bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒10‒11
forty papers selected by
Kelsey Fisher-Wellman
East Carolina University


  1. Cell. 2020 Sep 24. pii: S0092-8674(20)31091-6. [Epub ahead of print]
    Daw CC, Ramachandran K, Enslow BT, Maity S, Bursic B, Novello MJ, Rubannelsonkumar CS, Mashal AH, Ravichandran J, Bakewell TM, Wang W, Li K, Madaris TR, Shannon CE, Norton L, Kandala S, Caplan J, Srikantan S, Stathopulos PB, Reeves WB, Madesh M.
      Mg2+ is the most abundant divalent cation in metazoans and an essential cofactor for ATP, nucleic acids, and countless metabolic enzymes. To understand how the spatio-temporal dynamics of intracellular Mg2+ (iMg2+) are integrated into cellular signaling, we implemented a comprehensive screen to discover regulators of iMg2+ dynamics. Lactate emerged as an activator of rapid release of Mg2+ from endoplasmic reticulum (ER) stores, which facilitates mitochondrial Mg2+ (mMg2+) uptake in multiple cell types. We demonstrate that this process is remarkably temperature sensitive and mediated through intracellular but not extracellular signals. The ER-mitochondrial Mg2+ dynamics is selectively stimulated by L-lactate. Further, we show that lactate-mediated mMg2+ entry is facilitated by Mrs2, and point mutations in the intermembrane space loop limits mMg2+ uptake. Intriguingly, suppression of mMg2+ surge alleviates inflammation-induced multi-organ failure. Together, these findings reveal that lactate mobilizes iMg2+ and links the mMg2+ transport machinery with major metabolic feedback circuits and mitochondrial bioenergetics.
    Keywords:  Mrs2; calcium; cancer; channel; endoplasmic reticulum; inflammation; lactate; magnesium; metabolism; mitochondria
    DOI:  https://doi.org/10.1016/j.cell.2020.08.049
  2. Cell Metab. 2020 Oct 06. pii: S1550-4131(20)30486-1. [Epub ahead of print]
    Song JD, Alves TC, Befroy DE, Perry RJ, Mason GF, Zhang XM, Munk A, Zhang Y, Zhang D, Cline GW, Rothman DL, Petersen KF, Shulman GI.
      Alterations in muscle mitochondrial substrate preference have been postulated to play a major role in the pathogenesis of muscle insulin resistance. In order to examine this hypothesis, we assessed the ratio of mitochondrial pyruvate oxidation (VPDH) to rates of mitochondrial citrate synthase flux (VCS) in muscle. Contrary to this hypothesis, we found that high-fat-diet (HFD)-fed insulin-resistant rats did not manifest altered muscle substrate preference (VPDH/VCS) in soleus or quadriceps muscles in the fasting state. Furthermore, hyperinsulinemic-euglycemic (HE) clamps increased VPDH/VCS in both muscles in normal and insulin-resistant rats. We then examined the muscle VPDH/VCS flux in insulin-sensitive and insulin-resistant humans and found similar relative rates of VPDH/VCS, following an overnight fast (∼20%), and similar increases in VPDH/VCS fluxes during a HE clamp. Altogether, these findings demonstrate that alterations in mitochondrial substrate preference are not an essential step in the pathogenesis of muscle insulin resistance.
    Keywords:  Randle Cycle; citrate synthase; glucose oxidation; insulin resistance; metabolic flux; metabolic inflexibility; mitochondria; muscle metabolism; pyruvate dehydrogenase; respiratory quotient
    DOI:  https://doi.org/10.1016/j.cmet.2020.09.008
  3. Redox Biol. 2020 Sep 29. pii: S2213-2317(20)30942-3. [Epub ahead of print]37 101737
    López-Grueso MJ, Lagal DJ, García-Jiménez ÁF, Tarradas RM, Carmona-Hidalgo B, Peinado J, Requejo-Aguilar R, Bárcena JA, Padilla CA.
      Peroxiredoxin 6 (PRDX6) has been associated with tumor progression and cancer metastasis. Its acting on phospholipid hydroperoxides and its phospholipase-A2 activity are unique among the peroxiredoxin family and add complexity to its action mechanisms. As a first step towards the study of PRDX6 involvement in cancer, we have constructed a human hepatocarcinoma HepG2PRDX6-/- cell line using the CRISPR/Cas9 technique and have characterized the cellular response to lack of PRDX6. Applying quantitative global and redox proteomics, flow cytometry, in vivo extracellular flow analysis, Western blot and electron microscopy, we have detected diminished respiratory capacity, downregulation of mitochondrial proteins and altered mitochondrial morphology. Autophagic vesicles were abundant while the unfolded protein response (UPR), HIF1A and NRF2 transcription factors were not activated, despite increased levels of p62/SQSTM1 and reactive oxygen species (ROS). Insulin receptor (INSR), 3-phosphoinositide-dependent protein kinase 1 (PDPK1), uptake of glucose and hexokinase-2 (HK2) decreased markedly while nucleotide biosynthesis, lipogenesis and synthesis of long chain polyunsaturated fatty acids (LC-PUFA) increased. 254 Cys-peptides belonging to 202 proteins underwent significant redox changes. PRDX6 knockout had an antiproliferative effect due to cell cycle arrest at G2/M transition, without signs of apoptosis. Loss of PLA2 may affect the levels of specific lipids altering lipid signaling pathways, while loss of peroxidase activity could induce redox changes at critical sensitive cysteine residues in key proteins. Oxidation of specific cysteines in Proliferating Cell Nuclear Antigen (PCNA) could interfere with entry into mitosis. The GSH/Glutaredoxin system was downregulated likely contributing to these redox changes. Altogether the data demonstrate that loss of PRDX6 slows down cell division and alters metabolism and mitochondrial function, so that cell survival depends on glycolysis to lactate for ATP production and on AMPK-independent autophagy to obtain building blocks for biosynthesis. PRDX6 is an important link in the chain of elements connecting redox homeostasis and proliferation.
    Keywords:  CRISPR-Cas9; Carbohydrate metabolism; Cell cycle; Glucose metabolism; Lipokines; Mitochondria; NRF2; PCNA; Peroxiredoxin 6; Proteomics; Redox proteome
    DOI:  https://doi.org/10.1016/j.redox.2020.101737
  4. Nat Commun. 2020 10 05. 11(1): 4983
    Kang JH, Katsikis G, Li Z, Sapp KM, Stockslager MA, Lim D, Vander Heiden MG, Yaffe MB, Manalis SR, Miettinen TP.
      The energetic demands of a cell are believed to increase during mitosis, but the rates of ATP synthesis and consumption during mitosis have not been quantified. Here, we monitor mitochondrial membrane potential of single lymphocytic leukemia cells and demonstrate that mitochondria hyperpolarize from the G2/M transition until the metaphase-anaphase transition. This hyperpolarization was dependent on cyclin-dependent kinase 1 (CDK1) activity. By using an electrical circuit model of mitochondria, we quantify mitochondrial ATP synthesis rates in mitosis from the single-cell time-dynamics of mitochondrial membrane potential. We find that mitochondrial ATP synthesis decreases by approximately 50% during early mitosis and increases back to G2 levels during cytokinesis. Consistently, ATP levels and ATP synthesis are lower in mitosis than in G2 in synchronized cell populations. Overall, our results provide insights into mitotic bioenergetics and suggest that cell division is not a highly energy demanding process.
    DOI:  https://doi.org/10.1038/s41467-020-18769-y
  5. Cancers (Basel). 2020 Oct 01. pii: E2845. [Epub ahead of print]12(10):
    Chang YJ, Chen KW, Chen L.
      Increased ROS proto-oncogene 1 (ROS1) expression has been implicated in the invasiveness of human oral squamous cell carcinoma (OSCC). The cellular distribution of ROS1 has long-been assumed at the plasma membrane. However, a previous work reported a differential cellular distribution of mutant ROS1 derived from chromosomal translocation, resulting in increased carcinogenesis. We thus hypothesized that cellular distribution of upregulated ROS1 in OSCC may correlate with invasiveness. We found that ROS1 can localize to mitochondria in the highly invasive OSCC and identified a mitochondria-targeting signal sequence in ROS1. We also demonstrated that ROS1 targeting to mitochondria is required for mitochondrial fission phenotype in the highly invasive OSCC cells. OSCC cells expressing high levels of ROS1 consumed more oxygen and had increased levels of cellular ATP levels. Our results also revealed that ROS1 regulates mitochondrial biogenesis and cellular metabolic plasticity. Together, these findings demonstrate that ROS1 targeting to mitochondria enhances OSCC invasion through regulating mitochondrial morphogenesis and cellular respiratory.
