Muscle-UCP3 in the regulation of energy metabolism.

Uncoupling protein-3 (UCP3) is a mitochondria-regulatory protein with potential energy- homeostatic functions. This study explores the role of UCP3 in the regulation of muscle- and energy metabolism. UCP3 is critical for tuning substrate utilization, favoring lipid oxidation, particularly in conditions of high-fat availability. While UCP3 is non-essential for lipid oxidation during energy excess, it proves vital during fasting, indicating an energy-homeostatic trait. Preliminary evidence indicates UCP3' promotion of glucose uptake and oxidation, at least in conditions of high glucose/low fat availability. However, the dynamics of how fats and glucose differentially influence UCP3 remain undefined. UCP3 exhibits inducible proton transport and uncoupling activity, operating in a dual manner: a resting state with no/low activity and an activated state in the presence of activators. Uncoupling may enhance thermogenesis in specific conditions and in the presence of activators such as fatty acids, thyroid hormones, and catecholamines. This energy-dissipative activity adapts to varying energy availability, balancing energy dissipation with fatty acid oxidation to optimize whole-body energy homeostasis: fasting triggers UCP3 upregulation, enhancing lipid utilization while suppressing uncoupling. Additionally, UCP3 upregulation induces glucose and lipid disposal from the bloodstream and decreases tri-/diglyceride storage in muscle. This process improves mitochondrial functionality and insulin signaling, leading to enhanced systemicgluco-metabolic balance and protection from metabolic conditions. Reviewed evidence suggests that UCP3 plays a crucial role in adapting the system to changing energy conditions. However, the precise role of UCP3 in regulating metabolism requires further elucidation.

Uncoupling Protein 3 Promotes the Myogenic Differentiation of Type IIb Myotubes in C2C12 Cells.

Uncoupling protein 3 (Ucp3) is an important transporter within mitochondria and is mainly expressed in skeletal muscle, brown adipose tissue and the myocardium. However, the effects of Ucp3 on myogenic differentiation are still unclear. This study evaluated the effects of Ucp3 on myogenic differentiation, myofiber type and energy metabolism in C2C12 cells. Gain- and loss-of-function studies revealed that Ucp3 could increase the number of myotubes and promote the myogenic differentiation of C2C12 cells. Furthermore, Ucp3 promoted the expression of the type IIb myofiber marker gene myosin heavy chain 4 (Myh4) and decreased the expression of the type I myofiber marker gene myosin heavy chain 7 (Myh7). In addition, energy metabolism related to the expression of PPARG coactivator 1 alpha (Pgc1-α), ATP synthase, H+ transportation, mitochondrial F1 complex, alpha subunit 1 (Atp5a1), lactate dehydrogenase A (Ldha) and lactate dehydrogenase B (Ldhb) increased with Ucp3 overexpression. Ucp3 could promote the myogenic differentiation of type IIb myotubes and accelerate energy metabolism in C2C12 cells. This study can provide the theoretical basis for understanding the role of Ucp3 in energy metabolism.

The influence of six polymorphisms of uncoupling protein 3 (UCP3) gene and childhood obesity: a case-control study.

BACKGROUND: Obesity is defined as a multifactorial disease, marked by excessive accumulation of body fat, responsible for compromising the individual's health over the years. The energy balance is essential for the proper functioning of the body, as the individual needs to earn and spend energy in a compensatory way. Mitochondrial Uncoupling Proteins (UCP) help in energy expenditure through heat release and genetic polymorphisms could be responsible for reducing energy consumption to release heat and consequently generate an excessive accumulation of fat in the body. Thus, this study aimed to investigate the potential association between six UCP3 polymorphisms, that have not yet been represented in ClinVar®, and pediatric obesity susceptibility. METHODS: A case-control study was conducted with 225 children from Central Brazil. The groups were subdivided into obese (123) and eutrophic (102) individuals. The polymorphisms rs15763, rs1685354, rs1800849, rs11235972, rs647126, and rs3781907 were determined by real-time Polymerase Chain Reaction (qPCR). RESULTS: Biochemical and anthropometric evaluation of obese group showed higher levels of triglycerides, insulin resistance, and LDL-C and low level of HDL-C. Insulin resistance, age, sex, HDL-C, fasting glucose, triglyceride levels, and parents' BMI explained up to 50% of body mass deposition in the studied population. Additionally, obese mothers contribute 2 × more to the Z-BMI of their children than the fathers. The SNP rs647126 contributed to 20% to the risk of obesity in children and the SNP rs3781907 contribute to 10%. Mutant alleles of UCP3 increase the risk for triglycerides, total cholesterol, and HDL-C levels. The polymorphism rs3781907 is the only one that could not be a biomarker for obesity as the risk allele seem to be protective gains the increase in Z-BMI in our pediatric population. Haplotype analysis demonstrated two SNP blocks (rs15763, rs647126, and rs1685534) and (rs11235972 and rs1800849) that showed linkage disequilibrium, with LOD 76.3% and D' = 0.96 and LOD 57.4% and D' = 0.97, respectively. CONCLUSIONS: The causality between UCP3 polymorphism and obesity were not detected. On the other hand, the studied polymorphism contributes to Z-BMI, HOMA-IR, triglycerides, total cholesterol, and HDL-C levels. Haplotypes are concordant with the obese phenotype and contribute minimally to the risk of obesity.

