UCP3 Protein Content Research Articles

ACE I/D gene variant predicts ACE enzyme content in blood but not the ACE, UCP2, and UCP3 protein content in human skeletal muscle in the Gene SMART study.

Angiotensin-converting enzyme (ACE) is expressed in human skeletal muscle. The ACE I/D polymorphism has been associated with athletic performance in some studies. Studies have suggested that the ACE I/D gene variant is associated with ACE enzyme content in serum, and there is an interaction between ACE and uncoupling proteins 2 and 3 (UCP2 and UCP3). However, no studies have explored the effect of ACE I/D on ACE, UCP2, and UCP3 protein content in human skeletal muscle. Utilizing the Gene SMART cohort ( n = 81), we investigated whether the ACE I/D gene variant is associated with ACE enzyme content in blood and ACE, UCP2, and UCP3 protein content in skeletal muscle at baseline and following a session of high-intensity interval exercise (HIIE). Using a stringent and robust statistical analyses, we found that the ACE I/D gene variant was associated with ACE enzyme content in blood ( P < 0.005) at baseline but not the ACE, UCP2, and UCP3 protein content in muscle at baseline. A single session of HIIE tended (0.005 < P < 0.05) to increase blood ACE content immediately postexercise, whereas muscle ACE protein content was lower 3 h after a single session of HIIE ( P < 0.005). Muscle UCP3 protein content decreased immediately after a single session of HIIE ( P < 0.005) and remained low 3 h postexercise. However, those changes in the muscle were not genotype dependent. In conclusion, The ACE I/D gene variant predicts ACE enzyme content in blood but not the ACE, UCP2, and UCP3 protein content of human skeletal muscle. NEW & NOTEWORTHY This paper describes the association between ACE I/D gene variant and ACE protein content in blood and ACE, UCP2, and UCP3 protein content in skeletal muscle at baseline and after exercise in a large cohort of healthy males. Our data suggest that ACE I/D is a strong predictor of blood ACE content but not muscle ACE content.

Abstract 165: Saxagliptin Restores Vascular Mitochondrial Exercise Response in Diabetes

Exercise decreases cardiovascular disease (CVD) risk and all-cause mortality. We and others have defined that exercise stimulates mitochondrial biogenesis via upstream signaling through endothelial nitric oxide synthase (eNOS), sirtuins (SIRTs), and/or PPARγ co-activator alpha (PGC1-α). Further, this response is absent in diabetes and hypertension. We tested the hypothesis that pharmacological restoration of vascular signaling with the dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin will improve vascular mitochondrial adaptation to exercise through activation of eNOS, SIRTs, and/or PGC1-α. We examined the impact of an 8 day treadmill exercise intervention in the Goto-Kakizaki (GK) rat, a model of lean, type 2 diabetes (T2DM), and Wistar control rats. Four groups were examined: sedentary or exercise groups with or without saxagliptin. Twenty-four hours post-bout, aortas were probed for mitochondrial complexes I-V, as well upstream signaling molecules. In Wistar rats, the expression of mitochondrial complexes III, IV, and V, along with SIRT3 (p&lt;0.05), eNOS, and PCG1-α, increased with exercise. Conversely, in GK animals, exercise led to a decrease of complexes I, III, and IV, a decrease in the expression of COX IV (p&lt;0.05) and AMPK, and no effect on eNOS or SIRT3. In exercised GK rats treated with saxagliptin, the expression of all mitochondrial complexes increased, complex IV significantly (p&lt;0.05). Significant increases (p&lt;0.05) were also observed in cytochrome c, eNOS and nNOS, PGC1-α, and UCP3 protein content in GK rats treated with both exercise and saxagliptin. Body weight and insulin and glucose concentrations were not significantly different in GK animals across experimental groups, indicating that the effects observed are independent of changes in these parameters. In addition, saxagliptin added to a three week exercise intervention improved running time significantly compared to an exercise intervention alone. In summary, our data suggest that saxagliptin restores vascular mitochondrial adaptation to exercise in a rodent model of diabetes. In conclusion, these data are proof of concept of a targetable mitochondrial defect in the diabetic vasculature.

