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M Guerre-Millo

Publications and source records attributed to M Guerre-Millo.

At least 55 records · Page 3Linked to original sources
PubMed1992

Differential role of insulin receptor autophosphorylation sites 1162 and 1163 in the long-term insulin stimulation of glucose transport, glycogenesis, and protein synthesis.

The long-term regulatory effect of insulin on glucose transport activity and glucose transporter expression was examined in Chinese hamster ovary (CHO) transfectants that overexpress either human insulin receptors of the wild type (CHO-R cells) or human insulin receptors mutated at two major autophosphorylation sites, Tyr1162 and Tyr1163 (CHO-Y2 cells). Previous studies showed that, when acutely stimulated by insulin, CHO-Y2 cells exhibit decreased receptor kinase activity along with decreased signaling of several pathways, including that for glucose transport, as compared with CHO-R cells. We now report the following. (i) When treated for 24 h with insulin (10(-10) to 10(-6) M), CHO-R and CHO-Y2 cells displayed closely similar concentration-dependent increases in 2-deoxyglucose uptake. In both transfectants, the maximal insulin-induced increase (approximately 3.5-fold) in uptake was cycloheximide-sensitive and was paralleled by equivalent increases in the levels of GLUT-1 immunoreactive protein and mRNA. (ii) By contrast, under similar conditions, CHO-Y2 cells exhibited a marked decrease in their response to insulin for [U-14C]glucose incorporation into glycogen (decreased sensitivity and maximal responsiveness) and for [U-14C]leucine incorporation into protein (decreased sensitivity) as compared with CHO-R cells. (iii) After a 24-h treatment with 10(-7) M insulin, CHO-R (but not CHO-Y2) cells showed a decreased ability to respond to a subsequent acute insulin stimulation of either receptor exogenous kinase activity or 2-deoxyglucose uptake as compared with respective untreated controls. These results indicate that (i) insulin receptors mutated at Tyr1162 and Tyr1163 retain normal signaling of the long-term stimulatory effect of insulin on glucose transport activity and GLUT-1 expression, but not on glycogenesis and overall protein synthesis; (ii) these three insulin signaling pathways may be triggered by distinct domains of the insulin receptor beta-subunit; and (iii) wild-type (but not twin-tyrosine mutant) receptors undergo negative regulation by chronic insulin treatment for subsequent signaling of acute biological actions of insulin.

Animals↗
PubMed1991

Increased insulin action in rats with mild insulin deficiency induced by neonatal streptozotocin.

The effect of chronic moderate insulin deficiency on in vivo insulin action was studied in young rats after neonatal (day of birth) streptozotocin (n0-STZ model) at a time (4 wk) when basal hyperglycemia is not yet established. The insulin action was quantified in vivo during insulin-glucose clamps performed on anesthetized rats while in the postabsorptive state; under basal or hyperinsulinemic conditions, total glucose production and utilization were assessed with a [3- 3H]-glucose perfusion, and local glucose utilization was estimated by measuring 2-deoxy-D-[1-3H]glucose 6-phosphate accumulation in various tissues. Compared with controls, the 4-wk-old n0-STZ rats were normoglycemic and hypoinsulinemic (P less than 0.05). The basal glucose production rate in the diabetics was significantly greater (P less than 0.05). During the clamp studies, suppression of endogenous glucose production by submaximal (1 nmol/l) or maximal (30 nmol/l) hyperinsulinemia was similar in both groups. Overall glucose utilization in the diabetics was significantly higher in the basal state and, after submaximal or maximal hyperinsulinemia, it remained significantly greater (P less than 0.001) than the corresponding utilization in the controls. This was correlated with an increased stimulation of glucose utilization in soleus muscle, diaphragm, white adipose tissue, and brown adipose tissue. In vitro studies using inguinal adipocytes showed that the glucose oxidative pathway retained normal sensitivity to insulin in the n0-STZ rats while the glucose conversion into lipids was significantly higher at sub-maximal insulin concentration compared with the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

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↗
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

Tissue phospholipid fatty acid composition in genetically lean (Fa/-) or obese (fa/fa) Zucker female rats on the same diet.

