Function Of Uncoupling Protein Research Articles

Regulation of UCP2 in nonalcoholic fatty liver disease: From mechanisms to natural product

AbstractNonalcoholic fatty liver disease (NAFLD) is a chronic liver disease associated with lipid deposition in liver cells and/or subsequent inflammation, excluding other known causes. NAFLD is a subset of metabolic syndrome that ranges from simple steatohepatitis (NASH), fibrosis to cirrhosis and hepatocellular carcinoma (HCC). At present, the pathogenesis of NAFLD remains unclear. Among the many factors that shape these transitions, uncoupling protein 2 (UCP2) may be involved in every stage of the disease. UCP2 is a carrier protein that responds to fatty acids (FAs) in mitochondrial intima and has a wide tissue distribution. However, the biological function of UCP2 has not been fully elucidated, and most of our current knowledge comes from cell and animal experiments. These data suggest that UCP2 plays a role in lipid metabolism, oxidative stress, apoptosis, and even cancer. In this review, we summarize the structure, distribution, and biological function of UCP2 and its role in the progression of NAFLD, as well as natural products targeting UCP2 to improve NAFLD.

UCP2 promotes NSCLC proliferation and glycolysis via the mTOR/HIF-1α signaling.

Metabolic disturbance is a hallmark of cancers. Targeting key metabolic pathways and metabolism-related molecular could be a potential therapeutic approach. Uncoupling protein 2 (UCP2) plays a pivotal part in the malignancy of cancer and its capacity to develop resistance to pharmaceutical interventions. However, it is unclear about the mechanism of how UCP2 acts in the tumor growth and metabolic reprogramming process in non-small cell lung cancer (NSCLC). Here, we conducted qRT-PCR to investigate the expression of UCP2 in both NSCLC tissues and cell lines. Subsequent functional studies including colony formation assay, CCK-8 assay, and glycolysis assay were conducted to investigate the functions of UCP2 in NSCLC. The regulatory mechanism of UCP2 toward the mammalian target of rapamycin (mTOR) and hypoxia-inducible factor-1 alpha (HIF-1α) signaling in NSCLC was confirmed through western blotting. We observed a significant upregulation of UCP2 in both NSCLC tissues and cell lines. The increased expression of UCP2 has a strong association with a worse outlook. Silencing UCP2 remarkably dampened NSCLC cell proliferation and glycolysis capacities. Mechanically, UCP2 promoted NSCLC tumorigenesis partially via regulating the mTOR/HIF-1α axis. Taken together, we explored the functions as well as the mechanisms of the UCP2/mTOR/HIF-1α axis in NSCLC progression, uncovering potential biological signatures and targets for NSCLC treatment.

Mitochondrial Damage and Hypertension: Another Dark Side of Sodium Excess.

Essential or primary hypertension (HT) is a worldwide health problem with no definitive cure. Although the exact pathogenesis of HT is not known, genetic factors, increased renin-angiotensin and sympathetic system activity, endothelial dysfunction, oxidative stress, and inflammation play a role in its development. Environmental factors such as sodium intake are also important for BP regulation, and excess sodium intake in the form of salt (NaCl, sodium chloride) increases blood pressure in salt-sensitive people. Excess salt intake increases extracellular volume, oxidative stress, inflammation, and endothelial dysfunction. Recent evidence suggests that increased salt intake also disturbs mitochondrial function both structurally and functionally which is important as mitochondrial dysfunction is associated with HT. In the current review, we have summarized the experimental and clinical data regarding the impact of salt intake on mitochondrial structure and function. Excess salt intake damage mitochondrial structure (e.g., shorter mitochondria with less cristae, increased mitochondrial fission, increased mitochondrial vacuolization). Functionally, high salt intake impairs mitochondrial oxidative phosphorylation and electron transport chain, ATP production, mitochondrial calcium homeostasis, mitochondrial membrane potential, and mitochondrial uncoupling protein function. Excess salt intake also increases mitochondrial oxidative stress and modifies Krebs cycle protein expressions. Studies have shown that high salt intake impairs mitochondrial structure and function. These maladaptive mitochondrial changes facilitate the development of HT especially in salt-sensitive individuals. High salt intake impairs many functional and structural components of mitochondria. These mitochondrial alterations along with increased salt intake promote the development of hypertension.

