bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒08‒23
fifty-seven papers selected by
Kelsey Fisher-Wellman
East Carolina University


  1. Elife. 2020 Aug 17. pii: e58041. [Epub ahead of print]9
    Nowinski SM, Solmonson A, Rusin SF, Maschek JA, Bensard CL, Fogarty S, Jeong MY, Lettlova S, Berg JA, Morgan JT, Ouyang Y, Naylor BC, Paulo JA, Funai K, Cox JE, Gygi SP, Winge DR, DeBerardinis RJ, Rutter J.
      Cells harbor two systems for fatty acid synthesis, one in the cytoplasm (catalyzed by fatty acid synthase, FASN) and one in the mitochondria (mtFAS). In contrast to FASN, mtFAS is poorly characterized, especially in higher eukaryotes, with the major product(s), metabolic roles, and cellular function(s) being essentially unknown. Here we show that hypomorphic mtFAS mutant mouse skeletal myoblast cell lines display a severe loss of electron transport chain (ETC) complexes and exhibit compensatory metabolic activities including reductive carboxylation. This effect on ETC complexes appears to be independent of protein lipoylation, the best characterized function of mtFAS, as mutants lacking lipoylation have an intact ETC. Finally, mtFAS impairment blocks the differentiation of skeletal myoblasts in vitro. Together, these data suggest that ETC activity in mammals is profoundly controlled by mtFAS function, thereby connecting anabolic fatty acid synthesis with the oxidation of carbon fuels.
    Keywords:  biochemistry; chemical biology; mouse
    DOI:  https://doi.org/10.7554/eLife.58041
  2. Proc Natl Acad Sci U S A. 2020 Aug 14. pii: 202005976. [Epub ahead of print]
    Vais H, Payne R, Paudel U, Li C, Foskett JK.
      Ca2+ uptake by mitochondria regulates bioenergetics, apoptosis, and Ca2+ signaling. The primary pathway for mitochondrial Ca2+ uptake is the mitochondrial calcium uniporter (MCU), a Ca2+-selective ion channel in the inner mitochondrial membrane. MCU-mediated Ca2+ uptake is driven by the sizable inner-membrane potential generated by the electron-transport chain. Despite the large thermodynamic driving force, mitochondrial Ca2+ uptake is tightly regulated to maintain low matrix [Ca2+] and prevent opening of the permeability transition pore and cell death, while meeting dynamic cellular energy demands. How this is accomplished is controversial. Here we define a regulatory mechanism of MCU-channel activity in which cytoplasmic Ca2+ regulation of intermembrane space-localized MICU1/2 is controlled by Ca2+-regulatory mechanisms localized across the membrane in the mitochondrial matrix. Ca2+ that permeates through the channel pore regulates Ca2+ affinities of coupled inhibitory and activating sensors in the matrix. Ca2+ binding to the inhibitory sensor within the MCU amino terminus closes the channel despite Ca2+ binding to MICU1/2. Conversely, disruption of the interaction of MICU1/2 with the MCU complex disables matrix Ca2+ regulation of channel activity. Our results demonstrate how Ca2+ influx into mitochondria is tuned by coupled Ca2+-regulatory mechanisms on both sides of the inner mitochondrial membrane.
    Keywords:  EMRE; MICU1; calcium; electrophysiology; mitochondria
    DOI:  https://doi.org/10.1073/pnas.2005976117
  3. Cell Death Dis. 2020 Aug 18. 11(8): 645
    Dematteis G, Vydmantaitė G, Ruffinatti FA, Chahin M, Farruggio S, Barberis E, Ferrari E, Marengo E, Distasi C, Morkūnienė R, Genazzani AA, Grilli M, Grossini E, Corazzari M, Manfredi M, Lim D, Jekabsone A, Tapella L.
      The pathogenesis of Alzheimer's disease (AD), a slowly-developing age-related neurodegenerative disorder, is a result of the action of multiple factors including deregulation of Ca2+ homeostasis, mitochondrial dysfunction, and dysproteostasis. Interaction of these factors in astrocytes, principal homeostatic cells in the central nervous system, is still poorly understood. Here we report that in immortalized hippocampal astrocytes from 3xTg-AD mice (3Tg-iAstro cells) bioenergetics is impaired, including reduced glycolysis and mitochondrial oxygen consumption, and increased production of reactive oxygen species. Shotgun proteomics analysis of mitochondria-ER-enriched fraction showed no alterations in the expression of mitochondrial and OxPhos proteins, while those related to the ER functions and protein synthesis were deregulated. Using ER- and mitochondria-targeted aequorin-based Ca2+ probe we show that, in 3Tg-iAstro cells, ER was overloaded with Ca2+ while Ca2+ uptake by mitochondria upon ATP stimulation was reduced. This was accompanied by the increase in short distance (≈8-10 nm) contact area between mitochondria and ER, upregulation of ER-stress/unfolded protein response genes Atf4, Atf6 and Herp, and reduction of global protein synthesis rate. We suggest that familial AD mutations in 3Tg-iAstro cells induce mitochondria-ER interaction changes that deregulate astrocytic bioenergetics, Ca2+ homeostasis and proteostasis. These factors may interact, creating a pathogenic loop compromising homeostatic and defensive functions of astroglial cells predisposing neurons to dysfunction.
    DOI:  https://doi.org/10.1038/s41419-020-02911-1
  4. Int J Mol Sci. 2020 Aug 21. pii: E6021. [Epub ahead of print]21(17):
    Kwak CH, Jin L, Han JH, Han CW, Kim E, Cho M, Chung TW, Bae SJ, Jang SB, Ha KT.
      In cancer cells, aerobic glycolysis rather than oxidative phosphorylation (OxPhos) is generally preferred for the production of ATP. In many cancers, highly expressed pyruvate dehydrogenase kinase 1 (PDK1) reduces the activity of pyruvate dehydrogenase (PDH) by inducing the phosphorylation of its E1α subunit (PDHA1) and subsequently, shifts the energy metabolism from OxPhos to aerobic glycolysis. Thus, PDK1 has been regarded as a target for anticancer treatment. Here, we report that ilimaquinone (IQ), a sesquiterpene quinone isolated from the marine sponge Smenospongia cerebriformis, might be a novel PDK1 inhibitor. IQ decreased the cell viability of human and murine cancer cells, such as A549, DLD-1, RKO, and LLC cells. The phosphorylation of PDHA1, the substrate of PDK1, was reduced by IQ in the A549 cells. IQ decreased the levels of secretory lactate and increased oxygen consumption. The anticancer effect of IQ was markedly reduced in PDHA1-knockout cells. Computational simulation and biochemical assay revealed that IQ interfered with the ATP binding pocket of PDK1 without affecting the interaction of PDK1 and the E2 subunit of the PDH complex. In addition, similar to other pyruvate dehydrogenase kinase inhibitors, IQ induced the generation of mitochondrial reactive oxygen species (ROS) and depolarized the mitochondrial membrane potential in the A549 cells. The apoptotic cell death induced by IQ treatment was rescued in the presence of MitoTEMPO, a mitochondrial ROS inhibitor. In conclusion, we suggest that IQ might be a novel candidate for anticancer therapeutics that act via the inhibition of PDK1 activity.
    Keywords:  Warburg effect; apoptosis; glycolysis; ilimaquinone; pyruvate dehydrogenase kinase 1
    DOI:  https://doi.org/10.3390/ijms21176021
  5. Cell Death Dis. 2020 Aug 06. 11(8): 649
    Wan X, Wang C, Huang Z, Zhou D, Xiang S, Qi Q, Chen X, Arbely E, Liu CY, Du P, Yu W.
      The folate-coupled metabolic enzyme MTHFD2 (the mitochondrial methylenetetrahydrofolate dehydrogenase/cyclohydrolase) confers redox homeostasis and drives cancer cell proliferation and migration. Here, we show that MTHFD2 is hyperacetylated and lysine 88 is the critical acetylated site. SIRT3, the major deacetylase in mitochondria, is responsible for MTHFD2 deacetylation. Interestingly, chemotherapeutic agent cisplatin inhibits expression of SIRT3 to induce acetylation of MTHFD2 in colorectal cancer cells. Cisplatin-induced acetylated K88 MTHFD2 is sufficient to inhibit its enzymatic activity and downregulate NADPH levels in colorectal cancer cells. Ac-K88-MTHFD2 is significantly decreased in human colorectal cancer samples and is inversely correlated with the upregulated expression of SIRT3. Our findings reveal an unknown regulation axis of cisplatin-SIRT3-MTHFD2 in redox homeostasis and suggest a potential therapeutic strategy for cancer treatments by targeting MTHFD2.
    DOI:  https://doi.org/10.1038/s41419-020-02825-y
  6. Sci Rep. 2020 Aug 17. 10(1): 13899
    Sun J, Patel CB, Jang T, Merchant M, Chen C, Kazerounian S, Diers AR, Kiebish MA, Vishnudas VK, Gesta S, Sarangarajan R, Narain NR, Nagpal S, Recht L.
      Metabolic reprogramming in cancer cells, vs. non-cancer cells, elevates levels of reactive oxygen species (ROS) leading to higher oxidative stress. The elevated ROS levels suggest a vulnerability to excess prooxidant loads leading to selective cell death, a therapeutically exploitable difference. Co-enzyme Q10 (CoQ10) an endogenous mitochondrial resident molecule, plays an important role in mitochondrial redox homeostasis, membrane integrity, and energy production. BPM31510 is a lipid-drug conjugate nanodispersion specifically formulated for delivery of supraphysiological concentrations of ubidecarenone (oxidized CoQ10) to the cell and mitochondria, in both in vitro and in vivo model systems. In this study, we sought to investigate the therapeutic potential of ubidecarenone in the highly treatment-refractory glioblastoma. Rodent (C6) and human (U251) glioma cell lines, and non-tumor human astrocytes (HA) and rodent NIH3T3 fibroblast cell lines were utilized for experiments. Tumor cell lines exhibited a marked increase in sensitivity to ubidecarenone vs. non-tumor cell lines. Further, elevated mitochondrial superoxide production was noted in tumor cells vs. non-tumor cells hours before any changes in proliferation or the cell cycle could be detected. In vitro co-culture experiments show ubidecarenone differentially affecting tumor cells vs. non-tumor cells, resulting in an equilibrated culture. In vivo activity in a highly aggressive orthotopic C6 glioma model demonstrated a greater than 25% long-term survival rate. Based on these findings we conclude that high levels of ubidecarenone delivered using BPM31510 provide an effective therapeutic modality targeting cancer-specific modulation of redox mechanisms for anti-cancer effects.
    DOI:  https://doi.org/10.1038/s41598-020-70969-0
  7. Biochem Pharmacol. 2020 Aug 18. pii: S0006-2952(20)30438-X. [Epub ahead of print] 114202
    Ciccarone F, De Falco P, Rosa Ciriolo M.