The fatty acid composition of serum total lipids, of phospholipids of various organs (liver, heart, kidney), and of nervous structures (brain, retina, sciatic nerve, myelin, synaptosomes) have been compared in lean (Fa/-) and genetically obese (fa/fa) Zucker female rats. Both received a standard commercial diet including 37% of 18:2n-6 and 5% of n-3 polyunsaturated fatty acids (PUFA), 1.7% of which were in the form of 20:5n-3 and 22:6n-3. In comparison with lean rats, the results for the obese rats pointed out (i) no difference in the fatty acid composition of nervous structures; (ii) a decrease of 18:2n-6 (from -8% to -35%) and of 20:4n-6 (from -9% to -49%) in serum, liver and in kidney; this was compensated for by an increase in 20:3n-6 (from +30% to +320%) and in total n-3 PUFA (from +68% to +76%); (iii) a decrease of 20:4n-6 (-18%) and of 22:6n-3 (-24%) in heart compensated for by an increase in 18:2n-6 (+39%) and in 20:3n-6 (+233%); and (iv) constant levels of total PUFA (n-6 and n-3) in the various fractions studied, except in serum where this level decreased (-23%). Finally, except for the nervous structures, tissue phospholipids of obese rats included a lower proportion of 20:4n-6 and a higher proportion of 20:3n-6. This resulted in a significant reduction in the 20:4n-6/20:3n-6 ratio; by contrast, the 20:3n-6/18:2n-6 ratio increased. The results suggest that in Zucker rats, the obese character (fa/fa) affects the desaturation-elongation process of 18:2n-6 to 20:4n-6 by specifically decreasing delta 5-desaturase activity.

Animals↗
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↗
PubMed1987

Insulin receptor kinase is hyperresponsive in adipocytes of young obese Zucker rats.

Thirty-day-old obese Zucker rats have hyperresponsive adipose tissue, whereas their skeletal muscle normally responds to insulin in vitro. To further substantiate the role of insulin receptor tyrosine kinase in insulin action, we have studied the kinase activity of receptors obtained from adipocytes and skeletal muscle of these young obese Zucker rats. Insulin receptors, partially purified by wheat germ agglutinin agarose chromatography from plasma membranes of isolated adipocytes or from skeletal muscles, were studied in a cell-free system for auto-phosphorylation and for their ability to phosphorylate a synthetic glutamate-tyrosine copolymer. For an identical amount of receptors, the insulin stimulatory action on its beta-subunit receptor phosphorylation was markedly augmented in preparations from hyperresponsive adipocytes of obese animals compared with lean rats. Basal phosphorylation of adipocyte insulin receptors was nearly identical in lean and obese animals. Similarly the capacity of adipocyte insulin receptors to catalyze the phosphorylation of the synthetic substrate in response to insulin was increased. By contrast, the kinase activity of insulin receptors prepared from normally insulin-responsive skeletal muscle was similar in preparations of lean and obese rats. These results show that a state of hyperresponsiveness to insulin is correlated with a parallel increase of insulin receptor kinase activity suggesting an important role for this activity in insulin action.

Adipose Tissue↗
PubMed1987

Increased insulin mediated glucose metabolism in fat cells from I versus C57BL mice.

The purpose of this study was to determine whether adipocytes from I strain mice, which are characterized by a greater in vivo glucose tolerance than most other strains, had a higher capacity to utilize glucose in response to physiological concentrations of insulin. Using C57BL mice as a control strain, we examined the effect of insulin on glucose metabolism in epididymal and inguinal adipocytes from 2-month-old male mice. Body weight was only slightly less (7%) for the I mice than for the C57BL mice, but fat pad sizes were 60 and 20% less for epididymal and inguinal depots, respectively, in the I mice. Fat cell size was also smaller in epididymal adipocytes from the I mice than from the C57BL mice. Fat cell size of inguinal adipocytes was similar in the two strains. Without insulin the rates of [U-14C]glucose incorporation into CO2 or lipids were twofold higher in cells from the I mice than in those from the C57BL mice. Maximal insulin concentration (2.5 nM) increased glucose metabolism by 140 and 500% in epididymal and inguinal adipose cells, respectively, in the I mice versus 30 and 50% in the C57BL mice. The maximal effect of insulin was reached at a much higher insulin concentration in the I mice than in the C57BL mice. The activity of fatty acid synthetase was four- to sixfold higher in fat cells from I than in those from C57BL mice. These results demonstrate an increased insulin responsiveness of glucose metabolism in fat cells from the I mice related to an increased lipogenic capacity. Furthermore, they show that adipose tissue in mice exhibits significant regional differences in terms of insulin responsiveness of glucose metabolism.

Adipose Tissue↗
PubMed1986

Effect of lactation on insulin sensitivity of glucose metabolism in rat adipocytes.