    Keywords:  ROS1 oncogene; mitochondrial fission; mitochondrial respiratory capacity; oral cancer
    DOI:  https://doi.org/10.3390/cancers12102845
  6. Mol Cell. 2020 Sep 29. pii: S1097-2765(20)30648-1. [Epub ahead of print]
    Cai Z, Li CF, Han F, Liu C, Zhang A, Hsu CC, Peng D, Zhang X, Jin G, Rezaeian AH, Wang G, Zhang W, Pan BS, Wang CY, Wang YH, Wu SY, Yang SC, Hsu FC, D'Agostino RB, Furdui CM, Kucera GL, Parks JS, Chilton FH, Huang CY, Tsai FJ, Pasche B, Watabe K, Lin HK.
      Cancer metastasis accounts for the major cause of cancer-related deaths. How disseminated cancer cells cope with hostile microenvironments in secondary site for full-blown metastasis is largely unknown. Here, we show that AMPK (AMP-activated protein kinase), activated in mouse metastasis models, drives pyruvate dehydrogenase complex (PDHc) activation to maintain TCA cycle (tricarboxylic acid cycle) and promotes cancer metastasis by adapting cancer cells to metabolic and oxidative stresses. This AMPK-PDHc axis is activated in advanced breast cancer and predicts poor metastasis-free survival. Mechanistically, AMPK localizes in the mitochondrial matrix and phosphorylates the catalytic alpha subunit of PDHc (PDHA) on two residues S295 and S314, which activates the enzymatic activity of PDHc and alleviates an inhibitory phosphorylation by PDHKs, respectively. Importantly, these phosphorylation events mediate PDHc function in cancer metastasis. Our study reveals that AMPK-mediated PDHA phosphorylation drives PDHc activation and TCA cycle to empower cancer cells adaptation to metastatic microenvironments for metastasis.
    Keywords:  AMPK; PDHA; TCA cycle; breast cancer; cancer metastasis; metabolic stress
    DOI:  https://doi.org/10.1016/j.molcel.2020.09.018
  7. Cell Rep. 2020 Oct 06. pii: S2211-1247(20)31220-1. [Epub ahead of print]33(1): 108231
    Hollinshead KER, Parker SJ, Eapen VV, Encarnacion-Rosado J, Sohn A, Oncu T, Cammer M, Mancias JD, Kimmelman AC.
      Pancreatic ductal adenocarcinoma (PDAC) is characterized by extensive fibrosis and hypovascularization, resulting in significant intratumoral hypoxia (low oxygen) that contributes to its aggressiveness, therapeutic resistance, and high mortality. Despite oxygen being a fundamental requirement for many cellular and metabolic processes, and the severity of hypoxia in PDAC, the impact of oxygen deprivation on PDAC biology is poorly understood. Investigating how PDAC cells survive in the near absence of oxygen, we find that PDAC cell lines grow robustly in oxygen tensions down to 0.1%, maintaining mitochondrial morphology, membrane potential, and the oxidative metabolic activity required for the synthesis of key metabolites for proliferation. Disrupting electron transfer efficiency by targeting mitochondrial respiratory supercomplex assembly specifically affects hypoxic PDAC proliferation, metabolism, and in vivo tumor growth. Collectively, our results identify a mechanism that enables PDAC cells to thrive in severe, oxygen-limited microenvironments.
    Keywords:  COX7A2L; aspartate; electron transport chain; hypoxia; pancreatic cancer; respiration; supercomplexes
    DOI:  https://doi.org/10.1016/j.celrep.2020.108231
  8. Biochem Pharmacol. 2020 Oct 01. pii: S0006-2952(20)30489-5. [Epub ahead of print] 114253
    Carter JL, Hege K, Kalpage HA, Edwards H, Hüttemann M, Taub JW, Ge Y.
      Acute myeloid leukemia (AML) is a heterogeneous disease with variable presentation, molecular phenotype, and cytogenetic abnormalities and has seen very little improvement in patient survival over the last few decades. This heterogeneity supports poor prognosis partially through the variability in response to the standard chemotherapy. Further understanding of molecular heterogeneity has promoted the development of novel treatments, some of which target mitochondrial metabolism and function. This review discusses the relative dependency that AML cells have on mitochondrial function, and the ability to pivot this reliance to target important subsets of AML cells, including leukemia stem cells (LSCs). LSCs are tumor-initiating cells that are resistant to standard chemotherapy and promote the persistence and relapse of AML. Historically, LSCs have been targeted based on immunophenotype, but recent developments in the understanding of LSC metabolism has demonstrated unique abilities to target LSCs while sparing normal hematopoietic stem cells (HSCs) through inhibition of mitochondrial function. Here we highlight the use of small molecules that have been demonstrated to effectively target mitochondrial function. IACS-010759 and ME-344 target the electron transport chain (ETC) to inhibit oxidative phosphorylation (OXPHOS). The imipridone family (ONC201, ONC206, ONC212) of inhibitors target mitochondria through activation of ClpP mitochondrial protease and reduce function of essential pathways. These molecules offer a new mechanism for developing clinical therapies in AML and support novel strategies to target LSCs in parallel with conventional therapies.
    Keywords:  Acute myeloid leukemia; IACS-010759; ME-344; Mitochondria; ONC201; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.bcp.2020.114253
  9. Mitochondrial DNA A DNA Mapp Seq Anal. 2020 Oct 07. 1-10
    Towarnicki SG, Ballard JWO.
      Historically, mtDNA was considered a selectively neutral marker that was useful for estimating the population genetic history of the maternal lineage. Over time there has been an increasing appreciation of mtDNA and mitochondria in maintaining cellular and organismal health. Beyond energy production, mtDNA and mitochondria have critical cellular roles in signalling. Here we briefly review the structure of mtDNA and the role of the mitochondrion in energy production. We then discuss the predictions that can be obtained from quaternary structure modelling and focus on mitochondrial complex I. Complex I is the primary entry point for electrons into the electron transport system is the largest respiratory complex of the chain and produces about 40% of the proton flux used to synthesize ATP. A focus of the review is Drosophila's utility as a model organism to study the selective advantage of specific mutations. However, we note that the incorporation of insights from a multitude of systems is necessary to fully understand the range of roles that mtDNA has in organismal fitness. We speculate that dietary changes can illicit stress responses that influence the selective advantage of specific mtDNA mutations and cause spatial and temporal fluctuations in the frequencies of mutations. We conclude that developing our understanding of the roles mtDNA has in determining organismal fitness will enable increased evolutionary insight and propose we can no longer assume it is evolving as a strictly neutral marker without testing this hypothesis.
    Keywords:  Reactive oxygen species; diet; macronutrients; mito-nuclear interactions
    DOI:  https://doi.org/10.1080/24701394.2020.1830076
  10. Cancer Res. 2020 Oct 06. pii: canres.0397.2020. [Epub ahead of print]
    Barnoud T, Leung JC, Leu JI, Basu S, Poli ANR, Parris JLD, Indeglia A, Martynyuk T, Good M, Gnanapradeepan K, Sanseviero E, Moeller R, Tang HY, Cassel J, Kossenkov AV, Liu Q, Speicher DW, Gabrilovich DI, Salvino JM, George DL, Murphy ME.