      Aconitase 2 (ACO2) belongs to the tricarboxylic acid (TCA) cycle, which represents a key metabolic hub for cellular metabolism that is frequently altered in cancer for satisfying bioenergetic and biosynthetic requirements of proliferating cells. The promotion of ACO2 activity in breast cancer cell lines was shown to slow down proliferation imposing a switch from aerobic glycolysis to oxidative metabolism. The alteration of metabolic pathways in cancer also impinges on the sensitivity to chemotherapeutic interventions. In this work, we evidence that the presence of ACO2 sensitizes cells to the treatment with the genotoxic agents cisplatin (CDDP) and doxorubicin activating the apoptotic cell death mechanism. This response was driven by the accumulation of reactive oxygen species (ROS) following both ACO2 overexpression and CDDP exposure that permit the stabilization/activation of p53 in nuclear and mitochondrial compartments. Collectively, our results highlight that in ACO2 overexpressing cells the promotion of mitochondrial metabolism accounts for increased ROS production that was buffered by p53 mitochondrial recruitment and autophagy induction. However, these systems are not able to counteract the CDDP-mediated oxidative stress that becomes the Achilles heel for increasing susceptibility to apoptotic cell death.
    Keywords:  TCA cycle; autophagy; cisplatin; mitochondria; oxidative stress
    DOI:  https://doi.org/10.1016/j.bcp.2020.114202
  8. Commun Biol. 2020 Aug 18. 3(1): 451
    Wikström M, Springett R.
      The protonmotive mitochondrial respiratory chain, comprising complexes I, III and IV, transduces free energy of the electron transfer reactions to an electrochemical proton gradient across the inner mitochondrial membrane. This gradient is used to drive synthesis of ATP and ion and metabolite transport. The efficiency of energy conversion is of interest from a physiological point of view, since the energy transduction mechanisms differ fundamentally between the three complexes. Here, we have chosen actively phosphorylating mitochondria as the focus of analysis. For all three complexes we find that the thermodynamic efficiency is about 80-90% and that the degree of coupling between the redox and proton translocation reactions is very high during active ATP synthesis. However, when net ATP synthesis stops at a high ATP/ADP.Pi ratio, and mitochondria reach "State 4" with an elevated proton gradient, the degree of coupling drops substantially. The mechanistic cause and the physiological implications of this effect are discussed.
    DOI:  https://doi.org/10.1038/s42003-020-01192-w
  9. EBioMedicine. 2020 Aug 17. pii: S2352-3964(20)30319-4. [Epub ahead of print]59 102943
    Missiroli S, Perrone M, Genovese I, Pinton P, Giorgi C.
      Mitochondria are dynamic organelles that have essential metabolic activity and are regarded as signalling hubs with biosynthetic, bioenergetics and signalling functions that orchestrate key biological pathways. However, mitochondria can influence all processes linked to oncogenesis, starting from malignant transformation to metastatic dissemination. In this review, we describe how alterations in the mitochondrial metabolic status contribute to the acquisition of typical malignant traits, discussing the most recent discoveries and the many unanswered questions. We also highlight that expanding our understanding of mitochondrial regulation and function mechanisms in the context of cancer cell metabolism could be an important task in biomedical research, thus offering the possibility of targeting mitochondria for the treatment of cancer.
    Keywords:  Calcium; Cancer; Metabolism; Mitochondria; ROS
    DOI:  https://doi.org/10.1016/j.ebiom.2020.102943
  10. Oncotarget. 2020 Aug 04. 11(31): 3013-3024
    Turcios L, Marti F, Watt DS, Kril LM, Khurana A, Chapelin F, Liu C, Zwischenberger JB, Evers BM, Gedaly R.
      BACKGROUND: Hepatocellular Carcinoma (HCC) is the third most common cause of cancer related death worldwide. Adequate treatment options for patients with advanced HCC are currently limited.MATERIALS AND METHODS: We studied the anti-HCC effect of FH535 and a novel derivative Y3, on proliferation, mitochondrial function and cellular metabolism focusing on the three key substrates, glutamine, glucose, and fatty acids.
    RESULTS: FH535 and Y3 disrupted mitochondrial redox control in HCC cells that resulted from uncoupling mechanisms that increased proton leakage and decreased ATP production leading to apoptosis. The uncoupling effects of the sulfonamides in HCC cells were supported by the loss of activity of the methylated analogs. The accumulation of ROS significantly contributed to cell damage after the impaired autophagic machinery. These sulfonamides, FH535 and Y3, targeted glutamine and fatty acid metabolism and caused HCC cell reprograming towards the preferential use of glucose and the glycolytic pathway.
    CONCLUSIONS: FH535, and Y3, demonstrated potent anti-HCC activity by targeting OXPHOS, increasing dangerous levels of ROS and reducing ATP production. These sulfonamides target glutamine and FA metabolic pathways significantly increasing the cellular dependency on glycolysis.
    Keywords:  Wnt/β-catenin pathway; glutamine metabolism; hepatocellular carcinoma; mitochondria; proton uncouplers
    DOI:  https://doi.org/10.18632/oncotarget.27680
  11. Cells. 2020 Aug 19. pii: E1922. [Epub ahead of print]9(9):
    García-Bartolomé A, Peñas A, Illescas M, Bermejo V, López-Calcerrada S, Pérez-Pérez R, Marín-Buera L, Domínguez-González C, Arenas J, Martín MA, Ugalde C.
      Mitochondrial oxidative phosphorylation (OXPHOS) defects are the primary cause of inborn errors of energy metabolism. Despite considerable progress on their genetic basis, their global pathophysiological consequences remain undefined. Previous studies reported that OXPHOS dysfunction associated with complex III deficiency exacerbated the expression and mitochondrial location of cytoskeletal gelsolin (GSN) to promote cell survival responses. In humans, besides the cytosolic isoform, GSN presents a plasma isoform secreted to extracellular environments. We analyzed the interplay between both GSN isoforms in human cellular and clinical models of OXPHOS dysfunction. Regardless of its pathogenic origin, OXPHOS dysfunction induced the physiological upregulation of cytosolic GSN in the mitochondria (mGSN), in parallel with a significant downregulation of plasma GSN (pGSN) levels. Consequently, significantly high mGSN-to-pGSN ratios were associated with OXPHOS deficiency both in human cells and blood. In contrast, control cells subjected to hydrogen peroxide or staurosporine treatments showed no correlation between oxidative stress or cell death induction and the altered levels and subcellular location of GSN isoforms, suggesting their specificity for OXPHOS dysfunction. In conclusion, a high mitochondrial-to-plasma GSN ratio represents a useful cellular indicator of OXPHOS defects, with potential use for future research of a wide range of clinical conditions with mitochondrial involvement.
    Keywords:  GSN; OXPHOS dysfunction; actin cytoskeleton; biomarker; gelsolin isoforms; mitochondria; oxidative stress
    DOI:  https://doi.org/10.3390/cells9091922
  12. Nat Commun. 2020 Aug 17. 11(1): 4116
    Sharanek A, Burban A, Laaper M, Heckel E, Joyal JS, Soleimani VD, Jahani-Asl A.
      Glioblastoma contains a rare population of self-renewing brain tumor stem cells (BTSCs) which are endowed with properties to proliferate, spur the growth of new tumors, and at the same time, evade ionizing radiation (IR) and chemotherapy. However, the drivers of BTSC resistance to therapy remain unknown. The cytokine receptor for oncostatin M (OSMR) regulates BTSC proliferation and glioblastoma tumorigenesis. Here, we report our discovery of a mitochondrial OSMR that confers resistance to IR via regulation of oxidative phosphorylation, independent of its role in cell proliferation. Mechanistically, OSMR is targeted to the mitochondrial matrix via the presequence translocase-associated motor complex components, mtHSP70 and TIM44. OSMR interacts with NADH ubiquinone oxidoreductase 1/2 (NDUFS1/2) of complex I and promotes mitochondrial respiration. Deletion of OSMR impairs spare respiratory capacity, increases reactive oxygen species, and sensitizes BTSCs to IR-induced cell death. Importantly, suppression of OSMR improves glioblastoma response to IR and prolongs lifespan.
    DOI:  https://doi.org/10.1038/s41467-020-17885-z
  13. J Biol Chem. 2020 Aug 19. pii: jbc.AC120.014993. [Epub ahead of print]
    Perez M, Bak DW, Bergholtz SE, Crooks DR, Arimilli BS, Yang Y, Weerapana E, Linehan WM, Meier JL.
      An important context in which metabolism influences tumorigenesis is the genetic cancer syndrome hereditary leiomyomatosis and renal cell carcinoma (HLRCC), a disease in which mutation of the TCA cycle enzyme fumarate hydratase (FH) causes hyperaccumulation of fumarate. This electrophilic oncometabolite can alter gene activity at the level of transcription, via reversible inhibition of epigenetic dioxygenases, as well as posttranslationally, via covalent modification of cysteine residues. To better understand the potential for metabolites to influence posttranslational modifications important to tumorigenesis and cancer cell growth, here we report a chemoproteomic analysis of a kidney-derived HLRCC cell line. Using a general reactivity probe, we generated a dataset of proteomic cysteine residues sensitive to the reduction in fumarate levels caused by genetic re-introduction of active FH into HLRCC cell lines. This revealed a broad upregulation of cysteine reactivity upon FH rescue, which evidence suggests is caused by an approximately equal proportion of transcriptional and posttranslational modification-mediated regulation. Gene ontology analysis highlighted several new targets and pathways potentially modulated by FH mutation. Comparison of the new dataset to prior studies highlights considerable heterogeneity in the adaptive response of cysteine-containing proteins in different models of HLRCC. This is consistent with emerging studies indicating the existence of cell and tissue-specific cysteine-omes, further emphasizing the need for characterization of diverse models. Our analysis provides a resource for understanding the proteomic adaptation to fumarate accumulation, and a foundation for future efforts to exploit this knowledge for cancer therapy.
    Keywords:  chemical biology; inborn error of metabolism; metabolism; mitochondria; post-translational modification (PTM); proteomics; redox signaling; tricarboxylic acid cycle (TCA cycle) (Krebs cycle)
    DOI:  https://doi.org/10.1074/jbc.AC120.014993
  14. Int J Mol Sci. 2020 Aug 21. pii: E6014. [Epub ahead of print]21(17):
    Frattaruolo L, Brindisi M, Curcio R, Marra F, Dolce V, Cappello AR.
      Metabolic reprogramming is a hallmark of cancer, which implements a profound metabolic rewiring in order to support a high proliferation rate and to ensure cell survival in its complex microenvironment. Although initial studies considered glycolysis as a crucial metabolic pathway in tumor metabolism reprogramming (i.e., the Warburg effect), recently, the critical role of mitochondria in oncogenesis, tumor progression, and neoplastic dissemination has emerged. In this report, we examined the main mitochondrial metabolic pathways that are altered in cancer, which play key roles in the different stages of tumor progression. Furthermore, we reviewed the function of important molecules inhibiting the main mitochondrial metabolic processes, which have been proven to be promising anticancer candidates in recent years. In particular, inhibitors of oxidative phosphorylation (OXPHOS), heme flux, the tricarboxylic acid cycle (TCA), glutaminolysis, mitochondrial dynamics, and biogenesis are discussed. The examined mitochondrial metabolic network inhibitors have produced interesting results in both preclinical and clinical studies, advancing cancer research and emphasizing that mitochondrial targeting may represent an effective anticancer strategy.
