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D Ricquier

Publications and source records attributed to D Ricquier.

At least 73 records · Page 4Linked to original sources
PubMed1997

Kupffer cells are a dominant site of uncoupling protein 2 expression in rat liver.

The mechanisms underlying thermogenesis in liver are not well understood. They may involve proteins related to the mitochondrial uncoupling protein (UCP1) of brown adipocytes. In this paper, it is demonstrated that UCP1 is not expressed in any liver cell type of rat while UCP2, a recently cloned homologue of UCP1, is expressed at a very high level in Kupffer cells but not in hepatocytes. This high level of expression of UCP2 in Kupffer cells allowed cross immunoreactivity with antibodies directed against UCP1. This cross reactivity was confirmed by the detection of UCP2 with anti-UCP1 antibody, in western blotting analysis of transfected yeasts expressing rat UCP2. The high level expression of UCP2 in Kupffer cells suggests a particular function of UCP2 in macrophages.

Animals↗
PubMed1997

In vivo resistance of lipolysis to epinephrine. A new feature of childhood onset obesity.

A decreased mobilization of triglycerides may contribute to fat accumulation in adipocytes, leading to obesity. However, this hypothesis remains to be proven. In this study, epinephrine-induced lipid mobilization was investigated in vivo in nine markedly obese children (160+/-5% ideal body weight) aged 12.1+/-0.1 yr during the dynamic phase of fat deposition, compared with six age-matched nonobese children. As an in vivo index of lipolysis, we measured glycerol flux using a nonradioactive tracer dilution approach, and plasma free fatty acid concentrations. In the basal state, the obese children had a 30% lower rate of glycerol release per unit fat mass than the lean children. To study the regulation of lipolysis, epinephrine was infused stepwise at fixed doses of 0.75 and then 1. 50 microg/min in both groups. In lean children, glycerol flux and plasma free fatty acid increased to an average of 249-246% of basal values, respectively, in response to a mean plasma epinephrine of 396+/-41 pg/ml. The corresponding increase was only 55-72% in the obese children, although their mean plasma epinephrine reached 606+/-68 pg/ml. All obese and nonobese children, except an Arg64Trp heterozygote, were homozygotes for Trp at position 64 of their beta3-adrenoreceptor. The resistance of lipolysis to epinephrine showed no relationship with the Arg64 polymorphism of the beta3-adrenoreceptor gene. In summary, in vivo lipolysis, which mostly reflects the mobilization of lipid stores from subcutaneous adipose tissue, shows a decreased sensitivity to epinephrine in childhood onset obesity. Since our study was carried out in obese children during the dynamic phase of fat accumulation, the observed resistance to catecholamines might possibly be causative rather than the result of obesity.

Adolescent↗
PubMed1997

Uncoupling protein-2: a novel gene linked to obesity and hyperinsulinemia.

A mitochondrial protein called uncoupling protein (UCP1) plays an important role in generating heat and burning calories by creating a pathway that allows dissipation of the proton electrochemical gradient across the inner mitochondrial membrane in brown adipose tissue, without coupling to any other energy-consuming process. This pathway has been implicated in the regulation of body temperature, body composition and glucose metabolism. However, UCP1-containing brown adipose tissue is unlikely to be involved in weight regulation in adult large-size animals and humans living in a thermoneutral environment (one where an animal does not have to increase oxygen consumption or energy expenditure to lose or gain heat to maintain body temperature), as there is little brown adipose tissue present. We now report the discovery of a gene that codes for a novel uncoupling protein, designated UCP2, which has 59% amino-acid identity to UCP1, and describe properties consistent with a role in diabetes and obesity. In comparison with UCP1, UCP2 has a greater effect on mitochondrial membrane potential when expressed in yeast. Compared to UCP1, the gene is widely expressed in adult human tissues, including tissues rich in macrophages, and it is upregulated in white fat in response to fat feeding. Finally, UCP2 maps to regions of human chromosome 11 and mouse chromosome 7 that have been linked to hyperinsulinaemia and obesity. Our findings suggest that UCP2 has a unique role in energy balance, body weight regulation and thermoregulation and their responses to inflammatory stimuli.

Adipose Tissue↗
PubMed1997

Linkage between markers in the vicinity of the uncoupling protein 2 gene and resting metabolic rate in humans.

