M D Brand

..We found that there were no functionally-important bioenergetic differences between mitochondria bearing these haplogroups, using either isolated mitochondria or mitochondria within cells...

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..UCPs may also integrate inputs from different fuels in pancreatic beta-cells and modulate insulin secretion. They are exciting potential targets for treatment of obesity, cachexia, aging and diabetes...

..These correlations echo those seen in mammalian liver mitochondria, suggesting that they too are general for endotherms...

..More recently evolved roles of uncoupling proteins are in adaptive thermogenesis (UCP1) and perhaps as part of a signaling pathway to regulate insulin secretion in pancreatic beta cells (UCP2)...

..We conclude that half to two-thirds of the basal proton conductance of mitochondria is catalysed by the adenine nucleotide carrier, independently of its ATP/ADP exchange or fatty-acid-dependent proton-leak functions...

..Evidence that they export fatty acids physiologically is weak. UCP2 and UCP3 are important potential targets for treatment of aging, degenerative diseases, diabetes, and perhaps obesity...

..Recently, we have applied modular control analysis to modern DNA microarray expression profiling to measure the importance of different groups of mRNA transcripts in mediating physiological responses...

..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...

..Our findings indicate that the interaction of superoxide with UCPs may be a mechanism for decreasing the concentrations of reactive oxygen species inside mitochondria...

..In the absence of superoxide there is no GDP-sensitive component of the proton conductance from penguin muscle mitochondria demonstrating that avUCP plays no role in the basal proton leak...

..We conclude that superoxide (or its products) exerts its uncoupling effect by activating the proton transport mechanism of uncoupling proteins at the matrix side of the mitochondrial inner membrane...

..Our findings indicate that hydroxynonenal is not merely toxic, but may be a biological signal to induce uncoupling through UCPs and ANT and thus decrease mitochondrial ROS production...

..This difference was solely due to an elevated concentration of complex I in rat compared with pigeon heart mitochondria...

..We conclude that uncoupling in UCP3-tg mice is an artifact of transgenic expression, and that UCP3 does not catalyze the basal proton conductance of skeletal muscle mitochondria in the absence of activators such as superoxide...

..These results show that reactive alkenals activate the proton conductance of UCP1 more strongly when fatty acids are also added, with implications for both mechanistic and physiological models of UCP1 activation...

..We conclude that the uncoupling of yeast mitochondria by high levels of UCP3 expression is entirely an artifact and provides no evidence for any native uncoupling activity of the protein...

..We conclude that CoQ acted in mitochondria through production of superoxide, which mediated uncoupling, probably by acting through uncoupling protein 2...

..Thus, endogenous superoxide can activate the proton conductance of UCP3, which in turn limits mitochondrial superoxide production. These observations provide a departure point for studies under more physiological conditions...

..This observation might be important in the interpretation of results from experiments in which the functions of UCP1 homologues are verified by their ability to uncouple yeast mitochondria...

..These observations suggest that uncoupling of yeast mitochondria by UCP2 is an overexpression artifact leading to compromised mitochondrial integrity...

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..Specific uncoupling of muscle or brown adipocyte mitochondria remains an attractive target for the development of antiobesity drugs...

..The IC(50) for GDP is about 100 microM. These findings support the proposal that UCP3 attenuates endogenous radical production by the mitochondrial electron transport chain at high protonmotive force...

..Thus, the alterations in brown adipose tissue phospholipid acyl composition are revealed to be an independent part of the recruitment process, and their functional significance for thermogenesis should be elucidated...

..At least 75% of the total response of mitochondrial respiration to estivation was caused by primary changes in the kinetics of substrate oxidation, with only 25% or less of the response occurring through primary effects on ATP turnover...

..The physiological role of the proton leak, and of the uncoupling protein 1 homologues, remains similarly unclear...

..Thus, the fraction of cellular respiration devoted to different processes remained constant and the cellular energy balance was preserved in the hypometabolic state...

..We propose a model to relate adenine nucleotide translocase conformation to proton conductance in the presence or absence of 4-hydroxynonenal and/or carboxyatractylate...

..We also list other relevant articles of interest and suggest some key challenges for the field in the near future...

..We also introduce a method to determine coupling efficiencies noninvasively in attached cells and discuss theoretical and practical aspects of a modular-kinetic approach to describe and understand cellular bioenergetics...

..If a specific protein is responsible for the basal proton conductance of yeast mitochondria, its identity remains unknown...

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..We conclude that mitochondria from the long-lived pigeon display low rates of hydrogen peroxide production because they have low levels of complex I...

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..Given the broader importance of hepatic steatosis, the novel molecular mechanism revealed in this study should be examined in other forms of steatosis and nonalcoholic steatohepatitis...

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..However, they do not catalyse proton leak in the absence of such acute activation. They can also catalyse export of fatty acid and other anions, although the relationship of anion transport to proton transport remains controversial...

..These data suggest that lowering mitochondrial coupling by high expression of hUCP3 alters mNSC function in a way that appears to increase DILP-levels in fly heads and lead to a concomitant decrease in lifespan...

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..Here, we outline the background to these strategies and discuss how antioxidants targeted to mitochondria, or selective mitochondrial uncoupling, may be potential therapies for diabetes...