Expressions of mRNA and encoded proteins of mitochondrial uncoupling protein genes (UCP1, UCP2, and UCP3) in epicardial and mediastinal adipose tissue and associations with coronary artery disease.

Objective: To evaluate the expression of UCP1, UCP2, and UCP3 mRNA and encoded proteins in epicardial and mediastinal adipose tissues in patients with coronary artery disease (CAD). Subjects and methods: We studied 60 patients with CAD and 106 patients undergoing valve replacement surgery (controls). Expression levels of UCP1, UCP2, and UCP3 mRNA and encoded proteins were measured by quantitative real-time PCR and Western blot analysis, respectively. Results: : We found increased UCP1, UCP2, and UCP3 mRNA levels in the epicardial adipose tissue in the CAD versus the control group, and higher UCP1 and UCP3 mRNA expression in the epicardial compared with the mediastinal tissue in the CAD group. There was also increased expression of UCP1 protein in the epicardial tissue and UCP2 protein in the mediastinum tissue in patients with CAD. Finally, UCP1 expression was associated with levels of fasting plasma glucose, and UCP3 expression was associated with levels of high-density lipoprotein cholesterol and low-density cholesterol in the epicardial tissue. Conclusion: Our study supports the hypothesis that higher mRNA expression by UCP genes in the epicardial adipose tissue could be a protective mechanism against the production of reactive oxygen species and may guard the myocardium against damage. Thus, UCP levels are essential to maintain the adaptive phase of cardiac injury in the presence of metabolic disorders.

Oxidative damage and mitochondrial functionality in hearts from KO UCP3 mice housed at thermoneutrality.

The antioxidant role of mitochondrial uncoupling protein 3 (UCP3) is controversial. This work aimed to investigate the effects of UCP3 on the heart of mice housed at thermoneutral temperature, an experimental condition that avoids the effects of thermoregulation on mitochondrial activity and redox homeostasis, preventing the alterations related to these processes from confusing the results caused by the lack of UCP3. WT and KO UCP3 mice were acclimatized at 30 °C for 4 weeks and hearts were used to evaluate metabolic capacity and redox state. Tissue and mitochondrial respiration, the activities of the mitochondrial complexes, and the protein expression of mitochondrial complexes markers furnished information on mitochondrial functionality. The levels of lipid and protein oxidative damage markers, the activity of antioxidant enzymes, the reactive oxygen species levels, and the susceptibility to in vitro Fe-ascorbate-induced oxidative stress furnished information on redox state. UCP3 ablation reduced tissue and mitochondrial respiratory capacities, not affecting the mitochondrial content. In KO UCP3 mice, the mitochondrial complexes activities were lower than in WT without changes in their content. These effects were accompanied by an increase in the level of oxidative stress markers, ROS content, and in vitro susceptibility to oxidative stress, notwithstanding that the activities of antioxidant enzymes were not affected by UCP3 ablation. Such modifications are also associated with enhanced activation/phosphorylation of EIF2α, a marker of integrated stress response and endoplasmic reticulum stress (GRP778 BIP). The lack of UCP3 makes the heart more prone to oxidative insult by reducing oxygen consumption and increasing ROS. Our results demonstrate that UCP3 helps the cell to preserve mitochondrial function by mitigating oxidative stress.

Long-term GABA administration improves FNDC5, TFAM, and UCP3 mRNA expressions in the skeletal muscle and serum irisin levels in chronic type 2 diabetic rats.

