bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒07‒19
thirty-nine papers selected by
Kelsey Fisher-Wellman
East Carolina University


  1. Cell Metab. 2020 Jul 08. pii: S1550-4131(20)30320-X. [Epub ahead of print]
    Vasan K, Werner M, Chandel NS.
      Recent evidence in humans and mice supports the notion that mitochondrial metabolism is active and necessary for tumor growth. Mitochondrial metabolism supports tumor anabolism by providing key metabolites for macromolecule synthesis and generating oncometabolites to maintain the cancer phenotype. Moreover, there are multiple clinical trials testing the efficacy of inhibiting mitochondrial metabolism as a new cancer therapeutic treatment. In this review, we discuss the rationale of using these anti-cancer agents in clinical trials and highlight how to effectively utilize them in different tumor contexts.
    Keywords:  metformin; mitochondria
    DOI:  https://doi.org/10.1016/j.cmet.2020.06.019
  2. Sci Signal. 2020 Jul 14. pii: eaay1212. [Epub ahead of print]13(640):
    Cardenas C, Lovy A, Silva-Pavez E, Urra F, Mizzoni C, Ahumada-Castro U, Bustos G, Jaňa F, Cruz P, Farias P, Mendoza E, Huerta H, Murgas P, Hunter M, Rios M, Cerda O, Georgakoudi I, Zakarian A, Molgó J, Foskett JK.
      Spontaneous Ca2+ signaling from the InsP3R intracellular Ca2+ release channel to mitochondria is essential for optimal oxidative phosphorylation (OXPHOS) and ATP production. In cells with defective OXPHOS, reductive carboxylation replaces oxidative metabolism to maintain amounts of reducing equivalents and metabolic precursors. To investigate the role of mitochondrial Ca2+ uptake in regulating bioenergetics in these cells, we used OXPHOS-competent and OXPHOS-defective cells. Inhibition of InsP3R activity or mitochondrial Ca2+ uptake increased α-ketoglutarate (αKG) abundance and the NAD+/NADH ratio, indicating that constitutive endoplasmic reticulum (ER)-to-mitochondria Ca2+ transfer promoted optimal αKG dehydrogenase (αKGDH) activity. Reducing mitochondrial Ca2+ inhibited αKGDH activity and increased NAD+, which induced SIRT1-dependent autophagy in both OXPHOS-competent and OXPHOS-defective cells. Whereas autophagic flux in OXPHOS-competent cells promoted cell survival, it was impaired in OXPHOS-defective cells because of inhibition of autophagosome-lysosome fusion. Inhibition of αKGDH and impaired autophagic flux in OXPHOS-defective cells resulted in pronounced cell death in response to interruption of constitutive flux of Ca2+ from ER to mitochondria. These results demonstrate that mitochondria play a fundamental role in maintaining bioenergetic homeostasis of both OXPHOS-competent and OXPHOS-defective cells, with Ca2+ regulation of αKGDH activity playing a pivotal role. Inhibition of ER-to-mitochondria Ca2+ transfer may represent a general therapeutic strategy against cancer cells regardless of their OXPHOS status.
    DOI:  https://doi.org/10.1126/scisignal.aay1212
  3. J Biol Chem. 2020 Jul 14. pii: jbc.RA119.011229. [Epub ahead of print]
    Le CH, Benage LG, Specht KS, Li Puma LC, Mulligan CM, Heuberger AL, Prenni JE, Claypool SM, Chatfield KC, Sparagna GC, Chicco AJ.
      Barth syndrome (BTHS) is a mitochondrial myopathy resulting from mutations in the tafazzin (TAZ) gene encoding a phospholipid transacylase required for cardiolipin remodeling. Cardiolipin is phospholipid of the inner mitochondrial membrane essential for the function of numerous mitochondrial proteins and processes. However, it is unclear how tafazzin deficiency impacts cardiac mitochondrial metabolism. To address this question while avoiding confounding effects of cardiomyopathy on mitochondrial phenotype, we utilized Taz-shRNA "knockdown" (TazKD ) mice, which exhibit defective cardiolipin remodeling and respiratory supercomplex instability characteristic of human BTHS, but normal cardiac function into adulthood. Consistent with previous reports from other models, mitochondrial H2O2 emission and oxidative damage were greater in TazKD than in wild-type (WT) hearts, but there were no differences in oxidative phosphorylation coupling efficiency or membrane potential. Fatty acid and pyruvate oxidation capacities were 40-60% lower in TazKD mitochondria, but an upregulation of glutamate oxidation supported respiration rates approximating those with pyruvate and palmitoylcarnitine in WT. Deficiencies in mitochondrial CoA and shifts in the cardiac acyl-CoA profile paralleled changes in fatty acid oxidation enzymes and acyl-CoA thioesterases suggesting limitations of CoA availability or "trapping" in TazKD mitochondrial metabolism. Incubation of TazKD mitochondria with exogenous CoA partially rescued pyruvate and palmitoylcarnitine oxidation capacities, implicating dysregulation of CoA-dependent intermediary metabolism rather than respiratory chain defects in the bioenergetic impacts of tafazzin-deficiency. These findings support links among cardiolipin abnormalities, respiratory supercomplex instability and mitochondrial oxidant production, and shed new light on the distinct metabolic consequences of tafazzin-deficiency in the mammalian heart.
    Keywords:  Barth Syndrome (BTHS); X-linked mitochondrial disorder; bioenergetics; cardiolipin; cardioskeletal myopathy; lipid metabolism; mitochondrial disease; mitochondrial metabolism; phospholipid transacylase; tafazzin (TAZ)
    DOI:  https://doi.org/10.1074/jbc.RA119.011229
  4. Exp Neurol. 2020 Jul 09. pii: S0014-4886(20)30231-4. [Epub ahead of print] 113400
    Mnatsakanyan N, Jonas EA.
      The mitochondrial F1Fo ATP synthase is one of the most abundant proteins of the mitochondrial inner membrane, which catalyzes the final step of oxidative phosphorylation to synthesize ATP from ADP and Pi. ATP synthase uses the electrochemical gradient of protons (ΔμH+) across the mitochondrial inner membrane to synthesize ATP. Under certain pathophysiological conditions, ATP synthase can run in reverse to hydrolyze ATP and build the necessary ΔμH+ across the mitochondrial inner membrane. Tight coupling between these two processes, proton translocation and ATP synthesis, is achieved by the unique rotational mechanism of ATP synthase and is necessary for efficient cellular metabolism and cell survival. The uncoupling of these processes, dissipation of mitochondrial inner membrane potential, elevated levels of ROS, low matrix content of ATP in combination with other cellular malfunction trigger the opening of the mitochondrial permeability transition pore in the mitochondrial inner membrane. In this review we will discuss the new role of ATP synthase beyond oxidative phosphorylation. We will highlight its function as a unique regulator of cell life and death and as a key target in mitochondria-mediated neurodegeneration and neuroprotection.
    Keywords:  ATP synthase; Mitochondrial permeability transition pore; Neurodegeneration; Neuroprotection
    DOI:  https://doi.org/10.1016/j.expneurol.2020.113400
  5. Nat Commun. 2020 Jul 17. 11(1): 3606
    Nuevo-Tapioles C, Santacatterina F, Stamatakis K, Núñez de Arenas C, Gómez de Cedrón M, Formentini L, Cuezva JM.
      Mitochondrial metabolism has emerged as a promising target against the mechanisms of tumor growth. Herein, we have screened an FDA-approved library to identify drugs that inhibit mitochondrial respiration. The β1-blocker nebivolol specifically hinders oxidative phosphorylation in cancer cells by concertedly inhibiting Complex I and ATP synthase activities. Complex I inhibition is mediated by interfering the phosphorylation of NDUFS7. Inhibition of the ATP synthase is exerted by the overexpression and binding of the ATPase Inhibitory Factor 1 (IF1) to the enzyme. Remarkably, nebivolol also arrests tumor angiogenesis by arresting endothelial cell proliferation. Altogether, targeting mitochondria and angiogenesis triggers a metabolic and oxidative stress crisis that restricts the growth of colon and breast carcinomas. Nebivolol holds great promise to be repurposed for the treatment of cancer patients.
