A common polymorphism in the promoter of UCP2 contributes to the variation in insulin secretion in glucose-tolerant subjects

The Association of UCP2-866 G/A Genotype with Autoimmune Hypothyroidism in the Southwestern Saudi Arabia Population

Introduction

Autoimmune hypothyroidism (AHT) is a widespread disease that disproportionately affects women over men. It is characterized by the presence of autoantibodies that lead to the dysfunction of the thyroid gland. The exact cause of this process is unknown; however, some factors, such as genetic factors, may be to blame. The uncoupling protein 2 (UCP2) gene encodes uncoupling protein 2, which has been linked to several pathogeneses; however, the link between UCP2-866 G/A polymorphism and AHT has yet to be investigated. Thus, we investigate the potential relationship between UCP2-866 G/A polymorphism and AHT.

Methods

A total of 158 subjects participated in this study, they were either control or AHT patient, and genotyping was performed using a polymerase chain reaction.

Results

The frequencies of UCP2-866 G/G, G/A, and A/A in the control subject were 34%, 51%, and 15%, respectively, whereas these frequencies in the AHT were 43%, 46%, and 10%.

Conclusion

The study concludes a significant relationship between UCP2-866 G/A polymorphism and AHT, with a carrier subject of the -866 A allele being 3 times more likely to suffer from AHT than wild-type carriers in the study population.

Mitochondrial uncoupling protein 2 (UCP2) gene polymorphism - 866 G/A in the promoter region is associated with type 2 diabetes mellitus among Kashmiri population of Northern India

OBJECTIVE

The study aimed to evaluate the association of UCP2 gene polymorphism - 866 G/A and its expression with diabetes predisposition in the North Indian population.

METHODS

The study involved 850 subjects, including 425 each T2DM and control subjects. The serum metabolic and clinical parameters were estimated using standard protocols. The PCR-RFLP based genotyping was performed to determine UCP2 gene polymorphism, while the expression was measured by real-time quantitative PCR.

RESULTS

The genotypic and allelic frequencies showed a significant difference in cases compared to controls (p < 0.05). The diabetes patients had a 4.2-fold decrease in UCP2 gene expression. The expression was 29.8 and 8.4 fold lower in diabetes patients with homozygous (AA) and heterozygous (GA) mutation at - 866 locus of UCP2 nucleotide sequence, respectively. When categorized according to age and BMI, the T2DM subjects with age ≥ 50 and BMI ≥ 25 had a 5.53 and 8.2-fold decrease in UCP2 expression, respectively. The diabetes subjects with homozygous and heterozygous mutation demonstrated a pathological increase in serum metabolic and clinical parameters, which corroborated with UCP2 gene expression, indicating a strong association between the two. Intriguingly, we did not find any association between - 866 G/A polymorphism of UCP2 with serum insulin levels.

CONCLUSION

Our investigation is the first among the studies conducted in Jammu and Kashmir to work on adipose tissue and UCP2 gene polymorphism. The association of - 866 G/A SNP of the UCP2 gene with its expression in diabetes patients appears to be an important genetic determinant in the progression of T2DM. Moreover, age ≥ 50 years and BMI ≥ 25 could be considered risk factors for developing T2DM in the studied population.

Protective Role of Mitochondrial Uncoupling Proteins against Age-Related Oxidative Stress in Type 2 Diabetes Mellitus

The accumulation of oxidative damage to DNA and other biomolecules plays an important role in the etiology of aging and age-related diseases such as type 2 diabetes mellitus (T2D), atherosclerosis, and neurodegenerative disorders. Mitochondrial DNA (mtDNA) is especially sensitive to oxidative stress. Mitochondrial dysfunction resulting from the accumulation of mtDNA damage impairs normal cellular function and leads to a bioenergetic crisis that accelerates aging and associated diseases. Age-related mitochondrial dysfunction decreases ATP production, which directly affects insulin secretion by pancreatic beta cells and triggers the gradual development of the chronic metabolic dysfunction that characterizes T2D. At the same time, decreased glucose oxidation in skeletal muscle due to mitochondrial damage leads to prolonged postprandial blood glucose rise, which further worsens glucose homeostasis. ROS are not only highly reactive by-products of mitochondrial respiration capable of oxidizing DNA, proteins, and lipids but can also function as signaling and effector molecules in cell membranes mediating signal transduction and inflammation. Mitochondrial uncoupling proteins (UCPs) located in the inner mitochondrial membrane of various tissues can be activated by ROS to protect cells from mitochondrial damage. Mitochondrial UCPs facilitate the reflux of protons from the mitochondrial intermembrane space into the matrix, thereby dissipating the proton gradient required for oxidative phosphorylation. There are five known isoforms (UCP1-UCP5) of mitochondrial UCPs. UCP1 can indirectly reduce ROS formation by increasing glutathione levels, thermogenesis, and energy expenditure. In contrast, UCP2 and UCP3 regulate fatty acid metabolism and insulin secretion by beta cells and modulate insulin sensitivity. Understanding the functions of UCPs may play a critical role in developing pharmacological strategies to combat T2D. This review summarizes the current knowledge on the protective role of various UCP homologs against age-related oxidative stress in T2D.

Genipin, an Inhibitor of UCP2 as a Promising New Anticancer Agent: A Review of the Literature

Genipin is a protein cross-linking agent extracted from Gardenia (Gardenia jasminoides Ellis) fruits. This fruit has conventionally been used as a Chinese herbal medicine for the treatment of inflammation and jaundice and as an edible colorant in oriental countries. Uncoupling protein (UCP)-2 is a member of the family of uncoupling proteins, which are anion transporters positioned in the mitochondrial inner membrane. Genipin has been shown to have hepatoprotective activity, acting as an effective antioxidant and inhibitor of mitochondrial UCP2, and is also reported to exert significant anticancer effects. In this review, the author presents the latest progress of genipin as an anticancer agent and concisely describes its various mechanisms of action. In brief, genipin inhibits UCP2 to attenuate generation of reactive oxygen species (ROS), leading to ROS/c-Jun N-terminal kinase-dependent apoptosis of cancer cells. Genipin also increases the tissue inhibitors of matrix metalloproteases (MMP)-2, a kind of tumor promoter in a variety of cancers, as well as induces caspase-dependent apoptosis in in vitro and in vivo models. These findings suggest that genipin can serve as a promising novel antitumor agent that could be applicable for chemotherapy and/or chemoprevention for cancers.

SNPs for Genes Encoding the Mitochondrial Proteins Sirtuin3 and Uncoupling Protein 2 Are Associated With Disease Severity, Type 2 Diabetes, and Outcomes in Patients With Pulmonary Arterial Hypertension and This Is Recapitulated in a New Mouse Model Lacking Both Genes

Background

Isolated loss‐of‐function single nucleotide polymorphisms (SNPs) for SIRT3 (a mitochondrial deacetylase) and UCP2 (an atypical uncoupling protein enabling mitochondrial calcium entry) have been associated with both pulmonary arterial hypertension (PAH) and insulin resistance, but their collective role in animal models and patients is unknown.