P-014 Inhibition of mitochondrial uncoupling proteins irreversibly arrests human spermatozoa motility

Abstract Study question Are mitochondrial uncoupling proteins (UCPs) expressed in human spermatozoa and if yes, what is their role? Summary answer UCP1, UCP2, and UCP3 are expressed in human spermatozoa. The inhibition of UCPs irreversibly arrests human spermatozoa motility without compromising viability. What is known already UCPs are expressed in the mitochondrial inner membrane, where they act as channels between the intermembrane space and the matrix. Six UCP homologs had already been identified in mammals (UCP1-6). UCPs act as regulators of reactive oxygen species (ROS) production, general cellular redox state, and mitochondrial function. The altered expression or function of UCPs is positively linked with the onset of metabolic diseases, such as obesity and diabetes mellitus. Male infertility is closely related to metabolic diseases since the testis is susceptible to metabolic alterations and oxidative stress, however, the expression and function of UCPs in human spermatozoa are unknown. Study design, size, duration We performed a control-versus-treatment study. High motility spermatozoa were isolated through density gradient centrifugation from human normozoospermic seminal samples (n = 16) and incubated with genipin, a selective UCP inhibitor (0, 0.5, 5, and 50 µM), for 3 h at 37 °C. Cells and culture media were collected for analysis. Participants/materials, setting, methods UCP1-3 protein expression was detected by western blot and immunofluorescence. After UCPs inhibition, spermatozoa viability and motility were assessed. Mitochondrial membrane potential and ROS production were evaluated. Media were collected and the metabolic profile and antioxidant potential were analysed by 1H-NMR and FRAP, respectively. Main results and the role of chance We were able to identify the expression of UCP1, UCP2, and UCP3 in human spermatozoa. UCP1-3 are mainly located at the equatorial segment of the head, whereas UCP1 and UCP2 are also expressed at the spermatozoa midpiece, where mitochondria are located. The inhibition of UCPs by 50 µM genipin, resulting in the UCP3 inhibition, led to the complete and irreversible loss of motility that persisted despite washing or incubation with theophylline, a cAMP activator. These effects were associated with decreased mitochondrial membrane potential and lactate production. Interestingly, the loss of motility did not compromise spermatozoa viability. In addition, the inhibition of UCPs led to no alterations concerning ROS production, possibly due to the decreased mitochondrial activity and genipin antioxidant properties. Limitations, reasons for caution This is an in vitro study with a relatively small sample size. Genipin is considered a specific yet a general inhibitor of UCPs. The development and use of specific inhibitors for each homolog will further disclose their role in human spermatozoa motility and bioenergetics. Wider implications of the findings UCPs are expressed in human spermatozoa. UCPs are important regulators of human spermatozoa motility and metabolism. The discovery and characterization of UCPs’ role in human spermatozoa open the path for studies on ROS-related pathways and bioenergetics physiology of human spermatozoa. Trial registration number 'not applicable'

Dual transport function of uncoupling protein 3.

The mitochondrial membrane uncoupling protein UCP3 belongs to the SLC25 solute carrier family and transports protons across the inner mitochondrial membrane. Based on the knowledge that another uncoupling protein - UCP2 - transports C4 metabolites (malate, oxaloacetate, and aspartate)1 and there is high homology between UCP2 and UCP3, we hypothesized that UCP3 also transports these metabolites. To test this, we measured the transport of C4 metabolites against phosphate (32Pi) in proteoliposomes reconstituted with recombinant murine UCP3. We found that UCP3 transports primarily aspartate and sulfate, but also malate, malonate, oxaloacetate, and succinate. The transport rates from the exchange of 32Pi for extraliposomal aspartate and sulfate were 0.89 ± 0.33 and 0.61 ± 0.12 µmol/min/mg, respectively. We demonstrated that UCP3 preferentially transports malate, oxaloacetate, and aspartate against phosphate plus a proton from opposite side of the membrane, which does not exactly match the transport pattern of UCP2. Because UCP3 and UCP2 are expressed in different tissues2, we anticipate that their substrate specificity may differ. The putative physiological role of UCP3-mediated substrate transport in cells dependent on fatty acid oxidation is discussed. 1. Vozza A, et al. UCP2 transports C4 metabolites out of mitochondria, regulating glucose and glutamine oxidation. Proc. Natl. Acad. Sci. U S A 111, 960-965 (2014). 2. Pohl EE, Rupprecht A, Macher G, Hilse KE. Important Trends in UCP3 Investigation. Front Physiol. 10, 470 (2019).