    DOI:  https://doi.org/10.1038/s41467-020-17384-1
  6. Circ Res. 2020 Jul 14.
    Davidson MT, Grimsrud P, Lai L, Draper J, Fisher-Wellman KH, Narowski TM, Koves TR, Kelly DP, Muoio DM.
      Rationale: Circumstantial evidence links the development of heart failure to post-translational modifications of mitochondrial proteins, including lysine acetylation (Kac). Nonetheless, direct evidence that Kac compromises mitochondrial performance remains sparse. Objective: This study sought to explore the premise that mitochondrial Kac contributes to heart failure by disrupting oxidative metabolism.Methods and Results: A dual knockout (DKO) mouse line with deficiencies in carnitine acetyltransferase (CrAT) and sirtuin 3 (Sirt3), enzymes that oppose Kac by buffering the acetyl group pool and catalyzing lysine deacetylation, respectively, was developed to model extreme mitochondrial Kac in cardiac muscle, as confirmed by quantitative acetyl-proteomics. The resulting impact on mitochondrial bioenergetics was evaluated using a respiratory diagnostics platform that permits comprehensive assessment of mitochondrial function and energy transduction. Susceptibility of DKO mice to heart failure was investigated using transaortic constriction (TAC) as a model of cardiac pressure overload. The mitochondrial acetyl-lysine landscape of DKO hearts was elevated well beyond that observed in response to pressure overload or Sirt3 deficiency alone. Relative changes in the abundance of specific acetylated lysine peptides measured in DKO versus Sirt3 KO hearts were strongly correlated. A proteomics comparison across multiple settings of hyperacetylation revealed ∼86% overlap between the populations of Kac peptides affected by the DKO manipulation as compared to experimental heart failure. Despite the severity of cardiac Kac in DKO mice relative to other conditions, deep phenotyping of mitochondrial function revealed a surprisingly normal bioenergetics profile. Thus, of the >120 mitochondrial energy fluxes evaluated, including substrate-specific dehydrogenase activities, respiratory responses, redox charge, mitochondrial membrane potential and electron leak, we found minimal evidence of oxidative insufficiencies. Similarly, DKO hearts were not more vulnerable to dysfunction caused by TAC-induced pressure overload.Conclusions: The findings challenge the premise that hyperacetylation per se threatens metabolic resilience in the myocardium by causing broad-ranging disruption to mitochondrial oxidative machinery.
    Keywords:  carnitine; lysine acetylation; sirtuin
    DOI:  https://doi.org/10.1161/CIRCRESAHA.120.317293
  7. Cell Res. 2020 Jul 15.
    Liu J, Peng Y, Shi L, Wan L, Inuzuka H, Long J, Guo J, Zhang J, Yuan M, Zhang S, Wang X, Gao J, Dai X, Furumoto S, Jia L, Pandolfi PP, Asara JM, Kaelin WG, Liu J, Wei W.
      Whether glucose is predominantly metabolized via oxidative phosphorylation or glycolysis differs between quiescent versus proliferating cells, including tumor cells. However, how glucose metabolism is coordinated with cell cycle in mammalian cells remains elusive. Here, we report that mammalian cells predominantly utilize the tricarboxylic acid (TCA) cycle in G1 phase, but prefer glycolysis in S phase. Mechanistically, coupling cell cycle with metabolism is largely achieved by timely destruction of IDH1/2, key TCA cycle enzymes, in a Skp2-dependent manner. As such, depleting SKP2 abolishes cell cycle-dependent fluctuation of IDH1 protein abundance, leading to reduced glycolysis in S phase. Furthermore, elevated Skp2 abundance in prostate cancer cells destabilizes IDH1 to favor glycolysis and subsequent tumorigenesis. Therefore, our study reveals a mechanistic link between two cancer hallmarks, aberrant cell cycle and addiction to glycolysis, and provides the underlying mechanism for the coupling of metabolic fluctuation with periodic cell cycle in mammalian cells.
    DOI:  https://doi.org/10.1038/s41422-020-0372-z
  8. Nat Commun. 2020 Jul 13. 11(1): 3479
    Bennett JA, Mastrangelo MA, Ture SK, Smith CO, Loelius SG, Berg RA, Shi X, Burke RM, Spinelli SL, Cameron SJ, Carey TE, Brookes PS, Gerszten RE, Sabater-Lleal M, de Vries PS, Huffman JE, Smith NL, Morrell CN, Lowenstein CJ.
      Genetic factors contribute to the risk of thrombotic diseases. Recent genome wide association studies have identified genetic loci including SLC44A2 which may regulate thrombosis. Here we show that Slc44a2 controls platelet activation and thrombosis by regulating mitochondrial energetics. We find that Slc44a2 null mice (Slc44a2(KO)) have increased bleeding times and delayed thrombosis compared to wild-type (Slc44a2(WT)) controls. Platelets from Slc44a2(KO) mice have impaired activation in response to thrombin. We discover that Slc44a2 mediates choline transport into mitochondria, where choline metabolism leads to an increase in mitochondrial oxygen consumption and ATP production. Platelets lacking Slc44a2 contain less ATP at rest, release less ATP when activated, and have an activation defect that can be rescued by exogenous ADP. Taken together, our data suggest that mitochondria require choline for maximum function, demonstrate the importance of mitochondrial metabolism to platelet activation, and reveal a mechanism by which Slc44a2 influences thrombosis.
    DOI:  https://doi.org/10.1038/s41467-020-17254-w
  9. Anal Chem. 2020 Jul 14.
    Zhu N, Guo X, Pang S, Chang Y, Liu X, Shi Z, Feng S.
      Cancer incidence and mortality are fast growing worldwide. Recently, multiplexing imaging methods have been reported to be vital for cancer diagnosis and therapy. Fluorescence imaging, which has intrinsic capabilities for multiplexing imaging, is suitable and ripe for cancer imaging. In biomedical research, using a single probe for multiplexing imaging can avoid larger invasive effects and ensure the same spatio-temporal distributions and metabolisms of the probes, which has advantages over using multiple probes. Therefore, developing unimolecular fluorescent probes for multiplexing imaging of living cancer cells is meaningful. We herein report a unimolecular fluorescent probe (ZED) that simultaneously detects cysteine/homocysteine, hypochlorous acid, mitochondrial membrane potential (Δψm) and opening of the mitochondrial permeability transition (MPT) pore in cells. These four analytes are key indicators predominantly associated with multiple aspects of carcinogenesis and cancer therapy in living cells. Besides, ZED also differentiates MCF-7 cells from HBL-100 cells. The sensing process is fast, selective and sensitive in living cancer cells. As far as we know, ZED is the first probe that simultaneously detects four analytes in cells and the first probe that simultaneously detects Δψm and opening of the MPT pore in mitochondria.
    DOI:  https://doi.org/10.1021/acs.analchem.0c01046
  10. Sci Rep. 2020 Jul 16. 10(1): 11785
    Salsaa M, Pereira B, Liu J, Yu W, Jadhav S, Hüttemann M, Greenberg ML.
      The widely used mood stabilizer valproate (VPA) causes perturbation of energy metabolism, which is implicated in both the therapeutic mechanism of action of the drug as well as drug toxicity. To gain insight into these mechanisms, we determined the effects of VPA on energy metabolism in yeast. VPA treatment increased levels of glycolytic intermediates, increased expression of glycolysis genes, and increased ethanol production. Increased glycolysis was likely a response to perturbation of mitochondrial function, as reflected in decreased membrane potential and oxygen consumption. Interestingly, yeast, mouse liver, and isolated bovine cytochrome c oxidase were directly inhibited by the drug, while activities of other oxidative phosphorylation complexes (III and V) were not affected. These findings have implications for mechanisms of therapeutic action and toxicity.
