bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒05‒03
forty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Proc Natl Acad Sci U S A. 2020 Apr 27. pii: 201919250. [Epub ahead of print]
    Nilsson A, Haanstra JR, Engqvist M, Gerding A, Bakker BM, Klingmüller U, Teusink B, Nielsen J.
      Many cancer cells consume glutamine at high rates; counterintuitively, they simultaneously excrete glutamate, the first intermediate in glutamine metabolism. Glutamine consumption has been linked to replenishment of tricarboxylic acid cycle (TCA) intermediates and synthesis of adenosine triphosphate (ATP), but the reason for glutamate excretion is unclear. Here, we dynamically profile the uptake and excretion fluxes of a liver cancer cell line (HepG2) and use genome-scale metabolic modeling for in-depth analysis. We find that up to 30% of the glutamine is metabolized in the cytosol, primarily for nucleotide synthesis, producing cytosolic glutamate. We hypothesize that excreting glutamate helps the cell to increase the nucleotide synthesis rate to sustain growth. Indeed, we show experimentally that partial inhibition of glutamate excretion reduces cell growth. Our integrative approach thus links glutamine addiction to glutamate excretion in cancer and points toward potential drug targets.
    Keywords:  flux-balance analysis; genome-scale modeling; metabolic engineering; systems biology
  2. Proc Natl Acad Sci U S A. 2020 May 01. pii: 202001387. [Epub ahead of print]
    Jedrychowski MP, Lu GZ, Szpyt J, Mariotti M, Garrity R, Paulo JA, Schweppe DK, Laznik-Bogoslavski D, Kazak L, Murphy MP, Gladyshev VN, Gygi SP, Chouchani ET, Spiegelman BM.
      Oxidation of cysteine thiols by physiological reactive oxygen species (ROS) initiates thermogenesis in brown and beige adipose tissues. Cellular selenocysteines, where sulfur is replaced with selenium, exhibit enhanced reactivity with ROS. Despite their critical roles in physiology, methods for broad and direct detection of proteogenic selenocysteines are limited. Here we developed a mass spectrometric method to interrogate incorporation of selenium into proteins. Unexpectedly, this approach revealed facultative incorporation of selenium as selenocysteine or selenomethionine into proteins that lack canonical encoding for selenocysteine. Selenium was selectively incorporated into regulatory sites on key metabolic proteins, including as selenocysteine-replacing cysteine at position 253 in uncoupling protein 1 (UCP1). This facultative utilization of selenium was initiated by increasing cellular levels of organic, but not inorganic, forms of selenium. Remarkably, dietary selenium supplementation elevated facultative incorporation into UCP1, elevated energy expenditure through thermogenic adipose tissue, and protected against obesity. Together, these findings reveal the existence of facultative protein selenation, which correlates with impacts on thermogenic adipocyte function and presumably other biological processes as well.
    Keywords:  ROS; brown adipose tissue; cysteine; selenocysteine
  3. Cancer Discov. 2020 Apr 27. pii: CD-19-0597. [Epub ahead of print]
    Hou P, Kapoor A, Zhang Q, Li J, Wu CJ, Li J, Lan Z, Tang M, Ma X, Ackroyd JJ, Kalluri R, Zhang J, Jiang S, Spring DJ, Wang YA, DePinho RA.
      Oncogenic KRAS (KRAS*) is a key tumor maintenance gene in pancreatic ductal adenocarcinoma (PDAC), motivating pharmacological targeting of KRAS* and its effectors. Here, we explored mechanisms involving the tumor microenvironment (TME) as a potential basis for resistance to targeting KRAS*. Using the inducible KrasG12D p53 null (iKPC) PDAC mouse model, gain-of-function screens of epigenetic regulators identified HDAC5 as the top hit enabling KRAS* independent tumor growth. HDAC5-driven escaper tumors showed a prominent neutrophil-to-macrophage switch relative to KRAS*-driven tumors. Mechanistically, HDAC5 represses Socs3, a negative regulator of chemokine CCL2, resulting in increased CCL2 which recruits CCR2+ macrophages. Correspondingly, enforced Ccl2 promotes macrophage recruitment into the TME and enables tumor recurrence following KRAS* extinction. These tumor-associated macrophages (TAMs) in turn provide cancer cell with trophic support including TGFB to enable KRAS* bypass in a Smad4-dependent manner. Our work uncovers a KRAS* resistance mechanism involving immune cell remodeling of the PDAC TME.
  4. Cancer Discov. 2020 Apr 27. pii: CD-19-0959. [Epub ahead of print]
    Parker SJ, Amendola CR, Hollinshead KER, Yu Q, Yamamoto K, Encarnacion-Rosado J, Rose RE, LaRue MM, Sohn ASW, Biancur DE, Paulo JA, Gygi SP, Jones DR, Wang H, Philips MR, Bar-Sagi D, Mancias JD, Kimmelman AC.
      Pancreatic ductal adenocarcinoma (PDAC) evolves a complex microenvironment comprised of multiple cell types, including pancreatic stellate cells (PSCs). Previous studies have demonstrated that stromal supply of alanine, lipids, and nucleotides supports the metabolism, growth, and therapeutic resistance of PDAC. Here we demonstrate that alanine crosstalk between PSCs and PDAC is orchestrated by the utilization of specific transporters. PSCs utilize SLC1A4 and other transporter(s) to rapidly exchange and maintain environmental alanine concentrations. Moreover, PDAC cells upregulate SLC38A2 to supply their increased alanine demand. Cells lacking SLC38A2 fail to concentrate intracellular alanine and undergo a profound metabolic crisis resulting in markedly impaired tumor growth. Our results demonstrate that stromal-cancer metabolic niches can form through differential transporter expression, creating unique therapeutic opportunities to target metabolic demands of cancer.
  5. J Physiol. 2020 May 02.
    Glancy B, Kane DA, Kavazis AN, Goodwin ML, Willis WT, Gladden LB.
