increased during administration of glucocorticoids alone (placebo group) and during GH-treatment, whereas the glucocorticoid-induced increase was abolished during IGF-I plus GH (P < 0.03 vs. GH). Leucine oxidation (a parameter of irreversible protein catabolism) increased in the placebo group (+60 +/- 14.5%, P < 0.005, day 7 vs. day 1), remained unchanged in the GH group (+2.5 +/- 10%), and decreased in the combination group (-17.7 +/- 3.3%, P < 0.002, day 7 vs. day 1). Glucose MCR decreased in the group receiving placebo (P < 0.05) and remained unchanged during combined treatment with IGF-I plus GH. It is concluded that glucocorticoid-induced protein, catabolism (leucine oxidation) is abolished during coadministration of GH (anticatabolic effect), whereas treatment with IGF-I and GH results in a net anabolic effect without adverse effects on peripheral glucose clearance.

Adult↗
PubMed1997

The GLUT3 glucose transporter isoform is differentially expressed within human placental cell types.

The cellular localization of GLUT3 messenger ribonucleic acid (mRNA) and protein was examined in human term placenta using a combination of methodologies. In situ hybridization indicated that GLUT3 mRNA was present in the trophoblast cell layer and in vascular endothelium with a heterogeneous distribution pattern. GLUT3 protein migrating at an apparent molecular mass of 49 kDa was detected by immunoblotting in membranes from whole placenta and endothelial cells derived from intraplacental microvessels, but not in isolated trophoblast cells. This cell-specific pattern of expression was confirmed by immunocytochemical studies showing a prominent localization of GLUT3 protein in vascular endothelium. These findings indicate a differential distribution of GLUT3 mRNA and protein in the human placenta. Based on its cell-specific distribution at the fetal interface, GLUT3 protein could be of cardinal importance in the transport of glucose from the placenta to the fetal circulation.

Actins↗