    DOI:  https://doi.org/10.1038/s41598-020-68725-5
  11. Aging Cell. 2020 Jul 14. e13191
    Amartuvshin O, Lin CH, Hsu SC, Kao SH, Chen A, Tang WC, Chou HL, Chang DL, Hsu YY, Hsiao BS, Rastegari E, Lin KY, Wang YT, Yao CK, Chen GC, Chen BC, Hsu HJ.
      Changes in mitochondrial dynamics (fusion and fission) are known to occur during stem cell differentiation; however, the role of this phenomenon in tissue aging remains unclear. Here, we report that mitochondrial dynamics are shifted toward fission during aging of Drosophila ovarian germline stem cells (GSCs), and this shift contributes to aging-related GSC loss. We found that as GSCs age, mitochondrial fragmentation and expression of the mitochondrial fission regulator, Dynamin-related protein (Drp1), are both increased, while mitochondrial membrane potential is reduced. Moreover, preventing mitochondrial fusion in GSCs results in highly fragmented depolarized mitochondria, decreased BMP stemness signaling, impaired fatty acid metabolism, and GSC loss. Conversely, forcing mitochondrial elongation promotes GSC attachment to the niche. Importantly, maintenance of aging GSCs can be enhanced by suppressing Drp1 expression to prevent mitochondrial fission or treating with rapamycin, which is known to promote autophagy via TOR inhibition. Overall, our results show that mitochondrial dynamics are altered during physiological aging, affecting stem cell homeostasis via coordinated changes in stemness signaling, niche contact, and cellular metabolism. Such effects may also be highly relevant to other stem cell types and aging-induced tissue degeneration.
    Keywords:  BMP; Drp1; GSC; Marf; mitochondrial fission; mitochondrial fusion
    DOI:  https://doi.org/10.1111/acel.13191
  12. J Cell Mol Med. 2020 Jul 11.
    Olgar Y, Tuncay E, Degirmenci S, Billur D, Dhingra R, Kirshenbaum L, Turan B.
      The prevalence of death from cardiovascular disease is significantly higher in elderly populations; the underlying factors that contribute to the age-associated decline in cardiac performance are poorly understood. Herein, we identify the involvement of sodium/glucose co-transporter gene (SGLT2) in disrupted cellular Ca2+ -homeostasis, and mitochondrial dysfunction in age-associated cardiac dysfunction. In contrast to younger rats (6-month of age), older rats (24-month of age) exhibited severe cardiac ultrastructural defects, including deformed, fragmented mitochondria with high electron densities. Cardiomyocytes isolated from aged rats demonstrated increased reactive oxygen species (ROS), loss of mitochondrial membrane potential and altered mitochondrial dynamics, compared with younger controls. Moreover, mitochondrial defects were accompanied by mitochondrial and cytosolic Ca2+ ([Ca2+ ]i ) overload, indicative of disrupted cellular Ca2+ -homeostasis. Interestingly, increased [Ca2+ ]i coincided with decreased phosphorylation of phospholamban (PLB) and contractility. Aged-cardiomyocytes also displayed high Na+ /Ca2+ -exchanger (NCX) activity and blood glucose levels compared with young-controls. Interestingly, the protein level of SGLT2 was dramatically increased in the aged cardiomyocytes. Moreover, SGLT2 inhibition was sufficient to restore age-associated defects in [Ca2+ ]i -homeostasis, PLB phosphorylation, NCX activity and mitochondrial Ca2+ -loading. Hence, the present data suggest that deregulated SGLT2 during ageing disrupts mitochondrial function and cardiac contractility through a mechanism that impinges upon [Ca2+ ]i -homeostasis. Our studies support the notion that interventions that modulate SGLT2-activity can provide benefits in maintaining [Ca2+ ]i and cardiac function with advanced age.
    Keywords:  Ca2+ homeostasis; ageing-heart; cardiovascular function; mitochondria; reactive oxygen species; sarcoplasmic reticulum; sodium/glucose cotransporter 2
    DOI:  https://doi.org/10.1111/jcmm.15483
  13. Cell Death Differ. 2020 Jul 13.
    Filipe A, Chernorudskiy A, Arbogast S, Varone E, Villar-Quiles RN, Pozzer D, Moulin M, Fumagalli S, Cabet E, Dudhal S, De Simoni MG, Denis R, Vadrot N, Dill C, Giovarelli M, Szweda L, De Palma C, Pinton P, Giorgi C, Viscomi C, Clementi E, Missiroli S, Boncompagni S, Zito E, Ferreiro A.
      SEPN1-related myopathy (SEPN1-RM) is a muscle disorder due to mutations of the SEPN1 gene, which is characterized by muscle weakness and fatigue leading to scoliosis and life-threatening respiratory failure. Core lesions, focal areas of mitochondria depletion in skeletal muscle fibers, are the most common histopathological lesion. SEPN1-RM underlying mechanisms and the precise role of SEPN1 in muscle remained incompletely understood, hindering the development of biomarkers and therapies for this untreatable disease. To investigate the pathophysiological pathways in SEPN1-RM, we performed metabolic studies, calcium and ATP measurements, super-resolution and electron microscopy on in vivo and in vitro models of SEPN1 deficiency as well as muscle biopsies from SEPN1-RM patients. Mouse models of SEPN1 deficiency showed marked alterations in mitochondrial physiology and energy metabolism, suggesting that SEPN1 controls mitochondrial bioenergetics. Moreover, we found that SEPN1 was enriched at the mitochondria-associated membranes (MAM), and was needed for calcium transients between ER and mitochondria, as well as for the integrity of ER-mitochondria contacts. Consistently, loss of SEPN1 in patients was associated with alterations in body composition which correlated with the severity of muscle weakness, and with impaired ER-mitochondria contacts and low ATP levels. Our results indicate a role of SEPN1 as a novel MAM protein involved in mitochondrial bioenergetics. They also identify a systemic bioenergetic component in SEPN1-RM and establish mitochondria as a novel therapeutic target. This role of SEPN1 contributes to explain the fatigue and core lesions in skeletal muscle as well as the body composition abnormalities identified as part of the SEPN1-RM phenotype. Finally, these results point out to an unrecognized interplay between mitochondrial bioenergetics and ER homeostasis in skeletal muscle. They could therefore pave the way to the identification of biomarkers and therapeutic drugs for SEPN1-RM and for other disorders in which muscle ER-mitochondria cross-talk are impaired.
    DOI:  https://doi.org/10.1038/s41418-020-0587-z
  14. Photodiagnosis Photodyn Ther. 2020 Jul 14. pii: S1572-1000(20)30275-1. [Epub ahead of print] 101921
    Darvin P, Chandrasekharan A, Varadarajan SN, Chandrasekhar L, Maliakkal RT, S M JS, Varghese Jancy S, Santhoshkumar TR.
      BACKGROUND: Photodynamic therapy (PDT) is an emerging cancer treatment modality against tumors of superficial tissues. In vitro, in vivo, and clinical studies with different photosensitizers reveal diverging cell fates, including apoptosis, necrosis, autophagy, and non-specific forms of cell death. The mode of action and efficacy of PDT is mediated through free radical generation and is highly dependent on diverse variables such as nature, dose, metabolism of photosensitizer, irradiation energy, and irradiation cycle.AIM: Discovery of newer photosensitizers and optimization of PDT approaches to achieve a clinically relevant form of cell death called apoptosis requires better in vitro real-time methods. Oxidative damage and mitochondrial permeabilization are critical signaling events involved in photodamage and apoptosis. Hence, mitochondrial damage detection is an appropriate target signaling for mechanistic evaluation of PDT.
    METHODOLOGY: Here, we report mitochondria-targeted redox GFP expressing cells as a sensitive system to test and validate important variables of PDT using the photosensitizer 5-Aminolevulinic acid (5-ALA) as a model. An independent FRET-based caspase sensor cell was also used to study the impact of the photosensitizer dosage and irradiation duration on the mode of cell death.