The recent cloning of a gene that codes for a novel uncoupling protein, UCP2, which is expressed in a wide range of adult human tissues, has raised the possibility that it may be involved in regulation of energy balance. To explore this concept we have investigated potential linkage relationships between three microsatellite markers which encompass the UCP2 gene location on 11q13 with resting metabolic rate (RMR), body mass index, percentage body fat (%FAT) and fat mass (FM) in 640 individuals from 155 pedigrees from the Québec Family Study. Using a linkage analysis strategy based on sibling, avuncular, grandparental and cousin pairs, strong evidence of linkage was found between the marker D11S911 (P = 0.000002) and RMR, with more moderate evidence for D11S916 (P = 0.006) and D11S1321 (P = 0.02). Suggestive evidence of linkage was also observed between D11S1321 and %FAT (P = 0.04) and FM (P = 0.02). It is concluded that the three markers encompassing the UCP2 locus and spanning a 5 cM region on 11q13 are linked to resting energy expenditure in adult humans. The evidence is strong enough to warrant a search for DNA sequence variation in the gene itself.

Adult↗
PubMed1997

Leptin gene is expressed in rat brown adipose tissue at birth.

The ob gene product leptin is secreted from adipose tissue. Leptin has dramatic effects on food intake and energy expenditure in rodents. Brown adipose tissue is the first form of adipose tissue to appear during development, and is present at birth in most species. The development of a leptin feedback system in early life and the relative role of the brown and white adipose tissues have not yet been revealed. We have investigated the expression of ob/leptin mRNA in brown adipose tissue around birth and with respect to feeding. Northern blotting analysis and in situ hybridization experiments demonstrated the presence of leptin mRNA in brown adipose tissue at 0, 18, and 24 h after birth. The leptin mRNA level was decreased at 8 h postpartum in fed animals and at 18 or 24 h in the absence of feeding. In addition, circulating leptin was detected in the plasma of newborn rats at 0, 10, or 24 h after birth, whereas it was not detectable in 10 h-old animals that did not suckle at their mother. The presence at birth of ob mRNA and circulating leptin, as well as the early effect of suckling on ob mRNA levels, suggests the precocious involvement of leptin in the control of food intake.

Adipose Tissue, Brown↗
PubMed1996

Essential cis-acting elements in rat uncoupling protein gene are in an enhancer containing a complex retinoic acid response domain.

Transgenic mice were generated with a transgene containing the 211-base pair (bp) enhancer and 0.4 kilobase pairs of 5'-flanking DNA of the uncoupling protein (ucp) gene. Expression of this transgene was restricted to brown adipose tissue and was inducible by cold exposure or treatment of transgenic mice by norepinephrine, retinoic acid (RA), or CL-316,243 beta3-adrenoreceptor agonist. A search for retinoic acid response elements in the ucp gene enhancer was undertaken using mutagenesis and transfection of cultured cells with chloramphenicol acetyltransferase constructs. Deletion or mutations of several putative retinoic acid response elements were ineffective. Mutations of a TGAATCA region dramatically decreased the transcriptional activity in the presence of RA. In vitro this region was able to bind a complex containing proteins recognized by antibodies against Jun or Fos. Mutations of an adjacent region related to an inverted repeat of type 2 also markedly decreased RA effect. This region was able to bind in vitro retinoid X receptor alpha and retinoic acid receptor beta. The two regions form an activating region between bp -2421 and -2402 (referred to as the ucp gene-activating region), which has an enhancer activity but cannot confer RA response to a promoter. This response was obtained with a larger DNA fragment (bp -2489 to -2398) constituting a complex RA response domain.

Adipose Tissue, Brown↗
PubMed1996

Activation of the uncoupling protein by fatty acids is modulated by mutations in the C-terminal region of the protein.

The transport properties of the uncoupling protein (UCP) from brown adipose tissue have been studied in mutants where Cys304 has been replaced by either Gly, Ala, Ser, Thr, Ile or Trp. This position is only two residues away from the C-terminus of the protein, a region that faces the cytosolic side of the mitochondrial inner membrane. Mutant proteins have been expressed in Saccharomyces cerevisiae and their activity determined in situ by comparing yeast growth rates in the presence and absence of 2-bromopalmitate. Their bioenergetic properties have been studied in isolated mitochondria by determining the effects of fatty acids and nucleotides on the proton permeability and NADH oxidation rate. It is revealed that substitution of Cys304 by non-charged residues alters the response of UCP to fatty acids. The most effective substitution is Cys for Gly since it greatly enhances the sensitivity to palmitate, decreasing threefold the concentration required for half-maximal stimulation of respiration. The opposite extreme is the substitution by Ala which increases twofold the half-maximal concentration. We conclude that the C-terminal region participates in the fatty acid regulation of UCP activity. The observed correlation between yeast growth rates in the presence of bromopalmitate and the calculated activation constants for respiration in isolated mitochondria validates growth analysis as a method to screen the in situ activity of UCP mutants.

