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Biomedical subjects

M Lavau

Publications and source records attributed to M Lavau.

At least 37 records · Page 2Linked to original sources
PubMed1992

Gene expression of lipid storage-related enzymes in adipose tissue of the genetically obese Zucker rat. Co-ordinated increase in transcriptional activity and potentiation by hyperinsulinaemia.

The genetically obese Zucker rat displays excessive fat storage capacity which is due to a tissue-specific increase in the activities of a number of lipid storage-related enzymes in adipose tissue. The aim of this study was to investigate the molecular mechanism responsible for this phenomenon. Lean (Fa/fa) and obese (fa/fa) Zucker rats were studied during the early stages of adipose tissue overdevelopment, both before (at 16 days of age) and after (at 30 days of age) the emergence of hyperinsulinaemia, in order to delineate the effects of the fatty genotype independently of those of hyperinsulinaemia. Lipoprotein lipase (LPL), glycerophosphate dehydrogenase (GPDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and malic enzyme (ME) mRNA levels in the adipose tissue of lean and obese rats were assessed by Northern blot analysis, and the relative transcription rates of the corresponding genes were compared in the two genotypes by a nuclear run-on assay. In normoinsulinaemic 16-day-old pre-obese rats, mRNA levels were increased over control values (LPL, 5-fold; ME, 2-fold; GAPDH, 3-fold), in close correlation with genotype-mediated differences in enzyme activities. Stimulation of the transcription rates of the ME and GAPDH genes was observed in obese rats, which could fully account for differences in steady-state mRNA levels. At this age, GPDH activity, mRNA level and transcription rate were similar in the two genotypes. In hyperinsulinaemic 30-day-old obese rats, a 6-7-fold increase in both mRNA and the transcription rate of GPDH emerged, together with an amplification of the genotype-mediated differences observed in younger animals (GAPDH, 6-fold; ME, 7.9-fold; LPL, 10-fold). These results demonstrate that the obese genotype exerts a co-ordinated control on the expression of these genes in adipose tissue, mainly at the transcriptional level. This genotype effect is greatly amplified by the development of hyperinsulinaemia.

Adipose Tissue↗
PubMed1992

[Genes of the lipase family: comparison of nucleic and proteinic sequences].

Vertebrates' plasmatic apolipoproteins and a few number of lipases in their metabolism present sequence homologies. They are grouped in genes families. The four exons apolipoproteins gene family includes nine human genes: the divergence rate of their sequences allows to place the first ancestral gene very high in the phylogenetic tree of the evolution. However, a more recent duplication of apolipoprotein C-I gene dating from 40 millions years, may be a phylogenetic marker for the radiation of Monkeys. Pancreatic lipase and isoforms, lipoprotein-lipase and hepatic triacylglycerol-lipase form by their homologies a "superfamily" of genes, which also includes yolk proteins of Dipterians eggs. Sequence homologies of PL, LPL and HL are analysed and compared with multiple alignments of amino-acids and nucleotides on spreadsheets. From these comparisons we may characterize four classes of phylogenetic markers: 1) repetitive DNA sequence (Alu, B1, PRE-1) appeared during Mammals evolution, 2) short insertions or deletions (within N-terminal domain) and a gene conversion in guinea-pig lineage, 3) a progressive reduction of intron number during the lipases evolution, 4) several duplications of genes which have produced the five genes of this superfamily currently known in the human genome.

Amino Acid Sequence↗
PubMed1992

Genetic regulation of fatty acid synthetase expression in adipose tissue: overtranscription of the gene in genetically obese rats.

We have investigated the molecular mechanism of the overactivity of fatty acid synthetase (FAS) in adipose tissue from the genetically obese Zucker rat. Purified FAS from lean and obese rat adipose tissues displayed kinetics constants, molecular weight, and immunological properties that were identical. Western blot analysis revealed that FAS overactivity in obese versus lean rat adipose tissue was paralleled by a proportionate increase in FAS mass, i.e., 4-fold increase in suckling normoinsulinemic 16-day-old pups and 25-fold in weaned hyperinsulinemic 30-day-old rats. The determination of absolute FAS mass disclosed that FAS was quantitatively a major protein in obese rat adipose tissue accounting for 13% of cytosolic proteins versus 2% in lean rat at 30 days of age. FAS hyperabundance could be ascribed to an increased relative rate of FAS synthesis that was 6-fold higher in obese than in lean rat adipose tissue. Northern blot analysis demonstrated that FAS mRNA levels in obese rats were increased 4- and 14-fold over those of lean rats at 16 and 30 days of age, respectively, in very close proportion to the 3- and 15-fold increases in FAS gene transcription rates revealed by nuclear run-on assays. Southern analysis of genomic DNA did not allow for detecting amplification or any major structural changes in the FAS gene. It is concluded that FAS overactivity, shown here to be a life-long and general feature of all adipose tissue sites in the obese rat, arises primarily from FAS gene overtranscription.