    RESULTS: The study reveals that the cancer cells expressing mt-roGFP are extremely sensitive to monitor mitochondrial oxidation induced by PDT. The extent of mitochondrial redox changes induced by PDT can be determined using these sensor cells by real-time image-based approaches. These approaches provide sufficient temporal resolution that is required to fine-tune and optimize the PDT conditions. The degree of oxidation of the probe is highly dependent on the dosage of photosensitizer and duration of light irradiation, which determines the nature of cell death. A real-time caspase sensor probe further confirmed that the caspase-dependent and caspase-independent nature of cell death is in high correlation with the extent of mitochondrial oxidation. A condition that triggers rapid and extreme mito-oxidation seems to favor necrosis, while delayed and slowly progressing redox changes contribute to caspase-dependent apoptosis.
    CONCLUSION: The study confirms that temporal analysis of mitochondrial oxidation is a reliable biomarker for fine-tuning PDT conditions to achieve the desired outcome. This can be achieved using stable cancer cell lines expressing mitochondria-targeted roGFP by ratiometric imaging.
    Keywords:  Mitochondrial oxidation; PDT; apoptosis; necrosis; redox GFP
    DOI:  https://doi.org/10.1016/j.pdpdt.2020.101921
  15. Sci Rep. 2020 Jul 15. 10(1): 11643
    Dobson PF, Dennis EP, Hipps D, Reeve A, Laude A, Bradshaw C, Stamp C, Smith A, Deehan DJ, Turnbull DM, Greaves LC.
      The pathogenesis of declining bone mineral density, a universal feature of ageing, is not fully understood. Somatic mitochondrial DNA (mtDNA) mutations accumulate with age in human tissues and mounting evidence suggests that they may be integral to the ageing process. To explore the potential effects of mtDNA mutations on bone biology, we compared bone microarchitecture and turnover in an ageing series of wild type mice with that of the PolgAmut/mut mitochondrial DNA 'mutator' mouse. In vivo analyses showed an age-related loss of bone in both groups of mice; however, it was significantly accelerated in the PolgAmut/mut mice. This accelerated rate of bone loss is associated with significantly reduced bone formation rate, reduced osteoblast population densities, increased osteoclast population densities, and mitochondrial respiratory chain deficiency in osteoblasts and osteoclasts in PolgAmut/mut mice compared with wild-type mice. In vitro assays demonstrated severely impaired mineralised matrix formation and increased osteoclast resorption by PolgAmut/mut cells. Finally, application of an exercise intervention to a subset of PolgAmut/mut mice showed no effect on bone mass or mineralised matrix formation in vitro. Our data demonstrate that mitochondrial dysfunction, a universal feature of human ageing, impairs osteogenesis and is associated with accelerated bone loss.
    DOI:  https://doi.org/10.1038/s41598-020-68566-2
  16. Cells. 2020 Jul 10. pii: E1661. [Epub ahead of print]9(7):
    Nguyen TTT, Zhang Y, Shang E, Shu C, Quinzii CM, Westhoff MA, Karpel-Massler G, Siegelin MD.
      The heterogeneity of glioblastomas, the most common primary malignant brain tumor, remains a significant challenge for the treatment of these devastating tumors. Therefore, novel combination treatments are warranted. Here, we showed that the combined inhibition of TRAP1 by gamitrinib and histone deacetylases (HDAC1/HDAC2) through romidepsin or panobinostat caused synergistic growth reduction of established and patient-derived xenograft (PDX) glioblastoma cells. This was accompanied by enhanced cell death with features of apoptosis and activation of caspases. The combination treatment modulated the levels of pro- and anti-apoptotic Bcl-2 family members, including BIM and Noxa, Mcl-1, Bcl-2 and Bcl-xL. Silencing of Noxa, BAK and BAX attenuated the effects of the combination treatment. At the metabolic level, the combination treatment led to an enhanced reduction of oxygen consumption rate and elicited an unfolded stress response. Finally, we tested whether the combination treatment of gamitrinib and panobinostat exerted therapeutic efficacy in PDX models of glioblastoma (GBM) in mice. While single treatments led to mild to moderate reduction in tumor growth, the combination treatment suppressed tumor growth significantly stronger than single treatments without induction of toxicity. Taken together, we have provided evidence that simultaneous targeting of TRAP1 and HDAC1/2 is efficacious to reduce tumor growth in model systems of glioblastoma.
    Keywords:  Bcl-2 family; HDAC inhibitors; electron transport chain; gamitrinib; glioblastoma; tumor metabolism
    DOI:  https://doi.org/10.3390/cells9071661
  17. Commun Biol. 2020 Jul 17. 3(1): 389
    Allen ME, Pennington ER, Perry JB, Dadoo S, Makrecka-Kuka M, Dambrova M, Moukdar F, Patel HD, Han X, Kidd GK, Benson EK, Raisch TB, Poelzing S, Brown DA, Shaikh SR.
      Mitochondrial dysfunction contributes to cardiac pathologies. Barriers to new therapies include an incomplete understanding of underlying molecular culprits and a lack of effective mitochondria-targeted medicines. Here, we test the hypothesis that the cardiolipin-binding peptide elamipretide, a clinical-stage compound under investigation for diseases of mitochondrial dysfunction, mitigates impairments in mitochondrial structure-function observed after rat cardiac ischemia-reperfusion. Respirometry with permeabilized ventricular fibers indicates that ischemia-reperfusion induced decrements in the activity of complexes I, II, and IV are alleviated with elamipretide. Serial block face scanning electron microscopy used to create 3D reconstructions of cristae ultrastructure reveals that disease-induced fragmentation of cristae networks are improved with elamipretide. Mass spectrometry shows elamipretide did not protect against the reduction of cardiolipin concentration after ischemia-reperfusion. Finally, elamipretide improves biophysical properties of biomimetic membranes by aggregating cardiolipin. The data suggest mitochondrial structure-function are interdependent and demonstrate elamipretide targets mitochondrial membranes to sustain cristae networks and improve bioenergetic function.
    DOI:  https://doi.org/10.1038/s42003-020-1101-3
  18. Nat Commun. 2020 Jul 15. 11(1): 3546
    Au-Yeung CL, Yeung TL, Achreja A, Zhao H, Yip KP, Kwan SY, Onstad M, Sheng J, Zhu Y, Baluya DL, Co NN, Rynne-Vidal A, Schmandt R, Anderson ML, Lu KH, Wong STC, Nagrath D, Mok SC.
      Advanced ovarian cancer usually spreads to the omentum. However, the omental cell-derived molecular determinants modulating its progression have not been thoroughly characterized. Here, we show that circulating ITLN1 has prognostic significance in patients with advanced ovarian cancer. Further studies demonstrate that ITLN1 suppresses lactotransferrin's effect on ovarian cancer cell invasion potential and proliferation by decreasing MMP1 expression and inducing a metabolic shift in metastatic ovarian cancer cells. Additionally, ovarian cancer-bearing mice treated with ITLN1 demonstrate marked decrease in tumor growth rates. These data suggest that downregulation of mesothelial cell-derived ITLN1 in the omental tumor microenvironment facilitates ovarian cancer progression.
    DOI:  https://doi.org/10.1038/s41467-020-17383-2
  19. Mol Metab. 2020 Jul 09. pii: S2212-8778(20)30125-3. [Epub ahead of print] 101051
    Edmunds LR, Xie B, Mills AM, Huckestein BR, Undamatla R, Murali A, Pangburn MM, Martin J, Sipula I, Kaufman BA, Scott I, Jurczak MJ.
