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Uncoupling to survive? The role of mitochondrial inefficiency in ageing

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Abstract

Mitochondria are incompletely coupled, and during oxidative phosphorylation some of the redox energy in substrates is lost as heat. Incomplete coupling is mostly due to a natural leak of protons across the mitochondrial inner membrane. In rat hepatocytes the futile cycle of proton pumping and proton leak is responsible for 20-25% of respiration; in perfused rat muscle the value is 35-50%. Mitochondrial proton cycling is estimated to cause 20-25% of basal metabolic rate in rats. Proton cycling is equally prominent in hepatocytes from several different mammalian and ectotherm species, so it may be a general pathway of ecologically significant energy loss in all aerobes. Because it occurs in ectotherms, thermogenesis cannot be its primary function. Instead, an attractive candidate for the function of the universal and expensive energy-dissipating proton cycle is to decrease the production of superoxide and other reactive oxygen species (ROS). This could be important in helping to minimise oxidative damage to DNA and in slowing ageing. Mitochondria are the major source of cellular ROS, and increased mitochondrial proton conductance leads to oxidation of ubiquinone and decreased ROS production in isolated mitochondria. However, to date there is no direct evidence in cells or organisms that mitochondrial proton cycling lowers ROS production or oxidative damage or that it increases lifespan.

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... ROS production depends on the redox state of the electron transfer chain and proton motive force (PMF) F I G U R E 1 The whole organismal ROS production per unit oxygen consumed, F, as a function of h (A) and k (B) mitochondrial inner membrane leads to uncoupling, in which protons bypass the ATP synthase molecule and so shortcut the coupling of substrate oxidation to the phosphorylation of ADP to produce ATP. [18] By reducing PMF, the uncoupling process decreases the rate of ROS production. [18] However, the uncoupling-induced reductions of ROS production are different in the resting and the active states. ...
... [18] By reducing PMF, the uncoupling process decreases the rate of ROS production. [18] However, the uncoupling-induced reductions of ROS production are different in the resting and the active states. In the resting state, where PMF is high, the production of ROS is extremely sensitive to the strength of the membrane potential, that is, a slight uncoupling, which causes a slight reduction in potential, causes a substantial reduction in ROS production. ...
... It has been shown across a diversity of organisms (including snail, lizard, rat, and horse [18] ) that the degree of uncoupling, the fraction of oxygen consumption spent on offsetting the proton leak, ranges from 15%-25% (in the mitochondria of cells from snail hepatopancreas) to 35%-50% (in the mitochondria of rat muscle) with an average of 20%. ...
Article
It has been assumed that at the whole organismal level, the mitochondrial reactive oxygen species (ROS) production is proportional to the oxygen consumption. Recently, a number of researchers have challenged this assumption, based on the observation that the ROS production per unit oxygen consumed in the resting state of mitochondrial respiration is much higher than that in the active state. Here, we develop a simple model to investigate the validity of the assumption and the challenge of it. The model highlights the significance of the time budget that mitochondria operate in the different respiration states. The model suggests that under three physiologically possible conditions, the difference in ROS production per unit oxygen consumed between the respiration states does not upset the proportionality between the whole animal ROS production and oxygen consumption. The model also shows that mitochondrial uncoupling generally enhances the proportionality.
... In response to the low oxygen level of the Triassic period, there may have been two options for adaptation, as shown in Figure 1. Mammals took the first option, option A [20,21], whereas theropods took the second option, option B [22][23][24]. At that time, theropods may have totally changed their body plan by gene loss [7][8][9][10][11][12], which was dedicated for the purpose of maximizing the efficiency of oxygen usage [22][23][24], while mammals underwent only a very small model change [10,11]. This response determined the ecological status of mammals and theropods in the Mesozoic era, during which theropods outcompeted mammals and reptiles [1][2][3]. ...
... Mammals took the first option, option A [20,21], whereas theropods took the second option, option B [22][23][24]. At that time, theropods may have totally changed their body plan by gene loss [7][8][9][10][11][12], which was dedicated for the purpose of maximizing the efficiency of oxygen usage [22][23][24], while mammals underwent only a very small model change [10,11]. This response determined the ecological status of mammals and theropods in the Mesozoic era, during which theropods outcompeted mammals and reptiles [1][2][3]. ...
... Birds, and presumably theropods, must have adopted this system and may have faced ROS leakage during the upcoming periods [30]. In this model, animals may have increased oxygen consumption so as to maximize the efficiency of oxygen usage [22][23][24]. ROS leakage may be a potential adverse effect of this system [22][23][24]. ...
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Drift of oxygen concentrations in the atmosphere was one of the main drivers of the evolution of vertebrates. The drop in oxygen concentrations at the Permian–Triassic (PT) boundary may have been the biggest challenge to vertebrates. This hypoxic condition forced theropods to lose certain genes to maximize their efficiency of oxygen usage. Recent studies show that omentin and insulin-sensitive glucose transporter 4 (GLUT4) are missing in the bird genome. Since these gene products play essential roles in maintaining insulin sensitivity, this loss forced theropods to become insulin resistant. Insulin resistance may have been the key to allowing theropods to become hyperathletic under hypoxic conditions and to outcompete mammals during the Triassic period. A second challenge was the gradual increase in oxygen concentrations during the late Jurassic, Cretaceous, and Tertiary periods when reactive oxygen species (ROS) leakage from mitochondria became a problem. Since the simplest solution was the expansion of body size, some theropods became bigger to reduce ROS leakage per volume. Another solution was the development of a constitutively active countermeasure against ROS. A recent study shows that Neoaves have constitutively active nuclear factor erythroid 2-related factor 2 (NRF2) due to deletion of the C-terminal part of the KEAP1 protein, thus allowing Neoaves to express antioxidant enzymes to overcome ROS leakage.
... ROS are highly reactive molecules that have a number of functions (e.g., signalling, phagocytosis) (Murphy et al., 2011), but when in excess can cause oxidative damage to cellular lipids, proteins and DNA, leading to a state of oxidative stress (Finkel & Holbrook, 2000). As a result ROS are thought to be an important contributor to cellular ageing (Brand, 2000), and so to be a selective force in shaping the evolution of ageing and life history strategies (Beckman & Ames, 1998;Dowling & Simmons, 2009;Hou & Amunugama, 2015;Metcalfe & Alonso-Alvarez, 2010;Monaghan et al., 2009). The mitochondria are the major endogenous source of ROS in living cells, since ROS are continuously produced (in the form of the highly reactive superoxide molecule) as a byproduct from the ETS (Figure 1a; Brand, 2000;Murphy, 2009). ...
... As a result ROS are thought to be an important contributor to cellular ageing (Brand, 2000), and so to be a selective force in shaping the evolution of ageing and life history strategies (Beckman & Ames, 1998;Dowling & Simmons, 2009;Hou & Amunugama, 2015;Metcalfe & Alonso-Alvarez, 2010;Monaghan et al., 2009). The mitochondria are the major endogenous source of ROS in living cells, since ROS are continuously produced (in the form of the highly reactive superoxide molecule) as a byproduct from the ETS (Figure 1a; Brand, 2000;Murphy, 2009). In vitro assays have shown that the rate of ROS production positively correlates with the strength of the proton gradient across the IMM (and hence the degree of coupling) (Mailloux & Harper, 2011). ...
... In vitro assays have shown that the rate of ROS production positively correlates with the strength of the proton gradient across the IMM (and hence the degree of coupling) (Mailloux & Harper, 2011). As a consequence, a leakier IMM produces fewer ROS, as does the synthesis of ATP since this reduces the proton gradient (Brand, 2000;Mookerjee et al., 2010;Murphy, 2009;Roussel et al., 2019). It is important to note that the positive relationship between the proton gradient and the rate of ROS production is an accelerating rather than linear one, and so the ratio of ROS production F I G U R E 1 (a) Diagram illustrating the basic processes in the mitochondria that influence the production of reactive oxygen species (ROS) and hence telomere attrition. ...
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It is well known that oxidative stress is a major cause of DNA damage and telomere attrition. Most endogenous Reactive Oxygen Species (ROS) are produced in the mitochondria, producing a link between mitochondrial function, DNA integrity and telomere dynamics. In this review we will describe how ROS production, rates of damage to telomeric DNA and DNA repair are dynamic processes. The rate of ROS production depends on mitochondrial features such as the level of inner membrane uncoupling and the proportion of time that ATP is actively being produced. However, the efficiency of ATP production (the ATP/O ratio) is positively related to the rate of ROS production, so leading to a trade‐off between the body’s energy requirements and its need to prevent oxidative stress. Telomeric DNA is especially vulnerable to oxidative damage due to features such as its high guanine content; while repair to damaged telomere regions is possible through a range of mechanisms, these can result in more rapid telomere shortening. There is increasing evidence that mitochondrial efficiency varies over time and with environmental context, as do rates of DNA repair. We argue that telomere dynamics can only be understood by appreciating that the optimal solution to the trade‐off between energetic efficiency and telomere protection will differ between individuals and will change over time, depending on resource availability, energetic demands and life history strategy.
... However, LEAK respiration is a dissipative component for respiration associated with proton slip and leak and electron leak (Gnaiger, 2020). LEAK respiration is therefore not available for performing biochemical work, but has been suggested to be helpful in mitigating reactive oxygen species damage, which has been shown to increase with age (Brand, 2000). Further research is necessary to determine whether aged horses exhibit elevated reactive oxygen species production and oxidative stress in conjunction with increased LEAK respiration, and to determine whether decreasing oxidative stress facilitates a concomitant reduction in LEAK and improvement in mitochondrial efficiency. ...
... Additionally, complex I capacity has been associated with increased reactive oxygen species production (St-Pierre et al., 2002). Thus, a decrease in reliance on complex I activity may be favorable, particularly in aged horses, if they exhibit similar age-associated increases in oxidative stress to other species (Brand, 2000). ...
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In aged humans, low-intensity exercise increases mitochondrial density, function and oxidative capacity, decreases the prevalence of hybrid fibers, and increases lean muscle mass, but these adaptations have not been studied in aged horses. Effects of age and exercise training on muscle fiber type and size, satellite cell abundance, and mitochondrial volume density (citrate synthase activity; CS), function (cytochrome c oxidase activity; CCO), and integrative (per mg tissue) and intrinsic (per unit CS) oxidative capacities were evaluated in skeletal muscle from aged ( n = 9; 22 ± 5 yr) and yearling ( n = 8; 9.7 ± 0.7 mo) horses. Muscle was collected from the gluteus medius (GM) and triceps brachii at wk 0, 8, and 12 of exercise training. Data were analyzed using linear models with age, training, muscle, and all interactions as fixed effects. At wk 0, aged horses exhibited a lower percentage of type IIx ( p = 0.0006) and greater percentage of hybrid IIa/x fibers ( p = 0.002) in the GM, less satellite cells per type II fiber ( p = 0.03), lesser integrative and intrinsic ( p ≤ 0.04) CCO activities, lesser integrative oxidative phosphorylation capacity with complex I (P CI ; p = 0.02) and maximal electron transfer system capacity (E CI+II ; p = 0.06), and greater intrinsic P CI , E CI+II , and electron transfer system capacity with complex II (E CII ; p ≤ 0.05) than young horses. The percentage of type IIx fibers increased ( p < 0.0001) and of type IIa/x fibers decreased ( p = 0.001) in the GM, and the number of satellite cells per type II fiber increased ( p = 0.0006) in aged horses following exercise training. Conversely, the percentage of type IIa/x fibers increased ( p ≤ 0.01) and of type IIx fibers decreased ( p ≤ 0.002) in young horses. Integrative maximal oxidative capacity ( p ≤ 0.02), E CI+II ( p ≤ 0.07), and E CII ( p = 0.0003) increased for both age groups from wk 0 to 12. Following exercise training, aged horses had a greater percentage of IIx ( p ≤ 0.002) and lesser percentage of IIa/x fibers ( p ≤ 0.07), and more satellite cells per type II fiber ( p = 0.08) than young horses, but sustained lesser integrative and intrinsic CCO activities ( p ≤ 0.04) and greater intrinsic P CI , E CI+II , and E CII ( p ≤ 0.05). Exercise improved mitochondrial measures in young and aged horses; however, aged horses showed impaired mitochondrial function and differences in adaptation to exercise training.
... Abbreviations: AC, adenylate cyclase; B-A, β-adrenergic receptor; GC, guanylate cyclase; UCP-2, uncoupling protein this idea, because Ht was not decreased differentially in N and HH groups in the presence of genipin. According to the 'uncoupling to survive' hypothesis postulated by Brand (2000), UCP function could be involved in cardioprotective models, owing to the fact that its activation leads to physiological mitochondrial depolarization and a consequent reduction the production of reactive oxygen species by the respiratory chain (Brand, 2000;Mookerjee et al, 2010). However, this mechanism does not appear to be involved in the present results, because the HH heart does not respond to the UCP blocker genipin and it does not exhibit cardioprotection in response to HH treatment. ...
... Abbreviations: AC, adenylate cyclase; B-A, β-adrenergic receptor; GC, guanylate cyclase; UCP-2, uncoupling protein this idea, because Ht was not decreased differentially in N and HH groups in the presence of genipin. According to the 'uncoupling to survive' hypothesis postulated by Brand (2000), UCP function could be involved in cardioprotective models, owing to the fact that its activation leads to physiological mitochondrial depolarization and a consequent reduction the production of reactive oxygen species by the respiratory chain (Brand, 2000;Mookerjee et al, 2010). However, this mechanism does not appear to be involved in the present results, because the HH heart does not respond to the UCP blocker genipin and it does not exhibit cardioprotection in response to HH treatment. ...
