Expression Of UCP3 In Skeletal Muscle Research Articles

Differences in mitochondrial DNA inheritance and function align with body conformation in genetically lean and fat sheep.

Body weight and adiposity are determined by the balance between energy intake, energy expenditure, and nutrient deposition. We have identified differences in appetite-regulating peptides in sheep selectively bred to be either lean or fat, wherein gene expression for orexin and melanin-concentrating hormone are elevated in the lean group. Despite this, the underlying mechanisms leading to differences in body composition in the lean and fat lines remains unknown. We measured postprandial temperature in adipose tissue and muscle to ascertain whether a difference in thermogenesis is associated with the difference in body composition in genetically lean (n = 8) and fat (n = 12) ewes. Body weight was higher (P < 0.01) but percent fat mass was lower (P < 0.001) in the lean group. The percent lean mass was similar in lean and fat groups. Animals received intracerebroventricular cannulae and temperature probes implanted into the retroperitoneal fat and the hind-limb skeletal muscle (vastus lateralis). Animals were meal fed (1100-1600 h) to entrain postprandial thermogenesis. Food intake was similar between lean and fat animals. Postprandial thermogenesis was greater (P < 0.05) in the retroperitoneal adipose tissue of lean animals but not in skeletal muscle. Intracerebroventricular infusion of leptin reduced (P< 0.05) food intake by an equal extent in both groups. Postprandial expression of UCP1 mRNA was greater (P < 0.05) in retroperitoneal fat of lean animals, with similar UCP3 expression in skeletal muscle. Mitochondrial genome sequencing indicated haplotypic clustering in lean and fat animals within both the encoding and nonencoding regions. This demonstrates that differences in body composition may be underpinned by differences in thermogenesis, specifically within adipose tissue. Furthermore, thermogenic differences may be associated with specific mitochondrial DNA haplotypes, suggesting a strong genetic component inherited through the maternal lineage.

Deterioration of physical performance and cognitive function in rats with short‐term high‐fat feeding

Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a key determinant of endurance capacity, and can be altered by metabolic substrate supply, in that fatty acid oxidation is less efficient than glucose oxidation. It is unclear, however, whether consumption of a high-fat diet would be detrimental or beneficial for endurance capacity, due to purported glycogen-sparing properties. In addition, a high-fat diet over several months leads to cognitive impairment. Here, we tested the hypothesis that short-term ingestion of a high-fat diet (55% kcal from fat) would impair exercise capacity and cognitive function in rats, compared with a control chow diet (7.5% kcal from fat) via mitochondrial uncoupling and energy deprivation. We found that rats ran 35% less far on a treadmill and showed cognitive impairment in a maze test with 9 d of high-fat feeding, with respiratory uncoupling in skeletal muscle mitochondria, associated with increased uncoupling protein (UCP3) levels. Our results suggest that high-fat feeding, even over short periods of time, alters skeletal muscle UCP3 expression, affecting energy production and physical performance. Optimization of nutrition to maximize the efficiency of mitochondrial ATP production could improve energetics in athletes and patients with metabolic abnormalities.

Developmental programming of adult hyperinsulinemia, increased proinflammatory cytokine production, and altered skeletal muscle expression of SLC2A4 (GLUT4) and uncoupling protein 3

