bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒08‒18
forty-six papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Cell Rep. 2019 Aug 13. pii: S2211-1247(19)30928-3. [Epub ahead of print]28(7): 1845-1859.e5
    Nagdas S, Kashatus JA, Nascimento A, Hussain SS, Trainor RE, Pollock SR, Adair SJ, Michaels AD, Sesaki H, Stelow EB, Bauer TW, Kashatus DF.
      Mitochondria undergo fission and fusion to maintain homeostasis, and tumors exhibit the dysregulation of mitochondrial dynamics. We recently demonstrated that ectopic HRasG12V promotes mitochondrial fragmentation and tumor growth through Erk phosphorylation of the mitochondrial fission GTPase Dynamin-related protein 1 (Drp1). However, the role of Drp1 in the setting of endogenous oncogenic KRas remains unknown. Here, we show that Drp1 is required for KRas-driven anchorage-independent growth in fibroblasts and patient-derived pancreatic cancer cell lines, and it promotes glycolytic flux, in part through the regulation of hexokinase 2 (HK2). Furthermore, Drp1 deletion imparts a significant survival advantage in a model of KRas-driven pancreatic cancer, and tumors exhibit a strong selective pressure against complete Drp1 deletion. Rare tumors that arise in the absence of Drp1 have restored glycolysis but exhibit defective mitochondrial metabolism. This work demonstrates that Drp1 plays dual roles in KRas-driven tumor growth: supporting both glycolysis and mitochondrial function through independent mechanisms.
    Keywords:  Drp1; KRas; metabolism; mitochondria; pancreatic cancer
  2. Cell Metab. 2019 Aug 06. pii: S1550-4131(19)30379-1. [Epub ahead of print]
    Jain IH, Zazzeron L, Goldberger O, Marutani E, Wojtkiewicz GR, Ast T, Wang H, Schleifer G, Stepanova A, Brepoels K, Schoonjans L, Carmeliet P, Galkin A, Ichinose F, Zapol WM, Mootha VK.
      Leigh syndrome is a devastating mitochondrial disease for which there are no proven therapies. We previously showed that breathing chronic, continuous hypoxia can prevent and even reverse neurological disease in the Ndufs4 knockout (KO) mouse model of complex I (CI) deficiency and Leigh syndrome. Here, we show that genetic activation of the hypoxia-inducible factor transcriptional program via any of four different strategies is insufficient to rescue disease. Rather, we observe an age-dependent decline in whole-body oxygen consumption. These mice exhibit brain tissue hyperoxia, which is normalized by hypoxic breathing. Alternative experimental strategies to reduce oxygen delivery, including breathing carbon monoxide (600 ppm in air) or severe anemia, can reverse neurological disease. Therefore, unused oxygen is the most likely culprit in the pathology of this disease. While pharmacologic activation of the hypoxia response is unlikely to alleviate disease in vivo, interventions that safely normalize brain tissue hyperoxia may hold therapeutic potential.
    Keywords:  Leigh syndrome; anemia; carbon monoxide; hemoglobin; hyperoxia; hypoxia; mitochondria; oxygen; therapy
  3. Elife. 2019 Aug 14. pii: e49158. [Epub ahead of print]8
    Zhang Y, Lanjuin A, Chowdhury SR, Mistry M, Silva-García CG, Weir HJ, Lee CL, Escoubas CC, Tabakovic E, Mair W.
      Target of rapamycin complex 1 (TORC1) and AMP-activated protein kinase (AMPK) antagonistically modulate metabolism and aging. However, how they coordinate to determine longevity and if they act via separable mechanisms is unclear. Here, we show that neuronal AMPK is essential for lifespan extension from TORC1 inhibition, and that TORC1 suppression increases lifespan cell non autonomously via distinct mechanisms from global AMPK activation. Lifespan extension by null mutations in genes encoding raga-1 (RagA) or rsks-1 (S6K) is fully suppressed by neuronal-specific rescues. Loss of RAGA-1 increases lifespan via maintaining mitochondrial fusion. Neuronal RAGA-1 abrogation of raga-1 mutant longevity requires UNC-64/syntaxin, and promotes mitochondrial fission cell nonautonomously. Finally, deleting the mitochondrial fission factor DRP-1 renders the animal refractory to the pro-aging effects of neuronal RAGA-1. Our results highlight a new role for neuronal TORC1 in cell nonautonomous regulation of longevity, and suggest TORC1 in the central nervous system might be targeted to promote healthy aging.
    Keywords:  C. elegans; genetics; genomics
  4. Am J Physiol Cell Physiol. 2019 Aug 14.
    Chen Q, Thompson J, Hu Y, Dean J, Lesnefsky EJ.
      Activation of calpain1 (CPN1) and calpain2 (CPN2) contributes to cardiac injury during ischemia (ISC) and reperfusion (REP). Complex I activity is decreased in heart mitochondria following ISC-REP. CPN1 and CPN2 are ubiquitous calpains that exist in both cytosol (cs-CPN1&2) and mitochondria (mit-CPN1&2). Recent work shows that the complex I subunit (NDUFS7) is a potential substrate of the mit-CPN1. We asked if ISC-REP led to decreased complex I activity via proteolysis of the NDUFS7 subunit via activation of mit-CPN1&2. Activation of cs-CPN1&2 decreases mitophagy in hepatocytes following ISC-REP. We asked if activation of cs-CPN1&2 impaired mitophagy in the heart following ISC-REP. Buffer-perfused rat hearts underwent 25 min. global ISC and 30 min. REP. MDL-28170 (MDL, 10 µM) was used to inhibit CPN1&2. Cytosol, subsarcolemmal mitochondria (SSM), and interfibrillar mitochondria (IFM) were isolated at the end of heart perfusion. Cardiac ISC-REP led to decreased complex I activity with a decrease in the content of NDUFS7 in both SSM and IFM. ISC-REP also resulted in a decrease in cytosolic beclin1 content, a key component of the autophagy pathway required to form autophagosomes. MDL treatment protected the contents of cytosolic beclin1 and mitochondrial NDUFS7 in hearts following ISC-REP. These results support that activation of both cytosolic and mitochondrial calpains impairs mitochondria during cardiac ISC-REP. Mitochondria localized calpains impair complex I via cleavage of a key subunit. Activation of cytosolic calpains contributes to mitochondrial dysfunction by impairing removal of the impaired mitochondria through depletion of a key component of the mitophagy process.
    Keywords:  NADH:ubiquinone oxidoreductas; calpain inhibitor; electron transport chain; mitochondria
  5. BMC Mol Cell Biol. 2019 Aug 14. 20(1): 33
    Bowling JL, Skolfield MC, Riley WA, Nolin AP, Wolf LC, Nelson DE.
      BACKGROUND: The PINK1:Parkin pathway regulates the autophagic removal of damaged and dysfunctional mitochondria. While the response of this pathway to complete loss of ΔΨm, as caused by high concentrations of mitochondrial ionophores, has been well characterized, it remains unclear how the pathway makes coherent decisions about whether to keep or purge mitochondria in situations where ΔΨm is only partially lost or exhibits fluctuations, as has been observed in response to certain types of cellular stress.RESULTS: To investigate the responses of the PINK1:Parkin pathway to mitochondrial insults of different magnitude and duration, controlled titration of the mitochondrial protonophore, CCCP, was used to manipulate ΔΨm in live cells, and the dynamics of PINK1 and Parkin recruitment was measured by fluorescence microscopy. In contrast to the stable accumulation of PINK1 and Parkin seen at completely depolarized mitochondria, partial depolarization produced a transient pulse of PINK1 stabilization and rapid loss, which was driven by small fluctuations in ΔΨm. As the rate of Parkin dissociation from the mitochondria and phospho-polyubiquitin chain removal was comparatively slow, repetitive pulses of PINK1 were able to drive a slow step-wise accumulation of Parkin and phospho-polyubiquitin leading to deferred mitophagy.
    CONCLUSION: These data suggest that the PINK1:Parkin mitophagy pathway is able to exhibit distinct dynamic responses to complete and partial mitochondrial depolarization. In this way, the pathway is able to differentiate between irretrievably damaged mitochondria and those showing signs of dysfunction, promoting either rapid or delayed autophagy, respectively.
