bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒08‒02
thirty-four papers selected by
Kelsey Fisher-Wellman
East Carolina University


  1. Nature. 2020 Jul 29.
    Hernansanz-Agustín P, Choya-Foces C, Carregal-Romero S, Ramos E, Oliva T, Villa-Piña T, Moreno L, Izquierdo-Álvarez A, Cabrera-García JD, Cortés A, Lechuga-Vieco AV, Jadiya P, Navarro E, Parada E, Palomino-Antolín A, Tello D, Acín-Pérez R, Rodríguez-Aguilera JC, Navas P, Cogolludo Á, López-Montero I, Martínez-Del-Pozo Á, Egea J, López MG, Elrod JW, Ruíz-Cabello J, Bogdanova A, Enríquez JA, Martínez-Ruiz A.
      All metazoans depend on the consumption of O2 by the mitochondrial oxidative phosphorylation system (OXPHOS) to produce energy. In addition, the OXPHOS uses O2 to produce reactive oxygen species that can drive cell adaptations1-4, a phenomenon that occurs in hypoxia4-8 and whose precise mechanism remains unknown. Ca2+ is the best known ion that acts as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential10. Here we show that Na+ acts as a second messenger that regulates OXPHOS function and the production of reactive oxygen species by modulating the fluidity of the inner mitochondrial membrane. A conformational shift in mitochondrial complex I during acute hypoxia11 drives acidification of the matrix and the release of free Ca2+ from calcium phosphate (CaP) precipitates. The concomitant activation of the mitochondrial Na+/Ca2+ exchanger promotes the import of Na+ into the matrix. Na+ interacts with phospholipids, reducing inner mitochondrial membrane fluidity and the mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III. The inhibition of Na+ import through the Na+/Ca2+ exchanger is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences for cellular metabolism.
    DOI:  https://doi.org/10.1038/s41586-020-2551-y
  2. Biochim Biophys Acta Bioenerg. 2020 Jul 24. pii: S0005-2728(20)30126-2. [Epub ahead of print] 148276
    Rigoulet M, Bouchez CL, Paumard P, Ransac S, Cuvellier S, Duvezin-Caubet S, Mazat JP, Devin A.
      In living cells, growth is the result of coupling between substrate catabolism and multiple metabolic processes that take place during net biomass formation and maintenance processes. During growth, both ATP/ADP and NADH/NAD+ molecules play a key role. Cell energy metabolism hence refers to metabolic pathways involved in ATP synthesis linked to NADH turnover. Two main pathways are thus involved in cell energy metabolism: glycolysis/fermentation and oxidative phosphorylation. Glycolysis and mitochondrial oxidative phosphorylation are intertwined through thermodynamic and kinetic constraints that are reviewed herein. Further, our current knowledge of short-term and long term regulation of cell energy metabolism will be reviewed using examples such as the Crabtree and the Warburg effect.
    Keywords:  Cell energetic metabolism; Crabtree effect; Kinetics; Metabolism modeling; Mitochondria; Thermodynamics; Warburg effect
    DOI:  https://doi.org/10.1016/j.bbabio.2020.148276
  3. Int J Mol Sci. 2020 Jul 25. pii: E5276. [Epub ahead of print]21(15):
    Liu G, Luo Q, Li H, Liu Q, Ju Y, Song G.
      Cancer stem cells (CSCs) are considered to be the main cause of tumor recurrence, metastasis, and an unfavorable prognosis. Energy metabolism is closely associated with cell stemness. However, how the stemness of liver cancer stem cells (LCSCs) is regulated by metabolic/oxidative stress remains poorly understood. In this study, we compare the metabolic differences between LCSCs and the hepatocellular carcinoma cell line HCCLM3, and explore the relationship between metabolism and LCSC stemness. We found that LCSCs from the hepatocellular carcinoma cell HCCLM3 exhibited more robust glucose metabolism than HCCLM3, including glycolysis, oxidative phosphorylation (OXPHOS), and pyruvate produced by glycolysis entering mitochondria for OXPHOS. Moreover, 2-deoxy-D-glucose (2-DG) enhanced the LCSC stemness by upregulating OXPHOS. In contrast, Mdivi-1 reduced the levels of OXPHOS and weakened the stemness by inhibiting mitochondrial fission. Together, our findings clarify the relationship between energy metabolism and LCSC stemness and may provide theoretical guidance and potential therapeutic approaches for liver cancer.
    Keywords:  cancer stem cells; cell metabolism; glycolysis; hepatocellular carcinoma; oxidative phosphorylation
    DOI:  https://doi.org/10.3390/ijms21155276
  4. Int J Mol Sci. 2020 Jul 28. pii: E5374. [Epub ahead of print]21(15):
    Kruse R, Sahebekhtiari N, Højlund K.
      INTRODUCTION: Mitochondria are essential in energy metabolism and cellular survival, and there is growing evidence that insulin resistance in chronic metabolic disorders, such as obesity, type 2 diabetes (T2D), and aging, is linked to mitochondrial dysfunction in skeletal muscle. Protein profiling by proteomics is a powerful tool to investigate mechanisms underlying complex disorders. However, despite significant advances in proteomics within the past two decades, the technologies have not yet been fully exploited in the field of skeletal muscle proteome. Area covered: Here, we review the currently available studies characterizing the mitochondrial proteome in human skeletal muscle in insulin-resistant conditions, such as obesity, T2D, and aging, as well as exercise-mediated changes in the mitochondrial proteome. Furthermore, we outline technical challenges and limitations and methodological aspects that should be considered when planning future large-scale proteomics studies of mitochondria from human skeletal muscle. Authors' view: At present, most proteomic studies of skeletal muscle or isolated muscle mitochondria have demonstrated a reduced abundance of proteins in several mitochondrial biological processes in obesity, T2D, and aging, whereas the beneficial effects of exercise involve an increased content of muscle proteins involved in mitochondrial metabolism. Powerful mass-spectrometry-based proteomics now provides unprecedented opportunities to perform in-depth proteomics of muscle mitochondria, which in the near future is expected to increase our understanding of the complex molecular mechanisms underlying the link between mitochondrial dysfunction and insulin resistance in chronic metabolic disorders.
    Keywords:  Type 2 diabetes; insulin resistance; mitochondria; mitochondrial proteomics; skeletal muscle
    DOI:  https://doi.org/10.3390/ijms21155374
  5. Sci Signal. 2020 Jul 28. pii: eaaz8240. [Epub ahead of print]13(642):
    Li J, Agarwal E, Bertolini I, Seo JH, Caino MC, Ghosh JC, Kossenkov AV, Liu Q, Tang HY, Goldman AR, Languino LR, Speicher DW, Altieri DC.
      Mitochondria are signaling hubs in eukaryotic cells. Here, we showed that the mitochondrial FUN14 domain-containing protein-1 (FUNDC1), an effector of Parkin-independent mitophagy, also participates in cellular plasticity by sustaining oxidative bioenergetics, buffering ROS production, and supporting cell proliferation. Targeting this pathway in cancer cells suppressed tumor growth but rendered transformed cells more motile and invasive in a manner dependent on ROS-mediated mitochondrial dynamics and mitochondrial repositioning to the cortical cytoskeleton. Global metabolomics and proteomics profiling identified a FUNDC1 interactome at the mitochondrial inner membrane, comprising the AAA+ protease, LonP1, and subunits of oxidative phosphorylation, complex V (ATP synthase). Independently of its previously identified role in mitophagy, FUNDC1 enabled LonP1 proteostasis, which in turn preserved complex V function and decreased ROS generation. Therefore, mitochondrial reprogramming by a FUNDC1-LonP1 axis controls tumor cell plasticity by switching between proliferative and invasive states in cancer.