In this study, we aimed to investigate whether the anti-diabetic effects of γ-aminobutyric acid (GABA) and insulin can be mediated through the regulation of gene expression related to irisin production and mitochondrial biogenesis in type 2 diabetic mellitus (T2DM) rats. Four groups (n = 6) were used in this study: control, T2DM, T2DM + insulin, and T2DM + GABA groups. After T2DM induction for 3 months (high-fat diet + 35 mg/kg streptozotocin) and treatment with GABA or insulin for 3 months, circulating levels of FBG, triglyceride, LDL, Ox-LDL, and insulin as well as hepatic and serum irisin levels were measured. The mRNA expressions of fibronectin type III domain-containing protein 5 (FNDC5), mitochondrial transcription factor A (TFAM), and mitochondrial uncoupling protein 3 (UCP3) were also evaluated in the skeletal muscle of all groups. GABA therapy improved the FBG and insulin levels in diabetic rats. Insulin treatment significantly reduced FBG and failed to maintain glucose close to the control level. Insulin or GABA therapy significantly decreased the levels of LDL, Ox-LDL, and HOMA-IR index. Circulating irisin levels were markedly decreased in insulin-treated group, while irisin levels did not show significant changes in GABA-treated group compared with control group. GABA or insulin therapy increased mRNA expressions of TFAM and UCP3 in diabetic rats. GABA therapy also led to a significant increase in FNDC5 mRNA. Our findings suggest that the anti-diabetic effect of GABA may be mediated, in part, by a decrease in Ox-LDL levels and an increase in the levels of irisin as well as FNDC5, TFAM, and UCP3 gene expression in T2DM rats.

Uncoupling Proteins in Striated Muscle Tissue: Known Facts and Open Questions.

Significance: Uncoupling proteins (UCPs) are a family of proteins that allow proton leakage across the inner mitochondrial membrane. Although UCP1, also known as thermogenin, is well known and important for heat generation in brown adipose tissue, striated muscles express two distinct members of UCP, namely UCP2 and UCP3. Unlike UCP1, the main function of UCP2 and UCP3 does not appear to be heat production. Recent Advances: Interestingly, UCP2 is the main isoform expressed in cardiac tissues, whereas UCP3 is the dominant isoform in skeletal muscles. In the past years, researchers have started to investigate the regulation of UCP2 and UCP3 expression in striated muscles. Furthermore, concepts about the proposed functions of UCP2 and UCP3 in striated muscles are developed but are still a matter of debate. Critical Issues: Potential functions of UCP2 and UCP3 in striated muscles include a role in protection against mitochondria-dependent oxidative stress, as transporter for pyruvate, fatty acids, and protons into and out of the mitochondria, and in metabolic sensing. In this context, the different isoform expression of UCP2 and UCP3 in the skeletal and cardiac muscle may be related to different metabolic requirements of the two organs. Future Directions: The level of expression of UCP2 and UCP3 in striated muscles changes in different disease stages. This suggests that UCPs may become drug targets for therapy in the future. Antioxid. Redox Signal. 37, 324-335.

Association of UCP3 Polymorphisms with Nonalcoholic Steatohepatitis and Metabolic Syndrome in Nonalcoholic Fatty Liver Disease Brazilian Patients.

Background: We investigated the possible association of uncoupling protein 3 gene (UCP3) single nucleotide polymorphisms (SNPs) with nonalcoholic steatohepatitis (NASH) and metabolic syndrome (MetS) in nonalcoholic fatty liver disease (NAFLD) Brazilian patients. Methods:UCP3 SNPs rs1726745, rs3781907, and rs11235972 were genotyped in 158 biopsy-proven NAFLD Brazilian patients. Statistics was performed with JMP, R, and SHEsis softwares. Results: The TT genotype of rs1726745 was associated with less occurrence of MetS (P = 0.006) and with lower body mass index (BMI) in the entire NAFLD sample (P = 0.01) and in the NASH group (P = 0.02). The rs1726745-T was associated with lower values of AST (P = 0.001), ALT (P = 0.0002), triglycerides (P = 0.01), and total cholesterol (P = 0.02) in the entire NAFLD sample. Between groups, there were lower values of aminotransferases strictly in individuals with NASH (AST, P = 0.002; ALT, P = 0.0007) and with MetS (AST, P = 0.002; ALT, P = 0.001). The rs3781907-G was associated with lower GGT elevation values in the entire NAFLD sample (P = 0.002), in the NASH group (P = 0.004), and with MetS group (P = 0.003) and with protection for advanced fibrosis (P = 0.01). The rs11235972-A was associated with lower GGT values in the entire NAFLD sample (P = 0.006) and in the NASH group (P = 0.01) and with MetS group (P = 0.005), with fibrosis absence (P = 0.01) and protection for advanced fibrosis (P = 0.01). The TAA haplotype was protective for NASH (P = 0.002), and TGG haplotype was protective for MetS (P = 0.01). Conclusion:UCP3 gene variants were associated with protection against NASH and MetS, in addition to lower values of liver enzymes, lipid profile, BMI and, lesser fibrosis severity in the studied population.

