bims-camemi Biomed news
on Mitochondrial metabolism in cancer
Issue of 2019‒01‒20
forty-seven papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Cell Death Differ. 2019 Jan 18.
    Wen YA, Xiong X, Scott T, Li AT, Wang C, Weiss HL, Tan L, Bradford E, Fan TWM, Chandel NS, Barrett TA, Gao T.
      Cancer cells are known to upregulate aerobic glycolysis to promote growth, proliferation, and survival. However, the role of mitochondrial respiration in tumorigenesis remains elusive. Here we report that inhibition of mitochondrial function by silencing TFAM, a key transcription factor essential for mitochondrial DNA (mtDNA) replication and the transcription of mtDNA-encoded genes, markedly reduced tumor-initiating potential of colon cancer cells. Knockdown of TFAM significantly decreased mitochondrial respiration in colon cancer cells; however, the cellular levels of ATP remained largely unchanged as a result of increased glycolysis. This metabolic alteration rendered cancer cells highly susceptible to glucose deprivation. Interestingly, upregulation of glycolysis was independent of hypoxia-inducible factor-1 (HIF1) as TFAM knockdown cells fail to stabilize HIF1α under hypoxic conditions. Moreover, knockdown of TFAM results in decreased expression of genes-associated cancer stem cells downstream of Wnt/β-catenin signaling. Metabolic analysis reveals that the level of α-ketoglutarate (α-KG) was significantly upregulated in TFAM knockout cells. Silencing of prolyl hydroxylase domain-containing protein 2 (PHD2), a α-KG-dependent dioxyenase, rescued the expression of target genes of both HIF1α and Wnt/β-catenin. Furthermore, intestinal-specific knockout of TFAM prevents tumor formation in Apc-mutant mouse models of colon cancer. Taken together, our findings identify a novel role of mitochondria-mediated retrograde signaling in regulating Wnt signaling and tumor initiation in colon cancer.
    DOI:  https://doi.org/10.1038/s41418-018-0265-6
  2. Biochim Biophys Acta Mol Cell Biol Lipids. 2019 Jan 09. pii: S1388-1981(19)30003-4. [Epub ahead of print]
    Gürtler S, Wolke C, Otto O, Heise N, Scholz F, Laporte A, Elsner M, Jörns A, Weinert S, Döring M, Jansing S, Gardemann A, Lendeckel U, Schild L.
      The mitochondrial phospholipid cardiolipin (CL) has been implicated with mitochondrial morphology, function and, more recently, with cellular proliferation. Tafazzin, an acyltransferase with key functions in CL remodeling determining actual CL composition, affects mitochondrial oxidative phosphorylation. Here, we show that the CRISPR-Cas9 mediated knock-out of tafazzin (Taz) is associated with substantial alterations of various mitochondrial and cellular characteristics in C6 glioma cells. The knock-out of tafazzin substantially changed the profile of fatty acids incorporated in CL and the distribution of molecular CL species. Taz knock-out was further associated with decreased capacity of oxidative phosphorylation that mainly originates from impaired complex I associated energy metabolism in C6 glioma cells. The lack of tafazzin switched energy metabolism from oxidative phosphorylation to glycolysis indicated by lower respiration rates, membrane potential and higher levels of mitochondria-derived reactive oxygen species but keeping the cellular ATP content unchanged. The impact of tafazzin on mitochondria was also indicated by altered morphology and arrangement in tafazzin deficient C6 glioma cells. In the cells we observed tafazzin-dependent changes in the distribution of cellular fatty acids as an indication of altered lipid metabolism as well as in stability/morphology. Most impressive is the dramatic reduction in cell proliferation in tafazzin deficient C6 glioma cells that is not mediated by reactive oxygen species. Our data clearly indicate that defects in CL phospholipid remodeling trigger a cascade of events including modifications in CL linked to subsequent alterations in mitochondrial and cellular functions.
    Keywords:  CRISPR-Cas; Cardiolipin; Cell proliferation; Proliferation; Tafazzin
    DOI:  https://doi.org/10.1016/j.bbalip.2019.01.006
  3. FEBS J. 2019 Jan 18.
    Lunetti P, Di Giacomo M, Vergara D, De Domenico S, Maffia M, Zara V, Capobianco L, Ferramosca A.
      Mitochondrial dysfunction is a key feature of cancer and is frequently associated with increased aggressiveness and metastatic potential. Recent evidence has brought to light a metabolic re-wiring that takes place during the epithelial to mesenchymal transition (EMT), a process that drives the invasive capability of malignant tumors, and highlights a mechanistic link between mitochondrial dysfunction and EMT that has been only partially investigated. In the present study, we characterized mitochondrial function and bioenergetic status of cultured human breast cancer cell lines, including luminal-like and basal-like subtypes. Through a combination of biochemical and functional studies, we demonstrated that basal-like cell lines exhibit impaired, but not completely inactive, mitochondrial function, and rely on a consequent metabolic switch to glycolysis to support their ATP demand. These altered metabolic activities are linked to modifications of key electron transport chain proteins and a significant increase in levels of reactive oxygen species (ROS) compared to luminal cells. Furthermore, we observed that the stable knockdown of EMT markers caused functional changes in mitochondria that result in acquisition of a hybrid glycolysis/OXPHOS phenotype in cancer cells as a means to sustain their metabolic demand. This article is protected by copyright. All rights reserved.
    Keywords:   EMT ; Bioenergetic; breast cancer; mitochondria; oxidative stress
    DOI:  https://doi.org/10.1111/febs.14756
  4. Free Radic Biol Med. 2019 Jan 10. pii: S0891-5849(18)31303-0. [Epub ahead of print]
    Kikuchi R, Iwai Y, Tsuji T, Watanabe Y, Koyama N, Yamaguchi K, Nakamura H, Aoshiba K.
      The tumor microenvironment has previously been reported to be hypercapnic (as high as ~84mmHg), although its effect on tumor cell behaviors is unknown. In this study, high CO2 levels, ranging from 5% to 15%, protected lung cancer cells from anticancer agents, such as cisplatin, carboplatin and etoposide, by suppressing apoptosis. The cytoprotective effect of a high CO2 level was independent of acidosis and was due to mitochondrial metabolic reprogramming that reduced mitochondrial respiration, as assessed by oxygen consumption, oxidative phosphorylation, mitochondrial membrane and oxidative potentials, eventually leading to reduced reactive oxidant species production. In contrast, high CO2 levels did not affect cisplatin-mediated DNA damage responses or the expression of Bcl-2 family proteins. Although high CO2 levels inhibited glycolysis, this inhibition was not mechanistically involved in high CO2-mediated reductions in mitochondrial respiration, because a high CO2 concentration inhibited isolated mitochondria. A cytoprotective effect of high CO2 levels on mitochondria DNA-depleted cells was not noted, lending support to our conclusion that high CO2 levels act on mitochondria to reduce the cytotoxicity of anticancer agents. High CO2-mediated cytoprotection was also noted in a 3D culture system. In conclusion, the hypercapnic tumor microenvironment reprograms mitochondrial respiratory metabolism causing chemoresistance in lung cancer cells. Thus, tumor hypercapnia may represent a novel target to improve chemosensitivity.
    Keywords:  CO(2); Carboplatin; Cisplatin; Reactive oxygen species
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2019.01.014
  5. Mol Cell. 2019 Jan 11. pii: S1097-2765(18)31004-9. [Epub ahead of print]
    D'Amico D, Mottis A, Potenza F, Sorrentino V, Li H, Romani M, Lemos V, Schoonjans K, Zamboni N, Knott G, Schneider BL, Auwerx J.
      Little information is available about how post-transcriptional mechanisms regulate the aging process. Here, we show that the RNA-binding protein Pumilio2 (PUM2), which is a translation repressor, is induced upon aging and acts as a negative regulator of lifespan and mitochondrial homeostasis. Multi-omics and cross-species analyses of PUM2 function show that it inhibits the translation of the mRNA encoding for the mitochondrial fission factor (Mff), thereby impairing mitochondrial fission and mitophagy. This mechanism is conserved in C. elegans by the PUM2 ortholog PUF-8. puf-8 knock-down in old nematodes and Pum2 CRISPR/Cas9-mediated knockout in the muscles of elderly mice enhances mitochondrial fission and mitophagy in both models, hence improving mitochondrial quality control and tissue homeostasis. Our data reveal how a PUM2-mediated layer of post-transcriptional regulation links altered Mff translation to mitochondrial dynamics and mitophagy, thereby mediating age-related mitochondrial dysfunctions.
    Keywords:  RNA binding proteins; aging; fission/fusion; mitochondria; mitochondrial dynamics; mitophagy; neurodegeneration; protein aggregation diseases; proteostasis; ribonucleoprotein granules
    DOI:  https://doi.org/10.1016/j.molcel.2018.11.034
  6. Cell Rep. 2019 Jan 14. pii: S2211-1247(19)30018-X. [Epub ahead of print]
    Vincent AE, White K, Davey T, Philips J, Ogden RT, Lawess C, Warren C, Hall MG, Ng YS, Falkous G, Holden T, Deehan D, Taylor RW, Turnbull DM, Picard M.
