bims-camemi Biomed news
on Mitochondrial metabolism in cancer
Issue of 2019‒03‒31
fifty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Cell Rep. 2019 Mar 26. pii: S2211-1247(19)30293-1. [Epub ahead of print]26(13): 3709-3725.e7
    Tomar D, Jaña F, Dong Z, Quinn WJ, Jadiya P, Breves SL, Daw CC, Srikantan S, Shanmughapriya S, Nemani N, Carvalho E, Tripathi A, Worth AM, Zhang X, Razmpour R, Seelam A, Rhode S, Mehta AV, Murray M, Slade D, Ramirez SH, Mishra P, Gerhard GS, Caplan J, Norton L, Sharma K, Rajan S, Balciunas D, Wijesinghe DS, Ahima RS, Baur JA, Madesh M.
      Mitochondrial Ca2+ uniporter (MCU)-mediated Ca2+ uptake promotes the buildup of reducing equivalents that fuel oxidative phosphorylation for cellular metabolism. Although MCU modulates mitochondrial bioenergetics, its function in energy homeostasis in vivo remains elusive. Here we demonstrate that deletion of the Mcu gene in mouse liver (MCUΔhep) and in Danio rerio by CRISPR/Cas9 inhibits mitochondrial Ca2+ (mCa2+) uptake, delays cytosolic Ca2+ (cCa2+) clearance, reduces oxidative phosphorylation, and leads to increased lipid accumulation. Elevated hepatic lipids in MCUΔhep were a direct result of extramitochondrial Ca2+-dependent protein phosphatase-4 (PP4) activity, which dephosphorylates AMPK. Loss of AMPK recapitulates hepatic lipid accumulation without changes in MCU-mediated Ca2+ uptake. Furthermore, reconstitution of active AMPK, or PP4 knockdown, enhances lipid clearance in MCUΔhep hepatocytes. Conversely, gain-of-function MCU promotes rapid mCa2+ uptake, decreases PP4 levels, and reduces hepatic lipid accumulation. Thus, our work uncovers an MCU/PP4/AMPK molecular cascade that links Ca2+ dynamics to hepatic lipid metabolism.
    Keywords:  AMPK; MCU; bioenergetics; calcium; diabetes; hepatocyte; lipid metabolism; metabolic diseases; mitochondrial Ca(2+) uniporter; phosphatase
    DOI:  https://doi.org/10.1016/j.celrep.2019.02.107
  2. Autophagy. 2019 Mar 27. 1-20
    Fernandez-Mosquera L, Yambire KF, Couto R, Pereyra L, Pabis K, Ponsford AH, Diogo CV, Stagi M, Milosevic I, Raimundo N.
      Mitochondria are key organelles for cellular metabolism, and regulate several processes including cell death and macroautophagy/autophagy. Here, we show that mitochondrial respiratory chain (RC) deficiency deactivates AMP-activated protein kinase (AMPK, a key regulator of energy homeostasis) signaling in tissue and in cultured cells. The deactivation of AMPK in RC-deficiency is due to increased expression of the AMPK-inhibiting protein FLCN (folliculin). AMPK is found to be necessary for basal lysosomal function, and AMPK deactivation in RC-deficiency inhibits lysosomal function by decreasing the activity of the lysosomal Ca2+ channel MCOLN1 (mucolipin 1). MCOLN1 is regulated by phosphoinositide kinase PIKFYVE and its product PtdIns(3,5)P2, which is also decreased in RC-deficiency. Notably, reactivation of AMPK, in a PIKFYVE-dependent manner, or of MCOLN1 in RC-deficient cells, restores lysosomal hydrolytic capacity. Building on these data and the literature, we propose that downregulation of the AMPK-PIKFYVE-PtdIns(3,5)P2-MCOLN1 pathway causes lysosomal Ca2+ accumulation and impaired lysosomal catabolism. Besides unveiling a novel role of AMPK in lysosomal function, this study points to the mechanism that links mitochondrial malfunction to impaired lysosomal catabolism, underscoring the importance of AMPK and the complexity of organelle cross-talk in the regulation of cellular homeostasis. Abbreviation: ΔΨm: mitochondrial transmembrane potential; AMP: adenosine monophosphate; AMPK: AMP-activated protein kinase; ATG5: autophagy related 5; ATP: adenosine triphosphate; ATP6V0A1: ATPase, H+ transporting, lysosomal, V0 subbunit A1; ATP6V1A: ATPase, H+ transporting, lysosomal, V0 subbunit A; BSA: bovine serum albumin; CCCP: carbonyl cyanide-m-chlorophenylhydrazone; CREB1: cAMP response element binding protein 1; CTSD: cathepsin D; CTSF: cathepsin F; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; EBSS: Earl's balanced salt solution; ER: endoplasmic reticulum; FBS: fetal bovine serum; FCCP: carbonyl cyanide-p-trifluoromethoxyphenolhydrazone; GFP: green fluorescent protein; GPN: glycyl-L-phenylalanine 2-naphthylamide; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MCOLN1/TRPML1: mucolipin 1; MEF: mouse embryonic fibroblast; MITF: melanocyte inducing transcription factor; ML1N*2-GFP: probe used to detect PtdIns(3,5)P2 based on the transmembrane domain of MCOLN1; MTORC1: mechanistic target of rapamycin kinase complex 1; NDUFS4: NADH:ubiquinone oxidoreductase subunit S4; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; pcDNA: plasmid cytomegalovirus promoter DNA; PCR: polymerase chain reaction; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns(3,5)P2: phosphatidylinositol-3,5-bisphosphate; PIKFYVE: phosphoinositide kinase, FYVE-type zinc finger containing; P/S: penicillin-streptomycin; PVDF: polyvinylidene fluoride; qPCR: quantitative real time polymerase chain reaction; RFP: red fluorescent protein; RNA: ribonucleic acid; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; shRNA: short hairpin RNA; siRNA: small interfering RNA; TFEB: transcription factor EB; TFE3: transcription factor binding to IGHM enhancer 3; TMRM: tetramethylrhodamine, methyl ester, perchlorate; ULK1: unc-51 like autophagy activating kinase 1; ULK2: unc-51 like autophagy activating kinase 2; UQCRC1: ubiquinol-cytochrome c reductase core protein 1; v-ATPase: vacuolar-type H+-translocating ATPase; WT: wild-type.
    Keywords:  AMPK; MCOLN1; calcium; lysosomal Ca; lysosomes; mitochondria; mitochondrial respiratory chain deficiency
    DOI:  https://doi.org/10.1080/15548627.2019.1586256
  3. Cell Metab. 2019 Mar 15. pii: S1550-4131(19)30075-0. [Epub ahead of print]
    Benador IY, Veliova M, Liesa M, Shirihai OS.
      The isolation and biochemical characterization of lipid droplet (LD)-associated mitochondria revealed the capacity of the cell to produce and maintain distinct mitochondrial populations carrying disparate proteome and dissimilar capacities to oxidize fatty acids and pyruvate. With mitochondrial motility being a central parameter determining mitochondrial fusion, adherence to LDs provides a mechanism by which peridroplet mitochondria (PDM) remain segregated from cytoplasmic mitochondria (CM). The existence of metabolically distinct subpopulations provides an explanation for the capacity of mitochondria within the individual cell to be involved simultaneously in fatty acid oxidation and LD formation. The mechanisms that deploy mitochondria to the LD and the dysfunctions that result from unbalanced proportions of PDM and CM remain to be explored. Understanding the roles and regulation of mitochondrial tethering to LDs offers new points of intervention in metabolic diseases.
    Keywords:  adipose tissue; fat; fatty acid oxidation; lipid; lipid droplet; mitochondria; obesity; peridroplet mitochondria; triacylglyceride; triacylglycerol
    DOI:  https://doi.org/10.1016/j.cmet.2019.02.011
  4. Front Physiol. 2019 ;10 201
    Cortassa S, Aon MA, Sollott SJ.
      Appropriate substrate selection between fats and glucose is associated with the success of interventions that maintain health such as exercise or caloric restriction, or with the severity of diseases such as diabetes or other metabolic disorders. Although the interaction and mutual inhibition between glucose and fatty-acids (FAs) catabolism has been studied for decades, a quantitative and integrated understanding of the control and regulation of substrate selection through central catabolic pathways is lacking. We addressed this gap here using a computational model representing cardiomyocyte catabolism encompassing glucose (Glc) utilization, pyruvate transport into mitochondria and oxidation in the tricarboxylic acid (TCA) cycle, β-oxidation of palmitate (Palm), oxidative phosphorylation, ion transport, pH regulation, and ROS generation and scavenging in cytoplasmic and mitochondrial compartments. The model is described by 82 differential equations and 119 enzymatic, electron transport and substrate transport reactions accounting for regulatory mechanisms and key players, namely pyruvate dehydrogenase (PDH) and its modulation by multiple effectors. We applied metabolic control analysis to the network operating with various Glc to Palm ratios. The flux and metabolites' concentration control were visualized through heat maps providing major insights into main control and regulatory nodes throughout the catabolic network. Metabolic pathways located in different compartments were found to reciprocally control each other. For example, glucose uptake and the ATP demand exert control on most processes in catabolism while TCA cycle activities and membrane-associated energy transduction reactions exerted control on mitochondrial processes namely β-oxidation. PFK and PDH, two highly regulated enzymes, exhibit opposite behavior from a control perspective. While PFK activity was a main rate-controlling step affecting the whole network, PDH played the role of a major regulator showing high sensitivity (elasticity) to substrate availability and key activators/inhibitors, a trait expected from a flexible substrate selector strategically located in the metabolic network. PDH regulated the rate of Glc and Palm consumption, consistent with its high sensitivity toward AcCoA, CoA, and NADH. Overall, these results indicate that the control of catabolism is highly distributed across the metabolic network suggesting that fuel selection between FAs and Glc goes well beyond the mechanisms traditionally postulated to explain the glucose-fatty-acid cycle.
    Keywords:  central catabolism; computational modeling; control coefficients; glucose and fatty acids; metabolic control analysis; pyruvate dehydrogenase regulation
    DOI:  https://doi.org/10.3389/fphys.2019.00201
  5. Nat Commun. 2019 Mar 29. 10(1): 1432
    Calzada E, Avery E, Sam PN, Modak A, Wang C, McCaffery JM, Han X, Alder NN, Claypool SM.
      Of the four separate PE biosynthetic pathways in eukaryotes, one occurs in the mitochondrial inner membrane (IM) and is executed by phosphatidylserine decarboxylase (Psd1). Deletion of Psd1 is lethal in mice and compromises mitochondrial function. We hypothesize that this reflects inefficient import of non-mitochondrial PE into the IM. Here, we test this by re-wiring PE metabolism in yeast by re-directing Psd1 to the outer mitochondrial membrane or the endomembrane system and show that PE can cross the IMS in both directions. Nonetheless, PE synthesis in the IM is critical for cytochrome bc1 complex (III) function and mutations predicted to disrupt a conserved PE-binding site in the complex III subunit, Qcr7, impair complex III activity similar to PSD1 deletion. Collectively, these data challenge the current dogma of PE trafficking and demonstrate that PE made in the IM by Psd1 support the intrinsic functionality of complex III.