    Keywords:  cancer therapy; metabolic network; metabolic rewiring; mitochondria; targeting mitochondria
    DOI:  https://doi.org/10.3390/ijms21176014
  15. Autophagy. 2020 Aug 19.
    Han S, Jeong YY, Sheshadri P, Cai Q.
      Mitochondria sustain various essential functions at synaptic terminals. Synaptic mitochondria deficits have been implicated in early Alzheimer disease (AD) pathophysiology. Mitophagy, a selective autophagy for removal of damaged mitochondria, plays a key role in mitochondrial quality control in neurons. However, fundamental questions remain unanswered as to whether mitophagy regulates synaptic mitochondrial integrity and whether AD-associated early deficits in synaptic mitochondria are attributed to mitophagy failure. We have recently revealed that the integrity of synaptic mitochondria is maintained by a coordination of RHEB-mediated mitophagy with dynein- and SNAPIN-driven retrograde transport. We demonstrate that increased mitophagy initiation, coupled with defective retrograde transport, triggers mitophagy stress at AD synapses. Excitingly, SNAPIN-enhanced retrograde transport reduces synaptic mitophagy stress and ameliorates mitochondrial deficits, thereby counteracting synaptic damage in AD mouse brains. Therefore, our study provides new mechanistic insights into how mitophagy facilitates synaptic mitochondrial maintenance and how mitophagy failure exacerbates AD-linked mitochondrial defects and synaptic degeneration.
    Keywords:  Alzheimer; Nix; PRKN; RHEB; SNAPIN; mitophagosome; retrograde transport; synaptic degeneration; synaptic mitochondrial deficits; synaptic mitophagy
    DOI:  https://doi.org/10.1080/15548627.2020.1810919
  16. Nat Commun. 2020 Aug 18. 11(1): 4135
    Gutiérrez-Fernández J, Kaszuba K, Minhas GS, Baradaran R, Tambalo M, Gallagher DT, Sazanov LA.
      Complex I is the first and the largest enzyme of respiratory chains in bacteria and mitochondria. The mechanism which couples spatially separated transfer of electrons to proton translocation in complex I is not known. Here we report five crystal structures of T. thermophilus enzyme in complex with NADH or quinone-like compounds. We also determined cryo-EM structures of major and minor native states of the complex, differing in the position of the peripheral arm. Crystal structures show that binding of quinone-like compounds (but not of NADH) leads to a related global conformational change, accompanied by local re-arrangements propagating from the quinone site to the nearest proton channel. Normal mode and molecular dynamics analyses indicate that these are likely to represent the first steps in the proton translocation mechanism. Our results suggest that quinone binding and chemistry play a key role in the coupling mechanism of complex I.
    DOI:  https://doi.org/10.1038/s41467-020-17957-0
  17. Cancer Res. 2020 Aug 19. pii: canres.1255.2020. [Epub ahead of print]
    Rozeveld CN, Johnson KM, Zhang L, Razidlo GL.
      Oncogene-induced metabolic reprogramming is a hallmark of pancreatic cancer (PDAC), yet the metabolic drivers of metastasis are unclear. In PDAC, obesity and excess fatty acids accelerate tumor growth and increase metastasis. Here, we report that excess lipids, stored in organelles called lipid droplets (LD), are a key resource to fuel the energy-intensive process of metastasis. The oncogene KRAS controlled the storage and utilization of LD through regulation of hormone sensitive lipase (HSL), which was downregulated in human PDAC. Disruption of the KRAS-HSL axis reduced lipid storage, reprogrammed tumor cell metabolism, and inhibited invasive migration in vitro and metastasis in vivo. Finally, microscopy-based metabolic analysis revealed that migratory cells selectively utilize oxidative metabolism during the process of migration to metabolize stored lipids and fuel invasive migration. Taken together, these results reveal a mechanism that can be targeted to attenuate PDAC metastasis.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-20-1255
  18. Cancer Manag Res. 2020 ;12 6149-6163
    Cai Z, Deng Y, Ye J, Zhuo Y, Liu Z, Liang Y, Zhang H, Zhu X, Luo Y, Feng Y, Liu R, Chen G, Wu Y, Han Z, Liang Y, Jiang F, Zhong W.
      Purpose: Citrate synthase (CS) is a rate-limiting enzyme in the citrate cycle and is capable of catalyzing oxaloacetate and acetyl-CoA to citrate. CS has been uncovered to be upregulated in a variety of cancers, and its expression and clinical significance in prostate cancer (PCa) remain unknown.Methods: In this study, we examined the association between CS expression level and clinicopathological features of prostate cancer patients in a TMA cohort and the public cancer database (The Cancer Genome Atlas-Prostate Adenocarcinoma, TCGA-PRAD). The CS knockdown cell lines were constructed to study the effects of CS downregulation on proliferation, colony formation, migration, invasion, and cell cycle of prostate cancer cells in vitro. And the effect of CS downregulation on tumor growth in mice was studied in vivo. In addition, the metabolomics and mitochondrial function were detected in the CS knockdown cell lines.
    Results: CS expression level in PCa tissues was higher than that in normal tissues (P < 0.05). CS upregulation was significantly associated with high Gleason score (P < 0.05), advanced pathological stage (P < 0.001), and biochemical recurrence (P < 0.001). Functionally, decreased expression of CS inhibited PCa cell proliferation, colony formation, migration, invasion and cell cycle in vitro, and inhibited tumor growth in vivo. In addition, CS downregulation exerted potential inhibitory effects on the lipid metabolism and mitochondrial function of PCa cells.
    Conclusion: In conclusion, these findings suggested that CS upregulation may contribute to the aggressive progression and poor prognosis of PCa patients, which might be partially associated with its influences on the cell lipid metabolism and mitochondrial function.
    Keywords:  citrate synthase; lipid metabolism; prognosis; prostate cancer
    DOI:  https://doi.org/10.2147/CMAR.S255817
  19. Metabol Open. 2019 Dec;4 100020
    Grey JFE, Townley AR, Everitt NM, Campbell-Ritchie A, Wheatley SP.
      Analysis of cellular energetics is central to understanding metabolic diseases including diabetes and cancer. The two most commonly used methods to monitor cellular respiration are the Seahorse-XF system, and Glo™ assays, which are considered "gold standards". These commercial methods measure energetics indirectly and require considerable financial investment. Here we describe an alternative assay that enables accurate quantification of NADH turnover and that is affordable. This method measures resazurin reduction to resorufin at rising concentrations in the presence of purified mitochondrial extracts until NADH becomes a rate-limiting factor. This indicates the maximal level of NADH turnover in each sample and therefore infers metabolic activity. Here we compare MRC5, MCF7 and MDA231 cell lines which have differing metabolic profiles.
    Keywords:  Mitochondria; NADH; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.metop.2019.100020
  20. Redox Biol. 2020 Aug 06. pii: S2213-2317(20)30879-X. [Epub ahead of print] 101674
    Nolfi-Donegan D, Braganza A, Shiva S.
      The mitochondrial electron transport chain utilizes a series of electron transfer reactions to generate cellular ATP through oxidative phosphorylation. A consequence of electron transfer is the generation of reactive oxygen species (ROS), which contributes to both homeostatic signaling as well as oxidative stress during pathology. In this graphical review we provide an overview of oxidative phosphorylation and its inter-relationship with ROS production by the electron transport chain. We also outline traditional and novel translational methodology for assessing mitochondrial energetics in health and disease.
    Keywords:  Electron transport chain; Mitochondria; Mitochondrial reactive oxygen species; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.redox.2020.101674
  21. Theranostics. 2020 ;10(20): 9083-9099
    Liu HJ, Qin Y, Zhao ZH, Zhang Y, Yang JH, Zhai DH, Cui F, Luo C, Lu MX, Liu PP, Xu HW, Li K, Sun B, Chen S, Zhou HG, Yang C, Sun T.
      Rationale: Malignant ascites caused by cancer cells results in poor prognosis and short average survival time. No effective treatment is currently available for malignant ascites. In this study, the effects of lentinan (LNT)-functionalized selenium nanoparticles (Selene) on malignant ascites were evaluated. Furthermore, the mechanism of Selene targeting mitochondria of tumor cells were also investigated. Methods: Selene were synthesized and characterized by TEM, AFM and particle size analysis. The OVCAR-3 and EAC cells induced ascites models were used to evaluate the effects of Selene on malignant ascites. Proteomic analysis, immunofluorescence, TEM and ICP-MS were used to determine the location of Selene in tumor cells. Mitochondrial membrane potential, ROS, ATP content, and caspase-1/3 activity were detected to evaluate the effect of Selene on mitochondrial function and cell apoptosis. Immunofluorescence, Co-IP, pull-down, duolink, Western blot, and FPLC were used to investigate the pathway of Selene targeting mitochondria. Results: Selene could effectively inhibit ascites induced by OVCAR-3 and EAC cells. Selene was mainly located in the mitochondria of tumor cells and induced apoptosis of tumor cells. The LNT in Selene was involved in caveolae-mediated endocytosis through the interaction between toll-like receptor-4 (TLR4) and caveolin 1 (CAV1). Furthermore, the Selene in the endocytic vesicles could enter the mitochondria via the mitochondrial membrane fusion pathway, which was mediated by TLR4/TNF receptor associated factor 3 (TRAF3)/mitofusin-1 (MFN1) protein complex. Conclusion: Selene is a candidate anticancer drug for the treatment of malignant ascites. And TLR4/TRAF3/MFN1 may be a specific nano-drug delivery pathway that could target the mitochondria.
    Keywords:  lentinan; malignant ascites; mitochondria targeting pathway; ovarian cancer; selenium nanoparticles
    DOI:  https://doi.org/10.7150/thno.46467
  22. Methods Mol Biol. 2020 ;2184 197-213
    Teodoro JS, Machado IF, Castela AC, Rolo AP, Palmeira CM.
      The proton electrochemical gradient generated by respiratory chain activity accounts for over 90% of all available ATP and, as such, its evaluation and accurate measurements regarding its total values and fluctuations is an invaluable component in the understanding of mitochondrial functions. Consequently, alterations in electric potential across the inner mitochondrial membrane generated by differential protonic accumulations and transport are known as the mitochondrial membrane potential, or Δψ, and are reflective of the functional metabolic status of mitochondria. There are several experimental approaches to measure Δψ, ranging from fluorometric evaluations to electrochemical probes. Here we discuss the advantages and disadvantages of several of these methods, ranging from one that is dependent on the movement of a particular ion (tetraphenylphosphonium (TPP+) with a selective electrode) to the selection of a fluorescent dye from various types to achieve the same goal. The evaluation of the accumulation and movements of TPP+ across the inner mitochondrial membrane, or the fluorescence of accumulated dye particles, is a sensitive and accurate method of evaluating the Δψ in respiring mitochondria (either isolated or still inside the cell).
