Uncoupling Protein Content Research Articles

A low-protein, high-carbohydrate diet increases browning in perirenal adipose tissue but not in inguinal adipose tissue.

The aim of this study was to evaluate the browning and origin of fatty acids (FAs) in the maintenance of triacylglycerol (TG) storage and/or as fuel for thermogenesis in perirenal adipose tissue (periWAT) and inguinal adipose tissue (ingWAT) of rats fed a low-protein, high-carbohydrate (LPHC) diet. LPHC (6% protein, 74% carbohydrate) or control (C; 17% protein, 63% carbohydrate) diets were administered to rats for 15d. The tissues were stained with hematoxylin and eosin for histologic analysis. The content of uncoupling protein 1 (UCP1) was determined by immunofluorescence. Levels of T-box transcription factor (TBX1), PR domain containing 16 (PRDM16), adipose triacylglycerol lipase (ATGL), hormone-sensitive lipase, lipoprotein lipase (LPL), glycerokinase, phosphoenolpyruvate carboxykinase (PEPCK), glucose transporter 4, β3-adrenergic receptor (AR), β1-AR, protein kinase A (PKA), adenosine-monophosphate-activated protein kinase (AMPK), and phospho-AMPK were determined by immunoblotting. Serum fibroblast growth factor 21 (FGF21) was measured using a commercial kit (Student's t tests, P<0.05). The LPHC diet increased FGF21 levels by 150-fold. The presence of multilocular adipocytes, combined with the increased contents of UCP1, TBX1, and PRDM16 in periWAT of LPHC-fed rats, suggested the occurrence of browning. The contents of β1-AR and LPL were increased in the periWAT. The ingWAT showed higher ATGL and PEPCK levels, phospho-AMPK/AMPK ratio, and reduced β3-AR and PKA levels. These findings suggest that browning occurred only in the periWAT and that higher utilization of FAs from blood lipoproteins acted as fuel for thermogenesis. Increased glycerol 3-phosphate generation by glyceroneogenesis increased FAs reesterification from lipolysis, explaining the increased TG storage in the ingWAT.

Inhibition of Angiotensin Converting Enzyme Induces Beige Adipocytes through Angiotensin‐(1–7) in 3T1‐L1 Adipocytes and Obese Mice

The renin angiotensin system (RAS) has recently been recognized as an important factor in the regulation of energy balance. Adipocytes express all the components of renin angiotensin system (RAS), including Angiotensin‐(1–7) [Ang‐(1–7)] and Mas receptors. Ang‐(1–7), through Mas receptors, induces PPARy expression in 3T3‐L1 adipocytes and releases nitric oxide (NO) in diverse cells. White adipose tissue differentiates to beige adipose tissue through PPARy and NO stimulates mitochondrial biogenesis in brown adipose tissue (BAT). In recent years, beige adipocytes have been found, and they have some similar characteristics of BAT including a high thermogenic capacity due to a higher content of mitochondria and uncoupling protein 1 (UCP1). An increase of beige adipocytes has been associated with beneficial effects in health preventing obesity. The aim of this work is to determine if Ang‐(1–7) induces beige adipocytes in 3T3‐L1 cells and in high fat diet (HFD) mice. Captopril was used as a pharmacological strategy to increase Ang‐(1–7) concentrations. 3T3.L1 adipocytes were incubated with 3.16 μM of captopril during the maturation phase and then brown‐like genes and beige genes were measured by real‐time PCR. C57BL/6 mice were fed with a HFD for 24 weeks and captopril was administrated during the last four weeks in drinking water (5 mg/kg/day). Body weight, body composition, glucose tolerance test, cold resistance and energy expenditure were measured. Plasma Ang‐(1–7) was quantified with capilar electrophoresis and nitric oxide thorugh Griess reaction. Captopril increased the expression of UCP1 and beige marker genes in 3T3‐L1 adipocytes. In obese HFD‐mice, treatment with captopril reduced weight gain and decreased fat mass continuosly during the four weeks, although food intake was reduced only the first week, there was no change in remaining weeks. Moreover, HFD captopril‐treated group had improved glucose tolerance, increased energy expenditure and had an increase resistance to cold temperatures compared with the HFD group. On the other hand, HFD captopril‐treated group had increased plasma concentrations of Ang(1–7) and nitric oxide. In conclution, Ang‐(1–7) may be a new factor that induces browning process and partly explains the beneficial effects of ACE inhibitors in glucose and energy homeostasis.Support or Funding InformationCONACYT