Uncoupling proteins: are they involved in vitamin D3 protective effect against high-fat diet-induced cardiac apoptosis in rats?

This study aimed to assess the impact of high-fat diet (HFD) and vitamin D3 supplementation on cardiac apoptosis, inflammation, oxidative stress, and cardiac uncoupling proteins (UCPs) 2&3 expression. Forty rats were fed either (45%) or (10%) fat diet with or without vitamin D3 (500 U/kg/day) for 6 months, then cardiac tissue expression of Bax, Bcl2, Fas, Fas-L (markers for apoptotic pathways), TNF-α, MDA7, GPX1 (inflammatory and oxidative markers) and UCP 2&3 were assessed. Results revealed the enhancement of intrinsic and extrinsic cardiomyocyte apoptosis cascades and increased inflammatory and oxidative burdens on the heart in HFD rats. Downregulation of UCP2 and upregulation of UCP3 gene expression at 6 months. After vitamin D3 supplementation with HFD, cardiac apoptotic, inflammatory and oxidative markers were mitigated and expression of UCP3 was downregulated and UCP2 was upregulated. This work highlights the novel cardioprotective effect of vitamin D3 in the experimental model of HFD feeding through the downregulation of UCP3.

Detecting Single Nucleotide Polymorphisms in MEF2B and UCP3 and Elucidating Their Association with Sheep Growth Traits.

Herein we detected single nucleotide polymorphisms in MEF2B and UCP3 by DNA sequencing and the KASPar technology and analyzed their association with sheep growth traits. Two synonymous mutations, g.1826 C > T and g.10266 G > C, were detected, respectively, and they were found to be significantly associated with sheep growth traits (p < 0.05). In case of MEF2B g.1826 C > T, the average body weight and chest and cannon circumference of sheep with the CC genotype were significantly higher than those of sheep with the CT and TT genotypes (p < 0.05). Moreover, in case of UCP3 g.10266 G > C, the average body weight and chest and cannon circumference of sheep with the GG genotype were significantly higher than those of sheep with the GC and CC genotypes (p < 0.05). Moreover, the average body weight of sheep with the CC/GG genotype was higher compared with those of other genotype combinations. We also assessed MEF2B and UCP3 expression in different sheep tissues, confirming their expression in all examined tissues. To summarize, we believe that the polymorphisms identified in MEF2B and UCP3 can serve as molecular markers for sheep growth traits.

Ethnicity Differences in the Association of UCP1-3826A/G, UCP2-866G/A and Ala55Val, and UCP3-55C/T Polymorphisms with Type 2 Diabetes Mellitus Susceptibility: An Updated Meta-Analysis.

BACKGROUND: The relationship between uncoupling protein (UCP) 1-3 polymorphisms and susceptibility to type 2 diabetes mellitus (T2DM) has been extensively studied, while conclusions remain contradictory. Thus, we performed this meta-analysis to elucidate whether the UCP1-3826A/G, UCP2-866G/A, Ala55Val, and UCP3-55C/T polymorphisms are associated with T2DM. METHODS: Eligible studies were searched from PubMed, Cochrane Library, and Web of Science database before 12 July 2020. Pooled odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated to evaluate the strength of the association. Heterogeneity analysis, subgroup analysis, sensitivity analysis, and publication bias were also performed. RESULTS: A total of 38 case-control studies were included in this meta-analysis. The overall results revealed significant association between T2DM and the UCP2 Ala55Val polymorphism (recessive model: OR = 1.25, 95% CI 1.12-1.40, P < 0.01; homozygous model: OR = 1.33, 95% CI 1.03-1.72, P = 0.029, respectively). In subgroup analysis stratified by ethnicity, T2DM risk was increased with the UCP2 Ala55Val polymorphism (allele model: OR = 1.17, 95% CI 1.02-1.34, P = 0.023; recessive model: OR = 1.28, 95% CI 1.13-1.45, P < 0.01; homozygous model: OR = 1.39, 95% CI 1.05-1.86, P = 0.023, respectively), while decreased with the UCP2-866G/A polymorphism in Asians (dominant model: OR = 0.86, 95% CI 0.74-1.00, P = 0.045). CONCLUSIONS: Our results demonstrate that the UCP2-866G/A polymorphism is protective against T2DM, while the UCP2 Ala55Val polymorphism is susceptible to T2DM in Asians.