Amino Acid Sequence↗
PubMed1996

Evidence for numerous brown adipocytes lacking functional beta 3-adrenoceptors in fat pads from nonhuman primates.

Brown adipose tissue (BAT) is involved in the control of energy balance and has been demonstrated to be activated through beta 3-adrenoceptor (beta 3-AR) occupation in rodents. The ability to specifically activate energy expenditure via this receptor is of great interest for the treatment of obesity. Nevertheless, the extent of BAT and the presence of a functional beta 3-AR in humans are now debated, and this situation is difficult to clarify for evident practical and ethical reasons. We investigated the occurrence of brown adipocytes in fat deposits of prepubertal baboons using antibodies raised against uncoupling protein (UCP) in Western blotting and immunocytology experiments. UCP was detected in all types of fat pads studied and was revealed in multilocular cells. Pericardiac and axillary adipose tissues displayed large amounts of UCP and can be assimilated to typical BAT. Most of the other pads looked like white adipose tissue, but exhibited areas with clusters of brown adipocytes and, thus, can be assimilated to the convertible adipose tissue as previously described in rodents. The presence of beta 3-ARs was evaluated by both beta 2-agonist-stimulated lipolysis and messenger ribonucleic acid (mRNA) expression studies. There was no significant lipolytic effect of any of the beta 3-AR agonists tested (SR 58611A, BRL 37344, CGP 12177, or CL 316243) in either white or brown tissues. PCR analysis demonstrated that beta 3-AR mRNA expression is not related to the UCP content of fat pads and that beta 3-AR expression is low. This study demonstrates the presence of great proportions of brown adipocytes in adipose tissue and the heterogeneity of the fat pads in baboons. The lack of a metabolic effect of beta 3-agonists combined with the weak expression of beta 3-AR mRNAs raise the question of the role of beta 3-ARs in adipose tissues of primates.

Adipose Tissue, Brown↗
PubMed1996

The Bcl I polymorphism of the human uncoupling protein (ucp) gene is due to a point mutation in the 5'-flanking region.

The polymorphic Bcl I site in the human ucp gene associated to percentage fat gain over time in the Québec Family Study cohort (Oppert et al. Int J Obesity 1994; 18: 526-531) has been positioned to the 5'-flanking region. This polymorphism results from a unique A/G mutation. Oligonucleotides used to amplify the polymorphic region, and allowing future studies of any cohort of patients, are described.

Base Sequence↗
PubMed1996

Evidence from in vitro differentiating cells that adrenoceptor agonists can increase uncoupling protein mRNA level in adipocytes of adult humans: an RT-PCR study.

In vivo data have suggested that adrenergic signals can reactivate dormant brown adipocytes in adult humans. We report here a system based on primary cultures of perirenal adipocytes from human adults and reverse transcription-PCR of uncoupling protein mRNA. Norepinephrine and compounds classified as beta 3-adrenoceptor agonists in rodents increased uncoupling protein mRNA level in human adipocytes (presumably brown adipocytes). Although we did not demonstrate that the observed effect was mediated by beta 3-adrenoceptors, it is proposed that this system could be used to appreciate the ability of beta-adrenoceptor agonists to activate UCP gene transcription and help to select beta 3-adrenoceptor agonists and antagonists prior to in vivo trials; indeed, the difficulty in developing such drugs that are effective in humans may result from the fact that the screening of molecules has historically been made in rodents.

Adipocytes↗
PubMed1996

Polymorphisms of uncoupling protein (UCP) and beta 3 adrenoreceptor genes in obese people submitted to a low calorie diet.

OBJECTIVE: To investigate whether the genetic polymorphisms of the uncoupling protein (UCP) and beta 3 adrenergic receptor (beta 3 AR) were associated with differences of weight loss in obese patients submitted to a low calorie diet. DESIGN: Longitudinal, clinical intervention study of a 25% restriction in energy intake with respect to genotypes. SUBJECTS: 163 patients with a body mass index above 27. MEASUREMENTS: Body weight and body mass index at baseline and after 2.5 months, genotypes by polymerase chain reaction followed by enzymatic digestion. RESULTS: For the UCP polymorphism, two alleles, 1 and 2 were identified with respective frequencies of 0.27 and 0.73. The allele 1 was associated with lower body weight loss after diet: 4,6,5.7 and 7.1 kg for the 1-1, 1-2 and 2-2 genotypes respectively (P < 0.05). No difference in weight loss was found according to the beta 3 AR Trp64Arg mutation. CONCLUSIONS: A genetic variant of the UCP gene is associated with a resistance to low calorie diet. This result, together with previous data on body weight gain, supports the hypothesis of a role of UCP and brown adipose tissue in the body weight regulation in humans. The importance of the Trp64Arg mutation of the beta 3 AR in the resistance to low calorie diet is still to demonstrate.

