Interactions between physical activity and variants of the genes encoding uncoupling proteins −2 and −3 in relation to body weight changes during a 10-y follow-up

Solute Carrier Transporters as Potential Targets for the Treatment of Metabolic Disease

The solute carrier (SLC) superfamily comprises more than 400 transport proteins mediating the influx and efflux of substances such as ions, nucleotides, and sugars across biological membranes. Over 80 SLC transporters have been linked to human diseases, including obesity and type 2 diabetes (T2D). This observation highlights the importance of SLCs for human (patho)physiology. Yet, only a small number of SLC proteins are validated drug targets. The most recent drug class approved for the treatment of T2D targets sodium-glucose cotransporter 2, product of the SLC5A2 gene. There is great interest in identifying other SLC transporters as potential targets for the treatment of metabolic diseases. Finding better treatments will prove essential in future years, given the enormous personal and socioeconomic burden posed by more than 500 million patients with T2D by 2040 worldwide. In this review, we summarize the evidence for SLC transporters as target structures in metabolic disease. To this end, we identified SLC13A5/sodium-coupled citrate transporter, and recent proof-of-concept studies confirm its therapeutic potential in T2D and nonalcoholic fatty liver disease. Further SLC transporters were linked in multiple genome-wide association studies to T2D or related metabolic disorders. In addition to presenting better-characterized potential therapeutic targets, we discuss the likely unnoticed link between other SLC transporters and metabolic disease. Recognition of their potential may promote research on these proteins for future medical management of human metabolic diseases such as obesity, fatty liver disease, and T2D. SIGNIFICANCE STATEMENT: Given the fact that the prevalence of human metabolic diseases such as obesity and type 2 diabetes has dramatically risen, pharmacological intervention will be a key future approach to managing their burden and reducing mortality. In this review, we present the evidence for solute carrier (SLC) genes associated with human metabolic diseases and discuss the potential of SLC transporters as therapeutic target structures.

Association of uncoupling protein (Ucp) gene polymorphisms with cardiometabolic diseases

The hereditary aspect of obesity is a major focus of modern medical genetics. The genetic background is known to determine a higher-than-average prevalence of obesity in certain regions, like Oceania. There is evidence that dysfunction of brown adipose tissue (BAT) may be a risk factor for obesity and type 2 diabetes (T2D). A significant number of studies in the field focus on the UCP family. The Ucp genes code for electron transport carriers. UCP1 (thermogenin) is the most abundant protein of the UCP superfamily and is expressed in BAT, contributing to its capability of generating heat. Single nucleotide polymorphisms (SNPs) of Ucp1-Ucp3 were recently associated with risk of cardiometabolic diseases. This review covers the main Ucp SNPs A-3826G, A-1766G, A-112C, Met229Leu, Ala64Thr (Ucp1), Ala55Val, G-866A (Ucp2), and C-55 T (Ucp3), which may be associated with the development of obesity, disturbance in lipid metabolism, T2D, and cardiovascular diseases.

The UCP2 -866G/A, Ala55Val and UCP3 -55C/T polymorphisms are associated with premature coronary artery disease and cardiovascular risk factors in Mexican population

We examined the role of UCP gene polymorphisms as susceptibility markers for premature coronary artery disease (pCAD). The UCP2 Ala55Val (C/T rs660339), UCP2 -866G/A (rs659366), and UCP3 -55C/T (rs1800849) polymorphisms were genotyped in 948 patients with pCAD, and 763 controls. The distribution of the UCP2 A55V (C/T rs660339) and UCP3 -55 (rs1800849) was similar in patients and controls. However, under a recessive model, the UCP2 -866 (rs659366) A allele was associated with increased risk of developing pCAD (OR = 1.43, Pc = 0.003). On the other hand, patients with pCAD and UCP2 A55V (rs660339) TT showed high levels of visceral abdominal fat (VAF) (Pc = 0.002), low levels of subcutaneous abdominal fat (SAF) (Pc = 0.001) and high VAT/SAT ratio (Pc < 0.001). Also, patients with UCP2 -866 (rs659366) AA showed increased levels of VAF (Pc = 0.003), low levels of SAF (Pc = 0.001) and a high VAT/SAT ratio (Pc = 0.002), whereas patients with the UCP3 -55 (rs1800849) TT presented high levels of VAF (Pc = 0.002). The results suggest the association of the UCP2 -866 (rs659366) polymorphism with risk of developing pCAD. Some polymorphisms were associated with abdominal fat levels and cardiovascular risk factors.

