bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒05‒17
sixty-one papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. EMBO Mol Med. 2020 May 13. e11217
    Lahiguera Á, Hyroššová P, Figueras A, Garzón D, Moreno R, Soto-Cerrato V, McNeish I, Serra V, Lazaro C, Barretina P, Brunet J, Menéndez J, Matias-Guiu X, Vidal A, Villanueva A, Taylor-Harding B, Tanaka H, Orsulic S, Junza A, Yanes O, Muñoz-Pinedo C, Palomero L, Pujana MÀ, Perales JC, Viñals F.
      Mitochondrial metabolism and the generation of reactive oxygen species (ROS) contribute to the acquisition of DNA mutations and genomic instability in cancer. How genomic instability influences the metabolic capacity of cancer cells is nevertheless poorly understood. Here, we show that homologous recombination-defective (HRD) cancers rely on oxidative metabolism to supply NAD+ and ATP for poly(ADP-ribose) polymerase (PARP)-dependent DNA repair mechanisms. Studies in breast and ovarian cancer HRD models depict a metabolic shift that includes enhanced expression of the oxidative phosphorylation (OXPHOS) pathway and its key components and a decline in the glycolytic Warburg phenotype. Hence, HRD cells are more sensitive to metformin and NAD+ concentration changes. On the other hand, shifting from an OXPHOS to a highly glycolytic metabolism interferes with the sensitivity to PARP inhibitors (PARPi) in these HRD cells. This feature is associated with a weak response to PARP inhibition in patient-derived xenografts, emerging as a new mechanism to determine PARPi sensitivity. This study shows a mechanistic link between two major cancer hallmarks, which in turn suggests novel possibilities for specifically treating HRD cancers with OXPHOS inhibitors.
    Keywords:   BCRA ; OXPHOS ; PARP inhibitors; cancer metabolism; metformin
  2. Cell Metab. 2020 May 01. pii: S1550-4131(20)30190-X. [Epub ahead of print]
    Pirinen E, Auranen M, Khan NA, Brilhante V, Urho N, Pessia A, Hakkarainen A, Kuula J, Heinonen U, Schmidt MS, Haimilahti K, Piirilä P, Lundbom N, Taskinen MR, Brenner C, Velagapudi V, Pietiläinen KH, Suomalainen A.
      NAD+ is a redox-active metabolite, the depletion of which has been proposed to promote aging and degenerative diseases in rodents. However, whether NAD+ depletion occurs in patients with degenerative disorders and whether NAD+ repletion improves their symptoms has remained open. Here, we report systemic NAD+ deficiency in adult-onset mitochondrial myopathy patients. We administered an increasing dose of NAD+-booster niacin, a vitamin B3 form (to 750-1,000 mg/day; clinicaltrials.govNCT03973203) for patients and their matched controls for 10 or 4 months, respectively. Blood NAD+ increased in all subjects, up to 8-fold, and muscle NAD+ of patients reached the level of their controls. Some patients showed anemia tendency, while muscle strength and mitochondrial biogenesis increased in all subjects. In patients, muscle metabolome shifted toward controls and liver fat decreased even 50%. Our evidence indicates that blood analysis is useful in identifying NAD+ deficiency and points niacin to be an efficient NAD+ booster for treating mitochondrial myopathy.
    Keywords:  NAD(+); NAD(+) repletion; mitochondria; mitochondrial disease; mitochondrial myopathy; mtDNA deletions; niacin; respiratory chain deficiency; treatment; vitamin B3
  3. Autophagy. 2020 May 13. 1-20
    Vilmen G, Glon D, Siracusano G, Lussignol M, Shao Z, Hernandez E, Perdiz D, Quignon F, Mouna L, Poüs C, Gruffat H, Maréchal V, Esclatine A.
      Mitochondria respond to many cellular functions and act as central hubs in innate immunity against viruses. This response is notably due to their role in the activation of interferon (IFN) signaling pathways through the activity of MAVS (mitochondrial antiviral signaling protein) present at the mitochondrial surface. Here, we report that the BHRF1 protein, a BCL2 homolog encoded by Epstein-Barr virus (EBV), inhibits IFNB/IFN-β induction by targeting the mitochondria. Indeed, we have demonstrated that BHRF1 expression modifies mitochondrial dynamics and stimulates DNM1L/Drp1-mediated mitochondrial fission. Concomitantly, we have shown that BHRF1 is pro-autophagic because it stimulates the autophagic flux by interacting with BECN1/Beclin 1. In response to the BHRF1-induced mitochondrial fission and macroautophagy/autophagy stimulation, BHRF1 drives mitochondrial network reorganization to form juxtanuclear mitochondrial aggregates known as mito-aggresomes. Mitophagy is a cellular process, which can specifically sequester and degrade mitochondria. Our confocal studies uncovered that numerous mitochondria are present in autophagosomes and acidic compartments using BHRF1-expressing cells. Moreover, mito-aggresome formation allows the induction of mitophagy and the accumulation of PINK1 at the mitochondria. As BHRF1 modulates the mitochondrial fate, we explored the effect of BHRF1 on innate immunity and showed that BHRF1 expression could prevent IFNB induction. Indeed, BHRF1 inhibits the IFNB promoter activation and blocks the nuclear translocation of IRF3 (interferon regulatory factor 3). Thus, we concluded that BHRF1 can counteract innate immunity activation by inducing fission of the mitochondria to facilitate their sequestration in mitophagosomes for degradation.ABBREVIATIONS: 3-MA: 3-methyladenine; ACTB: actin beta; BCL2: BCL2 apoptosis regulator; CARD: caspase recruitment domain; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CI: compaction index; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole, dihydrochloride; DDX58/RIG-I: DExD/H-box helicase 58; DNM1L/Drp1: dynamin 1 like; EBSS: Earle's balanced salt solution; EBV: Epstein-Barr virus; ER: endoplasmic reticulum; EV: empty vector; GFP: green fluorescent protein; HEK: human embryonic kidney; IFN: interferon; IgG: immunoglobulin G; IRF3: interferon regulatory factor 3; LDHA: lactate dehydrogenase A; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; MMP: mitochondrial membrane potential; MOM: mitochondrial outer membrane; PINK1: PTEN induced kinase 1; RFP: red fluorescent protein; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TOMM20: translocase of outer mitochondrial membrane 20; VDAC: voltage dependent anion channel.
    Keywords:  Autophagy; BCL2; BECN1; BHRF1; DNM1L; EBV; IFN; MAVS; mitochondrial dynamics; mitophagy
  4. Elife. 2020 May 12. pii: e54090. [Epub ahead of print]9
    Alexander RK, Liou YH, Knudsen NH, Starost KA, Xu C, Hyde AL, Liu S, Jacobi D, Liao NS, Lee CH.
      Metabolic pathways and inflammatory processes are under circadian regulation. While rhythmic immune cell recruitment is known to impact infection outcomes, whether the circadian clock modulates immunometabolism remains unclear. We find the molecular clock Bmal1 is induced by inflammatory stimulants, including Ifn-g/lipopolysaccharide (M1) and tumor-conditioned medium, to maintain mitochondrial metabolism under these metabolically stressed conditions in mouse macrophages. Upon M1 stimulation, myeloid-specific Bmal1 knockout (M-BKO) renders macrophages unable to sustain mitochondrial function, enhancing succinate dehydrogenase (SDH)-mediated mitochondrial ROS production and Hif-1a-dependent metabolic reprogramming and inflammatory damage. In tumor-associated macrophages, the aberrant Hif-1a activation and metabolic dysregulation by M-BKO contribute to an immunosuppressive tumor microenvironment. Consequently, M-BKO increases melanoma tumor burden, while administrating an SDH inhibitor dimethyl malonate suppresses tumor growth. Therefore, Bmal1 functions as a metabolic checkpoint integrating macrophage mitochondrial metabolism, redox homeostasis and effector functions. This Bmal1-Hif-1a regulatory loop may provide therapeutic opportunities for inflammatory diseases and immunotherapy.
    Keywords:  cell biology; mouse
  5. Trends Biochem Sci. 2020 May 11. pii: S0968-0004(20)30091-8. [Epub ahead of print]
    Bykov YS, Rapaport D, Herrmann JM, Schuldiner M.
      While targeting of proteins synthesized in the cytosol to any organelle is complex, mitochondria present the most challenging of destinations. First, import of nuclear-encoded proteins needs to be balanced with production of mitochondrial-encoded ones. Moreover, as mitochondria are divided into distinct subdomains, their proteins harbor a number of different targeting signals and biophysical properties. While translocation into the mitochondrial membranes has been well studied, the cytosolic steps of protein import remain poorly understood. Here, we review current knowledge on mRNA and protein targeting to mitochondria, as well as recent advances in our understanding of the cellular programs that respond to accumulation of mitochondrial precursor proteins in the cytosol, thus linking defects in targeting-capacity to signaling.
    Keywords:  RNA-binding proteins; chaperones; mitochondrial precursor; mitochondrial protein import; mitochondrial targeting sequence; nascent-chain associated complex
  6. Int J Mol Sci. 2020 May 09. pii: E3363. [Epub ahead of print]21(9):
    Ghosh P, Vidal C, Dey S, Zhang L.
      Mitochondria are well known for their role in ATP production and biosynthesis of macromolecules. Importantly, increasing experimental evidence points to the roles of mitochondrial bioenergetics, dynamics, and signaling in tumorigenesis. Recent studies have shown that many types of cancer cells, including metastatic tumor cells, therapy-resistant tumor cells, and cancer stem cells, are reliant on mitochondrial respiration, and upregulate oxidative phosphorylation (OXPHOS) activity to fuel tumorigenesis. Mitochondrial metabolism is crucial for tumor proliferation, tumor survival, and metastasis. Mitochondrial OXPHOS dependency of cancer has been shown to underlie the development of resistance to chemotherapy and radiotherapy. Furthermore, recent studies have demonstrated that elevated heme synthesis and uptake leads to intensified mitochondrial respiration and ATP generation, thereby promoting tumorigenic functions in non-small cell lung cancer (NSCLC) cells. Also, lowering heme uptake/synthesis inhibits mitochondrial OXPHOS and effectively reduces oxygen consumption, thereby inhibiting cancer cell proliferation, migration, and tumor growth in NSCLC. Besides metabolic changes, mitochondrial dynamics such as fission and fusion are also altered in cancer cells. These alterations render mitochondria a vulnerable target for cancer therapy. This review summarizes recent advances in the understanding of mitochondrial alterations in cancer cells that contribute to tumorigenesis and the development of drug resistance. It highlights novel approaches involving mitochondria targeting in cancer therapy.