      Mitochondrial structures were probably observed microscopically in the 1840s, but the idea of oxidative phosphorylation (OXPHOS) within mitochondria did not appear until the 1930s. The foundation for research into energetics arose from Meyerhof's experiments on oxidation of lactate in isolated muscles recovering from electrical contractions in an O2 atmosphere. Today, we know that mitochondria are actually reticula and that the energy released from electron pairs being passed along the electron transport chain from NADH to O2 generates a membrane potential and pH gradient of protons that can enter the molecular machine of ATP Synthase to resynthesize ATP. Lactate stands at the crossroads of glycolytic and oxidative energy metabolism. Based on reported research and our own modeling in silico, we contend that lactate is not directly oxidized in the mitochondrial matrix. Instead, the interim glycolytic products (pyruvate and NADH) are held in cytosolic equilibrium with the products of the lactate dehydrogenase (LDH) reaction and the intermediates of the malate-aspartate and glycerol 3-phosphate shuttles. This equilibrium supplies the glycolytic products to the mitochondrial matrix for OXPHOS. LDH in the mitochondrial matrix is not compatible with the cytoplasmic/matrix redox gradient; its presence would drain matrix reducing power and substantially dissipate the proton motive force. OXPHOS requires O2 as the final electron acceptor, but O2 s upply is sufficient in most situations, including exercise and often acute illness. Recent studies suggest that atmospheric normoxia may constitute a cellular hyperoxia in mitochondrial disease. As research proceeds appropriate oxygenation levels should be carefully considered. Abstract figure legend Credit for the discovery of what would become known as mitochondria is given to Rudolf Albrecht von Kölliker in 1857; these structures were subsequently described in greater detail by Richard Altmann. In 1898, Benda used a derivation of the Greek words for 'thread' and 'granule' to name these structures 'mitochondria'. In 1907, Fletcher and Hopkins reported the disappearance of lactate in the presence of O2 in previously stimulated muscles. Approximately two decades later, Meyerhof's work on O2 consumption and lactate (La- ) resynthesis into glycogen during the recovery of isolated skeletal muscles from prior contractions was an early hint at the intersection of glycolysis and aerobic phosphorylation. Warburg related these phenomena to the metabolic physiology of cancer. Research by both Meyerhof and Emden led to discovery of the glycolytic pathway. In the 1930s, the work of Lundsgaard, Krebs, Kalckar, the Coris, Belitzer and Szent-Gyorgi, and subsequently Lipmann, Ochoa, Bensley & Hoerr and Claude in the 1940s led to establishing the bioenergetics of glycolysis and the TCA cycle and compounds of high phosphoryl transfer potential. The 1950s heralded the age of research using isolated, functioning mitochondria to explore bioenergetics, and featured prominently the work of Lehninger, Estabrook & Saktor, and Chance & Williams. In the 1960s, Peter Mitchell first proposed the chemiosmotic theory of oxidative phosphorylation, for which he was awarded the Nobel Prize. During this same decade, work by Borst clarified the malate-aspartate shuttle, wherein the exchange of anionic aspartate for undissociated glutamate (one negative charge exported from the matrix per exchange) is driven by the membrane potential (ΔΨ). Work by Skulachev in this decade and beyond further clarified mitochondrial bioenergetics and mitochondrial morphology. Boyer elucidated the nature of the ATP synthase, ultimately winning the Nobel Prize for his work. In the 1980s, David Nicholls further clarified mitochondrial bioenergetics, and the work of George Brooks initiated the era of the Cell-to-Cell Lactate Shuttle. Starting in the 1990s, research emerged suggesting that mitochondria are capable of transporting La- across the inner membrane and oxidizing it without the support of the cytosolic-mitochondrial electron shuttles (i.e. the malate-aspartate and glycerol-3-phosphate shuttles). The ultimate combustion of La- obviously takes place in the mitochondria; there is no question about that simple conclusion. However, our view is that La- is not directly oxidized by LDH in the mitochondrial matrix, but rather La- must first be converted to pyruvate (Pyr- ) in the cytosol or intermembrane space. Rationale for this view includes the high activity of the near-equilibrium enzyme LDH, which exceeds glycolytic capacity, the highly oxidized NAD+ /NADH ratio relative to the mitochondrial matrix, and the thermodynamic necessity for an energy-driven accumulation of shuttle species (e.g. ΔΨ-dependent aspartate-glutamate exchanger). Modeling in silico demonstrates that an active LDH in the matrix would render mitochondria nearly incapable of oxidizing Pyr- , a result which is inconsistent with decades of studies from hundreds of laboratories using both isolated mitochondria and permeabilized cells in which the mitochondrial reticulum remains intact. Healthy mitochondria function well, even at low O2 levels such that dysoxia is rare and low O2 is likely a minor factor in the increasing concentrations of La- typical with exercise or even many acute critical care situations.2 This article is protected by copyright. All rights reserved.
  6. J Mol Cell Cardiol. 2020 Apr 27. pii: S0022-2828(20)30119-X. [Epub ahead of print]
    Garbincius JF, Luongo TS, Elrod JW.
      Since the initial identification of the mitochondrial calcium uniporter (MCU) in 2011, several studies employing genetic models have attempted to decipher the role of mitochondrial calcium uptake in cardiac physiology. Confounding results in various mutant mouse models have led to an ongoing debate regarding the function of MCU in the heart. In this review, we evaluate and discuss the totality of evidence for mitochondrial calcium uptake in the cardiac stress response. We highlight recent reports that implicate MCU in the control of homeostatic cardiac metabolism and function. This review concludes with a discussion of current gaps in knowledge and remaining experiments to define how MCU contributes to contractile function, cell death, metabolic regulation, and heart failure progression.
    Keywords:  Calcium; Cardiac function; Energetics; Ischemia reperfusion; MCU; MICU1; Mitochondria; NCLX; Permeability transition
  7. Protein Cell. 2020 Apr 30.
    Zheng Q, Maksimovic I, Upad A, David Y.
      Epigenetic modifications, including those on DNA and histones, have been shown to regulate cellular metabolism by controlling expression of enzymes involved in the corresponding metabolic pathways. In turn, metabolic flux influences epigenetic regulation by affecting the biosynthetic balance of enzyme cofactors or donors for certain chromatin modifications. Recently, non-enzymatic covalent modifications (NECMs) by chemically reactive metabolites have been reported to manipulate chromatin architecture and gene transcription through multiple mechanisms. Here, we summarize these recent advances in the identification and characterization of NECMs on nucleic acids, histones, and transcription factors, providing an additional mechanistic link between metabolism and epigenetics.
    Keywords:  chromatin; epigenetics; human disease; metabolism; non-enzymatic modification
  8. Biomolecules. 2020 Apr 23. pii: E655. [Epub ahead of print]10(4):
    Palmieri F, Scarcia P, Monné M.
      In the 1980s, after the mitochondrial DNA (mtDNA) had been sequenced, several diseases resulting from mtDNA mutations emerged. Later, numerous disorders caused by mutations in the nuclear genes encoding mitochondrial proteins were found. A group of these diseases are due to defects of mitochondrial carriers, a family of proteins named solute carrier family 25 (SLC25), that transport a variety of solutes such as the reagents of ATP synthase (ATP, ADP, and phosphate), tricarboxylic acid cycle intermediates, cofactors, amino acids, and carnitine esters of fatty acids. The disease-causing mutations disclosed in mitochondrial carriers range from point mutations, which are often localized in the substrate translocation pore of the carrier, to large deletions and insertions. The biochemical consequences of deficient transport are the compartmentalized accumulation of the substrates and dysfunctional mitochondrial and cellular metabolism, which frequently develop into various forms of myopathy, encephalopathy, or neuropathy. Examples of diseases, due to mitochondrial carrier mutations are: combined D-2- and L-2-hydroxyglutaric aciduria, carnitine-acylcarnitine carrier deficiency, hyperornithinemia-hyperammonemia-homocitrillinuria (HHH) syndrome, early infantile epileptic encephalopathy type 3, Amish microcephaly, aspartate/glutamate isoform 1 deficiency, congenital sideroblastic anemia, Fontaine progeroid syndrome, and citrullinemia type II. Here, we review all the mitochondrial carrier-related diseases known until now, focusing on the connections between the molecular basis, altered metabolism, and phenotypes of these inherited disorders.
    Keywords:  SLC25.; disease; error of metabolism; membrane transport; mitochondrial carrier; mitochondrial carrier disease; mitochondrial disease; mitochondrial transporter; mutation
  9. Int Rev Cell Mol Biol. 2020 ;pii: S1937-6448(20)30047-2. [Epub ahead of print]352 xi-xv
    Spetz J, Galluzzi L.
    Keywords:  Apoptosis; Autophagy; Immunogenic cell death; Mitochondrial outer membrane permeabilization; Mitochondrial permeability transition; Necroptosis; Parthanatos; Pyroptosis
  10. Mech Ageing Dev. 2020 Apr 25. pii: S0047-6374(20)30050-6. [Epub ahead of print] 111254
    Wei-Chieh M, Ohkubo R, Widjaja A, Chen D.
      Stem cell aging contributes to aging-associated tissue degeneration and dysfunction. Recent studies reveal a mitochondrial metabolic checkpoint that regulates stem cell quiescence and maintenance, and dysregulation of the checkpoint leads to functional deterioration of aged stem cells. Here, we present the evidence supporting the mitochondrial metabolic checkpoint regulating stem cell aging and demonstrating the feasibility to target this checkpoint to reverse stem cell aging. We discuss the mechanisms by which mitochondrial stress leads to stem cell deterioration. We speculate the therapeutic potential of targeting the mitochondrial metabolic checkpoint for rejuvenating aged stem cells and improving aging tissue functions.