Adipose Tissue↗
PubMed1991

Differential regulation of adipose tissue glucose transporters in genetic obesity (fatty rat). Selective increase in the adipose cell/muscle glucose transporter (GLUT 4) expression.

Adipocytes from young obese Zucker rats exhibit a hyperresponsive insulin-mediated glucose transport, together with a marked increase in cytochalasin B binding as compared with lean rat adipocytes. Here, we examined in these cells the expression of two isoforms of glucose transporter, the erythroid (GLUT 1) and the adipose cell/muscle (GLUT 4) types, in rats aged 16 or 30 d, i.e., before and after the emergence of hyperinsulinemia. GLUT 1 protein and mRNA levels were identical in the two genotypes at both ages. In contrast, the levels of GLUT 4 protein in obese rat adipocytes were 2.4- and 4.5-fold those of lean littermates at 16 and 30 d of age, respectively, in perfect agreement with the genotype effect on insulin-stimulated glucose transport activity. The levels of GLUT 4 mRNA per fat pad were increased 2.3- and 6.2-fold in obese vs. lean rats 16- and 30-d-old, indicating a pretranslational level of regulation. The obese phenotype was not associated with overexpression of GLUT 4 mRNA in gastrocnemius muscle. This work indicates that the fa gene exerts a differential control on the expression of GLUT 1 and GLUT 4 in adipose tissue and provides evidence that independent of hyperinsulinemia, genotype is a major regulatory factor of GLUT 4 expression in this tissue.

Adipose Tissue↗
PubMed1991

Adrenalectomy in the Zucker fatty rat: effect on m-RNA for malic enzyme and glyceraldehyde 3-phosphate dehydrogenase.

The effects of adrenalectomy with or without replacement doses of corticosterone were examined on the levels of messenger RNA for malic enzyme (ME) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in adipose tissue and liver from Zucker fatty (fa/fa) and littermate lean rats. The levels of both GAPDH and ME mRNAs were increased in the obese rats. Adrenalectomy markedly reduced the m-RNA for GAPDH and ME in Zucker fatty rats to the low levels observed in adrenalectomized lean rats. Corticosterone treatment induced a greater and earlier increase in mRNA levels in adrenalectomized obese rats than in adrenalectomized lean rats. Since the fatty rat represents an autosomal recessive trait, these results are consistent with the hypothesis that the genetic defect is a loss of a modulator of steroid action which normally restricts the response of genes to glucorticoid hormones.

Adipose Tissue↗
PubMed1990

Long term regulation of glucose transporters by insulin in mature 3T3-F442A adipose cells. Differential effects on two glucose transporter subtypes.

The question of a long term regulatory role of insulin on adipocyte glucose transporter content was addressed using the differentiating or fully mature 3T3-F442A adipocytes. Glucose transport was measured in intact cells. Glucose transporter content in plasma membranes and low density microsomes (LDM) was assessed by cytochalasin B binding and Western analysis. In insulin- versus spontaneously differentiated adipocytes, glucose transport and glucose transporters content of plasma membranes and LDM were increased 5-, 4-, and 2-fold, respectively. Insulin deprivation for 24 h induced a redistribution of glucose transporters in those cells which then displayed 2-fold higher glucose transport and glucose transporter content in plasma membranes than spontaneously differentiated cells and 3-fold more glucose transporters in LDM. When fully insulin-differentiated adipocytes were insulin-deprived for 4 days, there was a marked decrease in glucose transporters in both membrane fractions that was fully reversible by reexposing the cells to insulin for 4 days. Glucose uptake changes were closely proportionate to changes in glucose transporter content of plasma membranes as assessed by an antiserum to the C-terminal peptide of the erythrocyte/HepG2/brain-type glucose transporter. When Western blots were immunoblotted with 1F8 monoclonal antibody, specific for glucose transporter in insulin responsive tissues, an abundant immunoreactive protein was detected in both plasma membranes and LDM but the amount of this glucose transporter did not change with insulin exposure in any membrane fractions. In conclusion, insulin plays a long term regulatory role on cultured adipocyte glucose transporter content through a selective effect on the erythrocyte/HepG2/brain-type glucose transporter.

