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

Binge alcohol induces NRF2-related antioxidant response in the skeletal muscle of female mice

BACKGROUND

Chronic alcohol enhances oxidative stress, but the temporal response of antioxidant genes in skeletal muscle following a binge drinking episode remains unknown.

METHODS

Experiment 1: C57BL/6Hsd female mice received an IP injection of saline (CON; n = 39) or ethanol (ETOH; n = 39) (5 g/kg). Gastrocnemius muscles were collected from baseline (untreated; n = 3), CON (n = 3), and ETOH (n = 3) mice every 4 h for 48 h. Experiment 2: Gastrocnemius muscles were collected from control-fed (CON-FED; n = 17), control-fasted (CON-FAST; n = 18), or alcohol-fed (ETOH-FED; n = 18) mice every 4hrs for 20hrs after saline or ethanol (5 g/kg).

RESULTS

EtOH enhanced Superoxide dismutase 1 (Sod1) and NADPH Oxidase 4 (Nox4) from 24 to 48hr after the binge, while Sod2 and Nox2 were suppressed. Nuclear factor erythroid-derived 2-like 2 (Nrf2) and Kelch-like ECH-associated protein 1 (Keap1) increased 12hrs after intoxication. Cytochrome P450 oxidoreductase (Por), Heme oxygenase 1 (Ho1), Peroxiredoxin 6 (Prdx6), Glutamate-cysteine ligase catalytic subunit (Gclc), Glutamate-cysteine ligase modifier subunit (Gclm), and Glutathione-disulfide reductase (Gsr) were increased by ETOH starting 12-16hrs post-binge. Fasting had similar effects on Nrf2 compared to alcohol, but downstream targets of NRF2, including Por, Ho1, Gclc, and Gclm, were differentially altered with fasting and EtOH.

CONCLUSION

These data suggest that acute alcohol intoxication induced markers of oxidative stress and antioxidant signaling through the NRF2 pathway and that there were effects of alcohol independent of a possible decrease in food intake caused by binge intoxication.

Muscle-UCP3 in the regulation of energy metabolism

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

Considerations for developing mitochondrial transplantation techniques for individualized medicine

Tweetable abstract Mitochondrial transplantation has been used to treat various diseases associated with mitochondrial dysfunction. Here, we highlight the considerations in quality control mechanisms that should be considered in the context of mitochondrial transplantation.

Phylogenetic conservation of the interdependent homeostatic relationship of sleep regulation and redox metabolism

Sleep is an essential and evolutionarily conserved process that affects many biological functions that are also strongly regulated by cellular metabolism. The interdependence between sleep homeostasis and redox metabolism, in particular, is such that sleep deprivation causes redox metabolic imbalances in the form of over-production of ROS. Likewise (and vice versa), accumulation of ROS leads to greater sleep pressure. Thus, it is theorized that one of the functions of sleep is to act as the brain's "antioxidant" at night by clearing oxidation built up from daily stress of the active day phase. In this review, we will highlight evidence linking sleep homeostasis and regulation to redox metabolism by discussing (1) the bipartite role that sleep-wake neuropeptides and hormones have in redox metabolism through comparing cross-species cellular and molecular mechanisms, (2) the evolutionarily metabolic changes that accompanied the development of sleep loss in cavefish, and finally, (3) some of the challenges of uncovering the cellular mechanism underpinning how ROS accumulation builds sleep pressure and cellularly, how this pressure is cleared.

Human mitochondrial uncoupling protein 3 functions as a metabolite transporter

Since its discovery, a major debate about mitochondrial uncoupling protein 3 (UCP3) has been whether its metabolic actions result primarily from mitochondrial inner membrane proton transport, a process that decreases respiratory efficiency and ATP synthesis. However, UCP3 expression and activity are induced by conditions that would seem at odds with inefficient 'uncoupled' respiration, including fasting and exercise. Here, we demonstrate that the bacterially expressed human UCP3, reconstituted into liposomes, catalyses a strict exchange of aspartate, malate, sulphate and phosphate. The R282Q mutation abolishes the transport activity of the protein. Although the substrate specificity and inhibitor sensitivity of UCP3 display similarity with that of its close homolog UCP2, the two proteins significantly differ in their transport mode and kinetic constants.

Oxidase enzyme genes are differentially expressed during Acanthamoeba castellanii encystment

Acanthamoeba castellanii, a ubiquitous protozoan, is responsible for significant diseases such as Acanthamoeba keratitis and granulomatous amoebic encephalitis. A crucial survival strategy of A. castellanii involves the formation of highly resistant cysts during adverse conditions. This study delves into the cellular processes underpinning encystment, focusing on gene expression changes related to reactive oxygen species (ROS) balance, with a particular emphasis on mitochondrial processes. Our findings reveal a dynamic response within the mitochondria during encystment, with the downregulation of key enzymes involved in oxidative phosphorylation (COX, AOX, and NADHalt) during the initial 48 h, followed by their overexpression at 72 h. This orchestrated response likely creates a pro-oxidative environment, facilitating encystment. Analysis of other ROS processing enzymes across the cell reveals differential expression patterns. Notably, antioxidant enzymes, such as catalases, glutaredoxins, glutathione S-transferases, peroxiredoxins, and thioredoxins, mirror the mitochondrial trend of downregulation followed by upregulation. Additionally, glycolysis and gluconeogenesis are downregulated during the early stages in order to potentially balance the metabolic requirement of the cyst. Our study underscores the importance of ROS regulation in Acanthamoeba encystment. Understanding these mechanisms offers insights into infection control and identifies potential therapeutic targets. This work contributes to unraveling the complex biology of A. castellanii and may aid in combatting Acanthamoeba-related infections. Further research into ROS and oxidase enzymes is warranted, given the organism's remarkable respiratory versatility.