Adult↗
PubMed1996

Additive effect of A-->G (-3826) variant of the uncoupling protein gene and the Trp64Arg mutation of the beta 3-adrenergic receptor gene on weight gain in morbid obesity.

OBJECTIVE: Obesity results from an imbalance between caloric intake and energy expenditure, which is partly genetically determined. We have investigated, using a PCR-RFLP assay, the effects on weight gain of two genetic variants of the uncoupling proteins and the beta 3-adrenoceptor, two major expressed proteins of the brown adipose tissue (BAT) involved in thermo-genesis. SUBJECTS: 238 morbidly obese and 91 non obese Caucasian subjects. RESULTS: A high prevalence (27%) in French Caucasians of the A-->G change variation located in the 5' flanking domain of the UCP gene was observed with no significant difference between morbidly obese patients and non obese subjects, suggesting that UCP gene is not a major gene for obesity. However, in the population of morbidly obese subjects, the presence of the A-->G allelic variant of the UCP gene showed to be an associated factor of high weight gain during adult life (odd-ratio: 1.4, P = 0.02). Such an association was previously described for the Trp64Arg mutation of the beta 3-AR gene. Furthermore, an additive effect of these two gene variants on weight gain was observed (Odd-Ratio: 4.95, trend test: P = 0.05). The attributable risks for UCP gene and beta 3-AR gene variants were respectively: 25% and 9%. CONCLUSION: These data support the hypothesis of a possible link between energy balance, BAT and weight gain in human.

Adipose Tissue, Brown↗
PubMed1995

Control of beta 3-adrenergic receptor gene expression in brown adipocytes in culture.

Brown adipose tissue is a mammalian thermogenic tissue. Its ability to dissipate energy as heat is due to a unique mitochondrial protein, uncoupling protein (UCP). Activation and expression of UCP is under control of the sympathetic nervous system acting through beta -adrenergic receptors (AR). In this study we used Siberian hamster brown adipocytes differentiated in vitro to investigate the expression of the fat specific beta 3-AR. Binding studies using the new labelled beta 3 adrenergic ligand [3H]SB 206606 showed a density of beta 3-AR in brown adipocyte plasma membranes comparable to that measured in vivo. beta 3-AR mRNA expression was very high in mature brown adipocytes and was started to be expressed during differentiation before UCP mRNA. Its half-life was approximately 50 min. Treatment of cells with non-specific beta adrenergic agonists, specific beta 3-adrenergic agonists, and dibutyryl cyclic AMP resulted in a marked down regulation of beta 3-AR mRNA level within several hours.

Adipose Tissue, Brown↗
PubMed1994

In vitro interactions between nuclear proteins and uncoupling protein gene promoter reveal several putative transactivating factors including Ets1, retinoid X receptor, thyroid hormone receptor, and a CACCC box-binding protein.

Previous studies of rat ucp (uncoupling protein) gene organization carried out in this laboratory identified regulatory sequences located in the 5'-flanking region. In this work, DNase I footprint analysis of the enhancer revealed two domains at base pairs (bp) -2444 to -2423 and bp -2352 to -2319. The former domain can bind in vitro, in a cooperative manner, factors related to nuclear factor 1 and Ets1; the latter domain contains a type 3 directly repeated sequence that was shown to be able to bind the retinoid X and triiodothyronine receptors. Moreover, a positive effect of retinoic acid on ucp mRNA levels in immortalized brown adipocytes was observed. DNase I footprint analysis identified two hypersensitive regions, A and B, at bp -509 to -472 and bp -403 to -350, respectively; region A contains a repeated CACCC box, and region B can bind protein related to Ets1. The A box differentially binds liver and brown adipose tissue nuclear proteins and could be involved in uncoupling protein induction. Further analysis showed three foot-printed boxes, C-E, at bp -182 to -159, -147 to -120, and -111 to -85, able to bind in vitro proteins related to nuclear factor 1, cAMP response element-binding protein, and Sp1, respectively.

Adipose Tissue, Brown↗
PubMed1994

A sequence related to a DNA recognition element is essential for the inhibition by nucleotides of proton transport through the mitochondrial uncoupling protein.