Adipose Tissue↗
PubMed1990

Impairment of adipsin expression is secondary to the onset of obesity in db/db mice.

The nature of the primary biochemical lesions in genetically obese mice, which might prove to be useful models for human obesity, remains totally obscure. The recent finding that the expression of adipsin was virtually suppressed in both db/db and ob/ob adult mice has opened new perspectives, suggesting a potential role for this defect in the pathogenesis of obesity. To be of etiological significance, adipsin deficiency must be present very early in life when excess fat storage starts to develop. We show here that at 10 days of age db/db pups exhibit significantly overdeveloped adipose tissue as compared with lean (+/db) pups but similar levels of both adipose tissue adipsin mRNA and serum adipsin. Adipsin expression was still normal in obese mice 15 days old but frankly deficient at 30 days of age when hyperinsulinemia has developed. Thus the defect in adipsin expression in db/db mice is a secondary feature which cannot be ascribed a role in the onset of obesity.

Adipose Tissue↗
PubMed1990

Increased growth hormone binding to liver membranes of obese Zucker rats.

Developmental changes in hepatic growth hormone binding sites were examined in the genetically obese male fa/fa rats and in the lean littermates. At 16 days, fa/fa pups are normoinsulinemic; the specific binding of 125I-hGH to liver membranes is comparable in the two genotypes. At 4 weeks and later on, plasma membranes and Golgi fractions of male obese Zucker rats have more GH binding sites than lean littermates. The GH pituitary content is comparable in the two genotypes from 2 to 8 weeks and in 14-week-old fa/fa rats it is half that in lean animals. In the two genotypes plasma IGFI dramatically increases during puberty. At 4 weeks, plasma IGFI level is significantly higher in fa/fa rats than in lean littermates. In this model of genetic obesity, an increased GH binding to liver membranes is observed after the third week of life, shortly after the onset of hyperinsulinemia in the fa/fa rat.

Animals↗
PubMed1990

Increased alpha 2-adrenergic binding sites and antilipolytic effect in adipocytes from genetically obese rats.

We have recently shown that functional alpha 2-adrenergic receptors, assessed by the alpha 2-agonist UK 14304, are present in rat white fat cells as in adipocytes of humans and other species. The aim of the present study was to further characterize rat fat cell alpha 2-adrenoceptors and to examine whether their number and biological effect were altered in fat cells from genetically obese Zucker rats. The maximal antilipolytic effect of UK 14304 was higher in obese than in lean littermates. Epinephrine, when its beta-component was blocked by propranolol, also induced an antilipolytic response that was higher in the obese rats. Similarly, 3H-labeled UK 14304 binding on adipocyte membranes was higher in obese than in lean animals. The radiolabeled alpha 2-antagonist [3H]idazoxan also recognized a higher number of sites in obese animals. However, epinephrine only partially competed for the 3H-labeled UK 14304 and [3H]idazoxan, suggesting that these imidazolinic radioligands labeled not only alpha 2-adrenoceptors but also nonadrenergic binding sites. By contrast, 3H-labeled RX 821002, an alpha 2-antagonist derived from the idazoxan family, did not recognize these sites and allowed accurate quantification of adipocyte alpha 2-adrenoceptors. The number of alpha 2-sites was higher in obese than in lean littermates (Bmax = 64 +/- 5 vs 39 +/- 2 fmol/mg protein, P less than 0.01) without change in affinity. The adipocyte alpha 2-adrenergic responsiveness showed a strong dependency on age and fattening between 5 and 10 weeks of age in both genotypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1989

Role of brown adipose tissue in glucose utilization in conscious pre-obese Zucker rats.