Understanding mechanisms of antioxidant action in health and disease

Several different reactive oxygen species (ROS) are generated in vivo. They have roles in the development of certain human diseases whilst also performing physiological functions. ROS are counterbalanced by an antioxidant defence network, which functions to modulate ROS levels to allow their physiological roles whilst minimizing the oxidative damage they cause that can contribute to disease development. This Review describes the mechanisms of action of antioxidants synthesized in vivo, antioxidants derived from the human diet and synthetic antioxidants developed as therapeutic agents, with a focus on the gaps in our current knowledge and the approaches needed to close them. The Review also explores the reasons behind the successes and failures of antioxidants in treating or preventing human disease. Antioxidants may have special roles in the gastrointestinal tract, and many lifestyle features known to promote health (especially diet, exercise and the control of blood glucose and cholesterol levels) may be acting, at least in part, by antioxidant mechanisms. Certain reactive sulfur species may be important antioxidants but more accurate determinations of their concentrations in vivo are needed to help assess their contributions.

Antioxidant effects of LEDT in dystrophic muscle cells: involvement of PGC-1α and UCP-3 pathways

PURPOSE

Reactive oxygen species and mitochondrial dysfunction play a crucial role in the pathophysiology of Duchenne muscular dystrophy (DMD). The light-emitting diode therapy (LEDT) showed beneficial effects on the dystrophic muscles. However, the mechanisms of this therapy influence the molecular pathways in the dystrophic muscles, particularly related to antioxidant effects, which still needs to be elucidated. The current study provides muscle cell-specific insights into the effect of LEDT, 48 h post-irradiation, on oxidative stress and mitochondrial parameters in the dystrophic primary muscle cells in culture.

METHODS

Dystrophic primary muscle cells were submitted to LEDT, at multiple wavelengths (420 nm, 470 nm, 660 nm and 850 nm), 0.5 J dose, and evaluated after 48 h based on oxidative stress markers, antioxidant enzymatic system and biogenesis, and functional mitochondrial parameters.

RESULTS

The mdx muscle cells treated with LEDT showed a significant reduction of H2O2 production and 4-HNE, catalase, SOD-2, and GR levels. Upregulation of UCP3 was observed with all wavelengths while upregulation of PGC-1α and a slight upregulation of electron transport chain complexes III and V was only observed following 850 nm LEDT. In addition, the mitochondrial membrane potential and mitochondrial mass mostly tended to be increased following LEDT, while parameters like O2·- production tended to be decreased.

CONCLUSION

The data shown here highlight the potential of LEDT as a therapeutic agent for DMD through its antioxidant action by modulating PGC-1α and UCP3 levels.

Milk fat globule size: Unraveling the intricate relationship between metabolism, homeostasis, and stress signaling

Fat is an important component of milk which delivers energy, nutrients, and bioactive molecules from the lactating mother to the suckling neonate. Milk fat consists of a complex mixture of different types of lipids; hundreds of fatty acids, triglycerides, phospholipids, sphingolipids, cholesterol and cholesteryl ester, and glycoconjugates, secreted by the mammary gland epithelial cells (MEC) in the form of a lipid-protein assembly termed the milk fat globule (MFG). The mammary gland in general, and specifically that of modern dairy cows, faces metabolic stress once lactation commences, which changes the lipogenic capacity of MECs directly by reducing available energy and reducing factors required for both lipid synthesis and secretion or indirectly by activating a proinflammatory response. Both processes have the capacity to change the morphometric features (e.g., number and size) of the secreted MFG and its precursor-the intracellular lipid droplet (LD). The MFG size is tightly associated with its lipidome and proteome and also affects the bioavailability of milk fat and protein. Thus, MFG size has the potential to regulate the bioactivity of milk and dairy products. MFG size also plays a central role in the functional properties of milk and dairy products such as texture and stability. To understand how stress affects the structure-function of the MFG, we cover: (i) The mechanism of production and secretion of the MFG and the implications of MFG size, (ii) How the response mechanisms to stress can change the morphometric features of MFGs, and (iii) The possible consequences of such modifications.

Factors Involved in the Evolution of the Basal Metabolic Rate over 30 Months After Roux-en-Y Gastric Bypass

INTRODUCTION

After Roux-en-Y gastric bypass (RYGB), the basal metabolic rate (BMR) falls. However, it is important to know how BMR per kilogram of body weight (BMR/kg) varies in the postoperative period. The present study evaluated the changes in the BMR/kg and its correlates over 30 months after RYGB.

METHODS

Eighty adult patients of both genders who underwent RYGB agreed to participate in the study. The following evaluations were performed before surgery (n=48) and 6 (n=27), 12 (n=28), 24 (n=40), and 30 months (n=29) after surgery: anthropometry, body composition (bioelectrical impedance), metabolic analysis (indirect calorimetry), and diet (food recall). Statistical analysis was performed (p = 0.05).

RESULTS

Although BMR decreased after surgery, BMR/kg increased significantly as compared to baseline from 12 months onward, peaking at 24 months and not significantly dipping at 30 months, suggesting stabilization of BMR/kg 2 years after surgery (pre, 10.68 ± 2.33 kcal/kg; 12 months, 12.46 ± 2.85 kcal/kg; 24 months, 18.78 ± 4.81 kcal/kg; 30 months, 18.12 ± 3.69 kcal/kg; p <0.001). Regarding the variables that influenced the BMR/kg, at 12 months, they were %LBM and intake of calcium-source foods (34%); at 24 months, it was protein intake (16%); and at 30 months, it was the intake of calcium-source foods (26.7%).

CONCLUSION

RYGB is associated with a significant increase in BMR when it is adjusted to body weight from 12 to 24 months postoperatively. Among the factors involved in the increase in BMR/kg are body composition and intake of protein-rich foods.