Methods and Results

In a prospective cohort of patients with PAH (n=60), we measured SNPs for both SIRT3 and UCP2, along with several clinical features (including invasive hemodynamic data) and outcomes. We found SIRT3 and UCP2 SNPs often both in the same patient in a homozygous or heterozygous manner, correlating positively with PAH severity and associated with the presence of type 2 diabetes and 10‐year outcomes (death and transplantation). To explore this mechanistically, we generated double knockout mice for Sirt3 and Ucp2 and found increasing severity of PAH (mean pulmonary artery pressure, right ventricular hypertrophy/dilatation and extensive vascular remodeling, including inflammatory plexogenic lesions, in a gene dose‐dependent manner), along with insulin resistance, compared with wild‐type mice. The suppressed mitochondrial function (decreased respiration, increased mitochondrial membrane potential) in the double knockout pulmonary artery smooth muscle cells was associated with apoptosis resistance and increased proliferation, compared with wild‐type mice.

Conclusions

Our work supports the metabolic theory of PAH and shows that these mice exhibit spontaneous severe PAH (without environmental or chemical triggers) that mimics human PAH and may explain the findings in our patient cohort. Our study offers a new mouse model of PAH, with several features of human disease that are typically absent in other PAH mouse models.

UCP2 as a Potential Biomarker for Adjunctive Metabolic Therapies in Tumor Management

Glioblastoma (GBM) remains one of the most lethal primary brain tumors in both adult and pediatric patients. Targeting tumor metabolism has emerged as a promising-targeted therapeutic strategy for GBM and characteristically resistant GBM stem-like cells (GSCs). Neoplastic cells, especially those with high proliferative potential such as GSCs, have been shown to upregulate UCP2 as a cytoprotective mechanism in response to chronic increased reactive oxygen species (ROS) exposure. This upregulation plays a central role in the induction of the highly glycolytic phenotype associated with many tumors. In addition to shifting metabolism away from oxidative phosphorylation, UCP2 has also been implicated in increased mitochondrial Ca²⁺ sequestration, apoptotic evasion, dampened immune response, and chemotherapeutic resistance. A query of the CGGA RNA-seq and the TCGA GBMLGG database demonstrated that UCP2 expression increases with increased WHO tumor-grade and is associated with much poorer prognosis across a cohort of brain tumors. UCP2 expression could potentially serve as a biomarker to stratify patients for adjunctive anti-tumor metabolic therapies, such as glycolytic inhibition alongside current standard of care, particularly in adult and pediatric gliomas. Additionally, because UCP2 correlates with tumor grade, monitoring serum protein levels in the future may allow clinicians a relatively minimally invasive marker to correlate with disease progression. Further investigation of UCP2’s role in metabolic reprogramming is warranted to fully appreciate its clinical translatability and utility.

Human Pluripotent Stem Cells to Model Islet Defects in Diabetes

Diabetes mellitus is characterized by elevated levels of blood glucose and is ultimately caused by insufficient insulin production from pancreatic beta cells. Different research models have been utilized to unravel the molecular mechanisms leading to the onset of diabetes. The generation of pancreatic endocrine cells from human pluripotent stem cells constitutes an approach to study genetic defects leading to impaired beta cell development and function. Here, we review the recent progress in generating and characterizing functional stem cell-derived beta cells. We summarize the diabetes disease modeling possibilities that stem cells offer and the challenges that lie ahead to further improve these models.

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.

Is Mitochondrial Dysfunction a Common Root of Noncommunicable Chronic Diseases?

Mitochondrial damage is implicated as a major contributing factor for a number of noncommunicable chronic diseases such as cardiovascular diseases, cancer, obesity, and insulin resistance/type 2 diabetes. Here, we discuss the role of mitochondria in maintaining cellular and whole-organism homeostasis, the mechanisms that promote mitochondrial dysfunction, and the role of this phenomenon in noncommunicable chronic diseases. We also review the state of the art regarding the preclinical evidence associated with the regulation of mitochondrial function and the development of current mitochondria-targeted therapeutics to treat noncommunicable chronic diseases. Finally, we give an integrated vision of how mitochondrial damage is implicated in these metabolic diseases.

Mitochondrial Dysfunction in Age-Related Metabolic Disorders

Aging is a natural biological process in living organisms characterized by receding bioenergetics. Mitochondria are crucial for cellular bioenergetics and thus an important contributor to age-related energetics deterioration. In addition, mitochondria play a major role in calcium signaling, redox homeostasis, and thermogenesis making this organelle a major cellular component that dictates the fate of a cell. To maintain its quantity and quality, mitochondria undergo multiple processes such as fission, fusion, and mitophagy to eliminate or replace damaged mitochondria. While this bioenergetics machinery is properly protected, the functional decline associated with age and age-related metabolic diseases is mostly a result of failure in such protective mechanisms. In addition, metabolic by-products like reactive oxygen species also aid in this destructive pathway. Mitochondrial dysfunction has always been thought to be associated with diseases. Moreover, studies in recent years have pointed out that aging contributes to the decay of mitochondrial health by promoting imbalances in key mitochondrial-regulated pathways. Hence, it is crucial to understand the nexus of mitochondrial dysfunction in age-related diseases. This review focuses on various aspects of basic mitochondrial biology and its status in aging and age-related metabolic diseases.

UCP2 gene polymorphisms in obesity and diabetes, and the role of UCP2 in cancer

Mitochondria are the primary sites for ATP synthesis and free radical generation in organisms. Abnormal mitochondrial metabolism contributes to many diseases, including obesity, diabetes and cancer. UCP2 is an ion/anion transporter located in mitochondrial inner membrane, and has a crucial role in regulating oxidative stress, cellular metabolism, cell proliferation and cell death. Polymorphisms of the UCP2 gene have been associated with diabetes and obesity because UCP2 is involved in energy expenditure and insulin secretion. Moreover, UCP2 gene expression is often amplified in cancers, and increased UCP2 expression contributes to cancer growth, cancer metabolism, anti-apoptosis and drug resistance. The present review summarizes the latest findings of UCP2 with respect to obesity, diabetes and cancer.

The -866G/A polymorphism in the promoter of the UCP2 gene is associated with risk for type 2 diabetes and with decreased insulin levels

BACKGROUND AND AIM

Oxidative stress and impaired insulin secretion is an underlying major risk factor for the development of type 2 diabetes (T2D). Uncoupling protein-2 (UCP2) is involved in the regulation of reactive oxygen species production, insulin secretion, and lipid metabolism. Based on this we aimed to find an association of UCP2 (G-866A) polymorphism with the risk of T2D in South Indian population.

METHODS

A total of 318 T2D patients and 312 controls were enrolled in this study. All the study subjects were genotyped for UCP2 (G-866A) polymorphism using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Fasting blood glucose, HbA1c, serum lipid profile, systolic and diastolic blood pressure were measured by standard biochemical methods. Fasting serum insulin level was measured by ELISA.

RESULTS

In UCP2 (G-866A) polymorphism, the distribution of GA (46%) and AA (14%) genotypes were significantly higher in T2D patients than the healthy controls. The frequency of GA and AA genotypes have high risk towards the development of T2D with an Odds Ratio (OR) of 1.55 (P = 0.01) and 2.04 (P = 0.01) respectively. Moreover, SNP-866 G>A allele was found to be significantly associated with T2D (OR = 1.48, P = 0.001, 95% CI = 1.16-1.88). Further, the UCP2 AA genotype showed significantly decreased level of insulin by the reduction in pancreatic β-cell function in T2D patients.

