bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒08‒30
fifty papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Life (Basel). 2020 Aug 26. pii: E164. [Epub ahead of print]10(9):
    Chapman J, Ng YS, Nicholls TJ.
      Mitochondria are complex organelles that harbour their own genome. Mitochondrial DNA (mtDNA) exists in the form of a circular double-stranded DNA molecule that must be replicated, segregated and distributed around the mitochondrial network. Human cells typically possess between a few hundred and several thousand copies of the mitochondrial genome, located within the mitochondrial matrix in close association with the cristae ultrastructure. The organisation of mtDNA around the mitochondrial network requires mitochondria to be dynamic and undergo both fission and fusion events in coordination with the modulation of cristae architecture. The dysregulation of these processes has profound effects upon mtDNA replication, manifesting as a loss of mtDNA integrity and copy number, and upon the subsequent distribution of mtDNA around the mitochondrial network. Mutations within genes involved in mitochondrial dynamics or cristae modulation cause a wide range of neurological disorders frequently associated with defects in mtDNA maintenance. This review aims to provide an understanding of the biological mechanisms that link mitochondrial dynamics and mtDNA integrity, as well as examine the interplay that occurs between mtDNA, mitochondrial dynamics and cristae structure.
    Keywords:  cristae; mitochondria; mitochondrial diseas; mitochondrial fission; mitochondrial fusion; mtDNA
    DOI:  https://doi.org/10.3390/life10090164
  2. Front Cell Dev Biol. 2020 ;8 715
    Kitada M, Xu J, Ogura Y, Monno I, Koya D.
      Nutrients are closely involved in the regulation of lifespan and metabolic health. Cellular activities, such as the regulation of metabolism, growth, and aging, are mediated by a network of nutrients and nutrient-sensing pathways. Among the nutrient-sensing pathways, the mechanistic target of rapamycin complex 1 (mTORC1) acts as the central regulator of cellular functions, which include autophagy. Autophagy plays a significant role in the removal of protein aggregates and damaged or excess organelles, including mitochondria, to maintain intracellular homeostasis, which is involved in lifespan extension and cardiometabolic health. Moreover, dietary methionine restriction may have a beneficial effect on lifespan extension and metabolic health. In contrast, methionine may activate mTORC1 and suppress autophagy. As the mechanism of methionine sensing on mTORC1, SAMTOR was identified as a sensor of S-adenosyl methionine (SAM), a metabolite of methionine, in the cytoplasm. Conversely, methionine may activate the mTORC1 signaling pathway through the activation of phosphatase 2A (PP2A) because of increased methylation in response to intracellular SAM levels. In this review, we summarized the recent findings regarding the mechanism via which methionine activates mTORC1.
    Keywords:  S-adenosyl methionine; SAMTOR; autophagy; mechanistic target of rapamycin complex 1; methionine; phosphatase 2A methylation
    DOI:  https://doi.org/10.3389/fcell.2020.00715
  3. Annu Rev Genet. 2020 Aug 28.
    Medini H, Cohen T, Mishmar D.
      Out of many intracellular bacteria, only the mitochondria and chloroplasts abandoned their independence billions of years ago and became endosymbionts within the host eukaryotic cell. Consequently, one cannot grow eukaryotic cells without their mitochondria, and the mitochondria cannot divide outside of the cell, thus reflecting interdependence. Here, we argue that such interdependence underlies the fundamental role of mitochondrial activities in the emergence of metazoans. Several lines of evidence support our hypothesis: (a) Differentiation and embryogenesis rely on mitochondrial function; (b) mitochondrial metabolites are primary precursors for epigenetic modifications (such as methyl and acetyl), which are critical for chromatin remodeling and gene expression, particularly during differentiation and embryogenesis; (c) mitonuclear coregulation adapted to accommodate both housekeeping and tissue-dependent metabolic needs. We discuss the evolution of the unique mitochondrial genetic system, mitochondrial metabolites, mitonuclear coregulation, and their critical roles in the emergence of metazoans and in human disorders. Expected final online publication date for the Annual Review of Genetics, Volume 54 is November 23, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
    DOI:  https://doi.org/10.1146/annurev-genet-021920-105545
  4. Nat Cell Biol. 2020 Aug 24.
    Gao Y, Nihira NT, Bu X, Chu C, Zhang J, Kolodziejczyk A, Fan Y, Chan NT, Ma L, Liu J, Wang D, Dai X, Liu H, Ono M, Nakanishi A, Inuzuka H, North BJ, Huang YH, Sharma S, Geng Y, Xu W, Liu XS, Li L, Miki Y, Sicinski P, Freeman GJ, Wei W.
      Immunotherapies that target programmed cell death protein 1 (PD-1) and its ligand PD-L1 as well as cytotoxic T-lymphocyte-associated protein 4 (CTLA4) have shown impressive clinical outcomes for multiple tumours. However, only a subset of patients achieves durable responses, suggesting that the mechanisms of the immune checkpoint pathways are not completely understood. Here, we report that PD-L1 translocates from the plasma membrane into the nucleus through interactions with components of the endocytosis and nucleocytoplasmic transport pathways, regulated by p300-mediated acetylation and HDAC2-dependent deacetylation of PD-L1. Moreover, PD-L1 deficiency leads to compromised expression of multiple immune-response-related genes. Genetically or pharmacologically modulating PD-L1 acetylation blocks its nuclear translocation, reprograms the expression of immune-response-related genes and, as a consequence, enhances the anti-tumour response to PD-1 blockade. Thus, our results reveal an acetylation-dependent regulation of PD-L1 nuclear localization that governs immune-response gene expression, and thereby advocate targeting PD-L1 translocation to enhance the efficacy of PD-1/PD-L1 blockade.
    DOI:  https://doi.org/10.1038/s41556-020-0562-4
  5. Biochem Biophys Res Commun. 2020 Sep 10. pii: S0006-291X(20)31471-6. [Epub ahead of print]530(1): 285-291
    Kikuchi N, Soga T, Nomura M, Sato T, Sakamoto Y, Tanaka R, Abe J, Morita M, Shima H, Okada Y, Tanuma N.
      Recent advances in cancer biology reveal the importance of metabolic changes in cancer; however, less is known about how metabolic pathways in tumors are regulated in vivo. Here, we report analysis of the lung cancer metabolism based on different surgical procedures, namely lobectomy and partial resection. In lobectomy, but not in partial resection, pulmonary arteries and veins are ligated prior to removal of tissues, rendering tissues ischemic. We show that tumors indeed undergo ischemia upon lobectomy and that the tumor metabolome differs markedly from that of tumors removed by partial resection. Comparison of the responses to ischemia in tumor and normal lung tissues revealed that lung cancer tissue exhibits greater TCA cycle and autophagic activity than do normal lung tissues in vivo in patients. Finally, we report that deleting ATG7, which encodes a protein essential for autophagy, antagonizes growth of tumors derived from lung cancer cell lines, suggesting that autophagy confers metabolic advantages to lung cancer. Our findings shed light on divergent metabolic responses to ischemia seen in tumors and normal tissues.
    Keywords:  Autophagy; Cancer metabolism; Ischemia; Lung cancer; Metabolome
    DOI:  https://doi.org/10.1016/j.bbrc.2020.07.082
  6. Am J Physiol Endocrinol Metab. 2020 Aug 24.
    Markby GR, Sakamoto K.
      In response to the increased energy demands of contractions, skeletal muscle adapts remarkably well through acutely regulating metabolic pathways to maintain energy balance and in the longer term by regulating metabolic reprogramming such as remodeling and expanding the mitochondrial network. This long-term adaptive response involves modulation of gene expression at least partly through the regulation of specific transcription factors and transcriptional coactivators. The AMP-activated protein kinase (AMPK)-peroxisome proliferator-activated receptor-γ co-activator 1a (PGC1a) pathway has long been known to orchestrate contraction-mediated adaptive responses, although AMPK-/PGC1a-independent pathways have also been proposed. Transcription factor EB (TFEB) and TFE3, known as important regulators of lysosomal biogenesis and autophagic processes, have emerged as new metabolic coordinators. The activity of TFEB/TFE3 is regulated through post-translational modifications (i.e. phosphorylation) and spatial organization. Under nutrient/energy stress, TFEB/TFE3 get dephosphorylated and translocate to the nucleus where they activate transcription of their target genes. It has recently been reported that exercise promotes nuclear translocation and activation of TFEB/TFE3 in mouse skeletal muscle through the Ca2+-stimulated protein phosphatase calcineurin. Skeletal muscle-specific ablation of TFEB exhibits impaired glucose homeostasis and mitochondrial biogenesis with reduced metabolic flexibility during exercise, and global TFE3 depletion results in diminished endurance and abolished exercise-induced metabolic benefits. Transcriptomic analysis of the muscle-specific TFEB-null mice has demonstrated that TFEB regulates the expression of genes involved in glucose metabolism and mitochondrial homeostasis. This review aims to summarize and discuss emerging roles for TFEB/TFE3 in metabolic and adaptive responses to exercise/contractile activity in skeletal muscle.
    Keywords:  AMPK; PGC1a; calcineurin; mTOR
    DOI:  https://doi.org/10.1152/ajpendo.00339.2020
  7. Pharmacol Res. 2020 Aug 23. pii: S1043-6618(20)31469-9. [Epub ahead of print] 105161
    English J, Son JM, Cardamone MD, Lee C, Perissi V.