    Keywords:  DiOC6(3); Membrane potential; Metabolic states; Mitochondria; Rh123; JC-1; TMRE; TMRM; TPP+-selective electrode
    DOI:  https://doi.org/10.1007/978-1-0716-0802-9_14
  23. JCI Insight. 2020 Aug 20. pii: 138729. [Epub ahead of print]5(16):
    Beckermann KE, Hongo R, Ye X, Young K, Carbonell K, Healey DCC, Siska PJ, Barone S, Roe CE, Smith CC, Vincent BG, Mason FM, Irish JM, Rathmell WK, Rathmell JC.
      Metabolic reprogramming dictates the fate and function of stimulated T cells, yet these pathways can be suppressed in T cells in tumor microenvironments. We previously showed that glycolytic and mitochondrial adaptations directly contribute to reducing the effector function of renal cell carcinoma (RCC) CD8+ tumor-infiltrating lymphocytes (TILs). Here we define the role of these metabolic pathways in the activation and effector functions of CD8+ RCC TILs. CD28 costimulation plays a key role in augmenting T cell activation and metabolism, and is antagonized by the inhibitory and checkpoint immunotherapy receptors CTLA4 and PD-1. While RCC CD8+ TILs were activated at a low level when stimulated through the T cell receptor alone, addition of CD28 costimulation greatly enhanced activation, function, and proliferation. CD28 costimulation reprogrammed RCC CD8+ TIL metabolism with increased glycolysis and mitochondrial oxidative metabolism, possibly through upregulation of GLUT3. Mitochondria also fused to a greater degree, with higher membrane potential and overall mass. These phenotypes were dependent on glucose metabolism, as the glycolytic inhibitor 2-deoxyglucose both prevented changes to mitochondria and suppressed RCC CD8+ TIL activation and function. These data show that CD28 costimulation can restore RCC CD8+ TIL metabolism and function through rescue of T cell glycolysis that supports mitochondrial mass and activity.
    Keywords:  Glucose metabolism; Immunology; Immunotherapy; Oncology; T cells
    DOI:  https://doi.org/10.1172/jci.insight.138729
  24. Cells. 2020 Aug 13. pii: E1900. [Epub ahead of print]9(8):
    Keller F, Bruch R, Schneider R, Meier-Hubberten J, Hafner M, Rudolf R.
      Most tumors consume large amounts of glucose. Concepts to explain the mechanisms that mediate the achievement of this metabolic need have proposed a switch of the tumor mass to aerobic glycolysis. Depending on whether primarily tumor or stroma cells undergo such a commutation, the terms 'Warburg effect' or 'reverse Warburg effect' were coined to describe the underlying biological phenomena. However, current in vitro systems relying on 2-D culture, single cell-type spheroids, or basal-membrane extract (BME/Matrigel)-containing 3-D structures do not thoroughly reflect these processes. Here, we aimed to establish a BME/Matrigel-free 3-D microarray cancer model to recapitulate the metabolic interplay between cancer and stromal cells that allows mechanistic analyses and drug testing. Human HT-29 colon cancer and CCD-1137Sk fibroblast cells were used in mono- and co-cultures as 2-D monolayers, spheroids, and in a cell-chip format. Metabolic patterns were studied with immunofluorescence and confocal microscopy. In chip-based co-cultures, HT-29 cells showed facilitated 3-D growth and increased levels of hexokinase-2, TP53-induced glycolysis and apoptosis regulator (TIGAR), lactate dehydrogenase, and: translocase of outer mitochondrial membrane 20 (TOMM20), when compared with HT-29 mono-cultures. Fibroblasts co-cultured with HT-29 cells expressed higher levels of mono-carboxylate transporter 4, hexokinase-2, microtubule-associated proteins 1A/1B light chain 3, and ubiquitin-binding protein p62 than in fibroblast mono-cultures, in both 2-D cultures and chips. Tetramethylrhodamin-methylester (TMRM) live-cell imaging of chip co-cultures revealed a higher mitochondrial potential in cancer cells than in fibroblasts. The findings demonstrate a crosstalk between cancer cells and fibroblasts that affects cellular growth and metabolism. Chip-based 3-D co-cultures of cancer cells and fibroblasts mimicked features of the reverse Warburg effect.
    Keywords:  LC3; MCT4; fibroblasts; mitochondria; optical tissue clearing; reverse Warburg effect
    DOI:  https://doi.org/10.3390/cells9081900
  25. Cancers (Basel). 2020 Aug 20. pii: E2358. [Epub ahead of print]12(9):
    Jo MJ, Kim BG, Park SH, Kim HJ, Jeong S, Kim BR, Kim JL, Na YJ, Jeong YA, Yun HK, Kim DY, Han J, Heo JY, Yoo YD, Lee DH, Oh SC.
      Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to behave as an attractive anti-cancer agent in various cancers. Despite its promise TRAIL has limitations such as short half-life and rapid development of resistance. In this regard, approaches to sensitizers of TRAIL that can overcome the limitations of TRAIL are necessary. However, the molecular targets and mechanisms underlying sensitization to TRAIL-induced apoptosis are not fully understood. Here, we propose that reactive oxygen species modulator-1 (Romo1) as an attractive sensitizer of TRAIL. Romo1 is a mitochondrial inner membrane channel protein that controls reactive oxygen species (ROS) production, and its expression is highly upregulated in various cancers, including colorectal cancer. In the present study, we demonstrated that Romo1 inhibition significantly increased TRAIL-induced apoptosis of colorectal cancer cells, but not of normal colon cells. The combined effect of TRAIL and Romo1 inhibition was correlated with the activation of mitochondrial apoptosis pathways. Romo1 silencing elevated the protein levels of BCL-2-associated X protein (Bax) by downregulating the ubiquitin proteasome system (UPS). Romo1 inhibition downregulated the interaction between Bax and Parkin. Furthermore, Romo1 knockdown triggered the mitochondrial dysfunction and ROS generation. We validated the effect of combination in tumor xenograft model in vivo. In conclusion, our study demonstrates that Romo1 inhibition induces TRAIL-mediated apoptosis by identifying the novel mechanism associated with the Bax/Parkin interaction. We suggest that targeting of Romo1 is essential for the treatment of colorectal cancer and may be a new therapeutic approach in the future and contribute to the drug discovery.
    Keywords:  Bax; Parkin; mitochondrial dysfunction; reactive oxygen species modulator-1; tumor necrosis factor-related apoptosis-inducing ligand
    DOI:  https://doi.org/10.3390/cancers12092358
  26. J Biol Chem. 2020 Aug 21. pii: jbc.RA120.013537. [Epub ahead of print]
    Chang L, Liu X, Diggle CP, Boyle JP, Hopkins PM, Shaw MA, Allen PD.
      Mutations in the skeletal muscle ryanodine receptor gene (RYR1) can cause susceptibility to malignant hyperthermia (MH), a potentially lethal genetic condition triggered by volatile anesthetics. MH is associated with hypermetabolism which has directed research interest into oxidative phosphorylation (OXPHOS) and muscle bioenergetics. The most common cause of MH in the United Kingdom is the c.7300G>A RYR1 variant, which is present in ~16% of MH families. Our study focuses on the MH susceptible G2435R-RYR1 knock-in mouse model, which is the murine equivalent of the human c.7300G>A genotype. Using a combination of transcriptomics, protein expression and functional analysis, we investigated adult muscle fiber bioenergetics in this mouse model. RNA sequencing data showed reduced expression of genes associated with mitochondria and fatty acid oxidation in RYR1 mutants when compared to wild-type (WT) controls. Mitochondrial function was assessed by measuring oxygen consumption rates in permeabilized muscle fibers. Comparisons between WT and homozygous G2435R-RYR1 mitochondria showed a significant increase in complex I-facilitated OXPHOS in mutant muscle. Furthermore, we observed a gene-dose specific increase in reactive oxygen species production in G2435R-RYR1 muscle fibers. Collectively these findings provide evidence of metabolic defects in G2435R-RYR1 knock-in mouse muscle under basal conditions. Differences in metabolic profile could be the result of differential gene expression in metabolic pathways, in conjunction with mitochondrial damage accumulated from chronic exposure to increased oxidative stress.
    Keywords:  bioenergetics; malignant hyperthermia; mitochondrial metabolism; mouse; muscle physiology; ryanodine receptor
    DOI:  https://doi.org/10.1074/jbc.RA120.013537
  27. EMBO J. 2020 Aug 20. e103889
    Finger Y, Habich M, Gerlich S, Urbanczyk S, van de Logt E, Koch J, Schu L, Lapacz KJ, Ali M, Petrungaro C, Salscheider SL, Pichlo C, Baumann U, Mielenz D, Dengjel J, Brachvogel B, Hofmann K, Riemer J.
      Plasticity of the proteome is critical to adapt to varying conditions. Control of mitochondrial protein import contributes to this plasticity. Here, we identified a pathway that regulates mitochondrial protein import by regulated N-terminal processing. We demonstrate that dipeptidyl peptidases 8/9 (DPP8/9) mediate the N-terminal processing of adenylate kinase 2 (AK2) en route to mitochondria. We show that AK2 is a substrate of the mitochondrial disulfide relay, thus lacking an N-terminal mitochondrial targeting sequence and undergoing comparatively slow import. DPP9-mediated processing of AK2 induces its rapid proteasomal degradation and prevents cytosolic accumulation of enzymatically active AK2. Besides AK2, we identify more than 100 mitochondrial proteins with putative DPP8/9 recognition sites and demonstrate that DPP8/9 influence the cellular levels of a number of these proteins. Collectively, we provide in this study a conceptual framework on how regulated cytosolic processing controls levels of mitochondrial proteins as well as their dual localization to mitochondria and other compartments.
    Keywords:  MIA40; adenylate kinase 2; dipeptidyl peptidase 9; mitochondrial protein import; quality control
    DOI:  https://doi.org/10.15252/embj.2019103889
  28. Sci Adv. 2020 Aug;6(32): eabc7288
    Ruan L, McNamara JT, Zhang X, Chang AC, Zhu J, Dong Y, Sun G, Peterson A, Na CH, Li R.
      Proteostasis declines with age, characterized by the accumulation of unfolded or damaged proteins. Recent studies suggest that proteins constituting pathological inclusions in neurodegenerative diseases also enter and accumulate in mitochondria. How unfolded proteins are managed within mitochondria remains unclear. Here, we found that excessive unfolded proteins in the mitochondrial matrix of yeast cells are consolidated into solid-phase inclusions, which we term deposits of unfolded mitochondrial proteins (DUMP). Formation of DUMP occurs in mitochondria near endoplasmic reticulum-mitochondria contact sites and is regulated by mitochondrial proteins controlling the production of cytidine 5'-diphosphate-diacylglycerol. DUMP formation is age dependent but accelerated by exogenous unfolded proteins. Many enzymes of the tricarboxylic acid cycle were enriched in DUMP. During yeast cell division, DUMP formation is necessary for asymmetric inheritance of damaged mitochondrial proteins between mother and daughter cells. We provide evidence that DUMP-like structures may be induced by excessive unfolded proteins in human cells.
    DOI:  https://doi.org/10.1126/sciadv.abc7288
  29. Stud Hist Philos Biol Biomed Sci. 2020 Aug 12. pii: S1369-8486(20)30030-3. [Epub ahead of print] 101290
    DiMarco M.
