Reduction of diet-induced obesity in transgenic mice overexpressing uncoupling protein 3 in skeletal muscle

Aims/hypothesis It has been suggested that uncoupling protein 3 (UCP3) can increase energy expenditure, thereby regulating body weight. Although studies on UCP3 knock-out mice suggest that lack of UCP3 function does not cause obesity or Type 2 diabetes, it is possible that up-regulation of UCP3 function improves these disorders or their clinical sequelae. A 10- to 20-fold increase of UCP3 gene expression is achievable through physiological or pharmacological stimuli. We examined the phenotype of transgenic mice with approximately 18-fold overexpression of mouse UCP3 mRNA in skeletal muscle.Methods We generated transgenic mice with approximately 18-fold overexpression of mouse UCP3 mRNA in skeletal muscle under control of the skeletal muscle-specific muscle creatine kinase gene promoter. The phenotype of these mice was analysed either on a standard diet or on a 4-week high-fat diet.Results In mice on standard chow, there was no difference in body weight, oxygen consumption and mitochondrial protonmotive force between transgenic mice and non-transgenic littermates. However, transgenic mice tended to have lower body weight, increased oxygen consumption and decreased mitochondrial protonmotive force than the control mice. Transgenic mice on a 4-week high-fat diet consumed much more oxygen and had noticeably less weight gain and less epididymal fat, as well as better glucose tolerance than non-transgenic littermates.Conclusions/interpretation Our study shows that 18-fold overexpression of UCP3 mRNA in the skeletal muscle reduced diet-induced obesity. An 18-fold increase of UCP3 mRNA can be attained by physiological or pharmacological stimuli, suggesting that UCP3 has therapeutic potential in the treatment of obesity.Abbreviations UCP3 uncoupling protein 3 - UCP2 uncoupling protein 2 - UCP1 uncoupling protein 1 - PPAR peroxisome-proliferator-activated receptor - MCK muscle creatine kinase - p mitochondrial protonmotive force     

瘦素、脂肪酸对大鼠胰岛细胞解偶联蛋白2 mRNA表达的影响

以瘦素、脂肪酸作用于体外培养的大鼠胰岛细胞，以甘油三酯含量，解偶联蛋白2 mRNA表达水平为指标，显示瘦素通过外周途径调节产热，脂肪酸可损害胰岛功能。     

Short-term beta-adrenergic regulation of leptin, adiponectin and interleukin-6 secretion in vivo in lean and obese subjects

Aim: Adipose tissue and skeletal muscle are endocrine organs, secreting substances that have been implicated in obesity‐related disorders. This study examined short‐term β‐adrenergic regulation of circulating leptin, adiponectin and interleukin‐6 (IL‐6) concentrations and secretion from abdominal subcutaneous adipose tissue and muscle (IL‐6) in vivo in lean and obese subjects. Methods: Systemic concentrations and net fluxes of leptin, adiponectin and IL‐6 across abdominal subcutaneous adipose tissue and forearm skeletal muscle (IL‐6) were assessed before and during β‐adrenergic stimulation (intravenous isoprenaline infusion) in 13 lean and 10 obese men. Results: Basal circulating leptin concentrations were higher in the obese (p < 0.001), while circulating adiponectin (p = 0.45) and IL‐6 concentrations (p = 0.41) were not different between groups. β‐Adrenergic stimulation decreased leptin concentrations in both groups (p < 0.01), but did not reduce net abdominal subcutaneous adipose tissue leptin release. Increased leptin clearance and/or decreased leptin secretion from other fat depots may explain the reduction in leptin concentrations. Adiponectin concentrations remained unchanged during β‐adrenergic stimulation in both groups. β‐Adrenergic stimulation increased IL‐6 concentration, which was more pronounced in the obese (p = 0.01 vs. lean). This cannot be explained by increased IL‐6 release per unit abdominal subcutaneous adipose tissue and muscle but might be because of the increased fat mass and fat‐free mass at whole‐body level. Conclusions: Short‐term β‐adrenergic stimulation decreases leptin concentrations, which cannot be explained by reduced net leptin release from abdominal subcutaneous adipose tissue, while it elevates IL‐6 concentration partly by increased release from this fat depot and muscle. Finally, β‐adrenergic stimulation has no short‐term regulatory role in adiponectin secretion.     