Article
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New findings: What is the central question of this study? Exposure to hypobaric hypoxia increased tolerance to hypoxia/reoxygenation, which is known as endogenous cardioprotection in heart of adult rats. This process involves the participation of the nitric oxide system and modulation of mitochondrial oxygen consumption. Taking in account the impact of the degree of somatic maturation on physiology, in the present work we evaluate the cardio energetic response in prepubertal rats exposed to hypobaric hypoxia. What is the main finding and its importance? Prepubertal rats, as opposite to adult ones, were unable to increase tolerance to hypoxia/reoxygenation by acute exposure to hypobaric hypoxia, which impaired cardiac contractile economy. This finding could be related to the failure for increasing nitric oxide synthase expression, and thus modulation of mitochondrial oxygen consumption and ATP production. Abstract: Studies in our laboratory showed that exposure of rats to hypobaric hypoxia (HH) increased the tolerance of heart to hypoxia/reoxygenation (H/R), involving mitochondrial and cytosolic NOS systems. The objective of the present study was to evaluate how the degree of somatic maturation could alter this healthy response. Prepubertal male rats were exposed 48 h to 4400 m simulated altitude in a hypobaric chamber. The mechanic-energetic activity in perfused hearts and the contractile functional capacity of nitric oxide synthase (NOS) in isolated left ventricle papillary muscles (PM) were evaluated during H/R. Cytosolic nitric oxide (NO), nitrites/nitrates (Nx- ) production, NOS isoforms expression, mitochondrial O2 consumption and ATP production were also evaluated. Heart left ventricular pressure (LVP) during H/R was not improved by HH. However the energetic activity (Ht) was increased. Thus, the contractile economy (LVP/Ht) got worse in HH. Nitric oxide did not modify PM contractility after H/R. Cytosolic p-eNOS -Ser1177and iNOS expression were decreased by HH but no changes were observed in NO production. Interestingly, HH increased Nx levels but O2 consumption and ATP production in mitochondria were not affected by HH. Conclusions: prepubertal rats exposed to HH preserved cardiac contractile function, but with a high energetic cost, modifying contractile economy. Although this could be related to the decreased NOS expression detected, cytosolic NO production was preserved, may be through the Nx metabolic pathway, without modifying mitochondrial ATP production and O2 consumption. In that scenario, the treatment was unable to increase tolerance to H/R as we observed in adult animals. This article is protected by copyright. All rights reserved.
... Therefore, the decline of the mitochondrial energy generation system could be one of the essential indicators characterizing the aging process. Energy producing system localized on the mitochondrial membrane is dependent on the formation of the proton gradient across the inner mitochondrial membrane, and all factors that make the inner membrane permeable decrease the efficiency of energy generation (Brand 2000). Reactive oxygen species (ROS) produced by mitochondria were proposed as the main factor participating in mitochondrial damage during aging (Benzi et al. 1992, Barja et al. 1994, Guerrieri et al. 1996, Lenaz et al. 1997, Davies et al. 2001, Barja 2004, Barja 2014. ...
... In mitochondria, calcium ions regulate MPTP. Increased Ca 2+ concentration, in addition to other changes (inorganic phosphate concentration, oxidative stress), causes MPTP opening and may lead to induction of cell death (Brand 2000). Reactive oxygen species decrease the calcium concentration needed for MPTP opening (Drahota et al. 2012a, Endlicher et al. ...
Article
Mitochondria play an important role in the cell aging process. Changes in calcium homeostasis and/or increased reactive oxygen species (ROS) production lead to the opening of mitochondrial permeability transition pore (MPTP), depolarization of the inner mitochondrial membrane, and decrease of ATP production. Our work aimed to monitor age-related changes in the Ca2+ ion effect on MPTP and the ability of isolated rat liver mitochondria to accumulate calcium. The mitochondrial calcium retention capacity (CRC) was found to be significantly affected by the age of rats. Measurement of CRC values of the rat liver mitochondria showed two periods when 3 to17-week old rats were tested. 3-week and 17-week old rats showed lower CRC values than 7-week old animals. Similar changes were observed while testing calcium-induced swelling of rat liver mitochondria. These findings indicate that the mitochondrial energy production system is more resistant to calcium-induced MPTP opening accompanied by the damaging effect of ROS in adult rats than in young and aged animals.
... Some data suggest that mice with higher daily energy expenditures and metabolic rates have higher uncoupled mitochondrial respiration mediated by adenine nucleotide translocase and uncoupling protein 3 (UCP-3) which provides the basis for the "uncoupled to survive" hypothesis (Brand, 2000). Essentially, this concept postulates that higher uncoupled mitochondrial respiration leads to longer lifespan and lower production of reactive oxygen species by means of a higher energy consumption (Speakman et al., 2004). ...
Article
In every population across the world, women live significantly longer than men; however, the underlying physiological processes that drive these sex differences in age-specific mortality are largely unknown. Recently, the role of adipose tissue in aging and longevity has been a focus of biomedical research in both humans and rodent models. Specifically, brown adipose tissue, a thermoregulatory tissue originally thought to not exist past infancy in humans, has been shown to potentially play a role in health throughout the lifespan. Females have larger adult brown adipose depots that are not just larger in size but also more efficient in non-shivering thermogenesis. This improved functioning of the brown adipose tissue may potentially lead to improved female health, and we hypothesize that this advantage may be of even bigger significance in the older population. Here, we briefly review what is known about sex differences in aging and how sex differences in brown adipose tissue may be contributing to the female lifespan advantage. These questions have usually been addressed in large experimental studies in rodents as a translational model of human aging. Overall, we propose that a better understanding of the thermogenesis-metabolism nexus is necessary in biomedical research, and sex differences in these factors may contribute to the female longevity bias seen in human populations.
... Consequently, incretins have been used as an adjunct therapy for diabetic retinopathy. While mild mitochondrial uncoupling has been shown to be beneficial for cell survival and ageing by reducing ROS production through reduced mitochondrial transmembrane potential [30][31][32], a severe mitochondrial uncoupling may produce a different effect. However, agents such as 2,4-dinitrophenol that are able to uncouple oxidative phosphorylation have been shown to improve cell metabolism and prolong lifespan [32]. ...
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The effects of early (5-day) onset of diabetes mellitus (DM) on retina ultrastructure and cellular bioenergetics were examined. The retinas of streptozotocin-induced diabetic rats were compared to those of non-diabetic rats using light and transmission electron microscopy. Tissue localization of glucagon-like-peptide-1 (GLP-1), exendin-4 (EXE-4), and catalase (CAT) in non-diabetic and diabetic rat retinas was conducted using immunohistochemistry, while the retinal and plasma concentration of GLP-1, EXE-4, and CAT were measured with ELISA. Lipid profiles and kidney and liver function markers were measured from the blood of non-diabetic and diabetic rats with an automated biochemical analyzer. Oxygen consumption was monitored using a phosphorescence analyzer, and the adenosine triphosphate (ATP) level was determined using the Enliten ATP assay kit. Blood glucose and cholesterol levels were significantly higher in diabetic rats compared to control. The number of degenerated photoreceptor cells was significantly higher in the diabetic rat retina. Tissue levels of EXE-4, GLP-1 and CAT were significantly (p = 0.002) higher in diabetic rat retina compared to non-diabetic controls. Retinal cellular respiration was 50% higher (p = 0.004) in diabetic (0.53 ± 0.16 µM O2 min−1 mg−1, n = 10) than in non-diabetic rats (0.35 ± 0.07 µM O2 min−1 mg−1, n = 11). Retinal cellular ATP was 76% higher (p = 0.077) in diabetic (205 ± 113 pmol mg−1, n = 10) than in non-diabetic rats (116 ± 99 pmol mg−1, n = 12). Thus, acute (5-day) or early onslaught of diabetes-induced hyperglycemia increased incretins and antioxidant levels and oxidative phosphorylation. All of these events could transiently preserve retinal function during the early phase of the progression of diabetes.
... Likewise, the increase of ROS could be regulated by uncoupling the electron transport chain through various mechanisms: (a) dissipation of the proton gradient through uncoupling proteins (UCP1-5), known as "proton leak"; (b) through "electron slip" or the H + -electron stoichiometric variation that produces enhanced H + transport for each electron. This loss of mψ means that the final reaction of electron transfer to form ATP, CO2 and H2O is likely to be thermodynamically more spontaneous, minimizing the loss associated with the production of ROS [66]. As such, physiological factors such as age favor OXPHOS inefficiency, generating more ROS, as seen by the ROS production at both mouse ages ( Figure 6). ...
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In recent years, the “non-autonomous motor neuron death” hypothesis has become more consolidated behind amyotrophic lateral sclerosis (ALS). It postulates that cells other than motor neurons participate in the pathology. In fact, the involvement of the autonomic nervous system is fundamental since patients die of sudden death when they become unable to compensate for cardiorespiratory arrest. Mitochondria are thought to play a fundamental role in the physiopathology of ALS, as they are compromised in multiple ALS models in different cell types, and it also occurs in other neurodegenerative diseases. Our study aimed to uncover mitochondrial alterations in the sympathoadrenal system of a mouse model of ALS, from a structural, bioenergetic and functional perspective during disease instauration. We studied the adrenal chromaffin cell from mutant SOD1G93A mouse at pre-symptomatic and symptomatic stages. The mitochondrial accumulation of the mutated SOD1G93A protein and the down-regulation of optic atrophy protein-1 (OPA1) provoke mitochondrial ultrastructure alterations prior to the onset of clinical symptoms. These changes affect mitochondrial fusion dynamics, triggering mitochondrial maturation impairment and cristae swelling, with increased size of cristae junctions. The functional consequences are a loss of mitochondrial membrane potential and changes in the bioenergetics profile, with reduced maximal respiration and spare respiratory capacity of mitochondria, as well as enhanced production of reactive oxygen species. This study identifies mitochondrial dynamics regulator OPA1 as an interesting therapeutic target in ALS. Additionally, our findings in the adrenal medulla gland from presymptomatic stages highlight the relevance of sympathetic impairment in this disease. Specifically, we show new SOD1G93A toxicity pathways affecting cellular energy metabolism in non-motor neurons, which offer a possible link between cell specific metabolic phenotype and the progression of ALS.
... Accordingly, doxorubicin-resistant cells also displayed much greater engagement of oxidative stress response than epirubicin-resistant cells. Interestingly, epirubicinresistant cells displayed an elevated level of uncoupled respiration, which may represent an alternate approach to minimizing ROS production in this model (Echtay et al., 2002;Brand, 2000). Indeed, targeting uncoupling proteins has previously been shown to sensitize multi-drug-resistant leukemia cells to both doxorubicin and epirubicin (Mailloux et al., 2010). ...
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Chemotherapy resistance is a critical barrier in cancer treatment. Metabolic adaptations have been shown to fuel therapy resistance; however, little is known regarding the generality of these changes and whether specific therapies elicit unique metabolic alterations. Using a combination of metabolomics, transcriptomics, and functional genomics, we show that two anthracyclines, doxorubicin and epirubicin, elicit distinct primary metabolic vulnerabilities in human breast cancer cells. Doxorubicin-resistant cells rely on glutamine to drive oxidative phosphorylation and de novo glutathione synthesis, while epirubicin-resistant cells display markedly increased bioenergetic capacity and mitochondrial ATP production. The dependence on these distinct metabolic adaptations is revealed by the increased sensitivity of doxorubicin-resistant cells and tumor xenografts to buthionine sulfoximine (BSO), a drug that interferes with glutathione synthesis, compared with epirubicin-resistant counterparts that are more sensitive to the biguanide phenformin. Overall, our work reveals that metabolic adaptations can vary with therapeutics and that these metabolic dependencies can be exploited as a targeted approach to treat chemotherapy-resistant breast cancer.
... Future research should, therefore, determine the mechanism driving the reduction in proton leak, which could include changes to the inner mitochondrial membrane, like the composition of the lipid bilayer, expression of the adenine nucleotide translocase, and/or suppression of uncoupling proteins (Zhao et al., 2019). Nevertheless, it should be noted that a decrease in proton leak in the absence of other changes will lead to an increase in ROS (Brand, 2000). ...
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It is well established that adult vertebrates acclimatizing to hypoxic environments undergo mitochondrial remodeling to enhance oxygen delivery, maintain ATP, and limit oxidative stress. However, many vertebrates also encounter oxygen deprivation during embryonic development. The effects of developmental hypoxia on mitochondrial function are likely to be more profound, because environmental stress during early life can permanently alter cellular physiology and morphology. To this end, we investigated the long-term effects of developmental hypoxia on mitochondrial function in a species that regularly encounters hypoxia during development—the common snapping turtle (Chelydra serpentina). Turtle eggs were incubated in 21% or 10% oxygen from 20% of embryonic development until hatching, and both cohorts were subsequently reared in 21% oxygen for 8 months. Ventricular mitochondria were isolated, and mitochondrial respiration and reactive oxygen species (ROS) production were measured with a microrespirometer. Compared to normoxic controls, juvenile turtles from hypoxic incubations had lower Leak respiration, higher P:O ratios, and reduced rates of ROS production. Interestingly, these same attributes occur in adult vertebrates that acclimatize to hypoxia. We speculate that these adjustments might improve mitochondrial hypoxia tolerance, which would be beneficial for turtles during breath-hold diving and overwintering in anoxic environments.
... Notably, at 24 hpi complexes I-IV of the electron transport chain were upregulated, whereas complex V transcripts were downregulated blocking the final step of electron transport and ATP synthesis. The resulting uncoupling of the electron transport chain can lead to a process known as "uncoupling to survive" [84], which increases reactive oxygen species production and, at low levels, can boost innate immune function [85]. However, it also has the potential to lead to mitochondrial membrane permeabilisation and trigger the apoptotic pathway, which was also overrepresented at 24 hpi ( Figure 3E). ...
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White Spot Disease (WSD) presents a major barrier to penaeid shrimp production. Mechanisms underlying White Spot Syndrome Virus (WSSV) susceptibility in penaeids are poorly understood due to limited information related to early infection. We investigated mRNA and miRNA transcription in Penaeus vannamei over 36 h following infection. Over this time course, 6192 transcripts and 27 miRNAs were differentially expressed—with limited differential expression from 3–12 h post injection (hpi) and a more significant transcriptional response associated with the onset of disease symptoms (24 hpi). During early infection, regulated processes included cytoskeletal remodelling and alterations in phagocytic activity that may assist WSSV entry and translocation, novel miRNA-induced metabolic shifts, and the downregulation of ATP-dependent proton transporter subunits that may impair cellular recycling. During later infection, uncoupling of the electron transport chain may drive cellular dysfunction and lead to high mortalities in infected penaeids. We propose that post-transcriptional silencing of the immune priming gene Dscam (downregulated following infections) by a novel shrimp miRNA (Pva-pmiR-78; upregulated) as a potential mechanism preventing future recognition of WSSV that may be suppressed in surviving shrimp. Our findings improve our understanding of WSD pathogenesis in P. vannamei and provide potential avenues for future development of prophylactics and treatments.