      Cellular homeostasis in eukaryotic cells requires synchronized coordination of multiple organelles. A key role in this stage is played by mitochondria, which have recently emerged as highly interconnected and multifunctional hubs that process and coordinate diverse cellular functions. Beyond producing ATP, mitochondria generate key metabolites and are central to apoptotic and metabolic signaling pathways. Because most mitochondrial proteins are encoded in the nuclear genome, the biogenesis of new mitochondria and the maintenance of mitochondrial functions and flexibility critically depend upon effective mitonuclear communication. This review addresses the complex network of signaling molecules and pathways allowing mitochondria-nuclear communication and coordinated regulation of their independent but interconnected genomes, and discusses the extent to which dynamic communication between the two organelles has evolved for mutual benefit and for the overall maintenance of cellular and organismal fitness.
    Keywords:  Acetyl-Coenzyme A (PubChem CID: 6302); Antimycin (PubChem CID: 12550); Carbonyl cyanide m-chlorophenylhydrazone (CCCP) (PubChem CID: 2603); Communication; Epigenetics; Humanin (PubChem CID: 16131438); Integrated Stress Response; Mitochondrial Retrograde Signaling; Mitonuclear; Nicotinamide riboside (PubChem CID: 439924); Oligoymycin (PubChem CID: 78358496); S-adenosylmethionine (SAM) (PubChem CID: 34756); Superoxide anion (PubChem CID: 5359597); alpha-Ketoglutarate (PubChem CID: 164533)
    DOI:  https://doi.org/10.1016/j.phrs.2020.105161
  8. J Biol Chem. 2020 Aug 28. pii: jbc.RA120.014483. [Epub ahead of print]
    Manhas N, Duong QV, Lee P, Richardson JD, Robertson JD, Moxley MA, Bazil JN.
      Succinate dehydrogenase (SDH) is an inner mitochondrial membrane protein complex that links the Krebs cycle to the electron transport system. It can produce significant amounts of superoxide (O2 .-) and hydrogen peroxide (H2O2); however, the precise mechanisms are unknown. This fact hinders the development of next-generation antioxidant therapies targeting mitochondria. To help address this problem, we developed a computational model to analyze and identify the kinetic mechanism of O2 .- and H2O2 production by SDH. Our model includes the major redox centers in the complex, namely FAD, three iron-sulfur clusters, and a transiently bound semiquinone. Oxidation state transitions involve a one- or two-electron redox reaction, each being thermodynamically constrained. Model parameters were simultaneously fit to many data sets using a variety of succinate oxidation and free radical production data. In the absence of respiratory chain inhibitors, model analysis revealed the 3Fe-4S iron-sulfur cluster as the primary O2 .- source. However, when the quinone reductase site is inhibited or the quinone pool is highly reduced, O2 .- is generated primarily by the FAD. In addition, H2O2 production is only significant when the enzyme is fully reduced, and fumarate is absent. Our simulations also reveal that the redox state of the quinone pool is the primary determinant of free radical production by SDH. In this study, we showed the importance of analyzing enzyme kinetics and associated side-reactions in a consistent, quantitative, and biophysically detailed manner using a diverse set of experimental data to interpret and explain experimental observations from a unified perspective.
    Keywords:  computational biology; computer modeling; enzyme kinetics; enzyme mechanism; free radicals; hydrogen peroxide; redox regulation; succinate dehydrogenase; superoxide ion; ubiquinone
    DOI:  https://doi.org/10.1074/jbc.RA120.014483
  9. Nat Commun. 2020 Aug 25. 11(1): 4236
    Henriques SF, Dhakan DB, Serra L, Francisco AP, Carvalho-Santos Z, Baltazar C, Elias AP, Anjos M, Zhang T, Maddocks ODK, Ribeiro C.
      The impact of commensal bacteria on the host arises from complex microbial-diet-host interactions. Mapping metabolic interactions in gut microbial communities is therefore key to understand how the microbiome influences the host. Here we use an interdisciplinary approach including isotope-resolved metabolomics to show that in Drosophila melanogaster, Acetobacter pomorum (Ap) and Lactobacillus plantarum (Lp) a syntrophic relationship is established to overcome detrimental host diets and identify Ap as the bacterium altering the host's feeding decisions. Specifically, we show that Ap uses the lactate produced by Lp to supply amino acids that are essential to Lp, allowing it to grow in imbalanced diets. Lactate is also necessary and sufficient for Ap to alter the fly's protein appetite. Our data show that gut bacterial communities use metabolic interactions to become resilient to detrimental host diets. These interactions also ensure the constant flow of metabolites used by the microbiome to alter reproduction and host behaviour.
    DOI:  https://doi.org/10.1038/s41467-020-18049-9
  10. iScience. 2020 Aug 13. pii: S2589-0042(20)30646-5. [Epub ahead of print]23(9): 101454
    Gerbec ZJ, Hashemi E, Nanbakhsh A, Holzhauer S, Yang C, Mei A, Tsaih SW, Lemke A, Flister MJ, Riese MJ, Thakar MS, Malarkannan S.
      During an immune response, natural killer (NK) cells activate specific metabolic pathways to meet the increased energetic and biosynthetic demands associated with effector functions. Here, we found in vivo activation of NK cells during Listeria monocytogenes infection-augmented transcription of genes encoding mitochondria-associated proteins in a manner dependent on the transcriptional coactivator PGC-1α. Using an Ncr1Cre-based conditional knockout mouse, we found that PGC-1α was crucial for optimal NK cell effector functions and bioenergetics, as the deletion of PGC-1α was associated with decreased cytotoxic potential and cytokine production along with altered ADP/ATP ratios. Lack of PGC-1α also significantly impaired the ability of NK cells to control B16F10 tumor growth in vivo, and subsequent gene expression analysis showed that PGC-1α mediates transcription required to maintain mitochondrial activity within the tumor microenvironment. Together, these data suggest that PGC-1α-dependent transcription of specific target genes is required for optimal NK cell function during the response to infection or tumor growth.
    Keywords:  Biological Sciences; Cancer; Cellular Physiology; Immunology
    DOI:  https://doi.org/10.1016/j.isci.2020.101454
  11. Dis Model Mech. 2020 Aug 28. pii: dmm.044925. [Epub ahead of print]
    Saskői É, Hujber Z, Nyírő G, Likó I, Mátyási B, Petővári G, Mészáros K, Kovács AL, Patthy L, Supekar S, Fan H, Sváb G, Tretter L, Sarkar A, Nazir A, Sebestyén A, Patócs A, Mehta A, Takács-Vellai K.
      The conserved B-subunit of succinate dehydrogenase (SDH) participates in the TCA cycle and mitochondrial electron transport. The Arg230His mutation in SDHB causes heritable pheochromocytoma/paraganglioma (PPGL). In C. elegans, we generated an in vivo PPGL model (SDHB-1 Arg244His; equivalent to human Arg230His) which manifests delayed development, shortened lifespan, attenuated ATP production and reduced mitochondrial number. Although succinate is elevated in both missense and null sdhb-1(gk165) mutants, transcriptomic comparison suggests very different causal mechanisms that are supported by metabolic analysis where only Arg244His (not null) worms elevate lactate/pyruvate levels, pointing to a missense-induced, 'Warburg'-like aberrant glycolysis. In silico predictions of the SDHA-B dimer structure demonstrate that Arg230His modifies the catalytic cleft despite the latter's remoteness from the mutation site. We hypothesise that Arg230His SDHB mutation rewires metabolism, reminiscent of metabolic reprogramming in cancer. Our tractable model provides a novel tool to investigate the metastatic propensity of this familial cancer and our approach may illuminate wider SDH pathology.
    Keywords:  C. elegans; Cancer; Familial Paraganglioma Syndrome (FPS); Succinate dehydrogenase; TCA cycle; Warburg-like glycolysis
    DOI:  https://doi.org/10.1242/dmm.044925
  12. Metabolites. 2020 Aug 26. pii: E346. [Epub ahead of print]10(9):
    Benito A, Hajji N, O'Neill K, Keun HC, Syed N.
      Metabolic regulation of immune cells has arisen as a critical set of processes required for appropriate response to immunological signals. While our knowledge in this area has rapidly expanded in leukocytes, much less is known about the metabolic regulation of brain-resident microglia. In particular, the role of alternative nutrients to glucose remains poorly understood. Here, we use stable-isotope (13C) tracing strategies and metabolomics to characterize the oxidative metabolism of β-hydroxybutyrate (BHB) in human (HMC3) and murine (BV2) microglia cells and the interplay with glucose in resting and LPS-activated BV2 cells. We found that BHB is imported and oxidised in the TCA cycle in both cell lines with a subsequent increase in the cytosolic NADH:NAD+ ratio. In BV2 cells, stimulation with LPS upregulated the glycolytic flux, increased the cytosolic NADH:NAD+ ratio and promoted the accumulation of the glycolytic intermediate dihydroxyacetone phosphate (DHAP). The addition of BHB enhanced LPS-induced accumulation of DHAP and promoted glucose-derived lactate export. BHB also synergistically increased LPS-induced accumulation of succinate and other key immunometabolites, such as α-ketoglutarate and fumarate generated by the TCA cycle. Finally, BHB upregulated the expression of a key pro-inflammatory (M1 polarisation) marker gene, NOS2, in BV2 cells activated with LPS. In conclusion, we identify BHB as a potentially immunomodulatory metabolic substrate for microglia that promotes metabolic reprogramming during pro-inflammatory response.