Behavioral and Environmental Modification of the Genetic Influence on Body Mass Index: A Twin Study

Body mass index (BMI) has a strong genetic basis, with a heritability around 0.75, but is also influenced by numerous behavioral and environmental factors. Aspects of the built environment (e.g., environmental walkability) are hypothesized to influence obesity by directly affecting BMI, by facilitating or inhibiting behaviors such as physical activity that are related to BMI, or by suppressing genetic tendencies toward higher BMI. The present study investigated relative influences of physical activity and walkability on variance in BMI using 5079 same-sex adult twin pairs (70 % monozygotic, 65 % female). High activity and walkability levels independently suppressed genetic variance in BMI. Estimating their effects simultaneously, however, suggested that the walkability effect was mediated by activity. The suppressive effect of activity on variance in BMI was present even with a tendency for low-BMI individuals to select into environments that require higher activity levels. Overall, our results point to community- or macro-level interventions that facilitate individual-level behaviors as a plausible approach to addressing the obesity epidemic among US adults.

Meta-analysis reveals the association of common variants in the uncoupling protein (UCP) 1-3 genes with body mass index variability

Background

The relationship between uncoupling protein (UCP) 1–3 polymorphisms and susceptibility to obesity has been investigated in several genetic studies. However, the impact of these polymorphisms on obesity is still under debate, with contradictory results being reported. Until this date, no meta-analysis evaluated the association of UCP polymorphisms with body mass index (BMI) variability. Thus, this paper describe a meta-analysis conducted to evaluate if the -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3) polymorphisms are associated with BMI changes.

Methods

A literature search was run to identify all studies that investigated associations between UCP1-3 polymorphisms and BMI. Weighted mean differences (WMD) were calculated for different inheritance models.

Results

Fifty-six studies were eligible for inclusion in the meta-analysis. Meta-analysis results showed that UCP2 55Val/Val genotype was associated with increased BMI in Europeans [Random Effect Model (REM) WMD 0.81, 95% CI 0.20, 1.41]. Moreover, the UCP2 Ins allele and UCP3-55T/T genotype were associated with increased BMI in Asians [REM WMD 0.46, 95% CI 0.09, 0.83 and Fixed Effect Model (FEM) WMD 1.63, 95% CI 0.25, 3.01]. However, a decreased BMI mean was observed for the UCP2-866 A allele in Europeans under a dominant model of inheritance (REM WMD −0.18, 95% CI −0.35, −0.01). There was no significant association of the UCP1-3826A/G polymorphism with BMI mean differences.

Conclusions

The meta-analysis detected a significant association between the UCP2-866G/A, Ins/Del, Ala55Val and UCP3-55C/T polymorphisms and BMI mean differences.

Association of the UCP polymorphisms with susceptibility to obesity: case-control study and meta-analysis

This paper describes a case-control study and a meta-analysis performed to evaluate if the following polymorphisms are associated with presence of obesity: -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3). The case-control study enrolled 282 obese and 483 non-obese patients with type 2 diabetes. A literature search was made to identify all studies that evaluated associations between UCP1-3 polymorphisms and obesity. In the case-control study the distributions of the UCP variants did not differ between obese and non-obese groups (P > 0.05). Forty-seven studies were eligible for the meta-analysis and the results showed that the UCP2 -866G/A and UCP3 -55C/T polymorphisms were associated with protection to obesity in Europeans (OR = 0.89, 95% CI 0.82-0.97 and OR = 0.88, 95% CI 0.80-0.97, respectively). The UCP2 Ala55 val polymorphism was associated with obesity in Asians (OR = 1.61, 95% CI 1.13-2.30). The UCP2 Ins/Del polymorphism was associated with obesity mainly in Europeans (OR = 1.19, 95% CI 1.00-1.42). There was no significant association of the UCP1 -3826A/G polymorphism with obesity. In our case-control study we were not able to demonstrate any association between UCP polymorphisms and obesity in T2DM patients; however, in the meta-analysis we detected a significant association of UCP2 -866G/A, Ins/Del, Ala55Val and UCP3 -55C/T polymorphisms with obesity.

A 45-bp insertion/deletion polymorphism of UCP2 gene is associated with metabolic syndrome

Background

Metabolic syndrome (MeS) is being recognized as a risk factor for insulin resistance and cardiovascular disease. The present study was aimed to find out the possible association between 45-bp I/D polymorphism of uncoupling protein 2 (UCP2) and MeS.

Methods

DNA was extracted from peripheral blood of 151 subjects with and 149 subjects without MeS. 45-bp I/D variant of UCP2 was detected using polymerase chain reaction (PCR).

Results

Our finding showed that 45-bp I/D polymorphism was associated with protection against MeS (OR = 0.56, 95% CI = 0.34-0.92, p = 0.020 D/I vs DD and OR = 0.54, 95% CI = 0.34-0.86, p = 0.009; D/I + I/I vs D/D). The I allele decreased the risk of MeS (OR = 0.62, 95% CI = 0.44-0.90, p = 0.011) in comparison with D allele.

Conclusion

In conclusion, our result suggests that 45-bp I/D polymorphism is associated with the risk of MeS, which remains to be cleared.