... The maintenance of a high ATP/O ratio and related efficiency may carry significant costs, especially increased production of reactive oxygen species (Brand, 2000), and/or a decreased carbon flux from mitochondria that can compromise aspects of cellular biosynthesis (Rolfe & Brand, 1997). Overall, there is strong evidence that mitochondrial efficiency (ATP/O ratio) can be adjusted plastically, in response to metabolic constraints and energy demands, leading to a dynamic interplay with the biological condition of an organism (Koch et al., 2021). ...
Article
Global warming is causing profound modifications of aquatic ecosystems and one major outcome appears to be a decline in adult size of many fish species. Over the last decade, sardine populations in the Gulf of Lions (NW Mediterranean Sea) have shown severe declines in body size and condition as well as disappearance of the oldest individuals, which could not be related to overfishing, predation pressure or epizootic diseases. In this study, we investigated whether this situation reflects a bottom‐up phenomenon caused by reduced size and availability of prey that could lead to energetic constraints. We fed captive sardines with food items of two different sizes eliciting a change in feeding mode (filter‐feeding on small items and directly capturing larger ones) at two different rations for several months, and then assessed their muscle bioenergetics to test for changes in cellular function. Feeding on smaller items was associated with a decline in body condition, even at high ration, and almost completely inhibited growth by comparison to sardines fed large items at high ration. Sardines fed on small items presented specific mitochondrial adjustments for energy sparing, indicating a major bioenergetic challenge. Moreover, mitochondria from sardines in poor condition had low basal oxidative activity but high efficiency of ATP production. Notably, when body condition was below a threshold value of 1.07, close to the mean observed in the wild, it was directly correlated with basal mitochondrial activity in muscle. The results show a link between whole‐animal condition and cellular bioenergetics in the sardine, and reveal physiological consequences of a shift in feeding mode. They demonstrate that filter‐feeding on small prey leads to poor growth, even under abundant food and an increase in the efficiency of ATP production. These findings may partially explain the declines in sardine size and condition observed in the wild.
... Indeed, caloric restriction in mice-a reliable pro-longevity factor-augments the expression of Ucp2 and Ucp3, promotes mitochondrial proton leak, and lowers ROS production [128,129]. The convergence of multiple longevity-related pathways on UCP2 and UCP3 speaks to the pro-survival roles of uncoupling, and supports the "uncoupling to survive" model [123,130]. ...
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Despite significant advances in our understanding of the mechanisms that underlie age-related physiological decline, our ability to translate these insights into actionable strategies to extend human healthspan has been limited. One of the major reasons for the existence of this barrier is that with a few important exceptions, many of the proteins that mediate aging have proven to be undruggable. The argument put forth here is that the amenability of ion channels and transporters to pharmacological manipulation could be leveraged to develop novel therapeutic strategies to combat aging. This review delves into the established roles for ion channels and transporters in the regulation of aging and longevity via their influence on membrane excitability, Ca2+ homeostasis, mitochondrial and endolysosomal function, and the transduction of sensory stimuli. The goal is to provide the reader with an understanding of emergent themes, and prompt further investigation into how the activities of ion channels and transporters sculpt the trajectories of cellular and organismal aging.
... Certain chemicals also known as oxidative phosphorylation uncoupling agents can increase the MMP and limit the ROS production by mitochondrial complex 1 (Liu 1997). Cells can sometimes undergo partial mitochondrial uncoupling, leading to decreased ROS production while maintaining sufficient ATP synthesis for delaying cellular senescence (Papa and Skulachev 1997;Brand 2000). ...
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A total mixture of 29 persistent organic pollutants (POPs) modelled from Scandinavian blood concentrations was used to expose human A-498 kidney cells for 24 h over a concentration range spanning below to above blood level (1/10x, 1x, 50x, 100x, 500x). Its constituent submixtures (PFAA, Br, Cl) and co-mixtures (PFAA + Br, PFAA + Cl, Br + Cl) were also tested. Valinomycin (12 µM) was used as a cytotoxic comparative compound. Cell number (CN), nuclear area (NA), nuclear intensity (NI), mitochondrial membrane potential (MMP), and mitochondrial mass (MM) were assessed using high content analysis (HCA). Only the co-mixtures (PFAA + Cl, PFAA + Br) at 50x and 50x, 500x decreased CN, respectively. NI was increased by the total mixture at 500x and Cl mixture at all concentrations tested. MMP was increased by the total mixture at 100x and 500x, PFAA at 1x, Br + Cl and PFAA + Cl at 100x and 500x, respectively. MM was decreased by the total mixture at 500x. In contrast, valinomycin decreased CN and surviving cells showed a decrease in MMP and an increase in MM. In conclusion, POP exposure altered mitochondrial metabolism and induced cell death via an alternative mechanism to valinomycin. Only specific combinations of individual chemical classes, but not the total mixture, affected cell number.
... The mitochondrial ND5 subunit of TT frogs had more α-helix than in CT frogs, which enlarges the region of transmembrane protein and could enhance the coupling degree of the mitochondrial ND5 subunit to a certain extent in the oxidative phosphorylation of TT frogs. Combined with the differences in ND5 expression and gene structure, ND5 gene transcript levels in CT frogs decreased significantly in tissues including liver, brain and kidney under low-temperature stress, potentially leading to less coupling of oxidative phosphorylation (i.e. more proton leakage) and resulting in less harmful reactive oxygen species and more heat, which could help to combat a cold environment [46][47][48]. ...
Article
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Abstract Background Hoplobatrachus rugulosus (Anura: Dicroglossidae) is distributed in China and Thailand and the former can survive substantially lower temperatures than the latter. The mitochondrial genomes of the two subspecies also differ: Chinese tiger frogs (CT frogs) display two identical ND5 genes whereas Thai tiger frogs (TT frogs) have two different ND5 genes. Metabolism of ectotherms is very sensitive to temperature change and different organs have different demands on energy metabolism at low temperatures. Therefore, we conducted studies to understand: (1) the differences in mitochondrial gene expression of tiger frogs from China (CT frogs) versus Thailand (TT frogs); (2) the differences in mitochondrial gene expression of tiger frogs (CT and TT frogs) under short term 24 h hypothermia exposure at 25 °C and 8 °C; (3) the differences in mitochondrial gene expression in three organs (brain, liver and kidney) of CT and TT frogs. Results Utilizing RT-qPCR and comparing control groups at 25 °C with low temperature groups at 8 °C, we came to the following results. (1) At the same temperature, mitochondrial gene expression was significantly different in two subspecies. The transcript levels of two identical ND5 of CT frogs were observed to decrease significantly at low temperatures (P liver > kidney. Conclusions We mainly drew the following conclusions: (1) The differences in the structure and expression of the ND5 gene between CT and TT frogs could result in the different tolerances to low temperature stress. (2) At low temperatures, the transcript levels of most of mitochondrial protein-encoding genes were down-regulated, which could have a significant effect in reducing metabolic rate and supporting long term survival at low temperatures. (3) The expression pattern of mitochondrial genes in different organs was related to mitochondrial activity and mtDNA replication in different organs.
... PFNA can upregulate the expression of fatty acid binding protein 1 liver (LFABP) and uncoupling protein 2 (UCP 2) while downregulating the gene transcription of NADH dehydrogenase subunit 1 (MT-ND 1), ATP synthase F0 subunit 6 (MT-ATP 6), superoxide dismutase 1 (SOD 1), and cytochrome c oxidase subunit I (COX 1) (Liu et al. 2015a). It has been reported that UCP2, MT-ND1 and SOD 1 play an important role in reducing ROS formation by transferring an electron in the respiratory chain and destroying free superoxide radicals, respectively (Brand 2000;Valentine et al. 2005;Zelko et al. 2002). ...
Article
Soil is an essential part of our ecosystem and plays a crucial role as a nutrient source, provides habitat for plants and other organisms. Overuse of antibiotics has accelerated the development and dissemination of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). ARB and ARGs are recognized as emerging environmental contaminants causing soil pollution and serious risks to public health. ARB and ARGs are discharged into soils through several pathways. Application of manure in agriculture is one of the primary sources of ARB and ARGs dissemination in the soil. Different sources of contamination by ARB and ARGs were reviewed and analyzed as well as dissemination mechanisms in the soil. The effects of ARB and ARGs on soil bacterial community were evaluated. Furthermore, the impact of different sources of manure on soil microbial diversity as well as the effect of antibiotics on the development of ARB and ARGs in soils was analyzed. Human health risk assessments associated with the spreading of ARB and ARGs in soils were investigated. Finally, recommendations and mitigation strategies were proposed.
... [22,32,33] The hypometric scaling of maintenance MR with body size is often found within and across species. [34] During periods of inactivity organisms must maintain the function of many basic cellular processes: mitochondria continue to consume oxygen when not manufacturing ATP, [35][36][37] maintaining ion gradients across cell membranes requires energy [38] and low-level biosynthesis all contribute to maintenance costs. 22] Yet these energy costs during inactivity are size-dependent-larger individuals almost always pay lower maintenance costs compared to small individuals per unit body size. ...
Article
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Sexual selection drives the evolution of some of the most exaggerated traits in nature. Studies on sexual selection often focus on the size of these traits relative to body size, but few focus on energetic maintenance costs of the tissues that compose them, and the ways in which these costs vary with body size. The relationships between energy use and body size have consequences that may allow large individuals to invest disproportionally more in sexually selected structures, or lead to the reduced per‐gram maintenance cost of enlarged structures. Although sexually selected traits can incur energetic maintenance costs, these costs are not universally high; they are dependent on the relative mass and metabolic activity of tissues associated with them. Energetic costs of maintenance may play a pervasive yet little‐explored role in shaping the relative scaling of sexually selected traits across diverse taxa. Large animals generally have lower relative rates of energy use compared to small ones. In many diverse groups, large animals also invest in disproportionately larger sexually selected traits. The economy of energy gained by large size may play an important role in shaping the positive scaling of sexually selected traits.
... Prior work demonstrated that T. californicus hybrids from SD and BB crosses had high levels of oxidative damage (Barreto and Burton 2013). Under the assumption that copepods in our cross also suffered from an increase in oxidative damage, it is possible that they were compensating for this effect through mitochondrial uncoupling (Brand 2000;Speakman et al. 2004), increasing mitochondria volume , or upregulating the activity of alternative oxidases (AOX) (Weaver 2019). These compensatory changes may stabilize the redox environment of the mitochondria against an increase in oxidative stress, thereby increasing respiration. ...
Article
Synopsis For decades, scientists have noted connections between individual condition and carotenoid-based coloration in terrestrial and aquatic animals. Organisms that produce more vibrant carotenoid-based coloration tend to have better physiological performance and behavioral displays compared with less colorful members of the same species. Traditional explanations for this association between ornamental coloration and performance invoked the need for color displays to be costly, but evidence for such hypothesized costs is equivocal. An alternative explanation for the condition-dependence of carotenoid-based coloration, the Shared-Pathway Hypothesis (SPH), was developed in response. This hypothesis proposes that red ketocarotenoid-based coloration is tied to core cellular processes involving a shared pathway with mitochondrial energy metabolism, making the concentration of carotenoids an index of mitochondrial function. Since the presentation of this hypothesis, empirical tests of the mechanisms proposed therein have been conducted in several species. In this manuscript, we review the SPH and the growing number of studies that have investigated a connection between carotenoid-based coloration and mitochondrial function. We also discuss future strategies for assessing the SPH to more effectively disentangle evidence that may simultaneously support evidence of carotenoid-resource tradeoffs.
... For this reason, uncoupling may limit the production of ROS by releasing excessive membrane proton potential. In rat hepatocytes, a futile cycle of H + pumping and proton leak may account for 20-25% of respiration [253] and even more in perfused rat muscle. Uncoupling may be achieved by activating proton leak through uncoupling proteins (UCP) [244] (for a different role postulated for uncoupling proteins, cf. ...
Article
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Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.
... To that end, others have found that primary fibroblast cells from dogs have lower mitochondrial membrane potential in longer-lived breeds, suggesting more uncoupling (Nicholatos et al. 2019). This is a similar pattern to the observed "uncoupling to survive" hypothesis (Brand 2000), which states that long-lived animals have uncoupled mitochondria to decrease the potential for ROS formation, minimizing oxidative damage and slowing aging. Speakman et al. (2004) found that mice with higher metabolism had skeletal muscle mitochondria that were more uncoupled, in support of this hypothesis, domestic dogs may also fall in this category. ...
Article
Synopsis Across Mammalia, body size and lifespan are positively correlated. However, in domestic dogs, the opposite is true: small dogs have longer lives compared with large dogs. Here, I present literature-based data on life-history traits that may affect dog lifespan, including adaptations at the whole-organism, and organ-level. Then, I compare those same traits to wild canids. Because oxidative stress is a byproduct of aerobic metabolism, I also present data on oxidative stress in dogs that suggests that small breed dogs accumulate significantly more circulating lipid peroxidation damage compared with large breed dogs, in opposition to lifespan predictions. Further, wild canids have increased antioxidant concentrations compared with domestic dogs, which may aid in explaining why wild canids have longer lifespans than similar-sized domestic dogs. At the cellular level, I describe mechanisms that differ across size classes of dogs, including increases in aerobic metabolism with age, and increases in glycolytic metabolic rates in large breed dogs across their lifespan. To address potential interventions to extend lifespan in domestic dogs, I describe experimental alterations to cellular architecture to test the “membrane pacemaker” hypotheses of metabolism and aging. This hypothesis suggests that increased lipid unsaturation and polyunsaturated fatty acids in cell membranes can increase cellular metabolic rates and oxidative damage, leading to potential decreased longevity. I also discuss cellular metabolic changes of primary fibroblast cells isolated from domestic dogs as they are treated with commercially available drugs that are linked to lifespan and health span expansion.