    DOI:  https://doi.org/10.1126/scisignal.aaz8240
  6. J Exp Clin Cancer Res. 2020 Jul 29. 39(1): 144
    Liu Z, Gu S, Lu T, Wu K, Li L, Dong C, Zhou Y.
      BACKGROUND: Esophageal squamous cell carcinoma (ESCC) is one of the most lethal forms of adult cancer with poor prognosis. Substantial evidence indicates that reactive oxygen species (ROS) are important modulators of aggressive cancer behavior. However, the mechanism by which ESCC cells integrate redox signals to modulate carcinoma progression remains elusive.METHODS: The expression of interferon alpha inducible protein 6 (IFI6) in clinical ESCC tissues and cell lines was detected by RT-PCR and Western blotting. The correlation between IFI6 expression levels and aggressive ESCC disease stage was examined by immunohistochemistry. Bioinformatic analysis was conducted to explore the potential function of IFI6 in ESCC. ESCC cell lines stably depleted of IFI6 and ectopically expressing IFI6 were established using lentiviruses expressing shRNAs and an IFI6 expression plasmid, respectively. The effects of IFI6 on ESCC cells were determined by cell-based analyses, including EdU assay, apoptotic assay, cellular and mitochondria-specific ROS detection, seahorse extracellular flux, and mitochondrial calcium flux assays. Blue native-polyacrylamide gel electrophoresis was used to determine mitochondrial supercomplex assembly. Transcriptional activation of NADPH oxidase 4 (NOX4) via ATF3 was confirmed by dual luciferase assay. In vivo tumor growth was determined in mouse xenograft models.
    RESULTS: We find that the expression of IFI6, an IFN-stimulated gene localized in the inner mitochondrial membrane, is markedly elevated in ESCC patients and a panel of ESCC cell lines. High IFI6 expression correlates with aggressive disease phenotype and poor prognosis in ESCC patients. IFI6 depletion suppresses proliferation and induces apoptosis by increasing ROS accumulation. Mechanistically, IFI6 ablation induces mitochondrial calcium overload by activating mitochondrial Ca2+ uniporter and subsequently ROS production. Following IFI6 ablation, mitochondrial ROS accumulation is also induced by mitochondrial supercomplex assembly suppression and oxidative phosphorylation dysfunction, while IFI6 overexpression produces the opposite effects. Furthermore, energy starvation induced by IFI6 inhibition drives endoplasmic reticulum stress through disrupting endoplasmic reticulum calcium uptake, which upregulates NOX4-derived ROS production in an ATF3-dependent manner. Finally, the results in xenograft models of ESCC further corroborate the in vitro findings.
    CONCLUSION: Our study unveils a novel redox homeostasis signaling pathway that regulates ESCC pathobiology and identifies IFI6 as a potential druggable target in ESCC.
    Keywords:  Endoplasmic reticulum stress; Esophageal squamous cell carcinoma; Interferon alpha inducible protein 6; Mitochondrial oxidative phosphorylation; Reactive oxygen species
    DOI:  https://doi.org/10.1186/s13046-020-01646-3
  7. Cells. 2020 Jul 23. pii: E1764. [Epub ahead of print]9(8):
    Pecinová A, Alán L, Brázdová A, Vrbacký M, Pecina P, Drahota Z, Houštěk J, Mráček T.
      Prostate cancer is one of the most prominent cancers diagnosed in males. Contrasting with other cancer types, glucose utilization is not increased in prostate carcinoma cells as they employ different metabolic adaptations involving mitochondria as a source of energy and intermediates required for rapid cell growth. In this regard, prostate cancer cells were associated with higher activity of mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), the key rate limiting component of the glycerophosphate shuttle, which connects mitochondrial and cytosolic processes and plays significant role in cellular bioenergetics. Our research focused on the role of mGPDH biogenesis and regulation in prostate cancer compared to healthy cells. We show that the 42 amino acid presequence is cleaved from N-terminus during mGPDH biogenesis. Only the processed form is part of the mGPDH dimer that is the prominent functional enzyme entity. We demonstrate that mGPDH overexpression enhances the wound healing ability in prostate cancer cells. As mGPDH is at the crossroad of glycolysis, lipogenesis and oxidative metabolism, regulation of its activity by intramitochondrial processing might represent rapid means of cellular metabolic adaptations.
    Keywords:  GPD2 gene; metabolic adaptation; mitochondrial glycerol-3-phosphate dehydrogenase (EC:1.1.5.3); prostate cancer
    DOI:  https://doi.org/10.3390/cells9081764
  8. Biochimie. 2020 Jul 25. pii: S0300-9084(20)30165-6. [Epub ahead of print]
    Belosludtsev KN, Belosludtseva NV, Kosareva EA, Talanov EY, Gudkov SV, Dubinin MV.
      Itaconic acid (methylene-succinic acid, ItA) is an unsaturated dicarboxylic acid that is secreted by mammalian macrophages in response to a pro-inflammatory stimulus and shows an anti-inflammatory/antibacterial effect. Being a mitochondrial metabolite, it exhibits an inhibitory activity on succinate dehydrogenase and subsequently induces mitochondrial dysfunction. The present study has shown that ItA dose-dependently inhibited ADP- and DNP-stimulated (uncoupled) respiration of rat liver mitochondria energized with succinate. This effect of ItA could be related to the suppression of the activity of complex II and the combined activity of complexes II + III of the respiratory chain. At the same time, ItA had no effect on the activity of the dicarboxylate carrier, which catalyzes the transport of succinate across the inner mitochondrial membrane. It was found that 4 mM ItA diminished the rates of ADP- and DNP-stimulated mitochondrial respiration supported by the substrates of complex I glutamate and malate. A study of the effect of ItA on the activity of complexes of the respiratory chain showed that it significantly decreases the activity of complex IV. It was observed that 4 mM ItA inhibited the rate of H2O2 production by mitochondria. At the same time, ItA promoted the opening of the cyclosporin A-sensitive Ca2+-dependent permeability transition pore. The latter was revealed as the decrease in the calcium retention capacity of mitochondria and the stimulation of release of cytochrome c from the organelles. ItA by itself promotes the cytochrome c release from mitochondria. Possible mechanisms of the effect of ItA on mitochondrial function are discussed.
    Keywords:  Dicarboxylate carrier; Itaconic acid; MPT pore; Mitochondria; Mitochondrial respiration; Oxidative phosphorylation; ROS production; Respiration chain complexes
    DOI:  https://doi.org/10.1016/j.biochi.2020.07.011
  9. Cell Death Discov. 2020 ;6 64
    Vial J, Huchedé P, Fagault S, Basset F, Rossi M, Geoffray J, Soldati H, Bisaccia J, Elsensohn MH, Creveaux M, Neves D, Blay JY, Fauvelle F, Bouquet F, Streichenberger N, Corradini N, Bergeron C, Maucort-Boulch D, Castets P, Carré M, Weber K, Castets M.
