bims-camemi Biomed news
on Mitochondrial metabolism in cancer
Issue of 2019‒03‒03
forty-seven papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Cell Rep. 2019 Feb 26. pii: S2211-1247(19)30143-3. [Epub ahead of print]26(9): 2257-2265.e4
    Meléndez-Rodríguez F, Urrutia AA, Lorendeau D, Rinaldi G, Roche O, Böğürcü-Seidel N, Ortega Muelas M, Mesa-Ciller C, Turiel G, Bouthelier A, Hernansanz-Agustín P, Elorza A, Escasany E, Li QOY, Torres-Capelli M, Tello D, Fuertes E, Fraga E, Martínez-Ruiz A, Pérez B, Giménez-Bachs JM, Salinas-Sánchez AS, Acker T, Sánchez Prieto R, Fendt SM, De Bock K, Aragonés J.
      Cellular aspartate drives cancer cell proliferation, but signaling pathways that rewire aspartate biosynthesis to control cell growth remain largely unknown. Hypoxia-inducible factor-1α (HIF1α) can suppress tumor cell proliferation. Here, we discovered that HIF1α acts as a direct repressor of aspartate biosynthesis involving the suppression of several key aspartate-producing proteins, including cytosolic glutamic-oxaloacetic transaminase-1 (GOT1) and mitochondrial GOT2. Accordingly, HIF1α suppresses aspartate production from both glutamine oxidation as well as the glutamine reductive pathway. Strikingly, the addition of aspartate to the culture medium is sufficient to relieve HIF1α-dependent repression of tumor cell proliferation. Furthermore, these key aspartate-producing players are specifically repressed in VHL-deficient human renal carcinomas, a paradigmatic tumor type in which HIF1α acts as a tumor suppressor, highlighting the in vivo relevance of these findings. In conclusion, we show that HIF1α inhibits cytosolic and mitochondrial aspartate biosynthesis and that this mechanism is the molecular basis for HIF1α tumor suppressor activity.
    Keywords:  GOT1; GOT2; HIF1α; aspartate biosynthesis; cancer; glutamine; oxygen; proliferation; renal cell carcinoma
  2. Sci Rep. 2019 Feb 26. 9(1): 2850
    Bundgaard A, James AM, Gruszczyk AV, Martin J, Murphy MP, Fago A.
      ATP depletion and succinate accumulation during ischemia lead to oxidative damage to mammalian organs upon reperfusion. In contrast, freshwater turtles survive weeks of anoxia at low temperatures without suffering from oxidative damage upon reoxygenation, but the mechanisms are unclear. To determine how turtles survive prolonged anoxia, we measured ~80 metabolites in hearts from cold-acclimated (5 °C) turtles exposed to 9 days anoxia and compared the results with those for normoxic turtles (25 °C) and mouse hearts exposed to 30 min of ischemia. In turtles, ATP and ADP decreased to new steady-state levels during fasting and cold-acclimation and further with anoxia, but disappeared within 30 min of ischemia in mouse hearts. High NADH/NAD+ ratios were associated with succinate accumulation in both anoxic turtles and ischemic mouse hearts. However, succinate concentrations and succinate/fumarate ratios were lower in turtle than in mouse heart, limiting the driving force for production of reactive oxygen species (ROS) upon reoxygenation in turtles. Furthermore, we show production of ROS from succinate is prevented by re-synthesis of ATP from ADP. Thus, maintenance of an ATP/ADP pool and low succinate accumulation likely protects turtle hearts from anoxia/reoxygenation injury and suggests metabolic interventions as a therapeutic approach to limit ischemia/reperfusion injury in mammals.
  3. Hum Mutat. 2019 Feb 22.
    Verrigni D, Nottia MD, Ardissone A, Baruffini E, Nasca A, Legati A, Bellacchio E, Fagiolari G, Martinelli D, Fusco L, Battaglia D, Trani G, Versienti G, Marchet S, Torraco A, Rizza T, Verardo M, D'Amico A, Diodato D, Moroni I, Lamperti C, Petrini S, Moggio M, Goffrini P, Ghezzi D, Carrozzo R, Bertini E.
      Mitochondria are highly dynamic organelles, undergoing continuous fission and fusion. The DNM1L gene encodes for the DRP1 protein, an evolutionary conserved member of the dynamin family, responsible for fission of mitochondria, and having a role in the division of peroxisomes, as well. DRP1 impairment is implicated in several neurological disorders and associated with either de novo dominant or compound heterozygous mutations. In five patients presenting with severe epileptic encephalopathy we identified 5 de novo dominant DNM1L variants, the pathogenicity of which was validated in a yeast model. Fluorescence microscopy revealed abnormally elongated mitochondria and aberrant peroxisomes in mutant fibroblasts, indicating impaired fission of these organelles. Moreover, a very peculiar finding in our cohort of patients was the presence, in muscle biopsy, of core like areas with oxidative enzyme alterations, suggesting an abnormal distribution of mitochondria in the muscle tissue. This article is protected by copyright. All rights reserved.
    Keywords:   DNM1L ; epileptic encephalopathy; mitochondrial disorders; mitochondrial dynamics; mitochondrial fission; muscle biopsy
  4. J Mol Cell Cardiol. 2019 Feb 26. pii: S0022-2828(19)30048-3. [Epub ahead of print]
    Thapa D, Xie B, Zhang M, Stoner MW, Manning JR, Huckestein BR, Edmunds LR, Mullett SJ, McTiernan CF, Wendell SG, Jurczak MJ, Scott I.
      Exposure to a high fat (HF) diet promotes increased fatty acid uptake, fatty acid oxidation and lipid accumulation in the heart. These maladaptive changes impact cellular energy metabolism and may promote the development of cardiac dysfunction. Attempts to increase cardiac glucose utilization have been proposed as a way to reverse cardiomyopathy in obese and diabetic individuals. Adropin is a nutrient-regulated metabolic hormone shown to promote glucose oxidation over fatty acid oxidation in skeletal muscle homogenates in vitro. The focus of the current study was to investigate whether adropin can regulate substrate metabolism in the heart following prolonged exposure to a HF diet in vivo. Mice on a long-term HF diet received serial intraperitoneal injections of vehicle or adropin over three days. Cardiac glucose oxidation was significantly reduced in HF animals, which was rescued by acute adropin treatment. Significant decreases in cardiac pyruvate dehydrogenase activity were observed in HF animals, which were also reversed by adropin treatment. In contrast to previous studies, this change was unrelated to Pdk4 expression, which remained elevated in both vehicle- and adropin-treated HF mice. Instead, we show that adropin modulated the expression of the mitochondrial acetyltransferase enzyme GCN5L1, which altered the acetylation status and activity of fuel metabolism enzymes to favor glucose utilization. Our findings indicate that adropin exposure leads to increased cardiac glucose oxidation under HF conditions, and may provide a future therapeutic avenue in the treatment of diabetic cardiomyopathy.
    Keywords:  Acetylation; Adropin; Fatty acid oxidation; Glucose oxidation; Metabolism; Mitochondria
  5. Front Physiol. 2019 ;10 78
    Janssen JJE, Grefte S, Keijer J, de Boer VCJ.
      Mitochondria are cellular organelles that control metabolic homeostasis and ATP generation, but also play an important role in other processes, like cell death decisions and immune signaling. Mitochondria produce a diverse array of metabolites that act in the mitochondria itself, but also function as signaling molecules to other parts of the cell. Communication of mitochondria with the nucleus by metabolites that are produced by the mitochondria provides the cells with a dynamic regulatory system that is able to respond to changing metabolic conditions. Dysregulation of the interplay between mitochondrial metabolites and the nucleus has been shown to play a role in disease etiology, such as cancer and type II diabetes. Multiple recent studies emphasize the crucial role of nutritional cofactors in regulating these metabolic networks. Since B-vitamins directly regulate mitochondrial metabolism, understanding the role of B-vitamins in mito-nuclear communication is relevant for therapeutic applications and optimal dietary lifestyle. In this review, we will highlight emerging concepts in mito-nuclear communication and will describe the role of B-vitamins in mitochondrial metabolite-mediated nuclear signaling.
    Keywords:  B-vitamins; TCA cycle metabolites; acyl-CoA; epigenetic modifications; mito-nuclear signaling; reactive oxygen species; sirtuins
  6. Autophagy. 2019 Feb 26.
    Safiulina D, Kuum M, Choubey V, Hickey MA, Kaasik A.