... Our data indicate that smaller queens receive more food from workers and have a higher metabolism, which was also corroborated by our transcriptome analyses. Surprisingly, the higher metabolism did not increase their susceptibility to paraquat-induced oxidative stress, pointing to a less direct relationship between metabolic activity and lifespan than commonly presumed (Speakman et al., 2004;Brand, 2000). Our transcriptome analysis revealed that queen morph-specific differences in gene expression are associated with longevity pathways such as malate metabolism, proteasome activity or insulin growth-factor signalling. ...
Article
During social evolution, life-history traits not only diverged, with social insect queens becoming highly fecund and long-lived compared to their sterile workers, but also individual traits lost their importance compared to colony-level traits. In solitary animals, fecundity is largely influenced by female size, whereas in eusocial insects, colony size and queen number can affect the egg-laying rate. Here we focussed on the ant Temnothorax rugatulus, which exhibits two queen morphs varying in size and reproductive strategy, correlating with their colony's social organization. We experimentally tested the influence of social structure, colony and body size on queen fecundity and investigated links between body size, metabolic rate and survival under paraquat-induced oxidative stress. To gain insights into the molecular physiology underlying the alternative reproductive strategies, we analysed fat body transcriptomes. Per-queen egg production was lower in polygynous colonies when fecundity was limited by worker care. Colony size was a determinant of fecundity rather than body size or queen number, highlighting the super-organismal properties of these societies. The smaller microgynes were more frequently fed by workers and exhibited an increase in metabolic activity, yet they were similarly resistant to oxidative stress. Small queens differentially expressed metabolic genes in the fat body indicating that shifts in molecular physiology and resource availability allow microgyne queens to compensate their small size with a more active metabolism without paying increased mortality costs. We provide novel insights into how life-history traits and their associations were modified during social evolution and adapted to queen reproductive strategies.
... Proton leak is closely linked to mitochondrial membrane potential: a higher membrane potential increases proton leak, while raised proton leak rate increases oxygen consumption and decreases membrane potential [61]. Decreasing membrane potential represents a protective mechanism by decreasing ROS production and protecting mitochondria from oxidative damage [62]. ROS, in turn, activate uncoupling, further supporting the protective mechanism of uncoupling [63]. ...
Conference Paper
Background: Sepsis represents life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis comprises various derangements including metabolic, immune and mitochondrial dysfunction and these are likely to be inter-related. The pharmacological impact of nutrition in sepsis is mostly overlooked. Depending on their hydrocarbon chain lengths, degree of unsaturation (number of double bonds between carbon atoms), number, position and orientation of their double bonds, lipids have differential effects on immune function and metabolism to either the potential benefit or detriment the patient. / Objectives: This study examines the literature surrounding nutrition in sepsis, with emphasis on lipids, and the potential therapeutic use of palmitate, butyrate and alpha-linolenic acid in modulating immune function, mitochondrial function and metabolism. / Methods: An in vitro model using human peripheral blood mononuclear cells exposed to lipopolysaccharide (LPS) or clinical strains of bacteria was used to determine the effects of palmitate (long-chain, saturated), butyrate (short-chain, saturated) and alpha-linolenic acid (ALA) (long-chain, unsaturated) on immune and mitochondrial function in sepsis via cytokine secretion, cell-specific flow cytometric analyses and mitochondrial respiration. A rat faecal peritonitis model was then utilised to investigate the impact of intravenous butyrate infusion on metabolism, immune function and mitochondrial function. / Results: Palmitate, butyrate and alpha-linolenic acid had pro-, anti-, and mixed inflammatory effects on cytokine secretion respectively. Butyrate, but not palmitate or alpha-linolenic acid, increased maximal mitochondrial respiration and spare respiratory capacity. Butyrate infusion in vivo stimulated fatty acid metabolism, but did not impact on immune function and may increase mitochondrial stress. / Conclusions: Palmitate and butyrate could potentially impact on sepsis pathology, but at different phases of sepsis. Beneficial in vitro effects of butyrate on immune and mitochondrial function could not be reproduced in vivo. Measuring plasma butyrate levels should be addressed in future studies.
... It is worth noting that some previous studies had reported contradictory results [35][36][37]; those studies suggest that NMR mitochondria are more uncoupled than other laboratory rodents, as indicated by their findings of a lower ΔΨ during state 4 respiration when compared to mice. Their observations support the "Uncoupling to Survive" hypothesis which proposes that mitochondrial uncoupling would result in decreased reactive oxygen species production, reducing oxidative stress with concomitant beneficial effects on longevity [78]. Further studies are warranted to explain interstudy variability and if this rather reflects disparate acclimation or other laboratory-specific experimental conditions. ...
Article
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Naked mole-rats (NMR) and Damaraland mole-rats (DMR) exhibit extraordinary longevity for their body size, high tolerance to hypoxia and oxidative stress and high reproductive output; these collectively defy the concept that life-history traits should be negatively correlated. However, when life-history traits share similar underlying physiological mechanisms, these may be positively associated with each other. We propose that one such potential common mechanism might be the bioenergetic properties of mole-rats. Here, we aim to characterize the bioenergetic properties of two African mole-rats. We adopted a top-down perspective measuring the bioenergetic properties at the organismal, cellular, and molecular level in both species and the biological significance of these properties were compared with the same measures in Siberian hamsters and C57BL/6 mice, chosen for their similar body size to the mole-rat species. We found mole-rats shared several bioenergetic properties that differed from their comparison species, including low basal metabolic rates, a high dependence on glycolysis rather than on oxidative phosphorylation for ATP production, and low proton conductance across the mitochondrial inner membrane. These shared mole-rat features could be a result of evolutionary adaptation to tolerating variable oxygen atmospheres, in particular hypoxia, and may in turn be one of the molecular mechanisms underlying their extremely long lifespans.
... However, mitochondrial uncoupling proteins (UCPs) are found in ectotherms (Rey et al., 2008;Woyda-Ploszczyca & Jarmuszkiewicz, 2017). UCPs are upregulated in some species of cold-acclimated ectotherms (fish, Mark et al., 2006;reptiles, Rey et al., 2008;amphibians, Trzcionka et al., 2008), which would reduce mitochondrial membrane potential and thus ROS generation (Brand, 2000). Because mitochondrial efficiency (ATP/oxygen ratio) relates to superoxide production, thermally induced variation in mitochondrial function will affect telomere attrition and damage to other macromolecules (Metcalfe & Olsson, 2021), including mitochondrial proteins and inner mitochondrial membranes. ...
Article
Ectotherms are classic models for understanding life-history tradeoffs, including the reproduction–somatic maintenance tradeoffs that may be reflected in telomere length and their dynamics. Importantly, life-history traits of ectotherms are tightly linked to their thermal environment, with diverse or synergistic mechanistic explanations underpinning the variation. Telomere dynamics potentially provide a mechanistic link that can be used to monitor thermal effects on individuals in response to climatic perturbations. Growth rate, age and developmental stage are all affected by temperature, which interacts with telomere dynamics in complex and intriguing ways. The physiological processes underpinning telomere dynamics can be visualized and understood using thermal performance curves (TPC). TPCs reflect the evolutionary history and the thermal environment during an individual's ontogeny. Telomere maintenance should be enhanced at or near the thermal performance optimum of a species, population and individual. The thermal sensitivity of telomere dynamics should reflect the interacting TPCs of the processes underlying them. The key processes directly underpinning telomere dynamics are mitochondrial function (reactive oxygen production), antioxidant activity, telomerase activity and telomere endcap protein status. We argue that identifying TPCs for these processes will significantly help design robust, repeatable experiments and field studies of telomere dynamics in ectotherms. Conceptually, TPCs are a valuable framework to predict and interpret taxon- and population-specific telomere dynamics across thermal regimes. The literature of thermal effects on telomeres in ectotherms is sparse and mostly limited to vertebrates, but our conclusions and recommendations are relevant across ectothermic animals.
... And how is this allocation achieved? The finding that ∼25% of available energy is dissipated largely unused (Brand, 2000) suggests that the practical problem of keeping biochemical gradients within a certain range may sometimes be more important than finding an appropriate allocation of the available energy. It would be recommendable for the future of allocation theory to investigate the extent to which resources can actually be allocated under specific, targeted physiological control. ...
Article
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The classical evolutionary theories of aging suggest that aging evolves due to insufficient selective pressure against it. In these theories, declining selection pressure with age leads to aging through genes or resource allocations, implying that aging could potentially be stalled were genes, resource allocation, or selection pressure somewhat different. While these classical evolutionary theories are undeniably part of a description of the evolution of aging, they do not explain the diversity of aging patterns, and they do not constitute the only possible evolutionary explanation. Without denying selection pressure a role in the evolution of aging, we argue that the origin and diversity of aging should also be sought in the nature and evolution of organisms that are, from their very physiological make up, unmaintainable. Drawing on advances in developmental biology, genetics, biochemistry, and complex systems theory since the classical theories emerged, we propose a fresh evolutionary-mechanistic theory of aging, the Danaid theory. We argue that, in complex forms of life like humans, various restrictions on maintenance and repair may be inherent, and we show how such restrictions are laid out during development. We further argue that there is systematic variation in these constraints across taxa, and that this is a crucial factor determining variation in aging and lifespan across the tree of life. Accordingly, the core challenge for the field going forward is to map and understand the mosaic of constraints, trade-offs, chance events, and selective pressures that shape aging in diverse ways across diverse taxa.
... This process contributes to about 30% of the oxygen consumption of cells, and occurs through the basal proton leak, uncoupling proteins (UCPs), and mitochondrial ADP/ATP carrier (AAC) (Brand et al., 1994;Bernardi 2019;Bertholet et al., 2019). The mitochondrial uncoupling reduces mitochondrial ΔΨ m , maintains electron flow through ETC and minimizes electronic "escape" to against RONS (Brand 2000;Pileggi et al., 2021). In addition, numerous studies have revealed other functions of mitochondria beyond the aforementioned. ...
Article
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Skeletal muscle fibers contain a large number of mitochondria, which produce ATP through oxidative phosphorylation (OXPHOS) and provide energy for muscle contraction. In this process, mitochondria also produce several types of “reactive species” as side product, such as reactive oxygen species and reactive nitrogen species which have attracted interest. Mitochondria have been proven to have an essential role in the production of skeletal muscle reactive oxygen/nitrogen species (RONS). Traditionally, the elevation in RONS production is related to oxidative stress, leading to impaired skeletal muscle contractility and muscle atrophy. However, recent studies have shown that the optimal RONS level under the action of antioxidants is a critical physiological signal in skeletal muscle. Here, we will review the origin and physiological functions of RONS, mitochondrial structure and function, mitochondrial dynamics, and the coupling between RONS and mitochondrial oxidative stress. The crosstalk mechanism between mitochondrial function and RONS in skeletal muscle and its regulation of muscle stem cell fate and myogenesis will also be discussed. In all, this review aims to describe a comprehensive and systematic network for the interaction between skeletal muscle mitochondrial function and RONS.
... Endothelial nitric oxide and PGC1α also have key roles. Decreased mitochondrial ROS production and macromolecular oxidative damage due, in part, to mitochondrial uncoupling might also explain the benefits of calorie restriction 219,220 . Moreover, calorie restriction stimulates mitochondrial turnover by boosting mitochondrial biogenesis and the clearance of damaged mitochondria via mitophagy 221,222 . ...
Article
Organismal ageing is accompanied by progressive loss of cellular function and systemic deterioration of multiple tissues, leading to impaired function and increased vulnerability to death. Mitochondria have become recognized not merely as being energy suppliers but also as having an essential role in the development of diseases associated with ageing, such as neurodegenerative and cardiovascular diseases. A growing body of evidence suggests that ageing and age-related diseases are tightly related to an energy supply and demand imbalance, which might be alleviated by a variety of interventions, including physical activity and calorie restriction, as well as naturally occurring molecules targeting conserved longevity pathways. Here, we review key historical advances and progress from the past few years in our understanding of the role of mitochondria in ageing and age-related metabolic diseases. We also highlight emerging scientific innovations using mitochondria-targeted therapeutic approaches.
... As noted previously, coupling of mitochondrial oxygen consumption to ATP production is tightly regulated within tissues. However, it is notable that tissues can modulate mitochondrial oxygen consumption and ATP production to fulfil other roles, such as heat generation by brown adipose tissue 27,28 . And that the contributions of different mitochondrial complexes and processes can be elucidated using metabolic poisons, as recently reported by the Sturmey group 25,29 . ...
Article
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We report a novel method to profile intrcellular oxygen concentration (icO2) during in vitro mammalian oocyte and preimplantation embryo development using a commercially available multimodal phosphorescent nanosensor (MM2). Abattoir-derived bovine oocytes and embryos were incubated with MM2 in vitro. A series of inhibitors were applied during live-cell multiphoton imaging to record changes in icO2 associated with mitochondrial processes. The uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) uncouples mitochondrial oxygen consumption to its maximum, while antimycin inhibits complex III to ablate mitochondrial oxygen consumption. Increasing oxygen consumption was expected to reduce icO2 and decreasing oxygen consumption to increase icO2. Use of these inhibitors quantifies how much oxygen is consumed at basal in comparison to the upper and lower limits of mitochondrial function. icO2 measurements were compared to mitochondrial DNA copy number analysed by qPCR. Antimycin treatment increased icO2 for all stages tested, suggesting significant mitochondrial oxygen consumption at basal. icO2 of oocytes and preimplantation embryos were unaffected by FCCP treatment. Inner cell mass icO2 was lower than trophectoderm, perhaps reflecting limitations of diffusion. Mitochondrial DNA copy numbers were similar between stages in the range 0.9–4 × 106 copies and did not correlate with icO2. These results validate the MM2 probe as a sensitive, non-toxic probe of intracellular oxygen concentration in mammalian oocytes and preimplantation embryos.
