Modulation of mitochondrial ion transport by inorganic polyphosphate - essential role in mitochondrial permeability transition pore

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

Inorganic polyphosphate regulates functions of thymocytes via activation of P2X purinoreceptors

Inorganic polyphosphate (polyP) is an ancient polymer, which was proven to be a signalling molecule in the mammalian brain, mediating the communication between astrocytes via activation of P2Y1 purinoreceptors and modulating the activity of neurons. There is very limited information regarding the ability of polyP to transmit the information as an agonist of purinoreceptors in other cells and tissues. Here, we show that application of polyP to the suspension of primary thymocytes increases the concentration of intracellular calcium. PolyP evoked calcium signal was dependent on the presence of P2X inhibitors but not P2Y1 inhibitor. PolyP dependent increase in intracellular calcium concentration caused mild mitochondrial depolarization, which was dependent on inhibitors of purinoreceptors, extracellular calcium and inhibitor of mitochondrial calcium uniporter but wasn't dependent on cyclosporin A. Application of polyP modulated cell volume regulation machinery of thymocytes in calcium dependent manner. Molecular docking experiments revealed that polyP can potentially bind to several types of P2X receptors with binding energy similar to ATP - natural agonist of P2X purinoreceptors. Further molecular dynamics simulations with P2X4 showed that binding of one molecule of polyP dramatically increases permeability of this receptor-channel for water molecules. Thus, in this research we for the first time showed that polyP can interact with P2X receptors in thymocytes and modulate physiological processes.

Inorganic polyphosphate's role in energy production and mitochondrial permeability transition pore opening in tick mitochondria

Inorganic polyphosphate (polyP) is a biopolymer composed of phosphoanhydride-linked orthophosphate molecules. PolyP is engaged in a variety of cellular functions, including mitochondrial metabolism. Here, we examined the effects of polyP on electron transport chain enzymes and F1 Fo ATP synthase in tick embryos during embryonic development. The study found that polyPs containing medium and long chains (polyP15 and polyP65 ) enhanced the activity of complex I, complex II, complex III, and F1 Fo ATP synthase, while short polyP chains (polyP3 ) had no effect. The study also examined the activity of exopolyphosphatases (PPX) in various energy-demand situations. PPX activity was stimulated when ADP concentrations are high, characterizing a low-energy context. When complexes I-III and F1 Fo ATP synthase inhibitors were added in energized mitochondria, PPX activity decreased, whereas the mitochondrial uncoupler FCCP had no impact on PPX activity. Additionally, the study investigated the effect of polyP on mitochondrial swelling, finding that polyP causes mitochondrial swelling by increasing calcium effects on the mitochondrial permeability transition pore. The findings presented here to increase our understanding of the function of polyP in mitochondrial metabolism and its relationship to mitochondrial permeability transition pore opening in an arthropod model.

The mitochondrial permeability transition: Recent progress and open questions

Major progress has been made in defining the basis of the mitochondrial permeability transition, a Ca²⁺ -dependent permeability increase of the inner membrane that has puzzled mitochondrial research for almost 70 years. Initially considered an artefact of limited biological interest by most, over the years the permeability transition has raised to the status of regulator of mitochondrial ion homeostasis and of druggable effector mechanism of cell death. The permeability transition is mediated by opening of channel(s) modulated by matrix cyclophilin D, the permeability transition pore(s) (PTP). The field has received new impulse (a) from the hypothesis that the PTP may originate from a Ca²⁺ -dependent conformational change of F-ATP synthase and (b) from the reevaluation of the long-standing hypothesis that it originates from the adenine nucleotide translocator (ANT). Here, we provide a synthetic account of the structure of ANT and F-ATP synthase to discuss potential and controversial mechanisms through which they may form high-conductance channels; and review some intriguing findings from the wealth of early studies of PTP modulation that still await an explanation. We hope that this review will stimulate new experiments addressing the many outstanding problems, and thus contribute to the eventual solution of the puzzle of the permeability transition.