      In their 1987 Nature publication, "Mitochondrial DNA and Human Evolution," Rebecca Cann, Mark Stoneking, and Allan C. Wilson gave a new reconstruction of human evolution on the basis of differences in mitochondrial DNA among contemporary human populations. This phylogeny included an African common ancestor for all human mitochondrial DNA (mtDNA) lineages, and Cann et al.'s reconstruction became known as the "Out of Africa" hypothesis. Since mtDNA is inherited exclusively through the maternal line, the common ancestor who was first branded African Eve later became known as Mitochondrial Eve (mtEve, for short). In this paper, I show that mtEve was not a single, successful, or purely scientific discovery. Instead, she was produced many times and in many ways, each of which informed the next. Importantly, though Wilson and colleagues heralded mitochondrial DNA as a source of certainty, objectivity, and consensus for evolutionary inference, their productions of Mitochondrial Eve depended as much on popular assumptions about the certainty of maternal inheritance as they did on new molecular and computational tools. This recognition lets us reevaluate the complex consequences of these productions, which, like mtEve herself, could not be confined to a purely social, material, or scientific dimension.
    DOI:  https://doi.org/10.1016/j.shpsc.2020.101290
  30. Cell Stem Cell. 2020 Aug 14. pii: S1934-5909(20)30359-3. [Epub ahead of print]
    Jones CL, Stevens BM, Pollyea DA, Culp-Hill R, Reisz JA, Nemkov T, Gehrke S, Gamboni F, Krug A, Winters A, Pei S, Gustafson A, Ye H, Inguva A, Amaya M, Minhajuddin M, Abbott D, Becker MW, DeGregori J, Smith CA, D'Alessandro A, Jordan CT.
      We previously demonstrated that leukemia stem cells (LSCs) in de novo acute myeloid leukemia (AML) patients are selectively reliant on amino acid metabolism and that treatment with the combination of venetoclax and azacitidine (ven/aza) inhibits amino acid metabolism, leading to cell death. In contrast, ven/aza fails to eradicate LSCs in relapsed/refractory (R/R) patients, suggesting altered metabolic properties. Detailed metabolomic analysis revealed elevated nicotinamide metabolism in relapsed LSCs, which activates both amino acid metabolism and fatty acid oxidation to drive OXPHOS, thereby providing a means for LSCs to circumvent the cytotoxic effects of ven/aza therapy. Genetic and pharmacological inhibition of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in nicotinamide metabolism, demonstrated selective eradication of R/R LSCs while sparing normal hematopoietic stem/progenitor cells. Altogether, these findings demonstrate that elevated nicotinamide metabolism is both the mechanistic basis for ven/aza resistance and a metabolic vulnerability of R/R LSCs.
    Keywords:  NAD+; NAMPT; acute myeloid leukemia; leukemia stem cells; metabolism; nicotinamide; oxidative phosphorylation; relapse; therapy resistance; venetoclax
    DOI:  https://doi.org/10.1016/j.stem.2020.07.021
  31. Nat Commun. 2020 Aug 21. 11(1): 4184
    Li F, Sun Q, Liu K, Zhang L, Lin N, You K, Liu M, Kon N, Tian F, Mao Z, Li T, Tong T, Qin J, Gu W, Li D, Zhao W.
      Oncogenic processes exert their greatest effect by targeting regulators of cell proliferation. Studying the mechanism underlying growth augmentation is expected to improve clinical therapies. The ovarian tumor (OTU) subfamily deubiquitinases have been implicated in the regulation of critical cell-signaling cascades, but most OTUs functions remain to be investigated. Through an unbiased RNAi screen, knockdown of OTUD5 is shown to significantly accelerate cell growth. Further investigation reveals that OTUD5 depletion leads to the enhanced transcriptional activity of TRIM25 and the inhibited expression of PML by altering the ubiquitination level of TRIM25. Importantly, OTUD5 knockdown accelerates tumor growth in a nude mouse model. OTUD5 expression is markedly downregulated in tumor tissues. The reduced OTUD5 level is associated with an aggressive phenotype and a poor clinical outcome for cancers patients. Our findings reveal a mechanism whereby OTUD5 regulates gene transcription and suppresses tumorigenesis by deubiquitinating TRIM25, providing a potential target for oncotherapy.
    DOI:  https://doi.org/10.1038/s41467-020-17926-7
  32. Proc Natl Acad Sci U S A. 2020 Aug 14. pii: 202010815. [Epub ahead of print]
    Yuly JL, Zhang P, Lubner CE, Peters JW, Beratan DN.
      For decades, it was unknown how electron-bifurcating systems in nature prevented energy-wasting short-circuiting reactions that have large driving forces, so synthetic electron-bifurcating molecular machines could not be designed and built. The underpinning free-energy landscapes for electron bifurcation were also enigmatic. We predict that a simple and universal free-energy landscape enables electron bifurcation, and we show that it enables high-efficiency bifurcation with limited short-circuiting (the EB scheme). The landscape relies on steep free-energy slopes in the two redox branches to insulate against short-circuiting using an electron occupancy blockade effect, without relying on nuanced changes in the microscopic rate constants for the short-circuiting reactions. The EB scheme thus unifies a body of observations on biological catalysis and energy conversion, and the scheme provides a blueprint to guide future campaigns to establish synthetic electron bifurcation machines.
    Keywords:  bioenergetics; chemiosmotic hypothesis; electron bifurcation; electron transfer; short-circuiting
    DOI:  https://doi.org/10.1073/pnas.2010815117
  33. FASEB J. 2020 Aug 17.
    Marchetti P, Fovez Q, Germain N, Khamari R, Kluza J.
      Mitochondrial metabolism must constantly adapt to stress conditions in order to maintain bioenergetic levels related to cellular functions. This absence of proper adaptation can be seen in a wide array of conditions, including cancer. Metabolic adaptation calls on mitochondrial function and draws on the mitochondrial reserve to meet increasing needs. Among mitochondrial respiratory parameters, the spare respiratory capacity (SRC) represents a particularly robust functional parameter to evaluate mitochondrial reserve. We provide an overview of potential SRC mechanisms and regulation with a focus on its particular significance in cancer cells.
    Keywords:  mitochondrial adaptation; mitochondrial dysfunction; mitochondrial flexibility; mitochondrial metabolism; mitochondrial stress; oxygen consumption; respiratory reserve capacity; spare reserve capacity; uncoupling ratio
    DOI:  https://doi.org/10.1096/fj.202000767R
  34. Redox Biol. 2020 Aug 07. pii: S2213-2317(20)30885-5. [Epub ahead of print]36 101680
    Wang Y, Hekimi S.
      Coenzyme Q10 (CoQ10; also known as ubiquinone) is a vital, redox-active membrane component that functions as obligate electron transporter in the mitochondrial respiratory chain, as cofactor in other enzymatic processes and as antioxidant. CoQ10 supplementation has been widely investigated for treating a variety of acute and chronic conditions in which mitochondrial function or oxidative stress play a role. In addition, it is used as replacement therapy in patients with CoQ deficiency including inborn primary CoQ10 deficiency due to mutations in CoQ10-biosynthetic genes as well as secondary CoQ10 deficiency, which is frequently observed in patients with mitochondrial disease syndrome and in other conditions. However, despite many tests and some promising results, whether CoQ10 treatment is beneficial in any indication has remained inconclusive. Because CoQ10 is highly insoluble, it is only available in oral formulations, despite its very poor oral bioavailability. Using a novel model of CoQ-deficient cells, we screened a library of FDA-approved drugs for an activity that could increase the uptake of exogenous CoQ10 by the cell. We identified the fungicide caspofungin as capable of increasing the aqueous solubility of CoQ10 by several orders of magnitude. Caspofungin is a mild surfactant that solubilizes CoQ10 by forming nano-micelles with unique properties favoring stability and cellular uptake. Intravenous administration of the formulation in mice achieves unprecedented increases in CoQ10 plasma levels and in tissue uptake, with no observable toxicity. As it contains only two safe components (caspofungin and CoQ10), this injectable formulation presents a high potential for clinical safety and efficacy.
    Keywords:  Caspofungin; Coenzyme Q; Micelle; Mitochondrial diseases; Ubiquinone
    DOI:  https://doi.org/10.1016/j.redox.2020.101680
  35. J Clin Endocrinol Metab. 2020 Aug 21. pii: dgaa571. [Epub ahead of print]
    Hoffmann C, Schneeweiss P, Randrianarisoa E, Schnauder G, Kappler L, Machann J, Schick F, Fritsche A, Heni M, Birkenfeld A, Niess AM, Häring HU, Weigert C, Moller A.
      CONTEXT: Exercise training improves glycemic control and increases mitochondrial content and respiration capacity in skeletal muscle. Rodent studies suggest that training increases mitochondrial respiration in adipose tissue.OBJECTIVE: To assess the effects of endurance training on respiratory capacities of human skeletal muscle and abdominal subcutaneous adipose tissue and to study the correlation with improvement in insulin sensitivity.
    DESIGN: Using high resolution respirometry, we analyzed biopsies from 25 sedentary (VO2 peak 25.1 ± 4.0 VO2 ml/(kg*min)) subjects (16 females, 9 males; 29.8 ± 8.4 yrs) with obesity (BMI 31.5 ± 4.3 kg/m 2 ), who did not have diabetes. They performed a supervised endurance training over 8 weeks (3 x 1 hour/week at 80% VO 2 peak).
    RESULTS: Based on change in insulin sensitivity after intervention, subjects were grouped in responders (>15% increase in ISIMatsuda) and low responders. The response in ISIMatsuda was correlated to a reduction of subcutaneous and visceral adipose tissue volume. Both groups exhibited similar increases in fitness, respiratory capacity, and in abundance of mitochondrial enzymes in skeletal muscle fibers. Respiratory capacities in subcutaneous adipose tissue were not altered by the intervention. Compared to muscle fibers, adipose tissue respiration showed a preference for β-oxidation and complex II substrates. Respiratory capacities were higher in adipose tissue from females.
    CONCLUSION: Our data show that the improvement of peripheral insulin sensitivity after endurance training is not directly related to an increase in mitochondrial respiratory capacities in skeletal muscle and occurs without an increase in the respiratory capacity of subcutaneous adipose tissue.
    Keywords:  Respiratory chain complex; VO2peak; diabetes prevention; sex-differences
    DOI:  https://doi.org/10.1210/clinem/dgaa571
  36. Nature. 2020 Aug 19.
    Ubellacker JM, Tasdogan A, Ramesh V, Shen B, Mitchell EC, Martin-Sandoval MS, Gu Z, McCormick ML, Durham AB, Spitz DR, Zhao Z, Mathews TP, Morrison SJ.