In silico investigation of uncoupling protein function in avian genomes.

The uncoupling proteins (UCPs) are involved in lipid metabolism and belong to a family of mitochondrial anionic transporters. In poultry, only one UCP homologue has been identified and experimentally shown to be associated with growth, feed conversion ratio, and abdominal fat according to its predominant expression in bird muscles. In endotherm birds, cell metabolic efficiency can be tuned by the rate of mitochondrial coupling. Thus, avUCP may be a key contributor to controlling metabolic rate during particular environmental changes. This study aimed to perform a set of in-silico investigations primarily focused on the structural, biological, and biomimetic functions of avUCP. Thereby, using in silico genome analyses among 8 avian species (chicken, turkey, swallow, manakin, sparrow, wagtail, pigeon, and mallard) and a series of bioinformatic approaches, we provide phylogenetic inference and comparative genomics of avUCPs and investigate whether sequence variation can alter coding sequence characteristics, the protein structure, and its biological features. Complementarily, a combination of literature mining and prediction approaches was also applied to predict the gene networks of avUCP to identify genes, pathways, and biological crosstalk associated with avUCP function. The results showed the evolutionary alteration of UCP proteins in different avian species. Uncoupling proteins in avian species are highly conserved trans membrane proteins as seen by sequence alignment, physio-chemical parameters, and predicted protein structures. Taken together, avUCP has the potential to be considered a functional marker for the identification of cell metabolic state, thermogenesis, and oxidative stress caused by cold, heat, fasting, transfer, and other chemical stimuli stresses in birds. It can also be deduced that avUCP, in migrant or domestic birds, may increase heat stress resistance by reducing fatty acid transport/b-oxidation and thermoregulation alongside antioxidant defense mechanisms. The predicted gene network for avUCP highlighted a cluster of 21 genes involved in response to stress and 28 genes related to lipid metabolism and the proton buffering system. Finally, among 11 enriched pathways, crosstalk of 5 signaling pathways including MAPK, adipocytokine, mTOR, insulin, ErbB, and GnRH was predicted, indicating a possible combination of positive or negative feedback among pathways to regulate avUCP functions. Genetic selection for fast-growing commercial poultry has unintentionally increased susceptibility to many kinds of oxidative stress, and so avUCP could be considered as a potential candidate gene for balancing energy expenditure and reactive oxygen species production, especially in breeding programs. In conclusion, avUCP can be introduced as a pleiotropic gene that requires the contribution of regulatory genes, hormones, pathways, and genetic crosstalk to allow its finely-tuned function.

Membrane Lipid Reshaping Underlies Oxidative Stress Sensing by the Mitochondrial Proteins UCP1 and ANT1.

Oxidative stress and ROS are important players in the pathogenesis of numerous diseases. In addition to directly altering proteins, ROS also affects lipids with negative intrinsic curvature such as phosphatidylethanolamine (PE), producing PE adducts and lysolipids. The formation of PE adducts potentiates the protonophoric activity of mitochondrial uncoupling proteins, but the molecular mechanism remains unclear. Here, we linked the ROS-mediated change in lipid shape to the mechanical properties of the membrane and the function of uncoupling protein 1 (UCP1) and adenine nucleotide translocase 1 (ANT1). We show that the increase in the protonophoric activity of both proteins occurs due to the decrease in bending modulus in lipid bilayers in the presence of lysophosphatidylcholines (OPC and MPC) and PE adducts. Moreover, MD simulations showed that modified PEs and lysolipids change the lateral pressure profile of the membrane in the same direction and by the similar amplitude, indicating that modified PEs act as lipids with positive intrinsic curvature. Both results indicate that oxidative stress decreases stored curvature elastic stress (SCES) in the lipid bilayer membrane. We demonstrated that UCP1 and ANT1 sense SCES and proposed a novel regulatory mechanism for the function of these proteins. The new findings should draw the attention of the scientific community to this important and unexplored area of redox biochemistry.