      Genetic and biochemical defects of mitochondrial function are a major cause of human disease, but their link to mitochondrial morphology in situ has not been defined. Here, we develop a quantitative three-dimensional approach to map mitochondrial network organization in human muscle at electron microscopy resolution. We establish morphological differences between human and mouse and among patients with mitochondrial DNA (mtDNA) diseases compared to healthy controls. We also define the ultrastructure and prevalence of mitochondrial nanotunnels, which exist as either free-ended or connecting membrane protrusions across non-adjacent mitochondria. A multivariate model integrating mitochondrial volume, morphological complexity, and branching anisotropy computed across individual mitochondria and mitochondrial populations identifies increased proportion of simple mitochondria and nanotunnels as a discriminant signature of mitochondrial stress. Overall, these data define the nature of the mitochondrial network in human muscle, quantify human-mouse differences, and suggest potential morphological markers of mitochondrial dysfunction in human tissues.
    Keywords:  3D morphometry; imaging; machine learning; mitochondrial disease; mitochondrion; nanotunnel; reconstruction; reticulum; serial block-face SEM; skeletal muscle
    DOI:  https://doi.org/10.1016/j.celrep.2019.01.010
  7. Oncol Lett. 2019 Jan;17(1): 697-705
    Fonseca J, Moradi F, Maddalena LA, Ferreira-Tollstadius B, Selim S, Stuart JA.
      Resveratrol (RES) is a polyphenol produced by certain plant species that has been well studied due to its ability to slow the growth of cancer cells. In numerous cell types and tissues, RES has been demonstrated to promote mitochondrial biogenesis, fusion, and oxidative phosphorylation. The present study investigated the interaction between RES's effects on growth and metabolism in PC3 prostate cancer cells, and demonstrated that RES-mediated growth inhibition is only observed under conditions in which a metabolic shift from glucose fermentation to mitochondrial respiration can occur. When this shift was prevented by growing cells in galactose medium or by pharmacologically inhibiting prolyl hydroxylase (PHD) in order to stabilize hypoxia inducible factor-1α, RES did not effect mitochondrial fusion, biogenesis, respiration or cell growth. Similar results were observed in PC3 cells expressing a mutant HIF-1α lacking the prolines that are hydroxylated by PHD to promote its degradation. Thus, RES appears to slow PC3 cell growth by interfering with glucose fermentation and promoting respiration. Consistent with this, RES was observed to be particularly effective at inhibiting PC3 cell growth under hypoxic conditions that precluded increased reliance on oxidative phosphorylation. These observations are important in understanding how RES may affect cancer cell growth in vivo where hypoxia is common in growing tumours.
    Keywords:  HIF-1; bioenergetics; cancer; fission; fusion; hypoxia-inducible factor; mitochondria; mitochondrial dynamics; resveratrol
    DOI:  https://doi.org/10.3892/ol.2018.9526
  8. Cell Rep. 2019 Jan 15. pii: S2211-1247(18)32015-1. [Epub ahead of print]26(3): 518-528.e6
    Kojima R, Kakimoto Y, Furuta S, Itoh K, Sesaki H, Endo T, Tamura Y.
      Mitochondria are dynamic organelles that constantly fuse and divide to maintain their proper morphology, which is essential for their normal functions. Energy production, a central role of mitochondria, demands highly folded structures of the mitochondrial inner membrane (MIM) called cristae and a dimeric phospholipid (PL) cardiolipin (CL). Previous studies identified a number of factors involved in mitochondrial dynamics, crista formation, and CL biosynthesis, yet it is still enigmatic how these events are interconnected and cooperated. Here, we first report that mitochondrial fusion-division dynamics are important to maintain CL abundance. Second, our genetic and biochemical analyses revealed that intra-mitochondrial PL transport plays an important role in crista formation. Finally, we show that simultaneous defects in MIM fusion and intra-mitochondrial PL transport cause a drastic decrease in crista structure, resulting in CL depletion. These results expand our understanding of the integrated functional network among the PL transport, crista formation, and CL biogenesis.
    Keywords:  cardiolipin; cristae; mitochondria; mitochondrial division; mitochondrial fusion; phospholipid; yeast
    DOI:  https://doi.org/10.1016/j.celrep.2018.12.070
  9. Nat Commun. 2019 Jan 18. 10(1): 329
    Ferreira JCB, Campos JC, Qvit N, Qi X, Bozi LHM, Bechara LRG, Lima VM, Queliconi BB, Disatnik MH, Dourado PMM, Kowaltowski AJ, Mochly-Rosen D.
      We previously demonstrated that beta II protein kinase C (βIIPKC) activity is elevated in failing hearts and contributes to this pathology. Here we report that βIIPKC accumulates on the mitochondrial outer membrane and phosphorylates mitofusin 1 (Mfn1) at serine 86. Mfn1 phosphorylation results in partial loss of its GTPase activity and in a buildup of fragmented and dysfunctional mitochondria in heart failure. βIIPKC siRNA or a βIIPKC inhibitor mitigates mitochondrial fragmentation and cell death. We confirm that Mfn1-βIIPKC interaction alone is critical in inhibiting mitochondrial function and cardiac myocyte viability using SAMβA, a rationally-designed peptide that selectively antagonizes Mfn1-βIIPKC association. SAMβA treatment protects cultured neonatal and adult cardiac myocytes, but not Mfn1 knockout cells, from stress-induced death. Importantly, SAMβA treatment re-establishes mitochondrial morphology and function and improves cardiac contractility in rats with heart failure, suggesting that SAMβA may be a potential treatment for patients with heart failure.
    DOI:  https://doi.org/10.1038/s41467-018-08276-6
  10. J Cell Physiol. 2019 Jan 13.
    Miller BA, Wang J, Song J, Zhang XQ, Hirschler-Laszkiewicz I, Shanmughapriya S, Tomar D, Rajan S, Feldman AM, Madesh M, Sheu SS, Cheung JY.
      The mechanisms by which Trpm2 channels enhance mitochondrial bioenergetics and protect against oxidative stress-induced cardiac injury remain unclear. Here, the role of proline-rich tyrosine kinase 2 (Pyk2) in Trpm2 signaling is explored. Activation of Trpm2 in adult myocytes with H2 O2 resulted in 10- to 21-fold increases in Pyk2 phosphorylation in wild-type (WT) myocytes which was significantly lower (~40%) in Trpm2 knockout (KO) myocytes. Pyk2 phosphorylation was inhibited (~54%) by the Trpm2 blocker clotrimazole. Buffering Trpm2-mediated Ca2+ increase with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) resulted in significantly reduced pPyk2 in WT but not in KO myocytes, indicating Ca2+ influx through activated Trpm2 channels phosphorylated Pyk2. Part of phosphorylated Pyk2 translocated from cytosol to mitochondria which has been previously shown to augment mitochondrial Ca2+ uptake and enhance adenosine triphosphate generation. Although Trpm2-mediated Ca2+ influx phosphorylated Ca2+ -calmodulin kinase II (CaMKII), the CaMKII inhibitor KN93 did not significantly affect Pyk2 phosphorylation in H2 O2 -treated WT myocytes. After ischemia/reperfusion (I/R), Pyk2 phosphorylation and its downstream prosurvival signaling molecules (pERK1/2 and pAkt) were significantly lower in KO-I/R when compared with WT-I/R hearts. After hypoxia/reoxygenation, mitochondrial membrane potential was lower and superoxide level was higher in KO myocytes, and were restored to WT values by the mitochondria-targeted superoxide scavenger MitoTempo. Our results suggested that Ca2+ influx via tonically activated Trpm2 phosphorylated Pyk2, part of which translocated to mitochondria, resulting in better mitochondrial bioenergetics to maintain cardiac health. After I/R, Pyk2 activated prosurvival signaling molecules and prevented excessive increases in reactive oxygen species, thereby affording protection from I/R injury.
    Keywords:  hypoxia-reoxygenation; ischemic cardiomyopathy; mitochondrial oxidants; oxidative injury; voltage-independent Ca2+ channels
    DOI:  https://doi.org/10.1002/jcp.28146
  11. J Nutr Biochem. 2018 Nov 22. pii: S0955-2863(18)30681-8. [Epub ahead of print]65 83-92
    Schnell DM, Walton RG, Vekaria HJ, Sullivan PG, Bollinger LM, Peterson CA, Thomas DT.
      Vitamin D has been connected with increased intramyocellular lipid (IMCL) and has also been shown to increase mitochondrial function and insulin sensitivity. Evidence suggests that perilipin 2 (PLIN2), a perilipin protein upregulated with calcitriol treatment, may be integral to managing increased IMCL capacity and lipid oxidation in skeletal muscle. Therefore, we hypothesized that PLIN2 is required for vitamin D induced IMCL accumulation and increased mitochondrial oxidative function. To address this hypothesis, we treated C2C12 myotubes with 100 nM calcitriol (the active form of vitamin D) and/or PLIN2 siRNA in a four group design and analyzed markers of IMCL accumulation and metabolism using qRT-PCR, cytochemistry, and oxygen consumption assay. Expression of PLIN2, but not PLIN3 or PLIN5 mRNA was increased with calcitriol, and PLIN2 induction was prevented with siRNA knockdown without compensation by other perilipins. PLIN2 knockdown did not appear to prevent lipid accumulation. Calcitriol treatment increased mRNA expression of triglyceride synthesizing genes DGAT1 and DGAT2 and also lipolytic genes ATGL and CGI-58. PLIN2 knockdown decreased the expression of CGI-58 and CPT1, and was required for calcitriol-induced upregulation of DGAT2. Calcitriol increased oxygen consumption rate while PLIN2 knockdown decreased oxygen consumption rate. PLIN2 was required for a calcitriol-induced increase in oxygen consumption driven by mitochondrial complex II. We conclude that calcitriol increases mitochondrial function in myotubes and that this increase is at least in part mediated by PLIN2.