    Keywords:  OXPHOS; heme; metabolism; mitochondria
  7. Trends Cell Biol. 2020 Jun;pii: S0962-8924(20)30055-6. [Epub ahead of print]30(6): 428-439
    Anderson NS, Haynes CM.
      Eukaryotic cells must accurately monitor the integrity of the mitochondrial network to overcome environmental insults and respond to physiological cues. The mitochondrial unfolded protein response (UPRmt) is a mitochondrial-to-nuclear signaling pathway that maintains mitochondrial proteostasis, mediates signaling between tissues, and regulates organismal aging. Aberrant UPRmt signaling is associated with a wide spectrum of disorders, including congenital diseases as well as cancers and neurodegenerative diseases. Here, we review recent research into the mechanisms underlying UPRmt signaling in Caenorhabditis elegans and discuss emerging connections between the UPRmt signaling and a translational regulation program called the 'integrated stress response'. Further study of the UPRmt will potentially enable development of new therapeutic strategies for inherited metabolic disorders and diseases of aging.
    Keywords:  integrated stress response; mitochondria; mitochondrial unfolded protein response; stress signaling
  8. Am J Physiol Endocrinol Metab. 2020 May 12.
    Pendleton AL, Antolic AT, Kelly AC, Davis MA, Camacho LE, Doubleday K, Anderson MJ, Langlais PR, Lynch RM, Limesand SW.
      Fetal sheep with placental insufficiency-induced intrauterine growth restriction (IUGR) have lower hind-limb oxygen consumption rates (OCR), indicating depressed mitochondrial oxidative phosphorylation capacity in their skeletal muscle. We hypothesized that OCRs are lower in skeletal muscle mitochondria from IUGR fetuses due to reduced electron transport chain (ETC) activity and lower abundances of Tricarboxylic Acid (TCA) cycle enzymes. IUGR sheep fetuses (n=12) were created with mid-gestation maternal hyperthermia and compared to control fetuses (n=12). At 132±1 days of gestation, biceps femoris muscles were collected, and the mitochondria were isolated. Mitochondria from IUGR muscle have 47% lower State 3 (Complex-I dependent) OCRs than controls, while State 4 (proton leak) OCRs were not different between groups. Furthermore, Complex I, but not Complex II or IV, enzymatic activity was lower in IUGR fetuses compared to controls. Proteomic analysis (n=6/group) identified 160 differentially expressed proteins between groups with 107 upregulated and 53 downregulated mitochondria proteins in IUGR fetuses compared to controls. Although no differences were identified in ETC subunit protein abundances, abundances of key TCA cycle enzymes (IDH3B, SUCLA2, and OGDH) were lower in IUGR mitochondria. IUGR mitochondria had a greater abundance of a hypoxia inducible protein, NADH dehydrogenase 1 alpha subcomplex 4-like 2, which is known to incorporate into Complex I and lower Complex I-mediated NADH oxidation. Our findings show that mitochondria from IUGR skeletal muscle adapts to hypoxemia and hypoglycemia by lowering Complex I activity and TCA cycle enzymes concentrations, which together act to lower OCR and NADH production/oxidation in IUGR skeletal muscle.
    Keywords:  electron transport chain; mitochondria; placental insufficiency; proteomics; tricarboxylic acid cycle
  9. Trends Biochem Sci. 2020 May 06. pii: S0968-0004(20)30092-X. [Epub ahead of print]
    Haws SA, Leech CM, Denu JM.
      Many chromatin-modifying enzymes require metabolic cofactors to support their catalytic activities, providing a direct path for fluctuations in metabolite availability to regulate the epigenome. Over the past decade, our knowledge of this link has grown significantly. What began with studies showing that cofactor availability drives global abundances of chromatin modifications has transitioned to discoveries highlighting metabolic enzymes as loci-specific regulators of gene expression. Here, we cover our current understanding of mechanisms that facilitate the dynamic and complex relationship between metabolism and the epigenome, focusing on the roles of essential metabolic and chromatin associated enzymes. We discuss physiological conditions where availability of these epimetabolites is dynamically altered, highlighting known links to the epigenome and proposing other plausible connections.
    Keywords:  acetylation; acylation; chromatin; circadian cycles; dietary challenges; methylation
  10. Cell Metab. 2020 May 05. pii: S1550-4131(20)30197-2. [Epub ahead of print]
    Bharath LP, Agrawal M, McCambridge G, Nicholas DA, Hasturk H, Liu J, Jiang K, Liu R, Guo Z, Deeney J, Apovian CM, Snyder-Cappione J, Hawk GS, Fleeman RM, Pihl RMF, Thompson K, Belkina AC, Cui L, Proctor EA, Kern PA, Nikolajczyk BS.
      Age is a non-modifiable risk factor for the inflammation that underlies age-associated diseases; thus, anti-inflammaging drugs hold promise for increasing health span. Cytokine profiling and bioinformatic analyses showed that Th17 cytokine production differentiates CD4+ T cells from lean, normoglycemic older and younger subjects, and mimics a diabetes-associated Th17 profile. T cells from older compared to younger subjects also had defects in autophagy and mitochondrial bioenergetics that associate with redox imbalance. Metformin ameliorated the Th17 inflammaging profile by increasing autophagy and improving mitochondrial bioenergetics. By contrast, autophagy-targeting siRNA disrupted redox balance in T cells from young subjects and activated the Th17 profile by activating the Th17 master regulator, STAT3, which in turn bound IL-17A and F promoters. Mitophagy-targeting siRNA failed to activate the Th17 profile. We conclude that metformin improves autophagy and mitochondrial function largely in parallel to ameliorate a newly defined inflammaging profile that echoes inflammation in diabetes.
    Keywords:  T cells; autophagy; inflammaging; metformin; mitochondria
  11. J Mol Cell Cardiol. 2020 May 07. pii: S0022-2828(20)30120-6. [Epub ahead of print]
    Liu JC.
      The uptake of Ca2+ into mitochondria is thought to be an important signal communicating the need for increased energy production. However, dysregulated uptake leading to mitochondrial Ca2+ overload can trigger opening of the mitochondrial permeability transition pore and potentially cell death. Thus mitochondrial Ca2+ entry is regulated via the activity of a Ca2+-selective channel known as the mitochondrial calcium uniporter. The last decade has seen enormous momentum in the discovery of the molecular identities of the multiple proteins comprising the uniporter. Increasing numbers of studies in cultured cells and animal models have provided insight into how disruption of uniporter proteins affects mitochondrial Ca2+ regulation and impacts tissue function and physiology. This review aims to summarize some of these recent findings, particularly in the context of the heart.
  12. Trends Biochem Sci. 2020 Jun;pii: S0968-0004(20)30055-4. [Epub ahead of print]45(6): 459-461
    Hobbs GA, Der CJ.
      The RAS oncoprotein drives elevated macropinocytosis, a metabolic process essential for cancer growth. A recent study by Ramirez et al. elucidated a mechanism whereby RAS controls V-ATPase association with the plasma membrane to drive RAC1 GTPase-dependent macropinocytosis. Potentially actionable targets to disrupt this RAS-dependent nutrient acquisition pathway were identified.
    Keywords:  KRAS; SLC4A7; V-ATPase; cancer metabolism; macropinocytosis
  13. Trends Cell Biol. 2020 Jun;pii: S0962-8924(20)30054-4. [Epub ahead of print]30(6): 478-490
    Stockwell BR, Jiang X, Gu W.
      Cell death is an essential feature of development in multicellular organisms, a critical driver of degenerative diseases, and can be harnessed for treating some cancers. Understanding the mechanisms governing cell death is critical for addressing its role in disease. Similarly, metabolism is essential for normal energy and biomolecule production, and goes awry in many diseases. Metabolism and cell death are tightly linked in the phenomenon of ferroptosis, a form of regulated cell death driven by peroxidation of phospholipids. Glutathione peroxidase 4 (GPX4) uses glutathione to protect cells from ferroptosis by eliminating phospholipid peroxides. Recent data have revealed glutathione/GPX4-independent axes for suppressing ferroptosis, and insight into the regulation of iron and mitochondria in ferroptosis. Ferroptosis has recently been implicated in multiple diseases, and functions as a tumor suppression mechanism. Ferroptosis induction is a promising approach in treating several conditions, including neoplastic diseases. Here, we summarize these recent advances.
    Keywords:  ferroptosis; iron; lipid peroxidation; metabolism; ubiquinone, cancer
  14. Front Endocrinol (Lausanne). 2020 ;11 232
    Schultz J, Warkus J, Wolke C, Waterstradt R, Baltrusch S.
      Background: Mitochondrial dynamics are important for glucose-stimulated insulin secretion in pancreatic beta cells. The mitochondrial elongation factor MiD51 has been proposed to act as an anchor that recruits Drp1 from the cytosol to the outer mitochondrial membrane. Whether MiD51 promotes mitochondrial fusion by inactivation of Drp1 is a controversial issue. Since both the underlying mechanism and the effects on mitochondrial function remain unknown, this study was conducted to investigate the role of MiD51 in beta cells. Methods: Overexpression and downregulation of MiD51 in mouse insulinoma 6 (MIN6) and mouse islet cells was achieved using the pcDNA expression vector and specific siRNA, respectively. Expression of genes regulating mitochondrial dynamics and autophagy was analyzed by quantitative Real-Time PCR, glucose-stimulated insulin secretion by ELISA, and cellular oxygen consumption rate by optode sensor technology. Mitochondrial membrane potential and morphology were visualized after TMRE and MitoTracker Green staining, respectively. Immunofluorescence analyses were examined by confocal microscopy. Results: MiD51 is expressed in insulin-positive mouse and human pancreatic islet and MIN6 cells. Overexpression of MiD51 resulted in mitochondrial fragmentation and cluster formation in MIN6 cells. Mitochondrial membrane potential, glucose-induced oxygen consumption rate and glucose-stimulated insulin secretion were reduced in MIN6 cells with high MiD51 expression. LC3 expression remained unchanged. Downregulation of MiD51 resulted in inhomogeneity of the mitochondrial network in MIN6 cells with hyperelongated and fragmented mitochondria. Mitochondrial membrane potential, maximal and glucose-induced oxygen consumption rate and insulin secretion were diminished in MIN6 cells with low MiD51 expression. Furthermore, reduced Mfn2 and Parkin expression was observed. Based on MiD51 overexpression and downregulation, changes in the mitochondrial network structure similar to those in MIN6 cells were also observed in mouse islet cells. Conclusion: We have demonstrated that MiD51 plays a pivotal role in regulating mitochondrial function and hence insulin secretion in MIN6 cells. We propose that this anchor protein of Drp1 is important to maintain a homogeneous mitochondrial network and to avoid morphologies such as hyperelongation and clustering which are inaccessible for degradation by autophagy. Assuming that insulin granule degradation frequently suppresses autophagy in beta cells, MiD51 could be a key element maintaining mitochondrial health.
