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

OBJECTIVE: 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. SUBJECTS: 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). DESIGN: 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. RESULTS: 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). CONCLUSION: 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.     

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

Aims/hypothesis. 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.¶Methods. 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.¶Results. 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.¶Conclusion/interpretation. 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. [Diabetologia (2000) 43: 1408–1416]     

Slow component of [V]O(2) kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

OBJECTIVE: In healthy individuals performing constant-load exercise at intensities above the lactate threshold a secondary rise in pulmonary oxygen uptake ([V]O(2)) occurs. [V]O(2) reaches a maximum and exhaustion rapidly prevails for a range of work rates lower than the maximal work rate achieved during a conventional rapid-incremental test. This phenomenon is called the slow component (SC) of [V]O(2) kinetics and represents an increase in [V]O(2) without an increase in work rate. Although still under debate, the magnitude of the SC is believed to be associated with the percentage of type II muscle fibres and their recruitment. In this study we investigated the relationship between the magnitude of the relative SC, citrate synthase activity, UCP2 and UCP3 mRNA levels and muscle fibre composition in both endurance-trained and recreationally active subjects. METHOD: The magnitude of the relative SC was measured in 12 endurance-trained (Tr) and 15 recreationally active (RA) male subjects. The magnitude of the relative SC was determined as the difference between the end-exercise [V]O(2) and 3 min [V]O(2) divided by the difference between end-exercise [V]O(2) and baseline [V]O(2). UCP2 and UCP3 mRNA expression in the vastus lateralis was measured by RT-PCR with beta-actin mRNA used as an internal control. These values were also normalized against cytochrome-b mRNA to control for training induced changes in mitochondria when comparing the Tr and RA groups. Type I, IIa and IIx skeletal muscle fibre composition was determined using a routine myosin ATPase histochemical staining technique. Citrate synthase (CS) activity was measured using spectrophotometric detection. RESULTS: The magnitude of the relative SC of the Tr group had the highest correlation with citrate synthase activity (r=-0.90, P<0.001) and that of the RA group with [V]O(2) peak (r=-0.68, P<0.01). For the Tr group other correlations with the magnitude of the relative SC included UCP3 mRNA levels (r=0.69, P<0.05) and the percentage of type I fibres (r=-0.58, P<0.05), while for the RA group they included UCP3 mRNA (r=0.58, P<0.05) and the percentage of type IIa muscle fibres (r=0.59, P<0.05). The Tr subjects had a lower relative SC (P=0.04) and a lower expression of UCP2 (P=0.04), and UCP3 mRNA (P=0.01) than the RA subjects. When the groups were combined the magnitude of the relative SC correlated with UCP3 mRNA (r=0.70, P<0.01), percentage of type IIa muscle fibres (r=0.60, P<0.01) and [V]O(2) peak (r=-0.73, P<0.01). Additionally UCP3 mRNA correlated with the percentage of type IIa muscle fibres (r=0.63, P<0.001). CONCLUSION: Citrate synthase activity and [V]O(2) peak are indicators of aerobic fitness. The high negative correlations between the magnitude of the relative SC and citrate synthase activity and [V]O(2) peak, of the Tr and RA subjects, respectively, suggests that the magnitude of the relative SC is inversely correlated with aerobic fitness. Additionally the correlations between UCP3 mRNA and the magnitude of the relative SC for both groups individually and combined suggest that the uncoupling activity of the UCP3 protein may also influence the magnitude of the relative SC.     

