Role Of Mitochondrial Reactive Oxygen Species Research Articles

Metabolic ROS Signaling: To Immunity and Beyond.

Metabolism is a critical determinant of immune cell functionality. Immunometabolism, by definition, is a multidisciplinary area of immunology research that integrates the knowledge of energy transduction mechanisms and biochemical pathways. An important concept in the field is metabolic switch, a transition of immune cells upon activation to preferential utilization of select catabolic pathways for their energy needs. Mitochondria are not inert in this process and contribute to the metabolic adaptation by different mechanisms which include increasing ATP production to match dynamic bioenergetic demands and serving as a signaling platform. The latter involves generation of reactive oxygen species (ROS), one of the most intensively studied mitochondrial processes. While the role of mitochondrial ROS in the context of oxidative stress is well established, ROS signaling in immunity is an emerging and quickly changing field. In this review, we discuss ROS signaling and immunometabolism concepts from the standpoint of bioenergetics. We also provide a critical insight into the methodology for ROS assessment, outlining current challenges in the field. Finally, based on our analysis of the literature data, we hypothesize that regulatory ROS production, as opposed to oxidative stress, is controlled by mitochondrial biogenesis rather than metabolic switches.

Mitochondrial Reactive Oxygen Species Contribute to Pathological Inflammation During Influenza A Virus Infection in Mice.

Aims: Reactive oxygen species (ROS) are highly reactive molecules generated in different subcellular sites or compartments, including endosomes via the NOX2-containing nicotinamide adenine dinucleotide phosphate oxidase during an immune response and in mitochondria during cellular respiration. However, while endosomal NOX2 oxidase promotes innate inflammation to influenza A virus (IAV) infection, the role of mitochondrial ROS (mtROS) has not been comprehensively investigated in the context of viral infections in vivo.Results: In this study, we show that pharmacological inhibition of mtROS, with intranasal delivery of MitoTEMPO, resulted in a reduction in airway/lung inflammation, neutrophil infiltration, viral titers, as well as overall morbidity and mortality in mice infected with IAV (Hkx31, H3N2). MitoTEMPO treatment also attenuated apoptotic and necrotic neutrophils and macrophages in airway and lung tissue. At an early phase of influenza infection, that is, day 3 there were significantly lower amounts of IL-1β protein in the airways, but substantially higher amounts of type I IFN-β following MitoTEMPO treatment. Importantly, blocking mtROS did not appear to alter the initiation of an adaptive immune response by lung dendritic cells, nor did it affect lung B and T cell populations that participate in humoral and cellular immunity.Innovation/Conclusion: Influenza virus infection promotes mtROS production, which drives innate immune inflammation and this exacerbates viral pathogenesis. This pathogenic cascade highlights the therapeutic potential of local mtROS antioxidant delivery to alleviate influenza virus pathology.

Mitochondrial ROS-induced lysosomal dysfunction impairs autophagic flux and contributes to M1 macrophage polarization in a diabetic condition.

Macrophage polarization toward the M1 phenotype and its subsequent inflammatory response have been implicated in the progression of diabetic complications. Despite adverse consequences of autophagy impairment on macrophage inflammation, the regulation of macrophage autophagy under hyperglycemic conditions is incompletely understood. Here, we report that the autophagy-lysosome system and mitochondrial function are impaired in streptozotocin (STZ)-induced diabetic mice and high glucose (HG)-stimulated RAW 264.7 cells. Mitochondrial dysfunction promotes reactive oxygen species (ROS) production and blocks autophagic flux by impairing lysosome function in macrophages under hyperglycemic conditions. Conversely, inhibition of mitochondrial ROS by Mito-TEMPO prevents HG-induced M1 macrophage polarization, and its effect is offset by blocking autophagic flux. The role of mitochondrial ROS in lysosome dysfunction and M1 macrophage polarization is also demonstrated in mitochondrial complex I defective RAW 264.7 cells induced by silencing NADH:ubiquinone oxidoreductase subunit-S4 (Ndufs4). These findings prove that mitochondrial ROS plays a key role in promoting macrophage polarization to inflammatory phenotype by impairing autophagy-lysosome system, which might provide clue to a novel treatment for diabetic complications.

Role of mitochondrial ROS in the brain: from physiology to neurodegeneration.

