bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒11‒15
forty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Am J Surg Pathol. 2020 Nov 05.
    Merino MJ, Ricketts CJ, Moreno V, Yang Y, Fan TWM, Lane AN, Meltzer PS, Vocke CD, Crooks DR, Linehan WM.
      Renal cell carcinoma (RCC) is a heterogenous disease composed of several different cancer types characterized by distinct histologies and genetic alterations, including mutation of the Krebs cycle enzyme genes for fumarate hydratase and succinate dehydrogenase (SDH). This report describes a patient with multifocal renal tumors that presented with a novel, biphasic histologic morphology with one component consisting of small cells growing in a diffuse pattern occasionally forming glandular and cystic structures, reminiscent of type 1 papillary RCC, and the other component having larger cells with abundant eosinophilic and clear cytoplasm and appearing in a solid pattern of growth. Genetic analysis of multiple tumors showed that all had a somatic mutation of the IDH2 gene that created the known pathogenic, gain-of-function p.R172M alteration that results in abnormal accumulation of the oncometabolite 2-hydroxyglutarate (2-HG). Analysis of multiple tumors demonstrated highly elevated levels of 2-HG and a CpG island methylator phenotype that is characteristic of 2-HG-related inhibition of the Ten-eleven translocation (TET) family of DNA demethylases. In combination with fumarate hydratase-deficient and succinate dehydrogenase-deficient RCCs that have increased levels of the fumarate and succinate oncometabolites, respectively, the mutation of isocitrate dehydrogenase 2 represents the third Krebs cycle enzyme alteration to be associated with oncometabolite-induced RCC tumorigenesis. This study associates the discovery of a new histologic presentation of RCC with the first report of an IDH2 gain-of-function mutation in RCC.
    DOI:  https://doi.org/10.1097/PAS.0000000000001611
  2. Cell Metab. 2020 Nov 06. pii: S1550-4131(20)30535-0. [Epub ahead of print]
    Zhang Y, Xu Y, Lu W, Ghergurovich JM, Guo L, Blair IA, Rabinowitz JD, Yang X.
      The emergence of cancer from diverse normal tissues has long been rationalized to represent a common set of fundamental processes. However, these processes are not fully defined. Here, we show that forced expression of glucose-6-phosphate dehydrogenase (G6PD) affords immortalized mouse and human cells anchorage-independent growth in vitro and tumorigenicity in animals. Mechanistically, G6PD augments the NADPH pool by stimulating NAD+ kinase-mediated NADP+ biosynthesis in addition to converting NADP+ to NADPH, bolstering antioxidant defense. G6PD also increases nucleotide precursor levels through the production of ribose and NADPH, promoting cell proliferation. Supplementation of antioxidants or nucleosides suffices to convert immortalized mouse and human cells into a tumorigenic state, and supplementation of both is required when their overlapping metabolic consequences are minimized. These results suggest that normal cells have a limited capacity for redox balance and nucleotide synthesis, and overcoming this limit might represent a key aspect of oncogenic transformation.
    Keywords:  G6PD; NAD kinase; NADPH; antioxidants; cancer metabolism; nucleosides; nucleotide synthesis; oncogenic transformation; pentose phosphate pathway; redox regulation
    DOI:  https://doi.org/10.1016/j.cmet.2020.10.002
  3. Mol Genet Metab. 2020 Oct 03. pii: S1096-7192(20)30200-6. [Epub ahead of print]
    Fullerton M, McFarland R, Taylor RW, Alston CL.
      Mitochondrial complex II (succinate:ubiquinone oxidoreductase) is the smallest complex of the oxidative phosphorylation system, a tetramer of just 140 kDa. Despite its diminutive size, it is a key complex in two coupled metabolic pathways - it oxidises succinate to fumarate in the tricarboxylic acid cycle and the electrons are used to reduce FAD to FADH2, ultimately reducing ubiquinone to ubiquinol in the respiratory chain. The biogenesis and assembly of complex II is facilitated by four ancillary proteins, all of which are autosomally-encoded. Numerous pathogenic defects have been reported which describe two broad clinical manifestations, either susceptibility to cancer in the case of single, heterozygous germline variants, or a mitochondrial disease presentation, almost exclusively due to bi-allelic recessive variants and associated with an isolated complex II deficiency. Here we present a compendium of pathogenic gene variants that have been documented in the literature in patients with an isolated mitochondrial complex II deficiency. To date, 61 patients are described, harbouring 32 different pathogenic variants in four distinct complex II genes: three structural subunit genes (SDHA, SDHB and SDHD) and one assembly factor gene (SDHAF1). Many pathogenic variants result in a null allele due to nonsense, frameshift or splicing defects however, the missense variants that do occur tend to induce substitutions at highly conserved residues in regions of the proteins that are critical for binding to other subunits or substrates. There is phenotypic heterogeneity associated with defects in each complex II gene, similar to other mitochondrial diseases.
    Keywords:  Complex II; Mitochondrial disease; Pathogenic variants; Succinate dehydrogenase
    DOI:  https://doi.org/10.1016/j.ymgme.2020.09.009
  4. IUBMB Life. 2020 Nov 12.
    Shteinfer-Kuzmine A, Verma A, Arif T, Aizenberg O, Paul A, Shoshan-Barmaz V.
      The cross-talk between the mitochondrion and the nucleus regulates cellular functions, including differentiation and adaptation to stress. Mitochondria supply metabolites for epigenetic modifications and other nuclear-associated activities and certain mitochondrial proteins were found in the nucleus. The voltage-dependent anion channel 1 (VDAC1), localized at the outer mitochondrial membrane (OMM) is a central protein in controlling energy production, cell growth, Ca2+ homeostasis, and apoptosis. To alter the cross-talk between the mitochondria and the nucleus, we used specific siRNA to silence the expression of VDAC1 in glioblastoma (GBM) U87-MG and U118-MG cell-derived tumors, and then monitored the nuclear localization of mitochondrial proteins and the methylation and acetylation of histones. Depletion of VDAC1 from tumor cells reduced metabolism, leading to inhibition of tumor growth, and several tumor-associated processes and signaling pathways linked to cancer development. In addition, we demonstrate that certain mitochondrial pro-apoptotic proteins such as caspases 3, 8, and 9, and p53 were unexpectedly overexpressed in tumors, suggesting that they possess additional non-apoptotic functions. VDAC1 depletion and metabolic reprograming altered their expression levels and subcellular localization, specifically their translocation to the nucleus. In addition, VDAC1 depletion also leads to epigenetic modifications of histone acetylation and methylation, suggesting that the interchange between metabolism and cancer signaling pathways involves mitochondria-nucleus cross-talk. The mechanisms regulating mitochondrial protein trafficking into and out of the nucleus and the role these proteins play in the nucleus remain to be elucidated.
    Keywords:  VDAC1; apoptosis; cancer; epigenetics; metabolism; mitochondria; nuclear
    DOI:  https://doi.org/10.1002/iub.2407
  5. PLoS Genet. 2020 Nov;16(11): e1009129
    Maddison DC, Alfonso-Núñez M, Swaih AM, Breda C, Campesan S, Allcock N, Straatman-Iwanowska A, Kyriacou CP, Giorgini F.
      The enzyme kynurenine 3-monooxygenase (KMO) operates at a critical branch-point in the kynurenine pathway (KP), the major route of tryptophan metabolism. As the KP has been implicated in the pathogenesis of several human diseases, KMO and other enzymes that control metabolic flux through the pathway are potential therapeutic targets for these disorders. While KMO is localized to the outer mitochondrial membrane in eukaryotic organisms, no mitochondrial role for KMO has been described. In this study, KMO deficient Drosophila melanogaster were investigated for mitochondrial phenotypes in vitro and in vivo. We find that a loss of function allele or RNAi knockdown of the Drosophila KMO ortholog (cinnabar) causes a range of morphological and functional alterations to mitochondria, which are independent of changes to levels of KP metabolites. Notably, cinnabar genetically interacts with the Parkinson's disease associated genes Pink1 and parkin, as well as the mitochondrial fission gene Drp1, implicating KMO in mitochondrial dynamics and mitophagy, mechanisms which govern the maintenance of a healthy mitochondrial network. Overexpression of human KMO in mammalian cells finds that KMO plays a role in the post-translational regulation of DRP1. These findings reveal a novel mitochondrial role for KMO, independent from its enzymatic role in the kynurenine pathway.