During lactation glucose metabolism in paraovarian adipocytes is characterized by a 40 and 80% decrease of glucose incorporation into CO2 and fatty acids in the presence of insulin. In contrast with the stimulation by insulin of glucose incorporation into lactate, glycerol remains unchanged. As a result, insulin sensitivity of total glucose metabolism (oxidation and lipid synthesis) is not altered in adipocytes from lactating rats.

Adipose Tissue↗
PubMed1985

Proposed mechanism for increased insulin-mediated glucose transport in adipose cells from young, obese Zucker rats. Large intracellular pool of glucose transporters.

The mechanism for hyperresponsive insulin-mediated glucose transport in adipose cells from 30-day-old obese Zucker rats was examined. Glucose transport was assayed by measuring 3-O-methylglucose transport, and the concentration of glucose transporters was estimated by measuring specific D-glucose-inhibitable cytochalasin B binding. Insulin increased glucose transport activity by approximately 17 fmol/cell/min in cells from obese rats compared to 3 fmol/cell/min in lean littermates. Insulin increased the concentration of glucose transporters in the plasma membrane fraction by about 15 pmol/mg of membrane protein in both groups. The insulin-mediated decrease in the concentration of transporters in the low-density microsomal fraction was 30 pmol/mg of membrane protein for the obese rats compared to 15 pmol/mg of membrane protein for the lean controls. An estimated number of glucose transporters was calculated using membrane protein and enzyme recoveries for each group. Insulin increased the number of transporters in the plasma membrane by 3 X 10(6) sites/cell for the obese rats and only 0.6 X 10(6) sites/cell for the lean controls. In addition, insulin decreased the number of transporters/cell in the intracellular membrane pool by approximately 4 X 10(6) sites/cell for the obese rats and 0.9 X 10(6) sites/cells for the lean rats. The total number of transporters/cell was about 7 X 10(6) sites/cell for the obese animals and 1.6 X 10(6) sites/cell for the lean controls. In the basal state, more than 80% of these transporters were located in the intracellular pool for both the lean and obese rats. Thus, the marked hyperresponsive insulin-mediated glucose transport observed in adipose cells from 30-day-old obese Zucker rats may be the consequence of a marked increase in the number of glucose transporters in the intracellular pool.

3-O-Methylglucose↗
PubMed1985

Effect of insulin on glucose transport and metabolism in isolated fat-cells of gonadal adipose tissue from mature age-matched male and female rats.

Insulin action on glucose transport and metabolism was studied in paraovarian adipocytes from 3-month-old female rats and compared with insulin action in epididymal adipocytes from closely age-matched males. At maximal insulin concentrations the stimulations of 2-deoxyglucose uptake (4-fold the basal value) and of [U-14C]glucose incorporation into CO2 and total lipids (3- and 2-fold the basal values respectively) were similar in adipocytes from rats of both sexes. At submaximal insulin concentrations (less than 0.2 nM) the ability of paraovarian adipocytes to transport and to metabolize glucose was higher than that of epididymal adipocytes; accordingly an increase in insulin binding was observed in paraovarian adipocytes as compared with epididymal adipocytes. These results show that paraovarian adipocytes from mature female rats were highly responsive to insulin, and exhibited a higher sensitivity to the hormone than did epididymal adipocytes from male rats of the same age.

Adipose Tissue↗
PubMed1985

Clearance of compounds of different molecular size in the human placenta in vitro.

The placental clearance of selected water-soluble molecules and antipyrine was evaluated using a dual perfusion of human placental lobules in vitro. When graded according to decreasing clearance, the sequence of the molecules was as follows: water = antipyrine greater than urea greater than p-aminohippuric acid greater than inulin greater than dextran 20 greater than dextran 70. A close correlation was obtained between the clearance and the free diffusion coefficient of these molecules. However, no restricted diffusion was observed in the molecular range studied. These results suggest an equivalent pore size larger than 90 A for the human placental membrane in vitro.

Aminohippuric Acids↗
PubMed1985

Increased insulin sensitivity and responsiveness of glucose metabolism in adipocytes from female versus male rats.