    DOI:  https://doi.org/10.1038/s41467-019-09425-1
  6. Elife. 2019 Mar 29. pii: e38986. [Epub ahead of print]8
    Xu J, Reznik E, Lee HJ, Gundem G, Jonsson P, Sarungbam J, Bialik A, Sanchez-Vega F, Creighton CJ, Hoekstra JG, Zhang L, Sajjakulnukit P, Kremer D, Tolstyka ZP, Casuscelli J, Stirdivant S, Tang J, Schultz N, Jeng PS, Dong Y, Su W, Cheng EH, Russo P, Coleman JA, Papaemmanuil E, Chen YB, Reuter VE, Sander C, Kennedy SR, Hsieh JJ, Lyssiotis C, Tickoo SK, Hakimi AA.
      While genomic sequencing routinely identifies oncogenic alterations for the majority of cancers, many tumors harbor no discernable driver lesion. Here, we describe the exceptional molecular phenotype of a genomically quiet kidney tumor, clear cell papillary renal cell carcinoma (CCPAP). In spite of a largely wild-type nuclear genome, CCPAP tumors exhibit severe depletion of mitochondrial DNA (mtDNA) and RNA and high levels of oxidative stress, reflecting a shift away from respiratory metabolism. Moreover, CCPAP tumors exhibit a distinct metabolic phenotype uniquely characterized by accumulation of the sugar alcohol sorbitol. Immunohistochemical staining of primary CCPAP tumor specimens recapitulates both the depletion of mtDNA-encoded proteins and a lipid-depleted metabolic phenotype, suggesting that the cytoplasmic clarity in CCPAP is primarily related to the presence of glycogen. These results argue for non-genetic profiling as a tool for the study of cancers of unknown driver.
    Keywords:  cancer biology; genetics; genomics; human
    DOI:  https://doi.org/10.7554/eLife.38986
  7. MBio. 2019 Mar 26. pii: e02550-18. [Epub ahead of print]10(2):
    Shi L, Jiang Q, Bushkin Y, Subbian S, Tyagi S.
      Macrophages are the primary targets of Mycobacterium tuberculosis infection; the early events of macrophage interaction with M. tuberculosis define subsequent progression and outcome of infection. M. tuberculosis can alter the innate immunity of macrophages, resulting in suboptimal Th1 immunity, which contributes to the survival, persistence, and eventual dissemination of the pathogen. Recent advances in immunometabolism illuminate the intimate link between the metabolic states of immune cells and their specific functions. In this review, we describe the little-studied biphasic metabolic dynamics of the macrophage response during progression of infection by M. tuberculosis and discuss their relevance to macrophage immunity and M. tuberculosis pathogenicity. The early phase of macrophage infection, which is marked by M1 polarization, is accompanied by a metabolic switch from mitochondrial oxidative phosphorylation to hypoxia-inducible factor 1 alpha (HIF-1α)-mediated aerobic glycolysis (also known as the Warburg effect in cancer cells), as well as by an upregulation of pathways involving oxidative and antioxidative defense responses, arginine metabolism, and synthesis of bioactive lipids. These early metabolic changes are followed by a late adaptation/resolution phase in which macrophages transition from glycolysis to mitochondrial oxidative metabolism, with a consequent dampening of macrophage proinflammatory and antimicrobial responses. Importantly, the identification of upregulated metabolic pathways and/or metabolic regulatory mechanisms with immunomodulatory functions during M1 polarization has revealed novel mechanisms of M. tuberculosis pathogenicity. These advances can lead to the development of novel host-directed therapies to facilitate bacterial clearance in tuberculosis by targeting the metabolic state of immune cells.
    Keywords:  arachidonic acid metabolism; arginine metabolism; bioactive lipids; glycolysis; host-directed therapy; immune response; immunometabolism; macrophage polarization; metabolic modulation; redox balancing
    DOI:  https://doi.org/10.1128/mBio.02550-18
  8. ASN Neuro. 2018 Jan-Dec;10:10 1759091418818261
    Chinopoulos C, Seyfried TN.
      Glioblastoma multiforme (GBM) is the most common and malignant of the primary adult brain cancers. Ultrastructural and biochemical evidence shows that GBM cells exhibit mitochondrial abnormalities incompatible with energy production through oxidative phosphorylation (OxPhos). Under such conditions, the mitochondrial F0-F1 ATP synthase operates in reverse at the expense of ATP hydrolysis to maintain a moderate membrane potential. Moreover, expression of the dimeric M2 isoform of pyruvate kinase in GBM results in diminished ATP output, precluding a significant ATP production from glycolysis. If ATP synthesis through both glycolysis and OxPhos was impeded, then where would GBM cells obtain high-energy phosphates for growth and invasion? Literature is reviewed suggesting that the succinate-CoA ligase reaction in the tricarboxylic acid cycle can substantiate sufficient ATP through mitochondrial substrate-level phosphorylation (mSLP) to maintain GBM growth when OxPhos is impaired. Production of high-energy phosphates would be supported by glutaminolysis-a hallmark of GBM metabolism-through the sequential conversion of glutamine → glutamate → alpha-ketoglutarate → succinyl CoA → succinate. Equally important, provision of ATP through mSLP would maintain the adenine nucleotide translocase in forward mode, thus preventing the reverse-operating F0-F1 ATP synthase from depleting cytosolic ATP reserves. Because glucose and glutamine are the primary fuels driving the rapid growth of GBM and most tumors for that matter, simultaneous restriction of these two substrates or inhibition of mSLP should diminish cancer viability, growth, and invasion.
    Keywords:  Warburg; bioenergetics; gliomas; therapies
    DOI:  https://doi.org/10.1177/1759091418818261
  9. Cell Physiol Biochem. 2019 ;52(3): 617-632
    Kim SR, Eirin A, Zhang X, Lerman A, Lerman LO.
      BACKGROUND/AIMS: Atherosclerotic renal artery stenosis (ARAS) may cause kidney injury and mitochondrial dysfunction, which is linked to cellular senescence. Elamipretide, a mitochondria-targeted peptide, improves renal function in ARAS, but whether it alleviates senescence is unknown. We hypothesized that elamipretide would reduce senescence stenotic kidney (STK) in ARAS.METHODS: Domestic pigs were randomized to control and unilateral ARAS untreated or treated with subcutaneous elamipretide (5d/wk) for 4 weeks starting after 6 weeks of ARAS or sham (n=6 each). After completion of treatment, STK renal blood flow (RBF) and glomerular filtration rate (GFR) were assessed in-vivo using multi-detector computed-tomography. Renal fibrosis and oxidative stress were analyzed in trichrome- and dihydroethidium-stained slides, respectively. Mitochondrial markers involved in the electrontransport chain (COX4, ATP/ADP ratio), biogenesis (PGC1α, PPARα), dynamics (MFN2, DRP1), and mitophagy (parkin, p62) were measured in the kidney using ELISA, western-blot, and immunohistochemistry. Cellular senescence (senescence-associated β-galactosidase and heterochromatin foci, phosphorylated-H2AX, and p16/21/53) and senescence-associated secretory phenotype (SASP; PAI-1, MCP-1, TGFβ, and TNFα) markers were studied by microscopy, quantitative reverse transcription-polymerase chain reaction, and western-blot.
    RESULTS: Blood pressure was elevated whereas STK-RBF and GFR were decreased in ARAS pigs, and tissue scarring was increased. ARAS induced STK cellular senescence and accumulated dysfunctional mitochondria, which were associated with cardiolipin loss, upregulated mitochondrial biogenesis, and defective mitophagy. Elamipretide normalized STK-RBF and GFR, alleviated fibrosis and oxidative stress, and restored mitochondrial cardiolipin, biogenesis, and mitophagy in ARAS, but did not change SASP markers, and attenuated only senescenceassociated β-galactosidase activity and p53 gene expression.
    CONCLUSION: Mitochondrial protection improved renal function and fibrosis in the ARAS STK, but only partly mitigated cellular senescence. This finding suggests that mitochondrial dysfunction may not be a major determinant of cellular senescence in the early stage of ARAS.
    Keywords:  Atherosclerotic renal artery stenosis; Elamipretide; Mitochondria; Senescence
    DOI:  https://doi.org/10.33594/000000044
  10. J Proteome Res. 2019 Mar 26.
    Betsinger CN, Cristea IM.
      As cellular metabolic hubs, mitochondria are the main energy producers for the cell. These organelles host essential energy producing biochemical processes, including the TCA cycle, fatty acid oxidation, and oxidative phosphorylation. An accumulating body of literature has demonstrated that a majority of mitochondrial proteins are decorated with diverse posttranslational modifications (PTMs). Given the critical roles of these proteins in cellular metabolic pathways and response to environmental stress or pathogens, understanding the role of PTMs in regulating their functions has become an area of intense investigation. A major family of enzymes that regulate PTMs within the mitochondria are sirtuins (SIRTs). Albeit until recently the least understood sirtuin, SIRT4 has emerged as an enzyme capable of removing diverse PTMs from its substrates, thereby modulating their functions. SIRT4 was shown to have ADP-ribosyltransferase, deacetylase, lipoamidase, and deacylase enzymatic activities. As metabolic dysfunction is linked to human disease, SIRT4 levels and activities have been implicated in modulating susceptibility to hyperinsulinemia and diabetes, liver disease, cancer, neurodegeneration, heart disease, aging, and pathogenic infections. Therefore, SIRT4 has emerged as a possible candidate for targeted therapeutics. Here, we discuss the diverse enzymatic activities and substrates of SIRT4 and its roles in human health and disease.
    DOI:  https://doi.org/10.1021/acs.jproteome.9b00086
  11. J Biol Chem. 2019 Mar 28. pii: jbc.RA118.006095. [Epub ahead of print]
    Hong SM, Lee YK, Park I, Kwon SM, Min S, Yoon G.
      Aerobic glycolysis and mitochondrial dysfunction are key metabolic features of cancer cells, but their interplay during cancer development remains unclear. We previously reported that human hepatoma cells with mitochondrial defects exhibit down-regulated lactate dehydrogenase subunit B (LDHB) expression. Here, using several molecular and biochemical assays and informatics analyses, we investigated how LDHB suppression regulates mitochondrial respiratory activity and contributes to liver cancer progression. We found that transcriptional LDHB down-regulation is an upstream event during suppressed oxidative phosphorylation (OXPHOS). We also observed that LDHB knockdown increases inhibitory phosphorylation of pyruvate dehydrogenase (PDH) via lactate-mediated PDH kinase (PDK) activation and thereby attenuates OXPHOS activity. Interestingly, monocarboxylate transporter 1 (MCT1) was the major lactate transporter in hepatoma cells, and its expression was essential for PDH phosphorylation by modulating intracellular lactate levels. Finally, bioinformatics analysis of the hepatocellular carcinoma cohort from The Cancer Genome Atlas revealed that a low LDHB/LDHA ratio is statistically significantly associated with poor prognostic outcomes. A low ratio was also associated with a significant enrichment in glycolysis genes and negatively correlated with PDK1 and 2 expression, supporting a close link between LDHB suppression and the PDK/PDH axis. These results suggest that LDHB suppression is a key mechanism that enhances glycolysis and is critically involved in the maintenance and propagation of mitochondrial dysfunction via lactate release in liver cancer progression.