COPD results in a reduction in UCP3 long mRNA and UCP3 protein content in types I and IIa skeletal muscle fibers

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

Epigallocatechin gallate attenuates diet-induced obesity in mice by decreasing energy absorption and increasing fat oxidation

OBJECTIVE: To examine the antiobesity effect of epigallocatechin gallate (EGCG), a green tea bioactive polyphenol in a mouse model of diet-induced obesity. METHODS: Obesity was induced in male New Zealand black mice by feeding of a high-fat diet. EGCG purified from green tea (TEAVIGO) was supplemented in the diet (0.5 and 1%). Body composition (quantitative magnetic resonance), food intake, and food digestibility were recorded over a 4-week period. Animals were killed and mRNA levels of uncoupling proteins (UCP1-3), leptin, malic enzyme (ME), stearoyl-CoA desaturase-1 (SCD1), glucokinase (GK), and pyruvate kinase (PK) were analysed in different tissues. Also investigated were acute effects of orally administered EGCG (500 mg/kg) on body temperature, activity (transponders), and energy expenditure (indirect calorimetry). RESULTS: Dietary supplementation of EGCG resulted in a dose-dependent attenuation of body fat accumulation. Food intake was not affected but faeces energy content was slightly increased by EGCG, indicating a reduced food digestibility and thus reduced long-term energy absorption. Leptin and SCD1 gene expression in white fat was reduced but SCD1 and UCP1 expression in brown fat was not changed. In liver, gene expression of SCD1, ME, and GK was reduced and that of UCP2 increased. Acute oral administration of EGCG over 3 days had no effect on body temperature, activity, and energy expenditure, whereas respiratory quotient during night (activity phase) was decreased, supportive of a decreased lipogenesis and increased fat oxidation. CONCLUSIONS: Dietary EGCG attenuated diet-induced body fat accretion in mice. EGCG apparently promoted fat oxidation, but its fat-reducing effect could be entirely explained by its effect in reducing diet digestibility.     

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

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

Effects of monounsaturated fatty acids v complex carbohydrates on serum lipoproteins and apoproteins in healthy men and women

The effects of a high-carbohydrate, high-fiber diet and an olive-oil-rich diet on the distribution of cholesterol over the various lipoproteins, on serum apolipoproteins, and on the composition of HDL2 and HDL3 were studied under strict dietary control. Forty-eight healthy subjects first consumed a high-saturated-fat diet [proportion of energy, en%] (saturated fat 20 en%, total fat 38 en%) for 17 days. For the next 36 days, 24 subjects consumed a diet high in complex carbohydrates (monounsaturated fat 9 en%, total fat 22 en%) and the other 24 consumed a high-fat, olive-oil-rich diet (monounsaturated fat 24 en%, total fat 41 en%). The amounts of protein (12% to 14 en%), polyunsaturated fat (4 to 5 en%), and cholesterol (31 to 35 mg/MJ) were similar in all three diets. Serum cholesterol levels fell by 0.44 mmol/L in subjects consuming the carbohydrate diet and by 0.52 mmol/L for those receiving the olive-oil-rich diet. VLDL-cholesterol levels rose by 0.08 mmol/L in the carbohydrate group and fell by 0.08 mmol/L in the olive oil group (P less than .05 for difference between test diets). HDL2 and LDL cholesterol levels fell to the same extent on both diets. HDL3 cholesterol fell by 0.09 mmol/L on the high-carbohydrate diet and increased by 0.01 mmol/L on the olive oil diet (P less than .05). There was no change in the composition of HDL3, suggesting that the fall was due to a decrease in the total number of circulating particles.(ABSTRACT TRUNCATED AT 250 WORDS)     

NO-1886 (ibrolipim), a lipoprotein lipase activator, increases the expression of uncoupling protein 3 in skeletal muscle and suppresses fat accumulation in high-fat diet-induced obesity in rats