UCP3 in muscle wasting, a role in modulating lipotoxicity?

UCP3 has been postulated to function in the defense against lipid-induced oxidative muscle damage (lipotoxicity). We explored this hypothesis during cachexia in rats (zymosan-induced sepsis), a condition characterized by increased oxidative stress and supply of fatty acids to the muscle. Muscle UCP3 protein content was increased 2, 6 and 11 days after zymosan injection. Plasma FFA levels were increased at day 2, but dropped below control levels on days 6 and 11. Muscular levels of the lipid peroxidation byproduct 4-hydroxy-2-nonenal (4-HNE) were increased at days 6 and 11 in zymosan-treated rats, supporting a role for UCP3 in modulating lipotoxicity during cachexia.

Understanding efficiency of human muscular movement exemplifies integrative and translational physiology

This issue of The Journal of Physiology contains a paper by Mogensen et al (2006) that is an excellent example of integrative physiology, addressing questions both at the subcellular and whole body levels that have implications for basic muscle energetics as well as athletic performance. Within a given population, muscular efficiency and thus work rate typically vary by as much as 20–30% when comparing individuals with low vs. high efficiency individuals despite controlling for oxygen consumption, training status, diet and other factors (Coyle et al. 1992). This represents a large amount of biological difference between individuals, which directly influences physical stress and work productivity. Elucidating the factors that determine and influence the energetic efficiency of human muscular movement in vivo, as currently measured by cycling or work efficiency, remains an important, open and challenging question. Work efficiency represents the product of two phenomena: (a) the efficiency with which the chemical energy of glucose and/or fat is converted to ATP through oxidative phosphorylation; and (b) the efficiency with which the chemical energy of ATP hydrolysis is converted to work. Mogensen et al (2006) convincingly demonstrate that differences in the efficiency of human muscular movement (e.g. gross cycling efficiency) observed among people cannot be explained by their in vitro differences in efficiency of oxidative phosphorylation within leg muscle mitochondria. Furthermore, mitochondrial efficiency was not different in endurance trained versus untrained individuals. This implies that the large differences among individuals in cycling efficiency appear to be due largely to the efficiency of transferring the chemical energy from ATP hydrolysis into physical work. The authors provide a good road map for translational physiologists to follow, especially when, as in the present case, the results don't support the initial hypothesis. Contrary to the initial hypothesis, cycling efficiency of people in vivo was not related to mitochondrial respiratory efficiency (i.e. phosphorylation ratio; P/O ratio) measured in vitro within isolated skeletal muscle mitochondria. The authors display keen insight into the literature and wisdom as they reconstruct how molecules of UCP3 or myosin might translate into the muscle functions currently observed. These appear to be the first such measurements made in vitro on humans of skeletal muscle mitochondrial efficiency measured during submaximal respiration. For this purpose, the authors developed a physiologically appropriate method involving constant rate ADP infusion across multiple flux rates to calculated the P/O at a common 50% value. However, their hard earned and physiologically sound data failed to support their theory leading to a host of new questions. The main new finding in the present study was that cycling efficiency was correlated to UCP3 protein content. It is hypothesized that other factors such as muscle fibre type influence UCP3 and thus muscle efficiency in vivo. However, the authors recognize the limitations in concluding a cause and effect relationship between UCP3 protein content and efficiency and go on to present a balanced argument including discussion against a direct role of UCP3 in determining muscle efficiency. This study again shows that cross-sectional endurance training status does not relate to mitochondrial efficiency (Tonkonogi et al. 2000; Fernstrom et al. 2004). Although oxidative phosphorylation can have direct influence on cycling efficiency, the authors acknowledge that it represents only part of the equation for work or cycling efficiency. We are left with an emerging picture that cycling efficiency appears related to percentage MHC I and somehow to UCP3 protein content. This study has made clear the fact that solving this puzzle requires use of techniques at the molecular and whole body levels, both of which can only be interpreted when controlling for the relative work rate.