    Keywords:  hepatocellular carcinoma; lactic acid; liver cancer; mitochondria; mitochondrial respiratory chain complex; pyruvate dehydrogenase complex (PDC)
    DOI:  https://doi.org/10.1074/jbc.RA118.006095
  12. J Appl Physiol (1985). 2019 Mar 28.
    Chao T, Burmeister DM, Corona BT, Greising SM.
      Volumetric muscle loss (VML) occurs after severe orthopaedic trauma, and results in loss of muscle fibers and function which can leave patients permanently disabled. While animals models of VML are useful to test possible therapeutic strategies, the pathophysiological characteristics of remaining skeletal muscle and changes in metabolism are not thoroughly understood. Herein, alterations of neuromuscular function, muscle fiber morphology, myosin heavy chain (MyHC) expression, and myofiber mitochondrial respiration were evaluated in an adult Yorkshire swine VML injury model. VML injured animals showed reduced peak isometric strength (p<0.05) and a shift towards smaller muscle fibers independent of fiber type (p<0.001). The muscle remaining after VML had a greater distribution of type I fibers and lower distribution of type II fibers (p<0.001). Skeletal muscle mitochondrial state 2 and state 3, reflecting complex I respiration, increased after injury (p<0.05) with a consistent trend to display higher oxygen flux per mg of tissue. However, this was largely driven by increased mitochondrial content after VML which is associated with higher mitochondrial fission (FIS-1 protein levels). T This study demonstrates an underlying perturbation of oxidative metabolism within the remaining musculature following surgical creation of an isolated, sterile VML injury in a porcine model that may be influential to the development of insidious pathophysiology and regenerative and rehabilitative therapies.
    Keywords:  Mitochondrial Respiration; Myosin Heavy Chain; Orthopaedic; Skeletal Muscle Injury; Trauma
    DOI:  https://doi.org/10.1152/japplphysiol.00026.2019
  13. Cell Metab. 2019 Mar 13. pii: S1550-4131(19)30125-1. [Epub ahead of print]
    Sullivan MR, Mattaini KR, Dennstedt EA, Nguyen AA, Sivanand S, Reilly MF, Meeth K, Muir A, Darnell AM, Bosenberg MW, Lewis CA, Vander Heiden MG.
      Tumors exhibit altered metabolism compared to normal tissues. Many cancers upregulate expression of serine synthesis pathway enzymes, and some tumors exhibit copy-number gain of the gene encoding the first enzyme in the pathway, phosphoglycerate dehydrogenase (PHGDH). However, whether increased serine synthesis promotes tumor growth and how serine synthesis benefits tumors is controversial. Here, we demonstrate that increased PHGDH expression promotes tumor progression in mouse models of melanoma and breast cancer, human tumor types that exhibit PHGDH copy-number gain. We measure circulating serine levels and find that PHGDH expression is necessary to support cell proliferation at lower physiological serine concentrations. Increased dietary serine or high PHGDH expression is sufficient to increase intracellular serine levels and support faster tumor growth. Together, these data suggest that physiological serine availability restrains tumor growth and argue that tumors arising in serine-limited environments acquire a fitness advantage by upregulating serine synthesis pathway enzymes.
    Keywords:  PHGDH; breast cancer; melanoma; serine
    DOI:  https://doi.org/10.1016/j.cmet.2019.02.015
  14. Integr Comp Biol. 2019 Mar 26. pii: icz015. [Epub ahead of print]
    Weaver RJ.
      The environment in which eukaryotes first evolved was drastically different from what they experience today, and one of the key limiting factors was the availability of oxygen for mitochondrial respiration. During the transition to a fully oxygenated Earth, other compounds such as sulfide posed a considerable constraint on using mitochondrial aerobic respiration for energy production. The ancestors of animals, and those that first evolved from the simpler eukaryotes have mitochondrial respiratory components that are absent from later-evolving animals. Specifically, mitochondria of most basal metazoans have a sulfide-resistant alternative oxidase (AOX), which provides a secondary oxidative pathway to the classical cytochrome pathway. In this essay, I argue that because of its resistance to sulfide, AOX respiration was critical to the evolution of animals by enabling oxidative metabolism under otherwise inhibitory conditions. I hypothesize that AOX allowed for metabolic flexibility during the stochastic oxygen environment of early Earth which shaped the evolution of basal metazoans. I briefly describe the known functions of AOX, with a particular focus on the decreased production of reactive oxygen species (ROS) during stress conditions. Then, I propose three evolutionary consequences of AOX-mediated protection from ROS observed in basal metazoans: 1) adaptation to stressful environments, 2) the persistence of facultative sexual reproduction, and 3) decreased mitochondrial DNA mutation rates. Recognizing the diversity of mitochondrial respiratory systems present in animals may help resolve the mechanisms involved in major evolutionary processes such as adaptation and speciation.
    DOI:  https://doi.org/10.1093/icb/icz015
  15. Mitochondrion. 2019 Mar 21. pii: S1567-7249(18)30235-6. [Epub ahead of print]
    El Hadi H, Vettor R, Rossato M.
      Cardiovascular disease is the leading cause of diabetes-related morbidity and mortality. It is widely accepted that heart failure risk is increased in diabetic patients even after adjusting for coronary artery disease and hypertension. Mitochondria are the center of fatty acid (FA) and glucose metabolism and thus are likely to be impacted by impaired metabolism associated with diabetes. Although the cause of this increased heart failure risk is multifactorial, increasing evidence points toward a crucial role for cardiomyocyte mitochondria dysfunction. Altered energy metabolism, defects in mitochondrial dynamics, increased oxidative stress, impaired calcium (Ca2+) handling and mitochondria-induced cell death are observed in mitochondria of diabetic myocardium. In addition, mitochondrial dysfunction appears to contribute substantially to the origin of arrhythmias in diabetic hearts. The current review will describe these mitochondrial abnormalities in cardiomyocytes attempting to provide an overview of underlying mechanisms. Finally, we briefly discuss the potential link between mitochondrial malfunction and arrhythmogenesis.
    Keywords:  Arrhythmogenesis; Cardiomyocyte; Metabolic disorder; Mitochondrial dynamics; Mitochondrial dysfunction; Oxidative stress; diabetes mellitus
    DOI:  https://doi.org/10.1016/j.mito.2019.03.005
  16. J Physiol. 2019 Mar 28.
    Kim Y, Yang DS, Katti P, Glancy B.
      KEY POINTS: Muscle mitochondrial networks changed from a longitudinal, fibre parallel orientation to a perpendicular configuration during postnatal development. Mitochondrial dynamics, mitophagy, and calcium uptake proteins were abundant during early postnatal development. Mitochondrial biogenesis and oxidative phosphorylation proteins were upregulated throughout muscle development. Postnatal muscle mitochondrial network formation is accompanied by a change in protein expression profile from mitochondria designed for coordinated cellular assembly to mitochondria highly specialized for cellular energy metabolism.ABSTRACT: Striated muscle mitochondria form connected networks capable of rapid cellular energy distribution. However, the mitochondrial reticulum is not formed at birth, and the mechanisms driving network development remain unclear. Here, we aimed to establish the network formation timecourse and protein expression profile during postnatal development of the murine muscle mitochondrial reticulum. Two-photon microscopy was used to observe mitochondrial network orientation in tibialis anterior (TA) muscles of live mice at postnatal (P) 1, 7, 14, 21, and 42 days, respectively. All muscle fibres maintained a longitudinal, fibre parallel mitochondrial network orientation early in development (P1-7). Mixed networks were most common at P14, but by P21, nearly all fibres had developed the perpendicular mitochondrial orientation observed in mature, glycolytic fibres. Tandem mass tag proteomics were then applied to examine changes in 6869 protein abundances in developing TA muscles. Mitochondrial proteins increased by 32% from P1 to P42. In addition, both nuclear- and mitochondrial-DNA encoded oxidative phosphorylation (OxPhos) components were increased during development while OxPhos assembly factors decreased. Though mitochondrial dynamics and mitophagy were induced at P1-7, mitochondrial biogenesis was enhanced after P14. Moreover, calcium signalling proteins and the mitochondrial calcium uniporter had highest expression early in postnatal development. In conclusion, mitochondrial networks transform from a fibre parallel to perpendicular orientation during the second and third weeks after birth in murine glycolytic skeletal muscle. This structural transition is accompanied by a change in protein expression profile from mitochondria designed for coordinated cellular assembly to mitochondria highly specialized for cellular energy metabolism. This article is protected by copyright. All rights reserved.
    Keywords:  mitochondrial development; postnatal muscle development; proteomics
    DOI:  https://doi.org/10.1113/JP277579
  17. Nat Rev Clin Oncol. 2019 Mar 26.
    Li X, Wenes M, Romero P, Huang SC, Fendt SM, Ho PC.
      The development of immunotherapies over the past decade has resulted in a paradigm shift in the treatment of cancer. However, the majority of patients do not benefit from immunotherapy, presumably owing to insufficient reprogramming of the immunosuppressive tumour microenvironment (TME) and thus limited reinvigoration of antitumour immunity. Various metabolic machineries and nutrient-sensing mechanisms orchestrate the behaviour of immune cells in response to nutrient availability in the TME. Notably, tumour-infiltrating immune cells typically experience metabolic stress as a result of the dysregulated metabolic activity of tumour cells, leading to impaired antitumour immune responses. Moreover, the immune checkpoints that are often exploited by tumour cells to evade immunosurveillance have emerging roles in modulating the metabolic and functional activity of T cells. Thus, repurposing of drugs targeting cancer metabolism might synergistically enhance immunotherapy via metabolic reprogramming of the TME. In addition, interventions targeting the metabolic circuits that impede antitumour immunity have been developed, with several clinical trials underway. Herein, we discuss how these metabolic circuits regulate antitumour immunity and the possible approaches to targeting these pathways in the context of anticancer immunotherapy. We also describe hypothetical combination treatments that could be used to better unleash the potential of adoptive cell therapies by enhancing T cell metabolism.
    DOI:  https://doi.org/10.1038/s41571-019-0203-7
  18. Br J Anaesth. 2019 Mar 19. pii: S0007-0912(19)30097-2. [Epub ahead of print]
    Chang L, Daly C, Miller DM, Allen PD, Boyle JP, Hopkins PM, Shaw MA.
      BACKGROUND: Individuals genetically susceptible to malignant hyperthermia (MH) exhibit hypermetabolic reactions when exposed to volatile anaesthetics. Mitochondrial dysfunction has previously been associated with the MH-susceptible (MHS) phenotype in animal models, but evidence of this in human MH is limited.METHODS: We used high resolution respirometry to compare oxygen consumption rates (oxygen flux) between permeabilised human MHS and MH-negative (MHN) skeletal muscle fibres with or without prior exposure to halothane. A substrate-uncoupler-inhibitor titration protocol was used to measure the following components of the electron transport chain under conditions of oxidative phosphorylation (OXPHOS) or after uncoupling the electron transport system (ETS): complex I (CI), complex II (CII), CI+CII and, as a measure of mitochondrial mass, complex IV (CIV).