Mutational analysis of the coding region of the uncoupling protein 2 gene in obese NIDDM patients: Impact of a common amino acid polymorphism on juvenile and maturity onset forms of obesity and insulin resistance

Summary Recently, a gene encoding a novel human uncoupling protein, designated UCP2, was discovered. The murine UCP2 was mapped to a region on mouse chromosome 7 which in several models has been shown to be linked to obesity and hyperinsulinaemia. Single strand conformation polymorphism (SSCP) analysis and direct sequencing of the coding region of the UCP2 gene in 35 obese Caucasian NIDDM patients of Danish ancestry revealed one nucleotide substitution, replacing an alanine with a valine at codon 55. The amino acid polymorphism was present in 24 of the 35 (69 %) examined subjects. The allelic frequency of the A/V55 variant was 48.3 % (95 % CI: 42.5–54.1 %) among 144 subjects with juvenile onset obesity, 45.6 % (40.5–50.7 %) among 182 subjects randomly selected at the draft board examination, and 45.5 % (37.1–53.9 %) among lean control subjects selected from the same study cohort. Within these cohorts there were no differences in BMI values at different ages among wild-type carriers and A/V55 carriers. In a population-based sample of 369 young healthy Caucasians the variant showed no association with alterations in BMI, waist-to-hip ratio, fat mass or weight gain during childhood or adolescence. The A/V55 polymorphism was not related to alterations in fasting values of serum insulin and C-peptide or to an impaired insulin sensitivity index. We conclude that genetic variability in the human UCP2 gene is not a common factor contributing to NIDDM in obese Danish Caucasian subjects and the common A/V55 amino acid polymorphism of the gene is not implicated in the pathogenesis of juvenile or maturity onset obesity or insulin resistance in Caucasians. [Diabetologia (1997) 40: 1227–1230] Received: 20 June 1997     

Role of age and uncoupling protein-2 in oxidative stress, RAGE/AGE interaction and inflammatory liver injury

The objective of this study is to clarify whether age-related oxidative stress enhances hepatic vulnerability via increased interaction of advanced glycation endproducts (AGE) with their receptor RAGE. To further address the role of uncoupling of mitochondrial respiration, mitochondrial uncoupling protein-2 wild-type (UCP2+/+) and knock out (UCP2−/−) mice were used and studied at an age of 8 (young), 38 (adult) and 76 weeks (senescent). First, we could show that UCP2 protein expression increased with age in UCP2+/+ mice. Second, in both mouse strains oxidative stress, as measured by malondialdehyde concentrations and the ratio of glutathione to glutathione disulfide, as well as hepatic RAGE expression and highly modified AGE accumulation significantly increased with age. This, however, was far more pronounced in UCP2−/− mice, in particular at the young age of 8 wk. In addition, the hepatic activity of the AGE precursor detoxifying enzyme glyoxalase-I was significantly decreased in 8 wk old UCP2−/− animals and concomitantly caused 2-fold higher levels of methylglyoxal-modified AGE in these animals. We further showed that the numbers of hepatic cells expressing sRAGE which acts as a decoy for RAGE ligands decreased with age and were markedly lower in the UCP2−/− than the UCP2+/+ mice. As a consequence, young 8 wk old UCP2−/− mice benefited from treatment with recombinant mouse RAGE to block the RAGE/AGE interaction, when challenged with galactosamine/lipopolysaccharide for the induction of acute liver injury. They showed less pronounced tissue damage and slightly lower mortality rate, while older UCP2+/+ and UCP2−/− mice revealed comparably high mortality rates and extent of liver injury, irrespective of their treatment with rRAGE. Taken together, the present study underlines the role of UCP2 in the age-related increase of oxidative stress and the oxidative stress-related RAGE/AGE interaction. In young animals, blockade of the RAGE/AGE interaction is of benefit, while in older animals, this protective effect is lost, supposedly due to the fact that with age other factors than enhanced hepatic glycation products predominantly determine liver injury and injury-related mortality rate.     