    DOI:  https://doi.org/10.1371/journal.pgen.1009129
  6. Elife. 2020 11 10. pii: e55994. [Epub ahead of print]9
    Gnanapradeepan K, Leu JI, Basu S, Barnoud T, Good M, Lee JV, Quinn WJ, Kung CP, Ahima R, Baur JA, Wellen KE, Liu Q, Schug ZT, George DL, Murphy ME.
      The Pro47Ser variant of p53 (S47) exists in African-descent populations and is associated with increased cancer risk in humans and mice. Due to impaired repression of the cystine importer Slc7a11, S47 cells show increased glutathione (GSH) accumulation compared to cells with wild -type p53. We show that mice containing the S47 variant display increased mTOR activity and oxidative metabolism, as well as larger size, improved metabolic efficiency, and signs of superior fitness. Mechanistically, we show that mTOR and its positive regulator Rheb display increased association in S47 cells; this is due to an altered redox state of GAPDH in S47 cells that inhibits its ability to bind and sequester Rheb. Compounds that decrease glutathione normalize GAPDH-Rheb complexes and mTOR activity in S47 cells. This study reveals a novel layer of regulation of mTOR by p53, and raises the possibility that this variant may have been selected for in early Africa.
    Keywords:  GAPDH; Pro47Ser; Rheb; cancer biology; human; mTOR; metabolism; mouse; p53
    DOI:  https://doi.org/10.7554/eLife.55994
  7. Nature. 2020 Nov 11.
    Lu XY, Shi XJ, Hu A, Wang JQ, Ding Y, Jiang W, Sun M, Zhao X, Luo J, Qi W, Song BL.
      Cholesterol is an essential lipid and its synthesis is nutritionally and energetically costly1,2. In mammals, cholesterol biosynthesis increases after feeding and is inhibited under fasting conditions3. However, the regulatory mechanisms of cholesterol biosynthesis at the fasting-feeding transition remain poorly understood. Here we show that the deubiquitylase ubiquitin-specific peptidase 20 (USP20) stabilizes HMG-CoA reductase (HMGCR), the rate-limiting enzyme in the cholesterol biosynthetic pathway, in the feeding state. The post-prandial increase in insulin and glucose concentration stimulates mTORC1 to phosphorylate USP20 at S132 and S134; USP20 is recruited to the HMGCR complex and antagonizes its degradation. The feeding-induced stabilization of HMGCR is abolished in mice with liver-specific Usp20 deletion and in USP20(S132A/S134A) knock-in mice. Genetic deletion or pharmacological inhibition of USP20 markedly decreases diet-induced body weight gain, reduces lipid levels in the serum and liver, improves insulin sensitivity and increases energy expenditure. These metabolic changes are reversed by expression of the constitutively stable HMGCR(K248R). This study reveals an unexpected regulatory axis from mTORC1 to HMGCR via USP20 phosphorylation and suggests that inhibitors of USP20 could be used to lower cholesterol levels to treat metabolic diseases including hyperlipidaemia, liver steatosis, obesity and diabetes.
    DOI:  https://doi.org/10.1038/s41586-020-2928-y
  8. Nat Metab. 2020 Nov 09.
    Leslie J, Macia MG, Luli S, Worrell JC, Reilly WJ, Paish HL, Knox A, Barksby BS, Gee LM, Zaki MYW, Collins AL, Burgoyne RA, Cameron R, Bragg C, Xu X, Chung GW, Brown CDA, Blanchard AD, Nanthakumar CB, Karsdal M, Robinson SM, Manas DM, Sen G, French J, White SA, Murphy S, Trost M, Zakrzewski JL, Klein U, Schwabe RF, Mederacke I, Nixon C, Bird T, Teuwen LA, Schoonjans L, Carmeliet P, Mann J, Fisher AJ, Sheerin NS, Borthwick LA, Mann DA, Oakley F.
      Fibrosis is a common pathological feature of chronic disease. Deletion of the NF-κB subunit c-Rel limits fibrosis in multiple organs, although the mechanistic nature of this protection is unresolved. Using cell-specific gene-targeting manipulations in mice undergoing liver damage, we elucidate a critical role for c-Rel in controlling metabolic changes required for inflammatory and fibrogenic activities of hepatocytes and macrophages and identify Pfkfb3 as the key downstream metabolic mediator of this response. Independent deletions of Rel in hepatocytes or macrophages suppressed liver fibrosis induced by carbon tetrachloride, while combined deletion had an additive anti-fibrogenic effect. In transforming growth factor-β1-induced hepatocytes, c-Rel regulates expression of a pro-fibrogenic secretome comprising inflammatory molecules and connective tissue growth factor, the latter promoting collagen secretion from HMs. Macrophages lacking c-Rel fail to polarize to M1 or M2 states, explaining reduced fibrosis in RelΔLysM mice. Pharmacological inhibition of c-Rel attenuated multi-organ fibrosis in both murine and human fibrosis. In conclusion, activation of c-Rel/Pfkfb3 in damaged tissue instigates a paracrine signalling network among epithelial, myeloid and mesenchymal cells to stimulate fibrogenesis. Targeting the c-Rel-Pfkfb3 axis has potential for therapeutic applications in fibrotic disease.
    DOI:  https://doi.org/10.1038/s42255-020-00306-2
  9. Proc Natl Acad Sci U S A. 2020 Nov 09. pii: 202019604. [Epub ahead of print]
    Kravtsova-Ivantsiv Y, Goldhirsh G, Ivantsiv A, Ben Itzhak O, Kwon YT, Pikarsky E, Ciechanover A.
      Nuclear factor-ĸB (NF-ĸB) transcription factor is a family of essential regulators of the immune response and cell proliferation and transformation. A typical factor is a heterodimer made of either p50 or p52, which are limited processing products of either p105 or p100, respectively, and a member of the Rel family of proteins, typically p65. The transcriptional program of NF-ĸB is tightly regulated by the composition of the dimers. In our previous work, we demonstrated that the ubiquitin ligase KPC1 is involved in ubiquitination and proteasomal processing of p105 to generate p50. Its overexpression and the resulting high level of p50 stimulates transcription of a broad array of tumor suppressors. Here we demonstrate that additional mechanisms are involved in the p50-mediated tumor-suppressive effect. p50 down-regulates expression of a major immune checkpoint inhibitor, the programmed cell death-ligand 1 (PD-L1), both in cells and in tumors. Importantly, the suppression is abrogated by overexpression of p65. This highlights the importance of the cellular quantities of the two different subunits of NF-ĸB which determine the composition of the dimer. While the putative p50 homodimer is tumor-suppressive, the "canonical" p50p65 heterodimer is oncogenic. We found that an additional mechanism is involved in the tumor-suppressive phenomenon: p50 up-regulates expression of the proinflammatory chemokines CCL3, CCL4, and CCL5, which in turn recruit into the tumors active natural killer (NK) cells and macrophages. Overall, p50 acts as a strong tumor suppressor via multiple mechanisms, including overexpression of tumor suppressors and modulation of the tumor microenvironment by recruiting active immune cells.
    Keywords:  NF-ĸB p50; PD-L1; chemokines; tumor suppression; ubiquitin ligase KPC1
    DOI:  https://doi.org/10.1073/pnas.2019604117
  10. Nat Rev Mol Cell Biol. 2020 Nov 13.
    Romani P, Valcarcel-Jimenez L, Frezza C, Dupont S.
      Mechanical forces shape cells and tissues during development and adult homeostasis. In addition, they also signal to cells via mechanotransduction pathways to control cell proliferation, differentiation and death. These processes require metabolism of nutrients for both energy generation and biosynthesis of macromolecules. However, how cellular mechanics and metabolism are connected is still poorly understood. Here, we discuss recent evidence indicating how the mechanical cues exerted by the extracellular matrix (ECM), cell-ECM and cell-cell adhesion complexes influence metabolic pathways. Moreover, we explore the energy and metabolic requirements associated with cell mechanics and ECM remodelling, implicating a reciprocal crosstalk between cell mechanics and metabolism.