    Keywords:  NLRP3; SIRT2; SIRT3; SIRT7; stem cell aging
  11. Diabetologia. 2020 Apr 29.
    Georgiadou E, Haythorne E, Dickerson MT, Lopez-Noriega L, Pullen TJ, da Silva Xavier G, Davis SPX, Martinez-Sanchez A, Semplici F, Rizzuto R, McGinty JA, French PM, Cane MC, Jacobson DA, Leclerc I, Rutter GA.
      AIMS/HYPOTHESIS: Mitochondrial oxidative metabolism is central to glucose-stimulated insulin secretion (GSIS). Whether Ca2+ uptake into pancreatic beta cell mitochondria potentiates or antagonises this process is still a matter of debate. Although the mitochondrial Ca2+ importer (MCU) complex is thought to represent the main route for Ca2+ transport across the inner mitochondrial membrane, its role in beta cells has not previously been examined in vivo.METHODS: Here, we inactivated the pore-forming subunit of the MCU, encoded by Mcu, selectively in mouse beta cells using Ins1Cre-mediated recombination. Whole or dissociated pancreatic islets were isolated and used for live beta cell fluorescence imaging of cytosolic or mitochondrial Ca2+ concentration and ATP production in response to increasing glucose concentrations. Electrophysiological recordings were also performed on whole islets. Serum and blood samples were collected to examine oral and i.p. glucose tolerance.
    RESULTS: Glucose-stimulated mitochondrial Ca2+ accumulation (p< 0.05), ATP production (p< 0.05) and insulin secretion (p< 0.01) were strongly inhibited in beta cell-specific Mcu-null (βMcu-KO) animals, in vitro, as compared with wild-type (WT) mice. Interestingly, cytosolic Ca2+ concentrations increased (p< 0.001), whereas mitochondrial membrane depolarisation improved in βMcu-KO animals. βMcu-KO mice displayed impaired in vivo insulin secretion at 5 min (p< 0.001) but not 15 min post-i.p. injection of glucose, whilst the opposite phenomenon was observed following an oral gavage at 5 min. Unexpectedly, glucose tolerance was improved (p< 0.05) in young βMcu-KO (<12 weeks), but not in older animals vs WT mice.
    CONCLUSIONS/INTERPRETATION: MCU is crucial for mitochondrial Ca2+ uptake in pancreatic beta cells and is required for normal GSIS. The apparent compensatory mechanisms that maintain glucose tolerance in βMcu-KO mice remain to be established.
    Keywords:  Calcium; Glucose homeostasis; Insulin secretion; Mitochondria; Mitochondrial Ca2+ uniporter (MCU); Pancreatic beta cells; Type 2 diabetes
  12. Biochim Biophys Acta Mol Basis Dis. 2020 Apr 22. pii: S0925-4439(20)30153-8. [Epub ahead of print] 165808
    Cho H, Cho YY, Shim MS, Lee JY, Lee HS, Kang HC.
      Mitochondria are considered one of the most important subcellular organelles for targeting and delivering drugs because mitochondria are the main location for various cellular functions and energy (i.e., ATP) production, and mitochondrial dysfunctions and malfunctions cause diverse diseases such as neurodegenerative disorders, cardiovascular disorders, metabolic disorders, and cancers. In particular, unique mitochondrial characteristics (e.g., negatively polarized membrane potential, alkaline pH, high reactive oxygen species (ROS) level, high glutathione level, high temperature, and paradoxical mitochondrial dynamics) in pathological cancers have been used as targets, signals, triggers, or driving forces for specific sensing/diagnosing/imaging of characteristic changes in mitochondria, targeted drug delivery on mitochondria, targeted drug delivery/accumulation into mitochondria, or stimuli-triggered drug release in mitochondria. In this review, we describe the distinctive structures, functions, and physiological properties of cancer mitochondria and discuss recent technologies of mitochondria-specific "key characteristic" sensing systems, mitochondria-targeted "drug delivery" systems, and mitochondrial stimuli-specific "drug release" systems as well as their strengths and weaknesses.
    Keywords:  Cancer targeting; Drug targeting; Mitochondria; Mitochondria targeting; Mitochondria-targeted drug delivery; Organelle targeting
  13. Cell Death Discov. 2020 ;6 27
    Leprivier G, Rotblat B.
      Glucose is a major requirement for biological life. Its concentration is constantly sensed at the cellular level, allowing for adequate responses to any changes of glucose availability. Such responses are mediated by key sensors and signaling pathway components that adapt cellular metabolism to glucose levels. One of the major hubs of these responses is mechanistic target of rapamycin (mTOR) kinase, which forms the mTORC1 and mTORC2 protein complexes. Under physiological glucose concentrations, mTORC1 is activated and stimulates a number of proteins and enzymes involved in anabolic processes, while restricting the autophagic process. Conversely, when glucose levels are low, mTORC1 is inhibited, in turn leading to the repression of numerous anabolic processes, sparing ATP and antioxidants. Understanding how mTORC1 activity is regulated by glucose is not only important to better delineate the biological function of mTOR, but also to highlight potential therapeutic strategies for treating diseases characterized by deregulated glucose availability, as is the case of cancer. In this perspective, we depict the different sensors and upstream proteins responsible of controlling mTORC1 activity in response to changes in glucose concentration. This includes the major energy sensor AMP-activated protein kinase (AMPK), as well as other independent players. The impact of such modes of regulation of mTORC1 on cellular processes is also discussed.
    Keywords:  Cell biology; Cell signalling
  14. Biochim Biophys Acta Bioenerg. 2020 Apr 23. pii: S0005-2728(20)30063-3. [Epub ahead of print] 148213
    Adjobo-Hermans MJW, de Haas R, Willems PHGM, Wojtala A, van Emst-de Vries SE, Wagenaars JA, van den Brand M, Rodenburg RJ, Smeitink JAM, Nijtmans LG, Sazanov LA, Wieckowski MR, Koopman WJH.
      Mutations in NDUFS4, which encodes an accessory subunit of mitochondrial oxidative phosphorylation (OXPHOS) complex I (CI), induce Leigh syndrome (LS). LS is a poorly understood pediatric disorder featuring brain-specific anomalies and early death. To study the LS pathomechanism, we here compared OXPHOS proteomes between various Ndufs4-/- mouse tissues. Ndufs4-/- animals displayed significantly lower CI subunit levels in brain/diaphragm relative to other tissues (liver/heart/kidney/skeletal muscle), whereas other OXPHOS subunit levels were not reduced. Absence of NDUFS4 induced near complete absence of the NDUFA12 accessory subunit, a 50% reduction in other CI subunit levels, and an increase in specific CI assembly factors. Among the latter, NDUFAF2 was most highly increased. Regarding NDUFS4, NDUFA12 and NDUFAF2, identical results were obtained in Ndufs4-/- mouse embryonic fibroblasts (MEFs) and NDUFS4-mutated LS patient cells. Ndufs4-/- MEFs contained active CI in situ but blue-native-PAGE highlighted that NDUFAF2 attached to an inactive CI subcomplex (CI-830) and inactive assemblies of higher MW. In NDUFA12-mutated LS patient cells, NDUFA12 absence did not reduce NDUFS4 levels but triggered NDUFAF2 association to active CI. BN-PAGE revealed no such association in LS patient fibroblasts with mutations in other CI subunit-encoding genes where NDUFAF2 was attached to CI-830 (NDUFS1, NDUFV1 mutation) or not detected (NDUFS7 mutation). Supported by enzymological and CI in silico structural analysis, we conclude that absence of NDUFS4 induces near complete absence of NDUFA12 but not vice versa, and that NDUFAF2 stabilizes active CI in Ndufs4-/- mice and LS patient cells, perhaps in concert with mitochondrial inner membrane lipids.
    Keywords:  Fibroblasts; Leigh syndrome; NADH:ubiquinone oxidoreductase; Proteomics
  15. Methods Protoc. 2020 Apr 27. pii: E32. [Epub ahead of print]3(2):
    Sim JJ, Jeong KY.