Effect of -55C/T Polymorphism of Uncoupling Protein 3 Gene on Risk for New-Onset Diabetes in Chinese Peritoneal Dialysis Patients: A Prospective Cohort Study.

BACKGROUND: A high-glucose load in therapy can cause new-onset diabetes (NOD) in peritoneal dialysis (PD) patients. Genetic variability may result in risk modulation. OBJECTIVES: This study aims to investigate the association between -55C/T polymorphism of uncoupling protein 3 (UCP3) gene and the risk of NOD in PD patients. METHODS: Nondiabetic incident PD patients between May 2005 and January 2017 were recruited (n = 154). -55C/T polymorphism of the UCP3 was genotyped in all participants at baseline. The cohort of wild group (-55CC) and mutant group (-55CT or -55TT) was built based on the genotypic difference. Insulin resistance was evaluated by the homeostasis model assessment method (HOMA-IR) during the follow-up. Binary logistic regression was performed to explore the association between HOMA-IR and genotypes. Competitive risk analysis was used to analyze the impact of -55C/T polymorphism of UCP3 on risk for NOD. RESULTS: The cohort was followed for up to 164.6 months (median: 58.3 months; interquartile range: 30.7 months). During the follow-up, 14 NODs occurred in the mutant group, while only 3 occurred in the wild group. Patients in the mutant group had higher HOMA-IR (Odd ratio: 2.210; 95% CI: 1.043-4.680; p = 0.038). Genotype with the variant T allele turned out to be an independent predictor for NOD morbidity (HR: 7.639; 95% CI: 1.798-32.451; p = 0.006). CONCLUSIONS: The variant of T allele of UCP3 -55C/T polymorphism was an independent predictor for NOD in PD patients. Early identification of the genotype may provide scientific basis for patients' clinic management.

Nox4 mediates skeletal muscle metabolic responses to exercise.

OBJECTIVE: The immediate signals that couple exercise to metabolic adaptations are incompletely understood. Nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) produces reactive oxygen species (ROS) and plays a significant role in metabolic and vascular adaptation during stress conditions. Our objective was to determine the role of Nox4 in exercise-induced skeletal muscle metabolism. METHODS: Mice were subjected to acute exercise to assess their immediate responses. mRNA and protein expression responses to Nox4 and hydrogen peroxide (H2O2) were measured by qPCR and immunoblotting. Functional metabolic flux was measured via ex vivo fatty acid and glucose oxidation assays using 14C-labeled palmitate and glucose, respectively. A chronic exercise regimen was also utilized and the time to exhaustion along with key markers of exercise adaptation (skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase activity) were measured. Endothelial-specific Nox4-deficient mice were then subjected to the same acute exercise regimen and their subsequent substrate oxidation was measured. RESULTS: We identified key exercise-responsive metabolic genes that depend on H2O2 and Nox4 using catalase and Nox4-deficient mice. Nox4 was required for the expression of uncoupling protein 3 (Ucp3), hexokinase 2 (Hk2), and pyruvate dehydrogenase kinase 4 (Pdk4), but not the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (Pgc-1α). Global Nox4 deletion resulted in decreased UCP3 protein expression and impaired glucose and fatty acid oxidization in response to acute exercise. Furthermore, Nox4-deficient mice demonstrated impaired adaptation to chronic exercise as measured by the time to exhaustion and activity of skeletal muscle citrate synthase and beta-hydroxyacyl-coA-dehydrogenase. Importantly, mice deficient in endothelial-Nox4 similarly demonstrated attenuated glucose and fatty acid oxidation following acute exercise. CONCLUSIONS: We report that H2O2 and Nox4 promote immediate responses to exercise in skeletal muscle. Glucose and fatty acid oxidation were blunted in the Nox4-deficient mice post-exercise, potentially through regulation of UCP3 expression. Our data demonstrate that endothelial-Nox4 is required for glucose and fatty acid oxidation, suggesting inter-tissue cross-talk between the endothelium and skeletal muscle in response to exercise.