UCP2 silencing restrains leukemia cell proliferation through glutamine metabolic remodeling.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T cell progenitors. Since relapsed T-ALL is associated with a poor prognosis improving initial treatment of patients is essential to avoid resistant selection of T-ALL. During initiation, development, metastasis and even in response to chemotherapy, tumor cells face strong metabolic challenges. In this study, we identify mitochondrial UnCoupling Protein 2 (UCP2) as a tricarboxylic acid (TCA) cycle metabolite transporter controlling glutamine metabolism associated with T-ALL cell proliferation. In T-ALL cell lines, we show that UCP2 expression is controlled by glutamine metabolism and is essential for their proliferation. Our data show that T-ALL cell lines differ in their substrate dependency and their energetic metabolism (glycolysis and oxidative). Thus, while UCP2 silencing decreases cell proliferation in all leukemia cells, it also alters mitochondrial respiration of T-ALL cells relying on glutamine-dependent oxidative metabolism by rewiring their cellular metabolism to glycolysis. In this context, the function of UCP2 in the metabolite export of malate enables appropriate TCA cycle to provide building blocks such as lipids for cell growth and mitochondrial respiration. Therefore, interfering with UCP2 function can be considered as an interesting strategy to decrease metabolic efficiency and proliferation rate of leukemia cells.

Mitochondrial uncoupling protein-2 reprograms metabolism to induce oxidative stress and myofibroblast senescence in age-associated lung fibrosis.

Mitochondrial dysfunction has been associated with age‐related diseases, including idiopathic pulmonary fibrosis (IPF). We provide evidence that implicates chronic elevation of the mitochondrial anion carrier protein, uncoupling protein‐2 (UCP2), in increased generation of reactive oxygen species, altered redox state and cellular bioenergetics, impaired fatty acid oxidation, and induction of myofibroblast senescence. This pro‐oxidant senescence reprogramming occurs in concert with conventional actions of UCP2 as an uncoupler of oxidative phosphorylation with dissipation of the mitochondrial membrane potential. UCP2 is highly expressed in human IPF lung myofibroblasts and in aged fibroblasts. In an aging murine model of lung fibrosis, the in vivo silencing of UCP2 induces fibrosis regression. These studies indicate a pro‐fibrotic function of UCP2 in chronic lung disease and support its therapeutic targeting in age‐related diseases associated with impaired tissue regeneration and organ fibrosis.

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.

Uncoupling Proteins and Regulated Proton Leak in Mitochondria.

Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field.

Theobromine enhances the conversion of white adipocytes into beige adipocytes in a PPARγ activation-dependent manner

The adipocytes play an important role in driving the obese-state—white adipose tissue (WAT) stores the excess energy as fat, wherein brown adipose tissue (BAT) is responsible for energy expenditure via the thermoregulatory function of uncoupling protein 1 (UCP1)—the imbalance between these two onsets obesity. Moreover, the anti-obesity effects of brown-like-adipocytes (beige) in WAT are well documented. Browning, the process of transformation of energy-storing into energy-dissipating adipocytes, is a potential preventive strategy against obesity and its related diseases. In the present study, to explore an alternative source of natural products in the regulation of adipocyte transformation, we assessed the potential of theobromine (TB), a bitter alkaloid of the cacao plant, inducing browning in mice (in vivo) and primary adipocytes (in vitro). Dietary supplementation of TB significantly increased skin temperature of the inguinal region in mice and induced the expression of UCP1 protein. It also increased the expression levels of mitochondrial marker proteins in subcutaneous adipose tissues but not in visceral adipose tissues. The microarray analysis showed that TB supplementation upregulated multiple thermogenic and beige adipocyte marker genes in subcutaneous adipose tissue. Furthermore, in mouse-derived primary adipocytes, TB upregulated the expression of the UCP1 protein and mitochondrial mass in a PPARγ ligand-dependent manner. It also increased the phosphorylation levels of PPARγ coactivator 1α without affecting its protein expression. These results indicate that dietary supplementation of TB induces browning in subcutaneous WAT and enhances PPARγ-induced UCP1 expression in vitro, suggesting its potential to treat obesity.