Although the lipoprotein lipase (LPL) activator NO-1886 shows antiobesity effects in high-fat-induced obese animals, the mechanism remains unclear. To clarify the mechanism, we studied the effects of NO-1886 on the expression of uncoupling protein (UCP) 1, UCP2, and UCP3 in rats. NO-1886 was mixed with a high-fat chow to supply a dose of 100 mg/kg to 8-month-old male Sprague-Dawley rats. The animals were fed the high-fat chow for 8 weeks. At the end of the administration period, brown adipose tissue (BAT), mesenteric fat, and soleus muscle were collected and levels of UCP1, UCP2, and UCP3 messenger RNA (mRNA) were determined. NO-1886 suppressed the body weight increase seen in the high-fat control group after the 8-week administration (585 +/- 39 vs 657 +/- 66 g, P < .05). NO-1886 also suppressed fat accumulation in visceral (46.9 +/- 10.4 vs 73.7 +/- 14.5 g, P < .01) and subcutaneous (43.1 +/- 18.1 vs 68.9 +/- 18.8 g, P < .05) tissues and increased the levels of plasma total cholesterol and high-density lipoprotein cholesterol in comparison to the high-fat control group. In contrast, NO-1886 decreased the levels of plasma triglycerides, nonesterified free fatty acid, glucose, and insulin. NO-1886 increased LPL activity in soleus muscle (0.082 +/- 0.013 vs 0.061 +/- 0.016 mumol of free fatty acid per minute per gram of tissue, P < .05). NO-1886 increased the expression of UCP3 mRNA in soleus muscle 3.14-fold (P < .01) compared with the high-fat control group without affecting the levels of UCP3 in mesenteric adipose tissue and BAT. In addition, NO-1886 did not affect the expression of UCP1 and UCP2 in BAT, mesenteric adipose tissue, and soleus muscle. In conclusion, NO-1886 increased the expression of UCP3 mRNA and LPL activity only in skeletal muscle. Therefore, a possible mechanism for NO-1886's antiobesity effects in rats may be the enhancement of LPL activity in skeletal muscle and the accompanying increase in UCP3 expression.     

Up-regulation of muscle uncoupling protein 3 gene expression in mice following high fat diet, dietary vitamin A supplementation and acute retinoic acid-treatment

OBJECTIVE: To analyse the impact of vitamin A supplementation of both a normal fat (NF) diet and a high fat (HF) diet and of acute retinoic acid (RA)-treatment on the expression of uncoupling protein 3 (UCP3) in mice. DESIGN: C57BL/6J mice were fed for 18 weeks a NF or a HF diet (10 and 45 energy% as fat, respectively), both with the normal vitamin A content or an excess vitamin A (8 mg and 320 mg retinyl palmitate/kg diet, respectively). Body weight and energy intake were recorded periodically. UCP3 mRNA and UCP3 protein levels in skeletal muscle (soleus/gastrocnemius) were analysed, as well as UCP1, UCP2 and UCP3 mRNA levels in interscapular brown adipose tissue (BAT), and UCP2 mRNA, UCP2 protein and leptin mRNA levels in white adipose tissue (WAT) depots. The effect of acute RA-treatment (100 mg/kg/day, 4 days) on UCP3 mRNA levels in skeletal muscle and BAT of NMRI mice was also assessed. RESULTS: Vitamin A supplementation of a NF diet led to increased levels of UCP3 mRNA and UCP3 protein in muscle, UCP1 mRNA in BAT, and UCP2 mRNA in inguinal WAT, but had no impact on body weight or adiposity of B6 mice. HF diet promoted obesity and increased levels of UCP3 mRNA and UCP3 protein in skeletal muscle, and of the mRNAs for all three UCPs in BAT. Supplementing the HF diet with vitamin A had little effect on the final obesity reached and did not lead to further increases of muscle UCP3 mRNA nor BAT UCP1 mRNA over the levels achieved with the non-supplemented HF diet. Adipose leptin mRNA levels were down regulated after vitamin A supplementation, independently of the fat content of the diet. Up-regulation of muscle, but not BAT, UCP3 mRNA levels was also found after acute RA-treatment in NMRI mice. CONCLUSION: The results provide evidence of a stimulatory effect of retinoids on muscle UCP3 expression in vivo, and a differential retinoid-regulation of the UCP3 gene in muscle and BAT.     