    Keywords:  Cell signalling; Mitophagy; PTEN-induced putative kinase 1 (PINK1); Parkin; Ubiquitin
  6. Biol Chem. 2019 Aug 01. pii: /j/bchm.just-accepted/hsz-2019-0264/hsz-2019-0264.xml. [Epub ahead of print]
    Moosavi B, Zhu XL, Yang WC, Yang GF.
      Succinate dehydrogenase (SDH), complex II or succinate:quinone oxidoreductase (SQR) is a crucial enzyme involved in both tricarboxylic acid cycle and oxidative phosphorylation, the two primary metabolic pathways for generating ATP. Impaired function of SDH results in deleterious disorders from cancer to neurodegeneration. SDH function is tailored in different cell types to meet the energy demands. Thus understanding how SDH function is regulated and how it operates in distinct cell types can support the development of therapeutic approaches against the diseases. In this article we discuss molecular pathways which regulate SDH function and describe extra roles played by SDH in specific cell types.
    Keywords:  complex II; mitochondria; respiratory chain complex; transcription; translation; tricarboxylic acid cycle
  7. Oncogene. 2019 Aug 12.
    Ghosh JC, Seo JH, Agarwal E, Wang Y, Kossenkov AV, Tang HY, Speicher DW, Altieri DC.
      Tumor mitochondria have heightened protein folding quality control, but the regulators of this process and how they impact cancer traits are not completely understood. Here we show that the ATP-directed mitochondrial protease, LonP1 is upregulated by stress conditions, including hypoxia, in tumor, but not normal cells. In mitochondria, LonP1 is phosphorylated by Akt on Ser173 and Ser181, enhancing its protease activity. Interference with this pathway induces accumulation of misfolded subunits of electron transport chain complex II and complex V, resulting in impaired oxidative bioenergetics and heightened ROS production. Functionally, this suppresses mitochondrial trafficking to the cortical cytoskeleton, shuts off tumor cell migration and invasion, and inhibits primary and metastatic tumor growth, in vivo. These data identify LonP1 as a key effector of mitochondrial reprogramming in cancer and potential therapeutic target.
  8. Nat Commun. 2019 Aug 13. 10(1): 3645
    Puri R, Cheng XT, Lin MY, Huang N, Sheng ZH.
      Chronic mitochondrial stress associates with major neurodegenerative diseases. Recovering stressed mitochondria constitutes a critical step of mitochondrial quality control and thus energy maintenance in early stages of neurodegeneration. Here, we reveal Mul1-Mfn2 pathway that maintains neuronal mitochondrial integrity under stress conditions. Mul1 deficiency increases Mfn2 activity that triggers the first phasic mitochondrial hyperfusion and also acts as an ER-Mito tethering antagonist. Reduced ER-Mito coupling leads to increased cytoplasmic Ca2+ load that activates calcineurin and induces the second phasic Drp1-dependent mitochondrial fragmentation and mitophagy. Overexpressing Mfn2, but not Mfn1, mimics Mul1-deficient phenotypes, while expressing PTPIP51, an ER-Mito anchoring protein, suppresses Parkin-mediated mitophagy. Thus, by regulating mitochondrial morphology and ER-Mito contacts, Mul1-Mfn2 pathway plays an early checkpoint role in maintaining mitochondrial integrity. Our study provides new mechanistic insights into neuronal mitochondrial maintenance under stress conditions, which is relevant to several major neurodegenerative diseases associated with mitochondrial dysfunction and altered ER-Mito interplay.
  9. Nature. 2019 Aug 14.
    Swatek KN, Usher JL, Kueck AF, Gladkova C, Mevissen TET, Pruneda JN, Skern T, Komander D.
      Protein ubiquitination is a multi-functional post-translational modification that affects all cellular processes. Its versatility arises from architecturally complex polyubiquitin chains, in which individual ubiquitin moieties may be ubiquitinated on one or multiple residues, and/or modified by phosphorylation and acetylation1-3. Advances in mass spectrometry have enabled the mapping of individual ubiquitin modifications that generate the ubiquitin code; however, the architecture of polyubiquitin signals has remained largely inaccessible. Here we introduce Ub-clipping as a methodology by which to understand polyubiquitin signals and architectures. Ub-clipping uses an engineered viral protease, Lbpro∗, to incompletely remove ubiquitin from substrates and leave the signature C-terminal GlyGly dipeptide attached to the modified residue; this simplifies the direct assessment of protein ubiquitination on substrates and within polyubiquitin. Monoubiquitin generated by Lbpro∗ retains GlyGly-modified residues, enabling the quantification of multiply GlyGly-modified branch-point ubiquitin. Notably, we find that a large amount (10-20%) of ubiquitin in polymers seems to exist as branched chains. Moreover, Ub-clipping enables the assessment of co-existing ubiquitin modifications. The analysis of depolarized mitochondria reveals that PINK1/parkin-mediated mitophagy predominantly exploits mono- and short-chain polyubiquitin, in which phosphorylated ubiquitin moieties are not further modified. Ub-clipping can therefore provide insight into the combinatorial complexity and architecture of the ubiquitin code.
  10. Free Radic Biol Med. 2019 Aug 08. pii: S0891-5849(19)30995-5. [Epub ahead of print]143 176-192
    Alquraishi M, Puckett DL, Alani DS, Humidat AS, Frankel VD, Donohoe DR, Whelan J, Bettaieb A.
      Pyruvate kinase M2 is a critical enzyme that regulates cell metabolism and growth under different physiological conditions. In its metabolic role, pyruvate kinase M2 catalyzes the last glycolytic step which converts phosphoenolpyruvate to pyruvate with the generation of ATP. Beyond this metabolic role in glycolysis, PKM2 regulates gene expression in the nucleus, phosphorylates several essential proteins that regulate major cell signaling pathways, and contribute to the redox homeostasis of cancer cells. The expression of PKM2 has been demonstrated to be significantly elevated in several types of cancer, and the overall inflammatory response. The unusual pattern of PKM2 expression inspired scientists to investigate the unrevealed functions of PKM2 and the therapeutic potential of targeting PKM2 in cancer and other disorders. Therefore, the purpose of this review is to discuss the mechanistic and therapeutic potential of targeting PKM2 with the focus on cancer metabolism, redox homeostasis, inflammation, and metabolic disorders. This review highlights and provides insight into the metabolic and non-metabolic functions of PKM2 and its relevant association with health and disease.
    Keywords:  Cancer; Glycolysis; Inflammation; Metabolic diseases; Oxidants; Pyruvate kinase M2; Redox homeostasis; Warburg effect
  11. Oncogene. 2019 Aug 13.
    Tang K, Yu Y, Zhu L, Xu P, Chen J, Ma J, Zhang H, Fang H, Sun W, Zhou L, Wei K, Li F, Lv J, Xie J, Liu Y, Huang B.
      Clinical applications of antiangiogenic agents profoundly affect tumor cell behaviors via the resultant hypoxia. To date, how the hypoxia regulates tumor cells remains unclear. Here, we show that hypoxia promotes the growth of human breast tumorigenic cells that repopulate tumors [tumor-repopulating cells (TRCs)] in vitro and in vivo. This stimulating effect is ascribed to hypoxia-induced reactive oxygen species (ROS) that activates Akt and NF-κB, dependent on the attenuated tricarboxylic acid (TCA) cycle. We find that fumarate is accumulated in the TCA cycle of hypoxic TRCs, leading to glutathione succination, NADPH/NADP+ decrease, and an increase in ROS levels. Mechanistically, hypoxia-increased HIF-1α transcriptionally downregulates the expression of mitochondrial phosphoenolpyruvate carboxykinase (PCK2), leading to TCA cycle attenuation and fumarate accumulation. These findings reveal that hypoxia-reprogrammed TCA cycle promotes human breast TRCs growth via a HIF-1α-downregulated PCK2 pathway, implying a need for a combination of an antiangiogenic therapy with an antioxidant modulator.