A Low-Protein, High-Carbohydrate Diet Stimulates Thermogenesis in the Brown Adipose Tissue of Rats via ATF-2.

The aim of this study was to evaluate thermogenesis in the interscapular brown adipose tissue (IBAT) of rats submitted to low-protein, high-carbohydrate (LPHC) diet and the involvement of adrenergic stimulation in this process. Male rats (~100 g) were submitted to LPHC (6%-protein; 74%-carbohydrate) or control (C; 17%-protein; 63%-carbohydrate) isocaloric diets for 15 days. The IBAT temperature was evaluated in the rats before and after the administration of noradrenaline (NA) (20 µg 100 g b w(-1) min(-1)). The expression levels of uncoupling protein 1 (UCP1) and other proteins involved in the regulation of UCP1 expression were determined by Western blot (Student's t test, P ≤ 0.05). The LPHC diet promoted a 1.1 °C increase in the basal temperature of IBAT when compared with the basal temperature in the IBAT of the C group. NA administration promoted a 0.3 °C increase in basal temperature in the IBAT of the C rats and a 0.5 °C increase in the IBAT of the LPHC group. The level of UCP1 increased 60% in the IBAT of LPHC-fed rats, and among the proteins involved in its expression, such as β3-AR and α1-AR, there was a 40% increase in the levels of p38-MAPK and a 30% decrease in CREB when compared to the C rats. The higher sympathetic flux to IBAT, which is a consequence of the administration of the LPHC diet to rats, activates thermogenesis and increases the expression of UCP1 in the tissue. Our results suggest that the increase in UCP1 content may occur via p38 MAPK and ATF2.

Plasticity in food intake, thermogenesis and body mass in the tree shrew (Tupaia belangeri) is affected by food restriction and refeeding

Physiological adjustments are important strategies for small mammals in response to variation in food availability. To determine the physiological mechanisms affected by food restriction and refeeding, tree shrews were restricted to 85% of initial food intake for 4 weeks and refedad libitumfor another 4 weeks. Changes in food intake, body mass, thermogenesis, body composition, mitochondrial cytochromecoxidase activity, uncoupling protein-1 content in brown adipose tissue and serum leptin levels were measured. The results showed that body mass, body fat mass and serum leptin levels significantly decreased in food restricted tree shrews, and increased when the restriction ended, showing a short “compensatory growth” rather than over-weight or obesity compared withad libitumcontrols. Resting metabolic rate, non-shivering thermogenesis, brown adipose tissue mass (mg), and uncoupling protein-1 content decreased significantly in response to food restriction, and returned to the control levels after the animals were refedad libitum, while the brown adipose tissue mass (%) and cytochromecoxidase activity remained stable during food restriction and refeeding. Food intake increased shortly after refeeding, which perhaps contributed to the rapid regaining of body mass. These results suggest thatTupaia belangerican adjust the status of its physiology integratively to cope with the lack of food by means of decreasing body mass, thermogenesis and serum leptin levels. Leptin may act as a starvation signal to predominantly mediate the reduction in body mass and energy expenditure.

Mitochondrial coupling and capacity of oxidative phosphorylation in skeletal muscle of Inuit and Caucasians in the arctic winter.