CONCLUSION

UCP2 (G-866A) polymorphism may play a crucial role in the pathogenesis of insulin secretion thus leads to the development of T2D.

Polymorphisms in the Uncoupling Protein 2 Gene Are Associated with Diabetic Retinopathy in Han Chinese Patients with Type 2 Diabetes

BACKGROUND

The uncoupling protein 2 (UCP2) gene plays an important role in the complications of type 2 diabetes (T2D). However, the association between variants in the UCP2 gene and diabetic retinopathy (DR) in Han Chinese T2D patients remains unclear.

METHODS

Two single-nucleotide polymorphisms (SNPs) [rs659366 (-866G/A) and a 45-bp insertion/deletion (I/D) in the 3'-UTR] in the UCP2 gene were genotyped in a study cohort of 209 T2D patients with DR and 199 T2D patients without DR by direct DNA sequencing.

RESULTS

Logistic regression analysis showed that the AA and GA genotypes of rs659366 were significantly associated with an increased risk for nonproliferative DR (NPDR) in the codominant model (corrected p-value <0.01) and the dominant model (corrected p-value = 0.006). Patients harboring the II and DI genotypes had a higher risk for PDR in the codominant model (corrected p-value = 0.011) and the dominant model (corrected p-value = 0.006), and the DI genotype showed a higher risk for NPDR in the dominant model (corrected p-value = 0.007) or codominant model (corrected p-value = 0.006). Further, haplotype analyses verified that the A-I haplotype is a risk haplotype for NPDR and PDR.

CONCLUSION

This study suggests that the UCP2 gene may be involved in the pathogenesis of NPDR and PDR in Han Chinese patients with T2D.

Mitochondrial Uncoupling Proteins: Subtle Regulators of Cellular Redox Signaling

SIGNIFICANCE

Mitochondria are the energetic, metabolic, redox, and information signaling centers of the cell. Substrate pressure, mitochondrial network dynamics, and cristae morphology state are integrated by the protonmotive force Δp or its potential component, ΔΨ, which are attenuated by proton backflux into the matrix, termed uncoupling. The mitochondrial uncoupling proteins (UCP1-5) play an eminent role in the regulation of each of the mentioned aspects, being involved in numerous physiological events including redox signaling. Recent Advances: UCP2 structure, including purine nucleotide and fatty acid (FA) binding sites, strongly support the FA cycling mechanism: UCP2 expels FA anions, whereas uncoupling is achieved by the membrane backflux of protonated FA. Nascent FAs, cleaved by phospholipases, are preferential. The resulting Δp dissipation decreases superoxide formation dependent on Δp. UCP-mediated antioxidant protection and its impairment are expected to play a major role in cell physiology and pathology. Moreover, UCP2-mediated aspartate, oxaloacetate, and malate antiport with phosphate is expected to alter metabolism of cancer cells.

CRITICAL ISSUES

A wide range of UCP antioxidant effects and participations in redox signaling have been reported; however, mechanisms of UCP activation are still debated. Switching off/on the UCP2 protonophoretic function might serve as redox signaling either by employing/releasing the extra capacity of cell antioxidant systems or by directly increasing/decreasing mitochondrial superoxide sources. Rapid UCP2 degradation, FA levels, elevation of purine nucleotides, decreased Mg²⁺, or increased pyruvate accumulation may initiate UCP-mediated redox signaling.

FUTURE DIRECTIONS

Issues such as UCP2 participation in glucose sensing, neuronal (synaptic) function, and immune cell activation should be elucidated. Antioxid. Redox Signal. 29, 667-714.

Obesity phenotype in relation to gene polymorphism among samples of Egyptian children and their mothers

Obesity is complex heterogeneous disease controlled by genes, environmental factors, and their interaction. Genetic factors account for 40-90% of the body mass index variations. Body mass index (BMI) of children correlates more closely with maternal than paternal BMI. So, this studu was aimed to investigate the role of leptin receptor LEPR Gln223Arg, the uncoupling protein 2 (UCP2 G 866 A) and insulin receptor gene (INSR exon 17) polymorphisms in the pathogenesis of obesity. A cross-sectional study executed on 130 children and their obese mothers; classified into 2 groups according to their BMI. The 2 groups were evaluated regarding the anthropometry. Restriction fragment length analysis for LEPR Gln223Arg, UCP2 -866 G/A and INSR exon 17 polymorphisms were applied. It was reported that increased risk of obesity was found in LEPR AG + AA genotype and the A allele. Significant statistical difference was detected only in female children. Concerning UCP2, the AG followed by the GG genotype was the most frequent in all groups and the G allele was the mostly present in obese mothers and obese male children but with no statistical significance. There was difference in the INSR genotype and alleles between groups, but this difference was not statistically significant. This study concluded that the LEPR Gln223Arg, UCP2 G 866 A and INSR exon 17 polymorphisms are related to obesity in Egyptian population. Further researches on larger population are recommended to ascertain the implications of LEPR, UCP2 and INSR polymorphisms in obesity.

Uncoupling Protein 2: A Key Player and a Potential Therapeutic Target in Vascular Diseases

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein that belongs to the uncoupling protein family and plays an important role in lowering mitochondrial membrane potential and dissipating metabolic energy with prevention of oxidative stress accumulation. In the present article, we will review the evidence that UCP2, as a consequence of its roles within the mitochondria, represents a critical player in the predisposition to vascular disease development in both animal models and in humans, particularly in relation to obesity, diabetes, and hypertension. The deletion of the UCP2 gene contributes to atherosclerosis lesion development in the knockout mice, also showing significantly shorter lifespan. The UCP2 gene downregulation is a key determinant of higher predisposition to renal and cerebrovascular damage in an animal model of spontaneous hypertension and stroke. In contrast, UCP2 overexpression improves both hyperglycemia- and high-salt diet-induced endothelial dysfunction and ameliorates hypertensive target organ damage in SHRSP. Moreover, drugs (fenofibrate and sitagliptin) and several vegetable compounds (extracts from Brassicaceae, berberine, curcumin, and capsaicin) are able to induce UCP2 expression level and to exert beneficial effects on the occurrence of vascular damage. As a consequence, UCP2 becomes an interesting therapeutic target for the treatment of common human vascular diseases.

Uncoupling protein 2 regulates daily rhythms of insulin secretion capacity in MIN6 cells and isolated islets from male mice

Objective

Upregulation of uncoupling protein 2 (UCP2) is associated with impaired glucose-stimulated insulin secretion (GSIS), which is thought to be an important contributor to pathological β cell failure in obesity and type 2 diabetes (T2D); however, the physiological function of UCP2 in the β cell remains undefined. It has been suggested, but not yet tested, that UCP2 plays a physiological role in β cells by coordinating insulin secretion capacity with anticipated fluctuating nutrient supply, such that upregulation of UCP2 in the inactive/fasted state inhibits GSIS as a mechanism to prevent hypoglycemia. Therefore, we hypothesized that daily cycles of GSIS capacity are dependent on rhythmic and predictable patterns of Ucp2 gene expression such that low Ucp2 in the active/fed phase promotes maximal GSIS capacity, whereas elevated Ucp2 expression in the inactive/fasted phase supresses GSIS capacity. We further hypothesized that rhythmic Ucp2 expression is required for the maintenance of glucose tolerance over the 24 h cycle.