Fetal glucocorticoid excess programs detrimental effects in the adult phenotype including hyperleptinemia and aberrant glycemic control. In this study, we determined the interactive effects of maternal dexamethasone (Dex) treatment and postnatal dietary omega-3 (n-3) fatty acids on adult proinflammatory cytokine production and skeletal muscle expression of genes central to glucose handling and fatty acid metabolism. Dex acetate was administered to pregnant rats (0.75 microg/ml drinking water) from day 13 to term. Offspring of treated and control mothers were cross-fostered to mothers on either a standard (Std) or high n-3 (Hn3) diet, and remained on these diets postweaning. Adult offspring exposed to Dex in utero exhibited fasting hyperinsulinemia when raised on the Std diet but not when raised on the Hn3 diet. Dex also programmed increased plasma tumour necrosis factor alpha and interleukin 1 beta (IL-1 beta), but the increase in IL-1 beta was also prevented by the Hn3 diet. In skeletal muscle, expression of insulin regulated Slc2a4 (formerly known as GLUT4) was elevated (up to 15-fold) after Dex in utero, and this resulted in elevated intracellular, but not membrane-associated, SLC2A4 protein. Fetal glucocorticoid excess also reduced adult skeletal muscle Ucp3 expression in all offspring, whereas skeletal muscle expression of both Ppard and Ppargc1a were increased in females but not males. In conclusion, our data show that fetal glucocorticoid excess programs adult hyperinsulinemia and increased proinflammatory cytokine production. Related changes in the skeletal muscle Slc2a4, Ucp3, and Ppard indicate that fetal glucocorticoid excess disturbs adult glucose/fatty acid transport and metabolism.

Roles of Norepinephrine, Free Fatty Acids, Thyroid Status, and Skeletal Muscle Uncoupling Protein 3 Expression in Sympathomimetic-Induced Thermogenesis

Thyroid hormone (TH) plays a fundamental role in thermoregulation, yet the molecular mediators of its effects are not fully defined. Recently, skeletal muscle (SKM) uncoupling protein (UCP) 3 was shown to be an important mediator of the thermogenic effects of the widely abused sympathomimetic agents 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy) and methamphetamine. Expression of UCP3 is regulated by TH. Activation of UCP3 is indirectly regulated by norepinephrine (NE) and is dependent upon the availability of free fatty acids (FFAs). We hypothesized that UCP3 may be a molecular link between TH and hyperthermia, requiring increased levels of both NE and FFAs to accomplish the thermogenic effect. Here, we demonstrate that MDMA (40 mg/kg s.c.) significantly increases plasma FFA levels 30 min after treatment. Pharmacologically increasing NE levels through the inhibition of phenylethanolamine N-methyltransferase with +/-2,3-dichloro-alpha-methylbenzylamine potentiated the hyperthermic effects of a 20 mg/kg dose of MDMA. Using Western blots and regression analysis, we further illustrated that chronic hyperthyroidism in rats potentiates the hyperthermic effects of MDMA and increases levels of SKM UCP3 protein in a linear fashion according to levels of circulating plasma TH. Conversely, chronic hypothyroidism results in a hypothermic response to MDMA that is directly proportionate to decreased UCP3 expression. Acute TH supplementation did not change the skeletal muscle UCP3 expression levels or temperature responses to MDMA. These findings suggest that, although MDMA-induced hyperthermia appears to result from increased NE and FFA levels, susceptibility is ultimately determined by TH regulation of UCP3-dependent thermogenesis.

Regulation of UCP1 and UCP3 in arctic ground squirrels and relation with mitochondrial proton leak

Uncoupling protein (UCP) 1 (UCP1) catalyzes a proton leak in brown adipose tissue (BAT) mitochondria that results in nonshivering thermogenesis (NST), but the extent to which UCP homologs mediate NST in other tissues is controversial. To clarify the role of UCP3 in mediating NST in a hibernating species, we measured Ucp3 expression in skeletal muscle of arctic ground squirrels in one of three activity states (not hibernating, not hibernating and fasted for 48 h, or hibernating) and housed at 5 degrees C or -10 degrees C. We then compared Ucp3 mRNA levels in skeletal muscle with Ucp1 mRNA and UCP1 protein levels in BAT in the same animals. Ucp1 mRNA and UCP1 protein levels were increased on cold exposure and decreased with fasting, with the highest UCP1 levels in thermogenic hibernators. In contrast, Ucp3 mRNA levels were not affected by temperature but were increased 10-fold during fasting and >3-fold during hibernation. UCP3 protein levels were increased nearly fivefold in skeletal muscle mitochondria isolated from fasted squirrels compared with nonhibernators, but proton leak kinetics in the presence of BSA were unchanged. Proton leak in BAT mitochondria also did not differ between fed and fasted animals but did show classical inhibition by the purine nucleotide GDP. Levels of nonesterified fatty acids were highest during hibernation, and tissue temperatures during hibernation were related to Ucp1, but not Ucp3, expression. Taken together, these results do not support a role for UCP3 as a physiologically relevant mediator of NST in muscle.