      Rhabdomyosarcoma (RMS) is the most frequent form of pediatric soft-tissue sarcoma. It is divided into two main subtypes: ERMS (embryonal) and ARMS (alveolar). Current treatments are based on chemotherapy, surgery, and radiotherapy. The 5-year survival rate has plateaued at 70% since 2000, despite several clinical trials. RMS cells are thought to derive from the muscle lineage. During development, myogenesis includes the expansion of muscle precursors, the elimination of those in excess by cell death and the differentiation of the remaining ones into myofibers. The notion that these processes may be hijacked by tumor cells to sustain their oncogenic transformation has emerged, with RMS being considered as the dark side of myogenesis. Thus, dissecting myogenic developmental programs could improve our understanding of RMS molecular etiology. We focused herein on ANT1, which is involved in myogenesis and is responsible for genetic disorders associated with muscle degeneration. ANT1 is a mitochondrial protein, which has a dual functionality, as it is involved both in metabolism via the regulation of ATP/ADP release from mitochondria and in regulated cell death as part of the mitochondrial permeability transition pore. Bioinformatics analyses of transcriptomic datasets revealed that ANT1 is expressed at low levels in RMS. Using the CRISPR-Cas9 technology, we showed that reduced ANT1 expression confers selective advantages to RMS cells in terms of proliferation and resistance to stress-induced death. These effects arise notably from an abnormal metabolic switch induced by ANT1 downregulation. Restoration of ANT1 expression using a Tet-On system is sufficient to prime tumor cells to death and to increase their sensitivity to chemotherapy. Based on our results, modulation of ANT1 expression and/or activity appears as an appealing therapeutic approach in RMS management.
    Keywords:  Cell death; Paediatric cancer
    DOI:  https://doi.org/10.1038/s41420-020-00302-1
  10. Exp Cell Res. 2020 Jul 24. pii: S0014-4827(20)30439-0. [Epub ahead of print] 112190
    Patergnani S, Guzzo S, Mangolini A, dell'Atti L, Pinton P, Aguiari G.
      The most common subtype of renal cell carcinoma (RCC) is the clear cell RCC (ccRCC) that accounts for 70-80% of cases. The fate of ccRCC is linked to alterations of genes that regulate TP53. The dysfunction of p53 affects several processes including autophagy, which is increased in different advanced carcinomas and could be associated with cancer progression. We report that different kidney cancer cell lines show higher levels of autophagy than control cells. The increased autophagy is associated with the upregulation of miR501-5p, which stimulates mTOR-independent autophagy by the activation of AMP kinase. AMPK activation occurs through the decrease of ATP generation caused by the downregulation of the mitochondrial calcium uniporter (MCU) that leads to the reduction of mitochondrial calcium uptake. Autophagy induction promotes the degradation of p53 through the autophagolysosomal machinery. Consistently, the inhibition of autophagy reduces both cell proliferation and migration enhancing the expression of p53, p21 and E-Cadherin as well as decreasing Vimentin synthesis. Taken together, these findings indicate that autophagy is involved in the progression of kidney cancer. Therefore, the pharmacological targeting of this process could be considered an interesting option for the treatment of advanced renal carcinoma.
    Keywords:  AMPK; Autophagy; Cell growth; Kidney cancer; MicroRNAs; p53
    DOI:  https://doi.org/10.1016/j.yexcr.2020.112190
  11. Nat Metab. 2020 Jul 27.
    Pinkosky SL, Scott JW, Desjardins EM, Smith BK, Day EA, Ford RJ, Langendorf CG, Ling NXY, Nero TL, Loh K, Galic S, Hoque A, Smiles WJ, Ngoei KRW, Parker MW, Yan Y, Melcher K, Kemp BE, Oakhill JS, Steinberg GR.
      Long-chain fatty acids (LCFAs) play important roles in cellular energy metabolism, acting as both an important energy source and signalling molecules1. LCFA-CoA esters promote their own oxidation by acting as allosteric inhibitors of acetyl-CoA carboxylase, which reduces the production of malonyl-CoA and relieves inhibition of carnitine palmitoyl-transferase 1, thereby promoting LCFA-CoA transport into the mitochondria for β-oxidation2-6. Here we report a new level of regulation wherein LCFA-CoA esters per se allosterically activate AMP-activated protein kinase (AMPK) β1-containing isoforms to increase fatty acid oxidation through phosphorylation of acetyl-CoA carboxylase. Activation of AMPK by LCFA-CoA esters requires the allosteric drug and metabolite site formed between the α-subunit kinase domain and the β-subunit. β1 subunit mutations that inhibit AMPK activation by the small-molecule activator A769662, which binds to the allosteric drug and metabolite site, also inhibit activation by LCFA-CoAs. Thus, LCFA-CoA metabolites act as direct endogenous AMPK β1-selective activators and promote LCFA oxidation.
    DOI:  https://doi.org/10.1038/s42255-020-0245-2
  12. Genes (Basel). 2020 Jul 26. pii: E855. [Epub ahead of print]11(8):
    González-Quintana A, García-Consuegra I, Belanger-Quintana A, Serrano-Lorenzo P, Lucia A, Blázquez A, Docampo J, Ugalde C, Morán M, Arenas J, Martín MA.
      Leigh syndrome (LS) usually presents as an early onset mitochondrial encephalopathy characterized by bilateral symmetric lesions in the basal ganglia and cerebral stem. More than 75 genes have been associated with this condition, including genes involved in the biogenesis of mitochondrial complex I (CI). In this study, we used a next-generation sequencing (NGS) panel to identify two novel biallelic variants in the NADH:ubiquinone oxidoreductase subunit A13 (NDUFA13) gene in a patient with isolated CI deficiency in skeletal muscle. Our patient, who represents the second family report with mutations in the CI NDUFA13 subunit, presented with LS lesions in brain magnetic resonance imaging, mild hypertrophic cardiomyopathy, and progressive spastic tetraparesis. This phenotype manifestation is different from that previously described in the first NDUFA13 family, which was predominantly characterized by neurosensorial symptoms. Both in silico pathogenicity predictions and oxidative phosphorylation (OXPHOS) functional findings in patient's skin fibroblasts (delayed cell growth, isolated CI enzyme defect, decreased basal and maximal oxygen consumption and as well as ATP production, together with markedly diminished levels of the NDUFA13 protein, CI, and respirasomes) suggest that these novel variants in the NDUFA13 gene are the underlying cause of the CI defect, expanding the genetic heterogeneity of LS.
    Keywords:  Leigh syndrome; NDUFA13 gene; OXPHOS assembly; OXPHOS diagnosis; mitochondrial OXPHOS dysfunction; mitochondrial complex I deficiency
    DOI:  https://doi.org/10.3390/genes11080855
  13. J Biol Chem. 2020 Jul 28. pii: jbc.RA120.014603. [Epub ahead of print]
    Ji Y, Zhang J, Lu Y, Yi Q, Chen M, Xie S, Mao X, Xiao Y, Meng F, Zhang M, Yang R, Guan MX.