    Keywords:  MiD51; mitochondrial dynamics; mitochondrial fission; mitophagy; pancreatic beta cells
  15. Cell Rep. 2020 May 12. pii: S2211-1247(20)30578-7. [Epub ahead of print]31(6): 107625
    Brunton H, Caligiuri G, Cunningham R, Upstill-Goddard R, Bailey UM, Garner IM, Nourse C, Dreyer S, Jones M, Moran-Jones K, Wright DW, Paulus-Hock V, Nixon C, Thomson G, Jamieson NB, McGregor GA, Evers L, McKay CJ, Gulati A, Brough R, Bajrami I, Pettitt SJ, Dziubinski ML, Barry ST, Grützmann R, Brown R, Curry E, , , Pajic M, Musgrove EA, Petersen GM, Shanks E, Ashworth A, Crawford HC, Simeone DM, Froeling FEM, Lord CJ, Mukhopadhyay D, Pilarsky C, Grimmond SE, Morton JP, Sansom OJ, Chang DK, Bailey PJ, Biankin AV.
      Pancreatic ductal adenocarcinoma (PDAC) can be divided into transcriptomic subtypes with two broad lineages referred to as classical (pancreatic) and squamous. We find that these two subtypes are driven by distinct metabolic phenotypes. Loss of genes that drive endodermal lineage specification, HNF4A and GATA6, switch metabolic profiles from classical (pancreatic) to predominantly squamous, with glycogen synthase kinase 3 beta (GSK3β) a key regulator of glycolysis. Pharmacological inhibition of GSK3β results in selective sensitivity in the squamous subtype; however, a subset of these squamous patient-derived cell lines (PDCLs) acquires rapid drug tolerance. Using chromatin accessibility maps, we demonstrate that the squamous subtype can be further classified using chromatin accessibility to predict responsiveness and tolerance to GSK3β inhibitors. Our findings demonstrate that distinct patterns of chromatin accessibility can be used to identify patient subgroups that are indistinguishable by gene expression profiles, highlighting the utility of chromatin-based biomarkers for patient selection in the treatment of PDAC.
    Keywords:  GATA6; GSK3B; HNF4A; PDAC subtypes; chromatin landscapes; intronic and distal promoters; metabolic targeting; therapeutic tolerance
  16. Cancer Cell. 2020 Apr 27. pii: S1535-6108(20)30204-X. [Epub ahead of print]
    Tajan M, Vousden KH.
      The concept that dietary changes could improve the response to cancer therapy is extremely attractive to many patients, who are highly motivated to take control of at least some aspect of their treatment. Growing insight into cancer metabolism is highlighting the importance of nutrient supply to tumor development and therapeutic response. Cancers show diverse metabolic requirements, influenced by factors such as tissue of origin, microenvironment, and genetics. Dietary modulation will therefore need to be matched to the specific characteristics of both cancers and treatment, a precision approach requiring a detailed understanding of the mechanisms that determine the metabolic vulnerabilities of each cancer.
    Keywords:  Diet; cancer; metabolism; nonessential amino acids; therapy
  17. Mol Cell Oncol. 2020 ;7(3): 1735284
    Lukey MJ, Greene KS, Cerione RA.
      The metabolic microenvironment of tumors is characterized by fluctuating and limited nutrient availability. To survive these conditions, cancer cell-intrinsic mechanisms sense and signal nutritional status. We describe how glutaminase (GLS) is destabilized by lysine succinylation and stabilized by the NAD+-dependent desuccinylase sirtuin 5 (SIRT5), coupling nutrient levels to metabolic flux.
    Keywords:  GLS; SIRT5; cancer-metabolism; glutamine; succinylation
  18. Blood. 2020 May 13. pii: blood.2019003257. [Epub ahead of print]
    Hesterberg RS, Beatty MS, Han Y, Fernandez MR, Akuffo AA, Goodheart WE, Yang C, Chang S, Colin C, Alontaga AY, McDaniel J, Mailloux AW, Billington JMR, Yue L, Russell S, Gillies RJ, Yun SY, Ayaz M, Lawrence NJ, Lawrence H, Yu XZ, Fu J, Darville LN, Koomen JM, Ren X, Messina J, Jiang K, Garrett TJ, Rajadhyaksha A, Cleveland JL, Epling-Burnette PK.
      Immunomodulatory drugs, such as thalidomide and related compounds, potentiate T-cell effector functions. Cereblon (CRBN), a substrate receptor of the DDB1-cullin-RING E3 ubiquitin ligase complex, is the only known molecular target for this drug class, where drug-induced ubiquitin-dependent degradation of "neo-substrates" such as IKAROS, AIOLOS, and CK1α accounts for their biological activity. Far less clear is whether these Cereblon E3 ligase modulating compounds disrupt the endogenous functions of CRBN. Strikingly, here we report that CRBN functions in a feedback loop that harnesses antigen-specific CD8+ T-cell effector responses. Specifically, Crbn deficiency in murine CD8+ T-cells augments their central metabolism manifest as elevated bioenergetics, with supraphysiological levels of polyamines secondary to enhanced glucose and amino acid transport, and with increased expression of metabolic enzymes, including the polyamine biosynthetic enzyme ornithine decarboxylase. Importantly, treatment with Celeblon-modulatingcompounds similarly augments central metabolism of human CD8+T-cell. Notably, the metabolic control of CD8+ T-cells by modulating compounds or Crbn deficiency is linked to increased and sustained expression of the master metabolic regulator MYC. Finally, Crbn deficient T-cells have augmented antigen-specific cytolytic activity versus melanoma tumor cells ex vivo and in vivo and drive accelerated and highly aggressive graft-versus-host disease. Therefore, CRBN functions to harness the activation of activated CD8+ T-cells and this phenotype can be exploited by treatment with drugs.
  19. Redox Biol. 2020 Apr 27. pii: S2213-2317(20)30347-5. [Epub ahead of print]34 101549
    Penjweini R, Roarke B, Alspaugh G, Gevorgyan A, Andreoni A, Pasut A, Sackett DL, Knutson JR.
      Oxidation-reduction chemistry is fundamental to the metabolism of all living organisms, and hence quantifying the principal redox players is important for a comprehensive understanding of cell metabolism in normal and pathological states. In mammalian cells, this is accomplished by measuring oxygen partial pressure (pO2) in parallel with free and enzyme-bound reduced nicotinamide adenine dinucleotide (phosphate) [H] (NAD(P)H) and flavin adenine dinucleotide (FAD, a proxy for NAD+). Previous optical methods for these measurements had accompanying problems of cytotoxicity, slow speed, population averaging, and inability to measure all redox parameters simultaneously. Herein we present a Förster resonance energy transfer (FRET)-based oxygen sensor, Myoglobin-mCherry, compatible with fluorescence lifetime imaging (FLIM)-based measurement of nicotinamide coenzyme state. This offers a contemporaneous reading of metabolic activity through real-time, non-invasive, cell-by-cell intracellular pO2 and coenzyme status monitoring in living cells. Additionally, this method reveals intracellular spatial heterogeneity and cell-to-cell variation in oxygenation and coenzyme states.
    Keywords:  FAD; FLIM; FLIRR; Free and bound NAD(P)H; Myo-mCherry; ORR
  20. Trends Endocrinol Metab. 2020 Jun;pii: S1043-2760(20)30050-3. [Epub ahead of print]31(6): 459-468
    Peek CB.
      Research over the past few decades has shed light on the mechanisms underlying the link between circadian disruption and the development of metabolic diseases such as obesity, type 2 diabetes, and cancer. However, how the clock network interacts with tissue-specificnutrient-sensing pathways during conditions of nutrient stress or pathological states remains incompletely understood. Recent work has demonstrated that the circadian clock can 'reprogram' the transcriptome to control distinct sets of genes during altered nutrient conditions, such as high fat diet, aging, and exercise. In this review, I discuss connections between circadian clock transcription factors and the oxygen- and nutrient-responsivehypoxia-inducible factor (HIF) pathway. I highlight recently uncovered mechanistic insights underlying these pathway interactions and address potential implications for the role of circadian disruption in metabolic diseases.
  21. Immunol Med. 2020 May 12. 1-6
    Iwasaki Y, Takeshima Y, Fujio K.
      Almost 160 years after the discovery of mitochondria, they are known for their production of energy and are called "the powerhouse of the cell". Recently, immune-metabolism has been revealed as a key factor controlling immune cell proliferation and differentiation. Resting lymphocytes generate energy through oxidative phosphorylation and fatty acid oxidation, whereas activated lymphocytes rapidly shift to glycolysis. Oxidative phosphorylation (OXPHOS) as well as mitochondrial reactive oxygen species (mtROS) generated through the electron transport chain (ETC) are involved in many immune cell functions. Moreover, mitochondria are dynamic organelles that can provide immunogenic molecules, such as mitochondrial DNA (mtDNA) resulting in innate immune system activation. Here, we describe the role of mitochondria in immune system regulation, highlighting metabolism-dependent and other immunogenic aspects.
    Keywords:  Mitochondrial dysfunction; OXPHOS; autoimmune diseases; mtDNA; mtROS
  22. Autophagy. 2020 May 13. 1-17
    Ko MS, Yun JY, Baek IJ, Jang JE, Hwang JJ, Lee SE, Heo SH, Bader DA, Lee CH, Han J, Moon JS, Lee JM, Hong EG, Lee IK, Kim SW, Park JY, Hartig SM, Kang UJ, Moore DD, Koh EH, Lee KU.