    RESULTS: Baseline comparisons without halothane exposure showed significantly increased mitochondrial mass (CIV, P=0.021) but lower flux control ratios in CI+CII(OXPHOS) and CII(ETS) of MHS mitochondria compared with MHN (P=0.033 and 0.005, respectively) showing that human MHS mitochondria have a functional deficiency. Exposure to halothane triggered a hypermetabolic response in MHS mitochondria, significantly increasing mass-specific oxygen flux in CI(OXPHOS), CI+CII(OXPHOS), CI+CII(ETS), and CII(ETS) (P=0.001-0.012), while the rates in MHN samples were unaltered by halothane exposure.
    CONCLUSIONS: We present evidence of mitochondrial dysfunction in human MHS skeletal muscle both at baseline and after halothane exposure.
    Keywords:  electron transport chain; malignant hyperthermia; mitochondria, oxidative phosphorylation; skeletal muscle; volatile anaesthetic
    DOI:  https://doi.org/10.1016/j.bja.2019.02.010
  19. Front Endocrinol (Lausanne). 2019 ;10 122
    Elmore SE, La Merrill MA.
      There is increasing evidence supporting the characterization of the pesticide DDT and its metabolite, DDE, as obesogens and metabolic disruptors. Elucidating the mechanism is critical to understanding whether the association of DDT and DDE with obesity and diabetes is in fact causal. One area of research investigating the etiology of metabolic diseases is mitochondrial toxicity. Several studies have found associations between mitochondrial defects and insulin resistance, cellular respiration, substrate utilization, and energy expenditure. Although the mitotoxicity of DDT and DDE was established 20-40 years ago, it was not viewed in the light of the diseases faced today; therefore, it is prudent to reexamine the mitotoxicity literature for mechanistic support of DDT and DDE as causal contributors to obesity and diabetes, as well as associated diseases, such as cancer and Alzheimer's disease. This review aims to focus on studies investigating the effect of DDT or DDE on mammalian mitochondrial oxidative phosphorylation. We illustrate that both DDT and DDE impair the electron transport chain (ETC) and oxidative phosphorylation. We conclude that there is reasonable data to suggest that DDT and DDE target specific complexes and processes within the mitochondria, and that these insults could in turn contribute to the role of DDT and DDE in mitochondria-associated diseases.
    Keywords:  DDE; DDT; electron transport chain; insulin resistance; mitotoxicity; obesity; pesticides
    DOI:  https://doi.org/10.3389/fendo.2019.00122
  20. Cell Rep. 2019 Mar 26. pii: S2211-1247(19)30291-8. [Epub ahead of print]26(13): 3784-3797.e8
    Chemello F, Grespi F, Zulian A, Cancellara P, Hebert-Chatelain E, Martini P, Bean C, Alessio E, Buson L, Bazzega M, Armani A, Sandri M, Ferrazza R, Laveder P, Guella G, Reggiani C, Romualdi C, Bernardi P, Scorrano L, Cagnin S, Lanfranchi G.
      Skeletal muscle is composed of different myofiber types that preferentially use glucose or lipids for ATP production. How fuel preference is regulated in these post-mitotic cells is largely unknown, making this issue a key question in the fields of muscle and whole-body metabolism. Here, we show that microRNAs (miRNAs) play a role in defining myofiber metabolic profiles. mRNA and miRNA signatures of all myofiber types obtained at the single-cell level unveiled fiber-specific regulatory networks and identified two master miRNAs that coordinately control myofiber fuel preference and mitochondrial morphology. Our work provides a complete and integrated mouse myofiber type-specific catalog of gene and miRNA expression and establishes miR-27a-3p and miR-142-3p as regulators of lipid use in skeletal muscle.
    Keywords:  lipids; miRNAs; mitochondria; single myofiber; skeletal muscle metabolism
    DOI:  https://doi.org/10.1016/j.celrep.2019.02.105
  21. Autophagy. 2019 Mar 25.
    Park JS, Lee DH, Lee YS, Oh E, Bae KH, Oh KJ, Kim H, Bae SH.
      Saturated fatty acid (SFA)-induced lipotoxicity is caused by the accumulation of reactive oxygen species (ROS), which is associated with damaged mitochondria. Moreover, lipotoxicity is crucial for the progression of nonalcoholic steatohepatitis (NASH). Autophagy is required for the clearance of protein aggregates or damaged mitochondria to maintain cellular metabolic homeostasis. The NFE2L2/NRF2 (nuclear factor, erythroid 2 like 2)-KEAP1 (kelch like ECH associated protein 1) pathway is essential for the elimination of ROS. ULK1 (unc-51 like autophagy activating kinase 1; yeast Atg1) is involved in the initiation of autophagy; however, its role in lipotoxicity-induced cell death in hepatocytes and mouse liver has not been elucidated. We now show that ULK1 potentiates the interaction between KEAP1 and the autophagy adaptor protein SQSTM1/p62, thereby mediating NFE2L2 activation in a manner requiring SQSTM1-dependent autophagic KEAP1 degradation. Furthermore, ULK1 is required for the autophagic removal of damaged mitochondria and to enhance binding between SQSTM1 and PINK1 (PTEN induced kinase 1). This study demonstrates the molecular mechanisms underlying the cytoprotective role of ULK1 against lipotoxicity. Thus, ULK1 could represent a potential therapeutic target for the treatment of NASH.
    Keywords:  KEAP1 (kelch like ECH-associated protein 1); NASH; SQSTM1/p62 (sequestosome 1); ULK1 (unc-51-like autophagy activating kinase 1); lipotoxicity
    DOI:  https://doi.org/10.1080/15548627.2019.1598751
  22. J Clin Invest. 2019 Mar 28. pii: 127579. [Epub ahead of print]130
    Piyarathna DWB, Balasubramanian A, Arnold JM, Lloyd SM, Karanam B, Castro P, Ittmann MM, Putluri N, Navone N, Jones JA, Yu W, Sandulache VC, Sikora AG, Michailidis G, Sreekumar A.
      BACKGROUND: African American (AA) patients have higher cancer mortality rates and shorter survival times compared to European American (EA) patients. Despite a significant focus on socioeconomic factors, recent findings strongly argue the existence of biological factors driving this disparity. Most of these factors have been described in a cancer-type specific context rather than a pan-cancer setting.METHODS: A novel in silico approach based on Gene Set Enrichment Analysis (GSEA) coupled to Transcription Factor enrichment was carried out to identify common biological drivers of pan-cancer racial disparity using The Cancer Genome Atlas (TCGA) dataset. Mitochondrial content in patient tissues was examined using a multi-cancer tissue microarray approach (TMA).
    RESULTS: Mitochondrial oxidative phosphorylation was uniquely enriched in AA tumors compared to EA tumors across various cancer types. AA tumors also showed strong enrichment for the ERR1-PGC1α-mediated transcriptional program, which has been implicated in mitochondrial biogenesis. TMA analysis revealed that AA cancers harbor significantly more mitochondria compared to their EA counterparts.
    CONCLUSIONS: These findings highlight changes in mitochondria as a common distinguishing feature between AA and EA tumors in a pan-cancer setting, and provide the rationale for the repurposing of mitochondrial inhibitors to treat AA cancers.
    Keywords:  Cancer; Metabolism; Oncology
    DOI:  https://doi.org/10.1172/JCI127579
  23. PLoS One. 2019 ;14(3): e0214287
    Esposito M, Hermann-Le Denmat S, Delahodde A.
      Eukaryotic organelles share different components and establish physical contacts to communicate throughout the cell. One of the best-recognized examples of such interplay is the metabolic cooperation and crosstalk between mitochondria and peroxisomes, both organelles being functionally and physically connected and linked to the endoplasmic reticulum (ER). In Saccharomyces cerevisiae, mitochondria are linked to the ER by the ERMES complex that facilitates inter-organelle calcium and phospholipid exchanges. Recently, peroxisome-mitochondria contact sites (PerMit) have been reported and among Permit tethers, one component of the ERMES complex (Mdm34) was shown to interact with the peroxin Pex11, suggesting that the ERMES complex or part of it may be involved in two membrane contact sites (ER-mitochondria and peroxisome- mitochondria). This opens the possibility of exchanges between these three membrane compartments. Here, we investigated in details the role of each ERMES subunit on peroxisome abundance. First, we confirmed previous studies from other groups showing that absence of Mdm10 or Mdm12 leads to an increased number of mature peroxisomes. Secondly, we showed that this is not simply due to respiratory function defect, mitochondrial DNA (mtDNA) loss or mitochondrial network alteration. Finally, we present evidence that the contribution of ERMES subunits Mdm10 and Mdm12 to peroxisome number involves two different mechanisms.
    DOI:  https://doi.org/10.1371/journal.pone.0214287
  24. Proc Natl Acad Sci U S A. 2019 Mar 29. pii: 201816023. [Epub ahead of print]
    Morita M, Siddiqui N, Katsumura S, Rouya C, Larsson O, Nagashima T, Hekmatnejad B, Takahashi A, Kiyonari H, Zang M, St-Arnaud R, Oike Y, Giguère V, Topisirovic I, Okada-Hatakeyama M, Yamamoto T, Sonenberg N.
      Whole-body metabolic homeostasis is tightly controlled by hormone-like factors with systemic or paracrine effects that are derived from nonendocrine organs, including adipose tissue (adipokines) and liver (hepatokines). Fibroblast growth factor 21 (FGF21) is a hormone-like protein, which is emerging as a major regulator of whole-body metabolism and has therapeutic potential for treating metabolic syndrome. However, the mechanisms that control FGF21 levels are not fully understood. Herein, we demonstrate that FGF21 production in the liver is regulated via a posttranscriptional network consisting of the CCR4-NOT deadenylase complex and RNA-binding protein tristetraprolin (TTP). In response to nutrient uptake, CCR4-NOT cooperates with TTP to degrade AU-rich mRNAs that encode pivotal metabolic regulators, including FGF21. Disruption of CCR4-NOT activity in the liver, by deletion of the catalytic subunit CNOT6L, increases serum FGF21 levels, which ameliorates diet-induced metabolic disorders and enhances energy expenditure without disrupting bone homeostasis. Taken together, our study describes a hepatic CCR4-NOT/FGF21 axis as a hitherto unrecognized systemic regulator of metabolism and suggests that hepatic CCR4-NOT may serve as a target for devising therapeutic strategies in metabolic syndrome and related morbidities.
    Keywords:  CCR4–NOT; FGF21; deadenylase; hepatokine; metabolic syndrome
    DOI:  https://doi.org/10.1073/pnas.1816023116
  25. Front Physiol. 2019 ;10 191
    Zhang X, Dash RK, Clough AV, Xie D, Jacobs ER, Audi SH.