Coenzyme Q10 and nicotinamide nucleotide transhydrogenase: Sentinels for mitochondrial hydrogen peroxide signaling

Mitochondria use hydrogen peroxide (H2O2) as a mitokine for cell communication. H2O2 output for signaling depends on its rate of production and degradation, both of which are strongly affected by the redox state of the coenzyme Q10 (CoQ) pool and NADPH availability. Here, we propose the CoQ pool and nicotinamide nucleotide transhydrogenase (NNT) have evolved to be central modalities for mitochondrial H2O2 signaling. Both factors play opposing yet equally important roles in dictating H2O2 availability because they are connected to one another by two central parameters in bioenergetics: electron supply and Δp. The CoQ pool is the central point of convergence for electrons from various dehydrogenases and the electron transport chain (ETC). The increase in Δp creates a significant amount of protonic backpressure on mitochondria to promote H2O2 genesis through CoQ pool reduction. These same factors also drive the activity of NNT, which uses electrons and the Δp to eliminate H2O2. In this way, electron supply and the magnitude of the Δp manifests as a redox connection between the two sentinels, CoQ and NNT, which serve as opposing yet equally important forces required for budgeting H2O2. Taken together, CoQ and NNT are sentinels linked through mitochondrial bioenergetics to manage H2O2 availability for interorganelle and intercellular redox signaling.

Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense

Mitochondria play multifaceted roles in cellular function, and impairments across domains of mitochondrial biology are known to promote cellular integrated stress response (ISR) pathways as well as systemic metabolic adaptations. However, the temporal dynamics of specific mitochondrial ISR related to physiological variations in tissue-specific energy demands remains unknown. Here, we conducted a comprehensive 24-hour muscle and plasma profiling of male and female mice with ectopic mitochondrial respiratory uncoupling in skeletal muscle (mUcp1-transgenic, TG). TG mice are characterized by increased muscle ISR, elevated oxidative stress defense, and increased secretion of FGF21 and GDF15 as ISR-induced myokines. We observed a temporal signature of both cell-autonomous and systemic ISR in the context of endocrine myokine signaling and cellular redox balance, but not of ferroptotic signature which was also increased in TG muscle. We show a progressive increase of muscle ISR on transcriptional level during the active phase (night time), with a subsequent peak in circulating FGF21 and GDF15 in the early resting phase. Moreover, we found highest levels of muscle oxidative defense (GPX and NQO1 activity) between the late active to early resting phase, which could aim to counteract excessive iron-dependent lipid peroxidation and ferroptosis in muscle of TG mice. These findings highlight the temporal dynamics of cell-autonomous and endocrine ISR signaling under skeletal muscle mitochondrial uncoupling, emphasizing the importance of considering such dissociation in translational strategies and sample collection for diagnostic biomarker analysis.

Empagliflozin induces the transcriptional program for nutrient homeostasis in skeletal muscle in normal mice

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) improve heart failure (HF) outcomes across a range of patient characteristics. A hypothesis that SGLT2i induce metabolic change similar to fasting has recently been proposed to explain their profound clinical benefits. However, it remains unclear whether SGLT2i primarily induce this change in physiological settings. Here, we demonstrate that empagliflozin administration under ad libitum feeding did not cause weight loss but did increase transcripts of the key nutrient sensors, AMP-activated protein kinase and nicotinamide phosphoribosyltransferase, and the master regulator of mitochondrial gene expression, PGC-1α, in quadriceps muscle in healthy mice. Expression of these genes correlated with that of PPARα and PPARδ target genes related to mitochondrial metabolism and oxidative stress response, and also correlated with serum ketone body β-hydroxybutyrate. These results were not observed in the heart. Collectively, this study revealed that empagliflozin activates transcriptional programs critical for sensing and adaptation to nutrient availability intrinsic to skeletal muscle rather than the heart even in normocaloric condition. As activation of PGC-1α is sufficient for metabolic switch from fatigable, glycolytic metabolism toward fatigue-resistant, oxidative mechanism in skeletal muscle myofibers, our findings may partly explain the improvement of exercise tolerance in patients with HF receiving empagliflozin.

One-carbon metabolizing enzyme ALDH1L1 influences mitochondrial metabolism through 5-aminoimidazole-4-carboxamide ribonucleotide accumulation and serine depletion, contributing to tumor suppression

Tumor cells generally require large amounts of nucleotides, and thus activate de novo purine synthesis (dnPS). In the dnPS reactions, 10-formyltetrahydorofolate (10-fTHF) supplied by one-carbon metabolism is utilized as a formyl group donor. We focused on aldehyde dehydrogenase 1 family member L1 (ALDH1L1), which metabolizes 10-fTHF to tetrahydrofolate and whose expression is often attenuated in hepatocellular carcinoma (HCC). We generated ALDH1L1-expressing HuH-7 cells to perform metabolome analysis and found that intracellular levels of serine were reduced and glycine was increased. In addition, 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP), a dnPS intermediate, accumulated due to the consumption of 10-fTHF by ALDH1L1, which inhibited ZMP formylation. Importantly, ALDH1L1-expressing cells showed reduced ZMP sensitivity and higher mitochondrial activity. The suppression of mitochondrial serine catabolism by ALDH1L1 expression was speculated to be closely related to this phenotype. Gene set enrichment analysis utilizing The Cancer Genome Atlas data revealed that genes related to oxidative phosphorylation were enriched in HCC patients with high ALDH1L1 expression. Moreover, drug sensitivity data analysis demonstrated that HCC cell lines with low expression of ALDH1L1 were sensitive to ZMP and cordycepin, a structural analog of ZMP and AMP. Our study revealed that ZMP and AMP analogs might be effective in the pharmacotherapy of HCC patients with low expression of ALDH1L1.