      Leber's hereditary optic neuropathy (LHON) is a maternal inheritance of eye disease due to the mitochondrial DNA mtDNA) mutations. We previously discovered a 3866T>C mutation within the gene for the ND1 subunit of complex I as possibly amplifying disease progression for patients bearing the disease-causing 11778G>A mutation, within the gene for the ND4 subunit of Complex I. However, whether and how the ND1 mutation exacerbates the ND4 mutation were unknown. In this report, we showed that four Chinese families bearing both m.3866T>C and m.11778G>A mutations exhibited higher penetrances of LHON than 6 Chinese pedigrees carrying only the m.3866T>C mutation or families harboring only the m.11778G>A mutation. The protein structure analysis revealed that the m.3866T>C (I187T) and m.11778G>A (R340H) mutations destabilized the specific interactions with other residues of ND1 and ND4, thereby altering the structure and function of complex I, respectively. Cellular data obtained using cybrids constructed by transferring mitochondria from the Chinese families into mtDNA-less (ro) cells demonstrated that the mutations perturbed the stability, assembly and activity of complex I, leading to changes in mitochondrial ATP levels and membrane potential, and increasing the production of reactive oxygen species. These mitochondrial dysfunctions promoted the apoptotic sensitivity of cells and decreased mitophagy. Cybrids bearing only m.3866T>C mutation displayed mild mitochondrial dysfunctions while those harboring both m.3866T>C and m.11778G>A mutations exhibited greater mitochondrial dysfunctions. These suggested that the m.3866T>C mutation acted as the synergy with m.11778G>A mutation, aggravating mitochondrial dysfunctions contributing to higher penetrance of LHON in these families carrying both mtDNA mutations.
    Keywords:  Leber’s hereditary optic neuropathy; Modifier; NADH: ubiquinone oxidoreductase; apoptosis; human genetics; mitochondrial DNA; mitochondrial disease; mitochondrial respiratory chain complex; mitophagy; molecular modeling; organelle; oxygen radicals; pathogenesis; penetrance; vision
    DOI:  https://doi.org/10.1074/jbc.RA120.014603
  14. J Physiol. 2020 Jul 31.
    Petrick HL, Brunetta HS, Pignanelli C, Nunes EA, van Loon LJC, Burr JF, Holloway GP.
      KEY POINTS: Ketone bodies are proposed to represent an alternative fuel source driving energy production, particularly during exercise. Biologically, the extent to which mitochondria utilize ketone bodies compared to other substrates remains unknown. We demonstrate in vitro that maximal mitochondrial respiration supported by ketone bodies is low when compared to carbohydrate-derived substrates in the left ventricle and red gastrocnemius muscle from rodents, and in human skeletal muscle. When considering intramuscular concentrations of ketone bodies and the presence of other carbohydrate and lipid substrates, biological rates of mitochondrial respiration supported by ketone bodies are predicted to be minimal. At the mitochondrial level, it is therefore unlikely that ketone bodies are an important source for energy production in cardiac and skeletal muscle, particularly when other substrates are readily available.ABSTRACT: Ketone bodies (KB) have recently gained popularity as an alternative fuel source to support mitochondrial oxidative phosphorylation and enhance exercise performance. However, given the low activity of ketolytic enzymes and potential inhibition from carbohydrate oxidation, it remains unknown if KBs can contribute to energy production. We therefore determined the ability of KBs (sodium DL-β-hydroxybutyrate, β-HB; lithium acetoacetate, AcAc) to stimulate in vitro mitochondrial respiration in the left ventricle (LV) and red gastrocnemius (RG) of rats, and in human vastus lateralis. Compared to pyruvate, the ability of KBs to maximally drive respiration was low in isolated mitochondria and permeabilized fibres (PmFb) from the LV (∼30-35% of pyruvate), RG (∼10-30%), and human vastus lateralis (∼2-10%). In PmFb, the concentration of KBs required to half-maximally drive respiration (LV: 889 μm β-HB, 801 μm AcAc; RG: 782 μm β-HB, 267 μm AcAc) were greater than KB content representative of the muscle microenvironment (∼100 μm). This would predict low rates (∼1-4% of pyruvate) of biological KB-supported respiration in the LV (8-14 pmol·sec-1 ·mg-1 ) and RG (3-6 pmol·sec-1 ·mg-1 ) at rest and following exercise. Moreover, KBs did not increase respiration in the presence of saturating pyruvate, submaximal pyruvate (100 μm) reduced the ability of physiological β-HB to drive respiration, and addition of other intracellular substrates (succinate, palmitoylcarnitine) decreased maximal KB-supported respiration. As a result, product inhibition likely limits KB oxidation. Altogether, the ability of KBs to drive mitochondrial respiration is minimal and they are likely outcompeted by other substrates, compromising their use as an important energy source. This article is protected by copyright. All rights reserved.
    Keywords:  bioenergetics; ketone bodies; metabolism; mitochondria
    DOI:  https://doi.org/10.1113/JP280032
  15. Med Oncol. 2020 Jul 28. 37(8): 72
    Lapa B, Gonçalves AC, Jorge J, Alves R, Pires AS, Abrantes AM, Coucelo M, Abrunhosa A, Botelho MF, Nascimento-Costa JM, Sarmento-Ribeiro AB.
      Cancer cells alter their metabolism by switching from glycolysis to oxidative phosphorylation (OXPHOS), regardless of oxygen availability. Metabolism may be a molecular target in acute myeloid leukemia (AML), where mutations in metabolic genes have been described. This study evaluated glycolysis and OXPHOS as therapeutic targets. The sensitivity to 2-deoxy-D-glucose (2-DG; glycolysis inhibitor) and oligomycin (OXPHOS inhibitor) was tested in six AML cell lines (HEL, HL-60, K-562, KG-1, NB-4, THP-1). These cells were characterized for IDH1/2 exon 4 mutations, reactive oxygen species, and mitochondrial membrane potential. Metabolic activity was assessed by resazurin assay, whereas cell death and cell cycle were assessed by flow cytometry. Glucose uptake and metabolism-related gene expression were analyzed by 18F-FDG and RT-PCR/qPCR, respectively. No IDH1/2 exon 4 mutations were detected. HEL cells had the highest 18F-FDG uptake and peroxides/superoxide anion levels, whereas THP-1 showed the lowest. 2-DG reduced metabolic activity in all cell lines with HEL, KG-1, and NB-4 being the most sensitive cells. Oligomycin decreased metabolic activity in a cell line-dependent manner, the THP-1 resistant and HL-60 being the most sensitive. Both inhibitors induced apoptosis and cell cycle arrest in a cell line- and compound-dependent manner. 2-DG decreased 18F-FDG uptake in HEL, HL-60, KG-1, and NB-4, while oligomycin increased the uptake in K-562. Metabolism gene expression had different responses to treatments. In conclusion, HEL and KG-1 show to be more glycolytic, whereas HL-60 was more OXPHOS dependent. Results suggest that AML cells reprogram their metabolism to overcome OXPHOS inhibition suggesting that glycolysis may be a better therapeutic target.
    Keywords:  2-Deoxy-D-glucose; Acute myeloid leukemia; Glycolysis; Oligomycin; Oxidative phosphorylation; Therapeutic target
    DOI:  https://doi.org/10.1007/s12032-020-01394-6
  16. Nat Metab. 2020 Jul 27.
    Zhang ZD, Milman S, Lin JR, Wierbowski S, Yu H, Barzilai N, Gorbunova V, Ladiges WC, Niedernhofer LJ, Suh Y, Robbins PD, Vijg J.
      Ageing is the greatest risk factor for most common chronic human diseases, and it therefore is a logical target for developing interventions to prevent, mitigate or reverse multiple age-related morbidities. Over the past two decades, genetic and pharmacologic interventions targeting conserved pathways of growth and metabolism have consistently led to substantial extension of the lifespan and healthspan in model organisms as diverse as nematodes, flies and mice. Recent genetic analysis of long-lived individuals is revealing common and rare variants enriched in these same conserved pathways that significantly correlate with longevity. In this Perspective, we summarize recent insights into the genetics of extreme human longevity and propose the use of this rare phenotype to identify genetic variants as molecular targets for gaining insight into the physiology of healthy ageing and the development of new therapies to extend the human healthspan.
