Uncoupling proteins: a role in protection against reactive oxygen species--or not?

Signals of energy availability in sleep: consequences of a fat-based metabolism

Humans can flexibly switch between two primary metabolic modes, usually distinguished by whether substrate supply from glucose can meet energy demands or not. However, it is often overlooked that when glucose use is limited, the remainder of energy needs may still be met more or less effectively with fat and ketone bodies. Hence a fat-based metabolism marked by ketosis is often conflated with starvation and contexts of inadequate energy (including at the cellular level), even when energy itself is in ample supply. Sleep and satiation are regulated by common pathways reflecting energy metabolism. A conceptual analysis that distinguishes signals of inadequate energy in a glucose-dominant metabolism from signals of a fat-based metabolism that may well be energy sufficient allows a reexamination of experimental results in the study of sleep that may shed light on species differences and explain why ketogenic diets have beneficial effects simultaneously in the brain and the periphery. It may also help to distinguish clinically when a failure of a ketogenic diet to resolve symptoms is due to inadequate energy rather than the metabolic state itself.

Cardiovascular Disease and miRNAs: Possible Oxidative Stress-Regulating Roles of miRNAs

MicroRNAs (miRNAs) have been highlighted as key players in numerous diseases, and accumulating evidence indicates that pathological expressions of miRNAs contribute to both the development and progression of cardiovascular diseases (CVD), as well. Another important factor affecting the development and progression of CVD is reactive oxygen species (ROS), as well as the oxidative stress they may impose on the cells. Considering miRNAs are involved in virtually every biological process, it is not unreasonable to assume that miRNAs also play critical roles in the regulation of oxidative stress. This narrative review aims to provide mechanistic insights on possible oxidative stress-regulating roles of miRNAs in cardiovascular diseases based on differentially expressed miRNAs reported in various cardiovascular diseases and their empirically validated targets that have been implicated in the regulation of oxidative stress.

Proton leak through the UCPs and ANT carriers and beyond: A breath for the electron transport chain

Mitochondria produce heat as a result of an ineffective H+ cycling of mitochondria respiration across the inner mitochondrial membrane (IMM). This event present in all mitochondria, known as proton leak, can decrease protonmotive force (Δp) and restore mitochondrial respiration by partially uncoupling the substrate oxidation from the ADP phosphorylation. During impaired conditions of ATP generation with F1FO-ATPase, the Δp increases and IMM is hyperpolarized. In this bioenergetic state, the respiratory complexes support H+ transport until the membrane potential stops the H+ pump activity. Consequently, the electron transfer is stalled and the reduced form of electron carriers of the respiratory chain can generate O2∙¯ triggering the cascade of ROS formation and oxidative stress. The physiological function to attenuate the production of O2∙¯ by Δp dissipation can be attributed to the proton leak supported by the translocases of IMM.

Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3

Myocardial ischemia-reperfusion (IR) injury may result in cardiomyocyte dysfunction. Mitochondria play a critical role in cardiomyocyte recovery after IR injury. The mitochondrial uncoupling protein 3 (UCP3) has been proposed to reduce mitochondrial reactive oxygen species (ROS) production and to facilitate fatty acid oxidation. As both mechanisms might be protective following IR injury, we investigated functional, mitochondrial structural, and metabolic cardiac remodeling in wild-type mice and in mice lacking UCP3 (UCP3-KO) after IR. Results showed that infarct size in isolated perfused hearts subjected to IR ex vivo was larger in adult and old UCP3-KO mice than in equivalent wild-type mice, and was accompanied by higher levels of creatine kinase in the effluent and by more pronounced mitochondrial structural changes. The greater myocardial damage in UCP3-KO hearts was confirmed in vivo after coronary artery occlusion followed by reperfusion. S1QEL, a suppressor of superoxide generation from site IQ in complex I, limited infarct size in UCP3-KO hearts, pointing to exacerbated superoxide production as a possible cause of the damage. Metabolomics analysis of isolated perfused hearts confirmed the reported accumulation of succinate, xanthine and hypoxanthine during ischemia, and a shift to anaerobic glucose utilization, which all recovered upon reoxygenation. The metabolic response to ischemia and IR was similar in UCP3-KO and wild-type hearts, being lipid and energy metabolism the most affected pathways. Fatty acid oxidation and complex I (but not complex II) activity were equally impaired after IR. Overall, our results indicate that UCP3 deficiency promotes enhanced superoxide generation and mitochondrial structural changes that increase the vulnerability of the myocardium to IR injury.

Role of UCP2 in the Energy Metabolism of the Cancer Cell Line A549

The uncoupling protein UCP2 is a mitochondrial carrier for which transport activity remains controversial. The physiological contexts in which UCP2 is expressed have led to the assumption that, like UCP1, it uncouples oxidative phosphorylation and thereby reduces the generation of reactive oxygen species. Other reports have involved UCP2 in the Warburg effect, and results showing that UCP2 catalyzes the export of matrix C4 metabolites to facilitate glutamine utilization suggest that the carrier could be involved in the metabolic adaptations required for cell proliferation. We have examined the role of UCP2 in the energy metabolism of the lung adenocarcinoma cell line A549 and show that UCP2 silencing decreased the basal rate of respiration, although this inhibition was not compensated by an increase in glycolysis. Silencing did not lead to either changes in proton leakage, as determined by the rate of respiration in the absence of ATP synthesis, or changes in the rate of formation of reactive oxygen species. The decrease in energy metabolism did not alter the cellular energy charge. The decreased cell proliferation observed in UCP2-silenced cells would explain the reduced cellular ATP demand. We conclude that UCP2 does not operate as an uncoupling protein, whereas our results are consistent with its activity as a C4-metabolite carrier involved in the metabolic adaptations of proliferating cells.

VDAC1 Knockout Affects Mitochondrial Oxygen Consumption Triggering a Rearrangement of ETC by Impacting on Complex I Activity

Voltage-Dependent Anion-selective Channel isoform 1 (VDAC1) is the most abundant isoform of the outer mitochondrial membrane (OMM) porins and the principal gate for ions and metabolites to and from the organelle. VDAC1 is also involved in a number of additional functions, such as the regulation of apoptosis. Although the protein is not directly involved in mitochondrial respiration, its deletion in yeast triggers a complete rewiring of the whole cell metabolism, with the inactivation of the main mitochondrial functions. In this work, we analyzed in detail the impact of VDAC1 knockout on mitochondrial respiration in the near-haploid human cell line HAP1. Results indicate that, despite the presence of other VDAC isoforms in the cell, the inactivation of VDAC1 correlates with a dramatic impairment in oxygen consumption and a re-organization of the relative contributions of the electron transport chain (ETC) enzymes. Precisely, in VDAC1 knockout HAP1 cells, the complex I-linked respiration (N-pathway) is increased by drawing resources from respiratory reserves. Overall, the data reported here strengthen the key role of VDAC1 as a general regulator of mitochondrial metabolism.

Therapeutic modulation of JAK-STAT, mTOR, and PPAR-γ signaling in neurological dysfunctions

The cytokine-activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) cascade is a pleiotropic pathway that involves receptor subunit multimerization. The mammalian target of rapamycin (mTOR) is a ubiquitously expressed serine-threonine kinase that perceives and integrates a variety of intracellular and environmental stimuli to regulate essential activities such as cell development and metabolism. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a prototypical metabolic nuclear receptor involved in neural differentiation and axon polarity. The JAK-STAT, mTOR, and PPARγ signaling pathways serve as a highly conserved signaling hub that coordinates neuronal activity and brain development. Additionally, overactivation of JAK/STAT, mTOR, and inhibition of PPARγ signaling have been linked to various neurocomplications, including neuroinflammation, apoptosis, and oxidative stress. Emerging research suggests that even minor disruptions in these cellular and molecular processes can have significant consequences manifested as neurological and neuropsychiatric diseases. Of interest, target modulators have been proven to alleviate neuronal complications associated with acute and chronic neurological deficits. This research-based review explores the therapeutic role of JAK-STAT, mTOR, and PPARγ signaling modulators in preventing neuronal dysfunctions in preclinical and clinical investigations.