      Altered lung tissue bioenergetics plays a key role in the pathogenesis of lung diseases. A wealth of information exists regarding the bioenergetic processes in mitochondria isolated from rat lungs, cultured pulmonary endothelial cells, and intact rat lungs under physiological and pathophysiological conditions. However, the interdependence of those processes makes it difficult to quantify the impact of a change in a single or multiple process(es) on overall lung tissue bioenergetics. Integrated computational modeling provides a mechanistic and quantitative framework for the bioenergetic data at different levels of biological organization. The objective of this study was to develop and validate an integrated computational model of lung bioenergetics using existing experimental data from isolated perfused rat lungs. The model expands our recently developed computational model of the bioenergetics of mitochondria isolated from rat lungs by accounting for glucose uptake and phosphorylation, glycolysis, and the pentose phosphate pathway. For the mitochondrial region of the model, values of kinetic parameters were fixed at those estimated in our recent model of the bioenergetics of mitochondria isolated from rat lungs. For the cytosolic region of the model, intrinsic parameters such as apparent Michaelis constants were determined based on previously published enzyme kinetics data, whereas extrinsic parameters such as maximal reaction and transport velocities were estimated by fitting the model solution to published data from isolated rat lungs. The model was then validated by assessing its ability to predict existing experimental data not used for parameter estimation, including relationships between lung nucleotides content, lung lactate production rate, and lung energy charge under different experimental conditions. In addition, the model was used to gain novel insights on how lung tissue glycolytic rate is regulated by exogenous substrates such as glucose and lactate, and assess differences in the bioenergetics of mitochondria isolated from lung tissue and those of mitochondria in intact lungs. To the best of our knowledge, this is the first model of lung tissue bioenergetics. The model provides a mechanistic and quantitative framework for integrating available lung tissue bioenergetics data, and for testing novel hypotheses regarding the role of different cytosolic and mitochondrial processes in lung tissue bioenergetics.
    Keywords:  cellular metabolism; glycolysis; isolated rat lungs; mitochondrial bioenergetics; thermodynamically-constrained modeling
    DOI:  https://doi.org/10.3389/fphys.2019.00191
  26. J Cell Sci. 2019 Mar 25. pii: jcs.230755. [Epub ahead of print]
    Spurlock B, Gupta P, Basu MK, Mukherjee A, Hjelmeland AB, Darley-Usmar V, Parker D, Foxall ME, Mitra K.
      Steady-state mitochondrial structure or morphology is primarily maintained by a balance of opposing fission and fusion events between individual mitochondria, which is collectively referred to as mitochondrial dynamics. The details of the bidirectional relationship between the status of mitochondrial dynamics (structure) and energetics (function) require methods to integrate these mitochondrial aspects. To study the quantitative relationship between the status of mitochondrial dynamics (fission, fusion, matrix continuity and diameter) and energetics (ATP and redox), we have developed an analytical approach called mito-SinCe2 After validating and providing proof of principal, we applied mito-SinCe2 on ovarian tumor initiating cells (ovTICs). Mito-SinCe2 analyses led to the hypothesis that mitochondria-dependent ovTICs interconvert between 3 states with distinct relationships between mitochondrial energetics and dynamics. Interestingly, fusion and ATP increase linearly with each other only once a certain level of fusion is attained. Moreover, mitochondrial dynamics status changes linearly either with ATP or with redox, but not simultaneously with both. Furthermore, mito-SinCe2 analyses can potentially predict new quantitative features of the opposing fission vs. fusion relationship and classify cells into functional classes based on their mito-SinCe2 states.
    Keywords:  Method; Microscopy; Mitochondrial ATP; Mitochondrial fission and fusion; Mitochondrial redox; Ovarian tumor initiating cells; Single cells
    DOI:  https://doi.org/10.1242/jcs.230755
  27. Nature. 2019 Mar 27.
    Yao W, Rose JL, Wang W, Seth S, Jiang H, Taguchi A, Liu J, Yan L, Kapoor A, Hou P, Chen Z, Wang Q, Nezi L, Xu Z, Yao J, Hu B, Pettazzoni PF, Ho IL, Feng N, Ramamoorthy V, Jiang S, Deng P, Ma GJ, Den P, Tan Z, Zhang SX, Wang H, Wang YA, Deem AK, Fleming JB, Carugo A, Heffernan TP, Maitra A, Viale A, Ying H, Hanash S, DePinho RA, Draetta GF.
      Pancreatic ductal adenocarcinoma (PDAC) remains recalcitrant to all forms of cancer treatment and carries a five-year survival rate of only 8%1. Inhibition of oncogenic KRAS (hereafter KRAS*), the earliest lesion in disease development that is present in more than 90% of PDACs, and its signalling surrogates has yielded encouraging preclinical results with experimental agents2-4. However, KRAS*-independent disease recurrence following genetic extinction of Kras* in mouse models anticipates the need for co-extinction strategies5,6. Multiple oncogenic processes are initiated at the cell surface, where KRAS* physically and functionally interacts to direct signalling that is essential for malignant transformation and tumour maintenance. Insights into the complexity of the functional cell-surface-protein repertoire (surfaceome) have been technologically limited until recently and-in the case of PDAC-the genetic control of the function and composition of the PDAC surfaceome in the context of KRAS* signalling remains largely unknown. Here we develop an unbiased, functional target-discovery platform to query KRAS*-dependent changes of the PDAC surfaceome, which reveals syndecan 1 (SDC1, also known as CD138) as a protein that is upregulated at the cell surface by KRAS*. Localization of SDC1 at the cell surface-where it regulates macropinocytosis, an essential metabolic pathway that fuels PDAC cell growth-is essential for disease maintenance and progression. Thus, our study forges a mechanistic link between KRAS* signalling and a targetable molecule driving nutrient salvage pathways in PDAC and validates oncogene-driven surfaceome annotation as a strategy to identify cancer-specific vulnerabilities.
    DOI:  https://doi.org/10.1038/s41586-019-1062-1
  28. Adv Exp Med Biol. 2019 ;1134 89-110
    Casajus Pelegay E, Puzzo F, Yilmazer A, Cagin U.
      Bioenergetic homeostasis is a vital process maintaining cellular health and has primary importance in neuronal cells due to their high energy demand markedly at synapses. Mitochondria, the metabolic hubs of the cells, are the organelles responsible for producing energy in the form of ATP by using nutrients and oxygen. Defects in mitochondrial homeostasis result in energy deprivation and can lead to disrupted neuronal functions. Mitochondrial defects adversely contribute to the pathogenesis of neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease (PD). Mitochondrial defects not only include reduced ATP levels but also increased reactive oxygen species (ROS) leading to cellular damage. Here, we detail the mechanisms that lead to neuronal pathologies involving mitochondrial defects. Furthermore, we discuss how to target these mitochondrial defects in order to have beneficial effects as novel and complementary therapeutic avenues in neurodegenerative diseases. The critical evaluation of these strategies and their potential outcome can pave the way for finding novel therapies for neurodegenerative pathologies.
    Keywords:  Animal models; Drug target; Longevity; Mitochondria; Neurodegenerative disease
    DOI:  https://doi.org/10.1007/978-3-030-12668-1_5
  29. Proc Natl Acad Sci U S A. 2019 Mar 28. pii: 201809964. [Epub ahead of print]
    Zhang J, Goliwas KF, Wang W, Taufalele PV, Bordeleau F, Reinhart-King CA.
      The ability of primary tumor cells to invade into adjacent tissues, followed by the formation of local or distant metastasis, is a lethal hallmark of cancer. Recently, locomoting clusters of tumor cells have been identified in numerous cancers and associated with increased invasiveness and metastatic potential. However, how the collective behaviors of cancer cells are coordinated and their contribution to cancer invasion remain unclear. Here we show that collective invasion of breast cancer cells is regulated by the energetic statuses of leader and follower cells. Using a combination of in vitro spheroid and ex vivo organoid invasion models, we found that cancer cells dynamically rearrange leader and follower positions during collective invasion. Cancer cells invade cooperatively in denser collagen matrices by accelerating leader-follower switching thus decreasing leader cell lifetime. Leader cells exhibit higher glucose uptake than follower cells. Moreover, their energy levels, as revealed by the intracellular ATP/ADP ratio, must exceed a threshold to invade. Forward invasion of the leader cell gradually depletes its available energy, eventually leading to leader-follower transition. Our computational model based on intracellular energy homeostasis successfully recapitulated the dependence of leader cell lifetime on collagen density. Experiments further supported model predictions that decreasing the cellular energy level by glucose starvation decreases leader cell lifetime whereas increasing the cellular energy level by AMP-activated kinase (AMPK) activation does the opposite. These findings highlight coordinated invasion and its metabolic regulation as potential therapeutic targets of cancer.
    Keywords:  bioenergetics; cancer invasion; cancer metabolism; collective migration; leader cell
    DOI:  https://doi.org/10.1073/pnas.1809964116
  30. Cell Calcium. 2019 Mar 06. pii: S0143-4160(19)30017-X. [Epub ahead of print]80 8-17
    Miller BA.
      The TRP ion channel TRPM2 has an essential function in cell survival and protects the viability of a number of cell types after oxidative stress. It is highly expressed in many cancers including breast, prostate, and pancreatic cancer, melanoma, leukemia, and neuroblastoma, suggesting it promotes cancer cell survival. TRPM2 is activated by production of ADP-ribose (ADPR) following oxidative stress, which binds to the C-terminus of TRPM2, resulting in channel opening. In a number of cancers including neuroblastoma, TRPM2 has been shown to preserve viability and mechanisms have been identified. Activation of TRPM2 results in expression of transcription factors and kinases important in cell proliferation and survival including HIF-1/2α, CREB, nuclear factor (erythroid-derived 2)-related factor-2 (Nrf2), and Pyk2, and Src phosphorylation. Together, HIF-1/2α and CREB regulate expression of genes encoding proteins with roles in mitochondrial function including members of the electron transport complex involved in ATP production. These contribute to lower mitochondrial ROS production while expression of antioxidants regulated by HIF-1/2α, FOXO3a, CREB, and Nrf2 is maintained. CREB is also important in control of expression of key proteins involved in autophagy. When TRPM2-mediated calcium influx is inhibited, mitochondria are dysfunctional, cellular bioenergetics are reduced, production of ROS is increased, and autophagy and DNA repair are impaired, decreasing tumor growth and increasing chemotherapy sensitivity. Inhibition of TRPM2 expression or function results in decreased tumor proliferation and/or viability in many malignancies including breast, gastric, pancreatic, prostate, head and neck cancers, melanoma, neuroblastoma, and T-cell and acute myelogenous leukemia. However, in a small number of malignancies, activation of TRPM2 rather than inhibition has been reported to reduce tumor cell survival. Here, TRPM2-mediated Ca2+ signaling and mechanisms of regulation of cancer cell growth and survival are reviewed and controversies discussed. Evidence suggests that targeting TRPM2 may be a novel therapeutic approach in many cancers.
    Keywords:  CREB; Cancer; HIF-1α; Mitochondria; ROS; TRPM2
    DOI:  https://doi.org/10.1016/j.ceca.2019.03.002
  31. J Cell Biol. 2019 Mar 26. pii: jcb.201808131. [Epub ahead of print]
    Ren M, Xu Y, Erdjument-Bromage H, Donelian A, Phoon CKL, Terada N, Strathdee D, Neubert TA, Schlame M.
      Mitochondria contain cardiolipin (CL), an organelle-specific phospholipid that carries four fatty acids with a strong preference for unsaturated chains. Unsaturation is essential for the stability and for the function of mitochondrial CL. Surprisingly, we found tetrapalmitoyl-CL (TPCL), a fully saturated species, in the testes of humans and mice. TPCL was absent from other mouse tissues but was the most abundant CL species in testicular germ cells. Most intriguingly, TPCL was not localized in mitochondria but was in other cellular membranes even though mitochondrial CL was the substrate from which TPCL was synthesized. During spermiogenesis, TPCL became associated with the acrosome, a sperm-specific organelle, along with a subset of authentic mitochondrial proteins, including Ant4, Suox, and Spata18. Our data suggest that mitochondria-derived membranes are assembled into the acrosome, challenging the concept that this organelle is strictly derived from the Golgi apparatus and revealing a novel function of mitochondria.