Uncoupling protein gene UCP1-3826A/G, UCP2 Ins/Del and UCP3-55C/T polymorphisms in obese Turkish children.

BACKGROUND: Mitochondrial uncoupling proteins (UCP) 1, 2 and 3 are members of the anion carrier protein family located in the inner mitochondrial membrane. There are various controversial reports on UCP genotypes and obesity in adults and children. This study aims to investigate the link between mostly studied UCP polymorphisms (UCP1-3826A/G, UCP2 Insertion/Deletion (Ins/Del) polymorphism of exon 8, and UCP3-55C/T Polymorphisms) and obesity in Turkish children. Furthermore, the relationships of UCP polymorphisms are also analyzed within the scope of metabolic parameters of obese children. METHODS: Molecular screening of the UCP1, UCP2, and UCP3 gene polymorphisms was carried out in 189 children aged 6 to 18 years, 102 of who had exogenous obesity (54 girls) and 87 of whom were healthy controls (48 girls). In the obese group, fasting lipids, glucose and insulin levels were measured. In 60 obese children, an oral glucose tolerance test (OGTT) was performed with 0, 30, 60, 90 and 120 minutes of sampling for plasma glucose and insulin levels. RESULTS: The frequency of UCP polymorphisms was similar in obese and non-obese children. In obese children, fasting lipids, glucose and insulin levels were not different among the UCP 1, 2 and 3 genotypes. While no relationship was found between the UCP 1 and 3 genotypes and glucose/insulin levels during OGTT, carriers of the Insertion allele with UCP2 Ins/Del polymorphism had significantly higher 30-minute insulin levels (p=0.018). CONCLUSIONS: Polymorphisms of the UCP1-3826A/G, UCP2 Ins/Del, and UCP3-55C/T are not associated with obesity and related pathologies in Turkish children. However, the presence of the Ins allele of the UCP2 gene has been found to have an unfavorable influence on early insulin excursion after glucose loading.

UCP3 reciprocally controls CD4+ Th17 and Treg cell differentiation.

Uncoupling proteins (UCPs) are members of the mitochondrial anion carrier superfamily that can mediate the transfer of protons into the mitochondrial matrix from the intermembrane space. We have previously reported UCP3 expression in thymocytes, mitochondria of total splenocytes and splenic lymphocytes. Here, we demonstrate that Ucp3 is expressed in peripheral naive CD4+ T cells at the mRNA level before being markedly downregulated following activation. Non-polarized, activated T cells (Th0 cells) from Ucp3-/- mice produced significantly more IL-2, had increased expression of CD25 and CD69 and were more proliferative than Ucp3+/+ Th0 cells. The altered IL-2 expression observed between T cells from Ucp3+/+ and Ucp3-/- mice may be a factor in determining differentiation into Th17 or induced regulatory (iTreg) cells. When compared to Ucp3+/+, CD4+ T cells from Ucp3-/- mice had increased FoxP3 expression under iTreg conditions. Conversely, Ucp3-/- CD4+ T cells produced a significantly lower concentration of IL-17A under Th17 cell-inducing conditions in vitro. These effects were mirrored in antigen-specific T cells from mice immunized with KLH and CT. Interestingly, the altered responses of Ucp3-/- T cells were partially reversed upon neutralisation of IL-2. Together, these data indicate that UCP3 acts to restrict the activation of naive T cells, acting as a rheostat to dampen signals following TCR and CD28 co-receptor ligation, thereby limiting early activation responses. The observation that Ucp3 ablation alters the Th17:Treg cell balance in vivo as well as in vitro suggests that UCP3 is a potential target for the treatment of Th17 cell-mediated autoimmune diseases.

Vitamin D-vitamin D receptor system down-regulates expression of uncoupling proteins in brown adipocyte through interaction with Hairless protein.