In 16-day-old conscious Zucker rats, at a time when pre-obese fa/fa rats were not yet hyperinsulinaemic compared with their lean Fa/fa littermates, the whole-body glucose-metabolism rate was decreased by 10% in pre-obese compared with lean pups. The markedly decreased glucose utilization found in brown adipose tissue (BAT) of pre-obese compared with lean pups accounted for at least 70% of the difference in whole-body glucose metabolism observed between the two genotypes. In pre-obese fa/fa rats, the 20% decrease in noradrenaline content of BAT reported in this study is consistent with the diminished glucose utilization by this tissue, and further supports the hypothesis of a defect in the sympathetic-nervous-system regulation of BAT metabolism as one of the primary causes for this genetic obesity.

Adipose Tissue, Brown↗
PubMed1989

Adipsin mRNA amounts are not decreased in the genetically obese Zucker rat.

Adipsin gene expression as assessed by mRNA amounts was examined in adipose tissue of genetically obese rats at the onset (16 days of age) or at later stages (30 and 60 days of age) of obesity. Amounts of mRNA were equivalent in obese and lean rats at 16 days of age. In adult rats, we observed a 2-fold decrease in adipsin mRNA in the obese rats compared with control lean rats, which was abolished by weaning the animals on a high-fat diet. Our data show that, in sharp contrast with genetically obese mice, adipsin mRNA is not suppressed in genetically obese Zucker rats.

Adipose Tissue↗
PubMed1989

Dependence on extracellular potassium of the positive inotropic response to St 587, a selective alpha-1 adrenoceptor agonist, in Zucker rat heart ventricle.

The effects of St 587, a selective alpha-1 adrenoceptor agonist, were investigated in non obese and obese Zucker rat heart ventricles. In both groups, the numbers and affinity constants for alpha-1 adrenoceptors were found to be similar. At 4 or 10 mM [K]o, St 587 failed to increase the developed tension whereas at 14 mM [K]o, St 587 significantly increased it in both groups of rats. This effect was reversed by prazosin; St 587 also increased action potential duration at 14 mM [K]o. [K]o is thus important for the occurrence of the inotropic effect of St 587 in 12 week-old Zucker rats, either non obese or obese with reduced beta-adrenoceptor responsiveness. This suggests the participation of phosphoinositide metabolism in the mechanism of St 587 inotropic effect in the rat.

Action Potentials↗
PubMed1989

Relationship between increased binding and insulin-like effects of human growth hormone in adipocytes from young fa/fa rats.

Binding and insulin-like effects of human GH (hGH) in inguinal adipocytes from young lean Fa/fa and obese fa/fa Zucker rats were studied. The binding of [125I]hGH per unit surface area is 2-fold higher in adipocytes prepared from 16- and 30-day-old fa/fa rats than in cells from lean littermates. A 3-h preincubation of the cells increases the hGH-binding capacity without changing the affinity of the binding, regardless of genotype. Freshly isolated adipocytes from 30-day-old lean rats fail to respond to hGH, whereas after preincubation of the cells, hGH produces a maximal 105% increase in glucose transport and a maximal 40% increase in glucose oxidation. In contrast, freshly isolated adipose cells from fa/fa rats are already responsive to hGH and the amplitude of the response is markedly elevated in preincubated cells, with a 430% stimulation of glucose transport. The concentration of hGH (1 nM) that inhibits 50% of [125I]hGH binding and that which produces half-maximal stimulation of glucose transport as well as glucose metabolism are not different, suggesting the absence of spare receptors for these insulin-like effects of hGH. Plots of GH effects on glucose transport as a function of receptor occupancy are linear, with a change in the slope after preincubation. Our results suggest a strong correlation between binding of hGH and actions on glucose transport and glucose metabolism in adipocytes of young Zucker rats.

Adipose Tissue↗
PubMed1988

Adipose-tissue-specific increase in glyceraldehyde-3-phosphate dehydrogenase activity and mRNA amounts in suckling pre-obese Zucker rats. Effect of weaning.

The regulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression was studied during the onset of obesity in the genetically obese (fa/fa) rat by determination of GAPDH activity and hybridizable mRNA amounts in adipose tissue and liver from suckling and weanling rats. GADPH activity remained low throughout the suckling period, and a burst of activity occurred after weaning in both lean and obese pups. As early as 7 days of age, adipose tissue from pre-obese rats displayed a significant increase in enzyme activity, whereas no difference could be detected in the liver. In both suckling (16 days of age) and weanling (30 days of age) obese rats a proportionate increase in GAPDH activity and mRNA amounts was observed in adipose tissue, but not in liver. It is concluded that the obese genotype influences GAPDH gene expression at a pretranslational level and in a tissue-specific manner. This phenomenon could partly contribute to the hyperactive fat accretion in the obese rat, since glycolysis is the major metabolic pathway for lipogenic substrates in adipose tissue.