    DOI:  https://doi.org/10.1038/s42255-020-0247-0
  17. Biochim Biophys Acta Bioenerg. 2020 Jul 23. pii: S0005-2728(20)30125-0. [Epub ahead of print]1861(11): 148275
    Bertgen L, Mühlhaus T, Herrmann JM.
      Why mitochondria still retain their own genome is a puzzle given the enormous effort to maintain a mitochondrial translation machinery. Most mitochondrially encoded proteins are membrane-embedded subunits of the respiratory chain. Their hydrophobicity presumably impedes their import into mitochondria. However, many mitochondrial genomes also encode protein subunits of the mitochondrial ribosome. These proteins lack transmembrane domains and hydrophobicity cannot explain why their genes remained in mitochondria. In this review, we provide an overview about mitochondrially encoded subunits of mitochondrial ribosomes of fungi, plants and protists. Moreover, we discuss and evaluate different hypotheses which were put forward to explain why (ribosomal) proteins remained mitochondrially encoded. It seems likely that the synthesis of ribosomal proteins in the mitochondrial matrix is used to regulate the assembly of the mitochondrial ribosome within mitochondria and to avoid problems that mitochondrial proteins might pose for cytosolic proteostasis and for the assembly of cytosolic ribosomes.
    Keywords:  Eukaryotes; Evolution; Gene transfer; Mitochondria; Respiratory chain; Ribosomes
    DOI:  https://doi.org/10.1016/j.bbabio.2020.148275
  18. Front Physiol. 2020 ;11 717
    Van Wijk R, Van Wijk EPA, Pang J, Yang M, Yan Y, Han J.
      Once regarded solely as the energy source of the cell, nowadays mitochondria are recognized to perform multiple essential functions in addition to energy production. Since the discovery of pathogenic mitochondrial DNA defects in the 1980s, research advances have revealed an increasing number of common human diseases, which share an underlying pathogenesis involving mitochondrial dysfunction. A major factor in this dysfunction is reactive oxygen species (ROS), which influence the mitochondrial-nuclear crosstalk and the link with the epigenome, an influence that provides explanations for pathogenic mechanisms. Regarding these mechanisms, we should take into account that mitochondria produce the majority of ultra-weak photon emission (UPE), an aspect that is often ignored - this type of emission may serve as assay for ROS, thus providing new opportunities for a non-invasive diagnosis of mitochondrial dysfunction. In this article, we overviewed three relevant areas of mitochondria-related research over the period 1960-2020: (a) respiration and energy production, (b) respiration-related production of free radicals and other ROS species, and (c) ultra-weak photon emission in relation to ROS and stress. First, we have outlined how these research areas initially developed independently of each other - following that, our review aims to show their stepwise integration during later stages of development. It is suggested that a further stimulation of research on UPE may have the potential to enhance the progress of modern mitochondrial research and its integration in medicine.
    Keywords:  aging; diagnosis; mitochondria; reactive oxygen species; stress; ultra-weak photon emission
    DOI:  https://doi.org/10.3389/fphys.2020.00717
  19. Nat Commun. 2020 Jul 30. 11(1): 3811
    Zhou W, Yao Y, Scott AJ, Wilder-Romans K, Dresser JJ, Werner CK, Sun H, Pratt D, Sajjakulnukit P, Zhao SG, Davis M, Nelson BS, Halbrook CJ, Zhang L, Gatto F, Umemura Y, Walker AK, Kachman M, Sarkaria JN, Xiong J, Morgan MA, Rehemtualla A, Castro MG, Lowenstein P, Chandrasekaran S, Lawrence TS, Lyssiotis CA, Wahl DR.
      Intratumoral genomic heterogeneity in glioblastoma (GBM) is a barrier to overcoming therapy resistance. Treatments that are effective independent of genotype are urgently needed. By correlating intracellular metabolite levels with radiation resistance across dozens of genomically-distinct models of GBM, we find that purine metabolites, especially guanylates, strongly correlate with radiation resistance. Inhibiting GTP synthesis radiosensitizes GBM cells and patient-derived neurospheres by impairing DNA repair. Likewise, administration of exogenous purine nucleosides protects sensitive GBM models from radiation by promoting DNA repair. Neither modulating pyrimidine metabolism nor purine salvage has similar effects. An FDA-approved inhibitor of GTP synthesis potentiates the effects of radiation in flank and orthotopic patient-derived xenograft models of GBM. High expression of the rate-limiting enzyme of de novo GTP synthesis is associated with shorter survival in GBM patients. These findings indicate that inhibiting purine synthesis may be a promising strategy to overcome therapy resistance in this genomically heterogeneous disease.
    DOI:  https://doi.org/10.1038/s41467-020-17512-x
  20. FASEB J. 2020 Jul 29.
    Rosa HS, Ajaz S, Gnudi L, Malik AN.
      Circulating mitochondrial DNA (mtDNA), widely studied as a disease biomarker, comprises of mtDNA located within mitochondria, indicative of mitochondrial function, and cell-free (cf) mtDNA linked to inflammation. The purpose of this study was to determine the ranges of, and relationship between, cellular and cf mtDNA in human blood. Whole blood from 23 controls (HC) and 20 patients with diabetes was separated into peripheral blood mononuclear cells (PBMCs), plasma, and serum. Total DNA was isolated and mtDNA copy numbers were determined using absolute quantification. Cellular mtDNA content in PBMCs was higher than in peripheral blood and a surprisingly high level of cf mtDNA was present in serum and plasma of HC, with no direct relationship between cellular and cf mtDNA content within individuals. Diabetes patients had similar levels of cellular mtDNA compared to healthy participants but a significantly higher cf mtDNA content. Furthermore, only in patients with diabetes, we observed a correlation between whole blood and plasma mtDNA levels, indicating that the relationship between cellular and cf mtDNA content is affected by disease status. In conclusion, when evaluating mtDNA in human blood as a biomarker of mitochondrial dysfunction, it is important to measure both cellular and cf mtDNA.
    Keywords:  absolute quantification; circulating nucleic acids; inflammation; mitochondria; qPCR
    DOI:  https://doi.org/10.1096/fj.202000959RR
  21. Ageing Res Rev. 2020 Jul 23. pii: S1568-1637(20)30263-4. [Epub ahead of print] 101128
    Shanmughapriya S, Langford D, Natarajaseenivasan K.
      Neurons and glia maintain central nervous system (CNS) homeostasis through diverse mechanisms of intra- and intercellular signaling. Some of these interactions include the exchange of soluble factors between cells via direct cell-to-cell contact for both short and long-distance transfer of biological materials. Transcellular transfer of mitochondria has emerged as a key example of this communication. This transcellular transfer of mitochondria are dynamically involved in the cellular and tissue response to CNS injury and play beneficial roles in recovery. This review highlights recent research addressing the cause and effect of intra- and intercellular mitochondrial transfer with a specific focus on the future of mitochondrial transplantation therapy. We believe that mitochondrial transfer plays a crucial role during bioenergetic crisis/deficit, but the quality, quantity and mode of mitochondrial transfer determines the protective capacity for the receiving cells. Mitochondrial transplantation is a new treatment paradigm and will overcome the major bottleneck of traditional approach of correcting mitochondria-related disorders.