      The protein chaperone HSP70 is overexpressed in many cancers including colorectal cancer (CRC), where overexpression is associated with poor survival. We report here the creation of a uniquely acting HSP70 inhibitor that targets multiple compartments in the cancer cell including mitochondria. This inhibitor was mitochondria-toxic and cytotoxic to CRC cells but not normal colon epithelial cells. Inhibition of HSP70 was efficacious as a single agent in primary and metastatic models of CRC and enabled identification of novel mitochondrial client proteins for HSP70. In a syngeneic CRC model, the inhibitor increased immune cell recruitment into tumors. Cells treated with the inhibitor secreted danger-associated molecular patterns (DAMP), including ATP and HMGB1, and functioned effectively as a tumor vaccine. Interestingly, the unique properties of this HSP70 inhibitor in the disruption of mitochondrial function and the inhibition of proteostasis both contributed to DAMP release. This HSP70 inhibitor constitutes a promising therapeutic opportunity in colorectal cancer and may exhibit anti-tumor activity against other tumor types.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-20-0397
  11. Nat Commun. 2020 10 07. 11(1): 5052
    May AI, Prescott M, Ohsumi Y.
      The mechanism and function of autophagy as a highly-conserved bulk degradation pathway are well studied, but the physiological role of autophagy remains poorly understood. We show that autophagy is involved in the adaptation of Saccharomyces cerevisiae to respiratory growth through its recycling of serine. On respiratory media, growth onset, mitochondrial initiator tRNA modification and mitochondrial protein expression are delayed in autophagy defective cells, suggesting that mitochondrial one-carbon metabolism is perturbed in these cells. The supplementation of serine, which is a key one-carbon metabolite, is able to restore mitochondrial protein expression and alleviate delayed respiratory growth. These results indicate that autophagy-derived serine feeds into mitochondrial one-carbon metabolism, supporting the initiation of mitochondrial protein synthesis and allowing rapid adaptation to respiratory growth.
    DOI:  https://doi.org/10.1038/s41467-020-18805-x
  12. FEBS J. 2020 Oct 08.
    Berndt N, Eckstein J, Heucke N, Wuensch T, Gajowski R, Stockmann M, Meierhofer D, Holzhütter HG.
      Metabolic reprogramming is a characteristic feature of cancer cells but there is no unique metabolic program for all tumors. Genetic and gene expression studies have revealed heterogeneous inter- and intra-tumor patterns of metabolic enzymes and membrane transporters. The functional implications of this heterogeneity remain often elusive. Here, we applied a systems biology approach to gain a comprehensive and quantitative picture of metabolic changes in individual hepatocellular carcinoma (HCC). We used protein intensity profiles determined by mass spectrometry in samples of ten human HCCs and the adjacent non-cancerous tissue to calibrate Hepatokin1, a complex mathematical model of liver metabolism. We computed the 24h profile of 18 metabolic functions related to carbohydrate, lipid and nitrogen metabolism. There was a general tendency among the tumors towards downregulated glucose uptake and glucose release albeit with large inter-tumor variability. This finding calls into question that the Warburg effect dictates the metabolic phenotype of HCC. All tumors comprised elevated β-oxidation rates. Urea synthesis was found to be consistently downregulated but without compromising the tumor's capacity for ammonia detoxification owing to increased glutamine synthesis. The largest inter-tumor heterogeneity was found for the uptake and release of lactate and the size of the cellular glycogen content. In line with the observed metabolic heterogeneity, the individual HCCs differed largely in their vulnerability against pharmacological treatment with metformin. Taken together, our approach provided a comprehensive and quantitative characterization of HCC metabolism that may pave the way for a computational a priori assessment of pharmacological therapies targeting metabolic processes of HCC.
    Keywords:  kinetic modeling; liver; mathematical model; metabolism; tumor metabolism
    DOI:  https://doi.org/10.1111/febs.15587
  13. Front Chem. 2020 ;8 783
    Pala L, Senn HM, Caldwell ST, Prime TA, Warrington S, Bright TP, Prag HA, Wilson C, Murphy MP, Hartley RC.
      There is considerable interest in developing drugs and probes targeted to mitochondria in order to understand and treat the many pathologies associated with mitochondrial dysfunction. The large membrane potential, negative inside, across the mitochondrial inner membrane enables delivery of molecules conjugated to lipophilic phosphonium cations to the organelle. Due to their combination of charge and hydrophobicity, quaternary triarylphosphonium cations rapidly cross biological membranes without the requirement for a carrier. Their extent of uptake is determined by the magnitude of the mitochondrial membrane potential, as described by the Nernst equation. To further enhance this uptake here we explored whether incorporation of a carboxylic acid into a quaternary triarylphosphonium cation would enhance its mitochondrial uptake in response to both the membrane potential and the mitochondrial pH gradient (alkaline inside). Accumulation of arylpropionic acid derivatives depended on both the membrane potential and the pH gradient. However, acetic or benzoic derivatives did not accumulate, due to their lowered pKa. Surprisingly, despite not being taken up by mitochondria, the phenylacetic or phenylbenzoic derivatives were not retained within mitochondria when generated within the mitochondrial matrix by hydrolysis of their cognate esters. Computational studies, supported by crystallography, showed that these molecules passed through the hydrophobic core of mitochondrial inner membrane as a neutral dimer. This finding extends our understanding of the mechanisms of membrane permeation of lipophilic cations and suggests future strategies to enhance drug and probe delivery to mitochondria.
    Keywords:  computational chemistry; membrane permeation; membrane potential; mitochondria; mitochondria-targeting; pH gradient; phosphonium
    DOI:  https://doi.org/10.3389/fchem.2020.00783
  14. Cell Metab. 2020 Oct 06. pii: S1550-4131(20)30490-3. [Epub ahead of print]32(4): 561-574.e7
    Carter CS, Huang SC, Searby CC, Cassaidy B, Miller MJ, Grzesik WJ, Piorczynski TB, Pak TK, Walsh SA, Acevedo M, Zhang Q, Mapuskar KA, Milne GL, Hinton AO, Guo DF, Weiss R, Bradberry K, Taylor EB, Rauckhorst AJ, Dick DW, Akurathi V, Falls-Hubert KC, Wagner BA, Carter WA, Wang K, Norris AW, Rahmouni K, Buettner GR, Hansen JM, Spitz DR, Abel ED, Sheffield VC.
      Aberrant redox signaling underlies the pathophysiology of many chronic metabolic diseases, including type 2 diabetes (T2D). Methodologies aimed at rebalancing systemic redox homeostasis have had limited success. A noninvasive, sustained approach would enable the long-term control of redox signaling for the treatment of T2D. We report that static magnetic and electric fields (sBE) noninvasively modulate the systemic GSH-to-GSSG redox couple to promote a healthier systemic redox environment that is reducing. Strikingly, when applied to mouse models of T2D, sBE rapidly ameliorates insulin resistance and glucose intolerance in as few as 3 days with no observed adverse effects. Scavenging paramagnetic byproducts of oxygen metabolism with SOD2 in hepatic mitochondria fully abolishes these insulin sensitizing effects, demonstrating that mitochondrial superoxide mediates induction of these therapeutic changes. Our findings introduce a remarkable redox-modulating phenomenon that exploits endogenous electromagneto-receptive mechanisms for the noninvasive treatment of T2D, and potentially other redox-related diseases.
    Keywords:  ROS; electromagnetic fields; glutathione; insulin resistance; liver; mitochondria; radical pair mechanism; redox; superoxide; type 2 diabetes
    DOI:  https://doi.org/10.1016/j.cmet.2020.09.012
  15. Oncotarget. 2020 Sep 22. 11(38): 3502-3514
    Smuder AJ, Roberts BM, Wiggs MP, Kwon OS, Yoo JK, Christou DD, Fuller DD, Szeto HH, Judge AR.
      Cancer cachexia is a syndrome characterized by profound cardiac and diaphragm muscle wasting, which increase the risk of morbidity in cancer patients due to failure of the cardiorespiratory system. In this regard, muscle relies greatly on mitochondria to meet energy requirements for contraction and mitochondrial dysfunction can result in muscle weakness and fatigue. In addition, mitochondria are a major source of reactive oxygen species (ROS) production, which can stimulate increased rates of muscle protein degradation. Therefore, it has been suggested that mitochondrial dysfunction may be an underlying factor that contributes to the pathology of cancer cachexia. To determine if pharmacologically targeting mitochondrial dysfunction via treatment with the mitochondria-targeting peptide SS-31 would prevent cardiorespiratory muscle dysfunction, colon 26 (C26) adenocarcinoma tumor-bearing mice were administered either saline or SS-31 daily (3 mg/kg/day) following inoculation. C26 mice treated with saline demonstrated greater ROS production and mitochondrial uncoupling compared to C26 mice receiving SS-31 in both the heart and diaphragm muscle. In addition, saline-treated C26 mice exhibited a decline in left ventricular function which was significantly rescued in C26 mice treated with SS-31. In the diaphragm, muscle fiber cross-sectional area of C26 mice treated with saline was significantly reduced and force production was impaired compared to C26, SS-31-treated animals. Finally, ventilatory deficits were also attenuated in C26 mice treated with SS-31, compared to saline treatment. These data demonstrate that C26 tumors promote severe cardiac and respiratory myopathy, and that prevention of mitochondrial dysfunction is sufficient to preclude cancer cachexia-induced cardiorespiratory dysfunction.
