bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒04‒07
forty-six papers selected by
Christian Frezza,

  1. G-quadruplex dynamics contribute to regulation of mitochondrial gene expression.
  2. Watch What You (Self-) Eat: Autophagic Mechanisms that Modulate Metabolism.
  3. Lymphocyte Activation Gene-3 Maintains Mitochondrial and Metabolic Quiescence in Naive CD4+ T Cells.
  4. Reversible induction of mitophagy by an optogenetic bimodular system.
  5. Cancer-associated fibroblasts promote prostate cancer malignancy via metabolic rewiring and mitochondrial transfer.
  6. Mitochondrial porin links protein biogenesis to metabolism.
  7. Metabolic Reprogramming in Astrocytes Distinguishes Region-Specific Neuronal Susceptibility in Huntington Mice.
  8. From nutritional wealth to autophagy: In vivo metabolic dynamics in the cytosol, mitochondrion and shuttles of IgG producing CHO cells.
  9. Translating in vivo metabolomic analysis of succinate dehydrogenase deficient tumours into clinical utility.
  10. The class 3 PI3K coordinates autophagy and mitochondrial lipid catabolism by controlling nuclear receptor PPARα.
  11. The Endoplasmic Reticulum-Mitochondria Encounter Structure Complex Coordinates Coenzyme Q Biosynthesis.
  12. Mitochondrial Permeability Uncouples Elevated Autophagy and Lifespan Extension.
  13. Dynamics of the mitochondrial permeability transition pore: Transient and permanent opening events.
  14. Telomere Dysfunction Induces Sirtuin Repression that Drives Telomere-Dependent Disease.
  15. Mitochondrial mRNA translation initiation contributes to oxidative metabolism in the myocardia of aged, obese mice.
  16. Hierarchical activation of compartmentalized pools of AMPK depends on severity of nutrient or energy stress.
  17. LRRK2 mutations impair depolarization-induced mitophagy through inhibition of mitochondrial accumulation of RAB10.
  18. Dynamic Recruitment of Single RNAs to Processing Bodies Depends on RNA Functionality.
  19. Modulation of mtDNA copy number ameliorates the pathological consequences of a heteroplasmic mtDNA mutation in the mouse.
  20. MiR-195 regulates mitochondrial function by targeting mitofusin-2 in breast cancer cells.
  21. HIF-1α Is a Metabolic Switch between Glycolytic-Driven Migration and Oxidative Phosphorylation-Driven Immunosuppression of Tregs in Glioblastoma.
  22. Angiotensin II suppresses autophagy and disrupts the ultrastructural morphology and function of mitochondria in mouse skeletal muscle.
  23. Natural killer cells limit the clearance of senescent lung adenocarcinoma cells.
  24. Autophagy regulates lipid metabolism through selective turnover of NCoR1.
  25. A unique dynamin-related protein is essential for mitochondrial fission in Toxoplasma gondii.
  26. Mitochondrial Protein Synthesis and mtDNA Levels Coordinated through an Aminoacyl-tRNA Synthetase Subunit.
  27. Metabolic Regulation of Dendritic Cell Differentiation.
  28. Monomethyltransferase SET8 facilitates hepatocellular carcinoma growth by enhancing aerobic glycolysis.
  29. Mitochondria-associated lactate dehydrogenase is not a biologically significant contributor to bioenergetic function in murine striated muscle.
  30. A new hyperpolarized 13C ketone body probe reveals an increase in acetoacetate utilization in the diabetic rat heart.
  31. Membrane Cholesterol Efflux Drives Tumor-Associated Macrophage Reprogramming and Tumor Progression.
  32. The Metabolic Landscape of Prostate Cancer.
  33. The Expanding and Unexpected Functions of Mitochondria Contact Sites.
  34. Tranexamic acid suppresses the release of mitochondrial DNA, protects the endothelial monolayer and enhances oxidative phosphorylation.
  35. Mitochondrial Dysfunction in Huntington's Disease; Interplay Between HSF1, p53 and PGC-1α Transcription Factors.
  36. A catalytic domain variant of Mitofusin requiring a wildtype paralog for function uncouples mitochondrial outer-membrane tethering and fusion.
  37. Immunometabolism in rheumatoid arthritis.
  38. Interleukin-1β Induces mtDNA Release to Activate Innate Immune Signaling via cGAS-STING.
  39. Targeting cancer cell metabolism in glioblastoma.
  40. LKB1 expressed in dendritic cells governs the development and expansion of thymus-derived regulatory T cells.
  41. Metabolic Adaptation Fuels Lymph Node Metastasis.
  42. Dihydronicotinamide riboside is a potent NAD+ concentration enhancer in vitro and in vivo.
  43. An allosteric mechanism for potent inhibition of human ATP-citrate lyase.
  44. Fatty Acid Desaturation Gets a NAD+ Reputation.
  45. High-throughput, label-free, single-cell photoacoustic microscopy of intratumoral metabolic heterogeneity.
  46. Oncogenic PIK3CA promotes cellular stemness in an allele dose-dependent manner.
  1. Sci Rep. 2019 Apr 03. 9(1): 5605
    G-quadruplex dynamics contribute to regulation of mitochondrial gene expression.
    M Falabella, J E Kolesar, C Wallace, D de Jesus, L Sun, Y V Taguchi, C Wang, T Wang, I M Xiang, J K Alder, R Maheshan, W Horne, J Turek-Herman, P J Pagano, C M St Croix, N Sondheimer, L A Yatsunyk, F B Johnson, B A Kaufman.
      Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Mitochondrial DNA (mtDNA) sequences that are predicted to form G4 are enriched on the heavy-strand and have been associated with formation of deletion breakpoints. Increasing evidence supports the ability of mtDNA to form G4 in cancer cells; however, the functional roles of G4 structures in regulating mitochondrial nucleic acid homeostasis in non-cancerous cells remain unclear. Here, we demonstrate by live cell imaging that the G4-ligand RHPS4 localizes primarily to mitochondria at low doses. We find that low doses of RHPS4 do not induce a nuclear DNA damage response but do cause an acute inhibition of mitochondrial transcript elongation, leading to respiratory complex depletion. We also observe that RHPS4 interferes with mtDNA levels or synthesis both in cells and isolated mitochondria. Importantly, a mtDNA variant that increases G4 stability and anti-parallel G4-forming character shows a stronger respiratory defect in response to RHPS4, supporting the conclusion that mitochondrial sensitivity to RHPS4 is G4-mediated. Taken together, our results indicate a direct role for G4 perturbation in mitochondrial genome replication, transcription processivity, and respiratory function in normal cells.
    DOI:  https://doi.org/10.1038/s41598-019-41464-y
  2. Cell Metab. 2019 Apr 02. pii: S1550-4131(19)30131-7. [Epub ahead of print]29(4): 803-826
    Watch What You (Self-) Eat: Autophagic Mechanisms that Modulate Metabolism.
    Vikramjit Lahiri, Wayne D Hawkins, Daniel J Klionsky.
      Autophagy is an evolutionarily conserved lysosome- or vacuole-dependent catabolic pathway in eukaryotes. Autophagy functions basally for cellular quality control and is induced to act as an alternative source of basic metabolites during nutrient deprivation. These functions of autophagy are intimately connected to the regulation of metabolism, and the metabolic status of the cell in turn controls the nature and extent of autophagic induction. Here, we highlight the co-regulation of autophagy and metabolism with a special focus on selective autophagy that, along with bulk autophagy, plays a central role in regulating and rewiring metabolic circuits. We outline the metabolic signals that activate these pathways, the mechanisms involved, and the downstream effects and implications while recognizing yet unanswered questions. We also discuss the role of autophagy in the development and maintenance of adipose tissue, an emerging player in systemic metabolic homeostasis, and describe what is currently known about the complex relationship between autophagy and cancer.
    Keywords:  AMPK; autophagy; ferritinophagy; homeostasis; lysosome; mTOR; macroautophagy; mitophagy; physiology; protein turnover; proteostasis; stress
    DOI:  https://doi.org/10.1016/j.cmet.2019.03.003
  3. Cell Rep. 2019 Apr 02. pii: S2211-1247(19)30311-0. [Epub ahead of print]27(1): 129-141.e4
    Lymphocyte Activation Gene-3 Maintains Mitochondrial and Metabolic Quiescence in Naive CD4+ T Cells.
    Dana M Previte, Christina P Martins, Erin C O'Connor, Meghan L Marre, Gina M Coudriet, Noah W Beck, Ashley V Menk, Rebecca H Wright, Hubert M Tse, Greg M Delgoffe, Jon D Piganelli.
      Lymphocyte activation gene-3 (LAG-3) is an inhibitory receptor expressed by CD4+ T cells and tempers their homeostatic expansion. Because CD4+ T cell proliferation is tightly coupled to bioenergetics, we investigate the role of LAG-3 in modulating naive CD4+ T cell metabolism. LAG-3 deficiency enhances the metabolic profile of naive CD4+ T cells by elevating levels of mitochondrial biogenesis. In vivo, LAG-3 blockade partially restores expansion and the metabolic phenotype of wild-type CD4+ T cells to levels of Lag3-/- CD4+ T cells, solidifying that LAG-3 controls these processes. Lag3-/- CD4+ T cells also demonstrate greater signal transducer and activator of transcription 5 (STAT5) activation, enabling resistance to interleukin-7 (IL-7) deprivation. These results implicate this pathway as a target of LAG-3-mediated inhibition. Additionally, enhancement of STAT5 activation, as a result of LAG-3 deficiency, contributes to greater activation potential in these cells. These results identify an additional mode of regulation elicited by LAG-3 in controlling CD4+ T cell responses.
    Keywords:  CD4(+) T cell; LAG-3; STAT5; metabolism; mitochondria
    DOI:  https://doi.org/10.1016/j.celrep.2019.03.004
  4. Nat Commun. 2019 Apr 04. 10(1): 1533
    Reversible induction of mitophagy by an optogenetic bimodular system.
    Pasquale D'Acunzo, Flavie Strappazzon, Ignazio Caruana, Giacomo Meneghetti, Anthea Di Rita, Luca Simula, Gerrit Weber, Francesca Del Bufalo, Luisa Dalla Valle, Silvia Campello, Franco Locatelli, Francesco Cecconi.