During evolution, mitochondrial DNA haplogroups of arctic populations may have been selected for lower coupling of mitochondrial respiration to ATP production in favor of higher heat production. We show that mitochondrial coupling in skeletal muscle of traditional and westernized Inuit habituating northern Greenland is identical to Danes of western Europe haplogroups. Biochemical coupling efficiency was preserved across variations in diet, muscle fiber type, and uncoupling protein-3 content. Mitochondrial phenotype displayed plasticity in relation to lifestyle and environment. Untrained Inuit and Danes had identical capacities to oxidize fat substrate in arm muscle, which increased in Danes during the 42days of acclimation to exercise, approaching the higher level of the Inuit hunters. A common pattern emerges of mitochondrial acclimatization and evolutionary adaptation in humans athigh latitude and high altitude where economy of locomotion may be optimized by preservation of biochemical coupling efficiency at modest mitochondrial density, when submaximum performance is uncoupled from VO2max and maximum capacities of oxidative phosphorylation.

OP1 - Molecular mechanisms of mitochondrial protection against oxidative damage in hibernators - the anti-aging effects of heterothermy

Natural hypothermia, in addition to allowing energy saving in hostile conditions, has been associated with delayed aging and increased longevity. However, the molecular basis responsible for observed correlations between the use of daily torpor/hibernation and indices of rate of aging is hitherto unclear. Considering central role of mitochondria dysfunction in the ageing process, we examined several mechanisms that might be involved in mitochondrial protection against oxidative damage during euthermia-hypothermia (and vice versa) transition, in brown adipose tissue (BAT) of the European Ground Squirrel ( Spermophilus citellus ). Results showed that in hibernation increased protein expression of Mn superoxide dismutase coincides with decreased content of ATP synthase and uncoupling protein 1. This suggests that BAT mitochondria during hibernation are protected from oxidative injuries by suppressed oxidative capacity, as well as by upregulated antioxidant defense. Also, the data indicate that such molecular pattern of changes is initiated already during prehibernating period. Namely, in this period we observed accumulations of hypoxia-inducible factor-1α (HIF-1α) and nuclear factor (erythroid 2-related)-like 2, which are probably responsible for suppressed oxidative metabolism, i.e. increased antioxidant capacity, respectively. Increased expression of the mitofusin 1 and detection of the megamitochondria in the prehibernating period indicate intensive mitofusion process in the BAT. This may be another mechanism of protection of mitochondrial content/function during euthermia-hypothermia transition. The results of the study suggest mechanisms that might be associated with increased resistance of “hibernating” mitochondria to the oxidative damage. Also, the data showed that biochemistry responsible for redox balance within the cell involves integration of antioxidant response and transcription control of overall metabolism. Finally, the results go in favor of the previous reports that suggested HIF-1 as a negative modulator of aging.

Effects of short photoperiod on energy intake, thermogenesis, and reproduction in desert hamsters (Phodopus roborovskii).

Desert hamsters (Phodopus roborovskii) are the least known species in the genus Phodopus with respect to ecology and physiology, and deserve scientific attention, particularly because of their small body size. Here, the responses of energy metabolism and reproductive function to short photoperiods in desert hamsters were investigated. Male and female desert hamsters were acclimated to either long day (LD) (L:D 16:8 h) or short day (SD) photoperiods (L:D 8:16 h) for three months, and then the females were transferred back to an LD photoperiod for a further five months, while at the end of the SD acclimation the males were killed and measurements were taken for serum leptin as well as molecular markers for thermogenesis. We found that like the other two species from the genus Phodopus, the desert hamsters under SD decreased body mass, increased adaptive thermogenesis as indicated by elevated mitochondrial protein content and uncoupling protein-1 content in brown adipose tissue, and suppressed reproduction compared to those under LD. However, different from the other two species, desert hamsters did not show any differences in energy intake or serum leptin concentration between LD and SD. These data suggest that different species from the same genus respond in different ways to the environmental signals, and the desert adapted species are not as sensitive to change in photoperiod as the other two species.

18F-FDG PET/CT monitoring of β3 agonist-stimulated brown adipocyte recruitment in white adipose tissue.

