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Figure S1. STS-induced death is enhanced in UCP2hi MIA PaCa-2 and UCP2hi U-87 MG cells.

Cancer cells tilt their energy production away from oxidative phosphorylation (OXPHOS) toward glycolysis during malignant progression, even when aerobic metabolism is available. Reversing this phenomenon, known as the Warburg effect, may offer a generalized anticancer strategy. In this study, we show that overexpression of the mitochondrial membrane transport protein UCP2 in cancer cells is sufficient to restore a balance toward oxidative phosphorylation and to repress malignant phenotypes. Altered expression of glycolytic and oxidative enzymes mediated the effects of this metabolic shift. Notably, UCP2 overexpression increased signaling from the master energy-regulating kinase, adenosine monophosphate-activated protein kinase, while downregulating expression of hypoxia-induced factor. In support of recent new evidence about UCP2 function, we found that UCP2 did not function in this setting as a membrane potential uncoupling protein, but instead acted to control routing of mitochondria substrates. Taken together, our results define a strategy to reorient mitochondrial function in cancer cells toward OXPHOS that restricts their malignant phenotype. Cancer Res; 74(14); 3971–82. ©2014 AACR.

BackgroundViruses are dependent on cellular energy metabolism for their replication, the drug Nitazoxanide (Alinia) was shown to interfere with both. An effect of Alinia on cellular energy metabolism is the uncoupling of mitochondrial oxidative phosphorylation (OXPHOS). Our hypothesis was that uncoupling grounds the antiviral properties of Alinia.MethodsAlinia or an unrelated uncoupler were applied to a viral releasing cell line to obtain the same increasing levels of uncoupling hence identical interference with OXPHOS.FindingsDecrease in infectious viral particles release reflected the intensity of interference irrespective of the nature of the drug and was significant with modest deviation (≤25%) from normal.InterpretationsA mild interference on cellular energy metabolism impacts significantly on viral replication cycle. This would explain Alinia’s antiviral properties in vitro moreover antiviral action of Alinia is supported by clinical trials.PerspectivesAltogether this indicates that moderate interference with mitochondrial bioenergetics should be considered as a ground for a therapeutic effect. In addition, Alinia would constitute example for a safe therapeutical use of an uncoupler, which deserves consideration for a wider range of applications.

HIV-1 eradication is hindered by viral persistence in cell reservoirs, established not only in circulatory CD4+T-cells but also in tissue-resident macrophages. The nature of macrophage reservoirs and mechanisms of persistence despite combined anti-retroviral therapy (cART) remain unclear. Using genital mucosa from cART-suppressed HIV-1-infected individuals, we evaluated the implication of macrophage immunometabolic pathways in HIV-1 persistence. We demonstrate that ex vivo, macrophage tissue reservoirs contain transcriptionally active HIV-1 and viral particles accumulated in virus-containing compartments, and harbor an inflammatory IL-1R+S100A8+MMP7+M4-phenotype prone to glycolysis. Reactivation of infectious virus production and release from these reservoirs in vitro are induced by the alarmin S100A8, an endogenous factor produced by M4-macrophages and implicated in “sterile” inflammation. This process metabolically depends on glycolysis. Altogether, inflammatory M4-macrophages form a major tissue reservoir of replication-competent HIV-1, which reactivate viral production upon autocrine/paracrine S100A8-mediated glycolytic stimulation. This HIV-1 persistence pathway needs to be targeted in future HIV eradication strategies.

Addition of hydrogen peroxide (H2O2) is a method commonly used to trigger cellular oxidative stress. However, the doses used (often hundreds of micromolar) are disproportionally high with regard to physiological oxygen concentration (low micromolar). In this study using polarographic measurement of oxygen concentration in cellular suspensions we show that H2O2 addition results in O2 release as expected from catalase reaction. This reaction is fast enough to, within seconds, decrease drastically H2O2 concentration and to annihilate it within a few minutes. Firstly, this is likely to explain why recording of oxidative damage requires the high concentrations found in the literature. Secondly, it illustrates the potency of intracellular antioxidant (H2O2) defense. Thirdly, it complicates the interpretation of experiments as subsequent observations might result from high/transient H2O2 exposure and/or from the diverse possible consequences of the O2 release.

Embryonic stem cells (ESC) have the unique ability to differentiate into all three germ cell layers. ESC transition through different states of pluripotency in response to growth factor signals and environmental cues before becoming terminally differentiated. Here, we demonstrated, by a multi-omic strategy, that the deubiquitinase USP9X regulates the developmental potential of ESC, and their transition from a naive to a more developmentally advance, or primed, state of pluripotency. We show that USP9X facilitates developmental gene expression and induces modifications of the mitochondrial bioenergetics, including decreased routing of pyruvate towards its oxidation and reduced respiration. In addition, USP9X binds to the pluripotency factor ESRRB, regulates its abundance and the transcriptional levels of a subset of its target genes. Finally, under permissive culture conditions, depletion of Usp9X accelerates cell differentiation in all cell lineages. We thus identified a new regulator of naive pluripotency and show that USP9X couples ESRRB pluripotency transcriptional network and cellular metabolism, both of which are important for ESC fate and pluripotency.