    Keywords:  C2C12; Lipid droplet; Metabolism; Mitochondria; PLIN2; Skeletal muscle; Vitamin D
    DOI:  https://doi.org/10.1016/j.jnutbio.2018.11.002
  12. Nature. 2019 Jan 16.
    Stegen S, Laperre K, Eelen G, Rinaldi G, Fraisl P, Torrekens S, Van Looveren R, Loopmans S, Bultynck G, Vinckier S, Meersman F, Maxwell PH, Rai J, Weis M, Eyre DR, Ghesquière B, Fendt SM, Carmeliet P, Carmeliet G.
      Endochondral ossification, an important process in vertebrate bone formation, is highly dependent on correct functioning of growth plate chondrocytes1. Proliferation of these cells determines longitudinal bone growth and the matrix deposited provides a scaffold for future bone formation. However, these two energy-dependent anabolic processes occur in an avascular environment1,2. In addition, the centre of the expanding growth plate becomes hypoxic, and local activation of the hypoxia-inducible transcription factor HIF-1α is necessary for chondrocyte survival by unidentified cell-intrinsic mechanisms3-6. It is unknown whether there is a requirement for restriction of HIF-1α signalling in the other regions of the growth plate and whether chondrocyte metabolism controls cell function. Here we show that prolonged HIF-1α signalling in chondrocytes leads to skeletal dysplasia by interfering with cellular bioenergetics and biosynthesis. Decreased glucose oxidation results in an energy deficit, which limits proliferation, activates the unfolded protein response and reduces collagen synthesis. However, enhanced glutamine flux increases α-ketoglutarate levels, which in turn increases proline and lysine hydroxylation on collagen. This metabolically regulated collagen modification renders the cartilaginous matrix more resistant to protease-mediated degradation and thereby increases bone mass. Thus, inappropriate HIF-1α signalling results in skeletal dysplasia caused by collagen overmodification, an effect that may also contribute to other diseases involving the extracellular matrix such as cancer and fibrosis.
    DOI:  https://doi.org/10.1038/s41586-019-0874-3
  13. Hum Mol Genet. 2019 Jan 11.
    Larrea D, Pera M, Gonelli A, Cabrera RQ, Akman HO, Guardia-Laguarta C, Velasco KR, Area-Gomez E, Dal Bello F, De Stefani D, Horvath R, Shy ME, Schon EA, Giacomello M.
      Charcot-Marie-Tooth disease (CMT) type 2A is an axonal form of peripheral neuropathy, due almost exclusively to dominant mutations in the nuclear gene encoding the mitochondrial protein mitofusin-2 (MFN2). However, there is no understanding of the relationship of clinical phenotype to genotype. MFN2 has two functions: it promotes inter-mitochondrial fusion and mediates ER-mitochondrial tethering at mitochondria-associated ER membranes (MAM). MAM regulates a number of key cellular functions, including lipid and calcium homeostasis, and mitochondrial behavior. To date, no studies have been performed to address whether mutations in MFN2 in CMT2A patient cells affect MAM function, which might provide insight into pathogenesis. Using fibroblasts from three CMT2AMFN2 patients with different mutations in MFN2, we found that some, but not all, examined aspects of ER-mitochondrial connectivity and of MAM function were indeed altered, and correlated with disease severity. Notably, however, respiratory chain function in those cells was unimpaired. Our results suggest that CMT2AMFN2 is a MAM-related disorder but is not a respiratory chain-deficiency disease. The alterations in MAM function described here could also provide insight into the pathogenesis of other forms of CMT.
    DOI:  https://doi.org/10.1093/hmg/ddz008
  14. J Heart Lung Transplant. 2018 Dec 21. pii: S1053-2498(18)31790-X. [Epub ahead of print]
    Wyss RK, Méndez-Carmona N, Sanz MN, Arnold M, Segiser A, Fiedler GM, Carrel TP, Djafarzadeh S, Tevaearai Stahel HT, Longnus SL.
      BACKGROUND: Cardioprotection and graft evaluation after ischemia-reperfusion (IR) are essential in facilitating heart transplantation with donation after circulatory death. Given the key role of mitochondria in IR, we aimed to investigate the tolerance of cardiac mitochondria to warm, global ischemia and to determine the predictive value of early reperfusion mitochondria-related parameters for post-ischemic cardiac recovery.METHODS: Isolated, working rat hearts underwent 0, 21, 24, 27, 30, or 33 minutes of warm, global ischemia, followed by 60 minutes of reperfusion. Functional recovery (developed pressure × heart rate) was determined at 60 minutes of reperfusion, whereas mitochondrial integrity was measured at 10 minutes of reperfusion.
    RESULTS: Functional recovery at 60 minutes of reperfusion decreased with ≥ 27 minutes of ischemia vs no ischemia (n = 7-8/group; p < 0.01). Cytochrome c, succinate release, and mitochondrial Ca2+ content increased with ≥ 27 minutes of ischemia vs no ischemia (p < 0.05). Ischemia at ≥ 21 minutes decreased mitochondrial coupling, adenosine 5'-triphosphate content, mitochondrial Ca2+ retention capacity, and increased oxidative damage vs no ischemia (p < 0.05). Reactive oxygen species (ROS) from reverse electron transfer increased with 21 and 27 minutes of ischemia vs no ischemia and 33 minutes of ischemia (p < 0.05), whereas ROS from forward electron transfer increased only with 33 minutes of ischemia vs no ischemia (p < 0.05). Mitochondrial coupling and adenosine 5'-triphosphate content correlated positively and cytochrome c, succinate, oxidative damage, and mitochondrial Ca2+ content correlated negatively with cardiac functional recovery (p < 0.05).
    CONCLUSIONS: Mitochondrial dysfunction occurs with shorter periods of ischemia than cardiac dysfunction. Mitochondrial coupling, ROS emission from reverse electron transfer, and calcium retention are particularly sensitive to early reperfusion injury, reflecting potential targets for cardioprotection. Indicators of mitochondrial integrity may be of aid in evaluating suitability of donation after circulatory death grafts for transplantation.
    Keywords:  cardioprotection; donation after circulatory death (DCD); functional recovery; heart transplantation; ischemia-reperfusion; mitochondria; reverse electron transfer
    DOI:  https://doi.org/10.1016/j.healun.2018.12.013
  15. Biol Chem. 2018 Dec 01. pii: /j/bchm.just-accepted/hsz-2018-0446/hsz-2018-0446.xml. [Epub ahead of print]
    Vriend J, Hoogstraten CA, Venrooij KR, Berge BTVD, Govers LP, Rooij AV, Huigen MCDG, Schirris TJJ, Russel FGM, Masereeuw R, Wilmer MJ.
      Organic anion transporter (OAT) 1 and 3 are, besides uptake transporters, key in several cellular metabolic pathways. The underlying mechanisms are largely unknown. Hence, we used human conditionally immortalized proximal tubule epithelial cells (ciPTEC) overexpressing OAT1 or OAT3 to gain insight into these mechanisms. In ciPTEC-OAT1 and -OAT3, extracellular lactate levels were decreased (by 77% and 71%, respectively), while intracellular ATP levels remained unchanged, suggesting a shift towards an oxidative phenotype upon OAT1 or OAT3 overexpression. This was confirmed by increased respiration of ciPTEC-OAT1 and -OAT3 (1.4-fold), a decreased sensitivity to respiratory inhibition, and characterized by a higher demand on mitochondrial oxidative capacity. In-depth profiling of tricarboxylic acid (TCA) cycle metabolites revealed reduced levels of intermediates converging into α-ketoglutarate in ciPTEC-OAT1 and -OAT3, which via 2-hydroxyglutarate metabolism explains the increased respiration. These interactions with TCA cycle metabolites were in agreement with metabolomic network modeling studies published earlier. Further studies using OAT or oxidative phosphorylation (OXPHOS) inhibitors confirmed our idea that OATs are responsible for increased use and synthesis of α-ketoglutarate. In conclusion, our results indicate an increased α-ketoglutarate efflux by OAT1 and OAT3, resulting in a metabolic shift towards an oxidative phenotype.
    Keywords:  OAT1; OAT3; TCA cycle; cellular energy metabolism; renal proximal tubule epithelial cells; α-ketoglutarate
    DOI:  https://doi.org/10.1515/hsz-2018-0446
  16. BMC Plant Biol. 2019 Jan 15. 19(1): 27
    Aguilera-Alvarado GP, Guevara-García ÁA, Estrada-Antolín SA, Sánchez-Nieto S.