      Autophagy-mediated degradation of mitochondria (mitophagy) is a key process in cellular quality control. Although mitophagy impairment is involved in several patho-physiological conditions, valuable methods to induce mitophagy with low toxicity in vivo are still lacking. Herein, we describe a new optogenetic tool to stimulate mitophagy, based on light-dependent recruitment of pro-autophagy protein AMBRA1 to mitochondrial surface. Upon illumination, AMBRA1-RFP-sspB is efficiently relocated from the cytosol to mitochondria, where it reversibly mediates mito-aggresome formation and reduction of mitochondrial mass. Finally, as a proof of concept of the biomedical relevance of this method, we induced mitophagy in an in vitro model of neurotoxicity, fully preventing cell death, as well as in human T lymphocytes and in zebrafish in vivo. Given the unique features of this tool, we think it may turn out to be very useful for a wide range of both therapeutic and research applications.
    DOI:  https://doi.org/10.1038/s41467-019-09487-1
  5. Oncogene. 2019 Apr 01.
    Cancer-associated fibroblasts promote prostate cancer malignancy via metabolic rewiring and mitochondrial transfer.
    Luigi Ippolito, Andrea Morandi, Maria Letizia Taddei, Matteo Parri, Giuseppina Comito, Alessandra Iscaro, Maria Rosaria Raspollini, Francesca Magherini, Elena Rapizzi, Julien Masquelier, Giulio G Muccioli, Pierre Sonveaux, Paola Chiarugi, Elisa Giannoni.
      Cancer-associated fibroblasts (CAFs) are the major cellular stromal component of many solid tumors. In prostate cancer (PCa), CAFs establish a metabolic symbiosis with PCa cells, contributing to cancer aggressiveness through lactate shuttle. In this study, we report that lactate uptake alters the NAD+/NADH ratio in the cancer cells, which culminates with SIRT1-dependent PGC-1α activation and subsequent enhancement of mitochondrial mass and activity. The high exploitation of mitochondria results in tricarboxylic acid cycle deregulation, accumulation of oncometabolites and in the altered expression of mitochondrial complexes, responsible for superoxide generation. Additionally, cancer cells hijack CAF-derived functional mitochondria through the formation of cellular bridges, a phenomenon that we observed in both in vitro and in vivo PCa models. Our work reveals a crucial function of tumor mitochondria as the energy sensors and transducers of CAF-dependent metabolic reprogramming and underscores the reliance of PCa cells on CAF catabolic activity and mitochondria trading.
    DOI:  https://doi.org/10.1038/s41388-019-0805-7
  6. Curr Genet. 2019 Apr 03.
    Mitochondrial porin links protein biogenesis to metabolism.
    Kim Nguyen Doan, Lars Ellenrieder, Thomas Becker.
      In this report, we summarize recent findings about a role of the outer membrane metabolite channel VDAC/porin in protein import into mitochondria. Mitochondria fulfill key functions for cellular energy metabolism. Their biogenesis involves the import of about 1000 different proteins that are produced as precursors on cytosolic ribosomes. The translocase of the outer membrane (TOM complex) forms the entry gate for mitochondrial precursor proteins. Dedicated protein translocases sort the preproteins into the different mitochondrial subcompartments. While protein transport pathways are analyzed to some detail, only little is known about regulatory mechanisms that fine-tune protein import upon metabolic signaling. Recently, a dual role of the voltage-dependent anion channel (VDAC), also termed porin, in mitochondrial protein biogenesis was reported. First, VDAC/porin promotes as a coupling factor import of carrier proteins into the inner membrane. Second, VDAC/porin regulates the formation of the TOM complex. Thus, the major metabolite channel in the outer membrane VDAC/porin connects protein import to mitochondrial metabolism.
    Keywords:  Mitochondria; Protein import; TOM complex; VDAC
    DOI:  https://doi.org/10.1007/s00294-019-00965-z
  7. Cell Metab. 2019 Mar 26. pii: S1550-4131(19)30132-9. [Epub ahead of print]
    Metabolic Reprogramming in Astrocytes Distinguishes Region-Specific Neuronal Susceptibility in Huntington Mice.
    Aris A Polyzos, Do Yup Lee, Rupsa Datta, Meghan Hauser, Helen Budworth, Amy Holt, Stephanie Mihalik, Pike Goldschmidt, Ken Frankel, Kelly Trego, Michael J Bennett, Jerry Vockley, Ke Xu, Enrico Gratton, Cynthia T McMurray.
      The basis for region-specific neuronal toxicity in Huntington disease is unknown. Here, we show that region-specific neuronal vulnerability is a substrate-driven response in astrocytes. Glucose is low in HdhQ(150/150) animals, and astrocytes in each brain region adapt by metabolically reprogramming their mitochondria to use endogenous, non-glycolytic metabolites as an alternative fuel. Each region is characterized by distinct metabolic pools, and astrocytes adapt accordingly. The vulnerable striatum is enriched in fatty acids, and mitochondria reprogram by oxidizing them as an energy source but at the cost of escalating reactive oxygen species (ROS)-induced damage. The cerebellum is replete with amino acids, which are precursors for glucose regeneration through the pentose phosphate shunt or gluconeogenesis pathways. ROS is not elevated, and this region sustains little damage. While mhtt expression imposes disease stress throughout the brain, sensitivity or resistance arises from an adaptive stress response, which is inherently region specific. Metabolic reprogramming may have relevance to other diseases.
    Keywords:  DNA repair; Huntington disease; astrocytes; double-strand break repair; fatty acids; metabolism; mitochondria; neurodegeneration; neurons; reprogramming
    DOI:  https://doi.org/10.1016/j.cmet.2019.03.004
  8. Metab Eng. 2019 Mar 28. pii: S1096-7176(18)30389-6. [Epub ahead of print]
    From nutritional wealth to autophagy: In vivo metabolic dynamics in the cytosol, mitochondrion and shuttles of IgG producing CHO cells.
    Lisa Junghans, Attila Teleki, Andy Wiranata Wijaya, Max Becker, Michael Schweikert, Ralf Takors.
      To fulfil the optimization needs of current biopharmaceutical processes the knowledge how to improve cell specific productivities is of outmost importance. This requires a detailed understanding of cellular metabolism on a subcellular level inside compartments such as cytosol and mitochondrion. Using IgG1 producing Chinese hamster ovary (CHO) cells, a pioneering protocol for compartment-specific metabolome analysis was applied. Various production-like growth conditions ranging from ample glucose and amino acid supply via moderate to severe nitrogen limitation were investigated in batch cultures. The combined application of quantitative metabolite pool analysis, 13C tracer studies and non-stationary flux calculations revealed that Pyr/H+ symport (MPC1/2) bore the bulk of the mitochondrial transport under ample nutrient supply. Glutamine limitation induced the concerted adaptation of the bidirectional Mal/aKG (OGC) and the Mal/HPO42- antiporter (DIC), even installing completely reversed shuttle fluxes. As a result, NADPH and ATP formation were adjusted to cellular needs unraveling the key role of cytosolic malic enzyme for NADPH production. Highest cell specific IgG1 productivities were closely correlated to a strong mitochondrial malate export according to the anabolic demands. The requirement to install proper NADPH supply for optimizing the production of monoclonal antibodies is clearly outlined. Interestingly, it was observed that mitochondrial citric acid cycle activity was always maintained enabling constant cytosolic adenylate energy charges at physiological levels, even under autophagy conditions.
    Keywords:  (13)C isotopic tracer studies; CHO; Cell line engineering targets; Compartment-specific metabolomics; Cytosolic fluxes; In vivo; Mitochondrial fluxes; Recombinant protein production
    DOI:  https://doi.org/10.1016/j.ymben.2019.02.005
  9. JCO Precis Oncol. 2018 Mar 29. 2 1-12
    Translating in vivo metabolomic analysis of succinate dehydrogenase deficient tumours into clinical utility.
    Ruth T Casey, Mary A McLean, Basetti Madhu, Benjamin G Challis, Rogier Ten Hoopen, Thomas Roberts, Graeme R Clark, Deborah Pittfield, Helen L Simpson, Venkata R Bulusu, Kieran Allinson, Lisa Happerfield, Soo-Mi Park, Alison Marker, Olivier Giger, Eamonn R Maher, Ferdia A Gallagher.
      Purpose: Mutations in the mitochondrial enzyme succinate dehydrogenase (SDH) subunit genes are associated with a wide spectrum of tumours including phaeochromocytoma and paraganglioma (PPGL) 1, 2, gastrointestinal stromal tumours (GIST) 3, renal cell carcinoma (RCC) 4 and pituitary adenomas5. SDH-related tumorigenesis is believed to be secondary to accumulation of the oncometabolite succinate. Our aim was to investigate the potential clinical applications of MRI spectroscopy (1H-MRS) in a range of suspected SDH-related tumours.Patients and methods: Fifteen patients were recruited to this study. Respiratory-gated single-voxel 1H-MRS was performed at 3T to quantify the content of succinate at 2.4 ppm and choline at 3.22 ppm.
    Results: A succinate peak was seen in six patients, all of whom had a germline SDHx mutation or loss of SDHB by immunohistochemistry. A succinate peak was also detected in two patients with a metastatic wild-type GIST (wtGIST) and no detectable germline SDHx mutation but a somatic epimutation in SDHC. Three patients without a tumour succinate peak retained SDHB expression, consistent with SDH functionality. In six cases with a borderline or absent peak, technical difficulties such as motion artefact rendered 1H-MRS difficult to interpret. Sequential imaging in a patient with a metastatic abdominal paraganglioma demonstrated loss of the succinate peak after four cycles of [177Lu]-DOTATATE, with a corresponding biochemical response in normetanephrine.
    Conclusions: This study has demonstrated the translation into clinical practice of in vivo metabolomic analysis using 1H-MRS in patients with SDH-deficient tumours. Potential applications include non-invasive diagnosis and disease stratification, as well as monitoring of tumour response to targeted treatments.