The anabolic effect of inorganic polyphosphate on chondrocytes is mediated by calcium signalling

Inorganic polyphosphates (polyP) are polymers composed of phosphate residues linked by energy-rich phosphoanhydride bonds. As polyP can bind calcium, the hypothesis of this study is that polyP enters chondrocytes and exerts its anabolic effect by calcium influx through calcium channels. PolyP treatment of cartilage tissue formed in 3D culture by bovine chondrocytes showed an increase in proteoglycan accumulation but only when calcium was also present at a concentration of 1.5 mM. This anabolic effect could be prevented by treatment with either ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid or the calcium channel inhibitors gadolinium and nifedipine. Calcium and polyP cotreatment of chondrocytes in monolayer culture resulted in calcium oscillations that were polyP chain length specific and were inhibited by gadolinium and nifedipine. The calcium influx resulted in increased gene expression of sox9, collagen type II, and aggrecan which was prevented by treatment with either calphostin, an inhibitor of protein kinase C, and W7, an inhibitor of calmodulin; suggesting activation of the protein kinase C-calmodulin pathway. Tracing studies using  4',6-diamidino-2-phenylindole, Mitotracker Red, and/or Fura-AM staining showed that polyP was detected in the nucleus, mitochondria, and intracellular vacuoles suggesting that polyP may also enter the cell. PolyP colocalizes with calcium in mitochondria. This study demonstrates that polyP requires the influx of calcium to regulate chondrocyte matrix production, likely via activating calcium signaling. These findings identify the mechanism regulating the anabolic effect of polyP in chondrocytes which will help in its clinical translation into a therapeutic agent for cartilage repair.

Inorganic Polyphosphate and F0F1-ATP Synthase of Mammalian Mitochondria

Inorganic polyphosphate is a polymer which plays multiple important roles in yeast and bacteria. In higher organisms the role of polyP has been intensively studied in last decades and involvements of this polymer in signal transduction, cell death mechanisms, energy production, and many other processes were demonstrated. In contrast to yeast and bacteria, where enzymes responsible for synthesis and hydrolysis of polyP were identified, in mammalian cells polyP clearly plays important role in physiology and pathology but enzymes responsible for synthesis of polyP or consumption of this polymer are still not identified. Here, we discuss the role of mitochondrial F₀F₁-ATP synthase in polyP synthesis with results, which confirm this proposal. We also discuss the role of other enzymes which may play important roles in polyP metabolism.

Inorganic Polyphosphate, Mitochondria, and Neurodegeneration

With an aging population, the presence of aging-associated pathologies is expected to increase within the next decades. Regrettably, we still do not have any valid pharmacological or non-pharmacological tools to prevent, revert, or cure these pathologies. The absence of therapeutical approaches against aging-associated pathologies can be at least partially explained by the relatively lack of knowledge that we still have regarding the molecular mechanisms underlying them, as well as by the complexity of their etiopathology. In fact, a complex number of changes in the physiological function of the cell has been described in all these aging-associated pathologies, including neurodegenerative disorders. Based on multiple scientific manuscripts produced by us and others, it seems clear that mitochondria are dysfunctional in many of these aging-associated pathologies. For example, mitochondrial dysfunction is an early event in the etiopathology of all the main neurodegenerative disorders, and it could be a trigger of many of the other deleterious changes which are present at the cellular level in these pathologies. While mitochondria are complex organelles and their regulation is still not yet entirely understood, inorganic polyphosphate (polyP) could play a crucial role in the regulation of some mitochondrial processes, which are dysfunctional in neurodegeneration. PolyP is a well-preserved biopolymer; it has been identified in every organism that has been studied. It is constituted by a series of orthophosphates connected by highly energetic phosphoanhydride bonds, comparable to those found in ATP. The literature suggests that the role of polyP in maintaining mitochondrial physiology might be related, at least partially, to its effects as a key regulator of cellular bioenergetics. However, further research needs to be conducted to fully elucidate the molecular mechanisms underlying the effects of polyP in the regulation of mitochondrial physiology in aging-associated pathologies, including neurodegenerative disorders. With a significant lack of therapeutic options for the prevention and/or treatment of neurodegeneration, the search for new pharmacological tools against these conditions has been continuous in past decades, even though very few therapeutic approaches have shown potential in treating these pathologies. Therefore, increasing our knowledge about the molecular mechanisms underlying the effects of polyP in mitochondrial physiology as well as its metabolism could place this polymer as a promising and innovative pharmacological target not only in neurodegeneration, but also in a wide range of aging-associated pathologies and conditions where mitochondrial dysfunction has been described as a crucial component of its etiopathology, such as diabetes, musculoskeletal disorders, and cardiovascular disorders.