      Although macroautophagy/autophagy deficiency causes degenerative diseases, the deletion of essential autophagy genes in adipocytes paradoxically reduces body weight. Brown adipose tissue (BAT) plays an important role in body weight regulation and metabolic control. However, the key cellular mechanisms that maintain BAT function remain poorly understood. in this study, we showed that global or brown adipocyte-specific deletion of pink1, a Parkinson disease-related gene involved in selective mitochondrial autophagy (mitophagy), induced BAT dysfunction, and obesity-prone type in mice. Defective mitochondrial function is among the upstream signals that activate the NLRP3 inflammasome. NLRP3 was induced in brown adipocyte precursors (BAPs) from pink1 knockout (KO) mice. Unexpectedly, NLRP3 induction did not induce canonical inflammasome activity. Instead, NLRP3 induction led to the differentiation of pink1 KO BAPs into white-like adipocytes by increasing the expression of white adipocyte-specific genes and repressing the expression of brown adipocyte-specific genes. nlrp3 deletion in pink1 knockout mice reversed BAT dysfunction. Conversely, adipose tissue-specific atg7 KO mice showed significantly lower expression of Nlrp3 in their BAT. Overall, our data suggest that the role of mitophagy is different from general autophagy in regulating adipose tissue and whole-body energy metabolism. Our results uncovered a new mitochondria-NLRP3 pathway that induces BAT dysfunction. The ability of the nlrp3 knockouts to rescue BAT dysfunction suggests the transcriptional function of NLRP3 as an unexpected, but a quite specific therapeutic target for obesity-related metabolic diseases.ABBREVIATIONS: ACTB: actin, beta; BAPs: brown adipocyte precursors; BAT: brown adipose tissue; BMDMs: bone marrow-derived macrophages; CASP1: caspase 1; CEBPA: CCAAT/enhancer binding protein (C/EBP), alpha; ChIP: chromatin immunoprecipitation; EE: energy expenditure; HFD: high-fat diet; IL1B: interleukin 1 beta; ITT: insulin tolerance test; KO: knockout; LPS: lipopolysaccharide; NLRP3: NLR family, pyrin domain containing 3; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RD: regular diet; ROS: reactive oxygen species; RT: room temperature; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); WT: wild-type.
    Keywords:  Brown adipocyte; inflammasome; pink1; transcriptional activation; white adipocyte
  23. Front Physiol. 2020 ;11 340
    Faienza F, Rizza S, Giglio P, Filomeni G.
    Keywords:  Parkinson's disease; S-nitrosylation; aging; cancer; mitochondria; tumor necrosis factor receptor-associated protein 1 (TRAP1)
  24. Front Cell Dev Biol. 2020 ;8 270
    Ravanelli S, den Brave F, Hoppe T.
      Mitochondria are essential organelles important for energy production, proliferation, and cell death. Biogenesis, homeostasis, and degradation of this organelle are tightly controlled to match cellular needs and counteract chronic stress conditions. Despite providing their own DNA, the vast majority of mitochondrial proteins are encoded in the nucleus, synthesized by cytosolic ribosomes, and subsequently imported into different mitochondrial compartments. The integrity of the mitochondrial proteome is permanently challenged by defects in folding, transport, and turnover of mitochondrial proteins. Therefore, damaged proteins are constantly sequestered from the outer mitochondrial membrane and targeted for proteasomal degradation in the cytosol via mitochondrial-associated degradation (MAD). Recent studies identified specialized quality control mechanisms important to decrease mislocalized proteins, which affect the mitochondrial import machinery. Interestingly, central factors of these ubiquitin-dependent pathways are shared with the ER-associated degradation (ERAD) machinery, indicating close collaboration between both tubular organelles. Here, we summarize recently described cellular stress response mechanisms, which are triggered by defects in mitochondrial protein import and quality control. Moreover, we discuss how ubiquitin-dependent degradation is integrated with cytosolic stress responses, particularly focused on the crosstalk between MAD and ERAD.
    Keywords:  C. elegans; Cdc48; Msp1; mitochondria; mitochondria-associated degradation (MAD); p97; proteostasis; ubiquitin
  25. Nat Commun. 2020 May 12. 11(1): 2375
    Ku AA, Hu HM, Zhao X, Shah KN, Kongara S, Wu D, McCormick F, Balmain A, Bandyopadhyay S.
      Synthetic lethal screens have the potential to identify new vulnerabilities incurred by specific cancer mutations but have been hindered by lack of agreement between studies. In the case of KRAS, we identify that published synthetic lethal screen hits significantly overlap at the pathway rather than gene level. Analysis of pathways encoded as protein networks could identify synthetic lethal candidates that are more reproducible than those previously reported. Lack of overlap likely stems from biological rather than technical limitations as most synthetic lethal phenotypes are strongly modulated by changes in cellular conditions or genetic context, the latter determined using a pairwise genetic interaction map that identifies numerous interactions that suppress synthetic lethal effects. Accounting for pathway, cellular and genetic context nominates a DNA repair dependency in KRAS-mutant cells, mediated by a network containing BRCA1. We provide evidence for why most reported synthetic lethals are not reproducible which is addressable using a multi-faceted testing framework.
  26. Front Mol Biosci. 2020 ;7 71
    Bhatia S, Wang P, Toh A, Thompson EW.
      Tumor cells demonstrate substantial plasticity in their genotypic and phenotypic characteristics. Epithelial-mesenchymal plasticity (EMP) can be characterized into dynamic intermediate states and can be orchestrated by many factors, either intercellularly via epigenetic reprograming, or extracellularly via growth factors, inflammation and/or hypoxia generated by the tumor stromal microenvironment. EMP has the capability to alter phenotype and produce heterogeneity, and thus by changing the whole cancer landscape can attenuate oncogenic signaling networks, invoke anti-apoptotic features, defend against chemotherapeutics and reprogram angiogenic and immune recognition functions. We discuss here the role of phenotypic plasticity in tumor initiation, progression and metastasis and provide an update of the modalities utilized for the molecular characterization of the EMT states and attributes of cellular behavior, including cellular metabolism, in the context of EMP. We also summarize recent findings in dynamic EMP studies that provide new insights into the phenotypic plasticity of EMP flux in cancer and propose therapeutic strategies to impede the metastatic outgrowth of phenotypically heterogeneous tumors.
    Keywords:  CTCs; EMP; EMT; hybrid EMT states; metabolism; metastasis; stem cell; tumor cell heterogeneity
  27. Nat Commun. 2020 May 15. 11(1): 2447
    Balachander S, Gombolay AL, Yang T, Xu P, Newnam G, Keskin H, El-Sayed WMM, Bryksin AV, Tao S, Bowen NE, Schinazi RF, Kim B, Koh KD, Vannberg FO, Storici F.
      Despite the abundance of ribonucleoside monophosphates (rNMPs) in DNA, sites of rNMP incorporation remain poorly characterized. Here, by using ribose-seq and Ribose-Map techniques, we built and analyzed high-throughput sequencing libraries of rNMPs derived from mitochondrial and nuclear DNA of budding and fission yeast. We reveal both common and unique features of rNMP sites among yeast species and strains, and between wild type and different ribonuclease H-mutant genotypes. We demonstrate that the rNMPs are not randomly incorporated in DNA. We highlight signatures and patterns of rNMPs, including sites within trinucleotide-repeat tracts. Our results uncover that the deoxyribonucleotide immediately upstream of the rNMPs has a strong influence on rNMP distribution, suggesting a mechanism of rNMP accommodation by DNA polymerases as a driving force of rNMP incorporation. Consistently, we find deoxyadenosine upstream from the most abundant genomic rCMPs and rGMPs. This study establishes a framework to better understand mechanisms of rNMP incorporation in DNA.
  28. Cell Rep. 2020 May 12. pii: S2211-1247(20)30585-4. [Epub ahead of print]31(6): 107632
    Na HJ, Akan I, Abramowitz LK, Hanover JA.
      Stem/progenitor cells exhibit high proliferation rates, elevated nutrient uptake, altered metabolic flux, and stress-induced genome instability. O-GlcNAcylation is an essential post-translational modification mediated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which act in a nutrient- and stress-responsive manner. The precise role of O-GlcNAc in adult stem cells and the relationship between O-GlcNAc and the DNA damage response (DDR) is poorly understood. Here, we show that hyper-O-GlcNacylation leads to elevated insulin signaling, hyperproliferation, and DDR activation that mimic the glucose- and oxidative-stress-induced response. We discover a feedback mechanism involving key downstream effectors of DDR, ATM, ATR, and CHK1/2 that regulates OGT stability to promote O-GlcNAcylation and elevate DDR. This O-GlcNAc-dependent regulatory pathway is critical for maintaining gut homeostasis in Drosophila and the DDR in mouse embryonic stem cells (ESCs) and mouse embryonic fibroblasts (MEFs). Our findings reveal a conserved mechanistic link among O-GlcNAc cycling, stem cell self-renewal, and DDR with profound implications for stem-cell-derived diseases including cancer.
    Keywords:  DDR; DNA damage response; Drosophila intestinal stem cell; ISC; MEF; O-GlcNAc transferase; O-GlcNAcase; O-GlcNAcylation; OGA; OGT; mESC; mouse embryonic fibroblast; mouse embryonic stem cell
  29. Redox Biol. 2020 Apr 25. pii: S2213-2317(20)30474-2. [Epub ahead of print]34 101548
    Noh MR, Kong MJ, Han SJ, Kim JI, Park KM.
      The development of hypertension is associated with mitochondrial redox balance disruptions. NADP+-dependent isocitrate dehydrogenase 2 (IDH2) plays an important role in the maintenance of mitochondrial redox balance by producing mitochondrial NADPH, which is an essential cofactor in the reduction of glutathione (from GSSG to GSH) to reduced form of glutathione (GSH). We investigated the association of IDH2 between the development of prolonged high-fat diet (HFD)-induced hypertension. Idh2 gene-deleted (Idh2-/-) male mice and wild-type (Idh2+/+) littermates were fed either HFD or low-fat diet (LFD). Some mice were administrated with Mito-TEMPO, a mitochondria-specific antioxidant. HFD feeding increased blood pressure (BP) in both Idh2-/- mice and Idh2+/+ mice. HFD-induced BP increase was greater in Idh2-/- than Idh2+/+ mice. HFD intake decreased IDH2 activity, NADPH levels, and the GSH/(GSH + GSSG) ratio in the renal mitochondria. However, HFD intake increased mitochondrial ROS levels, along with the accompanying oxidative stress and damage. HFD intake increased angiotensin II receptor 1 type 1 mRNA levels in the kidneys and plasma renin and angiotensin II concentrations. These HFD-induced changes were more prominent in Idh2-/- mice than Idh2+/+ mice. Mito-TEMPO mitigated the HFD-induced changes in both Idh2-/- and Idh2+/+ mice, with greater effects in Idh2-/- mice than Idh2+/+ mice. These results indicate that prolonged HFD intake disrupts the IDH2-NADPH-GSH-associated antioxidant system and activates the renin-angiotensin system in the kidney, leading to increased BP, suggesting that IDH2 is a critical enzyme in the development of hypertension and that the IDH2-associated antioxidant system could serve as a potential hypertension treatment target.