Evidence that single nucleotide polymorphism in the uncoupling protein 3 (UCP3) gene influences fat distribution in women of European and Asian origin

Abstract Aims/hypothesis. Uncoupling proteins are mitochondrial transmembrane carriers implicated in the regulation of energy balance. Dysfunction of UCP3 (the predominant uncoupling protein in skeletal muscle) might therefore be expected to reduce thermogenic capacity, alter energy homeostasis and influence predisposition to obesity and Type II (non-insulin-dependent) diabetes mellitus. A variant in the putative promoter region of UCP3 (–55 c→t) has recently been identified, and an association with obesity reported in French subjects. Our aim was to study the pathophysiological role of this variant in diabetes-related and obesity-related traits using two distinct ethnic populations. Methods. The –55 c→t variant was genotyped in 85 South Indian and 150 European parent-offspring trios ascertained through Type II diabetic probands and in 455 South Indian subjects initially recruited to an urban survey into the prevalence of diabetes. Results. In South Indian and European parent-offspring trios there was no preferential transmission of either allele at the –55 c→t polymorphism to diabetic offspring (South Indians, p = 0.60; Europeans, p = 0.15). When family members were analysed for intermediate traits, the t-allele was associated with increased waist-to-hip ratio but only in females (South Indian mothers p = 0.036, daughters p = 0.032: European mothers p = 0.037, daughters p = 0.14). These findings were replicated in South Indian females from the population-based survey (p = 0.039). Conclusion/interpretation. The consistent association between the t-allele at this locus and increased waist-to-hip ratio in women from three separate data sets indicates that variation at this polymorphism (or another locus with which it is in linkage disequilibrium) influences fat distribution but that this effect is restricted to females. [Diabetologia (2000) 43: 1558–1564] Received: 8 June 2000 and in final revised form: 6 September 2000     

Resistance to high-fat-diet-induced obesity and sexual dimorphism in the metabolic responses of transgenic mice with moderate uncoupling protein 3 overexpression in glycolytic skeletal muscles

Aims/hypothesis Uncoupling protein (UCP) 3 is a mitochondrial inner membrane protein expressed predominantly in glycolytic skeletal muscles. Its role in vivo remains poorly understood. The aim of the present work was to produce a mouse model with moderate overproduction and proper fibre-type distribution of UCP3. Methods Transgenic mice were created with a 16 kb region encompassing the human UCP3 gene. Mitochondrial uncoupling was investigated on permeabilised muscle fibres. Changes in body weight, adiposity and glucose or insulin tolerance were assessed in mice fed chow and high-fat diets. Indirect calorimetry was used to determine whole-body energy expenditure and substrate utilisation. Results Transgenic mice showed a twofold increase in UCP3 protein levels specifically in glycolytic muscles. Mitochondrial respiration revealed an increase of uncoupling in glycolytic but not in oxidative muscles. Transgenic mice gained less weight than wild-type littermates due to lower adipose tissue accretion when fed a high-fat diet. Animals showed a sexual dimorphism in metabolic responses. Female transgenic mice were more glucose-sensitive than wild-type animals, while male transgenic mice with high body weights had impaired glucose and insulin tolerance. Measurements of RQs in mice fed chow and high-fat diets suggested an impairment of metabolic flexibility in transgenic male mice. Conclusions/interpretation Our data show that physiological overproduction of UCP3 in glycolytic muscles results in mitochondrial uncoupling, resistance to high-fat diet-induced obesity and sex specificity regarding insulin sensitivity and whole-body substrate utilisation. C. Tiraby and G. Tavernier contributed equally to this study.     

Influence of norepinephrine,growth hormone and fasting on FFA mobilization and glucose metabolism in lean and obese subjects

Summary The influence of norepinephrine (NE), human growth hormone (HGH) and fasting on FFA mobilization and carbohydrate metabolism has been studied in 47 obese females and 72 nonobese control subjects (35 females and 37 males). — Weight-related doses of NE infused for 2 h (0.1 /kg/min) induced a much greater rise in plasma FFA and blood glucose concentrations in obese than in normal subjects. With a fixed dose (10 /min for 2 h), FFA response was still significantly higher in the overweight than in the lean subjects, while glucose réponses were similar in both groups. Among the control subjects, males and females behaved similarily. — The plasma FFA rise observed in the 4 h following thei. v. injection of HGH (10 mg) was not statistically different in obese females, normal males and normal females. — These results suggest that human obese adipose tissue has no impaired sensitivity toward the lipolytic action of NE and HGH. — During fasting, obese, when compared with normal subjects, showed a smaller increase in plasma FFA level together with a smaller decrease in glucose flux. The possible relationship between these 2 anomalies is discussed, considering that glucose deficiency has a major role in regulating FFA mobilization during fasting.

