Decreased uncoupling protein (UCP)3 is associated with insulin resistance in muscle of pre-diabetic and diabetic individuals, but the function of UCP3 remains unclear. Our goal was to elucidate mechanisms underlying the negative correlation between UCP3 and insulin resistance in muscle. We determined effects of physiologic UCP3 overexpression on glucose and fatty acid oxidation and on mitochondrial uncoupling and reactive oxygen species (ROS) production in L6 muscle cells. An adenoviral construct caused a 2.2-to 2.5-fold increase in UCP3 protein. Palmitate oxidation was increased in muscle cells incubated under normoglycemic or hyperglycemic conditions, whereas adenoviral green fluorescent protein infection or chronic low doses of the uncoupler dinitrophenol had no effect. Increased UCP3 did not affect glucose oxidation, whereas dinitrophenol and insulin treatments caused increases. Basal oxygen consumption, assessed in situ using self-referencing microelectrodes, was not significantly affected, whereas dinitrophenol caused increases. Mitochondrial membrane potential was decreased by dinitrophenol but was not affected by increased UCP3 expression. Finally, mitochondrial ROS production decreased significantly with increased UCP3 expression. Results are consistent with UCP3 functioning to facilitate fatty acid oxidation and minimize ROS production. As impaired fatty acid metabolism and ROS handling are important precursors in muscular insulin resistance, UCP3 is an important therapeutic target in type 2 diabetes. Diabetes 54: 2343-2350, 2005 I nsulin resistance in muscle is a primary component of type 2 diabetes, a disease with a prevalence that is increasing at an alarming rate in modern society. The importance of mitochondrial oxidative phosphorylation in the development of type 2 diabetes has recently been demonstrated through gene expression profiling studies in muscle of pre-diabetic, diabetic, and nondiabetic populations. Individuals with type 2 diabetes were shown to have reduced expression of genes for key proteins in oxidative metabolism and mitochondrial function in muscle (1). Furthermore, pre-diabetic individuals with insulin resistance but normal glucose tolerance display the same pattern of decreased expression of genes related to mitochondrial oxidative metabolism, consistent with the possibility that such characteristics are directly relevant to the origins and development of type 2 diabetes (2).One of the mitochondrial proteins having decreased mRNA expression in pre-diabetic and diabetic subjects is uncoupling protein (UCP)3 (2). Not only are the levels of mRNA for UCP3 decreased but also are the levels of UCP3 protein. Schrauwen et al. (3) demonstrated decreased UCP3 protein in vastus lateralis of type 2 diabetic patients and no significant association between UCP3 protein and BMI of patients.Mitochondrial UCPs belong to a large family of anion carrier proteins that facilitate the exchange of substrates across the mitochondrial inner membrane. Members of this family play essential roles in the t...

Uncoupling protein 3 (UCP3) expression is directly correlated to fatty acid oxidation in skeletal muscle. UCP3 has been hypothesized to facilitate high rates of fatty acid oxidation, but evidence thus far is lacking. Our aim was to investigate the effects of UCP3 overexpression and ablation on fatty acid uptake and metabolism in muscle of mice having congenic backgrounds. In mice constitutively expressing the UCP3 protein (human form) at levels just over twofold higher than normal (230% of wild-type levels), indirect calorimetry demonstrated no differences in total energy expenditure (VO2), but a shift toward increased fat oxidation compared with wild-type (WT) mice. Metabolic efficiency (gram weight gain/kcal ingested) was similar between Ucp3 overexpressors, WT and Ucp3 (-/-) mice. In muscle of Ucp3-tg mice, plasma membrane fatty acid binding protein (FABPpm) content was increased compared with WT mice. Although hormone-sensitive lipase activity was unchanged across the genotypes, there were increases in carnitine palmitoyltransferase I, beta-hydroxyacylCoA dehydrogenase, and citrate synthase activities and decreases in intramuscular triacylglycerol in muscle of Ucp3-tg mice. There were no differences in muscle mitochondrial content. High-energy phosphates and total muscle carnitine and CoA were also greater in Ucp3-tg compared with WT mice. Taken together, the findings demonstrate an increased capacity for fat oxidation in the absence of significant increases in thermogenesis in Ucp3-tg mice. Findings from Ucp3 (-/-) mice revealed few differences compared with WT mice, consistent with the possibility of compensatory mechanisms. In conjunction with our observed increases in CoA and carnitine in muscle of Ucp3 overexpressors, the findings support the hypothesized role for Ucp3 in facilitating fatty acid oxidation in muscle.