There is rising interest in recruitment of brown adipocytes into white adipose tissue (WAT) as a means to augment energy expenditure for weight reduction. We thus investigated the potential of (18)F-FDG uptake as an imaging biomarker that can monitor the process of WAT browning. C57BL/6 mice were treated daily with the β3 agonist CL316,243 (5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylic acid disodium salt), whereas controls received saline. (18)F-FDG small-animal PET/CT was serially performed at 1 h after CL316,243 injection. After sacrifice, interscapular brown adipose tissue (BAT) and WAT depots were extracted, weighed, and measured for (18)F-FDG uptake. Tissues underwent immunostaining, and UCP1 content was quantified by Western blotting. PET/CT showed low (18)F-FDG uptake in both BAT and inguinal WAT at baseline. BAT uptake was substantially increased by a single stimulation with CL316,243. Uptake in inguinal WAT was only modestly elevated by the first stimulation uptake but gradually increased to BAT level by prolonged stimulation. Ex vivo measurements recapitulated the PET findings, and measured (18)F-FDG uptake in other WAT depots was similar to inguinal WAT. WAT browning by prolonged stimulation was confirmed by a substantial increase in uncoupling protein 1 (UCP1), cytochrome-c oxidase 4 (COX4), and PR domain containing 16 (PRDM16) staining as markers of brown adipocytes. UCP1 content, which served as a measure for extent of browning, was low in baseline inguinal WAT but linearly increased over 10 d of CL316,243 injection. Finally, image-based and ex vivo-measured (18)F-FDG uptake in inguinal WAT correlated well with UCP1 content. (18)F-FDG PET/CT has the capacity to monitor brown adipocyte recruitment into WAT depots in vivo and may thus be useful for screening the efficacy of strategies to promote WAT browning.

Expression of uncoupling protein-2 remains increased within hibernating myocardium despite successful coronary artery bypass grafting at 4 wk post-revascularization

BackgroundWe have previously shown that mitochondrial uncoupling protein-2 (UCP-2) is increased in a swine model of hibernating myocardium (HM). Although UCP-2 reduces oxidant stress, it can promote inefficiency of the electron transport chain. In this study, we tested whether UCP-2 remains increased in revascularized HM (RHM) after coronary artery bypass grafting (CABG). MethodsSeven swine underwent thoracotomy with placement of a constrictor on the left anterior descending artery (LAD). Twelve weeks later, a left internal mammary artery graft was placed on the distal LAD. Four weeks post-CABG, computed tomography angiography documented patent grafts and function. At the terminal study, blood flow to the LAD and remote territories were assessed during high dose dobutamine and mitochondria isolated from both regions for analysis. Comparisons were made to a group of swine with HM who underwent constrictor placement without bypass grafting (n = 4). ResultsDuring dobutamine infusion, RHM demonstrated lower blood flows (2.44 ± 0.23 versus 3.43 ± 0.30 mL/min/g; P < 0.05) and reduced wall thickening (33 ± 9% versus 52 ± 13%; P < 0.05) compared with remote regions. RHM had lower respiratory control indices (3.7 ± 0.3 versus 4.3 ± 0.4; P < 0.05) with persistently increased UCP-2 content. ConclusionsDespite patent grafts, RHM demonstrates a submaximal response to dobutamine infusion and increased mitochondrial UCP-2 expression. These data support the notion that recovery of the mitochondria in RHM is delayed early post-CABG and may contribute to impaired oxygen consumption and contractile reserve during catecholamine challenges.

Alterations in proton leak, oxidative status and uncoupling protein 3 content in skeletal muscle subsarcolemmal and intermyofibrillar mitochondria in old rats.