Cycling efficiency in humans is related to low UCP3 content and to type I fibres but not to mitochondrial efficiency

The purpose of this study was to investigate the hypothesis that cycling efficiency in vivo is related to mitochondrial efficiency measured in vitro and to investigate the effect of training status on these parameters. Nine endurance trained and nine untrained male subjects (V(O2peak) = 60.4 +/- 1.4 and 37.0 +/- 2.0 ml kg(-1) min(-1), respectively) completed an incremental submaximal efficiency test for determination of cycling efficiency (gross efficiency, work efficiency (WE) and delta efficiency). Muscle biopsies were taken from m. vastus lateralis and analysed for mitochondrial respiration, mitochondrial efficiency (MEff; i.e. P/O ratio), UCP3 protein content and fibre type composition (% MHC I). MEff was determined in isolated mitochondria during maximal (state 3) and submaximal (constant rate of ADP infusion) rates of respiration with pyruvate. The rates of mitochondrial respiration and oxidative phosphorylation per muscle mass were about 40% higher in trained subjects but were not different when expressed per unit citrate synthase (CS) activity (a marker of mitochondrial density). Training status had no influence on WE (trained 28.0 +/- 0.5, untrained 27.7 +/- 0.8%, N.S.). Muscle UCP3 was 52% higher in untrained subjects, when expressed per muscle mass (P < 0.05 versus trained). WE was inversely correlated to UCP3 (r = -0.57, P < 0.05) and positively correlated to percentage MHC I (r = 0.58, P < 0.05). MEff was lower (P < 0.05) at submaximal respiration rates (2.39 +/- 0.01 at 50% V(O2max)) than at state 3 (2.48 +/- 0.01) but was neither influenced by training status nor correlated to cycling efficiency. In conclusion cycling efficiency was not influenced by training status and not correlated to MEff, but was related to type I fibres and inversely related to UCP3. The inverse correlation between WE and UCP3 indicates that extrinsic factors may influence UCP3 activity and thus MEff in vivo.

Long-term caloric restriction increases UCP3 content but decreases proton leak and reactive oxygen species production in rat skeletal muscle mitochondria

Calorie restriction (CR) without malnutrition increases life span and delays the onset of a variety of diseases in a wide range of animal species. However, the mechanisms responsible for the retardation of aging with CR are poorly understood. We proposed that CR may act, in part, by inducing a hypometabolic state characterized by decreased reactive oxygen species (ROS) production and mitochondrial proton leak. Here, we examine the effects of long-term CR on whole animal energetics as well as muscle mitochondrial energetics, ROS production, and ROS damage. CR was initiated in male FBNF1 rats at 6 mo of age and continued for 12 or 18 mo. Mean whole body VO2 was 34.6 (P < 0.01) and 35.6% (P < 0.001) lower in CR rats than in controls after 12 and 18 mo of CR, respectively. Body mass-adjusted VO2 was 11.1 and 29.5% lower (both P < 0.05) in CR rats than in controls after 12 and 18 mo of CR. Muscle mitochondrial leak-dependent (State 4) respiration was decreased after 12 mo compared with controls; however, after 18 mo of CR, there were slight but not statistically significant differences. Proton leak kinetics were affected by 12 mo of CR such that leak-dependent respiration was lower in CR mitochondria only at protonmotive force values exceeding 170 mV. Mitochondrial H2O2 production and oxidative damage were decreased by CR at both time points and increased with age. Muscle UCP3 protein content increased with long-term CR, consistent with a role in protection from ROS but inconsistent with the observed decrease or no change in proton leak.