    Keywords:  Translational; hereditary; imaging technique; metabolic cancer; metabolomics
    DOI:  https://doi.org/10.1200/PO.17.00191
  10. Nat Commun. 2019 Apr 05. 10(1): 1566
    The class 3 PI3K coordinates autophagy and mitochondrial lipid catabolism by controlling nuclear receptor PPARα.
    Anton Iershov, Ivan Nemazanyy, Chantal Alkhoury, Muriel Girard, Esther Barth, Nicolas Cagnard, Alexandra Montagner, Dominique Chretien, Elena I Rugarli, Herve Guillou, Mario Pende, Ganna Panasyuk.
      The class 3 phosphoinositide 3-kinase (PI3K) is required for lysosomal degradation by autophagy and vesicular trafficking, assuring nutrient availability. Mitochondrial lipid catabolism is another energy source. Autophagy and mitochondrial metabolism are transcriptionally controlled by nutrient sensing nuclear receptors. However, the class 3 PI3K contribution to this regulation is unknown. We show that liver-specific inactivation of Vps15, the essential regulatory subunit of the class 3 PI3K, elicits mitochondrial depletion and failure to oxidize fatty acids. Mechanistically, transcriptional activity of Peroxisome Proliferator Activated Receptor alpha (PPARα), a nuclear receptor orchestrating lipid catabolism, is blunted in Vps15-deficient livers. We find PPARα repressors Histone Deacetylase 3 (Hdac3) and Nuclear receptor co-repressor 1 (NCoR1) accumulated in Vps15-deficient livers due to defective autophagy. Activation of PPARα or inhibition of Hdac3 restored mitochondrial biogenesis and lipid oxidation in Vps15-deficient hepatocytes. These findings reveal roles for the class 3 PI3K and autophagy in transcriptional coordination of mitochondrial metabolism.
    DOI:  https://doi.org/10.1038/s41467-019-09598-9
  11. Contact (Thousand Oaks). 2019 Feb 22. 2 2515256418825409
    The Endoplasmic Reticulum-Mitochondria Encounter Structure Complex Coordinates Coenzyme Q Biosynthesis.
    Michal Eisenberg-Bord, Hui S Tsui, Diana Antunes, Lucía Fernández-Del-Río, Michelle C Bradley, Cory D Dunn, Theresa P T Nguyen, Doron Rapaport, Catherine F Clarke, Maya Schuldiner.
      Loss of the endoplasmic reticulum (ER)-mitochondria encounter structure (ERMES) complex that resides in contact sites between the yeast ER and mitochondria leads to impaired respiration; however, the reason for that is not clear. We find that in ERMES null mutants, there is an increase in the level of mRNAs encoding for biosynthetic enzymes of coenzyme Q6 (CoQ6), an essential electron carrier of the mitochondrial respiratory chain. We show that the mega complexes involved in CoQ6 biosynthesis (CoQ synthomes) are destabilized in ERMES mutants. This, in turn, affects the level and distribution of CoQ6 within the cell, resulting in reduced mitochondrial CoQ6. We suggest that these outcomes contribute to the reduced respiration observed in ERMES mutants. Fluorescence microscopy experiments demonstrate close proximity between the CoQ synthome and ERMES, suggesting a spatial coordination. The involvement of the ER-mitochondria contact site in regulation of CoQ6 biogenesis highlights an additional level of communication between these two organelles.
    Keywords:  ER-mitochondrial encounter structure; coenzyme Q; endoplasmic reticulum; mitochondrion (mitochondria)
    DOI:  https://doi.org/10.1177/2515256418825409
  12. Cell. 2019 Apr 04. pii: S0092-8674(19)30162-X. [Epub ahead of print]177(2): 299-314.e16
    Mitochondrial Permeability Uncouples Elevated Autophagy and Lifespan Extension.
    Ben Zhou, Johannes Kreuzer, Caroline Kumsta, Lianfeng Wu, Kimberli J Kamer, Lucydalila Cedillo, Yuyao Zhang, Sainan Li, Michael C Kacergis, Christopher M Webster, Geza Fejes-Toth, Aniko Naray-Fejes-Toth, Sudeshna Das, Malene Hansen, Wilhelm Haas, Alexander A Soukas.
      Autophagy is required in diverse paradigms of lifespan extension, leading to the prevailing notion that autophagy is beneficial for longevity. However, why autophagy is harmful in certain contexts remains unexplained. Here, we show that mitochondrial permeability defines the impact of autophagy on aging. Elevated autophagy unexpectedly shortens lifespan in C. elegans lacking serum/glucocorticoid regulated kinase-1 (sgk-1) because of increased mitochondrial permeability. In sgk-1 mutants, reducing levels of autophagy or mitochondrial permeability transition pore (mPTP) opening restores normal lifespan. Remarkably, low mitochondrial permeability is required across all paradigms examined of autophagy-dependent lifespan extension. Genetically induced mPTP opening blocks autophagy-dependent lifespan extension resulting from caloric restriction or loss of germline stem cells. Mitochondrial permeability similarly transforms autophagy into a destructive force in mammals, as liver-specific Sgk knockout mice demonstrate marked enhancement of hepatocyte autophagy, mPTP opening, and death with ischemia/reperfusion injury. Targeting mitochondrial permeability may maximize benefits of autophagy in aging.
    Keywords:  SGK; aging; autophagy; ischemia/reperfusion injury; longevity; mPTP; mTORC2; mitochondrial permeability
    DOI:  https://doi.org/10.1016/j.cell.2019.02.013
  13. Arch Biochem Biophys. 2019 Mar 28. pii: S0003-9861(18)30947-0. [Epub ahead of print]666 31-39
    Dynamics of the mitochondrial permeability transition pore: Transient and permanent opening events.
    Liron Boyman, Andrew K Coleman, Guiling Zhao, Andrew P Wescott, Humberto C Joca, B Maura Greiser, Mariusz Karbowski, Chris W Ward, W J Lederer.
      A gentle optical examination of the mitochondrial permeability transition pore (mPTP) opening events was carried out in isolated quiescent ventricular myocytes by tracking the inner membrane potential (ΔΨM) using TMRM (tetramethylrhodamine methyl ester). Zeiss Airyscan 880 ″super-resolution" or "high-resolution" imaging was done with very low levels of illumination (0.009% laser power). In cellular areas imaged every 9 s (ROI or regions of interest), transient depolarizations of variable amplitudes occurred at increasing rates for the first 30 min. The time to first depolarization events was 8.4 min (±1.1 SEM n = 21 cells). At longer times, essentially permanent and irreversible depolarizations occurred at an increasing fraction of all events. In other cellular areas surrounding the ROI, mitochondria were rarely illuminated (once per 5 min) and virtually no permanent depolarization events occurred for over 1 h of imaging. These findings suggest that photon stress due to the imaging itself plays an important role in the generation of both the transient mPTP opening events as well as the permanent mPTP opening events. Consistent with the evidence that photon "stress" in mitochondria loaded with virtually any photon absorbing substance, generates reactive oxygen species (ROS) [1-5], we show that cyclosporine-A (CsA, 10 μM) and the antioxidant n-acetyl cysteine (NAC, 10 mM), reduced the number of events by 80% and 93% respectively. Furthermore, CsA and NAC treatment led to the virtual disappearance of permanent depolarization events. Nevertheless, all transient depolarization events in any condition (control, CsA and NAC) appeared to repolarize with a similar half-time of 30 ± 6 s (n = 478) at 37 °C. Further experiments showed quantitatively similar results in cerebral vascular smooth muscle cells, using a different confocal system, and different photon absorbing reagent (TMRE; tetramethylrhodamine ethyl ester). In these experiments, using modest power (1% laser power) transient depolarization events were seen in only 8 out of 23 cells while with higher power (8%), all cells showed transient events, which align with the level of photon stress being the driver of the effect. Together, our findings suggest that photon-induced ROS is sufficient to cause depolarization events of individual mitochondria in quiescent cells; without electrical or mechanical activity to stimulates mitochondrial metabolism, and without raising the mitochondrial matrix Ca2+. In a broad context, these findings neither support nor deny the relevance or occurrence of ΔΨM depolarization events in specific putatively physiologic mitochondrial behaviors such as MitoFlashes [6,7] or MitoWinks [8]. Instead, our findings raise a caution with regards to the physiological and pathophysiological functions attributed to singular ΔΨM depolarization events when those functions are investigated using photon absorbing substances. Nevertheless, using photon stress as a tool ("Optical Stress-Probe"), we can extract information on the activation, reversibility, permanency and kinetics of mitochondrial depolarization. These data may provide new information on mPTP, help identify the mPTP protein complex, and establish the physiological function of the mPTP protein complex and their links to MitoFlashes and MitoWinks.
    Keywords:  Mitochondria; Mitochondrial inner membrane potential; Mitochondrial permeability transition pore; Ventricular myocytes
    DOI:  https://doi.org/10.1016/j.abb.2019.03.016
  14. Cell Metab. 2019 Mar 20. pii: S1550-4131(19)30129-9. [Epub ahead of print]
    Telomere Dysfunction Induces Sirtuin Repression that Drives Telomere-Dependent Disease.
    Hisayuki Amano, Arindam Chaudhury, Cristian Rodriguez-Aguayo, Lan Lu, Viktor Akhanov, Andre Catic, Yury V Popov, Eric Verdin, Hannah Johnson, Fabio Stossi, David A Sinclair, Eiko Nakamaru-Ogiso, Gabriel Lopez-Berestein, Jeffrey T Chang, Joel R Neilson, Alan Meeker, Milton Finegold, Joseph A Baur, Ergun Sahin.
      Telomere shortening is associated with stem cell decline, fibrotic disorders, and premature aging through mechanisms that are incompletely understood. Here, we show that telomere shortening in livers of telomerase knockout mice leads to a p53-dependent repression of all seven sirtuins. P53 regulates non-mitochondrial sirtuins (Sirt1, 2, 6, and 7) post-transcriptionally through microRNAs (miR-34a, 26a, and 145), while the mitochondrial sirtuins (Sirt3, 4, and 5) are regulated in a peroxisome proliferator-activated receptor gamma co-activator 1 alpha-/beta-dependent manner at the transcriptional level. Administration of the NAD(+) precursor nicotinamide mononucleotide maintains telomere length, dampens the DNA damage response and p53, improves mitochondrial function, and, functionally, rescues liver fibrosis in a partially Sirt1-dependent manner. These studies establish sirtuins as downstream targets of dysfunctional telomeres and suggest that increasing Sirt1 activity alone or in combination with other sirtuins stabilizes telomeres and mitigates telomere-dependent disorders.