      BACKGROUND: Seed germination is a crucial process in the plant life cycle when a dramatic variation of type and sugar content occurs just as the seed is hydrated. The production of hexose 6 phosphate is a key node in different pathways that are required for a successful germination. Hexokinase (HXK) is the only plant enzyme that phosphorylates glucose (Glc), so it is key to fueling several metabolic pathways depending on their substrate specificity, metabolite regulatory responses and subcellular localization. In maize, the HXK family is composed of nine genes, but only six of them (ZmHXK4-9) putatively encode catalytically active enzymes. Here, we cloned and functionally characterized putative catalytic enzymes to analyze their metabolic contribution during germination process.RESULTS: From the six HXKs analyzed here, only ZmHXK9 has minimal hexose phosphorylating activity even though enzymatic function of all isoforms (ZmHXK4-9) was confirmed using a yeast complementation approach. The kinetic parameters of recombinant proteins showed that ZmHXK4-7 have high catalytic efficiency for Glc, fructose (Fru) and mannose (Man), ZmHXK7 has a lower Km for ATP, and together with ZmHXK8 they have lower sensitivity to inhibition by ADP, G6P and N-acetylglucosamine than ZmHXK4-6 and ZmHXK9. Additionally, we demonstrated that ZmHXK4-6 and ZmHXK9 are located in the mitochondria and their location relies on the first 30 amino acids of the N-terminal domain. Otherwise, ZmHXK7-8 are constitutively located in the cytosol. HXK activity was detected in cytosolic and mitochondrial fractions and high Glc and Fru phosphorylating activities were found in imbibed embryos.
    CONCLUSIONS: Considering the biochemical characteristics, location and the expression of ZmHXK4 at onset of germination, we suggest that it is the main contributor to mitochondrial activity at early germination times, at 24 h other ZmHXKs also contribute to the total activity. While in the cytosol, ZmHXK7 could be responsible for the activity at the onset of germination, although later, ZmHXK8 also contributes to the total HXK activity. Our observations suggest that the HXKs may be redundant proteins with specific roles depending on carbon and ATP availability, metabolic needs, or sensor requirements. Further investigation is necessary to understand their specific or redundant physiological roles.
    Keywords:  Biochemical characterization; Cytosolic HXK; Germination; Hexokinase; Maize; Mitochondrial hexokinase
    DOI:  https://doi.org/10.1186/s12870-018-1605-x
  17. Cancer Res. 2019 Jan 18. pii: canres.2505.2018. [Epub ahead of print]
    Fan S, Tian T, Chen W, Lv X, Lei X, Zhang H, Sun S, Cai L, Pan G, He L, Ou Z, Lin X, Wang X, Perez MF, Tu Z, Ferrone S, Tannous BA, Li J.
      MicroRNAs (miRNA) that translocate from the nucleus to mitochondria are referred to as mitochondrial microRNAs (mitomiR). mitomiR have been shown to modulate the translational activity of the mitochondrial genome, yet their role in mitochondrial DNA(mtDNA) transcription remains to be determined. Here we report that the mitomiR-2392 regulates chemoresistance in tongue squamous cell carcinoma (TSCC) cells by reprogramming metabolism via downregulation of oxidative phosphorylation (OXPHOS) and upregulation of glycolysis. These effects were mediated through partial inhibition of mtDNA transcription by mitomiR-2392 rather than through translational regulation. This repression required specific miRNA-mtDNA base pairing and Argonaute 2 (AGO2). mitomiR-2392 recognized target sequences in the H-strand and partially inhibited polycistronic mtDNA transcription in a cell-specific manner. A retrospective analysis of TSCC patient tumors revealed a significant association of miR-2392 and regulated mitochondrial gene expression with chemosensitivity and overall survival. The clinical relevance of targeted mitochondrial genes was consistently validated by TCGA RNA sequencing in multiple types of cancer. Our study revealed for the first time the role of mitomiR in mtDNA transcription and its contribution to the molecular basis of tumor cell metabolism and chemoresistance.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-18-2505
  18. Cell Rep. 2019 Jan 15. pii: S2211-1247(18)32052-7. [Epub ahead of print]26(3): 759-774.e5
    Habich M, Salscheider SL, Murschall LM, Hoehne MN, Fischer M, Schorn F, Petrungaro C, Ali M, Erdogan AJ, Abou-Eid S, Kashkar H, Dengjel J, Riemer J.
      Disulfide formation in the mitochondrial intermembrane space (IMS) is an essential process. It is catalyzed by the disulfide relay machinery, which couples substrate import and oxidation. The machinery relies on the oxidoreductase and chaperone CHCHD4-Mia40. Here, we report on the driving force for IMS import and on a redox quality control mechanism. We demonstrate that unfolded reduced proteins, upon translocation into the IMS, initiate formation of a metastable disulfide-linked complex with CHCHD4. If this interaction does not result in productive oxidation, then substrates are released to the cytosol and degraded by the proteasome. Based on these data, we propose a redox quality control step at the level of the disulfide-linked intermediate that relies on the vectorial nature of IMS import. Our findings also provide the mechanistic framework to explain failures in import of numerous human disease mutants in CHCHD4 substrates.
    Keywords:  CHCHD4; Mia40; disulfide formation; disulfide relay; intermembrane space; oxidative folding; proteasome; quality control; vectorial import
    DOI:  https://doi.org/10.1016/j.celrep.2018.12.092
  19. Nucleic Acids Res. 2019 Jan 16.
    Alessio E, Buson L, Chemello F, Peggion C, Grespi F, Martini P, Massimino ML, Pacchioni B, Millino C, Romualdi C, Bertoli A, Scorrano L, Lanfranchi G, Cagnin S.
      Long non-coding RNAs (lncRNAs) are emerging as important players in the regulation of several aspects of cellular biology. For a better comprehension of their function, it is fundamental to determine their tissue or cell specificity and to identify their subcellular localization. In fact, the activity of lncRNAs may vary according to cell and tissue specificity and subcellular compartmentalization. Myofibers are the smallest complete contractile system of skeletal muscle influencing its contraction velocity and metabolism. How lncRNAs are expressed in different myofibers, participate in metabolism regulation and muscle atrophy or how they are compartmentalized within a single myofiber is still unknown. We compiled a comprehensive catalog of lncRNAs expressed in skeletal muscle, associating the fiber-type specificity and subcellular location to each of them, and demonstrating that many lncRNAs can be involved in the biological processes de-regulated during muscle atrophy. We demonstrated that the lncRNA Pvt1, activated early during muscle atrophy, impacts mitochondrial respiration and morphology and affects mito/autophagy, apoptosis and myofiber size in vivo. This work corroborates the importance of lncRNAs in the regulation of metabolism and neuromuscular pathologies and offers a valuable resource to study the metabolism in single cells characterized by pronounced plasticity.
    DOI:  https://doi.org/10.1093/nar/gkz007
  20. Circulation. 2019 Jan 14.
    Ma H, Yu S, Liu X, Zhang Y, Fakadej T, Liu Z, Yin C, Shen W, Locasale JW, Taylor JM, Qian L, Liu J.
      BACKGROUND: Hypertrophic response to pathological stimuli is a complex biological process that involves transcriptional and epigenetic regulation of the cardiac transcriptome. Though previous studies have implicated transcriptional factors and signaling molecules in pathological hypertrophy, the role of RNA-binding protein (RBP) in this process has received little attention.METHODS: Here we used transverse aortic constriction (TAC) and in vitro cardiac hypertrophy models to characterize the role of an evolutionary conserved RBP Lin28a in pathological cardiac hypertrophy. Next generation sequencing, RNA immunoprecipitation and gene expression analyses were applied to identify the downstream targets of Lin28a. Epistatic analysis, metabolic assays and flux analysis were further utilized to characterize the effects of Lin28a and its downstream mediator in cardiomyocyte hypertrophic growth and metabolic remodeling.
    RESULTS: Cardiac-specific deletion of Lin28a attenuated pressure overload-induced hypertrophic growth, cardiac dysfunction and alterations in cardiac transcriptome. Mechanistically, Lin28a directly bound to mitochondrial phosphoenolpyruvate carboxykinase 2 ( Pck2) mRNA and increased its transcript level. Increasing Pck2 was sufficient to promote hypertrophic growth similar to that caused by increasing Lin28a, whereas knocking down Pck2 attenuated norepinephrine-induced cardiac hypertrophy. Epistatic analysis demonstrated that Pck2 mediated, at least in part, the role of Lin28a in cardiac hypertrophic growth. Furthermore, metabolomic analyses highlighted role for Lin28a and Pck2 in promoting cardiac biosynthesis required for cell growth.
    CONCLUSIONS: Our study demonstrates that Lin28a promotes pathological cardiac hypertrophy and glycolytic reprograming, at least in part by binding to and stabilizing Pck2 mRNA.
    Keywords:  Biosynthesis; Glycolysis; Lin28a; Pathological cardiac hypertrophy; Pck2
    DOI:  https://doi.org/10.1161/CIRCULATIONAHA.118.037803
  21. Postepy Biochem. 2018 Oct 25. 64(3): 196-212
    Szewczyk A, Bednarczyk P, Jędraszko J, Kampa RP, Koprowski P, Krajewska M, Kucman S, Kulawiak B, Laskowski M, Rotko D, Sęk A, Walewska A, Żochowska M, Wrzosek A.
