bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒07‒12
thirty-five papers selected by
Kelsey Fisher-Wellman
East Carolina University


  1. Nature. 2020 Jul 08.
    Martínez-Reyes I, Cardona LR, Kong H, Vasan K, McElroy GS, Werner M, Kihshen H, Reczek CR, Weinberg SE, Gao P, Steinert EM, Piseaux R, Budinger GRS, Chandel NS.
      The mitochondrial electron transport chain (ETC) is necessary for tumour growth1-6 and its inhibition has demonstrated anti-tumour efficacy in combination with targeted therapies7-9. Furthermore, human brain and lung tumours display robust glucose oxidation by mitochondria10,11. However, it is unclear why a functional ETC is necessary for tumour growth in vivo. ETC function is coupled to the generation of ATP-that is, oxidative phosphorylation and the production of metabolites by the tricarboxylic acid (TCA) cycle. Mitochondrial complexes I and II donate electrons to ubiquinone, resulting in the generation of ubiquinol and the regeneration of the NAD+ and FAD cofactors, and complex III oxidizes ubiquinol back to ubiquinone, which also serves as an electron acceptor for dihydroorotate dehydrogenase (DHODH)-an enzyme necessary for de novo pyrimidine synthesis. Here we show impaired tumour growth in cancer cells that lack mitochondrial complex III. This phenotype was rescued by ectopic expression of Ciona intestinalis alternative oxidase (AOX)12, which also oxidizes ubiquinol to ubiquinone. Loss of mitochondrial complex I, II or DHODH diminished the tumour growth of AOX-expressing cancer cells deficient in mitochondrial complex III, which highlights the necessity of ubiquinone as an electron acceptor for tumour growth. Cancer cells that lack mitochondrial complex III but can regenerate NAD+ by expression of the NADH oxidase from Lactobacillus brevis (LbNOX)13 targeted to the mitochondria or cytosol were still unable to grow tumours. This suggests that regeneration of NAD+ is not sufficient to drive tumour growth in vivo. Collectively, our findings indicate that tumour growth requires the ETC to oxidize ubiquinol, which is essential to drive the oxidative TCA cycle and DHODH activity.
    DOI:  https://doi.org/10.1038/s41586-020-2475-6
  2. iScience. 2020 Jun 20. pii: S2589-0042(20)30482-X. [Epub ahead of print]23(7): 101295
    Bose HS, Marshall B, Debnath DK, Perry EW, Whittal RM.
      The first steroidogenic enzyme, cytochrome P450-side-chain-cleavage (SCC), requires electron transport chain (ETC) complexes III and IV to initiate steroid metabolic processes for mammalian survival. ETC complex II, containing succinate dehydrogenase (quinone), acts with the TCA cycle and has no proton pumping capacity. We show that complex II is required for SCC activation through the proton pump, generating an intermediate state for addition of phosphate by succinate. Phosphate anions in the presence of succinate form a stable mitochondrial complex with higher enthalpy (-ΔH) and enhanced activity. Inhibition of succinate action prevents SCC processing at the intermediate state and ablates activity and mitochondrial protein network. This is the first report directly showing that a protein intermediate state is activated by succinate, facilitating the ETC complex II to interact with complexes III and IV for continued mitochondrial metabolic process, suggesting complex II is essential for steroid metabolism regulation.
    Keywords:  Biochemistry; Biological Sciences; Molecular Biology
    DOI:  https://doi.org/10.1016/j.isci.2020.101295
  3. Sci Adv. 2020 Jun;6(26): eaba7509
    Calvo E, Cogliati S, Hernansanz-Agustín P, Loureiro-López M, Guarás A, Casuso RA, García-Marqués F, Acín-Pérez R, Martí-Mateos Y, Silla-Castro JC, Carro-Alvarellos M, Huertas JR, Vázquez J, Enríquez JA.
      Mitochondrial respiratory complexes assemble into supercomplexes (SC). Q-respirasome (III2 + IV) requires the supercomplex assembly factor (SCAF1) protein. The role of this factor in the N-respirasome (I + III2 + IV) and the physiological role of SCs are controversial. Here, we study C57BL/6J mice harboring nonfunctional SCAF1, the full knockout for SCAF1, or the wild-type version of the protein and found that exercise performance is SCAF1 dependent. By combining quantitative data-independent proteomics, 2D Blue native gel electrophoresis, and functional analysis of enriched respirasome fractions, we show that SCAF1 confers structural attachment between III2 and IV within the N-respirasome, increases NADH-dependent respiration, and reduces reactive oxygen species (ROS). Furthermore, the expression of AOX in cells and mice confirms that CI-CIII superassembly segments the CoQ in two pools and modulates CI-NADH oxidative capacity.
    DOI:  https://doi.org/10.1126/sciadv.aba7509
  4. J Cell Mol Med. 2020 Jul 07.
    Shao S, Qin T, Qian W, Yue Y, Xiao Y, Li X, Zhang D, Wang Z, Ma Q, Lei J.
      Caveolin-1 (Cav-1) is the principal structural component of caveolae, and its dysregulation occurs in cancer. However, the role of Cav-1 in pancreatic cancer (PDAC) tumorigenesis and metabolism is largely unknown. In this study, we aimed to investigate the effect of pancreatic stellate cell (PSC) Cav-1 on PDAC metabolism and aggression. We found that Cav-1 is expressed at low levels in PDAC stroma and that the loss of stromal Cav-1 is associated with poor survival. In PSCs, knockdown of Cav-1 promoted the production of reactive oxygen species (ROS), while ROS production further reduced the expression of Cav-1. Positive feedback occurs in Cav-1-ROS signalling in PSCs, which promotes PDAC growth and induces stroma-tumour metabolic coupling in PDAC. In PSCs, positive feedback in Cav-1-ROS signalling induced a shift in energy metabolism to glycolysis, with up-regulated expression of glycolytic enzymes (hexokinase 2 (HK-2), 6-phosphofructokinase (PFKP) and pyruvate kinase isozyme type M2 (PKM2)) and transporter (Glut1) expression and down-regulated expression of oxidative phosphorylation (OXPHOS) enzymes (translocase of outer mitochondrial membrane 20 (TOMM20) and NAD(P)H dehydrogenase [quinone] 1 (NQO1)). These events resulted in high levels of glycolysis products such as lactate, which was secreted by up-regulated monocarboxylate transporter 4 (MCT4) in PSCs. Simultaneously, PDAC cells took up these glycolysis products (lactate) through up-regulated MCT1 to undergo OXPHOS, with down-regulated expression of glycolytic enzymes (HK-2, PFKP and PKM2) and up-regulated expression of OXPHOS enzymes (TOMM20 and NQO1). Interrupting the metabolic coupling between the stroma and tumour cells may be an effective method for tumour therapy.
    Keywords:  pancreatic cancer; pancreatic stellate cells; positive feedback in Cav-1-ROS signalling; stroma-tumour metabolic coupling
    DOI:  https://doi.org/10.1111/jcmm.15596
  5. J Am Chem Soc. 2020 Jul 09.
    Muehlbauer ME, Saura P, Nuber F, Di Luca A, Friedrich T, Kaila VRI.
      The respiratory complex I transduces redox energy into an electrochemical proton gradient in aerobic respiratory chains, powering energy-requiring processes in the cell. However, despite recently resolved molecular structures, the mechanism of this gigantic enzyme remains poorly understood. By combining large-scale quantum and classical simulations with site-directed mutagenesis and biophysical experiments, we show here how the conformational state of buried ion-pairs and water molecules control the protonation dynamics in the membrane domain of complex I, and establish evolutionary conserved long-range coupling elements. We suggest that an electrostatic wave propagates in forward and reverse directions across the 200 Å long membrane domain during enzyme turnover, without significant dissipation of energy. Our findings demonstrate molecular principles that enable efficient long-range proton-electron coupling (PCET), and how perturbation of this PCET machinery may lead to development of mitochondrial disease.