      The Parkinson disease-associated proteins PINK1 and PRKN coordinate the ubiquitination of mitochondrial outer membrane proteins to tag them either for degradation or for autophagic clearance of the mitochondrion. The proteins include the mitochondrial trafficking proteins RHOT1 and RHOT2, the removal of which may be required for immobilization of mitochondria prior to mitophagy. Here, we demonstrate that RHOT1 and RHOT2 are not only substrates for PINK1-PRKN-dependent degradation but that they also play an active role in the process of mitophagy. RHOT1, and likely also RHOT2, may act as a docking site for inactive PRKN prior to mitochondrial damage, thus keeping PRKN in close proximity to its potential substrates and thereby facilitating mitophagy. We also show that RHOT1 functions as a calcium-sensing docking site for PRKN, and we suggest that calcium binding to RHOT is a key step in the calcium-dependent activation of mitophagy machinery.
    Keywords:  PRKN translocation; cytosolic calcium; mitochondrial trafficking; mitophagy; neuron
  7. Cell Metab. 2019 Feb 13. pii: S1550-4131(19)30020-8. [Epub ahead of print]
    Harris IS, Endress JE, Coloff JL, Selfors LM, McBrayer SK, Rosenbluth JM, Takahashi N, Dhakal S, Koduri V, Oser MG, Schauer NJ, Doherty LM, Hong AL, Kang YP, Younger ST, Doench JG, Hahn WC, Buhrlage SJ, DeNicola GM, Kaelin WG, Brugge JS.
      Cells are subjected to oxidative stress during the initiation and progression of tumors, and this imposes selective pressure for cancer cells to adapt mechanisms to tolerate these conditions. Here, we examined the dependency of cancer cells on glutathione (GSH), the most abundant cellular antioxidant. While cancer cell lines displayed a broad range of sensitivities to inhibition of GSH synthesis, the majority were resistant to GSH depletion. To identify cellular pathways required for this resistance, we carried out genetic and pharmacologic screens. Both approaches revealed that inhibition of deubiquitinating enzymes (DUBs) sensitizes cancer cells to GSH depletion. Inhibition of GSH synthesis, in combination with DUB inhibition, led to an accumulation of polyubiquitinated proteins, induction of proteotoxic stress, and cell death. These results indicate that depletion of GSH renders cancer cells dependent on DUB activity to maintain protein homeostasis and cell viability and reveal a potentially exploitable vulnerability for cancer therapy.
    Keywords:  GCLC; HSF1; UPR; antioxidants; cancer; deubiquitinase; glutamate-cysteine ligase catalytic subunit; glutathione; heat shock factor 1; high-throughput screening; oxidative stress; proteotoxic stress; unfolded protein response
  8. Neurochem Res. 2019 Feb 27.
    Bui D, Ravasz D, Chinopoulos C.
      The reaction catalyzed by succinate-CoA ligase in the mitochondrial matrix yields a high-energy phosphate when operating towards hydrolysis of the thioester bond of succinyl-CoA, known as mitochondrial substrate-level phosphorylation (mSLP). The catabolism of several metabolites converge to succinyl-CoA but through different biochemical pathways. Among them, threonine, serine and methionine catabolize to succinyl-CoA through the common intermediate, 2-ketobutyrate. During the course of this pathway 2-ketobutyrate will become succinyl-CoA through propionyl-CoA catabolism, obligatorily passing through an ATP-consuming step substantiated by propionyl-CoA carboxylase. Here, by recording the directionality of the adenine nucleotide translocase while measuring membrane potential we tested the hypothesis that catabolism of 2-ketobutyrate negates mSLP due to the ATP-consuming propionyl-CoA carboxylase step in rotenone-treated, isolated mouse liver and brain mitochondria. 2-Ketobutyrate produced a less negative membrane potential compared to NADH or FADH2-linked substrates, which was sensitive to inhibition by rotenone, atpenin and arsenate, implying the involvement of complex I, complex II and a dehydrogenase-most likely branched chain keto-acid dehydrogenase, respectively. Co-addition of 2-ketobutyrate with NADH- or FADH2-linked substrates yielded no greater membrane potential than in the presence of substrates alone. However, in the presence of NADH-linked substrates, 2-ketobutyrate prevented mSLP in a dose-dependent manner. Our results imply that despite that 2-ketobutyrate leads to succinyl-CoA formation, obligatory metabolism through propionyl-CoA carboxylase associated with ATP expenditure abolishes mSLP. The provision of metabolites converging to 2-ketobutyrate may be a useful way for manipulating mSLP without using pharmacological or genetic tools.
    Keywords:  2-Oxobutanoate; 2-Oxobutyrate; Alpha-ketobutyrate; Succinyl-CoA
  9. Nat Rev Immunol. 2019 Feb 26.
    O'Brien KL, Finlay DK.
      Natural killer (NK) cells are lymphocytes with important roles in innate and adaptive immune responses to tumours and viral infection. However, in certain chronic diseases, including obesity and cancer, NK cell functional responses are impaired. Recently, research has highlighted the importance of NK cell metabolism in facilitating robust NK cell effector functions. This Review describes our current understanding of mouse and human NK cell metabolism and the key signalling pathways that mediate metabolic responses in NK cells. Furthermore, it explores how defects in metabolism can contribute to the generation of dysfunctional NK cells in chronic disease. Finally, the potential for new therapeutic strategies targeting cellular metabolism is discussed.
  10. Br J Pharmacol. 2019 Feb 22.
    Cui C, Yang J, Fu L, Wang M, Wang X.
      With great Ca2+ buffering capacity, mitochondrion is one of the most important intracellular organelles in regulating Ca2+ dynamic oscillation. Mitochondrial calcium uniporter (MCU) is the primary mediator for Ca2+ influx into mitochondria to manipulate cell energy metabolism, reactive oxygen species (ROS) production and programmed cell death, all of which are critical for carcinogenesis and tumor progression. The understanding of the uniporter complex was significantly boosted by recent groundbreaking discoveries that identified the uniporter pore forming subunit MCU and its regulatory molecules, including MCU dominant negative beta subunit (MCUb), essential MCU regulator (EMRE), MCU regulator 1 (MCUR1), mitochondrial calcium uptake (MICU) 1, MICU2 and MICU3. These provide the possibilities and molecular platform to investigate MCU complex (uniplex)-mediated discordant Ca2+ signaling in physiology and pathology. This review aims to summarize the progress of the understanding regulatory mechanisms of uniplex, roles of uniplex-mediated Ca2+ signaling in cancer and potential pharmacological inhibitors of MCU.
    Keywords:  ROS; calcium; cancer; mitochondrial calcium uniporter; uniplex
  11. Redox Biol. 2019 Feb 21. pii: S2213-2317(19)30022-9. [Epub ahead of print] 101141
    Moshfegh CM, Collins CW, Gunda V, Vasanthakumar A, Cao JZ, Singh PK, Godley LA, Case AJ.
      While the role of mitochondrial metabolism in controlling T-lymphocyte activation and function is becoming more clear, the specifics of how mitochondrial redox signaling contributes to T-lymphocyte regulation remains elusive. Here, we examined the global effects of elevated mitochondrial superoxide (O2-) on T-lymphocyte activation using a novel model of inducible manganese superoxide dismutase (MnSOD) knock-out. Loss of MnSOD led to specific increases in mitochondrial O2- with no evident changes in hydrogen peroxide (H2O2), peroxynitrite (ONOO-), or copper/zinc superoxide dismutase (CuZnSOD) levels. Unexpectedly, both mitochondrial and glycolytic metabolism showed significant reductions in baseline, maximal capacities, and ATP production with increased mitochondrial O2- levels. MnSOD knock-out T-lymphocytes demonstrated aberrant activation including widespread dysregulation in cytokine production and increased cellular apoptosis. Interestingly, an elevated proliferative signature defined by significant upregulation of cell cycle regulatory genes was also evident in MnSOD knock-out T-lymphocytes, but these cells did not show accelerated proliferative rates. Global disruption in T-lymphocyte DNA methylation and hydroxymethylation was also observed with increased mitochondrial O2-, which was correlated to alterations in intracellular metabolite pools linked to the methionine cycle. Together, these results demonstrate a mitochondrial redox and metabolic couple that when disrupted may alter cellular processes necessary for proper T-lymphocyte activation.
    Keywords:  Adaptive immunity; Apoptosis; Cytokines; Hydroxymethylation; Immune; Manganese superoxide dismutase; Metabolism; Methylation; Oxidative stress; Proliferation; Redox
  12. J Neurosci Res. 2019 Feb 23.
    Klimova N, Long A, Kristian T.