      In this protocol, we introduced a method of measuring mitochondrial dysfunction to confirm the epithelial-mesenchymal transition (EMT) in pancreatic cancer cells under a hypoxic environment. There are many expertized and complicated methods to verify EMT. However, our methods have indicated that EMT can be identified by examining changes in reactive oxygen species (ROS) generation and membrane potential in mitochondria. To demonstrate whether the changes in the indicators of mitochondrial dysfunction are correlative to EMT, cell morphology, and expression of E-cadherin and N-cadherin were additionally observed. The results verified that a decrease in membrane potential and an increase in ROS in mitochondria were associated with EMT of pancreatic cancer cells. This protocol would be useful as a basis for providing an additional indicator for changes in the tumor microenvironment of pancreatic cancer cells relating to EMT under a hypoxic environment.
    Keywords:  ROS; epithelial–mesenchymal transition; hypoxia; membrane potential; mitochondria; pancreatic cancer cell
  16. Cell Rep. 2020 Apr 28. pii: S2211-1247(20)30516-7. [Epub ahead of print]31(4): 107567
    Doan KN, Grevel A, Mårtensson CU, Ellenrieder L, Thornton N, Wenz LS, Opaliński Ł, Guiard B, Pfanner N, Becker T.
      The mitochondrial outer membrane contains integral proteins with α-helical membrane anchors or a transmembrane β-barrel. The translocase of the outer membrane (TOM) cooperates with the sorting and assembly machinery (SAM) in the import of β-barrel proteins, whereas the mitochondrial import (MIM) complex inserts precursors of multi-spanning α-helical proteins. Single-spanning proteins constitute more than half of the integral outer membrane proteins; however, their biogenesis is poorly understood. We report that the yeast MIM complex promotes the insertion of proteins with N-terminal (signal-anchored) or C-terminal (tail-anchored) membrane anchors. The MIM complex exists in three dynamic populations. MIM interacts with TOM to accept precursor proteins from the receptor Tom70. Free MIM complexes insert single-spanning proteins that are imported in a Tom70-independent manner. Finally, coupling of MIM and SAM promotes early assembly steps of TOM subunits. We conclude that the MIM complex is a major and versatile protein translocase of the mitochondrial outer membrane.
    Keywords:  MIM complex; SAM complex; TOM complex; mitochondria; outer membrane; protein assembly; protein sorting; protein translocase
  17. Sci Rep. 2020 Apr 28. 10(1): 7157
    Tjaden B, Baum K, Marquardt V, Simon M, Trajkovic-Arsic M, Kouril T, Siebers B, Lisec J, Siveke JT, Schulte JH, Benary U, Remke M, Wolf J, Schramm A.
      N-Myc is a transcription factor that is aberrantly expressed in many tumor types and is often correlated with poor patient prognosis. Recently, several lines of evidence pointed to the fact that oncogenic activation of Myc family proteins is concomitant with reprogramming of tumor cells to cope with an enhanced need for metabolites during cell growth. These adaptions are driven by the ability of Myc proteins to act as transcriptional amplifiers in a tissue-of-origin specific manner. Here, we describe the effects of N-Myc overexpression on metabolic reprogramming in neuroblastoma cells. Ectopic expression of N-Myc induced a glycolytic switch that was concomitant with enhanced sensitivity towards 2-deoxyglucose, an inhibitor of glycolysis. Moreover, global metabolic profiling revealed extensive alterations in the cellular metabolome resulting from overexpression of N-Myc. Limited supply with either of the two main carbon sources, glucose or glutamine, resulted in distinct shifts in steady-state metabolite levels and significant changes in glutathione metabolism. Interestingly, interference with glutamine-glutamate conversion preferentially blocked proliferation of N-Myc overexpressing cells, when glutamine levels were reduced. Thus, our study uncovered N-Myc induction and nutrient levels as important metabolic master switches in neuroblastoma cells and identified critical nodes that restrict tumor cell proliferation.
  18. Proc Biol Sci. 2020 May 13. 287(1926): 20192713
    Gyllenhammer LE, Entringer S, Buss C, Wadhwa PD.
      Research on mechanisms underlying the phenomenon of developmental programming of health and disease has focused primarily on processes that are specific to cell types, organs and phenotypes of interest. However, the observation that exposure to suboptimal or adverse developmental conditions concomitantly influences a broad range of phenotypes suggests that these exposures may additionally exert effects through cellular mechanisms that are common, or shared, across these different cell and tissue types. It is in this context that we focus on cellular bioenergetics and propose that mitochondria, bioenergetic and signalling organelles, may represent a key cellular target underlying developmental programming. In this review, we discuss empirical findings in animals and humans that suggest that key structural and functional features of mitochondrial biology exhibit developmental plasticity, and are influenced by the same physiological pathways that are implicated in susceptibility for complex, common age-related disorders, and that these targets of mitochondrial developmental programming exhibit long-term temporal stability. We conclude by articulating current knowledge gaps and propose future research directions to bridge these gaps.
    Keywords:  bioenergetics; developmental programming; fetal programming; maternal–fetal–placental biology; mitochondria
  19. Proc Natl Acad Sci U S A. 2020 Apr 30. pii: 201918459. [Epub ahead of print]
    Karki S, Castillo K, Ding Z, Kerr O, Lamb TM, Wu C, Sachs MS, Bell-Pedersen D.
      The circadian clock in eukaryotes controls transcriptional and posttranscriptional events, including regulation of the levels and phosphorylation state of translation factors. However, the mechanisms underlying clock control of translation initiation, and the impact of this potential regulation on rhythmic protein synthesis, were not known. We show that inhibitory phosphorylation of eIF2α (P-eIF2α), a conserved translation initiation factor, is clock controlled in Neurospora crassa, peaking during the subjective day. Cycling P-eIF2α levels required rhythmic activation of the eIF2α kinase CPC-3 (the homolog of yeast and mammalian GCN2), and rhythmic activation of CPC-3 was abolished under conditions in which the levels of charged tRNAs were altered. Clock-controlled accumulation of P-eIF2α led to reduced translation during the day in vitro and was necessary for the rhythmic synthesis of select proteins in vivo. Finally, loss of rhythmic P-eIF2α levels led to reduced linear growth rates, supporting the idea that partitioning translation to specific times of day provides a growth advantage to the organism. Together, these results reveal a fundamental mechanism by which the clock regulates rhythmic protein production, and provide key insights into how rhythmic translation, cellular energy, stress, and nutrient metabolism are linked through the levels of charged versus uncharged tRNAs.
    Keywords:  Neurospora crassa; circadian clock; cpc-3; eIF2α; translation initiation
  20. Cell Biol Int. 2020 Apr 27.
    Wang B, Gan W, Han X, Li D.
      PRCC-TFE3 translocation renal cell carcinomas (tRCC) was a common subtype of TFE3 tRCCs in which TFE3 fusions were indicated as oncogene to promote tumor development. PRCC-TFE3 fusions are often accumulated in nucleus and related to poorer outcomes and higher stages (III/IV). In this study, we found that PRCC-TFE3 could positively regulate expression of both Dynamin-related protein 1 (Drp1) and fission protein1 (Fis1), and alter distribution of mitochondria, which could promote cell migration and invasion independent on matrix metalloproteinase-2 (MMP-2) and MMP-9. Together, our findings showed a new mechanism for PRCC-TFE3 tRCC cell migration and invasion by alteration of mitochondrial dynamics. Thus, targeting dysregulated Drp1-dependent mitochondrial fission may provide a novel strategy for suppressing the progression of PRCC-TFE3 tRCC. This article is protected by copyright. All rights reserved.
    Keywords:  PRCC-TFE3; invasion; migration; mitochondrial fission; tRCC
  21. Cell Metab. 2020 Apr 23. pii: S1550-4131(20)30183-2. [Epub ahead of print]
    Kulkarni AS, Gubbi S, Barzilai N.