Methods

We used synchronized MIN6 clonal β cells and isolated mouse islets from wild type (C57BL6) and mice with β cell knockout of Ucp2 (Ucp2-βKO; and respective Ins2-cre controls) to determine the endogenous expression pattern of Ucp2 over 24 h and its impact on GSIS capacity and glucose tolerance over 24 h.

Results

A dynamic pattern of Ucp2 mRNA expression was observed in synchronized MIN6 cells, which showed a reciprocal relationship with GSIS capacity in a time-of-day-specific manner. GSIS capacity was suppressed in islets isolated from wild type and control mice during the light/inactive phase of the daily cycle; a suppression that was dependent on Ucp2 in the β cell and was lost in islets isolated from Ucp2-βKO mice or wild type islets treated with a UCP2 inhibitor. Finally, suppression of GSIS capacity by UCP2 in the light phase was required for the maintenance of normal patterns of glucose tolerance.

Conclusions

Our study suggests that Ucp2/UCP2 in the β cell is part of an important, endogenous, metabolic regulator that controls the temporal capacity of GSIS over the course of the day/night cycle, which, in turn, regulates time-of-day glucose tolerance. Targeting Ucp2/UCP2 as a therapeutic in type 2 diabetes or any other metabolic condition must take into account the rhythmic nature of its expression and its impact on glucose tolerance over 24 h, specifically during the inactive/fasted phase.

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Ucp2 mRNA expression in MIN6 β cells and isolated islets is dynamic and rhythmic over 24 h.

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Daily cycles of glucose-stimulated insulin secretion capacity are dependent on rhythmic Ucp2 expression and UCP2 activity.

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Loss of rhythmic Ucp2 mRNA expression triggers glucose intolerance only in the light/inactive phase of the daily cycle.

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UCP2 is part of an endogenous diurnal metabolic regulator that coordinates islet function with the daily cycle of fasting and feeding.

Green Tea Polyphenol Epigallocatechin-3-gallate Suppresses Toll-like Receptor 4 Expression via Up-regulation of E3 Ubiquitin-protein Ligase RNF216

Toll-like receptor 4 (TLR4) plays an essential role in innate immunity through inflammatory cytokine induction. Recent studies demonstrated that the abnormal activation of TLR4 has a pivotal role in obesity-induced inflammation, which is associated with several diseases, including hyperinsulinemia, hypertriglyceridemia, and cardiovascular disease. Here we demonstrate that (-)-epigallocatechin-3-O-gallate, a natural agonist of the 67-kDa laminin receptor (67LR), suppressed TLR4 expression through E3 ubiquitin-protein ring finger protein 216 (RNF216) up-regulation. Our data indicate cyclic GMP mediates 67LR agonist-dependent RNF216 up-regulation. Moreover, we show that the highly absorbent 67LR agonist (-)-epigallocatechin-3-O-(3-O-methyl)-gallate (EGCG3″Me) significantly attenuated TLR4 expression in the adipose tissue. EGCG3″Me completely inhibited the high-fat/high-sucrose (HF/HS)-induced up-regulation of tumor necrosis factor α in adipose tissue and serum monocyte chemoattractant protein-1 increase. Furthermore, this agonist intake prevented HF/HS-induced hyperinsulinemia and hypertriglyceridemia. Taken together, 67LR presents an attractive target for the relief of obesity-induced inflammation.

Association of oxidative stress gene polymorphisms with presbycusis

INTRODUCTION

Presbycusis is characterised by etiopathological changes in the cochlea of the inner ear due to genetic and environmental factors and has a serious impact on quality of life. The present study was aimed to evaluate the role of oxidant stress gene polymorphisms in the development of presbycusis.

SUBJECTS AND METHODS

220 subjects with confirmed presbycusis from ENT specialists of MAA ENT hospital, Hyderabad, India from 2012 to 2014 were considered for the study. 270 age and sex matched controls were included in the study. Analysis of gene polymorphisms of SNPs cytochrome P450 1A1 (CYP1A1) 3801 T>C, 2455 A>G and 2453 A>C; glutathione S transferase (GST) T1 and M1; N-acetyl transferase (NAT2) 282 C>T and 857 G>A; uncoupled proteins (UCP1) (-3826) A>G and (UCP2) (866)G>A was carried out. Variations in the allelic and genotypic frequencies obtained were computed and analysed using appropriate statistical methods.

RESULTS

The results of the study indicated that CYP1A1 gene polymorphism at 2453 C>A (adjusted OR: 1.59, 95% CI: 1.01-2.87) and 2455 A>G (adjusted OR: 1.87, 95% CI: 1.07-3.37), double null genotype of GSTM1 and GSTT1 (adjusted OR: 8.88, 95% CI: 4.10-19.19), NAT2 gene at C282T (adjusted OR: 1.77, 95% CI: 1.02-3.11) and G590 A (adjusted OR: 1.83, 95% CI 1.20-3.63) and UCP2 (-866) G>A (adjusted OR: 12.39; 95% CI: 6.51-23.56) showed increased risk for presbycusis while CYP1A1 at 3801 T>C and UCP1 (-3286) A>G exhibited no association. The haplotype combinations of T-G-A of CYP1A1 at 3801, 2455 and 2453 positions as well as T-A of NAT2*6 at 282 and 590 positions were found to contribute significant risk for the onset of presbycusis.

CONCLUSIONS

Gene polymorphisms of CYP1A1 (A2455G, C2453A), NAT2*6 (C282T, G590 A), GST T1/M1 (double null genotype) and UCP2 (G-866 A) were found to contribute significant risk to presbycusis.

Common UCP2 variants contribute to serum urate concentrations and the risk of hyperuricemia

Elevated serum urate, which is regulated at multiple levels including genetic variants, is a risk factor for gout and other metabolic diseases. This study aimed to investigate the association between UCP2 variants and serum urate as well as hyperuricemia in a Chinese population. In total, 4332 individuals were genotyped for two common UCP2 variants, -866G/A and Ala55Val. These loci were not associated either serum urate level or with a risk of hyperuricemia in the total group of subjects. However, in females, -866G/A and Ala55Val were associated with a lower serum urate (P = 0.006 and 0.014, seperately) and played a protective role against hyperuricemia (OR = 0.80, P = 0.018; OR = 0.79, P = 0.016). These associations were not observed in the males. After further stratification, the two loci were associated with serum urate in overweight, but not underweight females. The haplotype A-T (-866G/A-Ala55Val) was a protective factor for hyperuricemia in the female subgroup (OR = 0.80, P = 0.017). This present study identified a novel gene, UCP2, that influences the serum urate concentration and the risk of hyperuricemia, and the degree of association varies with gender and BMI levels.

Association between parental history of diabetes and the incidence of type 2 diabetes mellitus differs according to the sex of the parent and offspring's body weight: A finding from a Japanese worksite-based cohort study

OBJECTIVE

To investigate differences in the association of parental history of diabetes with the risk of type 2 diabetes mellitus (T2DM) in the offspring according to the sex of the parent and the offspring's body weight.