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Einflu von Noradrenalin, Wachstumshormon und Fasten auf die FFS-Freisetzung und den Glucosestoffwechsel bei Übergewichtigen und Normalpersonen

Zusammenfassung Die Wirkung von Noradrenalin, Wachstumshormon und Fasten auf die Mobilisierung der freien Fettsäuren und den Glucosestoffweehsel wurde bei 47 übergewichtigen Frauen und 72 Kontrollpersonen (35 Frauen und 37 Männern) verglichen. — Nach einer zweistündigen Infusion mit 0,1 g/kg/min führte das Noradrenalin zu einem Anstieg der Plasma-FFS und des Blutzuckerspiegels, der bei den Übergewichtigen wesentlich stärker ausgeprägt war als bei den Normalpersonen. Mit einer konstanten Dosis von 10 g/min fiel die Steigerung der FFS bei den Adipösen immer noch signifikant höher aus, während der blutzuckersteigernde Effekt in beiden Kollektiven die gleiche Größenordnung erreichte. Die Kontrollpersonen zeigten keinen signifikanten Unterschied im Verhalten der beiden Geschlechter. — Die Erhöhung der FFS nach i.v. Verabreichung von menschlichem Wachstumshormon (10 mg) wurde über 4 Std. verfolgt, wobei sich keine Unterschiede zwischen den übergewichtigen Frauen und den Normalpersonen beider Geschlechter ergaben. — Diese Ergebnisse lassen vermuten, daß das Fettgewebe bei Adipösen eine normale Empfindlichkeit gegenüber der Wirkung von Noradrenalin und Somatotropin aufweist. — Fasten führte bei den übergewichtigen Patienten zu einem geringeren Anstieg der FFS und zu einer weniger ausgeprägten Reduktion des Glucoseabstroms als bei den Kontrollpersonen. Die möglichen Beziehungen zwischen den beiden Anomalien werden unter Berücksichtigung der Rolle diskutiert, die die der Glucosemangel bei der Fettmobilisierung während des Fastens spielt.

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Influence de la noradrénaline, de l'hormone de croissance et du jeûne sur la mobilisation des FFA et sur le métabolisme glucidique chez des sujets obèses et normaux

Résumé L'action de la noradrénaline, de l'hormone de croissance et du jeûne sur la mobilisation des FFA et sur le métabolisme glucidique a été comparée chez 47 femmes obèses et 72 sujets témoins (35 femmes et 37 hommes). — Perfusée pendant 2 h à une dose proportionnelle au poids (0.1 /kg/min), la noradrénaline provoque un accroissement des FFA plasmatiques et de la glycémie qui est beaucoup plus important chez les obèses que chez les normaux. Avec une dose fixe de 10 /min pendant 2 h, l'élévation des FFA est encore significativement plus élevée chez les sujets obèses alors que l'effet hyperglycémiant est de même amplitude dans les 2 groupes. Parmi les sujets témoins, il n'y a pas de différence significative entre les réponses des 2 sexes. — L'élévation des FFA mesurée pendant les 4 h suivant l'injection i.v. d'hormone de croissance humaine (10 mg) est comparable chez les femmes obèses et les sujets témoins des 2 sexes. — Ces données suggèrent que le tissu adipeux des obèses présente une sensibilité normale à l'action de la noradrénaline et de l'hormone de croissance. — Lorsqu'ils sont soumis au jeûne, les patients obèses présentent un accroissement moindre des FFA et une réduction moins marquée du flux glucosé que les sujets normaux. Les relations possibles entre ces deux anomalies sont discutées en tenant compte du rôle majeur que joue la carence en glucose dans la mobilisation lipidique au cours du jeûne.