      Biological aging involves an interplay of conserved and targetable molecular mechanisms, summarized as the hallmarks of aging. Metformin, a biguanide that combats age-related disorders and improves health span, is the first drug to be tested for its age-targeting effects in the large clinical trial-TAME (targeting aging by metformin). This review focuses on metformin's mechanisms in attenuating hallmarks of aging and their interconnectivity, by improving nutrient sensing, enhancing autophagy and intercellular communication, protecting against macromolecular damage, delaying stem cell aging, modulating mitochondrial function, regulating transcription, and lowering telomere attrition and senescence. These characteristics make metformin an attractive gerotherapeutic to translate to human trials.
    Keywords:  TAME; aging; aging hallmarks; health span; longevity; metabolism; metformin
  22. Mol Syst Biol. 2020 04;16(4): e9495
    Zhang C, Bjornson E, Arif M, Tebani A, Lovric A, Benfeitas R, Ozcan M, Juszczak K, Kim W, Kim JT, Bidkhori G, Ståhlman M, Bergh PO, Adiels M, Turkez H, Taskinen MR, Bosley J, Marschall HU, Nielsen J, Uhlén M, Borén J, Mardinoglu A.
      The prevalence of non-alcoholic fatty liver disease (NAFLD) continues to increase dramatically, and there is no approved medication for its treatment. Recently, we predicted the underlying molecular mechanisms involved in the progression of NAFLD using network analysis and identified metabolic cofactors that might be beneficial as supplements to decrease human liver fat. Here, we first assessed the tolerability of the combined metabolic cofactors including l-serine, N-acetyl-l-cysteine (NAC), nicotinamide riboside (NR), and l-carnitine by performing a 7-day rat toxicology study. Second, we performed a human calibration study by supplementing combined metabolic cofactors and a control study to study the kinetics of these metabolites in the plasma of healthy subjects with and without supplementation. We measured clinical parameters and observed no immediate side effects. Next, we generated plasma metabolomics and inflammatory protein markers data to reveal the acute changes associated with the supplementation of the metabolic cofactors. We also integrated metabolomics data using personalized genome-scale metabolic modeling and observed that such supplementation significantly affects the global human lipid, amino acid, and antioxidant metabolism. Finally, we predicted blood concentrations of these compounds during daily long-term supplementation by generating an ordinary differential equation model and liver concentrations of serine by generating a pharmacokinetic model and finally adjusted the doses of individual metabolic cofactors for future human clinical trials.
    Keywords:   NAFLD ; l-serine, N-acetyl-l-cysteine (NAC), nicotinamide riboside (NR), and l-carnitine; systems medicine
  23. Annu Rev Immunol. 2020 Apr 26. 38 147-170
    McCarville JL, Chen GY, Cuevas VD, Troha K, Ayres JS.
      Metabolism is one of the strongest drivers of interkingdom interactions-including those between microorganisms and their multicellular hosts. Traditionally thought to fuel energy requirements and provide building blocks for biosynthetic pathways, metabolism is now appreciated for its role in providing metabolites, small-molecule intermediates generated from metabolic processes, to perform various regulatory functions to mediate symbiotic relationships between microbes and their hosts. Here, we review recent advances in our mechanistic understanding of how microbiota-derived metabolites orchestrate and support physiological responses in the host, including immunity, inflammation, defense against infections, and metabolism. Understanding how microbes metabolically communicate with their hosts will provide us an opportunity to better describe how a host interacts with all microbes-beneficial, pathogenic, and commensal-and an opportunity to discover new ways to treat microbial-driven diseases.
    Keywords:  cancer; immune system; inflammation; metabolism; metabolites; microbiota
  24. Mitochondrion. 2020 Apr 22. pii: S1567-7249(20)30011-8. [Epub ahead of print]
    Braun HP.
      Mitochondrial Oxidative Phosphorylation (OXPHOS) provides ATP for driving cellular functions. In plants, OXPHOS takes place in the context of photosynthesis. Indeed, metabolism of mitochondria and chloroplasts is tightly linked. OXPHOS has several extra functions in plants. This review takes a view on the OXPHOS system of plants, the electron transfer chain (ETC), the ATP synthase complex and the numerous supplementary enzymes involved. Electron transport pathways are especially branched in plants. Furthermore, the "classical" OXPHOS complexes include extra subunits, some of which introduce side activities into these complexes. Consequently, and to a remarkable degree, OXPHOS is a multi-functional system in plants that needs to be efficiently regulated with respect to all its physiological tasks in the mitochondria, the chloroplasts, and beyond. Regulatory mechanisms based on posttranslational protein modifications and formation of supramolecular protein assemblies are summarized and discussed.
    Keywords:  ATP synthase; Arabidopsis thaliana; NADH dehydrogenase; Plant mitochondria; electron transfer chain; gamma-type carbonic anhydrase; oxidative phosphorylation; photosynthesis; respiratory protein complexes; respiratory supercomplexes
  25. Cell Death Discov. 2020 ;6 20
    Koch K, Hartmann R, Tsiampali J, Uhlmann C, Nickel AC, He X, Kamp MA, Sabel M, Barker RA, Steiger HJ, Hänggi D, Willbold D, Maciaczyk J, Kahlert UD.
      Cancer cells upregulate anabolic processes to maintain high rates of cellular turnover. Limiting the supply of macromolecular precursors by targeting enzymes involved in biosynthesis is a promising strategy in cancer therapy. Several tumors excessively metabolize glutamine to generate precursors for nonessential amino acids, nucleotides, and lipids, in a process called glutaminolysis. Here we show that pharmacological inhibition of glutaminase (GLS) eradicates glioblastoma stem-like cells (GSCs), a small cell subpopulation in glioblastoma (GBM) responsible for therapy resistance and tumor recurrence. Treatment with small molecule inhibitors compound 968 and CB839 effectively diminished cell growth and in vitro clonogenicity of GSC neurosphere cultures. However, our pharmaco-metabolic studies revealed that only CB839 inhibited GLS enzymatic activity thereby limiting the influx of glutamine derivates into the TCA cycle. Nevertheless, the effects of both inhibitors were highly GLS specific, since treatment sensitivity markedly correlated with GLS protein expression. Strikingly, we found GLS overexpressed in in vitro GSC models as compared with neural stem cells (NSC). Moreover, our study demonstrates the usefulness of in vitro pharmaco-metabolomics to score target specificity of compounds thereby refining drug development and risk assessment.
    Keywords:  CNS cancer; Cancer metabolism; Cancer stem cells; Predictive markers; Translational research
  26. Am J Physiol Heart Circ Physiol. 2020 May 01.
    Mia S, Kane MS, Latimer MN, Reitz CJ, Sonkar R, Benavides GA, Smith SR, Frank SJ, Martino TA, Zhang J, Darley-Usmar V, Young ME.
      Cell autonomous circadian clocks have emerged as temporal orchestrators of numerous biological processes. For example, the cardiomyocyte circadian clock modulates transcription, translation, posttranslational modifications, ion homeostasis, signaling cascades, metabolism, and contractility of the heart over the course of the day. Circadian clocks are composed of more than 10 interconnected transcriptional modulators, all of which have the potential to influence the cardiac transcriptome (and ultimately cardiac processes). These transcriptional modulators include BMAL1 and REV-ERBa/b; BMAL1 induces REV-ERBa/b, which in turn feeds back to inhibit BMAL1. Previous studies indicate that cardiomyocyte-specific BMAL1 knockout (CBK) mice exhibit a dysfunctional circadian clock (including decreased REV-ERBa/b expression) in the heart, associated with abnormalities in cardiac mitochondrial function, metabolism, signaling, and contractile function. Here, we hypothesized that decreased REV-ERBa/b activity is responsible for distinct phenotypic alterations observed in CBK hearts. To test this hypothesis, CBK (and littermate control) mice were administered with the selective REV-ERBa/b agonist, SR-9009 (100mg/Kg/day, for 8-days). SR-9009 administration was sufficient to normalize cardiac glycogen synthesis rates, cardiomyocyte size, interstitial fibrosis, and contractility in CBK hearts (without influencing mitochondrial complex activities, nor normalizing substrate oxidation and Akt/mTOR/GSK3b signaling). Collectively, these observations highlight a role for REV-ERBa/b as a mediator of a subset of circadian clock-controlled processes in the heart.