COPD Results in a Reduction in UCP3 Long mRNA and UCP3 Protein Content in Types I and IIa Skeletal Muscle Fibers

Findings recently have shown coupling protein-3 (UCP3) content to be decreased in the skeletal muscle of patients with chronic obstructive pulmonary disease (COPD). Uncoupling protein-3 mRNA exists as two isoforms: long (UCP3L) and short (UCP3S). The UCP3 protein is expressed the least in oxidative and the most in glycolytic muscle fibers. Levels of UCP3 have been associated positively with intramyocellular triglyceride (IMTG) contents in conditions of altered fatty acid metabolism. As a source for muscle free fatty acid metabolism, IMTG is decreased in COPD. The current study completely characterized all the parameters of UCP3 expression (ie, UCP3L and UCP3S mRNA expression in whole muscle samples) and UCP3 protein content as well as IMTG content in the different fiber types in patients with COPD and healthy control subjects. Using real-time polymerase chain reaction, UCP3 gene expression was quantified. Skeletal muscle fiber type and UCP3 protein and IMTG content were measured using immunofluorescence and Oil red oil staining, respectively. The findings showed that UCP3L mRNA expression was 44% lower (P < .005) in the patients with COPD than in the control subjects, whereas the UCP3S mRNA content was similar in the two groups. As compared with control subjects, UCP3 protein content was decreased by 89% and 83% and the IMTG content by 64% and 54%, respectively, in types I and IIa fibers (P < .0167) of patients with COPD, whereas they were unchanged in IIx fibers. The reduced UCP3 and IMTG content in the more oxidative fibers may be linked to the altered muscle fatty acid metabolism associated with COPD. Further studies are required to determine the exact role and clinical relevance of the reduced UCP3 content in patients with COPD.

Chronic low-frequency stimulation upregulates uncoupling protein-3 in transforming rat fast-twitch skeletal muscle.

The purpose of this investigation was to examine the temporal changes in uncoupling protein (UCP)-3 expression, as well as related adaptive changes in mitochondrial density and fast-to-slow fiber type transitions during chronically enhanced contractile activity. We examined the effects of 1-42 days of chronic low-frequency electrical stimulation (CLFS), applied to rat tibialis anterior (TA) for 10 h/day, on the expression of UCP-3 and concomitant changes in myosin heavy chain (MHC) protein expression and increases in oxidative capacity. UCP-3 protein content increased from 1 to 12 days, reaching 1.5-fold over control (P < 0.0005); it remained elevated for up to 42 days. In contrast, UCP-3 mRNA decreased in response to CLFS, reaching a level that was threefold lower than control (P < 0.0007). The activities of the mitochondrial reference enzymes citrate synthase (EC 4.1.3.7) and 3-hydroxyacyl-CoA-dehydrogenase (EC 1.1.1.35), which are known to increase in proportion to mitochondrial density, progressively increased up to an average of 2.3-fold (P < 0.00001). These changes were accompanied by fast-to-slow fiber type transitions, characterized by a shift in the pattern of MHC expression (P <0.0002): MHCI and MHCIIa expression increased by 1.7- and 4-fold, whereas MHCIIb displayed a 2.4-fold reduction. We conclude that absolute increases in UCP-3 protein content in the early adaptive phase were associated with the genesis of mitochondria containing a normal complement of UCP-3. However, during exposure to long-term CLFS, mitochondria were generated with a lower complement of UCP-3 and coincided with the emergence of a growing population of oxidative type IIA fibers.

Uncoupling protein 3 and physical activity: the role of uncoupling protein 3 in energy metabolism revisited.

Physical activity influences energy metabolism in human subjects by increasing activity-induced energy expenditure and resting metabolic rate for several hours after exercise. On the other hand, physical activity increases mechanical energy efficiency, suggesting that trained subjects would need less energy for daily activities. The underlying mechanism by which physical activity influences energy metabolism is largely unknown. The skeletal muscle-specific homologue of uncoupling protein (UCP) 1, UCP3, could possibly play a major role in energy expenditure. UCP3 is, like UCP1, able to uncouple respiration from ATP production. A strong link or association between the UCP3 gene and energy metabolism was found. Furthermore, UCP3 mRNA expression is related to sleeping metabolic rate, and thyroid hormone, a powerful stimulator of energy expenditure, up regulates UCP3. Finally, mice overexpressing UCP3 are hyperphagic but lean. These findings indicated that UCP3 is related to energy metabolism and that UCP3 could have a role in the effect of physical activity on energy expenditure. Thus, acute exercise up regulates UCP3, whereas endurance training results in the down-regulation of UCP3 protein content. Only a minimal amount of physical activity is needed for down-regulation of UCP3. Moreover, there is very strong evidence that UCP3 is negatively related to mechanical energy efficiency, suggesting that the down-regulation of UCP3 with training increases mechanical energy efficiency. Taken together, although the exact function of UCP3 is still unknown, exercise and training studies clearly show that under certain circumstances UCP3 is strongly related to human energy metabolism, possibly as a secondary effect of its (yet) unknown primary function.

