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Biomedical subjects

M Lavau

Publications and source records attributed to M Lavau.

At least 19 recordsLinked to original sources
PubMed1998

Leptin receptor gene in a large cohort of massively obese subjects: no indication of the fa/fa rat mutation. Detection of an intronic variant with no association with obesity.

The massive obesity caused in rodents by the disruption of the leptin-receptor signal through genetic defects at the level of either leptin (OB) or leptin receptor (OB-R) has raised the question of the relevance of these genes to morbid obesity in humans. In this study, we screened a large population of massively obese subjects for the presence of a leptin receptor mutation homologous to that of fa/fa rats, a single base substitution changing glutamine 269, a highly conserved glutamine found at position 270 in the human sequence. After polymerase chain reaction (PCR) amplification of a DNA region encompassing the end of exon 5, intron 5, and the beginning of exon 6, we performed restriction fragment length polymorphism analysis. Within the limitations of this approach where only mutations introducing restriction sites (5 of 8 possibilities) could be assessed, no evidence of mutation at the codon gln 270 was found in 343 massively obese subjects. However, a new OB-R gene variant in intron 5 was revealed by MaeII digestion of the PCR products. MaeII/hOB-R genotyping revealed no difference in the distribution of the genotypes between obese subjects and a group of 79 unrelated nonobese control subjects. In addition, no significant association between various obesity-related metabolic phenotypes and the presence of MaeII/hOB-R alleles was found. Thus, our results did not support a significant role for the MaeII/hOB-R gene variant in the development of the obese phenotype in the population we studied.

Adult↗
PubMed1997

Rab 3D in rat adipose cells and its overexpression in genetic obesity (Zucker fatty rat).

Members of the Rab 3 subfamily of low-molecular-mass GTP-binding proteins have been functionally implicated in regulated exocytosis. The aim of the present study was to examine the subcellular distribution of a member of this family, Rab 3D, in rat adipose cells, given the hypothesis that this protein might be involved in insulin-stimulated GLUT4 exocytosis. We show that Rab 3D immunoreactivity is associated predominantly with the high-density microsomal fraction, where the signal intensity is 3- and 7-fold greater than that in plasma membranes and low-density microsomes respectively. Rab 3D does not co-localize with GLUT4 on immuno-isolated intracellular vesicles and, unlike GLUT4, it is not redistributed in response to insulin. Thus, if Rab 3D plays a role in GLUT4 trafficking, it relies on mechanisms independent of relocation. We observed that Rab 3D is overexpressed in adipose cells of obese (fa/fa) Zucker rats, in a tissue- and isoform-specific manner. The pathophysiological significance of this defect remains elusive. This could form the molecular basis for altered adipose secretory function in obesity.

Adipose Tissue↗
PubMed1997

Time-dependent effects of insulin on lipid synthesis in cultured fetal rat hepatocytes: a comparison between lipogenesis and glycogenesis.

The lipogenic effect of insulin was studied in 18-day-old fetal rat hepatocytes after 2 to 3 days of culture in the presence of glucocorticoids when an acute stimulatory effect of insulin on glycogenesis was present. The rate of [1-14C]-acetate incorporation into lipids measured for 4 hours was much higher than with [U-14C]-glucose (30 v 3.8 nmol/h/mg protein). The stimulatory effect of insulin on lipid labeling remained weak (1.2-fold) and contrasted with its striking stimulatory effect on [U-14C]-glucose incorporation into glycogen (fourfold). When lipid labeling was assessed in longer experiments, increasing acetate concentrations in the medium stimulated the incorporation rate of [1-14C]-acetate into lipids (3.5-fold from 1 to 5 mmol/L after 36 hours) and decreased that of [U-14C]-glucose (by twofold). The stimulatory effect of insulin on the rate of lipid labeling developed with both precursors from 12 to 36 hours after insulin exposure (by approximately twofold) independently of acetate concentration and was not glucocorticoid-dependent, contrary to the glycogenic response. Addition of a glucose, load simultaneously with insulin increased the stimulation of lipogenesis when measured with [U-14C]-glucose (twofold to 3.7-fold). Besides contributing to an accumulation of larger and numerous lipid droplets in the cells, insulin increased fatty acid synthase activity by 26%, whereas malic enzyme was not affected. Thus, insulin-dependent lipogenesis in cultured fetal hepatocytes appears to be mostly regulated by a long-term mechanism, contrary to the glycogenic effect of insulin.

Acetates↗
PubMed1997

Reduction of insulin and triglycerides delays glomerulosclerosis in obese Zucker rats.