Type-2 iodothyronine 5'deiodinase (D2) in skeletal muscle of C57Bl/6 mice. II. Evidence for a role of D2 in the hypermetabolism of thyroid hormone receptor alpha-deficient mice

Mice with ablation of the Thra gene have cold intolerance due to an as yet undefined defect in the activation of brown adipose tissue (BAT) uncoupling protein (UCP). They develop an alternate form of facultative thermogenesis, activated at temperatures below thermoneutrality and associated with hypermetabolism and reduced sensitivity to diet-induced obesity. A consistent finding in Thra-0/0 mice is increased type-2 iodothyronine deiodinase (D2) mRNA in skeletal muscle and other tissues. With an improved assay to measure D2 activity, we show here that this enzyme activity is increased in proportion to the mRNA and as a function of the ambient cold. The activation is mediated by the sympathetic nervous system in Thra-0/0, as it is in wild-type genotype mice, but the sympathetic nervous system effect is greater in Thra-0/0 mice. Using D2-ablated mice (Dio2-/-), we reported elsewhere and show here that, in spite of sharing a severe deficiency in BAT thermogenesis with Thra-0/0 and UCP1-knockout mice, they do not have an increase in oxygen consumption, and they gain more weight than wild-type controls when fed a high-fat diet. UCP3 mRNA is highly responsive to thyroid hormone, and it is increased in Thra-0/0 mice, particularly when fed high-fat diets. We show here that muscle UCP3 mRNA in hypothyroid Thra-0/0 mice is responsive to small dose-short regimens of T(4), indicating a role for locally, D2-generated T(3). Lastly, we show that bile acids stimulate not only BAT but also muscle D2 activity, and this is associated with stimulation of muscle UCP3 mRNA expression provided T(4) is present. These observations strongly support the concept that enhanced D2 activity in Thra-0/0 plays a critical role in their alternate form of facultative thermogenesis, stimulating increased fat oxidation by increasing local T(3) generation in skeletal muscle.     

Regulation of uncoupling protein-2 and -3 by growth hormone in skeletal muscle and adipose tissue in growth hormone-deficient adults

The newly described uncoupling proteins, UCP2 and UCP3, may play a role in regulating energy expenditure (EE) in humans. GH deficiency (GHD) is associated with decreased lean body mass, increased adiposity, and reduced EE, which are reversed by GH treatment. In the present study we investigated whether GH treatment for 4 months influenced the expression of UCPs in skeletal muscle and adipose tissue in 22 GHD patients who were investigated before and after GH (n = 11) or placebo (n = 11) treatment. GH treatment increased the amount of lean body mass by 4.5% (P < 0.05) and decreased body fat mass by 12% (P < 0.05), whereas no changes in these parameters were observed after placebo treatment. The level of UCP3 messenger ribonucleic acid (mRNA) increased 3-fold (P < 0.005) in skeletal muscle and almost 2-fold (P < 0.05) in adipose tissue after GH treatment, with no changes observed after placebo treatment. Skeletal muscle UCP2 mRNA was slightly (25%), but significantly (P < 0.05), decreased, whereas the level of UCP2 mRNA in adipose tissue was unaffected after GH treatment. The T4 level was positively correlated with skeletal muscle UCP2 and UCP3 expression (r = 0.518; P < 0.05 and r = 0.463; P < 0.05, respectively). Furthermore, plasma free fatty acids were positively correlated with the expression of UCP2 (r = 0.573; P < 0.01) and UCP3 (r = 0.518; P < 0.05) in skeletal muscle. The marked increase in UCP3 expression after GH treatment indicates that the UCPs might play a role in the effects of GH on EE in GHD patients. Finally, the strong association between thyroid hormone and skeletal muscle UCP and the correlation between plasma free fatty acids and UCP expression in skeletal muscle indicate that these hormones/metabolites might influence UCP expression in humans as previously demonstrated in rodents.     