      Nicotinamide adenine dinucleotide (NAD+ ) is a central signaling molecule and enzyme cofactor that is involved in a variety of fundamental biological processes. NAD+ levels decline with age, neurodegenerative conditions, acute brain injury, and in obesity or diabetes. Loss of NAD+ results in impaired mitochondrial and cellular functions. Administration of NAD+ precursor, nicotinamide mononucleotide (NMN), has shown to improve mitochondrial bioenergetics, reverse age-associated physiological decline, and inhibit postischemic NAD+ degradation and cellular death. In this study, we identified a novel link between NAD+ metabolism and mitochondrial dynamics. A single dose (62.5 mg/kg) of NMN, administered to male mice, increases hippocampal mitochondria NAD+ pools for up to 24 hr posttreatment and drives a sirtuin 3 (SIRT3)-mediated global decrease in mitochondrial protein acetylation. This results in a reduction of hippocampal reactive oxygen species levels via SIRT3-driven deacetylation of mitochondrial manganese superoxide dismutase. Consequently, mitochondria in neurons become less fragmented due to lower interaction of phosphorylated fission protein, dynamin-related protein 1 (pDrp1 [S616]), with mitochondria. In conclusion, manipulation of mitochondrial NAD+ levels by NMN results in metabolic changes that protect mitochondria against reactive oxygen species and excessive fragmentation, offering therapeutic approaches for pathophysiologic stress conditions.
    Keywords:  ROS (reactive oxygen species); brain; dynamin-1-like protein; mitochondria; mitochondrial dynamics; nicotinamide adenine dinucleotide; nicotinamide mononucleotide; sirtuin 3; superoxide dismutase
  13. Oncogenesis. 2019 Feb 26. 8(3): 20
    Issaq SH, Mendoza A, Fox SD, Helman LJ.
      Despite a growing body of knowledge about the genomic landscape and molecular pathogenesis of sarcomas, translation of basic discoveries into targeted therapies and significant clinical gains has remained elusive. Renewed interest in altered metabolic properties of cancer cells has led to an exploration of targeting metabolic dependencies as a novel therapeutic strategy. In this study, we have characterized the dependency of human pediatric sarcoma cells on key metabolic substrates and identified a mechanism of adaptation to metabolic stress by examining proliferation and bioenergetic properties of rhabdomyosarcoma and Ewing sarcoma cells under varying concentrations of glucose and glutamine. While all cell lines tested were completely growth-inhibited by lack of glucose, cells adapted to glutamine deprivation, and restored proliferation following an initial period of reduced growth. We show that expression of glutamine synthetase (GS), the enzyme responsible for de novo glutamine synthesis, increased during glutamine deprivation, and that pharmacological or shRNA-mediated GS inhibition abolished proliferation of glutamine-deprived cells, while having no effect on cells grown under normal culture conditions. Moreover, the GS substrates and glutamine precursors glutamate and ammonia restored proliferation of glutamine-deprived cells in a GS-dependent manner, further emphasizing the necessity of GS for adaptation to glutamine stress. Furthermore, pharmacological and shRNA-mediated GS inhibition significantly reduced orthotopic xenograft tumor growth. We also show that glutamine supports sarcoma nucleotide biosynthesis and optimal mitochondrial bioenergetics. Our findings demonstrate that GS mediates proliferation of glutamine-deprived pediatric sarcomas, and suggest that targeting metabolic dependencies of sarcomas should be further investigated as a potential therapeutic strategy.
  14. Sci Rep. 2019 Feb 28. 9(1): 3073
    Lee CF, Caudal A, Abell L, Nagana Gowda GA, Tian R.
      Leigh syndrome is a mitochondrial disease characterized by neurological disorders, metabolic abnormality and premature death. There is no cure for Leigh syndrome; therefore, new therapeutic targets are urgently needed. In Ndufs4-KO mice, a mouse model of Leigh syndrome, we found that Complex I deficiency led to declines in NAD+ levels and NAD+ redox imbalance. We tested the hypothesis that elevation of NAD+ levels would benefit Ndufs4-KO mice. Administration of NAD+ precursor, nicotinamide mononucleotide (NMN) extended lifespan of Ndufs4-KO mice and attenuated lactic acidosis. NMN increased lifespan by normalizing NAD+ redox imbalance and lowering HIF1a accumulation in Ndufs4-KO skeletal muscle without affecting the brain. NMN up-regulated alpha-ketoglutarate (KG) levels in Ndufs4-KO muscle, a metabolite essential for HIF1a degradation. To test whether supplementation of KG can treat Ndufs4-KO mice, a cell-permeable KG, dimethyl ketoglutarate (DMKG) was administered. DMKG extended lifespan of Ndufs4-KO mice and delayed onset of neurological phenotype. This study identified therapeutic mechanisms that can be targeted pharmacologically to treat Leigh syndrome.
  15. Front Physiol. 2018 ;9 1914
    Haumann J, Camara AKS, Gadicherla AK, Navarro CD, Boelens AD, Blomeyer CA, Dash RK, Boswell MR, Kwok WM, Stowe DF.
      Mitochondrial (m) Ca2+ influx is largely dependent on membrane potential (ΔΨm), whereas mCa2+ efflux occurs primarily via Ca2+ ion exchangers. We probed the kinetics of Ca2+/H+ exchange (CHEm) in guinea pig cardiac muscle mitochondria. We tested if net mCa2+ flux is altered during a matrix inward H+ leak that is dependent on matrix H+ pumping by ATPm hydrolysis at complex V (FOF1-ATPase). We measured [Ca2+]m, extra-mitochondrial (e) [Ca2+]e, ΔΨm, pHm, pHe, NADH, respiration, ADP/ATP ratios, and total [ATP]m in the presence or absence of protonophore dinitrophenol (DNP), mitochondrial uniporter (MCU) blocker Ru360, and complex V blocker oligomycin (OMN). We proposed that net slow influx/efflux of Ca2+ after adding DNP and CaCl2 is dependent on whether the ΔpHm gradient is/is not maintained by reciprocal outward H+ pumping by complex V. We found that adding CaCl2 enhanced DNP-induced increases in respiration and decreases in ΔΨm while [ATP]m decreased, ΔpHm gradient was maintained, and [Ca2+]m continued to increase slowly, indicating net mCa2+ influx via MCU. In contrast, with complex V blocked by OMN, adding DNP and CaCl2 caused larger declines in ΔΨm as well as a slow fall in pHm to near pHe while [Ca2+]m continued to decrease slowly, indicating net mCa2+ efflux in exchange for H+ influx (CHEm) until the ΔpHm gradient was abolished. The kinetics of slow mCa2+ efflux with slow H+ influx via CHEm was also observed at pHe 6.9 vs. 7.6 by the slow fall in pHm until ΔpHm was abolished; if Ca2+ reuptake via the MCU was also blocked, mCa2+ efflux via CHEm became more evident. Of the two components of the proton electrochemical gradient, our results indicate that CHEm activity is driven largely by the ΔpHm chemical gradient with H+ leak, while mCa2+ entry via MCU depends largely on the charge gradient ΔΨm. A fall in ΔΨm with excess mCa2+ loading can occur during cardiac cell stress. Cardiac cell injury due to mCa2+ overload may be reduced by temporarily inhibiting FOF1-ATPase from pumping H+ due to ΔΨm depolarization. This action would prevent additional slow mCa2+ loading via MCU and permit activation of CHEm to mediate efflux of mCa2+. HIGHLIGHTS -We examined how slow mitochondrial (m) Ca2+ efflux via Ca2+/H+ exchange (CHEm) is triggered by matrix acidity after a rapid increase in [Ca2+]m by adding CaCl2 in the presence of dinitrophenol (DNP) to permit H+ influx, and oligomycin (OMN) to block H+ pumping via FOF1-ATP synthase/ase (complex V).-Declines in ΔΨm and pHm after DNP and added CaCl2 were larger when complex V was blocked.-[Ca2+]m slowly increased despite a fall in ΔΨm but maintained pHm when H+ pumping by complex V was permitted.-[Ca2+]m slowly decreased and external [Ca2+]e increased with declines in both ΔΨm and pHm when complex V was blocked.-ATPm hydrolysis supports a falling pHm and redox state and promotes a slow increase in [Ca2+]m.-After rapid Ca2+ influx due to a bolus of CaCl2, slow mCa2+ efflux by CHEm occurs directly if pHe is low.
    Keywords:  Ca2+ uptake/release; Ca2+/H+ exchange; H+ leak and pumping; cardiac mitochondria; complex V; mitochondrial Ca2+ uniporter
  16. Sci Signal. 2019 Feb 26. pii: eaau1788. [Epub ahead of print]12(570):
    Fu S, Zhu S, Tian C, Bai S, Zhang J, Zhan C, Xie D, Wang L, Li Z, Li J, Zhang H, Zhou R, Tian Z, Xu T, Bai L.