To evaluate the effect of insulin and/or triglycerides on the pathogenesis of glomerulosclerosis, acarbose (BAYg5421), an inhibitor of intestinal alpha-glucosidases, was administered as a dietary admix (40 mg/100 g chow) to Zucker obese rats (ZOA), from 1.5 months until sacrifice at 1.5, 5, 8, 10 and 15 months. Obese (ZO) and lean (ZL) rats served as controls. Despite a similar food intake, ZOA weighed less than ZO at all ages. Acarbose reduced serum triglycerides at all ages, and insulin until 10 months. Glycemia remained normal in all groups. Proteinuria developed with age and to a greater degree in ZO than in ZOA rats. In ZL, a faint proteinuria appeared only in the oldest animals. Glomerulosclerosis, tubular and interstitial lesions rapidly affected ZO kidneys. These lesions were reduced in ZOA until 10 months. Acarbose did not modify the hypertrophy of the glomeruli that developed after three months, but slowed down the expansion of the mesangial domain seen in ZO. Thus, by reducing the amount of ingested glucose, acarbose yielded a normal glycemia with a lesser production of insulin and reduced renal impairment. Therefore, insulin could be a key factor involved in the pathogenesis of glomerulosclerosis, either directly or through a control of triglyceride concentrations.

Acarbose↗
PubMed1996

Regulation of gene expression for lipogenic enzymes in the liver and adipose tissue of hereditary hypertriglyceridemic, insulin-resistant rats: effect of dietary sucrose and marine fish oil.

Hypertriglyceridemia is closely linked to insulin resistance. Increased dietary intake of n-3 polyunsaturated fatty acids reverses both hypertriglyceridemia and insulin resistance. To evaluate molecular mechanisms responsible for the hypotriglyceridemic effects of n-3 polyunsaturated fatty acids, the expression of genes for lipogenic enzymes in liver and white and brown adipose tissue was estimated in hereditary hypertriglyceridemic rats which underwent an euglycemic hyperinsulinemic clamp. Before the clamp, animals were fed a basal or a high (63%) sucrose diet with or without fish oil for two weeks. Results were compared to data obtained from control animals subjected to the identical protocol. In hereditary hypertriglyceridemic rats, gene expression for malic enzyme was increased in liver and in brown adipose tissue but not in white adipose tissue. The high sucrose diet raised malic enzyme mRNA levels in liver of both hereditary hypertriglyceridemic and control rats, and this effect was more pronounced in brown adipose tissue. Supplementing the high sucrose diet with fish oil led to a suppression of malic enzyme gene expression in liver and brown adipose tissue of control rats. However, this inhibitory effect was not as pronounced in the hereditary hypertriglyceridemic rats. Raised levels of fatty acid synthase mRNA in liver and brown adipose tissue of control rats fed high sucrose diet were suppressed by consumption of diet high in n-3 fatty acids. On the other hand, in hereditary hypertriglyceridemic rats fed high sucrose diet, fish oil supplementation failed to suppress increased levels of fatty acid synthase mRNA in liver and in brown adipose tissue. It appears that hereditary hypertriglyceridemic rats have elevated levels of mRNA for lipogenic enzymes in liver and brown adipose tissue and dietary control leading to an alteration of hypertriglyceridemia influences gene expression of lipogenic enzymes only under special dietary circumstances.

Adipose Tissue↗
PubMed1996

A GC-rich region containing Sp1 and Sp1-like binding sites is a crucial regulatory motif for fatty acid synthase gene promoter activity in adipocytes. Implication In the overactivity of FAS promoter in obese Zucker rats.

We have previously shown that the proximal 2-kb sequence of the fatty acid synthase (FAS) promoter transfected into rat adipocytes was highly sensitive to the cellular context, displaying an overactivity in obese (fa/fa) versus lean Zucker rat adipocytes. Using deletional analysis, we show here that FAS promoter activity mainly depends on a region from -200 to -126. This sequence exerts a strong negative effect on FAS promoter in adipocytes from lean rats but not in those from obese rats, resulting in a marked overtranscriptional activity in the latter cells. This region, fused to a heterologous promoter, the E1b TATA box, induced differential levels of gene reporter activity in lean and obese rat adipocytes, indicating it harbors fa-responsive element(s). Whatever the rat genotype, adipocyte nuclear proteins were shown to footprint the same protected sequence within the fa-responsive region, and supershift analysis demonstrated that Sp1 or Sp1-like proteins were bound to this DNA subregion. Compelling evidence that the Sp1 binding site contained in this sequence was implicated in the differential promoter activity in lean versus obese rats, was provided by the observation that mutations at this Sp1 site induced a 2.5-fold increase in FAS promoter activity in adipocytes from lean rats, whereas they had no effect in adipocytes from obese rats.