    DOI:  https://doi.org/10.1038/s41580-020-00306-w
  11. Metab Eng. 2020 Nov 05. pii: S1096-7176(20)30167-1. [Epub ahead of print]
    Yuzbasheva EY, Scarcia P, Yuzbashev TV, Messina E, Kosikhina IM, Palmieri L, Shutov AV, Taratynova MO, Amaro RL, Palmieri F, Sineoky SP, Agrimi G.
      During cultivation under nitrogen starvation, Yarrowia lipolytica produces a mixture of citric acid and isocitric acid whose ratio is mainly determined by the carbon source used. We report that mitochondrial succinate-fumarate carrier YlSfc1 controls isocitric acid efflux from mitochondria. YlSfc1 purified and reconstituted into liposomes transports succinate, fumarate, oxaloacetate, isocitrate and α-ketoglutarate. YlSFC1 overexpression determined the inversion of isocitric acid/citric acid ratio towards isocitric acid, resulting in 33.4 ± 1.9 g/L and 43.3 ± 2.8 g/L of ICA production in test-tube cultivation with glucose and glycerol, respectively. These titers represent a 4.0 and 6.3-fold increase compared to the wild type. YlSFC1 gene expression was repressed in the wild type strain grown in glucose-based medium compared to olive oil medium explaining the reason for the preferred citric acid production during Y. lipolytica growth on carbohydrates. Coexpression of YlSFC1 and adenosine monophosphate deaminase YlAMPD genes together with inactivation of citrate mitochondrial carrier YlYHM2 gene enhanced isocitric acid accumulation up to 41.4 ± 4.1 g/L with an isocitric acid/citric acid ratio of 14.3 in a small-scale cultivation with glucose as a carbon source. During large-scale cultivation with glucose pulse-feeding, the engineered strain produced 136.7 ± 2.5 g/L of ICA with a process selectivity of 88.1%, the highest reported titer and selectivity to date. These results represent the first reported isocitric acid secretion by Y. lipolytica as a main organic acid during cultivation on carbohydrate. Moreover, we demonstrate for the first time that the replacement of one mitochondrial transport system for another can be an efficient tool for switching product accumulation.
    Keywords:  Isocitric acid production; Mitochondrial carrier; Mitochondrial succinate–fumarate carrier; Yarrowia lipolytica; YlSfc1
    DOI:  https://doi.org/10.1016/j.ymben.2020.11.001
  12. J Cell Physiol. 2020 Nov 10.
    Hernandez S, Simoni-Nieves A, Gerardo-Ramírez M, Torres S, Fucho R, Gonzalez J, Castellanos-Tapia L, Hernández-Pando R, Tejero-Barrera E, Bucio L, Souza V, Miranda-Labra R, Fernández-Checa JC, Marquardt JU, Gomez-Quiroz LE, García-Ruiz C, Gutiérrez-Ruiz MC.
      Growth differentiation factor 11 (GDF11) has been characterized as a key regulator of differentiation in cells that retain stemness features. Recently, it has been reported that GDF11 exerts tumor-suppressive properties in hepatocellular carcinoma cells, decreasing clonogenicity, proliferation, spheroid formation, and cellular function, all associated with a decrement in stemness features, resulting in mesenchymal to epithelial transition and loss of aggressiveness. The aim of the present work was to investigate the mechanism associated with the tumor-suppressive properties displayed by GDF11 in liver cancer cells. Hepatocellular carcinoma-derived cell lines were exposed to GDF11 (50 ng/ml), RNA-seq analysis in Huh7 cell line revealed that GDF11 exerted profound transcriptomic impact, which involved regulation of cholesterol metabolic process, steroid metabolic process as well as key signaling pathways, resembling endoplasmic reticulum-related functions. Cholesterol and triglycerides determination in Huh7 and Hep3B cells treated with GDF11 exhibited a significant decrement in the content of these lipids. The mTOR signaling pathway was downregulated, and this was associated with a reduction in key proteins involved in the mevalonate pathway. In addition, real-time metabolism assessed by Seahorse technology showed abridged glycolysis as well as glycolytic capacity, closely related to an impaired oxygen consumption rate and decrement in adenosine triphosphate production. Finally, transmission electron microscopy revealed mitochondrial abnormalities, such as cristae disarrangement, consistent with metabolic changes. Results provide evidence that GDF11 impairs cancer cell metabolism targeting lipid homeostasis, glycolysis, and mitochondria function and morphology.
    Keywords:  GDF11; HCC; Huh7 cells; cholesterol; metabolism; mitochondria
    DOI:  https://doi.org/10.1002/jcp.30151
  13. Biol Direct. 2020 Nov 11. 15(1): 24
    Vance JE.
      This article supplements a recent Perspective by Scorrano et al. in Nature Communications [10 [ (1)]:1287] in which the properties and functions of inter-organelle membrane contact sites were summarized. It is now clear that inter-organelle membrane contact sites are widespread in eukaryotic cells and that diverse pairs of organelles can be linked via unique protein tethers. An appropriate definition of what constitutes an inter-organelle membrane contact site was proposed in the Perspective. In addition, the various experimental approaches that are frequently used to study these organelle associations, as well as the advantages and disadvantages of each of these methods, were considered. The nature of the tethers that link the pairs of organelles at the contact sites was discussed in detail and some biological functions that have been ascribed to specific membrane contact sites were highlighted. Nevertheless, the functions of most types of organelle contact sites remain unclear. In the current article I have considered some of the points raised in the Perspective but have omitted detailed information on the roles of membrane contact sites in biological functions such as apoptosis, autophagy, calcium homeostasis and mitochondrial fusion. Instead, I have provided some background on the initial discovery of mitochondria-endoplasmic reticulum membrane contact sites, and have focussed on the known roles of membrane contact sites in inter-organelle lipid transport. In addition, potential roles for membrane contact sites in human diseases are briefly discussed.
    Keywords:  Cholesterol transport; Endoplasmic reticulum; Membrane contact sites; Mitochondria; Mitochondria-associated membranes (MAM); Phospholipid transport; Plasma membrane
    DOI:  https://doi.org/10.1186/s13062-020-00279-y
  14. Trends Cancer. 2020 Nov 06. pii: S2405-8033(20)30281-8. [Epub ahead of print]
    Walker SA, Pham A, Nizzero S, Kim M, Riter B, Bletz J, Judge S, Phillips B, Noble D, Murray D, Wetzel E, Samson S, McMahon M, Flink C, Couch J, Tomlin C, Swanson K, Anderson ARA, Odde D, Shen H, Hughes S, Zahir N, Enderling H, Wolfram J.
      Physical sciences are often overlooked in the field of cancer research. The Physical Sciences in Oncology Initiative was launched to integrate physics, mathematics, chemistry, and engineering with cancer research and clinical oncology through education, outreach, and collaboration. Here, we provide a framework for education and outreach in emerging transdisciplinary fields.
    Keywords:  cancer awareness; developing field; science education and outreach; scientific network
    DOI:  https://doi.org/10.1016/j.trecan.2020.10.007
  15. Cell Metab. 2020 Nov 03. pii: S1550-4131(20)30554-4. [Epub ahead of print]
    Lv H, Lv G, Chen C, Zong Q, Jiang G, Ye D, Cui X, He Y, Xiang W, Han Q, Tang L, Yang W, Wang H.
      NAD+ metabolism is implicated in aging and cancer. However, its role in immune checkpoint regulation and immune evasion remains unclear. Here, we find nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ biogenesis, drives interferon γ (IFNγ)-induced PD-L1 expression in multiple types of tumors and governs tumor immune evasion in a CD8+ T cell-dependent manner. Mechanistically, NAD+ metabolism maintains activity and expression of methylcytosine dioxygenase Tet1 via α-ketoglutarate (α-KG). IFNγ-activated Stat1 facilitates Tet1 binding to Irf1 to regulate Irf1 demethylation, leading to downstream PD-L1 expression on tumors. Importantly, high NAMPT-expressing tumors are more sensitive to anti-PD-L1 treatment and NAD+ augmentation enhances the efficacy of anti-PD-L1 antibody in immunotherapy-resistant tumors. Collectively, these data delineate an NAD+ metabolism-dependent epigenetic mechanism contributing to tumor immune evasion, and NAD+ replenishment combined with PD-(L)1 antibody provides a promising therapeutic strategy for immunotherapy-resistant tumors.