Mitochondrial Respiration-Dependent ANT2-UCP2 Interaction

Adenine nucleotide translocases (ANTs) and uncoupling proteins (UCPs) are known to facilitate proton leak across the inner mitochondrial membrane. However, it remains to be unravelled whether UCP2/3 contribute to significant amount of proton leak in vivo. Reports are indicative of UCP2 dependent proton-coupled efflux of C4 metabolites from the mitochondrial matrix. Previous studies have suggested that UCP2/3 knockdown (KD) contributes to increased ANT-dependent proton leak. Here we investigated the hypothesis that interaction exists between the UCP2 and ANT2 proteins, and that such interaction is regulated by the cellular metabolic demand. Protein-protein interaction was evaluated using reciprocal co-immunoprecipitation and in situ proximity ligation assay. KD of ANT2 and UCP2 was performed by siRNA in human embryonic kidney cells 293A (HEK293A) cells. Mitochondrial and cellular respiration was measured by high-resolution respirometry. ANT2-UCP2 interaction was demonstrated, and this was dependent on cellular metabolism. Inhibition of ATP synthase promoted ANT2-UCP2 interaction whereas high cellular respiration, induced by adding the mitochondrial uncoupler FCCP, prevented interaction. UCP2 KD contributed to increased carboxyatractyloside (CATR) sensitive proton leak, whereas ANT2 and UCP2 double KD reduced CATR sensitive proton leak, compared to UCP2 KD. Furthermore, proton leak was reduced in double KD compared to UCP2 KD. In conclusion, our results show that there is an interaction between ANT2-UCP2, which appears to be dynamically regulated by mitochondrial respiratory activity. This may have implications in the regulation of mitochondrial efficiency or cellular substrate utilization as increased activity of UCP2 may promote a switch from glucose to fatty acid metabolism.

Mechanisms and mathematical modelling of ROS production by the mitochondrial electron transport chain

Reactive oxygen species (ROS) are recognised both as damaging molecules and intracellular signalling entities. In addition to its role in ATP generation, the mitochondrial electron transport chain (ETC) constitutes a relevant source of mitochondrial ROS, in particular during pathological conditions. Mitochondrial ROS homeostasis depends on species- and site-dependent ROS production, their bioreactivity, diffusion, and scavenging. However, our quantitative understanding of mitochondrial ROS homeostasis has thus far been hampered by technical limitations, including lack of truly site- and/or ROS-specific reporter molecules. In this context, the use of computational models is of great value to complement and interpret empirical data, as well as to predict variables that are difficult to assess experimentally. During the last decades, various mechanistic models of ETC-mediated ROS production have been developed. Although these often-complex models have generated novel insights, their parameterisation, analysis, and integration with other computational models is not straightforward. In contrast, phenomenological (sometimes termed "minimal") models use a relatively small set of equations to describe empirical relationship(s) between ROS-related and other parameters, and generally aim to explore system behaviour and generate hypotheses for experimental validation. In this review, we first discuss ETC-linked ROS homeostasis and introduce various detailed mechanistic models. Next, we present how bioenergetic parameters (e.g. NADH/NAD⁺ ratio, mitochondrial membrane potential) relate to site-specific ROS production within the ETC and how these relationships can be used to design minimal models of ROS homeostasis. Finally, we illustrate how minimal models have been applied to explore pathophysiological aspects of ROS.

The Uncoupling Proteins: A Systematic Review on the Mechanism Used in the Prevention of Oxidative Stress

Mitochondrial uncoupling proteins (UCP) 1-3 fulfill many physiological functions, ranging from non-shivering thermogenesis (UCP1) to glucose-stimulated insulin release (GSIS) and satiety signaling (UCP2) and muscle fuel metabolism (UCP3). Several studies have suggested that UCPs mediate these functions by facilitating proton return to the matrix. This would decrease protonic backpressure on the respiratory chain, lowering the production of hydrogen peroxide (H₂O₂), a second messenger. However, controlling mitochondrial H₂O₂ production to prevent oxidative stress by activating these leaks through these proteins is still enthusiastically debated. This is due to compelling evidence that UCP2/3 fulfill other function(s) and the inability to reproduce findings that UCP1-3 use inducible leaks to control reactive oxygen species (ROS) production. Further, other studies have found that UCP2/3 may serve as Ca²⁺. Therefore, we performed a systematic review aiming to summarize the results collected on the topic. A literature search using a list of curated keywords in Pubmed, BIOSIS Citation Index and Scopus was conducted. Potentially relevant references were screened, duplicate references eliminated, and then literature titles and abstracts were evaluated using Rayyan software. A total of 1101 eligible studies were identified for the review. From this total, 416 studies were evaluated based on our inclusion criteria. In general, most studies identified a role for UCPs in preventing oxidative stress, and in some cases, this may be related to the induction of leaks and lowering protonic backpressure on the respiratory chain. However, some studies also generated evidence that UCP2/3 may mitigate oxidative stress by transporting Ca²⁺ into the matrix, exporting lipid hydroperoxides, or by transporting C-4 metabolites. Additionally, some showed that activating UCP1 or 3 can increase mitochondrial ROS production, even though there is still augmented protection from oxidative stress. Conclusion: Overall, most available studies demonstrate that UCPs, particularly UCP2/3, prevent oxidative stress. However, the mechanism utilized to do so remains elusive and raises the question that UCP2/3 should be renamed, since they may still not be true “uncoupling proteins”.

Genetic associated complications of type 2 Diabetes Mellitus: a review

According to the International Diabetes Federation, the number of adults (age of 20-79) being diagnosed with Diabetes Mellitus (DM) have increased from 285 million in year 2009 to 463 million in year 2019 which comprises of 95% Type 2 DM patient (T2DM). Research have claimed that genetic predisposition could be one of the factors causing T2DM complications. In addition, T2DMcomplications cause an incremental risk to mortality. Therefore, this article aims to discuss some complications of T2DM in and their genetic association. The complications that are discussed in this article are diabetic nephropathy, diabetes induced cardiovascular disease, diabetic neuropathy, Diabetic Foot Ulcer (DFU) and Alzheimer's disease. According to the information obtained, genes associated with diabetic nephropathy (DN) are gene GABRR1 and ELMO1 that cause injury to glomerular. Replication of genes FRMD3, CARS and MYO16/IRS2 shown to have link with DN. The increase of gene THBS2, NGAL, PIP, TRAF6 polymorphism, ICAM-1 encoded for rs5498 polymorphism and C667T increase susceptibility towards DN in T2DM patient. Genes associated with cardiovascular diseases are Adiponectin gene (ACRP30) and Apolipoprotein E (APOE) polymorphism gene with ξ2 allele. Haptoglobin (Hp) 1-1 genotype and Mitochondria Superoxide Dismutase 2 (SOD2) plays a role in cardiovascular events. As for genes related to diabetic neuropathy, Janus Kinase (JAK), mutation of SCN9A and TRPA1 gene and destruction of miRNA contribute to pathogenesis of diabetic neuropathy among T2DM patients. Expression of cytokine IL-6, IL-10, miR-146a are found to cause diabetic neuropathy. Besides, A1a16Va1 gene polymorphism, an oxidative stress influence was found as one of the gene factors. Diabetic retinopathy (DR) is believed to have association with Monocyte Chemoattractant Protein-1 (MCP-1) and Insulin-like Growth Factor 1 (IGF1). Over-expression of gene ENPP1, IL-6 pro-inflammatory cytokine, ARHGAP22's protein rs3844492 polymorphism and TLR4 heterozygous genotype are contributing to significant pathophysiological process causing DR, while research found increases level of UCP1 gene protects retina cells from oxidative stress. Diabetic Foot Ulcer (DFU) is manifested by slowing in reepithelialisation of keratinocyte, persistence wound inflammation and healing impairment. Reepithelialisation disturbance was caused by E2F3 gene, reduction of Tacl gene encoded substance P causing persistence inflammation while expression of MMp-9 polymorphism contributes to healing impairment. A decrease in HIF-1a gene expression leads to increased risk of pathogenesis, while downregulation of TLR2 increases severity of wound in DFU patients. SNPs alleles has been shown to have significant association between the genetic dispositions of T2DM and Alzheimer's disease (AD). The progression of AD can be due to the change in DNA methylation of CLOCK gene, followed with worsening of AD by APOE4 gene due to dyslipidaemia condition in T2DM patients. Insulin resistance is also a factor that contributes to pathogenesis of AD.