    Keywords:  metabolic reprogramming; metabolomics; microglia; stable-isotope tracing; β-hydroxybutyrate
    DOI:  https://doi.org/10.3390/metabo10090346
  13. Essays Biochem. 2020 Aug 24. pii: EBC20190041. [Epub ahead of print]
    Judge A, Dodd MS.
      Metabolism consists of a series of reactions that occur within cells of living organisms to sustain life. The process of metabolism involves many interconnected cellular pathways to ultimately provide cells with the energy required to carry out their function. The importance and the evolutionary advantage of these pathways can be seen as many remain unchanged by animals, plants, fungi, and bacteria. In eukaryotes, the metabolic pathways occur within the cytosol and mitochondria of cells with the utilisation of glucose or fatty acids providing the majority of cellular energy in animals. Metabolism is organised into distinct metabolic pathways to either maximise the capture of energy or minimise its use. Metabolism can be split into a series of chemical reactions that comprise both the synthesis and degradation of complex macromolecules known as anabolism or catabolism, respectively. The basic principles of energy consumption and production are discussed, alongside the biochemical pathways that make up fundamental metabolic processes for life.
    Keywords:  biochemistry; glycolysis; metabolism
    DOI:  https://doi.org/10.1042/EBC20190041
  14. Redox Biol. 2020 Aug 13. pii: S2213-2317(20)30890-9. [Epub ahead of print]36 101685
    Shao C, Lu W, Du Y, Yan W, Bao Q, Tian Y, Wang G, Ye H, Hao H.
      NADPH is a pivotal cofactor that maintains redox homeostasis and lipogenesis in cancer cells and interference with NADPH production is a promising approach for treating cancer. However, how normal and cancer cells differentially exploit NADPH-producing pathways is unclear, and selective approaches to targeting NADPH are lacking. Here, we show that the assayed cancer cell lines preferentially depend on ME1-mediated NADPH production. ME1 knockdown increases intracellular ROS levels and impairs lipogenesis in cancer cells, leading to retarded proliferation and increased anoikis, while sparing normal cells. Notably, ME1 interference ultimately resulted in adaptive upregulation of mitochondrial IDH2 dependent of AMPK-FoxO1 activation to replenish the NADPH pool and mitigate cytosolic ROS. Combining ME1 ablation and IDH2 inhibition drastically reduces intracellular NADPH and prevents resistance to ME1 interference, resulting in increased apoptosis and impeded tumor growth and metastasis. This study demonstrates that cytosolic ME1 integrated with mitochondrial IDH2 is essential for tumor growth and metastasis, thereby highlighting the blockade of metabolic compensation by disrupting mitochondrial-cytosol NADPH transport as a promising approach to selectively targeting NADPH in cancer cells that rely on NADPH-driven antioxidant systems.
    Keywords:  IDH2; ME1; Metabolic adaptability; NADPH; ROS; Reductive carboxylation
    DOI:  https://doi.org/10.1016/j.redox.2020.101685
  15. Biomol Concepts. 2020 Aug 22. pii: /j/bmc.2020.11.issue-1/bmc-2020-0014/bmc-2020-0014.xml. [Epub ahead of print]11(1): 143-152
    Nath S.
      The mitochondrial permeability transition (MPT) has been one of the longstanding enigmas in biology. Its cause is currently at the center of an extensive scientific debate, and several hypotheses on its molecular nature have been put forward. The present view holds that the transition arises from the opening of a high-conductance channel in the energy-transducing membrane, the permeability transition pore (PTP), also called the mitochondrial megachannel or the multiconductance channel (MMC). Here, the novel hypothesis is proposed that the aqueous access channels at the interface of the c-ring and the a-subunit of FO in the FOF1-ATP synthase are repurposed during induction of apoptosis and constitute the elusive PTP/ MMC. A unifying principle based on regulation by local potentials is advanced to rationalize the action of the myriad structurally and chemically diverse inducers and inhibitors of PTP/MMC. Experimental evidence in favor of the hypothesis and its differences from current models of PTP/MMC are summarized. The hypothesis explains in considerable detail how the binding of Ca2+ to a β-catalytic site (site 3) in the F1 portion of ATP synthase triggers the opening of the PTP/MMC. It is also shown to connect to longstanding proposals within Nath's torsional mechanism of energy transduction and ATP synthesis as to how the binding of MgADP to site 3 does not induce PTP/MMC, but instead catalyzes physiological ATP synthesis in cell life. In the author's knowledge, this is the first model that explains how Ca2+ transforms the FOF1-ATP synthase from an exquisite energy-conserving enzyme in cell life into an energy-dissipating structure that promotes cell death. This has major implications for basic as well as for clinical research, such as for the development of drugs that target the MPT, given the established role of PTP/MMC dysregulation in cancer, ischemia, cardiac hypertrophy, and various neurodegenerative diseases.
    Keywords:  ATP synthase; Apoptosis; Calcium Ca2+; Magnesium Mg2+; Mitochondria; Nath’s torsional mechanism of energy transduction and ATP synthesis; Nath’s two-ion theory of energy coupling; Oxidative phosphorylation (OXPHOS); Permeability transition
    DOI:  https://doi.org/10.1515/bmc-2020-0014
  16. Front Immunol. 2020 ;11 1968
    Møller SH, Mellergaard M, Madsen M, Bermejo AV, Jepsen SD, Hansen MH, Høgh RI, Aldana BI, Desler C, Rasmussen LJ, Sustarsic EG, Gerhart-Hines Z, Daskalaki E, Wheelock CE, Hiron TK, Lin D, O'Callaghan CA, Wandall HH, Andresen L, Skov S.
      Immune surveillance of cancer cells is facilitated by the Natural Killer Group 2D (NKG2D) receptor expressed by different lymphocyte subsets. It recognizes NKG2D ligands that are rarely expressed on healthy cells, but upregulated by tumorigenesis, presenting a target for immunological clearance. The molecular mechanisms responsible for NKG2D ligand regulation remain complex. Here we report that cancer cell metabolism supports constitutive surface expression of the NKG2D ligand MHC class I chain-related proteins A (MICA). Knockout of the N-glycosylation gene N-acetylglucosaminyltransferase V (MGAT5) in HEK293 cells induced altered metabolism and continuous high MICA surface expression. MGAT5 knockout cells were used to examine the association of cell metabolism and MICA expression through genetic, pharmacological and metabolic assays. Findings were verified in cancer cell lines. Cells with constitutive high MICA expression showed enhanced spare respiratory capacity and elevated mitochondrial efflux of citrate, determined by extracellular flux analysis and metabolomics. MICA expression was reduced by inhibitors of mitochondrial function, FCCP and etomoxir e.g., and depended on conversion of citrate to acetyl-CoA and oxaloacetate by ATP citrate lyase, which was also observed in several cancer cell types. Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) analysis revealed that upregulated MICA transcription was associated with an open chromatin structure at the MICA transcription start site. We identify mitochondria and cytoplasmic citrate as key regulators of constitutive MICA expression and we propose that metabolic reprogramming of certain cancer cells facilitates MICA expression and NKG2D-mediated immune recognition.
    Keywords:  ATP citrate lyase; MHC class I chain-related proteins A; Natural Killer Group 2D; cancer metabolism; citrate; tumor immunology
    DOI:  https://doi.org/10.3389/fimmu.2020.01968
  17. Nat Rev Immunol. 2020 Aug 24.
    Certo M, Tsai CH, Pucino V, Ho PC, Mauro C.
      The microenvironment in cancerous tissues is immunosuppressive and pro-tumorigenic, whereas the microenvironment of tissues affected by chronic inflammatory disease is pro-inflammatory and anti-resolution. Despite these opposing immunological states, the metabolic states in the tissue microenvironments of cancer and inflammatory diseases are similar: both are hypoxic, show elevated levels of lactate and other metabolic by-products and have low levels of nutrients. In this Review, we describe how the bioavailability of lactate differs in the microenvironments of tumours and inflammatory diseases compared with normal tissues, thus contributing to the establishment of specific immunological states in disease. A clear understanding of the metabolic signature of tumours and inflammatory diseases will enable therapeutic intervention aimed at resetting the bioavailability of metabolites and correcting the dysregulated immunological state, triggering beneficial cytotoxic, inflammatory responses in tumours and immunosuppressive responses in chronic inflammation.
    DOI:  https://doi.org/10.1038/s41577-020-0406-2
  18. Cell Rep. 2020 Aug 25. pii: S2211-1247(20)31044-5. [Epub ahead of print]32(8): 108059
    Meul T, Berschneider K, Schmitt S, Mayr CH, Mattner LF, Schiller HB, Yazgili AS, Wang X, Lukas C, Schlesser C, Prehn C, Adamski J, Graf E, Schwarzmayr T, Perocchi F, Kukat A, Trifunovic A, Kremer L, Prokisch H, Popper B, von Toerne C, Hauck SM, Zischka H, Meiners S.