    DOI:  https://doi.org/10.1021/jacs.0c02789
  6. Aging Cell. 2020 Jul 06. e13187
    Liang W, Moyzis AG, Lampert MA, Diao RY, Najor RH, Gustafsson ÅB.
      Advancing age is a major risk factor for developing heart disease, and the biological processes contributing to aging are currently under intense investigation. Autophagy is an important cellular quality control mechanism that is reduced in tissues with age but the molecular mechanisms underlying the age-associated defects in autophagy remain poorly characterized. Here, we have investigated how the autophagic process is altered in aged mouse hearts. We report that autophagic activity is reduced in aged hearts due to a reduction in autophagosome formation. Gene expression profile analysis to evaluate changes in autophagy regulators uncovered a reduction in Atg9b transcript and protein levels. Atg9 proteins are critical in delivering membrane to the growing autophagosome, and siRNA knockdown of Atg9b in cells confirmed a reduction in autophagosome formation. Autophagy is also the main pathway involved in eliminating dysfunctional mitochondria via a process known as mitophagy. The E3 ubiquitin ligase Parkin plays a key role in labeling mitochondria for mitophagy. We also found increased levels of Parkin-positive mitochondria in the aged hearts, an indication that they have been labeled for mitophagy. In contrast, Nrf1, a major transcriptional regulator of mitochondrial biogenesis, was significantly reduced in aged hearts. Additionally, our data showed reduced Drp1-mediated mitochondrial fission and formation of enlarged mitochondria in the aged heart. Overall, our findings suggest that cardiac aging is associated with reduced autophagosome number, decreased mitochondrial turnover, and formation of megamitochondria.
    Keywords:  Atg9; Parkin; aging; autophagy; heart; mitochondria; mitophagy
    DOI:  https://doi.org/10.1111/acel.13187
  7. Cancer Res. 2020 Jul 10. pii: canres.0246.2020. [Epub ahead of print]
    Madala HR, Helenius IT, Zhou W, Mills E, Zhang Y, Liu Y, Metelo AM, Kelley ML, Punganuru S, Kim KB, Olenchock B, Rhee E, Intlekofer AM, Lliopoulos O, Chouchani E, Yeh JJ.
      Under conditions of inherent or induced mitochondrial dysfunction, cancer cells manifest overlapping metabolic phenotypes, suggesting that they may be targeted via a common approach. Here we use multiple oxidative phosphorylation (OXPHOS)-competent and -incompetent cancer cell pairs to demonstrate that treatment with alpha-ketoglutarate (aKG) esters elicits rapid death of OXPHOS-deficient cancer cells by elevating intracellular aKG concentrations, thereby sequestering nitrogen from aspartate through glutamic-oxaloacetic transaminase 1 (GOT1). Exhaustion of aspartate in these cells resulted in immediate depletion of adenylates, which plays a central role in mediating mTOR inactivation and inhibition of glycolysis. aKG esters also conferred cytotoxicity in a variety of cancer types if their cell respiration was obstructed by hypoxia or by chemical inhibition of the electron transport chain (ETC), both of which are known to increase aspartate and GOT1 dependencies. Further, preclinical mouse studies suggested that cell-permeable aKG displays a good biosafety profile, eliminates aspartate only in OXPHOS-incompetent tumors, and prevents their growth and metastasis. This study reveals a novel cytotoxic mechanism for the metabolite aKG and identifies cell-permeable aKG, either by itself or in combination with ETC inhibitors, as a potential anti-cancer approach.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-20-0246
  8. Nature. 2020 Jul 08.
    Jimenez-Blasco D, Busquets-Garcia A, Hebert-Chatelain E, Serrat R, Vicente-Gutierrez C, Ioannidou C, Gómez-Sotres P, Lopez-Fabuel I, Resch-Beusher M, Resel E, Arnouil D, Saraswat D, Varilh M, Cannich A, Julio-Kalajzic F, Bonilla-Del Río I, Almeida A, Puente N, Achicallende S, Lopez-Rodriguez ML, Jollé C, Déglon N, Pellerin L, Josephine C, Bonvento G, Panatier A, Lutz B, Piazza PV, Guzmán M, Bellocchio L, Bouzier-Sore AK, Grandes P, Bolaños JP, Marsicano G.
      Astrocytes take up glucose from the bloodstream to provide energy to the brain, thereby allowing neuronal activity and behavioural responses1-5. By contrast, astrocytes are under neuronal control through specific neurotransmitter receptors5-7. However, whether the activation of astroglial receptors can directly regulate cellular glucose metabolism to eventually modulate behavioural responses is unclear. Here we show that activation of mouse astroglial type-1 cannabinoid receptors associated with mitochondrial membranes (mtCB1) hampers the metabolism of glucose and the production of lactate in the brain, resulting in altered neuronal functions and, in turn, impaired behavioural responses in social interaction assays. Specifically, activation of astroglial mtCB1 receptors reduces the phosphorylation of the mitochondrial complex I subunit NDUFS4, which decreases the stability and activity of complex I. This leads to a reduction in the generation of reactive oxygen species by astrocytes and affects the glycolytic production of lactate through the hypoxia-inducible factor 1 pathway, eventually resulting in neuronal redox stress and impairment of behavioural responses in social interaction assays. Genetic and pharmacological correction of each of these effects abolishes the effect of cannabinoid treatment on the observed behaviour. These findings suggest that mtCB1 receptor signalling can directly regulate astroglial glucose metabolism to fine-tune neuronal activity and behaviour in mice.
    DOI:  https://doi.org/10.1038/s41586-020-2470-y
  9. FEBS Open Bio. 2020 Jul 06.
    Wu H, Zhang K, Chen Y, Li J, Strout MP, Gu X.
      Activation induced cytidine deaminase (AID) initiates somatic hypermutation and class switch recombination of immunoglobulin genes in B cells while off-targeted AID activity contributes to oncogenic mutations and chromosomal translocations associated with B cell malignancies. Paradoxically, only a minority of AID is allowed to access the nuclear genome but the majority of AID is retained in the cytoplasm. It is unknown whether cytoplasmic AID can access and target the mitochondrial genome (mtDNA). To address this issue, we developed high-fidelity 3DPCR (differential DNA denaturation PCR), which allowed the enrichment of genuine mtDNA mutations and therefore the identification of endogenous mtDNA mutation signatures in vitro. With this approach, we showed that AID targeting to mtDNA is a rare event in AID-expressing lymphoma lines. Further biochemical and microscopic analysis revealed that a fraction of cytosol AID is associated with the outer membrane of mitochondria, but unable to access the mitochondrial matrix. Together, our data suggested that the mitochondrial genome is protected from AID-mediated mutagenesis by physical segregation of AID from accessing mtDNA within mitochondrial matrix.
    Keywords:  3DPCR; Activation-induced cytidine deaminase; mitochondria; mtDNA
    DOI:  https://doi.org/10.1002/2211-5463.12927
  10. Cardiovasc Drugs Ther. 2020 Jul 09.
    Prag HA, Pala L, Kula-Alwar D, Mulvey JF, Luping D, Beach TE, Booty LM, Hall AR, Logan A, Sauchanka V, Caldwell ST, Robb EL, James AM, Xu Z, Saeb-Parsy K, Hartley RC, Murphy MP, Krieg T.