  12. FASEB J. 2019 Aug 15. fj201900234R
    Montgomery MK, Osborne B, Brandon AE, O'Reilly L, Fiveash CE, Brown SHJ, Wilkins BP, Samsudeen A, Yu J, Devanapalli B, Hertzog A, Tolun AA, Kavanagh T, Cooper AA, Mitchell TW, Biden TJ, Smith NJ, Cooney GJ, Turner N.
      Fatty acid receptors have been recognized as important players in glycaemic control. This study is the first to describe a role for the medium-chain fatty acid (MCFA) receptor G-protein-coupled receptor (Gpr) 84 in skeletal muscle mitochondrial function and insulin secretion. We are able to show that Gpr84 is highly expressed in skeletal muscle and adipose tissue. Mice with global deletion of Gpr84 [Gpr84 knockout (KO)] exhibit a mild impairment in glucose tolerance when fed a MCFA-enriched diet. Studies in mice and pancreatic islets suggest that glucose intolerance is accompanied by a defect in insulin secretion. MCFA-fed KO mice also exhibit a significant impairment in the intrinsic respiratory capacity of their skeletal muscle mitochondria, but at the same time also exhibit a substantial increase in mitochondrial content. Changes in canonical pathways of mitochondrial biogenesis and turnover are unable to explain these mitochondrial differences. Our results show that Gpr84 plays a crucial role in regulating mitochondrial function and quality control.-Montgomery, M. K., Osborne, B., Brandon, A. E., O'Reilly, L., Fiveash, C. E., Brown, S. H. J., Wilkins, B. P., Samsudeen, A., Yu, J., Devanapalli, B., Hertzog, A., Tolun, A. A., Kavanagh, T., Cooper, A. A., Mitchell, T. W., Biden, T. J., Smith, N. J., Cooney, G. J., Turner, N. Regulation of mitochondrial metabolism in murine skeletal muscle by the medium-chain fatty acid receptor Gpr84.
    Keywords:  insulin resistance; insulin secretion; mitochondrial function
  13. Nat Commun. 2019 Aug 12. 10(1): 3637
    Vennin C, Mélénec P, Rouet R, Nobis M, Cazet AS, Murphy KJ, Herrmann D, Reed DA, Lucas MC, Warren SC, Elgundi Z, Pinese M, Kalna G, Roden D, Samuel M, Zaratzian A, Grey ST, Da Silva A, Leung W, , Mathivanan S, Wang Y, Braithwaite AW, Christ D, Benda A, Parkin A, Phillips PA, Whitelock JM, Gill AJ, Sansom OJ, Croucher DR, Parker BL, Pajic M, Morton JP, Cox TR, Timpson P.
      Heterogeneous subtypes of cancer-associated fibroblasts (CAFs) coexist within pancreatic cancer tissues and can both promote and restrain disease progression. Here, we interrogate how cancer cells harboring distinct alterations in p53 manipulate CAFs. We reveal the existence of a p53-driven hierarchy, where cancer cells with a gain-of-function (GOF) mutant p53 educate a dominant population of CAFs that establish a pro-metastatic environment for GOF and null p53 cancer cells alike. We also demonstrate that CAFs educated by null p53 cancer cells may be reprogrammed by either GOF mutant p53 cells or their CAFs. We identify perlecan as a key component of this pro-metastatic environment. Using intravital imaging, we observe that these dominant CAFs delay cancer cell response to chemotherapy. Lastly, we reveal that depleting perlecan in the stroma combined with chemotherapy prolongs mouse survival, supporting it as a potential target for anti-stromal therapies in pancreatic cancer.
  14. Cell Death Differ. 2019 Aug 14.
    Vanzo R, Bartkova J, Merchut-Maya JM, Hall A, Bouchal J, Dyrskjøt L, Frankel LB, Gorgoulis V, Maya-Mendoza A, Jäättelä M, Bartek J.
      Autophagy is an evolutionarily conserved process that captures aberrant intracellular proteins and/or damaged organelles for delivery to lysosomes, with implications for cellular and organismal homeostasis, aging and diverse pathologies, including cancer. During cancer development, autophagy may play both tumour-supporting and tumour-suppressing roles. Any relationships of autophagy to the established oncogene-induced replication stress (RS) and the ensuing DNA damage response (DDR)-mediated anti-cancer barrier in early tumorigenesis remain to be elucidated. Here, assessing potential links between autophagy, RS and DDR, we found that autophagy is enhanced in both early and advanced stages of human urinary bladder and prostate tumorigenesis. Furthermore, a high-content, single-cell-level microscopy analysis of human cellular models exposed to diverse genotoxic insults showed that autophagy is enhanced in cells that experienced robust DNA damage, independently of the cell-cycle position. Oncogene- and drug-induced RS triggered first DDR and later autophagy. Unexpectedly, genetic inactivation of autophagy resulted in RS, despite cellular retention of functional mitochondria and normal ROS levels. Moreover, recovery from experimentally induced RS required autophagy to support DNA synthesis. Consistently, RS due to the absence of autophagy could be partly alleviated by exogenous supply of deoxynucleosides. Our results highlight the importance of autophagy for DNA synthesis, suggesting that autophagy may support cancer progression, at least in part, by facilitating tumour cell survival and fitness under replication stress, a feature shared by most malignancies. These findings have implications for better understanding of the role of autophagy in tumorigenesis, as well as for attempts to manipulate autophagy as an anti-tumour therapeutic strategy.
  15. Blood. 2019 Aug 15. pii: blood.2019001034. [Epub ahead of print]
    Tabe Y, Lorenzi PL, Konopleva M.
      Tumor cells rewire metabolic pathways to adapt to their increased nutritional demands for energy, reducing equivalents, and cellular biosynthesis. Alternations in amino acid metabolism are one modality for satisfying those demands. Amino acids are not only components of proteins but also intermediate metabolites fueling multiple biosynthetic pathways. Amino acid-depletion therapies use heterologous enzymes or recombinant or engineered human enzymes to decrease the concentration of amino acids upon which tumor cells have become dependent for survival. Notably, such therapies have minimal effect on normal cells due to their ability to synthesize the targeted amino acids under conditions of nutrient stress. Here we review novel aspects of amino acid metabolism in hematologic malignancies and deprivation strategies using heterologous or engineered enzymes, focusing on four key amino acids: arginine, asparagine, glutamine, and cysteine. We also present the roles of amino acid metabolism in the immunosuppressive tumor microenvironment and in drug resistance, and we present an argument for the reclassification of amino acid-depleting enzymes as targeted therapies.
  16. Trends Biochem Sci. 2019 Aug 08. pii: S0968-0004(19)30161-6. [Epub ahead of print]
    Nesci S, Pagliarani A.
      As pointed out by Gu et al. (Science 2019) in mammalian mitochondria, the H-shaped tetrameric structure of the ATP synthase, the cell powerhouse, consists of two V-shaped dimers linked by two IF1 in antiparallel arrangement. This supramolecular structure reveals new functional/structural roles of the enzyme complex in mitochondria.
    Keywords:  ATP synthase; cristae; mitochondria; subunit composition; tetrameric form
  17. Life Sci Alliance. 2019 08;pii: e201900308. [Epub ahead of print]2(4):
    Nagashima S, Takeda K, Ohno N, Ishido S, Aoki M, Saitoh Y, Takada T, Tokuyama T, Sugiura A, Fukuda T, Matsushita N, Inatome R, Yanagi S.
      Mitochondrial abnormalities are associated with developmental disorders, although a causal relationship remains largely unknown. Here, we report that increased oxidative stress in neurons by deletion of mitochondrial ubiquitin ligase MITOL causes a potential neuroinflammation including aberrant astrogliosis and microglial activation, indicating that mitochondrial abnormalities might confer a risk for inflammatory diseases in brain such as psychiatric disorders. A role of MITOL in both mitochondrial dynamics and ER-mitochondria tethering prompted us to characterize three-dimensional structures of mitochondria in vivo. In MITOL-deficient neurons, we observed a significant reduction in the ER-mitochondria contact sites, which might lead to perturbation of phospholipids transfer, consequently reduce cardiolipin biogenesis. We also found that branched large mitochondria disappeared by deletion of MITOL. These morphological abnormalities of mitochondria resulted in enhanced oxidative stress in brain, which led to astrogliosis and microglial activation partly causing abnormal behavior. In conclusion, the reduced ER-mitochondria tethering and excessive mitochondrial fission may trigger neuroinflammation through oxidative stress.