UCP2 -866G/A, Ala55Val and UCP3 -55C/T polymorphisms in association with obesity susceptibility - a meta-analysis study

AIMS/HYPOTHESIS

Variants of UCP2 and UCP3 genes have been reported to be associated with obesity, but the available data on the relationship are inconsistent. A meta-analysis was performed to determine whether there are any associations between the UCP2 -866G/A, Ala55Val, and UCP3 -55C/T polymorphisms and obesity susceptibility.

METHODS

The PubMed, Embase, Web of Science and CNKI, CBMdisc databases were searched for all relevant case-control studies. The fixed or random effect pooled measure was determined on the bias of heterogeneity test among studies. Publication bias was examined by the modified Begg's and Egger's test.

RESULTS

Twenty-two published articles with thirty-two outcomes were included in the meta-analysis: 12 studies with a total of 7,390 cases and 9,860 controls were analyzed for UCP2 -866G/A polymorphism with obesity, 9 studies with 1,483 cases and 2,067 controls for UCP2 Ala55Val and 8 studies with 2,180 cases and 2,514 controls for UCP3 -55C/T polymorphism. Using an additive model, the UCP2 -866G/A polymorphism showed no significant association with obesity risk in Asians (REM OR = 0.81, 95% CI: 0.65-1.01). In contrast, a statistically significant association was observed in subjects of European descent (FEM OR = 1.06, 95% CI: 1.01-1.12). But neither the UCP2 Ala55Val nor the UCP3 -55C/T polymorphism showed any significant association with obesity risk in either subjects of Asian (REM OR = 0.84, 95% CI: 0.67-1.06 for Ala55Val; REM OR = 0.94, 95% CI: 0.55-1.28 for -55C/T) or of European descent (REM OR = 1.04, 95% CI: 0.80-1.36 for Ala55Val; FEM OR = 1.08, 95% CI: 0.97-1.20 for -55C/T).

CONCLUSIONS AND INTERPRETATION

Our meta-analysis revealed that the UCP2 -866G/A polymorphism may be a risk factor for susceptibility to obesity in subjects of European descent, but not in individuals of Asian descent. And our results did not support the association between UCP2 Ala55Val, UCP3 -55C/T polymorphisms and obesity in the populations investigated. This conclusion warrants confirmation by further studies.

Associations between UCP1 -3826A/G, UCP2 -866G/A, Ala55Val and Ins/Del, and UCP3 -55C/T polymorphisms and susceptibility to type 2 diabetes mellitus: case-control study and meta-analysis

Background

Some studies have reported associations between five uncoupling protein (UCP) 1–3 polymorphisms and type 2 diabetes mellitus (T2DM). However, other studies have failed to confirm the associations. This paper describes a case-control study and a meta-analysis conducted to attempt to determine whether the following polymorphisms are associated with T2DM: -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3).

Methods

The case-control study enrolled 981 T2DM patients and 534 nondiabetic subjects, all of European ancestry. A literature search was run to identify all studies that investigated associations between UCP1–3 polymorphisms and T2DM. Pooled odds ratios (OR) were calculated for allele contrast, additive, recessive, dominant and co-dominant inheritance models. Sensitivity analyses were performed after stratification by ethnicity.

Results

In the case-control study the frequencies of the UCP polymorphisms did not differ significantly between T2DM and nondiabetic groups (P>0.05). Twenty-three studies were eligible for the meta-analysis. Meta-analysis results showed that the Ala55Val polymorphism was associated with T2DM under a dominant model (OR = 1.27, 95% CI 1.03–1.57); while the -55C/T polymorphism was associated with this disease in almost all genetic models: allele contrast (OR = 1.17, 95% CI 1.02–1.34), additive (OR = 1.32, 95% CI 1.01–1.72) and dominant (OR = 1.18, 95% CI 1.02–1.37). However, after stratification by ethnicity, the UCP2 55Val and UCP3 -55C/T alleles remained associated with T2DM only in Asians (OR = 1.25, 95% CI 1.02–1.51 and OR = 1.22, 95% CI 1.04–1.44, respectively; allele contrast model). No significant association of the -3826A/G, -866G/A and Ins/Del polymorphisms with T2DM was observed.

Conclusions

In our case-control study of people with European ancestry we were not able to demonstrate any association between the UCP polymorphisms and T2DM; however, our meta-analysis detected a significant association between the UCP2 Ala55Val and UCP3 -55C/T polymorphisms and increased susceptibility for T2DM in Asians.