    Keywords:  Hypertension; Isocitrate dehydrogenase 2; Mitochondria; Reactive oxygen species; Renin-angiotensin system
  30. DNA Cell Biol. 2020 May 12.
    Martín-Jiménez R, Lurette O, Hebert-Chatelain E.
      Mitochondria are the only organelles that contain their own genetic material (mtDNA). Mitochondria are involved in several key physiological functions, including ATP production, Ca2+ homeostasis, and metabolism of neurotransmitters. Since these organelles perform crucial processes to maintain neuronal homeostasis, mitochondrial dysfunctions can lead to various neurodegenerative diseases. Several mitochondrial proteins involved in ATP production are encoded by mtDNA. Thus, any mtDNA alteration can ultimately lead to mitochondrial dysfunction and cell death. Accumulation of mutations, deletions, and rearrangements in mtDNA has been observed in animal models and patients suffering from Parkinson's disease (PD). Also, specific inherited variations associated with mtDNA genetic groups (known as mtDNA haplogroups) are associated with lower or higher risk of developing PD. Consequently, mtDNA alterations should now be considered important hallmarks of this neurodegenerative disease. This review provides an update about the role of mtDNA alterations in the physiopathology of PD.
    Keywords:  Parkinson's disease; mitochondria; mtDNA
  31. Cell Rep. 2020 May 12. pii: S2211-1247(20)30576-3. [Epub ahead of print]31(6): 107623
    Davis JC, Alves TC, Helman A, Chen JC, Kenty JH, Cardone RL, Liu DR, Kibbey RG, Melton DA.
      Stem cell-derived β (SC-β) cells could provide unlimited human β cells toward a curative diabetes treatment. Differentiation of SC-β cells yields transplantable islets that secrete insulin in response to glucose challenges. Following transplantation into mice, SC-β cell function is comparable to human islets, but the magnitude and consistency of response in vitro are less robust than observed in cadaveric islets. Here, we profile metabolism of SC-β cells and islets to quantify their capacity to sense glucose and identify reduced anaplerotic cycling in the mitochondria as the cause of reduced glucose-stimulated insulin secretion in SC-β cells. This activity can be rescued by challenging SC-β cells with intermediate metabolites from the TCA cycle and late but not early glycolysis, downstream of the enzymes glyceraldehyde 3-phosphate dehydrogenase and phosphoglycerate kinase. Bypassing this metabolic bottleneck results in a robust, bi-phasic insulin release in vitro that is identical in magnitude to functionally mature human islets.
    Keywords:  GSIS; MIMOSA; differentiation; glucose-stimulated insulin secretion; metabolic profiling; stem cell metabolism; stem cell-derived β cell; β-cell metabolism
  32. Nat Chem Biol. 2020 May 11.
    Ghergurovich JM, García-Cañaveras JC, Wang J, Schmidt E, Zhang Z, TeSlaa T, Patel H, Chen L, Britt EC, Piqueras-Nebot M, Gomez-Cabrera MC, Lahoz A, Fan J, Beier UH, Kim H, Rabinowitz JD.
      Glucose is catabolized by two fundamental pathways, glycolysis to make ATP and the oxidative pentose phosphate pathway to make reduced nicotinamide adenine dinucleotide phosphate (NADPH). The first step of the oxidative pentose phosphate pathway is catalyzed by the enzyme glucose-6-phosphate dehydrogenase (G6PD). Here we develop metabolite reporter and deuterium tracer assays to monitor cellular G6PD activity. Using these, we show that the most widely cited G6PD antagonist, dehydroepiandosterone, does not robustly inhibit G6PD in cells. We then identify a small molecule (G6PDi-1) that more effectively inhibits G6PD. Across a range of cultured cells, G6PDi-1 depletes NADPH most strongly in lymphocytes. In T cells but not macrophages, G6PDi-1 markedly decreases inflammatory cytokine production. In neutrophils, it suppresses respiratory burst. Thus, we provide a cell-active small molecule tool for oxidative pentose phosphate pathway inhibition, and use it to identify G6PD as a pharmacological target for modulating immune response.
  33. Mitochondrion. 2020 May 05. pii: S1567-7249(20)30012-X. [Epub ahead of print]53 57-65
    Huang S, Li L, Petereit J, Millar AH.
      Plant mitochondria operate as the powerhouses for cellular energy production by using the combined functions of both imported and organelle-synthesised proteins. Homeostasis of mitochondrial proteins is controlled by both synthesis and degradation processes which together define protein turnover in this organelle. Better understanding of plant mitochondrial protein turnover will provide information on protein quality control inside these organelles and its importance for proper function and regulation of mitochondrial machinery. This review discusses methods used for measurement of turnover rates of plant mitochondrial proteins and presents our current understanding of these rates for key mitochondrial proteins and protein complexes. The assembly and maintenance of mitochondrial OXPHOS complexes, in particular Complexes I and V, will be discussed in detail based on the evidence for differential protein turnover rates of the same protein subunits in different mitochondrial fractions. The impact of the loss of specific plant mitochondrial proteases on proteolysis events and rates of mitochondrial protein turnover will be highlighted. The challenges and future directions for investigation of plant mitochondrial protein turnover are also discussed.
    Keywords:  Plant mitochondria; Proteases; Protein complex assembly; Protein turnover; Proteostasis
  34. ACS Chem Biol. 2020 May 12.
    Downes DP, Daurio NA, McLaren DG, Carrington P, Previs SF, Williams KB.
      Lipid oxidation and biosynthesis are crucial for cell survival, especially for rapidly proliferating cancer cells in a heterogeneous metabolic environment. Storage of high energy lipid reservoirs competitively advantages the cancer cell over non-neoplastic tissue. Disrupting lipid biosynthetic processes, through modulation of fatty acid (FA) esterification or de novo lipogenesis (DNL), is of interest in drug discovery. Mimicking the in vivo environment in vitro is also vital for testing the efficacy of potential drug compounds. We present here a stable isotope tracer-based approach for examining the impact of exogenous FA and oxygen tension on the pathways that affect lipid biosynthesis, including the rates of metabolic flux. By applying tandem mass spectrometry (MS/MS) analyses, to studies using parallel tracers, we characterized the impact of FA bioavailability on the positional enrichment within specific lipids. Our observations suggest that adding bioavailable FA as a carbon source preferentially biases the cellular metabolism away from DNL and towards esterification of free fatty acid pools. Additionally, we have found that this FA addition, under hypoxic conditions, led to biased increase in the total triglyceride pool (nearly 5-fold, as compared to phospholipids), regardless of the isotope tracer utilized. We discuss the implications of this metabolic flexibility on studies that aim to characterize apparent drug efficacy.
  35. J Biol Chem. 2020 May 11. pii: jbc.AW120.011105. [Epub ahead of print]
    Schaffer JE.
      Excess fatty acid accumulation in non-adipose tissues leads to cell dysfunction and cell death that is linked to the pathogenesis of inherited and acquired human diseases. Study of this process, known as lipotoxicity, has provided new insights into the regulation of lipid homeostasis and has revealed new molecular pathways involved in lipid-induced cellular stress. The discovery that disruption of specific small nucleolar RNAs protects against fatty acid-induced cell death and remodels metabolism in vivo opens new opportunities for understanding how nutrient signals influence cellular and systemic metabolic homeostasis through RNA biology.
    Keywords:  RNA; diabetes; diabetes complications; fatty acid; genetic screens; lipotoxicity; non-coding RNAs; snoRNAs; triacylglycerol
  36. Trends Cell Biol. 2020 May 05. pii: S0962-8924(20)30091-X. [Epub ahead of print]
    Baik AH, Jain IH.
      Oxygen is both vital and toxic to life. Molecular oxygen is the most used substrate in the human body and is required for several hundred diverse biochemical reactions. The discovery of the PHD-HIF-pVHL system revolutionized our fundamental understanding of oxygen sensing and cellular adaptations to hypoxia. It deepened our knowledge of the biochemical underpinnings of numerous diseases, ranging from anemia to cancer. Cellular dysfunction and tissue pathology can result from a mismatch of oxygen supply and demand. Recent work has shown that mitochondrial disease models display tissue hyperoxia and that disease pathology can be reversed by normalization of excess oxygen, suggesting that certain disease states can potentially be treated by modulating oxygen levels. In this review, we describe cellular and organismal mechanisms of oxygen sensing and adaptation. We provide a revitalized framework for understanding pathologies of too little or too much oxygen.
    Keywords:  hyperoxia; hypoxia; oxygen adaptation; oxygen metabolism; oxygen sensing
  37. J Neurosci. 2020 May 11. pii: JN-RM-2067-19. [Epub ahead of print]
    Watters O, Connolly NMC, König HG, Düssmann H, Prehn JHM.
      Mitochondrial clusters are found at regions of high energy demand, allowing cells to meet local metabolic requirements while maintaining neuronal homeostasis. AMP-activated protein kinase (AMPK), a key energy stress sensor, responds to increases in AMP/ATP ratio by activating multiple signalling cascades to overcome the energetic deficiency. In many neurological conditions, the distal axon experiences energetic stress independent of the soma. Here, we used microfluidic devices to physically isolate these two neuronal structures and to investigate whether localised AMPK signalling influenced axonal mitochondrial transport. Nucleofection of primary cortical neurons, derived from E16 mouse embryos (both sexes), with mito-GFP allowed monitoring of the transport dynamics of mitochondria within the axon, by confocal microscopy.Pharmacological activation of AMPK at the distal axon (0.1 mM AICAR) induced a depression of the mean frequency, velocity and distance of retrograde mitochondrial transport in the adjacent axon. Anterograde mitochondrial transport was less sensitive to local AMPK stimulus, with the imbalance of bi-directional mitochondrial transport resulting in accumulation of mitochondria at the region of energetic stress signal. Mitochondria in the axon-rich white matter of the brain rely heavily on lactate as a substrate for ATP synthesis. Interestingly, localised inhibition of lactate uptake (10 nM AR-C155858) reduced mitochondrial transport in the adjacent axon in all parameters measured, similar to that observed by AICAR treatment. Co-addition of compound C restored all parameters measured to baseline levels, confirming the involvement of AMPK. This study highlights a role of AMPK signalling in the depression of axonal mitochondrial mobility during localised energetic stress.SIGNIFICANCE STATEMENTAs the main providers of cellular energy, the dynamic transport of mitochondria within the neuron allows for clustering at regions of high energy demand. Here we investigate whether acute changes in energetic stress signal in the spatially isolated axon would alter mitochondrial transport in this local region. Both direct and indirect activation of AMP-activated protein kinase (AMPK) isolated to the distal axon induced a rapid, marked depression in local mitochondrial transport. This work highlights the ability of acute localised AMPK signalling to affect mitochondrial mobility within the axon, with important implications for white matter injury, axonal growth and axonal degeneration.