    Keywords:  liver disease; metabolism; p53; sirtuins; telomeres
    DOI:  https://doi.org/10.1016/j.cmet.2019.03.001
  15. Exp Gerontol. 2019 Mar 27. pii: S0531-5565(19)30144-5. [Epub ahead of print]121 62-70
    Mitochondrial mRNA translation initiation contributes to oxidative metabolism in the myocardia of aged, obese mice.
    David E Lee, Richard A Perry, Jacob L Brown, Megan E Rosa-Caldwell, Lemuel A Brown, Wesley S Haynie, Narasimhan Rajaram, Tyrone A Washington, Nicholas P Greene.
      Being both advanced in age and obese each contribute to cardiac hypertrophy in a unique manner. Electron transport complexes I and IV are implicated in deficient electron transport during cardiomyopathies and contain the majority of protein subunits that are transcribed and translated by machinery localized within the mitochondria.PURPOSE: To assess myocardial mt-mRNA translation factors in relation to mitochondrial content and mtDNA-encoded protein using a mouse model of aged obesity and to test the relationship of mt-mRNA translation initiation factor 2 (mtIF2) to oxidative capacity and the cellular oxidation-reduction (redox) state in cardiomyocytes.
    METHODS: Male C56BL/6 J mice fed lean or high fat diet were aged to either ~3 months or ~22 months, the heart was excised and analyzed using immunoblot and qPCR to assess differences in mitochondrial mRNA translation machinery. Using H9c2 cardiomyocytes, mtIF2 was knocked-down and oxidative metabolic characteristics assessed including oxidation/reduction state, bioenergetic flux, and hypoxic resistance was tested.
    RESULTS: Aged, obese mouse hearts were ~40% larger than young, lean controls and contained ~50% less mtIF2 protein alongside ~25-50% lower content of Cytb, a protein encoded by mtDNA. Reducing the level of mtIF2 by shRNA is associated with ~15-20% lower content of OXPHOS complex I and IV, ~30% lower optical redox ratio, ~40% oxygen reserve capacity, and ~20% less cell survival following hypoxia.
    CONCLUSION: We present evidence of altered mt-mRNA translation during cardiac hypertrophy in aged obesity. We build on these results by demonstrating the necessity of mtIF2 in maintaining oxidative characteristics of cardiac muscle cells.
    Keywords:  Bioenergetics; Cardiac hypertrophy; Hypoxia-reoxygenation; Mitochondrial quality; Optical redox imaging
    DOI:  https://doi.org/10.1016/j.exger.2019.03.009
  16. Cell Res. 2019 Apr 04.
    Hierarchical activation of compartmentalized pools of AMPK depends on severity of nutrient or energy stress.
    Yue Zong, Chen-Song Zhang, Mengqi Li, Wen Wang, Zhichao Wang, Simon A Hawley, Teng Ma, Jin-Wei Feng, Xiao Tian, Qu Qi, Yu-Qing Wu, Cixiong Zhang, Zhiyun Ye, Shu-Yong Lin, Hai-Long Piao, D Grahame Hardie, Sheng-Cai Lin.
      AMPK, a master regulator of metabolic homeostasis, is activated by both AMP-dependent and AMP-independent mechanisms. The conditions under which these different mechanisms operate, and their biological implications are unclear. Here, we show that, depending on the degree of elevation of cellular AMP, distinct compartmentalized pools of AMPK are activated, phosphorylating different sets of targets. Low glucose activates AMPK exclusively through the AMP-independent, AXIN-based pathway in lysosomes to phosphorylate targets such as ACC1 and SREBP1c, exerting early anti-anabolic and pro-catabolic roles. Moderate increases in AMP expand this to activate cytosolic AMPK also in an AXIN-dependent manner. In contrast, high concentrations of AMP, arising from severe nutrient stress, activate all pools of AMPK independently of AXIN. Surprisingly, mitochondrion-localized AMPK is activated to phosphorylate ACC2 and mitochondrial fission factor (MFF) only during severe nutrient stress. Our findings reveal a spatiotemporal basis for hierarchical activation of different pools of AMPK during differing degrees of stress severity.
    DOI:  https://doi.org/10.1038/s41422-019-0163-6
  17. Autophagy. 2019 Apr 04.
    LRRK2 mutations impair depolarization-induced mitophagy through inhibition of mitochondrial accumulation of RAB10.
    Fieke Wauters, Tom Cornelissen, Dorien Imberechts, Shaun Martin, Brianada Koentjoro, Carolyn Sue, Peter Vangheluwe, Wim Vandenberghe.
      Parkinson disease (PD) is a disabling, incurable disorder with increasing prevalence in the western world. In rare cases PD is caused by mutations in the genes for PINK1 (PTEN induced kinase 1) or PRKN (parkin RBR E3 ubiquitin protein ligase), which impair the selective autophagic elimination of damaged mitochondria (mitophagy). Mutations in the gene encoding LRRK2 (leucine rich repeat kinase 2) are the most common monogenic cause of PD. Here, we report that the LRRK2 kinase substrate RAB10 accumulates on depolarized mitochondria in a PINK1- and PRKN-dependent manner. RAB10 binds the autophagy receptor OPTN (optineurin), promotes OPTN accumulation on depolarized mitochondria and facilitates mitophagy. In PD patients with the two most common LRRK2 mutations (G2019S and R1441C), RAB10 phosphorylation at threonine 73 is enhanced, while RAB10 interaction with OPTN, accumulation of RAB10 and OPTN on depolarized mitochondria, depolarization-induced mitophagy and mitochondrial function are all impaired. These defects in LRRK2 mutant patient cells are rescued by LRRK2 knockdown and LRRK2 kinase inhibition. A phosphomimetic RAB10 mutant showed less OPTN interaction and less translocation to depolarized mitochondria than wild-type RAB10, and failed to rescue mitophagy in LRRK2 mutant cells. These data connect LRRK2 with PINK1- and PRKN-mediated mitophagy via its substrate RAB10, and indicate that the pathogenic effects of mutations in LRRK2, PINK1 and PRKN may converge on a common pathway.
    Keywords:  OPTN; PARK2; PINK1; PRKN; Parkinson disease; autophagy receptor; mitochondria; optineurin; parkin; selective autophagy
    DOI:  https://doi.org/10.1080/15548627.2019.1603548
  18. Mol Cell. 2019 Mar 23. pii: S1097-2765(19)30175-3. [Epub ahead of print]
    Dynamic Recruitment of Single RNAs to Processing Bodies Depends on RNA Functionality.
    Sethuramasundaram Pitchiaya, Marcio D A Mourao, Ameya P Jalihal, Lanbo Xiao, Xia Jiang, Arul M Chinnaiyan, Santiago Schnell, Nils G Walter.
      Cellular RNAs often colocalize with cytoplasmic, membrane-less ribonucleoprotein (RNP) granules enriched for RNA-processing enzymes, termed processing bodies (PBs). Here we track the dynamic localization of individual miRNAs, mRNAs, and long non-coding RNAs (lncRNAs) to PBs using intracellular single-molecule fluorescence microscopy. We find that unused miRNAs stably bind to PBs, whereas functional miRNAs, repressed mRNAs, and lncRNAs both transiently and stably localize within either the core or periphery of PBs, albeit to different extents. Consequently, translation potential and 3' versus 5' placement of miRNA target sites significantly affect the PB localization dynamics of mRNAs. Using computational modeling and supporting experimental approaches, we show that partitioning in the PB phase attenuates mRNA silencing, suggesting that physiological mRNA turnover occurs predominantly outside of PBs. Instead, our data support a PB role in sequestering unused miRNAs for surveillance and provide a framework for investigating the dynamic assembly of RNP granules by phase separation at single-molecule resolution.
    Keywords:  RNP granules; long non-coding RNAs; mRNAs; microRNAs; phase separation; processing bodies; single-molecule microscopy
    DOI:  https://doi.org/10.1016/j.molcel.2019.03.001
  19. Sci Adv. 2019 Apr;5(4): eaav9824
    Modulation of mtDNA copy number ameliorates the pathological consequences of a heteroplasmic mtDNA mutation in the mouse.
    R Filograna, C Koolmeister, M Upadhyay, A Pajak, P Clemente, R Wibom, M L Simard, A Wredenberg, C Freyer, J B Stewart, N G Larsson.
      Heteroplasmic mtDNA mutations typically act in a recessive way and cause mitochondrial disease only if present above a certain threshold level. We have experimentally investigated to what extent the absolute levels of wild-type (WT) mtDNA influence disease manifestations by manipulating TFAM levels in mice with a heteroplasmic mtDNA mutation in the tRNAAla gene. Increase of total mtDNA levels ameliorated pathology in multiple tissues, although the levels of heteroplasmy remained the same. A reduction in mtDNA levels worsened the phenotype in postmitotic tissues, such as heart, whereas there was an unexpected beneficial effect in rapidly proliferating tissues, such as colon, because of enhanced clonal expansion and selective elimination of mutated mtDNA. The absolute levels of WT mtDNA are thus an important determinant of the pathological manifestations, suggesting that pharmacological or gene therapy approaches to selectively increase mtDNA copy number provide a potential treatment strategy for human mtDNA mutation disease.
    DOI:  https://doi.org/10.1126/sciadv.aav9824
  20. RNA Biol. 2019 Apr 01.
    MiR-195 regulates mitochondrial function by targeting mitofusin-2 in breast cancer cells.
    Paresh Kumar Purohit, Ruairidh Edwards, Kostas Tokatlidis, Neeru Saini.