Physical activity and sex modulate obesity risk linked to 3111T/C gene variant of the CLOCK gene in an elderly population: the SUN Project

Genetic factors may interact with physical activity levels to modify obesity risk. Our aim was to explore the influence of rs1801260 single-nucleotide polymorphism (SNP) (3111T/C) of CLOCK gene on obesity risk, and to examine its potential interaction with lifestyle factors in an elderly population within the SUN ("Seguimiento Universidad de Navarra") Project. Subjects (n = 903, aged 69 ± 6 yrs) were recruited from the SUN Project. DNA was obtained from saliva, whereas lifestyle and dietary data were collected by validated self-report questionnaires. Genotype was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR) plus allele discrimination. A significant interaction was observed between the 3111T/C SNP of CLOCK gene and sex for overweight/obesity risk (p for sex × CLOCK interaction <.001). Our results showed that women carrying the C allele of CLOCK gene had a marginally significant lower risk of overweight/obesity compared with noncarrier-TT-subjects (odds ratio [OR]: .61, 95% confidence interval [CI]: .36-1.04; p = .069). Moreover, this association of the C allele with a decreased overweight/obesity risk might be enhanced in those women with a high physical activity level. Women practicing more than 16.8 metabolic equivalent tasks (hours per week) had a significantly lower overweight/obesity risk (OR: .36, 95% CI: .17-.79; p = .011). Furthermore, a significant interaction between the 3111T/C gene variant and physical activity (PA) for overweight/obesity risk was observed but only in women (p for PA × CLOCK interaction <.050). In conclusion, it appears that physical activity levels may act by modifying the association of the 3111T/C SNP (rs1801260) of the CLOCK gene with overweight/obesity risk in elderly women in the SUN Project.

UCP2 I/D modulated change in BMI during a lifestyle modification intervention study in Japanese subjects

AIM

Polymorphisms in uncoupling protein (UCP) genes have been strongly associated with energy expenditure and obesity. This study aimed at investigating the effects of UCP gene polymorphisms (UCP1 -3826A/G, UCP2A/V, UCP2 I/D, and UCP3 -55C/T) on change in body mass index (BMI) during a lifestyle modification program in Japanese subjects.

RESULTS

Intervention induced a significant decrease in energy intake (-8.6% ± 17.0%) and a significant increase in energy expenditure (7.7% ± 7.4%). As a result, participants experienced a significant decrease in their BMI of -1.8% ± 2.7%. In a multivariate regression analysis, only UCP2 D/I among the selected UCP gene polymorphisms was associated with a change in BMI independent of the effects of gender, age, baseline BMI, changes in energy intake, and expenditure. Further regression analysis revealed that, in contrast to the DD genotype group, the DI+II genotype group showed no significant association between weight loss and change in energy expenditure suggesting this polymorphism altered the effects of this parameter on change in BMI.

CONCLUSION

The study found UCP2 D/I to be associated with change in BMI by altering the effect of change in energy expenditure on change in BMI.

Uncoupling protein-2 45-base pair insertion/deletion polymorphism: is there an association with severe obesity and weight loss in morbidly obese subjects?

BACKGROUND

Uncoupling proteins are attractive candidate genes for obesity and type 2 diabetes mellitus. Our aim was to investigate the potential association of the uncoupling protein-2 (UCP2) 45-bp insertion/deletion (ins/del) polymorphism with obesity, as well as the potential effect of this polymorphism on weight loss variability in severely obese subjects.

METHODS

A total of 158 severely obese subjects (94 without and 64 with metabolic syndrome) and 91 age and sex-matched lean controls were recruited. A subgroup of 124 obese patients participated in a 3-month weight loss program. Anthropometric and metabolic variables were measured. Participants were genotyped for the UCP2 ins/del polymorphism.

RESULTS

Allelic frequency differed neither between obese subjects and controls (P=0.56), nor between obese subjects with versus without metabolic syndrome (P=0.58). At 3 months, metabolically healthy subjects carrying the insertion allele had significantly greater reduction in body mass index (P=0.029) and fat-free mass (P=0.013) and a borderline significant improvement in the homeostatic model assessment index (P=0.048).

CONCLUSION

There is no association of the UCP2 ins/del polymorphism with morbid obesity in our population, but this genotype appears to be linked with a favorable response to dietary changes in metabolically healthy obese subjects.

Four novel UCP3 gene variants associated with childhood obesity: effect on fatty acid oxidation and on prevention of triglyceride storage

OBJECTIVE

The objective of the study was to look for uncoupling protein 3 (UCP3) gene variants in early-onset severe childhood obesity and to determine their effect on long-chain fatty acid oxidation and triglyceride storage.