  18. Proc Natl Acad Sci U S A. 2019 Aug 14. pii: 201911252. [Epub ahead of print]
    Xu W, Boyd RM, Tree MO, Samkari F, Zhao L.
      In higher eukaryotic cells, mitochondria are essential subcellular organelles for energy production, cell signaling, and the biosynthesis of biomolecules. The mitochondrial DNA (mtDNA) genome is indispensable for mitochondrial function because it encodes protein subunits of the electron transport chain and a full set of transfer and ribosomal RNAs. MtDNA degradation has emerged as an essential quality control measure to maintain mtDNA and to cope with mtDNA damage resulting from endogenous and environmental factors. Among all types of DNA damage known, abasic (AP) sites, sourced from base excision repair and spontaneous base loss, are the most abundant endogenous DNA lesions in cells. In mitochondria, AP sites trigger rapid DNA loss; however, the mechanism and molecular factors involved in the process remain elusive. Herein, we demonstrate that the stability of AP sites is reduced dramatically upon binding to a major mtDNA packaging protein, mitochondrial transcription factor A (TFAM). The half-life of AP lesions within TFAM-DNA complexes is 2 to 3 orders of magnitude shorter than that in free DNA, depending on their position. The TFAM-catalyzed AP-DNA destabilization occurs with nonspecific DNA or mitochondrial light-strand promoter sequence, yielding DNA single-strand breaks and DNA-TFAM cross-links. TFAM-DNA cross-link intermediates prior to the strand scission were also observed upon treating AP-DNA with mitochondrial extracts of human cells. In situ trapping of the reaction intermediates (DNA-TFAM cross-links) revealed that the reaction proceeds via Schiff base chemistry facilitated by lysine residues. Collectively, our data suggest a novel role of TFAM in facilitating the turnover of abasic DNA.
    Keywords:  DNA damage; DNA repair; DNA turnover; DNA–protein cross-links; mitochondrial DNA degradation
  19. Oncogene. 2019 Aug 13.
    Han Y, Kim B, Cho U, Park IS, Kim SI, Dhanasekaran DN, Tsang BK, Song YS.
      Mitochondria undergo fission and fusion continually for survival through the course of cellular adaption processes in response to changes in the surrounding environment. Dysregulated mitochondrial dynamics has been reported in various diseases including cancer. Under hypoxic conditions (<1% O2), the relationship between mitochondrial dynamics and sensitivity to cisplatin (CDDP) was examined in ovarian cancer cells. We found that hypoxia promoted mitochondrial fission and CDDP resistance in ovarian cancer cells. Hypoxia-induced reactive oxygen species (ROS) caused an increase in mitochondrial fission, a response abolished by free radical scavenging with N-acetylcysteine (NAC) and Trolox. Also, treatment of hydrogen peroxide (H2O2) decreased inhibitory p-Drp1 (Ser637) content and increased mitochondrial fission. Suppression of mitochondrial fission enhanced the CDDP sensitivity of hypoxic ovarian cancer cells. Lastly, in tumor spheroids from malignant ascites or tissues of patients with advanced-stage ovarian cancer, pretreatment with Mdivi-1 increased the CDDP sensitivity. Taken together, our results implicate that hypoxia-induced ROS trigger mitochondrial fission and CDDP resistance through downregulation of p-Drp1 (Ser637) and Mfn1 in ovarian cancer cells. Inhibition of Drp1 by Mdivi-1 treatment or si-Drp1 transfection increased CDDP sensitivity of ovarian cancer cells under hypoxia. Therefore, mitochondrial dynamics of cancer cells adapting to the hypoxic tumor microenvironment could be a potential target for anticancer therapy.
  20. Elife. 2019 Aug 13. pii: e46312. [Epub ahead of print]8
    Kishimoto S, Brender JR, Crooks DR, Matsumoto S, Seki T, Oshima N, Merkle H, Lin P, Reed G, Chen AP, Ardenkjaer-Larsen JH, Munasinghe J, Saito K, Yamamoto K, Choyke PL, Mitchell J, Lane AN, Fan T, Linehan WM, Krishna MC.
      Metabolic differences among and within tumors can be an important determinant in cancer treatment outcome. However, methods for determining these differences non-invasively in vivo is lacking. Using pancreatic ductal adenocarcinoma as a model, we demonstrate that tumor xenografts with a similar genetic background can be distinguished by their differing rates of the metabolism of 13C labeled glucose tracers, which can be imaged without hyperpolarization using newly developed techniques for noise suppression. Using this method, cancer subtypes that appeared to have similar metabolic profiles based on steady state metabolic measurement can be distinguished from each other. The metabolic maps from 13C-glucose imaging localized lactate production and overall glucose metabolism to different regions of some tumors. Such tumor heterogeneity was not detectable in FDG-PET.
    Keywords:  cancer biology; mouse
  21. Cell Rep. 2019 Aug 13. pii: S2211-1247(19)30940-4. [Epub ahead of print]28(7): 1717-1728.e6
    Elhassan YS, Kluckova K, Fletcher RS, Schmidt MS, Garten A, Doig CL, Cartwright DM, Oakey L, Burley CV, Jenkinson N, Wilson M, Lucas SJE, Akerman I, Seabright A, Lai YC, Tennant DA, Nightingale P, Wallis GA, Manolopoulos KN, Brenner C, Philp A, Lavery GG.
      Nicotinamide adenine dinucleotide (NAD+) is modulated by conditions of metabolic stress and has been reported to decline with aging in preclinical models, but human data are sparse. Nicotinamide riboside (NR) supplementation ameliorates metabolic dysfunction in rodents. We aimed to establish whether oral NR supplementation in aged participants can increase the skeletal muscle NAD+ metabolome and if it can alter muscle mitochondrial bioenergetics. We supplemented 12 aged men with 1 g NR per day for 21 days in a placebo-controlled, randomized, double-blind, crossover trial. Targeted metabolomics showed that NR elevated the muscle NAD+ metabolome, evident by increased nicotinic acid adenine dinucleotide and nicotinamide clearance products. Muscle RNA sequencing revealed NR-mediated downregulation of energy metabolism and mitochondria pathways, without altering mitochondrial bioenergetics. NR also depressed levels of circulating inflammatory cytokines. Our data establish that oral NR is available to aged human muscle and identify anti-inflammatory effects of NR.
    Keywords:  aging; cell adhesion; inflammation; metabolism; nicotinamide adenine dinucleotide
  22. Am J Physiol Renal Physiol. 2019 Aug 14.
    Andres-Hernando A, Lanaspa MA, Kuwabara M, Orlicky DJ, Cicerchi C, Bales E, Garcia GE, Roncal-Jimenez CA, Sato Y, Johnson RJ.
      Obesity, as well as the metabolic syndrome, are well known risk factors for chronic kidney disease (CKD), but less is known about the mechanism(s) by which metabolic syndrome might accelerate kidney disease. We hypothesized that metabolic syndrome should accelerate the development of kidney disease and that it might be associated with alterations in energy metabolism.We studied the pound mouse (which develops early metabolic syndrome due to a leptin receptor deletion) and wild type littermates and compared the level of renal injury and muscle wasting following equivalent injury with oral adenine. Renal function, histology, and biochemical analyses were performed.The presence of metabolic syndrome was associated with earlier development of renal disease (12 months) and earlier mortality in pound mice compared to controls. Following administration of adenine, kidney disease was worse in pound mice and this was associated with greater tubular injury with a decrease in kidney mitochondria, lower tissue ATP levels, and worse oxidative stress. Pound mice with similar levels of renal function as adenine-treated wild type mice also showed worse sarcopenia, with lower tissue ATP and intracellular phosphate levels.In summary, our data demonstrate that Obesity and metabolic syndrome accelerate the progression of chronic kidney disease and worsen CKD-dependent sarcopenia. Both conditions are associated with renal alterations in energy metabolism and lower tissue ATP levels secondary to mitochondrial dysfunction and reduced mitochondrial number.