    Keywords:  chronobiology; gene expression; heart; metabolism; mitochondria
  27. Trends Cancer. 2020 May;pii: S2405-8033(20)30073-X. [Epub ahead of print]6(5): 359-361
    Quon E, Hart ML, Sullivan LB.
      Lactate dehydrogenase (LDH) accounts for the fermentative component of aerobic glycolysis, a near ubiquitous metabolic alteration in cancer. Recently, Oshima et al. developed a bioavailable LDH inhibitor that decreases tumor growth in mice and functions synergistically with mitochondrial respiration inhibitors. These findings suggest a cooperative mechanism of action that targets redox homeostasis.
  28. ISME J. 2020 Apr 29.
    Ankrah NYD, Wilkes RA, Zhang FQ, Zhu D, Kaweesi T, Aristilde L, Douglas AE.
      Insects feeding on the nutrient-poor diet of xylem plant sap generally bear two microbial symbionts that are localized to different organs (bacteriomes) and provide complementary sets of essential amino acids (EAAs). Here, we investigate the metabolic basis for the apparent paradox that xylem-feeding insects are under intense selection for metabolic efficiency but incur the cost of maintaining two symbionts for functions mediated by one symbiont in other associations. Using stable isotope analysis of central carbon metabolism and metabolic modeling, we provide evidence that the bacteriomes of the spittlebug Clastoptera proteus display high rates of aerobic glycolysis, with syntrophic splitting of glucose oxidation. Specifically, our data suggest that one bacteriome (containing the bacterium Sulcia, which synthesizes seven EAAs) predominantly processes glucose glycolytically, producing pyruvate and lactate, and the exported pyruvate and lactate is assimilated by the second bacteriome (containing the bacterium Zinderia, which synthesizes three energetically costly EAAs) and channeled through the TCA cycle for energy generation by oxidative phosphorylation. We, furthermore, calculate that this metabolic arrangement supports the high ATP demand in Zinderia bacteriomes for Zinderia-mediated synthesis of energy-intensive EAAs. We predict that metabolite cross-feeding among host cells may be widespread in animal-microbe symbioses utilizing low-nutrient diets.
  29. Biochim Biophys Acta Mol Basis Dis. 2020 Apr 27. pii: S0925-4439(20)30154-X. [Epub ahead of print] 165809
    Jabbari H, Roushandeh AM, Rostami MK, Razavi-Toosi MT, Shokrgozar MA, Jahanian-Najafabadi A, Kuwahara Y, Roudkenar MH.
      No real therapeutic modality is currently available for Acute kidney injury (AKI) and if any, they are mainly supportive in nature. Therefore, developing a new therapeutic strategy is crucial. Mitochondrial dysfunction proved to be a key contributor to renal tubular cell death during AKI. Thus, replacement or augmentation of damaged mitochondria could be a proper target in AKI treatment. Here, in an animal model of AKI, we auto-transplanted normal mitochondria isolated from healthy muscle cells to injured kidney cells through injection to renal artery. The mitochondria transplantation prevented renal tubular cell death, restored renal function, ameliorated kidney damage, improved regenerative potential of renal tubules, and decreased ischemia/reperfusion-induced apoptosis. Although further studies including clinical trials are required in this regard, our findings suggest a novel therapeutic strategy for treatment of AKI. Improved quality of life of patients suffering from renal failure and decreased morbidity and mortality rates would be the potential advantages of this therapeutic strategy.
    Keywords:  Acute kidney injury; Ischemia/reperfusion; Mitochondria transplantation; Novel treatment; Renal failure
  30. Nat Rev Cancer. 2020 Apr 27.
    Castel P, Rauen KA, McCormick F.
      Human oncoproteins promote transformation of cells into tumours by dysregulating the signalling pathways that are involved in cell growth, proliferation and death. Although oncoproteins were discovered many years ago and have been widely studied in the context of cancer, the recent use of high-throughput sequencing techniques has led to the identification of cancer-associated mutations in other conditions, including many congenital disorders. These syndromes offer an opportunity to study oncoprotein signalling and its biology in the absence of additional driver or passenger mutations, as a result of their monogenic nature. Moreover, their expression in multiple tissue lineages provides insight into the biology of the proto-oncoprotein at the physiological level, in both transformed and unaffected tissues. Given the recent paradigm shift in regard to how oncoproteins promote transformation, we review the fundamentals of genetics, signalling and pathogenesis underlying oncoprotein duality.
  31. Science. 2020 May 01. pii: eaat3987. [Epub ahead of print]368(6490):
    Knudsen NH, Stanya KJ, Hyde AL, Chalom MM, Alexander RK, Liou YH, Starost KA, Gangl MR, Jacobi D, Liu S, Sopariwala DH, Fonseca-Pereira D, Li J, Hu FB, Garrett WS, Narkar VA, Ortlund EA, Kim JH, Paton CM, Cooper JA, Lee CH.
      Repeated bouts of exercise condition muscle mitochondria to meet increased energy demand-an adaptive response associated with improved metabolic fitness. We found that the type 2 cytokine interleukin-13 (IL-13) is induced in exercising muscle, where it orchestrates metabolic reprogramming that preserves glycogen in favor of fatty acid oxidation and mitochondrial respiration. Exercise training-mediated mitochondrial biogenesis, running endurance, and beneficial glycemic effects were lost in Il13-/- mice. By contrast, enhanced muscle IL-13 signaling was sufficient to increase running distance, glucose tolerance, and mitochondrial activity similar to the effects of exercise training. In muscle, IL-13 acts through both its receptor IL-13Rα1 and the transcription factor Stat3. The genetic ablation of either of these downstream effectors reduced running capacity in mice. Thus, coordinated immunological and physiological responses mediate exercise-elicited metabolic adaptations that maximize muscle fuel economy.
  32. J Biol Chem. 2020 Apr 30. pii: jbc.RA120.013802. [Epub ahead of print]
    Dai Y, Sweeny EA, Schlanger S, Ghosh A, Stuehr DJ.
      Soluble guanylyl cyclase (sGC) is a key component of nitric oxide (NO)-cGMP signaling in mammals. Although heme must bind in the sGC β1 subunit (sGCβ) for sGC to function, how heme is delivered to sGCβ remains unknown. Given that glyceraldehyde 3-phosphate dehydrogenase (GAPDH) displays properties of a heme chaperone for inducible NO synthase, we investigated here whether heme delivery to apo-sGCβ involves GAPDH. We utilized an sGCβ reporter construct, tetra-Cys sGCβ (TC-sGCb), whose heme insertion can be followed by fluorescence quenching in live cells, assessed how lowering cell GAPDH expression impacts heme delivery, and examined whether expressing either a wild-type GAPDH or a GAPDH variant defective in heme binding recovers the heme delivery. We also studied interaction between GAPDH and sGCβ in cells and their complex formation and potential heme transfer using purified proteins. We found that (i) heme delivery to apo-sGCβ correlates with cellular GAPDH expression levels and depends on the ability of GAPDH to bind intracellular heme; (ii) apo-sGCβ associates with GAPDH in cells and dissociates when heme binds sGCβ; (iii) the purified GAPDH-heme complex binds to apo-sGCβ and transfers its heme to sGCβ. On the basis of these results, we propose a model whereby GAPDH obtains mitochondrial heme and then forms a complex with apo-sGCβ to accomplish heme delivery to sGCβ. Our findings illuminate a critical step in sGC maturation and uncover an additional mechanism that regulates its activity in health and disease.