Acanthamoeba castellanii Uncoupling Protein: A Complete Sequence, Activity, and Role in Response to Oxidative Stress

Uncoupling proteins (UCPs) are mitochondrial inner membrane transporters that mediate free-fatty-acid-induced, purine-nucleotide-inhibited proton leak into the mitochondrial matrix, thereby uncoupling respiratory substrate oxidation from ATP synthesis. The aim of this study was to provide functional evidence that the putative Acucp gene of the free-living protozoan amoeba, A. castellanii, encodes the mitochondrial protein with uncoupling activity characteristic of UCPs and to investigate its role during oxidative stress. We report the sequencing and cloning of a complete Acucp coding sequence, its phylogenetic analysis, and the heterologous expression of AcUCP in the S. cerevisiae strain InvSc1. Measurements of mitochondrial respiratory activity and membrane potential indicate that the heterologous expression of AcUCP causes AcUCP-mediated uncoupling activity. In addition, in a model of oxidative stress with increased reactive oxygen species levels (superoxide dismutase 1 knockout yeasts), AcUCP expression strongly promotes cell survival and growth. The level of superoxide anion radicals is greatly reduced in the ΔSOD1 strain expressing AcUCP. These results suggest that AcUCP targeted to yeast mitochondria causes uncoupling and may act as an antioxidant system. Phylogenetic analysis shows that the A. castellanii UCP diverges very early from other UCPs, but clearly locates within the UCP subfamily rather than among other mitochondrial anion carrier proteins.

UCP1 alleviates renal interstitial fibrosis progression through oxidative stress pathway mediated by SIRT3 protein stability

BACKGROUND

Renal interstitial fibrosis is a common pathway for the progressive development of chronic renal diseases (CKD) with different etiology, and is the main pathological basis leading to end-stage renal disease. Although the current research on renal interstitial fibrosis is gradually deepening, the diagnosis and treatment methods are still very lacking. Uncoupling protein 1 (UCP1) is a nuclear encoded protein in mitochondria inner membrane and plays an important role in regulating energy metabolism and mitochondrial homeostasis. However, the biological significance of UCP1 and potential regulatory mechanisms in the development of CKD remain unclear.

METHODS

Unilateral ureteral obstruction (UUO) model was used to construct the animal model of renal fibrosis, and TGF-β1 stimulation of HK2 cells was used to construct the vitro model of renal fibrosis. UCP1 expression was detected by Western blot, immunoblot analysis and immunohistochemistry. UCP1 was upregulated by UCP1 overexpressing lentivirus and UCP1 agonist CL316243. Western blot and immunofluorescence were used to detect epithelial mesenchymal transition (EMT)-related markers, such as collagen I, fibronectin, antioxidant enzyme SOD2 and CAT. Reactive oxygen species (ROS) production was detected by ROS detection kit. SIRT3 knockdown was performed by siRNA.

RESULTS

This study presents that UCP1 is significantly downregulated in patients with renal fibrosis and UUO model. Further studies discover that UCP1 overexpression and CL316243 treatments (UCP1 agonists) reversed EMT and extracellular matrix (ECM) accumulation in renal fibrosis models in vivo and in vitro. Simultaneously, UCP1 reduced the ROS production by increasing the stability of SIRT3. When SIRT3 was knocked down, the production of ROS decreased.

CONCLUSIONS

Elevating the expression of UCP1 can inhibit the occurrence of oxidative stress by stabilizing SIRT3, thereby reducing EMT and ECM accumulation, and ultimately alleviating renal interstitial fibrosis. It will provide new instructions and targets for the treatment of CKD.

Novel Strategies in the Early Detection and Treatment of Endothelial Cell-Specific Mitochondrial Dysfunction in Coronary Artery Disease

Although elevated cholesterol and other recognised cardiovascular risk factors are important in the development of coronary artery disease (CAD) and heart attack, the susceptibility of humans to this fatal process is distinct from other animals. Mitochondrial dysfunction of cells in the arterial wall, particularly the endothelium, has been strongly implicated in the pathogenesis of CAD. In this manuscript, we review the established evidence and mechanisms in detail and explore the potential opportunities arising from analysing mitochondrial function in patient-derived cells such as endothelial colony-forming cells easily cultured from venous blood. We discuss how emerging technology and knowledge may allow us to measure mitochondrial dysfunction as a potential biomarker for diagnosis and risk management. We also discuss the "pros and cons" of animal models of atherosclerosis, and how patient-derived cell models may provide opportunities to develop novel therapies relevant for humans. Finally, we review several targets that potentially alleviate mitochondrial dysfunction working both via direct and indirect mechanisms and evaluate the effect of several classes of compounds in the cardiovascular context.

Does diet and activity lead to difference in resting energy expenditure in obese women?

BACKGROUND

Obesity is considered as a risk factor for metabolic and chronic diseases. Reduction in resting energy expenditure (REE) may increase risk of obesity. Our study was carried out to investigate dietary, biochemical, anthropometric and body composition parameters and physical activity in obese women with normal and low resting energy expenditure.

METHODS

A total forty nine subjects (women, 30-50 years old) were enrolled and divided into three groups. Anthropometric, body composition parameters, resting energy expenditure, Fasting blood lipid profile, dietary intake and physical activity were measured.

RESULTS

Although, fat mass and fat-free mass were significantly increased in obese groups, there was no significant difference in body composition between two obese groups (p-value = 0.10, 0.27). Measured resting energy expenditure was significantly decreased in obese with low REE compare to other groups (p-value < 0.001). There was no significant difference in energy intake and macronutrients between groups. There was a significant difference in T3 between obese subjects with low REE compared to obese group with normal REE (p-value < 0.001). There was no significant difference in lipid profile between two obese groups. Also there was a significant difference in LDL, cholesterol and triacylglycerol between obese subjects with low REE compared to normal weight group. Moreover, there was a significant difference in cholesterol and triacylglycerol between obese subjects with normal REE compared to normal weight group. Our finding showed there was no significant difference in physical activity between three groups.

CONCLUSIONS

Dietary intake and physical activity may relate to metabolism and energy expenditure. It is interesting that in some obese people resting energy expenditure was much lower compared to other obese people; however, there was no significant difference in their body composition, age, sex, dietary intake, lipid profile and physical activity. Thus it should investigate the role of other factors involved in different REE in subjects with obesity.

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.