    DOI:  https://doi.org/10.1083/jcb.201808131
  32. Mitochondrion. 2019 Mar 26. pii: S1567-7249(18)30138-7. [Epub ahead of print]
    Mir DA, Balamurugan K.
      Mitochondria are involved in a variety of cellular metabolic processes and their functions are regulated by intrinsic and extrinsic stimuli. Recent studies have revealed functional diversity and importance of mitochondria in many cellular processes, including the innate immune response. This study evaluated the specific response and proteomic changes in host Caenorhabditis elegans mitochondria during Pseudomonas aeruginosa PAO1 infection. We performed an inclusive approach to determine the C. elegans mitochondria proteome. The protein fractions of mitochondria were analysed by tandem LC-MS/MS, 129 differentially regulated proteins were identified, indicating an involvement of various mitochondrial processes. The several known components of the oxidative phosphorylation (OXPHOS) machinery, the tricarboxylic acid (TCA) cycle, mitochondrial unfolded protein response (UPRmt) and stable mitochondria-encoded proteins were found to be differentially expressed. Our results in-depth provide new horizons for mitochondria-associated protein functions and the classification of mitochondrial diseases during host-pathogen interaction.
    Keywords:  Caenorhabditis elegans; Infection; Mitochondrial proteomic analysis; Pseudomonas aeruginosa PAO1
    DOI:  https://doi.org/10.1016/j.mito.2019.03.002
  33. J Neurosci. 2019 Mar 29. pii: 0894-18. [Epub ahead of print]
    McNair LF, Andersen JV, Aldana B, Hohnholt MC, Nissen JD, Sun Y, Fischer KD, Sonnewald U, Nyberg N, Webster SC, Kapur K, Rimmele TS, Barone I, Hawks-Mayer H, Lipton JO, Hodgson NW, Aoki CJ, Rosenberg PA, Waagepetersen HS.
      The glutamate transporter GLT-1 is highly expressed in astrocytes but also in neurons, primarily in axon terminals. We generated a conditional neuronal GLT-1 knockout using synapsin 1-Cre (synGLT-1 KO) to elucidate the metabolic functions of GLT-1 expressed in neurons, here focusing on the cerebral cortex. Both synaptosomal uptake studies and electron microscopic immunocytochemistry demonstrated knockdown of GLT-1 in the cerebral cortex in the synGLT-1 KO mice. Aspartate content was significantly reduced in cerebral cortical extracts as well as synaptosomes from cerebral cortex of synGLT-1 KO compared to control littermates. 13C-Labelling of tricarboxylic acid cycle intermediates originating from metabolism of [U-13C]-glutamate was significantly reduced in synGLT-1 KO synaptosomes. The decreased aspartate content was due to diminished entry of glutamate into the TCA cycle. Pyruvate recycling, a pathway necessary for full glutamate oxidation, was also decreased. ATP production was significantly increased, despite unaltered oxygen consumption, in isolated mitochondria from the synGLT-1 KO. Density of mitochondria in axon terminals and peri-synaptic astrocytes were increased in the synGLT-1 KO. Intramitochondrial cristae density of synGLT-1 KO mice was increased suggesting increased mitochondrial efficiency, perhaps in compensation for reduced access to glutamate. SynGLT-1 KO synaptosomes exhibited an elevated oxygen consumption rate when stimulated with veratridine, despite a lower baseline oxygen consumption rate in the presence of glucose. GLT-1 expressed in neurons appears to be required to provide glutamate to synaptic mitochondria and is linked to neuronal energy metabolism and mitochondrial function.SIGNIFICANCE STATEMENTAll synaptic transmitters need to be cleared from the extracellular space after release, and transporters are used to clear glutamate released from excitatory synapses. GLT-1 is the major glutamate transporter, and most GLT-1 is expressed in astrocytes. Only 5-10% is expressed in neurons, primarily in axon terminals. The function of GLT-1 in axon terminals remains unknown. Here, we used a conditional knockout approach to investigate the significance of the expression of GLT-1 in neurons. We found multiple abnormalities of mitochondrial function suggesting impairment of glutamate utilization by synaptic mitochondria in the neuronal GLT-1 knockout. These data suggest that GLT-1 expressed in axon terminals may be important in maintaining energy metabolism and biosynthetic activities mediated by presynaptic mitochondria.
    DOI:  https://doi.org/10.1523/JNEUROSCI.0894-18.2019
  34. Adv Genet. 2019 ;pii: S0065-2660(18)30037-3. [Epub ahead of print]103 91-118
    McEneaney LJ, Tee AR.
      Tuberous sclerosis complex (TSC) is a rare, autosomal dominant genetic condition caused by a mutation in either the TSC1 or TSC2 gene. Phenotypically, this leads to aberrant cell growth and the formation of benign tumors called hamartomas in multiple organs. Understanding the mechanisms of pathology that are caused through the presence of disease causing mutations is a real hurdle for many rare genetic disorders; a limiting factor that restricts knowledge of the disease and any hope of a future cure. Through the discovery of the TSC1 and TSC2 genes and the signaling pathways responsible for the pathology of TSC, a new drug target called mechanistic target of rapamycin complex 1 (mTORC1) was discovered. Rapamycin, an mTORC1 inhibitor, is now the only pharmacological therapy approved for the treatment of TSC. This chapter summarizes the success story of TSC and explores the future possibilities of finding a cure.
    Keywords:  ER stress; Energy homeostasis; Rapamycin; TSC; mTOR; mTORC1
    DOI:  https://doi.org/10.1016/bs.adgen.2018.11.003
  35. Science. 2019 03 29. pii: eaau0135. [Epub ahead of print]363(6434):
    Vodnala SK, Eil R, Kishton RJ, Sukumar M, Yamamoto TN, Ha NH, Lee PH, Shin M, Patel SJ, Yu Z, Palmer DC, Kruhlak MJ, Liu X, Locasale JW, Huang J, Roychoudhuri R, Finkel T, Klebanoff CA, Restifo NP.
      A paradox of tumor immunology is that tumor-infiltrating lymphocytes are dysfunctional in situ, yet are capable of stem cell-like behavior including self-renewal, expansion, and multipotency, resulting in the eradication of large metastatic tumors. We find that the overabundance of potassium in the tumor microenvironment underlies this dichotomy, triggering suppression of T cell effector function while preserving stemness. High levels of extracellular potassium constrain T cell effector programs by limiting nutrient uptake, thereby inducing autophagy and reduction of histone acetylation at effector and exhaustion loci, which in turn produces CD8+ T cells with improved in vivo persistence, multipotency, and tumor clearance. This mechanistic knowledge advances our understanding of T cell dysfunction and may lead to novel approaches that enable the development of enhanced T cell strategies for cancer immunotherapy.
    DOI:  https://doi.org/10.1126/science.aau0135
  36. Aging Cell. 2019 Mar 29. e12943
    Tang H, Inoki K, Brooks SV, Okazawa H, Lee M, Wang J, Kim M, Kennedy CL, Macpherson PCD, Ji X, Van Roekel S, Fraga DA, Wang K, Zhu J, Wang Y, Sharp ZD, Miller RA, Rando TA, Goldman D, Guan KL, Shrager JB.
      Aging leads to skeletal muscle atrophy (i.e., sarcopenia), and muscle fiber loss is a critical component of this process. The mechanisms underlying these age-related changes, however, remain unclear. We show here that mTORC1 signaling is activated in a subset of skeletal muscle fibers in aging mouse and human, colocalized with fiber damage. Activation of mTORC1 in TSC1 knockout mouse muscle fibers increases the content of morphologically abnormal mitochondria and causes progressive oxidative stress, fiber damage, and fiber loss over the lifespan. Transcriptomic profiling reveals that mTORC1's activation increases the expression of growth differentiation factors (GDF3, 5, and 15), and of genes involved in mitochondrial oxidative stress and catabolism. We show that increased GDF15 is sufficient to induce oxidative stress and catabolic changes, and that mTORC1 increases the expression of GDF15 via phosphorylation of STAT3. Inhibition of mTORC1 in aging mouse decreases the expression of GDFs and STAT3's phosphorylation in skeletal muscle, reducing oxidative stress and muscle fiber damage and loss. Thus, chronically increased mTORC1 activity contributes to age-related muscle atrophy, and GDF signaling is a proposed mechanism.
    Keywords:  aging; mTORC1; oxidative stress; signal transduction; skeletal muscle
    DOI:  https://doi.org/10.1111/acel.12943
  37. Cell Metab. 2019 Mar 05. pii: S1550-4131(19)30102-0. [Epub ahead of print]
    Wu Z, Isik M, Moroz N, Steinbaugh MJ, Zhang P, Blackwell TK.
      Chronic inflammation predisposes to aging-associated disease, but it is unknown whether immunity regulation might be important for extending healthy lifespan. Here we show that in C. elegans, dietary restriction (DR) extends lifespan by modulating a conserved innate immunity pathway that is regulated by p38 signaling and the transcription factor ATF-7. Longevity from DR depends upon p38-ATF-7 immunity being intact but downregulated to a basal level. p38-ATF-7 immunity accelerates aging when hyperactive, influences lifespan independently of pathogen exposure, and is activated by nutrients independently of mTORC1, a major DR mediator. Longevity from reduced insulin/IGF-1 signaling (rIIS) also involves p38-ATF-7 downregulation, with signals from DAF-16/FOXO reducing food intake. We conclude that p38-ATF-7 is an immunometabolic pathway that senses bacterial and nutrient signals, that immunity modulation is critical for DR, and that DAF-16/FOXO couples appetite to growth regulation. These conserved mechanisms may influence aging in more complex organisms.
    Keywords:  ATF-7; C. elegans; aging; dietary restriction; food intake; immunometabolism; innate immunity; insulin/IGF-1 signaling; longevity; p38 signaling
    DOI:  https://doi.org/10.1016/j.cmet.2019.02.013
  38. Biochim Biophys Acta Mol Basis Dis. 2019 Mar 25. pii: S0925-4439(19)30107-3. [Epub ahead of print]
    Duraisamy AJ, Mohammad G, Kowluru RA.
      Mitochondria are dynamic in structure, and undergo continuous fusion-fission to maintain their homeostasis. In diabetes, retinal mitochondria are swollen, their membrane are damaged and mitochondrial fusion protein, mitofusin 2 (Mfn2), is decreased. DNA methylation machinery is also activated and methylation status of genes implicated in mitochondrial damage and biogenesis is altered. This study aims to investigate the role of mitochondrial fusion in the development of diabetic retinopathy, and illustrate the molecular mechanism responsible for Mfn2 suppression. Using human retinal endothelial cells, manipulated for Mfn2, we investigated the role of fusion in mitochondrial structural and functional damage in diabetes. The molecular mechanism of its suppression in diabetic milieu was determined by investigating Mfn2 promoter DNA methylation, and confirmed using molecular and pharmacological inhibitors of DNA methylation. Similar studies were performed in the retinal microvasculature (prepared by hypotonic shock method) of diabetic rats, and human donors with documented diabetic retinopathy. Overexpression of Mfn2 prevented glucose-induced increase in mitochondrial fragmentation, decrease in complex III activity and increase in membrane permeability, mtDNA damage and apoptosis. High glucose hypermethylated Mfn2 promoter and decreased transcription factor (SP1) binding, and Dnmt inhibition protected Mfn2 promoter from these changes. In streptozotocin-induced diabetic rats, intravitreal administration of Dnmt1-siRNA attenuated Mfn2 promoter hypermethylation and restored its expression. Human donors with diabetic retinopathy confirmed Mfn2 promoter DNA hypermethylation. Thus, regulating Mfn2 and its epigenetic modifications by molecular/pharmacological means will protect mitochondrial homeostasis in diabetes, and could attenuate the development of retinopathy in diabetic patients.