METHODS

A prospective cohort study of 4446 middle-aged non-diabetic Japanese men and women were followed in Aichi Prefecture, central Japan, from 2002 to 2011. Subjects were categorized by their self-reported parental history of diabetes ("no parental history," "father only," "mother only," and "both"). The association of parental history of diabetes and incidence in the offspring was examined according to overweight status adjusted for age, sex, birth weight, smoking, alcohol consumption, physical activity, total energy intake, body mass index, and number of metabolic syndrome components.

RESULTS

During follow-up (median 8.9 years), 277 subjects developed T2DM. Parental history of diabetes was positively associated with T2DM incidence. However, stratified analysis by overweight status revealed that only maternal history was associated with increased T2DM incidence in non-overweight subjects (hazard ratio=2.35, 95% confidence interval: 1.41-3.91). While in overweight subjects, paternal history was significantly associated with higher T2DM incidence (hazard ratio=1.98, 95% confidence interval: 1.19-3.28).

CONCLUSIONS

Our results suggest that parental history of diabetes mellitus is associated with the incidence of T2DM in offspring differently according to the sex of the affected parent and the offspring's body weight.

Mitochondrial uncoupling proteins regulate angiotensin-converting enzyme expression: crosstalk between cellular and endocrine metabolic regulators suggested by RNA interference and genetic studies

Uncoupling proteins (UCPs) regulate mitochondrial function, and thus cellular metabolism. Angiotensin‐converting enzyme (ACE) is the central component of endocrine and local tissue renin–angiotensin systems (RAS), which also regulate diverse aspects of whole‐body metabolism and mitochondrial function (partly through altering mitochondrial UCP expression). We show that ACE expression also appears to be regulated by mitochondrial UCPs. In genetic analysis of two unrelated populations (healthy young UK men and Scandinavian diabetic patients) serum ACE (sACE) activity was significantly higher amongst UCP3‐55C (rather than T) and UCP2 I (rather than D) allele carriers. RNA interference against UCP2 in human umbilical vein endothelial cells reduced UCP2 mRNA sixfold (P < 0·01) whilst increasing ACE expression within a physiological range (<1·8‐fold at 48 h; P < 0·01). Our findings suggest novel hypotheses. Firstly, cellular feedback regulation may occur between UCPs and ACE. Secondly, cellular UCP regulation of sACE suggests a novel means of crosstalk between (and mutual regulation of) cellular and endocrine metabolism. This might partly explain the reduced risk of developing diabetes and metabolic syndrome with RAS antagonists and offer insight into the origins of cardiovascular disease in which UCPs and ACE both play a role.

The UCP2 -866 G>A promoter region polymorphism is associated with nonalcoholic steatohepatitis

BACKGROUND & AIMS

Uncoupling protein 2 - UCP2 - regulates mitochondrial lipid fluxes and reactive oxygen species production by the respiratory chain. The -866 G>A UCP2 promoter region polymorphism has been linked to insulin resistance and lipid metabolism. The aim of this study was to assess whether the -866 G>A UCP2 polymorphism predisposes to nonalcoholic steatohepatitis in patients at risk, and the relationship with lipid metabolism and hepatic UCP2 expression.

METHODS

We considered 688 Italian patients who underwent liver biopsy for suspected NASH, and 232 healthy controls. The UCP2 -866 G>A polymorphism was determined by allele specific oligonucleotide probes, hepatic UCP2 mRNA levels by quantitative real-time PCR.

RESULTS

UCP2 A/A genotype was associated with a reduced risk of nonalcoholic steatohepatitis (Odds Ratio 0.49, 95% C.I. 0.26-0.90; P = 0.02; adjusted for age, sex, BMI, impaired fasting glucose or diabetes, PNPLA3 I148M alleles and recruitment centre). The A/A genotype was associated with reduced risk of steatosis grade G2-G3 and nonalcoholic steatohepatitis in patients without (P = 0.003 and P = 0.01 respectively), but not in those with (P = NS) impaired fasting glucose/diabetes. The UCP2 A/A genotype was associated with higher hepatic UCP2 mRNA levels (adjusted P = 0.008). Concerning the metabolic traits, the UCP2 A/A genotype was associated with higher total serum cholesterol levels (adjusted P = 0.03), but not with serum HDL, triglycerides or impaired fasting glucose/diabetes.

CONCLUSIONS

UCP2 -866 A/A genotype is associated with increased hepatic UCP2 expression and reduced risk of nonalcoholic steatohepatitis, particularly in subjects with normal fasting glucose.

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.

UCP2, a mitochondrial protein regulated at multiple levels

An ever-increasing number of studies highlight the role of uncoupling protein 2 (UCP2) in a broad range of physiological and pathological processes. The knowledge of the molecular mechanisms of UCP2 regulation is becoming fundamental in both the comprehension of UCP2-related physiological events and the identification of novel therapeutic strategies based on UCP2 modulation. The study of UCP2 regulation is a fast-moving field. Recently, several research groups have made a great effort to thoroughly understand the various molecular mechanisms at the basis of UCP2 regulation. In this review, we describe novel findings concerning events that can occur in a concerted manner at various levels: Ucp2 gene mutation (single nucleotide polymorphisms), UCP2 mRNA and protein expression (transcriptional, translational, and protein turn-over regulation), UCP2 proton conductance (ligands and post-transcriptional modifications), and nutritional and pharmacological regulation of UCP2.

Mitochondrial dysfunction in metabolic syndrome and asthma

Though severe or refractory asthma merely affects less than 10% of asthma population, it consumes significant health resources and contributes significant morbidity and mortality. Severe asthma does not fell in the routine definition of asthma and requires alternative treatment strategies. It has been observed that asthma severity increases with higher body mass index. The obese-asthmatics, in general, have the features of metabolic syndrome and are progressively causing a significant burden for both developed and developing countries thanks to the westernization of the world. As most of the features of metabolic syndrome seem to be originated from central obesity, the underlying mechanisms for metabolic syndrome could help us to understand the pathobiology of obese-asthma condition. While mitochondrial dysfunction is the common factor for most of the risk factors of metabolic syndrome, such as central obesity, dyslipidemia, hypertension, insulin resistance, and type 2 diabetes, the involvement of mitochondria in obese-asthma pathogenesis seems to be important as mitochondrial dysfunction has recently been shown to be involved in airway epithelial injury and asthma pathogenesis. This review discusses current understanding of the overlapping features between metabolic syndrome and asthma in relation to mitochondrial structural and functional alterations with an aim to uncover mechanisms for obese-asthma.

Overexpression of the antioxidant enzyme catalase does not interfere with the glucose responsiveness of insulin-secreting INS-1E cells and rat islets

AIMS/HYPOTHESIS

Hydrogen peroxide (H2O2)-inactivating enzymes such as catalase are produced in extraordinarily low levels in beta cells. Whether this low expression might be related to a signalling function of H2O2 within the beta cell is unknown. A high level of H2O2-inactivating enzymes could potentially be incompatible with glucose-induced insulin secretion. Therefore the effect of catalase overexpression on mitochondrial function and physiological insulin secretion was studied in insulin-secreting INS-1E and primary islet cells.