    Keywords:  CKD; Mitochondria; Obesity; Renal Energy; Sarcopenia
  23. Free Radic Biol Med. 2019 Aug 10. pii: S0891-5849(19)31192-X. [Epub ahead of print]
    Lima TI, Guimarães DSPSF, Oliveira AG, Araujo H, Sponton CHG, Pinto NS, Saito A, Figueira ACM, Palameta S, Bajgelman MC, Calixto A, Pinto S, Mori MA, Orofino J, Perissi V, Mottis A, Auwerx J, Silveira LR.
      The ability to respond to fluctuations of reactive oxygen species (ROS) within the cell is a central aspect of mammalian physiology. This dynamic process depends on the coordinated action of transcriptional factors to promote the expression of genes encoding for antioxidant enzymes. Here, we demonstrate that the transcriptional coregulators, PGC-1α and NCoR1, are essential mediators of mitochondrial redox homeostasis in skeletal muscle cells. Our findings reveal an antagonistic role of these coregulators in modulating mitochondrial antioxidant induction through Sod2 transcriptional control. Importantly, the activation of this mechanism by either PGC-1α overexpression or NCoR1 knockdown attenuates mitochondrial ROS levels and prevents cell death caused by lipid overload in skeletal muscle cells. The opposing actions of coactivators and corepressors, therefore, exert a commanding role over cellular antioxidant capacity.
    Keywords:  Antioxidant enzymes; Mitochondria; Transcriptional coregulators
  24. Genes Dev. 2019 Aug 15.
    Venkateswaran N, Lafita-Navarro MC, Hao YH, Kilgore JA, Perez-Castro L, Braverman J, Borenstein-Auerbach N, Kim M, Lesner NP, Mishra P, Brabletz T, Shay JW, DeBerardinis RJ, Williams NS, Yilmaz OH, Conacci-Sorrell M.
      Tumors display increased uptake and processing of nutrients to fulfill the demands of rapidly proliferating cancer cells. Seminal studies have shown that the proto-oncogene MYC promotes metabolic reprogramming by altering glutamine uptake and metabolism in cancer cells. How MYC regulates the metabolism of other amino acids in cancer is not fully understood. Using high-performance liquid chromatography (HPLC)-tandem mass spectrometry (LC-MS/MS), we found that MYC increased intracellular levels of tryptophan and tryptophan metabolites in the kynurenine pathway. MYC induced the expression of the tryptophan transporters SLC7A5 and SLC1A5 and the enzyme arylformamidase (AFMID), involved in the conversion of tryptophan into kynurenine. SLC7A5, SLC1A5, and AFMID were elevated in colon cancer cells and tissues, and kynurenine was significantly greater in tumor samples than in the respective adjacent normal tissue from patients with colon cancer. Compared with normal human colonic epithelial cells, colon cancer cells were more sensitive to the depletion of tryptophan. Blocking enzymes in the kynurenine pathway caused preferential death of established colon cancer cells and transformed colonic organoids. We found that only kynurenine and no other tryptophan metabolite promotes the nuclear translocation of the transcription factor aryl hydrocarbon receptor (AHR). Blocking the interaction between AHR and kynurenine with CH223191 reduced the proliferation of colon cancer cells. Therefore, we propose that limiting cellular kynurenine or its downstream targets could present a new strategy to reduce the proliferation of MYC-dependent cancer cells.
    Keywords:  AFMID; AHR; MYC; SLC1A5; SLC7A5; cancer; kynurenine; organoid; tryptophan metabolism
  25. Nat Genet. 2019 Aug 12.
    Nissim S, Leshchiner I, Mancias JD, Greenblatt MB, Maertens O, Cassa CA, Rosenfeld JA, Cox AG, Hedgepeth J, Wucherpfennig JI, Kim AJ, Henderson JE, Gonyo P, Brandt A, Lorimer E, Unger B, Prokop JW, Heidel JR, Wang XX, Ukaegbu CI, Jennings BC, Paulo JA, Gableske S, Fierke CA, Getz G, Sunyaev SR, Wade Harper J, Cichowski K, Kimmelman AC, Houvras Y, Syngal S, Williams C, Goessling W.
      Pancreatic ductal adenocarcinoma is an aggressive cancer with limited treatment options1. Approximately 10% of cases exhibit familial predisposition, but causative genes are not known in most families2. We perform whole-genome sequence analysis in a family with multiple cases of pancreatic ductal adenocarcinoma and identify a germline truncating mutation in the member of the RAS oncogene family-like 3 (RABL3) gene. Heterozygous rabl3 mutant zebrafish show increased susceptibility to cancer formation. Transcriptomic and mass spectrometry approaches implicate RABL3 in RAS pathway regulation and identify an interaction with RAP1GDS1 (SmgGDS), a chaperone regulating prenylation of RAS GTPases3. Indeed, the truncated mutant RABL3 protein accelerates KRAS prenylation and requires RAS proteins to promote cell proliferation. Finally, evidence in patient cohorts with developmental disorders implicates germline RABL3 mutations in RASopathy syndromes. Our studies identify RABL3 mutations as a target for genetic testing in cancer families and uncover a mechanism for dysregulated RAS activity in development and cancer.
  26. Mitochondrion. 2019 Aug 13. pii: S1567-7249(19)30050-9. [Epub ahead of print]
    Ramzan R, Rhiel A, Weber P, Kadenbach B, Vogt S.
      Almost all energy consumed by higher organisms, either in the form of ATP or heat, is produced in mitochondria by respiration and oxidative phosphorylation through five protein complexes in the inner membrane. High-resolution x-ray analysis of crystallized cytochrome c oxidase (CytOx), the final oxygen-accepting complex of the respiratory chain, isolated by using cholate as detergent, revealed a dimeric structure with 13 subunits in each monomer. In contrast, CytOx isolated with non-ionic detergents appeared to be monomeric. Our data indicate in vivo a continuous transition between CytOx monomers and dimers via reversible phosphorylation. Increased intracellular calcium, as a consequence of stress, dephosphorylates and monomerises CytOx, whereas cAMP rephosphorylates and dimerises it. Only dimeric CytOx exhibits an "allosteric ATP-inhibition" which inhibits respiration at high cellular ATP/ADP-ratios and could prevent oxygen radical formation and the generation of diseases.
  27. Pharm Pat Anal. 2019 Aug 15.
    Katt WP, Cerione RA.
      Cancer metabolism is currently a hot topic. Since it was first realized that cancer cells rely upon an altered metabolic program to sustain their rapid proliferation, the enzymes that support those metabolic changes have appeared to be good targets for pharmacological intervention. Here, we discuss efforts pertaining to targets in cancer metabolism, focusing upon the tricarboxylic acid cycle and the mechanisms which feed nutrients into it. We describe a broad landscape of small-molecule inhibitors, targeting a dozen different proteins, each implicated in cancer progression. We hope that this will serve as a reference both to the areas being most highly examined today and, relatedly, the areas that are still ripe for novel intervention.
    Keywords:  TCA cycle; cancer; drug discovery; glutaminase; glutaminolysis; glycolysis; isocitrate dehydrogenase; metabolism; patents
  28. EMBO Rep. 2019 Aug 14. e47928
    Gordaliza-Alaguero I, Cantó C, Zorzano A.
      Cellular organelles are not static but show dynamism-a property that is likely relevant for their function. In addition, they interact with other organelles in a highly dynamic manner. In this review, we analyze the proteins involved in the interaction between mitochondria and other cellular organelles, especially the endoplasmic reticulum, lipid droplets, and lysosomes. Recent results indicate that, on one hand, metabolic alterations perturb the interaction between mitochondria and other organelles, and, on the other hand, that deficiency in proteins involved in the tethering between mitochondria and the ER or in specific functions of the interaction leads to metabolic alterations in a variety of tissues. The interaction between organelles is an emerging field that will permit to identify key proteins, to delineate novel modulation pathways, and to elucidate their implications in human disease.