Ectotherm mitochondrial economy and responses to global warming

Temperature is a key abiotic factor affecting ecology, biogeography, and evolution of species. Alterations of energy metabolism play an important role in adaptations and plastic responses to temperature shifts on different time scales. Mitochondrial metabolism affects cellular bioenergetics and redox balance making these organelles an important determinant of organismal performances such as growth, locomotion, or development. Here I analyze the impacts of environmental temperature on the mitochondrial functions (including oxidative phosphorylation, proton leak, production of reactive oxygen species(ROS), and ATP synthesis) of ectotherms and discuss the mechanisms underlying negative shifts in the mitochondrial energy economy caused by supraoptimal temperatures. Owing to the differences in the thermal sensitivity of different mitochondrial processes, elevated temperatures (beyond the species- and population-specific optimal range) cause reallocation of the electron flux and the protonmotive force (Δp) in a way that decreases ATP synthesis efficiency, elevates the relative cost of the mitochondrial maintenance, causes excessive production of ROS and raises energy cost for antioxidant defense. These shifts in the mitochondrial energy economy might have negative consequences for the organismal fitness traits such as the thermal tolerance or growth. Correlation between the thermal sensitivity indices of the mitochondria and the whole organism indicate that these traits experience similar selective pressures but further investigations are needed to establish whether there is a cause-effect relationship between the mitochondrial failure and loss of organismal performance during temperature change.

Chronic stress targets mitochondrial respiratory efficiency in the skeletal muscle of C57BL/6 mice

Episodes of chronic stress can result in psychic disorders like post-traumatic stress disorder, but also promote the development of metabolic syndrome and type 2 diabetes. We hypothesize that muscle, as main regulator of whole-body energy expenditure, is a central target of acute and adaptive molecular effects of stress in this context. Here, we investigate the immediate effect of a stress period on energy metabolism in Musculus gastrocnemius in our established C57BL/6 chronic variable stress (Cvs) mouse model. Cvs decreased lean body mass despite increased energy intake, reduced circadian energy expenditure (EE), and substrate utilization. Cvs altered the proteome of metabolic components but not of the oxidative phosphorylation system (OXPHOS), or other mitochondrial structural components. Functionally, Cvs impaired the electron transport chain (ETC) capacity of complex I and complex II, and reduces respiratory capacity of the ETC from complex I to ATP synthase. Complex I-OXPHOS correlated to diurnal EE and complex II-maximal uncoupled respiration correlated to diurnal and reduced nocturnal EE. Bioenergetics assessment revealed higher optimal thermodynamic efficiencies (ƞ-opt) of mitochondria via complex II after Cvs. Interestingly, transcriptome and methylome were unaffected by Cvs, thus excluding major contributions to supposed metabolic adaptation processes. In summary, the preclinical Cvs model shows that metabolic pressure by Cvs is initially compensated by adaptation of mitochondria function associated with high thermodynamic efficiency and decreased EE to manage the energy balance. This counter-regulation of mitochondrial complex II may be the driving force to longitudinal metabolic changes of muscle physiological adaptation as the basis of stress memory.

Role of oxidative stress and inflammation-related signaling pathways in doxorubicin-induced cardiomyopathy

Doxorubicin (DOX) is a powerful and commonly used chemotherapeutic drug, used alone or in combination in a variety of cancers, while it has been found to cause serious cardiac side effects in clinical application. More and more researchers are trying to explore the molecular mechanisms of DOX-induced cardiomyopathy (DIC), in which oxidative stress and inflammation are considered to play a significant role. This review summarizes signaling pathways related to oxidative stress and inflammation in DIC and compounds that exert cardioprotective effects by acting on relevant signaling pathways, including the role of Nrf2/Keap1/ARE, Sirt1/p66Shc, Sirt1/PPAR/PGC-1α signaling pathways and NOS, NOX, Fe²⁺ signaling in oxidative stress, as well as the role of NLRP3/caspase-1/GSDMD, HMGB1/TLR4/MAPKs/NF-κB, mTOR/TFEB/NF-κB pathways in DOX-induced inflammation. Hence, we attempt to explain the mechanisms of DIC in terms of oxidative stress and inflammation, and to provide a theoretical basis or new idea for further drug research on reducing DIC. Video Abstract.

An AMP Kinase-pathway dependent integrated stress response regulates ageing and longevity

The purpose of this article is to investigate the role of the AMP-kinase pathway (AMPK pathway) in the induction of a concomitant set of health benefits by exercise, numerous drugs, and health ingredients, all of which are adversely affected by ageing. Despite the AMPK pathway being frequently mentioned in relation to both these health effects and ageing, it appears challenging to understand how the activation of a single biochemical pathway by various treatments can produce such a diverse range of concurrent health benefits, involving so many organs. We discovered that the AMPK pathway functions as an integrated stress response system because of the presence of a feedback loop in it. This evolutionary conserved stress response system detects changes in AMP/ATP and NAD/NADH ratios, as well as the presence of potential toxins, and responds by activating a common protective transcriptional response that protects against aging and promotes longevity. The inactivation of the AMPK pathway with age most likely explains why ageing has a negative impact on the above-mentioned set of health benefits. We conclude that the presence of a feedback loop in the AMP-kinase pathway positions this pathway as an AMPK-ISR (AMP Kinase-dependent integrated stress response) system that responds to almost any type of (moderate) environmental stress by inducing various age-related health benefits and longevity.