... Therefore, the decline of the mitochondrial energy generation system could be one of the essential indicators characterizing the aging process. Energy producing system localized on the mitochondrial membrane is dependent on the formation of the proton gradient across the inner mitochondrial membrane, and all factors that make the inner membrane permeable decrease the efficiency of energy generation (Brand 2000). Reactive oxygen species (ROS) produced by mitochondria were proposed as the main factor participating in mitochondrial damage during aging (Benzi et al. 1992, Barja et al. 1994, Guerrieri et al. 1996, Lenaz et al. 1997, Davies et al. 2001, Barja 2004, Barja 2014. ...
Article
Mitochondria play an important role in the cell aging process. Changes in calcium homeostasis and/or increased reactive oxygen species (ROS) production lead to the opening of mitochondrial permeability transition pore (MPTP), depolarization of the inner mitochondrial membrane, and decrease of ATP production. Our work aimed to monitor age-related changes in the Ca2+ ion effect on MPTP and the ability of isolated rat liver mitochondria to accumulate calcium. The mitochondrial calcium retention capacity (CRC) was found to be significantly affected by the age of rats. Measurement of CRC values of the rat liver mitochondria showed two periods when 3 to 17-week old rats were tested. 3-week and 17-week old rats showed lower CRC values than 7-week old animals. Similar changes were observed while testing calcium-induced swelling of rat liver mitochondria. These findings indicate that the mitochondrial energy production system is more resistant to calcium-induced MPTP opening accompanied by the damaging effect of ROS in adult rats than in young and aged animals.
... This results in greater proton influx into the matrix and a reduction in the mitochondrial membrane potential (↓+), which leads to diminished O − 2 production. The "uncoupling to survive" hypothesis (Brand, 2000) suggests that mitochondrial uncoupling will favor longevity by diminishing oxidative damage and improving mitochondrial function, an antagonistic hallmark of mammalian aging (Lopez-Otin et al., 2013. Indeed, multiple studies in yeast, Caenorhabditis elegans, flies, rodents, and canines have shown that mild mitochondrial uncoupling reduces reactive oxygen species (ROS) production, delays the progression of age-related diseases (i.e., hepatic steatosis and diabetes) and extends lifespan (Barros et al., 2004;Caldeira da Silva et al., 2008;Fridell et al., 2005Fridell et al., , 2009Lemire et al., 2009;Neretti et al., 2009;Nicholatos et al., 2019;Perry et al., 2013Samuel et al., 2004Samuel et al., , 2007Ulgherait et al., 2020). ...
Article
Full-text available
Mild uncoupling of oxidative phosphorylation is an intrinsic property of all mitochondria and may have evolved to protect cells against the production of damaging reactive oxygen species. Therefore, compounds that enhance mitochondrial uncoupling are potentially attractive anti-aging therapies; however, chronic ingestion is associated with a number of unwanted side effects. We have previously developed a controlled-release mitochondrial protonophore (CRMP) that is functionally liver-directed and promotes oxidation of hepatic triglycerides by causing a subtle sustained increase in hepatic mitochondrial inefficiency. Here, we sought to leverage the higher therapeutic index of CRMP to test whether mild mitochondrial uncoupling in a liver-directed fashion could reduce oxidative damage and improve age-related metabolic disease and lifespan in diet-induced obese mice. Oral administration of CRMP (20 mg/[kg-day] × 4 weeks) reduced hepatic lipid content, protein kinase C epsilon activation, and hepatic insulin resistance in aged (74-week-old) high-fat diet (HFD)-fed C57BL/6J male mice, independently of changes in body weight, whole-body energy expenditure, food intake, or markers of hepatic mitochondrial biogenesis. CRMP treatment was also associated with a significant reduction in hepatic lipid peroxidation, protein carbonylation, and inflammation. Importantly, long-term (49 weeks) hepatic mitochondrial uncoupling initiated late in life (94-104 weeks), in conjugation with HFD feeding, protected mice against neoplastic disorders, including hepatocellular carcinoma (HCC), in a strain and sex-specific manner. Taken together, these studies illustrate the complex variation of aging and provide important proof-of-concept data to support further studies investigating the use of liver-directed mitochondrial uncouplers to promote healthy aging in humans.
... Oxygen consumption occurring via the ETS is being driven by protons leaking across the mitochondrial inner membrane rather than via ATP synthase. Low state 4 respiration tends to lead to high reactive oxygen species (ROS) production (Brand 2000); therefore, a higher state 4 in sexual species compared with hybrid asexual species may be an adaptive trait to mitigate oxidative damage. Investigation into potential differences in ROS production and oxidative damage between sexual and hybrid asexual species is needed to test this hypothesis. ...
Article
The scarcity of asexual reproduction in vertebrates alludes to an inherent cost. Several groups of asexual vertebrates exhibit lower endurance capacity (a trait predominantly sourced by mitochondrial respiration) compared with congeneric sexual species. Here we measure endurance capacity in five species of Aspidoscelis lizards and examine mitochondrial respiration between sexual and asexual species using mitochondrial respirometry. Our results show reduced endurance capacity, reduced mitochondrial respiration, and reduced phenotypic variability in asexual species compared with parental sexual species, along with a positive relationship between endurance capacity and mitochondrial respiration. Results of lower endurance capacity and lower mitochondrial respiration in asexual Aspidoscelis are consistent with hypotheses involving mitonuclear incompatibility.
... An increase in AOX expression would continue to consume oxygen for respiration, but would decrease ATP production due to reduced electron flow to Complex IV [81]. Similarly, the use of uncoupling proteins to reduce reactive oxygen species and maximize survival in the face of oxidative stress may also have resulted in a decrease in ATP [83][84][85]. If copepods in our study were using AOX or uncoupling enzymes to effectively combat oxidative stress due to hybridization and the poor yeast diet, it may explain why our most colorful lines also tended to produce less ATP (Fig 3). ...
Article
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The marine copepod, Tigriopus californicus , produces the red carotenoid pigment astaxanthin from yellow dietary precursors. This ‘bioconversion’ of yellow carotenoids to red is hypothesized to be linked to individual condition, possibly through shared metabolic pathways with mitochondrial oxidative phosphorylation. Experimental inter-population crosses of lab-reared T . californicus typically produces low-fitness hybrids is due in large part to the disruption of coadapted sets nuclear and mitochondrial genes within the parental populations. These hybrid incompatibilities can increase variability in life history traits and energy production among hybrid lines. Here, we tested if production of astaxanthin was compromised in hybrid copepods and if it was linked to mitochondrial metabolism and offspring development. We observed no clear mitonuclear dysfunction in hybrids fed a limited, carotenoid-deficient diet of nutritional yeast. However, when yellow carotenoids were restored to their diet, hybrid lines produced less astaxanthin than parental lines. We observed that lines fed a yeast diet produced less ATP and had slower offspring development compared to lines fed a more complete diet of algae, suggesting the yeast-only diet may have obscured effects of mitonuclear dysfunction. Astaxanthin production was not significantly associated with development among lines fed a yeast diet but was negatively related to development in early generation hybrids fed an algal diet. In lines fed yeast, astaxanthin was negatively related to ATP synthesis, but in lines fed algae, the relationship was reversed. Although the effects of the yeast diet may have obscured evidence of hybrid dysfunction, these results suggest that astaxanthin bioconversion may still be related to mitochondrial performance and reproductive success.
... This might be helpful to organisms living in cold environments. The low ROS production also protects the organisms against oxidative stress and ageing (Brand 2000;Stier et al. 2014;Zhou et al. 2014). Thus, the OXPHOS system can have broad impacts on organismal fitness and the genes involved may be subjected to selection for climate suitability. ...
Article
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What kind of genetic structure helps the rapid range expansion of the invasive species is fundamental to understand spread of invasion. The House crow (Corvus splendens), an ecological generalist, having a large native and introduced distribution range, is a good study model to investigate the genetic structure and adaptations underpinning the evolutionary potential for successful biological invasion. Thirteen mainland and one island native population from the Indian subcontinent were studied using four nuclear introns and mitochondrial genome to determine the phylogeographic structure and demographic history. A large, panmictic long-term expanding native population dating from the last glacial period (~ 30,000 ya) was inferred leading to great genetic diversity across the whole native range. The thirteen mitochondrial encoded proteins, directly involved in the energy supplying pathway, could underlie metabolic adaptations during range expansion under diverse climate conditions. Therefore, to investigate the molecular selection on these genes in native and introduced ranges, five previously studied introduced populations from Southeast Asia and Africa were included. The native populations originating from hot arid and humid tropical areas exhibited the signatures of positive selection on four codons located in three genes (ND5, Cytb and COX2), suggesting these may have evolved under environmental stresses in those regions. Our findings demonstrated the native range population as the reservoir of the species’ genetic diversity, mitogenomic patterns of the introduced populations related to native range of species and no varaints could be associated with climate in introduced range. Thus,inferred that the pre-adapted standing genetic variations evolved during dispersion over the native range are the predominant source of the high evolutionary potential and contribute to the successful invasion history. These findings will help to predict the future introduced range of the House crow.
... PFNA can upregulate the expression of fatty acid binding protein 1 liver (LFABP) and uncoupling protein 2 (UCP 2) while downregulating the gene transcription of NADH dehydrogenase subunit 1 (MT-ND 1), ATP synthase F0 subunit 6 (MT-ATP 6), superoxide dismutase 1 (SOD 1), and cytochrome c oxidase subunit I (COX 1) (Liu et al. 2015a). It has been reported that UCP2, MT-ND1 and SOD 1 play an important role in reducing ROS formation by transferring an electron in the respiratory chain and destroying free superoxide radicals, respectively (Brand 2000;Valentine et al. 2005;Zelko et al. 2002). ...
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Perchlorate is a persistent pollutant, generated via natural and anthropogenic processes, that possesses a high potential for endocrine disruption in humans and biota. It inhibits iodine fixation, a major reason for eliminating this pollutant from ecosystems. Remediation of perchlorate can be achieved with various physicochemical treatments, especially at low concentrations. However, microbiological approaches using microorganisms, such as those from the genera Dechloromonas, Serratia, Propionivibrio, Wolinella, and Azospirillum, are promising when perchlorate pollution is extensive. Perchlorate-reducing bacteria, isolated from harsh environments, for example saline soils, mine sediments, thermal waters, wastewater treatment plants, underground gas storage facilities, and remote areas, including the Antarctica, can provide removal yields from 20 to 100%. Perchlorate reduction, carried out by a series of enzymes, such as perchlorate reductase and superoxide chlorite, depends on pH, temperature, salt concentration, metabolic inhibitors, nutritional conditions, time of contact, and cellular concentration. Microbial degradation is cost-effective, simple to implement, and environmentally friendly, rendering it a viable method for alleviating perchlorate pollution in the environment.
... Even though it reduces the efficiency of ATP production, LEAK is an essential source of heat production, in mammals, but also potentially in birds [17,34]. LEAK can also reduce the oxidative damage associated with the production of reactive oxygen species (ROS) in mitochondria ('uncoupling to survive hypothesis' [35]). This leads to trade-offs between energy production, heat generation and oxidative balance [36], with LEAK accounting for 20-70% of cellular respiration, or up to 25% of the organismal basal metabolic rate [28,34,37]. ...
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Sound is an essential source of information in many taxa and can notably be used by embryos to programme their phenotypes for postnatal environments. While underlying mechanisms are mostly unknown, there is growing evidence for the involvement of mitochondria—main source of cellular energy (i.e. ATP)—in developmental programming processes. Here, we tested whether prenatal sound programmes mitochondrial metabolism. In the arid-adapted zebra finch, prenatal exposure to ‘heat-calls’—produced by parents incubating at high temperatures—adaptively alters nestling growth in the heat. We measured red blood cell mitochondrial function, in nestlings exposed prenatally to heat- or control-calls, and reared in contrasting thermal environments. Exposure to high temperatures always reduced mitochondrial ATP production efficiency. However, as expected to reduce heat production, prenatal exposure to heat-calls improved mitochondrial efficiency under mild heat conditions. In addition, when exposed to an acute heat-challenge, LEAK respiration was higher in heat-call nestlings, and mitochondrial efficiency low across temperatures. Consistent with its role in reducing oxidative damage, LEAK under extreme heat was also higher in fast growing nestlings. Our study therefore provides the first demonstration of mitochondrial acoustic sensitivity, and brings us closer to understanding the underpinning of acoustic developmental programming and avian strategies for heat adaptation.
... The longevity mice not only had elevated BMR but also raised total daily energy expenditures and elevated expenditure on physical activity (Speakman et al., 2004). The "uncoupled and surviving" hypothesis proposed that the increased mitochondrial proton cycling leads to oxidation of ubiquinone and decreased ROS production consistent with increased lifespan (Brand, 2000). It is just as likely that the longevity of these mice was owing to their raised expenditure on physical activity (Speakman et al., 2004). ...
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Objective: The aim of this study was to assess the relationship between basal metabolic rate (BMR) and all-cause mortality in southern Chinese adults. Methods: We prospectively examined the relationship between BMR and all-cause mortality in 12,608 Southern Chinese adults with age ≥ 35 years who participated in the National Key R&D Program from 2013–2014 to 2019–2020. Cox proportional hazard models were used to examine the association between BMR and all-cause mortality. Results: A total of 809 deaths (including 478 men and 331 women) occurred during a median follow-up period of 5.60 years. All-cause mortality was higher in elderly individuals than in non-elderly individuals (11.48 vs. 2.04%, P < 0.001) and was higher in male subjects than in female subjects (9.84 vs. 4.56%, P < 0.001). There was a significantly inverse relationship between BMR levels and all-cause mortality in elderly male individuals (adjusted-HR per SD increase: 0.80, 95% CI: 0.70–0.91, P < 0.001). Compared with BMR levels ≤ 1,115 kJ/day, there was lower all-cause mortality in third and highest BMR quartiles in the elderly male subjects (adjusted-HR: 0.71, 95% CI: 0.53–0.95, P = 0.022; adjusted-HR: 0.60, 95% CI: 0.43–0.84, P = 0.003, respectively). Conclusion: An elevated BMR was independently inversely associated with all-cause mortality in elderly male subjects in a southern Chinese population.