BackgroundWe considered of interest to evaluate how aging affects mitochondrial function in skeletal muscle.MethodsWe measured mitochondrial oxidative capacity and proton leak, together with lipid oxidative damage, superoxide dismutase specific activity and uncoupling protein 3 content, in subsarcolemmal and intermyofibrillar mitochondria from adult (six months) and old (two years) rats. Body composition, resting metabolic rate and plasma non esterified fatty acid levels were also assessed.ResultsOld rats displayed significantly higher body energy and lipids, while body proteins were significantly lower, compared to adult rats. In addition, plasma non esterified fatty acid levels were significantly higher, while resting metabolic rates were found to be significantly lower, in old rats compared to adult ones. Significantly lower oxidative capacities in whole tissue homogenates and in intermyofibrillar and subsarcolemmal mitochondria were found in old rats compared to adult ones. Subsarcolemmal and intermyofibrillar mitochondria from old rats exhibited a significantly lower proton leak rate, while oxidative damage was found to be significantly higher only in subsarcolemmal mitochondria. Mitochondrial superoxide dismutase specific activity was not significantly affected in old rats, while significantly higher content of uncoupling protein 3 was found in both mitochondrial populations from old rats compared to adult ones, although the magnitude of the increase was lower in subsarcolemmal than in intermyofibrillar mitochondria.ConclusionsThe decrease in oxidative capacity and proton leak in intermyofibrillar and subsarcolemmal mitochondria could induce a decline in energy expenditure and thus contribute to the reduced resting metabolic rate found in old rats, while oxidative damage is present only in subsarcolemmal mitochondria.

Effects of fasting and re-feeding on energy metabolism and thermogenesis in the tree shrew (Tupaia belangeri)

To investigate the effect of fasting and re-feeding on energy metabolism and thermogenesis in the tree shrew (Tupaia belangeri), the changes in body mass and body fat mass, resting metabolic rate (RMR), non-shivering thermogenesis (NST), body composition, mitochondrial cytochrome c oxidase (COX) activity in liver and brown adipose tissue (BAT), uncoupling protein-1 (UCP1) content of BAT, serum leptin level and post-fasting food intake were monitored and measured. The results showed that fasting induced a significant reduction in body mass and body fat mass. Body mass was restored to the control level in re-feeding tree shrew except for the body fat. RMR and NST decreased significantly in response to fasting, and returned to the control level after re-feeding. Fasting induced significant reduction in total, but not specific, COX activity (nmol O2/min/total tissue) in liver and BAT, and UCP1 content in BAT, which was reversed after re-feeding 48 h. Fasting of 12 h induced a rapid reduction in serum leptin content. There were no post-fasting compensatory increases in food intake. Interestingly, the tree shrew did not recover adipose tissue mass, nor serum leptin levels, upon re-feeding. These results suggest that T. belangeri can adjust the status of its physiology integratively to cope with the lack of food by means of decreasing body mass, adaptive thermogenesis and serum leptin levels, and serum leptin level acted as a starvation signal to mediate predominantly the reduction in body mass and energy expenditure.

Thermogenic Ability of Uncoupling Protein 1 in Beige Adipocytes in Mice

Chronic adrenergic activation leads to the emergence of beige adipocytes in some depots of white adipose tissue in mice. Despite their morphological similarities to brown adipocytes and their expression of uncoupling protein 1 (UCP1), a thermogenic protein exclusively expressed in brown adipocytes, the beige adipocytes have a gene expression pattern distinct from that of brown adipocytes. However, it is unclear whether the thermogenic function of beige adipocytes is different from that of classical brown adipocytes existing in brown adipose tissue. To examine the thermogenic ability of UCP1 expressed in beige and brown adipocytes, the adipocytes were isolated from the fat depots of C57BL/6J mice housed at 24°C (control group) or 10°C (cold-acclimated group) for 3 weeks. Morphological and gene expression analyses revealed that the adipocytes isolated from brown adipose tissue of both the control and cold-acclimated groups consisted mainly of brown adipocytes. These brown adipocytes contained large amounts of UCP1 and increased their oxygen consumption when stimulated with norepinephirine. Adipocytes isolated from the perigonadal white adipose tissues of both groups and the inguinal white adipose tissue of the control group were white adipocytes that showed no increase in oxygen consumption after norepinephrine stimulation. Adipocytes isolated from the inguinal white adipose tissue of the cold-acclimated group were a mixture of white and beige adipocytes, which expressed UCP1 and increased their oxygen consumption in response to norepinephrine. The UCP1 content and thermogenic ability of beige adipocytes estimated on the basis of their abundance in the cell mixture were similar to those of brown adipocytes. These results revealed that the inducible beige adipocytes have potent thermogenic ability comparable to classical brown adipocytes.