Inhibition of Mitochondrial Uncoupling Proteins Arrests Human Spermatozoa Motility without Compromising Viability

Mitochondrial uncoupling proteins (UCPs) are central in the regulation of mitochondrial activity and reactive oxygen species (ROS) production. High oxidative stress is a major cause of male infertility; however, UCPs expression and function in human spermatozoa are still unknown. Herein, we aimed to assess the expression and function of the different homologs (UCP1-6) in human spermatozoa. For this purpose, we screened for the mRNA expression of all UCP homologs. Protein expression and immunolocalization of UCP1, UCP2, and UCP3 were also assessed. Highly motile spermatozoa were isolated from human normozoospermic seminal samples (n = 16) and incubated with genipin, an inhibitor of UCPs (0, 0.5, 5, and 50 µM) for 3 h at 37 °C. Viability and total motility were assessed. Mitochondrial membrane potential and ROS production were evaluated. Media were collected and the metabolic profile and antioxidant potential were analyzed by ¹H-NMR and FRAP, respectively. The expression of all UCP homologs (UCP1-6) mRNA by human spermatozoa is herein reported for the first time. UCP1-3 are predominant at the head equatorial segment, 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, did not compromise sperm cell viability but resulted in irreversible total motility loss that persisted despite washing or incubation with theophylline, a cAMP activator. These effects were associated with decreased mitochondrial membrane potential and lactate production. No differences concerning UCP3 expression, however, were observed in spermatozoa from normozoospermic versus asthenozoospermic men (n = 6). The inhibition of UCPs did not increase ROS production, possibly due to the decreased mitochondrial activity and genipin antioxidant properties. In sum, UCPs are major regulators of human spermatozoa motility and metabolism. The discovery and characterization of UCPs' role in human spermatozoa can shed new light on spermatozoa ROS-related pathways and bioenergetics physiology.

Thermogenic Adipose Redox Mechanisms: Potential Targets for Metabolic Disease Therapies

Metabolic diseases, such as diabetes and non-alcoholic fatty liver disease (NAFLD), have several negative health outcomes on affected humans. Dysregulated energy metabolism is a key component underlying the pathophysiology of these conditions. Adipose tissue is a fundamental regulator of energy homeostasis that utilizes several redox reactions to carry out the metabolism. Brown and beige adipose tissues, in particular, perform highly oxidative reactions during non-shivering thermogenesis to dissipate energy as heat. The appropriate regulation of energy metabolism then requires coordinated antioxidant mechanisms to counterbalance the oxidation reactions. Indeed, non-shivering thermogenesis activation can cause striking changes in concentrations of both oxidants and antioxidants in order to adapt to various oxidative environments. Current therapeutic options for metabolic diseases either translate poorly from rodent models to humans (in part due to the challenges of creating a physiologically relevant rodent model) or tend to have numerous side effects, necessitating novel therapies. As increased brown adipose tissue activity results in enhanced energy expenditure and is associated with beneficial effects on metabolic health, such as decreased obesity, it has gathered great interest as a modulator of metabolic disease. One potential reason for the beneficial health effects may be that although non-shivering thermogenesis is enormously oxidative, it is also associated with decreased oxidant formation after its activation. However, targeting its redox mechanisms specifically to alter metabolic disease remains an underexplored area. Therefore, this review will discuss the role of adipose tissue in energy homeostasis, non-shivering thermogenesis in adults, and redox mechanisms that may serve as novel therapeutic targets of metabolic disease.

Glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system in old rats

Introduction: Aging is accompanied by cardiovascular disorders which is associated with an imbalance of pro- and antioxidant systems, the mitochondrial dysfunction, etc. Glutathione (GSH) plays a critical role in protecting cells from oxidative damage. The aim of the work was to study the effect of exogenous glutathione on the redox status of mitochondria, the content of H₂S and the function of the cardiovascular system in old rats. Methods: Experiments were performed on adult (6 months) and old (24 months) Wistar rats divided into three groups: adult, old and glutathionetreated old rats. Glutathione was injected intraperitoneally at a dose of 52 mg/kg. We investigated glutathione redox balance, H₂S levels, oxidative stress, the opening of the mitochondrial permeability transition pore (mPTP), the resistance of isolated heart to ischemia/reperfusion in Langendorff model, endothelium-dependent vasorelaxation of isolated aortic rings, and cardiac levels of 3-MST, CSE, and UCP3 mRNA were determined using real-time PCR analysis. Results: Our data shows that in old rats treated with glutathione, the balance of its oxidized and reduced form changes in the direction of a significant increase (by 53.6%) of the reduced form. Glutathione pretreatment significantly increased the H₂S levels, mtNOS activity, and UCP3 expression which considered as protective protein, and conversely, significantly decreased oxidative stress markers (the rate of O₂•^- generation, the levels of H₂O₂, diene conjugates and malone dialdehyde, in 2.5, 2.3, 2, and 1.6 times, respectively) in heart mitochondria. This was associated with the inhibition mitochondrial permeability transition pore opening and increased resistance of the isolated heart to ischemia/reperfusion in these animals. At the same time, in glutathione-treated old rats, we also observed restoration of endothelium-dependent vasorelaxation responses to acetylcholine, which were almost completely abolished by the NO-synthase inhibitor L-NAME. Conclusion: Thus, the pretreatment of old rats with glutathione restores the mitochondrial redox status and improves the function of the cardiovascular system.

Adrenal Dysfunction in Mitochondrial Diseases

Cortisol is central to several homeostatic mechanisms including the stress and immune response. Adrenal insufficiency and impaired cortisol production leads to severe, potentially fatal disorders. Several fundamental stages of steroidogenesis occur within the mitochondria. These dynamic organelles not only contribute ATP for steroidogenesis, but also detoxify harmful by-products generated during cortisol synthesis (reactive oxygen species). Mutations in nuclear or mitochondrial DNA that impair mitochondrial function lead to debilitating multi-system diseases. Recently, genetic variants that impair mitochondrial function have been identified in people with isolated cortisol insufficiency. This review aimed to clarify the association between mitochondrial diseases and adrenal insufficiency to produce cortisol. Mitochondrial diseases are rare and mitochondrial diseases that feature adrenal insufficiency are even rarer. We identified only 14 cases of adrenal insufficiency in people with confirmed mitochondrial diseases globally. In line with previous reviews, adrenal dysfunction was most prevalent in mitochondrial deletion syndromes (particularly Pearson syndrome and Kearns-Sayre syndrome) and with point mutations that compromised oxidative phosphorylation. Although adrenal insufficiency has been reported with mitochondrial diseases, the incidence reflects that expected in the general population. Thus, it is unlikely that mitochondrial mutations alone are responsible for an insufficiency to produce cortisol. More research is needed into the pathogenesis of adrenal disease in these individuals.