      PURPOSE: Mitochondrial reactive oxygen species (ROS) production upon reperfusion of ischemic tissue initiates the ischemia/reperfusion (I/R) injury associated with heart attack. During ischemia, succinate accumulates and its oxidation upon reperfusion by succinate dehydrogenase (SDH) drives ROS production. Inhibition of succinate accumulation and/or oxidation by dimethyl malonate (DMM), a cell permeable prodrug of the SDH inhibitor malonate, can decrease I/R injury. However, DMM is hydrolysed slowly, requiring administration to the heart prior to ischemia, precluding its administration to patients at the point of reperfusion, for example at the same time as unblocking a coronary artery following a heart attack. To accelerate malonate delivery, here we developed more rapidly hydrolysable malonate esters.METHODS: We synthesised a series of malonate esters and assessed their uptake and hydrolysis by isolated mitochondria, C2C12 cells and in mice in vivo. In addition, we assessed protection against cardiac I/R injury by the esters using an in vivo mouse model of acute myocardial infarction.
    RESULTS: We found that the diacetoxymethyl malonate diester (MAM) most rapidly delivered large amounts of malonate to cells in vivo. Furthermore, MAM could inhibit mitochondrial ROS production from succinate oxidation and was protective against I/R injury in vivo when added at reperfusion.
    CONCLUSIONS: The rapidly hydrolysed malonate prodrug MAM can protect against cardiac I/R injury in a clinically relevant mouse model.
    Keywords:  Drug delivery; Ischemia/reperfusion injury; Malonate; Mitochondria; Succinate
    DOI:  https://doi.org/10.1007/s10557-020-07033-6
  11. Aging (Albany NY). 2020 Jul 08. 12
    Wei JR, Dong J, Li L.
      Gamma-glutamyltransferase 5 (GGT5) is a member of the gamma-glutamyl transpeptidase gene family with the capacity of cleaving the gamma-glutamyl moiety of glutathione, but its role in cancer progression has never been revealed. In this study, we found that gene GGT5 was highly expressed in cancer-associated fibroblasts (CAFs) in lung adenocarcinoma, predicting the unfavorable survival of patients with lung adenocarcinoma. Cell growth, foci formation and spheres formation analyses showed that cancer cell proliferation was attenuated under treatment with the conditioned media from GGT5-silenced CAFs. Moreover, high expression of GGT5 in CAFs enhanced the drug resistance of cancer cells by increasing intracellular glutathione and reducing the intracellular reactive oxygen species in cancer cells. In mouse xenograft model, we proved that targeting GGT5 with a small-molecule inhibitor GGsTop could inhibit tumor growth and increase the chemosensitivity of cancer cells. Taken together, our study illuminates that high level of GGT5 in CAFs contributes to cancer cell survival and drug resistance, indicating that GGT5 may be a promising therapeutic target in lung adenocarcinoma.
    Keywords:  GGT5; ROS; cancer-associated fibroblast; glutathione; lung adenocarcinoma
    DOI:  https://doi.org/10.18632/aging.103429
  12. J Biol Chem. 2020 Jul 06. pii: jbc.RA120.013960. [Epub ahead of print]
    Li Y, Lou W, Grevel A, Böttinger L, Liang Z, Ji J, Patil VA, Liu J, Ye C, Hüttemann M, Becker T, Greenberg ML.
      Cardiolipin (CL) is the signature phospholipid of mitochondrial membranes, where it is synthesized locally and plays an important role in mitochondrial bioenergetics. Previous studies in the yeast model have indicated that CL is required for optimal iron homeostasis, which is disrupted by a mechanism not yet determined in the yeast CL mutant, crd1Δ. This finding has implications for the severe genetic disorder, Barth syndrome (BTHS), in which CL metabolism is perturbed because of mutations in the CL-remodeling enzyme, tafazzin. Here, we investigate the effects of tafazzin-deficiency on iron homeostasis in the mouse myoblast model of BTHS, TAZ-KO (tafazzin knockout) cells. Similarly to CL-deficient yeast cells, TAZ-KO cells exhibited elevated sensitivity to iron as well as to H2O2, which was alleviated by the iron chelator deferoxamine. TAZ-KO cells exhibited increased expression of the iron exporter ferroportin and decreased expression of the iron importer transferrin receptor, likely reflecting a regulatory response to elevated mitochondrial iron. Reduced activities of mitochondrial iron-sulfur cluster (Fe-S) enzymes suggested that the mechanism underlying perturbation of iron homeostasis was defective Fe-S biogenesis. We observed decreased levels of Yfh1/frataxin, an essential component of the Fe-S biogenesis machinery, in mitochondria from TAZ-KO mouse cells and in CL-deleted yeast crd1Δ cells, indicating that the role of CL in Fe-S biogenesis is highly conserved. Yeast crd1Δ cells exhibited decreased processing of the Yfh1 precursor upon import, which likely contributes to the iron homeostasis defects. Implications for understanding the pathogenesis of BTHS are discussed.
    Keywords:  Barth syndrome; cardiolipin; frataxin; iron; mitochondria; protein import
    DOI:  https://doi.org/10.1074/jbc.RA120.013960
  13. Elife. 2020 Jul 10. pii: e55513. [Epub ahead of print]9
    Chiao YA, Zhang H, Sweetwyne M, Whitson J, Ting YS, Basisty N, Pino LK, Quarles E, Nguyen NH, Campbell MD, Zhang T, Gaffrey MJ, Merrihew G, Wang L, Yue Y, Duan D, Granzier HL, Szeto HH, Qian WJ, Marcinek D, MacCoss MJ, Rabinovitch P.
      Diastolic dysfunction is a prominent feature of cardiac aging in both mice and humans. We show here that 8-week treatment of old mice with the mitochondrial targeted peptide SS-31 (elamipretide) can substantially reverse this deficit. SS-31 normalized the increase in proton leak and reduced mitochondrial ROS in cardiomyocytes from old mice, accompanied by reduced protein oxidation and a shift towards a more reduced protein thiol redox state in old hearts. Improved diastolic function was concordant with increased phosphorylation of cMyBP-C Ser282 but was independent of titin isoform shift. Late-life viral expression of mitochondrial-targeted catalase (mCAT) produced similar functional benefits in old mice and SS-31 did not improve cardiac function of old mCAT mice, implicating normalizing mitochondrial oxidative stress as an overlapping mechanism. These results demonstrate that pre-existing cardiac aging phenotypes can be reversed by targeting mitochondrial dysfunction and implicate mitochondrial energetics and redox signaling as therapeutic targets for cardiac aging.
    Keywords:  human biology; medicine; mouse
    DOI:  https://doi.org/10.7554/eLife.55513
  14. Theranostics. 2020 ;10(16): 7335-7350
    Du F, Cao T, Xie H, Li T, Sun L, Liu H, Guo H, Wang X, Liu Q, Kim T, Franklin JL, Graves-Deal R, Han W, Tian Z, Ge M, Nie Y, Fan D, Coffey RJ, Lu Y, Zhao X.