Effects of food restriction on body mass, thermogenesis and serum leptin level in Apodemus chevrieri (Mammalia: Rodentia: Muridae)

To investigate the effect of food restriction on the body mass, thermogenesis and serum leptin level in Apodemus chevrieri, the changes of body mass, body fat mass, resting metabolic rate (RMR), mitochondrial cytochrome coxidase (COX) activity both in liver and brown adipose tissue (BAT), uncoupling protein1 (UCP1) content of BAT, and serum leptin level were measured. The results showed that food restriction induced significant reductions in body mass and body fat mass. RMR decreased significantly in response to food restriction, and food restriction induced significant reduction in total mitochondrial protein content, COX activity both in liver and BAT, and UCP1 content in BAT. Food restriction also induced a reduction in serum leptin level. In contrast, length and mass with content in the small intestine in the food-restricted group was significantly higher relative to the control group. It suggests that the physiological regulations in energy metabolism to adaptively cope with a period of food shortage include decreasing body mass, reductions in the energy spent for RMR and thermogenesis, as well as the mobilization of fat storage. Leptin may play a potential role in physiological regulations in thermogenesis in response to food restriction.

Single and combined effects of acute and chronic non-thermal stressors on rat interscapular brown adipose tissue metabolic activity

The aim of this study was to examine whether the thermogenic potential of rat interscapular brown adipose tissue (IBAT) changes in response to acute and/or chronic exposure to non-thermal stressors (immobilization and isolation), by measuring the uncoupling protein 1 (UCP-1) content, MAO-A, SOD and CAT activities, as well as the number of IBAT sympathetic noradrenaline-containing nerve fibers. Both acute immobilization (2 h) and chronic isolation (21 days), as well as their combined effects, significantly increased the IBAT UCP-1 content in comparison to non-stressed animals. When applied individually, stressors increased the number of sympathetic fibers in comparison to controls, whereas in combination they decreased it. The activity of IBAT monoamine oxidase-A (MAO-A) decreased under the influence of each stressor independent of its type or duration. SOD activity coincided with MAO-A decrement, whereas CAT activity had an opposite pattern of changes. We conclude that acute and chronic exposure to non-thermal stressors, immobilization and isolation, respectively, affect the metabolic potential of rat IBAT, judging by the increase in UCP-1 content and sympathetic outflow. However, when acute immobilization was applied as a novel stressor to previously chronically isolated animals, an increase in the UCP-1 content was accompanied by a lower IBAT sympathetic outflow, suggesting that IBAT metabolic function under various stress condition is not solely dependent on SNS activity. [Projekat Ministarstva nauke Republike Srbije, br. 173023]. <br><br><font color="red"><b> This article has been corrected. Link to the correction <u><a href="http://dx.doi.org/10.2298/ABS150706080E">10.2298/ABS150706080E</a><u></b></font>

The thermogenic and metabolic responses to photoperiod manipulations in Apodemus chevrieri

Environmental cues play important roles in the regulation of an animal’s physiology and behavior. In the present study, we examined the effects of short photoperiod on body weight as well as on several physiological, hormonal, and biochemical measures indicative of thermogenic capacity to test our hypothesis that short photoperiod stimulates increases in thermogenesis without cold stress in Apodemus chevrieri. A. chevrieri were randomly assigned to either a long or short photoperiod for 4 weeks at constant temperature. The short photoperiod group of A. chevrieri showed increases in resting metabolic rate and nonshivering thermogenesis during the 4-week photoperiod acclimation. At the end, A. chevrieri at short photoperiod had lower body weights, higher levels of mitochondrial protein content and cytochrome C oxidase activity in liver and brown adipose tissues, and had higher levels of mitochondrial uncoupling protein-1 contents in brown adipose tissues. No difference in serum leptin levels were found between short and long photoperiod groups, but serum leptin levels were positively correlated with body mass and body fat mass, and negatively correlated with energy intake and uncoupling protein-1 content in brown adipose tissues, respectively. All results suggest that the short photoperiod may induce an increased thermogenesis capacity in A. chevrieri and that leptin is potentially involved in the photoperiod induced body mass regulation and thermogenesis in A. chevrieri.