Decreased Uncoupling Protein Expression and Intramyocytic Triglyceride Depletion in Formerly Obese Subjects

To examine the muscular uncoupling protein expression 2 (UCP2) and UCP3 gene expression in morbid obese subjects before and after bariatric surgery [bilio-pancreatic diversion (BPD)]. Eleven obese subjects (BMI = 49 +/- 2 kg/m(2)) were studied before BPD and 24 months after BPD. Skeletal muscle UCP2 and UCP3 mRNA was measured using reverse transcriptase-competitive polymerase chain reaction and UCP3 protein by Western blotting. Intramyocytic triglycerides were quantified by high-performance liquid chromatography. Twenty-four-hour energy expenditure and respiratory quotient (RQ) were measured in a respiratory chamber. After BPD, the average weight loss was approximately 38%. Nonprotein RQ was increased in the postobese subjects (0.73 +/- 0.00 vs. 0.83 +/- 0.02, p < 0.001). The intramyocytic triglyceride level dropped (3.66 +/- 0.16 to 1.60 +/- 0.29 mg/100 mg of fresh tissue, p < 0.0001) after BPD. Expression of UCP2 and UCP3 mRNA was significantly reduced (from 35.9 +/- 6.1% to 18.6 +/- 4.5% of cyclophilin, p = 0.02; from 60.2 +/- 14.0% to 33.4 +/- 8.5%, p = 0.03; respectively). UCP3 protein content was also significantly reduced (272.19 +/- 84.13 vs. 175.78 +/- 60.31, AU, p = 0.04). A multiple regression analysis (R(2) = 0.90) showed that IMTG levels (p = 0.007) represented the most powerful independent variable for predicting UCP3 variation. The strong correlation of UCP expression and decrease in IMTG levels suggests that triglyceride content plays an even more important role in the regulation of UCP gene expression than the circulating levels of free fatty acids or the achieved degree of weight loss.

The Effect of Burn Injury on UCP3 mRNA Expression and UCP3 Protein Content in Rat Skeletal Muscles

Journal Article The Effect of Burn Injury on UCP3 mRNA Expression and UCP3 Protein Content in Rat Skeletal Muscles Get access X. Sun, MD, PhD, X. Sun, MD, PhD 1Shriners Hospitals for Children and University of Cincinnati, Cincinnati, OH Search for other works by this author on: Oxford Academic Google Scholar C. H. Fang, MD, C. H. Fang, MD 1Shriners Hospitals for Children and University of Cincinnati, Cincinnati, OH Search for other works by this author on: Oxford Academic Google Scholar J. Oghene, BS J. Oghene, BS 1Shriners Hospitals for Children and University of Cincinnati, Cincinnati, OH Search for other works by this author on: Oxford Academic Google Scholar The Journal of Burn Care & Rehabilitation, Volume 24, Issue suppl_2, March-April 2003, Page S124, https://doi.org/10.1097/00004630-200303002-00163 Published: 01 March 2003