Mitochondria are key cell organelles in that they are responsible for energy production and control many processes from signalling to cell death. The function of the mitochondrial electron transport chain is coupled with the production of reactive oxygen species (ROS) in the form of superoxide anion or hydrogen peroxide. As a result of the constant production of ROS, mitochondria are protected by highly efficient antioxidant systems. The rapidly changing levels of ROS in mitochondria, coupled with multiple essential cellular functions, make ROS apt for physiological signalling. Thus, mutations, environmental toxins and chronic ischaemic conditions could affect the mitochondrial redox balance and lead to the development of pathology. In long-living and non-mitotic cells such as neurons, oxidative stress induced by overproduction of mitochondrial ROS or impairment of the antioxidant defence results in a dysfunction of mitochondria and initiation of the cell death cascade. Mitochondrial ROS overproduction and changes in mitochondrial redox homeostasis have been shown to be involved in both a number of neurological conditions and a majority of neurodegenerative diseases. Here, we summarise the involvement of mitochondrial ROS in the mechanism of neuronal loss of major neurodegenerative disorders.

The role of mitochondrial ROS in the aging brain.

The brain is the most complex human organ, consuming more energy than any other tissue in proportion to its size. It relies heavily on mitochondria to produce energy and is made up of mitotic and postmitotic cells that need to closely coordinate their metabolism to maintain essential bodily functions. During aging, damaged mitochondria that produce less ATP and more reactive oxygen species (ROS) accumulate. The current consensus is that ROS cause oxidative stress, damaging mitochondria and resulting in an energetic crisis that triggers neurodegenerative diseases and accelerates aging. However, in model organisms, increasing mitochondrial ROS (mtROS) in the brain extends lifespan, suggesting that ROS may participate in signaling that protects the brain. Here, we summarize the mechanisms by which mtROS are produced at the molecular level, how different brain cells and regions produce different amounts of mtROS, and how mtROS levels change during aging. Finally, we critically discuss the possible roles of ROS in aging as signaling molecules and damaging agents, addressing whether age-associated increases in mtROS are a cause or a consequence of aging.

The role of mitochondrial ROS in antibacterial immunity.

Reactive oxygen species (ROS) are essential participants of various innate immune cell responses against microorganisms and are also involved in many cellular regulatory pathways. It was believed that the main pool of ROS in the innate immune cells is generated by the NADPH oxidase enzymatic complex. However, it was discovered recently that mitochondrial ROS (mtROS) are equally important for the functioning of the immune system. mtROS play an important role in the development of the antimicrobial innate immune responses. The present mini-review summarizes the most recent data on the role of mtROS in the antibacterial immunity. The principles of mtROS formation and possible mechanisms of their generation under the activation of innate immunity are highlighted in this review. We also speculate on the possibilities of using activators of mtROS production in clinical practice.

ROS in Nature 2016: Part I

Nature (along with its several sister journals) is among the most highly influential journals that publish cutting edge scientific findings in diverse fields, including biomedical sciences. The purpose of the “ROS in Nature” series is to provide a platform to introduce the high profile research discoveries related to the molecular and cell biology of reactive oxygen species (ROS) published in Nature as well as some of its sister journals, including Nature Medicine, Nature Genetics, and Nature Communications. This “ROS in Nature 2016: Part I” paper highlights the major findings relevant to ROS bioscience, and these findings are reported in four articles in Nature over the past three months (January 1, 2016–March 31, 2016). The major findings from these articles include: (1) a novel role for mitochondrial ROS in regulating thermogenesis and energy expenditure in brown and beige fat; (2) an unexpected linkage between lipid dysfunction and impaired anticancer immunosurveillance, and an essential role for mitochondria-derived ROS in this linkage; (3) autophagy as a decisive stem–cell–fate regulator and an important role for cellular (likely mitochondria-derived) ROS in this process; and finally (4) the involvement of cellular (likely mitochondria-derived) ROS in GCN2-regulated gut inflammation. The elegant studies reported in the four Nature articles attest to the continued excitement about deciphering the detailed biochemistry and cell biology of ROS, species that result from the utilization of molecular oxygen in aerobic organisms. It is hoped that introducing such high profile research discoveries on ROS would help point to the new directions for innovative research in this rapidly evolving area of bioscience.