Mitochondrial Uncoupling Proteins (UCPs) as Key Modulators of ROS Homeostasis: A Crosstalk between Diabesity and Male Infertility?

Uncoupling proteins (UCPs) are transmembrane proteins members of the mitochondrial anion transporter family present in the mitochondrial inner membrane. Currently, six homologs have been identified (UCP1-6) in mammals, with ubiquitous tissue distribution and multiple physiological functions. UCPs are regulators of key events for cellular bioenergetic metabolism, such as membrane potential, metabolic efficiency, and energy dissipation also functioning as pivotal modulators of ROS production and general cellular redox state. UCPs can act as proton channels, leading to proton re-entry the mitochondrial matrix from the intermembrane space and thus collapsing the proton gradient and decreasing the membrane potential. Each homolog exhibits its specific functions, from thermogenesis to regulation of ROS production. The expression and function of UCPs are intimately linked to diabesity, with their dysregulation/dysfunction not only associated to diabesity onset, but also by exacerbating oxidative stress-related damage. Male infertility is one of the most overlooked diabesity-related comorbidities, where high oxidative stress takes a major role. In this review, we discuss in detail the expression and function of the different UCP homologs. In addition, the role of UCPs as key regulators of ROS production and redox homeostasis, as well as their influence on the pathophysiology of diabesity and potential role on diabesity-induced male infertility is debated.

Effect of 5-azacytidine (5-aza) on UCP2 expression in human liver and colon cancer cells.

The function of the uncoupling protein 2 (UCP2) is different for each cancer cell. However, the mechanism of expression is still unclear. DNA methylation affects protein expression and is one factor that transforms normal cells into cancer cells. In this study, the hepatocellular carcinoma Hep3B and HepG2 cells and colorectal cancer HT-29 cells were treated with 5-azacytidine (5-aza), a DNA demethylation agent, to observe the modification of UCP2 expression and the methylation degree in the UCP2 promoter region. Promoter basal activity and degree of UCP2 expression were measured in Hep3B, HepG2, and HT-29 cells. In addition, methylation-specific PCR (MSP) was performed to investigate the degree of methylation in the UCP2 promoter region. The methylation region in the UCP2 promoter was confirmed based on bisulfite sequencing. In Hep3B cells in which UCP2 mRNA was not transcribed, the promoter basal activity was significantly higher than in HT-29 or HepG2 cells in which UCP2 mRNA was transcribed. Treatment with 5-aza increased UCP2 expression in Hep3B and HT-29 cells; however, the expression in HepG2 cells was unchanged. The UCP2 promoter in Hep3B cells has numerous methylated regions compared with HT-29 and HepG2 cells. The results of the present study revealed that inhibition of UCP2 expression in Hep3B cells was due to methylation of the promoter region. Investigating the mechanism that induces UCP2 expression in cancer cells is important to understand the function of UCP2, which could aid in cancer treatment.

Genipin enhances the antitumor effect of elesclomol in A549 lung cancer cells by blocking uncoupling protein-2 and stimulating reactive oxygen species production.

The uncoupling protein-2 (UCP2) serves a role in tumor aggressiveness and anticancer resistance, which is considered to be associated with its ability to attenuate reactive oxygen species (ROS) production. We hypothesized that UCP2 may protect cancer cells from elesclomol-induced cytotoxicity, and that this may be overcome by blocking UCP2 function with genipin. In A549 lung cancer cells that exhibited high UCP2 expression, treatment with elesclomol alone induced limited changes in glucose uptake, ROS production and cell survival. By contrast, both UCP2 knockdown and genipin treatment mildly reduced glucose uptake, increased ROS production and decreased cell survival. Combining genipin and elesclomol further reduced glucose uptake and increased cellular and mitochondrial ROS production. Moreover, co-treatment with genipin and elesclomol reduced the colony forming capacity to 50.6±7.4% and the cell survival to 42.0±3.4% of that in the control cells (both P<0.001). Suppression of cell survival by treatment with elesclomol and genipin was enhanced in the presence of an exogenous ROS inducer and attenuated by a ROS scavenger. The cytotoxic effects of combining genipin and elesclomol were accompanied by reduced mitochondrial membrane potential and occurred through apoptosis as demonstrated by Annexin V assay and increased protein cleavage of PARP and caspase-3. Finally, in an A549 ×enograft mouse model, tumor growth was only modestly retarded by treatment with elesclomol or genipin alone, but was markedly suppressed by combining the two drugs compared with that in the control group (P=0.008). Therefore, high UCP2 expression may limit the antitumor effect of elesclomol by attenuating ROS responses, and this may be overcome by co-treatment with genipin; combining elesclomol and genipin may be an effective strategy for treating cancers with high UCP2.