    Keywords:  Kinesin; Miro; TRAK; extracellular vesicles; mitochondrial extrusion; mitochondrial transplantation; tunneling nanotubes
    DOI:  https://doi.org/10.1016/j.arr.2020.101128
  22. Cancers (Basel). 2020 Jul 25. pii: E2051. [Epub ahead of print]12(8):
    Moretton A, Loizou JI.
      Metabolism is a fundamental cellular process that can become harmful for cells by leading to DNA damage, for instance by an increase in oxidative stress or through the generation of toxic byproducts. To deal with such insults, cells have evolved sophisticated DNA damage response (DDR) pathways that allow for the maintenance of genome integrity. Recent years have seen remarkable progress in our understanding of the diverse DDR mechanisms, and, through such work, it has emerged that cellular metabolic regulation not only generates DNA damage but also impacts on DNA repair. Cancer cells show an alteration of the DDR coupled with modifications in cellular metabolism, further emphasizing links between these two fundamental processes. Taken together, these compelling findings indicate that metabolic enzymes and metabolites represent a key group of factors within the DDR. Here, we will compile the current knowledge on the dynamic interplay between metabolic factors and the DDR, with a specific focus on cancer. We will also discuss how recently developed high-throughput technologies allow for the identification of novel crosstalk between the DDR and metabolism, which is of crucial importance to better design efficient cancer treatments.
    Keywords:  DNA damage; DNA damage response; DNA repair; high-throughput technologies; metabolism
    DOI:  https://doi.org/10.3390/cancers12082051
  23. J Biol Chem. 2020 Jul 30. pii: jbc.RA120.012680. [Epub ahead of print]
    Huang LS, Kotha SR, Avasarala S, VanScoyk M, Winn RA, Pennathur A, Yashaswini PS, Bandela M, Salgia R, Tyurina YY, Kagan VE, Zhu X, Reddy SP, Sudhadevi T, Punathil-Kannan PK, Harijith A, Ramchandran R, Bikkavilli RK, Natarajan V.
      Lysocardiolipin acyltransferase (LYCAT), a cardiolipin (CL)-remodeling enzyme, is crucial for maintaining normal mitochondrial function and vascular development. Despite the well-characterized role for LYCAT in the regulation of mitochondrial dynamics, it's involvement in lung cancer, if any, remains incompletely understood. In this study, in silico analysis of TCGA lung cancer datasets revealed a significant increase in LYCAT expression, which was later corroborated in human lung cancer tissues and immortalized lung cancer cell lines via indirect immunofluorescence and immunoblotting, respectively. Stable knockdown of LYCAT in NSCLC cell lines not only reduced CL and increased monolyso CL levels but also reduced in vivo tumor growth, as determined by xenograft studies in athymic nude mice. Furthermore, blocking LYCAT activity using a LYCAT mimetic peptide, attenuated cell migration, suggesting a novel role for LYCAT activity in promoting NSCLC. Mechanistically, the pro-proliferative effects of LYCAT were mediated by an increase in mitochondrial fusion, and a G1/S cell cycle transition, both of which are linked to increased cell proliferation. Taken together, these results demonstrate a novel role for LYCAT in promoting NSCLC and suggests that targeting LYCAT expression or activity in NSCLC may provide new avenues for the therapeutic treatment of lung cancer.
    Keywords:  Cardiolipin; Cell migration; Cell proliferation; LYCAT; NSCLC; cardiolipin; cell cycle; cell migration; cell proliferation; lung cancer
    DOI:  https://doi.org/10.1074/jbc.RA120.012680
  24. Eur J Nucl Med Mol Imaging. 2020 Jul 27.
    Pelletier-Galarneau M, Petibon Y, Ma C, Han P, Kim SJW, Detmer FJ, Yokell D, Guehl N, Normandin M, El Fakhri G, Alpert NM.
      PURPOSE: Alteration in mitochondrial membrane potential (ΔΨm) is an important feature of many pathologic processes, including heart failure, cardiotoxicity, ventricular arrhythmia, and myocardial hypertrophy. We present the first in vivo, non-invasive, assessment of regional ΔΨm in the myocardium of normal human subjects.METHODS: Thirteen healthy subjects were imaged using [18F]-triphenylphosphonium ([18F]TPP+) on a PET/MR scanner. The imaging protocol consisted of a bolus injection of 300 MBq followed by a 120-min infusion of 0.6 MBq/min. A 60 min, dynamic PET acquisition was started 1 h after bolus injection. The extracellular space fraction (fECS) was simultaneously measured using MR T1-mapping images acquired at baseline and 15 min after gadolinium injection with correction for the subject's hematocrit level. Serial venous blood samples were obtained to calculate the plasma tracer concentration. The tissue membrane potential (ΔΨT), a proxy of ΔΨm, was calculated from the myocardial tracer concentration at secular equilibrium, blood concentration, and fECS measurements using a model based on the Nernst equation.
    RESULTS: In 13 healthy subjects, average tissue membrane potential (ΔΨT), representing the sum of cellular membrane potential (ΔΨc) and ΔΨm, was - 160.7 ± 3.7 mV, in excellent agreement with previous in vitro assessment.
    CONCLUSION: In vivo quantification of the mitochondrial function has the potential to provide new diagnostic and prognostic information for several cardiac diseases as well as allowing therapy monitoring. This feasibility study lays the foundation for further investigations to assess these potential roles. Clinical trial identifier: NCT03265431.
    Keywords:  Mitochondria; Mitochondrial membrane potential; Positron emission tomography; Tissue membrane potential; Triphenylphosphonium
    DOI:  https://doi.org/10.1007/s00259-020-04878-9
  25. Proc Natl Acad Sci U S A. 2020 Jul 31. pii: 202008021. [Epub ahead of print]
    Wei W, Ruvkun G.
      Mitochondrial fission and fusion are highly regulated by energy demand and physiological conditions to control the production, activity, and movement of these organelles. Mitochondria are arrayed in a periodic pattern in Caenorhabditis elegans muscle, but this pattern is disrupted by mutations in the mitochondrial fission component dynamin DRP-1. Here we show that the dramatically disorganized mitochondria caused by a mitochondrial fission-defective dynamin mutation is strongly suppressed to a more periodic pattern by a second mutation in lysosomal biogenesis or acidification. Vitamin B12 is normally imported from the bacterial diet via lysosomal degradation of B12-binding proteins and transport of vitamin B12 to the mitochondrion and cytoplasm. We show that the lysosomal dysfunction induced by gene inactivations of lysosomal biogenesis or acidification factors causes vitamin B12 deficiency. Growth of the C. elegans dynamin mutant on an Escherichia coli strain with low vitamin B12 also strongly suppressed the mitochondrial fission defect. Of the two C. elegans enzymes that require B12, gene inactivation of methionine synthase suppressed the mitochondrial fission defect of a dynamin mutation. We show that lysosomal dysfunction induced mitochondrial biogenesis, which is mediated by vitamin B12 deficiency and methionine restriction. S-adenosylmethionine, the methyl donor of many methylation reactions, including histones, is synthesized from methionine by S-adenosylmethionine synthase; inactivation of the sams-1 S-adenosylmethionine synthase also suppresses the drp-1 fission defect, suggesting that vitamin B12 regulates mitochondrial biogenesis and then affects mitochondrial fission via chromatin pathways.