      OBJECTIVE: PARKIN is an E3 ubiquitin ligase that regulates mitochondrial quality control through a process called mitophagy. Recent human and rodent studies suggest that loss of hepatic mitophagy may occur during the pathogenesis of obesity-associated fatty liver and contribute to changes in mitochondrial metabolism associated with this disease. Whole-body Prkn knockout mice are paradoxically protected against diet-induced hepatic steatosis; however, liver-specific effects of Prkn deficiency cannot be discerned in this model due to pleotropic effects of germline Prkn deletion on energy balance and subsequent protection against diet-induced obesity. We therefore generated the first liver-specific Prkn knockout mouse strain (LKO) to directly address the role of hepatic Prkn.METHODS: Littermate control (WT) and LKO mice were fed regular chow (RC) or high-fat diet (HFD) and changes in body weight and composition were measured over time. Liver mitochondrial content was assessed using multiple, complementary techniques and mitochondrial respiratory capacity assessed using Oroboros O2K platform. Liver fat was measured biochemically and assessed histologically, while global changes in hepatic gene expression were measured by RNA-seq. Whole-body and tissue-specific insulin resistance were assessed by hyperinsulinemic euglycemic clamp with isotopic tracers.
    RESULTS: Liver-specific deletion of Prkn had no effect on body weight or adiposity during RC or HFD feeding, however, hepatic steatosis was increased by 45% in HFD-fed LKO compared with WT mice (P<0.05). While there were no differences in mitochondrial content between genotypes on either diet, mitochondrial respiratory capacity and efficiency in liver were significantly reduced in LKO mice. Gene enrichment analyses from liver RNA-seq results suggested significant changes in pathways related to lipid metabolism and fibrosis in HFD-fed Prkn knockout mice. Finally, whole-body insulin sensitivity was reduced by 35% in HFD-fed LKO mice (P<0.05), which was primarily due to increased hepatic insulin resistance (60% of whole-body effect; P=0.11).
    CONCLUSIONS: These data demonstrate that PARKIN contributes to mitochondrial homeostasis in liver and plays a protective role against the pathogenesis of hepatic steatosis and insulin resistance.
    Keywords:  Parkin; bioenergetics; hepatic steatosis; insulin resistance; mitochondria; mitophagy
    DOI:  https://doi.org/10.1016/j.molmet.2020.101051
  20. J Neurochem. 2020 Jul 12.
    Juraszek B, Czarnecka-Herok J, Nałęcz KA.
      Gliomas are the most common primary malignant brain tumor in adults, but current treatment for glioblastoma multiforme (GBM) is insufficient. Even though glucose is the primary energetic substrate of glioma cells, they are capable of using fatty acids to generate energy. Fatty acid oxidation (FAO) in mitochondria requires L-carnitine for the formation of acylcarnitines by carnitine palmitoylotransferase 1 (CPT1) and further transport of acyl carnitine esters to mitochondrial matrix. Carnitine can be delivered to the cell by an organic cation/carnitine transporter - SLC22A5/OCTN2. In this study we show that SLC22A5 is up-regulated in glioma cells and that they vary in the amount of SLC22A5 in the plasma membrane. Research on glioma cells (lines U87MG, LN229, T98G) with various expression levels of SLC22A5 demonstrated a correlation between the FAO rate, the level of the transporter and the carnitine transport. Inhibition of carnitine transport by chemotherapeutics, such as vinorelbine and vincristine, led to inhibition of FAO, which was further intensified by etomoxir - a CPT1 inhibitor. This led to reduced viability and increased apoptosis in glioma cells. Modulation of SLC22A5 level by either silencing or up-regulation of SLC22A5 also affected glioma cell survival in a FAO-dependent way. These observations suggest that the survival of glioma cells is heavily reliant on both FAO and SLC22A5 activity, as well as that CPT1 and SLC22A5 might be possible drug targets.
    Keywords:  CPT1; SLC22A5; cancer metabolism; carnitine; fatty acid oxidation; glioma
    DOI:  https://doi.org/10.1111/jnc.15124
  21. Cells. 2020 Jul 14. pii: E1691. [Epub ahead of print]9(7):
    Kim J, Cheong JH.
      Despite the promise of cancer medicine, major challenges currently confronting the treatment of cancer patients include chemoresistance and recurrence. The existence of subpopulations of cancer cells, known as cancer stem cells (CSCs), contributes to the failure of cancer therapies and is associated with poor clinical outcomes. Of note, one of the recently characterized features of CSCs is augmented mitochondrial function. The cytoskeleton network is essential in regulating mitochondrial morphology and rearrangement, which are inextricably linked to its functions, such as oxidative phosphorylation (OXPHOS). The interaction between the cytoskeleton and mitochondria can enable CSCs to adapt to challenging conditions, such as a lack of energy sources, and to maintain their stemness. Cytoskeleton-mediated mitochondrial trafficking and relocating to the high energy requirement region are crucial steps in epithelial-to-mesenchymal transition (EMT). In addition, the cytoskeleton itself interplays with and blocks the voltage-dependent anion channel (VDAC) to directly regulate bioenergetics. In this review, we describe the regulation of cellular bioenergetics in CSCs, focusing on the cytoskeleton-mediated dynamic control of mitochondrial structure and function.
    Keywords:  cancer energy metabolism; cancer metabolism; cancer mitochondria; cancer stem cell; cytoskeleton; cytoskeleton-mitochondria; tubulin
    DOI:  https://doi.org/10.3390/cells9071691
  22. Mol Cancer Res. 2020 Jul 15. pii: molcanres.0570.2020. [Epub ahead of print]
    Nassar ZD, Mah CY, Centenera MM, Irani S, Sadowski MC, Scott JS, Nguyen EV, Nagarajan SR, Moldovan M, Lynn DJ, Daly RJ, Hoy AJ, Butler LM.
      HSP90 is a molecular chaperone required for stabilisation and activation of hundreds of client proteins, including many known oncoproteins. AUY922 (luminespib), a new generation HSP90 inhibitor, exhibits potent preclinical efficacy against several cancer types including prostate cancer (PCa). However, clinical use of HSP90 inhibitors for PCa has been limited by toxicity and treatment resistance. Here, we aimed to design an effective combinatorial therapeutic regimen that utilizes subtoxic doses of AUY922, by identifying potential survival pathways induced by AUY922 in clinical prostate tumors. We conducted a proteomic analysis of 30 patient-derived explants (PDEs) cultured in the absence and presence of AUY922, using quantitative mass spectrometry. AUY922 significantly increased the abundance of proteins involved in oxidative phosphorylation and fatty acid metabolism in the PDEs. Consistent with these findings, AUY922-treated PCa cell lines exhibited increased mitochondrial mass and activated fatty acid metabolism processes. We hypothesized that activation of fatty acid oxidation is a potential adaptive response to AUY922 treatment and that co-targeting this process will sensitize PCa cells to HSP90 inhibition. Combination treatment of AUY922 with a clinical inhibitor of fatty acid oxidation, perhexiline, synergistically decreased viability of several PCa cell lines, and had significant efficacy in PDEs. The novel drug combination treatment induced cell cycle arrest and apoptosis, and attenuated the heat shock response, a known mediator of HSP90 treatment resistance. This combination warrants further preclinical and clinical investigation as a novel strategy to overcome resistance to HSP90 inhibition. Implications: Metabolic pathways induced in tumor cells by therapeutic agents may be critical but targetable mediators of treatment resistance.
    DOI:  https://doi.org/10.1158/1541-7786.MCR-20-0570
  23. Elife. 2020 Jul 14. pii: e60346. [Epub ahead of print]9
    Roger F, Picazo C, Reiter W, Libiad M, Asami C, Hanzén S, Gao C, Lagniel G, Welkenhuysen N, Labarre J, Nyström T, Grotli M, Hartl M, Toledano MB, Molin M.
      Peroxiredoxins are H2O2 scavenging enzymes that also carry H2O2 signaling and chaperone functions. In yeast, the major cytosolic peroxiredoxin, Tsa1 is required for both promoting resistance to H2O2 and extending lifespan upon caloric restriction. We show here that Tsa1 effects both these functions not by scavenging H2O2, but by repressing the nutrient signaling Ras-cAMP-PKA pathway at the level of the protein kinase A (PKA) enzyme. Tsa1 stimulates sulfenylation of cysteines in the PKA catalytic subunit by H2O2 and a significant proportion of the catalytic subunits are glutathionylated on two cysteine residues. Redox modification of the conserved Cys243 inhibits the phosphorylation of a conserved Thr241 in the kinase activation loop and enzyme activity, and preventing Thr241 phosphorylation can overcome the H2O2 sensitivity of Tsa1-deficient cells. Results support a model of aging where nutrient signaling pathways constitute hubs integrating information from multiple aging-related conduits, including a peroxiredoxin-dependent response to H2O2.