      Mitochondria play a fundamental role in ATP synthesis within the majority of mammalian cells. Potassium channels present in the inner mitochondrial membrane are fine regulators of mitochondrial function, based on inner membrane K+ permeability. These channels are regulated by a plethora of factors and conditions in a way similar to plasma membrane potassium channels. Regulators of mitochondrial potassium channels include the membrane potential, calcium ions, free fatty acids and ATP levels within the cells. Recently, it was shown that these channels are regulated by the respiratory chain, stretching of the membrane and phosphorylation. The essential interest that has driven studies of mitochondrial potassium channels for nearly 25 years is their role in cytoprotection and in cell death. Mitochondrial potassium channels have been described in neurons, astrocytoma, cardiac and skeletal muscles, fibroblasts, keratinocytes and endothelial cells. In this overview, we summarize the current knowledge of mitochondrial potassium channels. This summary will be done with a special focus on studies performed over the last 20 years in the Laboratory of Intracellular Ion Channels at the Nencki Institute. These include studies on the electrophysiological and pharmacological properties of mitochondrial potassium channels and on their regulation by endogenous intracellular substances. Additionally, the regulation of mitochondrial potassium channels by the respiratory chain and by stretching of the inner mitochondrial membrane will be reviewed. Properties of mitochondrial potassium channels in various organisms will also be summarized.
  22. Mol Cancer Res. 2019 Jan 15. pii: molcanres.0347.2018. [Epub ahead of print]
    Balaban S, Nassar ZD, Zhang AY, Hosseini-Beheshti E, Centenera MM, Schreuder M, Lin HM, Aishah A, Varney B, Liu-Fu F, Lee LS, Nagarajan SR, Shearer RF, Hardie RA, Raftopulos NL, Kakani MS, Saunders DN, Holst J, Horvath LG, Butler LM, Hoy AJ.
      Prostate cancer cells exhibit altered cellular metabolism but, notably, not the hallmarks of Warburg metabolism. Prostate cancer cells exhibit increased de novo synthesis of fatty acids (FA); however, little is known about how extracellular FAs, such as those in the circulation, may support prostate cancer progression. Here, we show that increasing FA availability increased intracellular triacylglycerol content in cultured patient-derived tumor explants, LNCaP and C4-2B spheroids, a range of prostate cancer cells (LNCaP, C4-2B, 22Rv1, PC-3), and prostate epithelial cells (PNT1). Extracellular FAs are the major source (~83%) of carbons to the total lipid pool in all cell lines, compared to glucose (~13%) and glutamine (~4%), and FA oxidation rates are greater in prostate cancer cells compared to PNT1 cells, which preferentially partitioned extracellular FAs into triacylglycerols. Due to the higher rates of FA oxidation in C4-2B cells, cells remained viable when challenged by the addition of palmitate to culture media and inhibition of mitochondrial FA oxidation sensitized C4-2B cells to palmitate-induced apoptosis. Whereas in PC-3 cells, palmitate induced apoptosis, which was prevented by pre-treatment of PC-3 cells with FAs, and this protective effect required DGAT-1-mediated triacylglycerol synthesis. These outcomes highlight for the first-time heterogeneity of lipid metabolism in prostate cancer cells and the potential influence that obesity-associated dyslipidemia or host circulating has on prostate cancer progression. Implications: Extracellular-derived FAs are primary building blocks for complex lipids and heterogeneity in FA metabolism exists in prostate cancer that can influence tumor cell behavior.
    DOI:  https://doi.org/10.1158/1541-7786.MCR-18-0347
  23. FASEB J. 2019 Jan 17. fj201801862R
    Ballarò R, Beltrà M, De Lucia S, Pin F, Ranjbar K, Hulmi JJ, Costelli P, Penna F.
      Cancer cachexia is a multifactorial syndrome characterized by anorexia, body wasting, and muscle and adipose tissue loss, impairing patient's tolerance to anticancer treatments and survival. The aim of the present study was to compare the effects induced in mice by tumor growth alone (C26) or in combination with chemotherapy [C26 oxaliplatin and 5-fluorouracil (oxfu)] and to evaluate the potential of moderate exercise. Oxfu administration to C26 mice exacerbated muscle wasting and triggered autophagy or mitophagy, decreased protein synthesis, and induced mitochondrial alterations. Exercise in C26 oxfu mice counteracted the loss of muscle mass and strength, partially rescuing autophagy and mitochondrial function. Nevertheless, exercise worsened survival in C26 oxfu mice in late stages of cachexia. In summary, chemotherapy further impinges on cancer-induced alterations, worsening muscle wasting. An ideal multifactorial and early intervention to prevent cancer cachexia could take advantage of exercise, improving patient's energy metabolism, mobility, and quality of life.-Ballarò, R., Beltrà, M., De Lucia, S., Pin, F., Ranjbar, K., Hulmi, J. J., Costelli, P., Penna, F. Moderate exercise in mice improves cancer plus chemotherapy-induced muscle wasting and mitochondrial alterations.
    Keywords:  PGC-1α; autophagy; cancer cachexia; mitochondria; survival
    DOI:  https://doi.org/10.1096/fj.201801862R
  24. Glia. 2019 Jan 13.
    Nair S, Sobotka KS, Joshi P, Gressens P, Fleiss B, Thornton C, Mallard C, Hagberg H.
      Accumulating evidence suggests that changes in the metabolic signature of microglia underlie their response to inflammation. We sought to increase our knowledge of how pro-inflammatory stimuli induce metabolic changes. Primary microglia exposed to lipopolysaccharide (LPS)-expressed excessive fission leading to more fragmented mitochondria than tubular mitochondria. LPS-mediated Toll-like receptor 4 (TLR4) activation also resulted in metabolic reprogramming from oxidative phosphorylation to glycolysis. Blockade of mitochondrial fission by Mdivi-1, a putative mitochondrial division inhibitor led to the reversal of the metabolic shift. Mdivi-1 treatment also normalized the changes caused by LPS exposure, namely an increase in mitochondrial reactive oxygen species production and mitochondrial membrane potential as well as accumulation of key metabolic intermediate of TCA cycle succinate. Moreover, Mdivi-1 treatment substantially reduced LPS induced cytokine and chemokine production. Finally, we showed that Mdivi-1 treatment attenuated expression of genes related to cytotoxic, repair, and immunomodulatory microglia phenotypes in an in vivo neuroinflammation paradigm. Collectively, our data show that the activation of microglia to a classically pro-inflammatory state is associated with a switch to glycolysis that is mediated by mitochondrial fission, a process which may be a pharmacological target for immunomodulation.
    Keywords:  inflammation; metabolism; microglia; mitochondria; mitochondrial fission
    DOI:  https://doi.org/10.1002/glia.23587
  25. J Mol Cell Cardiol. 2019 Jan 09. pii: S0022-2828(18)31061-7. [Epub ahead of print]
    Nomura M, Liu J, Yu ZX, Yamazaki T, Yan Y, Kawagishi H, Rovira II, Liu C, Wolfgang MJ, Mukouyama YS, Finkel T.
      Atherosclerosis is a chronic disorder of the vessel wall. One key regulator of disease progression is lipid handling in macrophages. However, the role of macrophage mitochondrial-dependent fatty acid β-oxidation (FAO) in atherosclerosis is not well defined. To address this, we focused on carnitine palmitoyltransferase (CPT) 1 and 2, which play an essential role in the transport of long chain fatty acids (FAs) into the mitochondria. Using conditional alleles of these mitochondrial enzymes, we have generated myeloid-specific Cpt1a and Cpt2 knockout mutants (CPT1a M-KO and CPT2 M-KO). In culture, macrophages derived from CPT1a and CPT2 M-KO mice have impaired FAO, enhanced expression of the CD36 scavenger receptor, increased uptake of oxidized low-density lipoprotein (oxLDL), and augmented transformation into cholesterol-rich foam cells. In line with these in vitro observations, in the atherosclerosis-susceptible apolipoprotein E (ApoE) KO background, CPT2 M-KO mice demonstrated augmented atherosclerosis, accompanied by increased accumulation of aortic macrophages with elevated CD36 expression. These data suggest that macrophage FAO is athero-protective and that augmenting FAO may potentially slow atherosclerotic progression.
    DOI:  https://doi.org/10.1016/j.yjmcc.2019.01.003
  26. Mol Cell. 2019 Jan 17. pii: S1097-2765(18)31100-6. [Epub ahead of print]73(2): 197-198
    Chipuk JE.
      In this issue of Molecular Cell, Cho et al. (2019) identify a mechanism by which the mitochondrial division machinery provides selective pressure to identify dysfunctional organelles through the coordinated action of DRP1, Zip1, and Zn2+ transport into mitochondria.
    DOI:  https://doi.org/10.1016/j.molcel.2018.12.024
  27. Circulation. 2019 Jan 16.
    Wu S, Lu Q, Ding Y, Wu Y, Qiu Y, Wang P, Mao X, Huang K, Xie Z, Zou MH.
      BACKGROUND: FUN14 domain containing 1 (Fundc1), an outer mitochondrial membrane protein, is important for mitophagy and mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs). The roles of Fundc1 and MAMs in diabetic hearts remain unknown. The aims of this study therefore, were to determine if the diabetes-induced Fundc1 expression could increase MAM formation, and whether disruption of MAM formation improves diabetic cardiac function.METHODS: Levels of FUNDC1 were examined in the hearts from diabetic patients and nondiabetic donors. Levels of Fundc1-induced MAMs, and mitochondrial and heart function were examined in mouse neonatal cardiomyocytes exposed to high glucose (HG, 30 mmol/L Dglucose for 48 h), as well as in streptozotocin (STZ)-treated cardiac-specific Fundc1 knockout (KO) mice and cardiac-specific Fundc1 KO diabetic Akita mice.