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Skeletal muscle mitochondria of the African pygmy mouse Mus mattheyi exhibit markedly reduced oxygen consumption and ATP synthesis rates but a higher mitochondrial efficiency than what would be expected from allometric trends. In the present study, we assessed whether such reduction of mitochondrial activity in M. mattheyi can limit the oxidative stress associated with an increased generation of mitochondrial reactive oxygen species. We conducted a comparative study of mitochondrial oxygen consumption, H2O2 release, and electron leak (%H2O2/O) in skeletal muscle mitochondria isolated from the extremely small African pygmy mouse (M. mattheyi, ~5 g) and Mus musculus, which is a larger Mus species (~25 g). Mitochondria were energized with pyruvate, malate, and succinate, after which fluxes were measured at different steady-state rates of oxidative phosphorylation. Overall, M. mattheyi exhibited lower oxidative activity and higher electron leak than M. musculus, while the H2O2 release did not differ significantly between these two Mus species. We further found that the high coupling efficiency of skeletal muscle mitochondria from M. mattheyi was associated with high electron leak. Nevertheless, data also show that, despite the higher electron leak, the lower mitochondrial respiratory capacity of M. mattheyi limits the cost of a net increase in H2O2 release, which is lower than that expected for a mammals of this size.
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Pharmaceuticals and personal care products (PPCPs) are ubiquitous low-level contaminants in the aquatic environment. The molecular targets of many PPCPs play critical roles in evolutionarily conserved xenobiotic biotransformation and cellular energy production pathways. This chapter reviews the effects of PPCPs on metabolic processes in fish. We discuss PPCP-induced modulation of cytochrome P450-mediated drug metabolism and steroid hormone biosynthesis, effects on bioenergetics as indicated by the function of the mitochondrial electron transport system, and alteration of the metabolome. We also review the effects of PPCPs on physiological responses that are directly related to these subcellular metabolic processes, including growth, locomotion, and feeding and reproductive behavior. In addition, we identify directions for future research to address key data gaps. Although exposures of fish to environmentally relevant concentrations of PPCPs are generally sub-lethal, yet researchers have suggested that PPCP-induced modulation of physiological responses, driven by alteration of subcellular metabolic pathways, may lead to deficits in population fitness and survival of fish. Hence, we advocate continued research to elucidate the mechanisms of action of PPCPs on fish metabolic pathways, physiology, and behavior to guide ecological risk assessment of PPCPs in the aquatic environment.
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The increasing knowledge and awareness concerning the presence of pharmaceutical residues and their negative impact on the marine environment create a need to develop new tools to investigate and monitor their pathways. Multiresidue methods allow the determination of a vast number of target compounds from different classes of pharmaceuticals in a single analysis. The application of these methods to seawater samples is more complicated compared with freshwater analysis due to matrix impact and dilution of the target compounds. This chapter presents a review of the published research papers from the last decade and discusses the analytical methodologies presented there. Based on the current knowledge, authors also try to predict and point out the future trends and challenges in multiresidue analysis methodology.
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Naked mole-rats (NMR) and Damaraland mole-rats (DMR) are the only two eusocial mammals known. Both species exhibit extraordinary longevity for their body size, high tolerance to hypoxia and oxidative stress and high reproductive output; these collectively defy the concept that all life-history traits should be negatively correlated. However, when life-history traits share similar underpinning physiological mechanisms, these may be positively associated with each other. Here, we propose that the bioenergetic properties of mole-rats share a potential common mechanism. We adopted a top-down perspective measuring the bioenergetic properties at the organismal, cellular, and molecular level in both species and the biological significance of these properties were compared with the same measures in Siberian hamsters and C57BL/6 mice, chosen for their similar body size to the mole-rat species. We found mole-rats shared several bioenergetic properties that differed from their comparator species, including low basal metabolic rates, a high dependence on glycolysis rather than on oxidative phosphorylation for ATP production, and low proton conductance across the mitochondrial inner membrane. These shared mole-rat features could be a result of evolutionary adaptation to tolerating variable oxygen atmospheres, in particular hypoxia, and may in turn be one of the molecular mechanisms underlying their extremely long lifespans.
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The relationships between metabolic rate, body temperature (Tb), body composition and ageing are complex, and not fully resolved. In particular, Tb and metabolic rate often change in parallel, making disentangling their effects difficult. Here we show that in both sexes of mice and hamsters exposure to a temperature of 32.5 °C leads to a reduced lifespan, coincident with lowered metabolic rate and elevated Tb with no change in body composition. We exploit the unique situation that when small mammals are exposed to hot ambient temperatures their Tb goes up, at the same time that their metabolic rate goes down, allowing us to experimentally separate the impacts of Tb and metabolic rate on lifespan. The impact of ambient temperature on lifespan can be reversed by exposing the animals to elevated heat loss by forced convection, which reverses the effect on Tb but does not affect metabolic rate, demonstrating the causal effect of Tb on lifespan under laboratory conditions for these models. The impact of manipulations such as calorie restriction that increase lifespan may be mediated via effects on Tb, and measuring Tb may be a useful screening tool for putative therapeutics to extend the human lifespan.
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Persistent oxidative stress contributes to hallmarks of aging, including impaired proteostasis and mitochondrial dysfunction, while acute oxidative challenges resolved swiftly contribute to beneficial adaptations. Adaptive homeostasis is where acute exposures to sub-toxic stimuli kindle transient expansion of responses necessary to reestablish homeostasis. Elucidating mechanisms underlying adaptive homeostasis will provide novel targets for healthspan extension. Nuclear erythroid-related factor 2 (Nrf2) is a key regulator of cytoprotective gene transcription for redox homeostasis; nuclear respiratory factor 1 (NRF1) is a transcription factor that regulates expression of genes necessary for mitochondrial function. Regulation of both is compromised with advancing age. We hypothesized that NRF1 (NRF1a) and Nrf2 (Nrf2a) activators might improve adaptive homeostasis in C2C12 myoblasts by promoting mitochondrial proteome maintenance and function. Using stable isotope tracing, we assessed protein synthesis over a 16-hr treatment with NRF1a, Nrf2a, or both, with and without a hydrogen peroxide (H2O2) stress. We assessed mitochondrial function using high-resolution respirometry. Co-treatment of NRF1a and Nrf2a under H2O2 stress favored proteostatic maintenance (p<0.05). H2O2 stress decreased mitochondrial respiration and this decrease was not altered by NRF1a/Nrf2a co-treatment. These results suggest that simultaneously targeting Nrf2 and NRF1 may be a viable approach for reestablishing mitochondrial protein homeostasis following a stress, but that this adaptation may not improve respiratory capacity.
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Proton cycling across the mitochondrial inner membrane makes up a significant proportion (20–30%) of Standard Metabolic Rate (SMR) in rats. If proton cycling is equally important in other animals, those that metabolically depress to 25% or less of SMR have a problem: either their entire energy budget will be wasted by proton cycling, or they have to suppress the leak of protons across the mitochondrial membrane. Muscle mitochondria from metabolically depressed, hypoxic overwintering frogs (Rana temporaria) do have decreased proton leak rate. This is achieved not by decreasing the proton conductance of the membrane, but by lowering the protonmotive force (the driving force for the leak). Protonmotive force is lowered aerobically by restricting electron supply, and in anoxia by restricting mitochondrial ATPase activity. There is also a temperature component to the physiological depression of overwintering frogs. The proton conductance of frog muscle mitochondria decreases steeply with temperature. Frog hepatocytes also respond strongly to temperature, and decrease their proton cycling in parallel to other reactions, so preserving metabolic efficiency at different temperatures. Hepatopancreas cells from the land snail (Helix aspersa) provide a good new model system to study biochemical mechanisms of depression without the complications of temperature change. Cells from aestivating animals show a persistent metabolic depression to 30% of controls, partly through intrinsic effects and partly through the extrinsic effects of pH and pO2. In depressed cells, proton cycling decreases at least as much as cellular respiration rate. These results using frogs and snails show that mitochondrial proton cycling is strongly suppressed in metabolic depression, so that metabolic efficiency is maintained or even enhanced.
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Standard metabolic rate is 7-fold greater in the rat (a typical mammal) than in the bearded dragon, Amphibolurus vitticeps (a reptile with the same body mass and temperature). Rat hepatocytes respire 4-fold faster than do hepatocytes from the lizard. The inner membrane of isolated rat liver mitochondrial has a proton permeability that is 4-5-fold greater than the proton permeability of the lizard liver mitochondrial membrane per mg of mitochondrial protein. The greater permeability of rat mitochondria is not caused by differences in the surface area of the mitochondrial inner membrane, but differences in the fatty acid composition of the mitochondrial phospholipids may be involved in the permeability differences. Greater proton permeability of the mitochondrial inner membrane may contribute to the greater standard metabolic rate of mammals.
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The mitochondrial membrane potential in isolated hepatocytes was measured using the distribution of the lipophilic cation triphenylmethylphosphonium (TPMP+) with appropriate corrections for plasma membrane potential, cytoplasmic and mitochondrial binding of TPMP+, and other factors. The relationship between mitochondrial membrane potential and respiration rate in hepatocytes was examined as the respiratory chain was titrated with myxothiazol in the presence of oligomycin. This relationship was nonproportional and similar to results with isolated mitochondria respiring on succinate. This shows that there is an increased proton conductance of the mitochondrial inner membrane in situ at high values of membrane potential. From the respiration rate and mitochondrial membrane potential of hepatocytes in the absence of oligomycin, we estimate that the passive proton permeability of the mitochondrial inner membrane accounts for 20-40% of the basal respiration rate of hepatocytes. The relationship between log[TPMP+]tot/[TPMP+]e and respiration rate in thymocytes was also nonproportional suggesting that the phenomenon is not peculiar to hepatocytes. There is less mitochondrial proton leak in hepatocytes from hypothyroid rats. A large proportion of the difference in basal respiration rate between hepatocytes from normal and hypothyroid rats can be accounted for by differences in the proton permeability characteristics of the mitochondrial inner membrane.
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1A technique is described, based on the distribution of rubidium, acetate and methylammonium ions, for the simultaneous estimation of membrane potential and pH gradient across the inner membrane of mitochondria. The technique requires less than 0.5 mg mitochondrial protein and is independent of many factors which interfere with electrode determinations of protonmotive force (Δp).2With a limiting matrix volume of 0.4 μl/mg mitochondrial protein, the indicated value of Δp for rat liver mitochondria is 228 mV in state 4, 170 mV in state 3, and –0.6 mV in the presence of rotenone and uncoupler. The relative contributions of the pH gradient and membrane potential are dependent on the availability of electrophoretically and electroneutrally translocatable species in the incubation medium.3In a sucrose-based medium containing 0.5 mM KCl, rotenone and uncoupler, the technique indicated a membrane potential of + 85 mV and a pH gradient of + 1.46 (acidic in the matrix compartment). In state 4, under no conditions examined did the pH gradient contribute more than 50% of the total protonmotive force.4The hydrolysis of ATP generates an optimal Δp of 220 mV.5The proton conductance of the inner membrane is potential dependent, increasing when Δp is greater than 200 mV.6The extra-mitochondrial phosphate potential sustainable by respiration was found to change in parallel to Δp, but to exceed the latter parameter when based upon a stoichiometry of two protons translocated per ATP synthesised.
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Resting O2 consumption of hepatocytes isolated from mammals ranging in mass from 20-g mice to 200-kg horses decreases with increasing body mass. The substrate oxidation system increases in activity with increasing body mass and mitochondrial proton leak and phosphorylation system decrease in activity, resulting in a higher mitochondrial membrane potential in hepatocytes from larger mammals. The absolute rates of O2 consumption due to nonmitochondrial processes, substrate oxidation, mitochondrial proton leak, and the phosphorylation system decrease with increasing body mass. These decreases are due partly to a decrease in mitochondrial number per cell and partly to decrease in mitochondrial inner membrane proton leakiness and in ATP turnover by cells from larger mammals. Quantitatively, the proportion of total cell O2 consumption by nonmitochondrial processes (13%) and oxidation of substrates (87%) and the proportions used to drive mitochondrial proton leak (19%) and the phosphorylation system (68%) are the same for hepatocytes from all mammals investigated. The effect of matched decreases in the rates of proton leak and of ATP turnover is to keep the effective amount of ATP synthesized per unit of O2 consumed relatively constant with body mass, suggesting that the observed value is optimal.
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We have tested the hypothesis that the leak of protons across the mitochondrial inner membrane (proton leak) is a significant contributor to standard metabolic rate (SMR). We found that proton leak accounts for around one-half of the resting respiration rate of perfused rat skeletal muscle. Proton leak is known to make a significant (26%) contribution to the resting respiration rate of isolated rat hepatocytes (M. D. Brand, L.-F. Chien, E. K. Ainscow, D. F. S. Rolfe, and R. K. Porter. Biochim. Biophys. Acta 1187: 132-139, 1994). If the importance of proton leak in these isolated and perfused systems is similar to its importance in vivo, then using literature values for the contribution of liver and skeletal muscle to SMR, we can calculate that proton leak in liver and skeletal muscle alone accounts for 11-26% (mean 20%) of the SMR of the rat. If proton leak activity in the other tissues of the rat is similar to that in liver cells, then the contribution of proton leak to rat SMR would be 16-31% (mean 25%).
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Mitochondrial proton leak is an important component of cellular metabolism in animals and may account for as much as one quarter to one third of the Standard Metabolic Rate of the rat. The activity of the proton leak pathway is different in a wide range of animal species and in different thyroid states. Such differences imply some function for proton leak and candidates for this function include thermogenesis, protection against reactive oxygen species, endowment of metabolic sensitivity and maintenance of carbon fluxes.
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Recently, we proposed a hypothetical model of coexistence of "Reactive oxygen cycle" with Q cycle and H+ cycle in mitochondrial respiratory chain to combine both processes of univalent electron leak for production of superoxide and of proton leak across inner mitochondrial membrane. This review presents a more detailed description of this model and summaries the supporting experimental evidence obtained.