Association of UCP1 and UCP2 variants with diabetic retinopathy susceptibility in type-2 diabetes mellitus patients: a meta-analysis

BACKGROUND

Genetic association of uncoupling proteins (UCPs) variants with the susceptibility of diabetic retinopathy (DR) in diabetes mellitus (DM) patients has been reported but with controversy. Here we aimed to conduct a meta-analysis to confirm the association of different UCPs variants with DR.

METHODS

Three databases (Medline Ovid, Embase Ovid and CENTRAL) were applied in the literature search. Five genetic models, including allelic, homozygous, heterozygous, dominant and recessive models, were evaluated. Odds ratios (OR) were estimated under the random or fixed-effects models. Subgroup analyses, publication bias and sensitivity analyses were also conducted.

RESULTS

Eleven studies on 2 UCPs variants (UCP1 rs1800592 and UCP2 rs659366) were included. Our meta-analysis showed that UCP1 rs1800592 was not associated with DR in type-2 DM patients, and UCP2 rs659366 also showed no association with DR. In the subgroup analyses on the stage of DR, allele G of UCP1 rs1800592 significantly increased the susceptibility of proliferative diabetic retinopathy (PDR) in type-2 DM patients in the allelic (OR = 1.26, P = 0.03) and homozygous models (OR = 1.60, P = 0.04). Subgroup analysis on ethnicity did not found any significant association of rs1800592 and rs659366 with DR.

CONCLUSION

Our meta-analysis confirmed the association of UCP1 rs1800592 variant with PDR in patients with type-2 DM, suggesting its potential as a genetic marker for PDR prediction in population screening.

Mitochondria: Potential Targets for Osteoarthritis

Osteoarthritis (OA) is a common and disabling joint disorder that is mainly characterized by cartilage degeneration and narrow joint spaces. The role of mitochondrial dysfunction in promoting the development of OA has gained much attention. Targeting endogenous molecules to improve mitochondrial function is a potential treatment for OA. Moreover, research on exogenous drugs to improve mitochondrial function in OA based on endogenous molecular targets has been accomplished. In addition, stem cells and exosomes have been deeply researched in the context of cartilage regeneration, and these factors both reverse mitochondrial dysfunctions. Thus, we hypothesize that biomedical approaches will be applied to the treatment of OA. Furthermore, we have summarized the global status of mitochondria and osteoarthritis research in the past two decades, which will contribute to the research field and the development of novel treatment strategies for OA.

High-Resolution Respirometry Reveals MPP+ Mitochondrial Toxicity Mechanism in a Cellular Model of Parkinson's Disease

MPP⁺ is the active metabolite of MPTP, a molecule structurally similar to the herbicide Paraquat, known to injure the dopaminergic neurons of the nigrostriatal system in Parkinson’s disease models. Within the cells, MPP⁺ accumulates in mitochondria where it inhibits complex I of the electron transport chain, resulting in ATP depletion and neuronal impairment/death. So far, MPP⁺ is recognized as a valuable tool to mimic dopaminergic degeneration in various cell lines. However, despite a large number of studies, a detailed characterization of mitochondrial respiration in neuronal cells upon MPP⁺ treatment is still missing. By using high-resolution respirometry, we deeply investigated oxygen consumption related to each respiratory state in differentiated neuroblastoma cells exposed to the neurotoxin. Our results indicated the presence of extended mitochondrial damage at the inner membrane level, supported by increased LEAK respiration, and a drastic drop in oxygen flow devoted to ADP phosphorylation in respirometry measurements. Furthermore, prior to complex I inhibition, an enhancement of complex II activity was observed, suggesting the occurrence of some compensatory effect. Overall our findings provide a mechanistic insight on the mitochondrial toxicity mediated by MPP⁺, relevant for the standardization of studies that employ this neurotoxin as a disease model.

Uncoupling Protein 2 Increases Blood Pressure in DJ -1 Knockout Mice

Background The redox-sensitive chaperone DJ -1 and uncoupling protein 2 are protective against mitochondrial oxidative stress. We previously reported that renal-selective depletion and germline deletion of DJ -1 increases blood pressure in mice. This study aimed to determine the mechanisms involved in the oxidative stress-mediated hypertension in DJ -1 ^-/- mice. Methods and Results There were no differences in sodium excretion, renal renin expression, renal NADPH oxidase activity, and serum creatinine levels between DJ -1 ^-/- and wild-type mice. Renal expression of nitro-tyrosine, malondialdehyde, and urinary kidney injury marker-1 were increased in DJ -1 ^-/- mice relative to wild-type littermates. mRNA expression of mitochondrial heat shock protein 60 was also elevated in kidneys from DJ -1 ^-/- mice, indicating the presence of oxidative stress. Tempol-treated DJ -1 ^-/- mice presented higher serum nitrite/nitrate levels than vehicle-treated DJ -1 ^-/- mice, suggesting a role of the NO system in the high blood pressure of this model. Tempol treatment normalized renal kidney injury marker-1 and malondialdehyde expression as well as blood pressure in DJ -1 ^-/- mice, but had no effect in wild-type mice. The renal Ucp2 mRNA expression was increased in DJ -1 ^-/- mice versus wild-type and was also normalized by tempol. The renal-selective silencing of Ucp2 led to normalization of blood pressure and serum nitrite/nitrate ratio in DJ -1 ^-/- mice. Conclusions The deletion of DJ -1 leads to oxidative stress-induced hypertension associated with downregulation of NO function, and overexpression of Ucp2 in the kidney increases blood pressure in DJ -1 ^-/- mice. To our knowledge, this is the first report providing evidence of the role of uncoupling protein 2 in blood pressure regulation.

Novel Therapeutic Approaches of Ion Channels and Transporters in Cancer

The expression and function of many ion channels and transporters in cancer cells display major differences in comparison to those from healthy cells. These differences provide the cancer cells with advantages for tumor development. Accordingly, targeting ion channels and transporters have beneficial anticancer effects including inhibition of cancer cell proliferation, migration, invasion, metastasis, tumor vascularization, and chemotherapy resistance, as well as promoting apoptosis. Some of the molecular mechanisms associating ion channels and transporters with cancer include the participation of oxidative stress, immune response, metabolic pathways, drug synergism, as well as noncanonical functions of ion channels. This diversity of mechanisms offers an exciting possibility to suggest novel and more effective therapeutic approaches to fight cancer. Here, we review and discuss most of the current knowledge suggesting novel therapeutic approaches for cancer therapy targeting ion channels and transporters. The role and regulation of ion channels and transporters in cancer provide a plethora of exceptional opportunities in drug design, as well as novel and promising therapeutic approaches that may be used for the benefit of cancer patients.

Protective effect of d-tetramannuronic acid tetrasodium salt on UVA-induced photo-aging in HaCaT cells

UVA radiation from the sun is the main external stimulus in the pathogenesis of skin photo-aging. This process is associated with cellular oxidative stress. Here we aim at showing the protective effect of d-Tetramannuronic Acid Tetrasodium Salt (M4), a natural product, against UVA (30J/cm²) irradiation-induced oxidative stress and photo-aging in HaCaT cells, and to reveal the molecular mechanism underlying the protective efficacy. M4 pretreatment significantly increased HaCaT cell viability and MMP, suppressing UVA-induced ROS generation. Moreover, M4 treatment prevented the UVA-induced photo-aging of HaCaT cells (the reduction of cell viability, mitochondria dysfunction, and SIRT1/pGC-1α deregulation). Notably, the anti-photo-aging potential of M4 was directly associated with the increased expression of MMP and SIRT1, which was followed by the up-regulation of pGC-1α, D-LOOP, and Mt-TFA, and the transcriptional activation of NRF1/NRF2. Therefore, M4 is useful for the protection of skin cells from UVA-induced photo-aging.