Obesity is reaching epidemic proportions in developed countries and represents a signifi cant risk factor for cardiovascular disease, diabetes, and cancer ( 1 ). Enrolment in clinical and nonclinical obesity treatment programs is unprecedented. Success in obesity treatment programs is highly variable, related in part to compliance and program characteristics (e.g., type and duration of hypocaloric diets, educational components, and/or exercise-associated energy expenditure). While it is generally well accepted that there is substantial inter-individual variability in the susceptibility to weight gain in response to overfeeding ( 2, 3 ), less well understood is the impact of biological factors on weight loss success. However, studies of monozygotic twins have shown greater inter-pair than intra-pair variation in weight loss ( 4 ), consistent with the idea that there are important genetic determinants of weight loss success. We have studied the molecular and cellular determinants of variable weight loss in highly compliant subjects in an intensively supervised and interactive hypocaloric clinical obesity treatment program at the Ottawa Hospital. We previously reported differences in muscle mitochondrial energy ineffi ciencies between program participants exhibiting high versus low weight loss success ( 5 ). Here, we extend these fi ndings by demonstrating distinct differences in skeletal muscle gene expression profi les and in structural and metabolic characteristics between individuals who Abstract Inter-individual variability in weight gain and loss under energy surfeit and defi cit conditions, respectively, are well recognized but poorly understood phenomena. We documented weight loss variability in an intensively supervised clinical weight loss program and assessed skeletal muscle gene expression and phenotypic characteristics related to variable response to a 900 kcal regimen. Matched pairs of healthy, diet-compliant, obese diet-sensitive (ODS) and dietresistant (ODR) subjects were defi ned as those in the highest and lowest quintiles for weight loss rate. Physical activity energy expenditure was minimal and comparable. Following program completion and weight stabilization, skeletal muscle biopsies were obtained. Gene expression analysis of rectus femoris and vastus lateralis indicated upregulation of genes and gene sets involved in oxidative phosphorylation and glucose and fatty acid metabolism in ODS compared with ODR. In vastus lateralis , there was a higher proportion of oxidative (type I) fi bers in ODS compared with ODR women and lean controls, fi ber hypertrophy in ODS compared with ODR women and lean controls, and lower succinate dehydrogenase in oxidative and oxidative-glycolytic fi bers in all obese compared with lean subjects. Intramuscular lipid content was generally higher in obese versus lean, and specifi cally higher in ODS vs. lean women. Altogether, our fi ndings demonstrate differences in muscle gene expression and fi ber composition related to clinical weight loss success. Abbreviations: B...

The aim of the present study was to examine the role of several polyunsaturated fatty acids (PUFA) in the control of steroidogenesis in the goldfish testis. The release of fatty acids from testis tissue in response to the protein kinase C activator phorbol-12-myristate-13-acetate (PMA) and calcium ionophore A23187 was studied. After a 2-h incubation, goldfish testis tissue released detectable amounts of several fatty acids, particularly docosahexaenoic acid (DHA). Treatment with PMA (100 nM) and A23187 (1 microM) increased the release of arachidonic acid (AA) and, to a lesser extent, of eicosapentaenoic acid (EPA). Further experiments showed that AA (100 and 400 microM) and, to a lesser extent, eicosatrienoic acid (ETA; 400 microM)--but not EPA or DHA (both 400 microM)--stimulated testicular testosterone (T) production via an indomethacin (INDO; 40 microM)--sensitive pathway, suggesting that these effects may be mediated through conversion to prostaglandins (PG). E-series PGs formed directly from ETA, AA, or EPA (PGE1, PGE2, or PGE3, respectively) all stimulate T production, with relative potencies of PGE2 > PGE1 > PGE3. The inability to detect ETA release from testis incubates and the limited effect of EPA on steroid production suggest that PGE2 represents the predominant E-series PG formed under physiological conditions in the goldfish testis. The steroidogenic action of AA was blocked by treatment with EPA or DHA, and this effect is due, partly, to inhibition of PGE2 formation from AA.(ABSTRACT TRUNCATED AT 250 WORDS)

To establish if there are sex-specific differences in the utilization of specific fatty acids in salmon during migration, we monitored plasma nonesterified fatty acids (NEFA) in male and female early-run Stuart sockeye salmon, Oncorhynchus nerka, during their spawning migration in the Fraser River. Total plasma NEFA concentrations declined in both males and females to 60 and 40% of their respective initial levels. Palmitic (C 16:0), oleic (C 18:1), docosahexaenoic (C 22:6n3), and eicosapentaenoic (C 20:5n3) acids consistently represented between 66 and 77% of the total plasma NEFAs throughout the migration. These fatty acids are probably utilized as a source of energy to sustain swimming during the migration. A difference in monoene levels between sexes suggest that females utilized monoenes, particularly oleic acid, for yolk production. Fatty acid concentrations of the n6) series remained constant in both sexes; however, a sudden increase of C 20 polyunsaturate proportions of both the n3 and n6 series was observed at the time of gonadal maturation in both sexes. While plasma NEFAs are important as energy sources for migrating sockeye salmon, there is also a selective utilization of plasma NEFAs for gonadal development and reproduction that is reflected in altered NEFA profiles of male and female fish, respectively. Résumé : Nous avons surveillé la concentration plasmatique d'acides gras non estérifiés (AGNE) chez des saumons rouges, Oncorhynchus nerka, femelles et mâles qui passent dans la rivière Fraser au début de la remonte vers la Stuart pour déterminer si l'utilisation de ces acides gras diffère selon le sexe chez le saumon en migration. Nous avons constaté, tant chez les mâles que chez les femelles, une diminution de la concentration plasmatique des AGNE totaux, les valeurs ayant baissé à 60 et 40% de ce qu'elles étaient initialement. L'acide palmitique (C 16:0), l'acide oléique (C 18:1), l'acide docosahexanoïque (C 22:6n3) et l'acide eicosapentanoïque (C 20:5n3) ont représenté 66 et 77% des AGNE plasmatiques totaux durant toute la migration. Il est probable que ces acides gras fournissent l'énergie nécessaire à la nage soutenue durant la migration. Nous avons observé une différence entre les concentrations de monoènes des deux sexes, ce qui pourrait signifier que les femelles utilisent des monoènes, et plus particulìèrement l'acide oléique, pour la production du vitellus. Les concentrations d'acides gras de la série n6 sont restées constantes chez les deux sexes; toutefois, une brusque augmentation des proportions de polyinsaturés en C 20 des séries n3 et n6 est apparue chez les deux sexes au moment de la maturation des gonades. Les AGNE plasmatiques sont d'importantes sources d'énergie pour le saumon rouge en migration, mais certains sont aussi utilisés pour le développement gonadique et la reproduction, utilisation sélective que traduisent les changements du profil des AGNE observés chez mâles et chez les femelles. [Traduit par la Rédaction]