    Keywords:  SS-31; cachexia; diaphragm; elamipretide; heart
    DOI:  https://doi.org/10.18632/oncotarget.27748
  16. World J Biol Chem. 2020 Sep 27. 11(2): 52-61
    Kadenbach B.
      The generation of cellular energy in the form of ATP occurs mainly in mitochondria by oxidative phosphorylation. Cytochrome c oxidase (CytOx), the oxygen accepting and rate-limiting step of the respiratory chain, regulates the supply of variable ATP demands in cells by "allosteric ATP-inhibition of CytOx." This mechanism is based on inhibition of oxygen uptake of CytOx at high ATP/ADP ratios and low ferrocytochrome c concentrations in the mitochondrial matrix via cooperative interaction of the two substrate binding sites in dimeric CytOx. The mechanism keeps mitochondrial membrane potential ΔΨm and reactive oxygen species (ROS) formation at low healthy values. Stress signals increase cytosolic calcium leading to Ca2+-dependent dephosphorylation of CytOx subunit I at the cytosolic side accompanied by switching off the allosteric ATP-inhibition and monomerization of CytOx. This is followed by increase of ΔΨm and formation of ROS. A hypothesis is presented suggesting a dynamic change of binding of NDUFA4, originally identified as a subunit of complex I, between monomeric CytOx (active state with high ΔΨm, high ROS and low efficiency) and complex I (resting state with low ΔΨm, low ROS and high efficiency).
    Keywords:  Allosteric ATP-inhibition; Cytochrome c oxidase; Dimerization of cytochrome c oxidase; Efficiency of ATP synthesis; NDUFA4; Regulation of respiration; Reversible phosphorylation
    DOI:  https://doi.org/10.4331/wjbc.v11.i2.52
  17. Elife. 2020 10 05. pii: e56749. [Epub ahead of print]9
    Jin H, Wang S, Zaal EA, Wang C, Wu H, Bosma A, Jochems F, Isima N, Jin G, Lieftink C, Beijersbergen R, Berkers CR, Qin W, Bernards R.
      The dependency of cancer cells on glutamine may be exploited therapeutically as a new strategy for treating cancers that lack druggable driver genes. Here we found that human liver cancer was dependent on extracellular glutamine. However, targeting glutamine addiction using the glutaminase inhibitor CB-839 as monotherapy had a very limited anticancer effect, even against the most glutamine addicted human liver cancer cells. Using a chemical library, we identified V-9302, a novel inhibitor of glutamine transporter ASCT2, as sensitizing glutamine dependent (GD) cells to CB-839 treatment. Mechanically, a combination of CB-839 and V-9302 depleted glutathione and induced reactive oxygen species (ROS), resulting in apoptosis of GD cells. Moreover, this combination also showed tumor inhibition in HCC xenograft mouse models in vivo. Our findings indicate that dual inhibition of glutamine metabolism by targeting both glutaminase and glutamine transporter ASCT2 represents a potential novel treatment strategy for glutamine addicted liver cancers.
    Keywords:  CB-839; cancer biology; glutamine addiction; glutaminolysis; hepatocellular carcinoma; human
    DOI:  https://doi.org/10.7554/eLife.56749
  18. Sci Rep. 2020 Oct 05. 10(1): 16519
    Ravera S, Ghiotto F, Tenca C, Gugiatti E, Santamaria S, Ledda B, Ibatici A, Cutrona G, Mazzarello AN, Bagnara D, Cardillo M, Zarcone D, Darzynkiewicz Z, Ciccone E, Fais F, Bruno S.
      B-cell chronic lymphocytic leukemia (CLL) results from accumulation of leukemic cells that are subject to iterative re-activation cycles and clonal expansion in lymphoid tissues. The effects of the well-tolerated alkaloid Berberine (BRB), used for treating metabolic disorders, were studied on ex-vivo leukemic cells activated in vitro by microenvironment stimuli. BRB decreased expression of survival/proliferation-associated molecules (e.g. Mcl-1/Bcl-xL) and inhibited stimulation-induced cell cycle entry, irrespective of TP53 alterations or chromosomal abnormalities. CLL cells rely on oxidative phosphorylation for their bioenergetics, particularly during the activation process. In this context, BRB triggered mitochondrial dysfunction and aberrant cellular energetic metabolism. Decreased ATP production and NADH recycling, associated with mitochondrial uncoupling, were not compensated by increased lactic fermentation. Antioxidant defenses were affected and could not correct the altered intracellular redox homeostasis. The data thus indicated that the cytotoxic/cytostatic action of BRB at 10-30 μM might be mediated, at least in part, by BRB-induced impairment of oxidative phosphorylation and the associated increment of oxidative damage, with consequent inhibition of cell activation and eventual cell death. Bioenergetics and cell survival were instead unaffected in normal B lymphocytes at the same BRB concentrations. Interestingly, BRB lowered the apoptotic threshold of ABT-199/Venetoclax, a promising BH3-mimetic whose cytotoxic activity is counteracted by high Mcl-1/Bcl-xL expression and increased mitochondrial oxidative phosphorylation. Our results indicate that, while CLL cells are in the process of building their survival and cycling armamentarium, the presence of BRB affects this process.
    DOI:  https://doi.org/10.1038/s41598-020-73594-z
  19. Semin Cancer Biol. 2020 Oct 06. pii: S1044-579X(20)30203-0. [Epub ahead of print]
    Chen K, Lu P, Beeraka NM, Sukocheva OA, Madhunapantula SV, Liu J, Sinelnikov MY, Nikolenko VN, Bulygin KV, Mikhaleva LM, Reshetov IV, Gu Y, Zhang J, Cao Y, Somasundaram SG, Kirkland CE, Fan R, Aliev G.
      Epigenetic regulation of mitochondrial DNA (mtDNA) is an emerging and fast-developing field of research. Compared to regulation of nucler DNA, mechanisms of mtDNA epigenetic regulation (mitoepigenetics) remain less investigated. However, mitochondrial signaling directs various vital intracellular processes including aerobic respiration, apoptosis, cell proliferation and survival, nucleic acid synthesis, and oxidative stress. The later process and associated mismanagement of reactive oxygen species (ROS) cascade were associated with cancer progression. It has been demonstrated that cancer cells contain ROS/oxidative stress-mediated defects in mtDNA repair system and histone protection. Furthermore, mtDNA is vulnerable to damage caused by somatic mutations, resulting in the dysfunction of the mitochondrial respiratory chain and energy production, which fosters further generation of ROS and promotes oncogenicity. Mitochondrial proteins are encoded by the collective mitochondrial genome that comprises both nuclear and mitochondrial genomes coupled by crosstalk. Recent reports determined the defects in the collective mitochondrial genome that are conducive to breast cancer initiation and progression. Mutational damage to mtDNA, as well as its overproliferation and deletions, were reported to alter the nuclear epigenetic landscape. Unbalanced mitoepigenetics and adverse regulation of oxidative phosphorylation (OXPHOS) can efficiently facilitate cancer cell survival. Accordingly, several mitochondria-targeting therapeutic agents (biguanides, OXPHOS inhibitors, vitamin-E analogues, and antibiotic bedaquiline) were suggested for future clinical trials in breast cancer patients. However, crosstalk mechanisms between altered mitoepigenetics and cancer-associated mtDNA mutations remain largely unclear. Hence, mtDNA mutations and epigenetic modifications could be considered as a potential molecular marker for early diagnosis and targeted therapy of breast cancer. This review discusses the role of mitoepigenetic regulation in cancer cells and potential employment of mtDNA modifications as novel anti-cancer targets.