EXERCISE FOR MITOCHONDRIA

An important source of metabolic inefficiency is a futile cycle of protons across the mitochondrial inner membrane, a process called proton leak. In brown fat, proton leak is catalysed by a protein called uncoupling protein 1(UCP1), and two homologues of this protein have been discovered called UCP2 and UCP3. UCP2 is expressed in most tissues, while UCP3 is expressed mostly in skeletal muscle. Many studies have reported rapid and drastic increases in the level of UCP3 mRNA in skeletal muscle after a single bout of exercise, whilst others demonstrated decreases in UCP3 mRNA during longterm training. It was assumed that these changes had functional significance and that an increase in the level of UCP3 expression could protect muscle cells against elevated substrate supply following exercise by uncoupling substrate oxidation from ATP production, whereas a decrease during long-term training could augment metabolic efficiency. These data suggest changes in the composition of mitochondria in response to exercise such that they display markedly different UCP3 levels, relative to other mitochondrial proteins. Since exercise leads to an increase in the content of mitochondria in muscle fibers, and the expression of UCPs is most probably regulated in a manner similar to that of other mitochondrial proteins, Jones and collaborators hypothesized that UCP3 protein level in skeletal muscle increases during training as part of the increase in the content of mitochondria and that each mitochondrion preserves similar levels of UCP3 proteins. Additionally, they tested whether mitochondria rich type I muscle fibers have higher levels of UCP3 expression than type IIa or IIb fibers that have a lower mitochondrial content.To test their main hypothesis, the authors used rats accustomed to swimming. The exercise protocol consisted of two 3 hour swimming sessions separated by a resting period. The first group of rats performed the protocol for one day, the second for three days and the last group for ten days. The team collected muscle samples after each group's last training session and measured the muscles' UCP3 transcript and protein levels. The transcript level of UCP3 increased very rapidly after a single bout of exercise, while UCP3 protein level displayed a significant increase only after several hours. The level of UCP3 protein increased steadily over 10 days of swimming. Importantly, the increase in UCP3 protein level paralleled that of other mitochondrial proteins, indicating that exercise leads to a rise in the number of mitochondria in the muscle, rather than to a modification in the UCP3 protein content of pre-existing mitochondria.In a separate experiment using sedentary rats, the protein level of UCP3 was compared with that of other mitochondrial proteins in type I, IIa and IIb muscle fibers. The content of UCP3 was higher in type I fibers than in type IIa and IIb fibers, and this pattern is similar to that of other mitochondrial proteins. So the UCP3 protein content of each fiber type parallels their number of mitochondria.Overall, the results presented in this paper support the original hypothesis of the authors and suggest that modification in the expression level of UCPs under certain conditions could reflect changes in the content of mitochondria in cells, possibly due to alteration in cellular energy status.

The effect of mild cold exposure on UCP3 mRNA expression and UCP3 protein content in humans.

In rodents, adaptive thermogenesis in response to cold exposure and high-fat feeding is accomplished by the activation of the brown adipose tissue specific mitochondrial uncoupling protein, UCP1. The recently discovered human uncoupling protein 3 is a possible candidate for adaptive thermogenesis in humans. In the present study we examined the effect of mild cold exposure on the mRNA and protein expression of UCP3. Ten healthy male volunteers (age 24.4 +/- 1.6 y; height 1.83 +/- 0.02 m; weight 77.3 +/- 3.0 kg; percentage body fat 19 +/- 2). Subjects stayed twice in the respiration chamber for 60 h (20.00-8.00 h); once at 22 degrees C (72 degrees F), and once at 16 degrees C (61 degrees F). After leaving the respiration chamber, muscle biopsies were taken and RT-competitive-PCR and Western blotting was used to measure UCP3 mRNA and protein expression respectively. Twenty-four-hour energy expenditure was significantly increased at 16 degrees C compared to 22 degrees C (P<0.05). At 16 degrees C, UCP3T (4.6 +/- 1.0 vs 7.7 +/- 1.5 amol/microg RNA, P=0.07), UCP3L (2.0 +/- 0.5 vs 3.5 +/- 0.9 amol/microg RNA, P=0.1) and UCP3S (2.6 +/- 0.6 vs 4.2 +/- 0.7 amol/microg RNA, P=0.07) mRNA expression tended to be lower compared with at 22 degrees C, whereas UCP3 protein content was, on average, not different. However, the individual differences in UCP3 protein content (16-22 degrees C) correlated positively with the differences in 24 h energy expenditure (r=0.86, P<0.05). The present study suggests that UCP3 protein content is related to energy metabolism in humans and might help in the metabolic adaptation to cold exposure. However, the down-regulation of UCP3 mRNA with mild cold exposure suggests that prolonged cold exposure will lead to lower UCP3 protein content. What the function of such down-regulation of UCP3 could be is presently unknown.