      Mitochondrial dynamics is a highly dysregulated process in cancer. Apoptosis and mitochondrial fission are two concurrent events wherein increased mitochondrial fragmentation serves as a hallmark of apoptosis. We have shown earlier that miR-195 exerts pro-apoptotic effects in breast cancer cells. Herein, we have demonstrated miR-195 as a modulator of mitochondrial dynamics and function. Imaging experiments upon miR-195 treatment have shown that mitochondria undergo extensive fission. We validated mitofusin2 as a potential target of miR-195. Which may provide a molecular explanation for the respiratory defects induced by miR-195 over-expression in breast cancer cells? Active, but not total, mitochondrial mass, was reduced with increasing levels of miR-195. We have further shown that miR-195 enhances mitochondrial SOD-2 expression but does not affect PINK1 levels in breast cancer cells. Collectively, we have revealed that miR-195 is a modulator of mitochondrial dynamics by targeting MFN2 thereby impairing mitochondrial function. Concomitantly, it enhances the scavenger of reactive oxygen species (SOD-2) to maintain moderate levels of oxidative stress. Our findings suggest a therapeutic potential of miR-195 in both ER-positive as well as ER-negative breast cancer cells.
    Keywords:  - MiR-195; Breast cancer cells; Mitochondrial dysfunction; Mitofusin-2
    DOI:  https://doi.org/10.1080/15476286.2019.1600999
  21. Cell Rep. 2019 Apr 02. pii: S2211-1247(19)30345-6. [Epub ahead of print]27(1): 226-237.e4
    HIF-1α Is a Metabolic Switch between Glycolytic-Driven Migration and Oxidative Phosphorylation-Driven Immunosuppression of Tregs in Glioblastoma.
    Jason Miska, Catalina Lee-Chang, Aida Rashidi, Megan E Muroski, Alan L Chang, Aurora Lopez-Rosas, Peng Zhang, Wojciech K Panek, Alex Cordero, Yu Han, Atique U Ahmed, Navdeep S Chandel, Maciej S Lesniak.
      The mechanisms by which regulatory T cells (Tregs) migrate to and function within the hypoxic tumor microenvironment are unclear. Our studies indicate that specific ablation of hypoxia-inducible factor 1α (HIF-1α) in Tregs results in enhanced CD8+ T cell suppression versus wild-type Tregs under hypoxia, due to increased pyruvate import into the mitochondria. Importantly, HIF-1α-deficient Tregs are minimally affected by the inhibition of lipid oxidation, a fuel that is critical for Treg metabolism in tumors. Under hypoxia, HIF-1α directs glucose away from mitochondria, leaving Tregs dependent on fatty acids for mitochondrial metabolism within the hypoxic tumor. Indeed, inhibition of lipid oxidation enhances the survival of mice with glioma. Interestingly, HIF-1α-deficient-Treg mice exhibit significantly enhanced animal survival in a murine model of glioma, due to their stymied migratory capacity, explaining their reduced abundance in tumor-bearing mice. Thus HIF-1α acts as a metabolic switch for Tregs between glycolytic-driven migration and oxidative phosphorylation-driven immunosuppression.
    Keywords:  fatty acid oxidation; glioblastoma; glycolysis; immunosuppression; migration; oxidative phosphorylation; regulatory T cell
    DOI:  https://doi.org/10.1016/j.celrep.2019.03.029
  22. J Appl Physiol (1985). 2019 Apr 04.
    Angiotensin II suppresses autophagy and disrupts the ultrastructural morphology and function of mitochondria in mouse skeletal muscle.
    Kleiton Augusto Santos Silva, Thaysa Ghiarone, Kathy Schreiber, DeAna Grant, Tommi White, Madlyn I Frisard, Sergiy Sukhanov, Bysani Chandrasekar, Patrice Delafontaine, Tadashi Yoshida.
      Angiotensin II (Ang II)-induced skeletal muscle wasting is characterized by activation of the ubiquitin-proteasome system. However, the potential involvement of the proteolytic system macroautophagy/autophagy in this wasting process remains elusive. Autophagy is precisely regulated to maintain cell survival and homeostasis, thus its dysregulation ( i.e., overactivation or persistent suppression) could lead to detrimental outcomes in skeletal muscle. Here we show that infusion of Ang II for seven days in male FVB mice suppressed autophagy in skeletal muscle. Ang II blunted LC3B-I to LC3B-II conversion (an autophagosome marker), increased p62/SQSTM1 (an autophagy cargo receptor) protein expression, and decreased the number of autophagic vacuoles. Ang II inhibited ULK1 via inhibition of AMPK and activation of mTORC1, leading to reduced phosphorylation of beclin1Ser14 and ATG14Ser29, suggesting that Ang II impairs autophagosome formation in skeletal muscle. In line with Ang II-mediated suppression of autophagy, Ang II promoted accumulation of abnormal/damaged mitochondria, characterized by swelling and disorganized cristae and matrix dissolution, with associated increase in PINK1 protein expression. Ang II also reduced mitochondrial respiration, indicative of mitochondrial dysfunction. Together, these results demonstrate that Ang II reduces autophagic activity and disrupts mitochondrial ultrastructure and function, likely contributing to skeletal muscle wasting. Therefore, strategies that activate autophagy in skeletal muscle have the potential to prevent or blunt Ang II-induced skeletal muscle wasting in chronic diseases.
    Keywords:  Autophagosome; LC3B; beclin-1; mitochondrial respiration; proteolysis
    DOI:  https://doi.org/10.1152/japplphysiol.00898.2018
  23. Oncogenesis. 2019 Apr 01. 8(4): 24
    Natural killer cells limit the clearance of senescent lung adenocarcinoma cells.
    Kate L Stokes, Virna Cortez-Retamozo, Jonuelle Acosta, Brian Lauderback, Camila Robles-Oteiza, Michelle Cicchini, Mikael J Pittet, David M Feldser.
      Senescence is an important p53-controlled tumor suppressor program that not only opposes the proliferation of cancer cells but also promotes their immune-mediated clearance in certain contexts. In hepatocellular cancer, p53 induction promotes an innate immune cell-mediated clearance of senescent cells wherein natural killer (NK) cells seem to play the primary sentinel role. Whether NK cells also surveil cancer cells in other tumor types when p53 is activated to promote a senescence response is unknown. To identify the role that NK and other innate immune cell types have on the surveillance and destruction of lung adenocarcinoma cells, we developed an orthotopic transplantation model where p53 gene function could be restored to induce senescence after successful engraftment of tumor cells in the mouse lung. Contrary to precedent, we found that NK cells actually limited the efficient clearance of tumor cells from the mouse lung after p53 restoration. Instead, activation of p53 induced the infiltration of monocytes, neutrophils, and interstitial macrophages. Loss of NK cells further promoted expansion of these inflammatory cell types and tumor clearance after p53 restoration. These observations suggest that NK cell responses to p53 activation in lung adenocarcinoma is distinct from those found in other tumor types and that diverse innate immune cell populations may play context-dependent roles during tumor immune surveillance. Further, our data provide an impetus to understand the broader mechanisms that regulate cancer cell destruction by multiple cell types of the innate immune system and distinct cancer contexts.
    DOI:  https://doi.org/10.1038/s41389-019-0133-3
  24. Nat Commun. 2019 Apr 05. 10(1): 1567
    Autophagy regulates lipid metabolism through selective turnover of NCoR1.
    Tetsuya Saito, Akiko Kuma, Yuki Sugiura, Yoshinobu Ichimura, Miki Obata, Hiroshi Kitamura, Shujiro Okuda, Hyeon-Cheol Lee, Kazutaka Ikeda, Yumi Kanegae, Izumu Saito, Johan Auwerx, Hozumi Motohashi, Makoto Suematsu, Tomoyoshi Soga, Takehiko Yokomizo, Satoshi Waguri, Noboru Mizushima, Masaaki Komatsu.
      Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in β-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates β-oxidation and ketone bodies production.
    DOI:  https://doi.org/10.1038/s41467-019-08829-3
  25. PLoS Pathog. 2019 Apr;15(4): e1007512
    A unique dynamin-related protein is essential for mitochondrial fission in Toxoplasma gondii.
    Carmen Melatti, Manuela Pieperhoff, Leandro Lemgruber, Ehmke Pohl, Lilach Sheiner, Markus Meissner.
      The single mitochondrion of apicomplexan protozoa is thought to be critical for all stages of the life cycle, and is a validated drug target against these important human and veterinary parasites. In contrast to other eukaryotes, replication of the mitochondrion is tightly linked to the cell cycle. A key step in mitochondrial segregation is the fission event, which in many eukaryotes occurs by the action of dynamins constricting the outer membrane of the mitochondria from the cytosolic face. To date, none of the components of the apicomplexan fission machinery have been identified and validated. We identify here a highly divergent, dynamin-related protein (TgDrpC), conserved in apicomplexans as essential for mitochondrial biogenesis and potentially for fission in Toxoplasma gondii. We show that TgDrpC is found adjacent to the mitochondrion, and is localised both at its periphery and at its basal part, where fission is expected to occur. We demonstrate that depletion or dominant negative expression of TgDrpC results in interconnected mitochondria and ultimately in drastic changes in mitochondrial morphology, as well as in parasite death. Intriguingly, we find that the canonical adaptor TgFis1 is not required for mitochondrial fission. The identification of an Apicomplexa-specific enzyme required for mitochondrial biogenesis and essential for parasite growth highlights parasite adaptation. This work paves the way for future drug development targeting TgDrpC, and for the analysis of additional partners involved in this crucial step of apicomplexan multiplication.
    DOI:  https://doi.org/10.1371/journal.ppat.1007512
  26. Cell Rep. 2019 Apr 02. pii: S2211-1247(19)30329-8. [Epub ahead of print]27(1): 40-47.e5
    Mitochondrial Protein Synthesis and mtDNA Levels Coordinated through an Aminoacyl-tRNA Synthetase Subunit.
    Daria Picchioni, Albert Antolin-Fontes, Noelia Camacho, Claus Schmitz, Alba Pons-Pons, Marta Rodríguez-Escribà, Antigoni Machallekidou, Merve Nur Güler, Panagiota Siatra, Maria Carretero-Junquera, Alba Serrano, Stacy L Hovde, Philip A Knobel, Eva M Novoa, Maria Solà-Vilarrubias, Laurie S Kaguni, Travis H Stracker, Lluís Ribas de Pouplana.