METHODS

INS-1E and rat islet cells were lentivirally transduced to overexpress catalase in the cytosol (CytoCat) or in mitochondria (MitoCat). Cell viability and caspase-3 activation were assessed after cytokine incubation and hypoxia. Insulin secretion was quantified and expression of the gene encoding the mitochondrial uncoupling protein 2 (Ucp2) was measured in parallel to mitochondrial membrane potential and reactive oxygen species (ROS) formation.

RESULTS

The ability to secret insulin in a glucose-dependent manner was not suppressed by catalase overexpression, although the glucose-dependent increase in the mitochondrial membrane potential was attenuated in MitoCat cells along with an increased Ucp2 expression and reduced mitochondrial ROS formation. In addition, MitoCat overexpressing cells were significantly more resistant against pro-inflammatory cytokines and hypoxia than CytoCat and control cells.

CONCLUSIONS/INTERPRETATION

The results demonstrate that an improved antioxidative defence status of insulin-secreting cells allowing efficient H2O2 inactivation is not incompatible with proper insulin secretory responsiveness to glucose stimulation and provide no support for a signalling role of H2O2 in insulin-secreting cells. Interestingly, the results also document for the first time that the decreased ROS formation with increasing glucose concentrations is of mitochondrial origin.

Individualized therapy for type 2 diabetes: clinical implications of pharmacogenetic data

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance, abnormally elevated hepatic glucose production, and reduced glucose-stimulated insulin secretion. Treatment with antihyperglycemic agents is initially successful in type 2 diabetes, but it is often associated with a high secondary failure rate, and the addition of insulin is eventually necessary for many patients, in order to restore acceptable glycemic control and to reduce the risk of development and progression of disease complications. Notably, even patients who appear to have similar requirements of antidiabetic regimens show great variability in drug disposition, glycemic response, tolerability, and incidence of adverse effects during treatment. Pharmacogenomics is a promising area of investigation and involves the search for genetic polymorphisms that may explain the interindividual variability in antidiabetic therapy response. The initial positive results portend that genomic efforts will be able to shed important light on variability in pharmacologic traits. In this review, we summarize the current understanding of genetic polymorphisms that may affect the responses of subjects with T2DM to antidiabetic treatment. These genes belong to three major classes: genes involved in drug metabolism and transporters that influence pharmacokinetics (including the cytochrome P450 [CYP] superfamily, the organic anion transporting polypeptide [OATP] family, and the polyspecific organic cation transporter [OCT] family); genes encoding drug targets and receptors (including peroxisome proliferator-activated receptor gamma [PPARG], the adenosine triphosphate [ATP]-sensitive potassium channel [K(ATP)], and incretin receptors); and genes involved in the causal pathway of T2DM that are able to modify the effects of drugs (including adipokines, transcription factor 7-like 2 (T cell specific, HMG-box) [TCF7L2], insulin receptor substrate 1 [IRS1], nitric oxide synthase 1 (neuronal) adaptor protein [NOS1AP], and solute carrier family 30 (zinc transporter), member 8 [SLC30A8]). In addition to these three major classes, we also review the available evidence on novel genes (CDK5 regulatory subunit associated protein 1-like 1 [CDKAL1], insulin-like growth factor 2 mRNA binding protein 2 [IGF2BP2], potassium voltage-gated channel, KQT-like subfamily, member 1 [KCNQ1], paired box 4 [PAX4] and neuronal differentiation 1 [NEUROD1] transcription factors, ataxia telangiectasia mutated [ATM], and serine racemase [SRR]) that have recently been proposed as possible modulators of therapeutic response in subjects with T2DM.

Association between UCP2 A55V polymorphism and risk of cardiovascular events in patients with multi-vessel coronary arterial disease

Background

UCP2 (uncoupling protein 2) plays an important role in cardiovascular diseases and recent studies have suggested that the A55V polymorphism can cause UCP2 dysfunction. The main aim was to investigate the association of A55V polymorphism with cardiovascular events in a group of 611 patients enrolled in the Medical, Angioplasty or Surgery Study II (MASS II), a randomized trial comparing treatments for patients with coronary artery disease and preserved left ventricular function.

Methods

The participants of the MASS II were genotyped for the A55V polymorphism using allele-specific PCR assay. Survival curves were calculated with the Kaplan–Meier method and evaluated with the log-rank statistic. The relationship between baseline variables and the composite end-point of cardiac death, acute myocardial infarction (AMI), refractory angina requiring revascularization and cerebrovascular accident were assessed using a Cox proportional hazards survival model.

Results

There were no significant differences for baseline variables according genotypes. After 2 years of follow-up, dysglycemic patients harboring the VV genotype had higher occurrence of AMI (p=0.026), Death+AMI (p=0.033), new revascularization intervention (p=0.009) and combined events (p=0.037) as compared with patients carrying other genotypes. This association was not evident in normoglycemic patients.

Conclusions

These findings support the hypothesis that A55V polymorphism is associated with UCP2 functional alterations that increase the risk of cardiovascular events in patients with previous coronary artery disease and dysglycemia.

The pancreatic beta cells in human type 2 diabetes

Bell-cell (beta-cell) impairment is central to the development and progression of human diabetes, as a result of the combined effects of genetic and acquired factors. Reduced islet number and/or reduced beta cells amount in the pancreas of individuals with Type 2 diabetes have been consistently reported. This is mainly due to increased beta cell death, not adequately compensated for by regeneration. In addition, several quantitative and/or qualitative defects of insulin secretion have been observed in Type 2 diabetes, both in vivo and ex vivo with isolated islets. All this is associated with modifications of islet cell gene and protein expression. With the identification of several susceptible Type 2 diabetes loci, the role of genotype in affecting beta-cell function and survival has been addressed in a few studies and the relationships between genotype and beta-cell phenotype investigated. Among acquired factors, the importance of metabolic insults (in particular glucotoxicity and lipotoxicity) in the natural history of beta-cell damage has been widely underlined. Continuous improvements in our knowledge of the beta cells in human Type 2 diabetes will lead to more targeted and effective strategies for the prevention and treatment of the disease.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 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. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

Mitochondrial inhibitor as a new class of insulin sensitizer

Insulin resistance is a major risk factor for type 2 diabetes. AMP-activated protein kinase (AMPK) is a drug target in the improvement of insulin sensitivity. Several insulin-sensitizing medicines are able to activate AMPK through inhibition of mitochondrial functions. These drugs, such as metformin and STZ, inhibit ATP synthesis in mitochondria to raise AMP/ATP ratio in the process of AMPK activation. However, chemicals that activate AMPK directly or by activating its upstream kinases have not been approved for treatment of type 2 diabetes in humans. In an early study, we reported that berberine inhibited oxygen consumption in mitochondria, and increased AMP/ATP ratio in cells. The observation suggests an indirect mechanism for AMPK activation by berberine. Berberine stimulates glycolysis for ATP production that offsets the cell toxicity after mitochondria inhibition. The study suggests that mitochondrial inhibition is an approach for AMPK activation. In this review article, literature is critically reviewed to interpret the role of mitochondria function in the mechanism of insulin resistance, which supports that mitochondria inhibitors represent a new class of AMPK activator. The inhibitors are promising candidates for insulin sensitizers. This review provides a guideline in search for small molecule AMPK activators in the drug discovery for type 2 diabetes.