Enzymes of Polyphosphate Metabolism in Yeast: Properties, Functions, Practical Significance

Inorganic polyphosphates (polyP) are the linear polymers of orthophosphoric acid varying in the number of phosphate residues linked by the energy-rich phosphoanhydride bonds. PolyP is an essential component in living cells. Knowledge of polyP metabolizing enzymes in eukaryotes is necessary for understanding molecular mechanisms of polyP metabolism in humans and development of new approaches for treating bone and cardiovascular diseases associated with impaired mineral phosphorus metabolism. Yeast cells represent a rational experimental model for this research due to availability of the methods for studying phosphorus metabolism and construction of knockout mutants and strains overexpressing target proteins. Multicomponent system of polyP metabolism in Saccharomyces cerevisiae cells is presented in this review discussing properties, functioning, and practical significance of the enzymes involved in the synthesis and degradation of this important metabolite.

The emerging role of phosphorus in human health

Phosphorus, an essential nutrient, performs vital functions in skeletal and non-skeletal tissues and is pivotal for energy production. The last two decades of research on the physiological importance of phosphorus have provided several novel insights about its dynamic nature as a nutrient performing functions as a phosphate ion. Phosphorous also acts as a signaling molecule and induces complex physiological responses. It is recognized that phosphorus homeostasis is critical for health. The intake of phosphorus by the general population world-wide is almost double the amount required to maintain health. This increase is attributed to the incorporation of phosphate containing food additives in processed foods purchased by consumers. Research findings assessed the impact of excessive phosphorus intake on cells' and organs' responses, and highlighted the potential pathogenic consequences. Research also identified a new class of bioactive phosphates composed of polymers of phosphate molecules varying in chain length. These polymers are involved in metabolic responses including hemostasis, brain and bone health, via complex mechanism(s) with positive or negative health effects, depending on their chain length. It is amazing, that phosphorus, a simple element, is capable of exerting multiple and powerful effects. The role of phosphorus and its polymers in the renal and cardiovascular system as well as on brain health appear to be important and promising future research directions.

Inorganic polyphosphate is produced and hydrolyzed in F0F1-ATP synthase of mammalian mitochondria

Inorganic polyphosphate (polyP) is a polymer present in all living organisms. Although polyP is found to be involved in a variety of functions in cells of higher organisms, the enzyme responsible for polyP production and consumption has not yet been identified. Here, we studied the effect of polyP on mitochondrial respiration, oxidative phosphorylation and activity of F₀F₁-ATPsynthase. We have found that polyP activates mitochondrial respiration which does not coupled with ATP production (V₂) but inhibits ADP-dependent respiration (V₃). Moreover, PolyP can stimulate F₀F₁-ATPase activity in the presence of ATP and, importantly, can be hydrolyzed in this enzyme instead of ATP. Furthermore, PolyP can be produced in mitochondria in the presence of substrates for respiration and phosphate by the F₀F₁-ATPsynthase. Thus, polyP is an energy molecule in mammalian cells which can be produced and hydrolyzed in the mitochondrial F₀F₁-ATPsynthase.

Methanol extract and fraction of Anchomanes difformis root tuber modulate liver mitochondrial membrane permeability transition pore opening in rats

OBJECTIVE

Extracts of Anchomanes difformis (AD) are used in folkloric medicine to treat several diseases and infections. However, their roles in mitochondrial permeability transition pore opening are not known.