Vitamin D3 affects mitochondrial biogenesis through mitogen-activated protein kinase in polycystic ovary syndrome mouse model

Polycystic ovarian syndrome (PCOS) is a disorder characterized by oligomenorrhea, anovulation, and hyperandrogenism. Altered mitochondrial biogenesis can result in hyperandrogenism. The goal of this study was to examine the effect of vitamin D3 on mitochondrial biogenesis of the granulosa cells in the PCOS-induced mouse model. Vitamin D3 applies its effect via the mitogen-activated pathway kinase-extracellular signal-regulated kinases (MAPK-ERK1/2) pathway. The PCOS mouse model was induced by the injection of dehydroepiandrosterone (DHEA). Isolated granulosa cells were subsequently treated with vitamin D3, MAPK activator, and MAPK inhibitor. Gene expression levels were measured using real-time polymerase chain reaction. MAPK proteins were investigated by western blot analysis. We also determined reactive oxygen species (ROS) levels with 2', 7'-dichlorofluorescein diacetate. Mitochondrial membrane potential (mtMP) was also measured by TMJC1. Mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator 1-α and nuclear respiratory factor), antioxidant (superoxide dismutase, glutathione peroxidase, and catalase), and antiapoptotic (B-cell lymphoma-2) genes were upregulated in the PCOS mice that treated with vitamin D3 compared with the PCOS mice without any treatment. Vitamin D3 and MAPK activator-treated groups also reduced ROS levels compared with the nontreated PCOS group. In summary, vitamin D3 and MAPK activator increased the levels of mitochondrial biogenesis, MAPK pathway, and mtMP markers, while concomitantly decreased ROS levels in granulosa cells of the PCOS-induced mice. This study suggests that vitamin D3 may improve mitochondrial biogenesis through stimulation of the MAPK pathway in cultured granulosa cells of DHEA-induced PCOS mice which yet to be investigated.

The Role of Phosphatidylethanolamine Adducts in Modification of the Activity of Membrane Proteins under Oxidative Stress

Reactive oxygen species (ROS) and their derivatives, reactive aldehydes (RAs), have been implicated in the pathogenesis of many diseases, including metabolic, cardiovascular, and inflammatory disease. Understanding how RAs can modify the function of membrane proteins is critical for the design of therapeutic approaches in the above-mentioned pathologies. Over the last few decades, direct interactions of RA with proteins have been extensively studied. Yet, few studies have been performed on the modifications of membrane lipids arising from the interaction of RAs with the lipid amino group that leads to the formation of adducts. It is even less well understood how various multiple adducts affect the properties of the lipid membrane and those of embedded membrane proteins. In this short review, we discuss a crucial role of phosphatidylethanolamine (PE) and PE-derived adducts as mediators of RA effects on membrane proteins. We propose potential PE-mediated mechanisms that explain the modulation of membrane properties and the functions of membrane transporters, channels, receptors, and enzymes. We aim to highlight this new area of research and to encourage a more nuanced investigation of the complex nature of the new lipid-mediated mechanism in the modification of membrane protein function under oxidative stress.

Cold-Activated Lipid Dynamics in Adipose Tissue Highlights a Role for Cardiolipin in Thermogenic Metabolism

Thermogenic fat expends energy during cold for temperature homeostasis, and its activity regulates nutrient metabolism and insulin sensitivity. We measured cold-activated lipid landscapes in circulation and in adipose tissue by MS/MS^ALL shotgun lipidomics. We created an interactive online viewer to visualize the changes of specific lipid species in response to cold. In adipose tissue, among the approximately 1,600 lipid species profiled, we identified the biosynthetic pathway of the mitochondrial phospholipid cardiolipin as coordinately activated in brown and beige fat by cold in wild-type and transgenic mice with enhanced browning of white fat. Together, these data provide a comprehensive lipid bio-signature of thermogenic fat activation in circulation and tissue and suggest pathways regulated by cold exposure.

Mice overexpressing chromogranin A display hypergranulogenic adrenal glands with attenuated ATP levels contributing to the hypertensive phenotype

OBJECTIVE

Elevated circulating chromogranin A (CHGA) is observed in human hypertension. CHGA is critical for granulogenesis and exocytosis of catecholamine stores from secretory large dense core vesicles (LDCV). This study aims to understand the morphological, molecular and phenotypic changes because of excess CHGA and the mechanistic link eventuating in hyper-adrenergic hypertension.

METHODS

Blood pressure and heart rate was monitored in mouse models expressing normal and elevated level of CHGA by telemetry. Catecholamine and oxidative stress radicals were measured. Adrenal ultrastructure, LDCV content and mitochondrial abundance were compared and respiration analyzed by Seahorse assay. Effect of CHGA dosage on adrenal ATP content, electron transport chain components and uncoupling protein 2 (UCP-2) were compared in vivo and in vitro.

RESULTS

Mice with excess-CHGA displayed hypertensive phenotype, higher heart rate and increased sympathetic tone. They had elevated plasma catecholamine and adrenal ROS levels. Excess-CHGA caused an increase in size and abundance of LDCV and adrenal mitochondria. Nonetheless, they had attenuated levels of ATP. Isolated adrenal mitochondria from mice with elevated CHGA showed higher maximal respiration rates in the presence of protonophore, which uncouples oxidative phosphorylation. Elevated CHGA resulted in overexpression of UCP2 and diminished ATP. In vitro in chromaffin cells overexpressing CHGA, concomitant increase in UCP2 protein and decreased ATP was detected.

CONCLUSION

Elevated CHGA expression resulted in underlying bioenergetic dysfunction in ATP production despite higher mitochondrial mass. The outcome was unregulated negative feedback of LDCV exocytosis and secretion, resulting in elevated levels of circulating catecholamine and consequently the hypertensive phenotype.

Mitochondrial uncoupling proteins UCP4 and UCP5 from the Pacific white shrimp Litopenaeus vannamei

Mitochondrial uncoupling proteins (UCP) transport protons from the intermembrane space to the mitochondrial matrix uncoupling oxidative phosphorylation. In mammals, these proteins have been implicated in several cellular functions ranging from thermoregulation to antioxidant defense. In contrast, their invertebrate homologs have been much less studied despite the great diversity of species. In this study, two transcripts encoding mitochondrial uncoupling proteins were, for the first time, characterized in crustaceans. The white shrimp Litopenaeus vannamei transcript LvUCP4 is expressed in all tested shrimp tissues/organs, and its cDNA includes a coding region of 954 bp long which encodes a deduced protein 318 residues long and a predicted molecular weight of 35.3 kDa. The coding region of LvUCP5 transcript is 906 bp long, encodes a protein of 302 residues with a calculated molecular weight of 33.17 kDa. Both proteins share homology with insect UCPs, their predicted structures show the conserved motifs of the mitochondrial carrier proteins and were confirmed to be located in the mitochondria through a Western blot analysis. The genic expression of LvUCP4 and LvUCP5 was evaluated in shrimp at oxidative stress conditions and results were compared to some antioxidant enzymes to infer about their antioxidant role. LvUCP4 and LvUCP5 genes expression did not change during hypoxia/re-oxygenation, and no coordinated responses were detected with antioxidant enzymes at the transcriptional level. Results confirmed UCPs as the first uncoupling mechanism reported in this species, but their role in the oxidative stress response remains to be confirmed.

Molecular evolution of uncoupling proteins and implications for brain function

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier superfamily and catalyze important metabolic functions at the mitochondrial inner membrane. While the thermogenic role of UCP1 in brown fat of eutherian mammals is well established, the molecular functions of UCP1 in ectothermic vertebrates and of other UCP paralogs remain less clear. Here, we critically discuss the existence of brain UCPs and their potential roles. Applying phylogenetic classification of novel UCPs, we summarize the evidence for brain UCP1 among vertebrates, the role of UCP2 in specific brain areas, and the existence of brain-specific UCPs. The phylogenetic analyses and discussion on functional data should alert the scientific community that the molecular function of so-called UCP1 homologues is by far not clarified and possibly relates to neither thermogenesis nor mitochondrial uncoupling.