    Keywords:  S. cerevisiae; biochemistry; cell biology; chemical biology
    DOI:  https://doi.org/10.7554/eLife.60346
  24. Nat Immunol. 2020 Jul 13.
    Vardhana SA, Hwee MA, Berisa M, Wells DK, Yost KE, King B, Smith M, Herrera PS, Chang HY, Satpathy AT, van den Brink MRM, Cross JR, Thompson CB.
      The majority of tumor-infiltrating T cells exhibit a terminally exhausted phenotype, marked by a loss of self-renewal capacity. How repetitive antigenic stimulation impairs T cell self-renewal remains poorly defined. Here, we show that persistent antigenic stimulation impaired ADP-coupled oxidative phosphorylation. The resultant bioenergetic compromise blocked proliferation by limiting nucleotide triphosphate synthesis. Inhibition of mitochondrial oxidative phosphorylation in activated T cells was sufficient to suppress proliferation and upregulate genes linked to T cell exhaustion. Conversely, prevention of mitochondrial oxidative stress during chronic T cell stimulation allowed sustained T cell proliferation and induced genes associated with stem-like progenitor T cells. As a result, antioxidant treatment enhanced the anti-tumor efficacy of chronically stimulated T cells. These data reveal that loss of ATP production through oxidative phosphorylation limits T cell proliferation and effector function during chronic antigenic stimulation. Furthermore, treatments that maintain redox balance promote T cell self-renewal and enhance anti-tumor immunity.
    DOI:  https://doi.org/10.1038/s41590-020-0725-2
  25. Gastroenterol Rep (Oxf). 2020 Jun;8(3): 215-223
    Delgado-Deida Y, Alula KM, Theiss AL.
      Mitochondria are dynamic organelles that play a key role in integrating cellular signaling. Mitochondrial alterations are evident in all stages of tumorigenesis and targeting mitochondrial pathways has emerged as an anticancer therapeutic strategy. The Wnt-signaling pathway regulates many fundamental cellular functions such as proliferation, survival, migration, stem-cell maintenance, and mitochondrial metabolism and dynamics. Emerging evidence demonstrates that mitochondrial-induced regulation of Wnt signaling provides an additional mechanism to influence cell-fate decisions. Crosstalk between mitochondria and Wnt signaling presents a feedforward loop in which Wnt activation regulates mitochondrial function that, in turn, drives Wnt signaling. In this mini-review, we will discuss the recent evidence revealing the mitochondrial control of Wnt signaling and its implications for tumorigenesis and anticancer therapeutic targeting.
    Keywords:  PGAM5; cancer stem cells; metabolic reprogramming; metabolism; ββ-catenin
    DOI:  https://doi.org/10.1093/gastro/goaa025
  26. Stem Cell Reports. 2020 Jul 02. pii: S2213-6711(20)30239-3. [Epub ahead of print]
    Yue L, Pei Y, Zhong L, Yang H, Wang Y, Zhang W, Chen N, Zhu Q, Gao J, Zhi M, Wen B, Zhang S, Xiang J, Wei Q, Liang H, Cao S, Lou H, Chen Z, Han J.
      The pluripotency of stem cells determines their developmental potential. While the pluripotency states of pluripotent stem cells are variable and interconvertible, the mechanisms underlying the acquisition and maintenance of pluripotency remain largely elusive. Here, we identified that methylenetetrahydrofolate dehydrogenase (NAD+-dependent), methenyltetrahydrofolate cyclohydrolase (Mthfd2) plays an essential role in maintaining embryonic stem cell pluripotency and promoting complete reprogramming of induced pluripotent stem cells. Mechanistically, in mitochondria, Mthfd2 maintains the integrity of the mitochondrial respiratory chain and prevents mitochondrial dysfunction. In the nucleus, Mthfd2 stabilizes the phosphorylation of EXO1 to support DNA end resection and promote homologous recombination repair. Our results revealed that Mthfd2 is a dual-function factor in determining the pluripotency of pluripotent stem cells through both mitochondrial and nuclear pathways, ultimately ensuring safe application of pluripotent stem cells.
    Keywords:  DNA repair; Mthfd2; mitochondrial dysfunction; pluripotency; pluripotent stem cells
    DOI:  https://doi.org/10.1016/j.stemcr.2020.06.018
  27. Cell Rep. 2020 Jul 14. pii: S2211-1247(20)30883-4. [Epub ahead of print]32(2): 107902
    Liao PC, Wolken DMA, Serrano E, Srivastava P, Pon LA.
      The mitochondria-associated degradation pathway (MAD) mediates ubiquitination and degradation of mitochondrial outer membrane (MOM) proteins by the proteasome. We find that the MAD, but not other quality-control pathways including macroautophagy, mitophagy, or mitochondrial chaperones and proteases, is critical for yeast cellular fitness under conditions of paraquat (PQ)-induced oxidative stress in mitochondria. Specifically, inhibition of the MAD increases PQ-induced defects in growth and mitochondrial quality and decreases chronological lifespan. We use mass spectrometry analysis to identify possible MAD substrates as mitochondrial proteins that exhibit increased ubiquitination in response to PQ treatment and inhibition of the MAD. We identify candidate substrates in the mitochondrial matrix and inner membrane and confirm that two matrix proteins are MAD substrates. Our studies reveal a broader function for the MAD in mitochondrial protein surveillance beyond the MOM and a major role for the MAD in cellular and mitochondrial fitness in response to chronic, low-level oxidative stress in mitochondria.
    Keywords:  Saccharomyces cerevisiae; chronological lifespan; mitochondrial quality control; mitophagy; oxidative stress; paraquat; proteasome; proteostasis; reactive oxygen species; ubiquitin
    DOI:  https://doi.org/10.1016/j.celrep.2020.107902
  28. Stem Cells. 2020 Jul 11.
    Cieslar-Pobuda A, Ahrens TD, Caglayan S, Behringer S, Hannibal L, Staerk J.
      Embryonic stem cell (ESC) renewal and differentiation is regulated by metabolites that serve as co-factors for epigenetic enzymes. Increase of α-ketoglutarate (α-KG), a co-factor for histone and DNA demethylases, triggers multi-lineage differentiation in human ESCs. To gain further insight how the metabolic fluxes in pluripotent stem cells can be influenced by inactivating mutations in epigenetic enzymes, we generated human ESCs deficient for de novo DNA methyltransferases (DNMT) 3A and 3B. Our data reveal a bidirectional dependence between DNMT3B and α-KG levels: a-KG is significantly upregulated in cells deficient for DNMT3B, while DNMT3B expression is downregulated in human ESCs treated with α-KG. In addition, DNMT3B null human ESCs exhibit a disturbed mitochondrial fission and fusion balance and a switch from glycolysis to oxidative phosphorylation. Taken together, our data reveal a novel link between DNMT3B and the metabolic flux of human ESCs. © AlphaMed Press 2020 SIGNIFICANCE STATEMENT: The current study reveals a novel link between DNMT3B and the metabolic flux in human ESCs. Loss of DNMT3B disrupts the cells mitochondrial fusion and fission balance, reduces mitochondrial DNA levels, and elicits a switch from glycolysis to oxidative phosphorylation. The authors further show that loss of DNMT3B leads to an overexpression and hyperactivity of isocitrate dehydrogenases and buildup of α-ketoglutarate, as well as a significant upregulation of transcription factors during early neural differentiation. The observed increase in α-ketoglutarate levels can be reversed by re-expression of DNMT3B, demonstrating that its dysregulation is a direct consequence of DNMT3B-deficiency.