Influence of size at birth on the endocrine profiles and expression of uncoupling proteins in subcutaneous adipose tissue, lung, and muscle of neonatal pigs

Epidemiological studies suggest that infants of low birth weight show poor neonatal growth and increased susceptibility to adult diseases such as diabetes and lung disease. Uncoupling protein 2 and 3 (UCP2 and UCP3) have been implicated in the development of such diseases; pigs provide an ideal model to examine the influence of birth weight due to the natural variance in piglet weight within a litter. This study examined whether birth weight influences the expression of UCP2 and UCP3 in adipose tissue, skeletal muscle, and lung. Piglets from 11 litters were ranked according to birth weight and three from each litter assigned to small (SFD), normal (NFD), or large for dates (LFD) groups. Blood samples and morphometric measurements were taken over the first 14 days of life, and tissue samples were taken on day 7 or 14. Plasma hormone and metabolite concentrations and the expression of UCP2 and UCP3 mRNA in adipose tissue, skeletal muscle, and lung were measured. UCP2 and UCP3 expression in adipose tissue was lower in the SFD compared with the LFD group on day 7. UCP3 expression in skeletal muscle was higher than that of adipose tissue. Lung UCP2 and skeletal muscle UCP3 mRNA expression were unaffected by size at birth. Regression analysis indicated that UCP3 expression was differentially associated with IGF-1, leptin, and insulin. In conclusion, low birth weight is associated with tissue-specific effects on UCP expression. It remains to be established whether these subsequently contribute to pathological conditions such as diabetes.

Calcium and Dairy Products Inhibit Weight and Fat Regain during Ad Libitum Consumption Following Energy Restriction in Ap2-Agouti Transgenic Mice

We demonstrated previously that dietary calcium suppression of calcitriol reduces adipocyte Ca(2+), suppresses lipogenesis, and increases lipid utilization during energy restriction. Notably, dairy calcium sources exert markedly greater effects. To determine the effects of dietary calcium and dairy products on energy partitioning during subsequent refeeding, we induced obesity in aP2-agouti transgenic mice with a high-fat/high-sucrose diet, then restricted energy intake from a high-calcium (1.3%) diet for 6 wk to induce fat loss, and then provided free access to a low-calcium (0.4%) diet or to high-calcium (1.3%) diets that utilized either calcium-fortified foods or dairy products (milk or yogurt) for 6 wk. Refeeding the low-calcium diet caused the regain of all weight and fat, whereas all high-calcium diets reduced fat gain by 55% (P < 0.01). All high-calcium diets stimulated adipose tissue uncoupling protein (UCP)2 and skeletal muscle UCP3 expression (P < 0.001) and slightly increased core temperature (P = 0.136), but only the dairy-based diets elicited a marked (>10-fold, P < 0.001) increase in skeletal muscle peroxisome proliferator-activated receptor-alpha expression. All 3 high-calcium diets produced significant increases in lipolysis, decreases in fatty acid synthase expression and activity, and reduced fat regain (P < 0.03), but the 2 dairy-containing high-calcium diets exerted significantly greater effects on regain (P < 0.01). Thus, high-Ca diets elicit a shift in energy partitioning and reduction of weight gain during refeeding, with dairy Ca sources exerting markedly greater effects.

Uncoupling proteins and sleep deprivation.