     

An uncoupling protein 3 gene polymorphism associated with a lower risk of developing Type II diabetes and with atherogenic lipid profile in a French cohort

Aims/hypothesis. The UCP2-UCP3 gene region has been previously associated with obesity and diabetes. In a large representative cohort of Northern France (MONICA project), we studied the effect of a recently reported C/T polymorphism located in the 5' sequences of the UCP3 gene on anthropometric measurements and lipid profile. We also examined the association of this polymorphism with obesity and Type II (non-insulin-dependent) diabetes mellitus.¶Methods. The –55 C/T polymorphism of the UCP3 gene has been genotyped in 1155 subjects from the MONICA project. Association studies were done with diabetes, obesity and related phenotypes. Results were ascertained in a second cohort of well-characterized Type II diabetic and control subjects.¶Results. The variant T allele was associated with a decreased risk of developing Type II diabetes. Frequencies of the T allele were 13.3 % compared with 22 %, p = 0.04, in the diabetic and control groups, respectively. This observation was confirmed in the second cohort of French Type II diabetic (n = 171) and control (n = 124) subjects: 17.8 % compared with 25 %, p = 0.03. Moreover, subjects bearing the TT genotype had higher plasma total cholesterol and LDL-cholesterol concentrations (p = 0.0006 and p = 0.001, respectively) than subjects bearing wild or heterozygous genotypes.¶Conclusion/interpretation. The UCP3–55 C/T polymorphism was associated with a higher atherogenic profile and modified the risk for the development of Type II diabetes. [Diabetologia (2000) 43: 1424–1428]     

Effect of work-induced hypertrophy on muscle glucose metabolism in lean and obese mice

Summary The effect of work-induced hypertrophy (without any concomitant change in circulating parameters) on skeletal muscle metabolism was studied in lean mice and in goldthioglucose obese-mice. Soleus muscle was functionally overloaded in one leg by tenotomy of gastrocnemius muscle 4 days before muscle isolation, muscle in the other leg being used as control. Basal deoxyglucose uptake and glycolysis were markedly increased in overloaded muscles compared with control muscles, together with a ten-fold increase in fructose 2–6 bisphosphate content. In the presence of maximally effective insulin concentrations, deoxyglucose uptake and glycolysis were identical in overloaded and control muscles of lean mice, while the effects of overload and insulin were partly additive in muscles of goldthioglucose-obese mice. The sensitivity to insulin and insulin binding to muscles were not modified in overloaded muscles. Insulin-stimulated glycogenogenesis was decreased by about 50% probably due to a lower amount of glycogen synthase in overloaded than in control muscles. Thus, in muscles of goldthioglucose-obese mice work-induced hypertrophy increased the response to maximal insulin concentrations without modifying the altered insulin sensitivity and decreased insulin binding.     

A longitudinal magnetic resonance imaging (MRI) study of differences in abdominal fat distribution between normal mice,and lean overexpressers of mitochondrial uncoupling protein-3 (UCP-3)

Aim: To characterize evolution and distribution of abdominal adipose fat between 6 and 18 weeks of age in an animal model of energy consumption based on mice overexpressing the mitochondrial uncoupler protein 3 (UCP-3).
Methods: T2-weighted multislice MRI was performed six times during the 12 week study; visceral, subcutaneous and intermuscular fat depots were quantified.
Results: The overexpressor (UCP-3tg) mice consistently have less subcutaneous, visceral, interskeletal muscle and total fat throughout the experiment. Mean (standard error) volumes (ml) of the three distinct depots change between week 6 and week 18 as follows: wild type: subcutaneous 1.93 (0.28) to 6.18 (0.47), visceral 2.15 (0.34) to 6.37 (0.64), intermuscular 0.23 (0.04) to 0.53 (0.03); UCP-3tg: subcutaneous 1.47 (0.17) to 4.07 (0.57), visceral 1.18 (0.04) to 3.69 (0.59), intermuscular 0.23 (0.01) to 0.32 (0.04). Although they eat more (4.3 g compared with 3.4 g per day) the UCP-3tg's always weigh less than controls. In wild-type control animals, increases of all fat pools between week 6 and week 18 is highly significant, as it is for subcutaneous, visceral and total pools in the UCP-3tg animals. The UCP-3tg mice, however, show no significant absolute or relative increase in intermuscular fat; UCP-3 is predominantly overexpressed in skeletal muscle.
Conclusion: MRI provides an excellent approach to comparative studies of fat distribution in animal models of energy expenditure such as the UCP-3tg mouse.     