    DOI:  https://doi.org/10.1002/stem.3256
  29. Cell Metab. 2020 Jul 09. pii: S1550-4131(20)30318-1. [Epub ahead of print]
    Yoon H, Spinelli JB, Zaganjor E, Wong SJ, German NJ, Randall EC, Dean A, Clermont A, Paulo JA, Garcia D, Li H, Rombold O, Agar NYR, Goodyear LJ, Shaw RJ, Gygi SP, Auwerx J, Haigis MC.
      Rapid alterations in cellular metabolism allow tissues to maintain homeostasis during changes in energy availability. The central metabolic regulator acetyl-CoA carboxylase 2 (ACC2) is robustly phosphorylated during cellular energy stress by AMP-activated protein kinase (AMPK) to relieve its suppression of fat oxidation. While ACC2 can also be hydroxylated by prolyl hydroxylase 3 (PHD3), the physiological consequence thereof is poorly understood. We find that ACC2 phosphorylation and hydroxylation occur in an inverse fashion. ACC2 hydroxylation occurs in conditions of high energy and represses fatty acid oxidation. PHD3-null mice demonstrate loss of ACC2 hydroxylation in heart and skeletal muscle and display elevated fatty acid oxidation. Whole body or skeletal muscle-specific PHD3 loss enhances exercise capacity during an endurance exercise challenge. In sum, these data identify an unexpected link between AMPK and PHD3, and a role for PHD3 in acute exercise endurance capacity and skeletal muscle metabolism.
    Keywords:  Prolyl hydroxylase 3; acetyl-CoA carboxylase 2 modification; exercise capacity; fat catabolism
    DOI:  https://doi.org/10.1016/j.cmet.2020.06.017
  30. Cancer Invest. 2020 Jul 16. 1-46
    Thakur N, Sharma AK, Singh H, Singh S.
      mtDNA is the closed circular, ds-DNA present in mitochondria of eukaryotic cells and are inherited maternally. Besides being the power house of the cell, mitochondria are also responsible for the regulation of redox homeostasis, signaling, metabolism, immunity, survival and apoptosis. Lack of a 'Systematic Review' on mtDNA variations and cancers encouraged us to perform the present study. Pubmed', 'Embase' and 'Cochrane Library' databases were searched using keywords 'Mitochondrial DNA' OR 'mtDNA' OR 'mDNA' AND 'polymorphism' AND 'cancer' AND 'risk' to retrieve literature. Polymorphisms occupy first rank among mtDNA variations followed by CNV, MSI, mutations and hold a great potential to emerge as a key predictors for human cancers.
    Keywords:  cancer; mitochondrial DNA; polymorphism
    DOI:  https://doi.org/10.1080/07357907.2020.1797768
  31. Nat Commun. 2020 Jul 14. 11(1): 3506
    Deniz Ö, Ahmed M, Todd CD, Rio-Machin A, Dawson MA, Branco MR.
      Acute myeloid leukemia (AML) is characterised by a series of genetic and epigenetic alterations that result in deregulation of transcriptional networks. One understudied source of transcriptional regulators are transposable elements (TEs), whose aberrant usage could contribute to oncogenic transcriptional circuits. However, the regulatory influence of TEs and their links to AML pathogenesis remain unexplored. Here we identify six endogenous retrovirus (ERV) families with AML-associated enhancer chromatin signatures that are enriched in binding of key regulators of hematopoiesis and AML pathogenesis. Using both locus-specific genetic editing and simultaneous epigenetic silencing of multiple ERVs, we demonstrate that ERV deregulation directly alters the expression of adjacent genes in AML. Strikingly, deletion or epigenetic silencing of an ERV-derived enhancer suppresses cell growth by inducing apoptosis in leukemia cell lines. This work reveals that ERVs are a previously unappreciated source of AML enhancers that may be exploited by cancer cells to help drive tumour heterogeneity and evolution.
    DOI:  https://doi.org/10.1038/s41467-020-17206-4
  32. Oncogenesis. 2020 Jul 13. 9(7): 67
    Lin XH, Qiu BQ, Ma M, Zhang R, Hsu SJ, Liu HH, Chen J, Gao DM, Cui JF, Ren ZG, Chen RX.
      Transarterial embolization/transarterial chemoembolization (TAE/TACE) is the acceptable palliative treatment for hepatocellular carcinoma (HCC), mainly through ischemic necrosis induced by arterial embolization. However, how HCC cells survive under such ischemic hypoxic condition remains unclear, which can be exploited to potentiate TAE/TACE treatment. We hypothesized that targeting mitophagy can increase HCC cell apoptosis during hypoxia. HCC cells were subjected to hypoxia and then mitophagy was quantified. The role of dynamin-related protein 1 (DRP1) in hypoxia-induced HCC mitophagy was determined. Moreover, the synergistic effect of hypoxia and DRP1 inhibitor on HCC apoptosis was assessed in vitro and in vivo. Clinical association between DRP1 expression and outcome for HCC patients was validated. HCC cells that survived hypoxia showed significantly increased DRP1-mediated mitochondrial fission and mitophagy compared with cells in normoxia. Hypoxia induced mitophagy in surviving HCC cells by enhancing DRP1 expression and its translocation into the mitochondria and excessive mitochondrial fission into fragments. Blocking the DRP1 heightened the possibility of hypoxic cytotoxicity to HCC cells due to impaired mitophagy and increased the mitochondrial apoptosis, which involved decreased in mitochondrial membrane potential and mitochondrial release of apoptosis-inducing factor and cytochrome c. Additionally, DRP1 inhibitor Mdivi-1 suppressed the in vivo growth of hypoxia-exposed HCC cells. High expression of DRP1 was significantly associated with shorter survival in HCC patients. In conclusion, our results demonstrate that blocking DRP1-mediated mitochondrial fission and mitophagy increases the incidence of mitochondrial apoptosis of HCC cells during hypoxia, suggesting the new approach of targeting mitophagy to potentiate TAE/TACE.
    DOI:  https://doi.org/10.1038/s41389-020-00251-5
  33. Nat Ecol Evol. 2020 Jul 13.
    Fan L, Wu D, Goremykin V, Xiao J, Xu Y, Garg S, Zhang C, Martin WF, Zhu R.
      Though it is well accepted that mitochondria originated from an alphaproteobacteria-like ancestor, the phylogenetic relationship of the mitochondrial endosymbiont to extant Alphaproteobacteria is yet unresolved. The focus of much debate is whether the affinity between mitochondria and fast-evolving alphaproteobacterial lineages reflects true homology or artefacts. Approaches such as site exclusion have been claimed to mitigate compositional heterogeneity between taxa, but this comes at the cost of information loss, and the reliability of such methods is so far unproven. Here we demonstrate that site-exclusion methods produce erratic phylogenetic estimates of mitochondrial origin. Thus, previous phylogenetic hypotheses on the origin of mitochondria based on pretreated datasets should be re-evaluated. We applied alternative strategies to reduce phylogenetic noise by systematic taxon sampling while keeping site substitution information intact. Cross-validation based on a series of trees placed mitochondria robustly within Alphaproteobacteria, sharing an ancient common ancestor with Rickettsiales and currently unclassified marine lineages.
    DOI:  https://doi.org/10.1038/s41559-020-1239-x
  34. Cancer Metab. 2020 ;8 16
    Nakagawa T, Lanaspa MA, Millan IS, Fini M, Rivard CJ, Sanchez-Lozada LG, Andres-Hernando A, Tolan DR, Johnson RJ.
      Obesity and metabolic syndrome are strongly associated with cancer, and these disorders may share a common mechanism. Recently, fructose has emerged as a driving force to develop obesity and metabolic syndrome. Thus, we assume that fructose may be the mechanism to explain why obesity and metabolic syndrome are linked with cancer. Clinical and experimental evidence showed that fructose intake was associated with cancer growth and that fructose transporters are upregulated in various malignant tumors. Interestingly, fructose metabolism can be driven under low oxygen conditions, accelerates glucose utilization, and exhibits distinct effects as compared to glucose, including production of uric acid and lactate as major byproducts. Fructose promotes the Warburg effect to preferentially downregulate mitochondrial respiration and increases aerobic glycolysis that may aid metastases that initially have low oxygen supply. In the process, uric acid may facilitate carcinogenesis by inhibiting the TCA cycle, stimulating cell proliferation by mitochondrial ROS, and blocking fatty acid oxidation. Lactate may also contribute to cancer growth by suppressing fat oxidation and inducing oncogene expression. The ability of fructose metabolism to directly stimulate the glycolytic pathway may have been protective for animals living with limited access to oxygen, but may be deleterious toward stimulating cancer growth and metastasis for humans in modern society. Blocking fructose metabolism may be a novel approach for the prevention and treatment of cancer.