    RESULTS: FUNDC1 levels were significantly elevated in cardiac tissues from diabetic patients compared to those in non-diabetic donors. In cultured mouse neonatal cardiomyocytes, HG conditions increased levels of Fundc1, the inositol 1,4,5-trisphosphate type 2 receptor (Ip3r2), and MAMs. Genetic downregulation of either Fundc1 or Ip3r2 inhibited MAM formation, reduced ER-mitochondrial Ca2+ flux, and improved mitochondrial function in HG-treated cardiomyocytes. Consistently, adenoviral overexpression of Fundc1 promoted MAM formation, mitochondrial Ca2+ increase, and mitochondrial dysfunction in cardiomyocytes exposed to normal glucose (5.5 mmol/L D-glucose). Compared with non-diabetic controls, levels of Fundc1, Ip3r2, and MAMs were significantly increased in hearts from STZ-treated mice and Akita mice. Further, compared with control hearts, diabetes markedly increased co-immunoprecipitation of Fundc1 and Ip3r2. The binding of Fundc1 to Ip3r2 inhibits Ip3r2 ubiquitination and proteasomemediated degradation. Cardiomyocyte-specific Fundc1 deletion ablated diabetes-induced MAM formation, prevented mitochondrial Ca2+ increase, mitochondrial fragmentation, and apoptosis with improved mitochondrial functional capacity and cardiac function. In mouse neonatal cardiomyocytes, HG suppressed AMP-activated protein kinase (Ampk) activity. Furthermore, in cardiomyocytes of Prkaa2 KO mice, expression of Fundc1, MAM formation, and mitochondrial Ca2+ levels were significantly increased. Finally, adenoviral overexpression of a constitutively active mutant Ampk ablated HG-induced MAM formation and mitochondrial dysfunction.
    CONCLUSIONS: We conclude that diabetes suppresses Ampk, initiating Fundc1-mediated MAM formation, mitochondrial dysfunction, and cardiomyopathy, suggesting that Ampk-induced Fundc1 suppression is a valid target to treat diabetic cardiomyopathy.
    Keywords:  Ampk; Fundc1; MAMs; Mitochondrial dysfunction
    DOI:  https://doi.org/10.1161/CIRCULATIONAHA.118.033552
  28. Elife. 2019 Jan 14. pii: e41112. [Epub ahead of print]8
    Phillips CB, Tsai CW, Tsai MF.
      The mitochondrial calcium uniporter is a Ca2+ channel that regulates intracellular Ca2+ signaling, oxidative phosphorylation, and apoptosis. It contains the pore-forming MCU protein, which possesses a DIME sequence thought to form a Ca2+ selectivity filter, and also regulatory EMRE, MICU1, and MICU2 subunits. To properly carry out physiological functions, the uniporter must stay closed in resting conditions, becoming open only when stimulated by intracellular Ca2+ signals. This Ca2+-dependent activation, known to be mediated by MICU subunits, is not well understood. Here, we demonstrate that the DIME-aspartate mediates a Ca2+-modulated electrostatic interaction with MICU1, forming an MICU1 contact interface with a nearby Ser residue at the cytoplasmic entrance of the MCU pore. A mutagenesis screen of MICU1 identifies two highly-conserved Arg residues that might contact the DIME-Asp. Perturbing MCU-MICU1 interactions elicits unregulated, constitutive Ca2+ flux into mitochondria. These results indicate that MICU1 confers Ca2+-dependent gating of the uniporter by blocking/unblocking MCU.
    Keywords:  biochemistry; chemical biology; molecular biophysics; none; structural biology
    DOI:  https://doi.org/10.7554/eLife.41112
  29. Cell Rep. 2019 Jan 15. pii: S2211-1247(18)32018-7. [Epub ahead of print]26(3): 507-517.e3
    Badal KK, Akhmedov K, Lamoureux P, Liu XA, Reich A, Fallahi-Sichani M, Swarnkar S, Miller KE, Puthanveettil SV.
      Mechanisms that regulate the bi-directional transport of mitochondria in neurons for maintaining functional synaptic connections are poorly understood. Here, we show that in the pre-synaptic sensory neurons of the Aplysia gill withdrawal reflex, the formation of functional synapses leads to persistent enhancement in the flux of bi-directional mitochondrial transport. In the absence of a functional synapse, activation of cAMP signaling is sufficient to enhance bi-directional transport in sensory neurons. Furthermore, persistent enhancement in transport does not depend on NMDA and AMPA receptor signaling nor signaling from the post-synaptic neuronal cell body, but it is dependent on transcription and protein synthesis in the pre-synaptic neuron. We identified ∼4,000 differentially enriched transcripts in pre-synaptic neurons, suggesting a long-term change in the transcriptional program produced by synapse formation. These results provide insights into the regulation of bi-directional mitochondrial transport for synapse maintenance.
    Keywords:  Aplysia; axonal transport; bi-directional transport; cAMP signaling; gene expression; metabolism; mitochondria; single-cell analysis; synapse formation; synapse maintenance
    DOI:  https://doi.org/10.1016/j.celrep.2018.12.073
  30. J Cell Biol. 2019 Jan 16. pii: jcb.201901033. [Epub ahead of print]
    Leandro J, Houten SM.
      Saccharopine, a nonproteinogenic amino acid originally isolated from the yeast Saccharomyces cerevisiae, is an intermediate in lysine metabolism. In this issue, Zhou et al. (2019. J. Cell Biol. https://doi.org./10.1083/jcb.201807204) show that abnormal accumulation of saccharopine results in defective mitochondrial dynamics and function in worm and mouse models.
    DOI:  https://doi.org/10.1083/jcb.201901033
  31. Nat Commun. 2019 Jan 18. 10(1): 338
    Galván-Peña S, Carroll RG, Newman C, Hinchy EC, Palsson-McDermott E, Robinson EK, Covarrubias S, Nadin A, James AM, Haneklaus M, Carpenter S, Kelly VP, Murphy MP, Modis LK, O'Neill LA.
      Macrophages undergo metabolic changes during activation that are coupled to functional responses. The gram negative bacterial product lipopolysaccharide (LPS) is especially potent at driving metabolic reprogramming, enhancing glycolysis and altering the Krebs cycle. Here we describe a role for the citrate-derived metabolite malonyl-CoA in the effect of LPS in macrophages. Malonylation of a wide variety of proteins occurs in response to LPS. We focused on one of these, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In resting macrophages, GAPDH binds to and suppresses translation of several inflammatory mRNAs, including that encoding TNFα. Upon LPS stimulation, GAPDH undergoes malonylation on lysine 213, leading to its dissociation from TNFα mRNA, promoting translation. We therefore identify for the first time malonylation as a signal, regulating GAPDH mRNA binding to promote inflammation.
    DOI:  https://doi.org/10.1038/s41467-018-08187-6
  32. Am J Physiol Lung Cell Mol Physiol. 2019 Jan 17.
    Hogan SE, Rodriguez Salazar MP, Cheadle J, Glenn R, Medrano C, Petersen TH, Ilagan RM.
      Secreted exosomes are bioactive particles that elicit profound responses in target cells. Using targeted metabolomics and global microarray analysis, we identified a role of exosomes in promoting mitochondrial function in the context of pulmonary arterial hypertension (PAH). While chronic hypoxia results in a glycolytic shift in pulmonary artery smooth muscle cells (PASMC), exosomes restore energy balance and improve O2 consumption. These results were confirmed in a hypoxia-induced mouse model and a semaxinib/hypoxia rat model of PAH wherein exosomes improved the mitochondrial dysfunction associated with disease. Importantly, exosome exposure increased PASMC expression of pyruvate dehydrogenase (PDH) and glutamate dehydrogenase 1 (GLUD1), linking exosome treatment to the TCA cycle. Further, we show that while prolonged hypoxia induced sirtuin 4 (SIRT4) expression, an upstream inhibitor of both GLUD1 and PDH, exosomes reduced its expression. These data provide direct evidence of an exosome-mediated improvement in mitochondrial function and contribute new insights into the therapeutic potential of exosomes in PAH.
    Keywords:  Pulmonary hypertension; exosome; glutamate dehydrogenase; pyruvate dehydrogenase; sirtuin4
    DOI:  https://doi.org/10.1152/ajplung.00058.2018
  33. Redox Biol. 2018 Dec 17. pii: S2213-2317(18)31074-7. [Epub ahead of print] 101076
    Hirpara J, Eu JQ, Tan JKM, Wong AL, Clement MV, Kong LR, Ohi N, Tsunoda T, Qu J, Goh BC, Pervaiz S.