      Invariant natural killer T (iNKT) cells are innate-like T lymphocytes that express an invariant T cell receptor (TCR), which recognizes glycolipid antigens presented on CD1d molecules. These cells are phenotypically and functionally distinct from conventional T cells. When we characterized the metabolic activity of iNKT cells, consistent with their activated phenotype, we found that they had much less mitochondrial respiratory capacity but increased glycolytic activity in comparison to naïve conventional CD4+ T cells. After TCR engagement, iNKT cells further increased aerobic glycolysis, which was important for the expression of interferon-γ (IFN-γ). Glycolytic metabolism promoted the translocation of hexokinase-II to mitochondria and the activation of mammalian target of rapamycin complex 2 (mTORC2). Inhibiting glycolysis reduced the activity of Akt and PKCθ, which inhibited TCR recycling and accumulation within the immune synapse. Diminished TCR accumulation in the immune synapse reduced the activation of proximal and distal TCR signaling pathways and IFN-γ production in activated iNKT cells. Our studies demonstrate that glycolytic metabolism augments TCR signaling duration and IFN-γ production in iNKT cells by increasing TCR recycling.
  17. Cancer Metastasis Rev. 2019 Mar 01.
    Payen VL, Zampieri LX, Porporato PE, Sonveaux P.
      In cancer, mitochondrial functions are commonly altered. Directly involved in metabolic reprogramming, mitochondrial plasticity confers to cancer cells a high degree of adaptability to a wide range of stresses and to the harsh tumor microenvironment. Lack of nutrients or oxygen caused by altered perfusion, metabolic needs of proliferating cells, co-option of the microenvironment, control of the immune system, cell migration and metastasis, and evasion of exogenous stress (e.g., chemotherapy) are all, at least in part, influenced by mitochondria. Mitochondria are undoubtedly one of the key contributors to cancer development and progression. Understanding their protumoral (dys)functions may pave the way to therapeutic strategies capable of turning them into innocent entities. Here, we will focus on the production and detoxification of mitochondrial reactive oxygen species (mtROS), on their impact on tumorigenesis (genetic, prosurvival, and microenvironmental effects and their involvement in autophagy), and on tumor metastasis. We will also summarize the latest therapeutic approaches involving mtROS.
    Keywords:  Antioxidants; Cancer; Mitochondria; Mitochondrial reactive oxygen species (mtROS); Pro-oxidants; mitoQ
  18. Annu Rev Plant Biol. 2019 Mar 01.
    Meyer EH, Welchen E, Carrie C.
      Plant mitochondria play a major role during respiration by producing the ATP required for metabolism and growth. ATP is produced during oxidative phosphorylation (OXPHOS), a metabolic pathway coupling electron transfer with ADP phosphorylation via the formation and release of a proton gradient across the inner mitochondrial membrane. The OXPHOS system is composed of large, multiprotein complexes coordinating metal-containing cofactors for the transfer of electrons. In this review, we summarize the current state of knowledge about assembly of the OXPHOS complexes in land plants. We present the different steps involved in the formation of functional complexes and the regulatory mechanisms controlling the assembly pathways. Because several assembly steps have been found to be ancestral in plants-compared with those described in fungal and animal models-we discuss the evolutionary dynamics that lead to the conservation of ancestral pathways in land plant mitochondria. Expected final online publication date for the Annual Review of Plant Biology Volume 70 is April 29, 2019. Please see for revised estimates.
  19. Cell Physiol Biochem. 2019 ;52(2): 186-197
    Escribano-Lopez I, Bañuls C, Diaz-Morales N, Iannantuoni F, Rovira-Llopis S, Gomis R, Rocha M, Hernandez-Mijares A, Murphy MP, Victor VM.
      BACKGROUND/AIMS: Mitochondria-targeted antioxidants such as mitoquinone (MitoQ) have demonstrated protective effects against oxidative damage in several diseases. The increase in reactive oxygen species (ROS) production during glucose metabolism in β cells can be exacerbated under hyperglycaemic conditions such as type 2 diabetes (T2D), thus contributing to β cell function impairment. In the present work, we aimed to evaluate the effect of MitoQ on insulin secretion, oxidative stress, endoplasmic reticulum (ER) stress and nuclear factor kappa B (NFκB) signalling in a pancreatic β cell line under normoglycaemic (NG, 11.1 mM glucose), hyperglycaemic (HG, 25 mM glucose) and lipidic (palmitic acid (PA), 0.5mM) conditions.METHODS: We incubated the pancreatic β cell line INS-1E with or without MitoQ (0.5µM) under NG, HG and PA conditions. We then assessed the following parameters: glucose-induced insulin secretion, O₂ consumption (with a Clark-type electrode); mitochondrial function, oxidative stress parameters and calcium levels (by fluorescence microscopy); ER stress markers and NFκB-p65 protein levels (by western blotting).
    RESULTS: MitoQ increased insulin secretion and prevented the enhancement of ROS production and O₂ consumption and decrease in GSH levels that are characteristic under HG conditions. MitoQ also reduced protein levels of ER stress markers (GRP78 and P-eIF2α) and the proinflammatory nuclear transcription factor NFκB-p65, both of which increased under HG. MitoQ did not significantly alter ER stress markers under lipidic conditions.
    CONCLUSION: Our findings suggest that treatment with MitoQ modulates mitochondrial function, which in turn ameliorates endoplasmic reticulum stress and NFκB activation, thereby representing potential benefits for pancreatic β cell function.
    Keywords:  ER stress; MitoQ; Mitochondrial dysfunction; Oxidative stress; Pancreatic β cells; Type 2 Diabetes
  20. Methods Mol Biol. 2019 ;1936 333-342
    Campbell GR, Mahad DJ.
      Cytochrome c oxidase or mitochondrial respiratory chain complex IV is where over 90% of oxygen is consumed. The relationship between complex IV activity and mitochondrial proteins, which provides a guide to understanding the mechanisms in primary mitochondrial disorders, has been determined by histochemistry (complex IV activity) and immunohistochemistry in serial sections. In the central nervous system (CNS), mitochondrial activity and immunoreactivity have been determined in populations of cells in serial sections as capturing cells in more than one section is difficult. In this report, we describe a method to determine complex IV activity in relation to mitochondrial proteins at a single-cell level in the CNS. We performed complex IV histochemistry and immunohistochemistry consecutively in snap-frozen sections. Although the product of complex IV histochemistry reduces the sensitivity of standard immunohistochemistry (secondary antibody and ABC method), the biotin-free Menapath polymer detection system enables mitochondrial proteins to be detected following complex IV histochemistry. The co-occurring chromogens may then be separately visualized and analyzed using multispectral imaging. Our technique is applicable for exploring mitochondrial defects within single cells, including oligodendrocytes, in a variety of CNS disorders and animal models of those diseases.
    Keywords:  Cytochrome c oxidase; Immunohistochemistry and histochemistry; Mitochondria; Neurodegeneration
  21. J Biol Chem. 2019 Mar 01. pii: jbc.RA119.007687. [Epub ahead of print]
    Banba A, Tsuji A, Kimura H, Murai M, Miyoshi H.
      Site-specific suppressors of superoxide production (named S1QELs) in the quinone reaction site in mitochondrial respiratory complex I during reverse electron transfer have been previously reported; however, their mechanism of action remains elusive. Using bovine heart submitochondrial particles, we herein investigated the effects of S1QELs on complex I functions. We found that the inhibitory effects of S1QELs on complex I are distinctly different from those of other known quinone-site inhibitors. For example, the inhibitory potencies of S1QELs significantly varied depending on the direction of electron transfer (forward or reverse). S1QELs marginally suppressed the specific chemical modification of Asp-160 in the 49-kDa subunit, located deep in the quinone-binding pocket, by the tosyl chemistry reagent AL1. S1QELs also failed to suppress the binding of a photoreactive quinazoline-type inhibitor ([125I]AzQ) to the 49-kDa subunit. Moreover, a photoaffinity labeling experiment with photoreactive S1QEL derivatives indicated that they bind to a segment in the ND1 subunit that is not considered to make up the binding pocket for quinone or inhibitors. These results indicate that unlike known quinone-site inhibitors, S1QELs do not occupy the quinone- or inhibitor-binding pocket; rather, they may indirectly modulate the quinone redox reactions by inducing structural changes of the pocket through binding to ND1. We conclude that this indirect effect may be a prerequisite for S1QELs' direction-dependent modulation of electron transfer. This, in turn, may be responsible for the suppression of superoxide production during reverse electron transfer without significantly interfering with forward electron transfer.