Hyperosmotic conditions are associated to several pathological states. In this article, we evaluate the consequence of hyperosmotic medium on cellular energy metabolism. We demonstrate that exposure of cells to hyperosmotic conditions immediately reduces the mitochondrial oxidative phosphorylation rate. This causes an increase in glycolysis, which represses further respiration. This is known as the Warburg or Crabtree effect. In addition to aerobic glycolysis, we observed two other cellular responses that would help to preserve cellular ATP level and viability: A reduction in the cellular ATP turnover rate and a partial mitochondrial uncoupling which is expected to enhance ATP production by Krebs cycle. The latter is likely to constitute another metabolic adaptation to compensate for deficient oxidative phosphorylation that, importantly, is not dependent on glucose.

Sulfide (H 2 S in the gas form) is the third gaseous transmitter found in mammals. However, in contrast to nitric oxide (NO) or carbon monoxide (CO), sulfide is oxidized by a sulfide quinone reductase and generates electrons that enter the mitochondrial respiratory chain arriving ultimately at cytochrome oxidase, where they combine with oxygen to generate water. In addition, sulfide is also a strong inhibitor of cytochrome oxidase, similar to NO, CO and cyanide. The balance between the electron donor and the inhibitory role of sulfide is likely controlled by sulfide and oxygen availability. The present study aimed to evaluate if and how sulfide release and oxidation impacts on the cellular affinity for oxygen. Results : i ) when sulfide delivery approaches the maximal sulfide oxidation rate cells become exquisitely dependent on oxygen; ii ) a positive feedback makes the balance between sulfide-releasing and -oxidizing rates the relevant parameter rather than the absolute values of these rates, and; iii ) this altered dependence on oxygen is detected with sulfide concentrations that remain in the low micromolar range. Conclusions : i ) within the context of continuous release of sulfide stemming from cellular metabolism, alterations in the activity of the sulfide oxidation pathway fine-tunes the cell's affinity for oxygen, and; ii ) a decrease in the expression of the sulfide oxidation pathway greatly enhances the cell's dependence on oxygen concentration.

Until recently, hydrogen sulfide (H2S) was exclusively viewed a toxic gas and an environmental hazard, with its toxicity primarily attributed to the inhibition of mitochondrial Complex IV, resulting in a shutdown of mitochondrial electron transport and cellular ATP generation. Work over the last decade established multiple biological regulatory roles of H2S, as an endogenous gaseous transmitter. H2S is produced by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). In striking contrast to its inhibitory effect on Complex IV, recent studies showed that at lower concentrations, H2S serves as a stimulator of electron transport in mammalian cells, by acting as a mitochondrial electron donor. Endogenous H2S, produced by mitochondrially localized 3-MST, supports basal, physiological cellular bioenergetic functions; the activity of this metabolic support declines with physiological aging. In specialized conditions (calcium overload in vascular smooth muscle, colon cancer cells), CSE and CBS can also associate with the mitochondria; H2S produced by these enzymes, serves as an endogenous stimulator of cellular bioenergetics. The current article overviews the biochemical mechanisms underlying the stimulatory and inhibitory effects of H2S on mitochondrial function and cellular bioenergetics and discusses the implication of these processes for normal cellular physiology. The relevance of H2S biology is also discussed in the context of colonic epithelial cell physiology: colonocytes are exposed to high levels of sulfide produced by enteric bacteria, and serve as a metabolic barrier to limit their entry into the mammalian host, while, at the same time, utilizing it as a metabolic ‘fuel’. Linked Articles This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8

Generous donors: The dithioperoxyanhydrides (CH3 COS)2 , (PhCOS)2 , CH3 COSSCO2 Me and PhCOSSCO2 Me act as thiol-activated hydrogen sulfide donors in aqueous buffer solution. The most efficient donor (CH3 COS)2 can induce a biological response in cells, and advantageously replace hydrogen sulfide in ex vivo vascular studies.

Sulfide shows the same toxicity as cyanide. This toxic effect results from the inhibition of the complex IV of the mitochondrial respiratory chain (cytochrome oxidase) that reduces oxygen into water. With the isolated enzyme the toxic effect is exerted in the high nanomolar range. However, significant inhibition of cellular/mitochondrial respiration needs μM concentrations (5–20 μM). In contrast at lower concentrations (nM) sulfide is an hydrogen donor used as a substrate by mitochondria in a majority of tissues/cells. The enzyme involved is a sulfide quinone reductase (SQR) associated with a dioxygenase and a sulfur transferase. Therefore according to the concentration sulfide has two opposite effects on respiration: it increases oxygen consumption and drives ATP production at low (nM) concentration whereas at high (μM) concentration sulfide inhibits respiration and has adverse effects on cellular bioenergetics. The present estimation of the endogenous sulfide release rates, the occurence of SQR in a large majority of the tissues/cells explored so far and its high affinity for sulfide make the SQR and mitochondrial respiration the major pathway maintaining intracellular sulfide in an acceptable non toxic low range of concentrations. Therefore mitochondrial respiration is both the sulfide sink and the target of sulfide toxicity. This paves the way for positive feedback effects making the orientation towards one or another of the opposite consequences of a given sulfide exposure highly sensitive to various factors. SQR is thus likely to interfere with any endogenous sulfide signaling and definitely needs to be taken into account when pharmacological intervention involves sulfide donors. The lumen of the colon hosts a bacterial communauty releasing sulfide and a value of 60 μM is proposed for the concentration of free sulfide in the human colon. Accordingly, the epithelial cells (colonocytes) are exposed to toxic sulfide concentrations. These colonocytes show a high SQR activity and cellular bioenergetics adaptations to increase their tolerance to sulfide. The mechanisms involved in mitochondrial sulfide bioenergetics as well as their consequences with regard to the signaling role of sulfide and to the use of sulfide donors will be explained.