Our previous study showed that feeding mice with vitamin D deficiency diet markedly alleviated high-fat-diet-induced overweight, hyperinsulinemia, and hepatic lipid accumulation. Moreover, vitamin D deficiency up-regulated the expression of uncoupling protein 3 (Ucp3) in white adipose tissue (WAT) and brown adipose tissue (BAT). The present study aimed to further investigate the effects of vitamin D and vitamin D receptor (Vdr) on Ucp1-3 (Ucps) expression in brown adipocyte and the mechanism involved in it. Rat primary brown adipocytes were separated and purified. The effects of the 1,25(OH)2D3 (1,25-dihydroxyvitamin D3; the hormonal form of vitamin D) and Vdr system on Ucps expression in brown adipocytes were investigated in basal condition and activated condition by isoproterenol (ISO) and triiodothyronine (T3). Ucps expression levels were significantly down-regulated by 1,25(OH)2D3 in the activated brown adipocyte. Vdr silencing reversed the down-regulation of Ucps by 1,25(OH)2D3, whereas Vdr overexpression strengthened the down-regulation effects. Hairless protein did express in brown adipocyte and was localized in cell nuclei. 1,25(OH)2D3 increased Hairless protein expression in the cell nuclei. Hairless (Hr) silencing notably elevated Ucps expression in activated condition induced by ISO and T3. Moreover, immunoprecipitation results revealed that Vdr could interact with Hairless, which might contribute to decreasing expression of Vdr target gene Ucps. These data suggest that vitamin D suppresses expression of Ucps in brown adipocyte in a Vdr-dependent manner and the corepressor Hairless protein probably plays a role in the down-regulation.

Analysis of association between common variants of uncoupling proteins genes and diabetic retinopathy in a Chinese population.

BACKGROUND: The aim of this study was to explore the association between diabetic retinopathy (DR) and the variants of uncoupling proteins (UCPs) genes in a Chinese population of type 2 diabetes, in total and in patients of different glycemic status separately. METHODS: This case-control study included a total of 3107 participants from two datasets, among which 662 were DR patients (21.31%). Eighteen tag single nucleotide polymorphisms (SNPs) of UCP1, UCP2, and UCP3 were selected as genetic markers. TaqMan probes, Sequenom MassARRAY MALDI-TOF mass spectrometry platform and Affymetrix Genome-Wide Human SNP Array were used for genotyping. Online SHEsis software was used for association analysis. Bonferroni correction was used for multiple comparisons correction. RESULTS: Three SNPs of UCP1: rs7688743 (A allele, OR = 1.192, p = 0.013), rs3811787 (T allele, OR = 0.863, p = 0.023), and rs10011540 (G allele, OR = 1.368, p = 0.004) showed association with DR after the adjustment of glucose, but only rs10011540 was marginally significantly associated with DR when Bonferroni correction was strictly applied (padj = 0.048). In patients with uncontrolled glucose, rs7688743 (A allele, p = 0.012, OR = 1.309), rs10011540 (G allele, p = 0.033, OR = 1.432), and rs3811787 (T allele, p = 0.022, OR = 0.811) were associated with DR, while in participants with well controlled glucose, the rs2734827 of UCP3 was associated with DR (A allele, p = 0.017, OR = 0.532). Rs3811787 of UCP1 showed a protective effect to sight threatening DR (T allele, p = 0.007, OR = 0.490), and the association existed after the adjustment for environmental factors and the correction. In patients with uncontrolled glucose, the rs3811787 of UCP1 (T allele, p = 0.017, OR = 0.467) and the rs591758 of UCP3 (C allele, p = 0.026, OR = 0.103) were associated with STDR. While in those with well controlled glucose, only the rs7688743 of UCP1 showed a protective effect (A allele, p = 0.024, OR = 0.049). None of the associations remain significant when Bonferroni correction was strictly applied (all p < 0.05). CONCLUSIONS: The rs10011540 and rs3811787 of the UCP1 gene was marginally significantly associated with DR in Chinese type 2 diabetes patients. There might be different mechanisms of DR development in patients with different glycemic status.

Association of UCP1, UCP2 and UCP3 gene polymorphisms with cardiovascular disease risk factors in European adolescents: the HELENA study.