The uncoupling protein 2 -866G > a polymorphism is associated with the risk of ischemic stroke in Chinese type 2 diabetic patients

AIMS

To determine genetic predispsitions for diabetic cerebral ischemia, we investigated the relationship between the -866G>A polymorphism of uncoupling protein (UCP) 2 and the risk of ischemic stroke in two cohorts of type 2 diabetic patients.

METHODS

A total of 844 type 2 diabetic patients with 4-year prospective study were examined using a case-control methodology. And 404 cases with ischemical stroke, 440 cases without ischemical stroke. The -866G>A polymorphism in UCP2 was genotyped by TaqMan MGB probe method.

RESULTS

The -866G>A SNP in UCP2 was significantly associated with diabetic ischemical stroke (odds ratio [OR]= 1.94; 95% confidence interval [CI]= 0.68 to1.31; P < 0.037). Similar results were observed for baseline cases of IS. Stratification by sex confirmed an allelic association with IS in women, whereas no association was observed in men.

CONCLUSIONS

The A allele of the -866G>A variant of UCP2 was associated with increased risk of IS in Chinese diabetic women with type 2 diabetes in a 4-year prospective study. This association was independent of other common IS risk factors.

Uncoupling protein 2 gene polymorphisms are associated with obesity

Background

Uncoupling protein 2 (UCP2) gene polymorphisms have been reported as genetic risk factors for obesity and type 2 diabetes mellitus (T2DM). We examined the association of commonly observed UCP2 G(−866)A (rs659366) and Ala55Val (C > T) (rs660339) single nucleotide polymorphisms (SNPs) with obesity, high fasting plasma glucose, and serum lipids in a Balinese population.

Methods

A total of 603 participants (278 urban and 325 rural subjects) were recruited from Bali Island, Indonesia. Fasting plasma glucose (FPG), triglyceride (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C) and total cholesterol (TC) were measured. Obesity was determined based on WHO classifications for adult Asians. Participants were genotyped for G(−866)A and Ala55Val polymorphisms of the UCP2 gene.

Results

Obesity prevalence was higher in urban subjects (51%) as compared to rural subjects (23%). The genotype, minor allele (MAF), and heterozygosity frequencies were similar between urban and rural subjects for both SNPs. All genotype frequencies were in Hardy-Weinberg equilibrium. A combined analysis of genotypes and environment revealed that the urban subjects carrying the A/A genotype of the G(−866)A SNP have higher BMI than the rural subjects with the same genotype. Since the two SNPs showed strong linkage disequilibrium (D’ = 0.946, r² = 0.657), a haplotype analysis was performed. We found that the AT haplotype was associated with high BMI only when the urban environment was taken into account.

Conclusions

We have demonstrated the importance of environmental settings in studying the influence of the common UCP2 gene polymorphisms in the development of obesity in a Balinese population.

The frequent UCP2 -866G>A polymorphism protects against insulin resistance and is associated with obesity: a study of obesity and related metabolic traits among 17 636 Danes

CONTEXT

Uncoupling protein 2 (UCP2) is involved in regulating ATP synthesis, generation of reactive oxygen species and glucose-stimulated insulin secretion in β-cells. Polymorphisms in UCP2 may be associated with obesity and type 2 diabetes mellitus.

OBJECTIVE

To determine the influence of a functional UCP2 promoter polymorphism (-866G>A, rs659366) on obesity, type 2 diabetes and intermediary metabolic traits. Furthermore, to include these and previously published data in a meta-analysis of this variant with respect to its impact on obesity and type 2 diabetes.

DESIGN

We genotyped UCP2 rs659366 in a total of 17 636 Danish individuals and established case-control studies of obese and non-obese subjects and of type 2 diabetic and glucose-tolerant subjects. Meta-analyses were made in own data set and in publicly available data sets. Quantitative traits relevant for obesity and type 2 diabetes were analysed within separate study populations.

RESULTS

We found no consistent associations between the UCP2 -866G-allele and obesity or type 2 diabetes. Yet, a meta-analysis of data from 12 984 subjects showed an association with obesity (GA vs GG odds ratio (OR) (95% confidence interval (CI)): 0.894(0.826-0.968) P=0.00562, and AA vs GG OR(95% CI): 0.892(0.800-0.996), P=0.0415. Moreover, a meta-analysis for type 2 diabetes of 15 107 individuals showed no association. The -866G-allele was associated with elevated fasting serum insulin levels (P=0.002) and HOMA insulin resistance index (P=0.0007). Insulin sensitivity measured during intravenous glucose tolerance test in young Caucasian subjects (n=377) was decreased in carriers of the GG genotype (P=0.05).

CONCLUSIONS

The UCP2 -866G-allele is associated with decreased insulin sensitivity in Danish subjects and is associated with obesity in a combined meta-analysis.

Mitochondria and Oxidative Stress in the Cardiorenal Metabolic Syndrome

Mitochondria play a fundamental role in the maintenance of normal structure, function, and survival of tissues. There is considerable evidence for mitochondrial dysfunction in association with metabolic diseases including insulin resistance, obesity, diabetes, and the cardiorenal metabolic syndrome. The phenomenon of reactive oxygen species (ROS)-induced ROS release through interactions between cytosolic and mitochondrial oxidative stress contributes to a vicious cycle of enhanced oxidative stress and mitochondrial dysfunction. Activation of the cytosolic and mitochondrial NADPH oxidase system, impairment of the mitochondrial electron transport, activation of p66shc pathway-targeting mitochondria, endoplasmic reticular stress, and activation of the mammalian target of the rapamycin-S6 kinase pathway underlie dysregulation of mitochondrial dynamics and promote mitochondrial oxidative stress. These processes are further modulated by acetyltransferases including sirtuin 1 and sirtuin 3, the former regulating nuclear acetylation and the latter regulating mitochondrial acetylation. The regulation of mitochondrial functions by microRNAs forms an additional layer of molecular control of mitochondrial oxidative stress. Alcohol further exacerbates mitochondrial oxidative stress induced by overnutrition and promotes the development of metabolic diseases.

A/ASP/VAL allele combination of IGF1R, IRS2, and UCP2 genes is associated with better metabolic profile, preserved energy expenditure parameters, and low mortality rate in longevity

A large array of gene involved in human longevity seems to be in relationship with insulin/IGF1 pathway. However, if such genes interact each other, or with other genes, to reduce the age-related metabolic derangement and determine the long-lived phenotype has been poorly investigated. Thus, we tested the role of interchromosomal interactions among IGF1R, IRS2, and UCP2 genes on the probability to reach extreme old age in 722 unrelated Italian subjects (401 women and 321 men; mean age, 62.83 ± 25.30 years) enrolled between 1998 and 1999. In particular, the G/A-IGF1R, Gly/Asp-IRS2, and Ala/Val-UCP2 allele combination was tested for association with longevity, metabolic profile and energy expenditure parameters. The effect on all-cause and cause-specific mortality rate was also assessed after a mean follow-up of 6 years. The analysis revealed that AAV allele combination is associated with a decreased all-cause mortality risk (HR, 0.72; 95% CI, 0.63-0.91; p = 0.03) and with a higher probability to reach the extreme of old age (OR, 3.185; 95% CI, 1.63-6.19; p = 0.0006). The analysis also revealed lower HOMA-IR (Diff, -0.532, 95% CI, 0.886-0.17; p = 0.003), higher respiratory quotient (Diff, 0.0363, 95% CI, 0.014-0.05; p = 0.001), and resting metabolic rate (Diff, 101.80693, 95% CI, -5.26-204.278; p = 0.038) for AAV allele combination. In conclusion, A-IGF1R/Asp-IRS2/Val-UCP2 allele combination is associated with a decreased all-cause mortality risk and with an increased chance of longevity. Such an effect is probably due to the combined effect of IGF1R, IRS2, and UCP2 genes on energy metabolism and on the age-related metabolic remodeling capacity.