METHODS AND RESULTS

We identified four novel mutations in the UCP3 gene (V56M, A111V, V192I and Q252X) in 200 children with severe, early-onset obesity (body mass index-standard deviation score >2.5; onset: <4 years) living in Southern Italy. We evaluated the role of wild-type (wt) and mutant UCP3 proteins in palmitate oxidation and in triglyceride storage in human embryonic kidney cells (HEK293). Palmitate oxidation was ∼60% lower (P<0.05; P<0.01) and triglyceride storage was higher in HEK293 cells expressing the four UCP3 mutants than in cells expressing wt UCP3. Moreover, mutants V56M and Q252X exerted a dominant-negative effect on wt protein activity (P<0.01 and P<0.05, respectively). Telmisartan, an angiotensin II receptor antagonist used in the management of hypertension, significantly (P<0.05) increased palmitate oxidation in HEK293 cells expressing wt and mutant proteins (P<0.05; P<0.01), including the dominant-negative mutants.

CONCLUSIONS

These data indicate that protein UCP3 affects long-chain fatty acid metabolism and can prevent cytosolic triglyceride storage. Our results also suggest that telmisartan, which increases fatty acid oxidation in rat skeletal muscle, also improves UCP3 wt and mutant protein activity, including the dominant-negative UCP3 mutants.

Mitochondrial-nuclear epistasis: implications for human aging and longevity

There is substantial evidence that mitochondria are involved in the aging process. Mitochondrial function requires the coordinated expression of hundreds of nuclear genes and a few dozen mitochondrial genes, many of which have been associated with either extended or shortened life span. Impaired mitochondrial function resulting from mtDNA and nuclear DNA variation is likely to contribute to an imbalance in cellular energy homeostasis, increased vulnerability to oxidative stress, and an increased rate of cellular senescence and aging. The complex genetic architecture of mitochondria suggests that there may be an equally complex set of gene interactions (epistases) involving genetic variation in the nuclear and mitochondrial genomes. Results from Drosophila suggest that the effects of mtDNA haplotypes on longevity vary among different nuclear allelic backgrounds, which could account for the inconsistent associations that have been observed between mitochondrial DNA (mtDNA) haplogroups and survival in humans. A diversity of pathways may influence the way mitochondria and nuclear-mitochondrial interactions modulate longevity, including: oxidative phosphorylation; mitochondrial uncoupling; antioxidant defenses; mitochondrial fission and fusion; and sirtuin regulation of mitochondrial genes. We hypothesize that aging and longevity, as complex traits having a significant genetic component, are likely to be controlled by nuclear gene variants interacting with both inherited and somatic mtDNA variability.

Genetic Variance in Uncoupling Protein 2 in Relation to Obesity, Type 2 Diabetes, and Related Metabolic Traits: Focus on the Functional -866G>A Promoter Variant (rs659366)

Uncoupling proteins (UCPs) are mitochondrial proteins able to dissipate the proton gradient of the inner mitochondrial membrane when activated. This decreases ATP-generation through oxidation of fuels and may theoretically decrease energy expenditure leading to obesity. Evidence from Ucp((-/-)) mice revealed a role of UCP2 in the pancreatic β-cell, because β-cells without UCP2 had increased glucose-stimulated insulin secretion. Thus, from being a candidate gene for obesity UCP2 became a valid candidate gene for type 2 diabetes mellitus. This prompted a series of studies of the human UCP2 and UCP3 genes with respect to obesity and diabetes. Of special interest was a promoter variant of UCP2 situated 866bp upstream of transcription initiation (-866G>A, rs659366). This variant changes promoter activity and has been associated with obesity and/or type 2 diabetes in several, although not all, studies. The aim of the current paper is to summarize current evidence of association of UCP2 genetic variation with obesity and type 2 diabetes, with focus on the -866G>A polymorphism.

A Database of Gene-Environment Interactions Pertaining to Blood Lipid Traits, Cardiovascular Disease and Type 2 Diabetes

As the role of the environment - diet, exercise, alcohol and tobacco use and sleep among others - is accorded a more prominent role in modifying the relationship between genetic variants and clinical measures of disease, consideration of gene-environment (GxE) interactions is a must. To facilitate incorporation of GxE interactions into single-gene and genome-wide association studies, we have compiled from the literature a database of GxE interactions relevant to nutrition, blood lipids, cardiovascular disease and type 2 diabetes. Over 550 such interactions have been incorporated into a single database, along with over 1430 instances where a lack of statistical significance was found. This database will serve as an important resource to researchers in genetics and nutrition in order to gain an understanding of which points in the human genome are sensitive to variations in diet, physical activity and alcohol use, among other lifestyle choices. Furthermore, this GxE database has been designed with future integration into a larger database of nutritional phenotypes in mind.

Nutritional and hormonal regulation of uncoupling protein 2

Uncoupling proteins (UCPs) belong to a family of mitochondrial carrier proteins that are present in the mitochondrial inner membrane. Genetic and experimental studies have shown that UCP dysfunction can be involved in metabolic disorders and in obesity. Uncoupling protein-1 (UCP1; also known as thermogenin) was identified in 1988 and found to be highly expressed in brown adipose tissue. UCP1 allows the leak of protons in respiring mitochondria, dissipating the energy as heat; the enzyme has an important role in nonshivering heat production induced by cold exposure or food intake. In 1997, two homologs of UCP1 were identified and named UCP2 and UCP3. These novel proteins also lower mitochondrial membrane potential, but whether they can dissipate metabolic energy as heat as efficiently as UCP1 is open to dispute. Even after a decade of study, the physiological roles of these novel proteins have still not been completely elucidated. This review aims to shed light on the nutritional and hormonal regulation of UCP2 and on its physiological roles.