Fatty acid binding protein expression in different adipose tissue depots from lean and obese individuals

Aims/hypothesis: This study investigated the expression of adipose tissue fatty acid binding proteins (FABPs) in subcutaneous and visceral human adipose tissue depots from lean and obese individuals. Methods: Adipocyte lipid binding protein (ALBP) and keratinocyte lipid binding protein (KLBP) expression was quantified by western blot in subcutaneous and omental adipose tissue from 20 obese and 9 lean individuals. RNA expression was quantified by Northern blot in the obese subjects. Results: In the obese subjects, ALBP protein and RNA expression was higher in subcutaneous compared with omental adipose tissue (increases of 31 ± 14 % and 40 ± 13 % respectively, both p < 0.05), whereas in the lean group, KLBP protein levels were 32 ± 9 % lower in subcutaneous fat (p < 0.03). However, the ALBP/KLBP ratio was greater in subcutaneous compared to omental adipose tissue from both lean and obese subjects: increases of 187 ± 71 % (p = 0.01) and 52 ± 23 % (p = 0.17) respectively for the protein ratio, and 21 ± 6 % for RNA (p = 0.01, obese individuals). In lean subjects, insulin concentrations correlated positively with the ALBP/KLBP protein ratio in both depots (both p≤ 0.03). Conclusion/interpretation: There are regional differences in adipose tissue FABP expression, which could be influenced by obesity. However, the ALBP/KLBP ratio is greater in subcutaneous than visceral adipose tissue in lean as well as in obese subjects. Investigation of adipose tissue FABPs could further our understanding of the role of fatty acids in the insulin resistance syndrome. [Diabetologia (2001) 44: 1268–1273] Received: 1 February 2001 and in revised form: 25 June 2001     

Effect of thyroid hormone on uncoupling protein-3 mRNA expression in rat heart and skeletal muscle.

Thyroid hormones (triiodothyronine [T3] and thyroxine [T4]) stimulate UCP-3 expression in skeletal muscle. We examined whether thyroid hormone-induced changes in uncoupling protein (UCP)-3 mRNA expression are related to directs effects of T3 or reflect secondary effects of the hormone through stimulation of renin-angiotensin or beta-adrenergic systems. Hyperthyroidism was produced by three injections of 100 microg T3/100 g body weight on alternate days with or without concomitant treatment with either captopril (an angiotensin-converting enzyme [ACE] inhibitor), propranolol (a beta-blocker) or clenbuterol (a beta2-agonist). The relative abundance of UCP-3 mRNA was measured in ventricular myocardium and skeletal muscle (gastrocnemius and soleus). T3 resulted in a significant increase in the relative abundance of UCP-3 in heart and skeletal muscle (p < 0.05), and the effect was not altered by captopril or propanolol; the inhibitors alone had no effect of UCP-3 mRNA content. There was no synergistic or additive effect of T3 and clenbuterol on UCP-3 mRNA expression in skeletal muscle. Increased UCP-3 mRNA levels were associated with increased UCP-3 protein expression in skeletal muscle. We conclude that the effect of T3 on UCP-3 expression in cardiac and skeletal muscle is not dependent on either angiotensin II or the beta-adrenergic system and probably reflects a direct action of the hormone on UCP-3 gene expression.     

Metformin mitigates the impaired development of skeletal muscle in the offspring of obese mice

Background: Maternal obesity is linked with offspring obesity and type 2 diabetes. Skeletal muscle (SM) insulin resistance is central to the development of diabetes. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is inhibited in SM of fetuses born to obese mothers.Objective: The aim of this study was to evaluate the effect of maternal metformin administration on AMPK activity and reversion of adverse changes in offspring SM of obese mice.Design: Female weanling C57BL/6J mice received either control diet (CON, 6 mice) or high-fat diet (HFD; OB, 12 mice) for 8 weeks before mating. After mating, mice continued receiving their respective CON or OB diets. In addition, 6 of those 12 mice fed with fat diet also received metformin administration (2 mg per ml in drinking water) throughout gestation and lactation (MET). After weaning at postnatal 21 days, offspring were fed a HFD to mimic a postnatal obesogenic environment until necropsy.Results: Mothers receiving the fat diet developed obesity. OB offspring showed higher adiposity than CON and MET offspring. AMPK phosphorylation was lower in SM of OB offspring. β-Catenin and myogenic regulatory factors, MyoD and myogenin, were downregulated in OB muscle, whereas the adipogenic marker, peroxisome proliferator-activated receptor-γ, was upregulated compared with CON muscle. Metformin administration prevented these changes in OB offspring SM. OB but not MET offspring demonstrated glucose intolerance. Mitochondrial content decreased, and activities of citrate synthase and β-hydroxyacyl-CoA dehydrogenase also decreased in OB offspring SM, whereas they were recovered in MET offspring SM.Conclusion: Maternal metformin administration improves SM development in OB offspring.     