    Keywords:  chaperone; cyclic GMP (cGMP); guanylate cyclase (guanylyl cyclase); heme trafficking; mitochondria; nitric oxide
  33. Mol Cell. 2020 Apr 22. pii: S1097-2765(20)30228-8. [Epub ahead of print]
    Zasłona Z, O'Neill LAJ.
      Metabolites have functions in the immune system independent of their conventional roles as sources or intermediates in biosynthesis and bioenergetics. We are still in the pioneering phase of gathering information about the functions of specific metabolites in immunoregulation. In this review, we cover succinate, itaconate, α-ketoglutarate, and lactate as examples. Each of these metabolites has a different story of how their immunoregulatory functions were discovered and how their roles in the complex process of inflammation were revealed. Parallels and interactions are emerging between metabolites and cytokines, well-known immunoregulators. We depict molecular mechanisms by which metabolites prime cellular and often physiological changes focusing on intra- and extra-cellular activities and signaling pathways. Possible therapeutic opportunities for immune and inflammatory diseases are emerging.
  34. Neuromuscul Disord. 2020 Feb 29. pii: S0960-8966(20)30057-2. [Epub ahead of print]
    van den Ameele J, Fuge J, Pitceathly RDS, Berry S, McIntyre Z, Hanna MG, Lee M, Chinnery PF.
      In the absence of cure, the main objectives in the management of patients with mitochondrial disease are symptom control and prevention of complications. While pain is a complicating symptom in many chronic diseases and is known to have a clear impact on quality of life, its prevalence and severity in people with mitochondrial disease is unknown. We conducted a survey of pain symptoms in patients with genetically confirmed mitochondrial disease from two UK mitochondrial disease specialist centres. The majority (66.7%) of patients had chronic pain which was primarily of neuropathic nature. Presence of pain did not significantly impact overall quality of life. The m.3243A>G MTTL1 mutation was associated with higher pain severity and increased the likelihood of neuropathic pain compared to other causative nuclear and mitochondrial gene mutations. Although previously not considered a core symptom in people with mitochondrial disease, pain is a common clinical manifestation, frequently of neuropathic nature, and influenced by genotype. Therefore, pain-related symptoms should be carefully characterised and actively managed in this patient population.
    Keywords:  Genetics; Mitochondria; Mitochondrial disorders; Neuropathy; Pain
  35. Redox Biol. 2020 Apr 20. pii: S2213-2317(20)30328-1. [Epub ahead of print]34 101539
    Mota-Martorell N, Jove M, Pradas I, Sanchez I, Gómez J, Naudi A, Barja G, Pamplona R.
      Mitochondrial reactive oxygen species (ROS) production, specifically at complex I (Cx I), has been widely suggested to be one of the determinants of species longevity. The present study follows a comparative approach to analyse complex I in heart tissue from 8 mammalian species with a longevity ranging from 3.5 to 46 years. Gene expression and protein content of selected Cx I subunits were analysed using droplet digital PCR (ddPCR) and western blot, respectively. Our results demonstrate: 1) the existence of species-specific differences in gene expression and protein content of Cx I in relation to longevity; 2) the achievement of a longevity phenotype is associated with low protein abundance of subunits NDUFV2 and NDUFS4 from the matrix hydrophilic domain of Cx I; and 3) long-lived mammals show also lower levels of VDAC (voltage-dependent anion channel) amount. These differences could be associated with the lower mitochondrial ROS production and slower aging rate of long-lived animals and, unexpectedly, with a low content of the mitochondrial permeability transition pore in these species.
    Keywords:  Complex I; Droplet digital PCR; Longevity; Mammals; Mitochondria; NDUFS4 subunit; NDUFV2 subunit; VDAC; Western blot
  36. Nat Commun. 2020 May 01. 11(1): 2127
    Kim SR, Lee SG, Kim SH, Kim JH, Choi E, Cho W, Rim JH, Hwang I, Lee CJ, Lee M, Oh CM, Jeon JY, Gee HY, Kim JH, Lee BW, Kang ES, Cha BS, Lee MS, Yu JW, Cho JW, Kim JS, Lee YH.
      Sodium-glucose cotransporter 2 (SGLT2) inhibitors reduce cardiovascular events in humans with type 2 diabetes (T2D); however, the underlying mechanism remains unclear. Activation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome and subsequent interleukin (IL)-1β release induces atherosclerosis and heart failure. Here we show the effect of SGLT2 inhibitor empagliflozin on NLRP3 inflammasome activity. Patients with T2D and high cardiovascular risk receive SGLT2 inhibitor or sulfonylurea for 30 days, with NLRP3 inflammasome activation analyzed in macrophages. While the SGLT2 inhibitor's glucose-lowering capacity is similar to sulfonylurea, it shows a greater reduction in IL-1β secretion compared to sulfonylurea accompanied by increased serum β-hydroxybutyrate (BHB) and decreased serum insulin. Ex vivo experiments with macrophages verify the inhibitory effects of high BHB and low insulin levels on NLRP3 inflammasome activation. In conclusion, SGLT2 inhibitor attenuates NLRP3 inflammasome activation, which might help to explain its cardioprotective effects.
  37. Nat Commun. 2020 Apr 29. 11(1): 2086
    Kong LR, Ong RW, Tan TZ, Mohamed Salleh NAB, Thangavelu M, Chan JV, Koh LYJ, Periyasamy G, Lau JA, Le TBU, Wang L, Lee M, Kannan S, Verma CS, Lim CM, Chng WJ, Lane DP, Venkitaraman A, Hung HT, Cheok CF, Goh BC.
      Gain of function (GOF) DNA binding domain (DBD) mutations of TP53 upregulate chromatin regulatory genes that promote genome-wide histone methylation and acetylation. Here, we therapeutically exploit the oncogenic GOF mechanisms of p53 codon 158 (Arg158) mutation, a DBD mutant found to be prevalent in lung carcinomas. Using high throughput compound screening and combination analyses, we uncover that acetylating mutp53R158G could render cancers susceptible to cisplatin-induced DNA stress. Acetylation of mutp53R158G alters DNA binding motifs and upregulates TRAIP, a RING domain-containing E3 ubiquitin ligase which dephosphorylates IĸB and impedes nuclear translocation of RelA (p65), thus repressing oncogenic nuclear factor kappa-B (NF-ĸB) signaling and inducing apoptosis. Given that this mechanism of cytotoxic vulnerability appears inapt in p53 wild-type (WT) or other hotspot GOF mutp53 cells, our work provides a therapeutic opportunity specific to Arg158-mutp53 tumors utilizing a regimen consisting of DNA-damaging agents and mutp53 acetylators, which is currently being pursued clinically.
  38. Mol Biol Cell. 2020 Apr 29. mbcE19070413
    Black M, Arumugam P, Shukla S, Pradhan A, Ustiyan V, Milewski D, Kalinichenko VV, Kalin TV.
      Forkhead box M1 (FOXM1), a nuclear transcription factor which activates cell cycle regulatory genes, is highly expressed in a majority of human cancers. The function of FOXM1 independent of nuclear transcription is unknown. In the present study, we found the FOXM1 protein inside of the mitochondria. Using site-directed mutagenesis, we generated FOXM1 mutant proteins that localized to distinct cellular compartments, uncoupling the nuclear and mitochondrial functions of FOXM1. Directing FOXM1 into the mitochondria decreased mitochondrial mass, membrane potential, respiration and electron transport chain (ETC) activity. In mitochondria, the FOXM1 directly bound to and increased the pentatricopeptide repeat domain 1 (PTCD1) protein, a mitochondrial leucine-specific tRNA binding protein that inhibits leucine-rich ETC complexes. Mitochondrial FOXM1 did not change cellular proliferation. Thus, FOXM1 translocates into mitochondria and inhibits mitochondrial respiration by increasing PTCD1. We identify a new paradigm that FOXM1 regulates mitochondrial homeostasis in a process independent of nuclear transcription.