  38. EMBO Rep. 2020 May 10. e47872
    Grieschat M, Guzman RE, Langschwager K, Fahlke C, Alekov AK.
      CLC anion/proton exchangers control the pH and [Cl- ] of the endolysosomal system that is essential for cellular nutrient uptake. Here, we use heterologous expression and whole-cell electrophysiology to investigate the regulation of the CLC isoforms ClC-3, ClC-4, and ClC-5 by the adenylic system components ATP, ADP, and AMP. Our results show that cytosolic ATP and ADP but not AMP and Mg2+ -free ADP enhance CLC ion transport. Biophysical analysis reveals that adenine nucleotides alter the ratio between CLC ion transport and CLC gating charge and shift the CLC voltage-dependent activation. The latter effect is suppressed by blocking the intracellular entrance of the proton transport pathway. We suggest, therefore, that adenine nucleotides regulate the internal proton delivery into the CLC transporter machinery and alter the probability of CLC transporters to undergo silent non-transporting cycles. Our findings suggest that the CBS domains in mammalian CLC transporters serve as energy sensors that regulate vesicular Cl- /H+ exchange by detecting changes in the cytosolic ATP/ADP/AMP equilibrium. Such sensing mechanism links the endolysosomal activity to the cellular metabolic state.
    Keywords:  CBS domain; CLC transporter; adenine nucleotide regulation
  39. Nat Commun. 2020 May 11. 11(1): 2345
    Su Y, Ko ME, Cheng H, Zhu R, Xue M, Wang J, Lee JW, Frankiw L, Xu A, Wong S, Robert L, Takata K, Yuan D, Lu Y, Huang S, Ribas A, Levine R, Nolan GP, Wei W, Plevritis SK, Li G, Baltimore D, Heath JR.
      The determination of individual cell trajectories through a high-dimensional cell-state space is an outstanding challenge for understanding biological changes ranging from cellular differentiation to epigenetic responses of diseased cells upon drugging. We integrate experiments and theory to determine the trajectories that single BRAFV600E mutant melanoma cancer cells take between drug-naive and drug-tolerant states. Although single-cell omics tools can yield snapshots of the cell-state landscape, the determination of individual cell trajectories through that space can be confounded by stochastic cell-state switching. We assayed for a panel of signaling, phenotypic, and metabolic regulators at points across 5 days of drug treatment to uncover a cell-state landscape with two paths connecting drug-naive and drug-tolerant states. The trajectory a given cell takes depends upon the drug-naive level of a lineage-restricted transcription factor. Each trajectory exhibits unique druggable susceptibilities, thus updating the paradigm of adaptive resistance development in an isogenic cell population.
  40. Oncogene. 2020 May 12.
    Shmulevich R, Nissim TB, Wolf I, Merenbakh-Lamin K, Fishman D, Sekler I, Rubinek T.
      Klotho is a transmembrane protein, which can be shed and act as a circulating hormone and is involved in regulating cellular calcium levels and inhibition of the PI3K/AKT pathway. As a longevity hormone, it protects normal cells from oxidative stress, and as a tumor suppressor it inhibits growth of cancer cells. Mechanisms governing these differential activities have not been addressed. Altered cellular metabolism is a hallmark of cancer and dysregulation of mitochondrial activity is a hallmark of aging. We hypothesized that klotho exerts its differential effects through regulation of these two hallmarks. Treatment with klotho inhibited glycolysis, reduced mitochondrial activity and membrane potential only in cancer cells. Accordingly, global metabolic screen revealed that klotho altered pivotal metabolic pathways, amongst them glycolysis and tricarboxylic acid cycle in breast cancer cells. Alteration of metabolic activity and increased AMP/ATP ratio lead to LKB1-dependent AMPK activation. Indeed, klotho induced AMPK phosphorylation; furthermore, inhibition of LKB1 partially abolished klotho's tumor suppressor activity. By diminishing deltapsi (Δψ) klotho also inhibited mitochondria Ca2+ shuttling thereby impairing mitochondria communication with SOCE leading to reduced Ca2+ influx by SOCE channels. The reduced SOCE was followed by ER Ca2+ depletion and stress. These data delineate mechanisms mediating the differential effects of klotho toward cancer versus normal cells, and indicate klotho as a potent regulator of metabolic activity.
  41. Metabolites. 2020 May 13. pii: E193. [Epub ahead of print]10(5):
    Lei C, Chen J, Li H, Fan T, Zheng X, Wang H, Zhang N, Liu Y, Luo X, Wang J, Wang A.
      The activation of the Ras signaling pathway is a crucial process in hepatocarcinogenesis. Till now, no reports have scrutinized the role of dynamic metabolic changes in Ras oncogene-induced transition of the normal and precancerous liver cells to hepatocellular carcinoma in vivo. In the current study, we attempted a comprehensive investigation of Hras12V transgenic mice (Ras-Tg) by concatenating nontargeted metabolomics, transcriptomics analysis, and targeted-metabolomics incorporating [U-13C] glucose. A total of 631 peaks were detected, out of which 555 metabolites were screened. Besides, a total of 122 differently expressed metabolites (DEMs) were identified, and they were categorized and subtyped with the help of variation tendency analysis of the normal (W), precancerous (P), and hepatocellular carcinoma (T) liver tissues. Thus, the positive or negative association between metabolites and the hepatocellular carcinoma and Ras oncogene were identified. The bioinformatics analysis elucidated the hepatocarcinogenesis-associated significant metabolic pathways: glycolysis, mitochondrial citrate-malate shuttle, lipid biosynthesis, pentose phosphate pathway (PPP), cholesterol and bile acid biosynthesis, and glutathione metabolism. The key metabolites and enzymes identified in this analysis were further validated. Moreover, we confirmed the PPP, glycolysis, and conversion of pyruvate to cytosol acetyl-CoA by mitochondrial citrate-malate shuttle, in vivo, by incorporating [U-13C] glucose. In summary, the current study presented the comprehensive bioinformatics analysis, depicting the Ras oncogene-induced dynamic metabolite variations in hepatocarcinogenesis. A significant finding of our study was that the mitochondrial citrate-malate shuttle plays a crucial role in detoxification of lactic acid, maintenance of mitochondrial integrity, and enhancement of lipid biosynthesis, which, in turn, promotes hepatocarcinogenesis.
    Keywords:  Ras oncogene; hepatocarcinogenesis; metabolomics; mitochondrial citrate-malate shuttle; transcriptomics
  42. Nat Rev Cancer. 2020 May 13.
    Levine AJ.
      The evolutionarily conserved p53 protein and its cellular pathways mediate tumour suppression through an informed, regulated and integrated set of responses to environmental perturbations resulting in either cellular death or the maintenance of cellular homeostasis. The p53 and MDM2 proteins form a central hub in this pathway that receives stressful inputs via MDM2 and respond via p53 by informing and altering a great many other pathways and functions in the cell. The MDM2-p53 hub is one of the hubs most highly connected to other signalling pathways in the cell, and this may be why TP53 is the most commonly mutated gene in human cancers. Initial or truncal TP53 gene mutations (the first mutations in a stem cell) are selected for early in cancer development inectodermal and mesodermal-derived tissue-specific stem and progenitor cells and then, following additional mutations, produce tumours from those tissue types. In endodermal-derived tissue-specific stem or progenitor cells, TP53 mutations are functionally selected as late mutations transitioning the mutated cell into a malignant tumour. The order in which oncogenes or tumour suppressor genes are functionally selected for in a stem cell impacts the timing and development of a tumour.
  43. Cell Metab. 2020 May 11. pii: S1550-4131(20)30235-7. [Epub ahead of print]
    Aon MA, Bernier M, Mitchell SJ, Di Germanio C, Mattison JA, Ehrlich MR, Colman RJ, Anderson RM, de Cabo R.
      The impact of chronic caloric restriction (CR) on health and survival is complex with poorly understood underlying molecular mechanisms. A recent study in mice addressing the diets used in nonhuman primate CR studies found that while diet composition did not impact longevity, fasting time and total calorie intake were determinant for increased survival. Here, integrated analysis of physiological and multi-omics data from ad libitum, meal-fed, or CR animals was used to gain insight into pathways associated with improved health and survival. We identified a potential involvement of the glycine-serine-threonine metabolic axis in longevity and related molecular mechanisms. Direct comparison of the different feeding strategies unveiled a pattern of shared pathways of improved health that included short-chain fatty acids and essential PUFA metabolism. These findings were recapitulated in the serum metabolome from nonhuman primates. We propose that the pathways identified might be targeted for their potential role in healthy aging.
    Keywords:  aging; calorie restriction; calories; dietary interventions; dietary restriction; fasting; meal fed; metabolism; metabolomics; time-restricted feeding
  44. Sci Transl Med. 2020 May 13. pii: eaay7591. [Epub ahead of print]12(543):
    Yu X, Xu M, Meng X, Li S, Liu Q, Bai M, You R, Huang S, Yang L, Zhang Y, Jia Z, Zhang A.
      Acute kidney injury (AKI) is a worldwide public health problem with no specific and satisfactory therapies in clinic. The nuclear pregnane X receptor (PXR) is involved in the progression of multiple diseases, including metabolic diseases, atherosclerosis, hypertension, liver injury, etc. However, its role in kidney injury remains to be understood. In this study, we have investigated the role of PXR in AKI and underlying mechanism(s) involved in its function. PXR was robustly down-regulated and negatively correlated with renal dysfunction in human and animal kidneys with AKI. Silencing PXR in rats enhanced cisplatin-induced AKI and induced severe mitochondrial abnormalities, whereas activating PXR protected against AKI. Using luciferase reporter assays, genomic manipulation, and proteomics data analysis on the kidneys of PXR-/- rats, we determined that PXR targeted Aldo-keto reductase family 1, member B7 (AKR1B7) to improve mitochondrial function, thereby ameliorating AKI. We confirmed the protective role of PXR against kidney injury using genomic and pharmacologic approaches in an ischemia/reperfusion model of AKI. These findings demonstrate that disabling the PXR/AKR1B7/mitochondrial metabolism axis is an important factor that can contribute to AKI, whereas reestablishing this axis can be useful for treating AKI.