The polymorphisms of UCP2 and UCP3 genes associated with fat metabolism, obesity and diabetes

Uncoupling proteins (UCPs) belong to the family of mitochondrial transporter proteins that may uncouple the transport of protons across the inner mitochondrial membrane from electron transport and the synthesis of ATP from ADP, hence generating heat rather than energy. In mammals, more than five family members have been identified, including UCP1, UCP2, UCP3, UCP4 (or BMCP1/UCP5) and UCP5. The UCPs may play an important role in energy homeostasis and have become prominent in the fields of thermogenesis, obesity, diabetes and free-radical biology and have been considered candidate genes for obesity and insulin resistance. They have been as important potential targets for treatment of aging, degenerative diseases, diabetes and obesity. Recently, a series of studies showed the polymorphisms of UCPs gene association with the fat metabolism, obesity and diabetes. This review summarizes data supporting the roles of UCP2 and UCP3 in energy dissipation, as well as the genetic variety association with fat metabolism, obesity and diabetes in humans.

Gene-environment interaction and obesity

The epidemic of obesity has become a major public health problem. Common-form obesity is underpinned by both environmental and genetic factors. Epidemiological studies have documented that increased intakes of energy and reduced consumption of high-fiber foods, as well as sedentary lifestyle, were among the major driving forces for the epidemic of obesity. Recent genome-wide association studies have identified several genes convincingly related to obesity risk, including the fat mass and obesity associated gene and the melanocortin-4 receptor gene. Testing gene-environment interaction is a relatively new field. This article reviews recent advances in identifying the genetic and environmental risk factors (lifestyle and diet) for obesity. The evidence for gene-environment interaction, especially from observational studies and randomized intervention trials, is examined specifically. Knowledge about the interplay between genetic and environmental components may facilitate the choice of more effective and specific measures for obesity prevention based on the personalized genetic make-up.

Effects of UCP2 and UCP3 variants on the manifestation of overweight in Korean children

To investigate the associations of uncoupling protein (UCP)2 and UCP3 gene variants with overweight and related traits, we genotyped UCP2-866G>A, UCP2Ala55Val, and UCP3-55C>T in 737 Korean children and 732 adults and collected data regarding anthropometric status and blood biochemistry. Information concerning the children's lifestyles and dietary habits was collected. The UCP2-866G>A and UCP3-55C>T gene variants showed significant associations with BMI level, waist circumference, and body weight in the children but not in the adults. Compared with -866GG carriers, the -866GA and AA carriers showed a strong decreasing trend in the risk for overweight (odds ratio (OR), 0.67; 95% confidence interval (CI), 0.45-1.01; P = 0.053). In comparison with UCP3-55CC carriers, children carrying -55CT and TT showed a significant reduction in the risk of overweight (OR, 0.67; 95% CI, 0.46-0.98; P = 0.039). There was also evidence of interactions between the effects of the combined UCP2-UCP3 genotype and obesity-related metabolic traits. The greatest protective effect against overweight was seen in those with the combined genotype non-UCP2-866GG and non-UCP3-55CC, as compared with those carrying both UCP2-866GG and UCP3-55CC (OR,0.60; 95% CI, 0.38-0.95; P = 0.030). In the subgroup with a low level of physical activity, UCP3-55CC carriers had higher BMI values than UCP3-55T carriers (16.6 +/- 2.3 kg/m(2) vs. 16.1 +/- 1.9 kg/m(2), P = 0.016). Low physical activity may aggravate the susceptibility to overweight in UCP2-866GG and UCP3-55CC carriers.

The energetic implications of uncoupling protein-3 in skeletal muscle

Despite almost a decade of research since the identification of uncoupling protein-3 (UCP3), the molecular mechanisms and physiological functions of this mitochondrial anion carrier protein are not well understood. Because of its highly selective expression in skeletal muscle and the existence of mitochondrial proton leak in this tissue, early reports proposed that UCP3 caused a basal proton leak and increased thermogenesis. However, gene expression data and results from knockout and overexpression studies indicated that UCP3 does not cause basal proton leak or physiological thermogenesis. UCP3 expression is associated with increases in circulating fatty acids and in fatty acid oxidation (FAO) in muscle. Fatty acids are also well recognized as activators of the prototypic UCP1 in brown adipose tissue. This has led to hypotheses implicating UCP3 in mitochondrial fatty acid translocation. The corresponding hypothesized physiological roles include facilitated FAO and protection from the lipotoxic effects of fatty acids. Recent in vitro studies of physiological increases in UCP3 in muscle cells demonstrate increased FAO, and decreased reactive oxygen species (ROS) production. Detailed mechanistic studies indicate that ROS or lipid by-products of ROS can activate a UCP3-mediated proton leak, which in turn acts in a negative feedback loop to mitigate ROS production. Altogether, UCP3 appears to play roles in muscle FAO and mitigated ROS production. Future studies will need to elucidate the molecular mechanisms underlying increased FAO, as well as the physiological relevance of ROS-activated proton leak.