      Introduction: Colorectal cancer (CRC) frequently harbors KRAS mutations that result in chemoresistance and metastasis. MicroRNAs (miRNAs) are usually dysregulated and play important regulatory roles in tumor progression. However, the KRAS mutation-responsive miRNA profile in CRC remains uninvestigated. Methods: miR-139-5p was identified and evaluated by small RNA sequencing, qRT-PCR and in situ hybridization. The roles of miR-139-5p in CRC cells with and without KRAS mutation were determined by Cell Counting Kit-8 (CCK-8), colony formation, flow cytometry and transwell assays in vitro and by tumorigenesis and metastasis assays in vivo. Microarrays followed by bioinformatic analyses, luciferase reporter assays and Western blotting were applied for mechanistic studies. Results: miR-139-5p was significantly downregulated in KRAS-mutated CRC cells and tissues compared with their wild-type counterparts. Low miR-139-5p expression was associated with aggressive phenotypes and poor prognosis in CRC patients. miR-139-5p overexpression inhibited CRC cell proliferation, migration and invasion in vitro, sensitized tumors to chemotherapy, and impaired tumor growth and metastasis in vivo. Transcriptomic profiling identified multiple modulators in the Ras (JUN and FOS) and Wnt (CTNNB1 and DVL1) signaling pathways and the epithelial-to-mesenchymal transition (EMT) process (ZEB1) as direct targets of miR-139-5p, and inverse correlations were confirmed in CRC clinical tissues. Aberrantly activated Wnt signaling in KRAS-mutant cells was demonstrated to transcriptionally repress miR-139-5p through TCF4, forming a miR-139-5p/Wnt signaling double-negative feedback loop. Conclusions: We identified miR-139-5p as a KRAS-responsive miRNA and demonstrated its involvement in CRC progression. KRAS mutation disrupted the miR-139-5p/Wnt signaling reciprocal negative feedback mechanism, which might cause miR-139-5p downregulation and derepression of oncogenic signaling pathways and EMT. These results reveal a transcriptional regulatory mode of KRAS-driven malignant transformation and highlight miR-139-5p as a novel regulator of crosstalk between the Ras and Wnt signaling pathways in CRC.
    Keywords:  CRC; KRAS mutation; Ras signaling; Wnt/β-catenin signaling; miR-139-5p
    DOI:  https://doi.org/10.7150/thno.45971
  15. Mol Genet Metab. 2020 Jun 27. pii: S1096-7192(20)30150-5. [Epub ahead of print]
    Uittenbogaard M, Chiaramello A.
      Maternally inherited mitochondrial respiratory disorders are rare, progressive, and multi-systemic diseases that remain intractable, with no effective therapeutic interventions. Patients share a defective oxidative phosphorylation pathway responsible for mitochondrial ATP synthesis, in most cases due to pathogenic mitochondrial variants transmitted from mother to child or to a rare de novo mutation or large-scale deletion of the mitochondrial genome. The clinical diagnosis of these mitochondrial diseases is difficult due to exceptionally high clinical variability, while their genetic diagnosis has improved with the advent of next-generation sequencing. The mechanisms regulating the penetrance of the mitochondrial variants remain unresolved with the patient's nuclear background, epigenomic regulation, heteroplasmy, mitochondrial haplogroups, and environmental factors thought to act as rheostats. The lack of animal models mimicking the phenotypic manifestations of these disorders has hampered efforts toward curative therapies. Patient-derived cellular paradigms provide alternative models for elucidating the pathogenic mechanisms and screening pharmacological small molecules to enhance mitochondrial function. Recent progress has been made in designing promising approaches to curtail the negative impact of dysfunctional mitochondria and alleviate clinical symptoms: 1) boosting mitochondrial biogenesis; 2) shifting heteroplasmy; 3) reprogramming metabolism; and 4) administering hypoxia-based treatment. Here, we discuss their varying efficacies and limitations and provide an outlook on their therapeutic potential and clinical application.
    Keywords:  Hypoxia-directed intervention; Metabolic reprogramming; Mitochondrial genetics; Mitochondrial genome editing; Mitochondrial homeostasis; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.ymgme.2020.06.011
  16. Theranostics. 2020 ;10(16): 7193-7210
    Chen Y, Zhou Y, Han F, Zhao Y, Tu M, Wang Y, Huang C, Fan S, Chen P, Yao X, Guan L, Yu AM, Gonzalez FJ, Huang M, Bi H.
      Rationale: MicroRNAs are known to influence the development of a variety of cancers. Previous studies revealed that miR-1291 has antiproliferative functions in cancer cells. Carnitine palmitoyltransferase 1C (CPT1C) has a vital role in mitochondrial energy metabolism and modulation of cancer cell proliferation. Since both miR-1291 and CPT1C regulate tumor cell metabolism and cancer progression, we hypothesized that they might be regulated synergistically. Methods: A series of cell phenotype indicators, such as BrdU, colony formation, cell cycle, ATP production, ROS accumulation and cell ability to resist metabolic stress, were performed to clarify the effects of miR-1291 and ERRα expression on tumor cell proliferation and metabolism. A xenograft tumor model was used to evaluate cell tumorigenesis. Meta-analysis and bioinformatic prediction were applied in the search for the bridge-link between miR-1291 and CPT1C. RT-qPCR, western-blot and IHC analysis were used for the detection of mRNA and protein expression. Luciferase assays and ChIP assays were conducted for in-depth mechanism studies. Results: The expression of miR-1291 inhibited growth and tumorigenesis as a result of modulation of metabolism. CPT1C expression was indirectly and negatively correlated with miR-1291 levels. ESRRA was identified as a prominent differentially expressed gene in both breast and pancreatic cancer samples, and estrogen-related receptor α (ERRα) was found to link miR-1291 and CPT1C. MiR-1291 targeted ERRα and CPT1C was identified as a newly described ERRα target gene. Moreover, ERRα was found to influence cancer cell metabolism and proliferation, consistent with the cellular changes caused by miR-1291. Conclusion: This study demonstrated the existence and mechanism of action of a novel miR-1291-ERRα-CPT1C cancer metabolism axis that may provide new insights and strategies for the development of miRNA-based therapies for malignant cancers.
    Keywords:  carnitine palmitoyltransferase 1C; cell proliferation; estrogen-related receptor α; miR-1291; tumor metabolism
    DOI:  https://doi.org/10.7150/thno.44877
  17. Oncol Rep. 2020 Aug;44(2): 499-508
    Liu Y, Zhang Z, Li Q, Zhang L, Cheng Y, Zhong Z.
      Apurinic/apyrimidinic endonuclease 1 (APE1) is a primary nuclear‑localized multifunctional protein in osteosarcoma. However, the cytoplasmic localization of APE1 was found to be functional and to increase with cisplatin resistance, yet the molecular mechanism is unknown. In the present study, we explored the cisplatin resistance mechanism in osteosarcoma from the new perspective of APE1 extranuclear biological activity. Using cisplatin‑resistant and cisplatin‑sensitive osteosarcoma cell lines, we found that mitochondrial APE1 (mtAPE1) was overexpressed in cisplatin‑resistant cells but not in sensitive cells. Overexpression of mtAPE1 reduced cisplatin‑induced apoptosis, while knockdown of APE1 reversed this phenomenon and caused oxidative DNA damage via overproduction of reactive oxygen species (ROS). We further demonstrated that high mtAPE1 expression could downregulate ROS production by decreasing the phosphorylation of Rac1 (p‑Rac1), further promoting cisplatin resistance in osteosarcoma. Our findings suggest that mitochondrial APE1 promotes cisplatin resistance by decreasing ROS generation, which may provide new ideas for researching the molecular mechanism of osteosarcoma chemoresistance and strategies to overcome cisplatin resistance in osteosarcoma.