The contribution of uncoupling protein 2 to mitochondrial Ca2+ homeostasis in health and disease – A short revisit

Considering the versatile functions attributed to uncoupling protein 2 (UCP2) in health and disease, a profound understanding of the protein's molecular actions under physiological and pathophysiological conditions is indispensable. This review aims to revisit and shed light on the fundamental molecular functions of UCP2 in mitochondria, with particular emphasis on its intricate role in regulating mitochondrial calcium (Ca2+) uptake. UCP2′s modulating effect on various vital processes in mitochondria makes it a crucial regulator of mitochondrial homeostasis in health and disease.

Abstract P4-09-14: Evaluation of the relationship between antioxidant gene polymorphisms and breast cancer

Abstract Background: Myeloperoxidase (MPO) is a lysosomal enzyme found in monocytes, macrophages and primary granules of neutrophils. MPO participates in the biotransformation reaction of specific carcinogens by catalyzing the formation of hypochloric acid. The destruction of malignant and non-malignant cells is achieved via MPO enzyme. An important mechanism in oxidative stress regulation is the function of uncoupling proteins (UCP), which are among the mitochondrial membrane proteins. They control free radical formation. Theaim of thisstudywastodeterminetherelationshipbetweenpolymorphisms of myeloperoxidase (MPO), uncoupling protein 2 (UCP-2)genesanddevelopment of breastcancer. Methods: Thedistributions of genotypeandallelefrequencywascomparedamongthe groups.Thirty-seven caseswithbreastcancerandseventyhealthycontrolswereenrolled in thepresentstudy. Thestudyfocused on threefunctionalvariants; a variant in a variable number of 27 bp tandem repeatsin a variant in thepromoter region (G463A) of MPO gene and a variant in thepromoterregion(-866G/A) of UCP-2 gene. Wegenotypedthesevariantsusingthepolymerasechainreaction (PCR) and/or PCR- restrictionfragmentlengthpolymorphism (RFLP) method. Thedistribution of alleleand genotype in MPO and UCP-2 geneswerecomparedbetweencaseswithbreastcancer andhealthycontrolsusingchi-square test. Results: Significantlydecreasedbreastcancerriskswerefoundfor UCP-2 AA, and AG polymorphisms(For UCP-2 AA polymorphism OR=8.167; 95%CI:2.785-23.951; p=0.001, for UCP2 AG polymorphism OR=4.341; 95%CI:1.679-11.222; p=0.002).Significantly increasedbreastcancer risk wasfoundfor UCP-2 GG polymorphism (OR:5.0; 95%CI:2.207-11.327; p=0.001).Therewerenostatisticallysignificantdifference in any genotype of MPO whencaseswithbreastcancerandhealthycontrolswerecompared. Conclusion: In the current study, UCP-2 AA, AG and GG genotypes were found to be associated with breast cancer. In contrast, MPO GG, GA genotypes were not associated with breast cancer. Further studies are needed to determine whether these gene polymorphisms have a place in diagnosis or determining the risk of disease. Citation Format: Turkan Ozturk Topcu, Nilgun ısıksacan, Zisan Asal Kilic, Sacide Pehlivan, Meral Gunaldi. Evaluation of the relationship between antioxidant gene polymorphisms and breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-09-14.