      The aminoacylation of tRNAs by aminoacyl-tRNA synthetases (ARSs) is a central reaction in biology. Multiple regulatory pathways use the aminoacylation status of cytosolic tRNAs to monitor and regulate metabolism. The existence of equivalent regulatory networks within the mitochondria is unknown. Here, we describe a functional network that couples protein synthesis to DNA replication in animal mitochondria. We show that a duplication of the gene coding for mitochondrial seryl-tRNA synthetase (SerRS2) generated in arthropods a paralog protein (SLIMP) that forms a heterodimeric complex with a SerRS2 monomer. This seryl-tRNA synthetase variant is essential for protein synthesis and mitochondrial respiration. In addition, SLIMP interacts with the substrate binding domain of the mitochondrial protease LON, thus stimulating proteolysis of the DNA-binding protein TFAM and preventing mitochondrial DNA (mtDNA) accumulation. Thus, mitochondrial translation is directly coupled to mtDNA levels by a network based upon a profound structural modification of an animal ARS.
    Keywords:  LON; mitochondria; mtDNA; replication; seryl-tRNA synthetase; tRNA; translation
    DOI:  https://doi.org/10.1016/j.celrep.2019.03.022
  27. Front Immunol. 2019 ;10 410
    Metabolic Regulation of Dendritic Cell Differentiation.
    Zhimin He, Xinyi Zhu, Zhen Shi, Tao Wu, Li Wu.
      Dendritic cells (DCs) are important antigen-presenting cells (APCs) that play essential roles in bridging innate and adaptive immune responses. Differentiation stages of DC subsets from bone marrow progenitor cells have been well-defined during the past decades. Features that distinguish DC progenitor cells from each differentiation stages, related signaling pathways and transcription factors that are crucial for DC lineage commitment have been well-elucidated in numerous studies. Recently, growing evidence are showing that cellular metabolism, as one of the most fundamental process of cells, has essential role in the modulation of immune system. There have been multiple reports and reviews that focus on the metabolic modulations on DC functions, however little attention had been paid to the metabolic regulation of DC development and differentiation. In recent years, increasing evidence suggests that metabolic regulations also exert significant impact on DC differentiation, as well as on the homeostasis of tissue resident DCs. The focus of this review is to summarize the findings from recent studies on the metabolic regulation of DC differentiation and to discuss the impacts of the three major aspects of metabolism on the processes of DC development and differentiation, namely the changes in metabolic pathways, the molecular signaling pathways that modulate cell metabolism, and the effects of metabolites and nutrients. The aim of this review is to draw attentions to this important and exciting research field where the effects of metabolic process and their regulation in DC differentiation need to be further explored.
    Keywords:  cell differentiation; dendritic cell (DC); fatty acid (FA); glycolysis; mTOR pathway; metabolic regulation; mitochondria function; nutrients
    DOI:  https://doi.org/10.3389/fimmu.2019.00410
  28. Cell Death Dis. 2019 Apr 05. 10(4): 312
    Monomethyltransferase SET8 facilitates hepatocellular carcinoma growth by enhancing aerobic glycolysis.
    Xiangyuan Chen, Xiaowei Ding, Qichao Wu, Jie Qi, Minmin Zhu, Changhong Miao.
      Hepatocellular carcinoma (HCC) is one of the most aggressive cancers worldwide. Despite such a public health importance, efficient therapeutic agents are still lacking for this malignancy. Most tumor cells use aerobic glycolysis to sustain anabolic growth, including HCC, and the preference of glycolysis often leads to a close association with poorer clinical outcomes. The histone methyltransferase SET8 plays crucial roles in controlling cell-cycle progression, transcription regulation, and tumorigenesis. However, it remains largely undefined whether SET8 affects the glucose metabolism in HCC. Here, we report that upregulation of SET8 is positively correlated with a poor survival rate in HCC patients. Both in vitro and in vivo studies revealed that SET8 deficiency conferred an impaired glucose metabolism phenotype and thus inhibited the progression of HCC tumors. By contrast, SET8 overexpression aggravated the glycolytic alterations and tumor progression. Mechanistically, SET8 directly binds to and inactivates KLF4, resulting in suppression of its downstream SIRT4. We also provided further evidence that mutations in SET8 failed to restrain the transactivation of SIRT4 by KLF4. Our data collectively uncover a novel mechanism of SET8 in mediating glycolytic metabolism in HCC cells and may provide a basis for targeting SET8 as a therapeutic strategy in HCC.
    DOI:  https://doi.org/10.1038/s41419-019-1541-1
  29. Redox Biol. 2019 Mar 22. pii: S2213-2317(19)30253-8. [Epub ahead of print]24 101177
    Mitochondria-associated lactate dehydrogenase is not a biologically significant contributor to bioenergetic function in murine striated muscle.
    Kyle L Fulghum, Benjamin R Rood, Velma O Shang, Lindsey A McNally, Daniel W Riggs, Yu-Ting Zheng, Bradford G Hill.
      Previous studies indicate that mitochondria-localized lactate dehydrogenase (mLDH) might be a significant contributor to metabolism. In the heart, the presence of mLDH could provide cardiac mitochondria with a higher capacity to generate reducing equivalents directly available for respiration, especially during exercise when circulating lactate levels are high. The purpose of this study was to test the hypothesis that mLDH contributes to striated muscle bioenergetic function. Mitochondria isolated from murine cardiac and skeletal muscle lacked an appreciable ability to respire on lactate in the absence or presence of exogenous NAD+. Although three weeks of treadmill running promoted physiologic cardiac growth, mitochondria isolated from the hearts of acutely exercised or exercise-adapted mice showed no further increase in lactate oxidation capacity. In all conditions tested, cardiac mitochondria respired at >20-fold higher levels with provision of pyruvate compared with lactate. Similarly, skeletal muscle mitochondria showed little capacity to respire on lactate. Protease protection assays of isolated cardiac mitochondria confirmed that LDH is not localized within the mitochondrion. We conclude that mLDH does not contribute to cardiac bioenergetics in mice.
    Keywords:  Bioenergetics; Cardiac hypertrophy; Exercise; Glycolysis; Mitochondria; Respiration
    DOI:  https://doi.org/10.1016/j.redox.2019.101177
  30. Sci Rep. 2019 Apr 02. 9(1): 5532
    A new hyperpolarized 13C ketone body probe reveals an increase in acetoacetate utilization in the diabetic rat heart.
    Desiree Abdurrachim, Chern Chiuh Woo, Xing Qi Teo, Wei Xin Chan, George K Radda, Philip Teck Hock Lee.
      Emerging studies have recently shown the potential importance of ketone bodies in cardio-metabolic health. However, techniques to determine myocardial ketone body utilization in vivo are lacking. In this work, we developed a novel method to assess myocardial ketone body utilization in vivo using hyperpolarized [3-13C]acetoacetate and investigated the alterations in myocardial ketone body metabolism in diabetic rats. Within a minute upon injection of [3-13C]acetoacetate, the production of [5-13C]glutamate and [1-13C] acetylcarnitine can be observed real time in vivo. In diabetic rats, the production of [5-13C]glutamate was elevated compared to controls, while [1-13C]acetylcarnitine was not different. This suggests an increase in ketone body utilization in the diabetic heart, with the produced acetyl-CoA channelled into the tricarboxylic acid cycle. This observation was corroborated by an increase activity of succinyl-CoA:3-ketoacid-CoA transferase (SCOT) activity, the rate-limiting enzyme of ketone body utilization, in the diabetic heart. The increased ketone body oxidation in the diabetic hearts correlated with cardiac hypertrophy and dysfunction, suggesting a potential coupling between ketone body metabolism and cardiac function. Hyperpolarized [3-13C]acetoacetate is a new probe with potential for non-invasive and real time monitoring of myocardial ketone body oxidation in vivo, which offers a powerful tool to follow disease progression or therapeutic interventions.
    DOI:  https://doi.org/10.1038/s41598-019-39378-w
  31. Cell Metab. 2019 Mar 21. pii: S1550-4131(19)30128-7. [Epub ahead of print]
    Membrane Cholesterol Efflux Drives Tumor-Associated Macrophage Reprogramming and Tumor Progression.
    Pieter Goossens, Juan Rodriguez-Vita, Anders Etzerodt, Marion Masse, Olivia Rastoin, Victoire Gouirand, Thomas Ulas, Olympia Papantonopoulou, Miranda Van Eck, Nathalie Auphan-Anezin, Magali Bebien, Christophe Verthuy, Thien Phong Vu Manh, Martin Turner, Marc Dalod, Joachim L Schultze, Toby Lawrence.
      Macrophages possess intrinsic tumoricidal activity, yet tumor-associated macrophages (TAMs) rapidly adopt an alternative phenotype within the tumor microenvironment that is marked by tumor-promoting immunosuppressive and trophic functions. The mechanisms that promote such TAM polarization remain poorly understood, but once identified, they may represent important therapeutic targets to block the tumor-promoting functions of TAMs and restore their anti-tumor potential. Here, we have characterized TAMs in a mouse model of metastatic ovarian cancer. We show that ovarian cancer cells promote membrane-cholesterol efflux and depletion of lipid rafts from macrophages. Increased cholesterol efflux promoted IL-4-mediated reprogramming, including inhibition of IFNγ-induced gene expression. Genetic deletion of ABC transporters, which mediate cholesterol efflux, reverts the tumor-promoting functions of TAMs and reduces tumor progression. These studies reveal an unexpected role for membrane-cholesterol efflux in driving TAM-mediated tumor progression while pointing to a potentially novel anti-tumor therapeutic strategy.
    Keywords:  IL-4 signaling; cholesterol efflux; lipid rafts; ovarian cancer; tumor-associated macrophages
    DOI:  https://doi.org/10.1016/j.cmet.2019.02.016
  32. Eur Urol Oncol. 2019 Feb;pii: S2588-9311(18)30095-6. [Epub ahead of print]2(1): 28-36
    The Metabolic Landscape of Prostate Cancer.