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The free radical theory of aging, conceived in 1956, has turned 40 and is rapidly attracting the interest of the mainstream of biological research. From its origins in radiation biology, through a decade or so of dormancy and two decades of steady phenomenological research, it has attracted an increasing number of scientists from an expanding circle of fields. During the past decade, several lines of evidence have convinced a number of scientists that oxidants play an important role in aging. (For the sake of simplicity, we use the term oxidant to refer to all "reactive oxygen species," including O2-., H2O2, and .OH, even though the former often acts as a reductant and produces oxidants indirectly.) The pace and scope of research in the last few years have been particularly impressive and diverse. The only disadvantage of the current intellectual ferment is the difficulty in digesting the literature. Therefore, we have systematically reviewed the status of the free radical theory, by categorizing the literature in terms of the various types of experiments that have been performed. These include phenomenological measurements of age-associated oxidative stress, interspecies comparisons, dietary restriction, the manipulation of metabolic activity and oxygen tension, treatment with dietary and pharmacological antioxidants, in vitro senescence, classical and population genetics, molecular genetics, transgenic organisms, the study of human diseases of aging, epidemiological studies, and the ongoing elucidation of the role of active oxygen in biology.
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Birds have a maximum longevity (MLSP) much higher than mammals of similar body size in spite of their high metabolic rates. In this study, State 4 and State 3 rates of H2O2 production were lower in canary (MLSP = 24 years) and parakeet (MLSP = 21 years) than in mouse (MLSP = 3.5 years) heart mitochondria. Studies using specific inhibitors of the respiratory chain indicate that free radical generation sites at Complexes I and III are responsible for these differences. Main mechanisms lowering H2O2 production in these birds are a low rate of mitochondrial oxygen consumption in the parakeet and a low mitochondrial free radical leak in the canary. Strong increases in H2O2 production during active respiration (State 3) released by addition of ADP to pyruvate/malate-supplemented mitochondria are avoided in three species because the free radical leak decreases during the transition from State 4 to State 3 respiration. These results, together with those previously obtained in pigeons and in various mammalian species, suggest that the rate of mitochondrial free radical production correlates better with the rate of aging and the MLSP than the metabolic rate. They also suggest that a low rate of mitochondrial H2O2 production is a general characteristic of birds, animals showing very slow aging rates.
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Proton pumping across the mitochondrial inner membrane and proton leak back through the natural proton conductance pathway make up a futile cycle that dissipates redox energy. We measured respiration and average mitochondrial membrane potential in perfused rat hindquarter with maximal tetanic contraction of the left gastrocnemius-soleus-plantaris muscle group, and we estimate that the mitochondrial proton cycle accounted for 34% of the respiration rate of the preparation. Similar measurements in rat hepatocytes given substrates to cause a high rate of gluconeogenesis and ureagenesis showed that the proton cycle accounted for 22% of the respiration rate of these cells. Combining these in vitro values with literature values for the contribution of skeletal muscle and liver to standard metabolic rate (SMR), we calculate that the proton cycle in working muscle and liver may account for 15% of SMR in vivo. Although this value is less than the 20% of SMR we calculated previously using data from resting skeletal muscle and hepatocytes, it is still large, and we conclude that the futile proton cycle is a major contributor to SMR.
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There is a futile cycle of pump and leak of protons across the mitochondrial inner membrane. The contribution of the proton cycle to standard metabolic rate is significant, particularly in skeletal muscle, and it accounts for 20% or more of the resting respiration of a rat. The mechanism of the proton leak is uncertain: basal proton conductance is not a simple biophysical leak across the unmodified phospholipid bilayer. Equally, the evidence that it is catalysed by homologues of the brown adipose uncoupling protein, UCP1, is weak. The yeast genome contains no clear UCP homologue but yeast mitochondria have normal basal proton conductance. UCP1 catalyses a regulated inducible proton conductance in brown adipose tissue and the possibility remains open that UCP2 and UCP3 have a similar role in other tissues, although this has yet to be demonstrated.
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An energetically significant leak of protons occurs across the mitochondrial inner membranes of eukaryotic cells. This seemingly wasteful proton leak accounts for at least 20% of the standard metabolic rate of a rat. There is evidence that it makes a similar contribution to standard metabolic rate in a lizard. Proton conductance of the mitochondrial inner membrane can be considered as having two components: a basal component present in all mitochondria, and an augmentative component, which may occur in tissues of mammals and perhaps of some other animals. The uncoupling protein of brown adipose tissue, UCP1, is a clear example of such an augmentative component. The newly discovered UCP1 homologs, UCP2, UCP3, and brain mitochondrial carrier protein 1 (BMCP1) may participate in the augmentative component of proton leak. However, they do not appear to catalyze the basal leak, as this is observed in mitochondria from cells which apparently lack these proteins. Whereas UCP1 plays an important role in thermogenesis, the evidence that UCP2 and UCP3 do likewise remains equivocal.
Article
The cytochrome bc1 complex is the most widely occurring electron transfer complex capable of energy transduction. Cytochrome bc1 complexes are found in the plasma membranes of phylogenetically diverse photosynthetic and respiring bacteria, and in the inner mitochondrial membrane of all eucaryotic cells. In all of these species the bc1 complex transfers electrons from a low-potential quinol to a higher-potential c-type cytochrome and links this electron transfer to proton translocation. Most bacteria also possess alternative pathways of quinol oxidation capable of circumventing the bc1 complex, but these pathways generally lack the energy-transducing, protontranslocating activity of the bc1 complex. All cytochrome bc1 complexes contain three electron transfer proteins which contain four redox prosthetic groups. These are cytochrome b, which contains two b heme groups that differ in their optical and thermodynamic properties; cytochrome c1, which contains a covalently bound c-type heme; and a 2Fe-2S iron-sulfur protein. The mechanism which links proton translocation to electron transfer through these proteins is the proton motive Q cycle, and this mechanism appears to be universal to all bc1 complexes. Experimentation is currently focused on understanding selected structure-function relationships prerequisite for these redox proteins to participate in the Q-cycle mechanism. The cytochrome bc1 complexes of mitochondria differ from those of bacteria, in that the former contain six to eight supernumerary polypeptides, in addition to the three redox proteins common to bacteria and mitochondria. These extra polypeptides are encoded in the nucleus and do not contain redox prosthetic groups. The functions of the supernumerary polypeptides of the mitochondrial bc1 complexes are generally not known and are being actively explored by genetically manipulating these proteins in Saccharomyces cerevisiae.
Article
1. Pigeon heart mitochondria produce H(2)O(2) at a maximal rate of about 20nmol/min per mg of protein. 2. Succinate-glutamate and malate-glutamate are substrates which are able to support maximal H(2)O(2) production rates. With malate-glutamate, H(2)O(2) formation is sensitive to rotenone. Endogenous substrate, octanoate, stearoyl-CoA and palmitoyl-carnitine are by far less efficient substrates. 3. Antimycin A exerts a very pronounced effect in enhancing H(2)O(2) production in pigeon heart mitochondria; 0.26nmol of antimycin A/mg of protein and the addition of an uncoupler are required for maximal H(2)O(2) formation. 4. In the presence of endogenous substrate and of antimycin A, ATP decreases and uncoupler restores the rates of H(2)O(2) formation. 5. Reincorporation of ubiquinone-10 and ubiquinone-3 to ubiquinone-depleted pigeon heart mitochondria gives a system in which H(2)O(2) production is linearly related to the incorporated ubiquinone. 6. The generation of H(2)O(2) by pigeon heart mitochondria in the presence of succinate-glutamate and in metabolic state 4 has an optimum pH value of 7.5. In states 1 and 3u, and in the presence of antimycin A and uncoupler, the optimum pH value is shifted towards more alkaline values. 7. With increase of the partial pressure of O(2) to the hyperbaric region the formation of H(2)O(2) is markedly increased in pigeon heart mitochondria and in rat liver mitochondria. With rat liver mitochondria and succinate as substrate in state 4, an increase in the pO(2) up to 1.97MPa (19.5atm) increases H(2)O(2) formation 10-15-fold. Similar pO(2) profiles were observed when rat liver mitochondria were supplemented either with antimycin A or with antimycin A and uncoupler. No saturation of the system with O(2) was observed up to 1.97MPa (19.5atm). By increasing the pO(2) to 1.97MPa (19.5atm), H(2)O(2) formation in pigeon heart mitochondria with succinate as substrate increased fourfold in metabolic state 4, with antimycin A added the increase was threefold and with antimycin A and uncoupler it was 2.5-fold. In the last two saturation of the system with oxygen was observed, with an apparent K(m) of about 71kPa (0.7-0.8atm) and a V(max.) of 12 and 20nmol of H(2)O(2)/min per mg of protein. 8. It is postulated that in addition to the well-known flavin reaction, formation of H(2)O(2) may be due to interaction with an energy-dependent component of the respiratory chain at the cytochrome b level.
Article
Antimycin-inhibited bovine heart submitochondrial particles generate O2- and H2O2 with succinate as electron donor. H2O2 generation involves the action of the mitochondrial superoxide dismutase, in accordance with the McCord & Fridovich [(1969) j. biol. Chem. 244, 6049-6055] reaction mechanism. Removal of ubiquinone by acetone treatment decreases the ability of mitochondrial preparations to generate O2- and H2O2, whereas supplementation of the depleted membranes with ubiquinone enhances the peroxide-generating activity in the reconstituted membranes. Addition of superoxide dismutase to ubiquinone-reconstituted membranes is essential in order to obtain maximal rates of H2O2 generation since the acetone treatment of the membranes apparently inactivates (or removes) the mitochondrial superoxide dismutase. Parallel measurements of H2O2 production, succinate dehydrogenase and succinate-cytochrome c reductase activities show that peroxide generation by ubiquinone-supplemented membranes is a monotonous function of the reducible ubiquinone content, whereas the other two measured activities reach saturation at relatively low concentrations of reducible quinone. Alkaline treatment of submitochondrial particles causes a significant decrease in succinate dehydrogenase activity and succinate-dependent H2O2 production, which contrasts with the increase of peroxide production by the same particles with NADH as electron donor. Solubilized succinate dehydrogenase generates H2O2 at a much lower rate than the parent submitochondrial particles. It is postulated that ubisemiquinone (and ubiquinol) are chiefly responsible for the succinate-dependent peroxide production by the mitochondrial inner membrane.
Article
The cytochrome bc1 complex is the most widely occurring electron transfer complex capable of energy transduction. Cytochrome bc1 complexes are found in the plasma membranes of phylogenetically diverse photosynthetic and respiring bacteria, and in the inner mitochondrial membrane of all eucaryotic cells. In all of these species the bc1 complex transfers electrons from a low-potential quinol to a higher-potential c-type cytochrome and links this electron transfer to proton translocation. Most bacteria also possess alternative pathways of quinol oxidation capable of circumventing the bc1 complex, but these pathways generally lack the energy-transducing, protontranslocating activity of the bc1 complex. All cytochrome bc1 complexes contain three electron transfer proteins which contain four redox prosthetic groups. These are cytochrome b, which contains two b heme groups that differ in their optical and thermodynamic properties; cytochrome c1, which contains a covalently bound c-type heme; and a 2Fe-2S iron-sulfur protein. The mechanism which links proton translocation to electron transfer through these proteins is the proton motive Q cycle, and this mechanism appears to be universal to all bc1 complexes. Experimentation is currently focused on understanding selected structure-function relationships prerequisite for these redox proteins to participate in the Q-cycle mechanism. The cytochrome bc1 complexes of mitochondria differ from those of bacteria, in that the former contain six to eight supernumerary polypeptides, in addition to the three redox proteins common to bacteria and mitochondria. These extra polypeptides are encoded in the nucleus and do not contain redox prosthetic groups. The functions of the supernumerary polypeptides of the mitochondrial bc1 complexes are generally not known and are being actively explored by genetically manipulating these proteins in Saccharomyces cerevisiae.
Article
The proton conductance of the mitochondrial inner membrane increases at high protonmotive force in isolated mitochondria and in mitochondria in situ in rat hepatocytes. Quantitative analysis of its importance shows that about 20-30% of the oxygen consumption by resting hepatocytes is used to drive a heat-producing cycle of proton pumping by the respiratory chain and proton leak back to the matrix. The flux control coefficient of the proton leak pathway over respiration rate varies between 0.9 and zero in mitochondria depending on the rate of respiration, and has a value of about 0.2 in hepatocytes. Changes in the proton leak pathway in situ will therefore change respiration rate. Mitochondria isolated from hypothyroid animals have decreased proton leak pathway, causing slower state 4 respiration rates. Hepatocytes from hypothyroid rats also have decreased proton leak pathway, and this accounts for about 30% of the decrease in hepatocyte respiration rate. Mitochondrial proton leak may be a significant contributor to standard metabolic rate in vivo.
Article
The ATP/ADP-antiporter inhibitors and the substrate ADP suppress the uncoupling effect induced by low (10–20 μM) concentrations of palmitate in mitochondria from skeletal muscle and liver. The inhibitors and ADP are found to (a) inhibit the palmitate-stimulated respiration in the controlled state and (b) increase the membrane potential lowered by palmitate. The degree of efficiency decreases in the order: carboxyatractylate (CAtr) > ADP > bongkrekic acid, atractylate. GDP is ineffective, Mg > ADP is of much smaller effect, whereas ATP is effective at much higher concentration than is ADP. Inhibitor concentrations, which maximally suppress the palmitate-stimulated respiration, correspond to those needed for arresting the state 3 respiration. The extent of the CAtr-sensitive stimulation of respiration by palmitate has been found to decrease with an increase in palmitate concentration. Stimulation of the controlled respiration by p-trifluoromethoxycarbonylcyanide phenylhydrozone (FCCP) and gramicidin D at any concentrations of these uncouplers is CAtr-insensitive, whereas that caused by a low concentrations of 2,4-dinitrophenol and dodecyl sulfate is inhibited by CAtr.