    Keywords:  Complex I; bioenergetics; chemical biology; electron transfer chain; enzyme inhibitor; mitochondria; oxidative stress; photoaffinity labeling; ubiquinone
  22. Cell Metab. 2019 Feb 14. pii: S1550-4131(19)30022-1. [Epub ahead of print]
    Mao K, Ji F, Breen P, Sewell A, Han M, Sadreyev R, Ruvkun G.
      In Caenorhabditis elegans, mitochondrial dysfunction caused by mutation or toxins activates programs of detoxification and immune response. A genetic screen for mutations that constitutively induce C. elegans mitochondrial defense revealed reduction-of-function mutations in the mitochondrial chaperone hsp-6/mtHSP70 and gain-of-function mutations in the Mediator component mdt-15/MED15. The activation of detoxification and immune responses is transcriptionally mediated by mdt-15/MED15 and nuclear hormone receptor nhr-45. Mitochondrial dysfunction triggers redistribution of intestinal mitochondria, which requires the mitochondrial Rho GTPase miro-1 and its adaptor trak-1/TRAK1, but not nhr-45-regulated responses. Disabling the mdt-15/nhr-45 pathway renders animals more susceptible to a mitochondrial toxin or pathogenic Pseudomonas aeruginosa but paradoxically improves health and extends lifespan in animals with mitochondrial dysfunction caused by a mutation. Thus, some of the health deficits in mitochondrial disorders may be caused by the ineffective activation of detoxification and immune responses, which may be inhibited to improve health.
    Keywords:  detoxification and immune responses; lifespan; mitochondrion; xenobiotic surveillance
  23. Int J Radiat Biol. 2019 Mar 01. 1-25
    Vaupel P, Schmidberger H, Mayer A.
      PURPOSE: In the early 1920s, Warburg published experimental data on the enhanced conversion of glucose to pyruvate (followed by lactate formation) even in the presence of abundant oxygen (aerobic glycolysis, Warburg effect). He attributed this metabolic trait to a respiratory injury and considered this a universal metabolic alteration in carcinogenesis. This interpretation of the data was questioned since the early 1950s. Realistic causative mechanisms and consequences of the Warburg effect were described only during the past 15 years and are summarized in this article.CONCLUSIONS: There is clear evidence that mitochondria are not defective in most cancers. Aerobic glycolysis, a key metabolic feature of the Warburg phenotype, is caused by active metabolic reprogramming required to support sustained cancer cell proliferation and malignant progression. This metabolic switch is directed by altered growth factor signaling, hypoxic or normoxic activation of HIF-1α- transcription, oncogene activation or loss-of-function of suppressor genes, and is implemented in the hostile tumor microenvironment. The "selfish" reprogramming includes (a) overexpression of glucose transporters and of key glycolytic enzymes, and an accelerated glycolytic flux with subsequent accumulation and diversion of glycolytic intermediates for cancer biomass synthesis, (b) high-speed ATP production that meets the energy demand, and (c) accumulation of lactate which drives tumor progression and largely contributes to tumor acidosis, which in turn synergistically favors tumor progression and resistance to certain antitumor therapies, and compromises anti-tumor immunity. In all, the Warburg effect is the central contributor to the cancer progression machinery.
    Keywords:  Aerobic glycolysis; Warburg effect; cancer metabolism; cancer progression; glycolytic phenotype; metabolic reprogramming
  24. Proc Natl Acad Sci U S A. 2019 Feb 26. 116(9): 3530-3535
    Grenell A, Wang Y, Yam M, Swarup A, Dilan TL, Hauer A, Linton JD, Philp NJ, Gregor E, Zhu S, Shi Q, Murphy J, Guan T, Lohner D, Kolandaivelu S, Ramamurthy V, Goldberg AFX, Hurley JB, Du J.
      Glucose metabolism in vertebrate retinas is dominated by aerobic glycolysis (the "Warburg Effect"), which allows only a small fraction of glucose-derived pyruvate to enter mitochondria. Here, we report evidence that the small fraction of pyruvate in photoreceptors that does get oxidized by their mitochondria is required for visual function, photoreceptor structure and viability, normal neuron-glial interaction, and homeostasis of retinal metabolism. The mitochondrial pyruvate carrier (MPC) links glycolysis and mitochondrial metabolism. Retina-specific deletion of MPC1 results in progressive retinal degeneration and decline of visual function in both rod and cone photoreceptors. Using targeted-metabolomics and 13C tracers, we found that MPC1 is required for cytosolic reducing power maintenance, glutamine/glutamate metabolism, and flexibility in fuel utilization.
    Keywords:  MPC; glutamine; mitochondrial metabolism; pyruvate; retinal degeneration
  25. Heliyon. 2019 Feb;5(2): e01217
    Fan F, Sam R, Ryan E, Alvarado K, Villa-Cuesta E.
      Drosophila melanogaster is a powerful model to study mitochondrial respiratory chain defects, particularly succinate dehydrogenase (SDH) deficiency. Mutations in sdh genes cause degenerative disorders and often lead to death. Therapies for such pathologies are based on a combination of vitamins and dietary supplements, and are rarely effective. In Drosophila, mutations in several of the genes encoding SDH resemble the pathology of SDH deficiency in humans, enabling the Drosophila model to be used in finding treatments for this condition. Here we show that exposure to the drug rapamycin improves the survival of sdh mutant strains, the activity of SDH and the impaired climbing associated with sdh mutations. However, the production of reactive oxygen species, the oxygen consumption of isolated mitochondria and the resistance to hyperoxia were minimally affected. Our results contribute to the current research seeking a treatment for mitochondrial disease.
    Keywords:  Biochemistry; Cell biology; Genetics; Physiology
  26. Biochim Biophys Acta Mol Cell Res. 2019 Feb 22. pii: S0167-4889(19)30021-7. [Epub ahead of print]
    Moulin C, Caumont-Sarcos A, Ieva R.
      Mitochondria are pivotal organelles for cellular signaling and metabolism, and their dysfunction leads to severe cellular stress. About 70% of the mitochondrial proteome consists of preproteins synthesized in the cytosol with an amino-terminal cleavable presequence targeting signal. The TIM23 complex transports presequence signals towards the mitochondrial matrix. Ultimately, the mature protein segments are either transported into the matrix or sorted to the inner membrane. To ensure accurate preprotein import into distinct mitochondrial sub-compartments, the TIM23 machinery adopts specific functional conformations and interacts with different partner complexes. Regulatory subunits modulate the translocase dynamics, tailoring the import reaction to the incoming preprotein. The mitochondrial membrane potential and the ATP generated via oxidative phosphorylation are key energy sources in driving the presequence import pathway. Thus, mitochondrial dysfunctions have rapid repercussions on biogenesis. Cellular mechanisms exploit the presequence import pathway to monitor mitochondrial dysfunctions and mount transcriptional and proteostatic responses to restore functionality.
    Keywords:  Mitochondrial biogenesis; Mitochondrial homeostasis; PAM; Presequence import pathway; TIM23; TOM
  27. Mol Cancer Res. 2019 Feb 26. pii: molcanres.1068.2018. [Epub ahead of print]
    Pham-Danis C, Gehrke S, Danis E, Rozhok AI, Daniels MW, Gao D, Collins C, Di Paola JT, D'Alessandro A, DeGregori J.
      Mutations in oncogenes and tumor suppressor genes engender unique metabolic phenotypes crucial to the survival of tumor cells. Epidermal growth factor receptor (EGFR) signaling has been linked to the rewiring of tumor metabolism in non-small cell lung cancer (NSCLC). We have integrated the use of a functional genomics screen and metabolomics to identify metabolic vulnerabilities induced by EGFR inhibition. These studies reveal that following EGFR inhibition, EGFR-driven NSCLC cells become dependent on the urea cycle and in particular, the urea cycle enzyme CPS1. Combining knockdown of CPS1 with EGFR inhibition further reduces cell proliferation and impedes cell cycle progression. Profiling of the metabolome demonstrates that suppression of CPS1 potentiates the effects of EGFR inhibition on central carbon metabolism, pyrimidine biosynthesis, and arginine metabolism, coinciding with reduced glycolysis and mitochondrial respiration. We show that EGFR inhibition and CPS1 knockdown lead to a decrease in arginine levels and pyrimidine derivatives, and the addition of exogenous pyrimidines partially rescues the impairment in cell growth. Finally, we show that high expression of CPS1 in lung adenocarcinomas correlated with worse patient prognosis in publically available databases. These data collectively reveal that NSCLC cells have a greater dependency on the urea cycle to sustain central carbon metabolism, pyrimidine biosynthesis, and arginine metabolism to meet cellular energetics upon inhibition of EGFR. Implications: Our results reveal that the urea cycle may be a novel metabolic vulnerability in the context of EGFR inhibition, providing an opportunity to develop rational combination therapies with EGFR inhibitors for the treatment of EGFR-driven NSCLC.