BACKGROUND: Cardiovascular diseases (CVDs) are responsible for 31% of all deaths worldwide. Genetic predisposition to CVDs in adolescents remains largely unknown. The aim of this study was to examine the association of UCP1, UCP2 and UCP3 gene polymorphisms with CVD risk factors in European adolescents. METHOD: A cross-sectional study that involves 1.057 European adolescents (12-18 years old) from the HELENA study. A total of 18 polymorphisms of UCP1, UCP2 and UCP3 genes were genotyped. We measured serum total cholesterol, high-density lipoprotein,low-density lipoprotein, ApoA1, ApoB, leptin, triglycerides, glucose, insulin and blood pressure, and calculated HOMA (homeostatic model assessment), Quantitative Insulin Sensitivity Check Index (QUICKI) and a CVD risk score. RESULTS: The G allele of UCP2 rs2735572 and T allele of UCP2 rs17132534 were associated with higher diastolic blood pressure (P = 0.001; false discovery rate [FDR] = 0.009 and P = 8e-04; FDR = 0.009, respectively). We observed that the AATAG haplotype of UCP1 was associated with higher serum ApoB/ApoA1 (P = 0.008; FDR = 0.031) and ApoB levels (P = 0.008; FDR = 0.031). Moreover, the ACC haplotype of UCP3 was associated with a higher CVD risk score (P = 0.0036; FDR = 0.01). CONCLUSIONS: Two UCP2 polymorphisms and haplotypes of UCP1 and UCP3 were associated with CVD risk factors. These findings suggest that UCPs may have a role in the development of CVD already in adolescents.

Inorganic nitrate and nitrite supplementation fails to improve skeletal muscle mitochondrial efficiency in mice and humans.

BACKGROUND: Inorganic nitrate, abundant in leafy green vegetables and beetroot, is thought to have protective health benefits. Adherence to a Mediterranean diet reduces the incidence and severity of coronary artery disease, whereas supplementation with nitrate can improve submaximal exercise performance. Once ingested, oral commensal bacteria may reduce nitrate to nitrite, which may subsequently be reduced to nitric oxide during conditions of hypoxia and in the presence of "nitrite reductases" such as heme- and molybdenum-containing enzymes. OBJECTIVE: We aimed to explore the putative effects of inorganic nitrate and nitrite on mitochondrial function in skeletal muscle. METHODS: Mice were subjected to a nitrate/nitrite-depleted diet for 2 wk, then supplemented with sodium nitrate, sodium nitrite, or sodium chloride (1 g/L) in drinking water ad libitum for 7 d before killing. Skeletal muscle mitochondrial function and expression of uncoupling protein (UCP) 3, ADP/ATP carrier protein (AAC) 1 and AAC2, and pyruvate dehydrogenase (PDH) were assessed by respirometry and Western blotting. Studies were also undertaken in human skeletal muscle biopsies from a cohort of coronary artery bypass graft patients treated with either sodium nitrite (30-min infusion of 10 µmol/min) or vehicle [0.9% (wt:vol) saline] 24 h before surgery. RESULTS: Neither sodium nitrate nor sodium nitrite supplementation altered mitochondrial coupling efficiency in murine skeletal muscle, and expression of UCP3, AAC1, or AAC2, and PDH phosphorylation status did not differ between the nitrite and saline groups. Similar results were observed in human samples. CONCLUSIONS: Sodium nitrite failed to improve mitochondrial metabolic efficiency, rendering this mechanism implausible for the purported exercise benefits of dietary nitrate supplementation. This trial was registered at clinicaltrials.gov as NCT04001283.

Bta-miR-152 affects intracellular triglyceride content by targeting the UCP3 gene.

According to our previous studies, bta-miR-152, PRKAA1 and UCP3 are differentially expressed in mammary gland tissues of high milk fat and low milk fat cows, and the trend in bta-miR-152 expression is opposite from those of PRKAA1 and UCP3. To further identify the function and regulatory mechanism of bta-miR-152 in milk fat metabolism, we investigated the effect of bta-miR-152 on cellular triglyceride content in bovine mammary epithelial cells cultured in vitro, on the basis of bta-miR-152 overexpression and inhibition assays. The target genes of bta-miR-152 were identified through qPCR, Western blotting and dual luciferase reporter gene detection. Compared with that in the control group, the expression of UCP3 was significantly lower in the bta-miR-152 mimic group, the expression of PRKAA1 was decreased, and the intracellular TAG content was significantly increased. After transfection with bta-miR-152 inhibitor, the expression of UCP3 increased significantly, and the expression of PRKAA1 decreased, but the difference was not significant; in addition, the intracellular TAG content decreased significantly. Therefore, we concluded that bta-miR-152 affects the intracellular TAG content by targeting UCP3.