Article
1. Pigeon heart mitochondria produce H(2)O(2) at a maximal rate of about 20nmol/min per mg of protein. 2. Succinate-glutamate and malate-glutamate are substrates which are able to support maximal H(2)O(2) production rates. With malate-glutamate, H(2)O(2) formation is sensitive to rotenone. Endogenous substrate, octanoate, stearoyl-CoA and palmitoyl-carnitine are by far less efficient substrates. 3. Antimycin A exerts a very pronounced effect in enhancing H(2)O(2) production in pigeon heart mitochondria; 0.26nmol of antimycin A/mg of protein and the addition of an uncoupler are required for maximal H(2)O(2) formation. 4. In the presence of endogenous substrate and of antimycin A, ATP decreases and uncoupler restores the rates of H(2)O(2) formation. 5. Reincorporation of ubiquinone-10 and ubiquinone-3 to ubiquinone-depleted pigeon heart mitochondria gives a system in which H(2)O(2) production is linearly related to the incorporated ubiquinone. 6. The generation of H(2)O(2) by pigeon heart mitochondria in the presence of succinate-glutamate and in metabolic state 4 has an optimum pH value of 7.5. In states 1 and 3u, and in the presence of antimycin A and uncoupler, the optimum pH value is shifted towards more alkaline values. 7. With increase of the partial pressure of O(2) to the hyperbaric region the formation of H(2)O(2) is markedly increased in pigeon heart mitochondria and in rat liver mitochondria. With rat liver mitochondria and succinate as substrate in state 4, an increase in the pO(2) up to 1.97MPa (19.5atm) increases H(2)O(2) formation 10-15-fold. Similar pO(2) profiles were observed when rat liver mitochondria were supplemented either with antimycin A or with antimycin A and uncoupler. No saturation of the system with O(2) was observed up to 1.97MPa (19.5atm). By increasing the pO(2) to 1.97MPa (19.5atm), H(2)O(2) formation in pigeon heart mitochondria with succinate as substrate increased fourfold in metabolic state 4, with antimycin A added the increase was threefold and with antimycin A and uncoupler it was 2.5-fold. In the last two saturation of the system with oxygen was observed, with an apparent K(m) of about 71kPa (0.7-0.8atm) and a V(max.) of 12 and 20nmol of H(2)O(2)/min per mg of protein. 8. It is postulated that in addition to the well-known flavin reaction, formation of H(2)O(2) may be due to interaction with an energy-dependent component of the respiratory chain at the cytochrome b level.
Article
Cell respiration is associated with the risk of formation of oxygen radicals. Although various conditions of respiration have been described under which O2-radicals are generated it is not clear whether oxygen radical generation is an inevitable side effect of respiration. The answer is necessarily linked to an understanding of the mechanism and molecular site of oxygen radical generation. Redox-cycling ubiquinones of the mitochondrial respiratory chain have often been suggested to account for cellular O2-radical formation. However, there is an increasing body of evidence which refutes this assumption on thermodynamic grounds. The discovery of a novel respiratory enzyme of heart mitochondria, exogenous NADH-dehydrogenase, some years ago, has considerably aided understanding of mitochondrial O2-radical generation and the role of ubiquinones therein. This mitochondrial enzyme can be directly activated by cytosolic NADH. It has been shown that NADH consumption via this enzyme not only stimulates electron flow along components of the respiratory chain but that its activity is also linked to the release O2-. or the single electron reduction of adequate non-physiological oxidants. Anthraquinones which are increasingly used as antitumor drugs can enter this redox-shuttle and initiate radical chain reactions which may be partially responsible for the selective cardiotoxicity of these compounds. Metabolic conditions, causing abnormally high NADH levels in the cytosol, such as ischemia have been found to irreversibly transform intact mitochondria to active radical generators. The present review elucidates the finding of a general phenomenon which gives more insight into the mechanism and the site of O2-radical formation during normal cell respiration.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The non-linear relationship between respiration rate and protonmotive force in isolated mitochondria is explained entirely by delta p-dependent changes in the proton conductance of the mitochondrial inner membrane and is not caused by redox slip in the proton pumps. Mitochondrial proton leak occurs in intact cells and tissues: the futile cycle of proton pumping and proton leak accounts for 26% +/- 7% of the total oxygen consumption rate or 33% +/- 7% of the mitochondrial respiration rate of isolated hepatocytes (mean +/- S.D. for 43 rats); 52% of the oxygen consumption rate of resting perfused muscle and up to 38% of the basal metabolic rate of a rat, suggesting that heat production may be an important function in the proton leak in homeotherms. Together with non-mitochondrial oxygen consumption, it lowers the effective P/O ratio in cells from maximum possible values of 2.33 (palmitate oxidation) or 2.58 (glucose oxidation) to as low as 1.1 in liver or 0.8 in muscle. The effective P/O ratio increases in response to ATP demand; the ability to allow rapid switching of flux from leak to ATP turnover may be an even more important function of the leak reaction than heat production. The mitochondrial proton conductance in isolated mitochondria and in hepatocytes is greatly modulated by thyroid hormones, by phylogeny and by body mass. Usually the reactions of ATP turnover change in parallel so that the coupling ratio is not greatly affected. Changes in proton leak in tissues are brought about in the short term by changes in mitochondrial protonmotive force and in the longer term by changes in the surface area and proton permeability of the mitochondrial inner membrane. Permeability changes are probably caused by changes in the fatty acid composition of the membrane phospholipids.
Article
The standard metabolic rate of an animal is the rate of heat production under conditions that minimize known extra requirements for energy. In tissues and cells from aerobic organisms, energy expenditure can conveniently be measured as oxygen consumption. Measurements made using isolated rat hepatocytes have shown that a significant contribution to resting oxygen consumption (and hence heat production) is made by a futile cycle of proton pumping and proton leak across the mitochondrial inner membrane. Two important factors affecting standard metabolic rate, thyroid status and phylogeny, also affect the proton permeability. A third major factor affecting standard metabolic rate is body mass. Here we show that proton leak decreases with increasing body mass in mammals. We suggest that differences in proton leak may partly explain the differences in standard metabolic rate between mammals of different mass.
Article
The main energy-transducing metabolic systems originated and diversified very early in the evolution of life. This makes it difficult to unravel the precise steps in the evolution of the proteins involved in these processes. Recent molecular data suggest that homologous proteins of aerobic respiratory chains can be found in Bacteria and Archaea, which points to a common ancestor that possessed these proteins. Other molecular data predict that this ancestor was unlikely to perform oxygenic photosynthesis. This evidence, that aerobic respiration has a single origin and may have evolved before oxygen was released to the atmosphere by photosynthetic organisms, is contrary to the textbook viewpoint.
Article
The present investigation seeks to elucidate the molecular mechanism responsible of the transformation of redox-cycling ubiquinone (UQ) from a save electron carrier to an O2.- generator as observed in toluene-treated mitochondria as well as in mitochondria exposed to conditions of organ ischemia/reperfusion. Starting from the earlier finding that for thermodynamic grounds autoxidation of ubisemiquinone (SQ.-) requires the accessibility of protons, two possibilities were considered: a) protons from the aqueous phase may penetrate into the phospholipid bilayer and react with SQ.- due to a decreased hydrophobicity of the membrane, b) the physical state of the membrane remains unchanged while the binding of redox-cycling UQ is changed such that SQ.- will come into contact with the aqueous phase in the polar head group section. Spin probes were used to follow changes of the physical order of phospholipids of the inner mitochondrial membrane. Binding changes of mitochondrial SQ.- were assessed from power saturation experiments and spin-spin interactions with a Cr3+ salt of the aqueous phase were studied to recognize orientation changes via the polar head group section of the membrane. Our results show that autoxidation of SQ.- occurs in two different ways. In the case of membrane insertion of toluene, the physical property of the membrane was affected such that protons could penetrate and allow SQ.- to undergo autoxidation. In contrast, mitochondrial respiration of cytosolic NADH accumulating during ischemia involves a low saturating SQ.- species that readily autoxidizes due to its spatial orientation close to the aqueous face of the membrane. We conclude from these observations that in line with thermodynamics autoxidation of SQ.- in mitochondria requires protons that normally have no access.
Article
To proceed at a high rate, phosphorylating respiration requires ADP to be available. In the resting state, when the energy consumption is low, the ADP concentration decreases so that phosphorylating respiration ceases. This may result in an increase in the intracellular concentrations of O 2 as well as of one-electron O 2 reductants such as These two events should dramatically enhance non-enzymatic formation of reactive oxygen species, i.e. of , and OHׁ, and, hence, the probability of oxidative damage to cellular components. In this paper, a concept is put forward proposing that non-phosphorylating (uncoupled or non-coupled) respiration takes part in maintenance of low levels of both O 2 and the O 2 reductants when phosphorylating respiration fails to do this job due to lack of ADP. In particular, it is proposed that some increase in the H ⁺ leak of mitochondrial membrane in State 4 lowers , stimulates O 2 consumption and decreases the level of which otherwise accumulates and serves as one-electron O 2 reductant. In this connection, the role of natural uncouplers (thyroid hormones), recouplers (male sex hormones and progesterone), non-specific pore in the inner mitochondrial membrane, and apoptosis, as well as of non-coupled electron transfer chains in plants and bacteria will be considered.
Article
We have examined the substrate specificity and inhibitor sensitivity of H2O2 formation by rat heart mitochondria. Active H2O2 production requires both a high fractional reduction of Complex I (indexed by NADH/NAD+ + NADH ratio) and a high membrane potential, delta psi. These conditions are achieved with supraphysiological concentrations of succinate. With physiological concentrations of NAD-linked substrates, rates of H2O2 formation are much lower (less than 0.1% of respiratory chain electron flux) but may be stimulated by the Complex III inhibitor antimycin A, but not by myxothiazol. Addition of Mn2+ to give 10 nmol/mg of mitochondrial protein enhances H2O2 production with all substrate combinations, possibly by repleting mitochondrial superoxide dismutase with this cation. Contrary to previously published work, no increased activity of H2O2 production was found with heart mitochondria from senescent (24 month) rats, relative to young adults (6 month).
Article
On the basis of x-ray diffraction data to a resolution of 2.9 angstroms, atomic models of most protein components of the bovine cytochrome bc1 complex were built, including core 1, core 2, cytochrome b, subunit 6, subunit 7, a carboxyl-terminal fragment of cytochrome c1, and an amino-terminal fragment of the iron-sulfur protein. The positions of the four iron centers within the bc1 complex and the binding sites of the two specific respiratory inhibitors antimycin A and myxothiazol were identified. The membrane-spanning region of each bc1 complex monomer consists of 13 transmembrane helices, eight of which belong to cytochrome b. Closely interacting monomers are arranged as symmetric dimers and form cavities through which the inhibitor binding pockets can be accessed. The proteins core 1 and core 2 are structurally similar to each other and consist of two domains of roughly equal size and identical folding topology.
Article
Formation of H2O2 has been studied in rat heart mitochondria, pretreated with H2O2 and aminotriazole to lower their antioxidant capacity. It is shown that the rate of H2O2 formation by mitochondria oxidizing 6 mM succinate is inhibited by a protonophorous uncoupler, ADP and phosphate, malonate, rotenone and myxothiazol, and is stimulated by antimycin A. The effect of ADP is abolished by carboxyatractylate and oligomycin. Addition of uncoupler after rotenone induces further inhibition of H2O2 production. Inhibition of H2O2 formation by uncoupler, malonate and ADP+Pi is shown to be proportional to the delta psi decrease by these compounds. A threshold delta psi value is found, above which a very strong increase in H2O2 production takes place. This threshold slightly exceeds the state 3 delta psi level. The data obtained are in line with the concept [Skulachev, V.P., Q. Rev. Biophys. 29 (1996), 169-2021 that a high proton motive force in state 4 is potentially dangerous for the cell due to an increase in the probability of superoxide formation.
Article
We measured the proton leak across the inner membrane of liver mitochondria isolated from six different vertebrate species and from obese and control Zucker rats. Proton leak at 37 degrees C was similar in rat and pigeon, and in obese and control Zucker rats. Compared to rat, it was lower in cane toad, shingleback lizard, and the Madeiran lizard Lacerta dugessi. Proton leak at 20 degrees C was similar in xenopus toad and higher in rainbow trout, compared to rat. In general, proton permeability and substrate oxidation activity were greater in liver mitochondria from endotherms than those from ectotherms. Analysis of this and previous data showed that proton leak per milligram of mitochondrial protein correlated with standard metabolic rate, and proton leak per milligram of inner membrane phospholipid correlated with 11 phospholipid fatty acid compositional parameters, including unsaturation index.
Article
Mitochondria produce most of the energy in animal cells by a process called oxidative phosphorylation. Electrons are passed along a series of respiratory enzyme complexes located in the inner mitochondrial membrane, and the energy released by this electron transfer is used to pump protons across the membrane. The resultant electrochemical gradient enables another complex, adenosine 5'-triphosphate (ATP) synthase, to synthesize the energy carrier ATP. Important new mechanistic insights into oxidative phosphorylation have emerged from recent three-dimensional structural analyses of ATP synthase and two of the respiratory enzyme complexes, cytochrome bc1 and cytochrome c oxidase. This work, and new enzymological studies of ATP synthase's unusual catalytic mechanism, are reviewed here.
Article
Animal and plant uncoupling protein (UCP) homologues form a subfamily of mitochondrial carriers that are evolutionarily related and possibly derived from a proton/anion transporter ancestor. The brown adipose tissue (BAT) UCP1 has a marked and strongly regulated uncoupling activity, essential to the maintenance of body temperature in small mammals. UCP homologues identified in plants are induced in a cold environment and may be involved in resistance to chilling. The biochemical activities and biological functions of the recently identified mammalian UCP2 and UCP3 are not well known. However, recent data support a role for these UCPs in State 4 respiration, respiration uncoupling and proton leaks in mitochondria. Moreover, genetic studies suggest that UCP2 and UCP3 play a part in energy expenditure in humans. The UCPs may also be involved in adaptation of cellular metabolism to an excessive supply of substrates in order to regulate the ATP level, the NAD(+)/NADH ratio and various metabolic pathways, and to contain superoxide production. A major goal will be the analysis of mice that either lack the UCP2 or UCP3 gene or overexpress these genes. Other aims will be to investigate the possible roles of UCP2 and UCP3 in response to oxidative stress, lipid peroxidation, inflammatory processes, fever and regulation of temperature in certain specific parts of the body.
The uncoupling protein homologues
  • D Ricquier
  • F Bouillaud
Ricquier, D., Bouillaud, F., 2000. The uncoupling protein homologues: UCP1, UCP2, UCP3, StUCP and AtUCP. Biochem. J. 345, 161±179.
The proton leak across the mitochondrial inner membrane