Adipocytes↗
PubMed1995

Fatty genotype-induced increase in GLUT4 promoter activity in transfected adipocytes: delineation of two fa-responsive regions and glucose effect.

We have previously shown that adipocytes from genetically obese rats exhibited increases in GLUT4 protein and mRNA expressions. In order to elucidate the responsible defect we examined here the activity of GLUT4 promoter using adipocytes transiently transfected with -2212 + 164 rat GLUT4 gene fragment fused to luciferase reporter gene. GLUT4 promoter activity was several-fold higher in obese than in lean rat adipocytes (x4 in suckling 16 days old and x6 in weaned 30 days old rats), demonstrating the implication of transcription factors in the fatty genotype effect on GLUT4 expression. 5' deletion analysis of GLUT4 promoter allowed us to delineate two regions, -907 to -502 and -151 to -68, critical to the genotype effect, suggesting that they harbor fa-response element(s). In lean rat adipocytes GLUT4 promoter activity was not affected by the presence of glucose in the culture medium. In contrast, in obese rat adipocytes GLUT4 transcriptional activity was increased 3-fold from 0 to 5mM glucose, the concentration required for the full genotype effect, suggesting interactions between glucose and fa-dependent GLUT4 transactivator(s).

Adipocytes↗
PubMed1995

C/EBP alpha expression in adipose tissue of genetically obese Zucker rats.

The adipose tissue of genetically obese Zucker rats is characterized by coordinated tissue specific overtranscription of a subset of genes related to lipid storage such as Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH). We show that CCAAT/Enhancer Binding Protein alpha (C/EBP alpha) is an activator of GAPDH proximal promoter in transiently transfected mature rat adipocytes. C/EBP alpha mRNA levels were increased in adipose tissue but not in liver of obese as compared to lean rats at 30 days of age, i.e., when obesity is fully expressed. Nevertheless at 16 days of age, although overdevelopment of adipose tissue could be detected in preobese rats, C/EBP alpha mRNA levels were similar whatever the genotype. In conclusion C/EBP alpha mRNA is overexpressed in adipose tissue of obese rats, suggesting a possible role for this factor in the activation of lipid storage-related genes in adipose tissue of obese rats. However, C/EBP alpha overexpression is not temporally related to the onset of obesity.

Adipocytes↗
PubMed1995

Evidence of increased glyceraldehyde-3-phosphate dehydrogenase and fatty acid synthetase promoter activities in transiently transfected adipocytes from genetically obese rats.

Previous studies have shown that the adipose tissue of young genetically obese Zucker rats was characterized by a coordinate overtranscription of lipogenic genes, suggesting that the fa mutation triggers transcription factor(s) acting in common on the promoters of these genes. To test this hypothesis, we developed a system of transient transfection of rat adipocytes with constructs containing glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and fatty acid synthetase (FAS) promoters fused to gene reporter CAT. Those transfected cells expressed high levels of promoter-driven chloramphenicol acetyltransferase (CAT) activity through correctly initiated transcription as shown by primer extension analysis. Using this system we found a direct effect of insulin on GAPDH and FAS gene expression in rat adipocytes. In transfected adipocytes from obese compared to lean rats, activity of GAPDH and FAS promoters fused to CAT, was 2.6- and 8-fold increased, respectively. In contrast when reporter gene activity was driven by either phosphoenolpyruvate carboxykinase or beta-actin promoter, no difference could be observed between lean and obese, pointing out the promoter specificity of genotype effect. 5' deletion analysis of GAPDH promoter allowed us to narrow down the fa responsive region to nucleotide -488-329. As assessed by gel retardation and DNase I footprinting analysis, adipocyte nuclear protein interactions to this 159-bp fragment were found to be identical and to footprint the same 20-bp sequence. This study pointed out that overexpression of GAPDH and FAS genes in adipose tissue of genetically obese rats relies on promoter activation, through a 159-bp cis-acting region within the GAPDH promoter. The effects of the fa mutation on trans-acting factors binding to this region remain to be identified.

Adipocytes↗
PubMed1995

Regulation of glucose transporters in cultured rat adipocytes: synergistic effect of insulin and dexamethasone on GLUT4 gene expression through promoter activation.