      The proteasome is the main proteolytic system for targeted protein degradation in the cell and is fine-tuned according to cellular needs. Here, we demonstrate that mitochondrial dysfunction and concomitant metabolic reprogramming of the tricarboxylic acid (TCA) cycle reduce the assembly and activity of the 26S proteasome. Both mitochondrial mutations in respiratory complex I and treatment with the anti-diabetic drug metformin impair 26S proteasome activity. Defective 26S assembly is reversible and can be overcome by supplementation of aspartate or pyruvate. This metabolic regulation of 26S activity involves specific regulation of proteasome assembly factors via the mTORC1 pathway. Of note, reducing 26S activity by metformin confers increased resistance toward the proteasome inhibitor bortezomib, which is reversible upon pyruvate supplementation. Our study uncovers unexpected consequences of defective mitochondrial metabolism for proteasomal protein degradation in the cell, which has important pathophysiological and therapeutic implications.
    Keywords:  26S proteasome; Rpn6; TCA; aspartate; metabolic reprogramming; metformin; mitochondria; proteasome assembly factors; proteasome inhibitor resistance; pyruvate; respiratory complex I
    DOI:  https://doi.org/10.1016/j.celrep.2020.108059
  19. PLoS One. 2020 ;15(8): e0235551
    Kobylarz MJ, Goodwin JM, Kang ZB, Annand JW, Hevi S, O'Mahony E, McAllister G, Reece-Hoyes J, Wang Q, Alford J, Russ C, Lindeman A, Beibel M, Roma G, Carbone W, Knehr J, Loureiro J, Antczak C, Wiederschain D, Murphy LO, Menon S, Nyfeler B.
      VPS34 is a key regulator of endomembrane dynamics and cargo trafficking, and is essential in cultured cell lines and in mice. To better characterize the role of VPS34 in cell growth, we performed unbiased cell line profiling studies with the selective VPS34 inhibitor PIK-III and identified RKO as a VPS34-dependent cellular model. Pooled CRISPR screen in the presence of PIK-III revealed endolysosomal genes as genetic suppressors. Dissecting VPS34-dependent alterations with transcriptional profiling, we found the induction of hypoxia response and cholesterol biosynthesis as key signatures. Mechanistically, acute VPS34 inhibition enhanced lysosomal degradation of transferrin and low-density lipoprotein receptors leading to impaired iron and cholesterol uptake. Excess soluble iron, but not cholesterol, was sufficient to partially rescue the effects of VPS34 inhibition on mitochondrial respiration and cell growth, indicating that iron limitation is the primary driver of VPS34-dependency in RKO cells. Loss of RAB7A, an endolysosomal marker and top suppressor in our genetic screen, blocked transferrin receptor degradation, restored iron homeostasis and reversed the growth defect as well as metabolic alterations due to VPS34 inhibition. Altogether, our findings suggest that impaired iron mobilization via the VPS34-RAB7A axis drive VPS34-dependence in certain cancer cells.
    DOI:  https://doi.org/10.1371/journal.pone.0235551
  20. Autophagy. 2020 Aug 24. 1-15
    Lauterbach MA, Saavedra V, Mangan MSJ, Penno A, Thiele C, Latz E, Kuerschner L.
      1-Deoxysphingolipids (deoxySLs) are atypical sphingolipids of clinical relevance as they are elevated in plasma of patients suffering from hereditary sensory and autonomic neuropathy (HSAN1) or type 2 diabetes. Their neurotoxicity is described best but they inflict damage to various cell types by an uncertain pathomechanism. Using mouse embryonic fibroblasts and an alkyne analog of 1-deoxysphinganine (doxSA), the metabolic precursor of all deoxySLs, we here study the impact of deoxySLs on macroautophagy/autophagy, the regulated degradation of dysfunctional or expendable cellular components. We find that deoxySLs induce autophagosome and lysosome accumulation indicative of an increase in autophagic flux. The autophagosomal machinery targets damaged mitochondria that have accumulated N-acylated doxSA metabolites, presumably deoxyceramide and deoxydihydroceramide, and show aberrant swelling and tubule formation. Autophagosomes and lysosomes also interact with cellular lipid aggregates and crystals that occur upon cellular uptake and N-acylation of monomeric doxSA. As crystals entering the lysophagosomal apparatus in phagocytes are known to trigger the NLRP3 inflammasome, we also treated macrophages with doxSA. We demonstrate the activation of the NLRP3 inflammasome by doxSLs, prompting the release of IL1B from primary macrophages. Taken together, our data establish an impact of doxSLs on autophagy and link doxSL pathophysiology to inflammation and the innate immune system.ABBREVIATIONS: alkyne-doxSA: (2S,3R)-2-aminooctadec-17yn-3-ol; alkyne-SA: (2S,3R)-2- aminooctadec-17yn-1,3-diol; aSA: alkyne-sphinganine; ASTM-BODIPY: azido-sulfo-tetramethyl-BODIPY; CerS: ceramide synthase; CMR: clonal macrophage reporter; deoxySLs: 1-deoxysphingolipids; dox(DH)Cer: 1-deoxydihydroceramide; doxCer: 1-deoxyceramide; doxSA: 1-deoxysphinganine; FB1: fumonisin B1; HSAN1: hereditary sensory and autonomic neuropathy type 1; LC3: MAP1LC3A and MAP1LC3B; LPS: lipopolysaccharide; MEF: mouse embryonal fibroblasts; MS: mass spectrometry; N3635P: azido-STAR635P; N3Cy3: azido-cyanine 3; N3picCy3: azido-picolylcyanine 3; NLRP3: NOD-like receptor pyrin domain containing protein 3; P4HB: prolyl 4-hydroxylase subunit beta; PINK1: PTEN induced putative kinase 1; PYCARD/ASC: PYD and CARD domain containing; SPTLC1: serine palmitoyltransferase long chain base subunit 1; SQSTM1: sequestosome 1; TLC: thin layer chromatography.
    Keywords:  Autophagy; HSAN1; crystal; doxSA; innate immunity; lipid; macrophage
    DOI:  https://doi.org/10.1080/15548627.2020.1804677
  21. Proc Natl Acad Sci U S A. 2020 Aug 26. pii: 202000643. [Epub ahead of print]
    Tavares CDJ, Aigner S, Sharabi K, Sathe S, Mutlu B, Yeo GW, Puigserver P.
      The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) is a transcriptional coactivator that controls expression of metabolic/energetic genes, programming cellular responses to nutrient and environmental adaptations such as fasting, cold, or exercise. Unlike other coactivators, PGC-1α contains protein domains involved in RNA regulation such as serine/arginine (SR) and RNA recognition motifs (RRMs). However, the RNA targets of PGC-1α and how they pertain to metabolism are unknown. To address this, we performed enhanced ultraviolet (UV) cross-linking and immunoprecipitation followed by sequencing (eCLIP-seq) in primary hepatocytes induced with glucagon. A large fraction of RNAs bound to PGC-1α were intronic sequences of genes involved in transcriptional, signaling, or metabolic function linked to glucagon and fasting responses, but were not the canonical direct transcriptional PGC-1α targets such as OXPHOS or gluconeogenic genes. Among the top-scoring RNA sequences bound to PGC-1α were Foxo1, Camk1δ, Per1, Klf15, Pln4, Cluh, Trpc5, Gfra1, and Slc25a25 PGC-1α depletion decreased a fraction of these glucagon-induced messenger RNA (mRNA) transcript levels. Importantly, knockdown of several of these genes affected glucagon-dependent glucose production, a PGC-1α-regulated metabolic pathway. These studies show that PGC-1α binds to intronic RNA sequences, some of them controlling transcript levels associated with glucagon action.
    Keywords:  PGC-1α; RNA binding; glucagon; liver; mitochondria
    DOI:  https://doi.org/10.1073/pnas.2000643117
  22. Cell Res. 2020 Aug 24.
    Lv M, Chen M, Zhang R, Zhang W, Wang C, Zhang Y, Wei X, Guan Y, Liu J, Feng K, Jing M, Wang X, Liu YC, Mei Q, Han W, Jiang Z.
      CD8+ T cell-mediated cancer clearance is often suppressed by the interaction between inhibitory molecules like PD-1 and PD-L1, an interaction acts like brakes to prevent T cell overreaction under normal conditions but is exploited by tumor cells to escape the immune surveillance. Immune checkpoint inhibitors have revolutionized cancer therapeutics by removing such brakes. Unfortunately, only a minority of cancer patients respond to immunotherapies presumably due to inadequate immunity. Antitumor immunity depends on the activation of the cGAS-STING pathway, as STING-deficient mice fail to stimulate tumor-infiltrating dendritic cells (DCs) to activate CD8+ T cells. STING agonists also enhance natural killer (NK) cells to mediate the clearance of CD8+ T cell-resistant tumors. Therefore STING agonists have been intensively sought after. We previously discovered that manganese (Mn) is indispensable for the host defense against cytosolic dsDNA by activating cGAS-STING. Here we report that Mn is also essential in innate immune sensing of tumors and enhances adaptive immune responses against tumors. Mn-insufficient mice had significantly enhanced tumor growth and metastasis, with greatly reduced tumor-infiltrating CD8+ T cells. Mechanically, Mn2+ promoted DC and macrophage maturation and tumor-specific antigen presentation, augmented CD8+ T cell differentiation, activation and NK cell activation, and increased memory CD8+ T cells. Combining Mn2+ with immune checkpoint inhibition synergistically boosted antitumor efficacies and reduced the anti-PD-1 antibody dosage required in mice. Importantly, a completed phase 1 clinical trial with the combined regimen of Mn2+ and anti-PD-1 antibody showed promising efficacy, exhibiting type I IFN induction, manageable safety and revived responses to immunotherapy in most patients with advanced metastatic solid tumors. We propose that this combination strategy warrants further clinical translation.