The uncoupling protein (UCP) is uniquely expressed in brown adipose tissue, which is a thermogenic organ of mammals. The UCP uncouples mitochondrial respiration from ATP production by introducing a proton conducting pathway through the mitochondrial inner membrane. The activity of the UCP is regulated: nucleotide binding to the UCP inhibits proton conductance whereas free fatty acids increase it. The similarities between the UCP, the ADP/ATP carrier and the DNA recognition element found in the DNA binding domain of the estrogen receptor suggested that these proteins could share common features in their respective interactions with free nucleotides or DNA, and thus defined a putative 'nucleotide recognition element' in the UCP. This article provides demonstration of the validity of this hypothesis. The putative nucleotide recognition element corresponding to the amino acids 261-269 of the UCP was gradually destroyed, and these mutant proteins were expressed in yeast. Flow cytometry, measuring the mitochondrial membrane potential in vivo, showed increased uncoupling activities of these mutant proteins, and was corroborated with studies with isolated mitochondria. The deletion of the three amino acids Phe267, Lys268 and Gly269, resulted in a mutant where proton leak could be activated by fatty acids but not inhibited by nucleotides.

Amino Acid Sequence↗
PubMed1994

Expression of beta 1- and beta 3-adrenergic-receptor messages and adenylate cyclase beta-adrenergic response in bovine perirenal adipose tissue during its transformation from brown into white fat.

Possible modifications of the beta-adrenergic effector system during the development of bovine perirenal brown adipose tissue (BAT) in utero and its transformation into white-like adipose tissue after birth were studied. The parameters assessed were the level of expression of beta 1-, beta 2- and beta 3-adrenergic receptor (AR) mRNAs and the response of the plasma-membrane adenylate cyclase to (-)-isoprenaline and to the beta 3-agonist BRL 37344. The beta 3-AR mRNA was found to be expressed very early in utero, i.e. before the third month of foetal life. Then it increased dramatically (9-fold) between month 6 of foetal life and birth. A high beta 3-AR mRNA level was maintained after birth up to an age of 3 months. After conversion of BAT into white-like adipose tissue, i.e. in the adult bovine, the beta 3-AR mRNA expression became small or not detectable, and the beta 1-AR mRNA, which was expressed much less than the beta 3-AR mRNA in foetal life, became predominant. A response of the adenylate cyclase to (-)-isoprenaline was observed in foetal life (3.1-fold stimulation). It decreased after birth (1.8-fold stimulation) and then remained constant until adulthood. A response to BRL 37344 was also observed in foetal life (1.8-fold stimulation). It was maintained after birth, but disappeared in the adult. A possible relationship between the beta-AR expression and the adenylate cyclase response to (-)-isoprenaline on the one hand and the uncoupling-protein expression on the other is discussed. The bovine might represent a good model to understand the transition from brown to white fat in the human.

Adenylyl Cyclases↗
PubMed1994

Characterization of the novel brown adipocyte cell line HIB 1B. Adrenergic pathways involved in regulation of uncoupling protein gene expression.

The HIB 1B cell line, derived from a brown fat tumor of a transgenic mouse, is the first established brown adipocyte cell line capable of expressing the brown fat-specific mitochondrial uncoupling protein (UCP). UCP gene expression, which was virtually undetectable under basic conditions, was stimulated by acute catecholamine or cyclic AMP treatment to levels comparable to primary cultures of brown adipocytes. Elevation of UCP mRNA levels following stimulation was very rapid but transient, decreasing after about 4 hours with a half-life between 9 and 13 hours. Immunoblotting showed the presence of UCP in HIB 1B mitochondria, but expression was much lower than observed in BAT or primary cultures of brown adipocytes. Upon transfection of HIB 1B cells with a reporter gene containing the UCP promoter, the activity of the transgene was regulatable by cAMP and norepinephrine. Investigation of the possible adrenergic receptors involved in UCP stimulation showed that specific beta 3-adrenergic agonists were much less effective than nonspecific beta-adrenergic agonists and that mRNA levels of the atypical, fat-specific beta 3-adrenoceptor were lower than those observed in brown adipocytes differentiated in primary culture. From pharmacological evidence we conclude that beta 3-adrenergic receptors account for approximately 30-40% of catecholamine induced UCP gene stimulation, whereas about 60-70% is stimulated via the classical beta 1/2 adrenergic pathway. We conclude that HIB 1B cells represent a functional system for the study of mechanisms related to brown adipose thermogenesis.

Adipocytes↗