Can All Major ROS Forming Sites of the Respiratory Chain Be Activated By High FADH2 /NADH Ratios?: Ancient evolutionary constraints determine mitochondrial ROS formation

Aspects of peroxisome evolution, uncoupling, carnitine shuttles, supercomplex formation, and missing neuronal fatty acid oxidation (FAO) are linked to reactive oxygen species (ROS) formation in respiratory chains. Oxidation of substrates with high FADH₂ /NADH (F/N) ratios (e.g., FAs) initiate ROS formation in Complex I due to insufficient availability of its electron acceptor (Q) and reverse electron transport from QH₂ , e.g., during FAO or glycerol-3-phosphate shuttle use. Here it is proposed that the Q-cycle of Complex III contributes to enhanced ROS formation going from low F/N ratio substrates (glucose) to high F/N substrates. This contribution is twofold: 1) Complex III uses Q as substrate, thus also competing with Complex I; 2) Complex III itself will produce more ROS under these conditions. I link this scenario to the universally observed Complex III dimerization. The Q-cycle of Complex III thus again illustrates the tension between efficient ATP generation and endogenous ROS formation. This model can explain recent findings concerning succinate and ROS-induced uncoupling.

Uncoupling protein-1 deficiency promotes brown adipose tissue inflammation and ER stress

Inflammation and endoplasmic reticulum (ER) stress are hallmarks of metabolic syndrome. While these metabolic derangements have been well-investigated in white adipose tissue, their existence and etiology in brown adipose tissue (BAT) are poorly understood. Here, we aimed to investigate ER homeostasis and the inflammatory status and of BAT lacking uncoupling protein-1 (UCP1), a protein required for BAT thermogenesis. H&E staining illustrated lipid accumulation and crown-like structures surrounding adipocytes in BAT of UCP1-/- mice housed at room temperature compared to control mice. Further, immunohistological evaluation of F4/80 and gene expression studies demonstrated BAT macrophage infiltration and robust elevation of pro-inflammatory markers in UCP1-/- BAT. ER stress was also present in BAT of UCP1-/- mice, as evidenced by elevated gene expression and post-translational modifications of unfolded protein response components. After four weeks of thermoneutral housing, UCP1-/- mice did not exhibit elevated BAT inflammation and ER stress gene expression compared to WT mice, but depot expansion persisted. Collectively, we demonstrate that the effects of UCP1 deficiency in BAT are not restricted to mitochondrial uncoupling. We conclude that brown adipose tissue of UCP1-/- mice exhibits pro-inflammatory immune cell infiltration and perturbations in ER homeostasis and that this phenotype is driven by cold exposure rather than lipid accumulation.

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.

Targeting Mitochondrial Ion Channels to Fight Cancer

In recent years, several experimental evidences have underlined a new role of ion channels in cancer development and progression. In particular, mitochondrial ion channels are arising as new oncological targets, since it has been proved that most of them show an altered expression during tumor development and the pharmacological targeting of some of them have been demonstrated to be able to modulate cancer growth and progression, both in vitro as well as in vivo in pre-clinical mouse models. In this scenario, pharmacology of mitochondrial ion channels would be in the near future a new frontier for the treatment of tumors. In this review, we discuss the new advances in the field, by focusing our attention on the improvements in new drug developments to target mitochondrial ion channels.

Protective mechanisms involving enhanced mitochondrial functions and mitophagy against T-2 toxin-induced toxicities in GH3 cells

T-2 toxin is the most toxic member of trichothecene mycotoxin. So far, the mechanism of mitochondrial toxicity and protective mechanism in mammalian cells against T-2 toxin are not fully understood. In this study, we aimed to investigate the cellular and mitochondrial toxicity of T-2 toxin, and the cellular protective mechanisms in rat pituitary GH3 cells. We showed that T-2 toxin significantly increased reactive oxygen species (ROS) and DNA damage and caused apoptosis in GH3 cells. T-2 toxin induced abnormal cell morphology, cytoplasm and nuclear shrinkage, nuclear fragmentation and formation of apoptotic bodies and autophagosomes. The mitochondrial degradative morphologies included local or total cristae collapse and small condensed mitochondria. T-2 toxin decreased the mitochondrial membrane potential. However, T-2 toxin significantly increased the superoxide dismutase (SOD) activity and expression of antioxidant genes glutathione peroxidase 1 (GPx-1), catalase (CAT), mitochondria-specific SOD-2 and mitochondrial uncoupling protein-1, -2 and -3 (UCP-1, 2 and 3). Interestingly, T-2 toxin increased adenosine triphosphate (ATP) levels and mitochondrial complex I activity, and increased the expression of most of mitochondrial electron transport chain subunits tested and critical transcription factors controlling mitochondrial biogenesis and mitochondrial DNA transcription and replication. T-2 toxin increased mitophagic activity by increasing the expression of mitophagy-specific proteins NIP-like protein X (NIX), PTEN-induced putative kinase protein 1 (PINK1) and E3 ubiquitin ligase Parkin. T-2 toxin activated the protective protein kinase A (PKA) signaling pathway, which activated the nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/PINK1/Parkin pathway to mediate mitophagy. Taken together, our results suggested that the mammalian cells could increase their resistance against T-2 toxin by increasing the antioxidant activity, mitophagy and mitochondrial function.

Use the Protonmotive Force: Mitochondrial Uncoupling and Reactive Oxygen Species

Mitochondrial respiration results in an electrochemical proton gradient, or protonmotive force (pmf), across the mitochondrial inner membrane. The pmf is a form of potential energy consisting of charge (∆ψ_m) and chemical (∆pH) components, that together drive ATP production. In a process called uncoupling, proton leak into the mitochondrial matrix independent of ATP production dissipates the pmf and energy is lost as heat. Other events can directly dissipate the pmf independent of ATP production as well, such as chemical exposure or mechanisms involving regulated mitochondrial membrane electrolyte transport. Uncoupling has defined roles in metabolic plasticity and can be linked through signal transduction to physiologic events. In the latter case, the pmf impacts mitochondrial reactive oxygen species (ROS) production. Although capable of molecular damage, ROS also have signaling properties that depend on the timing, location, and quantity of their production. In this review, we provide a general overview of mitochondrial ROS production, mechanisms of uncoupling, and how these work in tandem to affect physiology and pathologies, including obesity, cardiovascular disease, and immunity. Overall, we highlight that isolated bioenergetic models-mitochondria and cells-only partially recapitulate the complex link between the pmf and ROS signaling that occurs in vivo.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

A fatty acid analogue targeting mitochondria exerts a plasma triacylglycerol lowering effect in rats with impaired carnitine biosynthesis

L-carnitine is important for the catabolism of long-chain fatty acids in the mitochondria. We investigated how the triacylglycerol (TAG)-lowering drug 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA) influenced lipid metabolism in carnitine-depleted, 3-(2,2,2-trimethylhydrazinium)propionate dehydrate (Mildronate; meldonium)-treated male Wistar rats. As indicated, carnitine biosynthesis was impaired by Mildronate. However, TAG levels of both plasma and liver were decreased by 1-triple TTA in Mildronate-treated animals. This was accompanied by increased gene expression of proteins involved in mitochondrial activity and proliferation and reduced mRNA levels of Dgat2, ApoB and ApoCIII in liver. The hepatic energy state was reduced in the group of Mildronate and 1-triple TTA as reflected by increased AMP/ATP ratio, reduced energy charge and induced gene expression of uncoupling proteins 2 and 3. The increase in mitochondrial fatty acid oxidation was observed despite low plasma carnitine levels, and was linked to strongly induced gene expression of carnitine acetyltransferase, translocase and carnitine transporter, suggesting an efficient carnitine turnover. The present data suggest that the plasma TAG-lowering effect of 1-triple TTA in Mildronate-treated rats is not only due to increased mitochondrial fatty acid oxidation reflected by increased mitochondrial biogenesis, but also to changes in plasma clearance and reduced TAG biosynthesis.