      The ability to selectively eradicate oncogene-addicted tumors while reducing systemic toxicity has endeared targeted therapies as a treatment strategy. Nevertheless, development of acquired resistance limits the benefits and durability of such a regime. Here we report evidence of enhanced reliance on mitochondrial oxidative phosphorylation (OXPHOS) in oncogene-addicted cancers manifesting acquired resistance to targeted therapies. To that effect, we describe a novel OXPHOS targeting activity of the small molecule compound, OPB-51602 (OPB). Of note, a priori treatment with OPB restored sensitivity to targeted therapies. Furthermore, cancer cells exhibiting stemness markers also showed selective reliance on OXPHOS and enhanced sensitivity to OPB. Importantly, in a subset of patients who developed secondary resistance to EGFR tyrosine kinase inhibitor (TKI), OPB treatment resulted in decrease in metabolic activity and reduction in tumor size. Collectively, we show here a switch to mitochondrial OXPHOS as a key driver of targeted drug resistance in oncogene-addicted cancers. This metabolic vulnerability is exploited by a novel OXPHOS inhibitor, which also shows promise in the clinical setting.
    Keywords:  Metabolic reprogramming; OXPHOS; Oncogene-addiction; STAT3
    DOI:  https://doi.org/10.1016/j.redox.2018.101076
  34. J Exerc Rehabil. 2018 Dec;14(6): 920-926
    No MH, Heo JW, Yoo SZ, Jo HS, Park DH, Kang JH, Seo DY, Han J, Kwak HB.
      Aging is a risk factor for heart disease and heart failure, which result from a progressive impairment of cardiac functions, including stroke volume, cardiac output, blood flow, and oxygen consumption. Age-related cardiac dysfunction is associated with impaired cardiac structures, such as the loss of myocytes, structural remodeling, altered calcium (Ca2+) handling, and contractile dysfunction. However, the mechanism by which aging affects mitochondrial function in the heart is poorly understood. The purpose of this study was to determine the effects of aging on mitochondrial function in the rat heart. Male Fischer 344 rats were randomly assigned to very young sedentary (VYS, 1 month), young sedentary (YS, 4 months), middle-aged sedentary (MS, 10 months), and old sedentary (OS, 20 months) groups. mitochondrial complex protein levels and mitochondrial function (e.g., mitochondrial hydrogen peroxide (H2O2) emission and Ca2+ retention capacity) were analyzed in the left ventricle. Aging was associated with decreased levels of OXPHOS (oxidative phosphorylation) protein expression of complex I to IV in the function of the electron transport chain. Aging increased the mitochondrial H2O2 emitting potential in the heart. In contrast, mitochondrial Ca2+ retention capacity gradually decreased with age. These data demonstrate that aging impairs mitochondrial function in cardiac muscle, suggesting that mitochondrial dysfunction with aging may be a primary factor for aging-induced cardiac dysfunction in the heart.
    Keywords:  Aging; Heart; Mitochondrial function; Mitochondrial oxidative phosphorylation
    DOI:  https://doi.org/10.12965/jer.1836550.275
  35. Cell Metab. 2019 Jan 02. pii: S1550-4131(18)30753-8. [Epub ahead of print]
    Patel S, Alvarez-Guaita A, Melvin A, Rimmington D, Dattilo A, Miedzybrodzka EL, Cimino I, Maurin AC, Roberts GP, Meek CL, Virtue S, Sparks LM, Parsons SA, Redman LM, Bray GA, Liou AP, Woods RM, Parry SA, Jeppesen PB, Kolnes AJ, Harding HP, Ron D, Vidal-Puig A, Reimann F, Gribble FM, Hulston CJ, Farooqi IS, Fafournoux P, Smith SR, Jensen J, Breen D, Wu Z, Zhang BB, Coll AP, Savage DB, O'Rahilly S.
      GDF15 is an established biomarker of cellular stress. The fact that it signals via a specific hindbrain receptor, GFRAL, and that mice lacking GDF15 manifest diet-induced obesity suggest that GDF15 may play a physiological role in energy balance. We performed experiments in humans, mice, and cells to determine if and how nutritional perturbations modify GDF15 expression. Circulating GDF15 levels manifest very modest changes in response to moderate caloric surpluses or deficits in mice or humans, differentiating it from classical intestinally derived satiety hormones and leptin. However, GDF15 levels do increase following sustained high-fat feeding or dietary amino acid imbalance in mice. We demonstrate that GDF15 expression is regulated by the integrated stress response and is induced in selected tissues in mice in these settings. Finally, we show that pharmacological GDF15 administration to mice can trigger conditioned taste aversion, suggesting that GDF15 may induce an aversive response to nutritional stress.
    Keywords:  GDF15; GFRAL; conditioned taste aversion; integrated stress response; overnutrion
    DOI:  https://doi.org/10.1016/j.cmet.2018.12.016
  36. Mol Biol Cell. 2019 Jan 16. mbcE18070466
    Kraft LM, Lackner LL.
      Mitochondrial anchors have functions that extend beyond simply positioning mitochondria. In budding yeast, mitochondria drive the assembly of the mitochondrial anchor protein Num1 into clusters, which serve to anchor mitochondria as well as dynein to the cell cortex. Here, we explore a conserved role for mitochondria in dynein anchoring by examining the tethering functions of the evolutionarily distant S. pombe Num1 homolog. In addition to its function in dynein anchoring, we find that S. pombe Num1 interacts with and tethers mitochondria to the plasma membrane in S. pombe and S. cerevisiae. Thus, the mitochondria and plasma membrane binding domains of the Num1 homologs, as well as the membrane features these domains recognize, are conserved. In S. pombe, we find that mitochondria impact the assembly and cellular distribution of Num1 clusters and that Num1 clusters actively engaged in mitochondrial tethering serve as cortical attachment sites for dynein. Thus, mitochondria play a critical and conserved role in the formation and distribution of dynein anchoring sites at the cell cortex and, as a consequence, impact dynein function. These findings shed light on an ancient mechanism of mitochondria-dependent dynein anchoring that is conserved over more than 450 million years of evolution, raising the intriguing possibility that the role mitochondria play in dynein anchoring and function extends beyond yeast to higher eukaryotes.
    DOI:  https://doi.org/10.1091/mbc.E18-07-0466
  37. Nat Rev Endocrinol. 2019 Jan 17.
    Gabriel BM, Zierath JR.
      Perturbed diurnal rhythms are becoming increasingly evident as deleterious events in the pathology of metabolic diseases. Exercise is well characterized as a crucial intervention in the prevention and treatment of individuals with metabolic diseases. Little is known, however, regarding optimizing the timing of exercise bouts in order to maximize their health benefits. Furthermore, exercise is a potent modulator of skeletal muscle metabolism, and it is clear that skeletal muscle has a strong circadian profile. In humans, mitochondrial function peaks in the late afternoon, and the circadian clock might be inherently impaired in myotubes from patients with metabolic disease. Timing exercise bouts to coordinate with an individual's circadian rhythms might be an efficacious strategy to optimize the health benefits of exercise. The role of exercise as a Zeitgeber can also be used as a tool in combating metabolic disease. Shift work is known to induce acute insulin resistance, and appropriately timed exercise might improve health markers in shift workers who are at risk of metabolic disease. In this Review, we discuss the literature regarding diurnal skeletal muscle metabolism and the interaction with exercise bouts at different times of the day to combat metabolic disease.
    DOI:  https://doi.org/10.1038/s41574-018-0150-x
  38. J Biol Chem. 2019 Jan 16. pii: jbc.AC119.007382. [Epub ahead of print]
    Shen K, Valenstein ML, Gu X, Sabatini DM.
      mTOR complex 1 (mTORC1) is a major regulator of cell growth and proliferation that coordinates nutrient inputs with anabolic and catabolic processes. Amino acid signals are transmitted to mTORC1 through the Rag GTPases, which directly recruit mTORC1 onto the lysosomal surface, its site of activation. The Rag GTPase heterodimer has a unique architecture that consists of two GTPase subunits, RagA or RagB bound to RagC or RagD. Their nucleotide-loading states are strictly controlled by several lysosomal or cytosolic protein complexes that directly detect and transmit the amino acid signals. GATOR1 (GTPase-activating protein (GAP) activity toward Rags-1), a negative regulator of the cytosolic branch of the nutrient-sensing pathway, comprises of three subunits: Depdc5 (DEP domain-containing protein 5), Nprl2 (NPR2-like GATOR1 complex subunit), and Nprl3 (NPR3-like GATOR1 complex subunit), and is a GAP for RagA. GATOR1 binds the Rag GTPases via two modes, an inhibitory mode that holds the Rag GTPase heterodimer and has previously been captured by structural determination, and a GAP mode that stimulates GTP hydrolysis by RagA but remains structurally elusive. Here, using site-directed mutagenesis, GTP hydrolysis assays, co-immunoprecipitation experiments, and structural analysis, we probed the GAP mode and found that a critical residue on Nprl2, Arg78, is the arginine finger that carries out GATOR1's GAP function. Substitutions of this arginine residue rendered mTORC1 signaling insensitive to amino acid starvation and are found frequently in cancers such as glioblastoma. Our results reveal the biochemical bases of mTORC1 inactivation through the GATOR1 complex.
    Keywords:  GATOR1 (GTPase-activating protein (GAP) activity toward Rags-1); GTPase activating protein (GAP); Nprl2 (NPR2-like GATOR1 complex subunit); Rag GTPase; amino acid; arginine finger; enzyme mechanism; mTOR complex (mTORC); nutrient sensing
    DOI:  https://doi.org/10.1074/jbc.AC119.007382
  39. Trends Biochem Sci. 2019 Jan 14. pii: S0968-0004(18)30273-1. [Epub ahead of print]
    Icard P, Fournel L, Wu Z, Alifano M, Lincet H.