Efficient Production of Antioxidants from Rape Pollen via a Chromatographic Strategy

Rape pollen has always been considered as a research hotspot in health foods and pharmaceuticals due to its abundance of natural active ingredients. In this work, a compound with antioxidant activity was directly isolated from the methanol extract of rape pollen using a two-step procedure, under the supervision of online HPLC−1,1-diphenyl-2-picrylhydrazyl (HPLC-DPPH) detection. Firstly, online HPLC−DPPH detection was used to identify the active peaks in the methanol extract of rape pollen, and then the methanol extract was pretreated via medium-pressure liquid chromatography (MPLC) to obtain the target fraction 3 (Fr3). Fr3 was further purified using HPLC to finally obtain the target fraction 3-1, which was identified as kaempferol 3,4′-di-O-β-D-glucopyranoside through NMR and mass spectrometry. To further explore the free radical scavenging activity of this compound, its DPPH scavenging ability was determined, and two proteins related to the antioxidant pathway were used for molecular docking. The results revealed that the chromatographic strategy used in this study was efficient and reliable in separating high−purity antioxidants from rape pollen. A strategy such as this, meanwhile, also holds promise for qualitatively identifying and specifically isolating active compounds from other natural products.

Transcription Factor Nrf2 and Mitochondria - Friends or Foes in the Regulation of Aging Rate

At the first sight, the transcription factor Nrf2 as a master regulator of cellular antioxidant systems, and mitochondria as the main source of reactive oxygen species (ROS), should play the opposite roles in determining the pace of aging. However, since the causes of aging cannot be confined to the oxidative stress, the role of Nrf2 role cannot be limited to the regulation of antioxidant systems, and moreover, the role of mitochondria is not confined to the ROS production. In this review, we discussed only one aspect of this problem, namely, the molecular mechanisms of interaction between Nrf2 and mitochondria that influence the rate of aging and the lifespan. Experimental data accumulated so far show that the Nrf2 activity positively affects both the mitochondrial dynamics and mitochondrial quality control. Nrf2 influences the mitochondrial function through various mechanisms, e.g., regulation of nuclear genome-encoded mitochondrial proteins and changes in the balance of ROS or other metabolites that affect the functioning of mitochondria. In turn, multiple regulatory proteins functionally associated with the mitochondria affect the Nrf2 activity and even form mutual regulatory loops with Nrf2. We believe that these loops enable the fine-tuning of the cellular redox balance and, possibly, of the cellular metabolism as a whole. It has been commonly accepted for a long time that all mitochondrial regulatory signals are mediated by the nuclear genome-encoded proteins, whereas the mitochondrial genome encodes only a few respiratory chain proteins and two ribosomal RNAs. Relatively recently, mtDNA-encoded signal peptides have been discovered. In this review, we discuss the data on their interactions with the nuclear regulatory systems, first of all, Nrf2, and their possible involvement in the regulation of the aging rate. The interactions between regulatory cascades that link the programs ensuring the maintenance of cellular homeostasis and cellular responses to the oxidative stress are a significant part of both aging and anti-aging programs. Therefore, understanding these interactions will be of great help in searching for the molecular targets to counteract aging-associated diseases and aging itself.

UCP2 as a Cancer Target through Energy Metabolism and Oxidative Stress Control

Despite numerous therapies, cancer remains one of the leading causes of death worldwide due to the lack of markers for early detection and response to treatment in many patients. Technological advances in tumor screening and renewed interest in energy metabolism have allowed us to identify new cellular players in order to develop personalized treatments. Among the metabolic actors, the mitochondrial transporter uncoupling protein 2 (UCP2), whose expression is increased in many cancers, has been identified as an interesting target in tumor metabolic reprogramming. Over the past decade, a better understanding of its biochemical and physiological functions has established a role for UCP2 in (1) protecting cells from oxidative stress, (2) regulating tumor progression through changes in glycolytic, oxidative and calcium metabolism, and (3) increasing antitumor immunity in the tumor microenvironment to limit cancer development. With these pleiotropic roles, UCP2 can be considered as a potential tumor biomarker that may be interesting to target positively or negatively, depending on the type, metabolic status and stage of tumors, in combination with conventional chemotherapy or immunotherapy to control tumor development and increase response to treatment. This review provides an overview of the latest published science linking mitochondrial UCP2 activity to the tumor context.

Relationships between Uncoupling Protein Genes UCP1, UCP2 and UCP3 and Irisin Levels in Residents of the Coldest Region of Siberia

Currently, it is known that irisin can participate in the processes of thermoregulation and browning of adipose tissue, and, therefore, it is possible that it is involved in the microevolutionary mechanisms of adaptation to a cold. The aim of this study is to investigate the relationship between the uncoupling protein genes (UCP1, UCP2, UCP3) and the irisin levels in the residents of the coldest region of Siberia. The sample consisted of 279 Yakut people (185 females, 94 males, average age 19.8 ± 2.03 years). The females plasma irisin concentration was 8.33 ± 2.74 mcg/mL and the males was 7.76 ± 1.86 mcg/mL. Comparative analysis of irisin levels with the genotypes of six studied SNP-markers in females revealed a significant association of irisin with rs1800849-UCP3. The TT genotype of rs1800849 was associated with elevated levels of irisin (p = 0.01). It was also found that this TT genotype in females was associated with reduced weight and height (p = 0.03). We searched for natural selection signals for the T-allele rs1800849-UCP3; as a result of which, it was found that this allele has a significantly high frequency of distribution in northern (45%, CI: 0.42–0.484) compared with southern Asian populations (28%, CI: 0.244–0.316) (p = 0.01). The results obtained indicate the probable involvement of irisin and the UCP3 gene in thermoregulation, and the spread of its allelic variants is probably related to adaptation to a cold climate.