    Keywords:  NAD(+) metabolism; NAMPT; PD-L1; Tet1; cancer immune evasion; cancer immunotherapy; epigenetics; immune checkpoint blockade; interferon γ
    DOI:  https://doi.org/10.1016/j.cmet.2020.10.021
  16. Transl Med Aging. 2020 ;4 117-120
    Mor DE, Murphy CT.
      Mitochondrial dysfunction is thought to contribute to neurodegeneration in Parkinson's disease (PD), yet the cellular events that lead to mitochondrial disruption remain unclear. Post-mortem studies of PD patient brains and the use of complex I inhibitors to model the disease previously suggested a reduction in mitochondrial activity as a causative factor in PD, but this may represent an endpoint in the disease process. In our recent studies, we identified a novel link between branched-chain amino acid metabolism and PD, and uncovered mitochondrial hyperactivity as a potential alternative mechanism of PD pathogenesis. Increased mitochondrial activity may occur in a subset of PD patients, or may be a more common early event that precedes the ultimate loss of mitochondrial function. Therefore, it may be that any imbalance in mitochondrial activity, either increased or decreased, could cause a loss of mitochondrial homeostasis that leads to disease. An effective therapeutic strategy may be to target specific imbalances in activity at selective stages of PD or in specific patients, with any efforts to reduce mitochondrial activity constituting a surprising new avenue for PD treatment.
    Keywords:  Branched-chain amino acid metabolism; Hyperactive mitochondria; Mitochondrial homeostasis; Parkinson’s disease
    DOI:  https://doi.org/10.1016/j.tma.2020.07.007
  17. Mol Cell. 2020 Oct 29. pii: S1097-2765(20)30725-5. [Epub ahead of print]
    Chen S, Liu S, Wang J, Wu Q, Wang A, Guan H, Zhang Q, Zhang D, Wang X, Song H, Qin J, Zou J, Jiang Z, Ouyang S, Feng XH, Liang T, Xu P.
      Mitochondrial morphology shifts rapidly to manage cellular metabolism, organelle integrity, and cell fate. It remains unknown whether innate nucleic acid sensing, the central and general mechanisms of monitoring both microbial invasion and cellular damage, can reprogram and govern mitochondrial dynamics and function. Here, we unexpectedly observed that upon activation of RIG-I-like receptor (RLR)-MAVS signaling, TBK1 directly phosphorylated DRP1/DNM1L, which disabled DRP1, preventing its high-order oligomerization and mitochondrial fragmentation function. The TBK1-DRP1 axis was essential for assembly of large MAVS aggregates and healthy antiviral immunity and underlay nutrient-triggered mitochondrial dynamics and cell fate determination. Knockin (KI) strategies mimicking TBK1-DRP1 signaling produced dominant-negative phenotypes reminiscent of human DRP1 inborn mutations, while interrupting the TBK1-DRP1 connection compromised antiviral responses. Thus, our findings establish an unrecognized function of innate immunity governing both morphology and physiology of a major organelle, identify a lacking loop during innate RNA sensing, and report an elegant mechanism of shaping mitochondrial dynamics.
    Keywords:  DRP1; RLR-MAVS; TBK1; antiviral immunity; cell fate determination; innate immunity; mitochondrial dynamics; mitochondrion; nucleic acid sensing; phosphorylation
    DOI:  https://doi.org/10.1016/j.molcel.2020.10.018
  18. Nat Commun. 2020 11 11. 11(1): 5711
    Hanada Y, Ishihara N, Wang L, Otera H, Ishihara T, Koshiba T, Mihara K, Ogawa Y, Nomura M.
      Mitochondria are multifunctional organelles that produce energy and are critical for various signaling pathways. Mitochondrial antiviral signaling (MAVS) is a mitochondrial outer membrane protein essential for the anti-RNA viral immune response, which is regulated by mitochondrial dynamics and energetics; however, the molecular link between mitochondrial metabolism and immunity is unclear. Here we show in cultured mammalian cells that MAVS is activated by mitochondrial fission factor (Mff), which senses mitochondrial energy status. Mff mediates the formation of active MAVS clusters on mitochondria, independent of mitochondrial fission and dynamin-related protein 1. Under mitochondrial dysfunction, Mff is phosphorylated by the cellular energy sensor AMP-activated protein kinase (AMPK), leading to the disorganization of MAVS clusters and repression of the acute antiviral response. Mff also contributes to immune tolerance during chronic infection by disrupting the mitochondrial MAVS clusters. Taken together, Mff has a critical function in MAVS-mediated innate immunity, by sensing mitochondrial energy metabolism via AMPK signaling.
    DOI:  https://doi.org/10.1038/s41467-020-19287-7
  19. Biology (Basel). 2020 Nov 07. pii: E380. [Epub ahead of print]9(11):
    de Goede KE, Driessen AJM, Van den Bossche J.
      Tumors consist of a wide variety of cells, including immune cells, that affect tumor progression. Macrophages are abundant innate immune cells in the tumor microenvironment (TME) and are crucial in regulating tumorigenicity. Specific metabolic conditions in the TME can alter the phenotype of tumor-associated macrophages (TAMs) in a direction that supports their pro-tumor functions. One of these conditions is the accumulation of metabolites, also known as oncometabolites. Interactions of oncometabolites with TAMs can promote a pro-tumorigenic phenotype, thereby sustaining cancer cell growth and decreasing the chance of eradication. This review focuses on the metabolic cancer-macrophage crosstalk in the TME. We discuss how cancer cell metabolism and oncometabolites affect macrophage phenotype and function, and conversely how macrophage metabolism can impact tumor progression. Lastly, we propose tumor-secreted exosome-mediated metabolic signaling as a potential factor in tumorigenesis. Insight in these processes may contribute to the development of novel cancer therapies.
    Keywords:  TAM; cancer; macrophages; metabolism; oncometabolite; tumor; tumor-associated macrophage
    DOI:  https://doi.org/10.3390/biology9110380
  20. Pharmaceutics. 2020 Nov 11. pii: E1083. [Epub ahead of print]12(11):
    Bottani E, Lamperti C, Prigione A, Tiranti V, Persico N, Brunetti D.
      Primary mitochondrial diseases (PMD) refer to a group of severe, often inherited genetic conditions due to mutations in the mitochondrial genome or in the nuclear genes encoding for proteins involved in oxidative phosphorylation (OXPHOS). The mutations hamper the last step of aerobic metabolism, affecting the primary source of cellular ATP synthesis. Mitochondrial diseases are characterized by extremely heterogeneous symptoms, ranging from organ-specific to multisystemic dysfunction with different clinical courses. The limited information of the natural history, the limitations of currently available preclinical models, coupled with the large variability of phenotypical presentations of PMD patients, have strongly penalized the development of effective therapies. However, new therapeutic strategies have been emerging, often with promising preclinical and clinical results. Here we review the state of the art on experimental treatments for mitochondrial diseases, presenting "one-size-fits-all" approaches and precision medicine strategies. Finally, we propose novel perspective therapeutic plans, either based on preclinical studies or currently used for other genetic or metabolic diseases that could be transferred to PMD.
    Keywords:  gene therapy; mitochondria; mitochondrial DNA; mitochondrial disorders; pharmacological therapy; precision medicine
    DOI:  https://doi.org/10.3390/pharmaceutics12111083
  21. Annu Rev Physiol. 2020 Nov 11.
    Barrett PQ, Guagliardo NA, Bayliss DA.