..Thus the lower mitochondrial respiration rate in hepatopancreas cells from aestivating snails was not caused by differences in mitochondrial volume or surface density but was associated with intrinsic changes in the mitochondria...

..It discusses the ways the approach has been used in organelles and cells to identify the sites of action of effectors, to measure the distribution of control by blocks of reactions, and to measure regulation by effectors...

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..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...

..However, ATP use by the F(1)F(0)-ATPase is limited in anoxia by a profound inhibition of the enzyme. Even so, ATP use by the F(1)F(0)-ATPase might account for approximately 9% of the ATP turnover in anoxic frog skeletal muscle...

..The application of modular control analysis to microarray data in order to partition and quantify the importance of mRNA clusters in mediating responses is described...

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..These findings indicate that enhanced longevity may be causally associated with low free radical production by mitochondria across species over two classes of vertebrate homeotherms...

..The significant recent progress describing the turnover of novel uncoupling proteins, as well as current views on the physiological roles and regulation of UCPs, is outlined...

..3) UCP3 may catalyse fatty acid transport. (4) UCP2 has a signalling role in pancreatic beta cells, where it attenuates insulin secretion. Other roles remain to be discovered...

..Although much work has been devoted to how these proteins are activated, little is known of the mechanisms that reverse this activation...

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..With this paper we aim to provide a brief account of the present state of affairs in this field, suggest a physiological role for UCP2, and highlight some of our own recent results...

..This phenotype is in direct contrast with the related proteins UCP1 and the adenine nucleotide translocase, which have long half-lives. Therefore UCP3 is turned over rapidly in multiple cell types in a proteasome-dependent manner...

..These results suggest that both endogenous HNE production and high membrane potential are required before mild uncoupling will be triggered to attenuate mitochondrial ROS production...

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..0-4.4 ng/million cells (2.7-14.5 ng/mg mitochondrial protein). This dynamic response to nutrients was achieved by varied expression rates against a background of a very short UCP2 protein half-life of about 1 h...

..Our data suggest that less than 10% of the superoxide originates from the flavin site during reverse electron transport from succinate...

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..We propose that the high mitochondrial proton leak in beta-cells is a mechanism which amplifies the effect of physiological UCP2 regulators on cytoplasmic ATP/ADP and hence on insulin secretion...

..Our results show two examples in which mitochondrial ROS production and life span are not correlated...

..The activity of UCP1 was similar in both Q-containing and -deficient yeast mitochondria. We conclude that Q is neither an obligatory cofactor nor an activator of proton transport by UCP1 when it is expressed in yeast mitochondria...

..The method is applicable to microarray, transcriptome, proteome and metabolome data...

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..Superoxide releases iron from iron-sulfur center proteins, which then generates carbon-centered radicals that initiate lipid peroxidation, yielding breakdown products that activate UCPs...

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..Analysis of the response of yeast relative fitness to 2-deoxy-D-glucose reveals that control is distributed between several mRNA clusters, but experimental error limits statistical significance...

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..Thus mild uncoupling may be particularly significant for ROS production from complex I on the matrix side of the mitochondrial inner membrane...

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..These observations provide the first demonstration that a mitochondrial inner membrane protein is degraded by the cytosolic ubiquitin-proteasome system...

..These results suggest that PGC1 beta may play a role in constitutive adrenergic-independent mitochondrial biogenesis...

..The approach allows a quantitative description of the relative importance of signal transduction pathways and the routes by which they activate a specific cellular process. It should be widely applicable...

..Contrary to the predictions of this hypothesis, mitochondria from Arctic haplogroups had similar or even greater coupling efficiency than mitochondria from tropical haplogroups...

..A brief overview of the methods for measuring reactive oxygen species production in isolated mitochondria and cells is also presented...

..They both uncouple mitochondrial respiration and inhibit substrate oxidation and ATP turnover. However, the topical effect and selective COX-2 inhibition may not be sufficient to cause NSAID-like damage to the GI tract...

..Individuals with high metabolism were therefore more uncoupled, had greater resting and total daily energy expenditures and survived longest - supporting the 'uncoupling to survive' hypothesis...

..These results suggest that mitochondrial proton conductance is unchanged during hibernation and that the reduced metabolism in hibernators is a partial consequence of tissue-specific depression of substrate oxidation...

..Furthermore, it demonstrates that changes in the amount of StUCP can alter the rate of proton conductance of potato mitochondria...

..We discuss the opportunities and pitfalls of targeting these processes as a treatment for obesity by decreasing coupling efficiency and increasing energy expenditure, either directly or through central mechanisms of energy homeostasis...

..If DR in Drosophila extends life span by reducing ROS production, then it does so through mechanisms that operate only in vivo...

..This activation induces mild uncoupling and so diminishes mitochondrial superoxide production, hence protecting against disease and oxidative damage at the expense of energy production...

..The effect of flight activity on insect life span differs considerably from the beneficial effects of exercise in mammals; these differences may be caused by physiological differences between the two taxa...

..Therefore MitoDNP did not act as a protonophore, probably because the efflux of deprotonated MitoDNP was inhibited...

..Taken together, this study characterises uncoupling protein activity in an ectotherm for the first time...

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