  28. J Cell Sci. 2019 Feb 27. pii: jcs.223925. [Epub ahead of print]
    Forte GM, Davie E, Lie S, Franz-Wachtel M, Ovens AJ, Wang T, Oakhill JS, Maček B, Hagan IM, Petersen J.
      AMP-activated kinase (AMPK) and Target Of Rapamycin (TOR) signalling coordinate cell growth, proliferation, metabolism, and cell survival with the nutrient environment of cells. The poor vasculature and nutritional stress experienced by cells in solid tumours raises the question: how do they assimilate sufficient nutrients to survive? Here, we show that human and fission yeast cells import ATP and AMP from their external environment to regulate AMPK and TOR signalling. Exposure of fission yeast and human cells to external AMP impeded cell growth, however, in yeast this restraining impact required AMPK. In contrast, external ATP rescued the growth defect of yeast mutants with reduced TORC1 signalling, furthermore, exogenous ATP transiently enhanced TORC1 signalling in both yeast and human cell lines. Addition of the PANX1 channel inhibitor probenecid blocked ATP import into human cell lines suggesting that this channel may be responsible for both ATP release and uptake in mammals. In light of these findings it is possible that the higher extracellular ATP concentration reported in solid tumours is both scavenged and recognized as an additional energy source beneficial for cells growth.
    Keywords:  AMP; AMPK; ATP; Fission yeast; Nutrient stress; Ssp2; TORC1; Tsc1; Tsc2 Schizosaccharomyces pombe
  29. Nutrients. 2019 Feb 27. pii: E504. [Epub ahead of print]11(3):
    Bradshaw PC.
      The reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) protects against redox stress by providing reducing equivalents to antioxidants such as glutathione and thioredoxin. NADPH levels decline with aging in several tissues, but whether this is a major driving force for the aging process has not been well established. Global or neural overexpression of several cytoplasmic enzymes that synthesize NADPH have been shown to extend lifespan in model organisms such as Drosophila suggesting a positive relationship between cytoplasmic NADPH levels and longevity. Mitochondrial NADPH plays an important role in the protection against redox stress and cell death and mitochondrial NADPH-utilizing thioredoxin reductase 2 levels correlate with species longevity in cells from rodents and primates. Mitochondrial NADPH shuttles allow for some NADPH flux between the cytoplasm and mitochondria. Since a decline of nicotinamide adenine dinucleotide (NAD⁺) is linked with aging and because NADP⁺ is exclusively synthesized from NAD⁺ by cytoplasmic and mitochondrial NAD⁺ kinases, a decline in the cytoplasmic or mitochondrial NADPH pool may also contribute to the aging process. Therefore pro-longevity therapies should aim to maintain the levels of both NAD⁺ and NADPH in aging tissues.
    Keywords:  C. elegans; Drosophila; NADP; NADPH; aging; glutathione; lifespan; longevity; mitochondrial; nicotinamide adenine dinucleotide phosphate; redox; thioredoxin
  30. Sci Signal. 2019 Feb 26. pii: eaau8544. [Epub ahead of print]12(570):
    Katsuno Y, Meyer DS, Zhang Z, Shokat KM, Akhurst RJ, Miyazono K, Derynck R.
      Tumors comprise cancer stem cells (CSCs) and their heterogeneous progeny within a stromal microenvironment. In response to transforming growth factor-β (TGF-β), epithelial and carcinoma cells undergo a partial or complete epithelial-mesenchymal transition (EMT), which contributes to cancer progression. This process is seen as reversible because cells revert to an epithelial phenotype upon TGF-β removal. However, we found that prolonged TGF-β exposure, mimicking the state of in vivo carcinomas, promotes stable EMT in mammary epithelial and carcinoma cells, in contrast to the reversible EMT induced by a shorter exposure. The stabilized EMT was accompanied by stably enhanced stem cell generation and anticancer drug resistance. Furthermore, prolonged TGF-β exposure enhanced mammalian target of rapamycin (mTOR) signaling. A bitopic mTOR inhibitor repressed CSC generation, anchorage independence, cell survival, and chemoresistance and efficiently inhibited tumorigenesis in mice. These results reveal a role for mTOR in the stabilization of stemness and drug resistance of breast cancer cells and position mTOR inhibition as a treatment strategy to target CSCs.
  31. Nat Commun. 2019 Feb 28. 10(1): 981
    Nishimura K, Johmura Y, Deguchi K, Jiang Z, Uchida KSK, Suzuki N, Shimada M, Chiba Y, Hirota T, Yoshimura SH, Kono K, Nakanishi M.
      Animal cells undergo rapid rounding during mitosis, ensuring proper chromosome segregation, during which an outward rounding force abruptly increases upon prometaphase entry and is maintained at a constant level during metaphase. Initial cortical tension is generated by the actomyosin system to which both myosin motors and actin network architecture contribute. However, how cortical tension is maintained and its physiological significance remain unknown. We demonstrate here that Cdk1-mediated phosphorylation of DIAPH1 stably maintains cortical tension after rounding and inactivates the spindle assembly checkpoint (SAC). Cdk1 phosphorylates DIAPH1, preventing profilin1 binding to maintain cortical tension. Mutation of DIAPH1 phosphorylation sites promotes cortical F-actin accumulation, increases cortical tension, and delays anaphase onset due to SAC activation. Measurement of the intra-kinetochore length suggests that Cdk1-mediated cortex relaxation is indispensable for kinetochore stretching. We thus uncovered a previously unknown mechanism by which Cdk1 coordinates cortical tension maintenance and SAC inactivation at anaphase onset.
  32. J Cell Mol Med. 2019 Feb 26.
    Zhang HS, Zhang ZG, Du GY, Sun HL, Liu HY, Zhou Z, Gou XM, Wu XH, Yu XY, Huang YH.
      Abnormal metabolism of tumour cells is closely related to the occurrence and development of breast cancer, during which the expression of NF-E2-related factor 2 (Nrf2) is of great significance. Metastatic breast cancer is one of the most common causes of cancer death worldwide; however, the molecular mechanism underlying breast cancer metastasis remains unknown. In this study, we found that the overexpression of Nrf2 promoted proliferation and migration of breast cancers cells. Inhibition of Nrf2 and overexpression of Kelch-like ECH-associated protein 1 (Keap1) reduced the expression of glucose-6-phosphate dehydrogenase (G6PD) and transketolase of pentose phosphate pathway, and overexpression of Nrf2 and knockdown of Keap1 had opposite effects. Our results further showed that the overexpression of Nrf2 promoted the expression of G6PD and Hypoxia-inducing factor 1α (HIF-1α) in MCF-7 and MDA-MB-231 cells. Overexpression of Nrf2 up-regulated the expression of Notch1 via G6PD/HIF-1α pathway. Notch signalling pathway affected the proliferation of breast cancer by affecting its downstream gene HES-1, and regulated the migration of breast cancer cells by affecting the expression of EMT pathway. The results suggest that Nrf2 is a potential molecular target for the treatment of breast cancer and targeting Notch1 signalling pathway may provide a promising strategy for the treatment of Nrf2-driven breast cancer metastasis.
    Keywords:  G6PD; HIF-1α; Notch1; Nrf2; breast cancer
  33. Mitochondrion. 2019 Feb 22. pii: S1567-7249(18)30241-1. [Epub ahead of print]
    Adam AAA, van der Mark VA, Ruiter JPN, Wanders RJA, Oude Elferink RPJ, Chamuleau RAFM, Hoekstra R.
      Hyperammonemia is an important contributing factor to hepatic encephalopathy in end-stage liver failure patients. Therefore reducing hyperammonemia is a requisite of bioartificial liver support (BAL). Ammonia elimination by human liver HepaRG cells occurs predominantly through reversible fixation into amino acids, whereas the irreversible conversion into urea is limited. Compared to human liver, the expression and activity of the three urea cycle (UC) enzymes carbamoyl-phosphate synthase1 (CPS1), ornithine transcarbamoylase (OTC) and arginase1, are low. To improve HepaRG cells as BAL biocomponent, its rate limiting factor of the UC was determined under two culture conditions: static and dynamic medium flow (DMF) achieved by shaking. HepaRG cells increasingly converted escalating arginine doses into urea, indicating that arginase activity is not limiting ureagenesis. Neither was OTC activity, as a stable HepaRG line overexpressing OTC exhibited a 90- and 15.7-fold upregulation of OTC transcript and activity levels, without improvement in ureagenesis. However, a stable HepaRG line overexpressing CPS1showed increased mitochondrial stress and reduced hepatic differentiation without promotion of the CPS1 transcript level or ureagenesis under static-culturing conditions, yet, it exhibited a 4.3-fold increased ureagenesis under DMF. This was associated with increased CPS1 transcript and activity levels amounting to >2-fold, increased mitochondrial abundance and hepatic differentiation. Unexpectedly, the transcript levels of several other UC genes increased up to 6.8-fold. We conclude that ureagenesis can be improved in HepaRG cells by CPS1 overexpression, however, only in combination with DMF-culturing, suggesting that both the low CPS1 level and static-culturing, possibly due to insufficient mitochondria, are limiting UC.