  39. Cell Rep. 2020 Apr 28. pii: S2211-1247(20)30520-9. [Epub ahead of print]31(4): 107571
    Xiao B, Zuo D, Hirukawa A, Cardiff RD, Lamb R, Sonenberg N, Muller WJ.
      Mechanistic target of rapamycin complex 1 (mTORC1) is a master modulator of cellular growth, and its aberrant regulation is recurrently documented within breast cancer. While the small GTPase Rheb1 is the canonical activator of mTORC1, Rheb1-independent mechanisms of mTORC1 activation have also been reported but have not been fully understood. Employing multiple transgenic mouse models of breast cancer, we report that ablation of Rheb1 significantly impedes mammary tumorigenesis. In the absence of Rheb1, a block in tumor initiation can be overcome by multiple independent mutations in Mtor to allow Rheb1-independent reactivation of mTORC1. We further demonstrate that the mTOR kinase is indispensable for tumor initiation as the genetic ablation of mTOR abolishes mammary tumorigenesis. Collectively, our findings demonstrate that mTORC1 activation is indispensable for mammary tumor initiation and that tumors acquire alternative mechanisms of mTORC1 activation.
    Keywords:  Rheb; breast; cancer; mTOR; mutation; tumorigenesis
  40. Nat Commun. 2020 May 01. 11(1): 2146
    Calvo-Rodriguez M, Hou SS, Snyder AC, Kharitonova EK, Russ AN, Das S, Fan Z, Muzikansky A, Garcia-Alloza M, Serrano-Pozo A, Hudry E, Bacskai BJ.
      Mitochondria contribute to shape intraneuronal Ca2+ signals. Excessive Ca2+ taken up by mitochondria could lead to cell death. Amyloid beta (Aβ) causes cytosolic Ca2+ overload, but the effects of Aβ on mitochondrial Ca2+ levels in Alzheimer's disease (AD) remain unclear. Using a ratiometric Ca2+ indicator targeted to neuronal mitochondria and intravital multiphoton microscopy, we find increased mitochondrial Ca2+ levels associated with plaque deposition and neuronal death in a transgenic mouse model of cerebral β-amyloidosis. Naturally secreted soluble Aβ applied onto the healthy brain increases Ca2+ concentration in mitochondria, which is prevented by blockage of the mitochondrial calcium uniporter. RNA-sequencing from post-mortem AD human brains shows downregulation in the expression of mitochondrial influx Ca2+ transporter genes, but upregulation in the genes related to mitochondrial Ca2+ efflux pathways, suggesting a counteracting effect to avoid Ca2+ overload. We propose lowering neuronal mitochondrial Ca2+ by inhibiting the mitochondrial Ca2+ uniporter as a novel potential therapeutic target against AD.
  41. Cell Death Differ. 2020 Apr 28.
    Simula L, Corrado M, Accordi B, Di Rita A, Nazio F, Antonucci Y, Di Daniele A, Caicci F, Caruana I, Soriano ME, Pigazzi M, Locatelli F, Cecconi F, Campello S.
      The Activation-Induced Cell Death (AICD) is a stimulation-dependent form of apoptosis used by the organism to shutdown T-cell response once the source of inflammation has been eliminated, while allowing the generation of immune memory. AICD is thought to progress through the activation of the extrinsic Fas/FasL pathway of cell death, leading to cytochrome-C release through caspase-8 and Bid activation. We recently described that, early upon AICD induction, mitochondria undergo structural alterations, which are required to promote cytochrome-C release and execute cell death. Here, we found that such alterations do not depend on the Fas/FasL pathway, which is instead only lately activated to amplify the cell death cascade. Instead, such alterations are primarily dependent on the MAPK proteins JNK1 and ERK1/2, which, in turn, regulate the activity of the pro-fission protein Drp1 and the pro-apoptotic factor Bim. The latter regulates cristae disassembly and cooperate with Drp1 to mediate the Mitochondrial Outer Membrane Permeabilization (MOMP), leading to cytochrome-C release. Interestingly, we found that Bim is also downregulated in T-cell Acute Lymphoblastic Leukemia (T-ALL) cells, this alteration favouring their escape from AICD-mediated control.
  42. Trends Cancer. 2020 Apr 23. pii: S2405-8033(20)30105-9. [Epub ahead of print]
    Singh AK, Yu X.
      Despite their ubiquitous expression, the inheritance of monoallelic germline mutations in breast cancer susceptibility gene type 1 or 2 (BRCA1/2) poses tissue-specific variations in cancer risks and primarily associate with familial breast and ovarian cancers. The molecular basis of this tissue-specific tumor incidence remains unknown and intriguing to cancer researchers. A plethora of recent reports support the idea that several nongenetic factors present in the tissue microenvironment could induce tumors in the mutant BRCA1/2 background. This Opinion article summarizes the recent advances on tissue-specific carcinogens and their complex crosstalk with the compromised DNA repair machinery of BRCA1/2-mutant cells. Finally, we present our perspective on the therapeutic and chemopreventive interpretations of these developments.
    Keywords:  BRCA1; BRCA2; carcinogens; hereditary cancers
  43. Carcinogenesis. 2020 Apr 29. pii: bgaa039. [Epub ahead of print]
    He F, Antonucci L, Karin M.
      Nuclear factor erythroid 2-related factor 2 (NRF2) is a master transcriptional regulator of genes whose products defend our cells for toxic and oxidative insults. Although NRF2 activation may reduce cancer risk by suppressing oxidative stress and tumor promoting inflammation, many cancers exhibit elevated NRF2 activity either due to mutations that disrupt the negative control of NRF2 activity or other factors. Importantly, NRF2 activation is associated with poor prognosis and NRF2 has turned out to be a key activator of cancer supportive anabolic metabolism. In this review, we summarize the diverse roles played by NRF2 in cancer focusing on metabolic reprogramming and tumor-promoting inflammation.
  44. Nat Microbiol. 2020 May;5(5): 655-667
    López-García P, Moreira D.
      The discovery of Asgard archaea, phylogenetically closer to eukaryotes than other archaea, together with improved knowledge of microbial ecology, impose new constraints on emerging models for the origin of the eukaryotic cell (eukaryogenesis). Long-held views are metamorphosing in favour of symbiogenetic models based on metabolic interactions between archaea and bacteria. These include the classical Searcy's and Hydrogen hypothesis, and the more recent Reverse Flow and Entangle-Engulf-Endogenize models. Two decades ago, we put forward the Syntrophy hypothesis for the origin of eukaryotes based on a tripartite metabolic symbiosis involving a methanogenic archaeon (future nucleus), a fermentative myxobacterial-like deltaproteobacterium (future eukaryotic cytoplasm) and a metabolically versatile methanotrophic alphaproteobacterium (future mitochondrion). A refined version later proposed the evolution of the endomembrane and nuclear membrane system by invagination of the deltaproteobacterial membrane. Here, we adapt the Syntrophy hypothesis to contemporary knowledge, shifting from the original hydrogen and methane-transfer-based symbiosis (HM Syntrophy) to a tripartite hydrogen and sulfur-transfer-based model (HS Syntrophy). We propose a sensible ecological scenario for eukaryogenesis in which eukaryotes originated in early Proterozoic microbial mats from the endosymbiosis of a hydrogen-producing Asgard archaeon within a complex sulfate-reducing deltaproteobacterium. Mitochondria evolved from versatile, facultatively aerobic, sulfide-oxidizing and, potentially, anoxygenic photosynthesizing alphaproteobacterial endosymbionts that recycled sulfur in the consortium. The HS Syntrophy hypothesis accounts for (endo)membrane, nucleus and metabolic evolution in a realistic ecological context. We compare and contrast the HS Syntrophy hypothesis to other models of eukaryogenesis, notably in terms of the mode and tempo of eukaryotic trait evolution, and discuss several model predictions and how these can be tested.