    DOI:  https://doi.org/10.1038/s41422-020-00395-4
  23. Nat Commun. 2020 Aug 27. 11(1): 4281
    Sohn BK, Basu U, Lee SW, Cho H, Shen J, Deshpande A, Johnson LC, Das K, Patel SS, Kim H.
      Controlling efficiency and fidelity in the early stage of mitochondrial DNA transcription is crucial for regulating cellular energy metabolism. Conformational transitions of the transcription initiation complex must be central for such control, but how the conformational dynamics progress throughout transcription initiation remains unknown. Here, we use single-molecule fluorescence resonance energy transfer techniques to examine the conformational dynamics of the transcriptional system of yeast mitochondria with single-base resolution. We show that the yeast mitochondrial transcriptional complex dynamically transitions among closed, open, and scrunched states throughout the initiation stage. Then abruptly at position +8, the dynamic states of initiation make a sharp irreversible transition to an unbent conformation with associated promoter release. Remarkably, stalled initiation complexes remain in dynamic scrunching and unscrunching states without dissociating the RNA transcript, implying the existence of backtracking transitions with possible regulatory roles. The dynamic landscape of transcription initiation suggests a kinetically driven regulation of mitochondrial transcription.
    DOI:  https://doi.org/10.1038/s41467-020-17793-2
  24. Am J Physiol Heart Circ Physiol. 2020 Aug 28.
    Oropeza-Almazan Y, Blatter LA.
      Cardiac alternans, defined as beat-to-beat alternations in action potential duration, cytosolic Ca transient (CaT) amplitude and cardiac contraction, is associated with atrial fibrillation (AF) and sudden cardiac death. At the cellular level, cardiac alternans is linked to abnormal intracellular calcium handling during excitation-contraction coupling. We investigated how pharmacological activation or inhibition of cytosolic Ca sequestration via mitochondrial Ca uptake and mitochondrial Ca retention affects the occurrence of pacing-induced CaT alternans in isolated rabbit atrial myocytes.Cytosolic CaTs were recorded using Fluo-4 fluorescence microscopy. Alternans was quantified as the alternans ratio (AR=1-CaTSmall/CaTLarge; CaTSmalland CaTLargeare the amplitudes of the small and large CaTs of a pair of alternating CaTs). Inhibition of mitochondrial Ca sequestration via mitochondrial Ca uniporter complex (MCUC) with Ru360 enhanced the severity of CaT alternans (AR increase) and lowered the pacing frequency threshold for alternans. In contrast, stimulation of MCUC mediated mitochondrial Ca uptake with spermine rescued alternans (AR decrease) and increased the alternans pacing threshold. Direct measurement of mitochondrial [Ca] in membrane permeabilized myocytes with Fluo-4 loaded mitochondria revealed that spermine enhanced and accelerated mitochondrial Ca uptake. Stimulation of mitochondrial Ca retention by preventing mitochondrial Ca efflux through the mitochondrial permeability transition pore with cyclosporin A also protected from alternans and increased the alternans pacing threshold. Pharmacological manipulation of MCUC activity did not affect sarcoplasmic reticulum Ca load. Our results suggest that activation of Ca sequestration by mitochondria protects from CaT alternans and could be a potential therapeutic target for cardiac alternans and AF prevention.
    Keywords:  Ca alternans; atrial fibrillation; mitochondrial calcium uniporter complex; mitochondrial calcium uptake
    DOI:  https://doi.org/10.1152/ajpheart.00375.2020
  25. Biochim Biophys Acta Rev Cancer. 2020 Aug 21. pii: S0304-419X(20)30140-2. [Epub ahead of print] 188421
    Tong Y, Gao WQ, Liu Y.
      Recent research on cancer metabolism has revealed that individual tumors have highly heterogeneous metabolic profiles that contribute to the connective metabolic networks within the tumor and its environment. Indeed, tumor-associated cells types, including tumor cells, cancer-associated fibroblasts (CAFs) and immune cells, reprogram their metabolism in many different ways due to diverse genetic backgrounds and complex environmental stimuli. This intratumoral metabolic heterogeneity and the derived metabolic interactions play an instrumental role in cancer progression. Understanding how this heterogeneity occurs may provide promising therapeutic strategies. Here, we review the diverse metabolic profiles of several important cell subpopulations in tumors and their impact on tumor progression and discuss the consequent metabolic interactions as well as the related therapeutic concerns.
    Keywords:  Cancer metabolism; Metabolic heterogeneity; Tumor microenvironment (TME)
    DOI:  https://doi.org/10.1016/j.bbcan.2020.188421
  26. Front Cell Neurosci. 2020 ;14 194
    Liao Y, Dong Y, Cheng J.
      Membrane tethering is an important communication method for membrane-packaged organelles. Mitochondria are organelles with a bilayer membrane, and the membrane contact between mitochondria and other organelles is indispensable for maintaining cellular homeostasis. Increased levels of molecular determinants that mediate the membrane contact between mitochondria and other organelles, and their functions, have been revealed in recent years. In this review article, we aim to summarize the findings on the tethering between mitochondria and other organelles in physiological or pathological conditions, and discuss their roles in cellular homeostasis, neural activity, and neurodegenerative diseases.
    Keywords:  determinant; membrane contact; mitochondria; neurological diseases; pathological condition; physiological condition
    DOI:  https://doi.org/10.3389/fncel.2020.00194
  27. J Cell Sci. 2020 Aug 25. pii: jcs.248468. [Epub ahead of print]
    Antón Z, Mullally G, Ford H, van der Kamp MW, Szczelkun MD, Lane JD.
      Current methodologies for targeting the mitochondrial genome for research and/or therapy development in mitochondrial diseases are restricted by practical limitations and technical inflexibility. A molecular toolbox for CRISPR-mediated mitochondrial genome editing is desirable, as this could enable targeting of mtDNA haplotypes using the precision and tuneability of CRISPR enzymes. "MitoCRISPR" systems described to date lack reproducibility and independent corroboration. We have explored the requirements for MitoCRISPR in human cells by CRISPR nuclease engineering, including the use of alternative mitochondrial protein targeting sequences and smaller paralogues, and the application of gRNA modifications for mitochondrial import. We demonstrate varied mitochondrial targeting efficiencies and effects on mitochondrial dynamics/function of different CRISPR nucleases, with Lachnospiraceae bacterium ND2006 (Lb) Cas12a being better targeted and tolerated than Cas9 variants. We also provide evidence of Cas9 gRNA association with mitochondria in HeLa cells and isolated yeast mitochondria, even in the absence of a targeting RNA aptamer. Our data link mitochondrial-targeted LbCas12a/crRNA with increased mtDNA copy number dependent upon DNA binding and cleavage activity. We discuss reproducibility issues and the future steps necessary for MitoCRISPR.
    Keywords:  Cas12a; Cas9; CrRNA; GRNA; Import; MitoCRISPR; Targeting
    DOI:  https://doi.org/10.1242/jcs.248468
  28. Curr Opin Physiol. 2019 Aug;10 96-101
    Drake JC, Yan Z.
      The profound energetic demand of prolonged exercise imposed upon skeletal muscle and the heart is met by oxidation of substrate within mitochondria. As such, several coordinated events are initiated in order to maintain mitochondria, collectively known as mitochondrial quality control. In this review, we discuss how mitochondrial quality control functions to maintain the integrity of the reticulum and energy production in response to prolonged exercise, as well as the relevant signaling events that dictate these responses. Based upon the prevailing data in the field, we propose a model where exercise-mediated quality control may be chiefly regulated through local mechanisms, thus allowing for the remarkable precision in mitochondrial quality control events.
    Keywords:  exercise; mitochondria; mitophagy; muscle; myofiber; quality control
    DOI:  https://doi.org/10.1016/j.cophys.2019.05.005
  29. Nat Metab. 2020 Aug 24.
    Todoric J, Di Caro G, Reibe S, Henstridge DC, Green CR, Vrbanac A, Ceteci F, Conche C, McNulty R, Shalapour S, Taniguchi K, Meikle PJ, Watrous JD, Moranchel R, Najhawan M, Jain M, Liu X, Kisseleva T, Diaz-Meco MT, Moscat J, Knight R, Greten FR, Lau LF, Metallo CM, Febbraio MA, Karin M.