    DOI:  https://doi.org/10.3892/or.2020.7633
  18. Elife. 2020 Jul 10. pii: e56782. [Epub ahead of print]9
    Lau AN, Li Z, Danai LV, Westermark AM, Darnell AM, Ferreira R, Gocheva V, Sivanand S, Lien EC, Sapp KM, Mayers JR, Biffi G, Chin CR, Davidson SM, Tuveson DA, Jacks T, Matheson NJ, Yilmaz O, Vander Heiden MG.
      Tumors are composed of many different cell types including cancer cells, fibroblasts, and immune cells. Dissecting functional metabolic differences between cell types within a mixed population can be challenging due to the rapid turnover of metabolites relative to the time needed to isolate cells. To overcome this challenge, we traced isotope-labeled nutrients into macromolecules that turn over more slowly than metabolites. This approach was used to assess differences between cancer cell and fibroblast metabolism in murine pancreatic cancer organoid-fibroblast co-cultures and tumors. Pancreatic cancer cells exhibited increased pyruvate carboxylation relative to fibroblasts, and this flux depended on both pyruvate carboxylase and malic enzyme 1 activity. Consequently, expression of both enzymes in cancer cells was necessary for organoid and tumor growth, demonstrating that dissecting the metabolism of specific cell populations within heterogeneous systems can identify dependencies that may not be evident from studying isolated cells in culture or bulk tissue.
    Keywords:  cancer biology; mouse
    DOI:  https://doi.org/10.7554/eLife.56782
  19. EMBO Rep. 2020 Jul 06. e201949801
    Han S, Jeong YY, Sheshadri P, Su X, Cai Q.
      Synaptic mitochondria are particularly vulnerable to physiological insults, and defects in synaptic mitochondria are linked to early pathophysiology of Alzheimer's disease (AD). Mitophagy, a cargo-specific autophagy for elimination of dysfunctional mitochondria, constitutes a key quality control mechanism. However, how mitophagy ensures synaptic mitochondrial integrity remains largely unknown. Here, we reveal Rheb and Snapin as key players regulating mitochondrial homeostasis at synapses. Rheb initiates mitophagy to target damaged mitochondria for autophagy, whereas dynein-Snapin-mediated retrograde transport promotes clearance of mitophagosomes from synaptic terminals. We demonstrate that synaptic accumulation of mitophagosomes is a feature in AD-related mutant hAPP mouse brains, which is attributed to increased mitophagy initiation coupled with impaired removal of mitophagosomes from AD synapses due to defective retrograde transport. Furthermore, while deficiency in dynein-Snapin-mediated retrograde transport recapitulates synaptic mitophagy stress and induces synaptic degeneration, elevated Snapin expression attenuates mitochondrial defects and ameliorates synapse loss in AD mouse brains. Taken together, our study provides new insights into mitophagy regulation of synaptic mitochondrial integrity, establishing a foundation for mitigating AD-associated mitochondria deficits and synaptic damage through mitophagy enhancement.
    Keywords:  Alzheimer's; mitophagosome; retrograde transport; synaptic mitochondrial deficits; synaptic mitophagy
    DOI:  https://doi.org/10.15252/embr.201949801
  20. Biomolecules. 2020 Jul 07. pii: E1008. [Epub ahead of print]10(7):
    Horten P, Colina-Tenorio L, Rampelt H.
      : Metabolite carriers of the mitochondrial inner membrane are crucial for cellular physiology since mitochondria contribute essential metabolic reactions and synthesize the majority of the cellular ATP. Like almost all mitochondrial proteins, carriers have to be imported into mitochondria from the cytosol. Carrier precursors utilize a specialized translocation pathway dedicated to the biogenesis of carriers and related proteins, the carrier translocase of the inner membrane (TIM22) pathway. After recognition and import through the mitochondrial outer membrane via the translocase of the outer membrane (TOM) complex, carrier precursors are ushered through the intermembrane space by hexameric TIM chaperones and ultimately integrated into the inner membrane by the TIM22 carrier translocase. Recent advances have shed light on the mechanisms of TOM translocase and TIM chaperone function, uncovered an unexpected versatility of the machineries, and revealed novel components and functional crosstalk of the human TIM22 translocase.
    Keywords:  TIM chaperones; TIM22; TOM; metabolite transport; mitochondrial biogenesis; mitochondrial carrier; mitochondrial pyruvate carrier; protein translocation; sideroflexin
    DOI:  https://doi.org/10.3390/biom10071008
  21. J Microbiol Biotechnol. 2020 Jul 06.
    Yoon YG.
      Recently, it was reported that entire mammalian mtDNA genomes could be transplanted into the mitochondrial networks of yeast, where they were accurately and stably maintained without rearrangement as intact genomes. Here, it was found that engineered mtDNA genomes could be readily transferred to and steadily maintained in the mitochondria of genetically modified yeast expressing the mouse mitochondrial transcription factor A (Tfam), one of the mitochondrial nucleoid proteins. The transferred mtDNA genomes were stably retained in the Tfam-expressing yeast cells for many generations. These results indicated that the engineered mouse mtDNA genomes introduced in yeast mitochondria could be relocated into the mitochondria of other cells and that the transferred genomes could be maintained within a mitochondrial environment that is highly amenable to mimicry of the biological conditions in mammalian mitochondria.
    Keywords:  N-ethylmaleimide; Tfam; mitochondrial transcription factor A; mtDNA; spheroplast; xenomitochondria
    DOI:  https://doi.org/10.4014/jmb.2004.04033
  22. Theranostics. 2020 ;10(16): 7178-7192
    Wang Z, Qin J, Zhao J, Li J, Li D, Popp M, Popp F, Alakus H, Kong B, Dong Q, Nelson PJ, Zhao Y, Bruns CJ.
      Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers worldwide and effective therapy remains a challenge. IFIT3 is an interferon-stimulated gene with antiviral and pro-inflammatory functions. Our previous work has shown that high expression of IFIT3 is correlated with poor survival in PDAC patients who receive chemotherapy suggesting a link between IFIT3 and chemotherapy resistance in PDAC. However, the exact role and molecular mechanism of IFIT3 in chemotherapy resistance in PDAC has been unclear. Methods: A group of transcriptome datasets were downloaded and analyzed for the characterization of IFIT3 in PDAC. Highly metastatic PDAC cell line L3.6pl and patient-derived primary cell TBO368 were used and IFIT3 knockdown and the corresponding knockin cells were established for in vitro studies. Chemotherapy-induced apoptosis, ROS production, confocal immunofluorescence, subcellular fractionation, chromatin-immunoprecipitation, co-immunoprecipitation and mass spectrometry analysis were determined to further explore the biological role of IFIT3 in chemotherapy resistance of PDAC. Results: Based on PDAC transcriptome data, we show that IFIT3 expression is associated with the squamous molecular subtype of PDAC and an increase in inflammatory response and apoptosis pathways. We further identify a crucial role for IFIT3 in the regulation of mitochondria-associated apoptosis during chemotherapy. Knockdown of IFIT3 attenuates the chemotherapy resistance of PDAC cells to gemcitabine, paclitaxel, and FOLFIRINOX regimen treatments, independent of individual chemotherapy regimens. While IFIT3 overexpression was found to promote drug resistance. Co-immunoprecipitation identified a direct interaction between IFIT3 and the mitochondrial channel protein VDAC2, an important regulator of mitochondria-associated apoptosis. It was subsequently found that IFIT3 regulates the post-translational modification-O-GlcNAcylation of VDAC2 by stabilizing the interaction of VDAC2 with O-GlcNAc transferase. Increased O-GlcNAcylation of VDAC2 protected PDAC cells from chemotherapy induced apoptosis. Conclusions: These results effectively demonstrate a central mechanism by which IFIT3 expression can affect chemotherapy resistance in PDAC. Targeting IFIT3/VDAC2 may represent a novel strategy to sensitize aggressive forms of pancreatic cancer to conventional chemotherapy regimens.