    Keywords:  contact sites; diabetes; endoplasmic reticulum; insulin resistance; lipid droplets
  29. Proc Natl Acad Sci U S A. 2019 Aug 15. pii: 201908228. [Epub ahead of print]
    Totaro A, Zhuang Q, Panciera T, Battilana G, Azzolin L, Brumana G, Gandin A, Brusatin G, Cordenonsi M, Piccolo S.
      Autophagy, besides ensuring energy metabolism and organelle renewal, is crucial for the biology of adult normal and cancer stem cells. However, it remains incompletely understood how autophagy connects to stemness factors and the nature of the microenvironmental signals that pattern autophagy in different cell types. Here we advance in these directions by reporting that YAP/TAZ transcriptionally control autophagy, being critical for autophagosomal degradation into autolysosomes. YAP/TAZ are downstream effectors of cellular mechanotransduction and indeed we found that cell mechanics, dictated by the physical property of the ECM and cytoskeletal tension, profoundly impact on autophagic flux in a YAP/TAZ-mediated manner. Functionally, by using pancreatic and mammary organoid cultures, we found that YAP/TAZ-regulated autophagy is essential in normal cells for YAP/TAZ-mediated dedifferentiation and acquisition of self-renewing properties. In tumor cells, the YAP/TAZ-autophagy connection is key to sustain transformed traits and for acquisition of a cancer stem cell state by otherwise more benign cells. Mechanistically, YAP/TAZ promote autophagic flux by directly promoting the expression of Armus, a RAB7-GAP required for autophagosome turnover and whose add-back rescues autophagy in YAP/TAZ-depleted cells. These findings expand the influence of YAP/TAZ mechanotransduction to the control of autophagy and, vice versa, the role of autophagy in YAP/TAZ biology, and suggest a mechanism to coordinate transcriptional rewiring with cytoplasmic restructuring during cell reprogramming.
    Keywords:  YAP/TAZ; autophagy; cell plasticity; mechanotransduction
  30. Nat Immunol. 2019 Aug 12.
    Guillamot M, Ouazia D, Dolgalev I, Yeung ST, Kourtis N, Dai Y, Corrigan K, Zea-Redondo L, Saraf A, Florens L, Washburn MP, Tikhonova AN, Malumbres M, Gong Y, Tsirigos A, Park C, Barbieri C, Khanna KM, Busino L, Aifantis I.
      The response to systemic infection and injury requires the rapid adaptation of hematopoietic stem cells (HSCs), which proliferate and divert their differentiation toward the myeloid lineage. Significant interest has emerged in understanding the signals that trigger the emergency hematopoietic program. However, the mechanisms that halt this response of HSCs, which is critical to restore homeostasis, remain unknown. Here we reveal that the E3 ubiquitin ligase Speckle-type BTB-POZ protein (SPOP) restrains the inflammatory activation of HSCs. In the absence of Spop, systemic inflammation proceeded in an unresolved manner, and the sustained response in the HSCs resulted in a lethal phenotype reminiscent of hyper-inflammatory syndrome or sepsis. Our proteomic studies decipher that SPOP restricted inflammation by ubiquitinating the innate signal transducer myeloid differentiation primary response protein 88 (MYD88). These findings unearth an HSC-intrinsic post-translational mechanism that is essential for reestablishing homeostasis after emergency hematopoiesis.
  31. Science. 2019 Aug 16. pii: eaaw9855. [Epub ahead of print]365(6454):
    Youle RJ.
      Mitochondria are organelles with their own genome that arose from α-proteobacteria living within single-celled Archaea more than a billion years ago. This step of endosymbiosis offered tremendous opportunities for energy production and metabolism and allowed the evolution of fungi, plants, and animals. However, less appreciated are the downsides of this endosymbiosis. Coordinating gene expression between the mitochondrial genomes and the nuclear genome is imprecise and can lead to proteotoxic stress. The clonal reproduction of mitochondrial DNA requires workarounds to avoid mutational meltdown. In metazoans that developed innate immune pathways to thwart bacterial and viral infections, mitochondrial components can cross-react with pathogen sensors and invoke inflammation. Here, I focus on the numerous and elegant quality control processes that compensate for or mitigate these challenges of endosymbiosis.
  32. Cell Rep. 2019 Aug 13. pii: S2211-1247(19)30953-2. [Epub ahead of print]28(7): 1659-1669.e5
    Rolland SG, Schneid S, Schwarz M, Rackles E, Fischer C, Haeussler S, Regmi SG, Yeroslaviz A, Habermann B, Mokranjac D, Lambie E, Conradt B.
      The induction of the mitochondrial unfolded protein response (UPRmt) results in increased transcription of the gene encoding the mitochondrial chaperone HSP70. We systematically screened the C. elegans genome and identified 171 genes that, when knocked down, induce the expression of an hsp-6 HSP70 reporter and encode mitochondrial proteins. These genes represent many, but not all, mitochondrial processes (e.g., mitochondrial calcium homeostasis and mitophagy are not represented). Knockdown of these genes leads to reduced mitochondrial membrane potential and, hence, decreased protein import into mitochondria. In addition, it induces UPRmt in a manner that is dependent on ATFS-1 but that is not antagonized by the kinase GCN-2. We propose that compromised mitochondrial protein import signals the induction of UPRmt and that the mitochondrial targeting sequence of ATFS-1 functions as a sensor for this signal.
    Keywords:  ATFS-1; C. elegans; GCN-2; UPR(mt); hsp-6; hsp-60; mitochondria
  33. Front Immunol. 2019 ;10 1611
    Jahchan NS, Mujal AM, Pollack JL, Binnewies M, Sriram V, Reyno L, Krummel MF.
      The tumor microenvironment (TME) of diverse cancer types is often characterized by high levels of infiltrating myeloid cells including monocytes, macrophages, dendritic cells, and granulocytes. These cells perform a variety of functions in the TME, varying from immune suppressive to immune stimulatory roles. In this review, we summarize the different myeloid cell populations in the TME and the intratumoral myeloid targeting approaches that are being clinically investigated, and discuss strategies that identify new myeloid subpopulations within the TME. The TME therapies include agents that modulate the functional activities of myeloid populations, that impact recruitment and survival of myeloid subpopulations, and that functionally reprogram or activate myeloid populations. We discuss the benefits, limitations and potential side effects of these therapeutic approaches.
    Keywords:  dendritic cell (DC); immune checkpoint blockade (ICB); macrophage; monocytes; myeloid cells; myeloid tuning; tumor associated macrophage (TAM); tumor micoenvironment
  34. Mol Metab. 2019 Jul 30. pii: S2212-8778(19)30431-4. [Epub ahead of print]
    Pietzke M, Meiser J, Vazquez A.
      BACKGROUND: Formate is a one-carbon molecule at the crossroad between cellular and whole body metabolism, between host and microbiome metabolism, and between nutrition and toxicology. This centrality confers formate with a key role in human physiology and disease that is currently unappreciated.SCOPE OF REVIEW: Here we review the scientific literature on formate metabolism, highlighting cellular pathways, whole body metabolism, and interactions with the diet and the gut microbiome. We will discuss the relevance of formate metabolism in the context of embryonic development, cancer, obesity, immunometabolism, and neurodegeneration.
    MAJOR CONCLUSIONS: We will conclude with an outlook of some open questions bringing formate metabolism into the spotlight.
    Keywords:  Cancer; Formate metabolism; Immune system; Neurodegeneration; Obesity; One-carbon-metabolism
  35. Nat Rev Immunol. 2019 Aug 12.
    Chapman NM, Boothby MR, Chi H.
      Naive T cells are actively maintained in a quiescent state that promotes their survival and persistence. On antigen stimulation, T cells exit quiescence to initiate clonal expansion and effector differentiation. Initial studies focused on the immune receptors and transcriptional regulators involved in T cell quiescence and activation, but recent findings highlight cell metabolism as a crucial regulator of these processes. Here we summarize these intrinsic metabolic programmes and also describe how cell-extrinsic factors, such as nutrients and regulatory T cells, directly and indirectly balance quiescence and activation programmes in conventional T cells. We propose that immunological cues and nutrients license and tune metabolic programmes and signalling networks that communicate in a bidirectional manner to promote quiescence exit. Understanding the programmes that regulate T cell quiescence will be key for developing novel approaches to modulate protective and pathological T cell responses in human diseases.