      Benign hepatosteatosis, affected by lipid uptake, de novo lipogenesis and fatty acid (FA) oxidation, progresses to non-alcoholic steatohepatitis (NASH) on stress and inflammation. A key macronutrient proposed to increase hepatosteatosis and NASH risk is fructose. Excessive intake of fructose causes intestinal-barrier deterioration and endotoxaemia. However, how fructose triggers these alterations and their roles in hepatosteatosis and NASH pathogenesis remain unknown. Here we show, using mice, that microbiota-derived Toll-like receptor (TLR) agonists promote hepatosteatosis without affecting fructose-1-phosphate (F1P) and cytosolic acetyl-CoA. Activation of mucosal-regenerative gp130 signalling, administration of the YAP-induced matricellular protein CCN1 or expression of the antimicrobial peptide Reg3b (beta) peptide counteract fructose-induced barrier deterioration, which depends on endoplasmic-reticulum stress and subsequent endotoxaemia. Endotoxin engages TLR4 to trigger TNF production by liver macrophages, thereby inducing lipogenic enzymes that convert F1P and acetyl-CoA to FA in both mouse and human hepatocytes.
    DOI:  https://doi.org/10.1038/s42255-020-0261-2
  30. J Mol Biol. 2020 Aug 22. pii: S0022-2836(20)30507-6. [Epub ahead of print]
    Wang C, Baradaran R, Long SB.
      The proteins MCU and EMRE form the minimal functional unit of the mitochondrial calcium uniporter complex in metazoans, a highly selective and tightly controlled Ca2+ channel of the inner mitochondrial membrane that regulates cellular metabolism. Here we present functional reconstitution of an MCU-EMRE complex from the red flour beetle, Tribolium castaneum, and a cryo-EM structure of the complex at 3.5 Å resolution. Using a novel assay, we demonstrate robust Ca2+ uptake into proteoliposomes containing the purified complex. Uptake is dependent on EMRE and also on the mitochondrial lipid cardiolipin. The structure reveals a tetrameric channel with a single ion pore. EMRE is located at the periphery of the transmembrane domain and associates primarily with the first transmembrane helix of MCU. Coiled coil and juxtamembrane domains within the matrix portion of the complex adopt markedly different conformations than in a structure of a human MCU-EMRE complex, suggesting that the structures represent different conformations of these functionally similar metazoan channels.
    Keywords:  Calcium channel; Flux assay; Ion channel; Membrane protein; Reconstitution
    DOI:  https://doi.org/10.1016/j.jmb.2020.08.013
  31. Nat Commun. 2020 Aug 25. 11(1): 4245
    Gong H, Gao Y, Zhou X, Xiao Y, Wang W, Tang Y, Zhou S, Zhang Y, Ji W, Yu L, Tian C, Lam SM, Shui G, Guddat LW, Wong LL, Wang Q, Rao Z.
      Diheme-containing succinate:menaquinone oxidoreductases (Sdh) are widespread in Gram-positive bacteria but little is known about the catalytic mechanisms they employ for succinate oxidation by menaquinone. Here, we present the 2.8 Å cryo-electron microscopy structure of a Mycobacterium smegmatis Sdh, which forms a trimer. We identified the membrane-anchored SdhF as a subunit of the complex. The 3 kDa SdhF forms a single transmembrane helix and this helix plays a role in blocking the canonically proximal quinone-binding site. We also identified two distal quinone-binding sites with bound quinones. One distal binding site is formed by neighboring subunits of the complex. Our structure further reveals the electron/proton transfer pathway for succinate oxidation by menaquinone. Moreover, this study provides further structural insights into the physiological significance of a trimeric respiratory complex II. The structure of the menaquinone binding site could provide a framework for the development of Sdh-selective anti-mycobacterial drugs.
    DOI:  https://doi.org/10.1038/s41467-020-18011-9
  32. Oncogene. 2020 Aug 27.
    Yang R, Zhao Y, Gu Y, Yang Y, Gao X, Yuan Y, Xiao L, Zhang J, Sun C, Yang H, Qin J, Li J, Zhang F, Zhang L, Ye J.
      Isocitrate dehydrogenase (IDH) mutation is the most important initiating event in gliomagenesis, and the increasing evidence shows that IDH mutation is associated with the metabolic reprogramming in the tumor. Dysregulated cholesterol metabolism is a hallmark of tumor cells, but the cholesterol homeostasis in IDH-mutated glioma is still unknown. In this study, we found that astrocyte-specific mutant IDH1(R132H) knockin reduced the cholesterol contents and damaged the structure of myelin in mouse brains. In U87 and U251 cells, the expression of mutant IDH1 consistently reduced the cholesterol levels. Furthermore, we found that IDH1 mutation enhanced the production of 24(S)-hydroxycholesterol (24-OHC), which is not only the metabolite of cholesterol elimination, but also functions as an endogenous ligand for the liver X receptors (LXRs). In IDH1-mutant glioma cells, the elevated 24-OHC activated LXRs, which consequently accelerated the low-density lipoprotein receptor (LDLR) degradation by upregulating the inducible degrader of the LDLR (IDOL). The reduced LDLR expressions in IDH1-mutant glioma cells abated the uptakes of low-density lipoprotein (LDL) to decrease the cholesterol influx. In addition, the activated LXRs also promoted the cholesterol efflux by elevating the ATP-binding cassette transporter A1 (ABCA1), ABCG1, and apolipoprotein E (ApoE) in both IDH1-mutant astrocytes and glioma cells. As a feedback, the reduced cholesterol levels stimulated the cholesterol biosynthesis, which made IDH1-mutated glioma cells more sensitive to atorvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase. The altered cholesterol homeostasis regulated by mutant IDH provides a pivotal therapeutical strategy for the IDH-mutated gliomas.
    DOI:  https://doi.org/10.1038/s41388-020-01439-0
  33. Nat Commun. 2020 Aug 28. 11(1): 4319
    Bennett NK, Nguyen MK, Darch MA, Nakaoka HJ, Cousineau D, Ten Hoeve J, Graeber TG, Schuelke M, Maltepe E, Kampmann M, Mendelsohn BA, Nakamura JL, Nakamura K.
      Disrupted energy metabolism drives cell dysfunction and disease, but approaches to increase or preserve ATP are lacking. To generate a comprehensive metabolic map of genes and pathways that regulate cellular ATP-the ATPome-we conducted a genome-wide CRISPR interference/activation screen integrated with an ATP biosensor. We show that ATP level is modulated by distinct mechanisms that promote energy production or inhibit consumption. In our system HK2 is the greatest ATP consumer, indicating energy failure may not be a general deficiency in producing ATP, but rather failure to recoup the ATP cost of glycolysis and diversion of glucose metabolites to the pentose phosphate pathway. We identify systems-level reciprocal inhibition between the HIF1 pathway and mitochondria; glycolysis-promoting enzymes inhibit respiration even when there is no glycolytic ATP production, and vice versa. Consequently, suppressing alternative metabolism modes paradoxically increases energy levels under substrate restriction. This work reveals mechanisms of metabolic control, and identifies therapeutic targets to correct energy failure.
    DOI:  https://doi.org/10.1038/s41467-020-18084-6
  34. Cell. 2020 Aug 18. pii: S0092-8674(20)30938-7. [Epub ahead of print]
    Johnstone SE, Reyes A, Qi Y, Adriaens C, Hegazi E, Pelka K, Chen JH, Zou LS, Drier Y, Hecht V, Shoresh N, Selig MK, Lareau CA, Iyer S, Nguyen SC, Joyce EF, Hacohen N, Irizarry RA, Zhang B, Aryee MJ, Bernstein BE.
      Widespread changes to DNA methylation and chromatin are well documented in cancer, but the fate of higher-order chromosomal structure remains obscure. Here we integrated topological maps for colon tumors and normal colons with epigenetic, transcriptional, and imaging data to characterize alterations to chromatin loops, topologically associated domains, and large-scale compartments. We found that spatial partitioning of the open and closed genome compartments is profoundly compromised in tumors. This reorganization is accompanied by compartment-specific hypomethylation and chromatin changes. Additionally, we identify a compartment at the interface between the canonical A and B compartments that is reorganized in tumors. Remarkably, similar shifts were evident in non-malignant cells that have accumulated excess divisions. Our analyses suggest that these topological changes repress stemness and invasion programs while inducing anti-tumor immunity genes and may therefore restrain malignant progression. Our findings call into question the conventional view that tumor-associated epigenomic alterations are primarily oncogenic.
    Keywords:  DNA methylation; chromatin; colon cancer; compartment; epigenetics; genome topology; nuclear architecture
    DOI:  https://doi.org/10.1016/j.cell.2020.07.030
  35. Nat Metab. 2020 Aug 24.
    Li L, Chen K, Wang T, Wu Y, Xing G, Chen M, Hao Z, Zhang C, Zhang J, Ma B, Liu Z, Yuan H, Liu Z, Long Q, Zhou Y, Qi J, Zhao D, Gao M, Pei D, Nie J, Ye D, Pan G, Liu X.
      Somatic cell reprogramming provides insight into basic principles of cell fate determination, which remain poorly understood. Here we show that the transcription factor Glis1 induces multi-level epigenetic and metabolic remodelling in stem cells that facilitates the induction of pluripotency. We find that Glis1 enables reprogramming of senescent cells into pluripotent cells and improves genome stability. During early phases of reprogramming, Glis1 directly binds to and opens chromatin at glycolytic genes, whereas it closes chromatin at somatic genes to upregulate glycolysis. Subsequently, higher glycolytic flux enhances cellular acetyl-CoA and lactate levels, thereby enhancing acetylation (H3K27Ac) and lactylation (H3K18la) at so-called 'second-wave' and pluripotency gene loci, opening them up to facilitate cellular reprogramming. Our work highlights Glis1 as a powerful reprogramming factor, and reveals an epigenome-metabolome-epigenome signalling cascade that involves the glycolysis-driven coordination of histone acetylation and lactylation in the context of cell fate determination.