    Keywords:  Chemotherapy resistance; IFIT3; PDAC; VDAC2; post-translational modification
    DOI:  https://doi.org/10.7150/thno.43093
  23. Cancer Res. 2020 Jul 09. pii: canres.3782.2019. [Epub ahead of print]
    Li F, Ng WL, Luster TA, Hu H, Sviderskiy VO, Dowling CM, Hollinshead KER, Zouitine P, Zhang H, Huang Q, Ranieri M, Wang W, Fang Z, Chen T, Deng J, Zhao K, So HC, Khodadadi-Jamayran A, Xu M, Karatza A, Pyon V, Li S, Pan Y, Labbe K, Almonte C, Poirier JT, Miller G, Possemato R, Qi J, Wong KK.
      Despite advancements in treatment options, the overall cure and survival rates for non-small cell lung cancers (NSCLC) remain low. While small-molecule inhibitors of epigenetic regulators have recently emerged as promising cancer therapeutics, their application in patients with NSCLC is limited. To exploit epigenetic regulators as novel therapeutic targets in NSCLC, we performed pooled epigenome-wide CRISPR knockout screens in vitro and in vivo and identified the histone chaperone nucleophosmin 1 (NPM1) as a potential therapeutic target. Genetic ablation of Npm1 significantly attenuated tumor progression in vitro and in vivo. Furthermore, KRAS-mutant cancer cells were more addicted to NPM1 expression. Genetic ablation of Npm1 rewired the balance of metabolism in cancer cells from predominant aerobic glycolysis to oxidative phosphorylation and reduced the population of tumor-propagating cells. Overall, our results support NPM1 as a therapeutic vulnerability in NSCLC.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-19-3782
  24. Cancers (Basel). 2020 Jul 04. pii: E1787. [Epub ahead of print]12(7):
    Sahinbegovic H, Jelinek T, Hrdinka M, Bago JR, Turi M, Sevcikova T, Kurtovic-Kozaric A, Hajek R, Simicek M.
      Cell-to-cell communication is a fundamental process in every multicellular organism. In addition to membrane-bound and released factors, the sharing of cytosolic components represents a new, poorly explored signaling route. An extraordinary example of this communication channel is the direct transport of mitochondria between cells. In this review, we discuss how intercellular mitochondrial transfer can be used by cancer cells to sustain their high metabolic requirements and promote drug resistance and describe relevant molecular players in the context of current and future cancer therapy.
    Keywords:  cancer; mitochondria; mitochondrial transfer; tumor microenvironment; tunneling nanotubes
    DOI:  https://doi.org/10.3390/cancers12071787
  25. Cancer Discov. 2020 Jul 08. pii: CD-19-1008. [Epub ahead of print]
    Aroua N, Boet E, Ghisi M, Nicolau-Travers ML, Saland E, Gwilliam R, de Toni F, Hosseini M, Mouchel PL, Farge T, Bosc C, Stuani L, Sabatier M, Mazed F, Larrue C, Jarrou L, Gandarillas S, Bardotti M, Picard M, Syrykh C, Laurent C, Gotanegre M, Bonnefoy N, Bellvert F, Portais JC, Nicot N, Azuaje F, Kaoma T, Joffre C, Tamburini J, Recher C, Vergez F, Sarry JE.
      Relapses driven by chemoresistant leukemic cell populations are the main cause of mortality for patients with acute myeloid leukemia (AML). Here, we show that the ectonucleotidase CD39 (ENTPD1) is upregulated in cytarabine (AraC)-resistant leukemic cells from both AML cell lines and patient samples in vivo and in vitro. CD39 cell surface expression and activity is increased in AML patients upon chemotherapy compared to diagnosis and enrichment in CD39-expressing blasts is a marker of adverse prognosis in the clinics. High CD39 activity promotes AraC resistance by enhancing mitochondrial activity and biogenesis through activation of a cAMP-mediated adaptive mitochondrial stress response. Finally, genetic and pharmacological inhibition of CD39 eATPase activity blocks the mitochondrial reprogramming triggered by AraC treatment and markedly enhances its cytotoxicity in AML cells in vitro and in vivo. Together, these results reveal CD39 as a new residual disease marker and a promising therapeutic target to improve chemotherapy response in AML.
    DOI:  https://doi.org/10.1158/2159-8290.CD-19-1008
  26. EBioMedicine. 2020 Jul 03. pii: S2352-3964(20)30243-7. [Epub ahead of print]57 102868
    Jaberi E, Tresse E, Grønbæk K, Weischenfeldt J, Issazadeh-Navikas S.
      BACKGROUND: Point mutations and structural variations (SVs) in mitochondrial DNA (mtDNA) contribute to many neurodegenerative diseases. Technical limitations and heteroplasmy, however, have impeded their identification, preventing these changes from being examined in neurons in healthy and disease states.METHODS: We have developed a high-resolution technique-Mitochondrial DNA Structural Variation Sequencing (MitoSV-seq)-that identifies all types of mtDNA SVs and single-nucleotide variations (SNVs) in single neurons and novel variations that have been undetectable with conventional techniques.
    FINDINGS: Using MitoSV-seq, we discovered SVs/SNVs in dopaminergic neurons in the Ifnar1-/- murine model of Parkinson disease. Further, MitoSV-seq was found to have broad applicability, delivering high-quality, full-length mtDNA sequences in a species-independent manner from human PBMCs, haematological cancers, and tumour cell lines, regardless of heteroplasmy. We characterised several common SVs in haematological cancers (AML and MDS) that were linked to the same mtDNA region, MT-ND5, using only 10 cells, indicating the power of MitoSV-seq in determining single-cancer-cell ontologies. Notably, the MT-ND5 hotspot, shared between all examined cancers and Ifnar1-/- dopaminergic neurons, suggests that its mutations have clinical value as disease biomarkers.
    INTERPRETATION: MitoSV-seq identifies disease-relevant mtDNA mutations in single cells with high resolution, rendering it a potential drug screening platform in neurodegenerative diseases and cancers.
    FUNDING: The Lundbeck Foundation, Danish Council for Independent Research-Medicine, and European Union Horizon 2020 Research and Innovation Programme.
    Keywords:  Disease biomarker; Mitochondrial DNA; Neurodegeneration; Neuron; Single-Cell Sequencing
    DOI:  https://doi.org/10.1016/j.ebiom.2020.102868
  27. Sci Rep. 2020 Jul 10. 10(1): 11423
    Contreras-Lopez RA, Elizondo-Vega R, Torres MJ, Vega-Letter AM, Luque-Campos N, Paredes-Martinez MJ, Pradenas C, Tejedor G, Oyarce K, Salgado M, Jorgensen C, Khoury M, Kronke G, Garcia-Robles MA, Altamirano C, Luz-Crawford P, Djouad F.
      Mesenchymal stem cell (MSC)-based therapy is being increasingly considered a powerful opportunity for several disorders based on MSC immunoregulatory properties. Nonetheless, MSC are versatile and plastic cells that require an efficient control of their features and functions for their optimal use in clinic. Recently, we have shown that PPARβ/δ is pivotal for MSC immunoregulatory and therapeutic functions. However, the role of PPARβ/δ on MSC metabolic activity and the relevance of PPARβ/δ metabolic control on MSC immunosuppressive properties have never been addressed. Here, we demonstrate that PPARβ/δ deficiency forces MSC metabolic adaptation increasing their glycolytic activity required for their immunoregulatory functions on Th1 and Th17 cells. Additionally, we show that the inhibition of the mitochondrial production of ATP in MSC expressing PPARβ/δ, promotes their metabolic switch towards aerobic glycolysis to stably enhance their immunosuppressive capacities significantly. Altogether, these data demonstrate that PPARβ/δ governs the immunoregulatory potential of MSC by dictating their metabolic reprogramming and pave the way for enhancing MSC immunoregulatory properties and counteracting their versatility.