A triggering effect of insulin on GLUT4 expression in adipocytes is consistently observed in vivo, whereas GLUT1 is roughly unaffected. However, in cultured rat adipocytes, insulin increases GLUT1 but fails to increase GLUT4, suggesting that additional factors are involved in vivo. This prompted us to evaluate the potential role of glucocorticoids as coregulators with insulin of glucose transporter expression using 3T3-F442A adipose cells and primary cultured rat adipocytes. In both systems, insulin increased and dexamethasone decreased GLUT1 messenger RNA (mRNA) and protein, an effect inhibited by the glucocorticoid antagonist RU 38486. When the two hormones were added together, the effect of dexamethasone was dominant in 3T3-F442A cells, but was totally antagonized in rat adipocytes. Moreover, in rat adipocytes, the GLUT1 gene transcription rate (run-on) was identical in the absence or presence of the two hormones. With regard to GLUT4 expression, neither insulin nor dexamethasone alone had any significant effect after 2 days of treatment. In contrast, the combined hormones markedly increased GLUT4 mRNA (+550% in rat adipocytes; +130% in 3T3-F442A cells) and protein (+164% in rat adipocytes; +79% in 3T3-F442A cells) with a 24- to 48-h delay after mRNA induction. Studies of the molecular mechanism(s) showed that exposure of rat adipocytes to dexamethasone plus insulin did not affect GLUT4 mRNA stability, but increased the GLUT4 gene transcription rate 3-fold. Transient transfections of rat adipocytes with the 5'-flanking 2.2-kilobase sequence of the rat GLUT4 gene fused to luciferase demonstrated that promoter activity was unchanged by insulin, increased 50% by dexamethasone, and increased 3-fold in the presence of both. These data show that insulin elicits an increase in GLUT4 gene expression provided glucocorticoids are present. Our results indicate that the synergism between insulin and glucocorticoids on GLUT4 gene transcription is mediated through GLUT4 promoter activation.

Adipocytes↗
PubMed1995

Sensitive northern blot hybridization using digoxigenin RNA probes for the mRNA detection of two glucose transporter isoforms.

Diseases involving glucose metabolism disorders are more and more prevalent. Therefore the question of glucose transporter gene expression is being addressed in experimental and clinical studies. Radioactive probes are generally used to assess glucose transporter mRNA levels, but these probes are short-lived, costly and harmful to the environment. Alternative methods that do not present these disadvantages, for example digoxigenin (DIG) labelled probes, might prove to be very interesting for the study of glucose transporter mRNA. The aim of the present work was to compare DIG-labelled cRNA probes to 32P-labelled cRNA probes in order to see whether or not the non-radioactive method can be used to assess glucose transporter gene expression. This work shows that DIG-labelled glucose transporter (GLUT1 and GLUT4) cRNAs are suitable probes for the assessment of these gene expressions. We have found that the DIG system offers a much higher sensitivity than the 32P system for both GLUT1 and GLUT4 mRNA detection. This represents a decisive advantage in human studies where tissue quantity is a limiting factor. In addition, stability, safety, time saving and cost reduction are other considerations that make DIG-labelled GLUT1 and GLUT4 cRNAs very attractive.

Animals↗
PubMed1994

Alteration in membrane lipid order and composition in metabolically hyperactive fatty rat adipocytes.

We have previously shown that adipose cells from young genetically obese Zucker rats are characterized by very high metabolic activity together with an increase in a wide range of membrane-mediated functions. The aim of the present study was to examine whether the physical properties of the membranes and the composition of the membrane lipids were altered in these cells. Plasma membranes and two intracellular membrane fractions were prepared by differential ultracentrifugation from inguinal adipose cells of 30-day-old obese (fa/fa) and lean (Fa/fa) littermates. The lipid order as measured by steady-state fluorescence polarization of diphenylhexatriene used as probe was markedly decreased in the plasma membranes of obese rat adipose cells. Consistent with this, the cholesterol-to-phospholipid ratio was significantly decreased, and the degree of unsaturation of the phospholipid fatty acids was significantly increased. In intracellular membranes, none of these parameters were altered by the different genotype. In fat cells from obese rats, both plasma and intracellular membranes exhibited a 2-fold decrease in the ratios of n-6/n-3 fatty acids mainly due to an enrichment in docosahexaenoic acid (22:6n-3). The data show that the fatty genotype is a determinant of membrane lipid order and composition in adipose cells. The alterations reported here for young obese Zucker rat adipocytes might be related to the metabolic hyperactivity of these cells.