In both humans and animals sleep deprivation (SD) produces an increase in food intake and in energy expenditure (EE). The increase in EE is a core element of the SD syndrome and, in rats, is negatively correlated with survival rate. However, the mechanisms involved are not understood. A large component of resting EE is accounted for by the mitochondrial proton leak, which is mediated by uncoupling proteins (UCPs). We measured UCP2, UCP3, and UCP5 mRNA levels in rats during the spontaneous sleep/waking cycle and after short (8 hours) and long (7 days) SD. During spontaneous sleep and waking there was no change in the level of mitochondrial uncoupling as measured by UCPs expression, either in the brain or in peripheral tissues. During SD, by contrast, UCP3 expression in skeletal muscle was elevated, but the increase was similar, compared to sleep, after both short-term and long-term SD. UCP2 expression, on the other hand, was strongly increased in the liver and skeletal muscle of long-term sleep deprived animals and much less so, or not at all, in yoked controls or in rats that lost only 8 hours of sleep. Since the skeletal muscle is the largest tissue in the body, an elevated muscular expression of UCP2 is likely to affect the overall resting EE and may thus contribute to its increase after SD.

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.

Enhanced diabetogenic effect of streptozotocin in mice overexpressing UCP-3 in skeletal muscle.

Diabetic patients exhibit varying degrees of increased muscle UCP-3 expression in skeletal muscle and, in rodents, the pancreatoxin streptozotocin (STZ) upregulates UCP-3 mRNA in skeletal and cardiac muscles. We have investigated the development of STZ-induced diabetes in transgenic mice overexpressing UCP-3 in skeletal muscle in order to provide further insight on the functional role of muscle UCP-3. UCP-3 transgenic mice treated with STZ (UCP3-STZ) showed a significant increase in blood glucose concentration 3 days after the last dose of STZ with a progressive induction of diabetes, attaining blood glucose concentrations of 24.7 +/- 1.5 mmol/L on day 17. Wild-type mice treated with STZ (WT-STZ) only started to show an increase in blood glucose concentration 6 days after the last dose of STZ and peaked on day 17 at a lower concentration than in the UCP-STZ mice. The pancreatic insulin content of UCP-3 control mice (UCP3-CON) was decreased relative to wild-type control mice (WT-CON), and STZ reduced the total pancreatic insulin content by 72% in WT-STZ mice and by 88% in UCP3-STZ mice. In an insulin tolerance test, blood glucose concentrations declined more in the UCP-3 transgenic mice than in the wild-type mice. Mice overexpressing UCP-3 in skeletal muscle have a lower pancreatic insulin content, but tend to be more insulin-sensitive. These twin actions result in an increased susceptibility to STZ-induced diabetes in UCP-3 transgenic mice.

The Effects of the β3-Adrenoceptor Agonist BRL 35135 on UCP Isoform mRNA Expression

The mitochondrial uncoupling protein UCP-1 uncouples respiration from ATP synthesis in brown adipose tissue (BAT) and thus energy is dissipated as heat. Recently two further isoforms have been identified which may play a similar role in other tissues. We have determined the effects of the rodent-selective β3-adrenoceptor (β3-AR) agonist BRL 35135, on β3-AR and UCP mRNA levels in tissues from lean and obese (fa/fa) Zucker rats. β3-AR mRNA levels were reduced infa/fawhite (WAT) and brown (BAT) adipose tissue relative to levels in lean littermates. BRL 35135 treatment increased expression levels of β3-AR mRNA in both genotypes. UCP-2 and UCP-3 mRNA levels in BAT, WAT and skeletal muscle were reduced by 2-3 fold in thefa/farats relative to the lean rats. We confirm that BRL 35135 increases BAT UCP-1 mRNA in lean rats, and find that BAT UCP-3 mRNA was reduced 3.2 fold, with no changes in UCP-2 expression. In WAT BRL 35135 increased UCP-2 and UCP-3 expression 2-3 fold in both lean andfa/farats. In lean rats, skeletal muscle UCP-3 mRNA was increased 2.3 fold by BRL 35135 whereas UCP-2 was reduced by 2.2 fold. BRL 35135 had no effects on UCP-2 and UCP-3 expression in skeletal muscle of thefa/farats. Our results demonstrate that mechanisms regulating UCP isoform synthesis infa/farats are impaired and that WAT could be involved in the thermogenic response of BRL 35135.