    DOI:  https://doi.org/10.1038/s41598-020-68347-x
  28. FASEB J. 2020 Jul 06.
    Tai YK, Ng C, Purnamawati K, Yap JLY, Yin JN, Wong C, Patel BK, Soong PL, Pelczar P, Fröhlich J, Beyer C, Fong CHH, Ramanan S, Casarosa M, Cerrato CP, Foo ZL, Pannir Selvan RM, Grishina E, Degirmenci U, Toh SJ, Richards PJ, Mirsaidi A, Wuertz-Kozak K, Chong SY, Ferguson SJ, Aguzzi A, Monici M, Sun L, Drum CL, Wang JW, Franco-Obregón A.
      Exercise modulates metabolism and the gut microbiome. Brief exposure to low mT-range pulsing electromagnetic fields (PEMFs) was previously shown to accentuate in vitro myogenesis and mitochondriogenesis by activating a calcium-mitochondrial axis upstream of PGC-1α transcriptional upregulation, recapitulating a genetic response implicated in exercise-induced metabolic adaptations. We compared the effects of analogous PEMF exposure (1.5 mT, 10 min/week), with and without exercise, on systemic metabolism and gut microbiome in four groups of mice: (a) no intervention; (b) PEMF treatment; (c) exercise; (d) exercise and PEMF treatment. The combination of PEMFs and exercise for 6 weeks enhanced running performance and upregulated muscular and adipose Pgc-1α transcript levels, whereas exercise alone was incapable of elevating Pgc-1α levels. The gut microbiome Firmicutes/Bacteroidetes ratio decreased with exercise and PEMF exposure, alone or in combination, which has been associated in published studies with an increase in lean body mass. After 2 months, brief PEMF treatment alone increased Pgc-1α and mitohormetic gene expression and after >4 months PEMF treatment alone enhanced oxidative muscle expression, fatty acid oxidation, and reduced insulin levels. Hence, short-term PEMF treatment was sufficient to instigate PGC-1α-associated transcriptional cascades governing systemic mitohormetic adaptations, whereas longer-term PEMF treatment was capable of inducing related metabolic adaptations independently of exercise.
    Keywords:  PEMF; brown adipose; mitochondria; muscle; white adipose
    DOI:  https://doi.org/10.1096/fj.201903005RR
  29. Nat Rev Cancer. 2020 Jul 06.
    Leone RD, Powell JD.
      Through the successes of checkpoint blockade and adoptive cellular therapy, immunotherapy has become an established treatment modality for cancer. Cellular metabolism has emerged as a critical determinant of the viability and function of both cancer cells and immune cells. In order to sustain prodigious anabolic needs, tumours employ a specialized metabolism that differs from untransformed somatic cells. This metabolism leads to a tumour microenvironment that is commonly acidic, hypoxic and/or depleted of critical nutrients required by immune cells. In this context, tumour metabolism itself is a checkpoint that can limit immune-mediated tumour destruction. Because our understanding of immune cell metabolism and cancer metabolism has grown significantly in the past decade, we are on the cusp of being able to unravel the interaction of cancer cell metabolism and immune metabolism in therapeutically meaningful ways. Although there are metabolic processes that are seemingly fundamental to both cancer and responding immune cells, metabolic heterogeneity and plasticity may serve to distinguish the two. As such, understanding the differential metabolic requirements of the diverse cells that comprise an immune response to cancer offers an opportunity to selectively regulate immune cell function. Such a nuanced evaluation of cancer and immune metabolism can uncover metabolic vulnerabilities and therapeutic windows upon which to intervene for enhanced immunotherapy.
    DOI:  https://doi.org/10.1038/s41568-020-0273-y
  30. Cancer Metab. 2020 ;8 13
    Kawashima M, Bensaad K, Zois CE, Barberis A, Bridges E, Wigfield S, Lagerholm C, Dmitriev RI, Tokiwa M, Toi M, Papkovsky DB, Buffa FM, Harris AL.
      Background: Humans produce heat through non-shivering thermogenesis, a metabolic process that occurs in inducible beige adipocytes expressing uncoupling protein 1 (UCP1). UCP1 dissipates the proton gradient of the mitochondrial inner membrane and converts that energy into heat. It is unclear whether cancer cells can exhibit autonomous thermogenesis. Previously, we found that the knockdown of hypoxia-inducible fatty acid binding protein 7 (FABP7) increased reactive oxygen species (ROS) in breast cancer cells. ROS are known to induce beige adipocyte differentiation.Methods: We investigated the association of tumor hypoxia, FABP7, and UCP1 across breast cancer patients using METABRIC and TCGA data sets. Furthermore, using a breast cancer cell line, HCC1806, we tested the effect of FABP7 knockdown on cellular physiology including thermogenesis.
    Results: We found a strong mutual exclusivity of FABP7 and UCP1 expression both in METABRIC and in TCGA, indicating major metabolic phenotypic differences. FABP7 was preferentially distributed in poorly differentiated-, estrogen receptor (ER) negative tumors. In contrast, UCP1 was highly expressed in normal ducts and well-differentiated-, ER positive-, less hypoxic tumors. In the cell line-based experiments, UCP1 and its transcriptional regulators were upregulated upon FABP7 knockdown. UCP1 was induced in about 20% of cancer cells, and the effect was increased further in hypoxia. UCP1 depolarized mitochondrial membranes at the site of expression. UCP1 induction was associated with the increase in proton leak, glycolysis, and maximal respiration, mimicking the typical energy profile of beige adipocytes. Most importantly, UCP1 induction elevated cancer cell temperature associated with increased vulnerability to hypoxia and γ-irradiation.
    Conclusions: We demonstrated that breast cancer cells can undergo thermogenesis through UCP1 induction. Disrupting FABP7-mediated fatty acid metabolism can unlock UCP1-mediated thermogenesis, potentially making it possible to develop therapies to target thermogenesis. Further study would be warranted to investigate the effect of rise in temperature of cancer cells on patients' outcomes and the relationship to other metabolic pathways.
    Keywords:  Breast cancer; FLIM; Fatty acid; Hypoxia; Modification of radiation sensitivity; Thermogenesis; UCP1
    DOI:  https://doi.org/10.1186/s40170-020-00219-4
  31. iScience. 2020 Jun 26. pii: S2589-0042(20)30433-8. [Epub ahead of print]23(6): 101247
    Kwon SM, Lee YK, Min S, Woo HG, Wang HJ, Yoon G.
      Mitochondrial ribosomes (mitoribosomes), the specialized translational machinery for mitochondrial genes, exclusively encode the subunits of the oxidative phosphorylation (OXPHOS) system. Although OXPHOS dysfunctions are associated with hepatic disorders including hepatocellular carcinoma (HCC), their underlying mechanisms remain poorly elucidated. In this study, we aimed to investigate the effects of mitoribosome defects on OXPHOS and HCC progression. By generating a gene signature from HCC transcriptome data, we developed a scoring system, i.e., mitoribosome defect score (MDS), which represents the degree of mitoribosomal defects in cancers. The MDS showed close associations with the clinical outcomes of patients with HCC and with gene functions such as oxidative phosphorylation, cell-cycle activation, and epithelial-mesenchymal transition. By analyzing immune profiles, we observed that mitoribosomal defects are also associated with immunosuppression and evasion. Taken together, our results provide new insights into the roles of mitoribosome defects in HCC progression.