    DOI:  https://doi.org/10.1038/s42255-020-0267-9
  36. Cell Metab. 2020 Aug 19. pii: S1550-4131(20)30415-0. [Epub ahead of print]
    McGettrick AF, O'Neill LAJ.
      HIF is a transcription factor that plays an essential role in the cellular response to low oxygen, orchestrating a metabolic switch that allows cells to survive in this environment. In immunity, infected and inflamed tissues are often hypoxic, and HIF helps immune cells adapt. HIF-α stabilization can also occur under normoxia during immunity and inflammation, where it regulates metabolism but in addition can directly regulate expression of immune genes. Here we review the role of HIF in immunity, including its role in macrophages, dendritic cells, neutrophils, T cells, and B cells. Its role in immunity is as essential for cellular responses as it is in its original role in hypoxia, with HIF being implicated in multiple inflammatory diseases and in immunosuppression in tumors.
    DOI:  https://doi.org/10.1016/j.cmet.2020.08.002
  37. Nat Commun. 2020 Aug 28. 11(1): 4337
    Aksentijević D, Karlstaedt A, Basalay MV, O'Brien BA, Sanchez-Tatay D, Eminaga S, Thakker A, Tennant DA, Fuller W, Eykyn TR, Taegtmeyer H, Shattock MJ.
      Intracellular Na elevation in the heart is a hallmark of pathologies where both acute and chronic metabolic remodelling occurs. Here, we assess whether acute (75 μM ouabain 100 nM blebbistatin) or chronic myocardial Nai load (PLM3SA mouse) are causally linked to metabolic remodelling and whether the failing heart shares a common Na-mediated metabolic 'fingerprint'. Control (PLMWT), transgenic (PLM3SA), ouabain-treated and hypertrophied Langendorff-perfused mouse hearts are studied by 23Na, 31P, 13C NMR followed by 1H-NMR metabolomic profiling. Elevated Nai leads to common adaptive metabolic alterations preceding energetic impairment: a switch from fatty acid to carbohydrate metabolism and changes in steady-state metabolite concentrations (glycolytic, anaplerotic, Krebs cycle intermediates). Inhibition of mitochondrial Na/Ca exchanger by CGP37157 ameliorates the metabolic changes. In silico modelling indicates altered metabolic fluxes (Krebs cycle, fatty acid, carbohydrate, amino acid metabolism). Prevention of Nai overload or inhibition of Na/Camito may be a new approach to ameliorate metabolic dysregulation in heart failure.
    DOI:  https://doi.org/10.1038/s41467-020-18160-x
  38. Am J Physiol Renal Physiol. 2020 Aug 24.
    Pokkunuri ID, Lokhandwala MF, Banday AA.
      Renal proximal tubular apoptosis plays a critical role in kidney health and disease. However, cellular molecules that trigger renal apoptosis remain elusive. Here, we evaluated the effect of inhibiting protein disulfide isomerase (PDI), a critical thioredoxin chaperone protein, on apoptosis, and the underlying mechanisms in human renal proximal tubular (HK2) cells. HK2 cells were transfected with PDI specific siRNA in the absence and presence of an antioxidant tempol. PDI siRNA transfection resulted in a decrease of ~70% in PDI protein expression and enzyme activity. PDI inhibition increased caspase-3 activity and induced profound cell apoptosis. Mitochondrial function, as assessed by mitochondrial cytochrome c levels, mitochondrial membrane potential, oxygen consumption, and ATP levels, was significantly reduced in the PDI inhibited cells. Also, PDI inhibition caused Nrf2 (nuclear factor E2 related factor 2, a redox-sensitive transcription factor) cytoplasmic sequestration, decreased superoxide dismutase, and glutathione S-transferase activities, and increased oxidative stress. In PDI inhibited cells, tempol reduced apoptosis, caspase-3 activity, and oxidative stress, and also restored Nrf2 nuclear translocation and mitochondrial function. Silencing Nrf2 in the cells abrogated the beneficial effect of tempol, while Keap1 silencing (Kelch-like ECH-associated protein 1, a Nrf2 regulatory protein) protected the cells from PDI inhibitory effects. Collectively, our data indicate that PDI inhibition diminishes Nrf2 nuclear translocation causing oxidative stress that further triggers mitochondrial dysfunction and renal cell apoptosis. These studies suggest an important role for PDI in renal cell apoptosis involving Nrf2 and mitochondrial dysfunction.
    Keywords:  Apoptosis; Keap1/Nrf2; Mitochondria; Oxidative Stress; PDI
    DOI:  https://doi.org/10.1152/ajprenal.00049.2020
  39. Nat Commun. 2020 Aug 27. 11(1): 4289
    Iske J, Seyda M, Heinbokel T, Maenosono R, Minami K, Nian Y, Quante M, Falk CS, Azuma H, Martin F, Passos JF, Niemann CU, Tchkonia T, Kirkland JL, Elkhal A, Tullius SG.
      Older organs represent an untapped potential to close the gap between demand and supply in organ transplantation but are associated with age-specific responses to injury and increased immunogenicity, thereby aggravating transplant outcomes. Here we show that cell-free mitochondrial DNA (cf-mt-DNA) released by senescent cells accumulates with aging and augments immunogenicity. Ischemia reperfusion injury induces a systemic increase of cf-mt-DNA that promotes dendritic cell-mediated, age-specific inflammatory responses. Comparable events are observed clinically, with the levels of cf-mt-DNA elevated in older deceased organ donors, and with the isolated cf-mt-DNA capable of activating human dendritic cells. In experimental models, treatment of old donor animals with senolytics clear senescent cells and diminish cf-mt-DNA release, thereby dampening age-specific immune responses and prolonging the survival of old cardiac allografts comparable to young donor organs. Collectively, we identify accumulating cf-mt-DNA as a key factor in inflamm-aging and present senolytics as a potential approach to improve transplant outcomes and availability.
    DOI:  https://doi.org/10.1038/s41467-020-18039-x
  40. Proc Natl Acad Sci U S A. 2020 Aug 24. pii: 202003537. [Epub ahead of print]
    Rao Y, Gammon S, Zacharias NM, Liu T, Salzillo T, Xi Y, Wang J, Bhattacharya P, Piwnica-Worms D.
      Hyperpolarized [1-13C]pyruvate magnetic resonance spectroscopic imaging (MRSI) is a noninvasive metabolic-imaging modality that probes carbon flux in tissues and infers the state of metabolic reprograming in tumors. Prevailing models attribute elevated hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion rates in aggressive tumors to enhanced glycolytic flux and lactate dehydrogenase A (LDHA) activity (Warburg effect). By contrast, we find by cross-sectional analysis using genetic and pharmacological tools in mechanistic studies applied to well-defined genetically engineered cell lines and tumors that initial hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion rates as well as global conversion were highly dependent on and critically rate-limited by the transmembrane influx of [1-13C]pyruvate mediated predominately by monocarboxylate transporter-1 (MCT1). Specifically, in a cell-encapsulated alginate bead model, induced short hairpin (shRNA) knockdown or overexpression of MCT1 quantitatively inhibited or enhanced, respectively, unidirectional pyruvate influxes and [1-13C]pyruvate-to-[1-13C]lactate conversion rates, independent of glycolysis or LDHA activity. Similarly, in tumor models in vivo, hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion was highly dependent on and critically rate-limited by the induced transmembrane influx of [1-13C]pyruvate mediated by MCT1. Thus, hyperpolarized [1-13C]pyruvate MRSI measures primarily MCT1-mediated [1-13C]pyruvate transmembrane influx in vivo, not glycolytic flux or LDHA activity, driving a reinterpretation of this maturing new technology during clinical translation. Indeed, Kaplan-Meier survival analysis for patients with pancreatic, renal, lung, and cervical cancers showed that high-level expression of MCT1 correlated with poor overall survival, and only in selected tumors, coincident with LDHA expression. Thus, hyperpolarized [1-13C]pyruvate MRSI provides a noninvasive functional assessment primarily of MCT1 as a clinical biomarker in relevant patient populations.
    Keywords:  MCT1; [1-13C]pyruvate; hyperpolarized NMR; imaging biomarker; monocarboxylate transporters
    DOI:  https://doi.org/10.1073/pnas.2003537117
  41. Nat Commun. 2020 Aug 27. 11(1): 4313
    Damal Villivalam S, You D, Kim J, Lim HW, Xiao H, Zushin PH, Oguri Y, Amin P, Kang S.
      It has been suggested that beige fat thermogenesis is tightly controlled by epigenetic regulators that sense environmental cues such as temperature. Here, we report that subcutaneous adipose expression of the DNA demethylase TET1 is suppressed by cold and other stimulators of beige adipocyte thermogenesis. TET1 acts as an autonomous repressor of key thermogenic genes, including Ucp1 and Ppargc1a, in beige adipocytes. Adipose-selective Tet1 knockout mice generated by using Fabp4-Cre improves cold tolerance and increases energy expenditure and protects against diet-induced obesity and insulin resistance. Moreover, the suppressive role of TET1 in the thermogenic gene regulation of beige adipocytes is largely DNA demethylase-independent. Rather, TET1 coordinates with HDAC1 to mediate the epigenetic changes to suppress thermogenic gene transcription. Taken together, TET1 is a potent beige-selective epigenetic breaker of the thermogenic gene program. Our findings may lead to a therapeutic strategy to increase energy expenditure in obesity and related metabolic disorders.