      Aldosterone excess is a pathogenic factor in many hypertensive disorders. The discovery of numerous somatic and germline mutations in ion channels in primary hyperaldosteronism underscores the importance of plasma membrane conductances in determining the activation-state of zona glomerulosa (zG) cells. Electrophysiological recordings describe an electrically quiescent behavior for dispersed zG cells. Yet, emerging data indicate that in native rosette structures in situ, zG cells are electrically excitable, generating slow periodic voltage spikes and coordinated bursts of Ca2+ oscillations. We revisit data to understand how a multitude of conductances may underlie voltage/Ca2+ oscillations, recognizing that zG layer self-renewal and cell heterogeneity may complicate this task. We review recent data to understand rosette architecture and apply maxims derived from computational network modeling to understand rosette function. The challenge going forward is to uncover how the rosette orchestrates the behavior of a functional network of conditional oscillators to control zG layer performance and aldosterone secretion. Expected final online publication date for the Annual Review of Physiology, Volume 83 is February 10, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
    DOI:  https://doi.org/10.1146/annurev-physiol-030220-113038
  22. Front Cell Dev Biol. 2020 ;8 580070
    Ren L, Chen X, Chen X, Li J, Cheng B, Xia J.
      Mesenchymal stem cells (MSCs) are pivotal to tissue homeostasis, repair, and regeneration due to their potential for self-renewal, multilineage differentiation, and immune modulation. Mitochondria are highly dynamic organelles that maintain their morphology via continuous fission and fusion, also known as mitochondrial dynamics. MSCs undergo specific mitochondrial dynamics during proliferation, migration, differentiation, apoptosis, or aging. Emerging evidence suggests that mitochondrial dynamics are key contributors to stem cell fate determination. The coordination of mitochondrial fission and fusion is crucial for cellular function and stress responses, while abnormal fission and/or fusion causes MSC dysfunction. This review focuses on the role of mitochondrial dynamics in MSC commitment under physiological and stress conditions. We highlight mechanistic insights into modulating mitochondrial dynamics and mitochondrial strategies for stem cell-based regenerative medicine. These findings shed light on the contribution of mitochondrial dynamics to MSC fate and MSC-based tissue repair.
    Keywords:  cell fate; mesenchymal stem cells; mitochondria; mitochondrial dynamics; mitochondrial fission; mitochondrial fusion
    DOI:  https://doi.org/10.3389/fcell.2020.580070
  23. Cell Rep. 2020 Nov 10. pii: S2211-1247(20)31364-4. [Epub ahead of print]33(6): 108375
    White PJ, Lapworth AL, McGarrah RW, Kwee LC, Crown SB, Ilkayeva O, An J, Carson MW, Christopher BA, Ball JR, Davies MN, Kjalarsdottir L, George T, Muehlbauer MJ, Bain JR, Stevens RD, Koves TR, Muoio DM, Brozinick JT, Gimeno RE, Brosnan MJ, Rolph TP, Kraus WE, Shah SH, Newgard CB.
      Glycine levels are inversely associated with branched-chain amino acids (BCAAs) and cardiometabolic disease phenotypes, but biochemical mechanisms that explain these relationships remain uncharted. Metabolites and genes related to BCAA metabolism and nitrogen handling were strongly associated with glycine in correlation analyses. Stable isotope labeling in Zucker fatty rats (ZFRs) shows that glycine acts as a carbon donor for the pyruvate-alanine cycle in a BCAA-regulated manner. Inhibition of the BCAA transaminase (BCAT) enzymes depletes plasma pools of alanine and raises glycine levels. In high-fat-fed ZFRs, dietary glycine supplementation raises urinary acyl-glycine content and lowers circulating triglycerides but also results in accumulation of long-chain acyl-coenzyme As (acyl-CoAs), lower 5' adenosine monophosphate-activated protein kinase (AMPK) phosphorylation in muscle, and no improvement in glucose tolerance. Collectively, these studies frame a mechanism for explaining obesity-related glycine depletion and also provide insight into the impact of glycine supplementation on systemic glucose, lipid, and amino acid metabolism.
    Keywords:  amino acids; metabolism; obesity; skeletal muscle
    DOI:  https://doi.org/10.1016/j.celrep.2020.108375
  24. Cell Metab. 2020 Nov 04. pii: S1550-4131(20)30553-2. [Epub ahead of print]
    Wang X, Wang H, Xu B, Huang D, Nie C, Pu L, Zajac GJM, Yan H, Zhao J, Shi F, Emmer BT, Lu J, Wang R, Dong X, Dai J, Zhou W, Wang C, Gao G, Wang Y, Willer C, Lu X, Zhu Y, Chen XW.
      Efficient delivery of specific cargos in vivo poses a major challenge to the secretory pathway, which shuttles products encoded by ∼30% of the genome. Newly synthesized protein and lipid cargos embark on the secretory pathway via COPII-coated vesicles, assembled by the GTPase SAR1 on the endoplasmic reticulum (ER), but how lipid-carrying lipoproteins are distinguished from the general protein cargos in the ER and selectively secreted has not been clear. Here, we show that this process is quantitatively governed by the GTPase SAR1B and SURF4, a high-efficiency cargo receptor. While both genes are implicated in lipid regulation in humans, hepatic inactivation of either mouse Sar1b or Surf4 selectively depletes plasma lipids to near-zero and protects the mice from atherosclerosis. These findings show that the pairing between SURF4 and SAR1B synergistically operates a specialized, dosage-sensitive transport program for circulating lipids, while further suggesting a potential translation to treat atherosclerosis and related cardio-metabolic diseases.
    Keywords:  COPII; cardio-metabolic disease; human genetics; lipid homeostasis; lipoprotein receptor; secretion
    DOI:  https://doi.org/10.1016/j.cmet.2020.10.020
  25. PLoS One. 2020 ;15(11): e0242174
    Sonavane M, Hayat F, Makarov M, Migaud ME, Gassman NR.
      Nicotinamide adenine dinucleotide (NAD+), the essential cofactor derived from vitamin B3, is both a coenzyme in redox enzymatic processes and substrate in non-redox events; processes that are intimately implicated in all essential bioenergetics. A decrease in intracellular NAD+ levels is known to cause multiple metabolic complications and age-related disorders. One NAD+ precursor is dihydronicotinamide riboside (NRH), which increases NAD+ levels more potently in both cultured cells and mice than current supplementation strategies with nicotinamide riboside (NR), nicotinamide mononucleotide (NMN) or vitamin B3 (nicotinamide and niacin). However, the consequences of extreme boosts in NAD+ levels are not fully understood. Here, we demonstrate the cell-specific effects of acute NRH exposure in mammalian cells. Hepatocellular carcinoma (HepG3) cells show dose-dependent cytotoxicity when supplemented with 100-1000 μM NRH. Cytotoxicity was not observed in human embryonic kidney (HEK293T) cells over the same dose range of NRH. PUMA and BAX mediate the cell-specific cytotoxicity of NRH in HepG3. When supplementing HepG3 with 100 μM NRH, a significant increase in ROS was observed concurrent with changes in the NAD(P)H and GSH/GSSG pools. NRH altered mitochondrial membrane potential, increased mitochondrial superoxide formation, and induced mitochondrial DNA damage in those cells. NRH also caused metabolic dysregulation, altering mitochondrial respiration. Altogether, we demonstrated the detrimental consequences of an extreme boost of the total NAD (NAD+ + NADH) pool through NRH supplementation in HepG3. The cell-specific effects are likely mediated through the different metabolic fate of NRH in these cells, which warrants further study in other systemic models.
    DOI:  https://doi.org/10.1371/journal.pone.0242174
  26. Proc Natl Acad Sci U S A. 2020 Nov 09. pii: 202017987. [Epub ahead of print]
    He J, Carroll J, Ding S, Fearnley IM, Montgomery MG, Walker JE.
      The adenosine triphosphate (ATP) synthase in human mitochondria is a membrane bound assembly of 29 proteins of 18 kinds organized into F1-catalytic, peripheral stalk (PS), and c8-rotor ring modules. All but two membrane components are encoded in nuclear genes, synthesized on cytoplasmic ribosomes, imported into the mitochondrial matrix, and assembled into the complex with the mitochondrial gene products ATP6 and ATP8. Intermediate vestigial ATPase complexes formed by disruption of nuclear genes for individual subunits provide a description of how the various domains are introduced into the enzyme. From this approach, it is evident that three alternative pathways operate to introduce the PS module (including associated membrane subunits e, f, and g). In one pathway, the PS is built up by addition to the core subunit b of membrane subunits e and g together, followed by membrane subunit f. Then this b-e-g-f complex is bound to the preformed F1-c8 module by subunits OSCP and F6 The final component of the PS, subunit d, is added subsequently to form a key intermediate that accepts the two mitochondrially encoded subunits. In another route to this key intermediate, first e and g together and then f are added to a preformed F1-c8-OSCP-F6-b-d complex. A third route involves the addition of the c8-ring module to the complete F1-PS complex. The key intermediate then accepts the two mitochondrially encoded subunits, stabilized by the addition of subunit j, leading to an ATP synthase complex that is coupled to the proton motive force and capable of making ATP.