Mitochondrial ROS govern the LPS-induced pro-inflammatory response in microglia cells by regulating MAPK and NF-κB pathways

Activation of microglia cells in the brain contributes to neurodegenerative processes promoted by many neurotoxic factors such as pro-inflammatory cytokines and nitric oxide (NO). Reactive oxygen species (ROS) actively affect microglia-associated neurodegenerative diseases through their role as pro-inflammatory molecules and modulators of pro-inflammatory processes. Although the ROS which involved in microglia activation are thought to be generated primarily by NADPH oxidase (NOX) and involved in the immune response, mitochondrial ROS have also been proposed as important regulators of the inflammatory response in the innate immune system. However, the role of mitochondrial ROS in microglial activation has yet to be fully elucidated. In this study, we demonstrate that inhibition of mitochondrial ROS by treatment with Mito-TEMPO effectively suppressed the level of mitochondrial and intracellular ROS. Mito-TEMPO treatment also significantly prevented LPS-induced increase in the TNF-α, IL-1β, IL-6, iNOS and Cox-2 in BV-2 and primary microglia cells. Furthermore, LPS-induced suppression of mitochondrial ROS generation not only affected LPS-stimulated activation of MAPKs, including ERK, JNK, and p38, but also regulated IκB activation and NF-κB nuclear localization. These results indicate that mitochondria constitute a major source of ROS generation in LPS-mediated activated microglia cells. Additionally, suppression of LPS-induced mitochondrial ROS plays a role in modulating the production of pro-inflammatory mediators by preventing MAPK and NF-κB activation in microglia cells. Our findings suggest that a potential strategy in the development of therapy for inflammation-associated degenerative neurological diseases involves targeting the regulation of mitochondrial ROS in microglial cells.

A midlife crisis for the mitochondrial free radical theory of aging

Since its inception more than four decades ago, the Mitochondrial Free Radical Theory of Aging (MFRTA) has served as a touchstone for research into the biology of aging. The MFRTA suggests that oxidative damage to cellular macromolecules caused by reactive oxygen species (ROS) originating from mitochondria accumulates in cells over an animal’s lifespan and eventually leads to the dysfunction and failure that characterizes aging. A central prediction of the theory is that the ability to ameliorate or slow this process should be associated with a slowed rate of aging and thus increased lifespan. A vast pool of data bearing on this idea has now been published. ROS production, ROS neutralization and macromolecule repair have all been extensively studied in the context of longevity. We review experimental evidence from comparisons between naturally long- or short-lived animal species, from calorie restricted animals, and from genetically modified animals and weigh the strength of results supporting the MFRTA. Viewed as a whole, the data accumulated from these studies have too often failed to support the theory. Excellent, well controlled studies from the past decade in particular have isolated ROS as an experimental variable and have shown no relationship between its production or neutralization and aging or longevity. Instead, a role for mitochondrial ROS as intracellular messengers involved in the regulation of some basic cellular processes, such as proliferation, differentiation and death, has emerged. If mitochondrial ROS are involved in the aging process, it seems very likely it will be via highly specific and regulated cellular processes and not through indiscriminate oxidative damage to macromolecules.

Mitochondrial ROS Fire Up T Cell Activation

Metabolic reprogramming has emerged as an important feature of immune cell activation. Two new studies, including Sena etal. (2013) in this issue of Immunity, identify mitochondrial reactive oxygen species (ROS) arising from metabolic reprogramming as signaling molecules in Tcell activation.

Mitochondrial Thioredoxin

The source of reactive oxygen species (ROS) produced in cardiovascular systems includes NADPH oxidase, xanthine oxidase, and uncoupling of endothelial NO synthase (eNOS) as well as mitochondria. In particular, NADPH oxidase has been considered a predominant source of ROS in the pathogenesis of hypertension, atherosclerosis, cardiac hypertrophy, and heart failure. Recent data suggest that angiotensin (Ang) II, a potent hypertensive hormone which is known to activate NADPH oxidase, induces mitochondrial dysfunction, which, in turn, promotes excess amounts of ROS, eg, superoxide (O2·−), hydrogen peroxide (H2O2), and peroxynitrite from mitochondria.1 This contributes to endothelial dysfunction by reducing NO bioavailability and activating apoptotic signaling, thereby progressing cardiovascular disease, neurodegenerative disease, and aging. The role of mitochondrial ROS is demonstrated by previous reports that transgenic mice overexpressing catalase targeted to the mitochondria exhibit an extended life span.2 Mice overexpressing peroxiredoxin 3, the mitochondria-specific peroxidase linked to thioredoxin 2 (Trx2), show improved survival after myocardial infarction.3 Furthermore, Ang II-converting enzyme inhibitors and Ang II type I receptor blockers prevent age-related mitochondrial dysfunction, hypertension-induced renal mitochondrial dysfunction, and cardiac mitochondrial dysfunction in the setting of acute ischemia.1 However, the role of mitochondria-derived ROS and its relationship with NADPH oxidase-derived ROS in Ang II-induced hypertension remain unclear. One of the major antioxidant defense systems against mitochondrial ROS (in particular, H2O2) is thiol-reducing systems, including thioredoxin (Trx), glutaredoxin, and the glutathione system. The Trx system (Trx, Trx reductase, and NADPH) reduces oxidized cysteine groups on protein through an …