This study was undertaken to examine whether there were sex-associated differences in the action of insulin on glucose metabolism in adipocytes. Insulin binding and the dose-response curves for glucose transport (assessed by measuring the cell-associated radioactivity after 15-s incubation with 50 microM [6-14C]glucose) and [U-14C]glucose (5 mM) metabolism into CO2 and lipids were compared in retroperitoneal adipocytes from age-matched (84 d) male and female rats. In addition, the activity of fatty acid synthetase, one of the key lipogenic enzymes, was determined. Fat cell size was not significantly larger in females than in males (0.238 vs. 0.209 microgram lipid per cell). At insulin concentrations less than or equal to 1.6 nM, adipocytes from females bound significantly more insulin than did adipocytes from males, due to an increased apparent affinity of the receptors for insulin. Accordingly, the sensitivity of glucose transport to insulin was greater in females than in males: insulin concentration eliciting half-maximal stimulation (ED50) = 0.19 nM vs. 0.41 nM. At maximal insulin stimulation the rates of glucose transport (12 times the basal values) were similar in the two sexes. In contrast, the maximal effect of insulin on glucose conversion to CO2 plus lipids was much greater in the adipocytes from females than males (increment over basal: 472 vs. 249 nmol/10(6) cells per 2 h). Fatty acid synthesis contributed approximately 40% of the incremental difference between the two types of adipocytes, while glyceride-glycerol synthesis contributed less than 10%. The insulin dose-response curves for adipocytes from females were shifted to the left for all the metabolic pathways investigated. The mean ED50 for total glucose metabolism in females was 50% of that in males (0.07 nM vs. 0.15 nM). Marked sex-associated differences in the action of insulin on glucose metabolism were also observed in subcutaneous inguinal adipocytes (increment over basal: 137 and 56 nmol/10(6) cells per 2 h, ED50 = 0.13 nM and 0.30 nM in females and males, respectively). The intracellular capacity to metabolize glucose through the fatty acid synthesis pathway, as assessed by FAS activity, was higher in adipocytes from females than in those from males and was greater in retroperitoneal than in inguinal adipocytes. Furthermore, by plotting the individual data, a highly significant correlation (r = 0.92, P less than 0.001) was found between the absolute effect of insulin on glucose metabolism at maximal stimulation and the fatty acid synthetase activity of the cells. These results indicate that the response of glucose metabolism to insulin in adipocytes from female as compared with male rats is characterized by two main features: (a) an increased sensitivity primarily due to an increase in insulin binding, and (b) an increased responsiveness closely associated with a postreceptor increase in the lipogenic capacity of the cell. These findings might be relevant to the differential disposition of male and female rats to develop fatness.

Adipose Tissue↗
PubMed1985

Increased capacity for fatty acid synthesis in white and brown adipose tissues from 7-day-old obese Zucker pups.

The activity of fatty acid synthetase was measured in liver, and white and brown adipose tissues of suckling lean and obese Zucker pups. In contrast to liver where no change could be observed, a significant increase in fatty acid synthetase activity was detected in both white and brown adipose tissues as early as 7 days of age. When the enzyme activity was expressed per inguinal fat pad whose weight was increased by 30 per cent in obese as compared to lean pups, a 50 per cent increase in fatty acid synthetase activity was observed. The increased activity was mediated through an increased enzyme content. Insulin levels were still identical in the two groups at 16 days of age but were significantly increased at days 17 and 18 in obese as compared to lean pups. The aetiological role of the increase in fatty acid synthetase, which is expressed in vivo, is discussed.

Adipose Tissue↗
PubMed1984

Effect of insulin on glucose metabolism in adipocytes from virgin and late-pregnant rats.

Under basal conditions (zero insulin), paraovarian adipocytes from 19-day-pregnant rats exhibited the same rates of [U-14C]glucose conversion into CO2 and total lipids as did those from age-matched virgin rats. The dose-response curves for insulin stimulation of glucose metabolism were similar in both groups: maximal response (+100% over basal values) and high sensitivity (half-maximal effect at 0.05 nM-insulin). The present results suggest that the insulin resistance in vivo that occurs during late pregnancy may involve circulating factors lost in vitro.

Adipose Tissue↗
PubMed1983

Flow-dependent transfer of antipyrine in the human placenta in vitro.

Placental transfer of antipyrine, a small liposoluble molecule, was investigated at varying flow rates using dual perfusion of human placental lobules. With a flow ratio equal to unity, the foetal transport fraction (foetal vein concentration X 100/maternal artery concentration) of antipyrine averaged 0.33. It has been suggested that effectiveness of exchange in the lobule perfused in vitro approximated that of a concurrent model with an antipyrine 'd' coefficient between 0.6 and 1.2, including shunting which diverted 16 p. 100 of foetal and 13 p. 100 of maternal flow rates from the exchange area. These observations have been discussed in relation to data obtained in other mammalian placentas and in man in vivo.

Antipyrine↗