Adipose Tissue↗
PubMed1988

Evidence of functional alpha 2-adrenergic receptors in adult-rat adipocytes by using the agonist UK 14304.

The aim of this study was to re-assess whether alpha 2-adrenergic receptors were present in rat adipocytes, by using UK 14304, a new and very selective alpha 2-agonist. The following observations demonstrate the presence of functional alpha 2-adrenoceptors in rat adipocytes. (1) Adipocyte lipolysis was dose-dependently inhibited by UK 14304 (maximal effect 80% at 1 microM-UK 14304, 45% at 10 microM-UK 14304, under basal or theophylline-stimulated conditions respectively). (2) UK 14304 bound specifically to purified plasma membranes, with Bmax. = 744 fmol/mg of protein and KD = 9 nM. (3) The effect of UK 14304 was suppressed by alpha 2-antagonists. (4) Adrenaline inhibited lipolysis upon beta-adrenergic blockade (propranolol). (5) The anti-lipolytic effect of UK 14304 was modulated by the age of the rats.

Adipose Tissue↗
PubMed1988

Increased lipoprotein lipase content in the adipose tissue of suckling and weaning obese Zucker rats.

The aim of this study was to determine whether the increase in lipoprotein lipase activity displayed by the adipose tissue of obese (fa/fa) rats as compared with that of lean (Fa/fa) rats could be ascribed to a change in the content or in the catalytic properties of the enzyme. The question was addressed in rats of two ages: in 7-day-old suckling and in 30-day-old post-weaning pups. Inguinal fat-pads were removed surgically (7 days of age) or after killing (30 days of age), and acetone-extract powders were prepared. The relative quantity of enzyme was assessed by immunotitration using an antiserum raised in goat against purified lipoprotein lipase from rat adipose tissue. The results indicate that increases in enzyme activity in obese animals were strictly paralleled by increases in the amount of enzyme in suckling as well as in post-weaning pups. Moreover, the apparent Km values of lipoprotein lipase for its substrate triacylglycerol were identical in the two genotypes. In conclusion, the genotype-mediated increase in lipoprotein lipase activity in adipose tissue of obese Zucker rats was fully accounted for by an increase in the content of the enzyme. In addition, this work documents the mechanism of the increase in lipoprotein lipase activity during weaning, which is mediated mainly through changes in the adipose-tissue enzyme content.

Adipose Tissue↗
PubMed1988

Insulin-dependent changes in subcellular distribution of liver insulin receptors in obese Zucker rats.

Acute hyperinsulinaemias induced by insulin and stimulants of insulin secretion have been shown to cause a translocation of liver insulin receptors from the cell surface to the intracellular compartment, with little or no change in total receptor number. To determine whether a similar phenomenon occurs in chronic hyperinsulinaemic states, we have carried out a longitudinal study of total, cell surface and intracellular liver insulin receptors in genetically obese Zucker rats, with spontaneously develop hyperinsulinaemia. Liver plasma membranes, Golgi-endosomal fractions, a microsomal fraction and a total particulate fraction were isolated in 2-14-week old obese (fa/fa) rats and examined for specific insulin binding relative to lean (Fa/?) age-matched animals. In 16-day old rats, which were still normoinsulinaemic, insulin binding was unchanged. Later on, as hyperinsulinaemia developed, three sequential changes in insulin binding activity were observed: first, a 25-30% increase in Golgi-endosomal fractions (20 days); then, a 50-60% decrease in Golgi-endosomal fractions (4-5 weeks); and finally, a 50% decrease in plasma membranes (11 weeks), microsomal fraction and total particulate fraction (14 weeks), accompanied by restoration in Golgi-endosomal fractions (8-11 weeks). Unlike insulin receptors, insulin extractable from Golgi-endosomal fractions at 4-5 weeks was unchanged or increased. We conclude that, although an early increase in the endocytosis of liver insulin receptors may occur in hyperinsulinaemic Zucker rats, this mechanism does not account for the later decrease in cell surface receptors observed in these animals.

Aging↗