Obesity and polymorphisms in genes regulating human adipose tissue

Obesity is the result of an imbalance between food intake and energy expenditure resulting in the storing of energy as fat. Adipose tissue contains the largest store of energy in the body and plays important roles in regulating energy partitioning. Developments in genomics, in particular microarray-based expression profiling, have provided scientists with a number of new candidate genes whose expression in adipose tissue is regulated by obesity. Integrating expression profiles with genome-wide linkage and/or association analyses is a promising strategy to identify new genes underlying susceptibility to obesity. This article provides a comprehensive review of adipose-tissue-expressed genes implicated in predisposition to human obesity. The authors consider the following genes of particular interest: peroxisome proliferator-activated receptor gamma and, potentially, INSIG2 acting in adipogenesis; the adrenoreceptors beta 2 and 3, as well as hormone-sensitive lipase acting on lipolysis; uncoupling protein 2 acting in mitochondria energy expenditure; and among secreted molecules the cytokine tumor necrosis factor alpha and the hormone leptin. With the rapid development in genome research, we predict that additional alleles in genes regulating adipose tissue function will be established as risk factors for common obesity in the coming years. This has important implications for the prevention of obesity and may also offer new therapeutic targets.

Gene-lifestyle interaction on risk of type 2 diabetes

The descriptive epidemiology of type 2 diabetes suggests that gene-lifestyle interactions are critical to the development of the condition. However, unravelling the molecular detail of these interactions is a complex task. The existing literature is based on small intervention studies or cross-sectional observational quantitative trait studies. Our systematic review of the literature identified some evidence of interactions, most notably for a common variant in the PPAR-gamma gene which appears to interact with the nature of dietary fat intake. Other interactions have been reported for adrenoceptors, uncoupling proteins, fatty acid binding proteins, apolipoproteins and lipoprotein lipase. There are, to date, no reports based on the ideal study design which is a case-control study nested within a cohort. To limit the likelihood of false discovery, such studies would need to be large and the search for interaction should be restricted to a priori biologically driven hypotheses. Additional study designs that examine differential response to lifestyle change or test interaction in the context of quantitative trait studies would complement the nested case-control approach, but the emphasis here should be on precision of measurement of both phenotype and lifestyle behaviour.

The human gene map for performance and health-related fitness phenotypes: the 2005 update

The current review presents the 2005 update of the human gene map for physical performance and health-related fitness phenotypes. It is based on peer-reviewed papers published by the end of 2005. The genes and markers with evidence of association or linkage with a performance or fitness phenotype in sedentary or active people, in adaptation to acute exercise, or for training-induced changes are positioned on the genetic map of all autosomes and the X chromosome. Negative studies are reviewed, but a gene or locus must be supported by at least one positive study before being inserted on the map. By the end of 2000, in the early version of the gene map, 29 loci were depicted. In contrast, the 2005 human gene map for physical performance and health-related phenotypes includes 165 autosomal gene entries and QTL, plus five others on the X chromosome. Moreover, there are 17 mitochondrial genes in which sequence variants have been shown to influence relevant fitness and performance phenotypes. Thus, the map is growing in complexity. Unfortunately, progress is slow in the field of genetics of fitness and performance, primarily because the number of laboratories and scientists focused on the role of genes and sequence variations in exercise-related traits continues to be quite limited.

Uncoupling protein-3: clues in an ongoing mitochondrial mystery

Uncoupling protein (UCP) 3 (UCP3) is a mitochondrial anion carrier protein with highly selective expression in skeletal muscle. Despite a great deal of interest, to date neither its molecular mechanism nor its biochemical and physiological functions are well understood. Based on its high degree of homology to the original UCP (UCP1), early studies examined a role for UCP3 in thermogenesis. However, evidence for such a function is lacking. Recent studies have focused on two distinct, but not mutually exclusive, hypotheses: 1) UCP3 mitigates reactive oxygen species (ROS) production, and 2) UCP3 is somehow involved in fatty acid (FA) translocation. While supportive evidence exists for both hypotheses, the interpretation of the corresponding evidence has created some controversy. Mechanistic studies examining mitigated ROS production have been largely conducted in vitro, and the physiological significance of the findings is questioned. Conversely, while physiological evidence exists for FA translocation hypotheses, the evidence is largely correlative, leaving causal relationships unexplored. This review critically assesses evidence for the hypotheses and attempts to link the outcomes from mechanistic studies to physiological implications. Important directions for future studies, using current and novel approaches, are discussed.