    Keywords:  Bioartificial liver; Carbamoyl-phosphate synthase1; Mitochondria; Transduction; Urea cycle
  34. Nature. 2019 Feb 27.
    Elia I, Rossi M, Stegen S, Broekaert D, Doglioni G, van Gorsel M, Boon R, Escalona-Noguero C, Torrekens S, Verfaillie C, Verbeken E, Carmeliet G, Fendt SM.
      The extracellular matrix is a major component of the local environment-that is, the niche-that determines cell behaviour1. During metastatic growth, cancer cells shape the extracellular matrix of the metastatic niche by hydroxylating collagen to promote their own metastatic growth2,3. However, only particular nutrients might support the ability of cancer cells to hydroxylate collagen, because nutrients dictate which enzymatic reactions are active in cancer cells4,5. Here we show that breast cancer cells rely on the nutrient pyruvate to drive collagen-based remodelling of the extracellular matrix in the lung metastatic niche. Specifically, we discovered that pyruvate uptake induces the production of α-ketoglutarate. This metabolite in turn activates collagen hydroxylation by increasing the activity of the enzyme collagen prolyl-4-hydroxylase (P4HA). Inhibition of pyruvate metabolism was sufficient to impair collagen hydroxylation and consequently the growth of breast-cancer-derived lung metastases in different mouse models. In summary, we provide a mechanistic understanding of the link between collagen remodelling and the nutrient environment in the metastatic niche.
  35. Blood. 2019 Feb 26. pii: blood-2018-10-808873. [Epub ahead of print]
    Filippi MD, Ghaffari S.
      The hematopoietic system produces new blood cells throughout life. Mature blood cells all derived from a pool of rare long-lived hematopoietic stem cells (HSCs) that are mostly quiescent but occasionally divide and self-renew to maintain the stem cell pool and to insure the continuous replenishment of blood cells. Mitochondria have recently emerged as critical not only for HSC differentiation and commitment but also for HSC homeostasis. Mitochondria are dynamic organelles that orchestrate a number of fundamental metabolic and signaling processes, producing most of the cellular energy via oxidative phosphorylation. HSCs have relatively high amount of mitochondria that are mostly inactive. Here, we review recent advances in our understanding of the role of mitochondria in HSC homeostasis and discuss among others how mitochondrial dynamism and quality control might be implicated in the HSC fate, self-renewal and regenerative potential.
  36. Mol Biol Cell. 2019 Feb 27. mbcE18110743
    Brier LW, Ge L, Stjepanovic G, Thelen AM, Hurley J, Schekman R.
      Autophagy is a conserved eukaryotic pathway critical for cellular adaptation to changes in nutrition levels and stress. The class III phosphatidylinositol 3-kinase complexes I and II (PI3KC3-C1 and C2) are essential for autophagosome initiation and maturation, respectively, from highly curved vesicles. We used a cell-free reaction that reproduces a key autophagy initiation step, LC3 lipidation, as a biochemical readout to probe the role of ATG14, a PI3KC3-C1-specific subunit implicated in targeting the complex to autophagy initiation sites. We reconstituted LC3 lipidation with recombinant PI3KC3-C1, -C2 or various mutant derivatives added to extracts derived from a CRISPR/Cas9-generated ATG14-knockout cell line. Both complexes C1 and C2 require the C-terminal helix of VPS34 for activity on highly curved membranes. However, only complex C1 supports LC3 lipidation through the curvature-targeting ALPS motif of ATG14. Furthermore, the ALPS motif and VPS34 catalytic activity are required for downstream recruitment of WIPI2, a protein that binds PtdIns3P and its product PtdIns(3,5)P2, and a WIPI-binding protein, ATG2A, but do not affect membrane association of ATG3 and ATG16L1, enzymes contributing directly to LC3 lipidation. These data reveal the nuanced role of the ATG14 ALPS in membrane curvature sensing, suggesting that the ALPS has additional roles in supporting LC3 lipidation.
  37. Nucleic Acids Res. 2019 Feb 27. pii: gkz129. [Epub ahead of print]
    Guiducci G, Paone A, Tramonti A, Giardina G, Rinaldo S, Bouzidi A, Magnifico MC, Marani M, Menendez JA, Fatica A, Macone A, Armaos A, Tartaglia GG, Contestabile R, Paiardini A, Cutruzzolà F.
      Enzymes of intermediary metabolism are often reported to have moonlighting functions as RNA-binding proteins and have regulatory roles beyond their primary activities. Human serine hydroxymethyltransferase (SHMT) is essential for the one-carbon metabolism, which sustains growth and proliferation in normal and tumour cells. Here, we characterize the RNA-binding function of cytosolic SHMT (SHMT1) in vitro and using cancer cell models. We show that SHMT1 controls the expression of its mitochondrial counterpart (SHMT2) by binding to the 5'untranslated region of the SHMT2 transcript (UTR2). Importantly, binding to RNA is modulated by metabolites in vitro and the formation of the SHMT1-UTR2 complex inhibits the serine cleavage activity of the SHMT1, without affecting the reverse reaction. Transfection of UTR2 in cancer cells controls SHMT1 activity and reduces cell viability. We propose a novel mechanism of SHMT regulation, which interconnects RNA and metabolites levels to control the cross-talk between cytosolic and mitochondrial compartments of serine metabolism.
  38. Nature. 2019 Feb 27.
    Liu X, Wang Y, Lu H, Li J, Yan X, Xiao M, Hao J, Alekseev A, Khong H, Chen T, Huang R, Wu J, Zhao Q, Wu Q, Xu S, Wang X, Jin W, Yu S, Wang Y, Wei L, Wang A, Zhong B, Ni L, Liu X, Nurieva R, Ye L, Tian Q, Bian XW, Dong C.
      T cells become dysfunctional when they encounter self antigens or are exposed to chronic infection or to the tumour microenvironment1. The function of T cells is tightly regulated by a combinational co-stimulatory signal, and dominance of negative co-stimulation results in T cell dysfunction2. However, the molecular mechanisms that underlie this dysfunction remain unclear. Here, using an in vitro T cell tolerance induction system in mice, we characterize genome-wide epigenetic and gene expression features in tolerant T cells, and show that they are distinct from effector and regulatory T cells. Notably, the transcription factor NR4A1 is stably expressed at high levels in tolerant T cells. Overexpression of NR4A1 inhibits effector T cell differentiation, whereas deletion of NR4A1 overcomes T cell tolerance and exaggerates effector function, as well as enhancing immunity against tumour and chronic virus. Mechanistically, NR4A1 is preferentially recruited to binding sites of the transcription factor AP-1, where it represses effector-gene expression by inhibiting AP-1 function. NR4A1 binding also promotes acetylation of histone 3 at lysine 27 (H3K27ac), leading to activation of tolerance-related genes. This study thus identifies NR4A1 as a key general regulator in the induction of T cell dysfunction, and a potential target for tumour immunotherapy.
  39. Biochim Biophys Acta Mol Basis Dis. 2019 Feb 22. pii: S0925-4439(19)30070-5. [Epub ahead of print]
    Singh K, Roy M, Prajapati P, Lipatova A, Sripada L, Gohel D, Singh A, Mane M, Godbole MM, Chumakov PM, Singh R.
      An increased level of proinflammatory cytokines, including TNF-α in tumor microenvironment regulates the bioenergetic capacity, immune evasion and survival of cancer cells. Emerging evidences suggest that mitochondrial immune signaling proteins modulates mitochondrial bioenergetic capacity, in addition to the regulation of innate immune response. The optimal oxidative phosphorylation (OxPhos) capacity is required for the maintenance of functional lysosomes and autophagy flux. NLRX1, a mitochondrial NOD family receptor protein, regulates mitochondrial function during apoptosis and tissue injury. However, its role in regulation of mitochondrial and lysosomal function to modulate autophagy flux during inflammatory conditions is not understood. In the current study, we investigated the role of NLRX1 in modulating TNF-α induced autophagy flux and mitochondrial turnover and its implication in regulating the invasive and metastatic capability of breast cancer cells. Expression analyses of clinical breast cancer samples and meta-analysis of multiple public databases revealed that NLRX1 expression is significantly increased in basal-like and metastatic breast carcinoma as compared to non-basal-like and primary breast cancer. Depletion of NLRX1 expression in triple-negative breast cancer cells, altered the organization and activity of OxPhos complexes in presence of TNF-α. NLRX1 depletion further impaired lysosomal function and hence the turnover of damaged mitochondria through mitophagy in presence of TNF-α. Importantly, loss of NLRX1 decreased OxPhos-dependent cell proliferation and migration ability of triple-negative breast cancer cells in presence of TNF-α. These evidences suggest an essential role of NLRX1 in maintaining the crosstalk of mitochondrial metabolism and lysosomal function to regulate invasion and metastasis capability of breast cancer cells.