    Keywords:  Mitoepigenetics; breast cancer; mitochondria; mtDNA; oxidative stress
    DOI:  https://doi.org/10.1016/j.semcancer.2020.09.012
  20. Nat Immunol. 2020 Oct 05.
    Yu YR, Imrichova H, Wang H, Chao T, Xiao Z, Gao M, Rincon-Restrepo M, Franco F, Genolet R, Cheng WC, Jandus C, Coukos G, Jiang YF, Locasale JW, Zippelius A, Liu PS, Tang L, Bock C, Vannini N, Ho PC.
      The metabolic challenges present in tumors attenuate the metabolic fitness and antitumor activity of tumor-infiltrating T lymphocytes (TILs). However, it remains unclear whether persistent metabolic insufficiency can imprint permanent T cell dysfunction. We found that TILs accumulated depolarized mitochondria as a result of decreased mitophagy activity and displayed functional, transcriptomic and epigenetic characteristics of terminally exhausted T cells. Mechanistically, reduced mitochondrial fitness in TILs was induced by the coordination of T cell receptor stimulation, microenvironmental stressors and PD-1 signaling. Enforced accumulation of depolarized mitochondria with pharmacological inhibitors induced epigenetic reprogramming toward terminal exhaustion, indicating that mitochondrial deregulation caused T cell exhaustion. Furthermore, supplementation with nicotinamide riboside enhanced T cell mitochondrial fitness and improved responsiveness to anti-PD-1 treatment. Together, our results reveal insights into how mitochondrial dynamics and quality orchestrate T cell antitumor responses and commitment to the exhaustion program.
    DOI:  https://doi.org/10.1038/s41590-020-0793-3
  21. Mol Cancer Ther. 2020 Oct 08. pii: molcanther.0420.2020. [Epub ahead of print]
    Raghavan S, Baskin DS, Sharpe MA.
      We previously reported the in vitro and in vivo efficacy of N,N-bis(2-chloroethyl)-2-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)propenamide, a prodrug that targeted the mitochondria of glioblastoma (GBM). The mitochondrial enzyme monoamine oxidase B (MAOB) is highly expressed in GBM and oxidizes an uncharged methyl-tetrahydropyridine (MP-) moiety into the mitochondrially-targeted cationic form, methyl-pyridinium (P+-). Coupling this MAOB-sensitive group to a nitrogen mustard produced a prodrug that damaged GBM mitochondria and killed GBM cells. Unfortunately, the intrinsic reactivity of the nitrogen-mustard group and low solubility of MP-MUS precluded clinical development. In our second generation prodrug, MP-Pt(IV) we coupled the MP-group to an unreactive cisplatin precursor. The enzymatic conversion of MP-Pt(IV) to P+-Pt(IV) was tested using recombinant human MAOA and rhMAOB. The generation of cisplatin from Pt(IV) by ascorbate was studied optically and using mass-spectroscopy. Efficacy toward primary GBM cells and tumors was studied in vitro and in an intracranial patient-derived xenograft mice GBM model. Our studies demonstrate that MP-Pt(IV) is selectively activated by MAOB. MP-Pt(IV) is highly toxic toward GBM cells in vitro. MP-Pt(IV) toxicity against GBM is potentiated by elevating mitochondrial ascorbate and can be arrested by MAOB inhibition. In in vitro studies, sub-lethal MP-Pt(IV) doses elevated mitochondrial MAOB levels in surviving GBM cells. MP-Pt(IV) is a potent chemotherapeutic in intracranial patient-derived xenograft mouse models of primary GBM and potentiates both temozolomide (TMZ) and TMZ-chemoradiation therapies. MP-Pt(IV) was well tolerated and is highly effective against GBM in both in vitro and in vivo models.
    DOI:  https://doi.org/10.1158/1535-7163.MCT-20-0420
  22. Proc Natl Acad Sci U S A. 2020 Oct 06. pii: 202009838. [Epub ahead of print]
    Mor DE, Sohrabi S, Kaletsky R, Keyes W, Tartici A, Kalia V, Miller GW, Murphy CT.
      Metabolic dysfunction occurs in many age-related neurodegenerative diseases, yet its role in disease etiology remains poorly understood. We recently discovered a potential causal link between the branched-chain amino acid transferase BCAT-1 and the neurodegenerative movement disorder Parkinson's disease (PD). RNAi-mediated knockdown of Caenorhabditis elegans bcat-1 is known to recapitulate PD-like features, including progressive motor deficits and neurodegeneration with age, yet the underlying mechanisms have remained unknown. Using transcriptomic, metabolomic, and imaging approaches, we show here that bcat-1 knockdown increases mitochondrial respiration and induces oxidative damage in neurons through mammalian target of rapamycin-independent mechanisms. Increased mitochondrial respiration, or "mitochondrial hyperactivity," is required for bcat-1(RNAi) neurotoxicity. Moreover, we show that post-disease-onset administration of the type 2 diabetes medication metformin reduces mitochondrial respiration to control levels and significantly improves both motor function and neuronal viability. Taken together, our findings suggest that mitochondrial hyperactivity may be an early event in the pathogenesis of PD, and that strategies aimed at reducing mitochondrial respiration may constitute a surprising new avenue for PD treatment.
    Keywords:  Caenorhabditis elegans; Parkinson’s disease; branched-chain amino acid metabolism; metformin; mitochondria
    DOI:  https://doi.org/10.1073/pnas.2009838117
  23. EMBO Rep. 2020 Oct 05. e51015
    Berndtsson J, Aufschnaiter A, Rathore S, Marin-Buera L, Dawitz H, Diessl J, Kohler V, Barrientos A, Büttner S, Fontanesi F, Ott M.
      Respiratory chains are crucial for cellular energy conversion and consist of multi-subunit complexes that can assemble into supercomplexes. These structures have been intensively characterized in various organisms, but their physiological roles remain unclear. Here, we elucidate their function by leveraging a high-resolution structural model of yeast respiratory supercomplexes that allowed us to inhibit supercomplex formation by mutation of key residues in the interaction interface. Analyses of a mutant defective in supercomplex formation, which still contains fully functional individual complexes, show that the lack of supercomplex assembly delays the diffusion of cytochrome c between the separated complexes, thus reducing electron transfer efficiency. Consequently, competitive cellular fitness is severely reduced in the absence of supercomplex formation and can be restored by overexpression of cytochrome c. In sum, our results establish how respiratory supercomplexes increase the efficiency of cellular energy conversion, thereby providing an evolutionary advantage for aerobic organisms.
    Keywords:  bioenergetics; competitive fitness; cryo-EM; mitochondria; respiratory chain supercomplexes
    DOI:  https://doi.org/10.15252/embr.202051015
  24. EMBO J. 2020 Oct 06. e101767
    Spannl S, Buhl T, Nellas I, Zeidan SA, Iyer KV, Khaliullina H, Schultz C, Nadler A, Dye NA, Eaton S.
      Changes in cell metabolism and plasma membrane potential have been linked to shifts between tissue growth and differentiation, and to developmental patterning. How such changes mediate these effects is poorly understood. Here, we use the developing wing of Drosophila to investigate the interplay between cell metabolism and a key developmental regulator-the Hedgehog (Hh) signalling pathway. We show that reducing glycolysis both lowers steady-state levels of ATP and stabilizes Smoothened (Smo), the 7-pass transmembrane protein that transduces the Hh signal. As a result, the transcription factor Cubitus interruptus accumulates in its full-length, transcription activating form. We show that glycolysis is required to maintain the plasma membrane potential and that plasma membrane depolarization blocks cellular uptake of N-acylethanolamides-lipoprotein-borne Hh pathway inhibitors required for Smo destabilization. Similarly, pharmacological inhibition of glycolysis in mammalian cells induces ciliary translocation of Smo-a key step in pathway activation-in the absence of Hh. Thus, changes in cell metabolism alter Hh signalling through their effects on plasma membrane potential.