Uncoupling proteins, dietary fat and the metabolic syndrome

There has been intense interest in defining the functions of UCP2 and UCP3 during the nine years since the cloning of these UCP1 homologues. Current data suggest that both UCP2 and UCP3 proteins share some features with UCP1, such as the ability to reduce mitochondrial membrane potential, but they also have distinctly different physiological roles. Human genetic studies consistently demonstrate the effect of UCP2 alleles on type-2 diabetes. Less clear is whether UCP2 alleles influence body weight or body mass index (BMI) with many studies showing a positive effect while others do not. There is strong evidence that both UCP2 and UCP3 protect against mitochondrial oxidative damage by reducing the production of reactive oxygen species. The evidence that UCP2 protein is a negative regulator of insulin secretion by pancreatic beta-cells is also strong: increased UCP2 decreases glucose stimulated insulin secretion ultimately leading to beta-cell dysfunction. UCP2 is also neuroprotective, reducing oxidative stress in neurons. UCP3 may also transport fatty acids out of mitochondria thereby protecting the mitochondria from fatty acid anions or peroxides. Current data suggest that UCP2 plays a role in the metabolic syndrome through down-regulation of insulin secretion and development of type-2 diabetes. However, UCP2 may protect against atherosclerosis through reduction of oxidative stress and both UCP2 and UCP3 may protect against obesity. Thus, these UCP1 homologues may both contribute to and protect from the markers of the metabolic syndrome.

The effects of uncoupling protein 3 haplotypes on obesity phenotypes and very low-energy diet-induced changes among overweight Korean female subjects

Responses to energy restriction tend to vary within the population because of genetic differences. In this study, we have genotyped 6 uncoupling protein 3 (UCP-3) polymorphisms (-55C/T, Int2-143G/C, Tyr99Tyr, Int3-47G/A, Int4-498C/T, and Tyr210Tyr) among 214 overweight Korean female subjects recruited from an obesity clinic. Three major haplotypes, identified with frequencies in excess of 0.04, were constructed from 6 single nucleotide polymorphisms. Association studies were then undertaken, involving the measurement of anthropometric characteristics and body composition both before and after 1 month of a energy-restriction regimen. At baseline, haplotype 1 (ht1) [CGTACC] was associated with elevated anthropometric characteristics, including body weight, waist-hip ratio, and body mass index, as well as body components, including body fat mass and body fat-free mass. After the completion of the 1-month weight control program, which involved a very low-energy (2900 kJ/d) diet, we analyzed the outcomes according to the UCP-3 genetic polymorphisms. Among the 3 principal haplotypes, ht1 [CGTACC] was significantly associated with an increased reduction in body weight, in the codominant (P=.022), dominant (P=.016), and recessive (P=.041) models. Body mass index reduction was associated with the ht1 haplotype in a similar fashion. Among the body components, changes in body fat mass were significantly associated with ht1 [CGTACC] (P=.028), but changes in body fat-free mass were not significantly associated with the UCP-3 polymorphism.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Association of UCP3 Gene –55C>T Polymorphism and Obesity in a Spanish Population

BACKGROUND/AIMS

The uncoupling protein 3 (UCP3) gene has been suggested as a possible determinant affecting obesity risk given its function in the regulation of energy metabolism. However, available genetic association studies have been inconsistent, which could be attributable to not considering individual lifestyle patterns, such as physical activity, a factor that affects UCP3 expression. The objective of this study was to assess the association between the UCP3 -55C>T polymorphism and the risk of obesity.

METHODS

Case-control study conducted in a sample of Spanish adults. 157 obese subjects (BMI > or = 30) and 150 controls (BMI < 25) participated in the study. UCP3 -55C>T polymorphism was identified by the polymerase chain reaction-restriction fragment length polymorphism methodology.

RESULTS

The odds ratio (OR) for obesity (95% confidence interval [CI]) according to the presence of UCP 3 gene -55C>T polymorphism (heterozygotes and homozygotes merged together), adjusting for age, sex, and recreational physical activity, was 0.61 (0.37-1.00), p = 0.05. Interestingly, this association was only manifest among those with higher recreational physical activity (OR: 0.46, 95% CI 0.21-0.99, p = 0.05) and not among those with lower physical activity (OR: 0.84, 95% CI 0.41-1.70, p = 0.84).

CONCLUSION

UCP3 -55C>T polymorphism carriers have apparently a lower risk of obesity when taking into consideration recreational energy expenditure. Interestingly, this inverse beneficial association may only occur in people with a high level of physical activity.