The Pancreatic β-Cell: A Bioenergetic Perspective

The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.

The molecular features of uncoupling protein 1 support a conventional mitochondrial carrier-like mechanism

Uncoupling protein 1 (UCP1) is an integral membrane protein found in the mitochondrial inner membrane of brown adipose tissue, and facilitates the process of non-shivering thermogenesis in mammals. Its activation by fatty acids, which overcomes its inhibition by purine nucleotides, leads to an increase in the proton conductance of the inner mitochondrial membrane, short-circuiting the mitochondrion to produce heat rather than ATP. Despite 40 years of intense research, the underlying molecular mechanism of UCP1 is still under debate. The protein belongs to the mitochondrial carrier family of transporters, which have recently been shown to utilise a domain-based alternating-access mechanism, cycling between a cytoplasmic and matrix state to transport metabolites across the inner membrane. Here, we review the protein properties of UCP1 and compare them to those of mitochondrial carriers. UCP1 has the same structural fold as other mitochondrial carriers and, in contrast to past claims, is a monomer, binding one purine nucleotide and three cardiolipin molecules tightly. The protein has a single substrate binding site, which is similar to those of the dicarboxylate and oxoglutarate carriers, but also contains a proton binding site and several hydrophobic residues. As found in other mitochondrial carriers, UCP1 has two conserved salt bridge networks on either side of the central cavity, which regulate access to the substrate binding site in an alternating way. The conserved domain structures and mobile inter-domain interfaces are consistent with an alternating access mechanism too. In conclusion, UCP1 has retained all of the key features of mitochondrial carriers, indicating that it operates by a conventional carrier-like mechanism.

Features of omental adipose tissue in endometrial cancer patients with 'standard' or 'metabolically healthy' obesity: associations with tumor process characteristics

Purpose

Adipose tissue products may contribute to endometrial cancer (EC) initiation and further growth that encourages the analysis of this issue in patients with different obesity phenotypes.

Methods/patients

Omental fat depot characteristics were studied in EC patients (n = 57) with “standard” (SO) or “metabolically healthy” (MHO) obesity. Collected omental samples were evaluated by immunohistochemistry /IHC/ for brown fat marker UCP1, CYP19 (aromatase) and macrophage infiltration markers (CD68, CD163, crown-like structures/CLS) expression. Total RNA extracted from the same samples was investigated for UCP1, CYP19, PTEN and adipokine omentin mRNA.

Results

Immunohistochemistry data revealed a statistically significant increase in aromatase and CD68 expression and tendency to increase of UCP1 expression in SO patients’ omental fat compared to samples obtained from MHO patients. Additionally, positive correlation of EC clinical stage with UCP1 protein and its mRNA content in omental fat was pronounced in MHO as well as SO group, while with omentin mRNA it was discovered only in patients with SO. An inclination to the correlation with better tumor differentiation was seen for UCP1 and CD68 protein expression in patients with MHO and with worse (high grade) differentiation—for CD68 expression in the group with SO.

Conclusions

In aggregate, this suggests that obesity phenotype has significant impact on omental fat tissue characteristics which is related to the clinical course of EC and may have practical consequences.

The conserved regulation of mitochondrial uncoupling proteins: From unicellular eukaryotes to mammals

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier protein family and mediate regulated proton leak across the inner mitochondrial membrane. Free fatty acids, aldehydes such as hydroxynonenal, and retinoids activate UCPs. However, there are some controversies about the effective action of retinoids and aldehydes alone; thus, only free fatty acids are commonly accepted positive effectors of UCPs. Purine nucleotides such as GTP inhibit UCP-mediated mitochondrial proton leak. In turn, membranous coenzyme Q may play a role as a redox state-dependent metabolic sensor that modulates the complete activation/inhibition of UCPs. Such regulation has been observed for UCPs in microorganisms, plant and animal UCP1 homologues, and UCP1 in mammalian brown adipose tissue. The origin of UCPs is still under debate, but UCP homologues have been identified in all systematic groups of eukaryotes. Despite the differing levels of amino acid/DNA sequence similarities, functional studies in unicellular and multicellular organisms, from amoebae to mammals, suggest that the mechanistic regulation of UCP activity is evolutionarily well conserved. This review focuses on the regulatory feedback loops of UCPs involving free fatty acids, aldehydes, retinoids, purine nucleotides, and coenzyme Q (particularly its reduction level), which may derive from the early stages of evolution as UCP first emerged.

Uncoupling Protein 2 Increases Susceptibility to Lipopolysaccharide-Induced Acute Lung Injury in Mice

Uncoupling protein 2 (UCP2) is upregulated in patients with systemic inflammation and infection, but its functional role is unclear. We up- or downregulated UCP2 expression using UCP2 recombinant adenovirus or the UCP2 inhibitor, genipin, in lungs of mice, and investigated the mechanisms of UCP2 in ALI. UCP2 overexpression in mouse lungs increased LPS-induced pathological changes, lung permeability, lung inflammation, and lowered survival rates. Furthermore, ATP levels and mitochondrial membrane potential were decreased, while reactive oxygen species production was increased. Additionally, mitogen-activated protein kinases (MAPKs) activity was elevated, which increased the sensitivity to LPS-induced apoptosis and inflammation. LPS-induced apoptosis and release of inflammatory factors were alleviated by pretreatment of the Jun N-terminal kinase (JNK) inhibitor SP600125 or the p38 MAPK inhibitor SB203580, but not by the extracellular signal-regulated kinase (ERK) inhibitor PD98059 in UCP2-overexpressing mice. On the other hand, LPS-induced alveolar epithelial cell death and inflammation were attenuated by genipin. In conclusion, UCP2 increased susceptibility to LPS-induced cell death and pulmonary inflammation, most likely via ATP depletion and activation of MAPK signaling following ALI in mice.

Resveratrol and the mitochondria: From triggering the intrinsic apoptotic pathway to inducing mitochondrial biogenesis, a mechanistic view

BACKGROUND

Mitochondria, the power plants of the cell, are known as a cross-road of different cellular signaling pathways. These cytoplasmic double-membraned organelles play a pivotal role in energy metabolism and regulate calcium flux in the cells. It is well known that mitochondrial dysfunction is associated with different diseases such as neurodegeneration and cancer. A growing body of literature has shown that polyphenolic compounds exert direct effects on mitochondrial ultra-structure and function. Resveratrol is known as one of the most common bioactive constituents of red wine, which improves mitochondrial functions under in vitro and in vivo conditions.

SCOPE OF REVIEW

This paper aims to review the molecular pathways underlying the beneficial effects of resveratrol on mitochondrial structure and functions. In addition, we discuss the chemistry and main sources of resveratrol.

MAJOR CONCLUSIONS

Resveratrol represents the promising effects on mitochondria in different experimental models. However, there are several reports on the detrimental effects elicited by resveratrol on mitochondria.

GENERAL SIGNIFICANCE

An understanding of the chemistry and source of resveratrol, its bioavailability and the promising effects on mitochondria brings a new hope to therapy of mitochondrial dysfunction-related diseases.

Mimicking respiratory phosphorylation using purified enzymes

The enzymes of oxidative phosphorylation is a striking example of the functional association of multiple enzyme complexes, working together to form ATP from cellular reducing equivalents. These complexes, such as cytochrome c oxidase or the ATP synthase, are typically investigated individually and therefore, their functional interplay is not well understood. Here, we present methodology that allows the co-reconstitution of purified terminal oxidases and ATP synthases in synthetic liposomes. The enzymes are functionally coupled via proton translocation where upon addition of reducing equivalents the oxidase creates and maintains a transmembrane electrochemical proton gradient that energizes the synthesis of ATP by the F1F0 ATP synthase. The method has been tested with the ATP synthases from Escherichia coli and spinach chloroplasts, and with the quinol and cytochrome c oxidases from E. coli and Rhodobacter sphaeroides, respectively. Unlike in experiments with the ATP synthase reconstituted alone, the setup allows in vitro ATP synthesis under steady state conditions, with rates up to 90 ATP×s(-1)×enzyme(-1). We have also used the novel system to study the phenomenon of "mild uncoupling" as observed in mitochondria upon addition of low concentrations of ionophores (e.g. FCCP, SF6847) and the recoupling effect of 6-ketocholestanol. While we could reproduce the described effects, our data with the in vitro system does not support the idea of a direct interaction between a mitochondrial protein and the uncoupling agents as proposed earlier.