    Keywords:  Cancer; Cancer Systems Biology; Immunology
    DOI:  https://doi.org/10.1016/j.isci.2020.101247
  32. Theranostics. 2020 ;10(16): 7070-7082
    Sun C, Wang F, Zhang Y, Yu J, Wang X.
      New insights into tumor-associated metabolic reprogramming have provided novel vulnerabilities that can be targeted for cancer therapy. Here, we propose a mass spectrometry imaging (MSI)-based metabolomic strategy to visualize the spatially resolved reprogramming of carnitine metabolism in heterogeneous breast cancer. Methods: A wide carnitine coverage MSI method was developed to investigate the spatial alternations of carnitines in cancer tissues of xenograft mouse models and human samples. Spatial expression of key metabolic enzymes that are closely associated with the altered carnitines was examined in adjacent cancer tissue sections. Results: A total of 17 carnitines, including L-carnitine, 6 short-chain acylcarnitines, 3 middle-chain acylcarnitines, and 7 long-chain acylcarnitines were imaged. L-carnitine and short-chain acylcarnitines are significantly reprogrammed in breast cancer. A classification model based on the carnitine profiles of 170 cancer samples and 128 normal samples enables an accurate identification of breast cancer. CPT 1A, CPT 2, and CRAT, which are extensively involved in carnitine system-mediated fatty acid β-oxidation pathway were also found to be abnormally expressed in breast cancer. Remarkably, the expressions of CPT 2 and CRAT were found for the first time to be altered in breast cancer. Conclusion: These data not only expand our understanding of the complex tumor metabolic reprogramming, but also provide the first evidence that carnitine metabolism is reprogrammed at both the metabolite and enzyme levels in breast cancer.
    Keywords:  breast cancer; carnitines; mass spectrometry imaging; metabolic reprogramming; metabolomics
    DOI:  https://doi.org/10.7150/thno.45543
  33. Antioxid Redox Signal. 2020 Jul 06.
    Jiang JW, Peng LY, Wang K, Huang C.
      SIGNIFICANCE: Metabolic reprogramming is considered to be a critical adaptive biological event that fulfills the energy and biomass demands for cancer cells. One hallmark of metabolic reprogramming is reduced oxidative phosphorylation and enhanced aerobic glycolysis. Such metabolic abnormalities contribute to the accumulation of reactive oxygen species (ROS), the byproducts of metabolic pathways. Emerging evidence suggests that ROS can in turn directly or indirectly affect the expression, activity or subcellular localization of metabolic enzymes, contributing to the moonlighting functions outside of their primary roles. This review summarizes the multi-functions of metabolic enzymes and the involved redox modification patterns, which further reveal the inherent connection between metabolism and cellular redox state. Recent Advances: These non-canonical functions of metabolic enzymes involve the regulation of epigenetic modifications, gene transcription, post-translational modification, cellular antioxidant capacity and many other fundamental cellular events. The multi-functional properties of metabolic enzymes further expand the metabolic dependencies of cancer cells, and confer cancer cells with a means of adapting to diverse environmental stimuli.CRITICAL ISSUES: Deciphering the redox-manipulated mechanisms with specific emphasis on the moonlighting function of metabolic enzymes is important for clarifying the pertinence between metabolism and redox processes.
    FUTURE DIRECTIONS: Investigation of the redox-regulated moonlighting functions of metabolic enzymes will shed new lights into the mechanism by which metabolic enzymes gain non-canonical functions, and yield new insights into the development of novel therapeutic strategies for cancer treatment by targeting metabolic-redox abnormalities.
    DOI:  https://doi.org/10.1089/ars.2020.8123
  34. Cancers (Basel). 2020 Jul 04. pii: E1797. [Epub ahead of print]12(7):
    Wang YH, Suk FM, Liao YJ.
      Hepatocellular carcinoma (HCC) is the most common primary malignant liver tumor with limited treatment. The ketogenic diet (KD) emerged as a metabolic therapy for cancer; however, the antitumor effect on HCC remains controversial. We previously reported that the ketogenesis rate-limiting enzyme, 3-hydroxymethylglutaryl-CoA synthase 2 (HMGCS2), was downregulated in most patients with HCC. The knockdown of HMGCS2 enhanced the proliferation and metastasis ability of HCC cells. However, the role of HMGCS2 in affecting KD-mediated metabolic effects remains unclear. Here, we report that KD feeding upregulates HMGCS2 expression and inhibits HCC tumor growth, while a reverse correlation between tumor size and HMGCS2 expression was observed. We found that HCC cells with HMGCS2 downregulation possess altered lipid metabolism that increases fatty acid, triglyceride, and cholesterol synthesis. Under KD feeding, a higher tumor growth rate was observed in HMGCS2 knockdown tumors, which had increased lipid synthesis-related marker expression and a positive correlation between lipid quantity and tumor weight. In conclusion, these results demonstrate that the downregulation of HMGCS2 attenuates the protective effect of the KD by shifting ketone production to enhance de novo lipogenesis in HCC. Our study elucidates a new molecular mechanism underlying the crosstalk between HMGCS2 expression and the KD in cancer treatment, which provides more information for precision medicine in developing personalized treatment strategies.
    Keywords:  HMGCS2; hepatocellular carcinoma; ketogenic diet; lipogenesis
    DOI:  https://doi.org/10.3390/cancers12071797
  35. Cancers (Basel). 2020 Jul 02. pii: E1757. [Epub ahead of print]12(7):
    Cuyàs E, Verdura S, Martin-Castillo B, Alarcón T, Lupu R, Bosch-Barrera J, Menendez JA.
      One of the greatest challenges in the cancer immunotherapy field is the need to biologically rationalize and broaden the clinical utility of immune checkpoint inhibitors (ICIs). The balance between metabolism and immune response has critical implications for overcoming the major weaknesses of ICIs, including their lack of universality and durability. The last decade has seen tremendous advances in understanding how the immune system's ability to kill tumor cells requires the conspicuous metabolic specialization of T-cells. We have learned that cancer cell-associated metabolic activities trigger shifts in the abundance of some metabolites with immunosuppressory roles in the tumor microenvironment. Yet very little is known about the tumor cell-intrinsic metabolic traits that control the immune checkpoint contexture in cancer cells. Likewise, we lack a comprehensive understanding of how systemic metabolic perturbations in response to dietary interventions can reprogram the immune checkpoint landscape of tumor cells. We here review state-of-the-art molecular- and functional-level interrogation approaches to uncover how cell-autonomous metabolic traits and diet-mediated changes in nutrient availability and utilization might delineate new cancer cell-intrinsic metabolic dependencies of tumor immunogenicity. We propose that clinical monitoring and in-depth molecular evaluation of the cancer cell-intrinsic metabolic traits involved in primary, adaptive, and acquired resistance to cancer immunotherapy can provide the basis for improvements in therapeutic responses to ICIs. Overall, these approaches might guide the use of metabolic therapeutics and dietary approaches as novel strategies to broaden the spectrum of cancer patients and indications that can be effectively treated with ICI-based cancer immunotherapy.
    Keywords:  diet; immune checkpoint inhibitors; immune checkpoints; metabolism; nutrition
    DOI:  https://doi.org/10.3390/cancers12071757