Organisation of the coding exons and mutational screening of the uncoupling protein 3 gene in subjects with juvenile-onset obesity

Summary Uncoupling proteins (UCPs) are mitochondrial transporters that uncouple the cellular respiration releasing stored energy as heat. Recently a third member of the UCP family was identified. Human UCP3 is different from UCP1 and UCP2 by its high and preferential expression in skeletal muscle and consequently the UCP3 gene is an attractive candidate gene for obesity. In this study we have determined the intron/exon organization of the coding region of the UCP3 gene and performed single strand conformation polymorphism (SSCP) analysis and direct sequencing of variants of the gene in 60 Caucasian subjects with juvenile-onset obesity. We detected 4 nucleotide substitutions in the intron regions and 2 silent amino acid variants. During the identification of the intron/exon structure of the gene in a normal healthy male subject with a BMI of 23.5 kg/m², a nucleotide substitution replacing a glycine with a serine was identified at codon 84. This variant was neither found among 156 subjects with juvenile-onset obesity nor among 205 control subjects. In a population based sample of 380 young healthy subjects the Gly/Ser84 variant was found in one female subject with a BMI of 25.5 kg/m² and a fat mass of 23.7 kg. We conclude it is unlikely that variants in the coding region of the UCP3 gene contribute to the pathogenesis of juvenile-onset obesity among Danish Caucasians. [Diabetologia (1998) 41: 241–244] Received: 8 October 1997 and in revised form: 30 October 1997     

Expression of human uncoupling protein-3 in Drosophila insulin-producing cells increases insulin-like peptide (DILP) levels and shortens lifespan

Uncoupling proteins (UCPs) can dissipate mitochondrial protonmotive force by increasing the proton conductance of the inner membrane and through this effect could decrease ROS production, ameliorate oxidative stress and extend lifespan. We investigated whether ubiquitous, pan-neuronal or neurosecretory cell-specific expression of human UCP3 (hUCP3) in adult Drosophila melanogaster affected lifespan. Low, ubiquitous expression of hUCP3 at levels found in rodent skeletal muscle mitochondria did not affect proton conductance in mitochondria isolated from whole flies, but high pan-neuronal expression of hUCP3 increased the proton conductance of mitochondria isolated from fly heads. Expression of hUCP3 at moderate levels in adult neurons led to a marginal lifespan-extension in males. However, high expression of hUCP3 in neuronal tissue shortened lifespan. The life-shortening effect was replicated when hUCP3 was expressed specifically in median neurosecretory cells (mNSC), which express three of the Drosophila insulin-like peptides (DILPs). Expression of hUCP3 in the mNSC did not alter expression of dilp2, dilp3 or dilp5 mRNA, but led to increased amounts of DILP2 in fly heads. These data suggest that lowering mitochondrial coupling by high expression of hUCP3 alters mNSC function in a way that appears to increase DILP-levels in fly heads and lead to a concomitant decrease in lifespan.     

Enzyme activities in quadriceps femoris muscle of obese diabetic male patients

Summary In biopsy samples of the lateral part of the quadriceps femoris muscle of 6 obese diabetic male patients and of 11 obese males with a normal glucose tolerance, the activities of 7 enzymes of energy metabolism were estimated: hexokinase, cytoplasmic glycerol-3-phosphate: NAD dehydrogenase, triosephosphate dehydrogenase, lactate dehydrogenase, citrate synthase, malate dehydrogenase and 3-hydroxyacyl-CoA dehydrogenase. The obese diabetic male patients exhibited decreased activities of enzymes of carbohydrate breakdown and cytoplasmic NAD regeneration. Enzymes connected functionally with aerobic metabolism were less affected. The unchanged activity of 3-hydroxyacyl-CoA dehydrogenase points to an increased role of fatty acid catabolism in the muscle.