  45. Cell Chem Biol. 2020 Apr 21. pii: S2451-9456(20)30118-5. [Epub ahead of print]
    Harvey EP, Hauseman ZJ, Cohen DT, Rettenmaier TJ, Lee S, Huhn AJ, Wales TE, Seo HS, Luccarelli J, Newman CE, Guerra RM, Bird GH, Dhe-Paganon S, Engen JR, Wells JA, Walensky LD.
      The BCL-2 family is composed of anti- and pro-apoptotic members that respectively protect or disrupt mitochondrial integrity. Anti-apoptotic overexpression can promote oncogenesis by trapping the BCL-2 homology 3 (BH3) "killer domains" of pro-apoptotic proteins in a surface groove, blocking apoptosis. Groove inhibitors, such as the relatively large BCL-2 drug venetoclax (868 Da), have emerged as cancer therapies. BFL-1 remains an undrugged oncogenic protein and can cause venetoclax resistance. Having identified a unique C55 residue in the BFL-1 groove, we performed a disulfide tethering screen to determine if C55 reactivity could enable smaller molecules to block BFL-1's BH3-binding functionality. We found that a disulfide-bearing N-acetyltryptophan analog (304 Da adduct) effectively targeted BFL-1 C55 and reversed BFL-1-mediated suppression of mitochondrial apoptosis. Structural analyses implicated the conserved leucine-binding pocket of BFL-1 as the interaction site, resulting in conformational remodeling. Thus, therapeutic targeting of BFL-1 may be achievable through the design of small, cysteine-reactive drugs.
    Keywords:  BCL-2 family; BFL-1/A1; BH3; anti-apoptotic; apoptosis; cancer; covalent inhibitor; disulfide tethering; mitochondria; small molecule
  46. Nat Cell Biol. 2020 May 11.
    Fuseya Y, Fujita H, Kim M, Ohtake F, Nishide A, Sasaki K, Saeki Y, Tanaka K, Takahashi R, Iwai K.
      The linear ubiquitin chain assembly complex (LUBAC), which consists of HOIP, SHARPIN and HOIL-1L, promotes NF-κB activation and protects against cell death by generating linear ubiquitin chains. LUBAC contains two RING-IBR-RING (RBR) ubiquitin ligases (E3), and the HOIP RBR is responsible for catalysing linear ubiquitination. We found that HOIL-1L RBR plays a crucial role in regulating LUBAC. HOIL-1L RBR conjugates monoubiquitin onto all LUBAC subunits, followed by HOIP-mediated conjugation of linear chains onto monoubiquitin, and these linear chains attenuate the functions of LUBAC. The introduction of E3-defective HOIL-1L mutants into cells augmented linear ubiquitination, which protected the cells against Salmonella infection and cured dermatitis caused by reduced LUBAC levels due to SHARPIN loss. Our results reveal a regulatory mode of E3 ligases in which the accessory E3 in LUBAC downregulates the main E3 by providing preferred substrates for autolinear ubiquitination. Thus, inhibition of HOIL-1L E3 represents a promising strategy for treating severe infections or immunodeficiency.
  47. Dev Cell. 2020 Apr 30. pii: S1534-5807(20)30306-3. [Epub ahead of print]
    Sanaki Y, Nagata R, Kizawa D, Léopold P, Igaki T.
      Metabolic diseases such as type 2 diabetes are associated with increased cancer incidence. Here, we show that hyperinsulinemia promotes epithelial tumorigenesis by abrogating cell competition. In Drosophila eye imaginal epithelium, oncogenic scribble (scrib) mutant cells are eliminated by cell competition when surrounded by wild-type cells. Through a genetic screen, we find that flies heterozygous for the insulin receptor substrate chico allow scrib cells to evade cell competition and develop into tumors. Intriguingly, chico is required in the brain's insulin-producing cells (IPCs) to execute cell competition remotely. Mechanistically, chico downregulation in IPCs causes hyperinsulinemia by upregulating a Drosophila insulin Dilp2, which activates insulin-mTOR signaling and thus boosts protein synthesis in scrib cells. A diet-induced increase in insulin levels also triggers scrib tumorigenesis, and pharmacological repression of protein synthesis prevents hyperinsulinemia-induced scrib overgrowth. Our findings provide an in vivo mechanistic link between metabolic disease and cancer risk via systemic regulation of cell competition.
    Keywords:  Drosophila; cancer; cell competition; hyperinsulinemia; insulin; tumor suppression
  48. Curr Stem Cell Res Ther. 2020 May 11.
    Lee HY, Hong IS.
      Recent studies on the mechanisms that link metabolic changes with stem cell fate have deepened our understanding of how specific metabolic pathways can regulate various stem cell functions during the development of an organism. Although it was originally thought to be merely a consequence of the specific cell state, metabolism is currently known to play a critical role in regulating the self-renewal capacity, differentiation potential, and quiescence of stem cells. Many studies in recent years have revealed that metabolic pathways regulate various stem cell behaviors (e.g., selfrenewal, migration, and differentiation) by modulating energy production through glycolysis or oxidative phosphorylation and by regulating the generation of metabolites, which can modulate multiple signaling pathways. Therefore, a more comprehensive understanding of stem cell metabolism could allow us to establish optimal culture conditions and differentiation methods that would increase stem cell expansion and function for cell-based therapies. However, little is known about how metabolic pathways regulate various stem cell functions. In this context, we review the current advances in metabolic research that have revealed functional roles for mitochondrial oxidative phosphorylation, anaerobic glycolysis, and oxidative stress during the self-renewal, differentiation and aging of various adult stem cell types. These approaches could provide novel strategies for the development of metabolic or pharmacological therapies to promote the regenerative potential of stem cells and subsequently promote their therapeutic utility.
    Keywords:  Stem cells; aging; differentiation; metabolism; pluripotency; quiescence; self-renewal
  49. J Invest Dermatol. 2020 May 07. pii: S0022-202X(20)31406-8. [Epub ahead of print]
    Nguyen MQ, Teh JLF, Purwin TJ, Chervoneva I, Davies MA, Nathanson KL, Cheng PF, Levesque MP, Dummer R, Aplin AE.
      Melanomas frequently harbor activating NRAS mutations leading to activation of MEK-ERK1/2 signaling; however, clinical efficacy of inhibitors to this pathway are limited by resistance. Tumors re-wire metabolic pathways in response to stress signals such as targeted inhibitors and drug resistance, but most therapeutic resistant pre-clinical models are generated in conditions that lack physiological metabolism. We generated human NRAS mutant melanoma xenografts that were resistant to the MEK inhibitor (MEKi), PD0325901, in vivo. MEKi-resistant (MEKiR) cells showed cross-resistance to the structurally distinct MEKi, trametinib, and elevated ERK1/2 phosphorylation and downstream signaling. Additionally, we observed upregulation of the serine synthesis pathway and phosphoglycerate dehydrogenase (PHGDH), a key enzyme in this pathway. Suppressing PHGDH in MEKiR cells together with MEKi treatment decreased oxidative stress tolerance and cell proliferation. Together, our data suggest targeting PHGDH as a potential strategy in overcoming MEKi resistance.
  50. Front Cell Dev Biol. 2020 ;8 274
    Su Y, Huang X, Huang Z, Huang T, Xu Y, Yi C.
      Signal transducer and activator of transcription 3 (STAT3) is a transcription factor (TF) that regulates a variety of biological processes, including a key role in mediating mitochondrial metabolism. It has been shown that STAT3 performs this function by translocating in minute amounts into mitochondria and interacting with mitochondrial proteins and genome. However, whether STAT3 localizes in mitochondria is still up for debate. To decipher the role of mitochondrial STAT3 requires a detailed understanding of its cellular localization. Using Percoll density gradient centrifugation, we surprisingly found that STAT3 is not located in the mitochondrial fraction, but instead, in the mitochondria-associated endoplasmic reticulum membrane (MAM) fraction. This was confirmed by sub-diffraction image analysis of labeled mitochondria in embryonic astrocytes. Also, we find that other TFs that have been previously found to localize in mitochondria are also found instead in the MAM fraction. Our results suggest that STAT3 and other transcriptional factors are, contrary to prior studies, consolidated specifically at MAMs, and further efforts to understand mitochondrial STAT3 function must take into consideration this localization, as the associated functional consequences offer a different interpretation to the questions of STAT3 trafficking and signaling in the mitochondria.
    Keywords:  ER; MAM; STAT3; mitochondrial localization; transcription factors
  51. Proc Natl Acad Sci U S A. 2020 May 15. pii: 201920546. [Epub ahead of print]
    Song D, Navalsky BE, Guan W, Ingersoll C, Wang T, Loro E, Eeles L, Matchett KB, Percy MJ, Walsby-Tickle J, McCullagh JSO, Medina RJ, Khurana TS, Bigham AW, Lappin TR, Lee FS.
      Tibetans have adapted to the chronic hypoxia of high altitude and display a distinctive suite of physiologic adaptations, including augmented hypoxic ventilatory response and resistance to pulmonary hypertension. Genome-wide studies have consistently identified compelling genetic signatures of natural selection in two genes of the Hypoxia Inducible Factor pathway, PHD2 and HIF2A The product of the former induces the degradation of the product of the latter. Key issues regarding Tibetan PHD2 are whether it is a gain-of-function or loss-of-function allele, and how it might contribute to high-altitude adaptation. Tibetan PHD2 possesses two amino acid changes, D4E and C127S. We previously showed that in vitro, Tibetan PHD2 is defective in its interaction with p23, a cochaperone of the HSP90 pathway, and we proposed that Tibetan PHD2 is a loss-of-function allele. Here, we report that additional PHD2 mutations at or near Asp-4 or Cys-127 impair interaction with p23 in vitro. We find that mice with the Tibetan Phd2 allele display augmented hypoxic ventilatory response, supporting this loss-of-function proposal. This is phenocopied by mice with a mutation in p23 that abrogates the PHD2:p23 interaction. Hif2a haploinsufficiency, but not the Tibetan Phd2 allele, ameliorates hypoxia-induced increases in right ventricular systolic pressure. The Tibetan Phd2 allele is not associated with hemoglobin levels in mice. We propose that Tibetans possess genetic alterations that both activate and inhibit selective outputs of the HIF pathway to facilitate successful adaptation to the chronic hypoxia of high altitude.