    Keywords:  endocannabinoids; glycolysis; hedgehog signalling; metabolism; plasma membrane potential
    DOI:  https://doi.org/10.15252/embj.2019101767
  25. Cell Metab. 2020 Oct 06. pii: S1550-4131(20)30492-7. [Epub ahead of print]32(4): 512-513
    Bartelt A, Weber C.
      Mitochondrial dysfunction is a hallmark of heart disease. Nicolás-Ávila et al. (2020) now find that cardiomyocytes eject dysfunctional mitochondria in exopher vesicles, which require elimination by specialized heart-resident macrophages, altogether supporting proper heart function.
    DOI:  https://doi.org/10.1016/j.cmet.2020.09.014
  26. Front Immunol. 2020 ;11 2153
    Cooke RE, Quinn KM, Quach H, Harrison S, Prince HM, Koldej R, Ritchie D.
      New diagnoses of multiple myeloma (MM) tend to occur after the age of 60, by which time thymic output is severely reduced. As a consequence, lymphocyte recovery after lymphopenia-inducing anti-MM therapies relies on homeostatic proliferation of peripheral T cells rather than replenishment by new thymic emigrants. To assess lymphocyte recovery and phenotype in patients with newly diagnosed MM (NDMM) and relapsed/refractory MM (RRMM), we tracked CD4+ and CD8+ T cell populations at serial time points throughout treatment and compared them to age-matched healthy donors (HD). Anti-MM therapies and autologous stem cell transplant (ASCT) caused a permanent reduction in the CD4:8 ratio, a decrease in naïve CD4+ T cells, and an increase in effector memory T cells and PD1-expressing CD4+ T cells. Transcriptional profiling highlighted that genes associated with fatty acid β-oxidation were upregulated in T cells in RRMM, suggesting increased reliance on mitochondrial respiration. High mitochondrial mass was seen in all T cell subsets in RRMM but with relatively suppressed reactive oxygen species and mitochondrial membrane potential, indicating mitochondrial dysfunction. These findings highlight that anti-MM and ASCT therapies perturb the composition of the T cell compartment and drive substantial metabolic remodeling, which may affect the fitness of T cells for immunotherapies. This is particularly pertinent to chimeric antigen receptor (CAR)-T therapy, which might be more efficacious if T cells were stored prior to ASCT rather than at relapse.
    Keywords:  T cell; aging; autologous stem cell transplant; metabolism; myeloma
    DOI:  https://doi.org/10.3389/fimmu.2020.02153
  27. Redox Biol. 2020 Sep 24. pii: S2213-2317(20)30941-1. [Epub ahead of print]37 101736
    Blasco N, Beà A, Barés G, Girón C, Navaridas R, Irazoki A, López-Lluch G, Zorzano A, Dolcet X, Llovera M, Sanchis D.
      The apoptotic nuclease EndoG is involved in mitochondrial DNA replication. Previous results suggested that, in addition to regulate cardiomyocyte hypertrophy, EndoG could be involved in cell proliferation. Here, by using in vivo and cell culture models, we investigated the role of EndoG in cell proliferation. Genetic deletion of Endog both in vivo and in cultured cells or Endog silencing in vitro induced a defect in rodent and human cell proliferation with a tendency of cells to accumulate in the G1 phase of cell cycle and increased reactive oxygen species (ROS) production. The defect in cell proliferation occurred with a decrease in the activity of the AKT/PKB-GSK-3β-Cyclin D axis and was reversed by addition of ROS scavengers. EndoG deficiency did not affect the expression of ROS detoxifying enzymes, nor the expression of the electron transport chain complexes and oxygen consumption rate. Addition of the micropeptide Humanin to EndoG-deficient cells restored AKT phosphorylation and proliferation without lowering ROS levels. Thus, our results show that EndoG is important for cell proliferation through the control of ROS and that Humanin can restore cell division in EndoG-deficient cells and counteracts the effects of ROS on AKT phosphorylation.
    Keywords:  Cell proliferation; Cell signaling; EndoG; Humanin; Mitochondria; Reactive oxygen species; Romo1
    DOI:  https://doi.org/10.1016/j.redox.2020.101736
  28. New Phytol. 2020 Oct 05.
    Jurdak R, Launay-Avon A, Paysant-Le Roux C, Bailly C.
      Ethylene and Reactive Oxygen Species (ROS) regulate seed dormancy alleviation, but the molecular basis of their action and crosstalk remains largely unknown. Here we studied the mechanism of Arabidopsis seed dormancy release by ethylene using cell imaging, genetic and transcriptomics approaches, in order to tackle its possible interaction with ROS homeostasis. We found that the effect of ethylene on seed germination required ROS production by the mitochondrial electron transport chain. Seed response to ethylene involved mitochondrial retrograde response (MRR) through nuclear ROS production and up-regulation of the MRR components AOX1a and ANAC013, but it also required the activation of the ethylene canonical pathway. Together our data allow deciphering the mode of action of ethylene on seed germination and the associated dynamics of ROS production. Our findings highlight the occurrence of retrograde signaling in seed germination.
    Keywords:  Arabidopsis; dormancy; ethylene; mitochondrial retrograde signaling; reactive oxygen species; seed
    DOI:  https://doi.org/10.1111/nph.16985
  29. Sci Rep. 2020 Oct 06. 10(1): 16534
    Tobias DK, Hazra A, Lawler PR, Chandler PD, Chasman DI, Buring JE, Lee IM, Cheng S, Manson JE, Mora S.
      Obesity is a risk factor for > 13 cancer sites, although it is unknown whether there is a common mechanism across sites. Evidence suggests a role for impaired branched-chain amino acid (BCAAs; isoleucine, leucine, valine) metabolism in obesity, insulin resistance, and immunity; thus, we hypothesized circulating BCAAs may be associated with incident obesity-related cancers. We analyzed participants in the prospective Women's Health Study without a history of cancer at baseline blood collection (N = 26,711, mean age = 54.6 years [SD = 7.1]). BCAAs were quantified via NMR spectroscopy, log-transformed, and standardized. We used Cox proportional regression models adjusted for age, race, smoking, diet, alcohol, physical activity, menopausal hormone use, Body Mass Index (BMI), diabetes, and other risk factors. The endpoint was a composite of obesity-related cancers, defined per the International Agency for Research on Cancer 2016 report, over a median 24 years follow-up. Baseline BMI ≥ 30 kg/m2 compared with BMI 18.5-25.0 kg/m2 was associated with 23% greater risk of obesity-related cancers (n = 2751 events; multivariable HR 1.23, 95% CI 1.11-1.37). However, BCAAs were not associated with obesity-related cancers (multivariable HR per SD = 1.01 [0.97-1.05]). Results for individual BCAA metabolites suggested a modest association for leucine with obesity-related cancers (1.04 [1.00-1.08]), and no association for isoleucine or valine (0.99 [0.95-1.03] and 1.00 [0.96-1.04], respectively). Exploratory analyses of BCAAs with individual sites included positive associations between leucine and postmenopausal breast cancer, and isoleucine with pancreatic cancer. Total circulating BCAAs were unrelated to obesity-related cancer incidence although an association was observed for leucine with incident obesity-related cancer.
    DOI:  https://doi.org/10.1038/s41598-020-73499-x
  30. BMJ Open Diabetes Res Care. 2020 Oct;pii: e001372. [Epub ahead of print]8(1):
    Seo M, Kim H, Noh H, Jeon JS, Byun DW, Kim SH, Kim HJ, Suh K, Park HK, Kwon SH.
      INTRODUCTION: Recent studies have suggested that extracellular circulating and urinary mitochondrial DNA (mtDNA) are associated with mitochondrial dysfunction in obesity and type 2 diabetes mellitus (T2DM). However, the changes to cell-free serum and urinary mtDNA after bariatric surgery in patients with obesity with T2DM have not been investigated to date.RESEARCH DESIGN AND METHODS: We prospectively recruited patients with obesity (n=18), and with obesity and T2DM (n=14) who underwent bariatric surgery, along with healthy volunteers (HV) as a control group (n=22). Serum and urinary mitochondrial nicotinamide adenine dinucleotide dehydrogenase subunit-1 (mtND-1) and cytochrome-c oxidase 3 (mtCOX-3) copy numbers were measured using quantitative PCR (qPCR). The mtDNA copy numbers of patients with obesity (with and without T2DM) were followed up 6 months after surgery.