    DOI:  https://doi.org/10.1038/s41467-020-18054-y
  42. Br J Pharmacol. 2020 Aug 25.
    Rahman J, Singh P, Merle NS, Niyonzima N, Kemper C.
      The complement system, well known for its central role in innate immunity, is currently emerging as an unexpected, cell-autonomous, orchestrator of normal cell physiology. Specifically, an intracellularly active complement system - the complosome - controls key pathways of normal cell metabolism during immune cell homeostasis and effector function. So far, we know little about the exact structure and localization of intracellular complement components within and among cells. A common scheme, however, is that they operate in crosstalk with other intracellular immune sensors, such as inflammasomes, and that they impact on the activity of key sub-cellular compartments. Among cell compartments, mitochondria appear to have built a particularly early and strong relationship with the complosome and extracellularly active complement - not surprising in view of the strong impact of the complosome on metabolism. In this review, we will hence summarize the current knowledge about the close complosome-mitochondria relationship and also discuss key questions surrounding this novel research area.
    Keywords:  CD46; Complement; OXPHOS; glycolysis; metabolism; mitochondria
    DOI:  https://doi.org/10.1111/bph.15238
  43. EMBO Rep. 2020 Aug 27. e50964
    Lightowlers RN, Chrzanowska-Lightowlers ZM, Russell OM.
      Transplantation of functional mitochondria directly into defective cells is a novel approach that has recently caught the attention of scientists and the general public alike. Could this be too good to be true?
    DOI:  https://doi.org/10.15252/embr.202050964
  44. Proc Natl Acad Sci U S A. 2020 Aug 24. pii: 202013543. [Epub ahead of print]
    Zhang H, Lyu Z, Fan Y, Evans CR, Barber KW, Banerjee K, Igoshin OA, Rinehart J, Ling J.
      Accurate protein synthesis is a tightly controlled biological process with multiple quality control steps safeguarded by aminoacyl-transfer RNA (tRNA) synthetases and the ribosome. Reduced translational accuracy leads to various physiological changes in both prokaryotes and eukaryotes. Termination of translation is signaled by stop codons and catalyzed by release factors. Occasionally, stop codons can be suppressed by near-cognate aminoacyl-tRNAs, resulting in protein variants with extended C termini. We have recently shown that stop-codon readthrough is heterogeneous among single bacterial cells. However, little is known about how environmental factors affect the level and heterogeneity of stop-codon readthrough. In this study, we have combined dual-fluorescence reporters, mass spectrometry, mathematical modeling, and single-cell approaches to demonstrate that a metabolic stress caused by excess carbon substantially increases both the level and heterogeneity of stop-codon readthrough. Excess carbon leads to accumulation of acid metabolites, which lower the pH and the activity of release factors to promote readthrough. Furthermore, our time-lapse microscopy experiments show that single cells with high readthrough levels are more adapted to severe acid stress conditions and are more sensitive to an aminoglycoside antibiotic. Our work thus reveals a metabolic stress that promotes translational heterogeneity and phenotypic diversity.
    DOI:  https://doi.org/10.1073/pnas.2013543117
  45. Cell Rep. 2020 Aug 25. pii: S2211-1247(20)31064-0. [Epub ahead of print]32(8): 108079
    Tur J, Pereira-Lopes S, Vico T, Marín EA, Muñoz JP, Hernández-Alvarez M, Cardona PJ, Zorzano A, Lloberas J, Celada A.
      Mitofusin 2 (Mfn2) plays a major role in mitochondrial fusion and in the maintenance of mitochondria-endoplasmic reticulum contact sites. Given that macrophages play a major role in inflammation, we studied the contribution of Mfn2 to the activity of these cells. Pro-inflammatory stimuli such as lipopolysaccharide (LPS) induced Mfn2 expression. The use of the Mfn2 and Mfn1 myeloid-conditional knockout (KO) mouse models reveals that Mfn2 but not Mfn1 is required for the adaptation of mitochondrial respiration to stress conditions and for the production of reactive oxygen species (ROS) upon pro-inflammatory activation. Mfn2 deficiency specifically impairs the production of pro-inflammatory cytokines and nitric oxide. In addition, the lack of Mfn2 but not Mfn1 is associated with dysfunctional autophagy, apoptosis, phagocytosis, and antigen processing. Mfn2floxed;CreLysM mice fail to be protected from Listeria, Mycobacterium tuberculosis, or LPS endotoxemia. These results reveal an unexpected contribution of Mfn2 to ROS production and inflammation in macrophages.
    Keywords:  apoptotic bodies; inflammation; lipopolysaccharide (LPS); macrophages; mitochondria; mitofusin; phagocytosis; protein degradation; reactive oxygen species (ROS); septic shock
    DOI:  https://doi.org/10.1016/j.celrep.2020.108079
  46. Cell. 2020 Aug 20. pii: S0092-8674(20)30943-0. [Epub ahead of print]
    Bock A, Annibale P, Konrad C, Hannawacker A, Anton SE, Maiellaro I, Zabel U, Sivaramakrishnan S, Falcke M, Lohse MJ.
      Cells relay a plethora of extracellular signals to specific cellular responses by using only a few second messengers, such as cAMP. To explain signaling specificity, cAMP-degrading phosphodiesterases (PDEs) have been suggested to confine cAMP to distinct cellular compartments. However, measured rates of fast cAMP diffusion and slow PDE activity render cAMP compartmentalization essentially impossible. Using fluorescence spectroscopy, we show that, contrary to earlier data, cAMP at physiological concentrations is predominantly bound to cAMP binding sites and, thus, immobile. Binding and unbinding results in largely reduced cAMP dynamics, which we term "buffered diffusion." With a large fraction of cAMP being buffered, PDEs can create nanometer-size domains of low cAMP concentrations. Using FRET-cAMP nanorulers, we directly map cAMP gradients at the nanoscale around PDE molecules and the areas of resulting downstream activation of cAMP-dependent protein kinase (PKA). Our study reveals that spatiotemporal cAMP signaling is under precise control of nanometer-size domains shaped by PDEs that gate activation of downstream effectors.
    Keywords:  FRET biosensors; G protein-coupled receptors; buffered diffusion; cell signaling; compartmentation; cyclic AMP; fluorescence fluctuation spectroscopy; nanodomains; phosphodiesterase; protein kinase A4
    DOI:  https://doi.org/10.1016/j.cell.2020.07.035
  47. Biochem Soc Trans. 2020 Aug 28. 48(4): 1379-1395
    Sauro HM.
      Linear metabolic pathways are the simplest network architecture we find in metabolism and are a good starting point to gain insight into the operating principles of metabolic control. Linear pathways possess some well-known properties, such as a bias of flux control towards the first few steps of the pathway as well as the lack of flux control at reactions close to equilibrium. In both cases, a rationale for these behaviors is given in terms of how elasticities transmit changes through a pathway. A discussion is given on the fundamental role that two reaction step sections play in a linear pathway when transmitting changes. For a pathway with irreversible steps, the deconstruction is straight forward and includes a product of local response coefficients that cascade along the pathway. When reversibility is included, the picture became more complex but a relationship in terms of the local response coefficients if derived that includes the reverse response coefficients and highlights the interplay between the forward and backward transmission of changes during a perturbation.
    Keywords:  linear pathway; metabolic control; metabolism
    DOI:  https://doi.org/10.1042/BST20190842
  48. BMC Bioinformatics. 2020 Aug 21. 21(Suppl 10): 349
    Manipur I, Granata I, Maddalena L, Guarracino MR.
      BACKGROUND: Biological networks are representative of the diverse molecular interactions that occur within cells. Some of the commonly studied biological networks are modeled through protein-protein interactions, gene regulatory, and metabolic pathways. Among these, metabolic networks are probably the most studied, as they directly influence all physiological processes. Exploration of biochemical pathways using multigraph representation is important in understanding complex regulatory mechanisms. Feature extraction and clustering of these networks enable grouping of samples obtained from different biological specimens. Clustering techniques separate networks depending on their mutual similarity.RESULTS: We present a clustering analysis on tissue-specific metabolic networks for single samples from three primary tumor sites: breast, lung, and kidney cancer. The metabolic networks were obtained by integrating genome scale metabolic models with gene expression data. We performed network simplification to reduce the computational time needed for the computation of network distances. We empirically proved that networks clustering can characterize groups of patients in multiple conditions.
    CONCLUSIONS: We provide a computational methodology to explore and characterize the metabolic landscape of tumors, thus providing a general methodology to integrate analytic metabolic models with gene expression data. This method represents a first attempt in clustering large scale metabolic networks. Moreover, this approach gives the possibility to get valuable information on what are the effects of different conditions on the overall metabolism.
    Keywords:  Metabolic networks; Network simplification; Networks clustering
    DOI:  https://doi.org/10.1186/s12859-020-03564-9