    Keywords:  Cancer; Fructose; Hypoxia; Lactate; Mitochondria; Polyol pathway; Uric acid
    DOI:  https://doi.org/10.1186/s40170-020-00222-9
  35. Nature. 2020 Jul 15.
    Caffa I, Spagnolo V, Vernieri C, Valdemarin F, Becherini P, Wei M, Brandhorst S, Zucal C, Driehuis E, Ferrando L, Piacente F, Tagliafico A, Cilli M, Mastracci L, Vellone VG, Piazza S, Cremonini AL, Gradaschi R, Mantero C, Passalacqua M, Ballestrero A, Zoppoli G, Cea M, Arrighi A, Odetti P, Monacelli F, Salvadori G, Cortellino S, Clevers H, De Braud F, Sukkar SG, Provenzani A, Longo VD, Nencioni A.
      Approximately 75% of all breast cancers express the oestrogen and/or progesterone receptors. Endocrine therapy is usually effective in these hormone-receptor-positive tumours, but primary and acquired resistance limits its long-term benefit1,2. Here we show that in mouse models of hormone-receptor-positive breast cancer, periodic fasting or a fasting-mimicking diet3-5 enhances the activity of the endocrine therapeutics tamoxifen and fulvestrant by lowering circulating IGF1, insulin and leptin and by inhibiting AKT-mTOR signalling via upregulation of EGR1 and PTEN. When fulvestrant is combined with palbociclib (a cyclin-dependent kinase 4/6 inhibitor), adding periodic cycles of a fasting-mimicking diet promotes long-lasting tumour regression and reverts acquired resistance to drug treatment. Moreover, both fasting and a fasting-mimicking diet prevent tamoxifen-induced endometrial hyperplasia. In patients with hormone-receptor-positive breast cancer receiving oestrogen therapy, cycles of a fasting-mimicking diet cause metabolic changes analogous to those observed in mice, including reduced levels of insulin, leptin and IGF1, with the last two remaining low for extended periods. In mice, these long-lasting effects are associated with long-term anti-cancer activity. These results support further clinical studies of a fasting-mimicking diet as an adjuvant to oestrogen therapy in hormone-receptor-positive breast cancer.
    DOI:  https://doi.org/10.1038/s41586-020-2502-7
  36. Am J Physiol Regul Integr Comp Physiol. 2020 Aug 01. 319(2): R148-R155
    Farhat E, Devereaux MEM, Pamenter ME, Weber JM.
      Naked mole-rats (NMRs) are mammalian champions of hypoxia tolerance that enter metabolic suppression to survive in low oxygen environments. Common physiological mechanisms used by animals to suppress metabolic rate include downregulating energy metabolism (ATP supply) as well as ion pumps (primary cellular ATP consumers). A recent goldfish study demonstrated that remodeling of membrane lipids may mediate these responses, but it is unknown if NMR employs the same strategies; therefore, we aimed to test the hypotheses that these fossorial mammals 1) downregulate the activity of key enzymes of glycolysis, tricarboxylic acid (TCA) cycle, and β-oxidation, 2) inhibit sodium-potassium-ATPase, and 3) alter membrane lipids in response to chronic hypoxia. We found that NMRs exposed to 11% oxygen for 4 wk had a lower metabolic rate by 34%. This suppression occurs concurrently with tissue-specific 25-99% decreases in metabolic enzymes activities, a 77% decrease in brain sodium/potassium-ATPase activity, and widespread changes in membrane cholesterol abundance. By reducing glycolytic and β-oxidation fluxes, NMRs decrease the supply of acetyl-CoA to the TCA cycle. By contrast, there is a 94% upregulation of citrate synthase in the heart, possibly to support circulation and thus oxygen supply to other organs. Taken together, these responses may reflect a coordinated physiological response to hypoxia, but a clear functional link between changes in membrane composition and enzyme activities could not be established. Nevertheless, this is the first demonstration that hypometabolic NMRs alter the lipid composition of their membranes in response to chronic in vivo exposure to hypoxia.
    Keywords:  enzymes; hypoxia tolerance; membrane lipids; metabolic suppression; sodium/potassium ATPase
    DOI:  https://doi.org/10.1152/ajpregu.00057.2020
  37. Nature. 2020 Jul;583(7816): 332
      
    Keywords:  Biological techniques; CRISPR-Cas9 genome editing; Genetics; Metabolism
    DOI:  https://doi.org/10.1038/d41586-020-02094-x
  38. Nat Commun. 2020 Jul 14. 11(1): 3520
    Mzoughi S, Fong JY, Papadopoli D, Koh CM, Hulea L, Pigini P, Di Tullio F, Andreacchio G, Hoppe MM, Wollmann H, Low D, Caldez MJ, Peng Y, Torre D, Zhao JN, Uchenunu O, Varano G, Motofeanu CM, Lakshmanan M, Teo SX, Wun CM, Perini G, Tan SY, Ong CB, Al-Haddawi M, Rajarethinam R, Hue SS, Lim ST, Ong CK, Huang D, Ng SB, Bernstein E, Hasson D, Wee KB, Kaldis P, Jeyasekharan A, Dominguez-Sola D, Topisirovic I, Guccione E.
      PRDM (PRDI-BF1 and RIZ homology domain containing) family members are sequence-specific transcriptional regulators involved in cell identity and fate determination, often dysregulated in cancer. The PRDM15 gene is of particular interest, given its low expression in adult tissues and its overexpression in B-cell lymphomas. Despite its well characterized role in stem cell biology and during early development, the role of PRDM15 in cancer remains obscure. Herein, we demonstrate that while PRDM15 is largely dispensable for mouse adult somatic cell homeostasis in vivo, it plays a critical role in B-cell lymphomagenesis. Mechanistically, PRDM15 regulates a transcriptional program that sustains the activity of the PI3K/AKT/mTOR pathway and glycolysis in B-cell lymphomas. Abrogation of PRDM15 induces a metabolic crisis and selective death of lymphoma cells. Collectively, our data demonstrate that PRDM15 fuels the metabolic requirement of B-cell lymphomas and validate it as an attractive and previously unrecognized target in oncology.
    DOI:  https://doi.org/10.1038/s41467-020-17064-0
  39. Elife. 2020 Jul 15. pii: e59991. [Epub ahead of print]9
    Wang C, Jacewicz A, Delgado BD, Baradaran R, Long SB.
      The mitochondrial calcium uniporter is a Ca2+-gated ion channel complex that controls mitochondrial Ca2+ entry and regulates cell metabolism. MCU and EMRE form the channel while Ca2+-dependent regulation is conferred by MICU1 and MICU2 through an enigmatic process. We present a cryo-EM structure of an MCU-EMRE-MICU1-MICU2 holocomplex comprising MCU and EMRE subunits from the beetle Tribolium castaneum in complex with a human MICU1-MICU2 heterodimer at 3.3 Å resolution. With analogy to how neuronal channels are blocked by protein toxins, a uniporter interaction domain on MICU1 binds to a channel receptor site comprising MCU and EMRE subunits to inhibit ion flow under resting Ca2+ conditions. A Ca2+-bound structure of MICU1-MICU2 at 3.1 Å resolution indicates how Ca2+-dependent changes enable dynamic response to cytosolic Ca2+ signals.
    Keywords:  biochemistry; chemical biology; human; molecular biophysics; structural biology
    DOI:  https://doi.org/10.7554/eLife.59991