    Francesca Giunchi, Michelangelo Fiorentino, Massimo Loda.
      CONTEXT: Neoplastic cells are characterized by metabolic alterations that sustain tumor growth. Interventions aimed at modifying metabolic rewiring of cancer cells are currently being investigated in several tumor types, including prostate cancer (PC).OBJECTIVE: To review relevant metabolic alterations reported for PC and potential diagnostic and therapeutic opportunities that could be exploited on the basis of these discoveries.
    EVIDENCE ACQUISITION: We performed a review of PubMed/Medline in March 2018 for PC in association with each of the following search terms: metabolomics; lipid, cholesterol, one-carbon, amino acid, and glucose metabolism. Fifty publications were selected for inclusion in this analysis.
    EVIDENCE SYNTHESIS: The reports included were grouped according to fatty acid and cholesterol metabolism (28 studies); one-carbon metabolism (9 studies); amino acid metabolism (6 studies); and glucose metabolism (7 studies). We report on multiple metabolic pathways that are dysregulated in prostate cancer. Metabolic alterations can result in at least one of the following changes: protein lipidation, oncogene activation, DNA methylation, cellular signaling, and protein-protein interactions.
    CONCLUSIONS: Metabolic alterations play a crucial role in PC development, progression, and resistance to therapy. Increasing knowledge of metabolic rewiring is revealing novel metabolic signatures in PC. These signatures could be utilized for PC diagnosis, as well as for the discovery of novel therapeutic interventions to overcome castration resistance.
    PATIENT SUMMARY: Metabolic alterations play a crucial role in the development and progression of prostate cancer and its resistance to therapy. Our knowledge of metabolic rewiring is increasing and revealing novel metabolic signatures in prostate cancer. These signatures could be used for diagnosis and for the discovery of novel therapeutic interventions aimed at overcoming castration resistance.
    Keywords:  Cholesterol; Fatty acid; Metabolism; Prostate cancer
    DOI:  https://doi.org/10.1016/j.euo.2018.06.010
  33. Trends Cell Biol. 2019 Mar 28. pii: S0962-8924(19)30040-6. [Epub ahead of print]
    The Expanding and Unexpected Functions of Mitochondria Contact Sites.
    Laura L Lackner.
      Mitochondria make functionally relevant contacts with most, if not all, other organelles in the cell. These contacts impact on mitochondrial behavior and function as well as on a wide variety of cellular functions. Many recent advances have been made in the rapidly growing field of mitochondria contact site biology, and these advances have expanded the known functions of mitochondria contact sites in exciting and unexpected ways.
    Keywords:  interorganelle contacts; membrane contact sites; mitochondria contact sites
    DOI:  https://doi.org/10.1016/j.tcb.2019.02.009
  34. J Cell Physiol. 2019 Apr 02.
    Tranexamic acid suppresses the release of mitochondrial DNA, protects the endothelial monolayer and enhances oxidative phosphorylation.
    Igor Prudovsky, Damien Carter, Doreen Kacer, Monica Palmeri, Tee Soul, Chloe Kumpel, Kathleen Pyburn, Karyn Barrett, Victoria DeMambro, Ilya Alexandrov, Irina Brandina, Robert Kramer, Joseph Rappold.
      Damage-associated molecular patterns, including mitochondrial DNA (mtDNA) are released during hemorrhage resulting in the development of endotheliopathy. Tranexamic acid (TXA), an antifibrinolytic drug used in hemorrhaging patients, enhances their survival despite the lack of a comprehensive understanding of its cellular mechanisms of action. The present study is aimed to elucidate these mechanisms, with a focus on mitochondria. We found that TXA inhibits the release of endogenous mtDNA from granulocytes and endothelial cells. Furthermore, TXA attenuates the loss of the endothelial monolayer integrity induced by exogenous mtDNA. Using the Seahorse XF technology, it was demonstrated that TXA strongly stimulates mitochondrial respiration. Studies using Mitotracker dye, cells derived from mito-QC mice, and the ActivSignal IPAD assay, indicate that TXA stimulates biogenesis of mitochondria and inhibits mitophagy. These findings open the potential for improvement of the strategies of TXA applications in trauma patients and the development of more efficient TXA derivatives.
    Keywords:  endothelial cell; mitochondria; mitochondrial DNA; mitophagy; tranexamic acid
    DOI:  https://doi.org/10.1002/jcp.28603
  35. Front Cell Neurosci. 2019 ;13 103
    Mitochondrial Dysfunction in Huntington's Disease; Interplay Between HSF1, p53 and PGC-1α Transcription Factors.
    Taylor A Intihar, Elisa A Martinez, Rocio Gomez-Pastor.
      Huntington's disease (HD) is a neurodegenerative disease caused by an expanded CAG repeat in the huntingtin (HTT) gene, causing the protein to misfold and aggregate. HD progression is characterized by motor impairment and cognitive decline associated with the preferential loss of striatal medium spiny neurons (MSNs). The mechanisms that determine increased susceptibility of MSNs to mutant HTT (mHTT) are not fully understood, although there is abundant evidence demonstrating the importance of mHTT mediated mitochondrial dysfunction in MSNs death. Two main transcription factors, p53 and peroxisome proliferator co-activator PGC-1α, have been widely studied in HD for their roles in regulating mitochondrial function and apoptosis. The action of these two proteins seems to be interconnected. However, it is still open to discussion whether p53 and PGC-1α dependent responses directly influence each other or if they are connected via a third mechanism. Recently, the stress responsive transcription factor HSF1, known for its role in protein homeostasis, has been implicated in mitochondrial function and in the regulation of PGC-1α and p53 levels in different contexts. Based on previous reports and our own research, we discuss in this review the potential role of HSF1 in mediating mitochondrial dysfunction in HD and propose a unifying mechanism that integrates the responses mediated by p53 and PGC-1α in HD via HSF1.
    Keywords:  Huntington (disease); PGC-1α; heat shock factor 1 (HSF1); mitochondrial dysfunction; p53
    DOI:  https://doi.org/10.3389/fncel.2019.00103
  36. J Biol Chem. 2019 Apr 01. pii: jbc.RA118.006347. [Epub ahead of print]
    A catalytic domain variant of Mitofusin requiring a wildtype paralog for function uncouples mitochondrial outer-membrane tethering and fusion.
    Emily A Engelhart, Suzanne Hoppins.
      Mitofusins (Mfn) are dynamin-related GTPases that mediate mitochondrial outer membrane fusion, a process that is required for mitochondrial and cellular health. In Mfn1 and Mfn2 paralogs, a conserved phenylalanine (Phe-202) located in the GTPase domain on a conserved beta strand and is part of an aromatic network in the core of this domain. To gain insight into the poorly understood mechanism of Mfn-mediated membrane fusion, here we characterize a Mitofusin mutant variant etiologically linked to Charcot Marie Tooth Syndrome. From analysis of mitochondrial structure in cells and mitochondrial fusion in vitro, we found that conversion of Phe-202 to leucine in either Mfn1 or Mfn2 diminishes the fusion activity of heterotypic complexes with both Mfn1 and Mfn2 and abolishes fusion activity of homotypic complexes. Using co-immunoprecipitation and native gel analysis, we further dissect the steps of mitochondrial fusion and demonstrate that the mutant variant has normal tethering activity, but impaired higher-order nucleotide-dependent assembly. The defective coupling of tethering to membrane fusion observed here suggests that nucleotide-dependent self-assembly of Mitofusin is required after tethering to promote membrane fusion.
    Keywords:  Charcot-Marie-Tooth disease (CMT); GTPase; dynamin related protein (DRP); fusion protein; membrane fusion; mitochondria; mitochondrial netowrk; organelle; structure-function; tethering
    DOI:  https://doi.org/10.1074/jbc.RA118.006347
  37. Immunol Med. 2018 Sep;41(3): 89-97
    Immunometabolism in rheumatoid arthritis.
    Takaichi Okano, Jun Saegusa, Soshi Takahashi, Yo Ueda, Akio Morinobu.
      Recent studies have revealed a relationship between cellular metabolism and cell function in immune cells. Cellular metabolism not only provides supplemental ATP, but also supports dynamic changes in cell proliferation and differentiation. For example, T cells exhibit subset-specific metabolic profiles, and require certain types of metabolism for their functions. Determining the metabolic profiles that support inflammatory immune responses may lead to novel treatment strategies for chronic inflammatory diseases such as rheumatoid arthritis (RA). However, the mechanisms by which metabolism modulates cell function have been unclear. Recent studies have begun to unveil unexpected non-metabolic functions for metabolic enzymes in the context of inflammation, including roles in signaling and gene regulation. Here we describe recent findings related to immunometabolism, the metabolome of RA patients, and the metabolically independent functions of glycolytic enzymes. We discuss how metabolic processes impact immune cells, especially T cells and fibroblast like synoviocytes, which are considered the orchestrators of autoimmune arthritis.
    Keywords:  Immunometabolism; T cell; fibroblast-like synoviocytes; rheumatoid arthritis
    DOI:  https://doi.org/10.1080/25785826.2018.1531186
  38. Mol Cell. 2019 Mar 22. pii: S1097-2765(19)30149-2. [Epub ahead of print]
    Interleukin-1β Induces mtDNA Release to Activate Innate Immune Signaling via cGAS-STING.
    Lauren D Aarreberg, Katharina Esser-Nobis, Connor Driscoll, Andrey Shuvarikov, Justin A Roby, Michael Gale.
      Interleukin-1 beta (IL-1β) is a pleiotropic mediator of inflammation and is produced in response to a wide range of stimuli. During infection, IL-1β production occurs in parallel with the onset of innate antimicrobial defenses, but the contribution of IL-1β signaling to cell-intrinsic immunity is not defined. Here, we report that exogenous IL-1β induces interferon regulatory factor 3 (IRF3) activation in human myeloid, fibroblast, and epithelial cells. IRF3 activation by IL-1β is dependent upon the DNA-sensing pathway adaptor, stimulator of interferon genes (STING), through the recognition of cytosolic mtDNA by cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS). IL-1β treatment results in interferon (IFN) production and activation of IFN signaling to direct a potent innate immune response that restricts dengue virus infection. This study identifies a new function for IL-1β in the onset or enhancement of cell-intrinsic immunity, with important implications for cGAS-STING in integrating inflammatory and microbial cues for host defense.