    Keywords:  ATP synthase; assembly; human mitochondria; peripheral stalk
    DOI:  https://doi.org/10.1073/pnas.2017987117
  27. Nucleic Acids Res. 2020 Nov 11. pii: gkaa1011. [Epub ahead of print]
    Rath S, Sharma R, Gupta R, Ast T, Chan C, Durham TJ, Goodman RP, Grabarek Z, Haas ME, Hung WHW, Joshi PR, Jourdain AA, Kim SH, Kotrys AV, Lam SS, McCoy JG, Meisel JD, Miranda M, Panda A, Patgiri A, Rogers R, Sadre S, Shah H, Skinner OS, To TL, Walker MA, Wang H, Ward PS, Wengrod J, Yuan CC, Calvo SE, Mootha VK.
      The mammalian mitochondrial proteome is under dual genomic control, with 99% of proteins encoded by the nuclear genome and 13 originating from the mitochondrial DNA (mtDNA). We previously developed MitoCarta, a catalogue of over 1000 genes encoding the mammalian mitochondrial proteome. This catalogue was compiled using a Bayesian integration of multiple sequence features and experimental datasets, notably protein mass spectrometry of mitochondria isolated from fourteen murine tissues. Here, we introduce MitoCarta3.0. Beginning with the MitoCarta2.0 inventory, we performed manual review to remove 100 genes and introduce 78 additional genes, arriving at an updated inventory of 1136 human genes. We now include manually curated annotations of sub-mitochondrial localization (matrix, inner membrane, intermembrane space, outer membrane) as well as assignment to 149 hierarchical 'MitoPathways' spanning seven broad functional categories relevant to mitochondria. MitoCarta3.0, including sub-mitochondrial localization and MitoPathway annotations, is freely available at http://www.broadinstitute.org/mitocarta and should serve as a continued community resource for mitochondrial biology and medicine.
    DOI:  https://doi.org/10.1093/nar/gkaa1011
  28. Cell Rep. 2020 Nov 10. pii: S2211-1247(20)31360-7. [Epub ahead of print]33(6): 108371
    Carey KL, Paulus GLC, Wang L, Balce DR, Luo JW, Bergman P, Ferder IC, Kong L, Renaud N, Singh S, Kost-Alimova M, Nyfeler B, Lassen KG, Virgin HW, Xavier RJ.
      Transcription factor EB (TFEB) activates lysosomal biogenesis genes in response to environmental cues. Given implications of impaired TFEB signaling and lysosomal dysfunction in metabolic, neurological, and infectious diseases, we aim to systematically identify TFEB-directed circuits by examining transcriptional responses to TFEB subcellular localization and stimulation. We reveal that steady-state nuclear TFEB is sufficient to activate transcription of lysosomal, autophagy, and innate immunity genes, whereas other targets require higher thresholds of stimulation. Furthermore, we identify shared and distinct transcriptional signatures between mTOR inhibition and bacterial autophagy. Using a genome-wide CRISPR library, we find TFEB targets that protect cells from or sensitize cells to lysosomal cell death. BHLHE40 and BHLHE41, genes responsive to high, sustained levels of nuclear TFEB, act in opposition to TFEB upon lysosomal cell death induction. Further investigation identifies genes counter-regulated by TFEB and BHLHE40/41, adding this negative feedback to the current understanding of TFEB regulatory mechanisms.
    Keywords:  BHLHE40; BHLHE41; TFEB; autophagy; gene regulation; lysosome; xenophagy
    DOI:  https://doi.org/10.1016/j.celrep.2020.108371
  29. Hum Genomics. 2020 Nov 09. 14(1): 41
    Krupenko NI, Sharma J, Pediaditakis P, Helke KL, Hall MS, Du X, Sumner S, Krupenko SA.
      BACKGROUND: Mitochondrial folate enzyme ALDH1L2 (aldehyde dehydrogenase 1 family member L2) converts 10-formyltetrahydrofolate to tetrahydrofolate and CO2 simultaneously producing NADPH. We have recently reported that the lack of the enzyme due to compound heterozygous mutations was associated with neuro-ichthyotic syndrome in a male patient. Here, we address the role of ALDH1L2 in cellular metabolism and highlight the mechanism by which the enzyme regulates lipid oxidation.METHODS: We generated Aldh1l2 knockout (KO) mouse model, characterized its phenotype, tissue histology, and levels of reduced folate pools and applied untargeted metabolomics to determine metabolic changes in the liver, pancreas, and plasma caused by the enzyme loss. We have also used NanoString Mouse Inflammation V2 Code Set to analyze inflammatory gene expression and evaluate the role of ALDH1L2 in the regulation of inflammatory pathways.
    RESULTS: Both male and female Aldh1l2 KO mice were viable and did not show an apparent phenotype. However, H&E and Oil Red O staining revealed the accumulation of lipid vesicles localized between the central veins and portal triads in the liver of Aldh1l2-/- male mice indicating abnormal lipid metabolism. The metabolomic analysis showed vastly changed metabotypes in the liver and plasma in these mice suggesting channeling of fatty acids away from β-oxidation. Specifically, drastically increased plasma acylcarnitine and acylglycine conjugates were indicative of impaired β-oxidation in the liver. Our metabolomics data further showed that mechanistically, the regulation of lipid metabolism by ALDH1L2 is linked to coenzyme A biosynthesis through the following steps. ALDH1L2 enables sufficient NADPH production in mitochondria to maintain high levels of glutathione, which in turn is required to support high levels of cysteine, the coenzyme A precursor. As the final outcome, the deregulation of lipid metabolism due to ALDH1L2 loss led to decreased ATP levels in mitochondria.
    CONCLUSIONS: The ALDH1L2 function is important for CoA-dependent pathways including β-oxidation, TCA cycle, and bile acid biosynthesis. The role of ALDH1L2 in the lipid metabolism explains why the loss of this enzyme is associated with neuro-cutaneous diseases. On a broader scale, our study links folate metabolism to the regulation of lipid homeostasis and the energy balance in the cell.
    Keywords:  ALDH1L2; Coenzyme A; Folate metabolism; Knockout mouse model; Metabolomics; NADPH; Oxidative stress; β-oxidation
    DOI:  https://doi.org/10.1186/s40246-020-00291-3
  30. Cell Rep. 2020 Nov 10. pii: S2211-1247(20)31352-8. [Epub ahead of print]33(6): 108363
    Qin Q, Zhao T, Zou W, Shen K, Wang X.
      Stringent targeting of membrane proteins to corresponding organelles is essential for organelle identity and functions. In addition to molecular pathways that target proteins to appropriate organelles, surveillance mechanisms clear mistargeted proteins from undesired destinations. Although Msp1 functions on the mitochondrial membrane to remove mistargeted proteins, the surveillance mechanism for the endoplasmic reticulum (ER) is not well understood. Here, we show that a conserved P5A-type ATPase CATP-8, which localizes to ER, removes ectopic mitochondrial tail-anchored (TA) and signal-anchored (SA) proteins from the ER. In catp-8 mutant, mitochondria fission protein FIS-1 mislocalizes to the ER membrane. Together with another mitochondria fission protein MFF-2, FIS-1 causes ER fragmentation in a Dynamin-related protein (DRP-1)-dependent manner. In addition, CATP-8 is essential for dendrite development. catp-8 mutant dramatically reduces the level of the dendrite guidance receptor DMA-1, leading to diminished dendritic arbors. Hence, P5A ATPase safeguards ER morphology and functions by preventing mitochondrial proteins mislocalization.
    DOI:  https://doi.org/10.1016/j.celrep.2020.108363
  31. Cell Metab. 2020 Nov 06. pii: S1550-4131(20)30546-5. [Epub ahead of print]
    Varanasi SK, Kumar SV, Rouse BT.