      Cancer cells, including melanoma cells, often metastasize regionally through the lymphatic system before metastasizing systemically through the blood1-4; however, the reason for this is unclear. Here we show that melanoma cells in lymph experience less oxidative stress and form more metastases than melanoma cells in blood. Immunocompromised mice with melanomas derived from patients, and immunocompetent mice with mouse melanomas, had more melanoma cells per microlitre in tumour-draining lymph than in tumour-draining blood. Cells that metastasized through blood, but not those that metastasized through lymph, became dependent on the ferroptosis inhibitor GPX4. Cells that were pretreated with chemical ferroptosis inhibitors formed more metastases than untreated cells after intravenous, but not intralymphatic, injection. We observed multiple differences between lymph fluid and blood plasma that may contribute to decreased oxidative stress and ferroptosis in lymph, including higher levels of glutathione and oleic acid and less free iron in lymph. Oleic acid protected melanoma cells from ferroptosis in an Acsl3-dependent manner and increased their capacity to form metastatic tumours. Melanoma cells from lymph nodes were more resistant to ferroptosis and formed more metastases after intravenous injection than did melanoma cells from subcutaneous tumours. Exposure to the lymphatic environment thus protects melanoma cells from ferroptosis and increases their ability to survive during subsequent metastasis through the blood.
    DOI:  https://doi.org/10.1038/s41586-020-2623-z
  37. Cell Tissue Res. 2020 Aug 17.
    Wang Y, Liu Y, Chen E, Pan Z.
      Mesenchymal stem cells (MSCs) hold enormous potential for the treatment of immune-related conditions and degenerative diseases, owing to their self-renewal and multilineage differentiation capabilities. Nevertheless, cellular senescence significantly impacts the quantity and quality of MSCs, limiting their clinical use. Mitochondria play essential roles in energy production by oxidative phosphorylation and metabolism of energy sources via the tricarboxylic acid cycle. Therefore, mitochondrial dysfunction is a primary cause of senescence in MSCs. Herein, we summarize the current knowledge regarding the mechanisms underlying mitochondrial dysfunction-associated cellular senescence. We also discuss potential methods to prevent or even reverse MSC senescence.
    Keywords:  Mesenchymal stem cells; Mitochondrial dysfunction; Mitophagy; Reactive oxygen species; Senescence
    DOI:  https://doi.org/10.1007/s00441-020-03272-z
  38. Mech Ageing Dev. 2020 Aug 17. pii: S0047-6374(20)30130-5. [Epub ahead of print] 111334
    Wan Y, Finkel T.
      Mitochondrial dysfunction and stem cell exhaustion are among the nine separate hallmarks of aging. Emerging evidence however suggests that mitochondrial activity can have a profound influence on the self-renewal and function of stem cells, thus mechanistically linking mitochondrial function and stem cell decline. In this review, we discuss how accumulation of mtDNA mutations or alterations in mitochondrial dynamics, turnover, and signaling can modulate age-dependent stem cell function. Finally, we also describe how mitochondrial substrate utilization influences stem and progenitor activity. Together, this growing body of evidence suggests that modulation of mitochondrial activity might provide a strategy to slow or reverse age-dependent stem cell decline, and potentially, slow or reverse human aging.
    DOI:  https://doi.org/10.1016/j.mad.2020.111334
  39. An Acad Bras Cienc. 2020 ;pii: S0001-37652020000300801. [Epub ahead of print]92(2): e20191340
    Yurre AR, Martins EGL, Lopez-Alarcon M, Cabral B, Vera N, Lopes JA, Galina A, Takiya CM, Lindoso RS, Vieyra A, SÁenz OC, Medei E.
      Type 2 diabetes mellitus (T2DM) is associated with an increase of premature appearance of several disorders such as cardiac complications. Thus, we test the hypothesis that a combination of a high fat diet (HFD) and low doses of streptozotocin (STZ) recapitulate a suitable mice model of T2DM to study the cardiac mitochondrial disturbances induced by this disease. Animals were divided in 2 groups: the T2DM group was given a HFD and injected with 2 low doses of STZ, while the CNTRL group was given a standard chow and a buffer solution. The combination of HFD and STZ recapitulate the T2DM metabolic profile showing higher blood glucose levels in T2DM mice when compared to CNTRL, and also, insulin resistance. The kidney structure/function was preserved. Regarding cardiac mitochondrial function, in all phosphorylative states, the cardiac mitochondria from T2DM mice presented reduced oxygen fluxes when compared to CNTRL mice. Also, mitochondria from T2DM mice showed decreased citrate synthase activity and lower protein content of mitochondrial complexes. Our results show that in this non-obese T2DM model, which recapitulates the classical metabolic alterations, mitochondrial function is impaired and provides a useful model to deepen study the mechanisms underlying these alterations.
    DOI:  https://doi.org/10.1590/0001-3765202020191340
  40. Anticancer Agents Med Chem. 2020 Aug 14.
    Xin Y, Guo W, Yang C, Huang Q, Zhang P, Zhang L, Jiang G.
      BACKGROUND: Photodynamic therapy (PDT) is a photoactivation or photosensitization process, wherein vitamin K3 (Vit K3) serves as a photosensitizer to produce reactive oxygen species (ROS) against bacteria at appropriate wavelengths. In this study, we used Vit K3 treatment combined with ultraviolet radiation A (UVA) to produce photodynamic effects on cervical cancer.METHODS: The dose-concentration relationship between Vit K3 treatment and UVA on tumor cells was analyzed through the Cell Counting Kit-8 method. Then, the morphological characteristics of apoptosis cells were observed through fluorescent staining and fluorescence microscopy. Apoptosis after treatment with Vit K3 treatment, UVA, and Vit K3 treatment plus UVA was further observed through Western blot analysis, flow cytometry, and TUNEL assay. The xenograft models from HeLa cells were established for the exploration of the photodynamic effect of Vit K3 treatment on cervical cancer in vivo.
    RESULTS: Vit K3 treatment plus UVA reduced tumor cell viability in a dose-dependent manner. Further studies indicated that Vit K3 treatment plus UVA can inhibit tumor growth and enhance the apoptosis of cervical cancer cells. In the combination group, the expression levels of cleaved caspase-3, cleaved caspase-9, B-cell lymphoma-extra large (Bcl-xl), and cytochrome c (cyt-c) increased obviously, whereas the expression level of B-cell lymphoma 2 (Bcl-2) decreased relative to the expression levels of UVA- or Vit K3-treated cells. In the vivo experiments, tumor growth was inhibited significantly in the VitK3 treatment plus UVA group. Additionally, we demonstrated that the combination therapy mediated an increase in cleaved caspase-3 and cleaved caspase-9 expression and decrease in Bcl-2 expression in vivo.
    CONCLUSION: Our results showed that Vit K3 treatment combined with UVA exerted photodynamic effects on cervical cancer cells by activating mitochondrial apoptosis pathways.
    Keywords:  Vitamin K3; apoptosis; caspase-9.; cervical cancer; photodynamic therapy; photosensitizer
    DOI:  https://doi.org/10.2174/1871520620666200814164629
  41. Int J Mol Sci. 2020 Aug 16. pii: E5880. [Epub ahead of print]21(16):
    Yamada M, Akashi K, Ooka R, Miyado K, Akutsu H.
      Mitochondria are energy-producing intracellular organelles containing their own genetic material in the form of mitochondrial DNA (mtDNA), which codes for proteins and RNAs essential for mitochondrial function. Some mtDNA mutations can cause mitochondria-related diseases. Mitochondrial diseases are a heterogeneous group of inherited disorders with no cure, in which mutated mtDNA is passed from mothers to offspring via maternal egg cytoplasm. Mitochondrial replacement (MR) is a genome transfer technology in which mtDNA carrying disease-related mutations is replaced by presumably disease-free mtDNA. This therapy aims at preventing the transmission of known disease-causing mitochondria to the next generation. Here, a proof of concept for the specific removal or editing of mtDNA disease-related mutations by genome editing is introduced. Although the amount of mtDNA carryover introduced into human oocytes during nuclear transfer is low, the safety of mtDNA heteroplasmy remains a concern. This is particularly true regarding donor-recipient mtDNA mismatch (mtDNA-mtDNA), mtDNA-nuclear DNA (nDNA) mismatch caused by mixing recipient nDNA with donor mtDNA, and mtDNA replicative segregation. These conditions can lead to mtDNA genetic drift and reversion to the original genotype. In this review, we address the current state of knowledge regarding nuclear transplantation for preventing the inheritance of mitochondrial diseases.
    Keywords:  Mitochondria DNA (mtDNA), nuclear transfer; maternal inheritance; mitochondria replacement (MR), nDNA–mtDNA compatibility; mitochondrial function; mtDNA genetic drift; mtDNA heteroplasmy; mtDNA replicative segregation; mtDNA–mtDNA compatibility
    DOI:  https://doi.org/10.3390/ijms21165880
  42. Methods Mol Biol. 2020 ;2184 233-263
    Sheppard AD, Lysaght J.
      The last century of research in tumor immunology has culminated in the advent of immunotherapy, most notably immune checkpoint inhibitors. These drugs have shown encouraging results across a multitude of malignancies and have shifted the paradigm of cancer treatment. However, no more than 40% of patients treated with these immune checkpoint blockade inhibitors respond. Thus, resistance is a barrier to therapy that remains poorly understood. All cells require energy and biosynthetic precursors for survival, growth, and functioning, where multiple metabolic pathways allow for flexibility in how nutrients are utilized. A defining hallmark of many cancers is altered cellular metabolism, creating an imbalanced demand for nutrients within the tumor microenvironment. Immunometabolism is increasingly understood to be vital to the functions and phenotypes of a myriad of immune cell subsets. In tumors, the high demand for nutrients by the tumor drives competition between tumor cells and infiltrating immune cells, culminating in dysfunctional immune responses. This chapter discusses the recent successes in cancer immunotherapy and highlights challenges to therapy. We also outline the major metabolic processes involved in the generation of an immune response, how this can become dysregulated in the context of the tumor microenvironment, and how this contributes to resistance to immunotherapy. Finally, we explore the potential for targeting immunometabolic pathways to improve immunotherapy, and examine current trials targeting various aspects of metabolism in an attempt to improve the outcomes from immunotherapy.
    Keywords:  Immunometabolism; Immunotherapy; Metabolism; Tumor microenvironment
    DOI:  https://doi.org/10.1007/978-1-0716-0802-9_17
  43. Antioxidants (Basel). 2020 Aug 16. pii: E758. [Epub ahead of print]9(8):
    Gordan R, Fefelova N, Gwathmey JK, Xie LH.