High body weight associated with impaired nonshivering thermogenesis but improved glucose tolerance in Mongolian gerbils (Meriones unguiculatus)

Overweight and obesity correspond with metabolic syndromes, such as glucose intolerance and type 2 diabetes. The objective of this study was to determine whether decreased thermogenesis mass and glucose intolerance are directly related to changes in body mass in Mongolian gerbils. High body weight gerbils displayed increase in total body fat mass especially epididymal fat pad, and decrease in nonshivering thermogenesis, as indicated by depressed mitochondrial protein content and uncoupling protein-1 content in brown adipose tissue. No variations of sirtuin 1 and subunit IV of cytochrome oxidase expression were found in brown adipose tissue and skeletal muscle between the two groups. High body weight gerbils showed increased serum leptin and insulin concentrations but surprisingly increased glucose tolerance, suggesting a difference from other obese species in the regulation of glucose metabolism. Serum leptin levels were negatively correlated with UCP1 content in BAT and positively correlated with energy intake and insulin concentration. Our data suggest that leptin may be involved in thermogenesis regulation, insulin secretion and glucose metabolism in HBW gerbils.

Insulin resistance improves metabolic and contractile efficiency in stressed rat heart

Insulin resistance is a prominent feature in heart failure, while hyperglycemia impairs cardiac contraction. We propose that decreased insulin-mediated glucose uptake by the heart preserves cardiac function in response to metabolic and hemodynamic stress. To test this hypothesis, we fed rats a high-sucrose diet (HSD). Energy substrate metabolism and cardiac work were determined ex vivo in a sequential protocol simulating metabolic and hemodynamic stress. Compared to chow-fed, control rats, HSD impaired myocardial insulin responsiveness and induced profound metabolic changes in the heart, characterized by reduced rates of glucose uptake (7.91 ± 0.30 vs. 10.73 ± 0.67 μmol/min/g dry weight; P<0.001) but increased rates of glucose oxidation (2.38 ± 0.17 vs. 1.50 ± 0.15 μmol/min/g dry weight; P<0.001) and oleate oxidation (2.29 ± 0.11 vs. 1.96 ± 0.12 μmol/min/g dry weight; P<0.05). Tight coupling of glucose uptake and oxidation and improved cardiac efficiency were associated with a reduction in glucose 6-phosphate and oleoyl-CoA levels, as well as a reduction in the content of uncoupling protein 3. Our results suggest that insulin resistance lessens fuel toxicity in the stressed heart. This calls for a new exploration of the mechanisms regulating substrate uptake and oxidation in the insulin-resistant heart.

Endurance training decreases the non‐linearity in the oxygen uptake–power output relationship in humans

In this study, we hypothesized that 5 weeks of cycling endurance training can decrease the magnitude of the non-proportional increase in oxygen uptake (V(O(2))) to power output relationship (V(O(2)) 'excess') at exercise intensities exceeding the lactate threshold (LT). Ten untrained, physically active men performed a bout of incremental cycling exercise until exhaustion before and after training. The mitochondrial DNA copy number, myosin heavy chain composition and content of uncoupling protein 3 and sarcoplasmic reticulum Ca(2+)-ATPases (SERCAs) were analysed in muscle biopsies taken from vastus lateralis before and after training. The training resulted in an enhancement of the power-generating capabilities at maximal oxygen uptake (V(O(2)max)) by ∼7% (P = 0.002) despite there being no changes in V(O(2)max) (P = 0.49). This effect was due to a considerable reduction in the magnitude of the V(O(2)) 'excess' (P < 0.05) above the LT. A decrease in plasma ammonia concentration was found during exercise after training (P < 0.05). A downregulation of SERCA2 in vastus lateralis (P = 0.006) was observed after training. No changes in myosin heavy chain composition, selected electron transport chain proteins, uncoupling protein 3 or the mitochondrial DNA copy number (P > 0.05) were found after training. We conclude that the training-induced increase in power-generating capabilities at V(O(2)max) was due to attenuation of the V(O(2)) 'excess' above the LT. This adaptive response seems to be related to the improvement of muscle metabolic stability, as judged by a lowering of plasma ammonia concentration. The enhancement of muscle metabolic stability after training could be caused by a decrease in ATP usage at a given power output owing to downregulation of SERCA2 pumps.