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.

Thermomagnetic Resonance Effect of the Extremely Low Frequency Electromagnetic Field on Three-Dimensional Cancer Models

In our recent studies, we have developed a thermodynamic biochemical model able to select the resonant frequency of an extremely low frequency electromagnetic field (ELF-EMF) specifically affecting different types of cancer, and we have demonstrated its effects in vitro. In this work, we investigate the cellular response to the ELF electromagnetic wave in three-dimensional (3D) culture models, which mimic the features of tumors in vivo. Cell membrane was modelled as a resistor–capacitor circuit and the specific thermal resonant frequency was calculated and tested on two-dimensional (2D) and three-dimensional (3D) cell cultures of human pancreatic cancer, glioblastoma and breast cancer. Cell proliferation and the transcription of respiratory chain and adenosine triphosphate synthase subunits, as well as uncoupling proteins, were assessed. For the first time, we demonstrate that an ELF-EMF hampers growth and potentiates both the coupled and uncoupled respiration of all analyzed models. Interestingly, the metabolic shift was evident even in the 3D aggregates, making this approach particularly valuable and promising for future application in vivo, in aggressive cancer tissues characterized by resistance to treatments.

Mito-Q promotes porcine oocytes maturation by maintaining mitochondrial thermogenesis via UCP2 downregulation

Mitochondrial thermogenesis is an adaptive response of cells to their surrounding stress. Oxidative stress is one of the common stresses during in vitro maturation (IVM) of oocytes, which leads to mitochondrial dysfunction. This study aimed to probe the effects of the mitochondria-targeted antioxidant Mito-Q on oocyte development and unravel the role of Mito-Q in mitochondrial ATP production and thermogenesis regulation. Our results showed that Mito-Q had a positive effect on porcine oocytes maturation and subsequent embryo development. During oocytes IVM, Mito-Q could reduce ATP levels and ROS, increase lipid droplets accumulation, induce autophagy, and maintain mitochondrial temperature stability. Moreover, in metaphase II (MII) oocytes, Mito-Q would induce mitochondrial uncoupling manifested by decreased ATP, attenuated mitochondrial membrane potential (MMP), and increased mitochondrial thermogenesis. Notably, the expression of mitochondrial uncoupling protein (UCP2) was significantly reduced in oocytes treated with Mito-Q. Further study indicated that specific depletion of UCP2 in oocytes also resulted in increased thermogenesis, decreased ATP and declined MMP, suggesting that UCP2 downregulation may participate in Mito-Q-induced mitochondrial uncoupling. In summary, our data demonstrate that Mito-Q promotes oocyte maturation in vitro and maintains the stability of mitochondrial thermogenesis by inhibiting UCP2 expression.

Mitochondrial and glucose metabolic dysfunctions in granulosa cells induce impaired oocytes of polycystic ovary syndrome through Sirtuin 3

Mitochondrial function and glucose metabolism play important roles in bidirectional signaling between granulosa cells (GCs) and oocytes. However, the factors associated with mitochondrial function and glucose metabolism of GCs in polycystic ovary syndrome (PCOS) are poorly understood, and their potential downstream effects on oocyte quality are still unknown. The aim of this study was to investigate whether there are alterations in mitochondrial-related functions and glucose metabolism in ovarian GCs of women with PCOS and the role of Sirtuin 3 (SIRT3) in this process. Here, we demonstrated that women with PCOS undergoing in vitro fertilization and embryo transfer had significantly lower rates of metaphase II oocytes, two-pronuclear fertilization, cleavage, and day 3 good-quality embryos. Germinal vesicle- and metaphase I-stage oocytes from women with PCOS exhibited increased mitochondrial reactive oxygen species (ROS), decreased mitochondrial membrane potential, and downregulation of glucose-6-phosphate dehydrogenase. GCs from women with PCOS presented significant alterations in mitochondrial morphology, amount, and localization, decreased membrane potential, reduced adenosine triphosphate (ATP) synthesis, increased mitochondrial ROS and oxidative stress, and insufficient oxidative phosphorylation (OXPHOS) together with decreased glycolysis. SIRT3 expression was significantly decreased in GCs of PCOS patients, and knockdown of SIRT3 in KGN cells could mimic the alterations in mitochondrial functions and glucose metabolism in PCOS GCs. SIRT3 knockdown changed the acetylation status of NDUFS1, which might induce altered mitochondrial OXPHOS, the generation of mitochondrial ROS, and eventually defects in the cellular insulin signaling pathway. These findings suggest that SIRT3 deficiency in GCs of PCOS patients may contribute to mitochondrial dysfunction, elevated oxidative stress, and defects in glucose metabolism, which potentially induce impaired oocytes in PCOS.

Uncoupling Proteins as Therapeutic Targets for Neurodegenerative Diseases

Most of the major retinal degenerative diseases are associated with significant levels of oxidative stress. One of the major sources contributing to the overall level of stress is the reactive oxygen species (ROS) generated by mitochondria. The driving force for ROS production is the proton gradient across the inner mitochondrial membrane. This gradient can be modulated by members of the uncoupling protein family, particularly the widely expressed UCP2. The overexpression and knockout studies of UCP2 in mice have established the ability of this protein to provide neuroprotection in a number of animal models of neurological disease, including retinal diseases. The expression and activity of UCP2 are controlled at the transcriptional, translational and post-translational levels, making it an ideal candidate for therapeutic intervention. In addition to regulation by a number of growth factors, including the neuroprotective factors LIF and PEDF, small molecule activators of UCP2 have been found to reduce mitochondrial ROS production and protect against cell death both in culture and animal models of retinal degeneration. Such studies point to the development of new therapeutics to combat a range of blinding retinal degenerative diseases and possibly other diseases in which oxidative stress plays a key role.