      Cell cycle progression and division is regulated by checkpoint controls and sequential activation of cyclin-dependent kinases (CDKs). Understanding of how these events occur in synchrony with metabolic changes could have important therapeutic implications. For biosynthesis, cancer cells enhance glucose and glutamine consumption. Inactivation of pyruvate kinase M2 (PKM2) promotes transcription in G1 phase. Glutamine metabolism supports DNA replication in S phase and lipid synthesis in G2 phase. A boost in glycolysis and oxidative metabolism can temporarily furnish more ATP when necessary (G1/S transition, segregation of chromosomes). Recent studies have shown that a few metabolic enzymes [PKM2, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB3), GAPDH] also periodically translocate to the nucleus and oversee cell cycle regulators or oncogene expression (c-Myc). Targeting these metabolic enzymes could increase the response to CDK inhibitors (CKIs).
    Keywords:  D cyclin; GAPDH; PFKFB3; PKM2; cell cycle; glycolysis
    DOI:  https://doi.org/10.1016/j.tibs.2018.12.007
  40. Curr Opin Clin Nutr Metab Care. 2019 Jan 14.
    Pedersen BK.
      PURPOSE OF REVIEW: Robust epidemiological evidence exists that lifelong regular exercise contributes to longevity. The aim of this review is to discuss recent findings regarding, which dose and type of physical activity promotes a long healthy life, free of disease.RECENT FINDINGS: Meeting the currently recommended amounts of leisure time physical aerobic activity of moderate intensity of at least 150 min/week provides most of the longevity benefit. However, a higher duration and intensity augments the beneficial effect on cardiovascular health and metabolism. Performing three to five times the recommended physical activity minimum reaches the maximal longevity benefit, that can be achieved. Although it is not dangerous to perform even higher amounts of exercise, the benefit may decrease. A high maximal oxygen uptake in mid-life is a strong marker of longevity, whereas muscle mass is a critical prognostic factor in aging and cancer.
    SUMMARY: Exercise training above the public health recommendations provides additional benefits regarding disease protection and longevity. Endurance exercise, including high-intensity training to improve cardiorespiratory fitness promotes longevity and slows down aging. Strength training should be added to slow down loss of muscle mass, associated with aging and disease.
    DOI:  https://doi.org/10.1097/MCO.0000000000000546
  41. J Cell Mol Med. 2019 Jan 16.
    Zhuang C, Zhuang C, Luo X, Huang X, Yao L, Li J, Li Y, Xiong T, Ye J, Zhang F, Gui Y.
      The abundant and reversible N6-methyladenosine (m6A) RNA modification and its modulators have important roles in regulating various gene expression and biological processes. Here, we demonstrate that fat mass and obesity associated (FTO), as an m6A demethylase, plays a critical anti-tumorigenic role in clear cell renal cell carcinoma (ccRCC). FTO is suppressed in ccRCC tissue. The low expression of FTO in human ccRCC correlates with increased tumour severity and poor patient survival. The Von Hippel-Lindau-deficient cells expressing FTO restores mitochondrial activity, induces oxidative stress and ROS production and shows impaired tumour growth, through increasing expression of PGC-1α by reducing m6A levels in its mRNA transcripts. Our work demonstrates the functional importance of the m6A methylation and its modulator, and uncovers a critical FTO-PGC-1α axis for developing effective therapeutic strategies in the treatment of ccRCC.
    Keywords:   FTO ; PGC-1α; ccRCC; m6A; mitochondria; oxidative stress
    DOI:  https://doi.org/10.1111/jcmm.14128
  42. J Cell Biol. 2019 Jan 14. pii: jcb.201806197. [Epub ahead of print]
    Chow HM, Cheng A, Song X, Swerdel MR, Hart RP, Herrup K.
      Ataxia-telangiectasia (A-T) is an autosomal recessive disease caused by mutation of the ATM gene and is characterized by loss of cerebellar Purkinje cells, neurons with high physiological activity and dynamic ATP demands. Here, we show that depletion of ATP generates reactive oxygen species that activate ATM. We find that when ATM is activated by oxidative stress, but not by DNA damage, ATM phosphorylates NRF1. This leads to NRF1 dimerization, nuclear translocation, and the up-regulation of nuclear-encoded mitochondrial genes, thus enhancing the capacity of the electron transport chain (ETC) and restoring mitochondrial function. In cells lacking ATM, cells replenish ATP poorly following surges in energy demand, and chronic ATP insufficiency endangers cell survival. We propose that in the absence of ATM, cerebellar Purkinje cells cannot respond adequately to the increase in energy demands of neuronal activity. Our findings identify ATM as a guardian of mitochondrial output, as well as genomic integrity, and suggest that alternative fuel sources may ameliorate A-T disease symptoms.
    DOI:  https://doi.org/10.1083/jcb.201806197
  43. Nature. 2019 Jan;565(7739): 296-297
    McWilliams TG, Suomalainen A.
      
    Keywords:  Cell biology; Genetics
    DOI:  https://doi.org/10.1038/d41586-019-00093-1
  44. Cancer Cell. 2019 Jan 14. pii: S1535-6108(18)30578-6. [Epub ahead of print]35(1): 1-2
    Hinz S, LaBarge MA.
      Potential for cancers to form metastases requires cell dissemination utilizing epithelial-to-mesenchymal transition (EMT) program. In this issue of Cancer Cell, Ishay-Ronen et al. show that plasticity intrinsic to the EMT program can be exploited to divert cancer cells into becoming post-mitotic adipocytes, thus preventing formation of metastases.
    DOI:  https://doi.org/10.1016/j.ccell.2018.12.007
  45. Autophagy. 2019 Jan 17.
    Zhang Y, Mun SR, Linares JF, Towers CG, Thorburn A, Diaz-Meco MT, Kwon YT, Kutateladze TG.
      SQSTM1/p62 facilitates responses to various cellular stresses and has been implicated in human diseases. This protein functions as a major cytoplasmic signaling hub and has multiple binding partners, including arginylated (Nt-R) proteins that are recognized by the ZZ domain of SQSTM1/p62 (SQSTM1/p62ZZ). We have determined the molecular mechanism of Nt-R recognition using a combination of biochemical and NMR approaches and obtained the crystal structure of SQSTM1/p62ZZ in complex with Nt-R. We found that binding of SQSTM1/p62ZZ to Nt-R induces SQSTM1/p62 puncta formation and macroautophagy/autophagy and identified a regulatory linker (RL) region of SQSTM1/p62 that associates with SQSTM1/p62ZZ in vitro. Our findings suggest a mechanism for SQSTM1/p62 autoregulation that can be essential in mediating autophagy.
    Keywords:  ZZ domain; arginylated substrates; autoregulation; macroautophagy; p62
    DOI:  https://doi.org/10.1080/15548627.2019.1569935
  46. Nat Commun. 2019 Jan 14. 10(1): 201
    Wang Y, Bai C, Ruan Y, Liu M, Chu Q, Qiu L, Yang C, Li B.
      Under hypoxia, most of glucose is converted to secretory lactate, which leads to the overuse of glutamine-carbon. However, under such a condition how glutamine nitrogen is disposed to avoid over-accumulating ammonia remains to be determined. Here we identify a metabolic flux of glutamine to secretory dihydroorotate, which is indispensable to glutamine-carbon metabolism under hypoxia. We found that glutamine nitrogen is necessary to nucleotide biosynthesis, but enriched in dihyroorotate and orotate rather than processing to its downstream uridine monophosphate under hypoxia. Dihyroorotate, not orotate, is then secreted out of cells. Furthermore, we found that the specific metabolic pathway occurs in vivo and is required for tumor growth. The identified metabolic pathway renders glutamine mainly to acetyl coenzyme A for lipogenesis, with the rest carbon and nitrogen being safely removed. Therefore, our results reveal how glutamine carbon and nitrogen are coordinatively metabolized under hypoxia, and provide a comprehensive understanding on glutamine metabolism.
    DOI:  https://doi.org/10.1038/s41467-018-08033-9
  47. Proc Natl Acad Sci U S A. 2019 Jan 17. pii: 201816056. [Epub ahead of print]
    Sferruzzi-Perri AN, Higgins JS, Vaughan OR, Murray AJ, Fowden AL.
      Mitochondria respond to a range of stimuli and function in energy production and redox homeostasis. However, little is known about the developmental and environmental control of mitochondria in the placenta, an organ vital for fetal growth and pregnancy maintenance in eutherian mammals. Using respirometry and molecular analyses, the present study examined mitochondrial function in the distinct transport and endocrine zones of the mouse placenta during normal pregnancy and maternal inhalation hypoxia. The data show that mitochondria of the two zones adopt different strategies in modulating their respiration, substrate use, biogenesis, density, and efficiency to best support the growth and energy demands of fetoplacental tissues during late gestation in both normal and hypoxic conditions. The findings have important implications for environmentally induced adaptations in mitochondrial function in other tissues and for compromised human pregnancy in which hypoxia and alterations in placental mitochondrial function are associated with poor outcomes like fetal growth restriction.
    Keywords:  fetus; hypoxia; metabolism; mitochondria; placenta
    DOI:  https://doi.org/10.1073/pnas.1816056116