    Keywords:  IFN; IL-1; IRF1; IRF3; STING; dengue virus; innate immunity; mitochondria
    DOI:  https://doi.org/10.1016/j.molcel.2019.02.038
  39. Nat Rev Cancer. 2019 Apr 03.
    Targeting cancer cell metabolism in glioblastoma.
    Sarah Crunkhorn.
      
    DOI:  https://doi.org/10.1038/s41568-019-0139-3
  40. Cell Res. 2019 Apr 02.
    LKB1 expressed in dendritic cells governs the development and expansion of thymus-derived regulatory T cells.
    Leonard R Pelgrom, Thiago A Patente, Alexey Sergushichev, Ekaterina Esaulova, Frank Otto, Arifa Ozir-Fazalalikhan, Hendrik J P van der Zande, Alwin J van der Ham, Stefan van der Stel, Maxim N Artyomov, Bart Everts.
      Liver Kinase B1 (LKB1) plays a key role in cellular metabolism by controlling AMPK activation. However, its function in dendritic cell (DC) biology has not been addressed. Here, we find that LKB1 functions as a critical brake on DC immunogenicity, and when lost, leads to reduced mitochondrial fitness and increased maturation, migration, and T cell priming of peripheral DCs. Concurrently, loss of LKB1 in DCs enhances their capacity to promote output of regulatory T cells (Tregs) from the thymus, which dominates the outcome of peripheral immune responses, as suggested by increased resistance to asthma and higher susceptibility to cancer in CD11cΔLKB1 mice. Mechanistically, we find that loss of LKB1 specifically primes thymic CD11b+ DCs to facilitate thymic Treg development and expansion, which is independent from AMPK signalling, but dependent on mTOR and enhanced phospholipase C β1-driven CD86 expression. Together, our results identify LKB1 as a critical regulator of DC-driven effector T cell and Treg responses both in the periphery and the thymus.
    DOI:  https://doi.org/10.1038/s41422-019-0161-8
  41. Cell Metab. 2019 Apr 02. pii: S1550-4131(19)30134-2. [Epub ahead of print]29(4): 785-786
    Metabolic Adaptation Fuels Lymph Node Metastasis.
    Jessalyn M Ubellacker, Sean J Morrison.
      Many cancers metastasize regionally through lymphatics before metastasizing systemically through blood vessels. However, metastasis through blood has been studied much more extensively than metastasis through lymph. Recently in Science, Lee et al. (2019) offered new insight into lymph node metastasis by showing that melanoma cells must undergo metabolic changes during this process and that it is driven by localized accumulation of bile acids.
    DOI:  https://doi.org/10.1016/j.cmet.2019.03.006
  42. J Biol Chem. 2019 Apr 04. pii: jbc.RA118.005772. [Epub ahead of print]
    Dihydronicotinamide riboside is a potent NAD+ concentration enhancer in vitro and in vivo.
    Yue Yang, Farheen Sultana Mohammed, Ning Zhang, Anthony A Sauve.
      Interest in pharmacological agents capable of increasing cellular NAD+ concentrations has stimulated investigations of nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). NR and NMN require large dosages for effect. Herein we describe synthesis of dihydronicotinamide riboside (NRH) and the discovery that NRH is a potent NAD+ concentration enhancing agent, which acts within as little as 1 hr after administration to mammalian cells to increase NAD+ concentrations by 2.5-10 fold over control values. Comparisons to NR and NMN show that in every instance NRH provides greater NAD+ increases at equivalent concentrations. NRH also provides substantial NAD+ increases in tissues when administered by intraperitoneal injection to  C57BL/6J mice. NRH substantially increases NAD+/NADH ratio in cultured cells and in liver, and no induction of apoptotic markers or significant increases in lactate levels in cells. Cells treated with NRH are resistant to cell death caused by NAD+-depleting genotoxins such as hydrogen peroxide and methylmethane sulfonate. Studies to identify its biochemical mechanism of action showed that it does not inhibit NAD+ consumption suggesting it acts as a biochemical precursor to NAD+. Cell lysates possess an ATP-dependent kinase activity which efficiently converts NRH to the compound NMNH, but independent of Nrk1 or Nrk2. These studies identify a putative new metabolic pathway to NAD+, and a potent pharmacologic agent for NAD+ concentration enhancement in cells and tissues.
    Keywords:  ADP-ribosylation; NAD biosynthesis; Nicotinamide riboside; biosynthesis; nicotinamide adenine dinucleotide (NAD); nicotinamide adenine dinucleotide (NADH)
    DOI:  https://doi.org/10.1074/jbc.RA118.005772
  43. Nature. 2019 Apr 03.
    An allosteric mechanism for potent inhibition of human ATP-citrate lyase.
    Jia Wei, Silvana Leit, Jun Kuai, Eric Therrien, Salma Rafi, H James Harwood, Byron DeLaBarre, Liang Tong.
      ATP-citrate lyase (ACLY) is a central metabolic enzyme and catalyses the ATP-dependent conversion of citrate and coenzyme A (CoA) to oxaloacetate and acetyl-CoA1-5. The acetyl-CoA product is crucial for the metabolism of fatty acids6,7, the biosynthesis of cholesterol8, and the acetylation and prenylation of proteins9,10. There has been considerable interest in ACLY as a target for anti-cancer drugs, because many cancer cells depend on its activity for proliferation2,5,11. ACLY is also a target against dyslipidaemia and hepatic steatosis, with a compound currently in phase 3 clinical trials4,5. Many inhibitors of ACLY have been reported, but most of them have weak activity5. Here we report the development of a series of low nanomolar, small-molecule inhibitors of human ACLY. We have also determined the structure of the full-length human ACLY homo-tetramer in complex with one of these inhibitors (NDI-091143) by cryo-electron microscopy, which reveals an unexpected mechanism of inhibition. The compound is located in an allosteric, mostly hydrophobic cavity next to the citrate-binding site, and requires extensive conformational changes in the enzyme that indirectly disrupt citrate binding. The observed binding mode is supported by and explains the structure-activity relationships of these compounds. This allosteric site greatly enhances the 'druggability' of ACLY and represents an attractive target for the development of new ACLY inhibitors.
    DOI:  https://doi.org/10.1038/s41586-019-1094-6
  44. Cell Metab. 2019 Apr 02. pii: S1550-4131(19)30135-4. [Epub ahead of print]29(4): 790-792
    Fatty Acid Desaturation Gets a NAD+ Reputation.
    Andrew J Lutkewitte, Shawn C Burgess, Brian N Finck.
      delta-5 desaturase and delta-6 desaturase are enzymes known to be involved in the synthesis of highly unsaturated fatty acids. In this issue, Kim et al. (2019) show that production of NAD+ by this desaturase reaction is an adaptive response to NAD+ depletion that may regulate cellular REDOX status.
    DOI:  https://doi.org/10.1016/j.cmet.2019.03.007
  45. Nat Biomed Eng. 2019 Apr 01.
    High-throughput, label-free, single-cell photoacoustic microscopy of intratumoral metabolic heterogeneity.
    Pengfei Hai, Toru Imai, Song Xu, Ruiying Zhang, Rebecca L Aft, Jun Zou, Lihong V Wang.
      Intratumoral heterogeneity, which is manifested in almost all of the hallmarks of cancer, including the significantly altered metabolic profiles of cancer cells, represents a challenge to effective cancer therapy. High-throughput measurements of the metabolism of individual cancer cells would allow direct visualization and quantification of intratumoral metabolic heterogeneity, yet the throughputs of current measurement techniques are limited to about 120 cells per hour. Here, we show that single-cell photoacoustic microscopy can reach throughputs of approximately 12,000 cells per hour by trapping single cells with blood in an oxygen-diffusion-limited high-density microwell array and by using photoacoustic imaging to measure the haemoglobin oxygen change (that is, the oxygen consumption rate) in the microwells. We demonstrate the capability of this label-free technique by performing high-throughput single-cell oxygen-consumption-rate measurements of cultured cells and by imaging intratumoral metabolic heterogeneity in specimens from patients with breast cancer. High-throughput single-cell photoacoustic microscopy of oxygen consumption rates should enable the faster characterization of intratumoral metabolic heterogeneity.
    DOI:  https://doi.org/10.1038/s41551-019-0376-5
  46. Proc Natl Acad Sci U S A. 2019 Apr 04. pii: 201821093. [Epub ahead of print]
    Oncogenic PIK3CA promotes cellular stemness in an allele dose-dependent manner.
    Ralitsa R Madsen, Rachel G Knox, Wayne Pearce, Saioa Lopez, Betania Mahler-Araujo, Nicholas McGranahan, Bart Vanhaesebroeck, Robert K Semple.
      The PIK3CA gene, which encodes the p110α catalytic subunit of PI3 kinase (PI3K), is mutationally activated in cancer and in overgrowth disorders known as PIK3CA-related overgrowth spectrum (PROS). To determine the consequences of genetic PIK3CA activation in a developmental context of relevance to both PROS and cancer, we engineered isogenic human induced pluripotent stem cells (iPSCs) with heterozygous or homozygous knockin of PIK3CA H1047R While heterozygous iPSCs remained largely similar to wild-type cells, homozygosity for PIK3CA H1047R caused widespread, cancer-like transcriptional remodeling, partial loss of epithelial morphology, up-regulation of stemness markers, and impaired differentiation to all three germ layers in vitro and in vivo. Genetic analysis of PIK3CA-associated cancers revealed that 64% had multiple oncogenic PIK3CA copies (39%) or additional PI3K signaling pathway-activating "hits" (25%). This contrasts with the prevailing view that PIK3CA mutations occur heterozygously in cancer. Our findings suggest that a PI3K activity threshold determines pathological consequences of oncogenic PIK3CA activation and provide insight into the specific role of this pathway in human pluripotent stem cells.
    Keywords:  PI3K; PROS; cancer; genetics; pluripotent stem cells
    DOI:  https://doi.org/10.1073/pnas.1821093116
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