Adipose Tissue↗
PubMed1994

Evidence for a sustained genetic effect on fat storage capacity in cultured adipose cells from Zucker rats.

Using mature adipocytes and preadipocytes from genetically obese Zucker rats, we investigated the cells' ability to maintain abnormal fat storage capacity when withdrawn from their in vivo environment. Long-term adipocyte cultures from obese rats displayed an increase in both glucose consumption (GC) and enzyme activities, including fatty acid synthase (4-fold), glycerol-3-phosphate dehydrogenase (4.5-fold), lipoprotein lipase (LPL; 6-fold), and malic enzyme (2.5-fold). Fully differentiated obese predipocytes exhibited a twofold increase in these enzyme activities, together with higher glucose metabolism. In obese cells, LPL mRNA was increased in both adipocytes (6-fold) and differentiated preadipocytes (2-fold). Insulin mediated an increase in GC and lipogenic enzymes in both adipocytes and preadipocytes regardless of the genotype; this effect was more marked in obese cells. Examining cultured adipocytes from rats fed a high-fat diet, we showed that the nutritional effect upon GC and lipogenic enzymes was abolished after culture. These results demonstrated that fatty mutation may be intrinsically expressed in prolonged cultured mature adipocytes and in newly differentiated adipocytes.

Adipose Tissue↗
PubMed1994

Effects of a fish oil-lard diet on rat plasma lipoproteins, liver FAS, and lipolytic enzymes.

The effects of a fish oil concentrate on blood lipids and lipoproteins were examined in relation to their effects on liver fatty acid synthase (FAS), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, adipose tissue lipoprotein lipase (LPL), and hepatic triglyceride lipase (H-TGL). For 15 days, 2-mo-old rats were fed a control diet (10% of calories from fat, 4% fat by weight) or diets with 50% of calories (25% wt/wt) provided by lard, lard and fish oil calories (35%/15%), or lard and corn oil (35%/15%). The high-lard diet increased plasma chylomicron and liver triglycerides. The high-lard diet greatly decreased FAS, HMG-CoA reductase, and LPL activities; it also reduced H-TGL activity. Compared with the lard diet, the lard-fish oil diet decreased plasma TG by drastically lowering chylomicron (4-fold, P < 0.001) and very-low-density lipoprotein levels (P < 0.001). It also reduced high-density lipoprotein levels. The lard-fish oil diet prevented hepatic triglyceride accumulation and decreased FAS activity and mass by 3.5-fold (P < 0.001) but did not further decrease HMG-CoA reductase activity. Adipose tissue LPL activity was 2.5-fold (P < 0.001) higher with the lard-fish oil diet than with the lard diet, and H-TGL activity decreased significantly (-32%, P < 0.01), despite unaltered levels of H-TGL mRNA. These effects were significant with only 10% fish oil concentrate in the lard diet. They were not observed with the lard-corn oil diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Sequence of rat lipoprotein lipase-encoding cDNA.

A rat lipoprotein lipase (LPL)-encoding cDNA (LPL) has been entirely sequenced and compared to the sequences of all the LPL cDNAs reported in other species. As expected, high homology was found between the coding exons. The putative catalytic triad, Ser132, Asp156, His241, according to human numbering, is conserved in rat. As is the case in mouse, an Asn444 present in human LPL is also missing. The major divergences between human, mouse and rat LPLs were observed in the untranslated exon 10, where (i) the rat cDNA exhibits a 157-bp insertion and an 81-bp deletion relative to human; (ii) neither the B1 repeat nor the homopurine stretch reported in mouse can be recognized, and (iii) the rat cDNA displays several A+T-rich stretches.

Amino Acid Sequence↗
PubMed1992

Differential polypeptide expression in adipose tissue of lean and obese Zucker rats. Evidence of specifically repressed peptides in 7-day-old pre-obese rats.

Using two-dimensional electrophoresis on total extracts of adipose tissue from young lean (Fa/fa) and obese (fa/fa) Zucker rats, we have investigated the existence of early events at the protein level, before obvious obesity. Our results indicate that the two genotypes do not differ at 3 days of age in terms of polypeptide pattern. By 7 days of age, two polypeptides are transiently repressed in the fatty genotype, leading us to suggest their potential involvement in the onset of obesity. However, most of the differences between the lean and obese rats are detected at 30 days of age, characterized by an increase in the accumulation of several peptides in the adipose tissue of obese rats, in good agreement with the multiple biochemical changes previously identified at this stage of the disease. These results present evidence of new peptides that may be of interest in the study of the obesity syndrome.

Adipose Tissue↗