      Metabolic reprogramming is a hallmark of T cell activation and function. As our understanding of T cell metabolism increases, so does our appreciation of its inherent complexity. The metabolic heterogeneity of T cells that reside in different locations, such as lymphoid and non-lymphoid tissues, presents a challenge to developing therapies that exploit metabolic vulnerabilities. The roots of metabolic heterogeneity are only beginning to be understood. Here, we propose four factors that contribute to the adaptation of T cells to their dynamic tissue environment: (1) functional status of T cells, (2) local factors unique to the tissue niche, (3) type of inflammation, and (4) time spent in a specific tissue. We review emerging concepts about tissue-specific metabolic reprogramming in T cells with particular attention to explain how such metabolic properties are used as an adaptation mechanism. Adaptation of immune cells to the local microenvironment is critical for their persistence and function. Here, Varanasi et al. review the role and types of metabolic adaptation acquired by T cells in tissues and how these adaptations might differ between tissue type, disease state, and functionality of a T cell.
    Keywords:  CD4 T cells; CD8 T cells; T cells; autoimmunity; cancer; fatty acids; hypoxia; immunology; infection; inflammation; metabolism; mitochondria; regulatory T cells
    DOI:  https://doi.org/10.1016/j.cmet.2020.10.013
  32. Aging Cell. 2020 Nov 09. e13268
    Okur MN, Fang EF, Fivenson EM, Tiwari V, Croteau DL, Bohr VA.
      Cockayne syndrome (CS) is a rare premature aging disease, most commonly caused by mutations of the genes encoding the CSA or CSB proteins. CS patients display cachectic dwarfism and severe neurological manifestations and have an average life expectancy of 12 years. The CS proteins are involved in transcription and DNA repair, with the latter including transcription-coupled nucleotide excision repair (TC-NER). However, there is also evidence for mitochondrial dysfunction in CS, which likely contributes to the severe premature aging phenotype of this disease. While damaged mitochondria and impaired mitophagy were characterized in mice with CSB deficiency, such changes in the CS nematode model and CS patients are not fully known. Our cross-species transcriptomic analysis in CS postmortem brain tissue, CS mouse, and nematode models shows that mitochondrial dysfunction is indeed a common feature in CS. Restoration of mitochondrial dysfunction through NAD+ supplementation significantly improved lifespan and healthspan in the CS nematodes, highlighting mitochondrial dysfunction as a major driver of the aging features of CS. In cerebellar samples from CS patients, we found molecular signatures of dysfunctional mitochondrial dynamics and impaired mitophagy/autophagy. In primary cells depleted for CSA or CSB, this dysfunction can be corrected with supplementation of NAD+ precursors. Our study provides support for the interconnection between major causative aging theories, DNA damage accumulation, mitochondrial dysfunction, and compromised mitophagy/autophagy. Together, these three agents contribute to an accelerated aging program that can be averted by cellular NAD+ restoration.
    Keywords:  AMPK; Cockayne syndrome; NAD+; accelerated ageing; aging; mitochondrial maintenance; mitophagy
    DOI:  https://doi.org/10.1111/acel.13268
  33. Nat Chem Biol. 2020 Nov 09.
    Kobayashi H, Hatakeyama H, Nishimura H, Yokota M, Suzuki S, Tomabechi Y, Shirouzu M, Osada H, Mimaki M, Goto YI, Yoshida M.
      Mitochondrial DNA (mtDNA) mutations are the major cause of mitochondrial diseases. Cells harboring disease-related mtDNA mutations exhibit various phenotypic abnormalities, such as reduced respiration and elevated lactic acid production. Induced pluripotent stem cell (iPSC) lines derived from patients with mitochondrial disease, with high proportions of mutated mtDNA, exhibit defects in maturation into neurons or cardiomyocytes. In this study, we have discovered a small-molecule compound, which we name tryptolinamide (TLAM), that activates mitochondrial respiration in cybrids generated from patient-derived mitochondria and fibroblasts from patient-derived iPSCs. We found that TLAM inhibits phosphofructokinase-1 (PFK1), which in turn activates AMPK-mediated fatty-acid oxidation to promote oxidative phosphorylation, and redirects carbon flow from glycolysis toward the pentose phosphate pathway to reinforce anti-oxidative potential. Finally, we found that TLAM rescued the defect in neuronal differentiation of iPSCs carrying a high ratio of mutant mtDNA, suggesting that PFK1 represents a potential therapeutic target for mitochondrial diseases.
    DOI:  https://doi.org/10.1038/s41589-020-00676-4
  34. Int J Biochem Cell Biol. 2020 Nov 06. pii: S1357-2725(20)30193-X. [Epub ahead of print] 105876
    Kopecka J, Godel M, Riganti C.
      Mevalonate pathway is a highly conserved pathway that produces isoprenoids and cholesterol, and it is often increased in cancer cells. Cholesterol, upstream metabolites including isoprenoids and cholesterol derivatives such as oxysterols modulate cell proliferation, motility, stemness and drug resistance. Moreover, when produced by cancer cells or immune infiltrating cells, they modulate the activity of immune populations of the tumor microenvironment. In this review, we will focus on the recent findings demonstrating that cholesterol derivatives may regulate tumor immune recognition or immune escape, playing a critical role in the immune surveillance. Since the mevalonate pathway is druggable, a deeper knowledge of the metabolic cross talks existing between the mevalonate pathway of cancer cells and immune cells may help to identify novel agents targeting cholesterol metabolism, able to boost the anti-tumor activity of the immune populations.
    Keywords:  cancer; cholesterol; immune modulation
    DOI:  https://doi.org/10.1016/j.biocel.2020.105876
  35. Bioessays. 2020 Nov 09. e2000169
    Kodama M, Nakayama KI.
      Carbon and nitrogen are essential elements for life. Glucose as a carbon source and glutamine as a nitrogen source are important nutrients for cell proliferation. About 100 years ago, it was discovered that cancer cells that have acquired unlimited proliferative capacity and undergone malignant evolution in their host manifest a cancer-specific remodeling of glucose metabolism (the Warburg effect). Only recently, however, was it shown that the metabolism of glutamine-derived nitrogen is substantially shifted from glutaminolysis to nucleotide biosynthesis during malignant progression of cancer-which might be referred to as a "second" Warburg effect. In this review, address the mechanism and relevance of this metabolic shift of glutamine-derived nitrogen in human cancer. We also examine the clinical potential of anticancer therapies that modulate the metabolic pathways of glutamine-derived nitrogen. This shift may be as important as the shift in carbon metabolism, which has long been known as the Warburg effect.
    Keywords:  de novo nucleotide biosynthesis; glutamine metabolism; glutaminolysis; meta-analysis; small cell lung cancer
    DOI:  https://doi.org/10.1002/bies.202000169
  36. Front Physiol. 2020 ;11 567796
    Corkey BE, Deeney JT.
      Key tissues are dysfunctional in obesity, diabetes, cardiovascular disease, fatty liver and other metabolic diseases. Focus has centered on individual organs as though each was isolated. Attention has been paid to insulin resistance as the key relevant pathosis, particularly insulin receptor signaling. However, many tissues play important roles in synergistically regulating metabolic homeostasis and should be considered part of a network. Our approach identifies redox as an acute regulator of the greater metabolic network. Redox reactions involve the transfer of electrons between two molecules and in this work refer to commonly shared molecules, reflective of energy state, that can readily lose electrons to increase or gain electrons to decrease the oxidation state of molecules including NAD(P), NAD(P)H, and thiols. Metabolism alters such redox molecules to impact metabolic function in many tissues, thus, responding to anabolic and catabolic stimuli appropriately and synergistically. It is also important to consider environmental factors that have arisen or increased in recent decades as putative modifiers of redox and reactive oxygen species (ROS) and thus metabolic state. ROS are highly reactive, controlled by the thiol redox state and influence the function of thousands of proteins. Lactate (L) and pyruvate (P) in cells are present in a ratio of about 10 reflective of the cytosolic NADH to NAD ratio. Equilibrium is maintained in cells because lactate dehydrogenase is highly expressed and near equilibrium. The major source of circulating lactate and pyruvate is muscle, although other tissues also contribute. Acetoacetate (A) is produced primarily by liver mitochondria where β-hydroxybutyrate dehydrogenase is highly expressed, and maintains a ratio of β-hydroxybutyrate (β) to A of about 2, reflective of the mitochondrial NADH to NAD ratio. All four metabolites as well as the thiols, cysteine and glutathione, are transported into and out of cells, due to high expression of relevant transporters. Our model supports regulation of all collaborating metabolic organs through changes in circulating redox metabolites, regardless of whether change was initiated exogenously or by a single organ. Validation of these predictions suggests novel ways to understand function by monitoring and impacting redox state.