    Keywords:  Diabetic retinopathy; Epigenetics; Mitochondria; Mitochondrial dynamics; Mitofusins
    DOI:  https://doi.org/10.1016/j.bbadis.2019.03.013
  39. Proc Natl Acad Sci U S A. 2019 Mar 25. pii: 201901376. [Epub ahead of print]
    Kumar A, Pyaram K, Yarosz EL, Hong H, Lyssiotis CA, Giri S, Chang CH.
      Cellular metabolism and signaling pathways are key regulators to determine conventional T cell fate and function, but little is understood about the role of cell metabolism for natural killer T (NKT) cell survival, proliferation, and function. We found that NKT cells operate distinct metabolic programming from CD4 T cells. NKT cells are less efficient in glucose uptake than CD4 T cells with or without activation. Gene-expression data revealed that, in NKT cells, glucose is preferentially metabolized by the pentose phosphate pathway and mitochondria, as opposed to being converted into lactate. In fact, glucose is essential for the effector functions of NKT cells and a high lactate environment is detrimental for NKT cell survival and proliferation. Increased glucose uptake and IFN-γ expression in NKT cells is inversely correlated with bacterial loads in response to bacterial infection, further supporting the significance of glucose metabolism for NKT cell function. We also found that promyelocytic leukemia zinc finger seemed to play a role in regulating NKT cells' glucose metabolism. Overall, our study reveals that NKT cells use distinct arms of glucose metabolism for their survival and function.
    Keywords:  NKT; OXPHOS; PLZF; glucose
    DOI:  https://doi.org/10.1073/pnas.1901376116
  40. Circ Res. 2019 Mar 29.
    Dunham-Snary KJ, Wu D, Potus F, Sykes EA, Mewburn JD, Charles RL, Eaton P, Sultanian RA, Archer SL.
      RATIONALE: Hypoxic pulmonary vasoconstriction (HPV) optimizes systemic oxygen delivery by matching ventilation to perfusion. HPV is intrinsic to pulmonary artery smooth muscle cells (PASMC). Hypoxia dilates systemic arteries, including renal arteries. Hypoxia is sensed by changes in mitochondrial-derived reactive oxygen species, notably H2O2 ([H2O2]mito). Decreases in [H2O2]mito elevate pulmonary vascular tone by increasing intracellular calcium ([Ca2+]i) through redox regulation of ion channels. Although HPV is mimicked by the Complex I inhibitor, rotenone, the molecular identity of the O2-sensor is unknown.OBJECTIVE: To determine the role of NADH dehydrogenase [ubiquinone] iron-sulfur protein 2 (Ndufs2), Complex I's rotenone binding site, in pulmonary vascular oxygen-sensing.
    METHODS AND RESULTS: Mitochondria-conditioned media (MCM) from pulmonary and renal mitochondria isolated from normoxic and chronically hypoxic rats, were infused into an isolated lung bioassay. MCM from normoxic lungs contained more H2O2 than MCM from chronic hypoxic lungs or kidneys and uniquely attenuated HPV via a catalase-dependent mechanism. In PASMC acute hypoxia decreased H2O2within 112{plus minus}7s, followed, within 205{plus minus}34s, by increased intracellular calcium concentration, [Ca2+]i. Hypoxia had no effects on [Ca2+]i in renal artery SMC (RASMC). Hypoxia decreases both cytosolic and mitochondrial H2O2 in PASMC while increasing cytosolic H2O2 in RASMC. Ndufs2 expression was greater in PASMC versus RASMC. Lung Ndufs2 cysteine residues became reduced during acute hypoxia and both hypoxia and reducing agents caused functional inhibition of Complex I. In PASMC, siNdufs2 decreased normoxic H2O2, prevented hypoxic increases in [Ca2+]i, and mimicked aspects of chronic hypoxia, including decreasing Complex I activity, elevating the NADH/NAD+ ratio and decreasing expression of the O2-sensitive ion channel, Kv1.5. Knocking down another Fe-S center within Complex I (Ndufs1) or other mitochondrial subunits proposed as putative oxygen sensors (Complex III's Rieske Fe-S center and COX4i2 in Complex IV) had no effect on hypoxic increases in [Ca2+]i. In vivo, siNdufs2 significantly decreased hypoxia- and rotenone-induced constriction while enhancing phenylephrine-induced constriction.
    CONCLUSIONS: Ndufs2 is essential for oxygen-sensing and HPV.
    Keywords:  Ndufs1; Ndufs2; hydrogen peroxide; oxygen-sensing; voltage-gated postassium channel (Kv1.5)
    DOI:  https://doi.org/10.1161/CIRCRESAHA.118.314284
  41. Nat Chem Biol. 2019 Mar 25.
    Chen AL, Lum KM, Lara-Gonzalez P, Ogasawara D, Cognetta AB, To A, Parsons WH, Simon GM, Desai A, Petrascheck M, Bar-Peled L, Cravatt BF.
      Phenotypic screening has identified small-molecule modulators of aging, but the mechanism of compound action often remains opaque due to the complexities of mapping protein targets in whole organisms. Here, we combine a library of covalent inhibitors with activity-based protein profiling to coordinately discover bioactive compounds and protein targets that extend lifespan in Caenorhabditis elegans. We identify JZL184-an inhibitor of the mammalian endocannabinoid (eCB) hydrolase monoacylglycerol lipase (MAGL or MGLL)-as a potent inducer of longevity, a result that was initially perplexing as C. elegans does not possess an MAGL ortholog. We instead identify FAAH-4 as a principal target of JZL184 and show that this enzyme, despite lacking homology with MAGL, performs the equivalent metabolic function of degrading eCB-related monoacylglycerides in C. elegans. Small-molecule phenotypic screening thus illuminates pure pharmacological connections marking convergent metabolic functions in distantly related organisms, implicating the FAAH-4/monoacylglyceride pathway as a regulator of lifespan in C. elegans.
    DOI:  https://doi.org/10.1038/s41589-019-0243-4
  42. Autophagy. 2019 Mar 28. 1-3
    Fang EF.
      Our latest publication on the inhibition of Alzheimer disease (AD) through mitophagy consolidates the 'defective mitophagy hypothesis of AD etiology'. Dementia (majorly AD) affects over 50 million people worldwide, and for AD there is no cure. AD leads to progressive loss of cognition, and pathological hallmarks of AD include aggregates of amyloid-β peptides extracellularly and MAPT (microtubule associated protein tau) intracellularly. However, there is no conclusive link between these pathological markers and cognitive symptoms. Anti-AD drug candidates have repeatedly failed, which led us to investigate other molecular etiologies to guide drug development. Mitochondria produce the majority of cellular ATP, affect Ca2+ and redox signaling, and promote developmental and synaptic plasticity. Mitochondrial dysfunction and accumulation of damaged mitochondria are common in brain tissues from AD patients and transgenic AD animal models, but the underlying molecular mechanisms are not fully understood. Damaged mitochondria are removed through multiple pathways, the major 2 being mitophagy and the ubiquitin proteasome pathway. Mitophagy is essential for clearance of damaged mitochondria to maintain mitochondrial homeostasis, ATP production, and neuronal activity and survival. These pieces of evidence converge on the 'defective mitophagy hypothesis of AD etiology', and the current cross-species study provides strong support for this hypothesis.
    Keywords:  Alzheimer’s disease; Mitophagy; aging; memory; mitochondria
    DOI:  https://doi.org/10.1080/15548627.2019.1596497
  43. Redox Biol. 2019 Mar 14. pii: S2213-2317(18)31233-3. [Epub ahead of print]24 101167
    Liu J, Lu W, Shi B, Klein S, Su X.
      Peroxisomes are ubiquitous cellular organelles required for specific pathways of fatty acid oxidation and lipid synthesis, and until recently their functions in adipocytes have not been well appreciated. Importantly, peroxisomes host many oxygen-consumption reactions and play a major role in generation and detoxification of reactive oxygen species (ROS) and reactive nitrogen species (RNS), influencing whole cell redox status. Here, we review recent progress in peroxisomal functions in lipid metabolism as related to ROS/RNS metabolism and discuss the roles of peroxisomal redox homeostasis in adipogenesis and adipocyte metabolism. We provide a framework for understanding redox regulation of peroxisomal functions in adipocytes together with testable hypotheses for developing therapies for obesity and the related metabolic diseases.
    Keywords:  Adipocytes; Lipid metabolism; Mitochondria; Peroxisomes; Redox
    DOI:  https://doi.org/10.1016/j.redox.2019.101167
  44. Cell Rep. 2019 Mar 26. pii: S2211-1247(19)30288-8. [Epub ahead of print]26(13): 3613-3628.e6
    El-Houjeiri L, Possik E, Vijayaraghavan T, Paquette M, Martina JA, Kazan JM, Ma EH, Jones R, Blanchette P, Puertollano R, Pause A.
      TFEB and TFE3 are transcriptional regulators of the innate immune response, but the mechanisms regulating their activation upon pathogen infection are poorly elucidated. Using C. elegans and mammalian models, we report that the master metabolic modulator 5'-AMP-activated protein kinase (AMPK) and its negative regulator Folliculin (FLCN) act upstream of TFEB/TFE3 in the innate immune response, independently of the mTORC1 signaling pathway. In nematodes, loss of FLCN or overexpression of AMPK confers pathogen resistance via activation of TFEB/TFE3-dependent antimicrobial genes, whereas ablation of total AMPK activity abolishes this phenotype. Similarly, in mammalian cells, loss of FLCN or pharmacological activation of AMPK induces TFEB/TFE3-dependent pro-inflammatory cytokine expression. Importantly, a rapid reduction in cellular ATP levels in murine macrophages is observed upon lipopolysaccharide (LPS) treatment accompanied by an acute AMPK activation and TFEB nuclear localization. These results uncover an ancient, highly conserved, and pharmacologically actionable mechanism coupling energy status with innate immunity.
    Keywords:  AMPK; FLCN; TFE3; TFEB; autophagy; innate immune response; lysosomal biogenesis; pathogen resistance; phagocytosis
    DOI:  https://doi.org/10.1016/j.celrep.2019.02.102
  45. Cell Death Dis. 2019 Mar 25. 10(4): 288
    Garrido-Maraver J, Celardo I, Costa AC, Lehmann S, Loh SHY, Martins LM.