      Iron (Fe) plays an essential role in many physiological processes. Hereditary hemochromatosis or frequent blood transfusions often cause iron overload (IO), which can lead to cardiomyopathy and arrhythmias; however, the underlying mechanism is not well defined. In the present study, we assess the hypothesis that IO promotes arrhythmias via reactive oxygen species (ROS) production, mitochondrial membrane potential (∆Ψm) depolarization, and disruption of cytosolic Ca dynamics. In ventricular myocytes isolated from wild type (WT) mice, both cytosolic and mitochondrial Fe levels were elevated following perfusion with the Fe3+/8-hydroxyquinoline (8-HQ) complex. IO promoted mitochondrial superoxide generation (measured using MitoSOX Red) and induced the depolarization of the ΔΨm (measured using tetramethylrhodamine methyl ester, TMRM) in a dose-dependent manner. IO significantly increased the rate of Ca wave (CaW) formation measured in isolated ventricular myocytes using Fluo-4. Furthermore, in ex-vivo Langendorff-perfused hearts, IO increased arrhythmia scores as evaluated by ECG recordings under programmed S1-S2 stimulation protocols. We also carried out similar experiments in cyclophilin D knockout (CypD KO) mice in which the mitochondrial permeability transition pore (mPTP) opening is impaired. While comparable cytosolic and mitochondrial Fe load, mitochondrial ROS production, and depolarization of the ∆Ψm were observed in ventricular myocytes isolated from both WT and CypD KO mice, the rate of CaW formation in isolated cells and the arrhythmia scores in ex-vivo hearts were significantly lower in CypD KO mice compared to those observed in WT mice under conditions of IO. The mPTP inhibitor cyclosporine A (CsA, 1 µM) also exhibited a protective effect. In conclusion, our results suggest that IO induces mitochondrial ROS generation and ∆Ψm depolarization, thus opening the mPTP, thereby promoting CaWs and cardiac arrhythmias. Conversely, the inhibition of mPTP ameliorates the proarrhythmic effects of IO.
    Keywords:  arrhythmia; calcium dynamics; heart; iron overload; mitochondria; oxidative stress
    DOI:  https://doi.org/10.3390/antiox9080758
  44. iScience. 2020 Aug 21. pii: S2589-0042(20)30618-0. [Epub ahead of print]23(8): 101428
    Ma Y, Zhu S, Lv T, Gu X, Feng H, Zhen J, Xin W, Wan Q.
      Mitochondrial DNA (mtDNA) encodes thirteen core components of OXPHOS complexes, and its steady expression is crucial for cellular energy homeostasis. However, the regulation of mtDNA expression machinery, along with its sensing mechanism to energetic stresses, is not fully understood. Here, we identified SQSTM1/p62 as an important regulator of mtDNA expression machinery, which could effectively induce mtDNA expression and the effects were mediated by p38-dependent upregulation of mitochondrial ribosomal protein L12 (MRPL12) in renal tubular epithelial cells (TECs), a highly energy-demanding cell type related to OXPHOS. We further identified a direct binding site within the MRPL12 promoter to ATF2, the downstream effector of p38. Besides, SQSTM1/p62-induced mtDNA expression is involved in both serum deprivation and hypoxia-induced mitochondrial response, which was further highlighted by kidney injury phenotype of TECs-specific SQSTM1/p62 knockout mice. Collectively, these data suggest that SQSTM1/p62 is a key regulator and energetic sensor of mtDNA expression machinery.
    Keywords:  Biological Sciences; Cell Biology; Functional Aspects of Cell Biology; Molecular Biology
    DOI:  https://doi.org/10.1016/j.isci.2020.101428
  45. Cold Spring Harb Perspect Med. 2020 Aug 17. pii: a035477. [Epub ahead of print]
    Stahl M, Epstein-Peterson ZD, Intlekofer AM.
      Leukemias and lymphomas acquire the capacity for unrestrained cell growth and proliferation in conjunction with loss of responsiveness to molecular programs that promote terminal differentiation. Malignant cells generate the building blocks required for rapid cell division through both increased acquisition of nutrients from the environment and reprogrammed intermediary metabolism to shunt these molecules into producing the protein, lipids, and nucleic acids that comprise cell biomass. These accelerated metabolic processes require energy in the form of ATP and reducing equivalents in the form of NADPH, which power biosynthetic reactions and buffer oxidative stress encountered by the metabolically active cancer cell. Cancer-associated metabolic alterations can also promote accumulation or depletion of specific metabolites that directly regulate cell fate and function, thereby coupling metabolic reprogramming to dedifferentiation and stemness. This review will focus on the mechanisms by which leukemia and lymphoma cells rewire cellular metabolism to support: (1) bioenergetics, (2) biomass accumulation, (3) redox balance, and (4) differentiation blockade. We will further highlight examples of how specific pathways of leukemia and lymphoma metabolism confer therapeutic vulnerabilities that can be targeted to inhibit growth or promote differentiation.
    DOI:  https://doi.org/10.1101/cshperspect.a035477
  46. J Aging Res. 2020 ;2020 4939310
    Hou X, Li Z, Higashi Y, Delafontaine P, Sukhanov S.
      Mitochondrial dysfunction is a hallmark of cellular aging. Mitophagy is a critical mitochondrial quality control mechanism that removes dysfunctional mitochondria and contributes to cell survival. Insulin-like growth factor 1 (IGF-1) promotes survival of smooth muscle cells (SMCs), but its potential effect on cellular aging is unknown yet. We found that IGF-1 decreased cell senescence, prevented DNA telomere shortening, increased mitochondrial membrane potential, activated cytochrome C oxidase, and reduced mitochondrial DNA damage in long-term cultured (aged) aortic SMC, suggesting an antiaging effect. IGF-1 increased mitophagy in aged cells, and this was associated with decreased expression of cyclin-dependent kinase inhibitors p16 and p21 and elevated levels of Nrf2 and Sirt3, regulators of mitophagy and mitochondrial biogenesis. SiRNA-induced inhibition of either Nrf2 or Sirt3 blocked IGF-1-induced upregulation of mitophagy, suggesting that the Nrf2/Sirt3 pathway was required for IGF-1's effect on mitophagy. PINK1 is a master regulator of mitophagy. PINK1 silencing suppressed mitophagy and inhibited IGF-1-induced antiaging effects in aged SMC, consistent with an essential role of mitophagy in IGF-1's effect on cellular aging. Thus, IGF-1 inhibited cellular aging via Nrf2/Sirt3-dependent activation of mitophagy. Our data suggest that activation of IGF-1 signaling is a novel potential strategy to activate mitophagy and slow cellular aging.
    DOI:  https://doi.org/10.1155/2020/4939310
  47. Proc Natl Acad Sci U S A. 2020 Aug 17. pii: 201921890. [Epub ahead of print]
    Björkeroth J, Campbell K, Malina C, Yu R, Di Bartolomeo F, Nielsen J.
      Several recent studies have shown that the concept of proteome constraint, i.e., the need for the cell to balance allocation of its proteome between different cellular processes, is essential for ensuring proper cell function. However, there have been no attempts to elucidate how cells' maximum capacity to grow depends on protein availability for different cellular processes. To experimentally address this, we cultivated Saccharomyces cerevisiae in bioreactors with or without amino acid supplementation and performed quantitative proteomics to analyze global changes in proteome allocation, during both anaerobic and aerobic growth on glucose. Analysis of the proteomic data implies that proteome mass is mainly reallocated from amino acid biosynthetic processes into translation, which enables an increased growth rate during supplementation. Similar findings were obtained from both aerobic and anaerobic cultivations. Our findings show that cells can increase their growth rate through increasing its proteome allocation toward the protein translational machinery.
    Keywords:  amino acid metabolism; metabolic engineering; protein translation; systems biology
    DOI:  https://doi.org/10.1073/pnas.1921890117
  48. FASEB J. 2020 Aug 20.
    Li C, Chen Q, Zhou Y, Niu Y, Wang X, Li X, Zheng H, Wei T, Zhao L, Gao H.
      The deregulation of S100A2 has been implicated in the pathogenesis of several types of cancers. However, the molecular mechanisms underlying the protumorigenic capacities of S100A2 have not been fully elucidated. Here, we demonstrated the molecular mechanisms underlying the roles of S100A2 in glycolysis reprogramming and proliferation of colorectal cancer (CRC) cells. The results indicated that S100A2 overexpression raises glucose metabolism and proliferation. Mechanistically, S100A2 activated the PI3K/AKT signaling pathway, upregulated GLUT1 expression, induced glycolytic reprogramming, and consequently increased proliferation. Clinical data showed significantly increased S100A2 levels in CRC tissues and the Oncomine database. In addition, analysis revealed a positive correlation between S100A2 and GLUT1 mRNA expression in CRC tissues. Together, these results demonstrate that the S100A2/GLUT1 axis can promote the progression of CRC by modulating glycolytic reprogramming. Our results further suggest that targeting S100A2 could present a promising therapeutic avenue for the prevention of colorectal cancer progression.
    Keywords:  GLUT1; Glycolysis; S100A2; metabolic reprogramming; proliferation
    DOI:  https://doi.org/10.1096/fj.202000555R
  49. Methods Mol Biol. 2020 ;2184 215-224
    Masson JJR, Ostrowski M, Duette G, Lee MKS, Murphy AJ, Crowe SM, Palmer CS.
      The analysis of mitochondrial dynamics within immune cells allows us to understand how fundamental metabolism influences immune cell functions, and how dysregulated immunometabolic processes impact biology and disease pathogenesis. For example, during infections, mitochondrial fission and fusion coincide with effector and memory T-cell differentiation, respectively, resulting in metabolic reprogramming. As frozen cells are generally not optimal for immunometabolic analyses, and given the logistic difficulties of analysis on cells within a few hours of blood collection, we have optimized and validated a simple cryopreservation protocol for peripheral blood mononuclear cells, yielding >95% cellular viability, as well as preserved metabolic and immunologic properties. Combining fluorescent dyes with cell surface antibodies, we demonstrate how to analyze mitochondrial density, membrane potential, and reactive oxygen species production in CD4 and CD8 T cells from cryopreserved clinical samples.
    Keywords:  CD4 and CD8 T cells; Immunometabolism; Mitochondrial density; Mitochondrial membrane potential; ROS
    DOI:  https://doi.org/10.1007/978-1-0716-0802-9_15
  50. NMR Biomed. 2020 Aug 16. e4381
    Bartlett MF, Fitzgerald LF, Nagarajan R, Kent JA.
      Several methods have been developed for using 31 P-MRS to calculate rates of oxidative ATP synthesis (ATPOX ) during muscular contractions based on assumptions that (1) the ATP cost of force generation (ATPCOST ) remains constant or (2) Michaelis-Menten coupling between cytosolic ADP and ATPOX does not change. However, growing evidence suggests that one, or both, of these assumptions are invalid during high-intensity fatigue protocols. Consequently, there is a need to examine the validity and accuracy of traditional ATPOX calculation methods under these conditions. To address this gap, we measured phosphate concentrations and pH in the vastus lateralis muscle of nine young adults during four rest-contraction-recovery trials lasting 24, 60, 120, and 240 s. The initial velocity of phosphocreatine resynthesis (ViPCr ) following each trial served as the criterion measure of ATPOX because this method makes no assumptions of constant ATPCOST or Michaelis-Menten coupling between changes in cytosolic ADP and ATPOX . Subsequently, we calculated ATPOX throughout the 240 s trial using several traditional calculation methods and compared estimations of ATPOX from each method with time-matched measurements of ViPCr . Method 1, which assumes that ATPCOST does not change, was able to model changes in ViPCr over time, but showed poor accuracy for predicting ViPCr across a wide range of ATPOX values. In contrast, Michaelis-Menten methods, which assume that the relationship between changes in cytosolic ADP and ATPOX remains constant, were invalid because they could not model the decline in ViPCr . However, adjusting these Michaelis-Menten methods for observed changes in maximal ATPOX capacity (i.e., Vmax ) permitted modeling of the decline in ViPCr and markedly improved accuracy. The results of these comprehensive analyses demonstrate that valid, accurate measurements of ATPOX can be obtained during high-intensity contractions by adjusting Michaelis-Menten ATPOX calculations for changes in Vmax observed from baseline to post-fatigue.