MATERIALS AND METHODS

The viability of mitochondria isolated from Wistar rat liver used in this experiment, was assessed by monitoring their swelling amplitude in the absence of calcium and reversal of calcium-induced pore opening by spermine. The effects of methanol extract and fraction of A. difformis (MEAD and MFAD, respectively) on Mitochondrial Membrane Permeability Transition (MMPT) pore opening, ATPase activity, cytochrome c release and ferrous-induced lipid peroxidation were assessed spectrophotometrically. Phytochemical constituents of MEAD and MFAD were assessed using Gas Chromatography- Mass Spectrometry (GC-MS).

RESULTS

The MEAD (10, 20, 40 and 80 μg/ ml) had no effect on MMPT pore opening in the absence of Ca²⁺, whereas MFAD at 80 μg/ml had a large amplitude pore opening effect. Both MEAD and MFAD reversed Ca²⁺‌‌-induced swelling with inhibition values of 18, 21, 24, 23% (for MEAD) and 41, 36, 35, and 26% (for MFAD) at 10, 20, 40 and 80 μg/ml, respectively. MFAD significantly enhanced F₁F₀ ATPase activity and caused cytochrome c release. Both MEAD and MFAD significantly inhibited ferrous-induced lipid peroxidation by 33.0, 64.0, 66, and 75% (for MEAD) and 24, 25, 30, and 45% (for MFAD), respectively. The GC-MS results revealed the presence of squalene as one of the major constituents of MEAD.

CONCLUSION

These findings suggest that MFAD can be used to induce cell death via mitochondrial permeability transition in isolated rat liver. Inhibition of lipid peroxidation by MEAD and MFAD showed that the pore opening effect of the extract and fraction was not mediated via peroxidation of mitochondrial membrane lipids.

Inorganic Polyphosphates As Storage for and Generator of Metabolic Energy in the Extracellular Matrix

Inorganic polyphosphates (polyP) consist of linear chains of orthophosphate residues, linked by high-energy phosphoanhydride bonds. They are evolutionarily old biopolymers that are present from bacteria to man. No other molecule concentrates as much (bio)chemically usable energy as polyP. However, the function and metabolism of this long-neglected polymer are scarcely known, especially in higher eukaryotes. In recent years, interest in polyP experienced a renaissance, beginning with the discovery of polyP as phosphate source in bone mineralization. Later, two discoveries placed polyP into the focus of regenerative medicine applications. First, polyP shows morphogenetic activity, i.e., induces cell differentiation via gene induction, and, second, acts as an energy storage and donor in the extracellular space. Studies on acidocalcisomes and mitochondria provided first insights into the enzymatic basis of eukaryotic polyP formation. In addition, a concerted action of alkaline phosphatase and adenylate kinase proved crucial for ADP/ATP generation from polyP. PolyP added extracellularly to mammalian cells resulted in a 3-fold increase of ATP. The importance and mechanism of this phosphotransfer reaction for energy-consuming processes in the extracellular matrix are discussed. This review aims to give a critical overview about the formation and function of this unique polymer that is capable of storing (bio)chemically useful energy.

Inorganic pyrophosphatase from the red flour beetle (Tribolium castaneum) modulates mitochondrial polyphosphate metabolism

Polyphosphates (polyPs) have been found in all cell types examined to date and play diverse roles, depending on the cell type. In eukaryotic organisms, polyPs have been mainly investigated in mammalian cells, with few studies on insects. In this study, we investigated mitochondrial polyphosphate metabolism in the red flour beetle, Tribolium castaneum. Substrate specificity for different chain lengths demonstrated the presence of two exopolyphosphatase isoforms in mitochondria. T. castaneum mitochondrial polyP levels decreased after injection with soluble pyrophosphatase (Tc-sPPase) dsRNA, while the membrane exopolyphosphate activity increased. Mitochondrial respiration modulated exopolyphosphatase activity only in wild-type beetles. Tripolyphosphate was able to increase the F-ATPase activity in wild-type and Tc-sPPase RNAi beetles. We suggest that inorganic pyrophosphatase modulates polyphosphate metabolism in mitochondria and affects the link between mitochondrial activity and polyphosphate metabolism in T. castaneum.