    Keywords:  Autophagy; Breast cancer; Inflammation; Lysosomes; Mitochondrial function; NLRX1
  40. Mol Cancer Ther. 2019 Mar;18(3): 693-705
    Teh JT, Zhu WL, Newgard CB, Casey PJ, Wang M.
      Metformin has been extensively studied for its impact on cancer cell metabolism and anticancer potential. Despite evidence of significant reduction in cancer occurrence in diabetic patients taking metformin, phase II cancer trials of the agent have been disappointing, quite possibly because of the lack of molecular mechanism-based patient stratification. In an effort to identify cancers that are responsive to metformin, we discovered that mitochondria respiratory capacity and respiratory reserve, which vary widely among cancer cells, correlate strongly to metformin sensitivity in both the in vitro and in vivo settings. A causal relationship between respiratory function and metformin sensitivity is demonstrated in studies in which we lowered respiratory capacity by either genetic knockdown or pharmacologic suppression of electron transport chain components, rendering cancer cells more vulnerable to metformin. These findings led us to predict, and experimentally validate, that metformin and AMP kinase inhibition synergistically suppress cancer cell proliferation.
  41. Cell Metab. 2019 Feb 14. pii: S1550-4131(19)30021-X. [Epub ahead of print]
    Thompson PJ, Shah A, Ntranos V, Van Gool F, Atkinson M, Bhushan A.
      Type 1 diabetes (T1D) is an organ-specific autoimmune disease characterized by hyperglycemia due to progressive loss of pancreatic beta cells. Immune-mediated beta cell destruction drives the disease, but whether beta cells actively participate in the pathogenesis remains unclear. Here, we show that during the natural history of T1D in humans and the non-obese diabetic (NOD) mouse model, a subset of beta cells acquires a senescence-associated secretory phenotype (SASP). Senescent beta cells upregulated pro-survival mediator Bcl-2, and treatment of NOD mice with Bcl-2 inhibitors selectively eliminated these cells without altering the abundance of the immune cell types involved in the disease. Significantly, elimination of senescent beta cells halted immune-mediated beta cell destruction and was sufficient to prevent diabetes. Our findings demonstrate that beta cell senescence is a significant component of the pathogenesis of T1D and indicate that clearance of senescent beta cells could be a new therapeutic approach for T1D.
    Keywords:  DNA damage; SASP; beta cells; cellular senescence; senolytics; type 1 diabetes
  42. Autophagy. 2019 Mar 01.
    Hao Y, Kacal M, Ouchida AT, Zhang B, Norberg E, Vakifahmetoglu-Norberg H.
      Chaperone-mediated autophagy is a lysosomal degradation pathway of select soluble proteins. Nearly one-third of the soluble proteins are predicted to be recognized by this pathway, yet only a minor fraction of this proteome has been identified as CMA substrates in cancer cells. Here, we undertook a quantitative multiplex mass spectrometry approach to study the proteome of isolated lysosomes in cancer cells during CMA-activated conditions. By integrating bioinformatics analyses, we identified and categorized proteins of multiple cellular pathways that were specifically targeted by CMA. Beyond verifying metabolic pathways, we showed that multiple components involved in select biological processes, including cellular translation, was specifically targeted for degradation by CMA. In particular, several proteins of the translation initiation complex were identified as bona fide CMA substrates in multiple cancer cell lines of distinct origin and we showed that CMA suppresses cellular translation. We further showed that the identified CMA substrates display high expression in multiple primary cancers compared to their normal counterparts. Combined, these findings uncover cellular processes affected by CMA and reveal a new role for CMA in the control of translation in cancer cells.
    Keywords:  autophagy; degradome; lysosome; proteome; translation
  43. Cell. 2019 Feb 08. pii: S0092-8674(19)30049-2. [Epub ahead of print]
    Dai J, Huang YJ, He X, Zhao M, Wang X, Liu ZS, Xue W, Cai H, Zhan XY, Huang SY, He K, Wang H, Wang N, Sang Z, Li T, Han QY, Mao J, Diao X, Song N, Chen Y, Li WH, Man JH, Li AL, Zhou T, Liu ZG, Zhang XM, Li T.
      The presence of DNA in the cytoplasm is normally a sign of microbial infections and is quickly detected by cyclic GMP-AMP synthase (cGAS) to elicit anti-infection immune responses. However, chronic activation of cGAS by self-DNA leads to severe autoimmune diseases for which no effective treatment is available yet. Here we report that acetylation inhibits cGAS activation and that the enforced acetylation of cGAS by aspirin robustly suppresses self-DNA-induced autoimmunity. We find that cGAS acetylation on either Lys384, Lys394, or Lys414 contributes to keeping cGAS inactive. cGAS is deacetylated in response to DNA challenges. Importantly, we show that aspirin can directly acetylate cGAS and efficiently inhibit cGAS-mediated immune responses. Finally, we demonstrate that aspirin can effectively suppress self-DNA-induced autoimmunity in Aicardi-Goutières syndrome (AGS) patient cells and in an AGS mouse model. Thus, our study reveals that acetylation contributes to cGAS activity regulation and provides a potential therapy for treating DNA-mediated autoimmune diseases.
    Keywords:  Aicardi-Goutiéres syndrome; Trex1; acetylation; aspirin; autoimmune disease; cGAS; interferonopathies
  44. Sci Rep. 2019 Feb 28. 9(1): 3153
    da Veiga Moreira J, Hamraz M, Abolhassani M, Schwartz L, Jolicœur M, Peres S.
      In the recent years, cancer research succeeded with sensitive detection methods, targeted drug delivery systems, and the identification of a large set of genes differently expressed. However, although most therapies are still based on antimitotic agents, which are causing wide secondary effects, there is an increasing interest for metabolic therapies that can minimize side effects. In the early 20th century, Otto Warburg revealed that cancer cells rely on the cytoplasmic fermentation of glucose to lactic acid for energy synthesis (called "Warburg effect"). Our investigations aim to reverse this effect in reprogramming cancer cells' metabolism. In this work, we present a metabolic therapy specifically targeting the activity of specific enzymes of central carbon metabolism, combining the METABLOC bi-therapeutic drugs combination (Alpha Lipoic Acid and Hydroxycitrate) to Metformin and Diclofenac, for treating tumors implanted in mice. Furthermore, a dynamic metabolic model describing central carbon metabolism as well as fluxes targeted by the drugs allowed to simulate tumors progression in both treated and non-treated mice, in addition to draw hypotheses on the effects of the drugs on tumor cells metabolism. Our model predicts metabolic therapies-induced reversed Warburg effect on tumor cells.
  45. Nat Commun. 2019 Mar 01. 10(1): 991
    Liu R, Li W, Tao B, Wang X, Yang Z, Zhang Y, Wang C, Liu R, Gao H, Liang J, Yang W.
      6-Phosphogluconate dehydrogenase (6PGD) is a key enzyme that converts 6-phosphogluconate into ribulose-5-phosphate with NADP+ as cofactor in the pentose phosphate pathway (PPP). 6PGD is commonly upregulated and plays important roles in many human cancers, while the mechanism underlying such roles of 6PGD remains elusive. Here we show that upon EGFR activation, 6PGD is phosphorylated at tyrosine (Y) 481 by Src family kinase Fyn. This phosphorylation enhances 6PGD activity by increasing its binding affinity to NADP+ and therefore activates the PPP for NADPH and ribose-5-phosphate, which consequently detoxifies intracellular reactive oxygen species (ROS) and accelerates DNA synthesis. Abrogating 6PGD Y481 phosphorylation (pY481) dramatically attenuates EGF-promoted glioma cell proliferation, tumor growth and resistance to ionizing radiation. In addition, 6PGD pY481 is associated with Fyn expression, the malignancy and prognosis of human glioblastoma. These findings establish a critical role of Fyn-dependent 6PGD phosphorylation in EGF-promoted tumor growth and radiation resistance.