    RESULTS: The copy numbers of urinary mtND-1 and mtCOX-3 in patients with obesity, with or without T2DM, were higher than those in the HVs. Moreover, urinary mtCOX-3 copy number increased in patients with obesity with T2DM compared with patients with obesity without T2DM (p=0.018). Meanwhile, serum mtCOX-3 copy numbers in HV were higher in both obesity patient groups (p=0.040). Bariatric surgery reduced urinary mtND-1 and mtCOX-3 copy numbers, as well as serum mtCOX-3 copy numbers only in patients with obesity with T2DM.
    CONCLUSION: These results suggest that T2DM induces greater kidney mitochondrial dysfunction in patients with obesity, which can be effectively restored with bariatric surgery.
    Keywords:  DNA; bariatric surgery; complementary; diabetes mellitus; obesity; type 2
    DOI:  https://doi.org/10.1136/bmjdrc-2020-001372
  31. J Alzheimers Dis. 2020 Sep 25.
    Yuan X, Wang L, Tendon N, Sun H, Tian J, Du H, Pascual JM, Guo L.
      BACKGROUND: Brain energy failure is an early pathological event associated with synaptic dysfunction in Alzheimer's disease (AD). Thus, mitigation or enhancement of brain energy metabolism may offer a therapeutic avenue. However, there is uncertainty as to what metabolic process(es) may be more appropriate to support or augment since metabolism is a multiform process such that each of the various metabolic precursors available is utilized via a specific metabolic pathway. In the brain, these pathways sustain not only a robust rate of energy production but also of carbon replenishment.OBJECTIVE: Triheptanoin, an edible odd-chain fatty acid triglyceride, is uncommon in that it replenishes metabolites in the tricarboxylic acid cycle (TCA) cycle via anaplerosis in addition to fueling the cycle via oxidation, thus potentially leading to both carbon replenishment and enhanced mitochondrial ATP production.
    METHODS: To test the hypothesis that triheptanoin is protective in AD, we supplied mice with severe brain amyloidosis (5×FAD mice) with dietary triheptanoin for four and a half months, followed by biological and biochemical experiments to examine mice metabolic as well as synaptic function.
    RESULTS: Triheptanoin treatment had minimal impact on systemic metabolism and brain amyloidosis as well as tauopathy while attenuating brain ATP deficiency and mitochondrial dysfunction including respiration and redox balance in 5×FAD mice. Synaptic density, a disease hallmark, was also preserved in hippocampus and neocortex despite profound amyloid deposition. None of these effects took place in treated control mice.
    CONCLUSION: These findings support the energy failure hypothesis of AD and justify investigating the mechanisms in greater depth with ultimate therapeutic intent.
    Keywords:  Alzheimer’s disease; amyloid-β; anaplerosis; mitochondrial function; triheptanoin
    DOI:  https://doi.org/10.3233/JAD-200594
  32. Mech Ageing Dev. 2020 Sep 30. pii: S0047-6374(20)30158-5. [Epub ahead of print] 111362
    Abreu P, Serna JDC, Munhoz AC, Kowaltowski AJ.
      Calorie restriction is known to promote healthy aging, which includes prevention of muscle loss. We investigated the effect of rodent calorie restriction on mitochondrial respiration and clonogenic capacity of muscle satellite stem cells, since metabolic alterations are known to regulate stem cell activity. Surprisingly, short or long-term calorie restriction do not change mitochondrial or glycolytic function. Nevertheless, both short- and long-term calorie restriction enhance myogenic colony formation. Overall, our results show that not all changes in satellite stem cell function are accompanied by metabolic remodeling.
    Keywords:  Bioenergetics; Diet; Metabolism; Mitochondria; Muscle stem cells
    DOI:  https://doi.org/10.1016/j.mad.2020.111362
  33. Sci Rep. 2020 10 07. 10(1): 16769
    Dewdney B, Alanazy M, Gillman R, Walker S, Wankell M, Qiao L, George J, Roberts A, Hebbard L.
      Hepatocellular carcinoma is rapidly becoming one of the leading causes of cancer-related deaths, largely due to the increasing incidence of non-alcoholic fatty liver disease. This in part may be attributed to Westernised diets high in fructose sugar. While many studies have shown the effects of fructose on inducing metabolic-related liver diseases, little research has investigated the effects of fructose sugar on liver cancer metabolism. The present study aimed to examine the metabolic effects of fructose on hepatocellular carcinoma growth in vitro and in vivo. Fructose sugar was found to reduce cell growth in vitro, and caused alterations in the expression of enzymes involved in the serine-glycine synthesis and pentose phosphate pathways. These biosynthesis pathways are highly active in cancer cells and they utilise glycolytic by-products to produce energy and nucleotides for growth. Hence, the study further investigated the efficacy of two novel drugs that inhibit these pathways, namely NCT-503 and Physcion. The study is the first to show that the combination treatment of NCT-503 and Physcion substantially inhibited hepatocellular carcinoma growth in vitro and in vivo. The combination of fructose diet and metabolism-inhibiting drugs may provide a unique metabolic environment that warrants further investigation in targeting hepatocellular carcinoma.
    DOI:  https://doi.org/10.1038/s41598-020-73653-5
  34. Aging Dis. 2020 Oct;11(5): 1260-1275
    Li W, Kui L, Demetrios T, Gong X, Tang M.
      Mitochondria are classically known to be cellular energy producers. Given the high-energy demanding nature of neurons in the brain, it is essential that the mitochondrial pool remains healthy and provides a continuous and efficient supply of energy. However, mitochondrial dysfunction is inevitable in aging and neurodegenerative diseases. In Alzheimer's disease (AD), neurons experience unbalanced homeostasis like damaged mitochondrial biogenesis and defective mitophagy, with the latter promoting the disease-defining amyloid β (Aβ) and p-Tau pathologies impaired mitophagy contributes to inflammation and the aggregation of Aβ and p-Tau-containing neurotoxic proteins. Interventions that restore defective mitophagy may, therefore, alleviate AD symptoms, pointing out the possibility of a novel therapy. This review aims to illustrate mitochondrial biology with a focus on mitophagy and propose strategies to treat AD while maintaining mitochondrial homeostasis.
    Keywords:  Alzheimer’s disease; NAD+; mitochondria dysfunction; mitophagy
    DOI:  https://doi.org/10.14336/AD.2020.0105
  35. Mol Cancer Ther. 2020 Oct 09. pii: molcanther.0119.2020. [Epub ahead of print]
    Huang Z, Kondoh E, Visco ZR, Baba T, Matsumura N, Dolan E, Whitaker RS, Konishi I, Fujii S, Berchuck A, Murphy SK.
      Spheroids exhibit drug resistance and slow proliferation, suggesting involvement in cancer recurrence. The protein kinase C inhibitor, UCN-01 (7-hydroxystaurosporine) has shown higher efficacy against slow proliferating and/or quiescent ovarian cancer cells. In this study, tumorigenic potential was assessed using anchorage independent growth assays and spheroid forming capacity, which was determined with ovarian cancer cell lines as well as primary ovarian cancers. Of 12 cell lines with increased anchorage-independent growth, eight formed spheroids under serum-free culture conditions. Spheroids showed reduced proliferation (p<0.0001) and Ki67 immunostaining (8% versus 87%) relative to monolayer cells. Spheroid formation was associated with increased expression of mitochondrial pathway genes (p≤0.001) from Affymetrix HT U133A gene expression data. UCN-01, a kinase inhibitor/mitochondrial uncoupler that has been shown to lead to Puma-induced mitochondrial apoptosis and ATP synthase inhibitor Oligomycin demonstrated effectiveness against spheroids, while spheroids were refractory to cisplatin and paclitaxel. By live in vivo imaging, ovarian cancer xenograft tumors were reduced after primary treatment with carboplatin. Continued treatment with carboplatin was accompanied by an increase in tumor signal while there was little or no increase in tumor signal observed with subsequent treatment with UCN-01 or Oltipraz. Taken together, our findings suggest that genes involved in mitochondrial function in spheroids may be an important therapeutic target in preventing disease recurrence.