How mitochondria produce reactive oxygen species

The production of ROS (reactive oxygen species) by mammalian mitochondria is important because it underlies oxidative damage in many pathologies and contributes to retrograde redox signalling from the organelle to the cytosol and nucleus. Superoxide (O2•−) is the proximal mitochondrial ROS, and in the present review I outline the principles that govern O2•− production within the matrix of mammalian mitochondria. The flux of O2•− is related to the concentration of potential electron donors, the local concentration of O2 and the second-order rate constants for the reactions between them. Two modes of operation by isolated mitochondria result in significant O2•− production, predominantly from complex I: (i) when the mitochondria are not making ATP and consequently have a high Δp (protonmotive force) and a reduced CoQ (coenzyme Q) pool; and (ii) when there is a high NADH/NAD+ ratio in the mitochondrial matrix. For mitochondria that are actively making ATP, and consequently have a lower Δp and NADH/NAD+ ratio, the extent of O2•− production is far lower. The generation of O2•− within the mitochondrial matrix depends critically on Δp, the NADH/NAD+ and CoQH2/CoQ ratios and the local O2 concentration, which are all highly variable and difficult to measure in vivo. Consequently, it is not possible to estimate O2•− generation by mitochondria in vivo from O2•−-production rates by isolated mitochondria, and such extrapolations in the literature are misleading. Even so, the description outlined here facilitates the understanding of factors that favour mitochondrial ROS production. There is a clear need to develop better methods to measure mitochondrial O2•− and H2O2 formation in vivo, as uncertainty about these values hampers studies on the role of mitochondrial ROS in pathological oxidative damage and redox signalling.

Mitochondrial complex III regulates hypoxic activation of HIF

Decreases in oxygen levels are observed in physiological processes, such as development, and pathological situations, such as tumorigenesis and ischemia. In the complete absence of oxygen (anoxia), mammalian cells are unable to generate sufficient energy for survival, so a mechanism for sensing a decrease in the oxygen level (hypoxia) before it reaches a critical point is crucial for the survival of the organism. In response to decreased oxygen levels, cells activate the transcription factors hypoxia-inducible factors (HIFs), which lead to metabolic adaptation to hypoxia, as well as to generate new vasculature to increase oxygen supply. How cells sense decreases in oxygen levels to regulate HIF activation has been hotly debated. Emerging evidence indicates that reactive oxygen species (ROS) generated by mitochondrial complex III are required for hypoxic activation of HIF. This review examines the current knowledge about the role of mitochondrial ROS in HIF activation, as well as implications of ROS-level regulation in pathological processes such as cancer.

Mitochondrial Swelling and Generation of Reactive Oxygen Species Induced by Photoirradiation Are Heterogeneously Distributed

Abstract: Abundant evidence has been gathered to show that overproduction of reactive oxygen species (ROS) can lead to the opening of the mitochondrial permeability transition pore (MPTP) and result in apoptosis in mammalian cells. The information regarding spatial and temporal regulation of intracellular ROS formation related to the MPTP opening, however, is relatively limited. In this study, we used a fluorescent probe, dihydro‐2′,7′‐dichloroforescin (DCF), to detect intracellular ROS levels in different compartments of the cell in a time‐resolved manner. The roles of mitochondrial ROS (mROS) in the MPTP opening and mitochondrial membrane potential drop were investigated by using H2DCFDA coloaded with a mitochondrial marker dye MitoTracker Red, and by a mitochondrial membrane potential dye tetramethyl rhodamine ethyl ester. We applied multiphoton laser scanning microscopy to avoid autooxidation and bleaching of DCF so that long‐term visualization of intracellular ROS formation could be performed. Moreover, we noted that the resting mROS levels of different mitochondria were not homogeneous. After cells had been exposed to photoirradiation, the intracellular ROS gradually increased but the heterogeneity of mROS was maintained. Later, swelling was observed in mitochondria that contained higher levels of ROS, indicating the opening of the MPTP. In cells in which all the mitochondria swelled, they were translocated to the perinuclear area, which became the site of ROS production. At this stage, mROS reached the highest level concomitantly with a complete loss of mitochondrial membrane potential, indicating full opening of the MPTP. At the end, photoirradiation resulted in apoptotic cell death. In summary, we demonstrated by multiphoton laser scanning microscopy that photoirradiation induces heterogeneous intracellular ROS formation and mitochondrial permeability transition pore opening in single intact cells. These observations imply the existence of a microdomain in the regulation of mROS formation and subsequent opening of the MPTP.