Adipose triglyceride lipase and hormone-sensitive lipase protein expression in subcutaneous adipose tissue is decreased after an isoenergetic low-fat high-complex carbohydrate diet in the metabolic syndrome

The objective was to determine the contribution of dietary fat quantity and composition to lipolysis and lipolytic gene expression in humans in relation to obesity, insulin resistance, and the metabolic syndrome (MetS). Men and women with the MetS were randomly assigned to one of four isoenergetic diets: a high-fat saturated fat diet (n=10), a high-fat monounsaturated fat diet (n=7), and two low-fat high-complex carbohydrate (LFHCC) diets, one supplemented with 1.24g/day long-chain n-3 PUFA (LFHCC: n=7, LFHCCn-3: n=8). Subcutaneous adipose tissue biopsies were taken before and after the 12-week dietary intervention period. ATGL and HSL mRNA and protein expression was determined. Whole body rate of appearance of free fatty acids (Ra(FFA)) was determined by intravenous infusion of [(2)H(2)]-palmitate in a subgroup of men (n=20). Adipose tissue ATGL and HSL mRNA and protein expression was not affected by alterations in dietary fat composition. Pooled analysis comparing the low- and high-fat diets showed that ATGL and HSL protein expression was significantly reduced after the LFHCC diets (P=.04), irrespective of long-chain n-3 PUFA. Moreover, LFHCC diets lowered fasting insulin, HOMA(IR), and (LDL)-cholesterol concentrations (P≤.05). Changes in ATGL and HSL protein expression was positively associated with changes in whole body Ra(FFA) (P<.03). The low-fat high-complex carbohydrate diets reduced ATGL and HSL protein expression and significantly improved circulating lipids and insulin sensitivity. Under isoenergetic conditions, dietary fat quantity, rather than composition, may be most important for modulating subcutaneous adipose tissue ATGL and HSL protein expression.     

Uncoupling proteins-2 and 3 influence obesity and inflammation in transgenic mice

OBJECTIVE: To test the hypothesis that either uncoupling protein-2 UCP2 or UCP3 or both together influence obesity and inflammation in transgenic mice. DESIGN: We generated 12 lines of transgenic mice for both human UCP2 and 3 using native promoters from a human bacterial artificial chromosome (BAC) clone. The BAC expresses no genes other than UCP2 and 3. Mice used for experiments are N4 or higher of backcross to C57BL/6J (B6). Each experiment used transgenic mice and their nontransgenic littermates. RESULTS: Northern blots confirmed expression on human UCP2 in adipose and spleen, while human UCP3 expression was detectable in gastrocnemius muscle. Western blots demonstrated a four-fold increase of UCP2 protein in spleens of Line 32 transgenic animals. Heterozygous mice of four lines showing expression of human UCP2 in spleen were examined for obesity phenotypes. There were no significant differences between Lines 1 and 32, but female transgenics of both lines had significantly smaller femoral fat depots than the control (littermate) mice (P=0.015 and 0.005, respectively). In addition, total fat of transgenic females was significantly less in Line 1 (P=0.05) and almost significantly different in Line 32 (P=0.06). Male Line 1 mice were leaner (P=0.04) while male Line 32 mice were almost significantly leaner (P=0.06). Heterozygous mice of Lines 35 and 44 showed no significant differences from the nontransgenic littermate controls. Effects of the UCP2/UCP3 transgene on obesity in Line 32 mice were confirmed by crossing transgenic mice with the B6.Cg-Ay agouti obese mice. B6.Cg-Ay carrying the UCP2/UCP3 transgene from Line 32 were significantly leaner than nontransgenic B6.Cg-Ay mice.Line 32 UCP2/UCP3 transgenics showed increased hypothalamic Neuropeptide (NPY) levels and food intake, with reduced spontaneous physical activity. Transgenic baseline interleukin4 (IL-4) and interleukin6 (IL-6) levels were low with lower or later increases after endotoxin injection compared to wild-type littermates. Endotoxin-induced fever was also diminished in transgenic male animals. Low-density lipoprotein (LDL) cholesterol levels were significantly higher in both Line 1 and 32 transgenics (P=0.05 and 0.001, respectively) after they had been placed on a moderate fat-defined diet containing 32% of calories from fat for 5 weeks. CONCLUSION: Moderate overexpression of UCP2 and 3 reduced fat mass and increased LDL cholesterol in two independent lines of transgenic mice. Thus, the reduced fat mass cannot be due to insertional mutagenesis since virtually identical fat pad weights and masses were observed with the two independent lines. Line 32 mice also have altered inflammation and mitochondrial function. We conclude that UCP2 and/or 3 have small but significant effects on obesity in mice, and that their mechanism of action may include alterations of metabolic rate.     