  36. Elife. 2019 Aug 16. pii: e47990. [Epub ahead of print]8
    Petkevicius K, Virtue S, Bidault G, Jenkins B, Çubuk C, Morgantini C, Aouadi M, Dopazo J, Serlie M, Koulman A, Vidal-Puig A.
      White adipose tissue (WAT) inflammation contributes to the development of insulin resistance in obesity. While the role of adipose tissue macrophage (ATM) pro-inflammatory signalling in the development of insulin resistance has been established, it is less clear how WAT inflammation is initiated. Here, we show that ATMs isolated from obese mice and humans exhibit markers of increased rate of de novo phosphatidylcholine (PC) biosynthesis. Macrophage-specific knockout of phosphocholine cytidylyltransferase A (CCTa), the rate-limiting enzyme of de novo PC biosynthesis pathway, alleviated obesity-induced WAT inflammation and insulin resistance. Mechanistically, CCTa-deficient macrophages showed reduced ER stress and inflammation in response to palmitate. Surprisingly, this was not due to lower exogenous palmitate incorporation into cellular PCs. Instead, CCTa-null macrophages had lower membrane PC turnover, leading to elevated membrane polyunsaturated fatty acid levels that negated the pro-inflammatory effects of palmitate. Our results reveal a causal link between obesity-associated increase in de novo PC synthesis, accelerated PC turnover and pro-inflammatory activation of ATMs.
    Keywords:  cell biology; human; human biology; medicine; mouse
  37. Neurochem Res. 2019 Aug 13.
    Zhang Q, Lei YH, Zhou JP, Hou YY, Wan Z, Wang HL, Meng H.
      As one of the major cell organelles responsible for ATP production, it is important that neurons maintain mitochondria with structural and functional integrity; this is especially true for neurons with high metabolic requirements. When mitochondrial damage occurs, mitochondria are able to maintain a steady state of functioning through molecular and organellar quality control, thus ensuring neuronal function. And when mitochondrial quality control (MQC) fails, mitochondria mediate apoptosis. An apparently key molecule in MQC is the transcriptional coactivator peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α). Recent findings have demonstrated that upregulation of PGC-1α expression in neurons can modulate MQC to prevent mitochondrial dysfunction in certain in vivo and in vitro aging or neurodegenerative encephalopathy models, such as Huntington's disease, Alzheimer's disease, and Parkinson's disease. Because mitochondrial function and quality control disorders are the basis of pathogenesis in almost all neurodegenerative diseases (NDDs), the role of PGC-1α may make it a viable entry point for the treatment of such diseases. This review focuses on multi-level MQC in neurons, as well as the regulation of MQC by PGC-1α in these major NDDs.
    Keywords:  Mitochondrial quality control; Neurodegenerative diseases; Neuroprotective effects; Peroxisome proliferator activated receptor γ coactivator-1α; Signaling pathway
  38. Nat Chem Biol. 2019 Aug 12.
    Patel SJ, Frey AG, Palenchar DJ, Achar S, Bullough KZ, Vashisht A, Wohlschlegel JA, Philpott CC.
      Hundreds of cellular proteins require iron cofactors for activity, and cells express systems for their assembly and distribution. Molecular details of the cytosolic iron pool used for iron cofactors are lacking, but iron chaperones of the poly(rC)-binding protein (PCBP) family play a key role in ferrous ion distribution. Here we show that, in cells and in vitro, PCBP1 coordinates iron via conserved cysteine and glutamate residues and a molecule of noncovalently bound glutathione (GSH). Proteomics analysis of PCBP1-interacting proteins identified BolA2, which functions, in complex with Glrx3, as a cytosolic [2Fe-2S] cluster chaperone. The Fe-GSH-bound form of PCBP1 complexes with cytosolic BolA2 via a bridging Fe ligand. Biochemical analysis of PCBP1 and BolA2, in cells and in vitro, indicates that PCBP1-Fe-GSH-BolA2 serves as an intermediate complex required for the assembly of [2Fe-2S] clusters on BolA2-Glrx3, thereby linking the ferrous iron and Fe-S distribution systems in cells.
  39. Nat Commun. 2019 Aug 14. 10(1): 3669
    Deelen J, Evans DS, Arking DE, Tesi N, Nygaard M, Liu X, Wojczynski MK, Biggs ML, van der Spek A, Atzmon G, Ware EB, Sarnowski C, Smith AV, Seppälä I, Cordell HJ, Dose J, Amin N, Arnold AM, Ayers KL, Barzilai N, Becker EJ, Beekman M, Blanché H, Christensen K, Christiansen L, Collerton JC, Cubaynes S, Cummings SR, Davies K, Debrabant B, Deleuze JF, Duncan R, Faul JD, Franceschi C, Galan P, Gudnason V, Harris TB, Huisman M, Hurme MA, Jagger C, Jansen I, Jylhä M, Kähönen M, Karasik D, Kardia SLR, Kingston A, Kirkwood TBL, Launer LJ, Lehtimäki T, Lieb W, Lyytikäinen LP, Martin-Ruiz C, Min J, Nebel A, Newman AB, Nie C, Nohr EA, Orwoll ES, Perls TT, Province MA, Psaty BM, Raitakari OT, Reinders MJT, Robine JM, Rotter JI, Sebastiani P, Smith J, Sørensen TIA, Taylor KD, Uitterlinden AG, van der Flier W, van der Lee SJ, van Duijn CM, van Heemst D, Vaupel JW, Weir D, Ye K, Zeng Y, Zheng W, Holstege H, Kiel DP, Lunetta KL, Slagboom PE, Murabito JM.
      Human longevity is heritable, but genome-wide association (GWA) studies have had limited success. Here, we perform two meta-analyses of GWA studies of a rigorous longevity phenotype definition including 11,262/3484 cases surviving at or beyond the age corresponding to the 90th/99th survival percentile, respectively, and 25,483 controls whose age at death or at last contact was at or below the age corresponding to the 60th survival percentile. Consistent with previous reports, rs429358 (apolipoprotein E (ApoE) ε4) is associated with lower odds of surviving to the 90th and 99th percentile age, while rs7412 (ApoE ε2) shows the opposite. Moreover, rs7676745, located near GPR78, associates with lower odds of surviving to the 90th percentile age. Gene-level association analysis reveals a role for tissue-specific expression of multiple genes in longevity. Finally, genetic correlation of the longevity GWA results with that of several disease-related phenotypes points to a shared genetic architecture between health and longevity.
  40. Cell Rep. 2019 Aug 13. pii: S2211-1247(19)30933-7. [Epub ahead of print]28(7): 1744-1757.e5
    Tang Z, Takahashi Y, He H, Hattori T, Chen C, Liang X, Chen H, Young MM, Wang HG.
      During autophagy, phagophores grow into double-membrane vesicles called autophagosomes, but the underlying mechanism remains unclear. Here, we show a critical role of Atg2A in phagophore expansion. Atg2A translocates to the phagophore at the mitochondria-associated ER membrane (MAM) through a C-terminal 45-amino acid domain that we have termed the MAM localization domain (MLD). Proteomic analysis identifies the outer mitochondrial membrane protein TOM40 as a MLD-interacting partner. The Atg2A-TOM40 interaction is responsible for MAM localization of Atg2A and requires the TOM receptor protein TOM70. In addition, Atg2A interacts with Atg9A by a region within its N terminus. Inhibition of either Atg2A-TOM40 or Atg2A-Atg9A interactions impairs phagophore expansion and accumulates Atg9A-vesicles in the vicinity of autophagic structures. Collectively, we propose a model that the TOM70-TOM40 complex recruits Atg2A to the MAM for vesicular and/or non-vesicular lipid transport into the expanding phagophore to grow the size of autophagosomes for efficient autophagic flux.
    Keywords:  Atg2; Atg9; TOM40; TOM70; autophagosome; autophagy; mitochondria-associated ER membrane; phagophore expansion
  41. Cancer Res. 2019 Aug 15. pii: canres.1246.2019. [Epub ahead of print]
    Wettersten HI, Weis SM, Pathria P, von Schalscha T, Minami T, Varner JA, Cheresh DA.