    Keywords:  ROS; adipocytes; energy metabolism; hepatocytes; metabolic regulation; network; redox; β-cells
    DOI:  https://doi.org/10.3389/fphys.2020.567796
  37. Trends Cell Biol. 2020 Nov 04. pii: S0962-8924(20)30195-1. [Epub ahead of print]
    Madan E, Peixoto ML, Dimitrion P, Eubank TD, Yekelchyk M, Talukdar S, Fisher PB, Mi QS, Moreno E, Gogna R.
      The comparison of fitness between cells leads to the elimination of less competent cells in the presence of more competent neighbors via cell competition (CC). This phenomenon has been linked with several cancer-related genes and thus may play an important role in cancer. Various processes are involved in the regulation of tumor initiation and growth, including tumor hypoxia, clonal stem cell selection, and immune cell response, all of which have been recently shown to have a potential connection with the mechanisms involved in CC. This review aims to unravel the relation between these processes and competitive cell interactions and how this affects disease progression.
    Keywords:  Flower; Myc; cell competition; hypoxic environment; p53; tumor heterogeneity
    DOI:  https://doi.org/10.1016/j.tcb.2020.10.002
  38. Science. 2020 Nov 13. 370(6518): 853-856
    Lamper AM, Fleming RH, Ladd KM, Lee ASY.
      Shutoff of global protein synthesis is a conserved response to cellular stresses. This general phenomenon is accompanied by the induction of distinct gene programs tailored to each stress. Although the mechanisms driving repression of general protein synthesis are well characterized, how cells reprogram the translation machinery for selective gene expression remains poorly understood. Here, we found that the noncanonical 5' cap-binding protein eIF3d was activated in response to metabolic stress in human cells. Activation required reduced CK2-mediated phosphorylation near the eIF3d cap-binding pocket. eIF3d controls a gene program enriched in factors important for glucose homeostasis, including members of the mammalian target of rapamycin (mTOR) pathway. eIF3d-directed translation adaptation was essential for cell survival during chronic glucose deprivation. Thus, this mechanism of translation reprogramming regulates the cellular response to metabolic stress.
    DOI:  https://doi.org/10.1126/science.abb0993
  39. Cancer Res. 2020 Nov 15. 80(22): 4886-4887
    Man J, Pajic M, Joshua AM.
      In this issue of Cancer Research, Rozeveld and colleagues present intriguing evidence of the importance of lipid droplets and hormone-sensitive lipase (HSL) in regulating the aggressive nature of pancreatic cancer. Initially demonstrating a dependency of preloaded lipids on an invasive phenotype, the authors then establish that oncogenic KRAS mutation downregulates HSL, thereby facilitating lipid storage during steady state. Thereafter, a phenotypic switch to oxidative metabolism with lipid utilization to fuel invasion and metastasis occurs. Experimentally, blocking the KRAS-HSL axis results in fewer lipid droplets, as well as metabolic reprogramming of the invasive cell phenotype, effectively reducing invasive capacity of KRAS-mutant pancreatic cancer. Of note, HSL overexpression in tumor cells also inhibited invasion, due to depletion of lipid droplets and the stored lipids, which are essential during invasion. Collectively, these novel findings highlight the importance of energy metabolism and its dynamic regulation in the evolution of the metastatic capacity of pancreatic cancer.See related article by Rozeveld et al., p. 4932.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-20-3082
  40. Crit Rev Biochem Mol Biol. 2020 Nov 12. 1-16
    Pareek V, Pedley AM, Benkovic SJ.
      The focus of this review is the human de novo purine biosynthetic pathway. The pathway enzymes are enumerated, as well as the reactions they catalyze and their physical properties. Early literature evidence suggested that they might assemble into a multi-enzyme complex called a metabolon. The finding that fluorescently-tagged chimeras of the pathway enzymes form discrete puncta, now called purinosomes, is further elaborated in this review to include: a discussion of their assembly; the role of ancillary proteins; their locus at the microtubule/mitochondria interface; the elucidation that at endogenous levels, purinosomes function to channel intermediates from phosphoribosyl pyrophosphate to AMP and GMP; and the evidence for the purinosomes to exist as a protein condensate. The review concludes with a consideration of probable signaling pathways that might promote the assembly and disassembly of the purinosome, in particular the identification of candidate kinases given the extensive phosphorylation of the enzymes. These collective findings substantiate our current view of the de novo purine biosynthetic metabolon whose properties will be representative of how other metabolic pathways might be organized for their function.
    Keywords:  metabolism de novo purine biosynthesis purinosome metabolon substrate channeling condensate signaling
    DOI:  https://doi.org/10.1080/10409238.2020.1832438
  41. Aging Cell. 2020 Nov 09. e13270
    Kowald A, Passos JF, Kirkwood TBL.
      The idea that senescent cells are causally involved in aging has gained strong support from findings that the removal of such cells alleviates many age-related diseases and extends the life span of mice. While efforts proceed to make therapeutic use of such discoveries, it is important to ask what evolutionary forces might have been behind the emergence of cellular senescence, in order better to understand the biology that we might seek to alter. Cellular senescence is often regarded as an anti-cancer mechanism, since it limits the division potential of cells. However, many studies have shown that senescent cells often also have carcinogenic properties. This is difficult to reconcile with the simple idea of an anti-cancer mechanism. Furthermore, other studies have shown that cellular senescence is involved in wound healing and tissue repair. Here, we bring these findings and ideas together and discuss the possibility that these functions might be the main reason for the evolution of cellular senescence. Furthermore, we discuss the idea that senescent cells might accumulate with age because the immune system had to strike a balance between false negatives (overlooking some senescent cells) and false positives (destroying healthy body cells).
    Keywords:  aging; anti-aging; cellular senescence; evolution; senolytics
    DOI:  https://doi.org/10.1111/acel.13270
  42. Cancer Discov. 2020 Nov 13.
      Exogenous serine-dependent pancreatic tumors secreted nerve growth factor to attract neurons.
    DOI:  https://doi.org/10.1158/2159-8290.CD-RW2020-165
  43. Proc Natl Acad Sci U S A. 2020 Nov 10. pii: 202016589. [Epub ahead of print]
    Tognini P, Samad M, Kinouchi K, Liu Y, Helbling JC, Moisan MP, Eckel-Mahan KL, Baldi P, Sassone-Corsi P.
      Food is a powerful entrainment cue for circadian clocks in peripheral tissues, and changes in the composition of nutrients have been demonstrated to metabolically reprogram peripheral clocks. However, how food challenges may influence circadian metabolism of the master clock in the suprachiasmatic nucleus (SCN) or in other brain areas is poorly understood. Using high-throughput metabolomics, we studied the circadian metabolome profiles of the SCN and medial prefrontal cortex (mPFC) in lean mice compared with mice challenged with a high-fat diet (HFD). Both the mPFC and the SCN displayed a robust cyclic metabolism, with a strikingly high sensitivity to HFD perturbation in an area-specific manner. The phase and amplitude of oscillations were drastically different between the SCN and mPFC, and the metabolic pathways impacted by HFD were remarkably region-dependent. Furthermore, HFD induced a significant increase in the number of cycling metabolites exclusively in the SCN, revealing an unsuspected susceptibility of the master clock to food stress.
    Keywords:  circadian clock; high-fat diet; metabolome reorganization; prefrontal cortex; suprachiasmatic nucleus
    DOI:  https://doi.org/10.1073/pnas.2016589117
  44. Cancer Discov. 2020 Nov 13.
      Cancer cell lines often used in research had transcriptomic heterogeneity reminiscent of tumors.
    DOI:  https://doi.org/10.1158/2159-8290.CD-RW2020-166