Alternative splicing of UCP1 by non-cell-autonomous action of PEMT

ObjectivePhosphatidylethanolamine methyltransferase (PEMT) generates phosphatidylcholine (PC), the most abundant phospholipid in the mitochondria and an important acyl chain donor for cardiolipin (CL) biosynthesis. Mice lacking PEMT (PEMTKO) are cold-intolerant when fed a high-fat diet (HFD) due to unclear mechanisms. The purpose of this study was to determine whether PEMT-derived phospholipids are important for the function of uncoupling protein 1 (UCP1) and thus for maintenance of core temperature. MethodsTo test whether PEMT-derived phospholipids are important for UCP1 function, we examined cold-tolerance and brown adipose (BAT) mitochondria from PEMTKO mice with or without HFD feeding. We complemented these studies with experiments on mice lacking functional CL due to tafazzin knockdown (TAZKD). We generated several conditional mouse models to study the tissue-specific roles of PEMT, including mice with BAT-specific knockout of PEMT (PEMT-BKO). ResultsChow- and HFD-fed PEMTKO mice completely lacked UCP1 protein in BAT, despite a lack of difference in mRNA levels, and the mice were accordingly cold-intolerant. While HFD-fed PEMTKO mice exhibited reduced mitochondrial CL content, this was not observed in chow-fed PEMTKO mice or TAZKD mice, indicating that the lack of UCP1 was not attributable to CL deficiency. Surprisingly, the PEMT-BKO mice exhibited normal UCP1 protein levels. Knockout of PEMT in the adipose tissue (PEMT-AKO), liver (PEMT-LKO), or skeletal muscle (PEMT-MKO) also did not affect UCP1 protein levels, suggesting that lack of PEMT in other non-UCP1-expressing cells communicates to BAT to suppress UCP1. Instead, we identified an untranslated UCP1 splice variant that was triggered during the perinatal period in the PEMTKO mice. ConclusionsPEMT is required for UCP1 splicing that yields functional protein. This effect is derived by PEMT in nonadipocytes that communicates to BAT during embryonic development. Future research will focus on identifying the non-cell-autonomous PEMT-dependent mechanism of UCP1 splicing.

Glutamine regulates mitochondrial uncoupling protein 2 to promote glutaminolysis in neuroblastoma cells

Mitochondrial uncoupling protein 2 (UCP2) is highly abundant in rapidly proliferating cells that utilize aerobic glycolysis, such as stem cells, cancer cells, and cells of the immune system. However, the function of UCP2 has been a longstanding conundrum. Considering the strict regulation and unusually short life time of the protein, we propose that UCP2 acts as a “signaling protein” under nutrient shortage in cancer cells. We reveal that glutamine shortage induces the rapid and reversible downregulation of UCP2, decrease of the metabolic activity and proliferation of neuroblastoma cells, that are regulated by glutamine per se but not by glutamine metabolism. Our findings indicate a very rapid (within 1 h) metabolic adaptation that allows the cell to survive by either shifting its metabolism to the use of the alternative fuel glutamine or going into a reversible, more quiescent state. The results imply that UCP2 facilitates glutamine utilization as an energetic fuel source, thereby providing metabolic flexibility during glucose shortage. The targeting UCP2 by drugs to intervene with cancer cell metabolism may represent a new strategy for treatment of cancers resistant to other therapies.

Bile acid supplementation decreases body mass gain in C57BL/6J but not 129S6/SvEvTac mice without increasing energy expenditure

Supplementation of cholate to a high fat diet can protect mice from diet-induced, increased body mass gain. It has been hypothesized that uncoupling protein 1 dependent, non-shivering thermogenesis in brown adipocytes provides the mechanism of increased energy expenditure to counteract excessive energy intake. We scrutinized this conjecture in wildtype mice and mice genetically devoid of a functional uncoupling protein 1 gene (C57BL/6J) as well as mice of the 129S6/SvEvTac strain that, in comparison, display an extraordinary capacity to recruit ectopic brown adipocytes. Protection from diet-induced, increased body mass gain by cholate supplementation was absent in 129S6/SvEvTac mice, a consequence of much lower bile acid absorption and spillover in this strain. Conversely, Ucp1-KO mice did not differ from C57BL/6J wildtype controls in any parameter assessed. Daily energy expenditure and resting metabolic rate of C57BL/6J mice remained unaffected by cholate supplementation. We conclude that protection of mice from diet-induced, increased body mass gain by cholate supplementation depends on the specific genetic background of C57BL/6J mice, does not involve increased energy expenditure and is independent of uncoupling protein 1 dependent non-shivering thermogenesis.