    Keywords:  interorganelle communication; methionine restriction; mitochondrial dynamics; vacuolar V-ATPase; vitamin B12
    DOI:  https://doi.org/10.1073/pnas.2008021117
  26. Aging (Albany NY). 2020 Jul 29. 12
    Wang C, Shi M, Ji J, Cai Q, Zhao Q, Jiang J, Liu J, Zhang H, Zhu Z, Zhang J.
      Cancer cells are characterized by metabolic alterations. Thereinto, Stearoyl-CoA Desaturase 1 (SCD1), an enzymatic node located in the conversion of saturated fatty acids into monounsaturated fatty acids (MUFAs), has been reported to accelerate the tumorigenesis of multiple cancers. However, its role in the metabolic process of gastric cancer remains largely unexplored. In this study, by in vitro, in vivo and in silico assessments, our results revealed that SCD1 exhibited the ability to promote tumor growth, migration and anti-ferroptosis of gastric cancer. The underlying mechanism might involve the alteration of cancer stemness and modulation of cell cycle-related proteins. Moreover, based on our findings, high expression of SCD1 might predict poor prognosis in gastric cancer patients. Our study provided new insights into the potential of SCD1 as a biomarker as well as a therapeutic target in the treatment of gastric cancer.
    Keywords:  SCD1; ferroptosis; gastric cancer; lipid metabolism; proliferation
    DOI:  https://doi.org/10.18632/aging.103598
  27. Front Oncol. 2020 ;10 947
    Serpa J.
      Cancer cells undergo a metabolic rewiring in order to fulfill the energy and biomass requirements. Cysteine is a pivotal organic compound that contributes for cancer metabolic remodeling at three different levels: (1) in redox control, free or as a component of glutathione; (2) in ATP production, via hydrogen sulfide (H2S) production, serving as a donor to electron transport chain (ETC), and (3) as a carbon source for biomass and energy production. In the present review, emphasis will be given to the role of cysteine as a carbon source, focusing on the metabolic reliance on cysteine, benefiting the metabolic fitness and survival of cancer cells. Therefore, the interplay between cysteine metabolism and other metabolic pathways, as well as the regulation of cysteine metabolism related enzymes and transporters, will be also addressed. Finally, the usefulness of cysteine metabolic route as a target in cancer treatment will be highlighted.
    Keywords:  cancer metabolic remodeling; cysteine; cysteine metabolism; cysteine transport; targeting cysteine route
    DOI:  https://doi.org/10.3389/fonc.2020.00947
  28. Dev Cell. 2020 Jul 15. pii: S1534-5807(20)30546-3. [Epub ahead of print]
    Williams R, Laskovs M, Williams RI, Mahadevan A, Labbadia J.
      The loss of protein homeostasis (proteostasis) is a primary driver of age-related tissue dysfunction. Recent studies have revealed that the failure of proteostasis with age is triggered by developmental and reproductive cues that repress the activity of proteostasis-related pathways in early adulthood. In Caenorhabditis elegans, reduced mitochondrial electron transport chain (ETC) function during development can override signals that promote proteostasis collapse in aged tissues. However, it is unclear precisely how these beneficial effects are mediated. Here, we reveal that in response to ETC impairment, the PP2A complex generates a dephosphorylated, mitochondrial stress-specific variant of the transcription factor HSF-1. This results in the selective induction of small heat shock proteins in adulthood, thereby protecting against age-related proteostasis collapse. We propose that mitochondrial signals early in life can protect the aging cytosolic proteome by tailoring HSF-1 activity to preferentially drive the expression of non-ATP-dependent chaperones.
    Keywords:  HSF1; PP2A; aging; mitochondria; molecular chaperones; protein aggregation; proteostasis; stress responses
    DOI:  https://doi.org/10.1016/j.devcel.2020.06.038
  29. iScience. 2020 Jul 10. pii: S2589-0042(20)30542-3. [Epub ahead of print]23(8): 101355
    Zhang Y, Guillermier C, De Raedt T, Cox AG, Maertens O, Yimlamai D, Lun M, Whitney A, Maas RL, Goessling W, Cichowski K, Steinhauser ML.
      Malignant tumors exhibit high degrees of genomic heterogeneity at the cellular level, leading to the view that subpopulations of tumor cells drive growth and treatment resistance. To examine the degree to which tumors also exhibit metabolic heterogeneity at the level of individual cells, we employed multi-isotope imaging mass spectrometry (MIMS) to quantify utilization of stable isotopes of glucose and glutamine along with a label for cell division. Mouse models of melanoma and malignant peripheral nerve sheath tumors (MPNSTs) exhibited striking heterogeneity of substrate utilization, evident in both proliferating and non-proliferating cells. We identified a correlation between metabolic heterogeneity, proliferation, and therapeutic resistance. Heterogeneity in metabolic substrate usage as revealed by incorporation of glucose and glutamine tracers is thus a marker for tumor proliferation. Collectively, our data demonstrate that MIMS provides a powerful tool with which to dissect metabolic functions of individual cells within the native tumor environment.
    Keywords:  Biological Sciences; Cancer Systems Biology
    DOI:  https://doi.org/10.1016/j.isci.2020.101355
  30. Viruses. 2020 Jul 27. pii: E811. [Epub ahead of print]12(8):
    Krishna G, Soman Pillai V, Valiya Veettil M.
      Epstein-Barr virus or human herpesvirus 4 (EBV/HHV-4) is a ubiquitous human virus associated with a wide range of malignant neoplasms. The interaction between EBV latent proteins and host cellular molecules often leads to oncogenic transformation, promoting the development of EBV-associated cancers. The present study identifies a functional role of GLS1 isoforms KGA and GAC in regulating mitochondrial energy metabolism to promote EBV-infected cell proliferation. Our data demonstrate increased expression of GLS1 isoforms KGA and GAC with mitochondrial localization in latently EBV-infected cells and de novo EBV-infected PBMCs. c-Myc upregulates KGA and GAC protein levels, which in turn elevate the levels of intracellular glutamate. Further analysis demonstrated upregulated expression of mitochondrial GLUD1 and GLUD2, with a subsequent increase in alpha-ketoglutarate levels that may mark the activation of glutaminolysis. Cell proliferation and viability of latently EBV-infected cells were notably inhibited by KGA/GAC, as well as GLUD1 inhibitors. Taken together, our results suggest that c-Myc-dependent regulation of KGA and GAC enhances mitochondrial functions to support the rapid proliferation of the EBV-infected cells, and these metabolic processes could be therapeutically exploited by targeting KGA/GAC and GLUD1 to prevent EBV-associated cancers.
    Keywords:  EBV; GAC; KGA; cell proliferation; glutaminolysis; mitochondrial metabolism
    DOI:  https://doi.org/10.3390/v12080811
  31. Nucleic Acids Res. 2020 Jul 27. pii: gkaa622. [Epub ahead of print]
    Røyrvik EC, Johnston IG.