      Tumor-associated macrophages (TAMs) are highly expressed within the tumor microenvironment of a wide range of cancers where they exert a pro-tumor phenotype by promoting tumor cell growth and suppressing anti-tumor immune function. Here, we showed that TAM accumulation in human and mouse tumors correlates with tumor cell expression of integrin αvβ3, a known driver of epithelial cancer progression and drug resistance. A monoclonal antibody targeting αvβ3 (LM609) exploited the co-enrichment of αvβ3 and TAMs to not only eradicate highly aggressive drug-resistant human lung and pancreas cancers in mice, but prevent the emergence of circulating tumor cells. Importantly, this anti-tumor activity in mice was eliminated following macrophage depletion. While LM609 had no direct effect on tumor cell viability, it engaged macrophages but not natural killer (NK) cells to induce antibody-dependent cellular cytotoxicity (ADCC) of αvβ3-expressing tumor cells despite their expression of the CD47 "don't eat me signal". In contrast to strategies designed to eliminate TAMs, these findings suggest that anti-αvβ3 represents a promising immunotherapeutic approach to redirect TAMs to serve as tumor killers for late-stage or drug-resistant cancers.
  42. Physiol Rev. 2019 Aug 15.
    Riera-Domingo C, Audigé A, Granja S, Cheng WC, Ho PC, Baltazar F, Stockmann C, Mazzone M.
      It is generally accepted that metabolism is able to shape the immune response. Only recently we are gaining awareness that the metabolic crosstalk between different tumor compartments strongly contributes to the harsh tumor microenvironment (TME) and ultimately impairs immune cell fitness and effector functions. The major aims of this review are: i) to provide an overview on the immune system in cancer; ii) to position oxygen shortage and metabolic competition as the ground of a restrictive TME and as important players in the anti-tumor immune response; iii) to define how immunotherapies affect hypoxia/oxygen-delivery and the metabolic landscape of the tumor and iv) vice versa, how oxygen and metabolites within the TME impinge on the success of immunotherapies. By analyzing preclinical and clinical endeavors, we will discuss how a metabolic characterization of the TME can identify novel targets and signatures that could be exploited in combination with standard immunotherapies and can help to predict the benefit of new and traditional immunotherapeutic drugs.
    Keywords:  Cancer; Hypoxia; Immunity; Immunotherapy; Metabolism
  43. Mitochondrion. 2019 Aug 13. pii: S1567-7249(19)30100-X. [Epub ahead of print]
    Kozhukhar N, Alexeyev MF.
      Mitochondrial transcription factor A (TFAM) plays an important role in mitochondrial DNA (mtDNA) transcription and replication. In some experimental settings, TFAM expression parallels parameters of mitochondrial biogenesis, which led to a widespread acceptance of TFAM as marker of mitochondrial biogenesis. We modulated TFAM expression in several experimental systems and observed that it fails to consistently parallel mtDNA copy number and expression of mtDNA-encoded polypeptides. We suggest that the use of TFAM as a marker of mitochondrial biogenesis should be avoided outside of systems in which its performance has been carefully validated.
  44. J Mol Biol. 2019 Aug 13. pii: S0022-2836(19)30508-X. [Epub ahead of print]
    Xavier GDS, Rutter GA.
      Metabolic and secretory heterogeneity are fundamental properties of pancreatic islet β cells. Emerging data suggest that stable differences in the transcriptome and proteome of individual cells may create cellular hierarchies which, in turn, establish coordinated functional networks. These networks appear to govern the secretory activity of the whole islet and be affected in some forms of diabetes mellitus. Functional imaging, e.g. of intracellular calcium dynamics, has led to the demonstration of "small worlds" behaviour, and the identification of highly connected "hub" (or "leader") cells, and of follower populations subservient to them. Subsequent inactivation of members of either population, for example using optogenetic approaches or photoablation, has confirmed the importance of hub cells as possible pacemakers. Hub cells appear to be enriched for the glucose phosphorylating enzyme glucokinase, and for genes encoding other enzymes involved in glucose metabolism, compared to follower cells. Recent findings have shown the relevance of cellular hierarchy in islets from multiple species including human, mouse and fish, and shown that it is preserved in vivo in the context of the fully vascularised and innervated islet. Importantly, connectivity is impaired by insults which mimic the diabetic milieu, including high glucose and/or fatty levels, and by the ablation of genes associated with type 2 diabetes risk in genome-wide association studies. We discuss here the evidence for the existence of these networks and their failure in disease settings. We also briefly survey the challenges in understanding their properties.
    Keywords:  Islets of Langerhans; heterogeneity; insulin; metabolism; β cells
  45. Sci Rep. 2019 Aug 12. 9(1): 11670
    Burmistrova O, Olias-Arjona A, Lapresa R, Jimenez-Blasco D, Eremeeva T, Shishov D, Romanov S, Zakurdaeva K, Almeida A, Fedichev PO, Bolaños JP.
      The glycolytic rate in neurons is low in order to allow glucose to be metabolized through the pentose-phosphate pathway (PPP), which regenerates NADPH to preserve the glutathione redox status and survival. This is controlled by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3), the pro-glycolytic enzyme that forms fructose-2,6-bisphosphate, a powerful allosteric activator of 6-phosphofructo-1-kinase. In neurons, PFKFB3 protein is physiologically inactive due to its proteasomal degradation. However, upon an excitotoxic stimuli, PFKFB3 becomes stabilized to activate glycolysis, thus hampering PPP mediated protection of redox status leading to neurodegeneration. Here, we show that selective inhibition of PFKFB3 activity by the small molecule AZ67 prevents the NADPH oxidation, redox stress and apoptotic cell death caused by the activation of glycolysis triggered upon excitotoxic and oxygen-glucose deprivation/reoxygenation models in mouse primary neurons. Furthermore, in vivo administration of AZ67 to mice significantly alleviated the motor discoordination and brain infarct injury in the middle carotid artery occlusion ischemia/reperfusion model. These results show that pharmacological inhibition of PFKFB3 is a suitable neuroprotective therapeutic strategy in excitotoxic-related disorders such as stroke.
  46. Biochem J. 2019 Aug 15. pii: BCJ20190500. [Epub ahead of print]
    Dewulf JP, Gerin I, Rider MH, Veiga-da-Cunha M, Van Schaftingen E, Bommer GT.
      Most fatty acids (FAs) are straight chains and are synthesized by fatty acid synthase (FASN) using acetyl-CoA and malonyl-CoA units. Yet, FASN is known to be promiscuous as it may use methylmalonyl-CoA instead of malonylCoA and thereby introduce methyl-branches. We have recently found that the cytosolic enzyme ECHDC1 degrades ethylmalonyl-CoA and methylmalonyl-CoA, which presumably result from promiscuous reactions catalyzed by acetyl-CoA carboxylase on butyryl- and propionyl-CoA. Here, we tested the hypothesis that ECHDC1 is a metabolite repair enzyme that serves to prevent the formation of methyl- or ethyl-branched FAs by FASN.Using purified enzyme, we found that FASN can incorporate not only methylmalonyl-CoA but also ethylmalonylCoA, producing methyl- or ethyl-branched FAs. Using a combination of gas-chromatography and liquid chromatography coupled to mass spectrometry, we observed that inactivation of ECHDC1 in adipocytes led to an increase in several methyl-branched FAs (present in different lipid classes), while its overexpression reduced them below wild type levels. In contrast, formation of ethyl-branched FAs was observed almost exclusively in ECHDC1 knockout cells, indicating that ECHDC1 and the low activity of FASN towards ethylmalonyl-CoA efficiently prevent their formation. We conclude that ECHDC1 performs a typical metabolite repair function by destroying methyl- and ethylmalonyl-CoA. This reduces the formation of methyl-branched FAs and prevents the formation of ethyl-branched FAs by FASN. The identification of ECHDC1 as a key modulator of the abundance of methyl-branched FAs opens the way to investigate their function.
    Keywords:  Branched-chain-fatty-acids; ECHDC1; Ethylmalonyl-CoA; Fatty acid synthase; Metabolite-repair; Methylmalonyl-CoA