    Keywords:  EGLN1; EPAS1; HIF; PHD2; high-altitude adaptation
  52. Nat Commun. 2020 May 12. 11(1): 2355
    Stehlik T, Kremp M, Kahnt J, Bölker M, Freitag J.
      Correct intracellular distribution of proteins is critical for the function of eukaryotic cells. Certain proteins are targeted to more than one cellular compartment, e.g. to mitochondria and peroxisomes. The protein phosphatase Ptc5 from Saccharomyces cerevisiae contains an N-terminal mitochondrial presequence followed by a transmembrane domain, and has been detected in the mitochondrial intermembrane space. Here we show mitochondrial transit of Ptc5 to peroxisomes. Translocation of Ptc5 to peroxisomes depended both on the C-terminal peroxisomal targeting signal (PTS1) and N-terminal cleavage by the mitochondrial inner membrane peptidase complex. Indirect targeting of Ptc5 to peroxisomes prevented deleterious effects of its phosphatase activity in the cytosol. Sorting of Ptc5 involves simultaneous interaction with import machineries of both organelles. We identify additional mitochondrial proteins with PTS1, which localize in both organelles and can increase their physical association. Thus, a tug-of-war-like mechanism can influence the interaction and communication of two cellular compartments.
  53. Blood. 2020 May 12. pii: blood.2019003940. [Epub ahead of print]
    Gu H, Chen C, Hao X, Su N, Huang D, Zou Y, Lin SH, Chen X, Zheng D, Liu L, Yu Z, Xie L, Zhang Y, He X, Lai X, Zhang X, Chen GQ, Zhao Y, Yang Y, Loscalzo J, Zheng J.
      The connections between energy metabolism and stemness of hematopoietic stem cells (HSCs) at different developmental stages remain largely unknown. We herein generate a transgenic mouse line for the genetically encoded NADH/NAD+ sensor (SoNar) and demonstrate that there exist three distinct fetal liver hematopoietic cell populations according to the ratios of SoNar fluorescence. SoNar-low cells have an enhanced level of mitochondrial respiration, but similar glycolytic level to SoNar-high cells. Interestingly, 10% of SoNar-low cells are enriched for 65% of total immunophenotypical fetal liver HSCs (FL-HSCs) and contain approximately 5-fold greater functional HSCs than that of SoNar-high counterparts. SoNar can monitor sensitively the dynamic changes of energy metabolism in HSCs both in vitro and in vivo. Mechanistically, STAT3 transactivates MDH1 to sustain the malate-aspartate NADH shuttle activity and the HSC self-renewal and differentiation. We reveal an unexpected metabolic program of FL-HSCs and provide a powerful genetic tool for metabolic studies of HSCs or other types of stem cells.
  54. JIMD Rep. 2020 May;53(1): 22-28
    Wilton KM, Morales-Rosado JA, Selcen D, Muthusamy K, Ewing S, Agre K, Nickels K, Klee EW, Ho ML, Morava E.
      Mitochondria play a variety of roles in the cell, far beyond their widely recognized role in ATP generation. One such role is the regulation and sequestration of calcium, which is done with the help of the mitochondrial calcium uniporter (MCU) and its regulators, MICU1 and MICU2. Genetic variations in MICU1 and MICU2 have been reported to cause myopathy, developmental disability and neurological symptoms typical of mitochondrial disorders. The symptoms of MICU1/2 deficiency have generally been attributed to calcium regulation in the metabolic and biochemical roles of mitochondria. Here, we report a female child with heterozygous MICU1 variants and multiple congenital brain malformations on MRI. Specifically, she shows anterior perisylvian polymicrogyria, dysmorphic basal ganglia, and cerebellar dysplasia in addition to white matter abnormalities. These novel findings suggest that MICU1 is necessary for proper neurodevelopment through a variety of potential mechanisms, including calcium-mediated regulation of the neuronal cytoskeleton, Miro1-MCU complex-mediated mitochondrial movement, or enhancing ATP production. This case provides new insight into the molecular pathogenesis of MCU dysfunction and may represent a novel diagnostic feature of calcium-based mitochondrial disease.
    Keywords:  MICU1; MICU1 deficiency; MPXPS; acute disseminated encephalomyelitis; genetic; mitochondria
  55. Front Oncol. 2020 ;10 658
    Zhu Z, Leung GKK.
      The bifunctional methylenetetrahydrofolate dehydrogenase/cyclohydrolase (MTHFD2) is a mitochondrial one-carbon folate metabolic enzyme whose role in cancer was not known until recently. MTHFD2 is highly expressed in embryos and a wide range of tumors but has low or absent expression in most adult differentiated tissues. Elevated MTHFD2 expression is associated with poor prognosis in both hematological and solid malignancy. Its depletion leads to suppression of multiple malignant phenotypes including proliferation, invasion, migration, and induction of cancer cell death. The non-metabolic functions of this enzyme, especially in cancers, have thus generated considerable research interests. This review summarizes current knowledge on both the metabolic functions and non-enzymatic roles of MTHFD2. Its expression, potential functions, and regulatory mechanism in cancers are highlighted. The development of MTHFD2 inhibitors and their implications in pre-clinical models are also discussed.
    Keywords:  cancer metabolism; epigenetic modification; metabolic enzyme; oncogenicity; one carbon metabolism
  56. Cancer Metab. 2020 ;8 5
    Oruganty K, Campit SE, Mamde S, Lyssiotis CA, Chandrasekaran S.
      Background: Tumor initiation and progression are associated with numerous metabolic alterations. However, the biochemical drivers and constraints that contribute to metabolic gene dysregulation are unclear.Methods: Here, we present MetOncoFit, a computational model that integrates 142 metabolic features that can impact tumor fitness, including enzyme catalytic activity, pathway association, network topology, and reaction flux. MetOncoFit uses genome-scale metabolic modeling and machine-learning to quantify the relative importance of various metabolic features in predicting cancer metabolic gene expression, copy number variation, and survival data.
    Results: Using MetOncoFit, we performed a meta-analysis of 9 cancer types and over 4500 samples from TCGA, Prognoscan, and COSMIC tumor databases. MetOncoFit accurately predicted enzyme differential expression and its impact on patient survival using the 142 attributes of metabolic enzymes. Our analysis revealed that enzymes with high catalytic activity were frequently upregulated in many tumors and associated with poor survival. Topological analysis also identified specific metabolites that were hot spots of dysregulation.
    Conclusions: MetOncoFit integrates a broad range of datasets to understand how biochemical and topological features influence metabolic gene dysregulation across various cancer types. MetOncoFit was able to achieve significantly higher accuracy in predicting differential expression, copy number variation, and patient survival than traditional modeling approaches. Overall, MetOncoFit illuminates how enzyme activity and metabolic network architecture influences tumorigenesis.
    Keywords:  Genomics; Machine learning; Metabolic modeling; Transcriptomics
  57. J Exp Biol. 2020 May 11. pii: jeb.223776. [Epub ahead of print]
    Bundgaard A, James AM, Harbour ME, Murphy MP, Fago A.
      The association of complex I (CI), complex III (CIII) and complex IV (CIV) of the mitochondrial electron transport chain into stable high-molecular weight supercomplexes (SCs) has been observed in several prokaryotes and eukaryotes, but among vertebrates it has only been examined in mammals. The biological role of these SCs is unclear but suggestions so far include enhanced electron transfer between complexes, decreased production of the reactive oxygen species (ROS) O2 ·- and H2O2, or enhanced structural stability. Here, we provide the first overview on the stability, composition and activity of mitochondrial SCs in representative species of several vertebrate classes to determine patterns of SC variation across endotherms and ectotherms. We found that the stability of the CICIII2 SC and the inclusion of CIV within SC varied considerably. Specifically, when solubilized by the detergent DDM, mitochondrial CICIII2 SCs were unstable in endotherms (birds and mammals) and highly stable in reptiles. Using mass-spectrometric complexomics, we confirmed that the CICIII2 is the major SC in the turtle, and that 90% of CI is found in this highly stable SC. Interestingly, the presence of stable SCs did not prevent mitochondrial H2O2 production and was not associated with elevated respiration rates of mitochondria isolated from the examined species. Together, these data show that SC stability varies among vertebrates and is greatest in poikilothermic reptiles and weakest in endotherms. This pattern suggests an adaptive role of SCs to varying body temperature, but not necessarily a direct effect on electron transfer or in the prevention of ROS production.
    Keywords:  Bioenergetics; Complexomics; Mass spectrometry; Mitochondria; Oxidative phosphorylation; Reactive oxygen species
  58. Trends Biochem Sci. 2020 Jun;pii: S0968-0004(20)30059-1. [Epub ahead of print]45(6): 545-546
    Radenkovic S, Vuckovic I, Lanza IR.
  59. J Cell Mol Med. 2020 May 14.
    Hernandez-Resendiz S, Prunier F, Girao H, Dorn G, Hausenloy DJ, .
      New treatments are needed to protect the myocardium against the detrimental effects of acute ischaemia/reperfusion (IR) injury following an acute myocardial infarction (AMI), in order to limit myocardial infarct (MI) size, preserve cardiac function and prevent the onset of heart failure (HF). Given the critical role of mitochondria in energy production for cardiac contractile function, prevention of mitochondrial dysfunction during acute myocardial IRI may provide novel cardioprotective strategies. In this regard, the mitochondrial fusion and fissions proteins, which regulate changes in mitochondrial morphology, are known to impact on mitochondrial quality control by modulating mitochondrial biogenesis, mitophagy and the mitochondrial unfolded protein response. In this article, we review how targeting these inter-related processes may provide novel treatment targets and new therapeutic strategies for reducing MI size, preventing the onset of HF following AMI.
    Keywords:  acute myocardial ischaemia/reperfusion injury; cardioprotection; mitochondrial morphology; mitochondrial unfolded protein response; mitophagy cardioprotection
  60. Cancer Discov. 2020 May 15.
      Loss of the gluconeogenic enzyme FBP1 promoted hepatocellular carcinoma development in mice.