      Mitochondrial DNA (mtDNA) encodes cellular machinery vital for cell and organism survival. Mutations, genetic manipulation, and gene therapies may produce cells where different types of mtDNA coexist in admixed populations. In these admixtures, one mtDNA type is often observed to proliferate over another, with different types dominating in different tissues. This 'segregation bias' is a long-standing biological mystery that may pose challenges to modern mtDNA disease therapies, leading to substantial recent attention in biological and medical circles. Here, we show how an mtDNA sequence's balance between replication and transcription, corresponding to molecular 'selfishness', in conjunction with cellular selection, can potentially modulate segregation bias. We combine a new replication-transcription-selection (RTS) model with a meta-analysis of existing data to show that this simple theory predicts complex tissue-specific patterns of segregation in mouse experiments, and reversion in human stem cells. We propose the stability of G-quadruplexes in the mtDNA control region, influencing the balance between transcription and replication primer formation, as a potential molecular mechanism governing this balance. Linking mtDNA sequence features, through this molecular mechanism, to cellular population dynamics, we use sequence data to obtain and verify the sequence-specific predictions from this hypothesis on segregation behaviour in mouse and human mtDNA.
    DOI:  https://doi.org/10.1093/nar/gkaa622
  32. Mol Metab. 2020 Jul 23. pii: S2212-8778(20)30128-9. [Epub ahead of print] 101054
    Sandeman LY, Kang WX, Wang X, Jensen KB, Wong D, Bo T, Gao L, Zhao J, Byrne CD, Page AJ, Proud CG.
      OBJECTIVES: Diet-driven obesity is increasingly widespread. Its consequences pose major challenges both to human health and health-care systems. There are two MAP kinase-interacting kinases (MNKs) in mice, MNK1 and MNK2. Previous studies showed that mice lacking either MNK1 or MNK2 were partially protected against high-fat diet (HFD)-induced weight gain and insulin resistance. The aims of this study were to evaluate the phenotype of mice lacking both MNKs when given a HFD, to assess whether pharmacological inhibition of MNK function also protects against diet-induced obesity (DIO) and its consequences and to probe the mechanisms underlying such protection.METHODS: Male wild-type (WT) C57Bl6 mice or mice lacking both MNK1 and MNK2 (double knockout, DKO) were fed HFD or control diet (CD) for up to 16 weeks. In a separate study, WT mice were also given HFD for 6 weeks, after which half were treated with the recently-developed MNK inhibitor ETC-206 daily for 10 more weeks, whilst maintained on a HFD. Metabolites and other parameters were measured, and the expression of selected mRNAs and proteins was assessed.
    RESULTS: MNK-DKO mice were almost completely protected from HFD-induced obesity. Higher energy expenditure (EE) in MNK-DKO mice was observed, which likely reflects the changes in a number of genes or proteins linked to lipolysis, mitochondrial function/biogenesis, oxidative metabolism and/or ATP consumption. The MNK inhibitor ETC-206 also prevented HFD-induced weight gain, confirming that the activity of the MNKs facilitates weight gain due to excessive caloric consumption.
    CONCLUSIONS: Disabling the MNKs in mice, either genetically or pharmacologically, strongly prevents weight gain on a calorie-rich diet. This likely results from increased energy utilisation, involving greater ATP consumption, mitochondrial oxidative metabolism and other processes.
    Keywords:  MNK; adipose tissue; diet-induced obesity; energy expenditure; lipid metabolism; mitochondria
    DOI:  https://doi.org/10.1016/j.molmet.2020.101054
  33. Biomed Pharmacother. 2020 Jul 24. pii: S0753-3322(20)30714-9. [Epub ahead of print]130 110521
    Yang SK, Han YC, He JR, Yang M, Zhang W, Zhan M, Li AM, Li L, Na-Song , Liu YT, Wu XQ, Zhang Q, Wang JW, Zhang H.
      OBJECTIVE: This study aimed to assess the effect and mechanism of SS31 on cisplatin-induced acute kidney injury (CP-AKI) both in vivo and in vitro.METHOD: Male mices and HK-2 cells were treated using cisplatin to establish models of CP-AKI. 32 C57BL/6 mices were randomly divided into four groups (control group, CP group, CP + normal saline group, CP + SS-31 group). Cisplatin was intraperitoneally injected once to the mice (25 mg/kg). SS31 was administrated for 10 days at dosages of 10 mg/kg per day. Kidney histological changes and level of reactive oxygen species(ROS) were detected. In vitro studies, HK-2 cells were incubated with cisplatin (50 u M) or combimed with SS-31(100 u M), the level of mitochondrial ROS, apoptosis rate and the the expression of NLRP3, Caspase-1 and IL-1β were tested.
    RESULTS: Renal tubulointerstitial apoptosis and oxidative stress were significantly increased in CP-AKI mice. Cisplatin caused elevation of serum creatinine (Scr), blood urea nitrogen (BUN) levels and enhanced IL-1β, caspase1 and NLRP3 expression, the electron microscopy examination showed mitochondria cristae swelling, mitochondrial spheres and partial ridge breakdown in renal tubular cell of CP-AKI mice. SS31 treatment could effectively suppress mitochondrial ROS, ameliorate these lesions and decrease the expression of NLRP3, IL-1β and Caspase1. In vitro studies, SS31 could restored the level of mitochondrial ROS and downregulate apoptosis rate in HK-2 cells, moreover, the elevated expression of NLRP3, IL-1β and Caspase-1were restored.
    CONCLUSION: SS31 could protect CP-AKI in mices, which might be due to an anti-oxidative and anti-apoptotic action via regulating mitochondrial ROS-NLRP3 pathway. NLRP3 inflammasome might be considered as a novel therapeutic target of CP-AKI.
    Keywords:  Acute kidney injury; Cisplatin; Mitochondria; SS-31
    DOI:  https://doi.org/10.1016/j.biopha.2020.110521
  34. Mitochondrion. 2020 Jul 24. pii: S1567-7249(20)30166-5. [Epub ahead of print]
    Long Toh Y, Wong E, Chae JW, Yi Yap N, Hui Ling Yeo A, Maung S, Chan A.
      Cancer-related fatigue (CRF) is characterized by a lack of energy, and mitochondrial dysfunction is postulated to contribute to its etiology. This prospective cohort study assesses the self-reported fatigue levels of early-stage breast cancer patients using the validated Multi-Dimensional Fatigue Symptom Inventory-Short Form (MFSI-SF) and blood samples drawn at three time points: before treatment, approximately 6 weeks, and 12 weeks after the initiation of chemotherapy. The aim of this study is to evaluate mitochondrial measures with CRF, over the course of chemotherapy using mitochondrial DNA (mtDNA content) and displacement loop (D-loop) region sequence variations at nucleotide positions 303, 489 and 514. The relative mtDNA copy number was determined via real-time quantitative polymerase chain reaction and compared between study time points and D-loop sequence variants. The association of mtDNA content with MFSI-SF total and sub-domain scores was analyzed in a sample of 155 patients (mean age ± SD: 51.7 ± 8.8 years). The median mtDNA content decreased over 12 weeks after the initiation of chemotherapy (p < 0.001). Baseline mtDNA content was lower for nucleotide position 303 in sequence variations than for the reference sequence (67.2 copies vs 79.1 copies, p = 0.03). Physical fatigue negatively correlated with mtDNA content in both unadjusted (β = -0.0075, p= 0.048) and adjusted models (β = -0.0062, p= 0.042), accounting for age, anxiety, insomnia, haemoglobin levels and body mass index. Our findings add to the literature indicating that mitochondrial function serves as an important target for mitigating CRF.
    Keywords:  Cancer-related fatigue; D-loop region; biomarker; breast cancer; mitochondrial DNA
    DOI:  https://doi.org/10.1016/j.mito.2020.07.004