Seasonal variations of body mass, thermogenesis and digestive tract morphology in Apodemus chevrieri in Hengduan mountain region

Seasonal changes in an animal’s morphology, physiology, and behavior are considered to be an adaptive strategy for survival and reproductive success. We hypothesize thatApodemus chevrieriwill change their thermogenesis seasonally and serum leptin will change with body mass or body fat mass. Seasonal variations in body mass (BM), basal metabolic rate (BMR), nonshivering thermogenesis (NST), digestive tract morphology, serum leptin and uncoupling protein 1 (UCP1) were measured in wild-trappedA. chevrieriin Hengduan mountain region. The results showed that the body weight ofA. chevrieriwas lowest in winter and highest in summer. Decreased BM in the winter was accompanied by increased energy intake and enhanced NST and UCP1 as well as by decreased body fat mass, adjusted digestive tract morphology and reduced levels of circulating leptin. Further, serum leptin were positively correlated with body weight and body fat mass, and negatively correlated with energy intake and UCP1 contents. These data suggest that wildA. chevrierido not depend on a decrease in BM, but instead increase their thermogenic capacity to cope with cold stress. Leptin may be involved in the seasonal regulation in energy balance and thermogenesis in fieldA. chevrieri.

Analysis of time-dependent adaptations in whole-body energy balance in obesity induced by high-fat diet in rats

BackgroundHigh-fat (HF) diet has been extensively used as a model to study metabolic disorders of human obesity in rodents. However, the adaptive whole-body metabolic responses that drive the development of obesity with chronically feeding a HF diet are not fully understood. Therefore, this study investigated the physiological mechanisms by which whole-body energy balance and substrate partitioning are adjusted in the course of HF diet-induced obesity.MethodsMale Wistar rats were fed ad libitum either a standard or a HF diet for 8 weeks. Food intake (FI) and body weight were monitored daily, while oxygen consumption, respiratory exchange ratio, physical activity, and energy expenditure (EE) were assessed weekly. At week 8, fat mass and lean body mass (LBM), fatty acid oxidation and uncoupling protein-1 (UCP-1) content in brown adipose tissue (BAT), as well as acetyl-CoA carboxylase (ACC) content in liver and epidydimal fat were measured.ResultsWithin 1 week of ad libitum HF diet, rats were able to spontaneously reduce FI to precisely match energy intake of control rats, indicating that alterations in dietary energy density were rapidly detected and FI was self-regulated accordingly. Oxygen consumption was higher in HF than controls throughout the study as whole-body fat oxidation also progressively increased. In HF rats, EE initially increased, but then reduced as dark cycle ambulatory activity reached values ~38% lower than controls. No differences in LBM were detected; however, epidydimal, inguinal, and retroperitoneal fat pads were 1.85-, 1.89-, and 2.54-fold larger in HF-fed than control rats, respectively. Plasma leptin was higher in HF rats than controls throughout the study, indicating the induction of leptin resistance by HF diet. At week 8, UCP-1 content and palmitate oxidation in BAT were 3.1- and 1.5-fold higher in HF rats than controls, respectively, while ACC content in liver and epididymal fat was markedly reduced.ConclusionThe thermogenic response induced by the HF diet was offset by increased energy efficiency and time-dependent reduction in physical activity, favoring fat accumulation. These adaptations were mainly driven by the nutrient composition of the diet, since control and HF animals spontaneously elicited isoenergetic intake.