    DOI:  https://doi.org/10.1158/1535-7163.MCT-20-0119
  36. Free Radic Biol Med. 2020 Oct 02. pii: S0891-5849(20)31271-5. [Epub ahead of print]161 60-70
    Takashi Y, Tomita K, Kuwahara Y, Roudkenar MH, Roushandeh AM, Igarashi K, Nagasawa T, Nishitani Y, Sato T.
      Most anti-cancer agents and radiotherapy exert their therapeutic effects via the production of free radicals. Ferroptosis is a recently described cell death process that is accompanied by iron-dependent lipid peroxidation. Hydrogen peroxide (H2O2) has been reported to induce cell death. However, it remains controversial whether H2O2-induced cell death is ferroptosis. In the present study, we aimed to elucidate the involvement of mitochondria in H2O2-induced ferroptosis and examined the molecules that regulate ferroptosis. We found that one mechanism underlying H2O2-induced cell death is ferroptosis, which occurs soon after H2O2 treatment (within 3 h after H2O2 treatment). We also investigated the involvement of mitochondria in H2O2-induced ferroptosis using mitochondrial DNA-depleted ρ0 cells because ρ0 cells produce more lipid peroxidation, hydroxyl radicals (•OH), and are more sensitive to H2O2 treatment. We found that ρ0 cells contain high Fe2+ levels that lead to •OH production by H2O2. Further, we observed that aquaporin (AQP) 3, 5, and 8 bind nicotinamide-adenine dinucleotide phosphate oxidase 2 and regulate the permeability of extracellular H2O2, thereby contributing to ferroptosis. Additionally, the role of mitochondria in ferroptosis was investigated using mitochondrial transfer in ρ0 cells. When mitochondria were transferred into ρ0 cells, the cells exhibited no sensitivity to H2O2-induced cytotoxicity because of decreased Fe2+ levels. Moreover, mitochondrial transfer upregulated the mitochondrial quality control protein prohibitin 2 (PHB2), which contributes to reduced AQP expression. Our findings also revealed the involvement of AQP and PHB2 in ferroptosis. Our results indicate that H2O2 treatment enhances AQP expression, Fe2+ level, and lipid peroxidation, and decrease mitochondrial function by downregulating PHB2, and thus, is a promising modality for effective cancer treatment.
    Keywords:  Aquaporin; Fe(2+); Ferroptosis; Hydrogen peroxide; Mitochondria
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2020.09.027
  37. Nucleic Acids Res. 2020 Oct 06. pii: gkaa804. [Epub ahead of print]
    Fontana GA, Gahlon HL.
      Deletions in mitochondrial DNA (mtDNA) are associated with diverse human pathologies including cancer, aging and mitochondrial disorders. Large-scale deletions span kilobases in length and the loss of these associated genes contributes to crippled oxidative phosphorylation and overall decline in mitochondrial fitness. There is not a united view for how mtDNA deletions are generated and the molecular mechanisms underlying this process are poorly understood. This review discusses the role of replication and repair in mtDNA deletion formation as well as nucleic acid motifs such as repeats, secondary structures, and DNA damage associated with deletion formation in the mitochondrial genome. We propose that while erroneous replication and repair can separately contribute to deletion formation, crosstalk between these pathways is also involved in generating deletions.
    DOI:  https://doi.org/10.1093/nar/gkaa804
  38. Transl Oncol. 2020 Sep 30. pii: S1936-5233(20)30370-3. [Epub ahead of print]14(1): 100878
    Albaret MA, Paré A, Malet L, De Souza G, Lavergne E, Goga D, De Pinieux G, Castellier C, Swalduz A, Robin V, Lavergne V, Mertani HC, Treilleux I, Vermot-Desroches C, Diaz JJ, Saintigny P.
      Keratin 8 (K8) expressed at the surface of cancer cells, referred as externalized K8 (eK8), has been observed in a variety of carcinoma cell lines. K8 has been previously reported to be expressed in poorly differentiated head and neck squamous cell carcinoma (HNSCC); however, its role during the invasive phase of upper aerodigestive tract tumorigenesis is unknown. Cohorts of HNSCC tumors for protein and mRNA expression and panel of cell lines were used for investigation. K8 was found to be externalized in a majority of HNSCC cell lines. Among the two main K8 protein isoforms only the 54 kDa was found to be present at the plasma membrane of HNSCC cells. The plasminogen-induced invasion of HNSCC cells was inhibited by the anti-eK8 D-A10 antagonist monoclonal antibody. Overexpression of K8 mRNA and protein were both correlated with tumor aggressive features and poor outcome. The effect of eK8 neutralization on invasion, its presence exclusively in cancer cells and the association of K8 expression with aggressive features and poor clinical outcome in HNSCC unravel eK8 as key player in invasion and a promising therapeutic target in HNSCC.
    DOI:  https://doi.org/10.1016/j.tranon.2020.100878
  39. Int J Obes (Lond). 2020 Oct 09.
    Alwarawrah Y, Nichols AG, Green WD, Eisner W, Kiernan K, Warren J, Hale LP, Beck MA, MacIver NJ.
      BACKGROUND: Obesity is associated with impaired primary and secondary immune responses to influenza infection, with T cells playing a critical role. T-cell function is highly influenced by the cellular metabolic state; however, it remains unknown how altered systemic metabolism in obesity alters T-cell metabolism and function to influence immune response. Our objective was to identify the altered cellular metabolic state of T cells from obese mice so that we may target T-cell metabolism to improve immune response to infection.METHODS: Mice were fed normal chow or high-fat diet for 18-19 weeks. Changes in T-cell populations were analyzed in both adipose tissue and spleens using flow cytometry. Splenic T cells were further analyzed for nutrient uptake and extracellular metabolic flux. As changes in T-cell mitochondrial oxidation were observed in obesity, obese mice were treated with metformin for 6 weeks and compared to lean control mice or obese mice undergoing weight loss through diet switch; immunity was measured by survival to influenza infection.
    RESULTS: We found changes in T-cell populations in adipose tissue of high-fat diet-induced obese mice, characterized by decreased proportions of Treg cells and increased proportions of CD8+ T cells. Activated CD4+ T cells from obese mice had increased glucose uptake and oxygen consumption rate (OCR), compared to T cells from lean controls, indicating increased mitochondrial oxidation of glucose. Treatment of isolated CD4+ T cells with metformin was found to inhibit OCR in vitro and alter the expression of several activation markers. Last, treatment of obese mice with metformin, but not weight loss, was able to improve survival to influenza in obesity.
    CONCLUSIONS: T cells from obese mice have an altered metabolic profile characterized by increased glucose oxidation, which can be targeted to improve survival against influenza infection.
    DOI:  https://doi.org/10.1038/s41366-020-00692-3
  40. J Photochem Photobiol B. 2020 Sep 24. pii: S1011-1344(20)30493-0. [Epub ahead of print]212 112043
    Khatun S, Biswas S, Mahanta AK, Joseph MM, Vidyalekshmi MS, Podder A, Maiti P, Maiti KK, Bhuniya S.
      Alkaline phosphatase (ALP) is an enzyme that actively plays a significant role in the various metabolic processes by transferring a phosphate group to the protein, nucleic acid, etc. The elevated level of ALP in blood plasma is the hallmark of inflammation/cancer. The hyperactive mitochondria in cancer cells produce an excess of ATP to fulfill the high energy demand. Thus, we have developed a fluorescent probe Mito-Phos for ALP, which can detect phosphatase expression in mitochondria in live cells. The probe Mito-Phos has shown ~15-fold fluorescence intensity increments at 450 nm in the presence of 500 ng/mL of ALP. It takes about 60 min to consume the whole amount of ALP (500 ng/mL) in physiological buffer saline. It can selectively react with ALP even in the presence of other probable cellular reactive components. It is highly biocompatible and nontoxic to the live cells. It has shown ALP expression in a dose-dependent manner by providing concomitant fluorescence images in the blue-channel region. It has localized exclusively in the mitochondria in live cells. The probe Mito-Phos is highly biocompatible with the ability to assess ALP expression in mitochondria in live cells.
    Keywords:  Alkaline phosphatase; Cancer cells; Fluorescence; MTT assay; Mitochondria
    DOI:  https://doi.org/10.1016/j.jphotobiol.2020.112043