Cellular calcification induced by inorganic polyphosphate involves ATP depletion and opening of the mitochondrial permeability transition pore (mPTP)

Inorganic polyphosphate (polyP) is a linear polymer containing tens to hundreds of orthophosphate residues linked by high-energy phosphoanhydride bonds. PolyP promotes osteocalcification and bone mineralization in both mouse and human osteoblastic cells. In the present study, we examined the molecular mechanism by which polyP affects mitochondrial metabolism to promote cellular calcification in MC3T3-E1 osteoblastic cells. The cellular content of adenosine triphosphate (ATP) was diminished one day after polyP treatment, and this was accompanied by increased conversion to adenosine diphosphate. Furthermore, mitochondrial membrane potential was significantly decreased in polyP-treated cells. These results suggest that the depletion of intracellular ATP and the decrease in mitochondrial membrane potential induced by polyP treatment may be a trigger to promote cell calcification.

Dual role of inorganic polyphosphate in cardiac myocytes: The importance of polyP chain length for energy metabolism and mPTP activation

We have previously demonstrated that inorganic polyphosphate (polyP) is a potent activator of the mitochondrial permeability transition pore (mPTP) in cardiac myocytes. PolyP depletion protected against Ca²⁺-induced mPTP opening, however it did not prevent and even exacerbated cell death during ischemia-reperfusion (I/R). The central goal of this study was to investigate potential molecular mechanisms underlying these dichotomous effects of polyP on mitochondrial function. We utilized a Langendorff-perfused heart model of I/R to monitor changes in polyP size and chain length at baseline, 20 min no-flow ischemia, and 15 min reperfusion. Freshly isolated cardiac myocytes and mitochondria from C57BL/6J (WT) and cyclophilin D knock-out (CypD KO) mice were used to measure polyP uptake, mPTP activity, mitochondrial membrane potential, respiration and ATP generation. We found that I/R induced a significant decrease in polyP chain length. We, therefore, tested, the ability of synthetic polyPs with different chain length to accumulate in mitochondria and induce mPTP. Both short and long chain polyPs accumulated in mitochondria in oligomycin-sensitive manner implicating potential involvement of mitochondrial ATP synthase in polyP transport. Notably, only short-chain polyP activated mPTP in WT myocytes, and this effect was prevented by mPTP inhibitor cyclosprorin A and absent in CypD KO myocytes. To the contrary, long-chain polyP suppressed mPTP activation, and enhanced ADP-linked respiration and ATP production. Our data indicate that 1) effect of polyP on cardiac function strongly depends on polymer chain length; and 2) short-chain polyPs (as increased in ischemia-reperfusion) induce mPTP and mitochondrial uncoupling, while long-chain polyPs contribute to energy generation and cell metabolism.

Signal transduction in astrocytes: Localization and release of inorganic polyphosphate

Inorganic polyphosphate (polyP) is present in every cell and is highly conserved from primeval times. In the mammalian cells, polyP plays multiple roles including control of cell bioenergetics and signal transduction. In the brain, polyP mediates signaling between astrocytes via activation of purinergic receptors, however, the mechanisms of polyP release remain unknown. Here we report identification of polyP-containing vesicles in cortical astrocytes and the main triggers that evoke vesicular polyP release. In cultured astrocytes, polyP was localized predominantly within the intracellular vesicular compartments which express vesicular nucleotide transporter VNUT (putative ATP-containing vesicles), but not within the compartments expressing vesicular glutamate transporter 2 (VGLUT2). The number of lysosomes which contain polyP was dependent on the conditions of astrocytes. Release of polyP from a proportion of lysosomes could be induced by calcium ionophores. In contrast, polyP release from the VNUT-containing vesicles could be triggered by various physiological stimuli, such as pH changes, polyP induced polyP release and other stimuli which increase [Ca2+ ] i . These data suggest that astrocytes release polyP predominantly via exocytosis from the VNUT-containing vesicles. © 2018 Wiley Periodicals, Inc.