    Keywords:  31P-MRS, ATP cost, bioenergetics, high-intensity exercise, mitochondria, muscle, oxidative capacity, oxidative phosphorylation
    DOI:  https://doi.org/10.1002/nbm.4381
  51. Trends Genet. 2020 Aug 17. pii: S0168-9525(20)30201-8. [Epub ahead of print]
    Riepsaame J.
      Precise gene editing of mitochondrial DNA (mtDNA) is essential for the generation of model systems to study rare mitochondrial diseases but was long deemed impossible - until now. A recent publication by Mok et al. describes a gene editing tool capable of installing point mutations in mtDNA, and it does not involve CRISPR.
    DOI:  https://doi.org/10.1016/j.tig.2020.08.001
  52. Proc Natl Acad Sci U S A. 2020 Aug 18. pii: 202010275. [Epub ahead of print]
    Khatib A, Solaimuthu B, Ben Yosef M, Abu Rmaileh A, Tanna M, Oren G, Schlesinger Frisch M, Axelrod JH, Lichtenstein M, Shaul YD.
      One of the emerging hallmarks of cancer illustrates the importance of metabolic reprogramming, necessary to synthesize the building blocks required to fulfill the high demands of rapidly proliferating cells. However, the proliferation-independent instructive role of metabolic enzymes in tumor plasticity is still unclear. Here, we provide evidence that glutathione peroxidase 8 (GPX8), a poorly characterized enzyme that resides in the endoplasmic reticulum, is an essential regulator of tumor aggressiveness. We found that GPX8 expression was induced by the epithelial-mesenchymal transition (EMT) program. Moreover, in breast cancer patients, GPX8 expression significantly correlated with known mesenchymal markers and poor prognosis. Strikingly, GPX8 knockout in mesenchymal-like cells (MDA-MB-231) resulted in an epithelial-like morphology, down-regulation of EMT characteristics, and loss of cancer stemness features. In addition, GPX8 knockout significantly delayed tumor initiation and decreased its growth rate in mice. We found that these GPX8 loss-dependent phenotypes were accompanied by the repression of crucial autocrine factors, in particular, interleukin-6 (IL-6). In these cells, IL-6 bound to the soluble receptor (sIL6R), stimulating the JAK/STAT3 signaling pathway by IL-6 trans-signaling mechanisms, so promoting cancer aggressiveness. We observed that in GPX8 knockout cells, this signaling mechanism was impaired as sIL6R failed to activate the JAK/STAT3 signaling pathway. Altogether, we present the GPX8/IL-6/STAT3 axis as a metabolic-inflammatory pathway that acts as a robust regulator of cancer cell aggressiveness.
    Keywords:  GPX8; JAK/STAT3 signaling; cancer metabolism; epithelial–mesenchymal transition
    DOI:  https://doi.org/10.1073/pnas.2010275117
  53. Life Sci. 2020 Aug 14. pii: S0024-3205(20)30999-1. [Epub ahead of print] 118247
    Wang N, Zhu P, Huang R, Wang C, Sun L, Lan B, He Y, Zhao H, Gao Y.
      PTEN-induced putative kinase 1 (PINK1) performs many important functions in cells and has been highlighted for its role in early-onset Parkinson's disease. In recent years, an increasing number of studies have revealed the involvement of PINK1 in regulation of a variety of cell physiological and pathophysiological processes, of which regulation of mitochondrial function remains the most prominent. As the "energy factory" of cells, mitochondria provide energy support for various cellular activities. Changes in mitochondrial function often have a fundamental and global impact on cellular activities. Moreover, mitochondrial dysfunction has been implicated in many diseases, especially those related to aging. Thus, a comprehensive study of PINK1 will help us better understand the various cell physiological and pathophysiological processes in which PINK1 is involved, including a variety of mitochondria-related diseases such as Parkinson's disease. This article will review the structural characteristics and expression regulation of PINK1, as well as its unique role in mitochondrial quality control (MQC) systems.
    Keywords:  MQC; Mitochondria; Mitochondrial dynamics; Mitochondrial function maintenance; Mitophagy; PINK1
    DOI:  https://doi.org/10.1016/j.lfs.2020.118247
  54. J Bioenerg Biomembr. 2020 Aug 17.
    Galkina KV, Finkelberg JM, Markova OV, Azbarova AV, Banerjee A, Kumari S, Sokolov SS, Severin FF, Prasad R, Knorre DA.
      Pleiotropic drug resistance (PDR) plasma membrane transporters mediate xenobiotic efflux from the cells and thereby help pathogenic microorganisms to withstand antimicrobial therapies. Given that xenobiotic efflux is an energy-consuming process, cells with upregulated PDR can be sensitive to perturbations in cellular energetics. Protonophores dissipate proton gradient across the cellular membranes and thus increase ATP spendings to their maintenance. We hypothesised that chronic exposure of yeast cells to the protonophores can favour the selection of cells with inactive PDR. To test this, we measured growth rates of the wild type Saccharomyces cerevisiae and PDR-deficient Δpdr1Δpdr3 strains in the presence of protonophores carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), pentachlorophenol (PCP) and niclosamide (NCA). Although the protonophore-induced respiration rates of these two strains were similar, the PDR-deficient strain outperformed the control one in the growth rate on non-fermentable carbon source supplemented with low concentrations of FCCP. Thus, active PDR can be deleterious under conditions of partially uncoupled oxidative-phosphorylation. Furthermore, our results suggest that tested anionic protonophores are poor substrates of PDR-transporters. At the same time, protonophores imparted azole tolerance to yeasts, pointing that they are potent PDR inducers. Interestingly, protonophore PCP led to a persistent increase in the levels of a major ABC-transporter Pdr5p, while azole clotrimazole induced only a temporary increase. Together, our data provides an insight into the effects of the protonophores in the eukaryotes at the cellular level and support the idea that cells with activated PDR can be selected out upon conditions of energy limitations.
    Keywords:  Drug interactions; Multiple drug resistance; Niclosamide; Protonophores; Uncouplers
    DOI:  https://doi.org/10.1007/s10863-020-09849-1
  55. Methods Mol Biol. 2020 ;2184 185-196
    Wei HJ, Letterio JJ, Pareek TK.
      Dendritic cells (DCs) are the bridge between innate and T cell-dependent adaptive immunity, and are promising therapeutic targets for cancer and immune-mediated disorders. In the recent past, DCs have gained significant interest to manipulate them for the treatment of cancer and immune-mediated disorders. This can be achieved by differentiating them into either immunogenic or tolerogenic DCs (TolDCs), by modulating their metabolic pathways, including glycolysis, oxidative phosphorylation, and fatty acid metabolism, to orchestrate their desired function. For immunogenic DCs, this maturation shifts the metabolic profile to a glycolytic metabolic state and leads to the use of glucose as a carbon source, whereas TolDCs prefer oxidative phosphorylation (OXPHOS) and fatty acid oxidation for their energy resource.Understanding the metabolic regulation of DC subsets and functions at large not only will improve our understanding of DC biology and immune regulation, but can also open up opportunities for treating immune-mediated ailments and cancers by tweaking endogenous T-cell responses through DC-based immunotherapies. Here we describe a method to analyze this dichotomous metabolic reprogramming of the DCs for generating reliable and effective DC cell therapy products. We, hereby, report how to measure the OXPHOS and glycolysis level of DCs. We focus on the metabolic reprogramming of TolDCs using a pharmacological nuclear factor (erythroid-derived 2)-like-2 factor (Nrf2) activator as an example to illustrate the metabolic profile of TolDCs.
    Keywords:  Dendritic cells; Glycolysis; Immunometabolism; Oxidative phosphorylation
    DOI:  https://doi.org/10.1007/978-1-0716-0802-9_13
  56. Metabol Open. 2019 Jun;2 100009
    Wu S, Fahmy N, Alachkar H.
      Background: Acute myeloid leukemia (AML) is characterized by rapid growth of abnormal blasts that overcrowd normal hematopoiesis. Defective mitochondrial biogenesis has been implicated in AML, which we believe is partly due to the deregulation of the mitochondrial transcription machinery (MTM) genes influencing the expression of mitochondrial genes. Here, we aim to characterize MTM gene upregulation in AML.Methods: Molecular and clinical patient data were retrieved from several public AML datasets. Kaplan-Meier survival curves were used to compare overall survival between patients, while Mann-Whitney U's non-parametric and Fisher's exact test were used for comparing continuous and categorical variables, respectively.
    Results: The MTM genes TFB1M, TFB2M, TFAM, and POLRMT were upregulated in patients with AML compared with healthy donors. Upregulation of one or more of these genes was associated with higher percentage of peripheral blood blasts (P = 0.002), normal cytogenetic status (P = 0.027) and NPM1 mutations (P = 0.009). Additionally, patients with high expression of MTM genes (Z ≥ 1) had shorter median overall survival compared with low MTM gene expression (Z < 1) (months: 11.8 vs 24.1, P = 0.027; multivariate survival analysis Cox Proportional Hazards model, HR: 1.82 (1.22-2.70); p-value: 0.003).
    Conclusion: The mitochondrial transcriptional machinery is upregulated and associated with worse clinical outcome in patients with AML and may present a viable therapeutic target.
    Keywords:  Acute myeloid leukemia; Gene expression regulation; Mitochondrial biogenesis; Mitochondrial transcription; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.metop.2019.100009
  57. Int J Mol Sci. 2020 Aug 14. pii: E5845. [Epub ahead of print]21(16):
    Bleve A, Durante B, Sica A, Consonni FM.
      Cancer progression generates a chronic inflammatory state that dramatically influences hematopoiesis, originating different subsets of immune cells that can exert pro- or anti-tumor roles. Commitment towards one of these opposing phenotypes is driven by inflammatory and metabolic stimuli derived from the tumor-microenvironment (TME). Current immunotherapy protocols are based on the reprogramming of both specific and innate immune responses, in order to boost the intrinsic anti-tumoral activity of both compartments. Growing pre-clinical and clinical evidence highlights the key role of metabolism as a major influence on both immune and clinical responses of cancer patients. Indeed, nutrient competition (i.e., amino acids, glucose, fatty acids) between proliferating cancer cells and immune cells, together with inflammatory mediators, drastically affect the functionality of innate and adaptive immune cells, as well as their functional cross-talk. This review discusses new advances on the complex interplay between cancer-related inflammation, myeloid cell differentiation and lipid metabolism, highlighting the therapeutic potential of metabolic interventions as modulators of anticancer immune responses and catalysts of anticancer immunotherapy.
    Keywords:  cancer immunotherapy; cholesterol; fatty acids; lipid metabolism; myeloid-derived suppressor cells (MDSCs); obesity; tumor-associated macrophages (TAMs)
    DOI:  https://doi.org/10.3390/ijms21165845