Variation in the uncoupling protein 2 and 3 genes and human performance

Uncoupling proteins 2 and 3 (UCP2 and UCP3) may negatively regulate mitochondrial ATP synthesis and, through this, influence human physical performance. However, human data relating to both these issues remain sparse. Examining the association of common variants in the UCP3/2 locus with performance phenotypes offers one means of investigation. The efficiency of skeletal muscle contraction, delta efficiency (DE), was assessed by cycle ergometry in 85 young, healthy, sedentary adults both before and after a period of endurance training. Of these, 58 were successfully genotyped for the UCP3-55C>T (rs1800849) and 61 for the UCP2-866G>A (rs659366) variant. At baseline, UCP genotype was unrelated to any physical characteristic, including DE. However, the UCP2-866G>A variant was independently and strongly associated with the DE response to physical training, with UCP2-866A allele carriers exhibiting a greater increase in DE with training (absolute change in DE of -0.2 ± 3.6% vs. 1.7 ± 2.8% vs. 2.3 ± 3.7% for GG vs. GA vs. AA, respectively; P = 0.02 for A allele carriers vs. GG homozygotes). In multivariate analysis, there was a significant interaction between UCP2-866G>A and UCP3-55C>T genotypes in determining changes in DE (adjusted R(2) = 0.137; P value for interaction = 0.003), which was independent of the effect of either single polymorphism or baseline characteristics. In conclusion, common genetic variation at the UCP3/2 gene locus is associated with training-related improvements in DE, an index of skeletal muscle performance. Such effects may be mediated through differences in the coupling of mitochondrial energy transduction in human skeletal muscle, but further mechanistic studies are required to delineate this potential role.

The role of uncoupling protein 2 (UCP2) on the development of type 2 diabetes mellitus and its chronic complications

It is well established that genetic factors play an important role in the development of type 2 diabetes mellitus (DM2) and its chronic complications, and that genetically susceptible subjects can develop the disease after being exposed to environmental risk factors. Therefore, great efforts have been made to identify genes associated with DM2. Uncoupling protein 2 (UCP2) is expressed in several tissues, and acts in the protection against oxidative stress; in the negative regulation of insulin secretion by beta cells, and in fatty acid metabolism. All these mechanisms are associated with DM2 pathogenesis and its chronic complications. Therefore, UCP2 is a candidate gene for the development of these disorders. Indeed, several studies have reported that three common polymorphisms in UCP2 gene are possibly associated with DM2 and/or obesity. Only a few studies investigated these polymorphisms in relation to chronic complications of diabetes, with inconclusive results.

UCP2 -866G/A and Ala55Val, and UCP3 -55C/T polymorphisms in association with type 2 diabetes susceptibility: a meta-analysis study

AIMS/HYPOTHESIS

A meta-analysis was performed to assess the association between the UCP2 -866G/A, UCP2 Ala55Val and UCP3 -55C/T polymorphisms and type 2 diabetes susceptibility.

METHODS

A literature-based search was conducted to identify all relevant studies. The fixed or random effect pooled measure was calculated mainly at the allele level to determine heterogeneity bias among studies. Further analyses were performed that stratified for ethnicity.

RESULTS

We examined 17 publications. Stratified analysis for ethnicity and sensitivity analysis revealed that there was no heterogeneity between studies for these variants. Using an additive model, no significant association of the UCP2 -866G/A polymorphism with type 2 diabetes risk was observed, either in participants of Asian (OR 1.05, 95% CI 0.96, 1.16) or of European (OR 1.03, 95% CI 0.99, 1.07) descent. Neither the UCP2 Ala55Val nor the UCP3 -55C/T polymorphism showed any significant association with type 2 diabetes risk in Europeans (OR 1.04, 95% CI 0.98, 1.09 for Ala55Val; OR 1.04, 95% CI 1.00, 1.09 for -55C/T). In contrast, a statistically significant association was observed for both polymorphisms in participants of Asian descent (OR 1.23, 95% CI 1.12, 1.36 for Ala55Val; OR 1.15, 95% CI 1.03, 1.28 for -55C/T).

CONCLUSIONS/INTERPRETATION

Our meta-analysis suggests that the UCP2 -866G/A polymorphism is unlikely to be associated with increased type 2 diabetes risk in the populations investigated. In contrast, our results indicate that the UCP2 Ala55Val and UCP3 -55C/T polymorphisms may indeed be risk factors for susceptibility to type 2 diabetes in individuals of Asian descent, but not in individuals of European descent. This conclusion warrants confirmation by further studies.

Glucose tolerance, insulin sensitivity and insulin release in European non-diabetic carriers of a polymorphism upstream of CDKN2A and CDKN2B

AIMS/HYPOTHESIS

The aim of this study was to investigate the association of the rs10811661 polymorphism near the CDKN2B/CDKN2A genes with glucose tolerance, insulin sensitivity and insulin release in three samples of white people with European ancestry.

METHODS

Sample 1 comprised 845 non-diabetic offspring of type 2 diabetes patients recruited in five European centres participating in the EUGENE2 study. Samples 2 and 3 comprised, respectively, 864 and 524 Italian non-diabetic participants. All individuals underwent an OGTT. Screening for the rs10811661 polymorphism was performed using a TaqMan allelic discrimination assay.

RESULTS

The rs10811661 polymorphism did not show a significant association with age, BMI and insulin sensitivity. Participants carrying the TT genotype showed a significant reduction in insulin release, measured by an OGTT-derived index, compared with carriers of the C allele, in the three samples. When these results were pooled with those of three published studies, and meta-analysed with a random-effects model, the T allele was significantly associated with reduced insulin secretion (-35.09 [95% CI 14.68-55.52], p = 0.0008 for CC+CT vs TT; and -29.45 [95% CI 9.51-49.38], p = 0.0038, for the additive model). In addition, in our three samples, participants carrying the TT genotype exhibited an increased risk for impaired glucose tolerance (IGT) compared with carriers of the C allele (OR 1.55 [95% CI 1.20-1.95] for the meta-analysis of the three samples).

CONCLUSIONS/INTERPRETATION

Our data, together with the meta-analysis of previously published studies, show that the rs10811661 polymorphism is associated with impaired insulin release and IGT, suggesting that this variant may contribute to type 2 diabetes by affecting beta cell function.

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.