Differences in proton leak kinetics, but not in UCP3 protein content, in subsarcolemmal and intermyofibrillar skeletal muscle mitochondria from fed and fasted rats

We have investigated the effect of 24-h fasting on basal proton leak and uncoupling protein (UCP) 3 expression at the protein level in subsarcolemmal and intermyofibrillar skeletal muscle mitochondria. In fed rats, the two mitochondrial populations displayed different proton leak, but the same protein content of UCP3. In addition, 24-h fasting, both at 24 and 29°C, induced an increase in proton leak only in subsarcolemmal mitochondria, while UCP3 content increased in both the populations. From the present data, it appears that UCP3 does not control the basal proton leak of skeletal muscle mitochondria.

Increased uncoupling proteins and decreased efficiency in palmitate-perfused hyperthyroid rat heart.

The physiological role of mitochondrial uncoupling proteins (UCPs) in heart and skeletal muscle is unknown, as is whether mitochondrial uncoupling of oxidative phosphorylation by fatty acids occurs in vivo. In this study, we found that UCP2 and UCP3 protein content, determined using Western blotting, was increased by 32 and 48%, respectively, in hyperthyroid rat heart mitochondria. Oligomycin-insensitive respiration rate, a measure of mitochondrial uncoupling, was increased in all mitochondria in the presence of palmitate: 36% in controls and 71 and 100% with 0.8 and 0.9 mM palmitate, respectively, in hyperthyroid rat heart mitochondria. In the isolated working heart, 0.4 mM palmitate significantly lowered cardiac output by 36% and cardiac efficiency by 38% in the hyperthyroid rat heart. Thus increased mitochondrial UCPs in the hyperthyroid rat heart were associated with increased uncoupling and decreased myocardial efficiency in the presence of palmitate. In conclusion, a physiological effect of UCPs on fatty acid oxidation has been found in heart at the mitochondrial and whole organ level.

The effect of weight reduction on skeletal muscle UCP2 and UCP3 mRNA expression and UCP3 protein content in Type II diabetic subjects.

The aim of this study was to examine the effect of weight loss on UCP2/UCP3 mRNA expression and UCP3 protein content in subjects with Type II (non-insulin-dependent) diabetes mellitus. We studied seven Type II diabetic subjects who followed a 10-week very low calorie diet. Expression of skeletal muscle UCP2 and UCP3 mRNA was measured using RT-competitive PCR and UCP3 protein content by western blotting, before and after the diet. Total and plasma fatty acid oxidation was measured using infusion of 13C labelled palmitate. Body weight decreased from 105.5 +/- 8.2 kg to 91.6 +/- 7.2 kg (p < 0.001), after 10 weeks of diet intervention. Expression of UCP2 and UCP3 mRNA were significantly reduced after 10 weeks of diet (p < 0.05) but UCP3 protein contents were not significantly altered. Notably, the change in UCP3L mRNA expression and UCP3 protein content after the very low calorie diet were negatively associated with changes in body weight (r = -0.97, p = 0.006 and r = -0.83, p = 0.043, respectively) and BMI (r = -0.99, p = 0.0007 and r = -0.9, p = 0.016, respectively). Furthermore, changes in UCP3L mRNA expression and UCP3 protein content induced by the diet were positively correlated with changes in cytosolic fatty acid-binding protein content (r = 0.93, p = 0.023 and r = 0.84, p = 0.039, respectively). No correlation between diet-induced changes in UCP3 protein and resting energy expenditure or plasma non-esterified fatty acid concentrations were found. The negative correlation between the change in UCP3 protein content after weight loss and the change in BMI, suggests that the decrease in UCP3 during weight loss could prevent further weight loss. The finding that the change in UCP3 protein content correlates with the change in skeletal muscle fatty acid-binding protein content, suggests a role for UCPs in the handling of lipids as a fuel.