Pharmacological Sequestration of Mitochondrial Calcium Uptake Protects Neurons Against Glutamate Excitotoxicity

Neuronal excitotoxicity which is induced by exposure to excessive extracellular glutamate is shown to be involved in neuronal cell death in acute brain injury and a number of neurological diseases. High concentration of glutamate induces calcium deregulation which results in mitochondrial calcium overload and mitochondrial depolarization that triggers the mechanism of cell death. Inhibition of mitochondrial calcium uptake could be potentially neuroprotective but complete inhibition of mitochondrial calcium uniporter could result in the loss of some physiological processes linked to Ca²⁺ in mitochondria. Here, we found that a novel compound, TG-2112x, can inhibit only the lower concentrations mitochondrial calcium uptake (induced by 100 nM-5 μM) but not the uptake induced by higher concentrations of calcium (10 μM and higher). This effect was not associated with changes in mitochondrial membrane potential and cellular respiration. However, a pre-treatment of neurons with TG-2112x protected the neurons against calcium overload upon application of toxic concentrations of glutamate. Thus, sequestration of mitochondrial calcium uptake protected the neurons against glutamate-induced mitochondrial depolarization and cell death. In our hands, TG-2112x was also protective against ionomycin-induced cell death. Hence, low rate mitochondrial calcium uptake plays an underestimated role in mitochondrial function, and its inhibition could protect neurons against calcium overload and cell death in glutamate excitotoxicity.

α-synuclein oligomers interact with ATP synthase and open the permeability transition pore in Parkinson's disease

Protein aggregation causes α-synuclein to switch from its physiological role to a pathological toxic gain of function. Under physiological conditions, monomeric α-synuclein improves ATP synthase efficiency. Here, we report that aggregation of monomers generates beta sheet-rich oligomers that localise to the mitochondria in close proximity to several mitochondrial proteins including ATP synthase. Oligomeric α-synuclein impairs complex I-dependent respiration. Oligomers induce selective oxidation of the ATP synthase beta subunit and mitochondrial lipid peroxidation. These oxidation events increase the probability of permeability transition pore (PTP) opening, triggering mitochondrial swelling, and ultimately cell death. Notably, inhibition of oligomer-induced oxidation prevents the pathological induction of PTP. Inducible pluripotent stem cells (iPSC)-derived neurons bearing SNCA triplication, generate α-synuclein aggregates that interact with the ATP synthase and induce PTP opening, leading to neuronal death. This study shows how the transition of α-synuclein from its monomeric to oligomeric structure alters its functional consequences in Parkinson's disease.

Rebalancing β-Amyloid-Induced Decrease of ATP Level by Amorphous Nano/Micro Polyphosphate: Suppression of the Neurotoxic Effect of Amyloid β-Protein Fragment 25-35

Morbus Alzheimer neuropathology is characterized by an impaired energy homeostasis of brain tissue. We present an approach towards a potential therapy of Alzheimer disease based on the high-energy polymer inorganic polyphosphate (polyP), which physiologically occurs both in the extracellular and in the intracellular space. Rat pheochromocytoma (PC) 12 cells, as well as rat primary cortical neurons were exposed to the Alzheimer peptide Aβ25-35. They were incubated in vitro with polyphosphate (polyP); ortho-phosphate was used as a control. The polymer remained as Na⁺ salt; or complexed in a stoichiometric ratio to Ca²⁺ (Na-polyP[Ca²⁺]); or was processed as amorphous Ca-polyP microparticles (Ca-polyP-MP). Ortho-phosphate was fabricated as crystalline Ca-phosphate nanoparticles (Ca-phosphate-NP). We show that the pre-incubation of PC12 cells and primary cortical neurons with polyP protects the cells against the neurotoxic effect of the Alzheimer peptide Aβ25-35. The strongest effect was observed with amorphous polyP microparticles (Ca-polyP-MP). The effect of the soluble sodium salt; Na-polyP (Na-polyP[Ca²⁺]) was lower; while crystalline orthophosphate nanoparticles (Ca-phosphate-NP) were ineffective. Ca-polyP-MP microparticles and Na-polyP[Ca²⁺] were found to markedly enhance the intracellular ATP level. Pre-incubation of Aβ25-35 during aggregate formation, with the polyP preparation before exposure of the cells, had a small effect on neurotoxicity. We conclude that recovery of the compromised energy status in neuronal cells by administration of nontoxic biodegradable Ca-salts of polyP reverse the β-amyloid-induced decrease of adenosine triphosphate (ATP) level. This study contributes to a new routes for a potential therapeutic intervention in Alzheimer’s disease pathophysiology.