      Mutations in the mitochondrial GTPase mitofusin 2 (MFN2) cause Charcot-Marie-Tooth disease type 2 (CMT2A), a form of peripheral neuropathy that compromises axonal function. Mitofusins promote mitochondrial fusion and regulate mitochondrial dynamics. They are also reported to be involved in forming contacts between mitochondria and the endoplasmic reticulum. The fruit fly, Drosophila melanogaster, is a powerful tool to model human neurodegenerative diseases, including CMT2A. Here, we have downregulated the expression of the Drosophila mitofusin (dMfn RNAi) in adult flies and showed that this activates mitochondrial retrograde signalling and is associated with an upregulation of genes involved in folic acid (FA) metabolism. Additionally, we demonstrated that pharmacological and genetic interventions designed to increase the FA metabolism pathway suppresses the phenotype of the dMfn RNAi flies. We conclude that strategies to increase FA metabolism may ameliorate diseases, such as peripheral neuropathies, that are associated with loss of mitochondrial function. A video abstract for this article is available at  https://youtu.be/fs1G-QRo6xI .
    DOI:  https://doi.org/10.1038/s41419-019-1496-2
  46. Sci Adv. 2019 Mar;5(3): eaav1850
    Jussupow A, Di Luca A, Kaila VRI.
      Cardiolipin modulates the activity of membrane-bound respiratory enzymes that catalyze biological energy transduction. The respiratory complex I functions as the primary redox-driven proton pump in mitochondrial and bacterial respiratory chains, and its activity is strongly enhanced by cardiolipin. However, despite recent advances in the structural biology of complex I, cardiolipin-specific interaction mechanisms currently remain unknown. On the basis of millisecond molecular simulations, we suggest that cardiolipin binds to proton-pumping subunits of complex I and induces global conformational changes that modulate the accessibility of the quinone substrate to the enzyme. Our findings provide key information on the coupling between complex I dynamics and activity and suggest how biological membranes modulate the structure and activity of proteins.
    DOI:  https://doi.org/10.1126/sciadv.aav1850
  47. Am J Cancer Res. 2019 ;9(2): 198-211
    Bost F, Kaminski L.
      The peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is a central modulator of cell metabolism. It regulates mitochondrial biogenesis and oxidative metabolism. Modifications and adaptations in cellular metabolism are hallmarks of cancer cells, thus, it is not surprising that PGC-1α plays a role in cancer. Several recent articles have shown that PGC-1α expression is altered in tumors and metastasis in relation to modifications in cellular metabolism. The potential uses of PGC-1α as a therapeutic target and a biomarker of the advanced form of cancer will be summarized in this review.
    Keywords:  PGC1 alpha; breast cancer; melanoma; metabolism; mitochondria; pancreatic cancer; prostate cancer
  48. Mol Immunol. 2019 Mar 20. pii: S0161-5890(19)30196-8. [Epub ahead of print]109 81-87
    Shen H, Shi LZ.
      IL-17-producing TH17 cells have been associated with autoimmune diseases such as multiple sclerosis (MS), psoriasis, Crohn's disease, and ulcerative colitis (Han et al., 2015), many of which lack effective therapies. Identifying effective approaches to selectively suppress TH17 cell development and function represents a legitimate strategy to cure these autoimmune disorders. TH17 cell differentiation requires rewiring of their metabolic program, transition from the oxidative phosphorylation-dominant catabolic phenotype in quiescent naïve T cells to glucose metabolism-orchestrated anabolic phenotype including lipogenesis. Here, we provide a focused review on the glycolytic-lipogenic pathway in TH17 development and pathogenicity. These studies reveal several metabolic checkpoints with specific regulation of TH17 cells (but not other T cell lineages), manifesting potential therapeutic opportunities to TH17 cell-mediated autoimmune diseases.
    Keywords:  Fatty acid synthesis; Glycolysis; HIF1α; T(H)17; mTOR
    DOI:  https://doi.org/10.1016/j.molimm.2019.03.005
  49. Cancer Res. 2019 Mar 26. pii: canres.1432.2018. [Epub ahead of print]
    Malakar P, Stein I, Saragovi A, Winkler R, Stern-Ginossar N, Berger M, Pikarsky E, Karni R.
      Reprogrammed glucose metabolism of enhanced aerobic glycolysis (or the Warburg effect) is known as a hallmark of cancer. The roles of long noncoding RNAs (lncRNA) in regulating cancer metabolism at the level of both glycolysis and gluconeogenesis are mostly unknown. We previously showed that lncRNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) acts as a proto-oncogene in hepatocellular carcinoma (HCC). Here we investigated the role of MALAT1 in regulating cancer glucose metabolism. MALAT1 upregulated the expression of glycolytic genes and downregulated gluconeogenic enzymes by enhancing the translation of the metabolic transcription factor TCF7L2. MALAT1-enhanced TCF7L2 translation was mediated by upregulation of SRSF1 and activation of the mTORC1-4EBP1 axis. Pharmacological or genetic inhibition of mTOR and Raptor or expression of a hypophosphorylated mutant version of eIF4E binding protein (4EBP1) resulted in decreased expression of TCF7L2. MALAT1 expression regulated TCF7L2 mRNA association with heavy polysomes, probably through the TCF7L2 5'UTR as determined by polysome fractionation and 5'UTR-reporter assays. Knockdown of TCF7L2 in MALAT1-overexpressing cells and HCC cell lines affected their metabolism and abolished their tumorigenic potential, suggesting that the effects of MALAT1 on glucose metabolism are essential for its oncogenic activity. Taken together, our findings suggest that MALAT1 contributes to HCC development and tumor progression by reprogramming tumor glucose metabolism.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-18-1432
  50. Proc Natl Acad Sci U S A. 2019 Mar 25. pii: 201820245. [Epub ahead of print]
    Weyemi U, Paul BD, Bhattacharya D, Malla AP, Boufraqech M, Harraz MM, Bonner WM, Snyder SH.
      Phosphorylation of histone H2AX is a major contributor to efficient DNA repair. We recently reported neurobehavioral deficits in mice lacking H2AX. Here we establish that this neural failure stems from impairment of mitochondrial function and repression of the mitochondrial biogenesis gene PGC-1α. H2AX loss leads to reduced levels of the major subunits of the mitochondrial respiratory complexes in mouse embryonic fibroblasts and in the striatum, a brain region particularly vulnerable to mitochondrial damage. These defects are substantiated by disruption of the mitochondrial shape in H2AX mutant cells. Ectopic expression of PGC-1α restores mitochondrial oxidative phosphorylation complexes and mitigates cell death. H2AX knockout mice display increased neuronal death in the brain when challenged with 3-nitropronionic acid, which targets mitochondria. This study establishes a role for H2AX in mitochondrial homeostasis associated with neuroprotection.
    Keywords:  DNA repair; histone H2AX; mitochondrial homeostasis; neuroprotection; oxidative stress
    DOI:  https://doi.org/10.1073/pnas.1820245116
  51. Mitochondrion. 2019 Mar 26. pii: S1567-7249(18)30187-9. [Epub ahead of print]
    Tobacyk J, Parajuli N, Shrum S, Crow JP, MacMillan-Crow LA.
      Mitochondria continually undergo fission and fusion which allow mitochondria to rapidly change their shape, size, and function throughout the cell life cycle. OMA1, a zinc metalloproteinase enzyme, is a key regulator of the mitochondrial fusion machinery. The paucity of information regarding OMA1 regulation and function largely stems from the fact that there is no direct method to quantitatively measure its activity. Using a fluorescence-based reporter assay, we developed a sensitive method to measure OMA1 enzymatic activity in whole cell lysates.
    Keywords:  Fluorescence-based reporter; Fusion; Mitochondria; OMA1; Proteases
    DOI:  https://doi.org/10.1016/j.mito.2019.03.001
  52. Nat Struct Mol Biol. 2019 Mar 25.
    Osawa T, Kotani T, Kawaoka T, Hirata E, Suzuki K, Nakatogawa H, Ohsumi Y, Noda NN.
      A key event in autophagy is autophagosome formation, whereby the newly synthesized isolation membrane (IM) expands to form a complete autophagosome using endomembrane-derived lipids. Atg2 physically links the edge of the expanding IM with the endoplasmic reticulum (ER), a role that is essential for autophagosome formation. However, the molecular function of Atg2 during ER-IM contact remains unclear, as does the mechanism of lipid delivery to the IM. Here we show that the conserved amino-terminal region of Schizosaccharomyces pombe Atg2 includes a lipid-transfer-protein-like hydrophobic cavity that accommodates phospholipid acyl chains. Atg2 bridges highly curved liposomes, thereby facilitating efficient phospholipid transfer in vitro, a function that is inhibited by mutations that impair autophagosome formation in vivo. These results suggest that Atg2 acts as a lipid-transfer protein that supplies phospholipids for autophagosome formation.
    DOI:  https://doi.org/10.1038/s41594-019-0203-4
  53. Aging Cell. 2019 Mar 25. e12950
    Palmer AK, Xu M, Zhu Y, Pirtskhalava T, Weivoda MM, Hachfeld CM, Prata LG, van Dijk TH, Verkade E, Casaclang-Verzosa G, Johnson KO, Cubro H, Doornebal EJ, Ogrodnik M, Jurk D, Jensen MD, Chini EN, Miller JD, Matveyenko A, Stout MB, Schafer MJ, White TA, Hickson LJ, Demaria M, Garovic V, Grande J, Arriaga EA, Kuipers F, von Zglinicki T, LeBrasseur NK, Campisi J, Tchkonia T, Kirkland JL.
      Adipose tissue inflammation and dysfunction are associated with obesity-related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug-inducible "suicide" genes driven by the p16Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra-abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity-related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity-related metabolic dysfunction and its complications.
    Keywords:  adipogenesis; aging; cellular senescence; dasatinib; quercetin; senolytics; type 2 diabetes
    DOI:  https://doi.org/10.1111/acel.12950
  54. Biometals. 2019 Mar 28.
    Rouault TA.
      In recent years, iron sulfur (Fe-S) proteins have been identified as key players in mammalian metabolism, ranging from long-known roles in the respiratory complexes and the citric acid cycle, to more recently recognized roles in RNA and DNA metabolism. Fe-S cofactors have often been missed because of their intrinsic lability and oxygen sensitivity. More Fe-S proteins have now been identified owing to detection of their direct interactions with components of the Fe-S biogenesis machinery, and through use of informatics to detect a motif that binds the co-chaperone responsible for transferring nascent Fe-S clusters to domains of recipient proteins. Dissection of the molecular steps involved in Fe-S transfer to Fe-S proteins has revealed that direct and shielded transfer occurs through highly conserved pathways that operate in parallel in the mitochondrial matrix and in the cytosolic/nuclear compartments of eukaryotic cells. Because Fe-S clusters have the unusual ability to accept or donate single electrons in chemical reactions, their presence renders complex chemical reactions possible. In addition, Fe-S clusters may function as sensors that interconnect activity of metabolic pathways with cellular redox status. Presence in pathways that control growth and division may enable cells to regulate their growth according to sufficiency of energy stores represented by redox capacity, and oxidation of such proteins could diminish anabolic activities to give cells an opportunity to restore energy supplies. This review will discuss mechanisms of Fe-S biogenesis and delivery, and methods that will likely reveal important roles of Fe-S proteins in proteins not yet recognized as Fe-S proteins.
    Keywords:  ABCB7 and Atm1; CIAO1; HSC20; IRP1 and IRP2; Iron sulfur proteins; LYR motif
    DOI:  https://doi.org/10.1007/s10534-019-00191-7