Mitochondrial oxidative metabolism and uncoupling proteins in the failing heart

Despite significant progress in cardiovascular medicine, myocardial ischemia and infarction, progressing eventually to the final end point heart failure (HF), remain the leading cause of morbidity and mortality in the USA. HF is a complex syndrome that results from any structural or functional impairment in ventricular filling or blood ejection. Ultimately, the heart's inability to supply the body's tissues with enough blood may lead to death. Mechanistically, the hallmarks of the failing heart include abnormal energy metabolism, increased production of reactive oxygen species (ROS) and defects in excitation-contraction coupling. HF is a highly dynamic pathological process, and observed alterations in cardiac metabolism and function depend on the disease progression. In the early stages, cardiac remodeling characterized by normal or slightly increased fatty acid (FA) oxidation plays a compensatory, cardioprotective role. However, upon progression of HF, FA oxidation and mitochondrial oxidative activity are decreased, resulting in a significant drop in cardiac ATP levels. In HF, as a compensatory response to decreased oxidative metabolism, glucose uptake and glycolysis are upregulated, but this upregulation is not sufficient to compensate for a drop in ATP production. Elevated mitochondrial ROS generation and ROS-mediated damage, when they overwhelm the cellular antioxidant defense system, induce heart injury and contribute to the progression of HF. Mitochondrial uncoupling proteins (UCPs), which promote proton leak across the inner mitochondrial membrane, have emerged as essential regulators of mitochondrial membrane potential, respiratory activity and ROS generation. Although the physiological role of UCP2 and UCP3, expressed in the heart, has not been clearly established, increasing evidence suggests that these proteins by promoting mild uncoupling could reduce mitochondrial ROS generation and cardiomyocyte apoptosis and ameliorate thereby myocardial function. Further investigation on the alterations in cardiac UCP activity and regulation will advance our understanding of their physiological roles in the healthy and diseased heart and also may facilitate the development of novel and more efficient therapies.

Transcriptional changes in Atlantic salmon (Salmo salar) after embryonic exposure to road salt

Road salt is extensively used as a deicing chemical in road maintenance during winter and has in certain areas of the world led to density stratifications in lakes and ponds, and adversely impacted aquatic organisms in the recipients of the road run-off. Aquatic vertebrates such as fish have been particularly sensitive during fertilisation, as the fertilisation of eggs involves rapid uptake of the surrounding water, reduction in egg swelling and in ovo exposure to high road salt concentrations. The present study aimed to identify the persistent molecular changes occurring in Atlantic salmon (Salmo salar) eggs after 24h exposure to high concentrations (5000 mg/L) of road salt at fertilisation. The global transcriptional changes were monitored by a 60k salmonid microarray at the eyed egg stage (cleavage stage, 255 degree days after fertilisation) and identified a high number of transcripts being differentially regulated. Functional enrichment, pathway and gene-gene interaction analysis identified that the differentially expressed genes (DEGs) were mainly associated with toxiciologically relevant processes involved in osmoregulation, ionregulation, oxidative stress, metabolism (energy turnover), renal function and developmental in the embryos. Quantitative rtPCR analysis of selected biomarkers, identified by global transcriptomics, were monitored in the eggs for an extended range of road salt concentrations (0, 50, 100, 500 and 5000 mg/L) and revealed a positive concentration-dependent increase in cypa14, a gene involved in lipid turnover and renal function, and nav1, a gene involved in neuraxonal development. Biomarkers for osmoregulatory responses such as atp1a2, the gene encoding the main sodium/potassium ATP-fueled transporter for chloride ions, and txdc9, a gene involved in regulation of cell redox homeostasis (oxidative stress), displayed apparent concentration-dependency with exposure, although large variance in the control group precluded robust statistical discrimination between the groups. A No Transcriptional Effect Level (NOTEL) of 50mg/L road salt was found to be several orders of magnitude lower than the adverse effects documented in developing fish embryos elsewhere, albeit at concentrations realistic in lotic systems receiving run-off from road salt. It remains to be determined whether these transcriptional changes may cause adverse effects in fish at ecologically relevant exposure concentrations of road salt.

The effect of delivery type on uncoupling protein-2 levels

OBJECTIVE

Uncoupling proteins (UCPs) are carrier proteins located in the mitochondrial inner membrane that disturb the proton gradient by re-transporting protons and that thus inhibit ATP synthesis. UCP-2 is found in in several tissues, particularly the brain. This study was performed to examine the effects of mode of delivery on UCP-2 in humans.

METHODS

The study was performed prospectively. Cord blood specimens were collected for measurement of blood gasses, full-blood count, total and direct bilirubin levels and UCP-2. UCP-2 levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit. Results were expressed as nanogram per milliliter.

RESULTS

The study was performed with 120 healthy term babies, 60 born by normal spontaneous vaginal delivery (NSVD) and 60 by cesarean/section (C/S). There was significant difference in UCP-2 levels between the two groups. UCP-2 levels were significantly higher in the cases born by NSVD then in the cases born by C/S.

CONCLUSION

This study showed that a correlation exists between mode of delivery and UCP-2 in humans. As UCP-2 is described as playing a significant role in the formation of nerve cells and deficiency of this protein during development of the brain may lead to behavioral problems extending to adulthood, we think that increasing UCP-2 levels through normal delivery will protect all organs, and particularly the brain, against oxidative damage and play a role in preventing organ dysfunctions.

Polymorphisms of the UCP2 Gene Are Associated with Glomerular Filtration Rate in Type 2 Diabetic Patients and with Decreased UCP2 Gene Expression in Human Kidney

INTRODUCTION

Uncoupling protein 2 (UCP2) reduces production of reactive oxygen species (ROS) by mitochondria. ROS overproduction is one of the major contributors to the pathogenesis of chronic diabetic complications, such as diabetic kidney disease (DKD). Thus, deleterious polymorphisms in the UCP2 gene are candidate risk factors for DKD. In this study, we investigated whether UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms were associated with DKD in patients with type 2 diabetes mellitus (T2DM), and whether they had an effect on UCP2 gene expression in human kidney tissue biopsies.

MATERIALS AND METHODS

In a case-control study, frequencies of the UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms as well as frequencies of the haplotypes constituted by them were analyzed in 287 T2DM patients with DKD and 281 T2DM patients without this complication. In a cross-sectional study, UCP2 gene expression was evaluated in 42 kidney biopsy samples stratified according to the presence of the UCP2 mutated -866A/55Val/Ins haplotype.

RESULTS

In the T2DM group, multivariate logistic regression analysis showed that the -866A/55Val/Ins haplotype was an independent risk factor for DKD (OR = 2.136, 95% CI 1.036-4.404), although neither genotype nor allele frequencies of the individual polymorphisms differed between case and control groups. Interestingly, T2DM patients carrying the mutated haplotype showed decreased estimated glomerular filtration rate (eGFR) when compared to subjects with the reference haplotype (adjusted P= 0.035). In kidney biopsy samples, UCP2 expression was significantly decreased in UCP2 mutated haplotype carriers when compared to kidneys from patients with the reference haplotype (0.32 ± 1.20 vs. 1.85 ± 1.16 n fold change; adjusted P< 0.000001).

DISCUSSION

Data reported here suggest that the UCP2 -866A/55Val/Ins haplotype is associated with an increased risk for DKD and with a lower eGFR in T2DM patients. Furthermore, this mutated haplotype was associated with decreased UCP2 gene expression in human kidneys.