The path from mitochondrial ROS to aging runs through the mitochondrial permeability transition pore

Excessive production of mitochondrial reactive oxygen species (mROS) is strongly associated with mitochondrial and cellular oxidative damage, aging, and degenerative diseases. However, mROS also induces pathways of protection of mitochondria that slow aging, inhibit cell death, and increase lifespan. Recent studies show that the activation of the mitochondrial permeability transition pore (mPTP), which is triggered by mROS and mitochondrial calcium overloading, is enhanced in aged animals and humans and in aging-related degenerative diseases. mPTP opening initiates further production and release of mROS that damage both mitochondrial and nuclear DNA, proteins, and phospholipids, and also releases matrix NAD that is hydrolyzed in the intermembrane space, thus contributing to the depletion of cellular NAD that accelerates aging. Oxidative damage to calcium transporters leads to calcium overload and more frequent opening of mPTP. Because aging enhances the opening of the mPTP and mPTP opening accelerates aging, we suggest that mPTP opening drives the progression of aging. Activation of the mPTP is regulated, directly and indirectly, not only by the mitochondrial protection pathways that are induced by mROS, but also by pro-apoptotic signals that are induced by DNA damage. We suggest that the integration of these contrasting signals by the mPTP largely determines the rate of cell aging and the initiation of cell death, and thus animal lifespan. The suggestion that the control of mPTP activation is critical for the progression of aging can explain the conflicting and confusing evidence regarding the beneficial and deleterious effects of mROS on health and lifespan.

Inorganic polyphosphate enhances radio-sensitivity in a human non-small cell lung cancer cell line, H1299

Inorganic polyphosphate is a linear polymer containing tens to hundreds of orthophosphate residues linked by high-energy phosphoanhydride bonds. Polyphosphate has been recognized as a potent anti-metastasis reagent. However, the molecular mechanism underlying polyphosphate action on cancer cells is poorly understood. In this study, we investigated the involvement of polyphosphate in radio-sensitivity using a human non-small cell lung cancer cell line, H1299. We found that polyphosphate treatment decreases cellular adenosine triphosphate levels, suggesting a disruption of energy metabolism. We also found that the induction of DNA double-strand breaks was enhanced in polyphosphate-treated cells after X-ray irradiation and colony formation assay revealed that cell survival decreased compared with that of the control groups. These findings suggest that polyphosphate is a promising radio-sensitizer for cancer cells. Therefore, we hypothesized that polyphosphate treatment disrupts adenosine triphosphate-mediated energy transfer for cellular survival and DNA repair, thereby reducing the cellular capability to resist X-ray irradiation.

Osmotic regulation of the mitochondrial permeability transition pore investigated by light scattering, fluorescence and electron microscopy techniques

Mitochondrial permeability transition (PT) is a phenomenon of an increase of the inner membrane permeability in response to an excessive matrix calcium accumulation. PTP is caused by the opening of the large weakly selective channel. Molecular composition and regulation of permeability transition pore (PTP) are not well understood. Here we used isolated mitochondria to investigate dependence of PTP activation on the osmotic pressure. We found that in low osmotic strength solution calcium-induced PTP is significantly inhibited. We propose that this effect is linked to the changes in the curvature of the mitochondrial inner membrane. This interpretation is consistent with the idea about the importance of ATP synthase dimerization in modulation of the PTP activity.