Reduced gene expression of UCP2 but not UCP3 in skeletal muscle of human obese subjects

Summary Massive overweight is an increasing health problem and underlies several complications which in turn result in premature death. The mechanisms underlying the imbalance between energy intake and energy expenditure, that lead to obesity in humans, are still only partly understood. In rodents, heat generation and the burning of calories by the mitochondrial uncoupling protein 1 (UCP1) are important for metabolic control. However, UCP1 is exclusively expressed in brown fat which is only present in limited amounts in human adults. The recent characterization of two new uncoupling proteins, UCP2 and UCP3, may elucidate potentially important pathways for energy expenditure regulation in man. The aim of this study was to investigate whether obesity is accompanied by aberrations in UCP2 and UCP3 regulation. Expression of these two genes was examined using in situ hybridization in six lean and six obese, but otherwise healthy, men. The UCP2 expression was decreased by 28 % (p = 0.001) in the abdominal muscle of the obese subjects. No differences in UCP3 expression were observed between obese and control subjects, although there was great variation in the expression between subjects. In conclusion, these data suggest an impaired activity of the mitochondrial uncoupling protein UCP2, but probably not UCP3, in obese subjects. This may result in decreased energy expenditure and contribute to the development and maintenance of obesity. [Diabetologia (1998) 41: 935–939] Received: 5 December 1997 and in revised form: 18 February 1998     

The effects of high-carbohydrate and high-fat diets on the serum lipid and lipoprotein concentrations of endurance athletes

We examined the effects of high-carbohydrate and high-fat diets on the serum lipid levels of distance runners. For seven days before each study, subjects consumed a diet containing 15% protein, 32% fat, and 53% carbohydrate. During 14-day experimental periods, a control group (n = 10) continued the same diet while two other groups consumed 69% of their calories as either carbohydrate (n = 13) or fat (n = 14). High-density lipoprotein (HDL)-cholesterol decreased 9% during the high-carbohydrate diet because of a 26% fall in the HDL2 fraction (1.063 to 1.125 g/mL). These changes were not accompanied by changes in the levels of apolipoproteins (apo) A-I or A-II. Total and low-density lipoprotein (LDL)-cholesterol initially decreased but subsequently exceeded pre-diet values while triglyceride concentrations increased 30% to 50%. Postheparin lipoprotein lipase activity (LPLA) fell 20%. Despite these dietary effects, HDL and HDL2 cholesterol concentrations in the athletes remained above values typical of sedentary men. The high-fat diet produced different effects on the serum lipids and lipoprotein levels of the athletes. HDL levels changed little during the study although HDL-cholesterol and apo A-I on the last diet day were both slightly above initial values. The high-fat diet provided 111 g of saturated fat per day but had surprisingly little effect on total and LDL-cholesterol whereas serum triglycerides fell by 10% to 20%. Postheparin LPLA increased 30% with fat feeding and the changes in LPLA correlated with alterations in triglyceride levels (r = -0.53, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)