Metabolically inert perfluorinated fatty acids directly activate uncoupling protein 1 in brown-fat mitochondria

The metabolically inert perfluorinated fatty acids perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) can display fatty acid-like activity in biological systems. The uncoupling protein 1 (UCP1) in brown adipose tissue is physiologically (re)activated by fatty acids, including octanoate. This leads to bioenergetically uncoupled energy dissipation (heat production, thermogenesis). We have examined here the possibility that PFOA/PFOS can directly (re)activate UCP1 in isolated mouse brown-fat mitochondria. In wild-type brown-fat mitochondria, PFOS and PFOA overcame GDP-inhibited thermogenesis, leading to increased oxygen consumption and dissipated membrane potential. The absence of this effect in brown-fat mitochondria from UCP1-ablated mice indicated that it occurred through activation of UCP1. A competitive type of inhibition by increased GDP concentrations indicated interaction with the same mechanistic site as that utilized by fatty acids. No effect was observed in heart mitochondria, i.e., in mitochondria without UCP1. The stimulatory effect of PFOA/PFOS was not secondary to non-specific mitochondrial membrane permeabilization or to ROS production. Thus, metabolic effects of perfluorinated fatty acids could include direct brown adipose tissue (UCP1) activation. The possibility that this may lead to unwarranted extra heat production and thus extra utilization of food resources, leading to decreased fitness in mammalian wildlife, is discussed, as well as possible negative effects in humans. However, a possibility to utilize PFOA-/PFOS-like substances for activating UCP1 therapeutically in obesity-prone humans may also be envisaged.

In the Early Stages of Diabetes, Rat Retinal Mitochondria Undergo Mild Uncoupling due to UCP2 Activity

In order to maintain high transmembrane ionic gradients, retinal tissues require a large amount of energy probably provided by a high rate of both, glycolysis and oxidative phosphorylation. However, little information exists on retinal mitochondrial efficiency. We analyzed the retinal mitochondrial activity in ex vivo retinas and in isolated mitochondria from normal rat retina and from short-term streptozotocin-diabetic rats. In normal ex vivo retinas, increasing glucose concentrations from 5.6mM to 30mM caused a four-fold increase in glucose accumulation and CO₂ production. Retina from diabetic rats accumulated similar amounts of glucose. However, CO₂ production was not as high. Isolated mitochondria from normal rat retina exhibited a resting rate of oxygen consumption of 14.6 ± 1.1 natgO (min.mg prot)^-1 and a respiratory control of 4.0. Mitochondria from 7, 20 and 45 days diabetic rats increased the resting rate of oxygen consumption and the activity of the electron transport complexes; under these conditions the mitochondrial transmembrane potential decreased. In spite of this, the ATP synthesis was not modified. GDP, an UCP2 inhibitor, increased mitochondrial membrane potential and superoxide production in controls and at 45 days of diabetes. The role of UCP2 is discussed. The results suggest that at the early stage of diabetes we studied, retinal mitochondria undergo adaptations leading to maintain energetic requirements and prevent oxidative stress.

The gene polymorphisms of UCP1 but not PPAR γ and TCF7L2 are associated with diabetic retinopathy in Chinese type 2 diabetes mellitus cases

PURPOSE

This study was designed to investigate the association between the polymorphisms in three insulin resistance-related genes, uncoupling protein-1 (UCP1), peroxisome proliferator-activated receptor γ (PPARγ) and transcription factor 7-like 2 (TCF7L2) and the susceptibility to diabetic retinopathy (DR) in a Chinese type 2 diabetes mellitus (T2DM) cohort.

METHODS

A total of 792 patients with T2DM were enrolled and categorized into two groups: (1) the DR group consisted of 448 patients, which was further subclassified into a proliferative DR (PDR) group with 220 patients and a non-proliferative DR (NPDR) group with 228 patients; (2) the diabetes without retinopathy (DNR) group, comprised 344 patients who had no signs of DR. Single-nucleotide polymorphisms (SNPs), rs1800592 in the UCP1 gene, rs1801282, rs3856806 and rs1249719 in the PPARγ gene and rs11196205 in the TCF7L2 gene were genotyped in this study.

RESULTS

For SNP rs1800592 of the UCP1 gene, the frequency of allele G and genotype GG was significantly higher in the PDR group than in the DNR group (allele OR: 1.32, 95% CI: 1.03-1.68, p = 0.03; genotype OR: 1.72, 95%CI: 1.06-2.79, p = 0.03). No evident association was found between the allele frequencies and genotype distributions of any individual SNP in the PPARγ or TCF7L2 genes and DR, PDR or NPDR. Haplotype analyses of the PPARγ gene did not provide any evidence for an association with DR, PDR or NPDR in this Chinese T2DM cohort.

CONCLUSIONS

This study suggests that the SNP rs1800592 in the UCP1 gene is associated with increased risk of PDR in the Chinese T2DM population.

Persistent reduced oxygen requirement following blood transfusion during recovery from hemorrhagic shock

Our study intended to determine the effects on oxygen uptake (VO2) of restoring a normal rate of O2 delivery following blood transfusion (BT) after a severe hemorrhage (H). Spontaneously breathing urethane anesthetized rats were bled by removing 20 ml/kg of blood over 30 min. Rats were then infused with their own shed blood 15 min after the end of H. At mid-perfusion, half of the rats received a unique infusion of the decoupling agent 2,4-dinitrophenol (DNP, 6 mg/kg). VO2 and arterial blood pressure (ABP) were continuously measured throughout the study, along with serial determination of blood lactate concentration [La]. Animals were euthanized 45 min after the end of reperfusion; liver and lungs were further analyzed for early expression of oxidative stress gene using RT-PCR. Our bleeding protocol induced a significant decrease in ABP and increase in [La], while VO2 dropped by half. The O2 deficit progressively accumulated during the period of bleeding reached -114 ± 53 ml/kg, just before blood transfusion. Despite the transfusion of blood, a significant O2 deficit persisted (-82 ± 59 ml/kg) 45 min after reperfusion. This slow recovery of VO2 was sped up by DNP injection, leading to a fast recovery of O2 deficit after reperfusion, becoming positive (+460 ± 132 ml/kg) by the end of the protocol, supporting the view that O2 supply is not the main controller of VO2 dynamics after BT. Of note is that DNP also enhanced oxidative stress gene expression (up-regulation of NADPH oxidase 4 in the lung for instance). The mechanism of slow recovery of O2 requirement/demand following BT and the resulting effects on tissues exposed to relatively high O2 partial pressure are discussed.

Low levels of lipopolysaccharide modulate mitochondrial oxygen consumption in skeletal muscle

OBJECTIVE

We have previously demonstrated that activation of toll-like receptor 4 (TLR4) in skeletal muscle results in an increased reliance on glucose as an energy source and a concomitant decrease in fatty acid oxidation under basal conditions. Herein, we examined the effects of lipopolysaccharide (LPS), the primary ligand for TLR4, on mitochondrial oxygen consumption in skeletal muscle cell culture and mitochondria isolated from rodent skeletal muscle.

MATERIALS/METHODS

Skeletal muscle cell cultures were exposed to LPS and oxygen consumption was assessed using a Seahorse Bioscience extracellular flux analyzer. Mice were also exposed to LPS and oxygen consumption was assessed in mitochondria isolated from skeletal muscle.

RESULTS

Acute LPS exposure resulted in significant reductions in Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP)-stimulated maximal respiration (state 3u) and increased oligomycin induced state 4 (state 4O) respiration in C2C12 and human primary myotubes. These findings were observed in conjunction with increased mRNA of uncoupling protein 3 (UCP3), superoxide dismutase 2 (SOD2), and pyruvate dehydrogenase activity. The LPS-mediated changes in substrate oxidation and maximal mitochondrial respiration were prevented in the presence of the antioxidants N-acetylcysteine and catalase, suggesting a potential role of reactive oxygen species in mediating these effects. Mitochondria isolated from red gastrocnemius and quadriceps femoris muscle from mice injected with LPS also demonstrated reduced respiratory control ratio (RCR), and ADP- and FCCP-stimulated respiration.

CONCLUSION

LPS exposure in skeletal muscle alters mitochondrial oxygen consumption and substrate preference, which is absent when antioxidants are present.